CN114436173A

CN114436173A - Forklift hydraulic transmission system and forklift transmission control system

Info

Publication number: CN114436173A
Application number: CN202210018052.6A
Authority: CN
Inventors: 孙保群; 孙冬; 盛楠; 汪韶杰; 夏光; 魏玉龙; 施益平
Original assignee: Anhui Zhanpeng Hydraulic Machinery Co ltd; Hefei Shinny Instrument Control Technology Co ltd; Hefei University of Technology
Current assignee: Anhui Zhanpeng Hydraulic Machinery Co ltd; Hefei Shinny Instrument Control Technology Co ltd; Hefei University of Technology
Priority date: 2022-01-07
Filing date: 2022-01-07
Publication date: 2022-05-06
Anticipated expiration: 2042-01-07
Also published as: CN114436173B

Abstract

The invention belongs to the field of transmission control of non-road mobile machines, and particularly relates to a forklift hydraulic transmission system and a forklift transmission control system, which comprise a first liquid supply oil way, a second liquid supply oil way, a walking driving oil way, an operation control oil way, a discharge control oil way, and a first valve, wherein the first valve is configured to at least have the following stations: at a first station, a first valve communicates a first liquid supply oil way with a walking driving oil way; the first valve communicates the first liquid supply with the operation control oil way; a second valve configured to have at least a station I, and a station II; and the displacement control valve is positioned between the second liquid supply oil way and the displacement control oil way. The system can realize pump valve combined control hydraulic stepless speed change transmission, valve control hydraulic transmission of fork truck jogging walking, fork frame lifting and mast tilting pump valve combined control transmission when the fork truck runs, and aims to improve the fork truck walking transmission efficiency and reduce the hydraulic transmission power loss of a fork truck hydraulic actuating mechanism.

Description

Forklift hydraulic transmission system and forklift transmission control system

Technical Field

The invention belongs to the field of transmission control of non-road mobile machines, and particularly relates to a manual and electro-hydraulic hybrid control forklift hydraulic transmission system and forklift transmission control system which take an internal combustion engine as power and adopt hydraulic transmission to provide power for walking micromotion, gantry inclination and fork lifting

Background

The forklift is mainly used for forklift loading, carrying and stacking of articles, is a typical non-road mobile machine, and mainly works in non-road scenes such as fields, warehouses and the like. The forklift generally adopts an electric motor and an internal combustion engine as power, wherein the electric motor is mainly applied to forklift products with less than 5 tons, and the internal combustion engine is widely applied to forklifts with various tonnage grades and is generally called as a diesel fork lift. In the working process, the forklift not only moves to carry goods, but also needs to complete engineering operations such as forking, lifting, stacking and the like of the goods through operation devices such as a gantry, a fork frame or an accessory. At present, the traveling power transmission of the diesel fork truck mainly adopts a hydraulic-mechanical transmission system, namely, the traveling transmission is realized by a transmission system formed by connecting a hydraulic torque converter, a gear and a shaft part in series, and the engineering operations of forking, lifting, stacking and the like of the diesel fork truck for goods are completed by providing hydraulic power for a hydraulic actuating mechanism through a vehicle-mounted hydraulic source.

In a hydraulic-mechanical walking transmission system of the diesel fork truck, the hydraulic torque converter has the function of realizing automatic torque conversion in a certain range, so that the self-adaptive stepless speed change in the starting and running processes of the fork truck is facilitated, but the transmission efficiency of the hydraulic torque converter is low, so that the walking transmission energy loss of the fork truck is large. The power transmission and control of the hydraulic actuating mechanism of the diesel fork truck are generally designed by configuring the parameters of a hydraulic source according to the maximum load working condition of the hydraulic actuating mechanism which consumes the maximum hydraulic power, and controlling the liquid supply parameters of the hydraulic source to the hydraulic actuating mechanism by adopting various hydraulic valve elements in the modes of shunting, throttling and the like according to the specific working condition of the hydraulic actuating mechanism so as to complete corresponding engineering operation. The scheme has the advantages that the hydraulic driving power requirements of all hydraulic actuating mechanisms can be met to the maximum extent, and the accurate control can be realized on various engineering operations, but the shunting and throttling processes of valve elements generally lead the shunted pressure oil pressure to directly flow back to the hydraulic oil tank, so that the hydraulic energy loss is formed; in addition, the hydraulic power is positively correlated with the hydraulic pressure and flow, a hydraulic actuating mechanism of the forklift adopts a linear hydraulic cylinder as an actuator, pressure oil is supplied to a hydraulic cylinder working cavity or the hydraulic cylinder working cavity discharges the oil during working, the discharged oil directly flows back to a hydraulic oil tank, and the discharged oil has certain oil pressure, so that hydraulic power loss is formed, and on the internal combustion forklift, the hydraulic power loss usually accounts for more than 40% of the hydraulic power provided by a hydraulic source.

Disclosure of Invention

In view of the defect of low transmission efficiency of the existing walking and engineering operation transmission of the diesel fork truck, the invention aims to provide a hydraulic transmission system of the fork truck and a transmission control system of the fork truck, wherein the hydraulic transmission system can realize pump valve combined control hydraulic stepless speed change transmission, valve control hydraulic transmission of micro-motion of the fork truck and pump valve combined control transmission of fork frame lifting and mast inclination when the fork truck runs, and aims to improve the walking transmission efficiency of the fork truck and reduce the hydraulic transmission power loss of a hydraulic actuating mechanism of the fork truck.

To achieve the above and other related objects, the present invention provides a forklift hydraulic transmission system, including:

the first liquid supply oil way is communicated with a hydraulic oil tank, and is provided with a variable pump which is in transmission connection with an output shaft of the internal combustion engine;

the second liquid supply oil way is communicated with the hydraulic oil tank, a fixed displacement pump is arranged on the second liquid supply oil way, and the fixed displacement pump is in transmission connection with an output shaft of the internal combustion engine;

the walking driving oil way is provided with a hydraulic motor, and an output shaft of the hydraulic motor is in transmission connection with the driving wheel;

the operation control oil way is connected with a lifting oil cylinder and an inclined oil cylinder at the front end of the forklift, and control valves for respectively controlling the lifting oil cylinder and the inclined oil cylinder are arranged on the operation control oil way;

a displacement control oil path, wherein a displacement adjusting oil cylinder is arranged on the displacement control oil path, and a piston rod of the displacement adjusting oil cylinder is in transmission connection with a displacement adjusting mechanism of the variable pump;

a first valve located between the first liquid supply oil passage and the travel drive oil passage and the work control oil passage, the first valve being configured to have at least the following positions:

the first valve is used for communicating the first liquid supply oil way with the walking driving oil way and disconnecting the first liquid supply oil way from the operation control oil way at a first station;

the first valve disconnects the first liquid supply oil way from the walking driving oil way and communicates the first liquid supply with the operation control oil way;

a second valve located between the second oil supply path and the travel drive path, the second valve being configured to have at least the following positions:

a second valve is used for communicating the second liquid supply oil way with the walking driving oil way at the station I;

the second valve disconnects the second liquid supply oil way from the walking driving oil way;

and the displacement control valve is positioned between the second liquid supply oil way and the displacement control oil way, is used for controlling connection/disconnection of the second liquid supply oil way and the displacement control oil way, and is configured to enable the opening degree of an oil outlet of the displacement control valve to be continuously adjustable.

In an optional embodiment of the invention, the first valve is configured to further have:

and in the third station, the first valve is used for communicating the first liquid supply oil way with the walking driving oil way and the operation control oil way respectively.

In an optional embodiment of the present invention, a reversing valve is disposed on the traveling driving oil path, and the reversing valve is configured to change a flow direction of the oil flowing through the hydraulic motor when the traveling driving oil path is communicated with the first liquid supply oil path, so as to implement forward and reverse rotation switching of the hydraulic motor.

In an optional embodiment of the present invention, a stop valve is further disposed on the travel driving oil path, the stop valve is configured to connect or disconnect an oil path between the directional valve and the hydraulic motor, and when the oil path between the directional valve and the hydraulic motor is disconnected, two oil ports of the hydraulic motor are simultaneously stopped, so that the hydraulic motor is in an oil trapping state.

In an optional embodiment of the invention, the station I of the second valve comprises a sub-station Ia and a sub-station Ib, and when the second valve is switched between the sub-station Ia and the sub-station Ib, the flow direction of the oil output by the second oil supply circuit when flowing through the hydraulic motor can be changed, so as to realize the forward and reverse rotation switching of the hydraulic motor.

In an optional embodiment of the present invention, when the second valve is in the station II, the two oil ports of the hydraulic motor are simultaneously closed, so that the hydraulic motor is in an oil trapping state.

In an optional embodiment of the present invention, the operation control oil path includes a first branch oil path and a second branch oil path, the first branch oil path and the second branch oil path are arranged in parallel, the first branch oil path is connected to the tilt cylinder, and a third valve is disposed on the first branch oil path, and the third valve is configured to control the tilt cylinder to switch between three positions, i.e., an extension position, a shortening position, and a pressure maintaining position; the second branch oil way is connected with the lifting oil cylinder, a fourth valve is arranged on the second branch oil way, and the fourth valve is configured to control the lifting oil cylinder to be switched among three stations of lifting, descending and pressure maintaining.

In an optional embodiment of the present invention, a flow control valve is further disposed on the operation control oil path, and the flow control valve is configured to continuously adjust a size of an internal oil passage thereof, so as to control an oil flow rate flowing from the first oil supply path to the operation control oil path.

In an optional embodiment of the present invention, an unloading valve is disposed between two oil ports of the variable displacement pump, and the unloading valve is configured to communicate the two oil ports of the variable displacement pump when the oil pressure of the first liquid supply oil path reaches a preset value, and an unloading button for controlling on/off of the unloading valve is further disposed on the unloading valve.

In order to achieve the above objects and other related objects, the present invention further provides a forklift transmission control system applied to the forklift hydraulic transmission system, wherein the first valve, the displacement control valve, the reversing valve, the stop valve and the flow direction control valve are electromagnetic slide valves; the second valve, the third valve and the fourth valve are manual slide valves;

the forklift transmission control system comprises:

the control signal input ends of the first valve, the displacement control valve, the reversing valve, the stop valve and the flow direction control valve are connected with the control signal output end of the electronic controller;

the second valve position sensor is used for detecting the valve position state of the second valve, and the signal output end of the second valve position sensor is connected with the signal input end of the electronic controller;

the third valve position sensor is used for detecting the valve position state of the third valve, and the signal output end of the third valve position sensor is connected with the signal input end of the electronic controller;

the fourth valve position sensor is used for detecting the valve position state of the fourth valve, and the signal output end of the fourth valve position sensor is connected with the signal input end of the electronic controller;

the adjusting oil cylinder piston rod position sensor is used for detecting the position of a piston rod of the displacement adjusting oil cylinder, and the signal output end of the adjusting oil cylinder piston rod position sensor is connected with the signal input end of the electronic controller;

the variable pump rotating speed sensor is used for detecting the rotating speed of the variable pump, and the signal output end of the variable pump rotating speed sensor is connected with the signal input end of the electronic controller;

the motor rotating speed sensor is used for detecting the rotating speed of the hydraulic motor, and the signal output end of the motor rotating speed sensor is connected with the signal input end of the electronic controller;

the execution oil pressure sensor is used for detecting the oil pressure of the operation control oil way, and the signal output end of the execution oil pressure sensor is connected with the signal input end of the electronic controller;

the braking force sensor is used for detecting the stepping depth of a braking pedal, and the signal output end of the braking force sensor is connected with the signal input end of the electronic controller;

the accelerator position sensor is used for detecting the treading depth of an accelerator pedal, and the signal output end of the accelerator position sensor is connected with the signal input end of the electronic controller;

and the gear sensor is used for detecting a gear signal, and the signal output end of the gear sensor is connected with the signal input end of the electronic controller.

The invention has the technical effects that:

through controlling the valve position of the first valve, the independent oil supply of the variable pump to the forklift running or operation execution module is realized, the interaction influence of hydraulic working parameters among different modules is effectively avoided, and the control difficulty of the hydraulic working parameters of each module is greatly reduced.

Because the closed hydraulic transmission system consisting of the variable pump and the bidirectional constant displacement motor is adopted in the forklift walking transmission chain, the transmission ratio of the pump to the motor is the ratio of the displacement of the constant displacement motor to the real-time displacement of the variable pump, through the adjustment of the displacement of the variable pump, the transmission ratio which is continuously changed from less than 1 to hundreds of times can be formed between the variable pump and the motor, the transmission ratio can be quickly well matched with the power requirements of working conditions such as starting, acceleration and uphill of the forklift under different loads, stepless speed change and accurate speed control can be realized in the conventional driving process of the forklift, and if the bidirectional constant displacement motor is replaced by the bidirectional variable displacement motor, the coverage range of the continuously changed transmission ratio between the bidirectional constant displacement motor and the bidirectional variable displacement motor can be larger.

Under the working condition of forklift running, in a forward and reverse transmission closed hydraulic loop formed between the variable pump and the motor, oil discharged by the motor has certain oil pressure and directly enters an oil suction port of the variable pump, so that the pressure difference between a variable pump suction port and an oil discharge port can be reduced, the volumetric efficiency of the variable pump is improved, and the power consumption is reduced.

When the forklift carries out engineering operation, the accurate control of the tilting speed and the tilting posture of the forklift gantry can be realized by adjusting the displacement of the variable pump and controlling the valve position of the third valve, and the accurate control of the position of the forklift gantry can be realized by adjusting the displacement of the variable pump, controlling the valve position of the fourth valve and adjusting the adjustable orifice of the fourth valve.

Through controlling the second valve position, utilize the pressure fluid that the constant delivery pump provided, can make fork truck go on the fine motion forward, backward at the engineering operation in-process, because the variable delivery pump provides the required hydraulic power of engineering operation alone this moment, fork truck fine motion power then is provided by the constant delivery pump, two hydraulic transmission routes are completely independent, mutual noninterference, are favorable to accurate control fork truck fine motion, also are convenient for carry out fork truck fine motion and engineering operation's combined operation simultaneously.

Under the fork truck walking operating mode, in the closed hydraulic transmission system that variable pump and motor are constituteed, utilize the displacement of variable pump to change the height of direct control speed of a motor vehicle, thereby fork truck reduces the variable pump discharge capacity gradually under certain speed of a vehicle and can make fork truck constantly slow down and produce the braking effect, thereby the fluid passageway between the first hydraulic fluid port of motor and the second hydraulic fluid port has been blocked when the variable pump discharge capacity is 0, make the motor be in "stranded oil" state and unable rotation, produce parking braking effect to fork truck.

Under the flameout state of the forklift engine, all valve elements are in the initial valve position, the displacement of the variable pump is 0, and at the moment, the motor is trapped in oil to generate the parking brake effect on the forklift.

Drawings

FIG. 1 is a schematic diagram of a forklift hydraulic drive system provided by an embodiment of the present invention;

FIG. 2 is a schematic diagram of a forklift hydraulic drive system and forklift drive control system provided by an embodiment of the present invention;

FIG. 3 is an enlarged schematic view of a first valve in a forklift hydraulic drive system and forklift drive control system provided by an embodiment of the present invention;

FIG. 4 is an enlarged schematic view of a second valve in the truck hydraulic drive system and truck drive control system provided by an embodiment of the present invention;

FIG. 5 is an enlarged schematic view of a third valve in the truck hydraulic drive system and truck drive control system provided by an embodiment of the present invention;

FIG. 6 is an enlarged schematic view of a fourth valve in the truck hydraulic drive system and truck drive control system provided by the embodiments of the present invention;

FIG. 7 is an enlarged schematic view of a stop valve in a forklift hydraulic drive system and forklift drive control system provided by an embodiment of the invention;

fig. 8 is an enlarged schematic view of the structural components of the displacement adjusting cylinder and the arrangement of the position sensor of the piston rod of the adjusting cylinder in the forklift hydraulic transmission system and the forklift transmission control system provided by the embodiment of the invention;

fig. 9 is an enlarged schematic view of the structural components of the hydraulic transmission system of the forklift and the tilt cylinder controlled by the transmission control system of the forklift according to the embodiment of the present invention;

fig. 10 is an enlarged schematic view of the structural components of the hydraulic transmission system of the forklift and the lift cylinder controlled by the transmission control system of the forklift according to the embodiment of the invention;

fig. 11 is a schematic diagram of the basic structural components of a forklift truck to which the forklift truck hydraulic drive system and the forklift truck drive control system according to the embodiment of the present invention are applied.

The specific meanings of the reference symbols in the figures are: AG, a discharge capacity adjusting oil cylinder; AGG adjusting the piston rod of the oil cylinder; agh, adjusting the cylinder piston; AGJ adjusting a shaft hinge of the oil cylinder; AGQ, adjusting a working cavity of the oil cylinder; AN AN unload button; BB. variable displacement pump; BBZ variable pump shaft; C1. a first gear; C2. a second gear; cj. fork carriage of fork truck; CS, forklift body; cb. variable pump gear; cd. fixed displacement pump gear; cm. motor gear; DB. quantitative pump; dbz, quantitative pump shaft; DG. lift cylinders; DGG, a piston rod of the lifting oil cylinder; DGH, lift cylinder piston; DW. drive wheel; FT. a return spring; GQ. lift cylinder working chamber; hts, forklift drive train; J2. a second valve adjustable orifice; J31. a third valve first adjustable orifice; J32. a third valve second adjustable orifice; J4. a fourth valve adjustable orifice; MD. a hydraulic motor; mdz, hydraulic motor shaft; MJ. forklift mast; OW. oil supply channel of other oil-using device; p1. first valve electrical drive power; p6, the electric driving power of the reversing valve; p7, controlling the electric driving power of the displacement control valve; p8, electrically driving power of the flow control valve; p9. stop valve electric drive power; pcu an electronic controller; pd. walking driving force; pi. engine power; qb. variable pump flow rate; qd. travel drive flow rate; qop, actuator traffic; SG. tilt cylinders; SGG, inclining a piston rod of the oil cylinder; sgh tilt cylinder piston; s2, a second valve position sensor; s v3, a third valve position sensor; s v4, a fourth valve position sensor; a sensor for adjusting the position of a piston rod of the oil cylinder; sap, accelerator position sensor; sb. variable pump speed sensor; a brake force sensor; s gs. a gear sensor; sm. hydraulic motor speed sensor; so. implement an oil pressure sensor; t. a hydraulic oil tank; v1. a first valve; v2. a second valve; v3. a third valve; v4. a fourth valve; v5. a fifth valve; v6. a diverter valve; v7. displacement control valves; v8. a flow control valve; v9. stop valve; VU. an unloader valve; VP. pressure maintaining valves; WQ. tilting the rodless cavity of the cylinder; YQ. tilting cylinder has rod cavity; z1. a first shaft; ZJ1. front axle hinge; ZJ2. rear axle hinge; e1. a first valve electrical port; e6. a reversing valve power connection port; e7. a displacement control valve electrical port; e8. the flow control valve is connected with an electric port; e9. a stop valve power connection port; iag, adjusting a position sensor interface of a piston rod of the oil cylinder; iap. throttle position sensor interface; ib. variable pump speed sensor interface; ibr, brake force sensor interface; ics, gear sensor interface; an engine electronic control unit communication interface; im. hydraulic motor speed sensor interface; an execution oil pressure sensor interface; iv2. a second valve position sensor interface; iv3. a third valve position sensor interface; iv4. a fourth valve position sensor interface; k11. a first valve first port; k12. a first valve second port; k13. a first valve third port; k14. a first valve fourth port; k15. a fifth oil port of the first valve; k21. a first oil port of the second valve; k22. a second valve second port; k23. a third oil port of the second valve; k24. a fourth oil port of the second valve; k25. a fifth oil port of the second valve; k31. a third valve first oil port; k32. a second oil port of a third valve; k33. a third oil port of a third valve; k34. a fourth oil port of the third valve; k41. a fourth valve first port; k42. a fourth valve second port; k43. a fourth valve third port; k51. a fifth valve first port; k52. a fifth valve second port; k61. a first oil port of the reversing valve; k62. a second oil port of the reversing valve; k63. a third oil port of the reversing valve; k64. a fourth oil port of the reversing valve; k71. a first oil port of the displacement control valve; k72. a second oil port of the displacement control valve; k73. a third oil port of the displacement control valve; k81. a first oil port of the flow control valve; k82. a second oil port of the flow control valve; k91. a first oil port of the stop valve; k92. a second oil port of the stop valve; k93. a third oil port of the stop valve; k94. a fourth oil port of the stop valve; ka. regulating oil cylinder oil port; kb1 variable pump suction; kb2, variable pump oil discharge port; kd. lifting cylinder working chamber oil port; kd1. constant displacement pump oil suction port; kd2. quantitative pump oil drain port; km1. a first oil port of the hydraulic motor; km2. a second oil port of the hydraulic motor; kp1. a first oil port of a pressure stabilizing valve; kp2. a second oil port of the pressure stabilizing valve; ks1, inclining a first oil port of the oil cylinder; ks2, inclining a second oil port of the oil cylinder; ku1, a first oil port of an unloading valve; ku2, a second oil port of the unloading valve; nb. variable pump speed; n1. input speed; nm. hydraulic motor speed; p1. a first valve actuation output interface; p6. a reversing valve drive output interface; p7. displacement control valve drive output interface; p8. flow control valve drive output interface; p9. stop valve drive output interface; sk1. oil ports of rod cavities of the tilting oil cylinders; and sk2. oil ports of rodless cavities of the inclined oil cylinders.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict.

It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention, and the drawings only show the components related to the present invention rather than the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.

Fig. 1 shows a basic embodiment for achieving the object of the invention, namely a hydraulic transmission system of a forklift truck, fig. 2 shows a further preferred embodiment, the type of the hydraulic components in the embodiment shown in fig. 2 is specifically defined, and the detailed components of the control system are given. The technical solution of the present invention will be described in detail with reference to the embodiment shown in fig. 2, and it should be understood that a person skilled in the art can develop a specific embodiment different from the embodiment shown in fig. 2 on the basis of the embodiment shown in fig. 1, and these extensions based on the embodiment shown in fig. 1 all belong to the protection scope of the present invention.

Referring to fig. 2-11, a hydraulic transmission control system for a forklift employing combined manual and electronic control, and more particularly, to a hydraulic transmission control system for performing hydraulic energy transfer control of a forklift transmission system HTS powered by an internal combustion engine, a lift cylinder DG of a forklift fork, and a tilt cylinder SG of a forklift mast;

as shown in fig. 2 and 11, the forklift transmission system HTS includes a first shaft Z1, a first gear C1, a second gear C2, a variable pump BB, a variable pump shaft BBZ, a variable pump gear Cb, a displacement adjusting cylinder AG, a fixed displacement pump DB, a fixed displacement pump shaft DBZ, a fixed displacement pump gear Cd, a motor MD, a motor shaft MDZ, a hydraulic oil tank T, and a forklift transmission casing KT, and in a forklift assembly state:

the first shaft Z1 is a power input shaft which is in transmission connection with an internal combustion engine EG in the forklift transmission system HTS, and a first gear C1 and a second gear C2 are fixedly arranged on the power input shaft in sequence and are rotatably supported on a forklift transmission casing KT; the variable pump BB is a positive displacement variable displacement hydraulic pump and mainly comprises a variable pump stator, a variable pump rotor and a displacement adjusting mechanism, wherein the variable pump stator is fixedly arranged on a machine body CS of the mobile machine, the variable pump rotor is arranged in the variable pump stator and coaxially sleeved at one end of a variable pump shaft BBZ, is in transmission connection with the variable pump stator and synchronously rotates, and a variable pump gear Cb is fixedly arranged at the other end of the variable pump shaft BBZ and is normally meshed with a second gear C2; the variable pump stator is provided with two oil ports, namely a variable pump oil suction port kb1 and a variable pump oil discharge port kb2, when the variable pump rotor rotates relative to the variable pump stator, the variable pump BB sucks oil from the variable pump oil suction port kb1 and discharges the oil from the oil discharge port kb2, the discharged oil amount per rotation of the variable pump rotor is defined as a variable pump displacement qb, the variable pump displacement qb is variable, the adjustment range is more than or equal to 0 and less than or equal to qb and less than or equal to qbmax, and the variable pump rotor comprises: qbmax is the maximum value of qb; the displacement adjusting mechanism of the variable displacement pump BB is used for adjusting qb; the oil flow output by the variable pump is defined as the variable pump flow Qb, and when the displacement of the variable pump is a certain fixed value of Qb > 0, the flow is in direct proportion to the rotating speed of a variable pump rotor; the displacement adjusting oil cylinder AG (see figure 8) is a single-action single-piston-rod hydraulic oil cylinder, and is integrally hinged on a forklift body CS through an adjusting oil cylinder shaft hinge AGJ; the displacement adjusting oil cylinder AG is provided with an adjusting oil cylinder piston rod AGG, an adjusting oil cylinder piston AGH, an adjusting oil cylinder working cavity AGQ and a return spring FT, and is provided with an adjusting oil cylinder oil port ka; one end of a piston rod AGG of the adjusting oil cylinder is fixedly arranged on the piston AGH of the adjusting oil cylinder, and the other end of the piston rod AGG extends out of the displacement adjusting oil cylinder AG and is in transmission connection with a displacement adjusting mechanism of the variable displacement pump BB; the adjusting oil cylinder oil port ka is communicated with the adjusting oil cylinder working cavity AGQ, the return spring FT is arranged in the displacement adjusting oil cylinder AG, the adjusting oil cylinder oil port ka is supplied with oil to increase the volume of the adjusting oil cylinder working cavity AGQ, push the adjusting oil cylinder piston AGH to increase the length of the adjusting oil cylinder piston rod AGG extending out of the displacement adjusting oil cylinder AG, meanwhile, the return spring FT is compressed to increase the elastic force of the adjusting oil cylinder piston rod AGG, when the adjusting oil cylinder working cavity AGQ discharges oil through the adjusting oil cylinder oil port ka, the volume of the adjusting oil cylinder working cavity AGQ can be reduced under the elastic force action of the return spring FT, meanwhile, the length of the adjusting oil cylinder piston rod AGG extending out of the displacement adjusting oil cylinder AG is reduced, and when the volume of the adjusting oil cylinder working cavity AGQ is minimum, the displacement adjusting oil cylinder AG is in an initial state; supplying or discharging oil to an oil-saving cylinder working cavity AGQ through an oil port ka of the adjusting oil cylinder, changing the length of an extending displacement of an adjusting cylinder piston rod AGG out of a displacement adjusting oil cylinder AG, and further actuating a displacement adjusting mechanism of a variable pump BB to adjust the displacement qb of the variable pump, wherein the single-rotation displacement of the variable pump BB is 0 when the oil is completely discharged from the oil-saving cylinder working cavity AGQ, and the single-rotation displacement of the variable pump BB reaches the maximum value qbmax when the oil is completely charged from the oil-saving cylinder working cavity AGQ; the fixed displacement pump DB is a positive displacement fixed displacement hydraulic pump and mainly comprises a fixed displacement pump stator and a fixed displacement pump rotor, wherein the fixed displacement pump stator is fixedly arranged on a mobile machine body CS, the fixed displacement pump rotor is arranged in the fixed displacement pump stator, coaxially sleeved at one end of the fixed displacement pump shaft DBZ, in transmission connection with and synchronously rotating with a fixed displacement pump shaft DBZ, and a fixed displacement pump gear Cd is fixedly arranged at the other end of a fixed displacement pump shaft DBZ and is normally meshed with the first gear C1; the fixed displacement pump stator is provided with two oil ports, namely a fixed displacement pump oil suction port kd1 and a fixed displacement pump oil discharge port kd2, and the fixed displacement pump oil suction port kd1 is communicated with a hydraulic oil tank T; when a rotor of the fixed displacement pump rotates relative to a stator of the fixed displacement pump, oil is sucked into the fixed displacement pump DB through a fixed displacement pump oil inlet kd1, and oil is discharged out of a fixed displacement pump oil outlet kd2, the amount of the oil discharged out of the fixed displacement pump rotor per rotation is defined as a fixed displacement qd of the fixed displacement pump, and the fixed displacement qd of the fixed displacement pump is a constant value; the flow rate of the oil output by the fixed displacement pump is defined as the flow rate of the fixed displacement pump, and the flow rate is in direct proportion to the rotating speed of a rotor of the fixed displacement pump; the motor MD is a positive displacement type fixed displacement bidirectional hydraulic motor and mainly comprises a motor stator and a motor rotor, the motor stator is fixedly arranged on a forklift body CS, and the motor rotor is arranged in the motor stator, coaxially sleeved at one end of the motor shaft MDZ, in transmission connection with the motor shaft MDZ and synchronously rotates; a motor stator is provided with a motor first oil port km1 and a motor second oil port km2, the motor rotor can be driven to rotate forwards by supplying oil to the motor first oil port km1, and the motor rotor can be driven to rotate reversely by supplying oil to the motor second oil port mk 2; in the assembled state of the fork-lift truck, the motor shaft MDZ is in transmission connection with the drive wheel DW in a mechanical transmission manner (see fig. 11).

The lifting oil cylinder DG (see the figures 10 and 11) is a single-rod single-action hydraulic oil cylinder which is integrally and fixedly arranged on a forklift gantry MJ and used for actuating a forklift fork CJ to lift or descend, and the lifting oil cylinder DG is provided with a lifting cylinder piston DGH, a lifting cylinder piston rod DGG, a lifting cylinder working cavity GQ and a lifting cylinder working cavity oil port kd; the lower end of a piston rod DGG of the lifting cylinder is fixedly connected with a piston DGH of the lifting cylinder, and the upper end of the piston rod DGG of the lifting cylinder extends out of a lifting cylinder DG and is in transmission connection with a fork frame CJ of the forklift; the oil port kd of the working cavity of the lifting cylinder is communicated with the working cavity GQ of the lifting cylinder, when the oil is supplied to the working cavity GQ of the lifting cylinder through the working cavity oil port kd of the lifting cylinder, a piston DGH of the lifting cylinder and a piston rod DGG of the lifting cylinder can move upwards and a fork frame CJ of the forklift can be lifted upwards, and when the working cavity GQ of the lifting cylinder drains oil through the working cavity oil port kd of the lifting cylinder, the piston DGH of the lifting cylinder and the piston rod DGG of the lifting cylinder can move downwards and the fork frame CJ of the forklift can descend under the action of gravity; when the fork frame CJ of the forklift is lifted or descended to any position, oil supply or drainage to the working cavity GQ of the lifting cylinder is stopped, and the position of the fork frame CJ can be maintained unchanged.

The tilt cylinder SG (see fig. 9 and 11) is a single-rod double-acting hydraulic cylinder integrally hinged to the forklift body CS through a rear axle hinge ZJ2, and is used for actuating the forklift mast MJ to swing forwards or backwards around a mast axle hinge MZJ hinged to the forklift body CS by the forklift mast MJ; the tilting cylinder SG is provided with a tilting cylinder piston rod SGG, a tilting cylinder piston SGH, a tilting cylinder rodless cavity WQ, a tilting cylinder rod cavity YQ, a tilting cylinder rod cavity oil port ks1 and a tilting cylinder rodless cavity oil port ks 2; one end of a piston rod SGG of the inclined oil cylinder is fixedly connected with the piston SGH of the inclined oil cylinder, and the other end of the piston rod SGG of the inclined oil cylinder extends out of the inclined oil cylinder SG and is hinged to a position, above a portal shaft hinge MZJ, of the forklift portal MJ through a front shaft hinge ZJ 1; the rod-free cavity oil port ks2 of the tilt oil cylinder is communicated with the rod-free cavity WQ of the tilt oil cylinder, the rod cavity oil port ks1 of the tilt oil cylinder is communicated with the rod cavity YQ of the tilt oil cylinder, when oil is supplied to the rod-free cavity WQ of the tilt oil cylinder through the rod cavity oil port ks2 of the tilt oil cylinder and oil is drained to the rod cavity YQ of the tilt oil cylinder through the rod cavity oil port ks1 of the tilt oil cylinder, the tilt oil cylinder piston SGH can be pushed to move to one side of the rod cavity YQ of the tilt oil cylinder, the length of the tilt oil cylinder piston rod SGG extending out of the tilt oil cylinder SG is increased, and then the forklift mast is swung forwards, when oil is drained to the rod cavity WQ of the tilt oil cylinder through the rod cavity oil port ks1 of the tilt oil cylinder, and the rod cavity oil port ks2 of the tilt oil cylinder is simultaneously pushed to move to one side of the rod cavity WQ of the tilt oil cylinder, the tilt oil cylinder piston rod piston H can be pushed to one side of the tilt oil cylinder, the rod cavity WQ extending out of the tilt oil cylinder is reduced, and then the forklift mast is swung backwards, when the rod cavity oil port ks1 of the tilt oil cylinder and the rodless cavity oil port ks2 of the tilt oil cylinder are simultaneously closed, the forklift gantry can be located at a certain fixed position; in practical application, in an assembly state, the forklift is provided with the tilting oil cylinders SG, the front axle hinge ZJ1, the rear axle hinge ZJ2 and the portal axle hinge MZJ in pairs, and the tilting oil cylinders SG, the front axle hinge ZJ1, the rear axle hinge ZJ2 and the portal axle hinge MZJ are symmetrically arranged on the forklift in the left and right direction; the forklift mast CJ is hinged to a forklift body CS through two mast shaft hinges MZJ which are symmetrically arranged in the left-right direction, the forklift mast CJ swings forwards and backwards around the axes of the left and right mast shaft hinges MZJ under the actuation of two tilt cylinders SG which are symmetrically arranged, the forklift mast is arranged in the forklift mast and can slide up and down along the forklift mast under the actuation of a lifting cylinder DG, and the forks HC are fixedly arranged on the forklift mast and synchronously move up and down along with the forklift mast.

As shown in fig. 2, the electro-hydraulic control system comprises valve-like elements, sensor-like elements and an information screen SC and an electronic controller PCU.

The valve-like elements include a first valve V1, a second valve V2, a third valve V3, a fourth valve V4, a fifth valve V5, a directional valve V6, a displacement control valve V7, a flow control valve V8, a stop valve V9, and an unloading valve VU and a pressure maintaining valve VP.

The first valve V1 (see fig. 3) is a 3-position 5-way proportional solenoid spool valve, and is provided with a first valve first port k11, a first valve second port k12, a first valve third port k13, a first valve fourth port k14, a first valve fifth port k15 and a first valve power connection port e 1; the first valve first port k11 is communicated with a variable pump oil outlet kb2 of a variable pump BB in the forklift transmission system HTS, and the first valve second port k12 is communicated with a variable pump oil inlet kb1 of the variable pump BB in the forklift transmission system HTS.

The internal communication relationship of the first valve V1 at different valve positions is as follows: when the valve is in the left position, the first valve first port k11 is communicated with the first valve fourth port k14, the first valve second port k12 is communicated with the first valve fifth port k15, and the first valve third port k13 is closed; during neutral position, the first valve first port k11 is communicated with the first valve third port k13 and the first valve fourth port k14 at the same time, the first valve second port k12 is communicated with the first valve fifth port k15, at this valve position, along with the movement of the valve core to the right position direction, the communication degree of the first valve first port k11 and the first valve third port k13 is not increased, and the communication degree of the first valve first port k11 and the first valve fourth port k14 is continuously decreased; when the valve is in the right position, the first valve first port k11 is communicated with the first valve third port k13, and the first valve second port k12, the first valve fourth port k14 and the first valve fifth port k15 are all closed; the initial valve position of the first valve V1 is the "left position".

The first valve electricity connecting port e1 is used for receiving first valve electric driving power P1 output by the electronic controller PCU to the first valve V1, the size of the first valve electric driving power P1 can be continuously adjusted from 0-100%, and the size of P1 determines the valve position of the first valve V1: the first valve V1 is in the left position when P1 < a1 is greater than or equal to 0, the first valve V1 is in the middle position when P1 < b1 is greater than or equal to a1, the first valve V1 is gradually moved to the right position along with the gradual increase of P1, and the first valve V1 is in the right position when P1 is greater than or equal to b1 and less than or equal to 100%, wherein: a1 is the starting power of the spool of the first valve V1, b1 is the full stroke power of the spool of the first valve V1, and the specific values of the two are determined by the electromagnetic-mechanical characteristics of the first valve V1.

The second valve V2 (see fig. 4) is a 3-position 5-way manual slide valve, and is provided with a second valve first port k21, a second valve second port k22, a second valve third port k23, a second valve fourth port k24 and a second valve fifth port k25, and a second valve adjustable throttle port J2 is further provided on the oil passage in the valve between the second valve first port k21 and the second valve second port k 22; the first oil port k21 of the second valve is communicated with an oil supply duct OW of other oil devices for the forklift, the second oil port k22 of the second valve is communicated with a fixed displacement pump oil outlet kd2 of a fixed displacement pump DB in a forklift transmission system HTS, the third oil port k23 of the second valve is simultaneously communicated with a fixed displacement pump oil inlet kd1 of the fixed displacement pump DB in the forklift transmission system HTS and the hydraulic oil tank T, the fourth oil port k24 of the second valve is communicated with a first oil port km1 of a motor MD in the forklift transmission system HTS, and the fifth oil port k25 of the second valve is communicated with a second oil port km2 of the motor MD in the forklift transmission system HTS.

The internal communication relationship when the second valve V2 is at different valve positions is as follows: in the neutral position, the first port k21 of the second valve is communicated with the second port k22 of the second valve, the third port k23 of the second valve, the fourth port k24 of the second valve and the fifth port k25 of the second valve are simultaneously closed, and in the valve position, the opening size of the adjustable flow port J2 of the second valve is automatically adjusted by the oil pressure of the first port k21 of the second valve and the second port k22 of the second valve in an internal control mode so as to maintain the oil pressure of the second port k22 of the second valve to be stable; when the valve is in the left position, the second valve second port k22 is communicated with the second valve first port k21 and the second valve fifth port k25 at the same time, the second valve third port k23 is communicated with the second valve fourth port k24, the opening degree of the second valve adjustable orifice J2 can be changed along with the movement of the valve core in the left position direction, and on the premise of maintaining the stable oil pressure at the second valve second port k22, the oil pressure and the flow of the second valve second port k22 flowing to the second valve first port k21 are gradually reduced, and the oil pressure and the flow of the second valve fifth port k25 are gradually increased; when the valve is in the right position, the second valve second port k22 is communicated with the second valve first port k21 and the second valve fourth port k24 at the same time, the second valve third port k23 is communicated with the second valve fifth port k25, the opening degree of the second valve adjustable orifice J2 can be changed along with the movement of the valve core to the right position, and on the premise of maintaining the stable oil pressure at the second valve second port k22, the oil pressure and the flow of the second valve second port k22 flowing to the second valve first port k21 are gradually reduced, and the oil pressure and the flow of the second valve fourth port k24 are gradually increased; the initial valve position of the second valve V2 is "neutral".

The third valve V3 (see fig. 5) is a 3-position 4-way manual slide valve, and is provided with a third valve first oil port k31, a third valve second oil port k32, a third valve third oil port k33 and a third valve fourth oil port k34, a third valve first adjustable throttle port J31 is arranged on the valve internal oil passage between the third valve first oil port k31 and the third valve third oil port k33, and a third valve second adjustable throttle port J32 is arranged on the valve internal oil passage between the third valve first oil port k31 and the third valve third oil port k 33; the first third valve oil port k31 is communicated with an oil port ks1 of a rod cavity of a tilt oil cylinder SG for tilting the forklift mast, the second third valve oil port k32 is communicated with an oil port ks2 of a rodless cavity of the tilt oil cylinder SG for tilting the forklift mast, and the third valve oil port k33 is communicated with a hydraulic oil tank T in a forklift transmission system HTS.

The internal communication relationship when the third valve V3 is at different valve positions is as follows: in the middle position, the first port k31 of the third valve, the second port k32 of the third valve, the third port k33 of the third valve and the fourth port k34 of the third valve are simultaneously closed; when the valve is in the left position, the third valve first port k31 is communicated with the third valve fourth port k34, the third valve second port k32 is communicated with the third valve third port k33, and in the valve position, along with the movement of the valve core in the left position direction, the opening degree of the third valve first adjustable throttle port J31 can be increased, so that the oil hydraulic pressure of the third valve second port k32 flowing to the third valve third port k33 is gradually reduced, and the flow is gradually increased; in the right position, the first port k31 of the third valve is communicated with the third port k33 of the third valve, the second port k32 of the third valve is communicated with the fourth port k34 of the third valve, and in the valve position, the opening degree of the second adjustable throttle port J32 of the third valve can be increased along with the movement of the valve core to the right position, so that the hydraulic pressure of the first port k31 of the third valve flowing to the third port k33 of the third valve is gradually reduced, and the flow is gradually increased; the initial valve position of the third valve V3 is "neutral".

The fourth valve V4 (see fig. 6) is a 3-position 3-way manual sliding valve, the fourth valve V4 is provided with a fourth valve first port k41, a fourth valve second port k42 and a fourth valve third port k43, and a fourth valve adjustable port J4 is further arranged on the valve oil passage between the fourth valve first port k41 and the fourth valve second port k 42; the fourth valve first port k41 is communicated with a lift cylinder working chamber port kd of a lift cylinder DG for lifting a fork of a forklift, the fourth valve second port k42 is simultaneously communicated with a third valve third port k33 and a hydraulic oil tank T, and the fourth valve third port k43 is communicated with a third valve fourth port k34.

The internal communication relationship of the fourth valve V4 at different valve positions is as follows: in the middle position, the fourth valve first port k41, the fourth valve second port k42 and the fourth valve third port k33 are simultaneously closed; the internal communication relationship of the fourth valve V4 is as follows: the fourth valve first port k41 is communicated with the fourth valve second port k42, the fourth valve third port k43 is cut off, and in the valve position, along with the leftward movement of the valve core, the opening degree of the fourth valve adjustable flow port J4 can be increased, so that the oil pressure of the fourth valve first port k41 flowing to the fourth valve second port k42 is gradually reduced, and the flow rate is gradually increased; the internal communication relationship of the fourth valve V4 at the right position is as follows: the fourth valve first port k31 is communicated with the fourth valve third port k43, and the fourth valve second port k42 is cut off; the initial valve position of the fourth valve V4 is "neutral".

The fifth valve V5 is a one-way hydraulic valve, and is provided with a fifth valve first port k51 and a fifth valve second port k52, the fifth valve first port k51 is communicated with the hydraulic oil tank T, and the fifth valve second port k52 is simultaneously communicated with a variable pump suction port kb1 and a first valve second port k12 of a variable pump BB in the forklift transmission system HTS; when the oil pressure at the first port k51 of the fifth valve is greater than the oil pressure at the second port k52 of the fifth valve, the fifth valve V5 is turned on, and otherwise, the fifth valve V5 is turned off.

The reversing valve V6 (see FIG. 7) is a 2-position 4-way electromagnetic reversing slide valve, the reversing valve V6 is provided with a reversing valve first oil port k61, a reversing valve second oil port k62, a reversing valve third oil port k63 and a reversing valve fourth oil port k64, and is also provided with a reversing valve electricity connection port e 6; the first port k61 of the change valve is communicated with the fourth port k14 of the first valve, and the second port k62 of the change valve is communicated with the fifth port k15 of the first valve.

The internal communication relationship when the reversing valve V6 is at different valve positions is as follows: when the valve is in the left position, the first oil port k61 of the reversing valve is communicated with the third oil port k63 of the reversing valve, and the second oil port k62 of the reversing valve is communicated with the fourth oil port k64 of the reversing valve; when the valve is at the right position, the first port k61 of the reversing valve is communicated with the fourth port k64 of the reversing valve, and the second port k62 of the reversing valve is communicated with the third port k63 of the reversing valve; the initial valve position of the direction valve V6 is "left position".

The reversing valve electricity connection port e6 is used for receiving reversing valve electric drive power P6 output by the electronic controller PCU to the reversing valve V6, the reversing valve electric drive power P6 has two states of power supply and power cut, when the reversing valve electric drive power P6 is in the power cut state, the reversing valve V6 is in the left position, and when the reversing valve electric drive power P6 is in the power supply state, the reversing valve V6 is in the right position.

The displacement control valve V7 is a 3-position 3-way electromagnetic proportional spool valve, and is provided with a first oil port k71 of the displacement control valve, a second oil port k72 of the displacement control valve, a third oil port k73 of the displacement control valve and a power connection port e7 of the displacement control valve; the first oil port k71 of the displacement control valve is simultaneously communicated with a fixed displacement pump oil outlet kd2 and a second oil port k22 of a fixed displacement pump DB in a forklift transmission system HTS, the second oil port k72 of the displacement control valve is simultaneously communicated with a second oil port k12 of the first valve, a second oil port k52 of the fifth valve and a variable displacement pump oil inlet kb1 of a variable displacement pump BB in the forklift transmission system, and the third oil port k73 of the displacement control valve is communicated with an adjusting oil cylinder oil port ka of a displacement adjusting oil cylinder AG in the forklift transmission system HTS.

The internal communication relationship when the displacement control valve V7 is at different valve positions is as follows: when the displacement control valve is at a left position, the first oil port k71 of the displacement control valve is cut off, and the second oil port k72 of the displacement control valve is communicated with the third oil port k73 of the displacement control valve; during the middle position, the first port k71 of the displacement control valve is communicated with the second port k72 of the displacement control valve and the third port k73 of the displacement control valve at the same time, and at the valve position, along with the movement of the valve core to the right position direction, the communication degree between the first port k71 of the displacement control valve and the second port k72 of the displacement control valve is gradually reduced, and the communication degree between the first port k73 of the displacement control valve and the third port k73 of the displacement control valve is gradually increased; when the displacement control valve is at the right position, the first oil port k71 of the displacement control valve is communicated with the second oil port k72 of the displacement control valve, and the third oil port k73 of the displacement control valve is cut off; the initial valve position of the displacement control valve V7 is the "left position".

The displacement control valve electric port e7 is used for receiving displacement control valve electric driving power P7 output by the electronic controller PCU to the displacement control valve V7, the size of the displacement control valve electric driving power P7 can be continuously adjusted from 0-100%, and the valve position of the displacement control valve V7 is determined by the size: when P7 is more than or equal to 0 and less than a7, the displacement control valve V7 is in the left position, when a7 is more than or equal to P7 and less than b7, the displacement control valve V7 is in the middle position, and the displacement control valve V7 gradually moves to the right position along with the gradual increase of the displacement control valve electric driving power P7, and when b7 is more than or equal to P7 and less than or equal to 100%, the displacement control valve V7 is in the right position, wherein: a7 is the starting power of the displacement control valve spool, b7 is the full stroke power of the displacement control valve spool, and the specific values of the two are determined by the electromagnetic-mechanical characteristics of the displacement control valve V7.

The flow control valve V8 is an electromagnetic proportional flow control slide valve, and is provided with a first oil port k81 of the flow control valve, a second oil port k82 of the flow control valve and an electric port e8 for connecting the flow control valve; the first port k81 of the flow control valve is communicated with the third port k13 of the first valve, the second port k82 of the flow control valve is simultaneously communicated with the fourth port k34 of the third valve and the third port k43 of the fourth valve, the conducting degree of the first port k81 of the flow control valve and the second port k82 of the flow control valve in the flow control valve V8 is determined by the position of the valve core of the flow control valve, and the conducting degree of the first port k81 of the flow control valve and the second port k82 of the flow control valve is gradually reduced along with the valve core of the flow control valve moving towards the left side until the valve core is completely cut off; the initial state of the flow control valve V8 is "fully on".

The flow control valve electricity connection port e8 is used for receiving flow control valve electric drive power P8 which is output to the 8 th valve V8 by the electronic controller PCU, the size of the flow control valve electric drive power P8 can be continuously adjusted from 0-100%, when the P8 is 0, the flow control valve V8 is in an initial state of 'full conduction', and when the P8 is more than 0 and less than or equal to 100%, the conduction degree of the flow control valve V8 is gradually reduced along with the gradual increase of the P8.

The stop valve V9 is a 2-position 4-way electromagnetic reversing slide valve, the stop valve V9 is provided with a stop valve first oil port k91, a stop valve second oil port k92, a stop valve third oil port k93, a stop valve fourth oil port k94 and a stop valve electric connection port e 9; the first cut-off valve port k91 is communicated with a fourth cut-off valve port k64, the second cut-off valve port k92 is communicated with a fifth cut-off valve port k25 and a second cut-off valve port km2 of a motor MD in a forklift transmission system HTS, the third cut-off valve port k93 is communicated with the third cut-off valve port k63, and the fourth cut-off valve port k94 is communicated with a fourth cut-off valve port k24 and a first cut-off valve port km1 of the motor MD in the forklift transmission system HTS;

the internal communication relationship when the stop valve V9 is at different valve positions is as follows: when the valve is in a left position, the first cut-off valve oil port k91 is communicated with the second cut-off valve oil port k92, and the third cut-off valve oil port k93 is communicated with the fourth cut-off valve oil port k 94; when the valve is at the right position, the first oil port k91, the second oil port k92, the third oil port k93 and the fourth oil port k94 of the stop valve are all cut off; the initial valve position of the stop valve V9 is a left position;

the cut-off valve power connection port e9 is used for receiving cut-off valve electric drive power P9 output to a cut-off valve V9 by an electronic controller PCU, the cut-off valve electric drive power P9 has two states of power supply and power cut-off, and a cut-off valve V9 is in a left position when the cut-off valve electric drive power P9 is in the power cut-off state and a cut-off valve V9 is in a right position when the cut-off valve electric drive power P9 is in the power supply state;

the unloading valve VU is AN external control type pressure relief slide valve, AN unloading valve first oil port ku1, AN unloading valve second oil port ku2 and AN unloading button AN are arranged on the unloading valve VU, the unloading valve first oil port ku1 is communicated with a first valve first oil port k11 and a variable pump oil outlet kb2 of a variable pump BB in a forklift transmission system HTS at the same time, and the unloading valve second oil port ku2 is communicated with a first valve second oil port k12, a fifth valve second oil port k52, a displacement control valve second oil port k72 and a variable pump oil inlet kb1 of the variable pump BB in the forklift transmission system HTS at the same time.

In the unloading valve VU, the conduction degree of a first oil port ku1 of the unloading valve and a second oil port ku2 of the unloading valve is determined by a 'unloading set value pu' of the unloading valve VU and the oil pressure at a first oil port ku1 of the unloading valve VU, when the oil pressure at the first oil port ku1 of the unloading valve is lower than the unloading set value pu, the space between the first oil port ku1 of the unloading valve and the second oil port ku2 of the unloading valve is cut off, when the oil pressure at the first oil port ku1 of the unloading valve reaches or is higher than the unloading set value pu, the first oil port ku1 of the unloading valve and the second oil port ku2 of the unloading valve start to be conducted, and the conduction degree of the first oil port ku1 of the unloading valve is increased along with the rise of the oil pressure at the first oil port ku1 of the unloading valve until the first oil port ku1 of the unloading valve is completely conducted; the initial state of the unloader valve VU is "OFF".

The unloading button AN is a manual button with two positions of pressing and pulling, when the unloading button AN is pressed, the valve inner channel between the first oil port ku1 and the second oil port ku2 of the unloading valve can be completely communicated, and when the unloading button AN is pulled out, the unloading valve VU is in the initial state; the normal position of the unload button AN is "pull out".

The pressure stabilizing valve VP is an external control type pressure relief slide valve, a pressure stabilizing valve first oil port kp1 and a pressure stabilizing valve second oil port kp2 are arranged on the pressure stabilizing valve VP, the pressure stabilizing valve first oil port kp1 is simultaneously communicated with a displacement control valve second oil port k71, a second valve second oil port k22 and a constant delivery pump oil outlet kd2 of a constant delivery pump DB in a forklift transmission system HTS, and the pressure stabilizing valve second oil port kp2 is simultaneously communicated with a second valve third oil port k23, a constant delivery pump oil inlet kd1 of the constant delivery pump DB in the forklift transmission system HTS and a hydraulic oil tank T.

In the pressure stabilizing valve VP, the conduction degree of a first oil port kp1 of the pressure stabilizing valve and a second oil port kp2 of the pressure stabilizing valve is determined by a pressure relief set value pp of the pressure stabilizing valve VP and the oil pressure at a first oil port kp1 of the pressure stabilizing valve VP, when the oil pressure at the first oil port kp1 of the pressure stabilizing valve is lower than the pressure relief set value pp, the connection between the first oil port kp1 of the pressure stabilizing valve and the second oil port kp2 of the pressure stabilizing valve is cut off, when the oil pressure at the first oil port kp1 of the pressure stabilizing valve reaches or is higher than the pressure relief set value pp, the first oil port kp1 of the pressure stabilizing valve and the second oil port kp2 of the pressure stabilizing valve start to be conducted, and the conduction degree of the first oil port kp1 of the pressure stabilizing valve is increased along with the rise of the oil pressure at the first oil port kp1 of the pressure stabilizing valve; the initial state of the pressure maintaining valve VP is "off".

The sensor elements comprise a second valve position sensor Sv2, a third valve position sensor Sv3, a fourth valve position sensor Sv4, a regulating cylinder piston rod position sensor Sag, a variable pump rotating speed sensor Sb, a motor rotating speed sensor Sm, an execution oil pressure sensor So, a braking force sensor Sbr, an accelerator position sensor Sap and a gear position sensor Sgs.

The second valve position sensor Sv2 is a displacement sensor, and the second valve position sensor Sv2 is arranged in cooperation with the second valve V2 and is fixedly arranged on the forklift body CS for monitoring the valve core position of the second valve V2.

The third valve position sensor Sv3 is a displacement sensor, and the third valve position sensor Sv3 and the third valve V3 are cooperatively arranged and fixedly arranged on the forklift body CS, and are used for monitoring the spool position of the third valve V3.

The fourth valve position sensor Sv4 is a displacement sensor, and the fourth valve position sensor Sv4 and the fourth valve V4 are arranged in a matching manner and are fixedly arranged on the forklift body CS, and are used for monitoring the valve core position of the fourth valve V4.

The adjusting oil cylinder piston rod position sensor Sag is a displacement sensor, is matched with an adjusting oil cylinder piston rod AGG in a forklift transmission system HTS, is shown in figure 7, is fixedly arranged on a forklift body CS, and is used for monitoring the length of the adjusting oil cylinder piston rod AGG extending out of a displacement adjusting oil cylinder AG.

The variable pump rotating speed sensor Sb is a rotating speed sensor, and is matched with a variable pump shaft BBZ in a forklift transmission system HTS and fixedly arranged on a forklift body CS for measuring the rotating speed of the variable pump shaft BBZ.

The motor speed sensor Sm is a speed sensor, and the motor speed sensor Sm is matched with a motor shaft MDZ in a forklift transmission system HTS and fixedly arranged on a forklift body CS for measuring the rotating speed of the motor shaft MDZ.

The actuating oil pressure sensor So is a fluid pressure sensor, is arranged on the oil passages of the second oil port k82 of the flow control valve and is simultaneously communicated with the third oil port k34 of the third valve and the third oil port k43 of the fourth valve, and is used for measuring the oil pressure in a lifting cylinder working cavity GQ of a lifting cylinder DG for realizing the lifting operation of a fork frame of the forklift truck and the oil pressure in a tilting cylinder rod cavity YQ or a tilting cylinder rodless cavity WQ of a tilting cylinder SG for realizing the tilting operation of a fork frame of the forklift truck.

The braking force sensor Sbr is a displacement sensor, and the braking force sensor Sbr is matched with a brake pedal of a forklift and fixedly arranged on a forklift body CS for monitoring the stepping depth of the brake pedal.

The accelerator position sensor Sap is a displacement sensor, is matched with a forklift accelerator pedal or an accelerator handle and is fixedly arranged on a forklift body CS for monitoring the trampling depth of the forklift accelerator pedal or the operating position of the accelerator handle.

The gear sensor Sgs is a sensor capable of generating 3 switching signals of ' forward ', neutral ' and ' reverse ', and is fixedly arranged on a forklift body CS and used for monitoring gear signals selected by a forklift driver.

The information screen SC is a plane display device and is used for displaying the related information of the forklift in real time;

the electronic control unit PCU is an electronic device for managing the power of the forklift, receives signals of various sensors in the invention and communicates with the electronic control unit ECU of the forklift engine, processes, calculates, compares and analyzes the received signals, and finishes corresponding power transmission control by giving electric driving power to one or more electromagnetic valves in the invention and sending a coordination control signal to the electronic control unit ECU of the engine after the real-time working condition of the forklift and the operation intention of a driver are clear; the electronic controller PCU is provided with a second valve position sensor interface iv2, a motor rotating speed sensor interface im, an adjusting oil cylinder piston rod position sensor interface iag, a variable pump rotating speed sensor interface ib, a gear sensor interface igs, an accelerator position sensor interface iap, a braking force sensor interface ibr, an engine electronic control unit communication interface iecu, a third valve position sensor interface iv3, an information screen interface isc, a fourth valve position sensor interface iv4 and an execution oil pressure sensor interface iso, and is also provided with a first valve power supply port p1, a reversing valve power supply port p6, a displacement control valve power supply port p7, a flow control valve power supply port p8 and a stop valve power supply port p 9;

the second valve position sensor interface iv2 is connected with a second valve position sensor Sv2 through a signal cable, the motor speed sensor interface im is connected with a motor speed sensor Sm through a signal cable, the adjusting cylinder piston rod position sensor interface iag is connected with an adjusting cylinder piston rod position sensor Sag through a signal cable, the variable pump speed sensor interface ib is connected with a variable pump speed sensor Sb through a signal cable, the gear sensor interface igs is connected with a gear sensor Sgs through a signal cable, the accelerator position sensor interface iap is connected with a valve position sensor Sap through a signal cable, the brake force sensor interface ibr is connected with a brake force sensor Sbr through a signal cable, the engine electric control unit communication interface iecu is connected with a forklift engine electric control unit ECU through a signal cable, the third valve position sensor interface iv3 is connected with a third valve position sensor Sv3 through a signal cable, the information screen interface isc is connected with an information screen SC through a signal cable, the fourth valve position sensor interface iv4 is connected with a fourth valve position sensor Sv4 through a signal cable, and the execution oil pressure sensor interface iso is connected with an execution oil pressure sensor So through a signal cable;

the first valve power supply port p1 is connected with a first valve power supply port e1 through a power transmission cable, and the first valve power supply port p1 outputs proportional control electric driving power; the reversing valve electricity service port p6 is connected with a reversing valve electricity service port e6 through a power transmission cable, and the reversing valve electricity service port p6 outputs switch type electric driving power; the displacement control valve electricity feeding port p7 is connected with a displacement control valve electricity feeding port e7 through an electricity transmission cable, and the displacement control valve electricity feeding port p7 outputs proportional control electric driving power; the flow control valve electricity feeding port p8 is connected with a flow control valve electricity feeding port e8 through a power transmission cable, and the flow control valve electricity feeding port p8 outputs proportional control electric drive power; the cut-off valve electricity supply port p9 is connected with the cut-off valve electricity supply port e9 through an electricity transmission cable, and the cut-off valve electricity supply port p9 outputs switch type control electric drive power.

After the forklift hydraulic transmission control system adopting manual and electronic combined control is carried and applied to the diesel fork truck, the working principle and the operation process are as follows:

1. fork engine start

In order to smoothly start the forklift engine, before the engine is started, it is necessary to ensure that all hydraulic valves in the system are in an 'initial valve position' and the displacement qb of a variable displacement pump in a forklift transmission system is 0, wherein the first valve V1, the reversing valve V6, the displacement control valve V7, the flow control valve V8 and the stop valve V9 are electromagnetic slide valves, all the valves are ensured to be in the initial valve position before the engine is started due to respective electromagnetic-mechanical characteristics, the unloading valve VU and the pressure maintaining valve VP are also ensured to be in the respective initial valve positions before the engine is started due to respective hydraulic-mechanical characteristics, but because the second valve V2, the third valve V3 and the fourth valve V4 are manual slide valves, the respective valve positions before the engine is started are positions when the forklift is finished in the previous work and the engine is shut down; when the vehicle power supply is switched on, the electronic controller PCU is powered on to start working but the engine is not started temporarily, firstly, the electronic controller PCU detects signals of a second valve position sensor Sv2, a third valve position sensor Sv3 and a fourth valve position sensor Sv4 to determine real-time valve positions of a second valve V2, a second valve V3 and a fourth valve V4, if a certain manual valve is not at the initial valve position, the electronic controller PCU transmits relevant information to a message screen to prompt a forklift driver to manually move a relevant slide valve to the initial valve position, then, the engine is started and enters an idling stable operation state, the power of the engine is transmitted to a first shaft Z1 of the forklift transmission system, wherein a part of the power is transmitted to the constant flow pump DB through a first gear C1, a constant flow pump gear HTS and a constant flow pump fixing DBZ to enable the constant flow pump DB to start oil suction from a hydraulic oil tank T through a constant flow pump Cd oil suction port kd1, the oil discharge port kd2 discharges pressure oil and supplies oil to other oil OW devices through a second valve V2, another part of the power transmitted to the first shaft Z1 is transmitted to the variable pump BB through the second gear C2, the variable pump gear Cb, and the variable pump shaft BBZ, but therefore the time variable pump displacement qb is 0, and the variable pump BB does not yet have the oil pumping capacity.

2. Forklift walking, accelerating and decelerating

When the forklift starts, accelerates and decelerates forwards, in an idle state of the forklift, firstly, an 'F' gear is selected on a gear sensor Sgs, then an accelerator pedal is stepped to a certain position, the gear sensor Sgs and an accelerator position sensor Sap send gear selection signals and accelerator pedal stepping position signals to an electronic controller PCU, each accelerator pedal stepping position corresponds to a target value of a forklift driver for controlling the speed, the electronic controller PCU outputs electric driving power P7 of a displacement control valve to a displacement control valve V7 to enable the electric driving power P7 to be more than or equal to a7 to enter a middle position, a first port k71 of the displacement control valve is enabled to be communicated with a second port k72 of the displacement control valve and a third port k73 of the displacement control valve at the same time, a part of pressure oil discharged from an oil discharge port kd2 of a constant displacement pump enters an oil saving control valve V7 from a first displacement control valve k71 of the displacement control valve, and a part of the oil is supplied to an AGH oil supply of a piston AGH of a pair of a cylinder through the third port k73 of the oil control valve, Pushing an adjusting oil cylinder piston rod AGG to extend outwards so as to enable the discharge capacity qb of the variable pump BB to gradually increase from 0 until reaching a qb calibration value corresponding to the stepping position of an accelerator pedal, and judging whether the qb reaches the calibration value or not by an electronic control unit PCU through monitoring signals of an adjusting oil cylinder piston rod position sensor Sag, wherein in the process, the variable pump BB sucks oil from a variable pump oil suction port kb1, discharges the pressure oil from a variable pump oil discharge port kb2, and supplies oil to a first oil port k11 of a first valve, a fourth oil port k14 of the first valve, a first oil port k61 of a reversing valve, a third oil port k63 of the reversing valve, a third oil port k93 of the stop valve and a fourth oil port k94 of the stop valve to a first oil port k1 of the motor, drives a rotor of the motor MD to rotate in the forward direction, and outputs power through a motor shaft MDZ so as to drive the forklift to start and accelerate to the speed corresponding to the stepping position of the accelerator pedal; in the working process of the motor MD, oil flowing out of a second oil port km2 of the motor returns to a variable pump oil suction port kb1 through a second oil port k92 of a stop valve, a first oil port k91 of the stop valve, a fourth oil port k64 of a reversing valve, a second oil port k62 of the reversing valve, a fifth oil port k15 of a first valve and a second oil port k12 of the first valve, and the other part of oil entering a displacement control valve V7 returns to the variable pump oil suction port kb1 through a second oil port k72 of the displacement control valve and the second oil port km2 of the motor to be converged;

when the forklift needs to accelerate after completing forward starting, the stepping depth of an accelerator pedal is continuously increased, and the electronic controller PCU can automatically perform the following operations according to a signal of an accelerator position sensor Sap: firstly, keeping an input rotating speed n1 unchanged (corresponding to the rotating speed of a forklift engine), increasing the electric driving power P7 of a displacement control valve to enable a displacement control valve V7 to move towards the right position direction of the displacement control valve V, increasing the oil supply amount of a regulating cylinder piston AGH, and increasing the displacement qb of a variable pump, so that the oil supply amount of the motor MD by a variable pump BB is increased, the rotating speed of a motor shaft MDZ is increased, and the forklift is accelerated; maintaining the displacement qb of the variable pump unchanged, sending a coordination control signal to an electronic control unit ECU of the engine to control the speed of the engine to be increased, increasing the input rotating speed n1 so as to increase the working rotating speed of the variable pump BB, increase the oil supply of the variable pump BB to the motor MD, increase the rotating speed of a driving motor shaft MDZ and accelerate a forklift; regulating the displacement qb of the variable pump and the rotating speed of the engine simultaneously to increase the oil supply of the motor MD by the variable pump BB, drive the rotating speed of the motor shaft MDZ to rise and accelerate the forklift; specifically, the operation is automatically selected by the electronic controller PCU according to the real-time working condition of the forklift.

When the forklift needs to decelerate at a certain advancing speed, the stepping depth of an accelerator pedal is reduced, and an electronic controller PCU can automatically perform the following operations according to a signal of an accelerator position sensor Sap: firstly, keeping an input rotating speed n1 unchanged, reducing the electric driving power P7 of a displacement control valve to enable a displacement control valve V7 to move towards the left position direction of the displacement control valve, reducing the oil supply amount of an oil-exchanging cylinder piston AGH and reducing the displacement qb of a variable pump, so that the oil supply amount of the variable pump BB to a motor MD is reduced, the rotating speed of a motor shaft MDZ is reduced, and a forklift is decelerated; maintaining the displacement qb of the variable pump unchanged, sending a coordination control signal to an electronic control unit ECU of the engine to control the deceleration of the engine, reducing the input rotating speed n1 and the working rotating speed of a variable pump BB, further reducing the oil supply of the engine to a motor MD, reducing the rotating speed of a motor shaft MDZ and decelerating a forklift; regulating the displacement qb of the variable pump and the rotating speed of the engine simultaneously to reduce the oil supply of the motor MD by the variable pump BB, so that the rotating speed of the motor shaft MDZ is reduced and the forklift is decelerated; specifically, the operation is automatically selected by the electronic controller PCU according to the real-time working condition of the forklift.

When the forklift starts, accelerates and decelerates in a reverse mode, in an idling state of the forklift, firstly, an 'R' gear is selected on a gear sensor Sgs, an electronic controller PCU outputs reversing valve electric drive power P6 to supply power to a reversing valve V6 to move to the right position after receiving a gear selection signal of the gear sensor Sgs, the communication relation between a variable pump oil suction port kb1 and a variable pump oil discharge port kb2 and a first oil port km1 of a motor and a second oil port km2 of the motor is changed, then the stepping depth of an accelerator pedal is gradually increased to a certain position, an accelerator position sensor Sap sends an accelerator pedal position signal to the electronic controller PCU, the electronic controller outputs electric drive power P7 not less than a7 to a displacement control valve V7 to enable the displacement control valve V7 to enter a middle position, the first oil port k71 of the displacement control valve is enabled to simultaneously communicate a second displacement oil port k72 of the displacement control valve and a third displacement control valve k73, a first displacement valve V85k 84 of a pressure of an oil port discharged by a constant displacement pump 46d 84 is controlled by a first displacement control valve 8584, in the process, the variable pump BB sucks oil from a variable pump oil suction port kb1, discharges pressure oil from a variable pump oil discharge port kb2, supplies oil to a motor second oil port km2 through a first valve oil port k11, a first valve fourth oil port k14, a first reversing valve oil port k61, a fourth reversing valve oil port k64, a first stop valve oil port k91 and a second stop valve oil port k92, drives a rotor of the motor MD to rotate reversely, and outputs power to drive the forklift to start and back up and accelerate to the speed corresponding to the stepping position of the accelerator pedal through a motor shaft MDZ; in the working process of the motor MD, oil flowing out of a first oil port km1 of the motor returns to a variable pump oil suction port kb1 through a fourth oil port k94 of a stop valve, a third oil port k93 of the stop valve, a third oil port k63 of a reversing valve, a second oil port k62 of the reversing valve, a fifth oil port k15 of a first valve and a second oil port k12 of the first valve, and the other part of oil entering a displacement control valve V7 is converged with the oil returning to the variable pump oil suction port kb1 through the first oil port km1 of the motor;

when the forklift needs to accelerate after finishing reversing and starting, the stepping depth of the accelerator pedal is continuously increased, and the automatic operation of the electronic controller PCU according to the signal of the accelerator position sensor Sap is the same as that of the forklift when the forklift moves forwards, which is not described herein.

When the forklift needs to decelerate at a certain reversing speed, the stepping depth of an accelerator pedal is reduced, and the automatic operation of the electronic controller PCU according to the signal of the accelerator position sensor Sap is the same as that of the forklift during forward deceleration, which is not described herein any more.

3. Forklift service brake

When the forklift needs braking in the walking process, a driver steps on the brake pedal after loosening the accelerator pedal to forcibly decelerate the forklift. When an accelerator pedal is loosened, the PCU maintains the valve positions of all the valves unchanged according to signals of an accelerator position sensor Sap, and simultaneously sends a coordinated control signal to an engine electronic control unit ECU to enable the engine to decelerate to enter an idling working condition, and the forklift enters a sliding state depending on inertia force; the forklift is driven by a closed hydraulic circuit consisting of a variable pump BB and a motor MD when running, under the action of inertia force, a forklift driving wheel DW drags a rotor of the motor MD to rotate, so that the motor MD has the function of the hydraulic pump, oil output by the motor is supplied to the variable pump BB and then drives the variable pump rotor to rotate, so that the variable pump BB has the function of the hydraulic motor, the engine is in transmission connection with a variable pump shaft BBZ, the rotating speed of the rotor of the variable pump BB is synchronous with the rotating speed of the rotor of the variable pump BB in the process that the engine is lowered to idle speed, so that the engine forms a braking action on the rotor of the motor MZ through the variable pump rotor, and the braking action is transmitted to the forklift driving wheel DW through a forklift traveling transmission chain to generate a braking effect on the forklift; when the brake pedal is stepped on, the stepping depth of the brake pedal corresponds to a target value of the braking force of a driver, the electronic controller PCU reduces the electric driving power P7 of the displacement control valve according to a signal of the braking force sensor Sbr to enable the displacement control valve V7 to move towards the left position of the displacement control valve V, so that the oil supply quantity of the oil exchange cylinder piston AGH through the third oil port k73 of the displacement control valve is reduced, the displacement qb of the variable displacement pump BB is reduced, the braking force formed by the forklift is increased, and the target braking force corresponding to the stepping depth of the brake pedal is achieved.

4. Parking brake for forklift

When the engine runs normally, parking brake is often needed to avoid any movement of the forklift. When parking braking is carried out, a brake pedal is stepped to the maximum depth, the electronic controller PCU reduces the electric driving power P7 of the displacement control valve to 0 according to a signal of the braking force sensor Sbr, the displacement control valve V7 is moved to the left position, the displacement qb of the variable displacement pump BB is reduced to 0, and meanwhile, the stop valve V9 is powered to move to the right position, so that the motor MD is in an oil trapping state due to the fact that two oil ports of the motor MD are all cut off, and a rotor and a forklift driving wheel DW cannot rotate, and therefore parking braking is formed on the forklift.

5. Micro-motion of forklift

The fine motion of the forklift is the small-range adjustment of the position of the forklift in a parking braking state when the forklift is used for loading and stacking articles.

When the forklift moves forwards slightly, the second valve V2 is shifted to the right position from the middle position manually, the second valve second port k22 is enabled to be communicated with the second valve first port k21 and the second valve fourth port k24 at the same time, the second valve fifth port k25 is enabled to be communicated with the second valve third port k23, the electronic controller PCU maintains the valve positions of the valves during parking braking according to the signal of a second valve position sensor Sv2, after pressure oil discharged from the fixed displacement pump oil discharge port kd2 enters the second valve V2 through the second valve second port k22, the pressure oil is respectively supplied to the oil supply gallery OW of other oil using devices through the second valve first port k21, and is supplied to the motor first km1 through the second valve fourth port k24, the MD 1 of the motor enables the rotor of the motor port to rotate forwards and drive the driving wheel DW to move forwards, the hydraulic pressure of the second valve port k 3578 and the hydraulic pressure of the fourth valve 21 of the forklift truck can be adjusted by adjusting the opening 36J 2 at the second valve port DW 35k 24 at the right position of the second valve V2, further adjusting the forward inching speed of the forklift, and moving the second valve V2 back to the middle position after the forklift is in place for inching so as to stop the forward inching of the forklift; in the process of micro-motion advancing of the forklift, oil flowing out of the second oil port km2 of the motor flows back to the hydraulic oil tank T through the fifth oil port k25 of the second valve and the third oil port k23 of the second valve.

When the forklift is reversed by inching, the second valve V2 is shifted to the left position from the left position, the second valve second port k22 is simultaneously communicated with the second valve first port k21 and the second valve fifth port k25, the second valve fourth port k24 is communicated with the second valve third port k23, the electronic controller PCU maintains the valve positions of the valves during parking braking according to the signal of a second valve position sensor Sv2, after pressure oil discharged from the fixed displacement pump oil discharge port kd2 enters the second valve V2 through the second valve second port k22, the oil is respectively supplied to the oil supply channel OW of other oil using devices through the second valve first port k21, and is supplied to the motor second km2 through the second valve fifth port k25, the oil supplied to the motor second 2 enables the rotor of the MD oil port to rotate reversely and drives the driving wheel of the forklift to reverse the forklift, the flow of the second valve port K25 and the hydraulic pressure of the second valve port DW 21 can be adjusted by adjusting the opening degree of the second valve J2 on the left position of the second valve V2, further adjusting the reversing micro-motion speed of the forklift, and moving the second valve V2 back to the middle position to stop the reversing micro-motion of the forklift after the forklift is in micro-motion position; in the process of micro-motion reversing of the forklift, oil flowing out of the first oil port km1 of the motor flows back to the hydraulic oil tank T through the fourth oil port k24 of the second valve and the third oil port k23 of the second valve.

6. Forklift mast inclination

When forklifts fork and stack articles, the inclined posture of the gantry is usually required to be adjusted in a parking or micro-motion state to adapt to relevant operations.

When the portal needs to be tilted forwards, the third valve V3 is manually displaced from the middle position to the right position, the third valve first port k31 is communicated with the third valve third port k33, the third valve second port k32 is communicated with the third valve fourth port k34, the electronic controller PCU maintains the valve positions of the valves during parking braking or fine movement of the forklift according to signals of the third valve sensor Sv3, the first valve electric driving power P1 ≧ b1 is output to the first valve V1 to be displaced from the left position to the right position, the first valve first port k11 is communicated with the first valve third port k13, the first valve second port k12, the first valve fourth port k14 and the first valve fifth port qk 15 to be simultaneously stopped, then the first valve electric driving power P7 ≧ a7 is output to the control valve V7 to be displaced from the left position to the middle position, the displacement of the variable displacement pump BB starts to be increased from 0, the displacement of the first oil outlet of the variable displacement pump Qk 13 is output by the first oil pump 13, the first oil outlet of the first valve 13 k2, The eighth first oil port k81, the flow control valve second oil port k82, the third valve fourth oil port k34, the third valve second oil port k32 and the tilt cylinder second oil port ks2 supply oil to the rodless cavity WQ of the tilt cylinder, the tilt cylinder piston SGH is pushed to move to one side of the rod cavity YQ of the tilt cylinder, the length of the tilt cylinder piston rod SGG extending out of the tilt cylinder SG is increased, and the forklift mast is further tilted forwards, meanwhile, under the action of the tilt cylinder piston SGH, oil in the rod cavity YQ of the tilt cylinder flows back to the hydraulic oil tank T through the first oil port ks1 of the tilt cylinder, the first oil port k31 of the third valve, the second adjustable throttle port J32 of the third valve and the third valve k33, when the mast is tilted in place, the third valve is displaced from the right to the middle position, so that all the oil ports are stopped, and the tilt posture of the mast can be kept unchanged immediately; in the process, the flow limiting effect of the second adjustable throttle opening J32 of the third valve controls the return speed of oil in a rod cavity YQ of the tilt cylinder, the movement of the third valve V3 at the right position can change the opening degree of the second adjustable throttle opening J32 of the third valve, so that the forward tilting speed of the portal frame is controlled, and meanwhile, the electronic controller PCU automatically adjusts the displacement qb of the variable displacement pump BB by adjusting the electric driving power P7 of the displacement control valve according to the monitored signal of the third valve position sensor Sv3, so that the oil supply of the rodless cavity WQ of the tilt cylinder by the variable displacement pump BB is adaptive to the tilting speed of the portal frame.

When the mast needs to be tilted backwards, the third valve V3 is manually displaced from the middle position to the left position, the third valve first port k31 is communicated with the third valve fourth port k34, the third valve second port k32 is communicated with the third valve third port k33, the electronic controller PCU maintains the valve positions of the valves during parking braking or fine movement of the forklift according to signals of the third valve sensor Sv3, outputs first valve electric driving power P1 ≧ b1 to the first valve V1 to be displaced from the left position to the right position, enables the first valve first port k11 to be communicated with the first valve third port k13, the first valve second port k12, the first valve fourth port k14 and the first valve fifth port k15 to be simultaneously stopped, then gradually increases the first valve electric driving power P8 from 0 until the control valve V6 is displaced to the middle position, the displacement b of the variable displacement pump BB starts to be increased from 0, the oil pressure is output, and the first oil discharge pressure of the variable pump BB is discharged through the first oil discharge port qkb 11, The first valve third oil port k13, the eighth first oil port k81, the flow control valve second oil port k82, the third valve fourth oil port k34, the third valve first oil port k31 and the tilt cylinder first oil port ks1 supply oil to the tilt cylinder rod chamber YQ, the tilt cylinder piston SGH is pushed to move to one side of the tilt cylinder rodless chamber WQ, the length of the tilt cylinder piston rod SGG extending out of the tilt cylinder SG is reduced, and the forklift mast is tilted backwards, meanwhile, oil in the tilt cylinder rodless chamber WQ flows back to the hydraulic oil tank T under the action of the tilt cylinder piston SGH through the tilt cylinder second oil port ks2, the third valve second oil port k32, the third valve first adjustable throttle port J31 and the third valve third oil port k33, when the mast is tilted in place, the third valve is moved back to the middle position from the left position to stop all the oil ports, and the instant tilt posture of the mast can be kept unchanged; in the process, the flow limiting effect of the first adjustable throttle opening J31 of the third valve controls the return speed of oil in the rodless cavity WQ of the tilt cylinder, the movement of the third valve V3 at the left position can change the opening degree of the first adjustable throttle opening J31 of the third valve, so that the forward tilting speed of the portal frame is controlled, and meanwhile, the electronic controller PCU automatically adjusts the displacement qb of the variable displacement pump BB by adjusting the electric driving power P7 of the displacement control valve according to the monitored signal of the third valve position sensor Sv3, so that the oil supply of the rod cavity YQ of the tilt cylinder by the variable displacement pump BB is adaptive to the portal frame tilting speed.

After the portal frame is inclined forwards or backwards to a proper position and locked, the electronic controller PCU automatically reduces the electric driving power P7 of the displacement control valve to 0 according to the signal of the third valve position sensor Sv3, so that the displacement qb of the variable pump is adjusted to 0, and the variable pump BB does not output pressure oil any more.

7. Fork lift of fork truck

The forklift is usually operated to fork or stack items at a certain height by adjusting the height of the fork in a parking or jogging state.

When the fork height needs to be raised, the fourth valve V4 is manually displaced from the middle position to the right position, the fourth valve first port k41 is communicated with the fourth valve third port k43, the fourth valve second port k42 is stopped, the PCU maintains the valve positions of the valves when the parking brake or the forklift is slightly moved according to the signal of the fourth valve position sensor Sv4, the first valve electric driving power P1 ≥ b1 is output to the first valve V1 to be simultaneously displaced from the left position to the right position, the first valve first port k11 is communicated with the first valve third port k 6336, the first valve second port k12, the first valve fourth port k14 and the first valve fifth port k15, the first valve electric driving power P7 is gradually increased from 0 until the control valve V7 is displaced to the middle position, the displacement b of the variable displacement pump BB is continuously increased from 0, the oil pressure is output, and the oil pressure of the first oil discharge port of the variable pump BB 23 is discharged through the first oil discharge port kb 23 kb 92, The first valve third oil port k13, the eighth first oil port k81, the flow control valve second oil port k82, the fourth valve third oil port k43, the fourth valve first oil port k41 and the lifting cylinder working chamber oil port kd supply oil to the lifting cylinder working chamber GQ, and pressure oil entering the lifting cylinder working chamber GQ pushes the lifting cylinder piston DGH and the lifting cylinder piston rod DGG to move upwards and enable the fork frame to ascend; in the process of lifting the fork frame, the movement of the fourth valve at the right position reflects the control intention of a driver on the lifting speed of the fork frame, the oil pressure measured by the execution oil pressure sensor So reflects the load size when the fork frame is lifted, the electronic controller PCU automatically adjusts the displacement qb of the variable displacement pump BB according to the monitored signal of the fourth valve position sensor Sv4 and the signal of the execution oil pressure sensor So by adjusting the electric driving power P7 of the displacement control valve So that the oil supply amount of the working chamber GQ of the lifting cylinder is adapted to the control intention of the driver on the lifting speed of the fork frame, simultaneously sends a coordination control signal to the electronic control unit ECU of the engine So that the output torque of the engine is adapted to the actual load when the fork frame is lifted to a target height, and manually returns the fourth valve from the right position to the middle position to stop all oil ports of the fork frame, at the moment, the electronic controller PCU automatically reduces the electric driving power P7 of the displacement control valve to 0 and adjusts the displacement qb of the variable displacement pump to 0 according to the signal of the fourth valve position sensor Sv4, so that the variable displacement pump BB can not output pressure oil any more.

When the height of the fork is required to be reduced, the fourth valve V4 is manually displaced to the left position from the left position, the fourth valve first oil port k41 is enabled to be communicated with the fourth valve second oil port k42, and the fourth valve third oil port k43 is stopped, the electronic controller PCU maintains the valve positions of the valves unchanged when parking braking or fine motion of the forklift is carried out according to the signal of the fourth valve position sensor Sv4, oil in the lifting cylinder working cavity GQ flows back to the hydraulic oil tank T through the lifting cylinder working cavity oil port kd, the fourth valve first oil port k41, the fourth valve adjustable throttle port J4 and the fourth valve second oil port k42, in the descending process of the fork, the fourth valve V4 is moved on the left position of the fourth valve V4, the opening degree of the fourth valve adjustable throttle port J4 can be adjusted, the return speed of the oil in the lifting cylinder working cavity GQ is controlled, and the descending speed of the fork is further controlled; when the fork descends to the target height, the fourth valve moves back to the middle position from the left position, and the fork height can be locked.

8. Combined operation of fork-lift truck

In order to improve work efficiency, the forklift often needs to adjust the inclination of the gantry or the height of the fork carriage in the walking process, which is conventionally called 'walking-working combined operation', and when the forklift is used for engineering working operation, the attitude of the gantry and the height of the fork carriage also need to be adjusted at the same time, which is conventionally called 'gantry-fork carriage combined operation'.

When the forklift is used for walking-operation combined operation, only the adjustment of the posture of the gantry or the height of the fork frame is allowed according to the general driving operation specification of the forklift, and the combined operation of the gantry and the fork frame is only allowed to be carried out under the working condition of parking or micro-motion of the forklift.

When the mast needs to be adjusted forwards or backwards in a combined manner in the forklift traveling process, the third valve V3 is manually moved from the middle position to the right position or the left position, the electronic controller PCU monitors a third valve displacement signal output by the third valve position sensor Sv3, the valve positions of the valves are maintained to be unchanged during traveling, first valve V1 is output first valve electric driving power P1 to enable the first valve V1 to be moved from the left position to the middle position, the first valve first port k11 is enabled to simultaneously communicate with the first valve third port k13 and the first valve fourth port k14, the first valve second port k12 is enabled to communicate with the first valve fifth port k15, variable pump flow Qb discharged from the variable pump second port kb2 enters the first valve V1 through the first valve first port k11 and then is shunted to the first valve third port k13 and the first valve fourth port k14, the driving flow Qd shunted by the first valve fourth port kb 14 is supplied to the first valve MD 58k actuating valve actuating cylinder MD 58k for adjusting the mast traveling attitude of the forklift traveling hydraulic actuator, after the portal frame is adjusted to the right position, the third valve V3 is manually moved back to the middle position from the right position or the left position, and the posture of the portal frame can be locked.

In the process of forklift traveling, when fork lifting adjustment needs to be jointly performed, the fourth valve V4 is manually shifted from the middle position to the right position, the electronic controller PCU monitors a fourth valve shift signal output by the fourth valve position sensor Sv4, then the valve positions of the valves are maintained unchanged during traveling, first valve V1 is output first valve electric driving power P1 to enable the first valve V1 to shift from the left position to the middle position, a first valve first port k11 is enabled to simultaneously communicate with a first valve third port k13 and a first valve fourth port k14, a first valve second port k12 is enabled to communicate with a first valve fifth port k15, variable pump flow Qb discharged from a variable pump second port kb2 enters a first valve V1 through the first valve first port k11 and then is shunted to a first valve third port k13 and a first valve fourth port k14, the flow Qd shunted by a first valve fourth port kb 14 drives a flow Qd to drive a first valve V1 to drive a fork lifting actuator MD lift cylinder to adjust the fork lift cylinder MD lift cylinder 13, after the fork is lifted to the target position, the height of the fork can be locked by manually displacing the fourth valve V4 from the right position to the middle position; in the process of running of the forklift, when the fork frame descending adjustment needs to be jointly carried out, the fourth valve V4 is directly moved into the left position from the left position manually, after the fork frame is lowered to the target position, the fourth valve V4 is manually moved back to the middle position from the right position, and then the height of the fork frame can be locked, in the process, the electronic controller PCU monitors a fourth valve displacement signal output by the fourth valve position sensor Sv4, and the valve positions of the valves are kept unchanged during running.

In the combined operation process, the electronic controller PCU monitors signals of the accelerator position sensor Sap, the third valve position sensor Sv3, the fourth valve position sensor Sv4, the adjusting cylinder piston rod position sensor Sag, the variable pump rotation speed sensor Sb, the motor rotation speed sensor Sm and the execution oil pressure sensor So in real time, reasonably distributes the traveling drive flow Qd and the actuator flow Qop by the variable pump flow Qb by adjusting the first valve electric drive power P1 to the first valve V1 and the eighth electric drive power P8 to the flow control valve V8, and simultaneously adjusts the variable pump discharge Qb by adjusting the displacement control valve electric drive power P7 to the displacement control valve V7 and sends a coordination control signal to the engine electronic control unit ECU to adjust the output rotation speed and the torque of the engine, So that the variable pump flow Qb and the oil pressure can meet the pressure oil parameters required by the combined operation.

According to the general driving operation specification of the forklift, the combined operation of the gantry and the fork frame is only carried out in the parking state of the forklift. When the combined operation of the gantry and the fork frame is performed, no matter the lifting or descending operation of the fork frame is performed in the process of adjusting the attitude of the gantry, or the adjustment of the attitude of the gantry is performed in the process of adjusting the height of the fork frame, as long as the third valve V3 and the fourth valve V4 are correspondingly and manually controlled, the specific implementation process of the system is the same as that of the processes of tilting the gantry of the forklift and lifting the fork frame of the forklift, and the detailed description is omitted here.

9. Fork truck parking brake

The parking brake is a brake that is required to prevent the forklift from moving after the engine is turned off.

Before the engine is shut down, no matter which valve position the second valve V2 is in, the second valve V2 is manually positioned in a middle position, the fourth oil port k24 of the second valve and the fifth oil port k25 of the second valve are all cut off, a channel between the first oil port km1 of the motor and the second oil port km2 of the motor is completely interrupted, so that oil cannot flow, the motor is in an oil trapping brake state that a rotor of the motor cannot rotate, parking brake force is formed on a forklift driving wheel DW, and then the engine is shut down.

10. Fault trailer

When the forklift fails to move autonomously, a rescue trailer needs to be implemented.

When the forklift needs to be towed in a fault, the second valve V2 is manually moved to the left position or the right position, the unloading button AN of the unloading valve VU is pressed simultaneously, the valve inner channel between the first oil port ku1 of the unloading valve and the second oil port ku2 of the unloading valve is completely communicated, the oil inlet kb1 of the variable pump is completely communicated through the oil way between the unloading valve VU and the oil outlet kb2 of the variable pump, the rotor of the variable pump BB can freely rotate, the first oil port km1 of the motor is completely communicated through the oil way between the second valve V2 and the second oil port 2 of the motor, the rotor of the motor MD can freely rotate, the brake on the forklift is released, and the forklift can be towed.

11. Fork truck real-time information display

Once the forklift engine is started, the information screen SC is automatically powered on, and relevant operations selected by a driver, the working state corresponding to the forklift, error correction and other information are displayed in real time during forklift operation.

In conclusion, the invention realizes independent oil supply of the variable pump to the forklift running or operation execution module by controlling the valve position of the first valve, effectively avoids the interaction influence of hydraulic working parameters among different modules, and greatly reduces the control difficulty of the hydraulic working parameters of each module. Because the closed hydraulic transmission system consisting of the variable pump and the bidirectional constant displacement motor is adopted in the forklift walking transmission chain, the transmission ratio of the pump to the motor is the ratio of the displacement of the constant displacement motor to the real-time displacement of the variable pump, through the adjustment of the displacement of the variable pump, the transmission ratio which is continuously changed from less than 1 to hundreds of times can be formed between the variable pump and the motor, the transmission ratio can be quickly well matched with the power requirements of working conditions such as starting, acceleration and uphill of the forklift under different loads, stepless speed change and accurate speed control can be realized in the conventional driving process of the forklift, and if the bidirectional constant displacement motor is replaced by the bidirectional variable displacement motor, the coverage range of the continuously changed transmission ratio between the bidirectional constant displacement motor and the bidirectional variable displacement motor can be larger. Under the working condition of forklift running, in a forward and reverse transmission closed hydraulic loop formed between the variable pump and the motor, oil discharged by the motor has certain oil pressure and directly enters an oil suction port of the variable pump, so that the pressure difference between a variable pump suction port and an oil discharge port can be reduced, the volumetric efficiency of the variable pump is improved, and the power consumption is reduced. When the forklift carries out engineering operation, the accurate control of the tilting speed and the tilting posture of the forklift gantry can be realized by adjusting the displacement of the variable pump and controlling the valve position of the third valve, and the accurate control of the position of the forklift gantry can be realized by adjusting the displacement of the variable pump, controlling the valve position of the fourth valve and adjusting the adjustable orifice of the fourth valve. Through controlling the second valve position, utilize the pressure fluid that the constant delivery pump provided, can make fork truck go on the fine motion forward, backward at the engineering operation in-process, because the variable delivery pump provides the required hydraulic power of engineering operation alone this moment, fork truck fine motion power then is provided by the constant delivery pump, two hydraulic transmission routes are completely independent, mutual noninterference, are favorable to accurate control fork truck fine motion, also are convenient for carry out fork truck fine motion and engineering operation's combined operation simultaneously. Under the fork truck walking operating mode, in the closed hydraulic transmission system is constituteed with the motor to the variable pump, utilize the displacement change direct control speed of a motor's height, thereby fork truck reduces the variable pump discharge capacity gradually under certain speed of a motor and can make fork truck constantly slow down and produce the braking effect, thereby the fluid passageway between the first hydraulic fluid port of motor and the second hydraulic fluid port has been blocked when the variable pump discharge capacity is 0, make the motor be in "stranded oil" state and unable rotation, produce parking braking effect to fork truck. Under the flameout state of the forklift engine, all valve elements are in the initial valve position, the displacement of the variable pump is 0, and at the moment, the motor is trapped in oil to generate the parking brake effect on the forklift.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

In the description herein, numerous specific details are provided, such as examples of components and/or methods, to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that an embodiment of the invention can be practiced without one or more of the specific details, or with other apparatus systems, assemblies, methods, components, materials, parts, and/or the like. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of embodiments of the invention.

Reference throughout this specification to "one embodiment," "an embodiment," or "a specific embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment, and not necessarily all embodiments, of the present invention. Thus, appearances of the phrases "in one embodiment," "in an embodiment," or "in a specific embodiment" in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics of any specific embodiment of the present invention may be combined in any suitable manner with one or more other embodiments. It is to be understood that other variations and modifications of the embodiments of the invention described and illustrated herein are possible in light of the teachings herein and are to be considered as part of the spirit and scope of the present invention.

It will also be appreciated that one or more of the elements shown in the figures can also be implemented in a more separated or integrated manner, or even removed for inoperability in some circumstances or provided for usefulness in accordance with a particular application.

Additionally, any reference arrows in the drawings/figures should be considered only as exemplary, and not limiting, unless otherwise expressly specified. Further, as used herein, the term "or" is generally intended to mean "and/or" unless otherwise indicated. Combinations of components or steps will also be considered as being noted where terminology is foreseen as rendering the ability to separate or combine is unclear.

As used in the description herein and throughout the claims that follow, "a," "an," and "the" include plural references unless otherwise indicated. Also, as used in the description herein and throughout the claims that follow, the meaning of "in …" includes "in …" and "on …" unless otherwise indicated.

The above description of illustrated embodiments of the invention, including what is described in the abstract of the specification, is not intended to be exhaustive or to limit the invention to the precise forms disclosed herein. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes only, various equivalent modifications are possible within the spirit and scope of the present invention, as those skilled in the relevant art will recognize and appreciate. As indicated, these modifications may be made to the present invention in light of the foregoing description of illustrated embodiments of the present invention and are to be included within the spirit and scope of the present invention.

The systems and methods have been described herein in general terms as the details aid in understanding the invention. Furthermore, various specific details have been given to provide a general understanding of the embodiments of the invention. One skilled in the relevant art will recognize, however, that an embodiment of the invention can be practiced without one or more of the specific details, or with other apparatus, systems, assemblies, methods, components, materials, parts, and/or the like. In other instances, well-known structures, materials, and/or operations are not specifically shown or described in detail to avoid obscuring aspects of embodiments of the invention.

Thus, although the present invention has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and it will be appreciated that in some instances some features of the invention will be employed without a corresponding use of other features without departing from the scope and spirit of the invention as set forth. Thus, many modifications may be made to adapt a particular situation or material to the essential scope and spirit of the present invention. It is intended that the invention not be limited to the particular terms used in following claims and/or to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include any and all embodiments and equivalents falling within the scope of the appended claims. Accordingly, the scope of the invention is to be determined solely by the appended claims.

Claims

1. A forklift hydraulic drive system, comprising:

and the displacement control valve is positioned between the second liquid supply oil path and the displacement control oil path, is used for controlling connection/disconnection of the second liquid supply oil path and the displacement control oil path, and is configured to enable the opening degree of a control port of the displacement control valve to be continuously adjustable.

2. The forklift hydraulic drive system of claim 1, wherein the first valve is configured to further have:

3. The forklift hydraulic transmission system according to claim 1, wherein a reversing valve is provided on the travel driving oil path, and the reversing valve is configured to change a flow direction of oil flowing through the hydraulic motor when the travel driving oil path communicates with the first liquid supply oil path, so as to switch the hydraulic motor between forward rotation and reverse rotation.

4. The forklift hydraulic transmission system according to claim 3, wherein a cut-off valve is further provided on the travel driving oil path, the cut-off valve is configured to connect or disconnect an oil path between the directional control valve and the hydraulic motor, and when the oil path between the directional control valve and the hydraulic motor is disconnected, both oil ports of the hydraulic motor are simultaneously cut off to place the hydraulic motor in an oil trapping state.

5. The hydraulic transmission system of the forklift truck as recited in claim 1, wherein the station I of the second valve comprises a sub-station Ia and a sub-station Ib, and when the second valve is switched between the sub-station Ia and the sub-station Ib, the flow direction of the oil output from the second oil supply circuit can be changed when the oil flows through the hydraulic motor, so that the forward and reverse rotation of the hydraulic motor can be switched.

6. The forklift hydraulic drive system of claim 1, wherein when the second valve is in the station II, both ports of the hydraulic motor are simultaneously blocked to place the hydraulic motor in a trapped state.

7. The forklift hydraulic transmission system according to claim 4, wherein the operation control oil passage includes a first branch oil passage and a second branch oil passage, the first branch oil passage and the second branch oil passage are arranged in parallel, the first branch oil passage is connected to the tilt cylinder, and a third valve is provided on the first branch oil passage, the third valve being configured to control the tilt cylinder to switch between three stations, i.e., an extension station, a shortening station, and a pressure maintaining station; the second branch oil way is connected with the lifting oil cylinder, a fourth valve is arranged on the second branch oil way, and the fourth valve is configured to control the lifting oil cylinder to be switched among three stations of lifting, descending and pressure maintaining.

8. The forklift hydraulic drive system of claim 7, wherein a flow control valve is further provided on the operation control oil passage, the flow control valve being configured to have a continuously adjustable opening of the transfer passage to control the flow of oil from the first oil supply passage to the operation control oil passage.

9. The forklift hydraulic transmission system according to claim 1, wherein an unloading valve is disposed between two oil ports of the variable displacement pump, the unloading valve is configured to communicate the two oil ports of the variable displacement pump when the oil pressure of the first liquid supply oil path reaches a preset value, and an unloading button for manually controlling the on/off of the unloading valve is further disposed on the unloading valve.

10. A forklift transmission control system applied to the forklift hydraulic transmission system according to claim 8, wherein the first valve, the displacement control valve, the reversing valve, the stop valve and the flow direction control valve are electromagnetic slide valves; the second valve, the third valve and the fourth valve are manual slide valves;

the forklift transmission control system comprises: