CN110001390B - Transmission system and control method - Google Patents

Abstract

The invention relates to the technical field of vehicles, in particular to a transmission system and a control method thereof, wherein the transmission system comprises an engine, a hydraulic pump, a hydraulic motor, a clutch, a main speed reduction mechanism, a differential mechanism and two half axle assemblies, the hydraulic pump is configured to be in transmission connection with the engine, two output ports of the hydraulic motor are respectively connected with two output ports of the hydraulic pump, the hydraulic motor and the hydraulic pump form a closed loop, one end of the clutch is connected with the hydraulic motor, the other end of the clutch is connected with the input end of the main speed reduction mechanism, the output end of the main speed reduction mechanism is connected with the differential mechanism, the differential mechanism is respectively connected with the two half axle assemblies, and the two half axle assemblies are respectively used for driving front wheels at two ends of a front bridge to rotate. The control method of the transmission system is applicable to the transmission system.

Description

Transmission system and control method

Technical Field

The invention relates to the technical field of vehicles, in particular to a transmission system and a control method thereof.

Background

For work vehicles, such as graders, bulldozers, etc., work is pulled through a driveline.

Taking a land leveler as an example, when the land leveler works flatly, the shovel blade is generally at a certain angle with the advancing direction of the whole machine so as to enable materials in front of the shovel blade to be in a rolling state, and the working resistance of the shovel blade is reduced; the front material of the shovel blade has a certain lateral force on the whole machine, and in order to eliminate part of the lateral force and reduce the sideslip phenomenon of the front axle tyre, the tyre inclination of the front axle is generally controlled to counteract part of the sideslip force. In narrow work sites, the turning radius can be further reduced by steering the front wheels and tilting the front wheels. Under the working conditions of slope operation or side ditch scraping and the like, the front wheel tilting function can enable the tire to be vertical to the horizontal plane, and the operation stability is enhanced, so that the front axle of the existing grader generally comprises three composite functions of front wheel steering, front wheel tilting and front axle swinging.

Meanwhile, the working device is pushed by traction force of machine walking, in the prior art, most land levellers are driven by rear axle wheels, and the front axle only has steering function and does not drive traction force. The maximum traction force of the grader is only determined by the rear axle wheel load and the attachment coefficient, and the front axle load of the grader generally accounts for about 30% of the weight of the whole grader, so that about 30% of the traction force of the grader is not exerted. And when the grader works in a fine leveling working condition, the requirements on the road surface flatness are higher, the road surface flatness is damaged due to the fact that the track is formed on the leveled road surface due to overlarge driving moment of the rear wheels when the common rear wheel is driven in the fine leveling working condition, the phenomenon is avoided when the front wheels are driven in an independent driving mode, the rear wheels are in neutral positions, the whole grader is towed by the front wheels, and the rear wheels cannot damage the road surface leveled by the road surface.

In order to meet the use requirements of the grader under different working conditions, a front wheel auxiliary driving system and a control scheme thereof are adopted in the prior art, and a double-pump and double-motor driving mode is adopted, so that front axle driving is realized by adding double low-speed large-torque motors (or motors and speed reducers) at two ends of a front axle and a hydraulic pump in the whole machine, and the traction force of the whole machine is improved. The double pump + double motor scheme can solve the problem that the motor rotation speed is unequal to the left and right when the front wheels are not loaded equally under certain conditions (such as during slope operation), so that the straight running of the grader is difficult to ensure, and the different flow and pressure requirements of the left and right front wheels during turning can be met by adjusting and controlling the displacement of the double pumps, but in order to realize the control of different displacement of the double pumps during wheel turning and whole machine articulated steering, a front wheel steering angle sensor and an articulated steering angle sensor are required to be added, and the cost is relatively high and is relatively complex in the aspects of straight running, differential speed, steering control and the like.

The second adopts the double motor scheme of single pump, it is lower to compare double pump + double motor scheme cost, but because the motor adopts the parallel mode, can cause the motor rotational speed inequality and hardly guarantee the straight line of grader and travel problem about the front wheel load inequality about, it is relatively poor simultaneously to be in the front wheel adhesion coefficient of certain side, when slipping appears, it is too much overspeed to cause the motor flow distribution of slipping side easily, and the other side wheel does not drive, thereby lead to the loss of drive traction, and when turning to, turn to inboard wheel rotational speed is low, wheel resistance is great, and turn to outside wheel rotational speed is fast, wheel resistance is less, the required flow is different, because the motor is parallelly connected about, the motor pressure is the same about, it is difficult to realize the differential about when making turns, control effect is unsatisfactory, inefficiency, only can realize two modes of full drive and rear drive, and can not adjust the advance rate according to operating mode demand under the full drive mode, thereby lead to result in the circulating power loss is big.

Disclosure of Invention

The invention aims at: the transmission system and the control method thereof are provided for solving the problem that the cost is high because the transmission system of the engineering vehicle adopts double pumps and double motors or single pump and double motors to drive front axle wheels in the prior art.

In one aspect, the present invention provides a transmission system comprising:

the device comprises an engine, a precursor mechanism and a rear drive mechanism;

the rear drive mechanism comprises a gearbox in transmission connection with the engine, a transmission shaft in connection with a first power taking port of the gearbox, and a drive rear axle in connection with the transmission shaft, wherein the drive rear axle is used for driving rear wheels to rotate;

the front driving mechanism comprises a hydraulic pump connected with a second power taking port of the gearbox, a hydraulic motor which forms a closed loop with the hydraulic pump, a clutch with one end connected with the hydraulic motor, a main speed reduction mechanism connected with the other end of the clutch, a differential mechanism connected with the output end of the main speed reduction mechanism, and two half shaft assemblies connected with the differential mechanism, wherein the two half shaft assemblies are respectively used for driving front wheels at two ends of a front bridge to rotate.

As a preferable mode of the transmission system, the hydraulic pump is a variable pump, the transmission system further comprises a pump control assembly, the pump control assembly is used for controlling the inclination angle of a swash plate of the variable pump, the hydraulic motor is a variable motor, and the transmission system further comprises a motor control assembly, and the motor control assembly is used for controlling the inclination angle of the swash plate of the variable motor.

As a preferred embodiment of the transmission system, the transmission system further comprises a parking brake for preventing or allowing power transmission between the propeller shaft and the rear drive axle.

In another aspect, the present invention provides a method for controlling a transmission system, which is applicable to any one of the transmission systems in the above aspects, wherein a brake mechanism driven by oil pressure is provided on a rear wheel, and the method includes:

selecting a driving mode, wherein the driving mode comprises a precursor mode, a rear-drive mode and a full-drive mode;

if the precursor mode is selected, judging whether a precursor mode starting condition is met, and if the precursor mode starting condition is met, only the precursor mechanism is in transmission connection with the engine;

the precursor mode starting conditions include: judging whether the whole machine is in a stop state, judging whether the gear of the gearbox is in the middle position, judging whether a parking brake is released, and acquiring the braking pressure Pb1 of the rear wheels and comparing the braking pressure Pb with the preset braking pressure Pb preset in the controller;

the precursor mode start condition is satisfied only when the complete machine is in a stopped state, the gear of the transmission is in a neutral position, the parking brake is released, and Pb1 < Pb all occur.

As a preferred embodiment of a control method of a transmission system, the control method of a transmission system further includes;

setting the rotation speed of the front wheels;

the controller adopts a PID algorithm to adjust the rotating speed of the front wheels to the rotating speed of the set front wheels through a pump control assembly and a motor control assembly.

6. The method of claim, further comprising, prior to determining whether a precursor mode start condition is met:

collecting oil pressure P1 of a low-pressure side in a closed loop of a hydraulic pump and a hydraulic motor;

the controller compares P1 with a preset oil pressure P;

if P1 > P, judging whether the precursor mode starting condition is satisfied.

As a preferred scheme of the control method of the transmission system, if a full-drive mode is selected, judging whether a full-drive mode starting condition is met, and if the full-drive mode starting condition is met, driving and connecting a rear drive mechanism and a front drive mechanism with the engine;

the full-drive mode starting conditions include: judging whether the parking brake is released, judging whether the gear of the gearbox is in the middle position, acquiring the braking pressure Pb2 of the rear wheel and comparing the braking pressure Pb 'with the preset braking pressure Pb' preset in the controller, and acquiring the rotating speed N1 of the front wheel and comparing the rotating speed N of the front wheel with the preset rotating speed N of the front wheel preset in the controller;

The all-drive mode start condition is satisfied only when the parking brake is released, the gear of the transmission is not in neutral, pb2 < Pb', and N1 < N all occur.

As a preferable scheme of the control method of the transmission system, if the starting condition of the full-drive mode is met, judging whether the running direction and the gear direction of the whole transmission system are the same;

if the two types of the engine are the same, the rear drive mechanism and the front drive mechanism are both in driving connection with the engine; if not, after waiting for the time T1, the back driving mechanism and the front driving mechanism are both in driving connection with the engine.

As a preferable mode of the control method of the transmission system, after the rear drive mechanism and the front drive mechanism are both in driving connection with the engine, the control method of the transmission system further includes:

setting a rotation speed ratio S of the front wheels and the rear wheels;

the rotational speed n2 of the rear wheels is obtained, and the controller adjusts the rotational speed of the front wheels to n3 through a pump control assembly and a motor control assembly by adopting a PID algorithm, wherein n3 = S x n2.

As a preferable mode of the control method of the transmission system, after the rotation speed of the front wheels is adjusted to n3, the control method of the transmission system further includes:

Acquiring the rotating speed n4 of the front wheel;

judging whether n4 is equal to 0;

if the time T2 of n4 which is continuously equal to 0 is greater than or equal to the preset time T preset in the controller, the full-drive mode is switched to the rear-drive mode, and the engine is in transmission connection with the rear-drive mechanism only.

As a preferred embodiment of the control method of the transmission system, the control method of the transmission system further includes:

if n4 is not equal to 0 or T2 is less than T, acquiring the oil temperature T of the high-pressure side in the closed loop of the hydraulic pump and the hydraulic motor and comparing the oil temperature T with a preset oil temperature T1 preset in the controller;

if t is more than or equal to t1 and S is more than or equal to 1; the rotation speed ratio of the front wheels to the rear wheels is adjusted to be S1, and S1 is smaller than 1;

and acquiring the rotating speed n5 of the rear wheel, and controlling the speed of the front wheel to n6 by a controller through the pump control assembly and the motor control assembly by adopting a PID algorithm, wherein n6 = S1 x n5.

The beneficial effects of the invention are as follows:

the invention provides a transmission system which comprises an engine, a hydraulic pump, a hydraulic motor, a clutch, a main speed reduction mechanism, a differential and two half shaft assemblies. The hydraulic pump is configured to be in transmission connection with the engine, and two output ports of the hydraulic motor are respectively connected with two output ports of the hydraulic pump, and the hydraulic motor and the hydraulic pump form a closed loop, and one end of the clutch is connected with the hydraulic motor, and the other end of the clutch is connected with the input end of the main speed reduction mechanism, and the output end of the main speed reduction mechanism is connected with the differential mechanism, and the differential mechanism is respectively connected with two half axle assemblies which are respectively used for driving front wheels at two ends of the front bridge to rotate. Compared with the prior art, the transmission system can drive the front wheels to rotate through the hydraulic pump and the hydraulic motor, and the cost can be effectively reduced.

Drawings

FIG. 1 is a schematic diagram of a transmission system according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a hydraulic system in a transmission system according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a front axle according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a front axle according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a front axle according to an embodiment of the present invention;

FIG. 6 is a schematic view of a grader according to an embodiment of the present invention;

FIG. 7 is a flowchart of a method of controlling a transmission system according to an embodiment of the present invention;

FIG. 8 is a second flowchart of a control method of the transmission system according to the embodiment of the present invention;

fig. 9 is a flowchart of a control method of the transmission system according to the embodiment of the present invention.

In the figure:

1. an engine; 2. a hydraulic pump; 3. a hydraulic motor; 4. a clutch; 5. a main speed reducing mechanism; 6. a differential;

7. a half shaft assembly; 71. differential half shafts; 72. a left cross shaft; 73. a hinged fork; 74. a right cross; 75. a speed reducer half shaft;

8. a front bridge; 9. a wheel-side speed reducing mechanism; 10. a gearbox; 11. a transmission shaft; 12. driving a rear axle; 13. a parking brake;

14. a first electro-hydraulic servo valve; 141. a first control end; 142. a second control end; 15. a first variable cylinder;

16. A second electro-hydraulic servo valve; 161. a third control end; 17. a second variable oil cylinder;

18. a flush valve; 19. flushing the overflow valve;

20. a make-up pump; 21. a one-way valve assembly; 22. an oil-compensating overflow valve; 23. a filter;

24. a third electro-hydraulic servo valve; 241. a fourth control end;

25. a left inclined frame; 26. a right inclined frame; 27. tilting the oil cylinder; 28. a tilt pull rod; 29. a left knuckle; 30. a right knuckle; 31. a left steering cylinder; 32. a right steering cylinder; 33. a steering tie rod.

Detailed Description

The following description of the embodiments of the present invention will be made apparent and fully in view of the accompanying drawings, in which some, but not all embodiments of the invention are shown. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, are merely for convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. Wherein the terms "first position" and "second position" are two different positions.

In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.

Referring to fig. 1 to 5, the present embodiment provides a transmission system, which includes an engine 1 and a front driving mechanism, wherein the front driving mechanism includes a hydraulic pump 2, a hydraulic motor 3, a clutch 4, a main reducing mechanism 5, a differential 6, and two half shaft assemblies 7. The hydraulic pump 2 is configured to be in transmission connection with the engine 1, the hydraulic motor 3 and the hydraulic pump 2 form a closed loop, one end of the clutch 4 is connected with the hydraulic motor 3, the other end of the clutch 4 is connected with the input end of the main speed reduction mechanism 5, the differential mechanism 6 is connected with the output end of the main speed reduction mechanism 5 and respectively connected with two half shaft assemblies 7, and the two half shaft assemblies 7 are respectively used for driving front wheels at two ends of the front bridge frame 8 to rotate.

In this embodiment, the rotation of the engine 1 drives the hydraulic pump 2 to rotate, the hydraulic pump 2 drives the hydraulic motor 3 to rotate, the hydraulic motor 3 outputs power to the main speed reduction mechanism 5 through the clutch 4, the power is transmitted to the two half shaft assemblies 7 through the differential mechanism 6 after the power is reduced through the main speed reduction mechanism 5, and the two half shaft assemblies 7 drive the front wheels to rotate. The clutch 4 is then used to control the transmission or disconnection of power between the hydraulic motor 3 and the final drive mechanism 5. Therefore, the transmission system can drive the front wheels to rotate through the hydraulic pump 2 and the hydraulic motor 3, and the cost can be effectively reduced.

The hydraulic pump 2 is a variable pump, the transmission system further comprises a pump control assembly, and the pump control assembly is used for controlling the inclination angle of a swash plate of the hydraulic pump 2, so that the displacement of the hydraulic pump 2 can be controlled. The pump control assembly comprises a first electrohydraulic servo valve 14 and a first variable oil cylinder 15, wherein the first electrohydraulic servo valve 14 is used for controlling the piston rod of the first variable oil cylinder 15 to move, and the piston rod of the first variable oil cylinder 15 is connected with a swash plate of the variable pump.

Specifically, control oil is accessed by an oil inlet of a first electrohydraulic servo valve 14, two oil outlets of the first electrohydraulic servo valve 14 are respectively connected with a first cavity and a second cavity of a first variable oil cylinder 15, and a piston rod of the first variable oil cylinder 15 is connected with a swash plate of a variable pump. The two ends of the first electrohydraulic servo valve 14 are respectively provided with a first control end 141 and a second control end 142, and the first control end 141 and the second control end 142 are electromagnetic relays; the first electro-hydraulic servo valve 14 includes three operating positions, a first operating position, a neutral position, and a second operating position. When only the first control end 141 is powered on, the first electrohydraulic servo valve 14 is located at the first working position, and the first cavity is filled with oil and the second cavity is drained; when only the second control end 142 is powered on, the first electro-hydraulic servo valve 14 is located at the second working position, and at this time, the first cavity discharges oil, and the second cavity feeds oil; when both the first control end 141 and the second control end 142 are powered off, at this time, both the first cavity and the second cavity drain, the first electrohydraulic servo valve 14 is located at the middle position, and the variable pump runs idle. When the first control end 141 is powered on, the variable pump rotates positively, and when the second control end 142 is powered on, the variable pump rotates reversely, so that switching is performed between the power on of the first control end 141 and the power on of the second control end 142, and the change of the pumping direction of the variable pump can be realized; the flow of hydraulic oil entering the first cavity or the second cavity of the variable piston through the oil inlet of the first electrohydraulic servo valve 14 can be controlled by controlling the current magnitude of the first control end 141 or the second control end 142, so that the inclination amplitude of the swash plate is controlled, and the displacement of the variable pump is adjusted.

It should be noted that in the present embodiment, when only the first control end 141 is powered, the hydraulic pump 2 drives the hydraulic motor 3 to drive the front wheels to rotate forward, and when only the second control end 142 is powered, the hydraulic pump 2 drives the hydraulic motor 3 to drive the front wheels to rotate backward.

The hydraulic motor 3 is a variable motor, and the transmission system further comprises a motor control assembly for controlling the inclination angle of the swash plate of the hydraulic motor 3. The motor control assembly comprises a second electrohydraulic servo valve 16 and a second variable oil cylinder 17, wherein the second electrohydraulic servo valve 16 is used for controlling the extension or retraction of a piston rod of the second variable oil cylinder 17, and the piston rod of the second variable oil cylinder 17 is connected with a swash plate of the variable motor.

The second electrohydraulic servo valve 16 and the second variable cylinder 17 may be configured to have the same structures as the first electrohydraulic servo valve 14 and the first variable cylinder 15, respectively, and in this embodiment, the second electrohydraulic servo valve 16 and the second variable cylinder 17 have different structures from the first electrohydraulic servo valve 14 and the first variable cylinder 15, respectively. Specifically, the second electrohydraulic servo valve 16 is a two-position three-way valve, which comprises an A working position and a B working position, a rod cavity and a rodless cavity are arranged on the second variable cylinder 17, a pressure spring is sleeved on a piston rod in the rod cavity, and the pressure spring is in a compression state. The rod cavity is connected with an oil inlet pipeline, the rodless cavity is connected with an oil inlet of the second electrohydraulic servo valve 16 through a pipeline, and two oil outlets of the second electrohydraulic servo valve 16 are respectively communicated with the oil pan and the rod cavity. The second electro-hydraulic servo valve 16 is provided with a third control end 161, the third control end 161 is an electromagnetic relay, and the third control end 161 is used for controlling the valve core of the second electro-hydraulic servo valve 16 to switch between an A working position and a B working position. When the third control end 161 is powered off, the second electrohydraulic servo valve 16 is located at the working position A, at this time, the rodless cavity of the second variable oil cylinder 17 is communicated with the oil pan, and the piston rod of the second variable oil cylinder 17 moves from the direction of the rod cavity to the direction of the rodless cavity under the action of the pressure spring, so that the piston rod of the second variable oil cylinder 17 drives the swash plate of the variable motor to rotate at the same time, thereby realizing the adjustment of the displacement of the variable motor. When the third control end 161 is powered on, the second electrohydraulic servo valve 16 is located at the B working position, the rodless cavity of the second variable oil cylinder 17 is communicated with the oil inlet pipeline, and the acting area of hydraulic oil in the rodless cavity and the piston is larger than the acting area of hydraulic oil in the rod cavity and the piston, so that under the action of pressure difference, the piston slides to the side with the rod cavity and compresses the pressure spring, the piston rod of the second variable oil cylinder 17 drives the swash plate of the variable motor to rotate at the same time, and the displacement of the variable motor is adjusted, and in the embodiment, the displacement of the variable motor is in a trend of becoming larger.

In this embodiment, two ports of the variable pump and two ports of the variable motor are respectively communicated through a first pipeline and a second pipeline, and a flushing valve 18 and a flushing overflow valve 19 connected with the flushing valve 18 are further arranged between the first pipeline and the second pipeline. The flushing valve 18 is close to the variable motor, two A and B ports of the flushing valve 18 are respectively communicated with a first pipeline and a second pipeline, a P port of the flushing valve 18 is communicated with the flushing overflow valve 19, the flushing valve 18 is a three-position three-way valve, two signal oil ports are formed in the flushing valve 18 and are respectively communicated with the first pipeline and the second pipeline through pipelines, in the working output process of the variable motor, one of the first pipeline and the second pipeline is communicated with high-pressure hydraulic oil, the other one of the first pipeline and the second pipeline is communicated with low-pressure hydraulic oil, and under the action of pressure difference, the valve core of the flushing valve 18 can be driven to move, so that the low-pressure oil can flow back to the oil pan through the flushing valve 18 and the flushing overflow valve 19.

A shuttle valve is further arranged between the first pipeline and the second pipeline, and an oil outlet of the shuttle valve is connected with an oil inlet of the second electrohydraulic servo valve 16 through an oil inlet pipeline.

The transmission system further comprises a supplementary oil pump 20 coaxially arranged with the variable pump, the supplementary oil pump 20 is driven to rotate by the engine 1, the supplementary oil pump 20 is connected with the oil pan, the supplementary oil pump 20 is respectively communicated with the first pipeline and the second pipeline through two one-way valve assemblies 21, and when hydraulic oil in the first pipeline (or the second pipeline) is low-pressure hydraulic oil, the hydraulic oil is pumped into the first pipeline (or the second pipeline) through the supplementary oil pump 20 and the corresponding system one-way valve 21. The oil supplementing pump 20 is also connected with a filter 23, the filter 23 is connected with an oil inlet of the first electro-hydraulic servo valve 14, impurities in hydraulic oil can be filtered through the filter 23, the oil supplementing pump 20 is also connected with an oil supplementing overflow valve 22, and when the oil pressure in an oil supplementing pipeline is higher, the hydraulic oil can overflow to an oil pan through the oil supplementing overflow valve 22.

In this embodiment, the clutch 4 may be a wet clutch, the clutch 4 is connected with a third electrohydraulic servo valve 24, and hydraulic oil is controlled to enter the clutch 4 by the third electrohydraulic servo valve 24, so as to control a driving disc and a driven disc of the clutch 4 to realize torque transmission between the variable motor and the main speed reducing mechanism 5 through friction combination. The third electrohydraulic servo valve 24 is a two-position three-way valve, an oil inlet of the third electrohydraulic servo valve 24 is connected with the filter 23 through a pipeline, two oil outlets of the third electrohydraulic servo valve 24 are respectively connected with the clutch 4 and the oil pan, a fourth control end 241 is arranged on the third electrohydraulic servo valve 24, the fourth control end 241 is an electromagnetic relay, when the fourth control end 241 is electrified, the third electrohydraulic servo valve 24 controls hydraulic oil to enter the clutch 4, and when the fourth control end 241 is electrified, the third electrohydraulic servo valve 24 controls hydraulic oil to enter the oil pan.

The final drive mechanism 5 and the clutch 4 are both integrated on the front bridge 8. The speed of the variable motor is reduced through the main speed reduction mechanism 5, the main speed reduction mechanism 5 comprises a driving bevel gear and a driven bevel gear which are meshed with each other, the driving bevel gear is connected with the clutch 4, the driven bevel gear is fixedly connected with the differential mechanism 6, and the driving gear of the differential mechanism 6 is driven to rotate through the driven bevel gear. The differential mechanism 6 is a prior art, and the structure thereof is not described herein, so that the front wheels are convenient to turn by arranging the differential mechanism 6.

Referring to fig. 3 and 4, in this embodiment, two wheel-side speed reducing mechanisms 9 are further disposed on the front bridge frame 8, the two half axle assemblies 7 are respectively connected with the input ends of the two wheel-side speed reducing mechanisms 9, and the output ends of the two wheel-side speed reducing mechanisms 9 are respectively connected with the wheels at the two ends of the front bridge frame 8. By providing the hub reduction mechanism 9, the driving torque to the front wheels can be further increased. Specifically, the axle shaft assembly 7 includes a differential axle shaft 71, a connecting component and a speed reducer axle shaft 75, the connecting component includes a left cross axle 72, a hinge fork 73 and a right cross axle 74, one end of the differential axle shaft 71 is connected with the differential 6, the other end of the differential axle shaft 71 is hinged with one end of the left cross axle 72, the other end of the left cross axle 72 is hinged with the hinge fork 73, the hinge fork 73 is hinged with one end of the right cross axle 74, the other end of the right cross axle 74 is hinged with one end of the speed reducer axle shaft 75, and the other end of the speed reducer axle shaft 75 is connected with the input end of the wheel side speed reducing mechanism 9. The front bridge frame 8 is provided with bearings and sealing rings on two sides of the differential mechanism 6, and the differential mechanism half shaft 71 is arranged in the bearings and the sealing rings in a penetrating way.

The wheel-side speed reducing mechanism 9 comprises an annular gear frame, a planet carrier assembly and a sun gear, wherein the annular gear frame is fixedly connected with a left steering knuckle 29 or a right steering knuckle 30 through bolts, and an annular gear is arranged on the inner side of the annular gear frame; the planet gears on the planet carrier assembly are located in and engaged with the ring gear, and the sun gear is engaged with the planet gears and is splined to the reducer half shaft 75. The planet carrier assembly is provided with a wheel rim shell fixedly at the outer side, and the wheel rim shell is used for installing a front wheel. Preferably, the reduction half shaft 75 and the sun gear are integrally formed.

The transmission system further comprises a tilting mechanism and a steering mechanism, wherein the tilting mechanism is arranged on the front bridge frame 8 and used for driving the front wheels to steer, the tilting mechanism is used for controlling the front wheels to tilt relative to the front bridge frame 8, the tilting mechanism comprises a left tilting frame 25, a right tilting frame 26, a tilting oil cylinder 27 and a tilting pull rod 28, and the steering mechanism comprises a left steering knuckle 29, a right steering knuckle 30, a left steering oil cylinder 3431, a right steering oil cylinder 32 and a steering pull rod 33. The left tilting frame 25 and the right tilting frame 26 are respectively pivoted at two ends of the front bridge frame 8, the left tilting frame 25 and the right tilting frame 26 are both connected with the tilting pull rod 28, the tilting oil cylinder 27 is installed on the front bridge frame 8 and used for driving the left tilting frame 25 or the right tilting frame 26 to rotate relative to the front bridge frame 8, the right steering knuckle 30 is pivoted on the right tilting frame 26, the left steering knuckle 29 is pivoted on the left tilting frame 25, the left steering knuckle 29 and the right steering knuckle 30 are respectively pivoted at two ends of the steering pull rod 33, the left steering knuckle 29 is also hinged with the output end of the left steering oil cylinder 3431, the body end of the left steering oil cylinder 3431 is hinged with the front bridge frame 8, the right steering knuckle 30 is also hinged with the output end of the right steering oil cylinder 32, and the body end of the right steering oil cylinder 32 is hinged with the front bridge frame 8. The left knuckle 29 and the right knuckle 30 are also connected to the two wheel-side reduction mechanisms 9, respectively.

In this embodiment, both ends of the tilt rod 28 are ball-hinged to the left tilt frame 25 and the right tilt frame 26, respectively. Four through holes with axes on the same plane are respectively arranged on the left inclined frame 25 and the right inclined frame 26, wherein two through holes are arranged at intervals up and down along the vertical direction, and the other two through holes are arranged at intervals along the front and back direction. The left knuckle 29 and the left tilt frame 25 are pivotally connected to two through holes in the up-down direction through a pin shaft, and the right knuckle 30 and the right tilt frame 26 are pivotally connected to two through holes in the up-down direction through a pin shaft; the two through holes in the front-rear direction of the left tilting frame 25 and the two through holes in the front-rear direction of the right tilting frame 26 are both pivotally connected to the front frame 8 via pins.

In the embodiment, the left steering cylinder 3431 and the right steering cylinder 32 control the left steering knuckle 29 and the right steering knuckle 30 to drive the front wheels to rotate, the left tilting frame 25 or the right tilting frame 26 is driven by the tilting cylinder 27 and the two steering knuckles are driven by the tilting tie rod 28 to synchronously tilt, and finally the synchronous tilting of the front wheels at the two ends of the front bridge 8 is realized, so that when the transmission system is used for a grader, partial lateral force applied by materials in front of a shovel blade to the whole machine can be eliminated, and the sideslip phenomenon of the front wheels is reduced; meanwhile, under the working conditions of slope operation or scraping ditches and the like, the front wheels can be perpendicular to the horizontal plane by controlling the inclination of the front wheels, so that the operation stability is enhanced.

In this embodiment, the left knuckle 29 and the right knuckle 30 are provided with bearings and sealing rings, and the two half shafts 75 of the speed reducer are respectively inserted into the bearings and sealing rings on the corresponding knuckles and are connected with the corresponding wheel-side speed reducing mechanisms 9 through splines.

The transmission system further comprises a rear drive mechanism, the rear drive mechanism comprises a gearbox 10, a transmission shaft 11 connected with a first force taking port of the gearbox 10, and a driving rear axle 12 connected with the transmission shaft 11, the driving rear axle 12 is used for driving rear wheels to rotate, and the hydraulic pump 2 is connected with a second force taking port of the gearbox 10. The junction of the propeller shaft 11 and the transaxle 12 is provided with a parking brake 13, and the parking brake 13 is used to prevent or allow power transmission between the propeller shaft 11 and the transaxle 12. The rear drive axle 12 and the parking brake 13 are both of the prior art, and the structure thereof will not be described herein, wherein the specific structure of the rear drive axle 12 is set according to the rear drive axle of the slewing bearing grader disclosed in the earlier patent with the application number CN 201620360528.4.

In the present embodiment, the transmission case 10 is not limited to being directly connected to the engine 1 through a torque converter or an elastic coupling, and a transfer case may be provided between the engine 1 and the transmission case 10. Accordingly, the hydraulic pump 2 is not limited to be mounted to the power take-off port of the transmission 10, and may be mounted to the power take-off port of the transfer case.

The transmission system further includes a selector switch that can be used to select a drive mode including a precursor mode, a rear drive mode, and a full drive mode.

In the default working mode, the selection switch is located at the position of the rear-drive mode, the fourth control end 241 is powered off, hydraulic oil combined with the clutch 4 is controlled to drain through the third electrohydraulic servo valve 24, the clutch 4 enables the driving end and the driven end to be disconnected under the action of a spring, the variable motor is disconnected from the transmission of the main speed reduction mechanism 5, the first control valve 141 and the second control valve 142 are powered off simultaneously, the variable pump and the variable motor idle, and the oil supplementing pump 20 supplies oil to the low-pressure side in the first pipeline or the second pipeline and washes the high-pressure side. The torque of the engine 1 is transmitted to a drive rear axle 12 through a gearbox 10 and a transmission shaft 11, so that the rear wheels are driven to rotate forwards, and a rear drive mode is formed.

When the selection switch selects the front drive mode, the gearbox 10 is in neutral gear, the fourth control end 241 is powered, the oil supplementing pump 20 provides control hydraulic oil to flow to the clutch 4 through the third electrohydraulic servo valve 24, the spring of the clutch 4 is compressed to enable the driving end and the driven end to be in friction combination, and accordingly the variable motor is in transmission combination with the main speed reduction mechanism 5, the first control end 141 and the third control end 161 are powered, and output torque of the variable motor is respectively transmitted to two front wheels through the main speed reduction mechanism 5, the differential mechanism 6, the two half shaft assemblies 7 and the two wheel edge speed reduction mechanisms 9, so that the front drive mode is formed. The rotation speeds of the two front wheels are different when the front wheels turn or the load of the two front wheels is different, such as when the two front wheels are in slope operation, and the differential speed of the two front wheels can be automatically realized through the differential mechanism 6.

When the selection switch selects the full drive mode, the fourth control end 241 is powered, the hydraulic oil supplied by the oil supplementing pump 20 flows to the clutch 4 through the third electrohydraulic servo valve 24, the spring of the clutch 4 is compressed to enable the driving end and the driven end to be in friction combination, so that the variable motor is in transmission combination with the main reduction mechanism 5, the first control end 141 and the third control end 161 are powered, a part of the power of the engine 1 is converted by the variable pump and is output through the variable motor, the part of the power is respectively transmitted to two front wheels through the main reduction mechanism 5, the differential mechanism 6, the two half shaft assemblies 7 and the two wheel side reduction mechanisms 9, and the other part of the power of the engine 1 is transmitted to the driving rear axle 12 through the gearbox 10 and the transmission shaft 11, so that the rear wheels are driven to rotate forwards. The rotation speeds of the two front wheels are different when the front wheels turn or the load of the two front wheels is different, such as when the two front wheels are in slope operation, and the differential speed of the two front wheels can be automatically realized through the differential mechanism 6.

It should be noted that when the selection switch selects the front wheel driving mode or the full driving mode, the first control terminal 141 is turned off and the second control terminal 142 is turned on when the reverse is required.

The transmission system further comprises a precursor speed adjusting knob, the rotating speed of the front wheels can be adjusted through the precursor speed adjusting knob, specifically, the controller reads the precursor speed adjusting knob to select and set the rotating speed value of the front wheels, and the controller obtains the current values of the first control end 141 and the third control end 161 according to the current value relation map of the rotating speed of the front wheels, which is preset in the controller, of the first control end 141 and the third control end 161, and controls the current values of the first control end 141 and the third control end 161 to change, so that the displacement of the hydraulic system changes, and the adjustment of the rotating speed of the front wheels is realized.

Referring to fig. 6, the present embodiment further provides a grader including the transmission system in the above scheme.

Referring to fig. 7 to 9, the present embodiment further provides a control method of a transmission system, which includes the following steps:

s10: selecting a driving mode, wherein the driving mode comprises a precursor mode, a rear-drive mode and a full-drive mode;

if the precursor mode is selected, S20 is executed.

S20: and judging whether the precursor mode starting condition is met.

If the precursor mode starting condition is met, executing S30; if the precursor mode start condition is not satisfied, S100 is executed.

S30: only the precursor mechanism is in driving connection with the engine 1.

S100: and (5) ending.

The precursor mode initiation conditions include: judging whether the whole machine is in a stopped state, judging whether the gear of the transmission 10 is in the neutral position, judging whether the parking brake 13 is released, and acquiring the braking pressure Pb1 of the rear wheels and comparing with a preset braking pressure Pb preset in the controller. The precursor mode starting condition is satisfied only when the complete machine is in a stopped state, the gear of the transmission 10 is in the neutral position, the parking brake 13 is released, and Pb1 < Pb all occur, and step S100 is executed when the complete machine is not in a stopped state, the gear of the transmission 10 is not in the neutral position, the parking brake 13 is not released, and any one of Pb1 not less than Pb occurs.

A driving mode selection button is arranged in the cab, corresponding buttons are respectively arranged corresponding to each driving mode, and a driver can select the corresponding driving mode through the buttons.

In the forward drive mode, only the forward drive mechanism is in driving connection with the engine 1, and at this time, no power is transmitted between the gearbox 10 and the transmission shaft 11 because the gear position of the gearbox 10 is in the neutral position. Thus, when the front drive mode is selected, it is necessary to confirm the gear of the transmission 10. And when the precursor mode is started, the whole machine cannot be in the rear-drive mode and the full-drive mode, and can enter under the condition of ensuring that the whole machine is in a stop state. The speed sensor arranged on the vehicle body can be used for measuring the speed of the whole machine, the detected speed value is transmitted to the controller, the controller judges whether the speed value is equal to 0, if the speed value is equal to 0, the whole machine is in a stop state at the moment, and if the speed value is not equal to 0, the whole machine is in a motion state at the moment. When judging whether the gear of the transmission 10 is in the neutral position, it is possible to detect by a first position sensor mounted on a gear lever of the transmission 10, specifically, a position of the first position sensor and a map of the gear of the transmission 10 may be preset in the controller, the position of the gear lever is detected by the first position sensor, and an electric signal representing the position of the gear lever is transmitted to the controller, the electric signal is converted into the position of the gear lever by the controller, and the gear of the gear lever is obtained from the map.

The determination of whether the parking brake 13 is released may be achieved by the controller in combination with a second position sensor mounted on the parking brake lever, specifically, a map of the position of the second position sensor and the braking position of the brake lever may be preset in the controller, the position of the brake lever may be detected by the second position sensor, and an electric signal representing the position of the brake lever may be transmitted to the controller, the electric signal may be converted into the position of the brake lever by the controller, if the position exists in the map, it indicates that the parking brake 13 is not released, and if the position does not exist in the map, it indicates that the parking brake 13 is released. The preset brake pressure Pb may be set according to actual conditions.

It will be appreciated that the rear wheels are provided with brake mechanisms which are driven by oil pressure. The oil pressure brake mechanism on the rear wheel is in the prior art, and is not described herein, the brake pressure Pb1 of the rear wheel is obtained, the pressure sensor arranged in the hydraulic oil inlet pipeline of the brake mechanism can be used for measuring, and the pressure sensor is connected with the controller, so that the measured data can be transmitted to the controller. Considering that the front drive mode is only auxiliary drive, if the brake pressure Pb1 is equal to or greater than Pb, the front drive mode is started at this time, the whole machine is kept still, or the advancing speed is extremely slow, so that the load of the hydraulic pump 2 and the hydraulic motor 3 is easily increased, the oil temperature of the high-pressure side in the closed loop of the hydraulic pump 2 and the hydraulic motor 3 is easily increased, the hydraulic pump 2 and the hydraulic motor 3 are adversely affected, and therefore, the brake oil pressure needs to be detected before the front drive mode is started to protect a front drive mechanism.

Optionally, S40 and S50 are also included after S30.

S40: the front wheel rotation speed is set.

S50: the controller adopts PID algorithm to adjust the rotation speed of the front wheels to the set rotation speed of the front wheels through the pump control assembly and the motor control assembly.

The PID algorithm is realized through a PID controller, the PID controller is the prior art, the specific structure of the PID controller is not repeated, the PID controller adopts a closed-loop automatic control theory, the uncertainty of control is reduced based on a feedback concept, and the elements of the feedback theory comprise three parts: measurement, comparison and execution. It is critical to measure the actual value of the controlled variable, compare it with the expected value, use this deviation to correct the response of the system, and perform regulation control. In this embodiment, the actual value of the controlled variable is the actual rotation speed of the front wheel, the expected value is the set rotation speed of the front wheel, and in the control process, the actual rotation speed of the front wheel is measured, the measured actual rotation speed value of the front wheel is compared with the set rotation speed of the front wheel, the current of the first control end 141 and the current of the third control end 161 are adjusted according to the difference value, so that the actual rotation speed of the front wheel is adjusted, and the rotation speed of the front wheel finally tends to or equals to the set rotation speed of the wheel through continuous adjustment.

Optionally, if the precursor mode is selected in S10, S11 and S12 are further included between S10 and S20:

s11: the oil pressure P1 on the low pressure side in the closed circuit of the hydraulic pump 2 and the hydraulic motor 3 is collected.

S12: the controller compares P1 with a preset oil pressure P.

If P1 > P, then S20 is executed; if P1 is equal to or less than P, S100 is executed.

If the oil pressure P1 at the low pressure side is less than or equal to P, air is liable to exist in the low pressure connecting lines of the hydraulic pump 2 and the hydraulic motor 3, and at this time, the hydraulic pump 2 and the hydraulic motor 3 are turned on to easily cause cavitation. Therefore, when P1 is less than or equal to P, the controller controls the precursor mode not to start. The preset oil pressure P may be set according to actual conditions.

In S10, if the full drive mode is selected, S60 is executed.

S60: judging whether the starting condition of the full-drive mode is met.

If the full-drive mode starting condition is met, executing S70; and if the full-drive mode starting condition is not satisfied, executing S100.

S70: the rear drive mechanism and the front drive mechanism are both in driving connection with the engine 1.

The starting conditions of the full-driving mode comprise: whether the parking brake 13 is released or not, whether the gear of the transmission 10 is in the neutral position or not, acquiring the braking pressure Pb2 of the rear wheels and comparing with the preset braking pressure Pb' preset in the controller, and acquiring the rotation speed N1 of the front wheels and comparing with the preset front wheel rotation speed N preset in the controller. The full drive mode start condition is satisfied only when the parking brake 13 is released, the gear of the transmission 10 is not in neutral, pb2 < Pb', and N1 < N all occur. When the parking brake 13 is not released, the gear of the transmission 10 is in neutral, any one of Pb2 Pb' and N1N occurs, the full drive mode start condition is not satisfied, and S100 will be executed.

In the full drive mode, the engine is in driving connection with both the rear drive and the front drive, and since the front drive needs to be started, it is also necessary to ensure that the parking brake 13 has been released before the full drive mode is started, and that the rear wheel brake pressure Pb2 needs to be less than Pb'. Since the rear drive mechanism needs to be activated at the same time, the gear position of the gearbox 10 needs to be ensured not to be in the neutral position. Considering that the front wheel driving mode is only auxiliary driving, the maximum speed of the front wheel driving mode capable of driving the front wheel to rotate is far lower than the maximum speed of the rear wheel driving mechanism capable of driving the front wheel to rotate, therefore, the front wheel rotating speed N1 and the preset front wheel rotating speed N need to be compared, the preset front wheel rotating speed N represents the maximum speed of the front wheel driving mechanism capable of driving the front wheel to rotate or represents x times of the maximum speed of the front wheel driving mechanism capable of driving the front wheel to rotate, x is more than 1 and less than or equal to 1.2, and when N1 is more than or equal to N, the front wheel driving mechanism is easy to damage when the front wheel driving mode is entered. The preset brake pressure Pb' and the preset front wheel rotation speed N may be set according to actual conditions. The gear direction refers to the final driving direction of the whole machine under the gear. The method for judging whether the running direction and the gear direction of the whole machine are the same comprises the following steps: the gear position of the clutch 4 and the map of the gear direction are stored in the controller in advance, the controller obtains the gear position of the gear lever through the first position sensor, obtains the running direction represented by the gear lever position according to the gear position and the map of the gear direction, obtains the rotating speed value of the whole machine through the rotating speed sensor arranged on the front wheel or the rear wheel, obtains the running direction of the whole machine through the positive and negative values of the obtained rotating speed value, and compares the running direction of the whole machine with the running direction represented by the gear lever position.

Optionally, if the full-drive mode starting condition is satisfied, the control method of the transmission system further includes S61 and S62.

S61: and judging whether the running direction of the whole machine is the same as the gear direction.

If the running direction of the whole machine is the same as the gear direction, executing S70; if the running direction of the whole machine is not the same as the gear direction, S62 is executed.

S62: after waiting for the time T1, S70 is performed.

Considering that the gear of the gearbox may be in the F gear (forward gear) or the R gear (reverse gear), and the actual running direction of the whole machine is also uncertain, for example, when the grader in the related art runs forward while keeping the speed below three gears, the grader can directly engage the reverse gear, and the grader gradually decelerates forward and reverses backward, so that the actual running direction of the whole machine needs to be ensured to be the same as the gear direction. This is because when the front-drive mode is started, it is necessary to ensure that the actual rotation direction of the front wheels coincides with the movement direction of the whole machine, otherwise, for the front-drive mechanism, the high-pressure side oil temperature in the closed circuit of the hydraulic pump 2 and the hydraulic motor 3 is liable to rise, which adversely affects the hydraulic pump 2 and the hydraulic motor 3.

When the running direction of the whole machine is different from the gear direction, the whole machine is possibly in a forward running state, but the gear of the clutch 4 is in the working condition of R gear, so after waiting time T1, the running direction of the whole machine is matched with the gear direction, and the precursor mechanism is ensured not to be damaged. The time T1 may be set according to the actual model of the whole machine. Preferably, S160 includes: waiting time T1, judging whether the running direction of the whole machine is the same as the gear direction, if so, executing S150, and if not, executing S160. Such a setting can avoid the problem of inaccurate T1 settings.

Optionally, after S70, the control method of the transmission system further includes steps S80 and S90:

s80: the rotation speed ratio S of the front wheels and the rear wheels is set.

S90: the method comprises the steps of obtaining the rotating speed n2 of a rear wheel, determining the rotating speed n3 of a corresponding front wheel according to n3=S.n2, and controlling the front wheel speed to n3 through a pump control assembly and a motor control assembly by a controller through a PID algorithm.

The rotation speed ratio of the front wheels and the rear wheels is also called as the advance rate, the value of S is 0.98-1.2, and various working conditions of the land balancing machine can be matched by setting the advance rate. For example, when the rear wheel side road surface of the grader is softer than the front wheel side road surface, the control S is greater than 1, at which time the rear wheel may be dragged forward by the front wheel, and accordingly the rear wheel may be prevented from collapsing the softer road surface. Similarly, when the road surface on the front wheel side of the grader is softer than the road surface on the rear wheel side, the control S is smaller than 1, and the front wheel can be dragged to move backwards through the rear wheel at the moment, so that the front wheel can be correspondingly prevented from collapsing the softer road surface. It should be noted that, in other embodiments, the lead rate may also adjust the rotational speed of the rear wheel according to the rotational speed of the front wheel, and accordingly, in step S80, in addition to manually setting the rotational speed ratio S of the front wheel and the rear wheel by the driver, the target rotational speed of the front wheel needs to be set, the controller adjusts the rotational speed of the front wheel to the target rotational speed by using the PID algorithm through the pump control assembly and the motor control assembly, and then adjusts the target rotational speed of the rear wheel according to the target rotational speed of the front wheel, where the target rotational speed of the rear wheel is equal to the quotient of the target rotational speed of the front wheel and S.

Optionally, after S90, the control method of the transmission system further includes steps S110 to S160.

S110: the rotation speed n4 of the front wheel is acquired.

S120: judging whether n4 is equal to 0; if n4=0; s130 is performed.

S130: the duration T2 of n4=0 is accumulated and compared with the preset time T.

If T2 is more than or equal to T; s140 is performed.

S140: the engine is only in transmission connection with the rear-drive mechanism when the full-drive mode is changed into the rear-drive mode.

The controller can judge the magnitudes of n4 and 0 by measuring the rotation speed n4 of the front wheel through the rotation speed sensor arranged on the front wheel, if n4 is equal to 0, the hydraulic pump 2 and the hydraulic motor 3 can be damaged after long time lasting, thus the hydraulic pump can be controlled by lasting the accumulated time T2, and if T2 is more than T, the hydraulic pump 2 and the hydraulic motor 3 can be prevented from being damaged by exiting the full drive mode and shifting to the back drive mode. It will be appreciated that when the cumulative time t2=t represents a significant risk of damage to the hydraulic pump 2 and the hydraulic motor 3, the time T may be set according to the actual situation, mainly taking into account the type of hydraulic pump 2 and hydraulic motor 3 of the complete machine. The method for accumulating n4=0 is that when the controller judges that n4=0, a timer connected with the controller is started, and if n4 is not equal to 0 in the accumulating process, the accumulating process is ended and defaults to time T2 < T. If the accumulated time exceeds or equals to T2, the controller executes step S140.

Optionally, after step S130, the control method of the transmission system further includes S150 to S210.

If n4+.0, or T2 < T, then S170 is performed.

S150: the oil temperature t at the high pressure side in the closed circuit of the hydraulic pump 2 and the hydraulic motor 3 is collected.

S160: comparing t with the preset oil temperature t 1.

If t is less than t1; s110 is performed; if t is more than or equal to t1; s170 is performed.

S170: and judging the sizes of S and 1.

If S is more than or equal to 1; s180 is performed.

S180: the rotation speed ratio of the front wheels and the rear wheels is adjusted to be S1, and S1 is smaller than 1.

S190: the rotational speed n5 of the rear wheel is obtained, the controller controls the front wheel speed to n6, n6=s1×n5 through the pump control assembly and the motor control assembly using the PID algorithm, and S110 is repeated.

When the lead rate is greater than 1, the front wheels drag the rear wheels to move, so that the load of the hydraulic pump 2 and the hydraulic motor 3 in the front wheel drive mechanism is large, the oil temperature in the high-pressure side pipeline in the closed circuit of the hydraulic pump 2 and the hydraulic motor 3 is easy to rise, however, the oil temperature rise is easy to damage the hydraulic pump 2 and the hydraulic motor 3, and thus the oil temperature in the high-pressure side pipeline in the closed circuit of the hydraulic pump 2 and the hydraulic motor 3 needs to be paid attention in real time, and when the oil temperature is greater than or equal to the preset oil temperature t1, the load of the hydraulic pump 2 and the hydraulic motor 3 in the front wheel drive mechanism is reduced by adjusting the value of the lead rate S to be less than 1, and the front wheels are pushed to move forward by the rear wheels, so that the front wheel drive mechanism is protected.

Optionally, in step S170, if S1 < 1, step 140 is performed.

If the value of the lead rate S is itself less than 1 and t is greater than or equal to t1, then it is indicated that adjusting the value of the lead rate S has failed to regulate the oil temperature, and it is necessary to exit the all-drive mode and enter the post-drive mode.

In S10, if the back drive mode is selected, S200 is executed.

S200: the engine 1 is only in driving connection with the rear drive mechanism.

Specifically, the controller controls the hydraulic pump 2 to stop by the pump control unit, controls the hydraulic motor 3 to stop by the motor control unit, and controls the clutch 4 to disconnect the power transmission between the hydraulic motor 3 and the final drive mechanism 5.

It is to be understood that the above examples of the present invention are provided for clarity of illustration only and are not limiting of the embodiments of the present invention. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the invention are desired to be protected by the following claims.

Claims (8)

1. A method of controlling a transmission system, the transmission system comprising: an engine (1), a front drive mechanism and a rear drive mechanism;

the rear drive mechanism comprises a gearbox (10) in transmission connection with the engine (1), a transmission shaft (11) connected with a first power taking port of the gearbox (10), and a drive rear axle (12) connected with the transmission shaft (11), wherein the drive rear axle (12) is used for driving rear wheels to rotate;

the front driving mechanism comprises a hydraulic pump (2) connected with a second power take-off port of the gearbox (10), a hydraulic motor (3) forming a closed loop with the hydraulic pump (2), a clutch (4) with one end connected with the hydraulic motor (3), a main speed reduction mechanism (5) connected with the other end of the clutch (4), a differential mechanism (6) connected with the output end of the main speed reduction mechanism (5), and two half shaft assemblies (7) connected with the differential mechanism (6), wherein the two half shaft assemblies (7) are respectively used for driving front wheels at two ends of a front bridge frame (8) to rotate;

the hydraulic pump (2) is a variable pump, the transmission system further comprises a pump control assembly, the pump control assembly is used for controlling the inclination angle of a swash plate of the variable pump, the hydraulic motor (3) is a variable motor, and the transmission system further comprises a motor control assembly, and the motor control assembly is used for controlling the inclination angle of the swash plate of the variable motor;

The transmission system further comprises a parking brake (13), the parking brake (13) being used for preventing or allowing power transmission between the transmission shaft (11) and the drive rear axle (12);

the control method of the transmission system is characterized in that a brake mechanism driven by oil pressure is arranged on a rear wheel, and the control method of the transmission system comprises the following steps:

selecting a driving mode, wherein the driving mode comprises a precursor mode, a rear-drive mode and a full-drive mode;

if the precursor mode is selected, judging whether a precursor mode starting condition is met, and if the precursor mode starting condition is met, only the precursor mechanism is in transmission connection with the engine (1);

the precursor mode starting conditions include: judging whether the whole machine is in a stop state, judging whether a gear of a gearbox (10) is in a middle position, judging whether a parking brake (13) is released, and acquiring the braking pressure Pb1 of a rear wheel and comparing the braking pressure Pb with a preset braking pressure Pb preset in a controller;

the precursor mode starting condition is satisfied only when the complete machine is in a stopped state, the gear of the gearbox (10) is in a neutral position, the parking brake (13) is released, and Pb1 < Pb all occur.

2. The control method of a power transmission system according to claim 1, characterized in that the control method of a power transmission system further comprises;

Setting the rotation speed of the front wheels;

the controller adopts a PID algorithm to adjust the rotating speed of the front wheels to the rotating speed of the set front wheels through a pump control assembly and a motor control assembly.

3. The control method of a power transmission system according to claim 2, characterized in that the control method of a power transmission system before determining whether a precursor mode start condition is satisfied further comprises:

collecting oil pressure P1 at the low pressure side in a closed loop of the hydraulic pump (2) and the hydraulic motor (3);

the controller compares P1 with a preset oil pressure P;

if P1 > P, judging whether the precursor mode starting condition is satisfied.

4. The control method of a transmission system according to claim 2, characterized in that if a full-drive mode is selected, it is determined whether a full-drive mode start condition is satisfied, and if the full-drive mode start condition is satisfied, both a rear drive mechanism and the front drive mechanism are in driving connection with the engine (1);

the full-drive mode starting conditions include: judging whether the parking brake (13) is released, judging whether a gear of the gearbox (10) is in a middle position, acquiring a braking pressure Pb2 of the rear wheels and comparing the braking pressure Pb with a preset braking pressure Pb' preset in the controller, and acquiring a rotating speed N1 of the front wheels and comparing the rotating speed N with a preset front wheel rotating speed N preset in the controller;

The full drive mode start condition is satisfied only when the parking brake (13) is released, the gear of the transmission (10) is not in neutral, pb2 < Pb', and N1 < N all occur.

5. The control method of a transmission system according to claim 4, wherein if the start condition of the all-drive mode is satisfied, it is determined whether the running direction of the entire machine and the shift direction are the same;

if the two types of the engine (1) are the same, the rear drive mechanism and the front drive mechanism are both in driving connection with the engine (1); if not, after waiting time T1, the back driving mechanism and the front driving mechanism are both in driving connection with the engine (1).

6. The control method of a transmission system according to claim 5, characterized in that, after the drive-behind mechanism and the drive-forward mechanism are both in driving connection with the engine (1), the control method of the transmission system further comprises:

setting a rotation speed ratio S of the front wheels and the rear wheels;

the rotational speed n2 of the rear wheels is obtained, and the controller adjusts the rotational speed of the front wheels to n3 through a pump control assembly and a motor control assembly by adopting a PID algorithm, wherein n3 = S x n2.

7. The control method of the power transmission system according to claim 6, characterized in that after the rotation speed of the front wheels is adjusted to n3, the control method of the power transmission system further comprises:

Acquiring the rotating speed n4 of the front wheel;

judging whether n4 is equal to 0;

if the time T2 of n4 which is continuously equal to 0 is greater than or equal to the preset time T preset in the controller, the full-drive mode is switched to the rear-drive mode, and the engine (1) is in transmission connection with the rear-drive mechanism only.

8. The control method of a power transmission system according to claim 7, characterized in that the control method of a power transmission system further comprises:

if n4 is not equal to 0 or T2 is less than T, acquiring the oil temperature T of the high-pressure side in the closed loop of the hydraulic pump (2) and the hydraulic motor (3) and comparing the oil temperature T with a preset oil temperature T1 preset in the controller;

if t is more than or equal to t1 and S is more than or equal to 1; the rotation speed ratio of the front wheels to the rear wheels is adjusted to be S1, and S1 is smaller than 1;

and acquiring the rotating speed n5 of the rear wheel, and controlling the speed of the front wheel to n6 by a controller through the pump control assembly and the motor control assembly by adopting a PID algorithm, wherein n6 = S1 x n5.