JPH01148661A - Power steering device for cargo working vehicle - Google Patents

Abstract

PURPOSE:To keep a force required for the operation of a steering handle nearly constant by providing a load sensitive regulating valve for controlling the feeding quantity of a working fluid into a control valve in proportion to the load of cargo which is loaded on a cargo-working device, in a hydraulic circuit from a pump driven by a prime mover to the control valve. CONSTITUTION:The delivery side of a pump 8 driven by a prime mover is connected to the flow-in port of a control valve 12 operated by a lift lever 7 via a first branch passage 11a by means of a flow-dividing valve 11, while also connected to the flow-in port of a variable flow regulating valve 14 as a load-sensitive regulating valve via a second branch passage 11b. The pilot port of the variable flow regulating valve 14 is connected to the bottom chamber of a lift cylinder 5 via a pipe line 17 to restrict a passing flow rate in proportion to the load applied to a cargo-working fork 6. The flow-out port of the variable flow regulating valve 14 is connected to a four-port control valve 18 which is operated in its opening/closing based on the operation of the steering handle 4 to control a power cylinder 21 via the valve 18.

Description

[Detailed Description of the Invention] Purpose of the Invention (Field of Industrial Application) The present invention relates to a power steering device for a cargo handling vehicle, which has a cargo handling device on the front side of the vehicle and steering wheels on the rear side of the vehicle. be. (Prior Art) In general, in a cargo handling vehicle, for example, a forklift trunk, which has a cargo handling device having a lifting member such as a cargo handling fork on the front side of the vehicle and a steering wheel on the rear side of the vehicle, the front side is A balance weight or the like is mounted on the rear side in order to balance the cargo load on the rear side with the own weight of the rear side. Therefore, when no cargo load is applied to the front side of the vehicle, a large load is applied to the steering wheel due to the weight of the rear side of the vehicle, making it difficult to turn the steering wheel support handle. On the other hand, in situations where a cargo load is applied to the front side of the vehicle, changes in the balance with the cargo load reduce the load on the steering wheels, making it easier to turn the steering wheel. That is, the force required to operate the handle varied greatly depending on the presence or absence of a cargo load. Therefore, as a power steering device that can alleviate the fluctuations in the operating force required for steering operation of such cargo handling vehicles and reduce power loss, for example,
The one disclosed in Japanese Patent No. 2-57563 has been proposed. As shown in FIG. 5, in this device, an oil tank 41
The hydraulic oil is sent to the switching valve 44 via the diverter valve 43 due to the operation of the pump 42, and further to the control valve 45 for the power cylinder.
It is sent to the bottom chamber of the power cylinder 46 via. Furthermore, by switching the spool of the control valve 45 based on the handle operation, hydraulic oil is sent to the piston rod chamber of the power cylinder 46, and hydraulic oil in the bottom chamber is returned to the oil tank 41. On the other hand, the hydraulic oil in the oil tank 41 is sent to the cargo handling control valve 47 via the diverter valve 43 based on the operation of the pump 42, and the piston of the tilt cylinder 49 is further used to rotate the support frame 48 of the cargo handling fork. Sent to the rod room, etc. Further, a pilot pipe line 50 extending from the switching valve 44 is connected between the piston rod chamber of the tilt cylinder 49 and the cargo handling control valve 47. Therefore, when no cargo load is applied to the cargo handling fork, the pressure in the piston rod chamber of the tilt cylinder 49 does not increase, and the pressure applied to the switching valve 44 via the pilot pipe 50 does not exceed the set pressure. , the switching valve 44 is opened, the hydraulic oil in the oil tank 41 is sent to the power cylinder 46, and the piston rod 46a expands and contracts to assist the steering operation of the steering wheels. Therefore, the force required to operate the handle is reduced, and the handle becomes easier to turn. On the other hand, when a cargo load is applied to the cargo handling fork, the pressure in the piston rod chamber of the tilt cylinder 49 increases, and the pressure applied to the switching valve 44 via the biloft pipe 50 becomes equal to or higher than the set pressure.゛As a result, the switching valve 44 is closed, and the hydraulic oil in the oil tank 41 is transferred to the power cylinder 4.
6, the piston rod 46a stops operating, and the steering drive of the steering wheel is no longer assisted. Therefore, the steering wheel does not become lighter than necessary. In this way, depending on the presence or absence of a cargo load, fluctuations in the operating force required for steering the vehicle are alleviated, and unnecessary operations of the power cylinder 46 are stopped to reduce power loss. Ta. (Problems to be Solved by the Invention) However, in the conventional device, the opening and closing of the switching valve 44 is switched depending on the level of pressure in the piston rod chamber of the tilt cylinder 49, and only the supply of hydraulic oil to the power cylinder 46 is performed. It was just changing the stop. For this reason, it has been impossible to control the operation of the power cylinder 46 by slightly varying it in proportion to the size of the cargo load. Therefore,
It was not possible to maintain the operating force of the handle approximately constant in an appropriate state depending on the size of the cargo load. This invention was made in view of the above-mentioned circumstances, and its purpose is to make it possible to fluctuately control the operation of a power cylinder in proportion to the size of the cargo load using a simple mechanical configuration. Therefore, it is an object of the present invention to provide a power steering device for a cargo handling vehicle that can maintain a substantially constant force required for steering wheel operation in an appropriate state. Structure of the Invention (Means for Solving Problems) In order to achieve the above object, the present invention includes a control valve that controls the flow of hydraulic oil from a pump driven by a prime mover, and a control valve that controls the flow of hydraulic oil from a pump driven by a prime mover. A power steering hydraulic circuit is provided, which operates with hydraulic oil to operate a power cylinder that assists the steering operation of the steering wheels, and the hydraulic circuit from the pump to the control valve is connected to the load loaded on the cargo handling equipment. A configuration is adopted in which a load-sensitive control valve is provided to control the amount of hydraulic oil supplied to the control valve in proportion to the load. (Function) Therefore, as the cargo load loaded on the cargo handling device increases or decreases, the opening/closing amount of the load-sensitive control valve is controlled in proportion to the magnitude of the cargo load. As a result, the amount of hydraulic oil supplied from the pump to the control valve is proportionally adjusted, and the power cylinder is controlled in accordance with the amount of hydraulic oil supplied. As a result, the steering assistance of the steering wheels is adjusted in proportion to the cargo load. (Example) Hereinafter, an example in which the present invention is embodied in a forklift truck will be described in detail with reference to FIGS. 1 to 4. As shown in FIG. 4, the front side of the vehicle 1 has a pair of left and right drive wheels 2 that are driven based on the operation of a predetermined prime mover (not shown).
A pair of left and right steering wheels 3 are arranged on the rear side of the vehicle (only one of them is shown).
A cargo handling device consisting of a lifting member such as a cargo handling fork 6 that is raised and lowered based on the operation of the lift cylinder 5 is disposed on the front side of the vehicle. Lift levers 7 are disposed in the driver's seat for raising and lowering the steering handle 4 of the steering wheel 3 and the cargo handling fork 6, respectively. Furthermore, a balance way 1a is mounted on the rear side of the vehicle 1 for balancing the cargo load applied to the front side of the vehicle 1 and the own weight of the rear side during cargo handling operations. Next, a power steering device provided to assist the steering operation of the steering wheels 3 of this vehicle 1 will be explained. As shown in FIG. 1, this device includes a pump 8 driven by the prime mover, the suction side of which is connected to an oil tank 10 via a pipe 9. Further, the discharge side of the pump 8 is connected to a diversion valve 11, and a first branch passage 11 of the diversion valve 11 is connected to the discharge side of the pump 8.
a is connected to the inflow port of a well-known control valve 12 which is controlled to open and close by operating the lift lever 7, and the outflow port of the counter valve 12 is connected to the lift cylinder 5 via a pipe 13.
is connected to the bottom chamber of. And lift lever 7
By controlling the supply of hydraulic oil to the lift cylinder 5 based on the operation, the piston rod 5a of the lift cylinder 5 is extended and contracted, and the fork 6 is moved up and down accordingly. On the other hand, the second branch path 11b of the diverter valve 11 is the inflow port 14a of the variable flow rate control valve 14 as a load-sensitive control valve.
2.3), and one end of a pipe line 15 is connected to the outflow boat 14b (see FIG. 2.3) of the control valve 14. Also, the branch bow) 14 of the variable flow rate control valve 14
c (see Figure 2.3) is connected to the oil tank 1 via the pipe 16.
0, and the pilot port 14d is also connected to the bottom chamber of the lift cylinder 5 via a biloft conduit 17. The other end of the pipe line 15 is connected to a first port of a four-point control valve 18 that is opened and closed based on the operation of the handle 4, and a second port of the control valve 18 is connected to a pipe. It is connected to the oil tank 10 via a passage 19 and a filter 20. Also, the third and fourth ports of the control valve 18 are connected to the steering wheel 3.
The power cylinder 21 is connected to a bottom chamber and a piston rod chamber, respectively, for assisting the steering operation of the power cylinder 21. A piston rod 21a of the power cylinder 21 is connected to the steering wheel 3 via a bell crank 22, a tie rod 23, and the like. Further, a variable flow rate control valve 14 is provided between the pipe line 15 and the pipe line 9.
A relief valve 24 is interposed to prevent the pressure of the hydraulic oil supplied from the pipe to the control valve 18 from exceeding a certain level, and a check valve for preventing backflow is provided between the pipe line 15 and the pipe line 17. 25 is interposed. Then, an oil tank 10, a pump 8, a variable flow rate control valve 14
, a control valve 18, a power cylinder 21, etc. constitute a power steering hydraulic circuit, and by opening and closing the control valve 18 in conjunction with the operation of the handle 4, the direction of the flow of hydraulic oil from the pump 8 is controlled. It will be done. As a result, the direction of flow of hydraulic oil to the power cylinder 21 is controlled, the piston rod 21a is expanded and contracted, and the steering operation of the steering wheel 3 is assisted. Also, the back pressure in the bottom chamber of the lift cylinder 5, which varies proportionally depending on the size of the cargo load loaded on the fork 6, is transmitted through the pilot pipe 17 to the pilot boat of the variable flow rate control valve 14 as pilot pressure. Acting on 14d,
In response to this, the flow rate adjustment of the variable flow rate control valve 14 is performed. Next, regarding the structure of the variable flow rate control valve 14, the second and third
This will be explained according to the diagram. Inside the main body case 26 constituting the variable flow rate control valve 14, first to third hollow parts 26C126d and 26e having the same inner diameter and partitioned by partition walls 26a and 26b are formed along the same axis. There is. A communication hole 26f is formed in the partition wall 26a to communicate between the first and second hollow portions 26c, 26a and to have a smaller diameter than each of the hollow portions 26c, 26d. The partition wall 26b also has a communication hole 26f that communicates between the second and third hollow parts 26d and 26a.
A communication hole 26g having a diameter smaller than that is formed. A pipe joint 27 is fitted and fixed into the opening of the first hollow portion 26c, and one end of the joint 27 serves as an inflow boat 14a. Further, an outflow boat 14b and a branch boat 14c are formed in parallel in the main body case 26 and communicate with the first hollow portion 26c. A cylindrical member 28 having a diameter smaller than that of the first hollow portion 26c is fitted and fixed within the first hollow portion 26c at its proximal flange portion 28a. A communication hole 28b is formed in a part of this flange portion 28a. Further, an oil passage 29 is formed between the proximal opening 28c of the cylindrical member 28 and the outflow boat 14b. Furthermore, on the outer periphery of the distal end side of the cylindrical member 28, a first hollow portion 2 is provided.
A cylindrical spool 30 for opening and closing communication between the branch bow 6c and the branch bow 14c is reciprocatably mounted. The spool 30 has an uneven large diameter portion 30a formed on its proximal end, and a communication hole 30b formed on its distal end. Further, on the cylindrical member 28, the base end of the spool 30 and the cylindrical member 28
A compression spring 31 is interposed between the flange portion 28a and the spool 30 based on the spring force, as shown in FIG. biased into position. In this state, a part of the hydraulic oil flowing in from the inflow boat 14a flows between the spool 30 and the first hollow part 26c through the communication hole 30b of the spool 30, and the inflow pressure of the hydraulic oil acts on the spool 30. do. Further, the spring force of the compression spring 31 is set to be smaller than the inflow pressure of the hydraulic oil, and the spool 30 is pressed against the spring force of the compression spring 31 based on the inflow pressure of the hydraulic oil.
As shown in FIG. 3, the spool 30 is separated from the pipe joint 27 and placed in an open position to open communication with the branch bow 14c. In this state, the inflow boat 14
The hydraulic oil flowing in from a flows out from the branch boat 14c. Further, the hydraulic oil flowing from the inflow bow) 14a flows into the cylindrical member 2.
8 and can flow out from the outflow boat 14b via the oil passage 29. A part of the hydraulic oil flows between the flange portion 28a and the spool 30 through the communication hole 28b of the flange portion 28a, and the inflow pressure of the hydraulic oil causes the spool 30 to be biased by the compression spring 31. Acts in the same direction as the direction. On the other hand, a pilot boat 14d is formed in the main body case 26 and communicates with the third hollow part 26e, and the hydraulic oil flowing into the third hollow part 26e via the boat 14d is supplied to the partition wall 26.
It is possible to flow into the second hollow part 26d through the communication hole 26g of b. A balance piston 32 that is pressed and moved based on the pilot pressure of hydraulic oil flowing from the pilot boat 14d is reciprocatably mounted in the second hollow portion 26d. That is, a pair of flange portions 32a are formed on the base end side of the balance piston 32, and a pair of flange portions 32a are formed in sliding contact with the inner circumferential surface of the second hollow portion 26d, and a rod portion 32b extends from the flange portions 32a.
passes through the communication hole 26f of the partition wall 26a and enters the first hollow portion 26.
It is disposed penetratingly within c. Further, the tip end 32c of the loft portion 32b has a conical shape, and the opening 2 of the cylindrical member 28 has a conical shape.
It is a needle valve that opens and closes 8c. Furthermore, a compression spring 33 that presses the flange portion 32a of the balance piston 32 is interposed in the second hollow portion 26d.
Based on the spring force, the flange portion 32a is urged into engagement with the partition wall 26b as shown in FIG. In this state, the tip end 32c of the balance piston 32 is connected to the cylindrical member 28.
The opening 28c of the opening 28c is opened. or,
When the balance piston 32 is pressed against the spring force of the compression spring 33 based on the pilot pressure of the hydraulic oil flowing in from the pilot boat 14d, the tip end 32c of the piston 32 becomes cylindrical as shown in FIG. The member 28 is placed in a closed position that closes the opening 28c. The opening amount of the opening 28C by the tip 32c of the balance piston 32 is a lift that varies in proportion to the magnitude of the pilot pressure applied to the balance piston 32, that is, the magnitude of the cargo load loaded on the fork 6. It is determined by the balance between the magnitude of the back pressure in the bottom chamber of the cylinder 5 and the magnitude of the spring force of the compression spring 33 applied to the balance piston 32 in the opposite direction to the direction of the pilot pressure. In other words, in response to an increase in the biloft pressure, the balance piston 32 is moved toward the closed position against the spring force of the compression spring 33, so that the opening 28
The opening amount of c becomes smaller. In addition, in response to the decrease in the viroft pressure, the balance piston 32 is moved toward the open position by the spring force of the compression spring 33, thereby opening the opening 2.
The opening amount of 8c becomes larger. Next, the operation of the power steering device configured as described above will be explained. First, when no cargo is loaded on the cargo handling fork 6 and no cargo load is applied, the back pressure in the bottom chamber of the lift cylinder 5 does not increase.
Pilot port 14d of variable flow rate control valve 14 via
Therefore, the balance piston 32 is placed in the open position based on the spring force of the compression spring 33, and the opening 28c of the cylindrical member 28 is opened by the maximum amount. As a result, the hydraulic oil flowing into the inflow port 14a of the variable flow control valve 14 based on the operation of the pump 8 smoothly flows through the opening 28c through the hollow part 28d of the cylindrical member 28, as shown by the arrow in FIG. Further, the maximum amount flows out from the outflow port 14b via the oil passage 29 and is sent to the control valve 18. Therefore, when steering the vehicle 1 using the steering wheel 4,
The maximum amount of hydraulic oil is supplied from the control valve 18 to the power cylinder 21, so that the piston rod 21a of the power cylinder 21 is expanded and contracted with a large hydraulic pressure, and the steering operation of the steering wheel 3 is assisted with a large force. As a result, handle 4
The force required to operate the handle 4 is reduced, making it easier to turn the handle 4 (
Become. At this time, based on the inflow pressure of the hydraulic oil flowing in from the inflow port 14a, the spool 30 is pressed with the same force from both the distal end side and the proximal end side. However, since the spring force of the compression spring 31 further acts on the proximal end side of the spool 30, the spool 30 is biased to the closed position that closes communication between the branch port 14C and the first hollow portion 26c. Therefore, the hydraulic oil flowing in from the inflow port 14a does not flow out from the branch port 14c, and all the hydraulic oil is supplied to the control valve 18. On the other hand, when a cargo is loaded on the cargo handling fork 6 and a cargo load is applied, the back pressure in the bottom chamber of the lift cylinder 5 increases in proportion to the magnitude of the cargo load. Therefore, the pilot pressure applied to the pilot port 14d of the variable flow rate control valve 14 via the biloft pipe 17 increases in proportion to the size of the cargo load. Therefore, the balance piston 32 resists the spring force of the compression spring 33 and is urged to move in proportion to the magnitude of the pilot pressure, and the opening amount of the opening 28c of the cylindrical member 28 is determined by the movement of the balance piston 32. It is adjusted proportionally according to the amount. As a result, the hydraulic oil that flows into the inflow boat 14a and flows into the opening 28c of the cylindrical member 28 flows to the oil passage 29 side by an amount proportional to the opening amount of the opening 28c, and flows into the outflow port 14.
b to the control valve 18. Therefore, when steering the vehicle 1 using the handle 4,
The opening 28c from the control valve 1B to the power cylinder 21
Hydraulic oil is supplied in an amount proportional to the opening amount, whereby the piston rod 21a of the power cylinder 21 is expanded and contracted with an appropriate hydraulic pressure, and the steering operation of the steering wheel 3 is assisted with an appropriate force. As a result, the force required to operate the handle 4 is kept approximately constant in an appropriate state. That is, when the cargo load is large, the auxiliary force for the steering operation based on the operation of the power cylinder 21 becomes small, and when the cargo load is small, the auxiliary force for the steering operation based on the operation of the power cylinder 21 becomes small. becomes appropriately large. Therefore, the steering wheel 4 does not become easier to cut than necessary. At this time, the spool 30 is pressed from both the distal end side and the proximal end side based on the inflow pressure of the hydraulic oil flowing in from the inflow port 14a. However, at this time, the amount of hydraulic oil flowing from the opening 28c of the cylindrical member 28 to the oil passage 29 side is small. decreases according to the amount of opening of the opening 28c, so the hydraulic pressure applied to the base end side of the spool 30 decreases accordingly. As a result, the inflow pressure applied to the proximal end of the spool 30 is relatively large (as shown in FIG. It is moved toward the open position where communication with the section 26C is opened. Therefore, a part of the hydraulic oil flowing in from the inflow port 14a flows out from the branch port 14C and returns to the oil tank 10. When the load increases and the pilot pressure applied to the balance piston 32 exceeds a predetermined pressure, the balance piston 32 is placed in the closed position.As a result,
The opening 28c of the tubular member 28 is substantially closed, which places the spool 30 in the open position and the inflow bow) 1
Almost all of the hydraulic oil flowing from 4a flows into branch port 14c.
It will flow out and return to the oil tank lO. As described above, in this embodiment, the amount of hydraulic fluid supplied to the power cylinder 21 is adjusted in proportion to the magnitude of the cargo load applied to the fork 6, and the magnitude of the hydraulic pressure acting on the power cylinder 21 is adjusted. Since it is adjustable, power cylinder 2
The auxiliary force for the steering operation based on the operation 1 can be appropriately varied. Therefore, regardless of the size of the cargo load, the force required to operate the handle 4 can be kept approximately constant in an appropriate state, and the operating feeling of the handle 4 can always be made good. Also, the power cylinder 21
Unnecessary power loss for operating the system can be reduced. In addition, in this embodiment, in order to detect changes in the size of the cargo load and control the size of the oil pressure acting on the power cylinder 21, changes in the oil pressure in the power steering hydraulic circuit are simply detected mechanically. Therefore, the configuration can be simpler than, for example, one that uses an electrical configuration for detection and control. Furthermore, in this embodiment, since the amount of hydraulic oil supplied to the control valve 18 is adjusted based on the pilot pressure that is sensitive to the back pressure in the bottom chamber of the lift cylinder 5, the amount of hydraulic oil supplied to the control valve 18 is adjusted according to the cargo load of the fork 6. The amount of hydraulic oil supplied can be stably adjusted. Note that this invention is not limited to the above embodiments,
For example, a pressure control valve other than the variable flow rate control valve 14 may be used as the load-sensitive control valve, or a part of the structure may be changed as appropriate without departing from the spirit of the invention. Effects of the Invention As detailed above, according to the present invention, by employing a simple mechanical configuration, it is possible to adjust the assisting force for steering operation in proportion to the size of the cargo load. This provides an excellent effect in that the force required to operate the handle can be maintained approximately constant in an appropriate state.

[Brief explanation of the drawing]

1 to 4 are drawings showing an embodiment embodying the invention, in which FIG. 1 is a hydraulic circuit diagram of the entire power steering device, and FIGS. 2 and 3 are diagrams of a variable flow control valve. A sectional view showing the operation, and FIG. 4 is a side view of the forklift trunk. FIG. 5 is a hydraulic circuit diagram of a conventional example. A vehicle 1, a steering wheel 3, a lift cylinder 5 and a fork 6 constituting a cargo handling device, a pump 8, a variable flow rate control valve 14 as a load-sensitive control valve, a control valve 18, and a power cylinder 2.
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Claims (1)

[Scope of Claims] 1. In a cargo handling vehicle having a cargo handling device on the front side of the vehicle and steering wheels on the rear side of the vehicle, a control valve for controlling the flow of hydraulic oil from a pump driven by a prime mover; , a power steering hydraulic circuit having a power cylinder operated by hydraulic oil controlled by the control valve to assist the steering operation of the steering wheel;
A load-sensitive control valve is provided in the hydraulic circuit extending from the pump to the control valve for controlling the amount of hydraulic fluid supplied to the control valve in proportion to the cargo load loaded on the cargo handling device. Power steering device for vehicles.