JPH07115646B2 - Power steering device for cargo handling vehicle - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering device for a cargo handling vehicle such as a forklift, and more particularly to a hydraulic power steering device using a power cylinder as an assist force.

(Prior Art) A conventional hydraulic power steering device used in a forklift is a hydraulic power pump sent from a hydraulic pump driven by an engine (an electric motor in a battery vehicle) is driven by a flow divider to a power steering system and a cargo handling system. It is common to steer the steered wheels by diverting the hydraulic fluid to the power steering system and supplying the hydraulic fluid sent to the power steering system to the power cylinder through a control valve operated by a steering wheel to operate the hydraulic fluid. A power steering device of this type is disclosed, for example, in Japanese Utility Model Publication No. 52-57563. Further, in the device disclosed in this publication, the steering is switched to the manual system by shutting off the hydraulic oil supply circuit to the power cylinder when loading a load.

(Problems to be Solved by the Invention) However, the conventional power steering device has a problem in that the steering force becomes too light when loading luggage. In other words, a large load is applied to the rear wheels, which are steered wheels when the steering wheel is empty, but the ground pressure on the steering wheel decreases when the fork is loaded, so the steering wheel is steered compared to when the steering wheel is empty. There is a problem that the force becomes too light and it easily staggers when traveling. Further, in the case of the method of switching to manual operation at the time of loading as in the above publication, the characteristic of the power steering is lost, and it becomes difficult to obtain an appropriate steering feeling.

Therefore, in view of the above problems, it is an object of the present invention to provide a power steering device for a cargo handling vehicle in which the followability of the power cylinder is changed between an empty state and a loaded state.

(Means for Solving Problems) In order to solve the above problems, the present invention is provided with a steering wheel on one side of a non-steering wheel and a load receiving portion for loading a load on the other side, and a handle. A power steering device for a cargo handling vehicle in which the steering wheel and the steering wheel are mechanically connected to each other, and a flow divider that supplies a fixed amount of hydraulic oil sent from a hydraulic pump to a power steering control valve operated by the handle, A main power cylinder connected to the control valve by a hydraulic line,
The auxiliary power cylinder connected to the main power cylinder by a hydraulic line and the hydraulic line connecting both power cylinders to each other are arranged to cut off the communication of the auxiliary power cylinder with the main power cylinder and A switching valve that can switch between a rest position in which both oil chambers communicate with each other and an operating position in which the auxiliary power cylinder communicates with the main power cylinder; and a switching valve that detects the presence or absence of a load or weight and A load detecting means for operating the switching valve, and the switching valve is set to a rest position at least when there is no load.

(Operation) In the empty state, the switching valve is held at the rest position communicating the both oil chambers of the sub power cylinder. Therefore, in this state, the hydraulic oil sent through the control valve when the handle is rotated is supplied only to the main power cylinder. On the other hand, when the cargo is loaded, the switching valve is switched to the operating position in which the auxiliary power cylinder and the main power cylinder communicate with each other. Therefore, in this state, the hydraulic oil sent through the control valve when the handle is rotated is supplied to both the main power cylinder and the sub power cylinder. That is, the amount of oil required to operate the power cylinder when loaded is greater than when it is not loaded, and the operating speed of the power cylinder slows down, resulting in a decrease in steering followability. Granted.

(Example) Hereinafter, the Example of this invention is concretely described based on drawing. First, the mechanical configuration of the power steering device will be briefly described with reference to FIG. The power steering apparatus according to the present embodiment is a cargo handling vehicle such as a forklift, that is, a steering wheel 7 is provided on one side (rear side) with a non-steering wheel (not shown) sandwiched therebetween, and luggage on the other side (front side). The present invention is applied to a cargo handling vehicle provided with a fork (not shown) as a load receiving portion for loading. In the figure, 1 is a steering wheel, 2 is a steering post, and 3 is a steering shaft in a steering post 2 (not shown). ) Pitman arm 4 which swings in association with the rotation is a drag link, one end of which is connected to pitman arm 3 and the other end of which is connected to bell crank 5. Reference numeral 6 denotes left and right tie rods, one end of which is connected to the bell crank 5 and the other end of which is connected to the steering wheel 7 via a knuckle 8. 9 and
Reference numeral 10 denotes a main power cylinder and a sub power cylinder which are symmetrically arranged and have the same volume.
One end of 10 is connected to the machine base side, and the other end is connected to the bell crank 6.

Next, the hydraulic circuit of the power steering device will be described with reference to FIG. In the figure, 11 is a hydraulic pump driven by an engine (electric motor in a battery vehicle) 12,
Reference numeral 13 is a flow divider that divides the hydraulic oil sent from the hydraulic pump 11 into a power steering system and a cargo handling system, and always supplies a constant amount of hydraulic oil to the power steering system,
It is set to supply the remaining surplus oil to the cargo handling system.

Reference numeral 14 denotes a power steering system supply pipe, which sends hydraulic oil from the flow divider 13 to a control valve 17 for power steering which is operated by the handle 1 via a brake booster 15 and a clutch booster 16.
Reference numeral 18 is a return conduit for the control valve 17.

Then, the control valve 17 is connected to the main power cylinder 9 by the hydraulic lines 19, 20, and the main power cylinder 9 and the sub power cylinder 10 are connected to the hydraulic lines 22, 23 via the pilot operated switching valve 21. Connected by. The switching valve 21 communicates the oil chambers of the sub power cylinder 10 with each other and shuts off the main power cylinder 9 from the rest position (a) and the operating position (b) that connects the power cylinders 9 and 10 to each other. ) With the tank 24 at the rest position (a), the switching operation is set based on the pressure of the cargo handling system. That is, in the present embodiment, the pilot line 25 for guiding the working fluid to the switching valve 21 is from the hydraulic line 28 connecting the lift control cylinder 27 and the cargo handling control valve 26 for controlling the working oil flow to the cargo handling actuator. I am taking it out.

The present embodiment is configured as described above, and its operation will be described below.

When the steering wheel 7 is heavily loaded, the lift cylinder 27
Since the working hydraulic pressures in the pressure conduit 28 and the pilot conduit 25 are low, the switching valve 21 is held in the illustrated rest position (a).
Therefore, the oil chambers on the rod side and the head side of the sub power cylinder 10 are in communication with each other and the tank 24, and the sub power cylinder 10 is in a free state. When the steering wheel 1 is rotated in this state, hydraulic oil from the control valve 17 for power steering is supplied only to the main power cylinder 9, and the steering wheel 7 is steered by this main power cylinder 9. At this time, the sub power cylinder 10 simply follows up and does not hinder the steering operation. That is, the steering when the cargo is empty is performed as before.

On the other hand, when a load with a light load on the steered wheels 7 is loaded, the hydraulic pressure in the pressure line 28 and the pilot line 25 of the lift cylinder 27 rises, the switching valve 21 is switched to the operating position (b), and the main power cylinder 9 and the sub power cylinder 10 communicate with each other. When the handle 1 is rotated in this state, the hydraulic oil from the control valve 17 is supplied to both the main power cylinder 9 and the sub power cylinder 10. For this reason,
The amount of oil required to operate the power cylinder is twice as much as when it is empty, and the operating speed is reduced. As a result, the followability of the steering is reduced and the operator feels heavier. Become.

That is, according to the power steering device of the present embodiment, the two power cylinders 9,
Appropriate steering force can be obtained by using 10 properly.

In the present embodiment, the pilot pressure of the lift cylinder is used as the cargo handling load detecting means for switching the switching valve 21, but the pilot cylinder pressure may be taken out from the tilt cylinder system. In addition, the switching valve 21 is an electromagnetic type,
It is also possible to change this to a configuration in which switching operation is performed based on a detection signal from a pressure detection means such as a pressure switch installed in the hydraulic circuit of the cargo handling system.

(Effects of the Invention) As described in detail above, according to the present invention, in a state where the steering wheel is heavily loaded, hydraulic oil is supplied only to the main power cylinder to perform normal power steering. In addition, when loading luggage with a small load on the steered wheels, hydraulic fluid is supplied to both the main power cylinder and the sub power cylinder to reduce the operating speed, thereby decreasing the steering followability. Since a suitable operation feeling can be obtained by giving an appropriate weight that can limit sudden steering wheel operation, stable traveling with less fluctuation can be achieved. Further, the power steering device of the present invention is a system that can be implemented by simply adding it without modifying the existing one, and can be easily applied to an existing vehicle.

[Brief description of drawings]

The drawings show an embodiment of the present invention, FIG. 1 is a hydraulic circuit diagram of a power steering device, and FIG. 2 is a plan view showing a mechanical configuration of the power steering device. 1 …… Handle 7 …… Steering wheel 9 …… Main power cylinder 10 …… Sub power cylinder 11 …… Hydraulic pump 17 …… Control valve 21 …… Switching valve 25 …… Pilot line 27 …… Lift cylinder

Claims (3)

[Claims] 1. A cargo handling vehicle in which a steering wheel is provided on one side of a non-steering wheel and a cargo receiving portion for loading a luggage is provided on the other side, and a steering wheel and the steering wheel are mechanically connected to each other. In this power steering device, a flow divider that supplies a fixed amount of hydraulic oil sent from a hydraulic pump to a power steering control valve operated by the handle, and a main power cylinder connected to the control valve by a hydraulic line, The auxiliary power cylinder is connected to the main power cylinder by a hydraulic line, and the auxiliary power cylinder is arranged in a hydraulic line connecting both power cylinders to each other. A rest position in which the oil chambers communicate with each other and the sub power cylinder with respect to the main power cylinder. A cargo-handling vehicle that includes a switching valve that can be switched to an operating position that allows passage, and load detection means that switches the switching valve by detecting the presence or absence of a load or the weight of the switching valve, and sets the switching valve to a rest position at least when there is no load. Power steering device. 2. The power steering apparatus for a cargo handling vehicle according to claim 1, wherein the changeover valve is a pilot operated changeover valve capable of changing over the pressure acting on the cargo handling cylinder as a pilot pressure. 3. The power steering apparatus for a cargo handling vehicle according to claim 1, wherein the changeover valve is an electromagnetic changeover valve that is switched by a pressure switch that detects a pressure acting on the cargo handling cylinder.