JPH0338467A - Hydraulic device of industrial vehicle - Google Patents

Abstract

PURPOSE:To improve capacity controllability of a pump by constituting the device from a controller for calculating and instructing amount of discharged oil per pump rotation required for power steering when force for operating a steering wheel exceeds the threshold value and a capacity variable mechanism for adjusting the amount of discharged oil of the pump based on the instruction signal. CONSTITUTION:A controller 9 always compares steering wheel torgue input from a torgue sensor 7 with the threshold value wherein if it exceeds the thresh old value, the controller 9 determines that it is intentional turning steering. Then based on the number of rotations of an engine 1 input from a rotation meter 8 at this time, amount of discharged oil per rotation of a pump with respect to the oil amount Q required for power steering is calculated and a control signal corresponding to the above amount is output to a capacity vari able mechanism 20 via a pump control amplifier 10. As a result gradient angle of a pump 2 is adjusted to supply only required amount of oil Q according to the number of rotations of the pump 2 to a power steering circuit 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic system for an industrial vehicle such as a forklift, and more particularly to a hydraulic system that controls the capacity of a hydraulic pump for power steering operation.

[Prior Art] A typical hydraulic system for a forklift equipped with power steering is, for example, as shown in FIG.
0, the tandem type hydraulic pumps 3 and 32 are driven, and the hydraulic fluid discharged from the large capacity hydraulic pump 31 is sent under pressure to the control valve 33, which then operates the required amount in response to a cargo handling operation (not shown). Oil is in lift cylinder 3
4 or the tilt cylinder 35. On the other hand, the hydraulic oil discharged from the small-capacity hydraulic pump 32 is used as the oil required for power steering by the flow device 36.
Only 1Q1 is supplied to the power steering circuit 37,
The surplus oil ff1Q2 is configured to be returned to the oil tank 38.

[Problems to be Solved by the Invention] As described above, in the conventional hydraulic system, the fixed displacement hydraulic pump 32 is used as a supply source of hydraulic oil to the power steering circuit 37, and moreover, Oil 11 is always secured by the flow device 36. Normally, the discharge capacity of the hydraulic pump 32 is set so that oil ff1Q1 necessary for power steering can be obtained when the engine 30 is idling.

That is, in such a hydraulic system, when the rotation speed of the engine 30 increases as shown in FIG.
Surplus oil ff1Q is returned to oil type 38 with the amount of discharged oil.
2 will inevitably increase, and even more so in a state where the power steering mechanism is not operating, such as when driving straight, the required curve ff1Q1 itself, which is secured, can only be a useless circulation of hydraulic fluid (the shaded area in the diagram). ). therefore,
Repetition of such wasteful circulation of hydraulic oil causes a loss of power and increases the oil temperature, which induces early deterioration of seal members and the like, causing serious defects in the hydraulic system.

The present invention aims to solve the technical problem of controlling the pump capacity in a timely manner by constantly grasping the presence or absence of actual steering and the varying rotational speed of the pump.

[Means for solving the problem] In order to solve the above problem, the present defense provides a variable displacement hydraulic pump connected to a power steering circuit, an operation force detector that detects the steering force, and a rotation speed of the pump. Input the rotation speed detector to be detected and the detection signals from both of the above detectors, and when the detected value of the steering wheel operating force exceeds the threshold,
A new system consisting of a control unit that calculates and commands the amount of oil discharged per one revolution of the pump required for power steering, and a variable capacity mechanism that adjusts the amount of oil discharged from the pump based on the command value of the 1til control unit. The configuration is adopted.

[Operations] According to the device of the present invention, the detected value of the steering force is first compared with a threshold value to determine whether the turning steering is intentional, and then the power is determined based on the reading of the pump (engine) rotation speed at that time. The amount of oil discharged per revolution of the pump required for steering is calculated, and the amount of oil discharged from the variable displacement hydraulic pump is adjusted via the variable capacity mechanism so that only the calculated amount of oil is supplied. In other words, the variable displacement hydraulic pump is controlled to supply the required amount of oil to the power steering circuit at the required timing.

[Example] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 shows a hydraulic system for a forklift to which the present invention is applied, and a well-known swash plate type axial piston pump (hereinafter simply referred to as pump) is used as a variable displacement hydraulic pump 2 driven by an engine 1. has been
The entire amount of hydraulic oil discharged from the pump 2 is supplied to a power steering circuit 4 via a supply pipe 3. Note that a semi-integral type power steering mechanism is used, and reference numeral 5 in the figure indicates a return pipe for hydraulic oil that is returned from the circuit 4 to the oil tank 6.

On the other hand, the steering shaft 6 is provided with a torque sensor 7 as a detector for detecting the steering force. According to the steering wheel torque detected by the torque sensor 7, for example, a fine operation accompanying straight-ahead driving is detected. A clear distinction is made between the phenomenon and intentional turning steering.

Figure 2 shows the relationship between the running state of the vehicle and the output voltage of the torque sensor 7, where ■ indicates a state in which the hand is completely removed from the steering wheel, ■ indicates a state in which the vehicle is traveling straight with only slight operation of the touched steering wheel, and ■ indicates a state in which the vehicle is traveling straight with only slight operation of the steering wheel. It represents the steering state for turning, and unlike the discrimination based on steering wheel rotation speed, etc., which does not make much difference between steering and non-steering, 1. The steering wheel torque can be clearly differentiated between the two using the threshold value C as a boundary, and it is possible to distinguish with high precision whether or not the vehicle is in a steering state.

Reference numeral 8 denotes a tachometer for detecting the rotational speed of the engine 1 (pump 2), and the tachometer 8 is connected to an input section of a control section (for example, a microcomputer) 9 together with the torque sensor 7. Also, 1. The output section of the control section 9 is connected to the variable capacity mechanism 20 of the pump 2 via the pump control amplifier 10.
is connected to, outputs a $ control signal to the variable capacity mechanism 20 in response to the detection signals of the torque sensor 7 and the tachometer 8,
The inclination angle of the swash plate can be adjusted.

FIG. 3 schematically shows the variable capacity mechanism 20. As shown in FIG.

The variable capacity mechanism 20 applies pilot pressure on the discharge side of the pump 2 to a control cylinder 22 disposed close to one side of the swash plate 21, and expands and contracts the piston rod 23 of the control cylinder 22, thereby adjusting the swash plate 21. The inclination angle θ is changed. control cylinder 22
Control of the pilot pressure for
5, its position is switched by a command signal from the pump control amplifier 10.

Note that 26 is a return spring connected to the other side of the swash plate 21, and 27 is a vibration-isolating pilot conduit loaded to stabilize the return spring 26.

FIG. 4 shows the control logic of the control section 9,
The control unit 9 constantly compares the steering wheel torque inputted from the torque sensor 7 with a threshold value C, and when the steering wheel torque F exceeds the threshold value C, determines that the turning steering is intentional. Based on the rotational speed of the engine 1 (pump 2) inputted from the tachometer 8 at the time, the amount q of oil discharged per one rotation of the pump for the oil ff1Q required for power steering is calculated, and the corresponding iil control signal is calculated. is output to the variable capacity mechanism 20 via the pump control amplifier 10.As a result, the swash plate inclination angle θ of the pump 2 is adjusted, and only the necessary indigo oil 1 corresponding to the rotation speed of the pump 2 is supplied to the power steering circuit 4. Supplied.

Of course, when the vehicle returns to running straight and the power steering mechanism does not need to be activated, the swash plate inclination angle θ of the pump 2 becomes zero, and unnecessary circulation of hydraulic oil is completely eliminated.

Incidentally, the variable capacity hydraulic pump is not limited to the swash plate type axial piston pump explained in the above embodiments, but it is naturally possible to use a slant axis type axial piston pump, and also, The variable displacement mechanism of the pump may also be configured such that, for example, a stepping motor is disposed so as to be interlocked with the swash plate, and the direction and amount of rotation of the stepping motor is controlled based on signal commands from the control section.

[Effects of the Invention] As described in detail above, according to the present invention, intentional turning steering that requires activation of the power steering mechanism is determined by detecting the steering force, and the rotational speed of the pump at that time is determined. Only the bending loss necessary for power steering is supplied.Since the amount of oil discharged per pump rotation can be adjusted, the pump surplus is proportional to the rise in engine (pump) rotation speed, unlike conventional pumps. Not only the amount of oil but also the unnecessary circulating oil when the power steering mechanism is not operating will be completely eliminated.

Therefore, in addition to simply preventing loss of power and improving fuel efficiency, the increase in oil temperature is extremely effectively suppressed, and each seal member is freed from thermal deterioration, which significantly improves the long-term stability of the hydraulic system. It is Uruchino who contributes.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a forklift hydraulic system to which the present invention is applied, Fig. 2 is a diagram showing the relationship between vehicle running conditions and torque sensor output voltage, and Fig. 3 is a schematic diagram of the variable capacity mechanism. FIG. 4 is an explanatory diagram schematically showing the control logic of the control unit, FIG. 5 is a circuit diagram of a conventional hydraulic system,
FIG. 6 is a diagram showing the relationship between the rotation speed of the pump (engine) and the amount of oil discharged from a conventional pump. 1... Engine 2... Variable displacement star-shaped hydraulic pump 4... Power steering circuit 7... Torque sensor 8... Tachometer 9... III m part 20... Variable capacity mechanism

Claims (1)

[Claims] (1) A variable displacement hydraulic pump connected to the power steering circuit, an operation force detector that detects the steering force, a rotation speed detector that detects the rotation speed of the pump, and detection from both of the above detectors. When a signal is input and the detected value of the steering wheel operating force exceeds a threshold value, a control unit calculates and commands the amount of oil discharged per one rotation of the pump required for power steering, and a command signal from the control unit calculates and commands the pump. A hydraulic system for industrial vehicles that consists of a variable capacity mechanism that adjusts the amount of oil discharged.