JPS6217334Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a steering device for a vehicle.

Vehicle steering devices include mechanical steering devices that are directly connected to a steering gear or the like, and power steering devices that use a hydraulic pump as a power source. In the former device, since the turning resistance of the wheels is directly applied to the steering wheel, the steering force required to overcome it increases in a certain relationship.Therefore, when the turning resistance exceeds a certain level, it becomes difficult to steer, and the turning resistance and steering force increase. The relationship to force is unique to the vehicle and cannot be changed. With the latter device, steering is possible even if the wheel turning resistance increases, but the engine output must naturally be increased to secure a power source, and the device itself is expensive, so it is not suitable for small size. It is not necessarily applicable to other vehicles.

For example, in the latter device, in order to prevent the engine from stopping due to insufficient output when the turning resistance of the wheels increases, a variable displacement type hydraulic pump is used for steering, and the discharge amount of the pump is controlled by the load pressure according to the wheel turning resistance. Japanese Unexamined Patent Publication No. 51-69837 discloses a system in which the theoretical displacement of the pump is changed according to changes in load pressure, and the pump is rotated with the optimum pump shaft input according to the output characteristics of the engine. has been disclosed. Therefore, if we consider the case where such a load pressure-sensitive variable displacement hydraulic pump is used in a simple manual hydraulic steering device that is not driven by an engine, it is possible to use a manually driven variable displacement hydraulic pump on an ordinary steering handle. A system in which the pump is driven by the steering torque applied by the operator to the steering wheel, converting it into fluid energy, which is guided to a hydraulic actuator and rotates by overcoming the wheel turning resistance via a link mechanism etc. The following are possible.
For example, in Fig. 1, the handle 2
A variable displacement hydraulic pump 1, such as a swash plate type axial piston pump, which can be rotated in forward and reverse directions is attached to the holder so as to be rotatable according to the rotation of the handle, and the pressure liquid discharged by the pump is delivered to the hydraulic actuator 3. The link mechanism 4 connected to the actuator is then operated to transmit the information to the wheels 5, and the suction and discharge side pipes of the pump are connected by a directional control valve 6 to generate a rotation resistance according to the wheel turning resistance. Only the liquid on the high pressure side flows into a control mechanism 7A to be described later, and the control mechanism includes a piston 9 sliding inside the cylinder and a spring 1 attached to the piston to bias it
0, the piston is the hydraulic pump 1
The swash plate 11 is engaged with the swash plate 11 to change its inclination angle α.

Describing the theory of the control system for the example shown in Figure 1, let us now assume that the steering torque is T, the steering force is f, the handle radius is rH, the hydraulic pump discharge pressure is P, and the discharge volume per revolution of the pump is q. Then, it is known that the following relationship exists: T=f・rH=P・q/2π (1).

Furthermore, if the turning resistance of the wheel is R and the proportionality constant is k, then the relationship between the resistance and the hydraulic pressure to overcome it, that is, the pump discharge pressure, is R=k・P (2) If the upper limit of the steering force f is fmax in equation (1), then since the steering wheel radius rH is constant, the upper limit Tmax of the steering torque T can be determined, and the above
In order to overcome a larger turning resistance R within the range of Tmax, the maximum value of the discharge pressure P that can be generated can be increased by decreasing the discharge volume q per pump revolution, and therefore, the maximum value of the discharge pressure P that can be generated can be increased. From equation (2), it is possible to steer with small torque even with large wheel turning resistance. In equation (1), when Tmax=P・q/2π=constant, P and q are expressed as A~ as shown in Figure 2.
There is a relationship expressed by the A' curve, and if the upper limit of the discharge volume q is determined to be _q3 , then the relationship between P and q can be controlled so as to follow A' in the figure. If the installed load of the spring 10 that biases the piston 9 is F, and the cross-sectional area of the piston 9 is S, then if the pressure P ₁ acting on the piston becomes P ₁ >F/S, the piston will not respond to the spring force. The inclination angle α of the swash plate 11 against
By changing , the discharge amount of the pump automatically changes along line A' in FIG.

Such a characteristic is generally called a constant torque characteristic, but considering that the input of steering torque is a manual operation force, it is difficult to determine whether the steering torque is applied when a forklift is unloaded or loaded, or when a tractor is loaded. Manual steering drive with a wide control range of pump discharge amount variation corresponding to the large difference in wheel turning resistance when driving on ordinary roads and driving in fields, and with a lower upper limit of steering torque compared to engine drive systems. In order to adapt the control mechanism 7A to the system shown in FIG. 1, the spring 10 of the control mechanism 7A must be large in size, which is an unavoidable drawback.

This invention aims to eliminate the above-mentioned drawbacks and provide a hydraulic steering device using manual steering force that is particularly suitable for small working vehicles such as tractors, and eliminates the need for a spring in the control mechanism that counters the load pressure. Alternatively, it is an object of the present invention to provide a steering device with a torque conversion mechanism that is sensitive to large changes in wheel turning resistance and that only requires a small spring.

That is, in the steering device of this invention, instead of the control mechanism 7A in the system shown in FIG. When a predetermined switching pressure value is reached, load pressure is applied to the large-diameter piston to move the rod to a predetermined intermediate discharge volume position, thereby changing the pump discharge amount in a stepwise manner. a first pilot-operated switching valve for reducing the switching pressure and applying the load pressure to the small diameter piston to further move the rod when the load pressure increases further to reach a predetermined pressure higher than the switching pressure value; Accordingly, a control mechanism is used which is provided with a second pilot-operated switching valve that further reduces the discharge amount of the pump.

In this way, in the present invention, the steering drive force is a manual operation force, and when the load pressure exceeds a certain set value, the pump discharge amount changes in steps, making it possible to lighten the steering wheel. In the case of forklifts and tractors targeted by this invention, the phenomenon of increased turning resistance occurs only when the vehicle is loaded or when running at low speeds such as in fields, so the number of rotations of the steering wheel is large to complete the necessary turn. It is based on the fact that there is absolutely no impediment.

Next, this invention will be explained with reference to the drawings of the embodiment.
In the steering device of this invention, instead of the control mechanism 7A in FIG. 1, the control mechanism 7B in FIG.
It connects the control mechanism 7C shown in the figure, and each control mechanism 7B, 7C will be described as follows.

In FIG. 4, the control mechanism 7B includes a large-diameter piston 13 and a small-diameter piston 14 disposed on a rod 12 that engages with and controls the swash plate 11 of the hydraulic pump 1. The former chamber is connected to the pilot operation switching valve 15, and the latter chamber is connected to the pilot operation switching valve 8.

When the large-diameter piston 13 receives a load pressure via a pilot-operated switching valve 15 that switches when the load pressure reaches a predetermined switching force _P1 , the swash plate 11
The rod 12 is moved to the right in the figure in order to set the piston at a certain discharge amount position, and the small diameter piston 14 is moved to this maximum position via the pilot operated switching valve 8 which is switched when the load pressure reaches the set maximum pressure _P3 . When receiving a high load pressure, the rod 12 is further moved to the right in the figure in order to raise the swash plate 11 to the unloading position.

That is, the switching valve 15 opens when the load pressure introduced via the directional control valve 6 reaches its set pressure P ₁ and introduces the load pressure into the sliding chamber 13', and the switching valve 8 opens when the load pressure introduced via the directional control valve 6 reaches the set pressure P1. When the set pressure P ₃ (>P ₁ ) is reached, it opens to introduce load pressure into the sliding chamber 14'. In this case, the large-diameter piston 13 is fitted on the rod 12 with a sliding bearing 13a so as to be able to slide relative to each other, but when it moves to the right in the figure due to the load pressure in the sliding chamber 13', Large diameter piston 13 is rod 1
The rod 12 collides with a stopper 12a fixed in the middle of the rod 2 at its inner diameter portion, and moves the rod 12 together to the right in the figure against a swash plate biasing spring (not shown) of the pump. When the large-diameter piston 13 reaches an inner wall stepped portion 18 provided halfway in the sliding chamber communicating with the opposite tank side corresponding to the discharge amount position, it does not move further to the right. On the other hand, by moving the small diameter piston 14 to the right in the figure, the rod 12 is slid relative to the inner diameter part of the large diameter piston 13, and is further moved to the right in the figure, and the swash plate 11 is cut off. It is becoming possible to do so. The small diameter piston 14 is retracted by the rod 12 being pushed back by the biasing spring of the swash plate 11 of the pump when the switching valve 8 is switched and the inside of the sliding chamber 14' communicates with the tank. At this time, when the rod 12 returns, the large diameter piston 13 collides with the stopper 12a of the rod and is moved back.

Further, in FIG. 5 showing still another example of the control mechanism, the control mechanism 7c presses the small diameter piston 14 of the rod 12 similar to the above example with the spring 16,
The switching valve 15 is connected to the sliding chamber 13', and another pilot operated switching valve 17 is connected to the sliding chamber 14'.

In this case, the switching valve 17 switches when the load pressure reaches another set pressure value P ₂ (>P ₁ ) lower than the maximum pressure P ₃ set by the switching valve 8 in the above example, and the subsequent load pressure increase On the other hand, the small diameter piston 14 moves the rod 12 to the right in the figure in order to raise the swash plate 11 according to an approximate constant torque characteristic by the spring force of the spring 16.

According to the present invention, in which the pump is controlled by the control mechanism 7B shown in FIG. 4, the pump discharge amount q is controlled by the --
--It can be controlled up to a predetermined pressure on the stairs, and when the pump pressure reaches P ₁ , the switching valve 15
opens and the large diameter piston 13 moves the rod 12 into the fourth position.
Slide the swash plate 1 to the right while facing the figure.
When the inclination angle of 1 becomes smaller and further rises to the maximum pressure P3, the switching valve ₈ opens and the small diameter piston 14 slides to the right, thereby further reducing the swash plate inclination angle. Note that by using another pilot-operated switching valve, it is possible to perform multi-stage control with one additional stage between _P1 and _P3 .

If the pump is controlled by the control mechanism 7c in FIG. 5, which is another example, the pump discharge amount q can be controlled as shown in A' in FIG. ₁ and the switching valve 17 is set to P ₂ , due to the spring force of the spring 16 pressing against the small diameter piston 14, the pressure approximately follows the curve -A' in Fig. ₂ when the pressure exceeds P 2. Change.

Therefore, according to this invention, the steering torque applied by the operator to the steering wheel drives the variable displacement hydraulic pump and is converted into liquid energy, and the energy actuates the hydraulic actuator and is transmitted through the link mechanism etc. The hydraulic pump senses and introduces the hydraulic pressure generated in proportion to the wheel turning resistance, and operates its control mechanism to turn the wheel against the wheel turning resistance. It is possible to reduce the steering torque by automatically switching the discharge volume at a certain load pressure, and there is no need to use a large spring in the pump control mechanism for this purpose. Since it can deal with changes in wheel turning resistance, the design is easy and the structure can be made compact.Also, by predicting the magnitude of the turning resistance in advance and automatically or manually changing the pump pressure to overcome it to the set pressure. It is also possible to control the discharge volume per pump revolution, and as the turning resistance increases, a large hydraulic pressure is required. ,
Since the pump drive torque, which is expressed as the product of the hydraulic pressure and the discharge amount, does not increase proportionally, the pump can be steered without increasing the steering force. Therefore, in agricultural tractors, when driving on general roads and in fields, or when forklifts and small vehicles are empty and loaded, the turning resistance from the vehicle is affected by the road surface condition and wheel load. Therefore, it is particularly effective because these vehicles generally run at low speeds, so even if the steering wheel rotation speed increases relative to the vehicle turning radius, there is no problem with driving, and even if the turning resistance is large, it is possible to turn with a small radius. Because you can
Along with the decrease in uncultivated land in the corners of fields,
This invention has many practical benefits, such as ease of turning operation in workplaces, aisles, etc.

[Brief explanation of the drawing]

Fig. 1 is an explanatory circuit diagram showing an example of a hydraulic steering device driven by manual steering force, and Fig. 2 shows the hydraulic pump discharge force P and the discharge volume q per pump rotation.
3 is a diagram showing the relationship between the turning resistance R of the wheels and the steering force f, FIG. 4 is an explanatory circuit diagram showing the control mechanism of the main part of an embodiment of the present invention, and FIG. FIG. 2 is an explanatory circuit diagram showing a control mechanism of a main part of another embodiment. 1: Hydraulic pump, 2: Handle, 3: Hydraulic actuator, 4: Link mechanism, 5: Wheel, 6: Directional control valve, 7A, 7B, 7C: Control mechanism, 8, 1
5, 17: Pilot operation switching valve, 9: Piston, 11: Swash plate, 12: Rod, 12a: Stopper, 13a: Sliding bearing, 14: Small diameter piston.

Claims (1)

[Scope of utility model registration request] A variable capacity hydraulic pump that can be rotated in forward and reverse directions is attached to the handle so that it can be rotated according to the rotation of the handle, and a hydraulic actuator that operates by introducing the pressure liquid discharged from the pump is operated via a link mechanism. The wheels are configured to turn, and only the high-pressure liquid generated in response to wheel turning resistance is sensed and introduced via a directional control valve provided in the pump, and the pump is configured to rotate per rotation of the pump in response to the liquid pressure. The control mechanism is equipped with a rod for controlling the discharge volume of the pump, a large-diameter piston and a small-diameter piston combined with the rod, and the hydraulic pressure is predetermined. When a predetermined switching pressure value is reached, the fluid pressure is applied to the large-diameter piston to move the rod to a predetermined intermediate discharge volume position, thereby increasing the discharge volume of the pump in steps. a first pilot-operated switching valve that reduces the switching pressure value to a predetermined value; A steering device for a work vehicle, comprising a second pilot operated switching valve that further reduces the discharge amount of the pump by further moving the rod.