JPH04103469A - Four-wheel steering system - Google Patents

Abstract

PURPOSE:To control steering of rear wheels without providing an electronic control device, by equipping the steering system with an oil pressure pump permitting the amount discharged during low-speed travel to become larger than the amount discharged during high-speed travel, and with a control valve performing change-over of an oil passage so as to cause the rear wheels to be steered in the opposite direction to the direction of front wheels. CONSTITUTION:The steering system is provided with an oil pressure pump 1 driven by an engine 7, the oil pressure pump 1 being equipped with a responsive-to-number-of- engine-revolution type flow control valve in which the degree of opening of the orifice is changed in response to the number of engine revolutions so that when the number of engine revolutions is small, the amount discharged may be increased and when that number is increased, the amount discharged may be greatly reduced. And an oil pressure cylinder 2 is disposed laterally at a rear position of the vehicle and opposite ends of a piston rod 4 are connected to wheel supports 12 of rear wheels 5 via tie rods, respectively. A control valve 3 is provided which is intended to control supply or discharge of a pressurized oil with respect to this oil pressure cylinder 2. The valve 3 is operated in interlocking relation with the rotation of a steering wheel 16, thereby turning the rear wheels in opposite direction to the direction of front wheels.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a four-wheel steering system, and more particularly, to a four-wheel steering system configured to steer the rear wheels in the opposite phase (in the opposite direction) to the front wheels when the steering wheel is turned during low-speed driving.

[Section that tries to invent or solve @]

For example, in the case of a four-wheel drive vehicle for off-road driving, the engine and transmission installed are generally large, so the chassis frame on which they are mounted must also be large with a wide gap between the left and right sight frames. It is often provided. Therefore, it is not possible to secure enough steering space between the chassis frame and the wheels placed on the side of the image, and since large tires are installed, the maximum wheel (front wheel) The reality is that the amount of steering has to be set smaller than that of a passenger car type vehicle. However, even when the steering wheel is turned to the maximum, the turning ability is not very good, and there is a lack of ease of driving. A way to solve the second problem is to install a four-wheel steering system so that when the steering wheel is turned off while driving at low speeds,
One possibility is to steer the rear wheels in the opposite direction (opposite phase) to the front wheels. This is because the turning radius can be reduced by reverse phase steering of the rear wheels. Various types of four-wheel steering devices have been proposed in the past. For example, Japanese Patent Application Laid-Open No. 61-85274 discloses a hydraulic cylinder that transmits the movement of a piston rod to the rear wheels to steer the rear wheels, a control valve that controls hydraulic pressure sent from a hydraulic pump to the hydraulic cylinder, and A variable steering ratio mechanism for controlling the steering ratio (ratio of the steering angle of the rear wheels to the steering angle of the front wheels), and an electronic control device that controls the variable steering ratio mechanism based on vehicle speed information from a vehicle speed sensor. In addition, the control valve is configured to switch oil passages and adjust oil pressure in accordance with the steering ratio and steering angle determined by the variable steering ratio mechanism. According to this four-wheel steering device, the rear wheels are steered by a predetermined amount in a predetermined direction according to the vehicle speed and the steering angle, and as described above, the rear wheels are not steered in the opposite phase during a low-speed turn. It can be done without any problem. However, since the four-wheel steering system disclosed in the above-mentioned publication is equipped with an electronic control device, it is not suitable for mounting on an off-road vehicle. When driving off-road, it is common for cars to be submerged in water when driving on roads (e.g., flooded waterways) or when crossing rivers, but electronic control units can be damaged or damaged if they get wet or submerged in water. This is because there is a high risk of damage to the electronic control unit, and it may also lead to failure of the electrical system surrounding the electronic control unit. In that case, the four-wheel steering system becomes inoperable. In addition, in the case of the four-wheel steering system disclosed in the above publication, in addition to the electronic control device, a variable steering ratio mechanism and a vehicle speed sensor are required, so the mechanism is complicated and the electronic control device is expensive. Therefore, there is also the problem that the cost of configuring the device is high. The present invention was devised under the above circumstances, and when the steering wheel is turned during low-speed driving, the rear wheels are steered in the opposite phase direction in response to the steering wheel being turned, thereby improving the turning ability. In addition to this, a four-wheel drive system has been developed that allows such control to be performed with a simple mechanism and without the need for an electronic control device, and that is sufficiently durable for use in off-road driving. The purpose is to provide a wheel steering device.

[Means to solve the problem]

In order to solve the above problems, the present invention takes the following technical measures. That is, the four-wheel steering system of the present invention includes a hydraulic pump configured such that the discharge amount during low-speed running is larger than the discharge amount during high-speed running, and a hydraulic pump that is operated by receiving the hydraulic pressure from the hydraulic pump. and a hydraulic cylinder that transmits the movement of the piston rod to the rear wheels to steer them, and is provided on the oil path between the hydraulic pump and the hydraulic cylinder, and is operatively connected to the steering shaft or steering gear. and a mount roll valve that is operated in conjunction with the rotation of the steering wheel and switches the oil passage between the cylinder right chamber and the cylinder left chamber of the hydraulic cylinder so as to steer the rear wheels in the opposite direction to the front wheels. It is characterized by having the following.

[Operation and effects of the invention]

When the hydraulic cylinder is activated, the rear wheels are steered by the movement of the piston rod. A control valve for this hydraulic cylinder is operated in conjunction with the rotation of the steering wheel, and switches the oil path to the hydraulic cylinder so that the rear wheels are steered in the opposite direction to the front wheels. Further, the hydraulic pump that supplies hydraulic pressure to the hydraulic cylinder is configured so that the discharge amount during low-speed running is greater than the discharge amount during high-speed running. In this case, the hydraulic cylinder should be set to operate to generate enough oil pressure for the suspension when driving at low speeds.
The rear wheels can be steered when driving at low speeds. That is, during low-speed cornering, the rear wheels can be steered in opposite phases. In the case of the present invention, such rear wheel steering control can be achieved without providing an electronic control device. As mentioned above, the control valve is structured to be linked to the rotation of the steering wheel, and the hydraulic pump is structured to have a large discharge volume when driving at low speeds, thereby making it possible to perform the above-mentioned steering control. There is. Therefore, it can be installed in off-road vehicles without any problems. This is because even if the car is submerged in water, there is no risk of failure due to electrical faults like electronic control type devices. Further, since an expensive electronic control device or a mechanism for controlling the steering ratio is not particularly required, the mechanism is simple and the device can be configured at low cost.

[Explanation of Examples]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the four-wheel steering system of the present invention includes a hydraulic pump 1, a hydraulic cylinder 2 which is operated by receiving the hydraulic pressure from the hydraulic pump 1, and a hydraulic cylinder 2 between the hydraulic pump 1 and the hydraulic cylinder 2. Control valve 3 installed on the oil path
and transmits the movement of the piston rod 4 of the hydraulic cylinder 2 to the rear wheel 5 when the hydraulic cylinder 2 is operated, so that the rear wheel 5 is steered in the opposite direction (opposite phase) to the front wheel 6. It is composed of In addition, illustration of the front wheel steering mechanism is omitted in the figure. Further, the type of this front wheel steering mechanism is not particularly limited, and various types of known types can be installed. In this example, the hydraulic pump 1 is driven by an engine 7. The hydraulic pump 1 is attached to a pump drive shaft 8 whose rotation is transmitted from a rotating shaft 7a taken out from an engine 7 by belt transmission. In the illustrated example, the pump drive shaft 8 is a pump 9 for a power steering device.
The drive shaft 8 is also used to drive the hydraulic pump 1. Further, as shown in FIG. 3, the hydraulic pump l is configured to increase in volume when the discharge amount or engine speed is low, and to become significantly smaller when the engine speed increases. This can be easily done by attaching to the hydraulic pump l an engine speed-sensitive flow control valve (as shown) in which the opening degree of the orifice changes depending on the engine speed (pump rotation speed). In this way, by varying the discharge amount of the hydraulic pump 1 depending on the engine speed, sufficient hydraulic pressure is generated to operate the hydraulic cylinder 2 at low speeds. Note that the discharge amount of the hydraulic pump l may be directly varied depending on the vehicle speed. For example, this means that a speed-sensitive control valve configured by providing a trochoid pump driven by a transmission as a vehicle speed sensor is connected to the hydraulic pump. This can be done by attaching it to 1. Further, the oil passage between the hydraulic pump 1 and the control valve 2 may be closed when the engine speed becomes high or at high speed. On the other hand, as shown in FIG. 1, the hydraulic cylinder 2 is disposed laterally at the rear of the vehicle, and is supported by an unsprung member such as an axle beam. A tie rod 10 is connected to both ends of the piston rod 4, and the tie rod 10 is further connected to a wheel support 12 of a rear wheel 5 supported rotatably around a king pin shaft 11. There is. Therefore, when the piston rod 4 is moved in the left-right direction, the rear wheels 5 are accordingly steered in a predetermined direction. Moreover, a centering spring 13 is built in the cylinder of the hydraulic cylinder 2. When the hydraulic pressure is released, the spring force of the centering spring 13 returns the piston rod 4 to the neutral position. Further, the control valve 3 is connected to a steering shaft 14 or a steering gear 15, and is configured to be operated in conjunction with rotation of a steering wheel 16. In this example, a spool valve is used as the control valve 3, and this is used as the steering shirt)! It operates by transmitting the rotation of step 4. As shown in FIG. 2, the control valve 3 includes a cylindrical valve housing 17 and a valve rod 18 fitted into the valve housing 17 so as to be slidable and rotatable in the axial direction. The valve housing 17 includes an inboard 19a into which oil sent from the hydraulic pump 1 is introduced. 9b1 and a return boat 21 for returning oil to the reservoir tank 20. Furthermore, each boat 1 in the valve housing 17
A cylinder right chamber boat 22 for sending oil to the cylinder right chamber 2a of the hydraulic cylinder 2 and a cylinder left chamber boat 22 for sending oil to the cylinder left chamber 2b are located at positions offset from 9.21 in the circumferential direction. A commercial boat 23 is provided. On the other hand, the hull blonde 18 has a threaded shaft portion 24 at the tip.
The threaded shaft portion 24 is screwed into the threaded hole portion 17a of the valve housing 17. Further, a gear 25 is attached to the base end of the valve rod 18, and rotation is transmitted to this gear 25 from a gear 26 attached to the steering shaft 14 via an intermediate gear 27. Therefore, the valve rod 18 is rotated in conjunction with the rotation of the steering shaft 14, and at this time is moved in the axial direction by receiving the feed of the screw in the screw fitting portion. Furthermore, oil passage opening grooves 28a and 28b are provided at two axially distant positions in the intermediate shaft portion of the valve rod 18, which are formed over the entire circumference. As shown in FIG. 2, the cylinder right chamber boat 22 and the cylinder left chamber boat 23 are communicated with the inboats 19a and 19b and the return boat 21 through the oil passage opening grooves 28a and 28b, respectively. In this state (hereinafter, this state will be referred to as a hydraulic non-operation state), the hydraulic cylinder 2 is not operated, and therefore the rear wheels 5 are not steered either. on the other hand,
In this state, the valve rod 18 is moved in the axial direction, and only one of the cylinder right chamber boat 22 or the cylinder left chamber boat 23 is communicated with the inboard 19 via the oil passage opening groove 28a or 28b. state (hereinafter referred to as
When this state is called a hydraulic operating state, the hydraulic cylinder 2 is operated and the rear wheels 5 are steered. When the steering wheel is turned to the right, the cylinder boat 23 for the left chamber communicates with the import 19 and enters the above-mentioned hydraulic operating state, and when the steering wheel is turned to the left, the cylinder boat 22 for the right chamber communicates with the inboard 19. It is set to be in communication with the above-mentioned hydraulically operating state. Thereby, when the steering wheel is turned, the rear wheels 5 are steered in a phase opposite to the front wheels 6. Further, in this example, as shown in FIG. 4, when the steering wheel is turned by a predetermined angle or more, the hydraulic pressure is activated and the rear wheels 5 begin to be steered. This can be set by adjusting the rotation ratio of the valve rod 18 to the steering shaft 14, the position of the oil passage opening groove, etc. The reason why the rear wheels 5 are steered when the steering angle exceeds a predetermined amount is as follows.
This is because the steering angle generally increases when turning at low speeds. Next, the operation of this four-wheel steering system will be explained. A hydraulic pump l that supplies hydraulic pressure to the hydraulic cylinder 2 generates hydraulic pressure that moves the piston rod 4 against the spring force of the centering spring 13 when the engine speed is low. That is, by operating the hydraulic cylinder 2, the rear wheels 5 can be steered. On the other hand, when the engine speed is high, the discharge amount of the hydraulic pump l is significantly reduced,
The piston rod 4 cannot be moved, or even if it can be moved it is only a small amount, in which case the rear wheel 5
The amount of steering is also kept to a very small amount that has almost no effect on maneuverability or running stability. In this way, when the engine speed is low to generate sufficient hydraulic pressure, in other words at low speed, when the steering wheel is turned by a predetermined angle or more, the control valve 3, which is activated in conjunction with this, operates the hydraulic cylinder. The oil passages are switched between the cylinder right chamber 2a and the cylinder left chamber 2b of No. 2, resulting in the above-mentioned hydraulic operating state. As a result, the piston rod 4 is moved and the rear wheels 5 are steered. In this case, when the steering wheel is turned to the right, the cylinder left chamber 2b is communicated with the import 19, and the rear wheel 5 is steered to the left. Room 2a or inboard 1
9, and the rear wheels 5 are steered to the right. That is, during low-speed cornering, the rear wheels 5 can be steered in a phase opposite to the front wheels 6. Also,
In this case, as the steering angle increases, the valve opening of the control valve 3 increases, and as shown in FIG. 4, the turning angle of the rear wheels 5 also increases. In addition, if the gear position of the transmission is high gear, even if a certain speed is being achieved, the engine speed is low, or in such a case, the rear wheels are steered to 5 or the opposite phase. No such inconvenience will occur. When driving at medium or high speeds, the amount of steering operation required when turning or changing lanes is generally small (in this example, if the steering angle is within a predetermined range, the control valve 3 remains in the above-mentioned hydraulic inactive state). This is because the hydraulic cylinder 2 cannot be operated.In the case of the present invention, even if the four-wheel steering device that is sensitive to vehicle speed and steering angle as described above is achieved, an electronic control device is not required. The control valve 3 is structured to be linked to the rotation of the steering wheel, and the hydraulic pump 1 is configured to be responsive to engine speed in this example, thereby making it possible to control the steering of the rear wheels as described above. Therefore, it can be installed in off-road vehicles without any problems, as there is no risk of failure when it gets wet with water, unlike electronically controlled devices.The scope of the present invention is as follows: The invention is not limited to the embodiments described above. For example, when the steering wheel is turned from the neutral position, the rear wheels or the opposite phase may be steered at the same time. Also, the type of control valve is also a particular consideration. Alternatively, it may be linked to the steering gear.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing a four-wheel steering device according to an embodiment of the present invention, FIG. 2 is a diagram showing a cross section of a control valve of the four-wheel steering device according to an embodiment, and FIG. 3 is a diagram showing an example of an embodiment of the present invention. FIG. 4 is a graph showing the relationship between the engine rotation speed and the discharge amount in the hydraulic pump according to the example, and FIG. 4 is a graph showing the relationship between the steering angle and the rear wheel turning angle according to the example. l...Hydraulic pump, 2...Hydraulic cylinder, 2a...
・Cylinder right chamber, 2b... Cylinder left chamber, 3... Control valve, 5... Rear wheel, 14... Steering shaft, 15... Steering gear, 16...
・Steering wheel.

Claims (1)

[Claims] (1) A hydraulic pump configured such that the discharge amount during low-speed running is larger than the discharge amount during high-speed running, and which is operated by receiving the hydraulic pressure from the hydraulic pump and controls the movement of the piston rod. A hydraulic cylinder is installed on the oil path between the hydraulic pump and the hydraulic cylinder, and is connected to the steering shaft or steering gear, and is linked to the rotation of the steering wheel. and a control valve that is operated to switch the oil passage between the right cylinder chamber and the left cylinder chamber of the hydraulic cylinder so as to steer the rear wheels in a direction opposite to that of the front wheels. Four-wheel steering device.