JPH0485176A - Steering system for automobile - Google Patents

Abstract

PURPOSE:To improve stability at time of rectilinear running and controllability at time of rest steering by installing a damping force lowering means, operating to form a bypass passage in a throttle passage with a pressure differential between two compressed oil chambers holding a piston of a power cylinder in between, in a steering damper in an additional manner. CONSTITUTION:When compressed oil is fed to a power cylinder 11 through a compressed oil passage 16L according to operation of a steering wheel 6, simultaneously it acts on a pilot port a1 through a pilot passage 40L, and a spool of a flow selector control valve 38 is displaced from a neutral position T0 to a first selector position T1 according to a pressure differential. In consequence, if it is through a bypass passage 37, both oil chambers 36L, 36R of a steering damper 30 are interconnected to each other, and when a cylinder tube 31 is displaced toward the right together with a rack shaft 2, oil in the oil chamber 35L at the left flows into the side of the oil chamber 36R at the right if being passed through the bypass passage 37 in addition to both orifices 35, 35. Therefore a damping coefficient in the steering damper 30 becomes lessened, thus damping force acting on the rack shaft 2 is lowered.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a steering system for an automobile that includes a power cylinder that assists steering force and a steering damper that aims to improve straight-line running stability. It is.

[Conventional technology]

2. Description of the Related Art Conventionally, in order to reduce steering force when driving at medium or low speeds, power cylinders that assist steering wheel operations using hydraulic pressure have been installed in steering devices of automobiles.

On the other hand, for example, in Japanese Patent Application Laid-Open No. 60-45473, a steering damper is installed between a tie rod connected to a steering wheel and the vehicle body, and the tie rod is connected to the steering damper in order to prevent the steering wheel from wobbling during high-speed driving. A configuration has been disclosed in which a damping force is applied to the vehicle, thereby improving stability during straight traveling.

[Problem to be solved by the invention]

However, the above-mentioned steering damper generates a damping force even during steering, and in particular, during a large steering angle steering such as stationary turning while traveling at low speed, a large damping force is generated depending on the operating speed. For this reason, there is a problem in that even in operations performed while being assisted by the power cylinder, the steering force cannot be sufficiently reduced, or the steering force may become stuck in the middle of the steering operation, impairing operability.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to improve the stability of an automobile when driving in a straight line, as well as improve the operability when steering, especially when turning stationary. The purpose of the present invention is to provide a steering device.

[Means to solve the problem]

Therefore, the automobile steering system of the present invention is provided with a power cylinder that is pushed by pressure oil supplied in response to the operation of the steering wheel to assist the operation of the steering wheel, and a cylinder tube that is filled with oil. A steering damper, in which a piston having a throttle flow path is slidably inserted, reciprocates in the width direction of the vehicle body in response to the steering angle of the steering wheel, and is connected to a transmission shaft that steers the steered wheels in accordance with the movement of the steering damper. A steering system for an automobile that is connected between the transmission shaft and the vehicle body to exert a damping force, which bypasses the throttle flow path by the pressure difference between the pressure oil chambers on both sides of the piston in the power cylinder. The steering damper is characterized in that a damping force reducing means operated to form a bypass flow path is attached to the steering damper.

[For production]

According to the above configuration, when the steering wheel is not operated and is located in the straight-ahead position, pressure oil is not supplied to the power cylinder, and therefore there is a pressure difference between the pressure oil chambers on both sides of the piston in the power cylinder. is maintained without.

As a result, the damping force lowering means is maintained in a non-operating state and no bypass flow path is formed, so that the steering damper is maintained in a state where a damping force corresponding to the throttle flow path acts on the transmission shaft.

On the other hand, if the steering wheel is operated and as a result, a pressure difference is created between the pressure oil chambers on both sides of the piston due to the supply of pressure oil to the power cylinder, this pressure difference activates the damping force reducing means. A bypass flow path that bypasses the throttle flow path is formed. Therefore, the oil in the cylinder tube of the steering damper can flow through the bypass flow path in addition to the throttle flow path, and the damping force of this steering damper is greater than when only the throttle flow path is used. also decreases.

In this way, when the steering wheel is being steered, a smaller damping force is automatically applied to the transmission shaft than when the steering wheel is not being steered. As a result, when the steering wheel is not being steered, wobbling of the steering wheel is effectively prevented and straight-line running stability is improved, and when the steering wheel is being steered, it is possible to operate with a smaller steering angle, which allows the steering wheel to be operated at a smaller steering angle. , it is possible to eliminate problems such as getting stuck due to excessive damping force, and improve operability.

〔Example〕

An embodiment of the present invention will be described below based on FIGS. 1 and 2.

As shown in FIG. 1, the front wheel steering device l is provided with a rank shaft (transmission shaft) 2 that can freely reciprocate in the width direction of the vehicle body (in the left-right direction in the figure). Left and right front wheels (steering wheels) 5, 5 are connected sequentially via tie rods 3, 3 and knuckle arms 4, 4. On the other hand, a pinion 8 is attached to the tip of a steering shaft 7 extending from the steering wheel 6, and this pinion 8 meshes with a rack portion 9 formed on the rack shaft 2 to constitute a so-called steering gear device. When you rotate the steering wheel 6,
The rack and pinion mechanism of the steering gear device moves the rack shaft 2 in the width direction of the vehicle body, thereby changing the direction of the front wheels 5, 5.

Further, a flange-shaped piston 12 of a power cylinder 11 is integrally connected to the rack shaft 2. The rack housing 13, which covers the rack shaft 2 and is fixed to the vehicle body, is formed as a cylindrical hydraulic cylinder tube 14 with a large diameter at a portion surrounding the piston 12. Inside this hydraulic cylinder tube 14, left and right pressure oil chambers 15L and 15R partitioned by the piston 12 are pressure oil passages 16L and 16R, respectively.
The control valve 17 is connected to a control valve 17 which is switched and operated in accordance with the rotation of the steering shaft 7. Further, this control valve 17 is connected to a hydraulic pump 20 and an oil tank 21 via a pressure oil supply passage 18 and a return oil passage 19, respectively.

The control valve 17 selects one pressure oil chamber 15L or 15R of the power cylinder 11 in response to the vehicle speed and the rotation of the steering shaft 7, and
B, and also connects the other pressure oil chamber 15R or 15L to the return oil passage 19, whereby the piston 12
, and the rack shaft 2 are configured to be driven from one pressure oil chamber 15L or 15R side to the other pressure oil chamber 15R or 15L side. As a result, the steering wheel 6
When rotating the wheel in either the forward or reverse direction, the rack shaft 2 is moved left and right while being assisted by the hydraulic pressure in the power cylinder 11, and the left and right front wheels 5 are rotated.
・It is designed to be able to steer 5.

The front wheel steering device 1 described above is further provided with a steering damper 30 disposed substantially parallel to the rack shaft 2. The steering damper 30 includes a sealed cylinder tube 31 filled with oil, and a piston 3 slidably inserted into the cylinder tube 31.
2. The tip of a piston rod 33 that extends from the piston 32 through the right end face of the cylinder tube 31 in the drawing is connected to the vehicle body.

Furthermore, the left end of the cylinder tube 31 in the figure is connected to the rack shaft 2 via a connecting rod 34, so that the cylinder tube 31 moves integrally with the rack shaft 2 in the width direction of the vehicle body. .

The piston 32 of the steering damper 30 is provided with a plurality of small orifices (throttled channels) 35, 35 in the case of the figure, which pass through the piston 32 from side to side, at axially symmetrical positions. ing.

A bypass passage 37 that interconnects these oil chambers 36L and 36R is further connected to the oil chambers 36L and 36R, which are partitioned left and right by the piston 32 in the cylinder tube 31, and a flow rate switch is made to this bypass passage 37. Three control valves (damping force reducing means) are provided.

The flow rate switching control valve 38 is a pilot-operated two-boat, three-position spool type switching valve, which blocks the bypass passage 37 at the neutral position T0, and at the first switching position T1 and the second switching position Tt. In each of these, a bypass flow path is formed in which the bypass passage 37 is communicated with the bypass passage 37 through variable throttles 39, 39, respectively. The switching operation of the spool from the neutral position T to the first switching position T1 and from the neutral position T0 to the second switching position iT2 is caused by the oil pressure supplied to each pilot port a1 and a2, These pilot ports at and a2 are connected to pressure oil passages 16L and 16R to the power cylinder 11 via pilot flow passages 40L and 40R, respectively.

Next, the operating state of the front wheel steering device I having the above configuration will be explained.

First, when the steering wheel 6 is in a non-steering state, that is, when the vehicle is maintained in a straight-ahead running state, the operation of the control valve 17 is controlled so that no pressure oil is supplied to the power cylinder 11. At this time, the pressure between the pressure oil chambers 15L and 15R is maintained in an equal pressure state. As a result, the flow rate switching control valve 38 is maintained at the neutral position T, since no pressure difference is maintained between the pilot bow (a+) and 82 in the flow rate switching control valve 38. For this reason, the steering damper 3
At 0, the oil chambers 36L and 36R are maintained in communication only through the orifices 35 and 35 of the piston 32. Therefore, in this state, the steering damper 30 functions as a damper having a high damping coefficient determined by the shapes of the orifices 35. For this reason, for example, disturbance acts on the front wheels 5, 5, and the rack shaft 2
When the rack shaft 2 is displaced, a large damping force corresponding to the displacement speed of the rack shaft 2 is applied from the steering damper 30 to the rack shaft 2. Therefore, the above-mentioned disturbance is attenuated and further absorbed by the steering damper 30, and stability when traveling straight is improved.

On the other hand, when the steering wheel 6 is operated,
Pressure oil corresponding to the vehicle speed and the operation speed of the steering wheel 6 is supplied to one pressure oil chamber 15L or 15R of the power cylinder 11 through the control valve 17 and through either pressure oil passage 16L or 16R depending on the steering direction. Ru. For example 1. When the steering wheel 6 is rotated so as to displace the rack shaft 2 to the right in FIG. , the control valve 17, and the pressure oil passage 16L, and the right pressure oil chamber 15R is supplied with the oil tank 2 through the pressure oil passage 16R, the control valve 17, and the return clean IW 19.
Connects to 1. As a result, a pressure difference is created between the repressurized oil chambers 15L and 15R sandwiching the piston 12 in the power cylinder 11, and this pressure difference acts as a force that pushes the piston 12 to the right. Assisted by this pushing force, the rack shaft 2 is displaced to the right in response to the rotation of the steering wheel 6, which causes the front wheels 5 and 5 to move toward the right.
is steered.

When pressure oil is supplied to the power cylinder 11 through the pressure oil path 16L in response to the operation of the steering wheel 6 as described above, this pressure oil also acts on the pilot port a through the pilot flow path 40L at the same time. As a result, the spool of the flow rate switching control valve 38 is displaced from the neutral position T0 toward the first switching position T in accordance with the pressure difference between the pilot ports a+a2. As a result, even through the bypass passage 37, the oil chambers 36L and 36R in the steering damper 30 are in a state of communication with each other.

As a result, the steering damper 30 along with the rack shaft 2
When the cylinder tube 31 is displaced rightward, the oil in the left oil chamber 36L flows toward the right oil chamber 36R through the bypass passage 37 in addition to the orifices 35, 35. Therefore, the damping coefficient of the steering damper 30 is smaller than when the bypass passage 37 is blocked, and the damping force acting on the rack shaft 2 is reduced.

In this way, when pressure oil is supplied to the power cylinder 11 in response to the operation of the steering wheel 6,
At the same time, the damping force at the steering damper 30 decreases. Therefore, the steering force of the steering wheel 6 is reduced, and the vehicle can be turned with easy operation.

Note that even when the steering wheel 6 is rotated so as to displace the rack shaft 2 to the left in FIG. The only difference is that the direction in which the spool is switched is different, but the operating state is the same as above, and the steering force is reduced.

In addition, in the above, the flow path area is gradually increased in the first switching position T and the second switching position T2 of the flow rate switching control valve 38 according to the pressure difference between the pilot ports a and ``a'', respectively. Variable throttles 39, 39 are provided.Therefore, when high pressure oil is supplied to the power cylinder 11 in order to generate a large pushing force in the power cylinder 11, such as during a stationary turning operation during low-speed driving, Oil easily flows through the bypass passage 37. That is, as shown in FIG. 2, the steering damper 30
is configured such that the damping coefficient gradually decreases as the pressure difference between the pressure oil chambers 15L and 15R of the power cylinder 11 increases. As a result, when an operation is performed to displace the rack shaft 2 at a high speed, such as during a stationary steering operation at low speed, the damping force by the steering damper 30 decreases, and therefore, when stationary steering is performed, etc., the damping force is reduced. The rudder force is reduced and there is no chance of getting caught, etc.
Allows for smooth operation.

In the above embodiment, the damping force reducing means was explained using the flow rate switching control valve 38 having a built-in variable throttle 39, but other types of switching valves such as pilot type relief valves may also be used. It is also possible to configure the

〔Effect of the invention〕

As described above, the automobile steering system of the present invention is operated to form a bypass flow path that bypasses the throttle flow path in the steering damper by the pressure difference between the pressure oil chambers on both sides of the piston in the power cylinder. The damping force reducing means is attached to the steering damper.

As a result, when the steering damper is located in the straight-ahead position, the damping force corresponding to the internal throttle flow path is maintained in a state that acts on the transmission shaft, while when the steering wheel is operated, the steering damper is Switching to reduce the damping force is automatically performed. As a result, the stability during straight running is improved, and smooth operation is possible when turning the vehicle stationary, resulting in improved operability.

[Brief explanation of the drawing]

1 and 2 show one embodiment of the present invention. FIG. 1 is a schematic diagram showing the overall configuration of a front wheel steering device. FIG. 2 is a graph showing an example of the damping characteristics of the steering damper in the front wheel steering device. 2 is a rank shaft (transmission shaft), 5 is a front wheel (steering wheel), 6 is a steering wheel, 11 is a power cylinder, 12 is a piston, 15L/15R is a pressure oil chamber 30 is a steering damper, 31 is a cylinder tube, 32 is a piston, 35
is an orifice (throttled flow path), 37 is a bypass passage, 38
is the flow rate switching control valve (damping force reducing means).

Claims (1)

[Claims] 1. A power cylinder is provided which is pushed by pressure oil supplied in response to the operation of the steering wheel to assist the operation of the steering wheel, and a piston having a throttle flow path in the cylinder tube filled with oil is provided. A steering damper, which is slidably inserted, reciprocates in the width direction of the vehicle body according to the steering angle of the steering wheel, and applies a damping force corresponding to the movement of the transmission shaft to steer the steered wheels. In an automobile steering system connected between a vehicle body and a vehicle body, the power cylinder is operated to form a bypass flow path that bypasses the throttle flow path due to a pressure difference between pressure oil chambers on both sides of the piston in the power cylinder. A steering system for an automobile, characterized in that a damping force reducing means is attached to the steering damper.