JPH0485174A - Steering system for automobile - Google Patents

Abstract

PURPOSE:To improve stability at the time of high speed running as well as to improve controllability at the time of rest steering by installing a frequency- dependent type steering damper, where damping force is varied according to size of a travel speed variation in a transfer shaft, in an interval between this transfer shaft steering wheel and a car body. CONSTITUTION:In a steering damper 30, the more left side than a partition wall 32 functions as a high damping force damper and the right as a low damping force damper, respectively. Each spring constant of both coil springs 46 and 48 becomes reversed of the size relation of each damping coefficient of these high and low damping force dampers. Each plate spring 55 covering respective orifices 42, 43 constitutes a check valve. Consequently, since steering operation at time of high speed running is slow, a travel speed variation in a rack shaft 2 is little and damping force to low frequency displacement works from the steering damper 30 to the rack shaft 2. At time of rest steering, there is interposed high frequency displacement, where the travel speed is largely varied at time of hand transferring, but only small damping force acts on it.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a steering system for an automobile equipped with a steering damper for the purpose of improving high-speed running stability.

[Conventional technology]

Conventionally, a structure in which a steering damper is installed between a tie rod connected to a steering wheel or a transmission shaft such as a rack shaft and the vehicle body has been adopted for the purpose of improving high-speed running stability. 60-45473, etc.). By applying a damping force to the rack shaft using the above-mentioned steering damper, it is possible to prevent the steering wheel from wobbling during high-speed driving, thereby improving stability during high-speed driving.

[Problem to be solved by the invention]

However, the above-mentioned steering damper generates a damping force even during steering, and this creates a problem in that the steering damper feels stuck and impairs operability, especially when steering at a large steering angle such as stationary turning while driving at low speeds. ing. In other words, the above-mentioned stationary steering operation is performed by moving the rack shaft in one direction while alternately holding the steering wheel between the left and right hands. In this case, when changing hands as described above, the movement of the rack shaft momentarily becomes almost stationary, and immediately after changing hands, the movement speed rapidly increases from the almost stationary state. In this way, an operation is performed in which a state in which the moving speed suddenly changes each time the hand is changed is intermittently repeated. As described above, when the speed of movement of the rack shaft is increased rapidly from a stationary state, an excessive damping force is applied from the steering damper, making the rack feel as if it is stuck.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to provide a steering system for an automobile that can improve stability during high-speed driving and improve operability when turning stationary. There is a particular thing.

[Means to solve the problem]

Therefore, the steering device for a vehicle of the present invention has a transmission shaft that reciprocates in the width direction of the vehicle body according to the steering angle of the steering wheel to steer the steered wheels, and a transmission shaft that is provided between the vehicle body and the transmission shaft according to the movement of the transmission shaft. In an automobile steering system connected to a steering damper that exerts a damping force on the transmission shaft, the damping force for high-frequency displacements with large changes in travel speed on the transmission shaft is greater than the damping force for low-frequency displacements with small changes in travel speed. The steering damper is also characterized in that it consists of a frequency-dependent damper that generates a small damping force.

[For production]

According to the above configuration, the steering wheel is operated relatively slowly when driving at high speeds, so in this case, the change in the moving speed of the transmission shaft is small, and therefore the damping force for low frequency displacement is applied to the steering wheel. The damper acts on the transmission shaft to provide an appropriate feeling of response, thereby improving stability during high-speed running.

On the other hand, during stationary steering, the transmission shaft is moved in one direction by a high-frequency displacement that causes a large change in movement speed when changing hands, etc., as described above. On the other hand, the above-mentioned steering damper exerts only a small damping force. Therefore, the conventional problem of getting stuck due to excessive damping force is eliminated, and operability is improved.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

As shown in FIG. 3, the front wheel steering device 1 is provided with a rack shaft (transmission shaft) 2 that can reciprocate in the width direction of the vehicle body (left and right directions 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, respectively. - 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 the steering wheel 6 is rotated, the rack shaft 2 is moved in the width direction of the vehicle body by the rack and pinion mechanism of the steering gear device.
As a result, the direction of the front wheels 5, 5 can be changed.

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 2o 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
8, 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 performing a steering operation, 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 can be steered.

The front wheel steering device 1 described above is further provided with a steering damper 30 disposed substantially parallel to the rack shaft 2. A partition wall 32 is provided in the closed cylinder tube 31 of the steering damper 30 and is perpendicular to the axial direction thereof, and two oil chambers 33 and 34 are formed on both sides of the partition wall 32. These oil chambers 3
First and second pistons 35 and 36, which are slidable in the axial direction, are fitted into the pistons 3 and 34, respectively. The tip of the first piston rond 38 extends from the first piston 35 in the left oil chamber 33 to the left through the end plate 37 that covers the left end of the left oil chamber 33, and the connecting rod 39 The second piston 36 in the oil chamber 34 on the right side in the figure is connected to the rack shaft 2 via
The tip of a second piston rod 41, which extends rightward through an end plate 40 covering the right end of the piston rod, is connected to the vehicle body.

As shown in FIG. 1, the first piston 35 has a first
The first
A pair of first orifices 42 in the shape of small holes are bored through the piston 35 from side to side. Similarly, the second piston 36 also has a pair of second orifices 43 in the shape of small holes.
43 is drilled. These second orifices 43, 43 are formed with a larger diameter than the first orifices 42, 42, so that the first piston 35 side and the second orifice
Each damping coefficient C, -C with respect to the piston 36 side.

is configured such that C,>C. Therefore, in the following, the left side of the partition wall 32 is a high damping force damper,
The right side will be described as a low attenuation Kadamba.

An intermediate spring bearing plate 44 is attached to the outer periphery of the cylinder tube 31 at a midway point in the axial direction that is substantially the same as the partition wall 32 . This intermediate spring holder includes a plate 44,
Cylinder tube 31 in first piston rod 38
The first spring holder attached to the left part is plate 4.
5, the first one surrounds the high damping force damper side from the outside.
A coil spring 46 is provided. Further, between the intermediate spring bearing plate 44 and the second spring bearing plate 47, which is attached to a portion of the second piston rod 41 to the right of the cylinder tube 31, there is a gap surrounding the low damping force damper side. A second coil spring 48 is provided. These first
・The second coil springs 46 and 48 have a spring constant of +'
Kz is configured such that K<K, contrary to the magnitude relationship of the damping coefficients C+'Cz of the high damping Kadamba and the low damping Kadamba.

In addition, each piston 35 in each of the oil chambers 33 and 34
Further outside the sliding contact surface of 36, there are oil chambers 33 and 36, respectively, which correspond to the movements of the first and second piston ronds 38 and 41, respectively.
Gas chambers 51 and 52 are provided for allowing volume changes of 34. In addition, the first and second spring receivers are plates 45 and 47.
Stopper members 53 and 54 made of synthetic rubber are attached to the axial center side of each surface of the cylinder tube 31, respectively. In addition, the first and second orifices 42 and 43 are diagonally bored so that the opening positions on both end faces of each piston 35 and 36 are slightly different in the radial direction. Leaf springs 55 . . . which cover the radially inward openings of the orifices 42 and 43 are attached to both end surfaces. That is, each of the orifices 42 and 43 has a check valve structure that allows oil to flow in the direction from the opening on the side not covered by the leaf spring 55 toward the opening on the side covered by the leaf spring 55. In addition, each pair of orifices 42, 42, 43, 43 in each piston 35, 36 has a structure in which the permissible flow directions are opposite to each other. Therefore, when each piston 35, 36 moves in the axial direction relative to the cylinder tube 31, it passes through one of the pair of orifices 42, 42, 43, 43 depending on the direction of movement. The oil in each oil chamber 33 and 34 flows,
Due to the difference in flow resistance at this time, the damping coefficients C, -C
Each damper is configured as a damper having two dampers.

In the above-mentioned steering damper 30, when the rack shaft 2 is held at a position corresponding to straight-ahead running, the cylinder tube 31 is moved by the first coil spring 46 acting on the plate 44, and the intermediate spring bearing attached to the cylinder tube 31 is The spring force F (Kl) of the second coil spring 48 and the spring force F (K,
) are located in a position that balances each other.

From this state, when the rack shaft 2, that is, the first piston rod 38 moves relatively slowly in response to the operation of the steering wheel 6, the cylinder tube 31 moves with this movement. The first piston 35 side of the high damping force damper also moves so that relative displacement with respect to the cylinder tube 31 occurs simultaneously on the second piston 36 side of the low damping force damper. In other words,
In the case of a structure where the first and second coil springs 46 and 48 are not provided and two dampers with different damping coefficients are connected in series, first, on the high damping force damper side, the piston and cylinder tube Almost no relative displacement occurs, and a relative displacement occurs only on the low damping force damper side, and after the piston inside this low damping force damper bottoms out against the end face of the cylinder tube, the relative displacement on the high damping force damper side occurs. It exhibits the behavior of causing relative displacement. That is, the damper effect is first applied by the low damping force damper, and then changes in order to the operating state of the high damping force damper.

However, in the steering damper 30 in the above embodiment, when the first piston rond 38 moves relatively slowly, the springs are adjusted according to the amount of deformation of the first and second coil springs 46 and 48 in the process of this movement. The forces F(Kl) and F(K2) further act, and the spring force F of the first coil spring 46 (the sum of the damping force F(C,) of KO and the high damping force damper, and the sum of the damping force F(C,) of the second coil spring 48 Spring force F (K2) and damping force F (C2) of the low damping force damper
A state is maintained in which the sum of Then, in a state where the first piston 35 in the high damping force damper generates a certain degree of relative displacement with respect to the cylinder tube 31, F(K,)
+ F (C1) and F (Kg) + F (C2) are each damped by a high damping force damper and a low damping force damper as each coil spring 46 and 48 so that the magnitude of the force is about the same as each other. The spring constant (Kl < Kt) is set in a relationship opposite to the magnitude relationship of the coefficient (Cr > Cz). As a result, as the first piston rod 38 moves, the cylinder tube 31 moves so that both the first piston 35 and the second piston 36 simultaneously move relative to the cylinder tube 31, and as a result, The sum of the damping forces simultaneously generated by the high damping force damper and the high damping force damper acts on the rack shaft 2.

On the other hand, the change in the moving speed of the rack shaft 2 increases, and
Displacement such that the amplitude becomes small, ↑ that is, the frequency is high (
When such a displacement occurs in the rack shaft 2, the position of the cylinder tube 31 is such that the damping force becomes more dominant than the spring force accompanying the deformation of each coil spring 46, 48, and the balance relationship as described above is maintained. It comes off. In particular, rack axis 2
When a high-frequency displacement occurs in the first piston 35 side of the high-damping Kadamba, it becomes difficult for oil to flow through the first orifice 42 having a small flow path diameter, resulting in a so-called hydraulic lock state. At this time, there is almost no relative movement between the first piston 35 and the cylinder tube 31, and the cylinder tube 31 moves toward the first piston rod 38.
move almost as one. Therefore, a relative movement approximately corresponding to this movement occurs only between the second piston 36 of the low damping force damper and the cylinder tube 31,
Damping force is generated only on this low damping force damper side. As a result, the damping force acting on the rack shaft 2 becomes smaller as a result of no damping action occurring on the high damping force damper side.

As mentioned above, the steering damper 3o is, for example, a second damper.
As shown in the figure, the damping force has a characteristic that the damping force automatically changes depending on the magnitude of the speed change of the rack shaft 2, that is, the change in the steering frequency. In other words, when the steering frequency is low, the high damping force damper and the low damping force damper generate damping forces at the same time, and the sum of these acts on the rack shaft 2. The damping effect of the damping force damper gradually decreases and the effect of the low damping force damper becomes dominant, and furthermore, for high frequency displacements that cause hydraulic lock in the high damping force damper, this high damping force Almost no damping force acts from the damper, and only a small damping force from the low damping force damper acts on the rack shaft 2.

As a result of the provision of the steering damper 30 that depends on the steering frequency as described above, steering stability is obtained during high-speed running, and the feeling of getting caught when turning the vehicle stationary is prevented. In other words, when driving at high speed, the steering operation is performed slowly, and the steering is light and the steering force is reduced, so the steering operation is relatively smooth, and the rack shaft 2 is therefore Operation is carried out under conditions where small low frequency displacements occur. In this case, a large damping force is generated by the steering damper 30, giving an appropriate feeling of response.
Improved stability.

On the other hand, when a stationary steering is performed in a low-speed driving state, this involves an operation of alternately holding the steering wheel between the right and left hands, for example, while the steering wheel is heavy, and when switching hands, the operating speed changes rapidly. That is, although the rack shaft 2 moves fully in one direction in a low-frequency displacement state as a whole, a behavior in which high-frequency displacement locally overlaps occurs in the middle. Conventionally, as described above, when the driver tries to operate the vehicle by changing hands, a large damping force is applied from the steering damper, resulting in a feeling of getting stuck. However, in the steering damper 30 of the above embodiment, the damping force is suppressed to a small value against displacement of high frequency components, so the above-mentioned stuck feeling is eliminated, and therefore, stationary steering operation is also possible. It can be done smoothly.

Note that the above embodiments do not limit the present invention, and various modifications can be made within the scope of the present invention. For example, the steering damper 30 as a frequency-dependent damper may include a spring system outside the cylinder tube 31. Although the frequency-dependent damper has been described with reference to a structure in which the damper is arranged in the cylinder tube, it is also possible to configure the frequency-dependent damper in other structures, such as having a spring system within the cylinder tube.

〔Effect of the invention〕

As described above, the automobile steering system of the present invention can handle high-frequency displacements with large changes in moving speed on the transmission shaft.
The steering damper is constructed of a frequency-dependent damper that generates a damping force smaller than the damping force for a low-frequency displacement with a small change in moving speed.

As a result, when driving at high speeds when the steering wheel is operated relatively slowly, the damping force for low frequency displacement acts from the steering damper on the transmission shaft, providing an appropriate feeling of response. Improved stability.

On the other hand, during stationary steering, the above-mentioned steering damper exerts only a small damping force during high-frequency displacement where the moving speed changes greatly when changing hands, etc., so the feeling of getting stuck due to excessive damping force that conventionally occurs is eliminated. This has the effect of improving operability.

[Brief explanation of drawings]

1 to 3 show one embodiment of the present invention. FIG. 1 is a sectional view of a main part showing the configuration of a steering damper. FIG. 2 is a graph showing an example of damping force characteristics of a steering damper. FIG. 3 is a schematic diagram showing the overall configuration of a steering system for an automobile having a steering damper. 2 is a rack shaft (transmission shaft), 5 is a front wheel (steering wheel), 6 is a steering wheel, and 30 is a steering damper.

Claims (1)

[Claims] 1. A damping force corresponding to the movement of the transmission shaft is provided between the vehicle body and a transmission shaft that reciprocates in the width direction of the vehicle body to steer the steered wheels according to the steering angle of the steering wheel. In an automobile steering system in which a steering damper is connected to the transmission shaft, the damping force is smaller for high-frequency displacements with large changes in travel speed on the transmission shaft than for low-frequency displacements with small changes in travel speed. A steering system for an automobile, characterized in that the steering damper is comprised of a frequency-dependent damper that generates force.