JP2864145B2 - Power steering device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic power steering apparatus that assists steering by using a force generated by a hydraulic actuator disposed in a steering mechanism.

[Conventional technology]

In recent years, the power steering device has been proposed as a device that can reduce the force required for steering operation for steering at the time of stopping and traveling at a low speed, and can reduce fatigue caused by long-time driving.
In addition to large vehicles, small vehicles such as ordinary passenger vehicles are also equipped. This power steering device is generally a hydraulic power steering device, which is provided with a hydraulic pump driven by an engine to generate operating hydraulic pressure, and disposed in a steering mechanism and fed from the hydraulic pump. Between the hydraulic actuator that generates the steering assist force by operating with pressure oil
A hydraulic control valve for controlling the supply and discharge of the pressure oil in accordance with the steering wheel operation is provided. The hydraulic control valve is mounted in the middle of a steering wheel shaft connected to the steering wheel, generates a relative angular displacement between the valve body and the casing according to a steering torque applied to the steering wheel, and a throttle formed between the two. 2. Description of the Related Art Rotary hydraulic control valves having a configuration that changes the area are often used.

Now, the steering of a car is performed against the road surface reaction force applied to the steered wheels, and when the road surface reaction force is large or at a stop or running at low speed, a large amount of force is required for steering operation for steering. On the other hand, when the vehicle is traveling at a high speed with a small road surface reaction force, the steering operation can be performed with a small force. Therefore, the power steering device is required to generate a steering assist force that becomes large or small according to the slowdown of the vehicle speed. Further, from the viewpoint of operation feeling at the time of steering operation, the power steering device is required to generate a steering assist force that shows a change mode proportional to a change in steering torque. In response to the former request, that is, a request for generation of a steering assist force that becomes large or small according to the vehicle speed slowdown,
For example, as disclosed in JP-A-52-112922,
Implements drooping that changes the amount of hydraulic oil supplied to the hydraulic actuator via the hydraulic control valve based on the detection result of the vehicle speed, and obtains a larger steering assist force for supplying a large amount of hydraulic oil at stop and at low speeds On the other hand, there is a power steering device that obtains a smaller steering assist force for supplying a small amount of pressure oil at a high speed. Further, as typified by Japanese Patent Publication No. 52-4807, the throttle shape of the hydraulic control valve is devised so that the change in the throttle area is small in a range where the steering torque is small, and the steering torque exceeds a predetermined value. The throttle area is changed abruptly, and the proportionally increasing area of the steering assist force in a small steering torque range, the proportionally increasing area of the steering assist force in a large steering torque range, and the steering torque of 0 are set. A large number of power steering devices have been proposed in the past in which a certain area near a point is obtained, and as shown in FIG. 6, a steering assist force increasing characteristic having two bent portions, that is, a so-called two-stage bending characteristic is obtained. ing.
According to this configuration, only a small steering assist force can be obtained with respect to the steering torque applied to the steering wheel at the time of high-speed running, while appropriate rigidity is given to the steering wheel to increase the straight running stability, while Alternatively, when driving at low speeds, a large steering assist force is assured by applying a steering torque about the transition point to the sudden increase region, and the force required for steering operation is greatly reduced, and when driving at a moderate speed, In this case, a favorable steering feeling can be obtained by a proportional increase mode in the gradually increasing region, and it is possible to meet the above two requirements.

[Problems to be solved by the invention]

However, in the former power steering device, that is, a power steering device that performs drooping of the amount of oil supplied to the hydraulic actuator, an existing vehicle speed sensor can be used for detecting the vehicle speed. Requires an electrical control circuit for opening and closing the oil amount control valve based on
Due to malfunction of the control circuit or the vehicle speed sensor due to the influence of external noise, or failure of the control circuit or the vehicle speed sensor, etc.
It is impossible to adjust the amount of oil during traveling, and there is a risk of causing an accident due to a sudden change in steering feeling.

Further, in the latter power steering device, that is, in the power steering device that realizes the two-stage breaking characteristic, it is difficult to set the inclination in the gradually increasing region mainly used when traveling at a medium speed, If this inclination is set to a large value with emphasis on the reduction of the steering operation force of the steering wheel, the straight running stability on the high-speed side is impaired, and conversely, if the inclination is set to a small value while emphasizing the stability on the high-speed side. However, there is a disadvantage that it is not possible to expect a sufficient steering assist force on the low speed side. The drawback is that
This can be solved by realizing a characteristic having one more bent portion in the gradually increasing region, but it is practically impossible to realize such a characteristic by changing the throttle shape of the hydraulic control valve. Actually, the inclination in the gradually increasing region is set ignoring some inconvenience on the high-speed side.

The present invention has been made in view of such circumstances, and enables generation of a steering assist force that increases or decreases in response to a slow vehicle speed without detecting a vehicle speed and requiring an electrical control circuit. And a power steering device that can eliminate the occurrence of malfunction due to malfunction and failure of the vehicle speed sensor. Further, by using together with a hydraulic control valve capable of realizing the two-stage break characteristic, a steering assist force gradually increasing portion is provided. It is another object of the present invention to provide a power steering device capable of obtaining one more bent portion in the middle of the vehicle, and realizing both stability on the high speed side and generation of sufficient steering assist force on the low speed side. I do.

[Means for solving the problem]

The power steering apparatus according to the present invention is configured such that, between a hydraulic actuator that generates a steering assist force and a hydraulic pump that generates an operating oil pressure thereof, the throttle area is changed according to the steering torque applied to the steering wheel, In a power steering apparatus provided with a hydraulic control valve for changing a supply hydraulic pressure to a hydraulic actuator through a gradually increasing region in a range where the steering torque is small and a rapid increasing region in a large range, the hydraulic control valve and the hydraulic control valve are provided. A predetermined hydraulic pressure passage is provided between the hydraulic pump and a hydraulic oil pump, and a bypass oil passage communicating with the suction side of the hydraulic pump, and a hydraulic fluid upstream of the hydraulic control valve is included in the gradually increasing region. While in the range, performs an operation of reducing the amount of oil passing through the bypass oil passage according to the increase of the oil pressure, and comprises a flow rate control valve that increases the rate of change in the gradually increasing region,
In addition, the hydraulic control valve is characterized in that the hydraulic control valve has a change rate of two or more different throttle areas which is large in a range where the steering torque is large and small in a range where the steering torque is small.

[Action]

In the present invention, paying attention to the fact that the hydraulic pressure on the upstream side of the hydraulic control valve increases in accordance with the operation of the hydraulic control valve accompanying the steering operation, a part of the discharge oil from the hydraulic pump that generates the operating hydraulic pressure is constantly Provide a bypass oil passage to bypass on the suction side,
By the operation of the flow control valve provided in the bypass oil passage, the amount of oil passing through the bypass oil passage is reduced in accordance with the increase in the upstream hydraulic pressure, and the pressure supplied to the hydraulic actuator via the hydraulic control valve is reduced. As in the case where the drooping is performed by increasing the oil amount, when the steering operation is performed at the time of stopping or at the time of low-speed running, a large steering assist force is obtained for the supply of a large amount of hydraulic oil, while the high-speed running is performed. When a steering operation is performed at a time, a small steering assist force is obtained by supplying a small amount of hydraulic oil, and a large or small steering assist force can be generated in accordance with a slow vehicle speed. At this time, the flow control valve operates within the range of the gradually increasing supply hydraulic pressure due to the operation of the hydraulic control valve, thereby having a bent portion in the middle of the gradually increasing region and increasing the rate of change of the supply hydraulic pressure. Is obtained. Further, in addition to this, by using a hydraulic control valve capable of realizing the above-described two-stage breaking characteristic, the flow control valve is operated within the range of the gradually increasing region by the hydraulic control valve, so that the hydraulic control valve operates in the middle of the gradually increasing region. In addition, a characteristic having one further bent portion is obtained, and the stability on the high-speed side and the generation of a sufficient steering assist force on the low-speed side are simultaneously realized.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments. FIG. 1 is a schematic diagram showing the overall configuration of a power steering device according to the present invention.

In the figure, 1 is a steering wheel (steering wheel) at the upper end.
2 is a steering shaft (steering column) which is coaxially fixed, and a pinion 3 fixed to the lower end of the steering shaft 1.
Are engaged with a rack shaft extending in the left-right direction of the vehicle body. Thus, when the steering wheel 2 is rotated, the steering shaft 1
Is rotated about its axis, and this rotation is converted into sliding in the axial direction of the rack shaft 4 meshing with the pinion 3, and the steered wheels (not shown) connected to the left and right ends of the rack shaft 4 change direction. Then, steering corresponding to the operation direction and the operation amount of the steering wheel 2 is performed.

Power steering device according to the present invention (hereinafter referred to as the present device)
Is a hydraulic cylinder 5 that generates a steering assist force, a hydraulic pump 6 that generates a hydraulic pressure supplied to the hydraulic cylinder 5, and a supply and discharge of hydraulic oil from the hydraulic pump 6 to the hydraulic cylinder 5
Is provided with a hydraulic control valve 7 which is controlled in accordance with the operation of.

The hydraulic cylinder 5 is coaxially fixed in the middle of the rack shaft 4 to a cylinder chamber 50 formed by sealing the inside of a cylindrical housing surrounding the rack shaft 4 over a suitable length in a liquid-tight manner. The provided piston plate 51 is slidably inserted therein, and oil chambers are formed on both sides of the piston plate 51. As a result, an oil pressure corresponding to the pressure difference of the oil introduced into the oil chambers on both sides of the piston plate 51 is applied in the axial direction of the rack shaft 4 to assist the sliding of the rack shaft 4 and the steering operation caused by the sliding. Is done. Further, the hydraulic control valve 7 is formed in the middle of the steering wheel shaft 1, and has two sets of throttle portions 70, the throttle opening of which changes according to the steering torque applied to the steering wheel shaft 1 in accordance with the turning operation of the steering wheel 2. It has 71. The hydraulic control valve 7 is interposed between the hydraulic pump 6 and the hydraulic oil storage tank T and the hydraulic cylinder 5 as shown in the drawing, and one oil chamber of the hydraulic cylinder 5 To the oil storage tank T via a throttle 71, and the other oil chamber is connected to the discharge side of the hydraulic pump 6 via a throttle 71 and the throttle 70. Through the oil storage tanks T. The throttle portions 70 and 71 cause the opening degrees to change in different directions due to the steering torque applied to the steering wheel shaft 1, respectively.
For example, when the degree of opening of one of the restricting portions 70 increases, the degree of opening of the other restricting portion 71 decreases. When the opening degree of the throttle 70 increases, most of the pressure oil discharged from the hydraulic pump 6 is introduced into one oil chamber of the hydraulic cylinder 5 through the throttle 70, and the hydraulic cylinder 5 Generates hydraulic pressure to the right. By this operation, the hydraulic oil in the other oil chamber is pushed out, returns to the hydraulic control valve 7, and returns to the oil storage tank T through the throttle 70. Conversely, when the opening of the throttle portion 71 increases, the hydraulic cylinder 5 generates a hydraulic pressure in the left direction in the figure. By the supply / discharge operation of the hydraulic control valve 7, the supply of the hydraulic oil from the hydraulic pump 6 to both the oil chambers of the hydraulic cylinder 5 is performed according to the direction of the steering torque applied to the steering wheel 2. A steering assist force in the direction of the steering torque is obtained by the hydraulic pressure generated by the hydraulic cylinder 5 accordingly. At this time, a part of the pressure oil discharged from the hydraulic pump 6 passes through the throttle portion 71 or 70 on the side whose opening is reduced, and together with the recirculation oil from the hydraulic cylinder 5, the oil storage tank T
When the above-described supply / discharge operation is performed by the hydraulic control valve 7, the hydraulic pressure on the upstream side of the hydraulic control valve 7, that is, the hydraulic pressure in the oil guide path 60 from the hydraulic pump 6 to the hydraulic control valve 7 is ,
Irrespective of the operation direction of the steering wheel 2, it increases with an increase in the steering torque applied to the steering wheel 2.

In the device of the present invention, the oil guide passage 60 is connected to the hydraulic pump 6
A bypass oil passage 61 communicating with the oil storage tank T is formed in the middle of the bypass oil passage 61. The bypass oil passage 61 is responsive to the oil pressure in the upstream side of the hydraulic control valve 7, that is, the oil guide passage 60. A flow control valve 8 is provided which operates.

FIG. 2 and FIG. 3 are schematic sectional views for explaining the operation of the flow control valve 8. As shown in these figures, a flow control valve 8 includes a housing 80 having a bottomed cylindrical shape, and a spool 81 which is slidably fitted in the housing 80 in the axial direction.
And The open end of the housing 80 is closed by screwing a screw cap 82, and the screw cap 82 and the spool 81 are closed.
Between them, a pressing spring 83 for urging them in directions away from each other is interposed. As shown in FIG. 2, the spool 81 is normally pressed against the bottom surface of the housing 80 by the urging force of the pressing spring 83. However, as shown in FIG. 3 can be slid until it comes into contact with the end of the screw cap 82 as shown in FIG. On the outer peripheral surface of the spool 81, annular grooves 81a and 81b are formed at substantially the center in the axial direction and at the bottom end of the housing 80 over the entire circumference thereof, and these are communicated with each other by a communication hole 81c. Have been. The housing 80 has an oil guide port 80a formed so as to penetrate the peripheral wall in and out.
And a discharge port 80b. The oil guide port 80a is connected to the oil guide passage 60 side of the bypass oil passage 61, and the discharge port 80b is similarly connected to the oil storage pump T side. Oil guide port 80
Both a and the discharge port 80b are opened inside the housing 80 at positions matching the annular groove 81a formed on the outer periphery of the central portion of the spool 81. Therefore, the oil passage 60
Is introduced into the housing 80 through the bypass oil passage 61 and the oil guide port 80a, and further into the annular groove 81a and the communication hole 8
It is introduced into the annular groove 81b via 1c and acts on the entire end surface of the spool 81, and presses the spool 81 in a direction against the urging force of the pressing spring 83. That is, the spool 81 is
The pressing force on the spool 81 due to the oil pressure inside the plate spring exceeds the initial urging force of the pressing spring 83 and starts sliding, and thereafter slides in proportion to the increase in the oil pressure.

On the other hand, as shown in FIGS. 2 and 3, the open end of the oil guide port 80a into the housing 80 is kept open regardless of the sliding position of the spool 81, while the discharge port The opening end of 80b is closed in accordance with the sliding of the spool 81, and is almost completely closed when the spool 81 reaches the sliding position shown in FIG. Thus the amount of oil is bypassed to the oil storage tank T via the bypass oil passage 61 (bypass oil amount) Q ₂ is proportionally reduced according to discharge port 80b by the sliding of the spool 81 is closed, lubricant guide path 60 and oil quantity supplied to the hydraulic cylinders 5 via the hydraulic control valve 7 (the main oil amount) Q ₁ is reversed, proportionally increases with increasing the sliding amount of the spool 81.

Thus, while the oil pressure in the oil guide path 60, that is, the oil pressure on the upstream side of the oil pressure control valve 7 is within a predetermined range, specifically, the spool 81 is pressed by the oil pressure.
Between but from the start of the slide until it hits the end surface of the screw cap 82, reducing the bypass oil amount Q ₂ in accordance with the oil pressure increase in lubricant guide path 60, the operation allowed to increase the main oil amount Q ₁ Eggplant 4 is a graph showing a change in state of the main oil amount Q ₁ and bypass oil amount Q ₂ for the hydraulic (circuit pressure) P of lubricant guide path 60. Bypass oil amount Q ₂ to which shown by a broken line in the figure, circuit pressure P is up to the predetermined pressure P _1, i.e., the spool 81 reaches the pressure to start the slide is kept constant, thereafter increasing the circuit pressure P proportionally decreased with becomes substantially 0 with reaching the pressure when the slide until it hits the end surface of the predetermined pressure P ₂ greater than P _1, i.e. the spool 81 screw cap 82. Thus the main oil amount Q ₁ shown by a solid line in the figure, circuit pressure P
There is maintained a small amount until it reaches the P _1, increased to the comparative example with an increase of the circuit pressure P in between P ₁ to P _2, the oil discharged from the hydraulic pump 6 after more than P ₂ The whole amount is supplied to the hydraulic control valve 7.

The pressure on the upstream side of the hydraulic control valve 7, that is, the circuit pressure P, increases the steering torque applied to the steering wheel 2 irrespective of the operation direction of the steering wheel 2 by the above-described supply / discharge operation by the hydraulic control valve 7. It increases with it. Therefore, the above-described flow control valve 8
The main oil amount Q ₁ , that is, the amount of oil supplied to the hydraulic cylinder 5 via the hydraulic control valve 7 is kept small when the steering torque applied to the steering wheel 2 is small. Up to the total discharge amount of the steering wheel increases with an increase in the steering torque. Therefore, during high-speed running in which a large steering torque is not applied to the steering wheel 2, since the amount of oil supplied through the hydraulic control valve 7 is small, the hydraulic pressure generated by the hydraulic cylinder 5, that is, the steering assist force When the vehicle is stopped or running at a low speed, a relatively large steering torque is applied to the steering wheel 2, and the hydraulic cylinder 5 generates a larger steering assist force for supplying a large amount of hydraulic oil. That is, in the device of the present invention, it is possible to generate the steering assist force that becomes higher or lower in response to the vehicle speed slowdown without the need for an electrical processing means such as a vehicle speed sensor and a control circuit that operates based on the detection result. In addition, the straight running stability at the time of high-speed running and the reduction of the operating force of the steering wheel 2 at the time of stopping or at the time of low-speed running are realized.

Further, as the hydraulic control valve 7, 2 as shown in FIG.
In the case of using one that can realize the step breaking characteristic, the following effects can be obtained. The two-stage breaking characteristic is such that the area of the two sets of throttle portions 70 and 71 of the hydraulic control valve 7 is smaller than the steering torque applied to the steering wheel 2 when the steering torque is small and large when the steering torque is large. This is realized by changing the rate of change at different rates. The hydraulic control valve 7 having the throttle portions 70 and 71 showing such a manner of changing the throttle area is disclosed in, for example, Japanese Patent Publication No. 52-4807 and Japanese Patent Application Laid-Open Nos. 57-197810 and 57-197810 by the present applicant. 59-1185
Many disclosures have been made, such as No. 77, and any of these may be used.

The present inventors, using a hydraulic control valve 7 having a two-stage folding characteristics, the amount of oil delivered to the hydraulic cylinders 5 via the hydraulic control valve 7, i.e. to change the main oil amount Q ₁ variously, As a result of examining the characteristics of each of them, the results shown in FIG. 5 were obtained. The hydraulic control valve 7 used at this time was proposed by the present inventors in Japanese Utility Model Application No. 63-106281.
The horizontal axis in this figure is the steering torque applied to the steering wheel 2, and the vertical axis is the hydraulic pressure on the upstream side of the hydraulic control valve 7, that is, the circuit pressure P.
As described above, a one-to-one correspondence is established between the circuit pressure P and the steering assist force generated by the hydraulic cylinder 5. Circuit pressure P as shown, regardless of the main oil amount Q _1, constant region shown in Figure 6 to increase the steering torque, but increases with a gradual increase region and surge zone, a main oil flow effect of Q ₁ is appeared on the slope of the increasing zone, the inclination increases with an increase in the main oil amount Q _1. When examining the circuit pressure P under appropriate steering torque in these increasing region, it became clear that the circuit pressure P exhibits substantially proportional increase to increase the main oil quantity Q _1. Therefore, for example, when the steering torque is in the range of 30 kgfcm or less, the main oil amount Q ₁
Was maintained at 2 / min, if the steering torque it is possible to proportionally increase until 5 / min the main oil amount Q ₁ in the range between to reach 50 kgf · cm, in thick lines in FIG. 5 As shown, a characteristic is obtained between the fixed region and the sudden increase region, which has two gradually increasing regions in which the rate of change of the circuit pressure P with respect to the change of the steering torque, that is, the rate of change of the steering assist force is different.
Transition of such main oil amount Q ₁ is, it is possible to perform the operation of the flow control valve 8 described above. That is, the amount of oil discharged from the hydraulic pump 6 to 5 / min, by respectively setting the bypass oil amount Q ₂ before the start sliding of the spool 81 to the 2 / min, main oil amount in the range steering torque is small Q ₁ can be kept at 2 / min, and the circuit pressure P ₁ at the time when the spool 81 starts sliding can be changed to a steering pressure of 30 kgf · cm on the characteristic curve of Q ₁ = 2 / min in FIG. The circuit pressure P corresponding to the torque is set, and the circuit pressure P ₂ when the spool 81 abuts on the screw cap 82 is changed to a circuit pressure corresponding to a steering torque of 50 kgf · cm on a characteristic curve of Q ₁ = 5 / min. by setting the P, the transition of the main oil amount Q ₁ such as described above are realized. Needless to say, the sliding start pressure and the sliding end pressure of the spool 81 can be freely set by selecting the pressure receiving area of the spool 81 and the spring constant of the pressing spring 83 for biasing the spool 81. That is, by using the hydraulic control valve 7 having the bypass oil passage 61 and the flow control valve 8 in the middle of the bypass oil passage 61 and obtaining a two-stage breaking characteristic, the gradually increasing region mainly used when traveling at a medium speed is used. On the way, a change characteristic of the steering assist force having one more bent portion is obtained, and both the straight running stability and improvement on the high speed side and the sufficient steering assist force on the low speed side are realized. You.

In the present embodiment, an example in which the present invention is applied to a vehicle having a rack and pinion type steering mechanism has been described, but the scope of application of the present invention is not limited to this.

〔effect〕

As described in detail above, in the device of the present invention, a bypass oil passage is provided between the hydraulic pump and the hydraulic actuator so as to bypass the suction side of the hydraulic pump, and an upstream side of the hydraulic control valve is provided in the middle of the bypass oil passage. A flow control valve responsive to oil pressure is provided, and while the oil pressure is within a predetermined range included in a gradual increase range of the supply oil pressure due to the operation of the oil pressure control valve, the amount of oil passing through the bypass oil passage according to the increase of the oil pressure Therefore, a bent portion is formed in the middle of the gradually increasing area, and a characteristic of increasing the change rate of the feed hydraulic pressure, that is, the steering assist force, is obtained. A large steering assist force is obtained in the feeding of the vehicle, and the steering assist force can be kept small by supplying a small amount of hydraulic oil at the time of high-speed traveling, and the generation of the steering assist force that becomes large and small according to the vehicle speed is reduced. Electric By using a hydraulic control valve which can realize a two-stage bending characteristic, a steering assist force having a further one-stage bending part in the middle of the gradually increasing region in the characteristic can be realized. Thus, the present invention has excellent effects, for example, such that a sufficient steering assist force can be generated on the low speed side within the middle speed range and the straight running stability can also be realized on the high speed side.

[Brief description of the drawings]

FIG. 1 is a schematic view showing the overall configuration of the apparatus of the present invention, FIGS. 2 and 3 are schematic sectional views for explaining the operation of the flow control valve, and FIG. 4 is a main flow generated by the operation of the flow control valve. FIG. 5 is a graph showing a change characteristic of the steering assist force obtained by the second invention of the present invention, and FIG. 6 is a graph showing a two-stage breaking characteristic. 2 ... steering wheel, 5 ... hydraulic cylinder, 6 ... hydraulic pump,
7 ... Hydraulic control valve, 8 ... Flow control valve, 60 ... Oil guideway,
61 ... Bypass oil passage, T ... Oil storage tank

Claims (2)

(57) [Claims] 1. A throttle area between a hydraulic actuator for generating a steering assist force and a hydraulic pump for generating an operating hydraulic pressure of the hydraulic actuator is changed according to a steering torque applied to a steering wheel.
In a power steering apparatus provided with a hydraulic control valve that changes a supply hydraulic pressure to the hydraulic actuator through a gradually increasing region in a range where the steering torque is small and a sudden increasing region in a large range, the hydraulic control valve includes: A bypass oil passage communicating between the hydraulic pump and the suction side of the hydraulic pump, and a bypass oil passage arranged in the middle of the bypass oil passage, wherein a hydraulic pressure upstream of the hydraulic control valve is included in the gradually increasing region. A flow control valve that performs an operation of reducing the flow rate of the bypass oil passage in accordance with the increase in the hydraulic pressure while increasing the rate of change in the gradually increasing region. Power steering device. 2. The power steering system according to claim 1, wherein the hydraulic control valve has two or more different throttle area change rates in a range where the steering torque is large and in a range where the steering torque is small. Taking device.