JP3952694B2 - Variable throttle valve and power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention includes a cylindrical spool that slides in the axial length direction by transmission from a rotational drive source such as a stepping motor, and a throttle portion formed on a fitting periphery of the housing and the spool. The present invention relates to a variable throttle valve configured to increase or decrease the throttle area, and to a power steering apparatus using this variable throttle valve.
[0002]
[Prior art]
For the purpose of obtaining hydraulic pressure for operation to be supplied to various hydraulic pressure (mainly hydraulic pressure) actuators, variable throttle valves that are provided in the hydraulic pressure circuit and provide throttle resistance are widely used. . Many of the variable throttle valves of this type include a cylindrical spool that is slidably held in the axial direction inside a housing, and a throttle portion formed on a fitting circumference between the spool and the housing. The throttle opening is increased or decreased by sliding the spool, and a throttle resistance corresponding to the throttle opening is provided in the middle of the hydraulic circuit, and a desired hydraulic pressure is provided upstream or downstream of itself. And used to obtain a liquid amount.
[0003]
As one application of such a variable throttle, there is a hydraulic power steering device (power steering device) that assists steering of a vehicle with oil pressure. The hydraulic power steering device is provided in a steering mechanism of a vehicle to generate a steering assist force, and to supply pressure oil according to a steering torque applied to a steering wheel (steering wheel) for steering. A hydraulic control valve that performs a draining operation, and pressure oil for operation supplied from a hydraulic pump as a hydraulic power source is supplied to the hydraulic actuator via the hydraulic control valve. In response, the hydraulic pressure (steering assisting force) generated by the hydraulic actuator is applied to the steering mechanism to perform an operation to reduce the labor burden on the driver required for steering.
[0004]
In such a power steering apparatus, the correspondence relationship (auxiliary force characteristics) between the steering torque applied to the steered wheels and the steering assist force obtained in accordance therewith is uniquely determined by the operation characteristics of the hydraulic control valve. An assist force characteristic in which the steering assist force increases proportionally with an increase in the steering torque is obtained, but this assist force characteristic is not a preferable characteristic in actual steering of the vehicle.
[0005]
The steering of the vehicle is performed against the road surface reaction force acting on the steering wheel (generally the front wheel), and this road surface reaction force depends on the running conditions such as the vehicle speed and the steering angle. Change to large or small. Therefore, when the operation characteristic of the hydraulic control valve is selected when the steering is greatly stopped or stopped at a low speed, that is, when the road surface reaction force is large, the operation characteristics of the hydraulic control valve will be Steering is performed with a slight force applied, and there is a problem that the straight running stability is impaired.On the other hand, the operation characteristics are selected assuming that steering is performed at a low speed during high-speed driving, that is, when the road reaction force is small. In such a case, there arises a problem that a sufficient steering assist force cannot be obtained at the time of steering that requires a great amount of force, that is, so-called stationary.
[0006]
Various configurations have been proposed in the past for solving such problems and obtaining a good steering feeling regardless of the running state, such as the slow speed of the vehicle, the magnitude of the steering angle, etc. There is a power steering apparatus using the variable aperture described above. This power steering device is provided with the above-described variable throttle valve in the middle of a hydraulic circuit that returns from a hydraulic pump as a hydraulic source to an oil tank as a drain destination through the hydraulic control valve and hydraulic actuator. The throttle opening of the variable throttle valve is increased / decreased controlled based on the detection result of the running state such as the vehicle speed and the steering angle, and the hydraulic pressure and oil amount on the outlet side or the inlet side of the hydraulic control valve are changed, A desirable assisting force characteristic adapted to the running state is obtained.
[0007]
[Problems to be solved by the invention]
As described above, in the variable throttle valve used in the hydraulic power steering apparatus, in order to achieve a desired assist force characteristic with high accuracy, the sliding position of the spool is adjusted to increase or decrease the throttle opening. In order to meet this requirement, U.S. Pat. No. 4,730,687 discloses a stepping motor capable of controlling the rotational position with high accuracy as a driving source for sliding the spool. A variable throttle valve using a rotational drive source is used.
[0008]
However, this variable throttle valve connects a screw shaft to the output end of the stepping motor, while forming a screw hole in the axial center of the spool, and screwing the screw shaft into the screw hole. The rotation of the screw shaft due to the transmission of the shaft is converted into the sliding of the spool using the screwing of the screw hole screwed into the shaft, and the power loss accompanying this conversion is large, and it is used as a drive source. There is a problem that the stepping motor becomes larger.
[0009]
In addition, in order to smoothly slide the spool, it is necessary to secure an appropriate screwing gap between the screw shaft and the screw hole. In this case, the rotation control of the stepping motor is highly accurate. Even if it is realized, there is a problem that an error due to the gap occurs in the sliding position of the spool, and the desired position accuracy cannot be obtained, and when the screwing gap is made zero to solve this problem As a result, the power loss increases due to the increase in the frictional resistance at the screwing portion, and the stepping motor as a drive source is further increased in size.
[0010]
In particular, the variable throttle valve used in the hydraulic power steering device as described above does not require a connecting pipe to the hydraulic control valve, and the housing of the hydraulic control valve can be easily secured. However, the variable throttle valve provided with the large stepping motor as the driving means as described above has a problem that it is difficult to arrange the variable throttle valve in parallel with the hydraulic control valve.
[0011]
The present invention has been made in view of such circumstances, and by adopting a highly efficient motion conversion mechanism that converts the rotation of the rotational drive source into sliding in the axial direction of the spool with high accuracy, the smoothness of the spool is improved. That achieves the desired hydraulic pressure with high accuracy by using it in combination with various hydraulic circuits. Provides a variable throttle valve that can be operated, and further provides a power steering device that can realize auxiliary force characteristics adapted to the running state by arranging this variable throttle valve in parallel with a hydraulic control valve for supplying and discharging pressure oil. The purpose is to do.
[0012]
[Means for Solving the Problems]
  The variable throttle valve according to the first aspect of the present invention is formed on the fitting circumference of a cylindrical spool fitted and held in the housing in the axial direction by transmission from a rotational drive source. In the variable throttle valve that increases or decreases the throttle opening of the throttle partThe spool has an insertion hole formed at a position eccentric with respect to the axial center of the spool, and a holding chamber which is continuously provided so as to increase the diameter of one side of the insertion hole so as to be substantially coaxial with the spool. AndConnected to the output end of the rotational drive source,InsertionA screw shaft inserted through the hole;Holding roomAnd a feed bearing in which an engagement protrusion provided on the inner peripheral surface of the screw is engaged with a thread groove on the outer surface of the screw shaft at one place in the circumferential direction. .
[0013]
  In the present invention, when the screw shaft is rotated by transmission from a rotational drive source such as a stepping motor, a feed bearing is formed by engaging engagement protrusions provided on the inner peripheral surface of the screw shaft with a screw groove on the outer periphery of the screw shaft. The spool that holds the feed bearing is pressed by the axial component of the acting force applied along the inclination of the thread groove along with the rolling, and the spool is axially moved inside the housing. It slides, and the throttle opening degree of the throttle part formed between the housings is increased or decreased. At this time, the motion conversion from the rotation of the stepping motor to the sliding of the spool is performed smoothly and with high efficiency under the rolling resistance of the feed bearing.A holding chamber that holds the feed bearing is formed coaxially with the spool, and the screw shaft is inserted into an insertion hole that is eccentric to one side of the holding chamber, and the screw shaft rotates while maintaining smooth sliding of the spool. Spooling of the spool accompanying movement is prevented without providing a dedicated means.
[0016]
  The first aspect of the present invention2The variable throttle valve according to the invention is the firstIn one inventionAn urging means for applying an urging force to the spool from one side in the axial length direction to reinforce the engagement between the thread groove and the feed bearing is provided.
[0017]
In the present invention, a biasing force directed to the other side is applied by a biasing means such as a spring that elastically contacts one side in the axial direction of the spool, and the feed bearing that is internally fitted and held in the spool is formed in the thread groove on the outer periphery of the screw shaft. By pressing, a preload is applied to the engaging portions of both, and the motion conversion described above is performed with high accuracy.
[0018]
  Furthermore, the first of the present invention3A power steering apparatus according to the invention includes a hydraulic actuator that applies a steering assist force to a steering mechanism of a vehicle, and a hydraulic control valve that supplies and discharges pressure oil for operating the hydraulic actuator according to a steering operation. In the take-off device, the hydraulic control valve is interposed between the hydraulic pressure source or the oil discharge destination.According to the first or second inventionA variable throttle valve, and a control unit that increases or decreases the throttle opening of the variable throttle valve according to the traveling state of the vehicle.
[0019]
  In the present invention, the first is provided between the hydraulic control valve that performs the supply and discharge operation of the pressure oil according to the steering operation with respect to the hydraulic actuator for assisting steering, and the hydraulic source or the oil discharge destination.Or the variable throttle valve of the second inventionThis variable aperture is interposedvalveThe throttle opening degree is increased / decreased controlled according to the traveling state of the vehicle, and the operating characteristic of the hydraulic control valve is changed to realize the assisting force characteristic adapted to the traveling state.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof. 1 and 2 are longitudinal sectional views showing the configuration of a variable throttle valve according to the present invention.
[0021]
As shown in these drawings, the variable throttle valve 1 according to the present invention includes a housing 10 in which a spool chamber 10a having a circular cross section is formed so as to pass through an axial center portion thereof, and is slidable in the axial direction within the spool chamber 10a. And a stepping motor 12 serving as a drive source for the spool 11.
[0022]
The opening on one side of the spool chamber 10a is sealed by a stopper plug 13 screwed and fixed thereto, and the spool 11 held inside the spool chamber 10a is connected to the inner end face of the stopper plug 13. Is urged toward the other side by a pressing spring 14 interposed therebetween.
[0023]
On the other hand, on the other side of the spool chamber 10a, a diameter-enlarged portion 15 having an inner diameter increased over an appropriate length is connected to one side in the radial direction with an appropriate length eccentricity. Is fitted with a short cylindrical cylinder 16. Further, on the other side of the enlarged diameter portion 15, a motor chamber 17 having a circular cross section having an enlarged inner diameter is continuously provided concentrically with the enlarged diameter portion 15. The stepping motor 12 is housed in a cover member 18 that is fixed by screws so as to cover the opening.
[0024]
The output shaft of the stepping motor 12 housed in this way is coaxially connected to one end of the screw shaft 19 inside the enlarged diameter portion 15. The screw shaft 19 is sealed at the outer periphery of the midway portion with an X-ring that is fitted and held in the seal cylinder 16, and is extended into the spool chamber 10a to be connected to the spool 11 held in the spool chamber 10a. It is inserted and rotated around an axis eccentric with respect to the axis of the spool chamber 10a by transmission from the stepping motor 12.
[0025]
FIG. 3 is an enlarged cross-sectional view of a portion where the screw shaft 19 is inserted into the spool 11. As shown in the figure, the spool 11 is provided with an insertion hole 11a that is formed in the axial length direction so as to penetrate an appropriate length eccentrically in the radial direction, and the screw shaft 19 is inserted into the insertion hole 11a. Has been made. On one side of the insertion hole 11a, a holding chamber 11b whose inner diameter is expanded over an appropriate length is connected to the spool 11 so as to be substantially coaxial with the inside of the holding chamber 11b. The feed bearing R is fitted and fixed.
[0026]
As shown in the figure, the feed bearing R is a ball bearing in which a large number of balls are interposed between an inner ring and an outer ring, and an engagement protrusion having a semicircular cross section is provided on the inner peripheral surface of the inner ring. . A screw groove 19a having a semicircular cross section is formed on the outer peripheral surface of the screw shaft 19 over substantially the entire length of the extension into the spool chamber 10a. The screw groove 19a includes the feed bearing 19a. Engaging protrusions provided around the inner periphery of R are engaged at one place in the circumferential direction, specifically, at a circumferential position approaching the screw shaft 19 due to the eccentricity of the holding chamber 11b with respect to the insertion hole 11a. is there.
[0027]
FIG. 4 is an operation explanatory view of the feed bearing R, and shows a cross section in a direction orthogonal to FIG. As described above, the feed bearing R is engaged with the screw groove 19a on the outer periphery of the screw shaft 19 inserted inside the feed bearing R via the engaging protrusions provided on the inner peripheral surface. In this state, when the screw shaft 19 is rotated by the transmission from the stepping motor 12, the feed bearing R rolls while maintaining the engagement state with the screw groove 19a at the engagement point indicated by A in the figure. A force F along the inclination of the thread groove 19a acts on this engagement point A, and the spool 11 that holds the feed bearing R has an axial component F of the acting force F.₁And circumferential component force F₂Act
[0028]
Here, the insertion hole 11a through which the screw shaft 19 is inserted is eccentric with respect to the axis of the spool 11 and the spool chamber 10a that holds the spool 11 as described above. Force F₂Is held without being rotated inside the spool chamber 10a by the action of the axial component force F₁In accordance with the change in the position of the engagement point A along the inclination of the thread groove 19a, it slides in the axial length direction as indicated by white arrows in FIGS. Since the direction and amount of this sliding correspond to the direction and amount of rotation of the screw shaft 19, the sliding position of the spool 11 can be freely changed by controlling the rotation of the stepping motor 12 that is the drive source of the screw shaft 19. can do.
[0029]
As described above, the spool 11 is urged toward the other side, that is, the mounting side of the stepping motor 12 by the push spring 14 interposed between the stopper plug 13 that seals one side of the spool chamber 10a. The urging force applies a preload to the engaging portion between the feed bearing R held on the spool 11 and the thread groove 19a on the outer periphery of the screw shaft 19, thereby strengthening the engagement between them. As a result, sliding of the spool 11 accompanying the rotation of the screw shaft 19 occurs without displacement under the action of the preload, and the spool 11 responds to the rotation of the stepping motor 12 that can perform rotation control with high accuracy. Positioning with high accuracy.
[0030]
On the other hand, the motion conversion from the rotation of the screw shaft 19 to the sliding of the spool 11 is performed smoothly under the rolling resistance of the feed bearing R, so that high conversion efficiency is obtained even in the state where the preload is applied. Thus, the stepping motor 12 as a drive source can be downsized.
[0031]
An annular throttle groove 11c is provided around the outer peripheral surface of the spool 11 that slides in this manner, and the throttle groove 11c communicates with the inner insertion hole 11a through a communication passage that penetrates the peripheral wall of the spool 11. I'm allowed. An annular throttle groove 10c is provided on the inner peripheral surface of the spool chamber 10a for fitting and holding the spool 11, and communicates with the outside through an introduction hole 10b that penetrates the peripheral wall of the housing 10. The throttle groove 10c and the throttle groove 11c on the outer periphery of the spool 11 constitute a throttle portion that changes the communication area (throttle area) according to the sliding displacement of the spool 11.
[0032]
FIG. 1 shows a state in which the spool 11 is separated from the stopper plug 13. At this time, the throttle groove 11c on the outer periphery of the spool 11 overlaps with the throttle groove 10c on the inner periphery of the spool chamber 10a over a wide width. The aperture area becomes large. FIG. 2 shows a state in which the spool 11 approaches the stopper plug 13 and abuts against the inner end of the stopper plug 13. At this time, the throttle groove 11c on the outer periphery of the spool 11 has a throttle groove on the inner periphery of the spool chamber 10a. Slightly overlaps with the groove 10c, and the area of restriction between them is minimized.
[0033]
As described above, the stopper plug 13 is screwed and fixed to the opening end on one side of the spool chamber 10a, and the position of the inner end of the stopper plug 13 contacting the spool 11 can be freely set by changing the screwing length. It is. That is, the stopper plug 13 can be used as a means for setting the sliding position of the spool 11 that minimizes the throttle area of the throttle portion from the outside of the housing 10.
[0034]
A lead-out hole 10d communicating with the vicinity of the inner end of the stopper plug 13 is formed through the peripheral wall of the housing 10. A notch portion 11d is provided at a circumferential end position corresponding to the lead-out hole 10d at the same end portion of the spool 11, and the lead-out hole 10d slides on the spool 11 by alignment with the notch portion 11d. Regardless of the position, the spool chamber 10a is always in communication.
[0035]
In the variable throttle valve 1 configured as described above, the opening end of the introduction hole 10b to the outside of the housing 10 is connected to an oil supply source to introduce the oil supply from the oil supply source, while the lead-out hole 10d is out of the housing. Is connected to an oil discharge destination of pressure oil and used in an appropriate hydraulic circuit (hydraulic pressure circuit) so as to lead out the oil discharged to the oil discharge destination. In this state of use, the oil introduced into the introduction hole 10b passes through the throttle portion between the throttle groove 10c communicating with the introduction hole 10b and the throttle groove 11c on the outer periphery of the spool 11, and communicates with the throttle groove 11c. The oil flows into the spool chamber 10a through the insertion hole 11a on the inner side of the spool 11, and is led out to the oil drainage destination through the lead-out hole 10d opened inside the spool chamber 10a.
[0036]
The pressure oil flowing in this way is subjected to a throttle resistance that changes in magnitude according to the throttle opening of the throttle when passing through the throttle. This throttle resistance is small when the throttle opening is large as shown in FIG. 1, and is large when the throttle opening is small as shown in FIG. It changes continuously in response. Accordingly, on the upstream side of the introduction hole 10b, it is possible to obtain a hydraulic pressure that increases according to the sliding displacement of the spool 11 from the seal cylinder 16 side toward the stopper plug 13, and on the downstream side of the lead-out hole 10d. Therefore, it is possible to obtain a hydraulic pressure that decreases conversely according to the sliding displacement in the same direction.
[0037]
Here, in the variable throttle valve 1 according to the present invention, the sliding of the spool 11 inside the spool chamber 10a causes the rotation of the stepping motor 12 capable of controlling the position with high accuracy to the preload by the pressing spring 14. Since it is converted by the rolling of the feed bearing R generated along the thread groove 19a on the outer periphery of the screw shaft 19 under application, the hydraulic pressure obtained as described above can be realized with high accuracy according to this sliding. It can be used conveniently for various purposes.
[0038]
FIG. 5 is a schematic diagram showing an overall configuration of a rack and pinion type power steering apparatus including the variable throttle valve 1 according to the present invention. The rack and pinion type steering device has a pinion 21 fixed to the lower end of a steering wheel shaft 2 coaxially connected to the lower side of a steering wheel (steering wheel) 20. The rotation of the steering wheel 20 for steering is converted into sliding in the axial direction of the rack shaft 22, and each knuckle is connected to each end of the rack shaft 22. It has a known configuration in which steering is performed by changing the direction of a pair of left and right steering wheels (generally front wheels) 23 and 23 connected via an arm.
[0039]
A power steering apparatus that assists such a steering operation with hydraulic pressure is provided in the lower part of the steering wheel shaft 2 in the middle of a hydraulic circuit that circulates between a hydraulic pump P serving as a hydraulic pressure source and an oil tank T that stores hydraulic oil. The hydraulic control valve 3 configured and the steering assist power cylinder S configured in the middle of the rack shaft 22 are arranged, and the operating pressure oil supplied from the hydraulic pump P is used to operate the steering wheel 20. The hydraulic control valve 3 is fed to the power cylinder S by a later-described operation according to the pressure, and the rack shaft 22 is pressed in the axial direction by the hydraulic pressure (steering assisting force) generated by the power cylinder S in response to the feeding. In other words, the steering is performed as described above by sliding the rack shaft 22, and the variable throttle valve 1 according to the present invention is arranged in parallel on the downstream side of the hydraulic control valve 3.
[0040]
FIG. 6 is a longitudinal sectional view of the vicinity of the components of the hydraulic control valve 3. In the figure, 2a is a hollow input shaft, and 2b is a pinion shaft, which are cylindrical valve housings H.₁Is rotatably supported on the same axis and constitutes the lower part of the steering wheel shaft 2. The lower end of the input shaft 2a is fitted into the upper end of the pinion shaft 2b at an appropriate length and is supported so as to be relatively rotatable. Both the shafts 2a and 2b are inserted into the hollow portion of the input shaft 2a. 4 are connected coaxially.
[0041]
The upper part of the input shaft 2a is a valve housing H.₁A suitable length protrudes from the upper part of the wheel and is connected to the steering wheel 20. The pinion 21 is formed in the lower half of the pinion shaft 2b, and the pinion 21 is connected to the valve housing H.₁The rack shaft 22 is arranged so as to cross the lower portion of the rack shaft 22.
[0042]
Thus, when the steering wheel 20 is turned, the rotation of the steering wheel shaft 2 is transmitted to the pinion shaft 2b via the input shaft 2a and the torsion bar 4, and meshed with the pinion 21 in the lower half portion thereof. Steering is performed by converting the rack shaft 22 to slide in the axial length direction. At this time, the steering applied to the steered wheel 20 with the torsion bar 4 being twisted between the input shaft 2a and the pinion shaft 2b. A relative angular displacement corresponding to the torque occurs.
[0043]
The hydraulic control valve 3 performs an operation of controlling supply / discharge of the pressure oil supplied to the power cylinder S using the relative angular displacement generated in this manner, and the valve housing H₁Is provided with a cylindrical valve body 30 that is coaxially pivotably fitted therein, and a valve spool 31 that is fitted inside thereof.
[0044]
One side of the valve body 30 is engaged with a dowel pin 2c formed on the outer periphery of the upper end portion of the pinion shaft 2b, and rotates together with the pinion shaft 2b. Further, the valve spool 31 is integrally formed on the outer periphery of the midway part of the input shaft 2a fitted inside the valve body 30. As a result, a relative angular displacement generated between the input shaft 2a and the pinion shaft 2b in accordance with the operation of the steering wheel 20 between the valve body 30 and the valve spool 31 of the hydraulic control valve 3 is applied to the steering wheel 20. A relative angular displacement is generated according to the direction and magnitude of the steering torque. On the fitting periphery of the valve body 30 and the valve spool 31, a throttle portion that changes the throttle area in accordance with the relative angular displacement is provided in parallel.
[0045]
In such a hydraulic control valve 3, the pressure oil supplied from the hydraulic pump P is supplied to the valve housing H.₁The pressure oil is distributed according to the change in the area of the throttle portion arranged on the fitting circumference of the valve body 30 and the valve spool 31, and is introduced into the valve housing. H₁One oil chamber S of a power cylinder S that is sent to one of a pair of cylinder ports (not shown) formed in_R(Or S_L) (See FIG. 7). Along with the supply of the pressure oil, the power cylinder S is connected to the other oil chamber S_L(Or S_RThe hydraulic pressure corresponding to the pressure difference generated between the rack shaft 22 and the rack shaft 22 is applied as a steering assist force as described above.
[0046]
Valve housing H₁Is formed in the upper part of the valve body 30 and is connected to the oil tank T through the tank port 33, and the oil on the other side is formed by the operation of the power cylinder S described above. Room S_L(Or S_RThe hydraulic oil pushed out from (3) is returned to the hydraulic control valve 3 through the corresponding cylinder port, and then returned to the oil tank T through the return chamber 34 and the tank port 33.
[0047]
The variable throttle valve 1 according to the present invention has a valve housing H so as to correspond to the formation position of the reflux chamber 34.₁The housing 10 is fixed to a mounting seat 35 provided outside, and the introduction hole 10b is formed outside the hydraulic control valve 3 by means of separate communication holes 36 and 37 provided to cross the mounting seat 35. The outlet 10d is attached in communication with the reflux chamber 34. The hydraulic oil returning to the hydraulic control valve 3 is received through the introduction hole 10b as described above, and after passing through the throttle portion, it is led out. It is used to lead to the reflux chamber 34 through the hole 10d. In FIG. 6, in order to avoid complication of the drawings, reference is made to details only for the main components (housing 10, spool 11, stepping motor 12, stopper plug 13 and pressing spring 14) with reference numerals in the variable throttle valve 1. The reference numerals are omitted.
[0048]
An operation command from the control unit 5 for characteristic control is given to the stepping motor 12 serving as a drive source of the variable throttle valve 1. The control unit 5 includes detection results of various sensors that detect the traveling state of the vehicle, such as a vehicle speed sensor 50 that detects the traveling speed of the vehicle and a steering angle sensor 51 that detects the steering angle of the steering wheels 23 and 23. The stepping motor 12 is driven in accordance with an operation command issued by the control unit 5 based on these detection results, and slides the spool 11 to increase or decrease the throttle opening of the throttle unit. It has been.
[0049]
FIG. 7 is a hydraulic circuit diagram of the power steering apparatus configured as described above. In this figure, the hydraulic control valve 3 includes a hydraulic pump P as a hydraulic source and a pair of oil chambers S of the power cylinder S._L, S_RAnd these oil chambers S_L, S_RAnd the two throttle portions S that change in area in different directions depending on the steering torque applied to the steering wheel 20.₁, S₂The variable throttle valve 1 that is represented as shown above and is mounted as described above is interposed between the hydraulic control valve 3 and the oil tank T, and has a throttle portion S that changes in area according to the traveling state._ThreeRepresented as:
[0050]
In the hydraulic circuit configured as described above, one throttle portion S of the hydraulic control valve 3 according to the operation of the steering wheel 20.₁Squeezing area of the other squeezing part S₂As described above, the pressure oil supplied from the hydraulic pump P is reduced by the throttle portion S as indicated by an arrow in the figure.₂Oil chamber S of the power cylinder S communicating with the side of_RThe power cylinder S is supplied to the oil chamber S_RFrom oil chamber S_LSteering assist force toward is generated.
[0051]
On the other hand, the operation of the power cylinder S causes the other oil chamber S to move._LThe hydraulic oil pushed out from the refrigerant flows back to the hydraulic control valve 3 as indicated by an arrow in the drawing, and a throttle section S having an increased throttle area on one side of the reflux section.₂And return to the oil tank T communicating with the same side. This reflux oil is used as the throttle part S of the variable throttle valve 1 used as described above._ThreeThe throttle section S_ThreeAs a result, the diaphragm portion S₂The downstream hydraulic pressure, that is, the back pressure of the hydraulic control valve 3 increases in accordance with the throttle resistance. Thus, in the power cylinder S, the oil chamber S_LThe internal pressure of the oil chamber increases, and this internal pressure and the other oil chamber S_RThe steering assist force generated by the differential pressure with respect to the supply hydraulic pressure is limited.
[0052]
Therefore, if the increase / decrease of the throttle opening degree of the variable throttle valve 1 according to the operation command from the control unit 5 is increased or decreased according to the slow speed of the vehicle detected by the vehicle speed sensor 50, the vehicle is traveling at high speed. As a result, the throttle resistance by the variable throttle valve 1 is increased, and the steering assist force generated by the power cylinder S is reduced. As a result, steering is performed by a slight force applied to the steering wheel during high speed traveling, and the straight running stability is impaired. On the contrary, during low-speed traveling or when stopped, the throttle resistance by the variable throttle valve 1 becomes small, and the steering assist force generated by the power cylinder S becomes large. Therefore, the desired assisting force characteristic can be realized.
[0053]
Further, if the throttle opening of the variable throttle valve 1 is increased / decreased according to the detection result of the driving state including the magnitude of the steering angle detected by the steering angle sensor 51, more desirable assistance corresponding to the driving state of the vehicle in detail. Force characteristics can be realized. Further, the variable throttle valve 1 according to the present invention may be interposed upstream of the hydraulic control valve 3, and it goes without saying that the same effect can be obtained.
[0054]
The variable throttle valve 1 according to the present invention has two throttle portions on the fitting circumference of the valve body 30 and the valve spool 31, as disclosed in Japanese Patent Laid-Open No. 8-159323 by the applicant of the present application. In the power steering apparatus provided with the special hydraulic control valve provided, it is possible to use the power steering apparatus by interposing it on the downstream side or the upstream side of one set of throttle portions. Further, the rack shown in the above embodiment Not only the pinion type power steering apparatus but also other types of power steering apparatuses such as a ball screw type can be used in exactly the same manner in order to obtain a desired auxiliary force characteristic.
[0055]
【The invention's effect】
  As described above in detail, in the variable throttle valve according to the first aspect of the present invention, the spool slides in the axial direction.The feed bearing is placed in a holding chamber that is substantially coaxial.Keep fit inside,thisSince the feed bearing is configured to engage with the thread groove on the outer periphery of the screw shaft rotated by transmission from the rotational drive source at one place in the circumferential direction, the sliding of the spool from the rotation of the screw shaft. Can be smoothly and efficiently performed under the rolling resistance of the feed bearing that rolls along the thread groove, and the throttle opening degree can be increased and decreased with high accuracy. It becomes possible to realize this together with downsizing.
[0056]
  MaTheFormed at an eccentric position with respect to the spool axisSince the screw shaft is inserted and held in the insertion hole,By turning the screw shaftWhile maintaining smooth sliding of the spool,Prevent spool rotation without using any special meansIs possible andThe configuration can be simplified.
[0057]
  The second2In the variable throttle valve according to the present invention, the spool is provided with a biasing means for applying a biasing force from one side in the axial direction to the spool. It is possible to perform the above-described motion conversion with high accuracy.
[0058]
  In addition3In the power steering apparatus according to the invention, the first to first downstreams or upstreams of the hydraulic control valve that supplies and discharges the pressure oil to the steering assist hydraulic actuator.2Since the variable throttle valve of the present invention is arranged side by side and the throttle opening degree of the variable throttle valve is increased or decreased according to the running state of the vehicle, the operation of the hydraulic control valve is performed by increasing or decreasing the throttle opening degree of the variable throttle valve The present invention has an excellent effect such that it is possible to easily realize the assisting force characteristic adapted to the traveling state by complementing the characteristic.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a configuration of a variable throttle valve according to the present invention.
FIG. 2 is a longitudinal sectional view showing a configuration of a variable throttle valve according to the present invention.
FIG. 3 is an enlarged cross-sectional view of a portion through which a screw shaft is inserted into a spool.
FIG. 4 is an operation explanatory diagram of a feed bearing;
FIG. 5 is a schematic diagram showing an overall configuration of a rack and pinion type power steering apparatus including a variable throttle valve according to the present invention.
6 is a longitudinal sectional view of the vicinity of the components of the hydraulic control valve of the power steering apparatus shown in FIG.
7 is a hydraulic circuit diagram of the power steering apparatus shown in FIG. 5. FIG.
[Explanation of symbols]
1 Variable throttle valve
2 Rudder axle
3 Hydraulic control valve
4 Torsion bar
5 Control unit
10 Housing
10c Aperture groove
11 Spool
11c Aperture groove
12 Stepping motor
13 Stopper plug
14 Pressing spring
19 Screw shaft
19a Thread groove
20 helm
21 Pinion
22 Rack shaft
30 Valve body
31 Valve spool
P Hydraulic pump
S Power cylinder
T Oil tank

Claims (3)

A variable throttle that increases or decreases the throttle opening of the throttle formed on the fitting circumference of a cylindrical spool that is fitted and held inside the housing, sliding in the axial length direction by transmission from a rotary drive source In the valve
The spool has an insertion hole formed at a position eccentric with respect to the axial center of the spool, and a holding chamber which is continuously provided so as to increase the diameter of one side of the insertion hole so as to be substantially coaxial with the spool. And
A screw shaft connected to the output end of the rotational drive source and inserted through the insertion hole;
A feed bearing that is fitted and held in the holding chamber , and is engaged with a thread groove on the outer surface of the screw shaft at one location in the circumferential direction. Characteristic variable throttle valve. The spool to the biasing force applied from a side of the axial direction, according to claim 1 Symbol placement of the variable throttle valve comprises a biasing means for enhancing the engagement of the bearing feed and the screw groove. In a power steering apparatus comprising a hydraulic actuator that applies a steering assist force to a steering mechanism of a vehicle, and a hydraulic control valve that supplies and discharges pressure oil for operating the hydraulic actuator according to a steering operation,
The variable throttle valve according to claim 1 or 2 , wherein the variable throttle valve is interposed between the hydraulic control valve and a hydraulic pressure source or an oil discharge destination.
A power steering apparatus comprising: control means for increasing / decreasing the throttle opening of the variable throttle valve in accordance with the traveling state of the vehicle.

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