JP3717293B2 - Servo valve of power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a servo valve for a power steering apparatus in which an input shaft and an output shaft are connected via a torsion bar.
[0002]
[Prior art]
In a servo valve of this type of power steering device, a torsion bar is provided between an input shaft connected to a steering wheel operated by a driver and an output shaft connected to wheels via a rack and pinion mechanism, for example. Are connected through.
During steering, the pressure oil flow path is switched according to the relative displacement between the input shaft and the output shaft generated by twisting the torsion bar, and the power cylinder is supplied and discharged to obtain a steering assist force. Yes.
[0003]
On the other hand, during non-steering (straight running), the torsion bar is rarely twisted by operating force from the input shaft side, but due to slight force from the wheels, such as road surface unevenness or tire imbalance The torsion bar may be slightly twisted when the force due to the generated vibration or the like is transmitted from the output shaft side. The twist generated in this manner causes the servo valve to work slightly, which may make the traveling direction unstable.
[0004]
Therefore, conventionally, in order to increase the steering rigidity in the neutral state, a plunger penetrating the input shaft in the radial direction is provided, and the plunger is pressed against the axial direction intermediate portion of the torsion bar by external hydraulic pressure according to the traveling state. A servo valve for the power steering apparatus is provided (see, for example, Japanese Patent Publication No. 53-41851 and Japanese Patent Publication No. 61-41787).
[0005]
[Problems to be solved by the invention]
However, a hydraulic mechanism that loads the hydraulic pressure to the plunger and a mechanism that controls the operation of the hydraulic mechanism in accordance with the running state are required. The structure is very complicated, and a large amount of space is required. There was a problem of increasing the size.
SUMMARY OF THE INVENTION An object of the present invention is to provide a servo valve for a power steering apparatus that can secure a steering rigidity when neutral without causing an increase in size with a simple structure.
[0006]
[Means for Solving the Problems]
As a means for solving the problems to achieve the above object,
According to a first aspect of the present invention, there is provided a servo valve for a power steering apparatus in which a cylindrical first shaft and a second shaft are coupled by a torsion bar. The servo valve is coupled to the first shaft so as to be integrally rotatable. A cylindrical body that surrounds the periphery of the cylinder, an opening formed in the cylindrical body, and an accommodation hole formed along the radial direction in the axially intermediate portion of the torsion bar are accommodated so as to be able to advance and retract. A plunger including a spring member, and the top of the plunger is elastically engaged with the edge of the opening by the biasing force of the spring member so as to increase the torsional rigidity of the torsion bar during non-steering. It is characterized by this.
[0007]
In this aspect, when the top of the plunger is elastically engaged with the edge of the opening of the cylindrical body during non-steering, the axial intermediate portion of the torsion bar and the first shaft, for example, the input shaft are connected, The torsional rigidity of the torsion bar can be increased by shortening the effective length involved in the torsion bar torsion. Therefore, it is possible to increase the steering rigidity when not steering, that is, when the valve is neutral. In addition, a mechanism for increasing the torsional rigidity of the torsion bar can be incorporated into the torsion bar itself with a simple structure, so that the desired steering performance can be achieved without increasing the size of the power steering apparatus.
[0008]
Moreover, if it is going to process the recessed part etc. which engage with a plunger in the internal peripheral surface itself of a 1st axis | shaft, processing will be very difficult. On the other hand, in this aspect, since the cylindrical body before being incorporated in the first shaft may be drilled in the radial direction, the processing becomes very simple.
The term “plunger including a spring member for biasing” includes a plunger that is elastically biased by the spring member and engages with an edge of the opening, and a plunger that itself has elasticity. It is. Further, the first axis may be an input axis or an output axis.
[0009]
According to a second aspect of the present invention, in the first aspect, the cylindrical body includes a fixed portion fixed to the first shaft side fixed end portion of the torsion bar, and the opening portion of the plunger from the accommodation hole. It has a size that prevents removal.
In this configuration, the torsion bar in which the plunger is incorporated in the accommodation hole can be covered with a cylindrical body so as to be unitized, and this unitization facilitates assembly of the power steering apparatus, thereby reducing manufacturing costs. can do.
[0010]
According to a third aspect of the present invention, in the first or second aspect, the plunger engages the edge of the opening with the top of the cylindrical body in which at least a part of the compression coil spring as the spring member is inserted. It consists of things.
In order to increase the set load of the compression coil spring, it is necessary to increase the effective diameter of the compression coil spring to increase the wire diameter and the amount of bending at the time of setting. However, in the case where a ball is used as the plunger, if the diameter of the receiving hole is increased in order to increase the effective diameter of the compression coil spring, the ball diameter inevitably increases, resulting in a set space with respect to the length direction of the compression coil spring. Becomes very narrow, and on the contrary, the wire diameter must be reduced and the set load cannot be increased.
[0011]
In contrast, in this embodiment, since the compression coil spring is inserted into the cylindrical plunger, even if the diameter of the accommodation hole is increased to the vicinity of the limit of the torsional stress of the torsion bar, the compression coil spring is set. The length can be secured long enough. Therefore, the set load can be increased by securing a large wire diameter and deflection amount of the compression coil spring, and consequently, the torsion torque displacement point of the torsion bar can be set in a region where the torsion bar has a large twist angle. .
[0012]
According to a fourth aspect of the present invention, in the first, second, or third aspect, the receiving hole penetrates the axially intermediate portion of the torsion bar in the radial direction, and the plunger is disposed in a reverse direction. An urging spring member is interposed between each other.
In this aspect, since the pair of plungers are operated in the opposite directions by the single spring member, the torsion bar is not unnecessarily bent.
[0013]
According to a fifth aspect of the present invention, in the first, second, or third aspect, a pair of the accommodation holes are provided side by side in the axial direction of the torsion bar, and the plungers accommodated in the pair of accommodation holes respectively. The urging is performed in the opposite directions by the corresponding spring members.
In this aspect, since the pair of plungers respectively accommodated in the separate accommodation holes are urged by the corresponding pair of spring members, the two spring members are used in parallel. Compared with the case where the pair of plungers accommodated in the accommodation holes are urged, a set load twice as large can be obtained.
[0014]
According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the top portion of the plunger has a cam surface that urges itself to the center of the opening by engaging with the edge of the opening. The hardness of the top of the plunger is higher than the hardness of the edge of the opening.
For smooth operation of the plunger, the top of the plunger biased by the spring member engages with the edge of the opening, thereby providing a cam-like effect for urging the top of the plunger to the center of the opening. It is necessary to have it. This cam-like effect brings about an effect of smoothly retreating the plunger into the accommodation hole when a rotational displacement occurs between the axial intermediate portion of the torsion bar and the cylindrical body. By the way, since the edge part of an opening part becomes the inner peripheral side of a cylindrical body, it is difficult to chamfer this edge part, As a result, the edge part of an opening part tends to become edge shape. Therefore, an inclined cam surface is necessarily provided on the top of the plunger.
[0015]
In this case, if the hardness of the edge of the opening is higher than the hardness of the top of the plunger, the cam surface at the top of the plunger will be worn away and the inclination angle will change, and the cam surface with the changed inclination angle will There is a risk that the edge portion of the opening that is in the shape of a bite will bite and lock. If locked, the so-called two-stage characteristic of the torsion bar is lost, and the cylindrical body also undergoes plastic deformation.
[0016]
On the other hand, in the present invention, since the hardness of the top of the plunger is relatively high, it is difficult for the top of the plunger to be worn, so that the inclination angle of the cam surface can be kept constant. Also, even if the edge of the opening is worn, it wears so as to be adapted to the inclination angle of the cam surface, so that it does not bite into each other, and the rotation direction of the torsion bar with which both are engaged The position (that is, the position when the valve is neutral) can always be kept constant.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the internal configuration of a servo valve of a power steering apparatus according to an embodiment of the present invention. Referring to FIG. 1, the servo valve 1 is applied to a rack and pinion type power steering apparatus having a rack bar 3 driven by a pinion 2, and a driving handle is a steering column (not shown). Is connected to a cylindrical input shaft 4.
[0018]
The rack bar 3 also serves as a piston rod of a power cylinder as a hydraulic actuator that generates a steering assist force. A tie rod (not shown) is connected to both ends of the piston rod. An operating force applied to the input shaft 4 from the steering wheel is transmitted to the pinion 2, and the rotation of the pinion 2 causes the tie rod to change the direction of the steering wheel (not shown) via the rack bar 3.
[0019]
In the housing 5, the input shaft 4 and the output shaft 6 on which the pinion 2 is formed are rotatably supported via a bearing (not shown). The input shaft 4 and the output shaft 6 are connected by a torsion bar 7 so as to be relatively rotatable. As for the housing 5, only the upper housing that houses the input shaft 4 is shown, and the lower housing that houses the pinion 2 is not shown.
[0020]
Referring to FIG. 2 which is an enlarged view of the main part of FIG. 1, the cylindrical input shaft 4 is surrounded by a valve sleeve 8 connected to the output shaft 6 so as to be integrally rotatable. By forming the path, a known rotary type valve mechanism 9 is configured that generates and supplies a steering assist force by supplying and discharging pressure oil from a pressure source such as a pump to a pair of oil chambers of the power cylinder. In the valve mechanism 9, the input shaft 4 and the valve sleeve 8 rotate relative to each other at the time of steering to control the flow path and supply and discharge the pressure oil to and from the power cylinder. Reflux to the side.
[0021]
Opposing end portions 7a and 7b of the torsion bar 7 are connected to the input shaft 4 and the output shaft 6 so as to be integrally rotatable by a pin 10 and a press-fitted serration 11, respectively. Further, the torsion bar 7 is formed with a large diameter portion 12 as an axially intermediate portion. The large-diameter portion 12 is formed with a plunger accommodation hole 13 penetrating in the radial direction, which accommodates a pair of plungers 14 and 14 so as to advance and retract. These plungers 14 and 14 are arranged in opposite directions, and a compression coil spring 15 is interposed between them. Both plungers 14, 14 are connected to the input shaft 4 side through a torsion bar case 16 as a cylindrical body, which will be described later, when the valve is in a neutral position. This is to increase the torsional rigidity of the torsion bar 7.
[0022]
On the other hand, the portion from the fixed end 7a to the input shaft 4 which is one of the opposing ends 7a and 7b of the torsion bar 7 to the large diameter portion 12 as an intermediate portion is covered with a torsion bar case 16 as a cylindrical body. ing. The torsion bar case 16 has a fixed portion 20 as a first end fixed to the fixed end 7 a of the torsion bar 7 by a pin 17. As a result, the torsion bar case 16 rotates substantially integrally with the input shaft 4. In addition, in said fixing | fixed part 20, connection strength can also be improved by brazing etc. with respect to the outer periphery of the torsion bar 7. FIG.
[0023]
2 and 3, the torsion bar case 16 has a large-diameter portion 18 as a second end along the periphery of the large-diameter portion 12. A pair of openings 19 that respectively engage with the pair of plungers 14 and 14 are formed through. These openings 19 are provided at positions where the plunger 14 can be engaged when the valve is in a neutral state during non-steering. Each opening 19 has a size that prevents the plunger 14 from being pulled out of the plunger receiving hole 13. That is, the diameter of the opening 19 is made smaller than the diameter of the plunger receiving hole 13.
[0024]
As the torsion bar case 16, for example, a general carbon steel pipe for piping can be used at a low cost.
The plunger 14 is formed of a cylindrical body into which at least a part of the compression coil spring 15 is inserted, and the top portion 21 is engaged with an edge portion 22 as an engaging portion of the opening portion 19. The top portion 21 of the plunger 14 includes a conical surface portion 23 as a cam surface that engages with the edge portion 22 of the opening portion 19, and a spherical surface portion 24 that is continuous with the tip end side of the conical surface portion 23. The inclined conical surface portion 23 of the plunger 14 urged by the compression coil spring 15 engages with the edge 22 of the opening 19, thereby obtaining a cam-like effect for holding the plunger 14 at the center of the opening 19. It is supposed to be. As the inclination angle of the conical surface portion 23 as the cam surface, for example, a range of 35 to 55 degrees, particularly 45 degrees is preferable.
[0025]
Note that the top portion 21 of the plunger 14 avoids contact with the inner peripheral surface of the input shaft 4 while being engaged with the edge portion 22 of the opening portion 19 because the input portion and the reaction force are used. This is to eliminate the torque deviation, that is, hysteresis.
Moreover, it is preferable that the top of the plunger 14 is harder than the torsion bar case 16. For example, it is preferable that the hardness of the top of the plunger 14 is HRC55 or more in terms of Rockwell hardness, and the hardness of the torsion bar case 16 is HRC25-30. In order to achieve the above hardness, it is preferable to quench the top portion 21 of the plunger 14.
[0026]
According to the present embodiment, there are the following excellent advantages. That is,
The plunger 14 urged by the compression coil spring 15 during non-steering (during straight traveling) is engaged with the edge 22 of the opening 19 to connect the intermediate portion in the axial direction of the torsion bar 7 and the input shaft 4. Thereby, the effective length involved in torsion of the torsion bar 7 can be shortened, and the torsional rigidity of the torsion bar 7 can be increased. Therefore, the steering rigidity when not steering, that is, when the valve is neutral can be increased.
[0027]
In addition, a mechanism for increasing the torsional rigidity of the torsion bar 7 can be incorporated in the torsion bar 7 itself with a simple structure of a plunger 14 with a built-in spring. Therefore, the desired steering performance can be achieved without increasing the size of the servo valve 1. Can be achieved.
Moreover, since the engaging part for engaging the plunger 14 is comprised by the opening part 19 formed in the torsion bar case 16, processing becomes very easy. This is because, in this case, the torsion bar case 16 before being incorporated in the input shaft 4 may be drilled in the radial direction to form the opening 19, so that the inner peripheral surface of the input shaft 4 is directly processed. Compared with the case of applying, the processing becomes very simple.
[0028]
Further, the torsion bar 7 incorporating the compression coil spring 15 and the plungers 14 and 14 can be covered with the torsion bar case 16 so as to be unitized, and the assembly of the servo valve 1 is facilitated. be able to. Further, since the compression coil spring 15 is inserted into the cylindrical plunger 14, the set length of the compression coil spring 15 is set even if the diameter of the plunger accommodation hole 13 is increased to near the limit of the torsional stress of the torsion bar 7. A sufficient length can be ensured. As a result, it is possible to secure a large wire diameter and deflection amount of the compression coil spring 15 and increase the set load. As a result, as shown in FIG. 4, the torsion bar 7 is in a region where the twist angle θ of the torsion bar 7 is larger. The displacement points B and C of the torsion torque T of 7 can be set.
[0029]
Further, since the pair of plungers 14 and 14 are operated in the opposite directions by the single compression coil spring 15, the torsion bar 7 is not unnecessarily bent.
Further, since the top portion 21 of the plunger 14 is harder than the torsion bar case 16, the conical surface portion 23 as a cam surface formed on the top portion 21 of the plunger 14 does not wear and the edge portion of the opening portion 19 of the torsion bar case 16. As a result, the contact angle between the two can be maintained substantially constant, the two do not lock, and the displacement points B and C of the torsion torque T are substantially constant. Can be maintained.
[0030]
Next, FIG. 5 shows a main part of the second embodiment of the present invention. Referring to the figure, in the present embodiment, a pair of plunger accommodating holes 25, 26 extending in the radial direction are provided side by side in the axial direction of torsion bar 7, and each plunger accommodating hole 25, 26 has a single A plunger 27 and a single compression coil spring 28 were accommodated. The pair of plunger receiving holes 25 and 26 are formed to have a predetermined depth in opposite directions, and both plungers 27 and 27 are biased in opposite directions by the corresponding compression coil springs 28 and 28. .
[0031]
In the present embodiment, in addition to the same effects as the embodiment of FIG. 1, since the two compression coil springs 28 and 28 are used in parallel, a single compression coil spring is used. Compared to the case, a double set load can be obtained. As a result, the steering rigidity when the valve is neutral can be further improved.
In the first and second embodiments, a ball plunger can be used.
[0032]
In the first and second embodiments, the plungers 14 and 27 are not in contact with the inner peripheral surface of the input shaft 4, but may be brought into contact with each other. Further, a recess for engaging the plunger may be formed directly on the inner peripheral surface of the input shaft.
Next, FIG. 6 shows a third embodiment. This embodiment is characterized in that the plunger itself has elasticity. The plunger 29 includes a main body portion 30 held in the plunger housing hole 13 and a projecting plate spring 31 as a spring member fixed to the end surface of the main body portion 30. In this plunger 29, the top part is comprised by the leaf | plate spring 31, and the leaf | plate spring 31 elastically engages with the edge 22 of the opening part 19 of the torsion bar case 16 as a cylindrical body.
[0033]
In addition, this invention is not limited to said each embodiment, For example, it is also possible to use a ball plunger as a plunger.
In the above embodiments, the plungers 14 and 27 are not in contact with the inner peripheral surface of the input shaft 4, but they may be in contact with each other. Further, in each of the above-described embodiments, the present invention is applied to a rack and pinion type hydraulic power steering apparatus. However, the present invention is also applicable to a ball screw type power steering apparatus and an electric power steering apparatus. In addition, various modifications can be made within the scope of the present invention.
[0034]
【The invention's effect】
According to the first aspect of the present invention, the torsion bar is twisted by shortening the effective length involved in torsion of the torsion bar by connecting the axially intermediate portion of the torsion bar to the first shaft by using the plunger during non-steering. As a result of improving the rigidity, the steering rigidity when the valve is neutral can be improved. In addition, this can be realized without increasing the size of the entire apparatus only by incorporating a simple structure of a plunger with a built-in spring member into the torsion bar itself. In particular, since a so-called two-stage characteristic is established with a single torsion bar, the neutral position of the servo valve is not affected at all, and assembly is possible with a simple centering operation. In addition, since it is only necessary to perform a drilling process in the radial direction on the cylindrical body before being incorporated in the first shaft, the processing becomes very simple as compared with the case where the inner peripheral surface of the first shaft is processed.
[0035]
In the invention of claim 2, the torsion bar in which the plunger is incorporated in the accommodation hole can be covered with a cylindrical body to be unitized, and the assembly of the power steering apparatus is facilitated, thereby reducing the manufacturing cost. can do.
In the invention according to claim 3, since the spring member made of the compression coil spring is inserted into the cylindrical plunger, even if the diameter of the accommodation hole is increased to the vicinity of the limit of the torsional stress of the torsion bar, A sufficiently long set length can be secured. As a result, the set load can be increased by securing a large wire diameter and the amount of bending, and consequently, the displacement point of the torsion torque of the torsion bar can be set in a region where the torsion angle of the torsion bar is large.
[0036]
In the invention according to claim 4, since the pair of plungers are operated in the opposite directions by the single spring member, the torsion bar is not unnecessarily bent.
In the invention according to claim 5, since two spring members are used in parallel, a set load twice as large as that obtained when a single spring member is used can be obtained. The rigidity can be further improved.
[0037]
In the invention of claim 6, since the top of the plunger is hard to wear and the cam surface can be maintained at a constant inclination angle, the top of the plunger does not bite into the opening and locks, and is stable over a long period of time. Operation can be ensured.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing an internal configuration of a servo valve of a power steering apparatus according to an embodiment of the present invention.
FIG. 2 is an enlarged view of a main part of FIG.
FIG. 3 is a cross-sectional view taken along line AA in FIG.
FIG. 4 is a graph showing a relationship between a twist angle of steering and a twist torque.
FIG. 5 is a cross-sectional view of a main part of a servo valve of a power steering apparatus as another embodiment of the present invention.
FIG. 6 is a cross-sectional view of a main part of a servo valve of a power steering apparatus as still another embodiment of the present invention.
[Explanation of symbols]
4 Input shaft (first axis)
6 Output shaft (second shaft)
7 Torsion bar 7a Fixed end 9 Valve mechanism 10, 11 Pin 12 Large diameter part (Axial intermediate part)
13 receiving hole 14 plunger 15 compression coil spring (spring member)
16 Torsion bar case (tubular body)
17 Pin 18 Expanded portion 19 Opening portion 20 Fixing portion 21 Top portion 22 Edge portion 23 Conical surface portion (cam surface)
25, 26 Accommodating hole 27 Plunger 28 Compression coil spring (spring member)
29 Plunger 30 Body 31 Leaf spring (top, spring member)

Claims (6)

In the servo valve of the power steering apparatus that connects the cylindrical first shaft and the second shaft by a torsion bar,
A cylindrical body that is connected to the first shaft so as to be integrally rotatable, and surrounds the periphery of the torsion bar;
An opening formed in the tubular body;
A plunger including a spring member for biasing, which is housed in a housing hole formed along the radial direction in the axial direction intermediate portion of the torsion bar, and includes a spring member for biasing;
The top of the plunger is elastically engaged with the edge of the opening by the biasing force of the spring member so as to increase the torsional rigidity of the torsion bar during non-steering. Servo valve. The cylindrical body includes a fixed portion that is fixed to a first shaft side fixed end portion of a torsion bar, and the opening has a size that prevents the plunger from being removed from the accommodation hole. Item 2. A servo valve for a power steering apparatus according to Item 1. 3. The power rudder according to claim 1, wherein the plunger is configured to engage a top portion of a cylindrical body into which at least a part of a compression coil spring as a spring member is inserted with an edge portion of the opening. Servo valve of the take-off device. The accommodation hole penetrates the axial intermediate portion of the torsion bar in the radial direction, and the plunger is disposed in a reverse direction, and a biasing spring member is interposed therebetween. A servo valve for a power steering apparatus according to claim 1, 2 or 3. A pair of the accommodation holes are provided side by side in the axial direction of the torsion bar, and the plungers accommodated in the pair of accommodation holes are urged in opposite directions by the corresponding spring members. The servo valve of the power steering apparatus according to claim 1, 2, or 3. The top of the plunger has a cam surface that urges itself to the center of the opening by engagement with the edge of the opening;
The servo valve of the power steering apparatus according to any one of claims 1 to 5, wherein the hardness of the top of the plunger is higher than the hardness of the edge of the opening.

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