JPS625824B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a steering device for a vehicle.

Conventionally, there are various types of steering devices for automobiles and the like, and in the United States, where there are many large vehicles, the ball screw type is often used, and in relatively small European cars, the rack and pinion type is adopted. In Japan, some car models use the rack and pinion type, but most others use the ball screw type. However, due to recent energy saving trends, front-wheel drive vehicles are increasing, and there is also a tendency for rack and pinion vehicles to increase due to issues such as steering stability. In addition, although ball screw type steering devices with variable gear ratios are popular, even rack and pinion type steering devices are now required to have variable gear ratios like the ball screw type. A rack and pinion type variable gear ratio steering device is disclosed in Japanese Utility Model Application No. 114827/1983,
Although proposed in Japanese Patent Publication No. 150129 and Japanese Patent Publication No. 52-29049, etc., the former two have intermediate gears and cannot avoid having a larger gearbox compared to the conventional rack and pinion type. This is a result that runs counter to the trend toward smaller size and lighter weight. The latter has the disadvantage that the rack structure is complicated and gear cutting is not easy. In any case, the characteristics of the rack and pinion type, which are simple in structure, easy to process, small and lightweight, and low manufacturing cost, are lost.

The present invention was developed for the purpose of providing a variable gear ratio steering system without sacrificing the features of the rack and pinion steering system as described above. To achieve the above object, the present invention includes a pinion shaft 1 connected to a handle shaft of a vehicle, which has a threaded pinion 11 at one end;
A screw rack 21 that meshes with the screw pinion 11
a rack shaft 2 connected to a link for steering the wheels and movable in the axial direction as the pinion shaft 1 rotates; and as the rack shaft 2 moves in the axial direction,
By rotating the rack shaft 2, the screw pinion 11
Rack axis 2 according to the reference pitch of screw rack 21
This is a steering device for a vehicle that has a variable gear ratio and a guide device that increases and decreases the amount of movement. The characteristics of its configuration, compared to the conventional rack and pinion type, are:
The steering device has a screw rack shaft replacing the rack, a screw pinion shaft replacing the pinion, and a device for guiding the movement of the screw rack shaft to provide a variable gear ratio. To explain this with respect to the embodiments shown in the figures, the first embodiment shown in Figs. 1 and 2 shows the straight running state of the vehicle, that is, the neutral position of the steering device, and the pinion shaft 1 connected to the steering wheel shaft is A screw pinion 11 is provided, and is rotatably supported by the gear case 3 by needle roller bearings 12 and ball bearings 13 mounted on both sides of the screw pinion 11. The screw pinion 11 has an hourglass shape and meshes with a screw rack 21 provided on the rack shaft 2. The screw rack 21 is machined with gears leaving a part of its circumference, and is not machined with gears on the entire circumference like a general worm. Since the rotation of the screw rack 21 is regulated by a guide device, which will be described later, there is no need to cut the gears around the entire circumference. A tubular cam 4 is welded to the rack shaft 2 so as to surround the rack shaft 2, and the wall of the tube on the screw pinion 11 side is shaved off to form a cam surface 4A. The gear case 3 that accommodates the pinion shaft 1 and the rack shaft 2 has a pipe section 31 extending in the direction of the rack shaft 2, and at both ends of the pipe section 31 are fixing parts 32 fixed to the vehicle via brackets (not shown). There are 33. The rack shaft 2 has a support member 8 provided at a position facing the screw pinion 11 of the gear case 3, and a pipe member 31.
It is supported by a bearing 22 fitted on one end side, and connected to a link (not shown) for steering the vehicle via ball joints 23 fixed to both ends of the rack shaft 2, respectively. ing. The support member 8 is slidably fitted into the gear case 3, and has a lid 19 fixed to the gear case 3 with bolts 20 at both ends, and a cam integrated with the rack shaft 2 via a spring 7 in contact with the support member 8. 4 is supported. An adjustment bolt 9 is screwed into the lid 19, and its tip is fitted with a washer 10.
The threaded pinion 11 contacts the support member 8 via the threaded pinion 11, and regulates the meshing clearance between the threaded pinion 11 and the threaded rack 21. The engagement between the threaded pinion 11 and the threaded rack 21 is centered by shifting the position of a ball bearing 13 that pivotally supports one end of the pinion shaft 1. That is, the ball bearing 13 is fixed to the adjusting nut 14 screwed into the gear case 3 by a snap ring 17 and a retaining member 18 that prevents the snap ring 17 from coming off, without any clearance in the axial direction. By moving the nut 14 back and forth, the axial position of the ball bearing 13 moves, and the pinion shaft 1 formed in the inner raceway of the ball bearing 13 moves accordingly, and the center of the screw pinion 11 and the screw rack 21 is moved. matches. Cam followers 5, 6 are provided adjacent to both sides of the screw pinion 11. One cam follower 6
is formed integrally with the pinion shaft 1, but the other cam follower 5 is formed separately and fits into the shaft diameter portion of the pinion shaft 1 into which the needle roller bearing 12 is fitted. A disc spring 24 is interposed between the screw pinion 11 and the cam follower 5. The two cam followers 5, 6 have conical outer surfaces with a smaller diameter on the opposite side from the screw pinion 11, and contact the cam surface 4A with this conical outer surface. In particular, one cam follower 5 is securely pressed against the disc spring 24. Note that it goes without saying that the other cam follower 6 may also be constructed separately. Cam follower 5,6
It is desirable to make the diameter of the conical outer surface equal to the diameter of the meshing pitch circle between the screw rack 21 and the screw pinion 11, thereby making rolling contact with the cam surface 4A with little slippage. The cam followers 5, 6 and the cam 4 form a guide device for guiding the movement of the rack 2. This is because the rotation of the handle shaft is transmitted to the rack shaft 2 due to the engagement between the screw rack 21 and the screw pinion 11, and the rack shaft 2 rotates, but the rotational motion is restricted within a certain range by the guide device. It guides axial movement. That is, the rotational movement of the rack shaft 2 regulated by the guide device causes the axial movement of the screw rack 21 to lag or advance relative to the rotation of the screw pinion 11. As a result, the rack axis 2
The amount of axial movement of the rack shaft 2 due to the reference pitch between the screw pinion 11 and the screw rack 21 is regulated so that there is no rotational movement, and the rotational movement of the rack shaft 2 is regulated within a certain range by this cam device. It is a variable gear ratio in which the amount of movement in the axial direction increases or decreases (the ratio at which the amount of rotation of the pinion shaft 1 changes relative to the amount of movement in the axial direction of the rack shaft 2).

The guide device of the first embodiment is for a manual variable gear ratio steering device, and has the lowest gear ratio when the vehicle is running straight, that is, at the neutral position of the steering device, and the steering device can steer the required angle left and right. This will give you the best gear ratio. The curve of the cam surface 4A shown in FIG. 1 includes straight portions at the center and at both ends. The figure shows the cam surface on the front side, and a cam surface with the unevenness of the cam surface on the front side reversed is formed on the back side. In the case of this figure where the rack shaft 2 and pinion shaft 1 are orthogonal, the lowest part on the front side and the highest part on the back side are at the same position in the axial direction. Next, the relationship between the shape of the cam surface and the gear ratio will be explained. Figure 3 is an explanatory diagram in which the horizontal axis represents the axial movement amount l of the rack shaft 2, and the vertical axis represents the rotation θ of the rack shaft 2 caused by cam guidance, and the line shown here corresponds to the cam curve. Equivalent to.
The line .theta.=0, that is, the rotation of the rack shaft is regulated to zero by the guide device. screw rack 21
Let the pitch circle diameter be D, the torsion angle of the screw rack 21 be β, the lead of the rack be L, and the circumference be π, then L=π・D・tanβ……(1) Do not allow the rack shaft 2 to rotate In this case, the relationship between the rotation of the pinion shaft 1 and the axial movement of the rack shaft 2 is constant, so the gear ratio does not change and the rack shaft moves at the reference pitch between the screw pinion and the screw rack. A collecting device is obtained. The gear ratio at this time is Go.

The next line indicates that the rotation angle θ increases at a constant ratio to the axial movement l of the rack shaft 2, that is, the rack shaft 2 is rotated by the guide device by a constant angle per one revolution of the screw pinion 11. A permissible cam shape is shown in FIG. The shape of this cam is reversed between the front side and the rear side indicated by dotted lines, as in the case of FIG.

The axial movement of the rack axis may be faster or slower than that of the line. That is, when the screw rack 21 is a left-handed screw and the rack shaft 2 moves to the left, rotating the rack shaft 2 counterclockwise when viewed from the right side in FIG. 4 will advance the rack, and rotating clockwise will cause the rack shaft to retract. Assume that the amount of advance of the rack shaft 2 per unit rotation angle of the pinion shaft caused by the rotation of the rack shaft is △l, and the total amount of movement of the rack shaft per unit rotation angle of the pinion shaft is l', and the amount of advance If the amount of movement when there is no (the amount of movement due to the reference pitch) is l ₀ , then l' = l ₀ + △l (2).

Even in this case, the relationship between the rotation of the pinion shaft 1 and the axial movement of the rack shaft 2 is constant, so a steering device with a constant gear ratio is obtained, and if the gear ratio is _G1 , the pinion, rack and link If the specifications of the relationship are the same, G ₁ <G ₀ . The amount of delay△
When there is l (for example, when the cam surface in Fig. 4 has the opposite slope), l″=l ₀ −△l ………(2)′, and if the gear ratio is G ₂ , then G ₂ > G becomes ₀ .

The gear ratio G of this type of steering device is the ratio of the rotation angle of the pinion shaft 1 to the rotation angle of the knuckle arm. Axis 2
When the rotation angle of the knuckle arm is l/2πA×360°, the rotation angle of the pinion shaft 1 is 1° in unit rotation angle. Therefore, the gear ratio is defined as However, in an actual mechanism, the knuckle arm is in rotational motion, the rack axis is in linear motion, and there is also suspension motion, and the relationship between gear ratios changes in a complex manner, so we have simplified it for ease of understanding. , using the definition of G ₀ above.

Similarly, G ₀ =2・π・A/360・l ₀ ......(4) From equations (3) and (4), G/G ₀ = l ₀ /l, that is, G=G ₀ ×l ₀ / l ......(5) Letting the rotation angle of the rack shaft 2 per unit rotation angle of the pinion shaft 1 be θ ₀ , the advancement amount Δl of the rack shaft 2 for any rotation angle of the pinion shaft 1 is If the pitch circle diameter is D, △l=π・D・tanβ/360×θ ₀ ………(6
) Substituting equations (2) and (6) into equation (5), we get D and β are constant due to gear specifications, and l ₀ is also a constant value, so θ ₀ is the only variable, and if the constants are collectively denoted as C, equation (7) becomes G = G ₀・( 1/1+C・θ ₀ ) ......(8) The next line is for the variable gear ratio shown in the first embodiment, and the E-L and N-H parts are straight lines, Shows the range of equal gear ratios.

The range between RO and N indicates the range of the variable gear ratio, and at point C, θ ₀ =0 and G=G ₀ .

Between Lo and Ha is an interval in which θ ₀ is positive. During the hinge period, the direction of rotation of the rack shaft is reversed and θ ₀ is negative.

Therefore, 1/1+C・θ ₀ in equation (8) is 1 between loha and
is smaller than , and is larger than 1 between harini, so between roha, G < G ₀ between harini, G ₀ <
It becomes G. Therefore, the lowest constant gear ratio is obtained between E and E, the highest constant gear ratio is obtained between N and H, and a gradually increasing gear ratio is obtained between R and N. Similarly, when the rack shaft 2 moves to the left from the neutral position, gear ratios are obtained in which B and B', C and H', D and D', and E and E' change in the same way. , the change in gear ratio is shown in Fig. 5. That is, the gear ratio G' ₁ is the lowest when the vehicle is traveling straight, and the gear ratio G' ₂ is the highest at a position where the rotation angle of the pinion shaft is large.

Similarly to the line in _the embodiment shown in FIG. 6, the line in FIG. ₃ shows the shape of the cam surface of the steering device with a variable gear ratio. Since ₀ is a positive and convex curve, and the front and rear sides thereof are straight lines, the highest gear ratio is obtained at the position beyond _l2 , and the lowest gear ratio is obtained at the _l1 - _l1 position.

The line indicates a cam surface shape for a power steering device that has the highest gear ratio near the neutral position (near straight travel) and smaller gear ratios at the left and right positions.

FIG. 7 shows another embodiment of the guide device, in which the cam 4
0 is a protrusion 40 provided along the axial direction of the rack shaft 2
A, and the protrusion 40A is formed by twisting left and right in FIG. 7 with respect to the axis 2A of the rack shaft 2 in order to obtain a variable gear ratio. The cam 40 is welded to the rack shaft 2. The cam follower 50 is a support member 8
0, and is rotatably supported by a shaft 81, and is a rolling element having a groove 50A that fits into the protrusion 40A. Screw pinion 11 and screw rack 2
1 is the same as the first embodiment, and the support structure of the pinion shaft 1, the attachment of the support fitting to the gear case 3, etc. are also the same. 8 and 9 also show other embodiments of the guide device, and the protrusion 40A of the embodiment of FIG.
Instead, a groove 140A is provided, and the rolling elements 150 and 250, which are equipped with protrusions 150A and 250A that fit into the groove 140A on the support member 80, are used as cam followers. The structure is similar to that of a bearing. Note that these cam followers are not rolling elements, but gear case 3.
etc. may be fixed. Alternatively, the cam may be fixed to the gear case 3 and the cam follower may be provided on the rack shaft 2. Furthermore, if there is sufficient strength in the diameter of the rack shaft, a groove may be carved into the rack shaft 2 to form a cam.

The steering device of the present invention configured as described above includes a threaded pinion connected to the steering wheel shaft of the vehicle, and a threaded rack that engages with the threaded pinion, and is connected to a link for steering the vehicle, and slides in the axial direction. Although it has a movable rack shaft and a guide device for guiding the rotational movement of the rack shaft, the screw pinion and screw rack do not have a special shape and, by known gear cutting methods, rather than the current rack and pinion. It can be easily machined, and the number of man-hours is reduced, as the threaded rack of the example requires gear cutting while leaving a part of the circumference, and it is difficult to machine the rack with conventional rack and pinion type variable gear ratio steering devices. Gear cutting is extremely easy compared to the previous method. Although the increase in the number of man-hours required to process the guide device will affect manufacturing costs, compared to the conventional process for manufacturing easy variable gear ratios, the cost increase will be relatively small, making it possible to provide an inexpensive variable gear ratio steering device. effective. In conventional rack and pinion type steering devices, increasing the gear ratio requires reducing the pinion diameter, which poses problems in terms of strength and was only used for small vehicles.

However, since the present invention uses a threaded pinion and a threaded rack, the tooth height is substantially higher than that of the conventional rack pinion, which improves the meshing ratio and provides more strength for the teeth. The mesh will also become smoother. Furthermore, since the threaded rack of the embodiment is toothed leaving only a part of the circumference, there is a cut-up portion, which further improves the strength. For this reason, the number of teeth on the screw pinion can be reduced and the tooth module can be made smaller, making it possible to make the screw pinion smaller.This has the advantage of providing a large gear ratio, and can also be used in vehicles with severe load conditions. There is an effect that can be done. Furthermore, the absence of an edge portion at the radial end of the rack also has an advantageous effect on strength. In the present invention, the amount of axial movement of the rack shaft relative to the rotation of the pinion shaft can be controlled by the guide device.

Furthermore, the guide device of the present invention is composed of a cam that is fixed to the rack shaft in a shape that includes the threaded rack portion, and has a cam surface on a part thereof, and a cam follower that rotates and guides the cam surface. It is easy to manufacture a cam with desired cam characteristics, and smooth cam characteristics can be obtained by rotational guidance.

Therefore, by selecting the cam characteristics of the guide device, it is possible to widen the variable range of the gear ratio, and it is possible to avoid unreasonable design changes to the tooth profile and difficult gear cutting as in the conventional rack and pinion type or ball screw type. It has the advantage that there is no need to wrinkle it during processing.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG.
Figure 3 is an explanatory diagram showing the height of the cam surface in terms of the rotation angle of the rack shaft at each position in the axial direction of the rack shaft. Figure 4 is a cam shown by the line in Figure 3. , FIG. 5 is an explanatory diagram showing the change in gear ratio obtained by the guide device of the first embodiment, FIG. 6 is a side view of the cam indicated by the line in FIG. 3, and FIG. is another embodiment of the guide device.
FIG. 8 is a cross-sectional view of the main part showing another embodiment of the guide device, and FIG. 9 is a cross-sectional view of the main part showing another embodiment similar to FIG. . Explanation of symbols: 1: Pinion axis, 2: Rack axis,
3: Gear case, 4: Cam, 5, 6: Cam follower, 11: Screw pinion, 21: Screw rack.

Claims (1)

[Scope of Claims] 1. A pinion shaft 1 having a threaded pinion 11 at one end and connected to a steering wheel shaft of a vehicle, and a threaded rack 21 that meshes with the threaded pinion 11 and connected to a link for steering the vehicle, The pinion shaft 1
a rack shaft 2 that is movable in the axial direction as the rotation of the rack shaft 2;
A variable guide device that regulates the rotational movement of the rack shaft 2 as the rack shaft 2 moves in the axial direction and increases or decreases the amount of movement of the rack shaft 2 according to the reference pitch of the screw pinion 11 and the screw rack 21. The guiding device is a steering device for a vehicle equipped with a gear ratio, and the guide device is fixed to the rack shaft 2 in a shape that wraps the rack shaft 2 except for a threaded rack 21, and includes cams 4, 40 having a cam surface 4A on a part thereof. , a cam follower 5, 50, 150, 250 that rotates and guides the cam surface 4A. 2. The steering device for a vehicle according to claim 1, wherein the threaded rack 21 is machined with gears leaving only a part of the circumference. 3. The cam 4 has a cam surface 4A on its edge,
The cam follower 5 that rotationally guides the cam surface 4A is
A steering device for a vehicle according to claim 1, wherein the steering device is rotatably supported on the pinion shaft. 4. The cam 40 has a protrusion 40A in its center portion that extends in the axial direction while being twisted with respect to a line parallel to the axis of the rack shaft 2, and the cam follower 50 that rotationally guides the protrusion 40A has a concave groove. has 50A,
The steering device for a vehicle according to claim 1, wherein the steering device is rotatably supported on a support member 80 by a shaft 81. 5 The cam has the rack shaft 2 in its central portion.
It has grooves 140A and 240A that extend in the axial direction and are twisted with respect to a line parallel to the axis of the groove 140.
The cam follower that rotationally guides A, 240A has rolling elements 150, 2 having protrusions 150A, 250A.
50, a steering device for a vehicle according to claim 1, wherein the steering device is rotatably supported on a support member 80 by a shaft 81. 6. The vehicle according to any one of claims 3 to 5, wherein the cam has a shape such that the variable gear ratio obtained by rotating the rack shaft 2 is the lowest when the vehicle is traveling straight. steering gear. 7. The vehicle according to any one of claims 3 to 5, wherein the cam has a shape such that the variable gear ratio obtained by rotating the rack shaft 2 is highest when the vehicle is traveling straight. steering gear.