Reduction gear with gap correction for electric power steering

Abstract

To provide a worm reduction gear which can reduce impact sound that is generated in reverse operation of a steering, rattling-like noise and vibration (backlash noise / rattling noise).SOLUTION: The present invention comprises: a case (17a); a worm disposed in an accommodation part (17b) of the case and having a base end part connected to an input shaft; a worm wheel connected to an output shaft and configured to be driven for rotation by the worm; a base end side bearing that holds the base end part of the worm in the accommodation part; a tip side bearing that holds a tip part of the worm and is arranged at a cylindrical tip part of the accommodation part; and a spring (30) fixed to the tip part of the accommodation part around the tip side bearing, the spring having at least one elastic blade (32, 33) which is positioned and formed so as to abut on the case to apply a force to the tip side bearing in a direction toward the worm.SELECTED DRAWING: Figure 9B

Description

[Technical field]

[0001] The present invention relates to the field of electric power steering of automobiles, and more particularly to a reducer capable of transmitting the torque generated by an electric assist motor to a mechanical steering link connecting the steering wheel of an automobile to the steered wheels. [Background technology]

[0002] An electric power steering device for a motor vehicle generally has mechanical components including a steering wheel rotatably connected to a steering column, the end of which remote from the steering wheel supports a steering pinion which engages with a rack slidably mounted in a steering case. The two opposing ends of the rack are respectively connected to the left and right steering wheels of the vehicle via rods. To assist the force applied by the driver of the vehicle to the steering wheel, the steering system includes an electric assist motor which rotates in two directions, the output shaft of which is connected to a mechanical steering link between the steering column and the steered wheels of the vehicle via a reducer to transmit a motor torque (and possibly also a resistive torque) to assist the steering column. The electric assist motor is controlled by an on-board electronic computer which receives and processes various signals from sensors, including in particular a sensor of the torque applied to the steering column by the driver of the vehicle.

[0003] Various reduction gears are known, in particular with a worm and a worm wheel. Patent document 1 describes a worm reducer with a gap compensation spring (backlash reducing spring) including an elastic blade (elastic tongue). This spring is formed to clamp the bearing of the worm located opposite the motor in an elongated housing machined in the case housing the reducer and move with said bearing. The housing is closed with a waterproof plug. The elastic blade is configured to hold the worm against the worm wheel and compensates for the gap between the worm and the worm wheel. This gap is due, among other things, to geometrical variations inherent in the manufacture of machine parts, to temperature fluctuations and to wear during normal operation. The part of the case housing the spring is a complex elongated shape with a cavity for housing the elastic blade. This complex shape can only be obtained by additional machining operations that are more complex and time-consuming than the other machining operations necessary to form the housing of the reducer in the case, and that require very high precision in shape and positioning. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-117049 A Summary of the Invention [Problem to be solved by the invention]

[0005] It is therefore desirable to provide a worm reducer that can reduce the impact and rattle type noises and vibrations ("backlash noise / rattle noise") that occur when traveling on uneven ground (such as cobblestones, uneven roads, road joints, etc.) or when steering is reversed. It is also desirable for such a reducer to have a long life while allowing for a reduction in the number of parts, the complexity of the machining, and the size. [Means for solving the problem]

[0006] One embodiment relates to a reducer having a case, a worm disposed within an accommodating portion of the case and having a base end connected to an input shaft, a worm wheel connected to an output shaft and configured to be rotated by the worm, a base end bearing that holds the base end of the worm within the accommodating portion, a tip end bearing that holds a tip end of the worm and is disposed in a cylindrical tip end of the accommodating portion, and a spring fixed to the tip end of the accommodating portion around the tip end bearing, the spring including at least one elastic blade disposed and formed to abut against the case and apply a force to the tip end bearing in a direction toward the worm wheel.

[0007] With this configuration, the spring is fixed to the case and the tip bearing moves within the spring. This reduces friction and wear of the housing due to the movement of the spring or bearing within the housing, which is typically made of aluminum. Friction occurs primarily between the spring and the tip bearing, which is typically made of steel, and the coefficient of friction between two steel parts is less than the coefficient of friction between an aluminum part and a steel part. Furthermore, by changing the shape and elasticity of the spring, the side gap between the spring and the tip bearing can be eliminated.

[0008] In addition, the cylindrical shape of the spring-side tip of the housing facilitates manufacturing. As a result, the machining of the tip of the housing can be performed in the same process as the machining of the housing of the base-end bearing on the motor side, and thus the need to open the tip of the housing for this machining is eliminated. This ensures that the two bearings are perfectly coaxial. This non-through machining eliminates the need for plugs and possible joints and their assembly work.

[0009] If the space between the spring and the case is small, the two blades will only deform slightly without exceeding their elastic limit.

[0010] In cases where the reducer or the input and output shafts may be subjected to impacts, this configuration makes it possible to reduce impact noise or vibrations and rattles that occur in the reducer when driving on uneven ground or when reversing steering.

[0011] According to one embodiment, in order to prevent the spring from rotating in the receiving part, the spring has a protrusion arranged to engage in a recess formed in the tip of the receiving part.

[0012] In this manner, the spring can be easily prevented from rotating within the case without the need for complex machining.

[0013] According to one embodiment, the protrusion has a U-shaped portion extending radially outwardly of the spring.

[0014] Therefore, the direction of action of the blades can be easily changed by simply changing the position of the spring projections. In fact, this change of direction is useful for adapting the reducer to geometrical reducer characteristics such as the cross angle, the helix angle, the pressure angle, etc.

[0015] According to one embodiment, the spring has flat sides positioned and shaped to guide the tip bearing toward and away from the worm wheel and eliminate side gaps between the spring and the tip bearing.

[0016] In this way, the worm can be held accurately on the central surface of the worm wheel, preventing errors in the crossing angle that could impair the quality of the meshing. Furthermore, by eliminating such gaps, noise that is likely to be generated when the reducer and input / output shafts are subjected to impact can be reduced.

[0017] According to one embodiment, the flat side has a tab extending radially inwardly of the spring which cooperates with a distal bearing to lock the spring in an axial distal direction.

[0018] Thus, the tabs that axially hold the spring in the distal bearing can be formed by bending over the protruding parts of the flats in the annular part of the spring, without affecting the cylindrical shape of the main part of the spring, and the presence of the tabs extending the flats also strengthens these flats.

[0019] According to one embodiment, each resilient blade has a curvature and varies in width between its fixed and free ends and is adjusted to follow the variation curve of the force exerted by the blade on the tip bearing as a function of the position of the tip bearing on the spring.

[0020] In this way, the impact noise can be reduced by adjusting the shape and curvature of each elastic blade.

[0021] According to one embodiment, the variation curve of the force exerted by each resilient blade on the tip bearing as a function of the tip bearing's position on the spring changes linearly with a relatively small slope, and then becomes more abrupt near the end of the tip bearing's stroke in the direction towards the worm wheel.

[0022] According to one embodiment, the spring has an annular portion extending over an angular region comprised between 240° and 300°, and each elastic blade has a free end and a fixed end fixed to the annular portion.

[0023] According to one embodiment, the spring has two elastic blades whose width is less than the height of the spring and which are arranged to intersect in an area diametrically opposite the contact area between the worm and the worm wheel.

[0024] In this way, the (two) contact forces applied by the spring to the front bearing are balanced and directed towards the worm wheel.

[0025] The embodiment also relates to a power steering system for a motor vehicle having a reduction gear coupled between an assist motor and a rotating member of a steering system of the motor vehicle, the reduction gear being the reduction gear described above.

[0026] According to one embodiment, the worm wheel of the reducer is fixed to a steering column of the steering system.

[0027] According to one embodiment, the worm wheel of the reducer is fixed to a pinion shaft that is connected to a rack and pinion of the steering system.

[0028] According to one embodiment, the worm wheel of the reducer is fixed to a pinion shaft which is connected to an additional rack and pinion of the steering system.

[0029] According to one embodiment, the worm wheel of the reducer is fixed to a force feedback steering column of a steering system in which there is no mechanical link between the steering wheel and the steered wheels of the vehicle.

[0030] According to one embodiment, the power steering includes another reducer having a worm wheel, the worm wheel of the reducer and the worm wheel of the other reducer being respectively connected to a rack and pinion of the steering system.

[0031] The present invention will be better understood from the following description taken in conjunction with the accompanying drawings, in which like reference numbers correspond to structurally and / or functionally identical or similar elements, and in which: [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 is a schematic diagram of a conventional automobile steering system equipped with an electric power assist. [Diagram 2] FIG. 2 is a schematic diagram of another conventional automobile steering system equipped with an electric power assist. [Diagram 3] FIG. 3 is a schematic diagram of another conventional automobile steering system equipped with an electric power assist. [Figure 4] FIG. 4 is a schematic diagram of another automobile steering system equipped with an electric power assist. [Diagram 5] FIG. 5 is a schematic perspective view of another automobile steering system equipped with an electric power assist. [Figure 6] FIG. 6 is a schematic cross-sectional view of a conventional worm reduction gear. [Figure 7] FIG. 7 is a cross-sectional view of a gap compensation spring according to the prior art used in the reducer of FIG. [Figure 8] FIG. 8 is a schematic vertical cross-sectional view of a worm reduction gear according to one embodiment. [Figure 9A] FIG. 9A is a schematic cross-sectional view of a worm reducer according to one embodiment, showing the gap compensation spring without the worm. [Figure 9B] FIG. 9B is a schematic cross-sectional view of a worm reducer according to an embodiment, showing the gap compensation spring with the worm. [Figure 10] FIG. 10 is a schematic side view of a gap compensation spring according to one embodiment. [Figure 11] FIG. 11 is a schematic perspective view of a gap compensation spring according to one embodiment. [Figure 12] FIG. 12 is a schematic perspective view of a gap compensation spring according to one embodiment. [Figure 13] FIG. 13 is a schematic perspective view of a portion of a gap compensation spring according to one embodiment. [Figure 14] FIG. 14 is a schematic perspective view of a portion of a gap compensation spring according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] 1, 2 and 3 show prior art steering devices 1a, 1b, 1c for automobiles equipped with an electrically power-assisted device.

[0034] FIG. 1 shows a C-EPS type column power steering 1a ("column type electric power steering (EPS)"). FIG. 2 shows a dual pinion DP-EPS type power steering ("dual pinion EPS"). FIG. 3 shows a P-EPS type power steering ("pinion type EPS"). Each of the devices 1a, 1b, and 1c has a steering column 3 connected to a steering wheel 2 and an intermediate shaft 5 connected to a steering shaft 3 by a dial joint 4. The intermediate shaft 5 is connected to a steering pinion 7a by a dial joint 6 and a pinion shaft 7. The steering pinion 7a meshes with a rack bar 8 slidably attached to a steering case 9. Two opposing ends of the rack bar 8 are connected to left and right steering wheels 11 by rods 10, respectively. When the steering wheel is rotated, the steering column is rotated. This rotation is converted into a translational motion by the rack bar 8, which changes the direction of the wheels 11.

[0035] To assist the force applied manually to the steering wheel 2 by the driver of the vehicle, each power steering device 1a, 1b, 1c has a motor system SM with a bidirectionally rotating electric assist motor M and a reducer 17. The output shaft of the motor M is connected to the power steering of the vehicle by the reducer 17 so as to transmit the motor torque (and possibly also the resistance torque) to the steering. The motor system SM also has a control unit (on-board electronic computer) ECU that receives and processes various signals from sensors, in particular the torque sensor 13, and supplies control signals to the control circuit DC of the engine M. The reducer 17 can be of the type with a worm, formed by a worm shaft 18 and a worm wheel 19 fixed to the power steering of the vehicle. The torque sensor 13 has, for example, a torsion bar 12 interconnecting the upper and lower parts of the steering shaft of the vehicle. A motion detector 13 connected to the torsion bar 12 measures the relative rotational movement between the upper and lower parts of the steering shaft on either side of the torsion bar 12.

[0036] In a C-EPS type power steering device (FIG. 1), a worm wheel 19 of a reduction gear 17 is fixed to a steering column 3 , and a torsion bar 12 is interposed between an upper portion and a lower portion of the column 3 .

[0037] In a DP-EPS type power steering device (FIG. 2), a worm wheel 19 of a reduction gear 17 is fixed to a shaft 7c that is connected to a rack bar 8 by another pinion 7b. A torsion bar 12 is interposed between an upper portion and a lower portion of the pinion shaft 7.

[0038] In a P-EPS type power steering device (FIG. 3), the worm wheel 19 of the reduction gear 17 is fixed to the pinion shaft 7, and the torsion bar 12 is interposed between the upper and lower portions of the pinion shaft 7.

[0039] 4 and 5 show other steering devices 1d, 1e for automobiles with an electrically power-assisted device of the SBW (Steer-by-Wire) type. In these two devices, the steering wheel 2 is no longer mechanically linked to the rack bar 8, but is connected via two motor systems SM1, SM2, which can be the same as the motor system SM described above. The motor systems SM1, SM2 are mechanically linked to the rack bar 8 by shafts 7c, 7d and pinions 7a, 7b, respectively. A torque sensor 13 is associated with the steering column 3, and both control units ECU of the systems SM1, SM2 receive signals from the sensor 13.

[0040] The device 1e (FIG. 5) comprises a third motor system SM3 coupled to the steering column 3 for supplying a resistive or motor torque to the steering wheel 2. The control unit ECU of this system SM3 is connected to the control units ECU of the systems SM1, SM2 and supplies force feedback to the steering wheel 2 according to control signals generated by the systems SM1, SM2.

[0041] FIG. 6 shows in more detail a worm reducer 117 according to the prior art, comprising a worm wheel 19 and a worm 18. The reducer can be mounted on the steering column 3 (FIG. 1), on an additional pinion 7b (FIGS. 2, 4, 5) or on the pinion shaft 7 (FIG. 3). The worm shaft 18 is arranged coaxially with respect to an output shaft 20 of the electric motor M and is connected to the output shaft 20 of the electric motor M in such a way that mechanical power provided by the motor is transmitted to the shaft 18 to rotate it about its axis. The shaft 18 connected to the motor M has a base end 18a and a distal end 18b connected by a central portion 18c. The central portion 18c is provided with teeth (not shown) adapted to mesh with complementary teeth provided on the outer circumference of a coaxial wheel 19 fixed to the steering column 3. The ends 18a, 18b of the shaft 18 are held in the case 117a of the reducer 117 by a base end bearing 22 and a tip end bearing 23, for example of a ball bearing or roller bearing type. The bearings 22, 23 each have an inner ring 24, 25 that contacts one of the ends 18a, 18b of the shaft 18, and an outer ring 26, 27. The ring (outer ring) 26 of the base end bearing 22 is fixed in the case, and the ring (outer ring) 27 of the tip end bearing 23 can move linearly in the case 117a to follow the movement of the worm 18. The tip end bearing 23 is held in the housing of the case 117a by a gap compensation spring 130. The spring 130 has a curved elastic blade 133 that is housed in a cavity 136 formed in the periphery of the housing that houses the outer ring 27 of the tip end bearing 23. Therefore, the elastic blade 133 presses the tip bearing 23 in the direction X1 (shown in FIGS. 6 and 7) of the wheel 19.

[0042] FIG. 7 shows the spring 130. The spring 130 has an annular portion 131 that surrounds most of the outer ring 27 of the distal bearing 23, and a spring blade 133. The spring 130 can be held on the outer ring 27 of the distal bearing 23 by tabs 134 that extend radially from the base and distal ends of the annular portion of the spring 130. The elastic blades 133 each have a free end and an end connected to each side edge of the annular portion 131 by an abutment portion 132. The elastic blades 133 and the abutment portion 132 are housed in a cavity 136 formed in the case 117a of the reducer 117. The spring 130 is formed into a spring blade, for example, by bending and / or stamping. The abutment portion 132 is formed to cooperate with the inner wall of the cavity 136 to prevent the spring 130 from rotating in the case 117a. The elastic blades 133 are formed such that their free ends come into contact with the bottom of the cavity 136 to press the bearing 23 toward the worm wheel 19. The elastic blades 133 are configured to cross each other near their free ends at the bottom of the cavity 136. The elastic blades 133 thus form a mechanism for compensating for the meshing gap of the reducer 117 including the worm wheel 19 and the worm 18. This gap compensation makes it possible to absorb geometrical variations inherent in the manufacture of the parts constituting the reducer 117, temperature changes, wear during normal operation, and the like.

[0043] However, the accommodation of the reducer in the case 117a, which has an elongated shape along an axis determined by the direction X1 and has a cavity 136, is machined in an additional lengthy operation (contouring), which requires much higher precision in terms of shape and positioning compared to other types of machining of the case 117a.

[0044] The accommodation portion of the reducer inside the case 17a needs to be sealed after assembly, particularly in systems that need to be installed under a cover, such as P-EPS and DP-EPS systems.

[0045] FIG. 8 shows a reducer 17 according to an embodiment including a worm 18 and a worm wheel 19. The reducer 17 differs from the reducer 117 in that the spring 130 is replaced with a spring 30 and the case 117a is replaced with a case 17a. FIG. 8 shows the worm 18 and the worm wheel 19 assembled in the housing of the case 17a. The worm wheel 19 is fixed to the steering column 3 and is attached coaxially with the steering column 3. The worm 18 is held in the case 17a by a base end bearing 22 and a tip end bearing 23, and is connected to the shaft of the motor M by a coupling member 42. The tip end bearing 23 is guided in the case 17a by a spring 30 formed to apply a force to the tip end bearing 23 to press the tip end of the worm 18 toward the wheel 19 in the X1 direction. The case 17a has a housing 17b in which the worm 18 and the bearings 22 and 23 are arranged. The receiving portion 17b has a substantially cylindrical distal end 17c for receiving a spring 30 which surrounds the distal bearing 23. The bearings 22, 23 are, for example, of the ball bearing type.

[0046] Figures 9A and 9B show the spring 30 in the case 17a, and Figure 9B also shows the bearing 23 and the worm 18. Figures 10 to 12 show the spring according to one embodiment in isolation. In Figures 9 to 12, the spring 30 is in the form of a collar that is generally cylindrical and open between two generatrices of the cylindrical shape, and has an open annular part 31, i.e. an annular part 31 that extends over an annular area that is smaller than 360° and is included, for example, between 240° and 300°, for example 270° (plus or minus 10%).

[0047] The annular portion 31 has an annular proximal edge 38, an annular distal edge 39 and opposing side ends 37, each of which is extended in part by a resilient curved blade 32, 33. The blades 32, 33 have a width less than half the height of the spring 30 and extend a length less than the distance between the longitudinal edges 37, such that the cylindrical shape is closed and intersects, for example, at the mid-distance between the longitudinal edges 37. The spring 30 is therefore symmetrical with respect to a plane XZ passing through the longitudinal axis Z of the worm 8 and perpendicular to the axis of rotation of the wheel 19.

[0048] At the tip edge 39 of the spring 30, tabs 34, 34a extend radially inward of the annular portion 31. The tabs 34 are provided to lock the spring 30 to the tip bearing 23 in the axial base direction. The spring 30 is locked in the tip direction by a shoulder formed at or near the bottom of the housing portion 17b. The bearing 23 can be held in the axial base direction by an annular shoulder 18a provided at the tip of the worm 18. The bearing 23 is further locked in the axial tip direction by being pressed into the worm 18. The blades 32, 33 are arranged and formed to apply a force to the tip bearing 23 in the direction X1 toward the worm wheel 19 by being supported inside the case 17a.

[0049] The tabs 34, 34a are extensions of flats 35, 35a, respectively, of the annular portion 31. The side flats 35 are arranged and shaped to laterally lock the spring 30 within the case 17a to eliminate any side gaps between the bearing 23 and the worm 18, and to guide the movement of the bearing 23 in the direction X1 and the opposite direction. The annular portion 31 has a protrusion intended to engage a recess 36 formed in the case 17a to prevent rotation (about the Z axis) of the spring 30 within the case 17a.

[0050] According to one embodiment, this protrusion is formed by folding the strip forming the annular portion 31 in a U-shape and moving the flat portion 35a radially outward of the annular portion (FIGS. 9A, 9B). The recess 36 in the case 17a can also lock the spring 30 axially distally.

[0051] In this way, the spring 30 is fixed with respect to the case 17a. The flat 35a is, for example, located radially opposite the intersection of the blades 32, 33. The flat 35a also serves as an index that allows the direction of the force applied by the blades 32, 33 to the bearing 23 to be determined with respect to the case 17a. The direction of the force applied by the blades 32, 33 can be fine-tuned by adjusting this shape 35a of the annular part 31 of the spring 30 with respect to the direction X1, which shape can be formed, for example, by stamping and / or bending the spring blades. It should be noted that the flat 35a does not come into contact with the case, and only the side that connects the flat 35a to the rest of the spring determines the angular position of the spring 30 around the Z axis.

[0052] According to one embodiment, the flats 35 are strengthened by forming bends in the flats 35. However, it should be noted that the bent tabs extending the flats 35, 35a also contribute to the strengthening of these sections.

[0053] The elastic blades 32, 33 receive an auxiliary torque and are pressed against the case 17a when the worm 18 moves in the opposite direction to the wheel 19, so that the elastic blades 32, 33 spread and retreat. This spreading causes very small local deformation of the elastic blades 32, 33, thereby minimizing the risk of plastic deformation and fatigue failure of the elastic blades.

[0054] The curvature of the elastic blades 32, 33 towards the bearing 23 and their shape which changes in cross section along the blade are designed to generate a force whose magnitude depends on the stroke. According to one embodiment, the curvature and shape of the blades 32, 33 are designed to generate a force whose magnitude changes with the stroke, first linearly with a small gradient and then increasing more rapidly at the end of the stroke. Thus, when approaching the rest position of the bearing 23 in the case 17a, the force generated increases abruptly due to the blades widening (shortening of the lever arm). This reduces possible impact noise due to the bearing 23 coming into hard contact with the case 17a at the end of the stroke.

[0055] At the time of contact, the radius of curvature of the outer surface of the bearing 23, the radius of curvature of the expanded (extended) blades 32, 33, and the radius of curvature of the housing part of the case 17a are close to each other. As a result, the contact is made with the pressure well distributed, and excessively localized pressure stress concentration that may adversely affect the life of the spring 30, especially the blades 32, 33, is avoided.

[0056] In the embodiment shown in FIG. 13, the flats 35 of the spring 30 are replaced by straight ribs 35' which function in the same way, and these ribs can be manufactured by stamping an annular section inwards.

[0057] In the embodiment shown in FIG. 14, the tab 35a of the spring 30 is replaced by a spatula-shaped part 40 that allows easy installation of the spring in the case. When the spring 30 is installed, a guide is temporarily placed in the housing of the wheel 19. This guide ensures communication between a passage and positioning notch located at the entrance of the housing 17b and a notch located at the tip 36 of the housing 17b. Between these two notches is a window / intersection (meshing area) between the hole with the worm 18 and the chamber with the wheel 19. This spatula shape 40 allows easy entry / guiding and passage of the guide / tip 36.

[0058] It will be apparent to those skilled in the art that the present invention is subject to various embodiments and various applications. In particular, the present invention is not limited to the shape of the spring 30 described above. In fact, the spring 30 may have only one elastic blade configured to apply a force to the tip bearing 23 in the direction of the worm wheel 19.

[0059] Additionally, the spring may be retained in the case by means other than a protrusion engaging a recess in the case, thus for example the spring may be formed with a recess and the case with a protrusion.

[0060] Furthermore, the reduction gear may be used in mechanical devices other than the power steering device of an automobile.

Claims

1. It is a speed reducer, Case (17a) and A worm (18) is disposed within the housing portion (17b) of the case and has a base end connected to the input shaft, A worm wheel (19) is connected to the output shaft (3, 7, 7c) and is configured to be rotationally driven by the worm, A base end bearing (22) holds the base end of the worm within the housing, A tip-side bearing (23) that holds the tip of the worm, the tip-side bearing being positioned at the cylindrical tip (17c) of the housing (17b), A spring (30) fixed to the tip of the housing around the tip bearing, having at least one elastic blade (32, 33) arranged and formed to contact the case and apply force to the tip bearing in the direction toward the worm wheel (X1), A gearbox having a gear reducer.

2. In the gearbox according to claim 1, A reduction gear having a projection (35a) configured to engage with a recess (36) formed at the tip (17c) of the housing (17b) in order to prevent the spring (30) from rotating within the housing.

3. In the gearbox according to claim 2, The aforementioned protrusion (35a) is a reduction gear having a U-shaped portion that extends radially outward from the spring (30).

4. In the gearbox according to claim 1, The spring (30) guides the front end bearing (23) in the direction toward the worm wheel (19) (X1) and in the opposite direction, and the gearbox has a flat side portion (35) that is arranged and formed to eliminate the side gap between the spring and the front end bearing.

5. In the gearbox according to claim 4, The flat side portion (35) is a reduction gear in which a tab (34) that cooperates with the tip bearing extends radially inward of the spring, locking the spring (30) toward the axial tip.

6. In the gearbox according to claim 1, Each elastic blade has a curved portion and its width changes between its fixed end and free end, and is adjusted to follow a fluctuation curve of the force applied to the tip bearing (23) by the blade as a function of the position of the tip bearing in the spring.

7. In the gearbox described in claim 6, A reduction gear in which, as a function of the position of the tip bearing in the spring (30), the fluctuation curve of the force applied to the tip bearing (23) by each elastic blade (32, 33) changes linearly with a relatively small slope, and then increases more sharply near the end of the stroke of the tip bearing in the direction toward the worm wheel (19) (X1).

8. In the gearbox according to any one of claims 1 to 7, The spring (30) has an annular portion extending over an angular region between 240° and 300°, and each elastic blade (32, 33) has a free end and a fixed end fixed to the annular portion in the reduction gear.

9. In the gearbox according to any one of claims 1 to 7, The spring (30) has two elastic blades (32, 33) configured to be narrower than the height of the spring (30) and intersect in a region radially opposite to the contact region between the worm (18) and the worm wheel (19).

10. A power steering system for an automobile having a reduction gear (17) connected between the assist motor (M) and the rotating members (3, 7, 8) of the automobile's steering system (1a, 1b, 1c), The power steering system for an automobile, wherein the reduction gear is a reduction gear described in any one of claims 1 to 7.

11. In the power steering according to claim 10, A power steering system in which the worm wheel (19) of the reduction gear (17) is fixed to the steering column (3) of the steering system (1a).

12. In the power steering according to claim 10, A power steering system in which the worm wheel (19) of the reduction gear (17) is fixed to a pinion shaft (7) connected to the rack (8) pinion (7a) of the steering system (1c).

13. In the power steering according to claim 10, A power steering system in which the worm wheel (19) of the reduction gear (17) is fixed to a pinion shaft (7c) connected to an additional rack (8) pinion (7b) of the steering system (1b).

14. In the power steering according to claim 10, A power steering system in which the reduction gear (17) and the worm wheel (19) are fixed to a force feedback steering column (3) of a steering system (1e) in which there is no mechanical link between the steering wheel (2) and the steering wheels of an automobile.

15. In the power steering according to claim 10, A power steering system comprising the worm and another reduction gear having the worm wheel, wherein the worm wheel (19) of the reduction gear and the worm wheel (19) of the other reduction gear are respectively connected to the rack (8) and pinion (7a, 7b) of the steering system (1d, 1e).

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