Steering system for rotating a steerable wheel

Abstract

The invention relates to a steering system for rotating steerable wheels, comprising a one-piece output unit which is connected to a steering wheel such that rotation of the steering wheel causes the output unit to rotate about an axis. The output unit has an output shaft coupled to the steerable wheel such that rotation of the output unit influences steering of the steerable wheel. The output unit supports the planetary gear. The sun gear is connected with the electric motor such that torque from the electric motor causes the sun gear to rotate relative to the output unit. The sun gear meshes with the planetary gears such that rotation of the sun gear causes the planetary gears to rotate and operate around the sun gear. The output unit is urged to rotate about the axis in response to rotation of the planetary gears and operation about the sun gear.

Description

Technical Field

[0001] The present invention relates to a steering system for turning a steerable wheel. Background Art

[0002] A known vehicle steering system includes a gearbox and a motor. The gearbox includes an output shaft that is rotatable to affect the rotational movement of a steerable wheel. A pinion is operably connected to the output shaft such that rotation of the pinion about an axis of rotation causes the output shaft to rotate. The pinion is rotatably supported on two ball bearings in the gearbox that are aligned along the axis of rotation of the pinion. A steering column interconnects the pinion with a vehicle steering wheel.

[0003] In addition, the motor can be operated to affect the rotation of the output shaft so as to provide steering assistance. The motor is operably connected to the output shaft through one or more planetary gear stages mounted in the gearbox. The output shaft of the motor, the output shaft and each planetary gear stage are aligned along a single axis in the gearbox. A steering system having this general structure is disclosed in US Pat. No. 11,498,616. Summary of the invention

[0004] According to one aspect of the invention, alone or in combination with any other aspect, a steering system for turning a steerable wheel includes a one-piece output unit connected to a steering wheel so that rotation of the steering wheel causes the output unit to rotate around an axis. The output unit has an output shaft coupled to the steerable wheel so that rotation of the output unit affects the steering of the steerable wheel. The output unit supports a planetary gear. The sun gear is connected to an electric motor so that torque from the electric motor causes the sun gear to rotate relative to the output unit. The sun gear meshes with the planetary gears so that rotation of the sun gear causes the planetary gears to rotate and run around the sun gear. The output unit is caused to rotate around the axis in response to the rotation of the planetary gears and the running around the sun gear.

[0005] According to another aspect of the present invention, alone or in combination with any other aspect, a one-piece output portion has a bracket for a planetary gear stage, a worm wheel extending from an axial end face of the bracket along an axis, and an output shaft extending from an axial end face of the bracket along the axis. The bracket is connected to a motor so that the motor causes the output unit to rotate around the axis via the bracket. The worm wheel is connected to a steering wheel via a threaded transmission member so that the rotation of the steering wheel causes the output unit to rotate around the axis. The output shaft is configured to be coupled to a steerable wheel so that the rotation of the output unit affects the steering of the steerable wheel. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The foregoing and other features and advantages of the present invention will become apparent to those skilled in the art by reading the following description with reference to the accompanying drawings, in which:

[0007] Figure 1 is a schematic rear view of an exemplary steering system for turning a steerable wheel;

[0008] Figure 2 yes Figure 1 Rear view of the EPS unit of the steering system;

[0009] Figure 3 is along Figure 2 a cross-sectional view taken along line 3-3 of ;

[0010] Figure 4 yes Figure 3 A separate view of part 4;

[0011] Figure 5 yes Figure 3 A separate view of part 5;

[0012] Figure 6 yes Figure 2 A cross-sectional view of a portion of an EPS unit;

[0013] Figure 7 yes Figure 2 An exploded view of a portion of an EPS unit;

[0014] Figure 8 yes Figure 2 A front perspective view of components of an EPS unit;

[0015] Fig. 9 yes Figure 6 a separate view of portion 9 of ; and

[0016] Fig.10 is along Figure 2 A cross-sectional view taken along line 10-10. DETAILED DESCRIPTION

[0017] The present invention relates to a steering system for turning a steerable wheel. Figure 1 Schematically illustrated is an exemplary steering system 10 for turning a steerable wheel 12. The steering system 10 may be used, for example, in a commercial vehicle. The steering system 10 includes an input shaft 14 and an electric powered steering unit (“EPS unit”) 16 for providing steering assistance. The input shaft 14 extends from a first end 18 to a second end 20 ( Figure 3 ). The steering wheel 22 is connected to the first end 18. For example, the steering wheel 22 can be connected to the first end 18 via a steering column, one or more shafts, one or more joints (such as a universal joint), or any combination thereof. The threaded transmission member 24 ( Figure 3 ) is connected to or disposed on the second end 20. The rotation of the steering wheel 22 causes the torque to be transmitted to the screw transmission member 24 through the input shaft 14. In other words, the screw transmission member 24 is caused to rotate under the influence of the torque transmitted through the input shaft 14.

[0018] The steering linkage 26 is connected to the steerable wheel 12. As shown, the steering linkage 26 includes a first steering member 28, a second steering member 30, and a third steering member 32. The first steering member 28 is connected to the output shaft 34 of the EPS unit 16. The first steering member 28 can be, for example, a pitman arm. The second steering member 30 is connected to the first steering member 28 and can be, for example, a tie rod. The third steering member 32 is connected to one of the steerable wheels 12 and the second steering member 30. The third steering member 32 can be, for example, a pitman arm.

[0019] The EPS unit 16 provides steering assistance in response to rotation of the steering wheel 22 by affecting movement of the steering linkage 26 and, therefore, movement of the steerable wheels 12. See further Figure 2 , the EPS unit 16 includes an electric motor 36 (eg, a reversible electric motor) and a gearbox 38 connected to the motor.

[0020] like Figure 3 As shown, the gearbox 38 has a housing 40 in which the threaded transmission member 24 is rotatably supported. The housing 40 can be formed as a single integral piece or assembled from separate sub-components. A cover 42 is connected to the housing 40 and receives the input shaft 14 in a manner that allows relative rotation between the input shaft 14 and the cover. Therefore, the first end 18 of the input shaft 14 can be outside the housing 40, while the second end 20 can be inside the housing 40. The torsion bar 44 and the output shaft 46 help to transfer the rotation of the second end 20 of the input shaft 14 to the threaded transmission member 24. The input shaft 14, the torsion bar 44, and the output shaft 46 can be coaxial with each other.

[0021] A torsion bar 44 extends within the input shaft 14 and the output shaft 46. A first end 48 of the torsion bar 44 is fixed for rotation with the input shaft 14, while a second end 50 of the torsion bar is fixed for rotation with the output shaft 46. When the input shaft 14 is rotated by the steering wheel 22, the torsion bar 44 allows a predetermined amount of relative rotation between the input shaft and the output shaft 46 before the input shaft and the output shaft rotate together.

[0022] The output shaft 46 has a first end 52 that extends into the second end 20 of the input shaft 14. The second end 54 of the output shaft 46 extends into a recess 56 of the threaded drive 24. The second end 54 can engage with the threaded drive 24 (e.g., by a spline) so that rotation of the output shaft 46 is transmitted to the threaded drive. Therefore, rotation of the output shaft 46 responsively causes or prompts the threaded drive 24 to rotate relative to the housing 40 about the threaded drive's axis of rotation A1 (also referred to herein as the "first axis of rotation").

[0023] The first end 58 and the second end 60 of the threaded drive 24 are each rotatably supported in the housing 40 by bearings 62, 64. Each bearing 62, 64 is a tapered roller bearing having an inner race or cone 66 that circumferentially engages the threaded drive 24, an outer race or cup 68 that circumferentially engages the inner surface of the housing 40 or the inner surface in the housing, and a plurality of tapered rollers 70 radially disposed between the cone and the cup. The cone 66 can be fixed to the threaded drive 24 in a non-rotatable manner, while the cup 68 can be fixed to its corresponding inner surface in a non-rotatable manner. Therefore, when the threaded drive 24 rotates relative to the housing 40, the cone 66 can rotate relative to the cup 68. Each bearing 62, 64 can also include a retainer 72 for its corresponding tapered roller 70. Although each bearing 62 , 64 is shown as a tapered roller bearing, at least one of the bearings 62 , 64 may be any other desired bearing such as, for example, a ball bearing, an angular contact ball bearing, a spherical roller bearing, a cylindrical roller bearing, and a needle bearing.

[0024] The preload of each bearing 62, 64 can be adjusted by a bearing adjuster 74. Figure 3 to Figure 4 As shown, the bearing adjuster includes external threads 76 for threadingly engaging internal threads 78 of the housing 40. The bearing adjuster 74 can be substantially cylindrical such that at least one of the first end 58 of the threaded drive 24 and the second end 54 of the output shaft 46 can extend into and / or through the bearing adjuster 74.

[0025] The bearing adjuster 74 may contact or be caused to contact the cup 68 of the bearing 62. When in contact with the cup 68, screwing the bearing adjuster 74 in (i.e., driving the bearing adjuster toward the bearing 64) causes the cup 68 of the bearing 62 to move toward the other bearing 64 relative to the cone 66 of the bearing 62. This relative movement reduces one or more clearances between the elements of the bearing 62 and thus increases the preload of the bearing 62. Conversely, screwing out the bearing adjuster 74 (i.e., driving the bearing adjuster away from the bearing 64) increases the clearance and reduces the preload of the bearing 62.

[0026] Threading the bearing adjuster 74 in also causes the threaded drive 24 to move along the first axis of rotation A1 toward the bearing 64 via the bearing 62. This movement causes the cone 66 of the bearing 64 to move away from the bearing 62 relative to the cup 68 of the bearing 64, which reduces the one or more gaps between the elements of the bearing 64 and increases the preload of the bearing 64. Conversely, unthreading the bearing adjuster 74 increases the gap and reduces the preload of the bearing 64.

[0027] The amount of torque required to rotate the threaded drive 24 about its axis of rotation A1 corresponds, at least in part, to the level of preload in the bearings 62, 64. In particular, increasing the preload increases the amount of torque required to rotate the threaded drive 24. This is because the friction between the elements of the bearings 62, 64 increases as the preload in the bearings increases.

[0028] Thus, the bearing preload and the "rotation to torque" of the threaded drive can be set or adjusted as needed by screwing in / in or screwing out / out the bearing adjuster 74. In certain gearbox 38 configurations, it can be advantageous for the threaded drive 24 to have a relatively high torque rotation value. This is at least in part because having a high torque rotation value and preload reduces the amount of noise, vibration and / or harshness ("NVH") in the gearbox 38. For example, when the bearings 62, 64 have a high preload, the threaded drive 24 can be substantially prevented from being undesirably pushed axially (e.g., along its rotational axis A1) in response to a change in the rotational direction of the threaded drive and / or in response to an impact force. A threaded drive 24 that is pushed axially may cause or increase NVH in the gearbox.

[0029] However, in other gearbox configurations, such as the gearbox 38 configuration shown in the figures, relatively low torque rotational values ​​are desired. The gearbox 38, as a low torque rotational system, may include features for reducing NVH. For example, Figure 3 to Figure 4 As shown, the gearbox 38 may include a resilient element 80 positioned in the recess 56 of the threaded drive 24. The resilient element 80 extends between a bottom 82 of the recess 56 and the second end 54 of the output shaft 46. Although the resilient element 80 directly contacts each of the threaded drive 24 (e.g., at the bottom 82 of the recess 56) and the output shaft 24, some gearbox 38 configurations may include one or more intermediate elements disposed between at least one of the threaded drive and the output shaft and the resilient element. The resilient element 80 may be a wave spring, a coil spring, or any other suitable spring.

[0030] The resilient element 80 may be at least partially compressed between the threaded drive 24 and the output shaft 46 such that the resilient element applies a predetermined axial force to the threaded drive in a direction away from the output shaft. Axial loading of the threaded drive 24 reduces / damps any axial movement of the threaded drive. Damping the axial movement of the threaded drive 24 eliminates NVH in the gearbox 38 or at least reduces it to an acceptable level without having to increase the preload of the bearings and / or the torque rotation value of the threaded drive 24.

[0031] like Figure 3 As shown, the threaded drive 24 may be in the form of or include a worm that meshingly engages with a worm wheel 84 such that rotation of the threaded drive 24 responsively causes or prompts the worm wheel to rotate relative to the housing 40. The worm wheel 84 may be operably connected to the output shaft 34. Thus, rotation of the steering wheel 22 causes torque to be transmitted to the output shaft 34 through the input shaft 14, the threaded drive 24, and the worm wheel 84. Thus, under the influence of the torque originating from the steering wheel 22, the output shaft 34 may rotate or be prompted to rotate.

[0032] The screw drive 24 can be pressed against the worm gear 84 by pressure via the pressure device 86 of the gear box 38. Figure 3 and Figure 5 As shown, the pressure device 86 includes a reaction plate 88, a resilient element 90, and a piston 92 inserted into a recess 94 of the housing 40. The reaction plate 88 abuts a first shoulder 96 of the housing 40 on one side and a cover 98 closing the recess 94 on the other side. The reaction plate 88 may include external threads for threaded engagement with internal threads of the housing 40. Thus, undesired movement of the reaction plate 88 relative to the housing 40 is substantially prevented.

[0033] The resilient element 90 extends between the reaction plate 88 and the piston 92. Although the resilient element 90 directly contacts each of the reaction plate 88 and the piston 92, some pressure device 86 configurations may include one or more intermediate elements interposed between at least one of the reaction plate and the piston and the resilient element. The resilient element 90 may be a wave spring, a coil spring, or any other suitable spring.

[0034] The piston 92 can move relative to the housing 40 in the recess 94. For example, the piston 92 can move along the recess 94 in a direction transverse to the first rotational axis A1 toward and away from the worm gear 84. However, the geometry of the recess 94 / housing 40 and the piston 92 can be configured to substantially restrict the piston to movement in a direction transverse to the first rotational axis A1. In addition, the movement of the piston 92 can be limited at one end by the reaction plate 88 and at the other end by the second shoulder 100 of the housing 40.

[0035] The piston 92 includes a first recess 102 that faces substantially in a direction transverse to the first rotation axis A1. The resilient element 90 is positioned (e.g., completely positioned) in the first recess 102. At least one of the reaction plate 88 and the cover 98 may also extend into the first recess 102. The resilient element 90 is at least partially compressed between the reaction plate 88 and the piston 92, so that the resilient element provides a pressure (generated by the internal deflection of the resilient element) to the piston that urges the piston away from the reaction plate.

[0036] The piston 92 also includes a second recess 104 that faces substantially in the direction of the first axis of rotation A1. The cup 68 of the bearing 64 circumferentially engages the inner surface of the piston 92 in the second recess 104, so that the bearing 64 moves toward and away from the worm gear 84 with the piston. Thus, the bearing 64 takes the form of a "floating bearing" that can move toward and away from the worm gear 84 in a direction transverse to the first axis of rotation A1. On the other hand, the bearing 62 is a "fixed bearing" because the bearing is mounted in the housing 40 so that the bearing is substantially prevented from moving toward and away from the worm gear 84 relative to the housing 40.

[0037] The pressure of the resilient element 90 urges the piston 92 and the bearing 64 to move away from the reaction plate 88 and toward the worm gear 84. Through the bearing 64, the second end 60 of the threaded drive 24 supported by the bearing 64 is urged toward the worm gear 84. As the second end 60 is pressed toward the worm gear 84, the second end 60 pivots toward the worm gear about the pivot axis 106 defined by the bearing 62 until the threaded drive 24 is in close mesh with the worm gear. Thus, the pressure generated by the resilient element 90 causes or urges the second end 60 of the threaded drive 24 to pivot about the pivot axis 106 until the threaded drive is in close mesh with the worm gear 84.

[0038] When the threaded drive 24 and the worm gear 84 are tightly engaged, the bearings 62, 64 are intentionally at least slightly misaligned (i.e., not coaxial) because the bearing 64 moves under pressure relative to the housing 40. For example, the cup axis 108 of the cup 68 of the bearing 64 may be oriented in a direction transverse to the first rotational axis A1 relative to the cup axis 110 of the bearing 62 ( Figure 4 ) offset. In addition, due to its pivoting movement, the rotation axis A1 of the threaded drive 24 is at a non-zero angle relative to the cup axis 110 of the bearing 62.

[0039] The mounting arrangement of the bearings 62, 64 may be selected in view of the intentional misalignment of the bearings. In other words, it may be advantageous to arrange the bearings 62, 64 in a manner that is relatively insensitive to bearing misalignment. An example of such a mounting arrangement is a direct mounting arrangement. Thus, if Figures 3 to 5As shown, the bearings 62, 64 can be arranged in a direct mounting arrangement. Therefore, each bearing 62, 64 is arranged so that the small end 112 of its tapered roller 70 is "outward" or directed away from the other bearing 62, 64.

[0040] The torque transmitted from the steering wheel 22 to the threaded drive 24 can generate a separation force between the threaded drive 24 and the worm wheel 84, which causes the threaded drive to pivot away from the worm wheel. The pressure of the elastic element 90 is designed to overcome a low separation force (i.e., a separation force equal to or lower than the predetermined separation force) and maintain the threaded drive 24 in close engagement with the worm wheel 84. The low separation force can be generated by a steering wheel torque equal to or lower than the predetermined torque. Therefore, when the steering wheel torque is equal to or lower than the predetermined torque, the threaded drive 24 and the worm wheel 84 remain in close engagement. Because the bearings 62 and 64 are not aligned, the internal stress of the bearing is within an acceptable range, while the steering wheel torque remains low.

[0041] However, the internal stress of the misaligned bearings 62, 64 may increase as the steering wheel torque rises above a predetermined torque threshold. To counteract this potential increase in internal stress, the pressure device 86 may be configured so that the pressure of the elastic element 90 is overcome by a high separation force (i.e., a separation force that is higher than the predetermined separation force). The high separation force may be generated by a steering wheel torque that is higher than the predetermined torque. Therefore, the high separation force causes the threaded drive 24 (e.g., its second end 60) to at least partially pivot away from the worm gear 84 to a position where the bearings 62, 64 are aligned with each other. In other words, the high separation force causes the second end 60 of the threaded drive 24 to pivot to a position coaxial with the cup axes 108, 110. Aligning the bearings 62, 64 at least partially reduces the internal stress of the bearings and thus helps to keep the internal stress of the bearings within an acceptable range under high steering wheel torque. Due to the pivoting caused by the high separation force, the rotation axis A1 of the threaded drive 24 may also be coaxial with the cup axes 108, 110, the input shaft 14, the torsion bar 44, and the output shaft 46.

[0042] The gearbox 38 may be configured such that the second end 60 of the threaded drive 24 may be pivoted away from the worm gear 84 only by a disengaging force until the piston 92 abuts the reaction plate 88. Thus, the maximum distance that the second end 60 of the threaded drive 24 may be pivoted away from the worm gear 84 may be defined by the maximum distance that the piston 92 may travel toward the reaction plate 88. Furthermore, the gearbox 38 may be configured such that the cup axes 108, 110 are coaxial when the piston 92 contacts the reaction plate 88.

[0043] Once the steering wheel torque returns to or below the predetermined torque threshold, the pressure of the resilient element 90 overcomes the separation force and causes the threaded drive 24 to pivot back into tight meshing with the worm wheel 84. In addition, as the teeth of the worm wheel and / or the threaded drive wear, the pressure can also compensate for the wear of the teeth of the threaded drive 24 and / or the wear of the worm wheel 84 by causing the threaded drive to pivot further toward the worm wheel. Thus, even if the teeth of the worm wheel and / or the threaded drive wear, the tight meshing engagement between the threaded drive 24 and the worm wheel 84 can be maintained by the pressure.

[0044] The maximum distance that the second end 60 of the threaded drive 24 can be pivoted toward the worm gear 84 (e.g., to compensate for wear) can be limited by the maximum distance that the piston 92 can travel toward the worm gear. Thus, the threaded drive 24 can be pivoted toward the worm gear 84 until the threaded drive is tightly engaged with the worm gear and / or until the piston 92 contacts the second shoulder 100.

[0045] Although Figures 3 to 5 The gearbox 38 is shown as having both the elastic element 80 and the pressure device 86 , but the gearbox 38 may be configured to include only one of the elastic element 80 and the pressure device 86 or to include neither the elastic element nor the pressure device.

[0046] like Figures 2 to 3 As shown, the steering system 10 also includes a controller 114 and one or more vehicle condition sensors 116, which cooperate to control the EPS unit 16 based on the sensed vehicle condition. In one example, the vehicle condition sensor 116 may include a torque sensor and / or a position sensor electrically connected to the controller 114. When a torque sensor is provided, the torque sensor senses the torque applied to the steering wheel 22 and generates a signal indicative of the torque. When a position sensor is provided, the position sensor senses the rotational position of the steering wheel 22 and generates a signal indicative of the steering wheel position. It should be understood that the vehicle condition sensor 116 may be located inside the housing 40 (such as Figure 3 as shown) or outside the housing.

[0047] The signal from the vehicle condition sensor 116 is sent to the controller 114. The controller 114 analyzes the output of the vehicle condition sensor 116 and affects the operation of the motor 36 of the EPS unit 16 based on the output of the sensor. It is also contemplated that only the torque measurement or only the steering wheel position measurement may be used to affect the operation of the motor 16. The controller 114 may also have inputs that vary based on sensed lateral acceleration of the vehicle or other vehicle operating conditions. In any case, the signal received by the controller 114 determines the speed and / or torque of the motor 36, and thereby determines the torque output by the motor output shaft 118 ( Figure 6 ) is transmitted to the gearbox 38 to assist the rotation of the steerable wheels 12.

[0048] like Figure 6 to Figure 7 As shown, the output shaft 118 extends into the gearbox 38 along the second axis of rotation A2 and extends toward the first planetary gear stage 120. The first planetary gear stage 120 includes a sun gear 122 fixed to the output shaft 118 and rotatable therewith. The sun gear 122 is integrally formed with the output shaft 118 as a single, unitary piece, although the sun gear may be formed separately from the output shaft and subsequently attached to the output shaft. The planet gears 124 are meshingly engaged with the sun gear 122 and with a ring gear 126 that is non-rotatably fixed in the housing 40. Rotating the output shaft 118 and the sun gear 122 fixed thereto about the second axis of rotation A2 responsively rotates the planet gears 124 or causes the planet gears to rotate and run about the sun gear (and thus the second axis of rotation) while maintaining their meshing engagement with the ring gear 126. Although three planet gears 124 are shown, the first planetary gear stage 120 may include any number of planet gears.

[0049] The planet gears 124 are rotatably supported on a carrier 128 that rotates about a second axis of rotation A2 as the planet gears rotate and orbit about the sun gear 122. The carrier 128 is radially spaced from the housing 40 and is positioned radially between the sun gear 122 and the ring gear 126. The first planet gear stage 120 may have a gear reduction ratio from the sun gear 122 to the carrier 128 of, for example, about 3:1 to about 10:1, although the second planet gear stage may have any desired gear reduction ratio.

[0050] The first planetary gear stage 120 is operably connected to the second planetary gear stage 142 within the housing 40. However, unlike a typical gearbox arrangement, the first planetary gear stage 120 and the second planetary gear stage 142 are not directly connected to each other, nor are they aligned along a single axis. Instead, the first planetary gear stage 120 is operably connected in series with the second planetary gear stage 142 via one or more intermediate gears. Thus, the intermediate gear(s) transfer torque from the first planetary gear stage 120 to the second planetary gear stage 142. In other words, the one or more intermediate gears serve as an intermediary for transferring the rotation of the first planetary gear stage 120 to the second planetary gear stage 142.

[0051] like Figure 6 to Figure 7 As shown, the one or more intermediate gears may include a first intermediate gear 130 that is fixed for rotation with the carrier 128. Therefore, the first intermediate gear 130 can rotate about the second rotation axis A2 with the carrier 128. The end of the first intermediate gear 130 opposite the carrier 86 can be rotatably supported in the housing 40 by a bearing 132 (e.g., a ball bearing).

[0052] The second intermediate gear 134 is rotatably mounted in the housing 40 and meshingly engaged with the first intermediate gear 130. Therefore, the rotation of the first intermediate gear 130 responsively causes the second intermediate gear 134 to rotate about the third rotation axis A3.

[0053] The third intermediate gear 136 is rotatably supported in the housing 40 by bearings 138, 140. The third intermediate gear 136 is also meshingly engaged with the second intermediate gear 134. The rotation of the second intermediate gear 134 responsively causes the third intermediate gear 136 to rotate about the fourth rotation axis A4. Although only one intermediate gear 134 is shown between the first intermediate gear 130 and the third intermediate gear 136, the gearbox 38 may include any number of intermediate gears located between the first intermediate gear and the third intermediate gear.

[0054] The second planetary gear stage 142 includes a sun gear 144 that is fixed to the third intermediate gear 136 in a non-rotatable manner. Specifically, the sun gear 144 may include a first end 146 extending into an opening 148 of the third intermediate gear 136, wherein the first end is engaged with the third intermediate gear in a non-rotatable manner. Therefore, the sun gear 144 can rotate around the fourth rotation axis A4 together with the third intermediate gear 136. The planetary gear 150 is meshedly engaged with the sun gear 144 and the teeth 152. The teeth 152 are on the housing 40, adjacent to the second planetary gear stage 142 and extend circumferentially around the fourth rotation axis A4. Therefore, the teeth 152 are integrally formed with the housing 40 as a single integral piece. However, the teeth 152 may be provided on a component (e.g., a ring gear) that is separate from the housing 40 and attached to the housing.

[0055] Rotation of the sun gear 144 about the fourth axis of rotation A4 responsively rotates or causes the planet gears 150 to rotate and orbit the sun gear (and thus the fourth axis of rotation) while maintaining meshing engagement with the teeth 152. Although three planet gears 150 are shown, the second planetary gear stage 142 may include any number of planet gears.

[0056] The planet gears 150 are rotatably supported on a carrier 154 that rotates about a fourth axis of rotation A4 as the planet gears rotate and run around the sun gear 144. The carrier 154 is radially spaced from the housing 40 and is radially positioned between the sun gear 144 and the teeth 152. The second planet gear stage 142 may have a gear reduction ratio from the sun gear 144 to the carrier 154 of, for example, about 3:1 to about 10:1, although the second planet gear stage may have any desired gear reduction ratio. It should be understood that the gearbox 38 may include additional planet gear stages (not shown) to achieve a desired gear reduction ratio through the gearbox.

[0057] The output shaft 34 is connected to the bracket 154 so that the bracket and the output shaft rotate together about the fourth rotation axis A4 relative to the housing 40. The output shaft 34 can be rotatably supported in the housing 40 by at least one bearing 156. The output shaft 34 extends from the housing 40 and includes a spline 158 on the exterior of the housing for connecting with the steering linkage 26.

[0058] The worm gear 84 is fixed to the bracket 154 of the second planetary gear stage 142 and can rotate therewith around the fourth rotation axis A4. As a result, the rotation of the steering wheel 22 is transmitted to the output shaft 34 via the threaded transmission 24, the worm gear 84 and the bracket 154. Although the worm gear 84 and its teeth are shown as extending completely around the fourth rotation axis A4, the worm gear can be configured so that the worm gear and / or the teeth of the worm gear only partially extend around the fourth rotation axis. For example, the worm gear 84 and / or its teeth can extend circumferentially around the fourth rotation axis A4 from about 150 degrees to about 180 degrees, although the worm gear 84 and / or its teeth can be configured to extend around the fourth rotation axis Any desired degree.

[0059] like Figures 6 to 8 As shown, the output shaft 34, the worm gear 84 and the bracket 154 are integrally formed together as a single unitary piece to define a one-piece output unit 160 of the gearbox 38. Forming the output shaft 34, the worm gear 84 and the bracket 154 as a single piece helps reduce angular backlash in the gearbox 38 and eliminates any potential alignment issues between these parts that may occur if they are separated from each other. The bracket 154 (i.e., the bracket portion of the output unit) has a recess 162 into which the sun gear 144 extends. Specifically, the sun gear 144 extends through a first portion 162a of the recess 162 along the fourth rotation axis A4 and extends into a second portion 162b of the recess, which second portion may have a smaller diameter than the first portion. The second end 164 of the sun gear 144 may be rotatably supported in the second portion 162b of the recess 162 via a bearing 166 (e.g., a needle bearing) so that the sun gear and the bracket 154 can rotate relative to each other around the fourth rotation axis A4.

[0060] The carrier 154 also includes circumferentially spaced windows 168 that extend radially through the carrier. The number of windows 168 can be equal to the number of planet gears 150, because each planet gear can be positioned in a corresponding window, although at least one of the windows can be configured to accommodate multiple planet gears therein. Therefore, the planet gears 150 extend through the windows 168 so that they mesh with the sun gear 144 in the first portion 162a of the recess 162 and mesh with the teeth 152 that circumferentially surround the carrier 154. The planet gears 150 are connected to the carrier 154 and retained in the windows by shafts 170 that extend through the windows 168 in the direction of the fourth rotation axis A4. The shafts 170 can be supported in openings 172 on the carrier 154.

[0061] The bracket 154 also includes an axial end face 174, which faces away from the third intermediate gear 136 in the direction of the fourth rotation axis A4. The output shaft 34 (i.e., the output shaft portion of the output unit 160) extends from the axial end face 174 along the fourth rotation axis A4. Therefore, one end of the output shaft 34 is connected to the bracket 154 (and connected to the worm gear 84 via the bracket) in the housing 40, and the other end of the output shaft is outside the housing. The worm gear 84 (i.e., the worm gear portion of the output unit 160) also extends from the axial end face 174 along the fourth rotation axis A4 so that it at least partially circumferentially surrounds a portion of the output shaft 34. The worm gear 84, which is integrally formed as a part of the output unit 160, defines an external tooth on the output unit that meshes with the threaded transmission member. Therefore, in response to the torque from each of the steering wheel 22 and the motor 36, the output unit 160 is caused to rotate around the fourth rotation axis A4.

[0062] See also Figure 6 and Fig. 9 , the output unit 160 is rotatably supported at one end (e.g., at or adjacent to the output shaft 34) via a bearing 156, and rotatably supported at the other end (e.g., at or adjacent to the bracket 154) via a bearing 140. Specifically, the bearing 156 is a tapered roller bearing having an inner race or cone 66 circumferentially engaged with the output shaft 34, an outer race or cup 68 circumferentially engaged with the inner surface 176 of the housing 40, and a plurality of tapered rollers 70 radially disposed between the cone and the cup. The cone 66 may be non-rotatably fixed to the output shaft 34, and the cup 68 may be non-rotatably fixed to the inner surface 176. Therefore, when the output shaft 34 rotates relative to the housing 40, the cone 66 may rotate relative to the cup 68. The bearing 156 may also include a cage 72 for its corresponding tapered roller 70. At least a portion of the bearing 156 is located radially between the output shaft 34 and the worm gear 84, although the bearing may be disposed at any other desired location on the outer shaft.

[0063] The bearing 140 is also a tapered roller bearing having an inner race or cone 66 circumferentially engaged with the third intermediate gear 136 (e.g., an outer shoulder 178 of the third intermediate gear), an outer race or cup 68 circumferentially engaged with the inner surface 180 of the carrier 154, and a plurality of tapered rollers 70 radially disposed between the cone and the cup. The bearing 140 may also include a retainer 72 for its respective tapered rollers 70. The inner surface 180 of the carrier 154 may define a third portion 162c of the recess 162, which may have a larger diameter than the first portion 162a of the recess. A portion of the third intermediate gear 136 extends into the recess 162 of the carrier 154, such that the inner surface 178 circumferentially surrounds the outer shoulder 180 of the third intermediate gear 136. Thus, the bearing 140 is radially located between the carrier 154 and the third intermediate gear 136. The cone 66 may be fixed to the outer shoulder 180 of the third intermediate gear 136 in a non-rotatable manner, and the cup 68 may be fixed to the inner surface 180 of the bracket 154 in a non-rotatable manner. In this case, when the bracket 154 and the third intermediate gear 136 rotate relative to each other, the cone 66 and the cup 68 rotate relative to each other.

[0064] Thus, the carrier 154 (and thus the output unit 160) and the third intermediate gear 136 are rotatably supported to each other via the bearing 140. The third intermediate gear 136 is also rotatably supported in the housing 40 via the bearing 138. The bearing 138 is a tapered roller bearing having an inner race or cone 66 circumferentially engaged with a support surface 182 in the housing 40, an outer race or cup 68 circumferentially engaged with an inner surface 184 of the third intermediate gear 136, and a plurality of tapered rollers 70 radially disposed between the cone and the cup. The bearing 138 may also include a cage 72 for its respective tapered rollers 70. The inner surface 184 of the third intermediate gear 136 may define a portion of the opening 148 of the third intermediate gear. The support surface 182 may be located on a support plate 186 that is inserted and fixed in a non-rotatable manner in the housing 40. The support plate 186 can be at least partially retained within the housing 40 via the cover 190 and / or via a threaded interface between the support plate and the housing. A portion of the support surface 182 extends into the opening 148 so that the inner surface 184 of the third intermediate gear 136 circumferentially surrounds the support surface. Therefore, the bearing 138 is radially located between the support plate 186 and the third intermediate gear 136. The cone 66 can be fixed to the support surface 182 in a non-rotatable manner, and the cup 68 can be fixed to the inner surface 184 of the third intermediate gear 136 in a non-rotatable manner. In this case, when the third intermediate gear 136 rotates relative to the support plate 186, the cup 68 rotates relative to the cone 66.

[0065] In view of the above, it can be understood that the output unit 160 is rotatably supported on the housing 40 via the bearing 156, the third intermediate gear 136 is rotatably supported on the support plate 186 via the bearing 138, and the output unit and the third intermediate gear are rotatably supported to each other via the bearing 140. Therefore, the output unit 160 and the third intermediate gear 136 are mainly supported in the housing 40 via the bearings 138, 140, 156. Although the bearing 166 is radially positioned between the bracket 154 and the sun gear 144, the bearing is not provided for supporting the output unit 160. In fact, in certain configurations of the gearbox 38, the bearing 166 may be omitted. In such a configuration, the sun gear 144 may terminate outside the second portion 162b of the recess 162 (e.g., the second end 164 of the sun gear may be located in the first portion 162a of the recess), and the second portion of the recess may be completely omitted.

[0066] However, in Figure 6 and Fig. 9 In the illustrated configuration of the gearbox 38, the first end 146 of the sun gear 144 is non-rotatably fixed to the third intermediate gear 136, and the second end 164 of the sun gear extends into the carrier 154, where the second end of the sun gear is rotatably supported via a bearing 166, so that the sun gear and the output unit 160 can rotate relative to each other. The extension of the sun gear 144 into the carrier helps to keep the output unit 160 and the third intermediate gear 136 aligned on the fourth rotation axis A4. The deviation of the output unit 160 (e.g., the carrier 154) and / or the third intermediate gear 136 from alignment can increase the stress on the bearings 138, 140, 156. Therefore, the connection of the sun gear 144 to the carrier 154 via the bearing 166 helps to reduce the stress on the bearings 138, 140, 156 by keeping the output unit 160 and the third intermediate gear 136 at least partially in proper alignment. Therefore, the bearing 166 is provided for alignment and stress purposes, rather than being provided for support purposes as the bearings 138, 140, 156.

[0067] It should be understood that while any of the bearings 138, 140, 156 may be different types of bearings (e.g., ball bearings, angular contact ball bearings, spherical roller bearings, cylindrical roller bearings, or needle bearings), the bearing being a tapered roller bearing provides certain advantages. For example, a ball bearing has point contact between its balls and each of the inner and outer races, while a tapered roller bearing has line contact between the tapered rollers and each of the cone and cup. Line contact provides better stress distribution in the bearing than point contact because the load / stress in the bearing is distributed over a relatively large area, as opposed to being applied to a single point. In addition, tapered roller bearings are designed to support relatively high axial and radial loads. If the bearings 138, 140, 156 were ball bearings or angular contact ball bearings, they would have to be much larger than they are currently in order to provide the same axial load / radial load support that they provide in their tapered roller bearing form.

[0068] Typically, the EPS unit 16, or at least its gearbox 38, is mounted to a support structure (e.g., a frame) of the vehicle between one of the steerable wheels 12 and the support structure such that an axial width 188 of the EPS unit 16 extends between the frame and the steerable wheel. The axial space between the frame and the steerable wheel may be quite limited. Therefore, in order to reduce the axial width 188 of the EPS unit 16, the EPS unit separates the motor 36, the output shaft 118, and the first planetary gear stage 120 via intermediate gears 130, 134, 136 onto a different axis of rotation than the second planetary gear stage 142 and the output unit 160. Arranging the motor 36, the output shaft 118, the first planetary gear stage 120, the second planetary gear stage 142, and the output unit 160 on a single axis of rotation will significantly increase the axial width 188 of the EPS unit 16. Therefore, the specific arrangement of the features of the EPS unit 16 makes the axial width 188 smaller than what would otherwise be produced.

[0069] In addition, if Figure 7 and Fig.10 As shown, each of the rotational axes A2, A3, A4 may intersect a single orientation axis A5 that extends transversely (e.g., perpendicularly) to each of the rotational axes A2, A3, A4. Due to this orientation, other dimensions of the gearbox 38 (e.g., a depth dimension of the gearbox that is substantially perpendicular to the axial width 188 of the gearbox) may remain relatively small without increasing the axial width. Although the first rotational axis A2, the second rotational axis A3, and the third rotational axis A4 are shown as being parallel to each other, at least one of the rotational axes A2, A3, A4 may be at an angle relative to at least another of the rotational axes A2, A3, A4 and / or may be offset from the orientation axis A5.

[0070] During operation, the operator rotates the steering wheel 22, thereby causing the screw drive 24 to rotate about the first rotation axis A1. This in turn causes the worm gear 84 (and thus the output unit 160) to rotate about the fourth rotation axis A4. At the same time, the controller 114 actuates the motor 36 in response to the signal received from the vehicle condition sensor (s) 116 to rotate the output shaft 118 about the second rotation axis A2, which causes the carrier 128 to rotate about the second rotation axis via the sun gear 122 and the planetary gears 124. As a result, the first intermediate gear 130 fixed to the carrier 128 is also caused to rotate about the second rotation axis A2.

[0071] The rotating first intermediate gear 130 causes the second intermediate gear 134 to rotate about the third rotation axis A3, which responsively causes the third intermediate gear 136 to rotate about the fourth rotation axis A4. The sun gear 144, which is non-rotatably fixed to the third intermediate gear 136, rotates together with the third intermediate gear 136 about the fourth rotation axis A4. The sun gear 144 causes the carrier 154 (and thus the attached output shaft 34) to rotate about the fourth rotation axis A4 via the planetary gears 150. Therefore, the force from the motor 36 is transmitted to the output shaft 34 through the various features. The total gear reduction ratio from the output shaft 118 of the motor 36 to the output shaft 34 can be, for example, about 75:1 to about 600:1, although the gearbox 38 can be configured to have any desired total gear reduction ratio.

[0072] like Figure 1 As shown, when the output shaft 34 rotates about the fourth rotation axis A4, the first steering member 28 fixed thereto is also caused to rotate about the fourth rotation axis A4. The first steering member 28 moves the second steering member 30 in an L manner, and the second steering member pivots the third steering member 32 in an R manner to steer (e.g., rotate) the wheel 12.

[0073] In addition to providing steering assist, the EPS unit 16 , via its connection of the motor 36 to the steering wheel 22 , may be configured to provide feedback or steering feel to the operator.

[0074] What has been described above are examples of the present invention. Of course, it is not possible to describe every conceivable combination of components or methods for the purpose of describing the present invention, but one of ordinary skill in the art will recognize that many other combinations and arrangements of the present invention are feasible. Therefore, the present invention is intended to encompass all such changes, modifications and variations that fall within the spirit and scope of the appended claims.

Claims

1. A steering system for turning a steerable wheel, the steering system comprising: a one-piece output unit connected to the steering wheel so that rotation of the steering wheel causes the output unit to rotate about an axis, the output unit having an output shaft coupled to the steerable wheels so that rotation of the output unit affects the steering of the steerable wheels, the output unit supporting a planetary gear; and A sun gear connected to an electric motor so that torque from the electric motor causes the sun gear to rotate relative to the output unit, the sun gear meshes with the planetary gears so that rotation of the sun gear causes the planetary gears to rotate and run around the sun gear, and the output unit is caused to rotate around an axis in response to the rotation of the planetary gears and the operation around the sun gear.

2. The steering system according to claim 1, wherein: The steering system further includes a threaded transmission member meshing with the external teeth of the output unit, wherein the threaded transmission member connects the output unit with the steering wheel.

3. The steering system according to claim 2, wherein: The external teeth partially circumferentially surround the shaft.

4. The steering system according to claim 1, wherein: The planetary gear stage is located in the housing, and the planetary gears mesh with the internal teeth of the housing.

5. The steering system according to claim 1, wherein: The sun gear extends into a recess in the carrier.

6. The steering system according to claim 5, wherein: The output unit includes a window extending radially therethrough, the planet gears extending through the window such that the planet gears mesh with teeth circumferentially surrounding the carrier.

7. The steering system according to claim 6, wherein: The output unit supports a plurality of planetary gears, each planetary gear being received in a corresponding window of the output unit.

8. The steering system according to claim 6, wherein: In a first portion of the recess, the sun gear is rotatably supported via a bearing, and in a second portion of the recess, the planet gears mesh with the sun gear, the second portion having a larger diameter than the first portion.

9. The steering system according to claim 1, wherein: The planet gears extend through a window of the output unit, the window extending radially through the output unit.

10. The steering system according to claim 9, wherein: The planetary gear is connected to the carrier via a shaft and is held in the window, the shaft extending through the window in the direction of the axis.

11. The steering system according to claim 1, wherein: The steering system further includes an electric steering unit including the electric motor and a gear box, wherein the output unit is at least partially located in a housing of the gear box.

12. A steering system for turning a steerable wheel, the steering system comprising a one-piece output part, the output part having: a carrier for the planetary gear stage, the carrier being connected to the motor so that the motor causes the output unit to rotate about the axis via the carrier, a worm wheel extending from an axial end surface of the bracket along an axis, the worm wheel being connected to a steering wheel via a threaded transmission member, so that rotation of the steering wheel causes the output unit to rotate about the axis, and An output shaft extends along an axis from an axial end surface of the bracket, and the output shaft is configured to be coupled to a steerable wheel so that rotation of the output unit affects the steering of the steerable wheel.

13. The steering system according to claim 12, wherein: The steering system further includes an electric steering unit including the electric motor and a gear box, wherein the output unit is at least partially located in a housing of the gear box.

14. The steering system according to claim 12, wherein: The steering system also includes a sun gear, which is connected to the electric motor so that the torque from the electric motor causes the sun gear to rotate relative to the output unit, the sun gear is meshed with a plurality of planetary gears so that the rotation of the sun gear causes the planetary gears to rotate and run around the sun gear, the output unit supports the planetary gears, and the output unit is caused to rotate around the axis in response to the rotation of the planetary gears and the operation around the sun gear.

15. The steering system according to claim 14, wherein: The planet gears extend through corresponding windows in the carrier such that the planet gears mesh with teeth circumferentially surrounding the carrier.

16. The steering system according to claim 12, wherein: The worm gear at least partially circumferentially surrounds the output shaft.

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