Steering system for use when turning steerable vehicle wheels

Abstract

A steering system for use in turning steerable vehicle wheels includes a one-piece output unit connected to a steering wheel, such that the rotation of the steering wheel forces the output unit to rotate about an axis. The output unit has an output shaft coupled to the steerable vehicle wheels in such a way that the rotation of the output unit affects the steering of the steerable vehicle wheels. The output unit supports a planetary gear. A sun gear is connected to an electric motor, so that torque from the electric motor forces the sun gear to rotate relative to the output unit. The sun gear is meshed with the planet gear, so that the rotation of the sun gear forces the planet gear to rotate and orbit the sun gear. The output unit is forced to rotate about the axis in response to the planet gear rotating and orbiting the sun gear.

Description

Technical area

[0001] The present invention relates to a steering system for use in turning steerable vehicle wheels. Background of the invention

[0002] A common vehicle steering system includes a transmission and a motor. The transmission includes an output shaft that is rotatable to influence rotational movements of steerable vehicle wheels. A pinion gear is operatively connected to the output shaft, such that rotation of the pinion gear about a rotational axis causes the output shaft to rotate. The pinion gear is rotatably mounted within the transmission on two ball bearings aligned along the pinion's rotational axis. A steering column connects the pinion gear and a vehicle steering wheel.

[0003] Additionally, the motor is operative to influence the rotation of the output shaft to provide steering assistance. The motor is operatively connected to the output shaft via one or more planetary gear sets mounted within the transmission. Each motor output shaft, the output shaft, and each planetary gear set are aligned along a single axis within the transmission. A steering system with this general construction is disclosed in U.S. Patent No. 11,498,616. Brief description of the invention

[0004] According to one aspect of the invention, alone or in combination with any other aspect, a steering system for use in turning steerable vehicle wheels includes a one-piece output unit connected to a steering wheel such that rotation of the steering wheel forces the output unit to rotate about an axis. The output unit has an output shaft coupled to the steerable vehicle wheels such that rotation of the output unit affects the steering of the steerable vehicle wheels. The output unit supports a planetary gear. A sun gear is connected to an electric motor such that torque from the electric motor forces the sun gear to rotate relative to the output unit. The sun gear is meshed with the planetary gear such that rotation of the sun gear forces the planetary gear to rotate and orbit the sun gear.The output unit is forced to rotate around the axis in response to the planetary gear rotating and orbiting the sun gear.

[0005] According to another aspect of the invention, alone or in combination with any other aspect, a one-piece output comprises a carrier for a planetary gear stage, a worm gear extending along the axis from an axial end face of the carrier, and an output shaft extending along the axis from the axial end face of the carrier. The carrier is connected to a motor such that the motor forces the output unit to rotate about an axis via the carrier. The worm gear is connected to a steering wheel via a pinion such that rotation of the steering wheel forces the output unit to rotate about the axis. The output shaft is configured to be coupled to steerable vehicle wheels such that rotation of the output unit influences the steering of the steerable vehicle wheels. Short description of the drawings

[0006] The above and other features and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings in which: Fig. 1 is a schematic rear view of an exemplary steering system for use in turning steerable vehicle wheels; Fig. 2 is a rear view of an EPS unit of the steering system of Fig. 1; Fig. 3 is a cross-sectional view taken along line 3-3 of Fig. 2; Fig. 4 is an isolated view of section 4 of Fig. 3; Fig. 5 is an isolated view of section 5 of Fig. 3; Fig. Figure 6 is a cross-sectional view of a portion of the EPS unit of Fig. 2; Fig. Figure 7 is an exploded view of a portion of the EPS unit of Fig. 2; Fig. Figure 8 is a front perspective view of an element of the EPS unit of Fig. 2; Fig. 9 is an isolated view of section 9 of Fig. 6; and Fig. 10 is a cross-sectional view taken along line 10-10 of Fig. 2. Detailed description

[0007] The present invention relates to a steering system for use in turning steerable vehicle wheels. An exemplary steering system 10 for use in turning steerable vehicle wheels 12 is shown schematically in Fig. 1. The steering system 10 may be used, for example, in a commercial vehicle. The steering system 10 includes an input shaft 14 and an electrically driven steering unit ("EPS unit") 16 for providing steering assistance. The input shaft 14 extends from a first end 18 to a second end 20 ( Fig. 3). A steering wheel 22 is connected to the first end 18. For example, the steering wheel 22 may be connected to the first end 18 via a steering column, one or more shafts, one or more joints (e.g., universal joints), or any combination thereof. A pinion 24 ( Fig. 3) is connected to or provided at the second end 20. Rotation of the steering wheel 22 transmits torque through the input shaft 14 to the pinion gear 24. In other words, the pinion gear 24 is forced to rotate under the influence of the torque transmitted through the input shaft 14.

[0008] A steering linkage 26 is connected to the steerable vehicle wheels 12. As shown, the steering linkage 26 includes first, second, and third steering links 28, 30, 32. The first steering link 28 is connected to an output shaft 34 of the EPS unit 16. The first steering link 28 can be, for example, a pitman arm. The second steering link 30 is connected to the first steering link 28 and can be, for example, a steering link rod. The third steering link 32 is connected to the second steering link 30 and one of the steerable wheels 12. The third steering link 32 can be, for example, a steering lever.

[0009] The EPS unit 16 provides steering assistance by influencing the movement of the steering linkage 26 - and therefore the steerable wheels 12 - in response to the rotation of the steering wheel 22. Further referring to Fig. 2, the EPS unit 16 includes an electric motor 36 (e.g., a reversible electric motor) and a transmission 38 connected to the motor.

[0010] As in Fig. 3, the transmission 38 includes a housing 40 in which the pinion gear 24 is rotatably mounted. The housing 40 may be formed as a single monolithic piece or assembled from separate subcomponents. A cap 42 is connected to the housing 40 and receives the input shaft 14 in a manner that allows relative rotation therebetween. The first end 18 of the input shaft 14 may thus be located outside the housing 40, while the second end 20 may be located inside the housing 40. A torsion bar 44 and an output shaft 46 help transmit the rotation of the second end 20 of the input shaft 14 to the pinion gear 24. The input shaft 14, the torsion bar 44, and the output shaft 46 may be coaxial with each other.

[0011] The torsion bar 44 extends within the input shaft 14 and the output shaft 46. A first end 48 of the torsion bar 44 is fixedly connected for rotation to the input shaft 14, while a second end 50 of the torsion bar is fixedly connected for rotation to the output shaft 46. When the input shaft 14 is rotated by the steering wheel 22, the torsion bar 44 allows a prescribed amount of relative rotation between the input shaft and the output shaft 46 before the input shaft and the output shaft rotate together.

[0012] The output shaft 46 has a first end 52 that extends into the second end 20 of the input shaft 14. A second end 54 of the output shaft 46 extends into a recess 56 of the pinion gear 24. The second end 54 may engage the pinion gear 24 (e.g., via splines) in such a manner that rotation of the output shaft 46 is transmitted to the pinion gear. Therefore, rotation of the output shaft 46 reactively causes or forces the pinion gear 24 to rotate about a pinion rotational axis A1 (also referred to herein as "a first rotational axis") relative to the housing 40.

[0013] A first and second end 58, 60 of the pinion gear 24 is each rotatably supported in the housing 40 by a bearing 62, 64. Each bearing 62, 64 is a tapered roller bearing having an inner race or cone 66 circumferentially engaging the pinion gear 24, an outer race or cup 68 circumferentially engaging an inner surface of or within the housing 40, and a plurality of tapered rollers 70 radially disposed between the cone and the cup. The cones 66 may be rotatably fixed to the pinion gear 24, while the cups 68 may be rotatably fixed to their respective inner surfaces. The cones 66 may thus rotate relative to the cups 68 while the pinion gear 24 rotates relative to the housing 40. Each bearing 62, 64 may also include a cage 72 for its respective tapered rollers 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 a ball bearing, an angular contact ball bearing, a spherical roller bearing, a cylindrical roller bearing, and a needle bearing.

[0014] The preload of each bearing 62, 64 can be adjusted via a bearing adjuster 74. As shown in Fig. 3-4, the bearing adjuster includes external threads 76 for threaded engagement with internal threads 78 of the housing 40. The bearing adjuster 74 may be substantially cylindrical so that the first end 58 of the pinion gear 24 and / or the second end 54 of the output shaft 46 may extend into and / or through the bearing adjuster 74.

[0015] The bearing adjuster 74 can be in contact with, or brought into contact with, the cup 68 of the bearing 62. When in contact with the cup 68, threading in / screwing the bearing adjuster 74 (i.e., driving the bearing adjuster toward the bearing 64) forces the cup 68 of the bearing 62 toward the other bearing 64 relative to the cone 66 of the bearing 62. Such relative movement reduces one or more clearances between the elements of the bearing 62, thus increasing the preload of the bearing 62. In contrast, threading out / screwing out the bearing adjuster 74 (i.e., driving the bearing adjuster away from the bearing 64) increases the clearances and reduces the preload of the bearing 62.

[0016] Via the bearing 62, threading / screwing in the bearing adjuster 74 also forces the pinion gear 24 to move along the first rotational axis A1 toward the bearing 64. Such movement forces the cone 66 of the bearing 64 away from the bearing 62 relative to the cup 68 of the bearing 64, reducing one or more gaps between the elements of the bearing 64 and increasing the preload of the bearing 64. In contrast, threading / screwing out the bearing adjuster 74 increases the gaps and reduces the preload of the bearing 64.

[0017] The amount of torque required to rotate the pinion 24 about its axis of rotation A1 corresponds at least in part to the amount of preload in the bearings 62, 64. In particular, increasing the preload increases the amount of torque required to rotate the pinion 24. This is because the friction between the elements of the bearings 62, 64 increases as the preload(s) in the bearings increase.

[0018] Therefore, the bearing preload(s) and pinion torque-to-rotation can be set or adjusted as desired by threading / unthreading the bearing adjuster 74. In certain configurations of the transmission 38, it may be advantageous to have a relatively high torque-to-rotation value for the pinion 24. This is at least in part because having a high torque-to-rotation value and a high preload reduces the amount of noise, vibration, and / or harshness ("NVH") in the transmission 38. For example, when the bearings 62, 64 have a high preload, the pinion 24 can be substantially prevented from being undesirably axially shifted (e.g., along its rotational axis A1) in response to a change in the pinion's rotational direction and / or in response to impact forces. An axially shifted pinion 24 has the potential to cause or increase NVH in the transmission.

[0019] However, in other transmission configurations, such as the configuration of transmission 38 shown in the figures, a relatively low torque-to-rotation value is desired. Transmission 38, which is a low torque-to-rotation system, may include features to reduce NVH. For example, as shown in Fig. 3-4, the transmission 38 may include a resilient member 80 positioned within the recess 56 of the pinion gear 24. The resilient member 80 extends between a bottom surface 82 of the recess 56 and the second end 54 of the output shaft 46. Although the resilient member 80 directly contacts both the pinion gear 24 (e.g., at the bottom surface 82 of the recess 56) and the output shaft 46, certain configurations of the transmission 38 may include one or more intermediate members disposed between the resilient member and the pinion gear and / or the output shaft. The resilient member 80 may be a wave spring, a coil spring, or any other suitable spring.

[0020] The resilient member 80 can be at least partially compressed between the pinion gear 24 and the output shaft 46 such that the resilient member exerts a predetermined axial force on the pinion gear in a direction away from the output shaft. The axial loading of the pinion gear 24 reduces / damps any of the pinion gear's axial movements. Damping the axial movements of the pinion gear 24 eliminates or at least reduces NVH in the transmission 38 to an acceptable level without requiring an increase in the bearing preload and / or the torque-to-rotation ratio of the pinion gear 24.

[0021] As in Fig. 3, the pinion gear 24 may be in the form of or include a worm shaft that meshes with a worm gear 84 such that rotation of the pinion gear reactively rotates or forces the worm gear to rotate relative to the housing 40. The worm gear 84 may be operatively connected to the output shaft 34. Therefore, rotation of the steering wheel 22 transmits torque to the output shaft 34 via the input shaft 14, the pinion gear 24, and the worm gear 84. The output shaft 34 may thus rotate or be forced to rotate under the influence of torque emanating from the steering wheel 22.

[0022] The pinion 24 can be forced by a pressing force in the direction of the worm wheel 84 via a pressing device 86 of the gear 38. As in Fig. 3 and Fig. As shown in Figure 5, the pressing device 86 includes a reaction plate 88, a resilient member 90, and a plunger 92 that is inserted into a recess 94 of the housing 40. The reaction plate 88 abuts both a first shoulder 96 of the housing 40 on one side and a cap 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. This substantially prevents the reaction plate 88 from undesired movement relative to the housing 40.

[0023] The resilient member 90 extends between the reaction plate 88 and the plunger 92. Although the resilient member 90 directly contacts both the reaction plate 88 and the plunger 92, certain configurations of the pressing device 86 may include one or more intermediate members disposed between the resilient member and the reaction plate and / or the plunger. The resilient member 90 may be a wave spring, a coil spring, or any other suitable spring.

[0024] The plunger 92 is movable within the recess 94 relative to the housing 40. For example, the plunger 92 may move along the recess 94 toward and away from the worm gear 84 in a direction transverse to the first rotational axis A1. However, the geometries of the recess / housing 94 / 40 and the plunger 92 may be configured to substantially limit the plunger to movement in the direction transverse to the first rotational axis A1. Further, these movements of the plunger 92 may be limited by the reaction plate 88 at one end and a second shoulder 100 of the housing 40 at the other end.

[0025] The plunger 92 includes a first recess 102 that faces substantially in a direction transverse to the first rotational axis A1. The resilient member 90 is positioned in (e.g., completely within) the first recess 102. The reaction plate 88 and / or the cap 98 may also extend into the first recess 102. The resilient member 90 is at least partially compressed between the reaction plate 88 and the plunger 92, such that the resilient member provides the compressive force (generated via the internal bias of the resilient member) to the plunger that urges the plunger away from the reaction plate.

[0026] The plunger 92 also includes a second recess 104 that points substantially in the direction of the first rotational axis A1. The cup 68 of the bearing 64 circumferentially engages an inner surface of the plunger 92 in the second recess 104, such that the bearing 64 moves along with the plunger toward and away from the worm gear 84. The bearing 64 thus takes the form of a "floating bearing" that can be moved toward and away from the worm gear 84 in a direction transverse to the first rotational axis A1. The bearing 62, on the other hand, is a "fixed bearing" in the sense that it is mounted in the housing 40 in such a way as to be substantially prevented from moving toward and away from the worm gear 84 relative to the housing 40.

[0027] The compressive force of the elastic element 90 forces the plunger 92 and the bearing 64 away from the reaction plate 88 and toward the worm gear 84. The second end 60 of the pinion 24, supported by the bearing 64, is forced toward the worm gear 84 by the bearing 64. As the second end 60 is forced toward the worm gear 84, the second end 60 pivots about a pivot axis 106 defined by the bearing 62 toward the worm gear until the pinion 24 is closely meshed with the worm gear. The compressive force generated by the elastic element 90 thus causes or forces the second end 60 of the pinion 24 to pivot about the pivot axis 106 until the pinion is closely meshed with the worm gear 84.

[0028] Since the bearing 64 moves relative to the housing 40 under the pressing force, the bearings 62, 64 are intentionally misaligned (ie, not coaxial) by a small margin when the pinion 24 and the worm gear 84 are closely meshed. For example, a cup axis 108 of the cup 68 of the bearing 64 may be oriented in a direction transverse to the first rotational axis A1 with respect to a cup axis 110 ( Fig. 4) of the bearing 62. Due to its pivoting movement, the rotational axis A1 of the pinion 24 is at an angle other than zero degrees with respect to the cup axis 110 of the bearing 62.

[0029] The mounting arrangement of the bearings 62, 64 can be selected with regard to their intentional misalignment. In other words, it may be advantageous to arrange the bearings 62, 64 in a manner that is relatively less sensitive to bearing misalignment. An example of such a mounting arrangement is a direct mounting arrangement. The bearings 62, 64, as shown in Fig. 3-5, can thus be arranged in a direct mounting arrangement. Therefore, each bearing 62, 64 is arranged so that the small ends 112 of its tapered rollers 70 point "outward" or away from the other bearing 62, 64.

[0030] Torque transmitted from the steering wheel 22 to the pinion gear 24 can create separation forces between the pinion gear 24 and the worm gear 84, forcing the pinion gear to pivot away from the worm gear. The compressive force of the resilient member 90 is configured to overcome low separation forces (i.e., separation forces at or below a predetermined separation force) and keep the pinion gear 24 closely meshed with the worm gear 84. Low separation forces can be created by steering wheel torques at or below a predetermined torque. Therefore, when the steering wheel torque is at or below the predetermined torque, the pinion gear 24 and the worm gear 84 are held in close mesh. The internal stress of the bearings 62, 64 due to their misalignment is within an acceptable range while the steering wheel torque remains low.

[0031] However, the internal stress of the misaligned bearings 62, 64 may increase as the steering wheel torque increases above the predetermined torque threshold. To combat this potential increase in internal stress, the pressing device 86 may be configured so that the pressing force of the resilient member 90 is overcome by high separation forces (i.e., separation forces in excess of the predetermined separation force). High separation forces may be generated by steering wheel torques in excess of the predetermined torque. These high separation forces thus force the pinion gear 24 (e.g., its second end 60) to pivot at least partially 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 forces force the second end 60 of the pinion gear 24 to pivot to a position where the bucket axes 108, 110 are coaxial.Aligning the bearings 62, 64 at least partially reduces the internal stress of the bearings and thus helps keep the internal stress of the bearings within the acceptable range under high steering wheel torques. The rotational axis A1 of the pinion 24 may also be coaxial with the bucket axes 108, 110, the input shaft 14, the torsion bar 44, and the output shaft 46 due to the pivoting caused by the high separation forces.

[0032] The gearbox 38 can be configured so that the second end 60 of the pinion 24 can only be pivoted away from the worm gear 84 by the separating forces until the plunger 92 abuts the reaction plate 88. The maximum distance the second end 60 of the pinion 24 can be pivoted away from the worm gear 84 can thus be defined by the maximum distance the plunger 92 can travel to the reaction plate 88. Furthermore, the gearbox 38 can be configured so that the bucket axes 108, 110 are coaxial when the plunger 92 contacts the reaction plate 88.

[0033] The pressing force of the elastic element 90 overcomes the separating forces and pivots the pinion gear 24 back into close meshing with the worm gear 84 once the steering wheel torque returns to or below the predetermined torque threshold. Additionally, the pressing force can also compensate for wear on the teeth of the pinion gear 24 and / or the worm gear 84 by forcing the pinion gear to continue pivoting toward the worm gear as the teeth of the pinion gear and / or the worm gear wear. Therefore, the close meshing between the pinion gear 24 and the worm gear 84 can be maintained by the pressing force even as the teeth of the pinion gear and / or the worm gear wear.

[0034] The maximum distance by which the second end 60 of the pinion 24 can be pivoted relative to the worm gear 84 (e.g., to compensate for wear) can be defined by the maximum distance by which the plunger 92 can travel relative to the worm gear. Therefore, the pinion 24 can be pivoted relative to the worm gear 84 until the pinion is closely meshed with the worm gear and / or until the plunger 92 contacts the second shoulder 100.

[0035] Although the gearbox of Fig. 3-5 as having both the elastic member 80 and the pressing device 86, the transmission 38 may be configured to include only one or neither of the elastic member 80 and the pressing device 86.

[0036] As in Fig. 2-3, the steering system 10 further includes a controller 114 and one or more vehicle condition sensors 116 that cooperate to control the EPS unit 16 based on sensed vehicle conditions. In one example, the vehicle condition sensors 116 may include a torque sensor and / or a position sensor electrically connected to the controller 114. The torque sensor, if provided, senses the torque applied to the steering wheel 22 and generates a signal indicative of the torque. The position sensor, if provided, senses the rotational position of the steering wheel 22 and generates a signal indicative of the steering wheel position. It is understood that the vehicle condition sensors 116 may be mounted within the housing 40 (as shown in Fig. 3) or can be positioned outside the housing.

[0037] The signals from the vehicle condition sensors 116 are sent to the controller 114. The controller 114 analyzes the outputs of the vehicle condition sensors 116 and influences the operation of the motor 36 of the EPS unit 16 as a function of the output of the sensors. It is also contemplated that only the torque measurements or only the steering wheel position measurements may be used to influence the operation of the motor 16. The controller 114 may also have inputs that vary as a function of a sensed lateral acceleration of the vehicle or other vehicle operating conditions. In any event, the signals received by the controller 114 dictate the speed and / or torque of the motor 36 and thereby dictate the speed and torque delivered through an output shaft 118 ( Fig. 6) of the engine to the transmission 38 to assist the rotation of the steerable vehicle wheels 12.

[0038] As in Fig. 6-7, the output shaft 118 extends along a second rotational axis A2 into the transmission 70 and to a first planetary gear set 120. The first planetary gear set 120 includes a sun gear 122 secured to and rotatable with the output shaft 118. The sun gear 122 is integrally formed with the output shaft 118 as a single monolithic piece, although the sun gear may be formed separately from and subsequently attached to the output shaft. Planetary gears 124 are in meshing engagement with the sun gear 122 and with a ring gear 126 rotatably fixed within the housing 40. Rotating the output shaft 118 and the captive sun gear 122 about the second rotational axis A2 reactively rotates or forces the planetary gears 124 to rotate and orbit the sun gear (and accordingly the second rotational axis) while maintaining their meshing engagement with the ring gear 126.Although three planetary gears 124 are shown, the first planetary gear stage 120 may include any number of planetary gears.

[0039] The planet gears 124 are rotatably supported on a carrier 128, which rotates about the second rotational axis A2, while the planet gears rotate and orbit the sun gear 122. The carrier 128 is radially spaced from the housing 40 and positioned radially between the sun gear 122 and the ring gear 126. The first planetary gear stage 120 may have a reduction ratio from the sun gear 122 to the carrier 128 of, for example, about 3:1 to about 10:1, although the second planetary gear stage may have any desired reduction ratio.

[0040] The first planetary gear set 120 is operatively connected to a second planetary gear set 142 within the housing 40. However, unlike typical gear arrangements, the first and second planetary gear sets 120, 142 are not directly connected to each other, nor are they aligned along a single axis. Instead, the first planetary gear set 120 is operatively connected in series with the second planetary gear set 142 via one or more intermediate gears. The one or more intermediate gears thus transmit torque from the first planetary gear set 120 to the second planetary gear set 142. In other words, the one or more intermediate gears act as an intermediary for transmitting rotation of the first planetary gear set 120 to the second planetary gear set 142.

[0041] As in Fig. 6-7, the one or more intermediate gears may include a first intermediate gear 130 fixedly connected for rotation with the carrier 128. The first intermediate gear 130 is thus rotatable with the carrier 128 about the second rotation axis A2. One end of the first intermediate gear 130 opposite the carrier 86 may be rotatably supported in the housing 40 by a bearing 132 (e.g., a ball bearing).

[0042] A second intermediate gear 134 is rotatably mounted in the housing 40 and is in meshing engagement with the first intermediate gear 130. Therefore, rotation of the first intermediate gear 130 reactively causes the second intermediate gear 134 to rotate about a third rotational axis A3.

[0043] A third idler gear 136 is rotatably supported in the housing 40 by bearings 138, 140. The third idler gear 136 is also in meshing engagement with the second idler gear 134. Rotation of the second idler gear 134 reactively causes the third idler gear 136 to rotate about a fourth rotational axis A4. Although only one idler gear 134 is shown between the first and third idler gears 130, 136, the transmission 38 may include any number of idler gears between the first and third idler gears.

[0044] The second planetary gear stage 142 includes a sun gear 144 that is rotatably connected to the third intermediate gear 136. In particular, the sun gear 144 may include a first end 146 that extends into an opening 148 of the third intermediate gear 136, the first end engaging the third intermediate gear in a rotatably connected manner. The sun gear 144 is thus rotatable with the third intermediate gear 136 about the fourth axis of rotation A4. Planetary gears 150 are in meshing engagement with the sun gear 144 and teeth 152. The teeth 152 are located on the housing 40 adjacent to the second planetary gear stage 142 and extend circumferentially about the fourth axis of rotation A4. The teeth 152 are thus formed integrally with the housing 40 as a single monolithic piece. However, the teeth 152 may be provided on a component (e.g., a ring gear) that is separate from and attached to the housing 40.

[0045] Rotating the sun gear 144 about the fourth rotational axis A4 reactively rotates or forces the planet gears 150 to rotate and orbit the sun gear (and accordingly, the fourth rotational axis) 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.

[0046] The planet gears 150 are rotatably supported on a carrier 154, which rotates about the fourth rotational axis A4, while the planet gears rotate and orbit the sun gear 144. The carrier 154 is radially spaced from the housing 40 and radially positioned between the sun gear 144 and the teeth 152. The second planetary gear stage 142 may have a reduction ratio from the sun gear 144 to the carrier 154 of, for example, about 3:1 to about 10:1, although the second planetary gear stage may have any desired reduction ratio. It is understood that the transmission 38 may include additional planetary gear stages (not shown) to achieve a desired reduction ratio through the transmission.

[0047] The output shaft 34 is connected to the carrier 154 such that the carrier and the output shaft rotate together about the fourth rotational axis A4 relative to the housing 40. The output shaft 34 may be rotatably supported in the housing 40 by at least one bearing 156. The output shaft 34 extends from the housing 40 and includes keyways 158 outside the housing for connection to the steering linkage 26.

[0048] The worm gear 84 is secured to the carrier 154 of the second planetary gear set 142 and is thus rotatable about the fourth axis of rotation A4. As a result, the rotation of the steering wheel 22 is transmitted to the output shaft 34 via the pinion 24, the worm gear 84, and the carrier 154. Although the worm gear 84 and its teeth are shown as extending fully circumferentially about the fourth axis of rotation A4, the worm gear may be configured such that the worm gear and / or the worm gear teeth extend only partially circumferentially about the fourth axis of rotation. For example, the worm gear 84 and / or its teeth may extend approximately 150 degrees to approximately 180 degrees circumferentially about the fourth axis of rotation A4, although the worm gear 84 and / or its teeth may be configured to extend any number of degrees around the fourth axis of rotation.

[0049] As in Fig. 6-8, the output shaft 34, the worm gear 84, and the carrier 154 are integrally formed together as a single monolithic piece to define a one-piece output unit 160 of the transmission 38. Forming the output shaft 34, the worm gear 84, and the carrier 154 as a single piece helps reduce angular backlash in the transmission 38 and eliminates any potential alignment problems between these parts that might otherwise arise if they were separated. The carrier 154 (i.e., the support portion of the output unit) includes a recess 162 into which the sun gear 144 extends. Specifically, the sun gear 144 extends along the fourth rotational axis A4 through a first portion 162a of the recess 162 and into a second portion 162b of the recess, which may have a smaller diameter than the first portion.A 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 carrier 154 may rotate relative to each other about the fourth axis of rotation A4.

[0050] The carrier 154 also includes circumferentially spaced windows 168 extending radially therethrough. The number of windows 168 may be equal to the number of planet gears 150, as each planet gear may be positioned in a corresponding window, although at least one of the windows may be configured to receive a plurality of planet gears therein. The planet gears 150 thus extend through the windows 168 so as to mesh with the sun gear 144 in the first portion 162a of the recess 162 and mesh with the teeth 152 circumferentially surrounding the carrier 154. The planet gears 150 are connected to the carrier 154 and are held in the windows by shafts 170 that extend through the windows 168 in the direction of the fourth rotational axis A4. The shafts 170 may be journalled in openings 172 on the carrier 154.

[0051] The carrier 154 further includes an axial end surface 174 that faces in the direction of the fourth rotational axis A4 away from the third intermediate gear 136. The output shaft 34 (i.e., the output shaft portion of the output unit 160) extends along the fourth rotational axis A4 from the axial end surface 174. Therefore, one end of the output shaft 34 is connected to the housing 40 of the carrier 154 (and, via the carrier, to the worm gear 84), while the other end of the output shaft lies outside the housing. The worm gear 84 (i.e., the worm gear portion of the output unit 160) also extends along the fourth rotational axis A4 from the axial end surface 174 so as to at least partially circumferentially surround a portion of the output shaft 34. The worm gear 84, which is integrally formed as a part of the output unit 160, defines external teeth on the output unit that mesh with the pinion.The output unit 160 is thus driven to rotate about the fourth rotational axis A4 in response to torque from both the steering wheel 22 and the motor 36.

[0052] With reference to Fig. 6 and Fig. 9, the output unit 160 is rotatably supported at one end (e.g., at or adjacent to the output shaft 34) by bearing 156 and at the other end (e.g., at or adjacent to the carrier 154) by bearing 140. In particular, the bearing 156 is a tapered roller bearing having an inner race or cone 66 circumferentially engaging the output shaft 34, an outer race or cup 68 circumferentially engaging an 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 rotatably fixed to the output shaft 34, while the cup 68 may be rotatably fixed to the inner surface 176. The cone 66 may thus rotate relative to the cup 68 while the output shaft 34 rotates relative to the housing 40. The bearing 156 may also include a cage 72 for its respective tapered rollers 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 provided on the outer shaft at any other desired location.

[0053] The bearing 140 is also a tapered roller bearing having an inner race or cone 66 circumferentially engaging the third idler gear 136 (e.g., an outer shoulder 178 of the third idler gear), an outer race or cup 68 circumferentially engaging an 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 cage 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.The bearing 140 is thus located radially between the carrier 154 and the third intermediate gear 136. The cone 66 may be rotatably connected to the external shoulder 180 of the third intermediate gear 136, while the cup 68 may be rotatably connected to the inner surface 180 of the carrier 154. In such a case, the cone 66 and the cup 68 rotate relative to each other, while the carrier 154 and the third intermediate gear 136 rotate relative to each other.

[0054] Accordingly, the carrier 154 (and thus the output unit 160) and the third idler gear 136 are rotatably supported by the bearing 140. The third idler gear 136 is also rotatably supported in the housing 40 by the bearing 138. The bearing 138 is a tapered roller bearing having an inner race or cone 66 circumferentially engaging a support surface 182 in the housing 40, an outer race or cup 68 circumferentially engaging an inner surface 184 of the third idler 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 idler gear 136 may define a portion of the third idler gear opening 148. The support surface 182 may rest on a support plate 186 which is inserted into the housing 40 and is rotatably connected therein.The support plate 186 may be at least partially retained within the housing 40 via a cap 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 such that the inner surface 184 of the third idler gear 136 circumferentially surrounds the support surface. The bearing 138 is thus radially disposed between the support plate 186 and the third idler gear 136. The cone 66 may be rotatably fixed to the support surface 182, while the cup 68 may be rotatably fixed to the inner surface 184 of the third idler gear 136. In such a case, the cup 68 rotates relative to the cone 66, while the third idler gear 136 rotates relative to the support plate 186.

[0055] 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 one another via the bearing 140. Accordingly, the output unit 160 and the third intermediate gear 136 are supported in the housing 40 primarily via the bearings 138, 140, 156. Although the bearing 166 is positioned radially between the carrier 154 and the sun gear 144, this bearing is not provided to support the output unit 160. Indeed, in certain configurations of the transmission 38, the bearing 166 may be omitted. In such configurations, 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 omitted entirely.

[0056] In the configuration of the gearbox 38, which in Fig. 6 and Fig. However, as shown in Figure 9, the first end 146 of the sun gear 144 is rotatably connected to the third idler gear 136, and the second end 164 of the sun gear extends into the carrier 154 where it is rotatably supported via the bearing 166, allowing the sun gear and the output unit 160 to rotate relative to each other. The extension of the sun gear 144 into the carrier helps maintain the output unit 160 and the third idler gear 136 in alignment on the fourth rotational axis A4. The deflection of the output unit 160 (e.g., the carrier 154) and / or the third idler gear 136 from alignment can increase the load on the bearings 138, 140, 156. The connection of the sun gear 144 to the carrier 154 via the bearing 166 thus helps to reduce the stress on the bearings 138, 140, 156 by at least partially maintaining the output unit 160 and the third intermediate gear 136 in the correct alignment.Accordingly, instead of being provided for support purposes like bearings 138, 140, 156, bearing 166 is provided for alignment and tension purposes.

[0057] It should be understood that although any of the bearings 138, 140, 156 could be a different type of bearing (e.g., a ball bearing, an angular contact ball bearing, a spherical roller bearing, a cylindrical roller bearing, or a needle bearing), there are certain advantages to the bearings being tapered roller bearings. For example, ball bearings have point contact between their balls and each of the inner and outer races, while tapered roller bearings have line contact between the tapered rollers and each of the cones and cups. Line contact provides better stress distribution in bearings than point contact because loads / stress in the bearings are spread over a relatively large area rather than being exerted at a single point. Furthermore, tapered roller bearings are designed to support relatively high axial and radial loads.If bearings 138, 140, 156 were ball or angular contact ball bearings, they would be much larger than they currently are to provide the same axial / radial load support as they provide in their tapered roller bearing form.

[0058] Typically, the EPS unit 16, or at least its transmission 38, is mounted on a support structure (e.g., a frame) of a vehicle between the support structure and one of the steerable vehicle wheels 12, such that an axial width 188 of the EPS unit 16 extends between the frame and the steerable vehicle wheel. The axial space between the frame and the steerable vehicle wheel can be quite limited. Therefore, to reduce the axial width 188 of the EPS unit 16, the EPS unit, via the intermediate gears 130, 134, 136, divides the motor 36, the output shaft 118, and the first planetary gear set 120 onto a different axis of rotation than the second planetary gear set 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 would significantly increase the axial width 188 of the EPS unit 16.Therefore, the particular arrangement of the features of the EPS unit 16 results in the axial width 188 being less than would otherwise be possible.

[0059] Furthermore, as in Fig. 7 and Fig. 10, each of the rotational axes A2, A3, A4 may intersect a single alignment axis A5 that extends transversely (e.g., perpendicularly) to each of the rotational axes A2, A3, A4. Due to this alignment, 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 be kept relatively small without increasing the axial width. Although the first, second, and third rotational axes A2, A3, A4 are shown as being parallel to one another, at least one of the rotational axes A2, A3, A4 may be at an angle with respect to at least one other of the rotational axes A2, A3, A4 and / or may be offset from the alignment axis A5.

[0060] During operation, the operator turns the steering wheel 22, thereby forcing the pinion gear 24 to rotate about the first rotational axis A1. This, in turn, forces the worm gear 84 to rotate about the fourth rotational axis A4 (and, accordingly, the output unit 160). At the same time, in response to signals received from the one or more vehicle condition sensors 116, the controller 114 actuates the motor 36 to rotate the output shaft 118 about the second rotational axis A2, which forces the carrier 128 to rotate about the second rotational axis via the sun gear 122 and the planetary gears 124. As a result, the first intermediate gear 130, which is fixedly connected to the carrier 128, is also forced to rotate about the second rotational axis A2.

[0061] The rotating first idler gear 130 forces the second idler gear 134 to rotate about the third rotational axis A3, which reactively forces the third idler gear 136 to rotate about the fourth rotational axis A4. The sun gear 144, which is rotatably connected to the third idler gear 136, rotates with the third idler gear 136 about the fourth rotational axis A4. The sun gear 144 forces the carrier 154 (and thus the attached output shaft 34) to rotate about the fourth rotational axis A4 via the planetary gears 150. Therefore, power from the motor 36 is transmitted to the output shaft 34 via the various features. For example, a total reduction ratio from the output shaft 118 of the motor 36 to the output shaft 34 may be about 75:1 to about 600:1, although the transmission 38 may be configured to have any desired total reduction ratio.

[0062] As in Fig.As shown in Figure 1, when the output shaft 34 rotates about the fourth axis of rotation A4, the first steering member 28 attached thereto is similarly forced to rotate about the fourth axis of rotation A4. The first steering member 28 moves the second steering member 30 in the manner L, which pivots the third steering member 32 in the manner R to steer (e.g., turn) the vehicle wheels 12.

[0063] In addition to providing steering assistance, 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.

[0064] What has been described above are examples of the present invention. It is obviously not possible to describe every conceivable combination of components or methodologies for the purpose of describing the present invention, but one of ordinary skill in the art will recognize that many other combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to include all such changes, modifications, and variations that fall within the spirit and scope of the appended claims.

Claims

[1] A steering system for use in turning steerable vehicle wheels, the steering system comprising: a one-piece output unit connected to a steering wheel such that rotation of the steering wheel forces the output unit to rotate about an axis, the output unit having an output shaft coupled to the steerable vehicle wheels such that rotation of the output unit influences the steering of the steerable vehicle wheels, the output unit supporting a planetary gear; and a sun gear connected to an electric motor such that torque from the electric motor forces the sun gear to rotate relative to the output unit, the sun gear being meshed with the planet gear such that rotation of the sun gear forces the planet gear to rotate and orbit the sun gear, the output unit being forced to rotate about the axis in response to the planet gear rotating and orbiting the sun gear. [2] The steering system of claim 1, further comprising a pinion gear meshed with external teeth of the output unit, the pinion gear connecting the output unit to the steering wheel. [3] Steering system according to claim 2, wherein the external teeth at least partially circumferentially surround the shaft. [4] Steering system according to claim 1, wherein the planetary gear stage is located in a housing, the planetary gear being toothed with internal teeth of the housing. [5] Steering system according to claim 1, wherein the sun gear extends into a recess of the carrier. [6] A steering system according to claim 5, wherein the output unit includes a window extending radially therethrough, the planetary gear extending through the window such that the planetary gear is meshed with teeth circumferentially surrounding the carrier. [7] A steering system according to claim 6, wherein the output unit supports a plurality of the planetary gears, each planetary gear being received in a corresponding window of the output unit. [8] Steering system according to claim 6, wherein the sun gear is rotatably mounted in a first portion of the recess via a bearing, wherein the planet gear is toothed with the sun gear in a second portion of the recess, wherein the second portion has a larger diameter than the first portion. [9] A steering system according to claim 1, wherein the planetary gear extends through a window of the output unit, the window extending radially through the output unit. [10] A steering system according to claim 9, wherein the planetary gear is connected to the carrier and is held in the window by a shaft extending in the direction of the axis through the windows. [11] Steering system according to claim 1, further comprising an electrically driven steering unit comprising the electric motor and a transmission, wherein the output unit is at least partially located in a housing of the transmission. [12] A steering system for use in turning steerable vehicle wheels, the steering system comprising: a one-piece output with a carrier for a planetary gear stage, the carrier being connected to a motor so that the motor forces the output unit to rotate about an axis via the carrier, a worm wheel extending along the axis from an axial end face of the carrier, the worm wheel being connected to a steering wheel via a pinion, so that rotation of the steering wheel forces the output unit to rotate about the axis, and an output shaft extending along the axis from the axial end surface of the carrier, the output shaft being adapted to be coupled to steerable vehicle wheels such that rotation of the output unit influences the steering of the steerable vehicle wheels. [13] Steering system according to claim 12, further comprising an electrically driven steering unit comprising the electric motor and a transmission, wherein the output unit is at least partially located in a housing of the transmission. [14] The steering system of claim 12, further comprising a sun gear connected to the electric motor such that torque from the electric motor forces the sun gear to rotate relative to the output unit, the sun gear being meshed with a plurality of planetary gears such that rotation of the sun gear forces the planetary gears to rotate and orbit the sun gear, the output unit supporting the planetary gears, the output unit being forced to rotate about the axis in response to the planetary gears rotating and orbiting the sun gear. [15] A steering system according to claim 14, wherein the planetary gears extend through corresponding windows in the carrier so that the planetary gears are meshed with teeth circumferentially surrounding the carrier. [16] Steering system according to claim 12, wherein the worm gear at least partially surrounds the output shaft.

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