ELECTRIC SERVO CONTROL SYSTEM WITH A BALL SCREW DRIVE DEVICE

Abstract

An electric power steering arrangement includes an electric motor, a gear set, and a ball screw drive arrangement. The gear set couples the electric motor and a nut of the ball screw drive arrangement such that the electric motor is operable to rotate the nut relative to a ball shaft. A plurality of bearings can orbit along a helical path defined between the nut and a ball shaft of the ball screw drive arrangement as the nut rotates relative to the ball shaft to displace the ball shaft relative to the nut.

Description

FIELD OF THE INVENTION

[0001] The present subject matter generally relates to power steering systems for commercial vehicles. BACKGROUND OF THE INVENTION

[0002] Conventional commercial vehicles typically include hydraulic power steering. Common hydraulic power steering systems include a hydraulic piston actuated by pressurized hydraulic fluid from a pump. A steering wheel and the hydraulic piston are both coupled to a steering linkage, and the pressurized hydraulic fluid from the pump selectively extends and retracts the hydraulic piston to supplement the torque applied to the steering linkage by a driver turning the steering wheel.

[0003] While existing hydraulic power steering systems work well in conventional commercial vehicles, the use of hydraulic power steering in electric and / or hybrid commercial vehicles presents challenges. An electric power steering system for commercial vehicles would be appropriate. BRIEF DESCRIPTION OF THE INVENTION

[0004] Aspects and advantages of the invention will be set forth in part in the description which follows, or may be obvious from the description, or may be learned by practice of the invention.

[0005] The present subject matter relates generally to an electric power steering system for commercial vehicles. The electric power steering system includes a ball screw assembly having a ball nut and a ball shaft that together define a helical path. An electric motor is coupled to the ball nut and can rotate the ball nut relative to the ball shaft. To translate the ball shaft relative to the ball nut, a plurality of bearings can orbit through the helical path as the ball nut rotates relative to the ball shaft. A pair of ball joints are attached to opposite ends of the ball shaft, and a pair of bellows are attached over the ball joints. During translation of the ball shaft, air in the bellows flows through an axial passage in the ball shaft between the bellows to assist in pressure equalization within the bellows.Such internal airflow within the electric power steering system can advantageously prevent inflation or deflation of the bellows, e.g., without requiring conventional ventilation of outside air into and out of the bellows. Thus, the present subject matter can electrify the power steering of heavy-duty vehicles in a safe, robust, and / or cost-effective manner.

[0006] In one embodiment, an electric power steering assembly includes an electric motor, a gear set, and a ball screw assembly. The ball screw assembly includes a ball nut and a ball shaft that together define a helical track. The gear set couples the electric motor and the ball nut such that the electric motor is operable to rotate the ball nut relative to the ball shaft. To translate the ball shaft relative to the ball nut, a plurality of bearings may orbit through the helical track as the ball nut rotates relative to the ball shaft. The electric power steering assembly also includes a pair of ball joints and a pair of bellows. Each of the pair of ball joints is attached to the ball shaft at a respective end portion of the ball shaft. Each of the pair of bellows is attached over a respective one of the pair of ball joints.The ball shaft defines an axial passage, and air can flow between the pair of bellows through the axial passage.

[0007] According to a first exemplary aspect, each of the pair of ball joints may include a journal and a bushing. The journal may be received in the bushing in each of the pair of ball joints, and the bushing of each of the pair of ball joints may be attached to the ball shaft at the respective end portion of the ball shaft.

[0008] According to a second exemplary aspect, the bushing of each of the pair of ball joints may define a connecting passage. The connecting passage of each pair of ball joints may extend between and connect the axial passage of the ball shaft and an interior of a respective one of the pair of bellows.

[0009] According to a third exemplary aspect, the bushing of each of the pair of ball joints may be bolted to the ball shaft at the respective end portion of the ball shaft.

[0010] According to a fourth exemplary aspect, the connecting passage of each of the pair of ball joints may include a first portion and a second portion. The first portion may extend from the axial passage of the ball shaft into a journal of the bushing, and the second portion may extend from the interior of the respective one of the pair of bellows into the journal of the bushing. The first portion may be oriented at an angle relative to the second portion in each of the pair of ball joints, and the angle may be no less than sixty degrees and no less than one hundred and twenty degrees.

[0011] According to a fifth exemplary aspect, the axial passage may extend between opposite end portions of the ball shaft.

[0012] According to a sixth exemplary aspect, the axial passage may extend parallel to a central axis of the ball shaft.

[0013] According to a seventh exemplary aspect, a cross-sectional area of ​​the axial passage in a plane perpendicular to a central axis of the spherical shaft may be not less than seventy square millimeters and not more than one thousand two hundred square millimeters.

[0014] According to an eighth exemplary aspect, the axial passage and the interior of the pair of bellows may together define a sealed air chamber with respect to the ambient air around the electric power steering assembly.

[0015] According to a ninth exemplary aspect, the ball screw assembly may further include a housing. The ball nut may be rotatably mounted within the housing. The ball shaft may be translationally displaceable relative to the housing. An outer surface of the ball shaft may have at least one toothing received by the housing to limit rotation of the ball shaft relative to the housing.

[0016] According to a tenth exemplary aspect, the gear set may include a first gear, a second gear, and a third gear. The first gear may be coupled to a rotor of the electric motor. The third gear may mesh with a gearing on the ball nut. The second gear may be arranged between the first and third gears in a power flow path between the first and third gears. The second gear may be connectable to a steering column.

[0017] According to an eleventh exemplary aspect, the electric power steering assembly may further include a bevel gear having a first bevel gear and a second bevel gear. The first bevel gear may mesh with the second bevel gear. The first bevel gear may be connectable to the steering column, and the second bevel gear may be connected to the second gear of the gear set.

[0018] According to a twelfth exemplary aspect, the second gear may mesh with the first and third gears.

[0019] According to a thirteenth exemplary aspect, a length of the spherical shaft may be not less than five hundred millimeters and not more than one thousand millimeters.

[0020] According to a fourteenth exemplary aspect, a vehicle may include the electric power steering assembly.

[0021] According to a fifteenth exemplary aspect, the vehicle may be a Class 8 commercial vehicle based on the gross vehicle weight rating.

[0022] Each of the example aspects listed above may be combined with one or more of the other example aspects listed above in certain embodiments. For example, all fifteen of the example aspects listed above may be combined with each other in some embodiments. As another example, any combination of two, three, four, five, six, or more of the fifteen example aspects listed above may be combined in other embodiments. Thus, the example aspects listed above may be used in combination with each other in some embodiments. Alternatively, the example aspects listed above may be implemented individually in other embodiments. Accordingly, it should be understood that various embodiments may be realized using the example aspects listed above.

[0023] These and other features, aspects, and advantages of the present invention will become more fully understood by reference to the following description and the appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] A full and enabling disclosure of the present invention, including the best mode thereof directed to one of ordinary skill in the art, is set forth in the description which refers to the accompanying figures. Fig. 1 is a side view of a vehicle according to an embodiment of the present subject matter. Fig. 2 is a perspective view of an electric power steering system according to an embodiment of the present subject matter. Fig. 3 is a partially sectioned side view of the exemplary electric power steering system of Fig. 2. Fig. 4 is a perspective cutaway view of a ball shaft of the exemplary electric power steering system of Fig. 2. Fig. 5 is a perspective cutaway view of a ball joint of the exemplary electric power steering system of Fig. 2. Fig. 6 is a perspective view of the ball shaft associated with a housing of the exemplary electric power steering system of Fig. 2 is engaged. Fig. 7 and Fig. 8 are perspective views of a gear set of the exemplary electric power steering system of Fig. 2. Fig. 7A is a schematic view of a planetary gear set of the exemplary electric power steering system of Fig. 2. DETAILED DESCRIPTION

[0025] Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided to illustrate the invention and not to limit the invention. Indeed, it will be obvious to those skilled in the art that various modifications and variations can be made to the present invention without departing from the scope and spirit of the invention. For example, features illustrated or described as part of one embodiment may be used with another embodiment to yield a still further embodiment. It is therefore intended that the present invention cover such modifications and variations that come within the scope of the appended claims and their equivalents.

[0026] As used herein, the terms "include / comprise" and "including / having" are intended to be inclusive in a manner similar to the term "comprising." Likewise, the term "or" is intended to be broadly inclusive (i.e., "A or B" is intended to mean "A or B or both"). The approximate terms used in the specification and claims are used to modify any quantitative representation that could permissibly vary without altering the basic function to which it relates. Accordingly, a value modified by one or more terms such as "approximately," "about," and "substantially" is not intended to be limited to the precise value stated. In at least some cases, the approximate terms may correspond to the accuracy of an instrument for measuring the value. For example, the approximate terms may refer to being within a ten percent (10%) margin.

[0027] Embodiments of the present disclosure relate to an electric power steering system for heavy-duty commercial vehicles. The electric power steering system may include a ball screw assembly. The use of the ball screw assembly may advantageously provide mechanical force amplification between an electric motor and / or a vehicle steering wheel and steering knuckles of the commercial vehicle. Furthermore, the electric power steering system may provide a mechanically robust, safe, and cost-effective power steering system for heavy-duty commercial vehicles.

[0028] Fig. 1 illustrates a side view of the vehicle 100. As in Fig. 1, the vehicle 100 includes a tractor unit 102 and a trailer 104 and is generally referred to as a "trailer combination." As one example, the vehicle 100 may be a Class 8 commercial vehicle based on a gross vehicle weight rating. The vehicle 100 is provided only as an example. For example, in alternative embodiments, the vehicle 100 may include one, two, or more additional trailers. Furthermore, although described below in connection with the vehicle 100, it should be understood that the present subject matter may be used in or with any other suitable vehicle, including passenger vehicles such as cars, vans, trucks, etc., or commercial vehicles such as buses, box trucks, farm vehicles, construction vehicles, etc., in other embodiments.

[0029] The vehicle 100 can define a longitudinal direction LG. A front part FV of the vehicle 100 and a rear part RV of the vehicle 100 can be spaced apart from one another along the longitudinal direction LG. Thus, the vehicle 100 can extend between the front and rear parts FV, ​​RV of the vehicle 100 along the longitudinal direction LG. The front part FV of the vehicle 100 can be positioned in front of the rear part RV of the vehicle 100 along a forward travel direction FDOT. The tractor 102 can be positioned at the front part FV of the vehicle 100.

[0030] The tractor 102 may be pivotally connected to the trailer 104 via a hitch 106 and is operable to tow the trailer 104. Various cargoes may be stored in the trailer 104. In alternative embodiments, the trailer 104 may be open, e.g., a flatbed, depending on the items stored on the trailer 104. The tractor 102 may include various components for towing the trailer 104, including an engine system 110, a transmission system 112, a steering system 200, a braking system 116, etc. During operation, an operator may sit in a cab 108 of the tractor 102.

[0031] The engine system 110, the transmission system 112, and the braking system 116 may generally be configured in any conventional manner. For example, the engine system 110 may generally include a suitable prime mover, such as an electric motor and / or an internal combustion engine, operable to propel the vehicle 100. The engine system 110 may be disposed within the tractor 102 and connected to the transmission system 112. The transmission system 112 is disposed within the power flow between the engine system 110 and the wheels 101 of the vehicle 100. The transmission system 112 is operable to provide various speed and torque ratios between an input and an output of the transmission system 112. Thus, for example, the transmission system 112 may provide a mechanical power boost to assist the propulsion of the vehicle 100 by the engine system 110.The braking system 116 is operable to decelerate the vehicle 100. For example, the braking system 116 may include friction brakes configured to selectively reduce the rotational speed of the wheels 101. The braking system 116 may also be configured as a regenerative braking system that converts kinetic energy of the wheels 101 into electrical power. The operation of the motor system 110, the transmission system 112, and the braking system 116 is well known to those skilled in the art and is not described in detail here for brevity.

[0032] The steering system 200 is operable to adjust the direction of travel of the vehicle 100. For example, the steering system 200 may be coupled to the front wheels 101 of the vehicle 100 and operable to turn the front wheels 101 in response to rotation of a steering device 118 (e.g., a steering wheel) in the cab 108 by a driver of the commercial vehicle and / or operation of a prime mover (e.g., electric motor 210) in the steering system 200. Thus, the steering wheel 118 may generally be connected to the steering system 200 by a steering column 120 extending between and coupling the steering wheel 118 and the steering system 200, such that rotation of the steering wheel 118 causes rotation of the steering column 120 and translational displacement of a shaft (e.g., ball shaft 234) of the steering system 200, which changes a heading angle of the front wheels 101 relative to a forward direction of travel FDOT.The electric motor 210 may be configured to apply torque to assist a driver in turning the steering column 120. For example, the amount of torque applied by the electric motor 210 may be varied based on a speed of the vehicle 100. The total force or torque acting on the steering column 120 (e.g., by a driver and / or electric motor 210) may be measured using one or more shaft sensors 292 (. Fig. 2). The one or more shaft sensors 292 may include one or more transducers configured to output an electrical signal proportional to the dynamic or torque applied to the steering column 120. Alternatively or additionally, the one or more shaft sensors 292 may include angular position sensors for detecting the angular position of the steering column 120, wherein the angular position of the steering column 120 (e.g., from a neutral position) is indicative of the torque acting on the steering column 120.

[0033] Fig. 2 is a perspective view of an electric power steering system 200 according to an embodiment of the present subject matter. The electric power steering system 200 may be mounted within the vehicle 100, e.g., on a frame of the vehicle 100. Accordingly, the electric power steering system 200 is described below in connection with the vehicle 100 of Fig. 1. However, it should be understood that the electric power steering system 200 may be used in or with any other suitable vehicle, including passenger vehicles such as cars, vans, trucks, etc., or commercial vehicles such as buses, box trucks, farm vehicles, construction vehicles, etc., in other embodiments. The electric power steering system 200 may generally be configured for use in or with commercial vehicles greater than 26,000 lbs., greater than seven and a half tons (7.5 t), or other heavy-duty trucks.

[0034] As discussed in more detail below, the electric power steering system 200 includes components for providing mechanical power amplification to an electric motor, for example, to enable the electric motor to supplement torque applied to a steering linkage by a driver turning a steering wheel. The electric power steering system 200 may also have numerous advantages over hydraulic power steering systems. For example, the electric power steering system 200 may enable the implementation of automatic driver assistance features, such as lane keeping, lane departure corrections, and autonomous driving. Furthermore, the electric power steering system 200 may consume power only when in use. In contrast, hydraulic power steering systems require a pump that runs continuously with the prime mover, the internal combustion engine.

[0035] Various views and components of the electric power steering system 200 are also shown in the Fig. 2 to 8. Now on the Fig. 2 and Fig. 3, the electric power steering system 200 may include an electric motor 210, a gear set 220, and a ball screw assembly 230. The electric motor 210 may be coupled to the ball screw assembly 230 via the gear set 220. For example, the rotational motion of the electric motor 210 may be transmitted to the ball screw assembly 230 via the gear set 220. Furthermore, the ball screw assembly 230 may convert the rotational motion of the electric motor 210 to translate the tie rods 202. Each tie rod 202 may be located between a ball shaft 234 ( Fig. 3) extend between and connect the ball screw assembly 230 and a corresponding steering knuckle (not shown) of the vehicle 100. Specifically, an outer end 203 of each tie rod 202 may be attached to a steering arm of the respective steering knuckle, and an inner end 204 of each tie rod 202 may be connected to the ball shaft 234. The translational displacement of the ball shaft 234 may thus rotate the steering knuckles via the tie rods 202 and rotate the front wheels 101 of the vehicle 100.

[0036] The electric power steering system 200 may be configured for installation in vehicles with an independent front suspension. Thus, the electric power steering system 200 may include a pair of ball joints 240. The ball joints 240 may help enable pivoting of the tie rods 202 relative to the ball screw assembly 230, which may be mounted to a frame of the vehicle 100. Furthermore, as the front wheels 101 move relative to the frame and ball screw assembly 230 on the front suspension, the ball joints 240 may allow the tie rods 202 to pivot relative to the ball screw assembly 230.

[0037] The ball joints 240 may be attached to the ball shaft 234 at opposite end portions of the ball shaft 234. The ball joints 240 may be configured to allow free rotation in two planes while limiting translational displacement in any direction. As shown in the Fig. 3 and Fig. 5, each ball joint 240 may include a journal 242 and a bushing 244. The journal 242 may have a spherical end 243 received in the bushing 244, and the journal 242 may rotate relative to the bushing 244 in two planes while being prevented from translating away from the bushing 244. One of the journal 242 and the bushing 244 may be attached to the ball shaft 234, and the other of the journal 242 and the bushing 244 may be attached to the tie rod 202. In the embodiment shown in the Fig. 3 and Fig. 5, the bushing 244 is attached to the ball shaft 234 (e.g., bolted, welded, glued, riveted, etc.), and the journal 242 is attached to the tie rod 202; however, it should be understood that such mounting arrangement may be reversed in alternative embodiments.

[0038] With further reference to the Fig. 2 and Fig. 3, the electric power steering system 200 may further include a pair of bellows or gaiters 250. Each bellows 250 may be mounted over a respective one of the ball joints 240. The gaiters 250 may protect the ball shaft 234 and the ball joints 240 and limit dust and other debris from interfering with the operation of the ball shaft 234 and the ball joints 240. One end of the gaiters 250 may be fixed to a housing 231 of the ball screw assembly 230, and the opposite end of the gaiters 250 may be fixed to the tie rod 202. The bellows 250 may deform (e.g., expand and contract) as the tie rod 202 pivots relative to the ball shaft 234 and as the ball shaft 234 translates to rotate steering knuckles about the tie rods 202 and rotate the front wheels 101 of the vehicle 100.

[0039] Now on Fig. 4, the ball screw assembly 230 includes a ball nut 232 and a ball shaft 234. The ball shaft 234 may be received within the ball nut 232. The ball nut 232 and the ball shaft 234 may together define a helical track 236. For example, the ball shaft 234 may define a portion of the helical track 236 on an outer surface of the ball shaft 234, and the ball nut 232 may define the other portion of the helical track 236 on an inner surface of the ball nut 232. The portion of the helical track 236 defined by the ball shaft 234 may face the portion of the helical track 236 defined by the ball nut 232, such that the helical track 236 is formed radially between the ball nut 232 and the ball shaft 234.

[0040] The ball nut 232 is rotatable relative to the ball shaft 234. For example, the ball nut 232 may be rotatably mounted within the housing 231, e.g., on tapered roller bearings, and the gear set 220 may couple the electric motor 210 and the ball nut 232 such that the electric motor 210 is operable to rotate the ball nut 232 relative to the ball shaft 234. During the rotation of the ball nut 232 relative to the ball shaft 234, the ball shaft 234 may also translate relative to the ball nut 232. In particular, a plurality of bearings 238, such as spherical ball bearings, may be arranged within the helical track 236. The bearings 238 can rotate through the helical track 236, and the bearings 238 can drive the translational displacement of the ball shaft 234 relative to the ball nut 232 during rotation of the ball nut 232 relative to the ball shaft 234.The bearings 238 can rotate repeatedly in a closed circuit through the helical track 236.

[0041] In certain embodiments, a length of the ball shaft 234 may be no less than three hundred millimeters (300 mm) and no more than nine hundred millimeters (900 mm), such as seven hundred and twenty-five millimeters (725 mm). Such sizing of the ball shaft 234 may advantageously provide an axially compact ball screw assembly 230, while simultaneously sizing the ball shaft 234 for translational translation to rotate steering knuckles via tie rods 202 and to rotate the front wheels 101 of the vehicle 100. Furthermore, the ball screw assembly 230 may be more axially compact than known rack and pinion assemblies for front-wheel steering systems.

[0042] During translational displacement of the ball shaft 234, the ends of the ball shaft 234 can extend and retract relative to the housing 231 of the ball screw assembly 230. Furthermore, one end of the ball shaft 234 can extend away from the housing 231, and the opposite end of the ball shaft 234 can retract toward the housing 231. Such movement of the ball shaft 234 can also deform the bellows 250. For example, the bellows 250 at the end of the ball shaft 234 extending from the housing 231 can expand, and the bellows 250 at the end of the ball shaft 234 retracting toward the housing 231 can contract. Such expansion and contraction of the bellows 250 can change the air pressure within the bellows 250. Thus, the electric power steering system 200 may include features that allow air to move between the bellows 250 through the ball shaft 234.

[0043] As in Fig. 4, the ball shaft 234 may define an axial passage 260. For example, the axial passage 260 may extend between opposite end portions of the ball shaft 234. Furthermore, the ball shaft 234 may extend axially between a first end portion 268 and a second end portion 269, and the axial passage 260 may extend through the ball shaft 234 between the first and second end portions 268, 269 of the ball shaft 234. The axial passage 260 may, in certain embodiments, extend parallel to and be oriented along a central axis of the ball shaft 234.

[0044] Air can flow through the axial passage 260 between the bellows 250. For example, air can flow through the axial passage 260 from the first end portion 268 of the ball shaft 234 to the second end portion 269 of the ball shaft 234, or vice versa. The axial passage 260 can also be dimensioned to facilitate air flow through the axial passage 260. For example, a cross-sectional area of ​​the axial passage 260, e.g., in a plane perpendicular to the central axis of the ball shaft 234, can be no less than seventy square millimeters (70 mm 2 ) and not more than one thousand two hundred square millimeters (1200 mm 2 ). Such dimensioning of the axial passage 260 can advantageously allow a relatively unrestricted air flow through the ball shaft 234 without compromising the strength of the ball shaft 234.

[0045] The axial passage 260 and the interior 252 of the bellows 250 may collectively define a sealed air chamber from the ambient air around the electric power steering assembly 200. The axial passage 260 may provide an airflow path between the interior 252 of the bellows 250 to allow air pressure equalization between the interior 252 of the bellows 250. As noted above, the expansion and contraction of the bellows 250 may change the air pressure within the bellows 250. Thus, the axial passage 260 may advantageously support the proper operation of the bellows 250. Furthermore, the axial passage 260 may also allow the electric power steering system 200 to not include vent(s) that allow air in the bellows 250 to enter or exit the bellows 250.However, it should be understood that in certain embodiments, one or more vents may be added to the bellows 250 to assist in the operation of the axial passage 260 while equalizing the air pressure within the bellows 250. The vent(s) may include a membrane that allows airflow but limits or prevents the transfer of water and other fluids through the vent(s).

[0046] The ball joints 240 may also include features that allow air to move between the bellows 250 through the ball shaft 234. For example, one of the journal 242 and the bushing 244 of the ball joints 240 may define a connecting passage 262. Air may flow between the bellows 250 through the connecting passages 262. For example, the connecting passages 262 of the ball joints 240 may extend between and connect the axial passage 260 of the ball shaft 234 and the interior 252 of the bellows 250. Thus, air from the interior 252 of the bellows 250 can enter the axial passage 260 of the ball shaft 234 through the connecting passage 262, and air from the axial passage 260 of the ball shaft 234 can enter the interior 252 of the bellows 250 through the connecting passage 262. It should be understood that in certain embodiments, the ball joints 240 may not include a connecting passage 262.Thus, in certain embodiments, e.g., in addition to or alternatively to the connecting passage 262, radial bores or other connecting passages may be formed to provide an airflow path between the axial passage 260 and the interior 252 of the bellows 250.

[0047] As in Fig. 5, the connecting passage 262 may include a first portion 264 and a second portion 266. The first portion 264 of the connecting passage 262 may extend from the axial passage 260 of the ball shaft 234 into a pin 246 of the socket 244. The pin 246 of the socket 244 may be threaded or otherwise attached to the ball shaft 234. The second portion 266 of the connecting passage 262 may extend from the interior 252 of the bellows 250 into the pin 246 of the socket 244. The first portion 264 may be oriented at an angle α with respect to the second portion 266 in the ball joint 240. The angle α may not be less than sixty degrees (60°) and not less than one hundred and twenty degrees (120°), such as ninety degrees (90°).Such an angle α may advantageously help to facilitate the flow of air into and out of the axial passage 260 via the connecting passage 262, while at the same time not hindering the mounting of the ball joints 240 on the ball shaft 234.

[0048] As can be seen from the foregoing, the output movement, e.g., linear translational displacement, of the ball shaft 234 can change the air volume within the bellows 250. For example, while the air volume in one of the bellows 250 decreases, the air volume in the other of the bellows 250 may increase at approximately the same rate. The axial passage 260 can allow air transfer between the bellows 250 to accommodate such air volume changes. Without such air transfer or sufficient external ventilation, the bellows 250 would undesirably inflate or deflate. The axial passage 260 (e.g., and the connecting passages 262) can thus advantageously allow air transfer between the bellows 250 during operation of the electric power steering system 200.

[0049] With reference to the Fig. 5 and Fig. 6, the ball screw assembly 230 may also include features for limiting or preventing rotation of the ball shaft 234 relative to the housing 231. For example, an outer surface 281 of the ball shaft 234 may include at least one spline tooth 280. In certain embodiments, the ball shaft 234 may include one, two, three, four, five, six, or more spline teeth 280. The spline teeth 280 may be circumferentially distributed around the ball shaft 234 and extend axially on the ball shaft 234. The housing 231 may define a plurality of grooves 282. The grooves 282 may be shaped complementarily to the spline teeth 280, and each spline tooth 280 may be received in a respective one of the grooves 282.Mutual engagement between the ball shaft 234 and the housing 231 at the splines 280 within the grooves 282 can limit or prevent rotation of the ball shaft 234 relative to the housing 231, while simultaneously allowing translational displacement of the ball shaft 234 relative to the housing 231. An axial length of the grooves 282 can be no less than six millimeters (6 mm) and no more than fifty millimeters (50 mm). An axial length of the splines 280 can be no less than a stroke length of the ball shaft 234 relative to the housing 231.

[0050] As can be seen from the foregoing, the splines 280 on the ball shaft 234 may engage the grooves 282 on the housing 231. Such an interface between the ball shaft 234 and the housing 231 may advantageously prevent rotation of the ball shaft 234 relative to the housing 231, e.g., due to torque applied by rotation of the ball nut 232 relative to the ball shaft 234.

[0051] The grooves 282 may be positioned at one end of the housing 231. For example, the housing 231 may extend between a first end portion 286 and a second end portion 287. The grooves 282 may be positioned at a first end portion 286 of the housing 231. Thus, in certain embodiments, the friction between the ball shaft 234 and the housing 231 at the splines 280 within the grooves 282 may be limited to a small portion of the length of the ball shaft 234. The third gear 226, which couples the gear set 220 to the ball nut 232, may be positioned at a second end portion 287 of the housing 231. Thus, for example, the grooves 282 and the third gear 226 may be axially spaced and / or positioned at opposite end portions of the housing 231.

[0052] A grease nipple 288 may also be provided on the housing 231, e.g., near the grooves 282 on the first end portion 286 of the housing 231. The interface between the ball shaft 234 and the housing 231 may be lubricated by grease fed into the housing 231 via the grease nipple 288. Such lubrication may advantageously enable smooth translational displacement of the ball shaft 234 relative to the housing 231.

[0053] As noted above, the gear set 220 may couple the electric motor 210 and the ball nut 232, and the electric motor 210 may be operable to rotate the ball nut 232 relative to the ball shaft 234 via the gear set 220. Now to the Fig. 7, Fig. 7A and Fig. Referring to Figure 8, the gear set 220, as shown, may include a first gear 222, a second gear 224, and a third gear 226. The first gear 222, the second gear 224, and the third gear 226 may collectively form part of a power flow path between the electric motor 210 and the ball nut 232.

[0054] The first gear 222 may be coupled to a rotor 211 of the electric motor 210. For example, the first gear 222 may be coupled to the rotor 211 of the electric motor 210 via a planetary gear set 214, as described in more detail below, and the third gear 226 may be coupled to the ball nut 232. The third gear 226 may be fixed relative to the ball nut 232. In certain embodiments, the third gear 226 may be formed separately and attached to the ball nut 232, e.g., via a spline. In other embodiments, the third gear 226 may be formed integrally with the ball nut 232, e.g., such that the third gear 226 is formed on the ball nut 232. For example, the ball nut 232 may be milled, ground, planed, shaped, or otherwise suitably machined to form the third gear 226.The second gear 224 may be arranged between the first and third gears 222, 226 in the power flow path of the gear set 220. For example, the second gear 224 may mesh with the first and third gears 222, 226.

[0055] The planetary gear set 214 may be arranged in the power flow between the electric motor 210 and the gear set 220. Thus, for example, the planetary gear set 214 may be configured to transmit the rotation of the electric motor 210 to the gear set 220. The planetary gear set 214 may include a sun gear 215, a plurality of planet gears 216, a planet carrier 217, and a ring gear 218 ( Fig. 7A). The planet gears 216 mesh with both the sun gear 215 and the ring gear 218. Thus, for example, the planet gears 216 may be positioned between the sun gear 215 and the ring gear 218 within the planetary gear set 214. It should be understood that while the planetary gear set 214 includes one set of planet gears 216 and is thus a negative or minus planetary gear set in the illustrated embodiment, in alternative embodiments the planetary gear set 214 may include an additional set of planet gears and is thus a positive or plus planetary gear set.

[0056] The sun gear 215, the planet carrier 217 or the ring gear 218 of the planetary gear set 214 can be connected to a rotor 211 of the electric motor 210 and can be rotatable therewith ( Fig. 2). Thus, for example, one of the sun gear 215, the planet carrier 217, and the ring gear 218 of the planetary gear set 214 may correspond to an input of the planetary gear set 214 during operation of the electric motor 210 when windings within the electric motor 210 rotate the rotor 211. Furthermore, one of the sun gear 215, the planet carrier 134, and the ring gear 218 of the planetary gear set 214 may rotate when windings within the electric motor 210 rotate the rotor 211. In certain embodiments, the sun gear 215 is connected to and rotatable with the rotor 211. For example, the sun gear 215 may be integrally formed with the rotor 211, e.g., such that the teeth of the sun gear 215 are formed on the rotor 211. For example, one end of the rotor 211 may be milled, ground, planed, shaped, or otherwise suitably machined to form a sun gear 215 on the rotor 211.Alternatively, the sun gear 215 may be formed separately and subsequently connected to the rotor 211, e.g., directly on the rotor 211 or with one or more intermediate elements, such as a shaft.

[0057] Another one of the sun gear 215, the planet carrier 217, and the ring gear 218 of the planetary gear set 214 (e.g., other than the one of the sun gear 215, the planet carrier 217, and the ring gear 218 that is connected to and rotatable with the rotor 211) may be connected to and rotatable with the first gear 222 of the gear set 220. Thus, for example, another one of the sun gear 215, the planet carrier 217, and the ring gear 218 of the planetary gear set 214 may correspond to an output of the planetary gear set 214 during operation of the electric motor 210, and the first gear 222 may correspond to an input for the gear set 220 during operation of the electric motor 210. In addition, the other of the sun gear 215, the planet carrier 217, and the ring gear 218 of the planetary gear set 214, which is connected to the first gear 142, can rotate when windings within the electric motor 210 cause the rotor 211 to rotate.In certain embodiments, the planet carrier 217 is connected to and rotatable with the first gear 142. For example, the planet carrier 217 may be connected to the first gear 222, e.g., directly or via a suitable shaft or other intermediate components.

[0058] The planetary gear set 214 may be configured to provide a reduction gear between the electric motor 210 and the gear set 220. For example, a gear ratio of the planetary gear set 214 may be no less than 7.5:1 and no greater than 8.5:1, such as 8:1. Thus, the planetary gear set 214 may provide a mechanical force boost between the electric motor 210 and the gear set 220. The gear set 220 may also be configured to provide a reduction gear between the planetary gear set 214 and the ball screw assembly 230. For example, a gear ratio of the gear set 220 may be no less than 1:1 and no greater than 2:1, such as 1.5:1. Thus, the gear set 220 may provide a mechanical force boost between the planetary gear set 214 and the ball screw assembly 230.To provide such mechanical power amplification, a root diameter of the second gear 224 may be larger than a root diameter of the third gear 226, and the root diameter of the third gear 226 may be larger than the root diameter of the first gear 222.

[0059] Now on the Fig. 3, Fig. 4 and Fig. 8, the electric power steering system 200 may include a bevel gear 270. An input 276 of the bevel gear 270 may be connected to the steering column 120 ( Fig. 1). An output 278 of the bevel gear 270 may be connected to the second gear 224 of the gear set 220. The bevel gear 270 may include a first bevel gear 272 and a second bevel gear 274. The first bevel gear 272 may mesh with the second bevel gear 274. The first bevel gear 272 may be connectable to the steering column 120 at the input 276 of the bevel gear 270, and the second bevel gear 274 may be connectable to the second gear 224 of the gear set 220 at the output 278 of the bevel gear 270. Thus, the bevel gear 270 may couple the steering column 120 to the gear set 220. Furthermore, the bevel gear 270 can transmit the rotation of the steering column 120 to the gear set 220 and thus to the ball screw assembly 230 while simultaneously changing an angle of such rotation.In certain embodiments, a gear ratio of the bevel gear 270 may be no less than 0.25:1 and no greater than 0.75:1, such as about 0.5:1.

[0060] As in the Fig. 2 and Fig. 3, the ball screw assembly 230, the electric motor 210, and the bevel gear 270 may be positioned on the same axial side of the gear set 220. Such an arrangement of the ball screw assembly 230, the electric motor 210, and the bevel gear 270 may advantageously provide an axially compact electric power steering system 200. Furthermore, the electric power steering system 200 may be more axially compact than known rack and pinion assemblies for front-wheel steering systems.

[0061] The planetary gear set 214, the gear set 220, and the ball screw assembly 230 may cooperate and be configured to provide a mechanical power boost to the electric motor 210, e.g., to enable the electric motor 210 to supplement driver torque to facilitate turning the wheels 101 of the vehicle 100, as described in more detail below.

[0062] The bevel gear 270 may be coupled to a steering wheel 118 of the vehicle 100. For example, the steering wheel 118 may be coupled to the second gear 224 via the steering column 120 of the vehicle 100, which extends between and connects the steering wheel 118 and the first bevel gear 272 at the input 276 of the bevel gear 270. A driver of the vehicle 100 may rotate the steering wheel 118 to rotate the first bevel gear 272 via the steering column 120, which transmits the rotation of the steering wheel 118 to the first bevel gear 272. By meshing the first and second bevel gears 272, 274, the rotation of the steering column 120 is transmitted to the second bevel gear 274 at the output 278 of the bevel gear 270. Within the electric power steering system 200, the output 278 of the bevel gear 270 is coupled to the second gear 224 of the gear set 220 so that the rotation of the second bevel gear 274 is transmitted to the gear set 220.

[0063] The electric power steering system 200 includes features for supplementing the torque applied by the driver to the steering column 120 by turning the steering wheel 118, e.g., to assist the driver in steering the vehicle 100. In particular, the electric motor 210 is operable to rotate the ball nut 232, e.g., to supplement the torque applied by the driver to the second gear 224 of the gear set 220 by turning the steering wheel 118. As noted above, the electric motor 210 may be coupled to the ball nut 232 via the planetary gear set 214 and the gear set 220, such that rotation of the electric motor 210 may rotate the ball nut 232 via the planetary gear set 214 and the gear set 220. For example, the electric motor 210 may be operated to rotate the rotor 211, and a first of the components of the planetary gear set 214 (e.g., the sun gear 215) may rotate during operation of the electric motor 210.The rotation of the first of the components of the planetary gear set 214 (e.g., the sun gear 215) can cause a second of the components of the planetary gear set 214 (e.g., the planet carrier 217) to rotate. Due to the coupling of the second of the components of the planetary gear set 214 (e.g., the planet carrier 217) to the first gear 222 of the gear set 220, the planetary gear set 214 can transmit the rotation of the electric motor 210 to the gear set 220, such that the first gear 222 rotates during operation of the electric motor 210. The second gear 224, in turn, can transmit the rotation of the first gear 222 to the third gear 226 within the gear set 220, and the ball nut 232 can rotate due to the connection of the third gear 226 to the ball nut 232. Accordingly, the ball nut 232 may rotate during operation of the electric motor 210, e.g.with a mechanical power boost for the electric motor 210, which is provided by the planetary gear set 214 and the gear set 220.

[0064] During the rotation of the ball nut 232 relative to the ball shaft 234, the ball shaft 234 can also translate relative to the ball nut 232. Thus, the ball screw assembly 230 can convert the rotational motion of the electric motor 210 to translate the tie rods 202 coupled to the ball shaft 234. Furthermore, the translational displacement of the ball shaft 234 can rotate steering knuckles via tie rods 202 and turn the front wheels 101 of the vehicle 100. Thus, when a driver turns the steering wheel 118 and / or when the electric motor 210 is operated to rotate the ball nut 232, the ball screw assembly 230 can translate the ball shaft 234 to rotate steering knuckles via tie rods 202 and turn the front wheels 101 of the vehicle 100.

[0065] To control the operation of the electric motor 210, the electric power steering system 200 may include a controller 290 and / or a power steering sensor 292. The controller 290 may include a memory and a microprocessor, such as a general-purpose or special-purpose microprocessor operable to execute programming instructions or microcontrol code associated with the operation of the electric power steering system 200. The memory may be a random access memory, such as DRAM, or a read-only memory, such as ROM or FLASH. In one embodiment, the processor executes programming instructions stored in the memory. The memory may be a separate component from the processor or may be integrated into the processor. Alternatively, the controller 290 may be constructed without using a microprocessor, e.g.,using a combination of discrete analog and / or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, and the like) to perform control functionality, rather than relying on software. The electric motor 210 and the power steering sensor 292 may communicate with the controller 290 via one or more signal lines or shared communication buses. The controller 290 may also communicate with other systems within the vehicle 100 via a CAN (Controller Area Network) bus.

[0066] The power steering sensor 292 may be configured to detect a steering torque and / or a steering angle of the steering column 120. In response to inputs from the power steering sensor 292, the controller 290 may operate the electric motor 210 to rotate the ball nut 232. Furthermore, the power steering sensor 292 may detect a driver of the vehicle 100 turning the steering wheel 118, and the controller 290 may activate the electric motor 210 to supplement the driver torque applied to the second gear 224 to facilitate turning the wheels 101 of the vehicle 100. Further, the power steering sensor 292 may detect the direction and degree in which the driver turns the steering wheel 118, and the controller 290 may operate the electric motor 210 to drive the rotor 211 a certain number of rotations in a certain direction, both of which complement the direction and degree detected by the power steering sensor 292.

[0067] As can be seen from the foregoing, the electric power steering system 200 includes components (e.g., the planetary gear set 214, the gear set 220, and the ball screw assembly 230) for mechanical reduction between the electric motor 210 and / or the steering wheel 118 and the output shaft 150, e.g., to convert the low torque and high speed of the electric motor 210 into a useful higher torque and low speed to effectively steer a heavy commercial vehicle.

[0068] The electric power steering system 200 can provide a mechanically robust, safe, and cost-effective electric power steering system for heavy-duty vehicles. Furthermore, the electric power steering system 200 can advantageously: (1) electrify the power steering of heavy-duty vehicles; (2) provide the necessary mechanical power boost for an electric motor for steering heavy-duty vehicles; (3) provide a compact power steering system; (4) provide a robust and safe electric power steering system for heavy-duty vehicles; and / or (5) provide a cost-effective electric steering system for heavy-duty vehicles.

[0069] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims and may include other examples that occur to one skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the language of the claims, or if they include equivalent structural elements with only insubstantial differences from the language of the claims. LIST OF REFERENCE SYMBOLS 100 commercial vehicles 101 wheels 102 tractor 104 followers 106 cabin 110 engine system 112 Transmission system 116 Brake system 118 Steering device 120 steering column 200 steering system 202 tie rod 203 Outer End 204 Inner End 210 electric motor 211 Rotor 212 engine housing 214 planetary gear set 215 Sun gear 216 carriers 218 ring gear 220 gear set 222 First gear 224 Second gear 226 Third gear 230 ball screw assembly 231 housings 232 ball nut 234 ball shaft 236 Helical track 238 warehouses 240 ball joints 242 bearing journals 244 socket 246 cones 250 bellows 252 Interior 260 Axial passage 262 connecting passage 264 First Part (Connecting Passage) 266 Second part (connecting passage) 268 First end part (ball shaft) 269 ​​Second end part (ball shaft) 270 bevel gears 272 First bevel gear 274 Second bevel gear 276 Entrance 278 Exit 280 splines 281 exterior area 282 grooves 283 interior surface 284 Soft Stops 286 First end part (housing) 287 Second end part (housing) 288 grease nipples 290 Control 292 Power steering sensor LG longitudinal direction FV front part zip back FDOT Forward Direction α angle

Claims

[1] Electric power steering assembly comprising: an electric motor; a gear set; a ball screw assembly comprising: a ball nut and a ball shaft which together define a helical path, wherein the gear set couples the electric motor and the ball nut such that the electric motor is operable to rotate the ball nut relative to the ball shaft, and a plurality of bearings that can rotate through the helical track when the ball nut rotates relative to the ball shaft in order to translate the ball shaft relative to the ball nut; a pair of ball joints, each of the pair of ball joints being attached to the ball shaft at a respective end portion of the ball shaft; and a pair of bellows, each of the pair of bellows being mounted via a respective one of the pair of ball joints, wherein the ball shaft defines an axial passage and air can flow between the pair of bellows through the axial passage. [2] The electric power steering assembly of claim 1, wherein each of the pair of ball joints includes a journal and a bushing, the journal being received in the bushing in each of the pair of ball joints, the bushing of each of the pair of ball joints being attached to the ball shaft at the respective end portion of the ball shaft. [3] The electric power steering assembly of claim 2, wherein the bushing of each of the pair of ball joints defines a connecting passage, the connecting passage of each of the pair of ball joints extending between and connecting the axial passage of the ball shaft and an interior of a respective one of the pair of bellows. [4] An electric power steering assembly according to claim 3, wherein the socket of each of the pair of ball joints is bolted to the ball shaft at the respective end portion of the ball shaft. [5] An electric power steering assembly according to claim 3, wherein the connecting passage of each of the pair of ball joints comprises a first part and a second part, the first part extending from the axial passage of the ball shaft into a journal of the socket, the second part extending from the interior of a respective one of the pair of bellows into the journal of the socket, the first part being oriented at an angle with respect to the second part in each of the pair of ball joints, the angle being not less than sixty degrees and not less than one hundred and twenty degrees. [6] An electric power steering assembly according to claim 1, wherein the axial passage extends between opposite end portions of the ball shaft. [7] An electric power steering assembly according to claim 6, wherein the axial passage extends parallel to a central axis of the ball shaft. [8] The electric power steering assembly according to claim 1, wherein a cross-sectional area of ​​the axial passage in a plane perpendicular to a center axis of the ball shaft is not less than seventy square millimeters and not more than one thousand two hundred square millimeters. [9] The electric power steering assembly of claim 1, wherein the axial passage and the interior of the pair of bellows together define a sealed air chamber with respect to the ambient air around the electric power steering assembly. [10] The electric power steering assembly of claim 1, wherein the ball screw assembly further comprises a housing, the ball nut being rotatably mounted within the housing, the ball shaft being translationally displaceable relative to the housing, an outer surface of the ball shaft including at least one spline tooth received by the housing to limit rotation of the ball shaft relative to the housing. [11] An electric power steering assembly according to claim 1, wherein: the gear set comprises a first gear, a second gear and a third gear; the first gear is coupled to a rotor of the electric motor; the third gear meshes with a toothing on the ball nut; the second gear is arranged between the first and third gears in a power flow path between the first and third gears; and the second gear can be connected to a steering column. [12] The electric power steering assembly of claim 11, further comprising a bevel gear having a first bevel gear and a second bevel gear, the first bevel gear meshing with the second bevel gear, the first bevel gear connectable to the steering column, the second bevel gear connected to the second gear of the gear set. [13] The electric power steering assembly of claim 11, wherein the second gear meshes with the first and third gears. [14] The electric power steering assembly according to claim 1, wherein a length of the ball shaft is not less than five hundred millimeters and not more than one thousand millimeters. [15] A vehicle comprising the electric power steering assembly of claim 1. [16] A vehicle according to claim 15, wherein the vehicle is a Class 8 commercial vehicle based on the gross vehicle weight rating. [17] Electric power steering assembly comprising: an electric motor; a gear set comprising a first gear, a second gear, and a third gear, the first gear coupled to a rotor of the electric motor, the second gear connectable to a steering column and disposed between the first and third gears in a power flow path between the first and third gears; a ball screw assembly comprising: a ball nut and a ball shaft which together define a helical path, wherein the third gear meshes with a toothing on the ball nut so that the electric motor is operable to rotate the ball nut relative to the ball shaft, and a plurality of bearings that can rotate through the helical track when the ball nut rotates relative to the ball shaft in order to translate the ball shaft relative to the ball nut; a pair of ball joints, each of the pair of ball joints comprising a journal and a bushing, the journal being received in the bushing in each of the pair of ball joints, the bushing of each of the pair of ball joints being attached to the ball shaft at a respective end portion of the ball shaft; and a pair of bellows, each of the pair of bellows being mounted via a respective one of the pair of ball joints, wherein the ball shaft defines an axial passage between opposite end portions of the ball shaft, the bushing of each of the pair of ball joints defines a connecting passage, the connecting passage of each of the pair of ball joints extends between and connects the axial passage of the ball shaft and an interior of a respective one of the pair of bellows, and air can flow between the pair of bellows through the axial passage. [18] An electric power steering assembly according to claim 17, wherein the axial passage extends parallel to a central axis of the ball shaft.

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