System for low-friction transmission A system for low-friction transmission

Abstract

A drivetrain for a vehicle includes a first helical pinion gear having a helix angle coupled to a first shaft and configured to receive an input torque. The drivetrain includes a second helical pinion gear having a first helix angle coupled to a second shaft and configured to receive the input torque. The second shaft is disposed within the first shaft and is rotatable within the first shaft. The drivetrain includes a differential assembly having a third helical gear and a fourth helical gear, the third helical gear having the first helix angle and coupled to the first helical pinion gear, the fourth helical gear having a helix angle and coupled to the second helical pinion gear. The third helical gear and the fourth helical gear are coupled to a differential gear set to drive first and second output shafts associated with the vehicle.

Description

Technical Field

[0001] The technical field generally relates to systems for transmissions in vehicles, and more specifically to systems for low-friction transmissions in battery electric vehicles. Background Technology

[0002] In the example of a battery electric vehicle (BEV), the drivetrain transmits power from an electric motor to the wheels associated with the BEV. In some cases, the drivetrain may include one or more gears and shafts that cooperate to transfer torque from the electric motor to the wheels at different speeds. In these cases, mechanical friction may occur between the gears and shafts, which may necessitate the use of additional torque from the electric motor to drive them. Using this additional torque may reduce the BEV's driving range or may require additional or larger capacity batteries to power the electric motor.

[0003] Therefore, it is desirable to provide a low-friction transmission system for battery electric vehicles, wherein friction within the transmission device is reduced, thereby increasing the driving range of the battery electric vehicle or enabling a reduction in the capacity of the battery associated with the battery electric vehicle. Furthermore, other desirable features and characteristics of the invention will become apparent from the following detailed description and the appended claims, in conjunction with the accompanying drawings and the foregoing technical and background information. Summary of the Invention

[0004] According to various embodiments, a drivetrain system for a vehicle is provided. The drivetrain includes a first helical pinion having a helix angle, coupled to a first shaft and configured to receive input torque. The drivetrain also includes a second helical pinion having a first helix angle, coupled to a second shaft and configured to receive input torque. The second shaft is disposed within and rotatable within the first shaft. The drivetrain includes a differential assembly having a third helical gear and a fourth helical gear, the third helical gear having a first helix angle and coupled to the first helical pinion, and the fourth helical gear having a helix angle and coupled to the second helical pinion. The third and fourth helical gears are coupled to a differential gear set to drive a first and a second output shaft associated with the vehicle.

[0005] An input shaft assembly is coupled to a propulsion system associated with a vehicle and is configured to provide input torque. A first shaft includes a first helical gear coupled to the input shaft assembly to receive input torque, and the first helical gear has a helix angle. The input shaft assembly includes an input shaft and an output shaft, and the input shaft includes a third helical pinion having a first helix angle and coupled to the first helical gear. A second shaft includes a second helical gear coupled to the input shaft assembly to receive input torque, and the second helical gear has a helix angle. The input shaft assembly includes an input shaft and an output shaft, and the input shaft includes a fourth helical pinion having a helix angle and coupled to the second helical gear. The input shaft assembly includes an input shaft disposed within an output shaft associated with the vehicle's propulsion system, and the input shaft is configured to rotate with the output shaft at the same speed as the input shaft. The input shaft includes a third helical pinion having a helix angle and a fourth helical pinion having a first helix angle. The input shaft includes a plurality of splines that engage a central bore on the output shaft to couple the input shaft to the output shaft. The helix angle and the first helix angle are opposite and equal angles.

[0006] A vehicle is also provided. The vehicle includes a propulsion system having an output shaft. The vehicle includes a transmission system. The transmission system includes an input shaft assembly coupled to the output shaft and a transmission shaft assembly coupled to the input shaft assembly. The transmission shaft assembly includes a first transmission shaft and a second transmission shaft, the first transmission shaft having a first helical pinion and a first helical gear configured to be driven by the input shaft assembly, and the second transmission shaft having a second helical pinion and a second helical gear configured to be driven by the input shaft assembly. The first helical gear and the first helical pinion have a helix angle, and the second helical gear and the second helical pinion have a first helix angle. The transmission system includes a differential assembly coupled to the transmission shaft assembly. The differential assembly includes a third helical gear and a fourth helical gear coupled to a differential gear set. The third helical gear is configured to be driven by the first helical pinion, the fourth helical gear is configured to be driven by the second helical pinion, and the differential gear set is configured to drive the first output shaft and the second output shaft.

[0007] The helix angle and the first helix angle are opposite and equal angles. The third helical gear has the first helix angle, and the fourth helical gear has the first helix angle. The input shaft assembly includes an input shaft disposed within the output shaft, and the input shaft is configured to rotate with the output shaft at the same speed as the input shaft. The input shaft is coupled to the output shaft at a coupling point to transmit power from the output shaft to the input shaft. The input shaft includes a third helical pinion with a helix angle and a fourth helical pinion with a first helix angle. The third helical pinion is configured to drive the first helical gear. The fourth helical pinion is configured to drive the second helical gear. The input shaft includes multiple splines that engage a central bore of the output shaft to connect the input shaft for rotation with the output shaft. A second transmission shaft is positioned within a central transmission bore of the first transmission shaft. Attached Figure Description

[0008] Exemplary embodiments will be described below in conjunction with the following figures, wherein the same numerals denote the same elements, and wherein:

[0009] Figure 1 This is a functional block diagram illustrating a vehicle including a low-friction transmission system according to various embodiments;

[0010] Figure 2 This is a perspective schematic diagram of a low-friction transmission system according to various embodiments, wherein the bearing associated with the low-friction transmission system is shown as a partial cross-section;

[0011] Figure 3 It is along Figure 2 A cross-sectional view of the input shaft assembly of a low-friction transmission system obtained from line 3-3;

[0012] Figure 4 It is along Figure 2 A cross-sectional view of the transmission shaft assembly of a low-friction drive system obtained from line 4-4;

[0013] Figure 5 It is along Figure 2 A cross-sectional view of the differential assembly of a low-friction transmission system obtained from line 5-5.

[0014] Figure 6 This is a cross-sectional view of a low-friction transmission system, where the cross-sectional view of the input shaft assembly is along... Figure 2 The cross-sectional view of the transmission shaft assembly is obtained from line 3-3. Figure 2 Line 4-4 is obtained, and the cross-sectional view of the differential assembly is along... Figure 2 The line 5-5 was obtained; and

[0015] Figure 7 According to various embodiments, it is used for Figure 1 A partially exploded perspective view of another exemplary low-friction drive system for a vehicle. Detailed Implementation

[0016] The following detailed description is exemplary in nature only and is not intended to limit application and use. Furthermore, it is not intended to be bound by any express or implied theory presented in the foregoing introduction, brief overview, or the following detailed description. As used herein, the term "module" refers to any hardware, software, firmware, electronic control components, processing logic, and / or processor device, individually or in any combination, including, but not limited to: application-specific integrated circuits (ASICs), electronic circuits, processors (shared, dedicated, or grouped) and memories executing one or more software or firmware programs, combinational logic circuits, and / or other suitable components that provide the described functionality.

[0017] Embodiments of this disclosure can be described herein in terms of functional and / or logical block components and various processing steps. It should be understood that such block components can be implemented by any number of hardware, software, and / or firmware components configured to perform specified functions. For example, embodiments of this disclosure can employ various integrated circuit components, such as memory elements, digital signal processing elements, logic elements, lookup tables, etc., which can perform various functions under the control of one or more microprocessors or other control devices. Furthermore, those skilled in the art will understand that embodiments of this disclosure can be practiced in conjunction with any number of systems, and the systems described herein are merely exemplary embodiments of this disclosure.

[0018] For the sake of brevity, conventional techniques relating to signal processing, data transmission, signaling, control, machine learning models, radar, lidar, image analysis, and other functional aspects of the system (and its individual operating components) may not be described in detail herein. Furthermore, the connecting lines shown in the various figures included herein are intended to represent exemplary functional relationships and / or physical connections between various elements. It should be noted that many alternative or additional functional relationships or physical connections may exist in the embodiments of this disclosure.

[0019] Reference Figure 1 According to various embodiments, a low-friction drive system, generally indicated as 100, is associated with vehicle 10. In one example, vehicle 10 is a battery-powered electric vehicle; however, it should be understood that the following disclosure is applicable to other electric motor-driven devices. Figure 1 As shown, vehicle 10 generally includes a chassis 12, a body 14, front wheels 16, and rear wheels 18. The body 14 is mounted on the chassis 12 and substantially surrounds the components of vehicle 10. The body 14 and chassis 12 may together form a frame. Wheels 16-18 are rotatably connected to the chassis 12 near corresponding corners of the body 14. In various embodiments, vehicle 10 is an autonomous or semi-autonomous vehicle. As will be understood, the low-friction drive system 100 can be implemented in other non-autonomous systems and is not limited to this embodiment. In the illustrated embodiment, vehicle 10 is depicted as a battery-electric passenger vehicle, but it should be understood that any other vehicle, including motorcycles, trucks, SUVs, RVs, etc., may also be used.

[0020] As shown in the figure, the vehicle 10 generally includes a propulsion system 20, a low-friction drive system 100, a steering system 24, a braking system 26, a sensor system 28, an actuator system 30, and at least one controller 34. In various embodiments, the propulsion system 20 may include an electric motor, such as an electric motor or a traction motor. The propulsion system 20 has an output shaft or outer shaft 22 coupled to the low-friction drive system 100.

[0021] Braking system 26 is configured to provide braking torque to wheels 16 and 18. In various embodiments, braking system 26 may include friction braking, brake-by-wire braking, regenerative braking systems such as motors, and / or other suitable braking systems.

[0022] Steering system 24 affects the position of wheels 16 and / or 18. Although depicted for illustrative purposes as including steering wheel 24a, in some embodiments contemplated within the scope of this disclosure, steering system 24 may not include steering wheel.

[0023] Sensor system 28 includes one or more sensing devices 40a-40n that sense observable conditions of the external and / or internal environment of vehicle 10. In various embodiments, sensing devices 40a-40n include, but are not limited to, radar (e.g., long-range, medium-range / short-range), lidar, global positioning system, optical cameras (e.g., forward, 360-degree, rearward, lateral, stereo, etc.), thermal (e.g., infrared) cameras, ultrasonic sensors, odometer sensors (e.g., encoders), and / or other sensors that may be utilized in conjunction with systems and methods according to this subject matter. Sensor system 28 communicates with controller 34 via a communication medium.

[0024] The actuator system 30 includes one or more actuator devices 42a-42n that control one or more vehicle features, such as, but not limited to, the propulsion system 20, the steering system 24, and the braking system 26. In various embodiments, the vehicle 10 may also include… Figure 1 Interior and / or exterior vehicle features not shown, such as various doors, trunk and cabin features, such as air, music, lighting, touchscreen display components, active safety seats or haptic seats, etc.

[0025] The controller 34 includes at least one processor 44 and a computer-readable storage device or medium 46. The processor 44 can be any custom or commercially available processor, central processing unit (CPU), graphics processing unit (GPU), application-specific integrated circuit (ASIC) (e.g., a custom ASIC implementing a neural network), field-programmable gate array (FPGA), an auxiliary processor among several processors associated with the controller 34, a semiconductor-based microprocessor (in the form of a microchip or chipset), any combination thereof, or any device generally used for executing instructions. For example, the computer-readable storage device or medium 46 can include volatile and non-volatile memory in the form of read-only memory (ROM), random access memory (RAM), and non-fail-to-reset memory (KAM). KAM is a persistent or non-volatile memory that can be used to store various operational variables when the processor 44 is powered off. The computer-readable storage device or medium 46 may be implemented using any of a number of known memory devices, such as PROM (programmable read-only memory), EPROM (electric PROM), EEPROM (electrically erasable PROM), flash memory, or any other electrical, magnetic, optical, or combined memory device capable of storing data (some of which represents executable instructions used by controller 34 to control vehicle 10).

[0026] Reference Figure 2 The low-friction drive system 100 is shown in more detail below. In one example, the low-friction drive system 100 includes an input shaft assembly 102, a transmission shaft assembly 104, and a differential assembly 106. The low-friction drive system 100 may also include a housing to enclose the components of the low-friction drive system 100. The input shaft assembly 102 receives input torque from the propulsion system 20. In one example, the input shaft assembly 102 includes an input shaft or inner shaft 110, an outer shaft 22, one or more bearings 114, a first pinion 116, a second pinion 118, and a coupling system 120.

[0027] Reference Figure 3The diagram shows a cross-section of the input shaft assembly 102. The inner shaft 110 is connected to the outer shaft 22 via a coupling system 120 to rotate at the same speed as the outer shaft 22. In one example, the inner shaft 110, outer shaft 22, the first or outer transmission shaft 180 and the second transmission shaft or inner transmission shaft 182 of the transmission shaft assembly 104, and the first output shaft 274 and the second output shaft 276 of the differential assembly 106 are torsionally tuned, cooperating with the rest of the low-friction drivetrain 100 to substantially cancel or eliminate axial loads acting on the low-friction drivetrain 100. By eliminating axial loads, the mechanical friction associated with the low-friction drivetrain 100 is significantly reduced, which improves the operating efficiency of the propulsion system 20 and the low-friction drivetrain 100. In one example, given the arrangement of the input shaft assembly 102 and the transmission shaft assembly 104, a finite element analysis is performed based on a predetermined output torque required for a predetermined rotation angle of the output shafts 274, 276 of the differential assembly 106. Finite element analysis determined the connection point 112 between the inner shaft 110 and the outer shaft 22, which resulted in the cancellation of axial loads acting on the input shaft assembly 102, the transmission shaft assembly 104, and the differential assembly 106. Generally, the torsional stiffness of the inner shaft 110 and the outer shaft 22 at the connection point 112 is the same as the torsional stiffness at the first helical differential gear 250 and the second helical differential gear 262 of the differential assembly 106. By providing the same torsional stiffness at the connection point 112 between the inner shaft 110 and the outer shaft 22, and at the first helical differential gear 250 and the second helical differential gear 262 of the differential assembly 106, the axial loads acting on the input shaft assembly 102, the transmission shaft assembly 104, and the differential assembly 106 are canceled out by the opposing helical gear teeth on the corresponding gears of the first pinion 116, the second pinion 118, the first helical gear 160, the second helical gear 174, the first transmission pinion 184, the second transmission pinion 186, the first helical differential gear 250, and the second helical differential gear 262, as will be discussed. In one example, the connection point 112 is defined near one of the bearings 114. It should be noted that in other examples, torsional tuning of the low-friction drivetrain 100 may result in the inner shaft 110 being connected to the outer shaft 22 at different locations along the length of the inner shaft 110. The connection point 112 is the point where power is diverted from the outer shaft 22 to the inner shaft 110.

[0028] The inner shaft 110 is cylindrical and may be hollow. The inner shaft 110 is made of metal or a metal alloy and may be forged, extruded, cast, etc. Generally, the inner shaft 110 and the outer shaft 22 are each made of metal or a metal alloy, including but not limited to shaft steel. The inner shaft 110 includes a first input shaft end 122 and an opposing second input shaft end 124. The first input shaft end 122 is coupled to the coupling system 120 and supported by one of the bearings 114 for rotation with the outer shaft 22. A second pinion 118 is coupled to the second input shaft end 124. In one example, the second input shaft end 124 includes a plurality of pinion splines 126 that engage with a plurality of mating pinion splines 127 defined within the second pinion 118.

[0029] In this example, the inner shaft 110 is received within the outer shaft 22 such that the outer shaft 22 surrounds a portion of the inner shaft 110, and the second input shaft end 124 extends beyond the outer shaft 22. At the second input shaft end 124, the inner shaft 110 includes a plurality of pinion splines 126. The plurality of pinion splines 126 engage a second pinion 118 to the inner shaft 110. The second pinion 118 may include a plurality of mating pinion splines 127 that engage with the pinion splines 126 of the inner shaft 110 to engage the second pinion 118 to the inner shaft 110. Generally, the outer shaft 22, driven by the propulsion system 20, drives the first pinion 116 and the second pinion 118 at the same speed and torque as the inner shaft 110. It should be noted that in other embodiments, the second pinion 118 may be engaged to the inner shaft 110 via a locking cone or the like.

[0030] In this example, the inner shaft 110 also includes a plurality of shaft splines 131. The shaft splines 131 are defined on the inner shaft 110 at the connection point 112. In this example, the shaft splines 131 are defined on the inner shaft 110 near, but spaced apart from, the second input shaft end 124. The center bore 134 of the outer shaft 22 is substantially smooth. The inner shaft 110 is connected to the outer shaft 22 by the coupling system 120, such that the shaft splines 131 form grooves in the center bore 134 of the outer shaft 22, thereby securing the inner shaft 110 to the outer shaft 22 at the connection point 112, allowing the inner shaft 110 and the outer shaft 22 to rotate together. The outer shaft 22 includes a first output shaft end 130 and an opposing second output shaft end 132. The outer shaft 22 also defines a center bore 134 from the first output shaft end 130 to the second output shaft end 132, which is connected to the inner shaft 110.

[0031] In this example, the input shaft assembly 102 includes two bearings 114. One bearing 114 is adjacent to or coupled to the outer shaft 22 at the first output shaft end 130, and the other bearing 114 is adjacent to or coupled to the outer shaft 22 at the second output shaft end 132. The bearings 114 support the outer shaft 22 for rotation. In this example, each bearing 114 is a roller bearing; however, any bearing can be used, including but not limited to ball bearings. The bearings 114 can be coupled to a housing associated with the low-friction drive system 100.

[0032] A first pinion 116 is coupled to an outer shaft 22. The first pinion 116 is made of metal or a metal alloy and may be forged, cast, additively manufactured, etc. The first pinion 116 has a first pinion inner diameter 150 and a first pinion outer diameter 152. The first pinion inner diameter 150 is positioned about an inner shaft 110. In one example, the first pinion 116 includes a first pinion end 154 opposite a second pinion end 157. The first pinion end 154 is coupled to the outer shaft 22 such that the first pinion 116 is driven by the outer shaft 22, and the second pinion end 157 is spaced apart from a second pinion 118. In one example, the first pinion 116 is a helical gear and has a plurality of helical teeth 156 defined on the first pinion outer diameter 152. (Return to Reference) Figure 2 The first pinion 116 has a central axis C, and the helical gear teeth 156 are arranged with a first helix angle 158, which is defined between the central axis C and a line tangent to one of the plurality of helical gear teeth 156. In this example, the first helix angle 158 is approximately -10 degrees to -50 degrees. The first pinion 116 is driven by the outer shaft 22 and drives the first helical gear 160 of the transmission shaft assembly 104.

[0033] The second pinion 118 is coupled to the inner shaft 110. The second pinion 118 is made of metal or a metal alloy and can be forged, cast, additively manufactured, etc. The second pinion 118 has a second pinion inner diameter 162 and a second pinion outer diameter 164. The second pinion 118 also has a first pinion end 166 opposite to the second pinion end 168. The second pinion inner diameter 162 defines a central bore extending from the first pinion end 166 to the second pinion end 168, which includes a plurality of mating pinion splines 127. In one example, the second pinion 118 is a helical gear and has a plurality of second helical gear teeth 170 defined on the second pinion outer diameter 164. (Return to reference) Figure 2The second pinion 118 has a central axis C2, and the second helical gear teeth 170 are arranged with a second helix angle 172, which is defined between the central axis C2 and a line tangent to one of the plurality of second helical gear teeth 170. In this example, the second helix angle 172 is between 10 and 50 degrees, and is opposite to and equal to the first helix angle 158. For example, if the first helix angle 158 is negative 45 degrees, then the second helix angle 172 is 45 degrees. By providing a second helix angle 172 that is opposite to and equal to the first helix angle 158, the axial load acting on the input shaft assembly 102 is reduced or canceled due to the opposite directions of the first helix angle 158 and the second helix angle 172, and the torsional tuning of the inner shaft 110 and the outer shaft 22. By eliminating or canceling the axial load acting on the input shaft assembly 102, the first pinion 116 and the second pinion 118 reduce the mechanical friction associated with the input shaft assembly 102. The second pinion 118 is driven by the inner shaft 110 and drives the second helical gear 174 of the transmission shaft assembly 104.

[0034] The coupling system 120 secures the inner shaft 110 to the outer shaft 22 at the engagement point 112, so that the inner shaft 110 rotates at the same speed as the outer shaft 22 and transmits the same torque from the inner shaft 110 to each of the first pinion 116 and the second pinion 118. In one example, the coupling system 120 is a locking nut; however, other techniques can be used to couple the inner shaft 110 to the outer shaft 22, including but not limited to forgings. Generally, the coupling system 120 creates a compression fit between the inner shaft 110 and the outer shaft 22, which causes the shaft spline 131 to engage with the center hole 134 of the outer shaft 22 to couple the inner shaft 110 to the outer shaft 22.

[0035] Transmission shaft assembly 104 is coupled between input shaft assembly 102 and differential assembly 106. Transmission shaft assembly 104 transmits speed and torque from input shaft assembly 102 to differential assembly 106. In one example, transmission shaft assembly 104 includes a first helical gear 160, a second helical gear 174, an outer transmission shaft 180, an inner transmission shaft 182, a first transmission pinion 184, a second transmission pinion 186, and one or more bearings 188.

[0036] Reference Figure 4A first helical gear 160 is coupled to an outer transmission shaft 180. The first helical gear 160 is made of metal or a metal alloy and can be forged, cast, additively manufactured, etc. The first helical gear 160 has a first gear inner diameter 190 and a first gear outer diameter 192. The first gear inner diameter 190 is coupled to or integrally formed with the outer transmission shaft 180 and drives the outer transmission shaft 180. In one example, the first gear inner diameter 190 includes a plurality of mating splines 194 that mate with a plurality of splines 196 of the outer transmission shaft 180 to securely couple the first helical gear 160 to the outer transmission shaft 180. In one example, the first helical gear 160 has a plurality of helical gear teeth 198. The helical gear teeth 198 are coupled to or defined on the first gear outer diameter 192. (Return to Reference) Figure 2 The first helical gear 160 has a central axis C3, and the helical gear teeth 198 are arranged with a second helix angle 172, which is defined between the central axis C3 and a line tangent to one of the helical gear teeth 198. The first helical gear 160 is driven by a first pinion 116 and drives the outer transmission shaft 180.

[0037] Return to reference Figure 4 A second helical gear 174 is coupled to an inner transmission shaft 182. The second helical gear 174 is made of metal or a metal alloy and can be forged, cast, additively manufactured, etc. The second helical gear 174 has a second gear inner diameter 200 and a second gear outer diameter 202. The second gear inner diameter 200 is coupled to and drives the inner transmission shaft 182. The second gear inner diameter 200 includes a plurality of second mating splines 204 that mate with a plurality of second splines 206 of the inner transmission shaft 182 to securely connect the second helical gear 174 to the inner transmission shaft 182. In one example, the second helical gear 174 has a plurality of second helical gear teeth 210. The second helical gear teeth 210 are defined on the second gear outer diameter 202. (Return to Reference) Figure 2 The second helical gear 174 has a central axis C4, and the second helical gear teeth 210 are arranged with a first helix angle 158, which is defined between the central axis C4 and a line tangent to one of the teeth of the second helical gear 210. The second helical gear 174 is driven by a second pinion 118 and drives the inner transmission shaft 182. By providing the first helical gear 160 with a second helix angle 172 that is opposite to and equal to that of the second helical gear 174 having the first helix angle 158, the axial load acting on the transmission shaft assembly 104 is reduced or canceled because the directions of the first helix angle 158 and the second helix angle 172 are opposite. By eliminating or canceling the axial load acting on the transmission shaft assembly 104, the first helical gear 160 and the second helical gear 174 reduce the mechanical friction associated with the transmission shaft assembly 104.

[0038] The outer transmission shaft 180 includes a first transmission shaft end 220 and an opposing second transmission shaft end 222. The outer transmission shaft 180 also defines a central transmission hole 224 extending from the first transmission shaft end 220 to the second transmission shaft end 222, sized to receive the inner transmission shaft 182. The central transmission hole 224 is the inner diameter of the outer transmission shaft 180, and a plurality of splines 196 are defined around the outer diameter 225 of the outer transmission shaft 180. The outer transmission shaft 180 is made of metal or a metal alloy and can be forged, extruded, cast, etc. In this example, the outer transmission shaft 180 has a larger diameter than the inner transmission shaft 182, allowing the inner transmission shaft 182 to rotate within and independently of the outer transmission shaft 180. A first helical gear 160 is coupled to the first transmission shaft end 220 of the outer transmission shaft 180, and a first transmission pinion 184 is coupled to the second transmission shaft end 222 of the outer transmission shaft 180. In one example, the second transmission shaft end 222 includes a plurality of transmission splines 226 surrounding the outer diameter 225, which engage with a plurality of pinion splines 227 to connect the first transmission pinion 184 to the second transmission shaft end 222 of the outer transmission shaft 180.

[0039] The inner transmission shaft 182 includes a third transmission shaft end 230 and an opposing fourth transmission shaft end 232. The inner transmission shaft 182 also defines a second central transmission hole 234 extending from the third transmission shaft end 230 to the fourth transmission shaft end 232, which reduces the weight associated with the inner transmission shaft 182. A plurality of second splines 206 define the outer diameter 236 of the inner transmission shaft 182. The inner transmission shaft 182 is made of metal or a metal alloy and can be forged, extruded, cast, etc. In this example, the inner transmission shaft 182 is received by and rotatable within an outer transmission shaft 180. A second helical gear 174 is coupled to the third transmission shaft end 230 of the inner transmission shaft 182 via second splines 204, 206, and a second transmission pinion 186 is coupled to the fourth transmission shaft end 232 of the inner transmission shaft 182. In one example, the fourth transmission shaft end 232 includes a plurality of second transmission splines 237 surrounding the outer diameter 236, which engage with a plurality of second pinion splines 239 to connect the second transmission pinion 186 to the fourth transmission shaft end 232 of the inner transmission shaft 182.

[0040] A first transmission pinion 184 is coupled to an outer transmission shaft 180. The first transmission pinion 184 is made of metal or a metal alloy and can be forged, cast, additively manufactured, etc. The first transmission pinion 184 has a first transmission pinion inner diameter 240 and a first transmission pinion outer diameter 242. A pinion spline 227 is defined on the first transmission pinion inner diameter 240. The first transmission pinion 184 also has a first transmission end 244 opposite to a second transmission end 246, and a central pinion bore 245 is defined through the first transmission end 244 to the second transmission end 246. The inner diameter 240 of the first transmission pinion is sized to allow the inner transmission shaft 182 to rotate within and independently of the first transmission pinion 184. The second transmission end 246 is spaced apart from the second transmission pinion 186. In one example, the first transmission pinion 184 is a helical gear and has a plurality of helical gear teeth 248 defined on the first transmission pinion outer diameter 242. (Return to Reference) Figure 2 The first transmission pinion 184 has a central axis C5, and the helical gear teeth 248 are arranged with a second helix angle 172, which is defined between the central axis C5 and a line tangent to one of the helical gear teeth 248. The first transmission pinion 184 is driven by the outer transmission shaft 180 and drives the first helical differential gear 250 of the differential assembly 106.

[0041] Return to reference Figure 4 The second transmission pinion 186 is coupled to the inner transmission shaft 182. The second transmission pinion 186 is made of metal or a metal alloy and can be forged, cast, additively manufactured, etc. The second transmission pinion 186 has an inner diameter 252 and an outer diameter 254. A spline 239 is defined on the inner diameter 252 and connects the second transmission pinion 186 to the inner transmission shaft 182. The second transmission pinion 186 also has a third transmission end 256 opposite to a fourth transmission end 258. The third transmission end 256 is adjacent to the first transmission pinion 184 and inhibits or restricts axial movement of the outer transmission shaft 180 relative to the inner transmission shaft 182. The fourth transmission end 258 is spaced apart from one of the bearings 188. In one example, the second transmission pinion 186 is a helical gear and has a plurality of second helical gear teeth 260 defined on the outer diameter 254. (Return to reference) Figure 2The second transmission pinion 186 has a central axis C6, and the second helical gear teeth 260 are arranged with a first helix angle 158, which is defined between the central axis C6 and a line tangent to one of the teeth of the second helical gear 260. The second transmission pinion 186 is driven by the inner transmission shaft 182 and drives the second helical differential gear 262 of the differential assembly 106. By providing the first transmission pinion 184 with a second helix angle 172 that is opposite to and equal to that of the second transmission pinion 186 having the first helix angle 158, the axial load acting on the transmission shaft assembly 104 is reduced or canceled due to the opposite directions of the first helix angle 158 and the second helix angle 172, and the torsional tuning of the inner shaft 110 and the outer shaft 22. By eliminating or canceling the axial load acting on the transmission shaft assembly 104, the first transmission pinion 184 and the second transmission pinion 186 reduce the mechanical friction associated with the transmission shaft assembly 104.

[0042] In this example, the transmission shaft assembly 104 includes two bearings 188. One bearing 188 is coupled to a first transmission shaft end 220 of the outer transmission shaft 180, and the other bearing 188 is coupled to a second transmission shaft end 222 of the outer transmission shaft 180. The bearings 188 support the outer transmission shaft 180 for rotation. In this example, each bearing 188 is a roller bearing; however, any bearing can be used, including but not limited to ball bearings. The bearings 188 can be coupled to a housing associated with the low-friction drive system 100.

[0043] Differential assembly 106 is coupled to transmission shaft assembly 104. Transmission shaft assembly 104 transmits speed and torque to differential assembly 106. In one example, differential assembly 106 includes a first helical differential gear 250, a second helical differential gear 262, a differential gear set 270, a first output shaft 274, a second output shaft 276, and one or more bearings 278.

[0044] The first helical differential gear 250 is coupled to and driven by the first transmission pinion 184. The first helical differential gear 250 is made of metal or a metal alloy and can be forged, cast, additively manufactured, etc. In one example, the first helical differential gear 250 is a helical ring gear. (See reference...) Figure 5 The first helical differential gear 250 has a first differential gear inner diameter 280 and a first differential gear outer diameter 282. The first differential gear inner diameter 280 is coupled to the differential gear set 270 and cooperates with the second helical differential gear 262 to drive the differential gear set 270. A plurality of helical gear teeth 284 are defined on the first differential gear outer diameter 282. (Return to reference) Figure 2The first helical differential gear 250 has a central axis C7, and the helical gear teeth 284 are arranged with a first helix angle 158, which is defined between the central axis C7 and a line tangent to one of the teeth of the helical gear 284.

[0045] The second helical differential gear 262 is coupled to and driven by the second transmission pinion 186. The second helical differential gear 262 is made of metal or a metal alloy and can be forged, cast, additively manufactured, etc. In one example, the second helical differential gear 262 is a helical ring gear. (See reference...) Figure 5 The second helical differential gear 262 has a second differential gear inner diameter 290 and a second differential gear outer diameter 292. The second differential gear inner diameter 290 is coupled to the differential gear set 270 and cooperates with the first helical differential gear 250 to drive the differential gear set 270. A plurality of helical gear teeth 294 are defined on the second differential gear outer diameter 292. (Return to reference) Figure 2 The second helical differential gear 262 has a central axis C8, and the helical gear teeth 294 are arranged with a second helix angle 172, which is defined between the central axis C8 and a line tangent to one of the helical gear teeth 294. By providing the second helical differential gear 262 with a second helix angle 172 that is opposite to and equal to that of the first helical differential gear 250 having a first helix angle 158, the axial load acting on the differential assembly 106 is reduced or canceled due to the opposite directions of the first helix angle 158 and the second helix angle 172, and the torsional tuning of the inner shaft 110 and the outer shaft 22. By eliminating or canceling the axial load acting on the differential assembly 106, the first helical differential gear 250 and the second helical differential gear 262 reduce the mechanical friction associated with the differential assembly 106.

[0046] Return to reference Figure 5 In one example, the differential gear set 270 includes a carrier 300, a first sun gear 302, a second sun gear 304, and a pair of planetary gears 306. The carrier 300 is coupled to each of a first helical differential gear 250 and a second helical differential gear 262. The carrier 300 is driven by the first helical differential gear 250 and the second helical differential gear 262. The carrier 300 is coupled to the planetary gears 306. Rotation of the carrier 300 about the axis of the carrier 300 causes rotation of the planetary gears 306. The carrier 300 can have any desired shape and is made of metal or a metal alloy. The carrier 300 can be cast, additively manufactured, forged, etc.

[0047] The first sun gear 302 is coupled to the first output shaft 274. In one example, the first sun gear 302 is a bevel gear comprising a plurality of first bevel gear teeth 310. The first sun gear 302 is made of metal or a metal alloy and may be cast, machined, forged, additively manufactured, etc. The first bevel gear teeth 310 engage with a plurality of planetary bevel gear teeth 312 of the planetary gear 306, such that the planetary gear 306 drives the first sun gear 302 by rotation of the carrier 300. Rotation of the first sun gear 302 in turn causes the first output shaft 274 to rotate, thereby moving or rotating the corresponding front wheel 16.

[0048] The second sun gear 304 is coupled to the second output shaft 276. In one example, the second sun gear 304 is a bevel gear comprising a plurality of second bevel gear teeth 314. The second sun gear 304 is made of metal or a metal alloy and can be cast, machined, forged, additively manufactured, etc. The second bevel gear teeth 314 engage with the planetary bevel gear teeth 312 of the planetary gear 306, such that the planetary gear 306 drives the second sun gear 304 by the rotation of the carrier 300. The rotation of the second sun gear 304, in turn, causes the second output shaft 276 to rotate, thereby moving or rotating the corresponding front wheel 16.

[0049] Each planetary gear 306 is connected to a carrier 300. In one example, each planetary gear 306 is a bevel gear and includes planetary bevel gear teeth 312. Each planetary gear 306 is made of free metal or metal alloy and can be cast, machined, forged, additively manufactured, etc. Each planetary gear 306 drives a first sun gear 302 and a second sun gear 304. Each planetary gear 306 is also connected to the carrier 300 to be rotatable about a planetary gear axis. When the first output shaft 274 rotates at a different speed than the second output shaft 276, for example during the turning of the front wheel 16, each planetary gear 306 can rotate about a planetary gear axis via either the first sun gear 302 or the second sun gear 304.

[0050] The first output shaft 274 is connected to the first sun gear 302. The first sun gear 302 is fixedly connected to the first output shaft 274, such that the rotation of the first sun gear 302 drives the first output shaft 274. The first output shaft 274 is made of metal or metal alloy, and is cast, machined, forged, etc. The first output shaft 274 is connected to the corresponding front wheel 16.

[0051] The second output shaft 276 is connected to the second sun gear 304. The second sun gear 304 is fixedly connected to the second output shaft 276, such that the rotation of the second sun gear 304 drives the second output shaft 276. The second output shaft 276 is made of metal or a metal alloy, and is cast, machined, forged, etc. The second output shaft 276 is connected to the corresponding front wheel 16.

[0052] In this example, the differential assembly 106 includes two bearings 278. One bearing 278 is connected to the carrier 300 near the first output shaft 274, and the other bearing 278 is connected to the carrier 300 near the second output shaft 276. In this example, each bearing 278 is a roller bearing; however, any bearing can be used, including but not limited to ball bearings. The bearings 278 support the carrier 300 for rotation. The bearings 278 can be coupled to a housing associated with the low-friction drivetrain 100.

[0053] In one example, refer to Figure 2 To assemble the low-friction transmission system 100, with the connection point 112 between the inner shaft 110 and the outer shaft 22 predetermined, the inner shaft 110 is connected to the outer shaft 22 of the propulsion system 20 at the connection point 112. A first pinion 116 and a second pinion 118 are connected to the inner shaft 110. A bearing 114 is connected to the outer shaft 22. A coupling system 120 is connected to the inner shaft 110 to securely connect the inner shaft 110 to the outer shaft 22. An inner transmission shaft 182 is positioned within the outer transmission shaft 180. A first helical gear 160 is connected to the outer transmission shaft 180, and a first transmission pinion 184 is connected to the outer transmission shaft 180. A second helical gear 174 is connected to the inner transmission shaft 182, and a second transmission pinion 186 is connected to the inner transmission shaft 182. A bearing 188 is connected to the inner transmission shaft 182. With planetary gear 306 engaged with carrier 300, differential gear set 270 is assembled, and first helical differential gear 250 is engaged with carrier 300. Second helical differential gear 262 is engaged with carrier 300. Output shafts 274, 276 are engaged with the corresponding front wheels 16. If desired, one or more housings may be engaged around low-friction drivetrain 100 to enclose it.

[0054] When the low-friction transmission system 100 is assembled into the propulsion system 20 and connected to the front wheel 16, when the propulsion system 20 drives the outer shaft 22, refer to Figure 6The inner shaft 110 rotates at the same speed and torque as the outer shaft 22. The rotation of the inner shaft 110 drives the first pinion 116 and the second pinion 118. The rotation of the first pinion 116 drives the first helical gear 160, which in turn drives the outer transmission shaft 180. The rotation of the second pinion 118 drives the second helical gear 174, which in turn drives the inner transmission shaft 182. The rotation of the outer transmission shaft 180 drives the first transmission pinion 184, which in turn drives the first helical differential gear 250. The rotation of the inner transmission shaft 182 drives the second transmission pinion 186, which in turn drives the second helical differential gear 262. The rotation of the first helical differential gear 250 and the second helical differential gear 262 causes the carrier 300 to rotate. The rotation of the carrier 300 causes the planetary gear 306 to rotate, which in turn causes the first sun gear 302 and the second sun gear 304 to rotate. The rotation of the first sun gear 302 drives the first output shaft 274, which in turn causes the corresponding front wheel 16 to rotate. The rotation of the second sun gear 304 drives the second output shaft 276, which in turn causes the corresponding front wheel 16 to rotate.

[0055] When the inner shaft 110 is connected to the outer shaft 22 at the predetermined connection point 112 based on the torsional tuning of the low-friction transmission system 100, return to reference. Figure 2 Due to the opposite first helix angle 158 and second helix angle 172, the first pinion 116 and second pinion 118 cooperate to counteract the axial load acting on the input shaft assembly 102; due to the corresponding opposite first helix angle 158 and second helix angle 172, the first helical gear 160, the second helical gear 174, the first transmission pinion 184, and the second transmission pinion 186 cooperate to counteract the axial load acting on the transmission shaft assembly 104; and due to the opposite first helix angle 158 and second helix angle 172, the first helical differential gear 250 and the second helical differential gear 262 cooperate to counteract the axial load acting on the differential assembly 106. By counteracting the axial loads acting on the input shaft assembly 102, the transmission shaft assembly 104, and the differential assembly 106, mechanical friction is reduced, which improves the efficiency of the low-friction drive system 100. By improving the efficiency of the low-friction drive system 100, the driving range of the electric motor associated with the propulsion system 20 can be increased, or a smaller battery can be used to power the propulsion system 20. In addition, the use of helical gears 116, 118, 160, 174, 184, 186, 250, and 262 can reduce the noise associated with the operation of the low-friction transmission system 100, because helical gears are generally quieter than other gears (such as spur gears) during operation.

[0056] It should be noted that although the low-friction drive system 100 is described herein as comprising multiple torsionalally tuned shafts, the low-friction drive system 100 can be configured in different ways to transmit torque from the propulsion system 20 to the front wheel 16. For example, refer to Figure 7 This illustrates a low-friction transmission system 400. Because the low-friction transmission system 400 includes components related to... Figures 1 to 6 The low-friction transmission system 100 discusses components that are the same or substantially similar to those components, therefore the same reference numerals will be used to denote the same or substantially similar components.

[0057] In one example, the low-friction drivetrain 400 includes an input shaft assembly 102, a transmission shaft assembly 404, and a differential assembly 106. The low-friction drivetrain 400 may also include a housing to enclose the components of the low-friction drivetrain 400. The input shaft assembly 102 receives input torque from the propulsion system 20. Figure 7 In one example, the low-friction drivetrain 400 includes an input shaft assembly 102 and a differential assembly 106, which are torsionalally tuned and axially balanced such that axial loads acting on the input shaft assembly 102 and the differential assembly 106 are substantially offset to reduce friction associated with the low-friction drivetrain 400. A transmission shaft assembly 404 is coupled between the input shaft assembly 102 and the differential assembly 106. The transmission shaft assembly 404 transmits speed and torque from the input shaft assembly 102 to the differential assembly 106. In one example, the transmission shaft assembly 404 includes a first helical gear 160, a second helical gear 174, an outer transmission shaft 180, an inner transmission shaft 182, a first transmission pinion 184, a second transmission pinion 186, and a bearing 188. In this example, the inner transmission shaft 182 is not located within the outer transmission shaft 180 but is spaced apart from the first transmission shaft 182.

[0058] Due to the assembly and use of the low-friction transmission system 400 and related to Figures 1 to 6 The assembly and use of the low-friction drive system 100 discussed are essentially the same; therefore, the differences in the assembly and use of the low-friction drive system 400 will be briefly discussed. In the example of the low-friction drive system 400, with the input shaft assembly 102 assembled, a first helical gear 160 and a first transmission pinion 186 are connected to the outer transmission shaft 180. A second helical gear 174 and a second transmission pinion 186 are connected to the inner transmission shaft 182. The first helical gear 160 is connected to the first pinion 116, and the first transmission pinion 184 is connected to the second helical differential gear 262 to transmit torque from the input shaft assembly 102 to the differential assembly 106. The second helical gear 174 is connected to the second pinion 118, and the second transmission pinion 186 is connected to the first helical differential gear 250 to transmit torque from the input shaft assembly 102 to the differential assembly 106.

[0059] Furthermore, it should be noted that while the propulsion system 20 is described herein as including a single electric motor driving the outer shaft 22, in other embodiments, the propulsion system 20 may include multiple electric motors, such as two electric motors. In the example where the propulsion system 20 includes two electric motors, the first electric motor may include an outer shaft 22 and an inner shaft 110, the inner shaft 110 being coupled to a first pinion 116 to drive the first pinion 116, while the output shaft of the second electric motor may be coupled to a second pinion 118 to drive the second pinion 118. In the example using two electric motors, the differential assembly 106 can be omitted, and the first helical differential gear 250 can directly drive the first output shaft 274, and the second helical differential gear 262 can directly drive the second output shaft 276. This arrangement counteracts axial loads, and since the left and right wheels 16 are now disconnected, advanced functions such as torque vectoring control may be possible.

[0060] It should be noted that although this document describes low-friction drive systems 100 and 400 as including splines 126, 127, 131, 194, 196, 204, 206, 226, 227, 237, and 239, splines 126, 127, 131, 194, 196, 204, 206, 226, 227, 237, and 239 can be optional. For example, splines 126, 127, 131, 194, 196, 204, 206, 226, 227, 237, and 239 can be used in conjunction with low-friction drive systems 100 and 400 for high-torque applications.

[0061] Although at least one exemplary embodiment has been presented in the foregoing detailed description, it should be understood that numerous variations exist. It should also be understood that the exemplary embodiments or multiple exemplary embodiments are merely examples and are not intended to limit the scope, applicability, or configuration of this disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient roadmap for implementing the exemplary embodiments or multiple exemplary embodiments. It should be understood that various changes can be made to the function and arrangement of the elements without departing from the scope of this disclosure as set forth in the appended claims and their legal equivalents.

Claims

1. A transmission system for a vehicle, comprising: A first helical pinion with a helix angle is coupled to a first shaft and configured to receive input torque; A second helical pinion having a first helix angle is coupled to a second shaft and configured to receive the input torque, the second shaft being disposed within the first shaft and capable of rotating within the first shaft; as well as A differential assembly includes a third helical gear and a fourth helical gear, the third helical gear having the first helix angle and coupled to a first pinion, and the fourth helical gear having the helix angle and coupled to a second pinion. The third and fourth helical gears are coupled to a differential gear set to drive a first and a second output shaft associated with the vehicle. The helix angle and the first helix angle are opposite and equal angles.

2. The drivetrain of claim 1, further comprising an input shaft assembly coupled to a propulsion system associated with the vehicle, and the input shaft assembly being configured to provide the input torque.

3. The transmission system of claim 2, wherein the first shaft further comprises a first helical gear coupled to the input shaft assembly to receive the input torque, and the first helical gear has the helix angle.

4. The transmission system according to claim 3, wherein the input shaft assembly includes an input shaft and an output shaft, and the input shaft includes a third helical pinion having the first helix angle and connected to the first helical gear.

5. The transmission system of claim 2, wherein the second shaft further comprises a second helical gear coupled to the input shaft assembly to receive the input torque, the second helical gear having the first helix angle, the input shaft assembly comprising an input shaft and an output shaft, and the input shaft comprising a fourth helical pinion having the helix angle and coupled to the second helical gear.

6. The drivetrain of claim 2, wherein the input shaft assembly includes an input shaft disposed within an output shaft associated with the propulsion system of the vehicle, and the input shaft is configured to rotate together with the output shaft at the same speed as the input shaft.

7. The transmission system of claim 6, wherein the input shaft includes a third helical pinion having the helix angle, a fourth helical pinion having the first helix angle, and the input shaft includes a plurality of splines that engage a center hole of the output shaft to connect the input shaft to the output shaft.

8. A vehicle comprising: A propulsion system with an output shaft; The transmission system includes: An input shaft assembly connected to the output shaft; A transmission shaft assembly connected to the input shaft assembly, the transmission shaft assembly including a first shaft and a second shaft, the second shaft being disposed within and rotatable within the first shaft, the first shaft having a first helical gear and a first helical pinion configured to be driven by the input shaft assembly, the second shaft having a second helical gear and a second helical pinion configured to be driven by the input shaft assembly, the first helical gear and the first helical pinion having a helix angle, and the second helical gear and the second helical pinion having a first helix angle; and A differential assembly connected to the transmission shaft assembly includes a third helical gear and a fourth helical gear. The third helical gear has the first helix angle and is connected to a first pinion. The fourth helical gear has the first helix angle and is connected to a second pinion. The third and fourth helical gears are connected to a differential gear set to drive a first and a second output shaft associated with the vehicle. The helix angle and the first helix angle are opposite and equal angles.

9. The vehicle of claim 8, wherein the input shaft assembly includes an input shaft disposed within the output shaft, the input shaft being configured to rotate together with the output shaft at the same speed as the input shaft, the input shaft being coupled to the output shaft at a coupling point to transmit power from the output shaft to the input shaft, and the second shaft being positioned within a central transmission bore of the first shaft.

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