Heavy load transmission architecture design

Abstract

A transmission assembly suitable for use with an electric power device. The transmission assembly includes a number of advantageous features. For example, the transmission assembly may include a robust enclosure having integral mounting features, a bearing assembly that supports the input shaft in a simple support configuration, a thrust mechanism for counteracting counter axial loads generated between the input shaft and the main shaft, and an asymmetric clutch assembly.

Description

[0001] Related Applications

[0002] This application claims priority to Indian Provisional Patent Application Serial No. 202211033623 filed on June 13, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to transmissions and, more particularly, to heavy duty transmissions suitable for electric vehicle applications. Background Art

[0004] Transmission assemblies are known. Typically, a transmission assembly receives power from a powerplant via a rotating output shaft and outputs power via one or more outputs, with the ability to change the gear ratio between the input and output ends. In some examples, the powerplant is an internal combustion engine, while in other examples, the powerplant is an electric motor. When the powerplant is an electric motor in an electric vehicle (EV) application, the transmission assembly may experience different operating conditions and loads, which may reduce the reliability of the transmission assembly. This is especially true for buses, trucks, and off-highway heavy-duty vehicles. Electric machine features such as high speed and high low-end constant torque can meet shallow first gear requirements. The combination of high speed, high load, and very high low gear utilization is unique in the EV application duty cycle compared to traditional engine-driven transmissions. Therefore, traditional transmissions are not suitable for EV applications with traditional configurations. Therefore, it is a challenge to design an architecture to meet all of these requirements within a given space. Summary of the invention

[0005] A transmission assembly may include: a dual countershaft type transmission powertrain gear assembly having an input shaft assembly and an output shaft assembly, the powertrain gear assembly having at least one mechanism for changing the gear ratio between the input shaft assembly and the output shaft assembly; a housing assembly for accommodating the powertrain gear assembly, the housing assembly including a single-piece housing portion, the single-piece housing portion defining: a node mounting structure for mounting the transmission assembly to a vehicle; a mounting device for fixing an electronic control unit; and a mounting device for a shifter assembly.

[0006] In some examples, the enclosure includes a mounting arrangement for supporting a power take-off (PTO) unit.

[0007] In some examples, the enclosure assembly includes a modular mounting interface for receiving adapters of different configurations.

[0008] In some examples, the enclosure assembly further includes a main housing secured to the open end of the enclosure.

[0009] In some examples, the main housing supports the pump assembly and includes at least one lubrication passage.

[0010] In some examples, the at least one lubrication passage is cast within the shallow main housing.

[0011] In some examples, the enclosure is formed from a metallic material.

[0012] In some examples, the enclosure is formed from aluminum.

[0013] In some examples, the PTO unit and the output shaft arrangement are located at a first end of the enclosure.

[0014] In some examples, the PTO unit is driven directly by a layshaft of the powertrain assembly. In some examples, the PTO unit is driven by a lower layshaft.

[0015] A transmission assembly may include: an input shaft assembly, which includes an input shaft extending between a first end and a second end; an output shaft assembly, which includes an output shaft; a powertrain gear assembly, which includes at least one mechanism for changing the gear ratio between the input shaft assembly and the output shaft assembly, wherein the powertrain gear assembly includes a head gear directly connected to the input shaft adjacent to the first end; a bearing assembly, which includes a first bearing assembly supporting the head gear and a second bearing assembly supporting the input shaft adjacent to the second end, wherein the second bearing assembly and the second end of the input shaft are located within an inner cavity of the output shaft.

[0016] In some examples, the head gear has a first connection interface and a second connection interface with the input shaft.

[0017] In some examples, the first connection interface is a spline connection and the second connection interface is a press-fit interface.

[0018] In some examples, the first bearing assembly is press fit onto the head gear.

[0019] In some examples, a thrust mechanism is provided for counteracting opposing axial loads generated between the input shaft and the main shaft.

[0020] In some examples, the main shaft partially surrounds and is coaxially aligned with the input shaft, wherein the thrust mechanism is located between an axial end of the main shaft and an axial surface of one or both of the head gear and the input shaft. In one feature, the main shaft floats between the input shaft and the output shaft and is also held in place by a floating main shaft gear between the countershafts.

[0021] In some examples, the thrust mechanism is supported by one or both of the overrunning gear and the input shaft.

[0022] In some examples, the thrust mechanism is located axially between the first bearing assembly and the second bearing assembly.

[0023] In some examples, the thrust mechanism is at least partially disposed in a cavity formed between the head gear and the input shaft.

[0024] In some examples, a power take-off (PTO) unit is provided.

[0025] A transmission assembly may include: an input shaft assembly, which includes an input shaft extending between a first end and a second end; an output shaft assembly, which includes an output shaft; a powertrain gear assembly, which includes at least one mechanism for changing the gear ratio between the input shaft assembly and the output shaft assembly, wherein the powertrain gear assembly includes an overrunning gear directly connected to the input shaft adjacent the first end; and a thrust mechanism for offsetting opposing axial loads generated between the input shaft and the output shaft.

[0026] In some examples, the thrust mechanism is supported by one or both of the overrunning gear and the input shaft.

[0027] In some examples, the thrust mechanism is located axially between a first bearing assembly and a second bearing assembly supporting the input shaft.

[0028] In some examples, the thrust mechanism is at least partially disposed in a cavity formed between the head gear and the input shaft.

[0029] In some examples, a power take-off (PTO) unit is provided.

[0030] In some examples, the thrust mechanism includes a plurality of cylindrical rollers disposed between a pair of thrust washers.

[0031] In some examples, the thrust mechanism includes bearings positioned about the input shaft.

[0032] In some examples, the thrust mechanism includes a tapered race adjacent to one of a pair of thrust washers and a spherical washer adjacent to the tapered race.

[0033] In some examples, the thrust mechanism includes a wave spring positioned between the overmount gear and one of the pair of thrust washers.

[0034] In some examples, the input shaft assembly is configured to operate at speeds up to 5,000 revolutions per minute.

[0035] A transmission assembly may include: an input shaft assembly, which includes an input shaft extending between a first end and a second end; an output shaft assembly, which includes an output shaft; and a gear train assembly for changing a gear ratio between the input shaft and the output shaft, the gear train assembly including: a head gear fixed to the input shaft, the head gear meshing with a first countershaft gear and defining a first internal drive interface; a drive gear meshing with a second countershaft gear and defining a second internal drive interface; a main shaft, which meshes with the output shaft, the main shaft defining a first external drive interface; and a clutch assembly, which includes a sleeve member slidably disposed around the main shaft, the sleeve member defining a third internal drive interface engaged with the first external drive interface of the main shaft, the sleeve member defining a first external gear spline for engaging with the first internal drive interface and a second external gear spline for engaging with the second internal gear, wherein the first external gear spline has a first diameter and the second external gear spline has a second diameter different from the first diameter.

[0036] In some examples, the first diameter is smaller than the second diameter.

[0037] In some examples, the first external gear splines are spaced apart from the second external gear splines to form a channel for receiving a shift fork.

[0038] In some examples, when the sleeve member is in the first position, the first external gear spline is at least partially received within the head gear.

[0039] In some examples, when the sleeve member is in the second position, the second external gear splines are at least partially received within the drive gear.

[0040] In some examples, the sleeve member abuts the thrust washer when in the second position.

[0041] In some examples, when in the first position, the sleeve member abuts the head gear surface.

[0042] In some examples, a thrust mechanism is provided for counteracting opposing axial loads generated between the input shaft and the main shaft.

[0043] In some examples, the thrust mechanism is at least partially received within the sleeve member when the sleeve member is in the first position.

[0044] In some examples, when the sleeve member is in the first position, the first external gear spline is at least partially received in the head gear.

[0045] In some examples, a power take-off (PTO) unit is provided.

[0046] Other objects and advantages will be set forth in part in the description that follows, and in part will be obvious from the description, or can be learned by practicing the teachings presented herein. Objects and advantages will also be realized and obtained by means of the elements and combinations particularly pointed out in the appended claims. It should be understood that the foregoing general description and the following detailed description are exemplary and illustrative only and do not limit the claimed invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a first perspective view of a transmission assembly having features of an example according to aspects of the principles of the present disclosure, the transmission assembly being configured for operation with a PTO unit.

[0048] Figure 2 yes Figure 1 A second perspective view of a transmission assembly is shown configured to be mounted with a PTO unit.

[0049] Figure 2A yes Figure 1 A second perspective view of the transmission assembly is shown.

[0050] Figure 3 yes Figure 1 A perspective exploded view of the transmission assembly is shown.

[0051] Figure 4 yes Figure 1 A first perspective view of a rear enclosure portion of a transmission assembly is shown.

[0052] Figure 5 is a second perspective view of the capsule.

[0053] Figure 6 yes Figure 1 An end view of an adapter housing of a transmission assembly is shown.

[0054] Figure 7 yes Figure 6 A partial cross-sectional side view of the adapter is shown.

[0055] Figure 8 yes Figure 1 An end view of the shallow main housing of the transmission assembly is shown.

[0056] Fig. 9 yes Figure 1 A cross-sectional view of a transmission assembly is shown.

[0057] Fig.10 yes Figure 1 A partial cross-sectional view of a transmission assembly is shown illustrating the bearing support of an input shaft of the transmission assembly.

[0058] Fig.11 yes Figure 1A partial cross-sectional view of a transmission assembly is shown schematically illustrating the transfer of PTO loads.

[0059] Fig.12 yes Figure 1 A partial cross-sectional view of the transmission assembly is shown schematically illustrating the radial and moment loads on the input shaft and attached overdrive gear under PTO loading conditions.

[0060] Fig.13 yes Figure 1 A partial side cross-sectional view of a transmission assembly is shown illustrating the connection between the overrunning gear and the input shaft.

[0061] Fig.14 yes Figure 1 A partial cross-sectional end view of a transmission assembly is shown illustrating the connection between the overmount gear and the input shaft.

[0062] Fig.15 yes Figure 1 A partial side cross-sectional view of a transmission assembly is shown illustrating the thrust mechanism, alignment aspects, and operating forces.

[0063] Fig.16 yes Figure 1 A partial side cross-sectional view of the transmission assembly is shown, further illustrating the thrust mechanism.

[0064] Fig.17 yes Figure 1 A partial side cross-sectional view of the transmission assembly is shown, further illustrating the thrust mechanism.

[0065] Fig.18 yes Figure 1 A partial side cross-sectional view of a transmission assembly is shown illustrating normal operating torques and moments.

[0066] Fig.19 yes Figure 1 A partial side cross-sectional view of a transmission assembly is shown illustrating PTO operating torque and moments.

[0067] Fig. 20 yes Figure 1 A partial side cross-sectional view of the transmission assembly is shown, further illustrating a spindle abutment surface for the spindle assembly.

[0068] Fig.21 yes Figure 1 A partial side cross-sectional view of a transmission assembly is shown illustrating the thrust forces generated in a driven state.

[0069] Fig. 22 yes Figure 1 A partial side cross-sectional view of a transmission assembly is shown illustrating thrust generated during a coasting condition.

[0070] Fig.23 yes Figure 1 A partial side cross-sectional view of a transmission assembly is shown illustrating a sliding clutch assembly of the transmission assembly.

[0071] Fig.24 yes Fig.23 A perspective view of the slip clutch of the assembly is shown.

[0072] Fig.25 yes Fig.24 A cross-sectional side view of a slip clutch is shown.

[0073] Fig.26 yes Fig.24 A partial end view of a slip clutch is shown.

[0074] Fig. 27 yes Fig.24 A partial side cross-sectional view of a slip clutch is shown.

[0075] Fig.28 yes Fig.24 A cross-sectional end view of a slip clutch is shown.

[0076] Fig.29 yes Figure 1 A perspective view of a thrust washer of a transmission assembly is shown.

[0077] Fig.30 yes Fig.24 A partial view of a slip clutch is shown, illustrating the reverse taper angle.

[0078] Fig.31 yes Fig.23 A partial cross-sectional view of the head gear is shown.

[0079] Fig.32 yes Fig.31 A cross-sectional end view of the head mounted gear is shown.

[0080] Fig.33 yes Figure 1 A partial cross-sectional side view of a transmission assembly is shown illustrating the maximum thrust area between the sliding sleeve and the thrust washer.

[0081] Fig.34 yes Figure 1 A partial cross-sectional side view of a transmission assembly is shown, illustrating clearance with the thrust assembly.

[0082] Fig.35 yes Figure 1 A perspective view of a transmission assembly is shown with the closeout housing shown transparent to illustrate the lubrication delivery path.

[0083] Fig.36 yes Fig.35 A second perspective view of the transmission assembly is shown.

[0084] Fig.37 yes Fig.35 A partial perspective view of a transmission assembly is shown.

[0085] Fig.38 yes Fig.37 A cross-sectional view of a portion of a transmission assembly is shown.

[0086] Fig.39 yes Fig.37 A cross-sectional view of a portion of a transmission assembly is shown.

[0087] Fig.40 yes Figure 1 A cross-sectional view of a portion of a transmission assembly is shown, further illustrating the lubrication delivery path.

[0088] Fig.40A yes Figure 1 A cross-sectional view of a portion of a transmission assembly is shown, further illustrating the lubrication delivery path.

[0089] Fig.41 yes Figure 1 A cross-sectional view of a portion of a transmission assembly is shown, and as Fig.36 and 42 , further showing the lubrication delivery path.

[0090] Fig.42 yes Figure 1 A cross-sectional view of a pump assembly of a transmission assembly.

[0091] Fig.43 yes Figure 1 A partially exploded perspective view of a portion of a transmission assembly showing closure and sealing features of the assembly. DETAILED DESCRIPTION

[0092] The present disclosure relates to transmission assemblies for use in a variety of applications.

[0093] Transmission assembly 10 overall description

[0094] Reference Figure 1-34 , an exemplary transmission assembly 10 of the present disclosure is shown. In the example presented, and as in Figure 1-3 As best seen in Figures 9 and 10 , the transmission assembly 10 is configured as a dual layshaft design.

[0095] In one aspect, the transmission assembly 10 is provided with a housing assembly 100 for housing internal components of the transmission assembly 10 and for supporting external components fixed to the housing 100. As shown, the housing assembly 100 externally supports a main power output assembly 110 and a power take-off unit (PTO) 120, a shifter assembly 130, an electronic controller 140 for controlling the shifter assembly 130 and communicating with the vehicle (e.g., via a CAN bus), and an I / P sensor 142. At an end opposite to the main power output assembly 110 and the PTO 120, a shallow main housing 150 is fixed to the housing assembly 100, and an adapter housing 160 is fixed to the shallow main housing.

[0096] Internally, the transmission assembly is configured with a powertrain 165 that includes an input shaft assembly 170, a main shaft assembly 180 extending on the input shaft 170, and an output shaft assembly 190 splined to the main shaft assembly 180. In one aspect, the assemblies 170, 180, and 190 are coaxially aligned together. An overgear 200 is mounted to the input shaft assembly 170, and first and second sliding clutch assemblies 210, 220 are splined to the main shaft assembly 180 in a sliding manner. Also shown are progressively larger drive gear assemblies 230, 240, and 250 that are coaxially aligned with the main shaft assembly 180. The transmission assembly 10 also includes a pair of countershafts 260, 270 that are disposed on opposite sides of the shaft assemblies 170, 180, 190 and have progressively smaller associated gears or gear assemblies 262 / 272, 264 / 274, 266 / 276, 268 / 278. In the example shown, gears 262 / 272 and 264 / 274 are formed independently of and mounted to their respective shafts 260, 270, while gears 266 / 276, 268 / 278 are formed integrally with their respective shafts 260, 270. According to the configuration, gear assembly 262 / 272 meshes with head mounted gear assembly 200, gear assembly 264 / 274 meshes with drive gear 230, gear assembly 266 / 276 meshes with drive gear 240, and gear assembly 268 / 278 meshes with drive gear 250. In the example presented, the disclosed gears are helical gears, wherein the gears are provided with teeth cut at an oblique angle to the axis of rotation of the gears, such that the contact line between the intermeshing gears is also oblique or non-parallel to the axis of rotation. It should be noted that the clutch assemblies 210 , 220 are provided with outwardly facing spur teeth or splines that interact with corresponding inwardly facing spur teeth or splines on the head gear 200 and the drive gears 230 , 240 , 250 .

[0097] In operation, the shifter assembly 130 operates the shift shaft assembly 135 to selectively operate the first and second sliding clutch assemblies 210, 220, so that the first clutch assembly 210 engages the main shaft assembly 180 with the head gear assembly 200 or the drive gear 230 to respectively achieve the third and fourth gear ratios between the input shaft assembly 170 and the output shaft assembly 190, or the second clutch assembly 220 engages the main shaft assembly 180 with the drive gear 240 or the drive gear 250 to respectively achieve the first and second gear ratios between the input shaft assembly 170 and the output shaft assembly 190. In the illustrated configuration, the countershaft 270 provides power to the PTO 120 via the spline connection 270a, which receives rotational power at a gear ratio set between the head gear 200 and the gear assembly 262. Fig. 9A Four different gears or gear ratios are schematically depicted between which the transmission assembly 10 is operable. Fig.11 The power transmission from the input shaft 170 to the PTO load is schematically shown, and Fig.12 The resulting load forces are shown.

[0098] The transmission assembly 10 is also shown to include an internal pump assembly 290 driven by the powertrain for circulating lubricating fluid throughout the assembly. The transmission assembly 10 is also shown to include various bearing assemblies for supporting the shaft assemblies. For example, bearing assembly 300 is shown to support the output shaft assembly 190, bearing assembly 310 is shown to support the head gear 200 and the input shaft assembly 170, bearing assembly 320 is shown to support the input shaft assembly 170 within the output shaft assembly 190, bearing assemblies 330, 340 are shown to support the layshaft 260, and bearing assemblies 350, 360 are shown to support the layshaft 270. In the example shown, the bearing assemblies are shown as radial bearings, such as radial ball bearings and radial needle bearings. Other bearing types are also possible. Reference Fig. 9 and 43, it can be seen that anti-rotation features 332, 342, 352, 362 are provided for receiving bearing assemblies 330, 340, 350, 360, respectively. Anti-rotation features 332, 352 are received in openings in rear enclosure portion 102, while anti-rotation features 342, 362 are received in openings in shallow main housing 150. In one example, the anti-rotation features are formed of a different material than the enclosure material and provide a more dimensionally stable structure for supporting bearings 330, 340, 350, 360. In one example, rear enclosure portion 102 and shallow main housing 150 are formed of aluminum, anti-rotation features 332, 342, 352, 362 are formed of cast iron, and bearing assemblies 330, 340, 350, 360 are made of steel. With this arrangement, the anti-rotation feature is formed of a material having a low coefficient of thermal expansion compared to the material of the enclosure portion and the main housing, thereby improving the installation of the bearing assembly, which reduces or eliminates the problem of bearing creep at elevated temperatures under operating conditions. As shown, the anti-rotation features 332, 342, 352, 362 are provided with rib structures that interact with the rib structures formed in the rear enclosure portion 102 and the shallow main housing 150 so that when the anti-rotation feature is inserted into the rear enclosure portion 102 and the shallow main housing 150, the anti-rotation feature cannot rotate relative to the enclosure. Anti-rotation features 302 and 312 may also be provided for bearings 300 and 310. In the example shown, the anti-rotation features 302, 312 are provided in the form of O-rings that are disposed between the enclosure opening and the bearing assemblies 300, 310.

[0099] The transmission assembly is also shown to include cover assemblies 370 , 380 and 390 for covering openings in the rear enclosure portion 102 associated with the output shaft 190 and the countershafts 260 , 270 , respectively.

[0100] In one aspect, a thrust mechanism 280 is disposed between the input shaft assembly 170 and the main shaft assembly 180. The thrust mechanism 280 will be described in greater detail in a later section of this disclosure.

[0101] Encapsulation Subsystem Architecture

[0102] Reference Figure 1-8 , the enclosure subsystem architecture is now described in more detail. In one aspect, the enclosure assembly 100 may be characterized as including a single main rear enclosure portion 102 to which a shallow main housing 150 is attached, and may also be characterized as additionally including an adapter housing 160. The enclosure assembly 100 may also be characterized as including a cover assembly 370, 380, 390.

[0103] Reference Figure 4 and 5, the rear enclosure portion 102 is shown separately. In one aspect, the architecture of the enclosure assembly 100 is configured as a dual layshaft design and has sufficient structural integrity and comprehensive NVH aspects (noise, vibration, harshness) for electric vehicle applications with a torque capacity of 2600Nm or greater. In this configuration, the rear enclosure portion 102 is compatible with an adapter housing 160, which has an SAE #1 and #2 configuration for accommodating a corresponding flywheel and providing a bolt connection device for fixing to the vehicle and / or power plant. In one aspect, the rear enclosure portion 102 has a nominal or average wall thickness of 5.5 mm and strength-enhancing ribs, which help to give the rear enclosure portion 102 the above-mentioned structural characteristics. The rear enclosure portion 102 also has a curved surface design with smooth transitions between surfaces to eliminate or reduce the accumulation of debris, dust, ice and water, for example. In one example, the rear enclosure portion 102 is formed of a metal material such as low-pressure die-cast A-356 aluminum.

[0104] The enclosure assembly 100 has many other advantageous features. For example, the enclosure assembly 100 has: a node mounting arrangement; a mounting arrangement for the electronic control unit (ECU) 140; a lubricated creep track; a lubrication channel, a rear mounted PTO interface design; and a design that meets a pass-by noise level target of 79 dBA. In addition, the disclosed design improves ease of assembly, provides easy access to the shift system and pump assembly and powertrain components, and makes the total system weight less than 200 kg. The disclosed design also includes mounting position configurations derived from SAE node mounting and OEM requirements. In addition, a sealing joint interface feature is provided to account for heat changes caused by gear meshing. Another feature is a restriction or anti-rotation mechanism between the housing and the bearing to avoid bearing creep.

[0105] The disclosed enclosure assembly 100 has many advantages over conventional enclosure assembly configurations. For example, the disclosed design provides integrated covers for the front countershaft and input shaft - limited space accessibility due to SAE #2; flexible adapter enclosure design, where a variety of different motor configurations can be used, including non-standard motor interfaces, input shaft lengths and spline configurations; adaptability of the adapter housing between SAE #2 and SAE #1 flanges; lubricated creep track, which avoids the need for additional sealing joints (in-pump installation); easy assembly (accessibility) of powertrain components, shifting system and pump assembly; adaptability to powertrain architectures with higher center distance (CD) of 155 mm; node mounting arrangement according to SAE J1134; provision of rear-biased PTO; and easy serviceability at the OEM end.

[0106] Reference Figure 3-5, it can be seen that the rear enclosure portion 102 is provided with a first opening 102a and a bolt hole arrangement structure 102b for fixing to the shallow main housing 150, and is provided with openings 102c, 102d, 102e coaxially aligned with the shaft assemblies 170, 180, 190. These openings are provided with bolt hole arrangements 102f, 102g, 102h so that in addition to the main power output assembly 110 and the PTO 120, the cover assemblies 370, 380, 390 can also be fixed to the rear enclosure portion 102. The rear enclosure portion 102 is also provided with a top opening 102i and a bolt hole arrangement structure 102j for receiving and fixing the shifter assembly 130. In one aspect, the rear enclosure portion 102 is also provided with a direct mounting device 108, having separate mounting points 108a, 108b, 108c, so that the ECU 140 can be directly mounted to the rear enclosure portion 102. By providing a direct mounting arrangement in the configuration shown, reliability, accessibility, and NVH performance of the ECU may be improved while reducing cost by avoiding the need for a separate mounting bracket. The rear enclosure portion 102 may have further ports and mounting features to support various other features of the transmission assembly 10 .

[0107] In one aspect, the rear enclosure portion 102 is provided with a pair of opposing node mounting flange structures 104 that are integrally formed with the rear enclosure portion 102. In one aspect, the node mounting flange structures 104 are SAE J1134 node mounting flanges with 4xM20 bolt configurations on both sides. The node mounting flange structures 104 provide rigid support for the transmission assembly 10 and are connected to the vehicle chassis via brackets and rubber reinforcements. The node mounting flange structures 104 are also provided with drainage features 104a to help drain water and / or ice that accumulates on top of the transmission assembly 10.

[0108] In one aspect, the enclosure is provided with a lifting device 106 having sub-devices 106a, 106b. Sub-devices 106a and 106b may be configured as through holes for receiving pins or hooks, or as threaded openings for receiving bolts or other types of threaded members. All or part of the lifting device 106 may also be used to provide rigid support for the transmission harness to prevent loosening due to vibration.

[0109] As previously described, the PTO 120 can be mounted to the rear enclosure portion 102 via the mounting arrangement 102h. The provision of the PTO 120 enables the transmission assembly 10 to operate auxiliary applications. In the example shown, an insert 122 is provided between the rear enclosure portion 102 and the PTO 120 to facilitate the installation of the PTO 120. By providing a direct mounting location for the PTO to the rear enclosure portion 102, a significant amount of space can be saved. Therefore, the disclosed design can be configured to more easily meet OEM requirements.

[0110] Lubrication circuit

[0111] refer to Figures 6 to 8 and Figures 35 to 42 , further describing in detail the features associated with the lubrication circuit. As previously described, the transmission assembly 10 includes an internal pump assembly 290, which is supported by the shallow main housing 150 and therein. In one aspect, the pump assembly 290 includes an inlet 290a and an outlet 290b. The pump assembly also includes an inner meshing rotor / cycloidal rotor 292 for generating pressure and flow from the inlet 290a to the outlet 290b. In one aspect, the inlet 290a is a portion of a support base 290c attached to the shallow main housing 150 and is surrounded by the bottom portion of the rear housing portion 102, which defines an oil sump area. Therefore, the pump assembly 290 draws lubricant that is gathered or collected at the bottom of the rear housing portion 102 into the inlet 290a and delivers the fluid to the outlet 290b. In one aspect, the pump assembly 290 includes a gear 294 connected to the cycloidal rotor 292 via a shaft 295. Gear 294 is driven by a drive gear 296 which is pressed or otherwise attached to gear 262 associated with countershaft 260. Thus, the impeller speed has a fixed ratio relative to the input shaft speed. From pump assembly 290, lubricant flows from outlet 290b into creep track 152 (cast in shallow main housing 150 as shown) and into lower lubrication tube 156. In one aspect, tube 156 is supported into the pump housing at the front end and into the rear housing at the rear end and directs oil to the rear bearing cap passage ports to assist in lubricating the countershaft rear bearing 330. Creep track 152 provides a lubricant flow path for the front bearing assemblies 310, 340, 360 and is connected to upper lubrication tube 154 where lubricant is delivered to the rear bearing assembly 330 after delivering the lubricant to the gear mesh points between the gears via intermediate ports. In one aspect, tube 154 is connected into the shallow main housing 150 and supported by features in the rear housing to direct lubricant to the lower countershaft rear bearing 350 through the bearing cap 390. The lower lubrication tube 156 delivers lubricant to the bearing 350 after delivering the lubricant to the gear mesh point between the gears via the intermediate port. The lubricant also flows through the internal passage 171 in the input shaft 172, through the path 171a in the input shaft 172 and the lubrication path 162 defined in the adapter plate 160, and then flows to the thrust mechanism 280, the thrust washer and the bearing assembly 320, 300, and then returns to the oil pan portion of the rear housing portion 102. The adapter plate 160 is also configured with ports to release the lubricant into the oil pan. Reference Fig.40A The lubrication circuit is also shown to include a pressure relief passage 163 in the adapter plate 160 that drains excess oil back to the oil pan while reducing back pressure on the front seal 173 associated with the input shaft 172 . Fig.40AAlso shown is a plug 175 provided at one end of the channel 171 . Fig.13 The plug 175 is shown in more detail, where it can be seen that an O-ring seal 175 a is also provided in the groove of the plug 175 to form a seal between the passage 171 and the plug 175 .

[0112] Input shaft and head gear

[0113] Reference Figure 9-15 , aspects of the input shaft and head-mounted gear assembly are now described in more detail. Misalignment / misalignment / misplacement of the prime mover drive shaft with respect to the transmission centerline is a very critical factor in defining the reliability of the transmission. In addition, the unbalance and misalignment forces generated due to PTO and pump operations make the transmission input shaft design more challenging for the durability of the transmission. The robust input shaft design disclosed herein plays a decisive role in minimizing the risks associated with such misalignment / misalignment. The disclosed input shaft assembly design has a splined head-mounted drive gear and a simple support bearing at the rear end of the transmission, thereby creating a robust architecture to reduce radial displacement of the head-mounted drive gear, thereby improving reliability. By supporting the ends of the input shaft with two bearing assemblies and increasing the overlap of the head-mounted bearing and the input shaft, the required stiffness is provided to the system compared to the traditional cantilevered input shaft design.

[0114] Reference Fig.10 As can be seen, the input shaft assembly 170 includes an input shaft 172 extending between a first end 172a and a second end 172b. The first end 172a is provided with an interface, shown here as an inwardly facing spline, for engaging with a power unit or prime mover. The second end 172b extends into a cavity 192a of an output shaft 192 of the output shaft assembly 190, thereby obtaining a compact shaft arrangement. As previously described, the head gear 200 is fixedly mounted to the input shaft 172 and supported by the bearing assembly 310, while the second end 172b of the shaft 172 is supported by the bearing assembly 320. Therefore, the input shaft 172 has a simple support configuration. This support helps to evenly distribute radial forces over a longer shaft span, thereby limiting radial shaft displacement and providing better alignment relative to the center of the gearbox.

[0115] In one aspect, the head gear 200 is fixed to the input shaft 172, and its arrangement ensures a perfect center match between the input shaft 172 and the head gear 200, while ensuring a reliable and high-strength connection for optimal torque transmission. In the example shown, the input shaft 172 is provided with an outer surface 174, which defines a spline section 174a, a larger diameter smooth shoulder section 174b, and a shoulder 174c extending from the shoulder section. The head gear 200 is provided with an inner surface 202, which defines a spline section 202a, a shoulder section 202b, and an end face 202c. The shoulder sections 174b, 202b are configured so that the head gear 200 must be press-fit onto the input shaft 172, thereby ensuring that the two components are fully coaxially aligned. The shoulder 174c and the end face 202c provide stop surfaces for the head gear 200, so that full engagement between the components can be ensured and verified. The head gear 200 and the input shaft 172 are further secured together via the interaction between the spline section 174a on the input shaft 172 and the spline section 202a on the head gear 200. The spline connection ensures that full torque transfer from the input shaft 172 to the head gear 200 is achieved. These combined features together provide a high-strength, fully aligned arrangement. This arrangement has the further benefit of ensuring equal torque transfer to each layshaft assembly 260, 270.

[0116] In one aspect, the head gear 200 is further provided with an outer surface 204 that defines a radial surface 204a and an axial surface 204b to provide corresponding press fit and stop surfaces for the bearing assembly 310. The final assembly of the bearing assembly 310, the head gear 200, and the input shaft 172, with the input shaft 172 supported at the other end by the bearing assembly 320, results in a robust configuration with increased stiffness to handle various loads within the assembly. For example, referring to Fig.11 and 12 , the bearing assemblies 310 and 320 are advantageously capable of providing sufficient radial bearing force (FR-B) to accommodate the unbalanced radial (FR-PTO) and moment / torque (FM-PTO) loads (PTO loads) that are inevitably generated by the operation of the PTO 120 via the layshaft 270.

[0117] In one aspect, the head gear 200 and the input shaft 172 together define a cavity 208 for receiving the thrust mechanism 280 therebetween. The cavity 208 may be characterized as being defined by surfaces 174d, 174e, and 174f on the input shaft 172 and surfaces 204c, 204d on the head gear 200. By providing the cavity 208, a compact assembly may be achieved in which the provision of the thrust mechanism 280 does not result in an overall increase in the axial length of the assembly.

[0118] Reference Fig.15, it can be seen that the thrust mechanism 280 is axially located between the head gear 200 and the axial end of the main shaft assembly 180, and the center lines of the thrust mechanism 280, the input shaft 172 and the output shaft assembly 190 are coaxially aligned. The simple support provided to the input shaft 172 as described above helps to ensure this alignment. In operation, the driven gear axial force F1 acts on a first side of the thrust mechanism in a first direction (axially in a direction from the output shaft assembly 190 toward the thrust mechanism 280), and the drive gear axial force F2 acts on a second opposite side of the thrust mechanism in an opposite second direction. Therefore, the thrust mechanism 280 acts to counteract the convergence of opposing axial thrust loads generated during operation. The thrust mechanism will be further described in the next section. In the sliding state, the thrust of the thrust mechanism 280 is transmitted to the thrust washer 289a via the shoulder or protrusion 180a on the main shaft assembly 180, and then transmitted to the output shaft assembly 190 via the gear 230, the thrust washer 289b, the gear 240, the clutch assembly 220, the thrust washer 289d, the gear 250, and the thrust washer 289e.

[0119] Thrust mechanism

[0120] Reference Figure 16-22 , various aspects of the thrust mechanism are now described in more detail. In operation, due to the constant lead gear design, the driving gears on the input shaft assembly 170 and the main shaft assembly 180 produce equal opposing axial thrusts (e.g., ~30kN) under driving and coasting conditions. In electric vehicle applications, the time operating in coasting conditions is considerable compared to vehicles using internal combustion engines. If the support bearings are designed to withstand thrust loads under both driving and coasting conditions, the increase in coasting time poses a challenge to meeting the reliability requirements of the support bearings. Reference Fig.21 , shows a driving condition where axial thrust is generated by the head gear 200 and any main shaft gears. In this case, these forces are equal and mutually transmitted and received at the rollers of the thrust mechanism 280, thereby canceling each other out within the system. The thrust mechanism 280 is loaded in this condition and is designed to have sufficient thrust capacity. Reference Fig. 22 , shows a coasting condition where the thrust forces generated by the head gear 200 and any main shaft gears are equal and directed in opposite directions to each other. The support bearings of the thrust mechanism 280 are designed to withstand the thrust forces under this condition. Under this condition, the thrust roller bearings are unloaded and the wave springs discussed below provide sufficient preload to avoid any possibility of roller slippage.

[0121] In addition, because the disclosed architecture is designed to achieve the most complete gear reduction within a single housing, the support bearing load is significantly increased compared to traditional architectures (e.g., where the reduction is distributed between two housings). As described above, the addition of the thrust mechanism 280 offsets the driving thrust within the system, thereby allowing the support bearing to be designed for sliding loads only, thereby ensuring that the support bearing meets its reliability within a given range. In addition, due to the use of electric motors as prime movers, electric vehicle applications have very high differential speeds (approximately 4200 RPM) between the input and output sides. Compared to traditional guide or sliding bearing arrangements for thrust, the disclosed thrust mechanism 280 advantageously provides a rolling contact interface that can operate at high relative speeds with minimal friction losses.

[0122] To achieve the above advantages, the thrust mechanism 280 is configured with a plurality of cylindrical thrust rollers 282, which are disposed between a pair of thrust washers 283, 284. A tapered raceway 285 is disposed near the thrust washer 284, and a spherical washer 286 is disposed axially between the tapered raceway 285 and the spindle assembly 180. In one aspect, the spherical washer 286 avoids edge loading of the thrust mechanism due to shaft misalignment, and also maintains line contact therebetween to minimize friction losses. A wave spring 287 is also shown, which is axially located between the thrust washer 283 and the head gear 200. The wave spring 287 generates a slight axial force in the direction of the spherical washer 286 that resists the thrust washer 283. The thrust mechanism also includes a bearing 288 (e.g., a needle bearing) radially located between the tapered raceway 285 and the input shaft 172. The bearing 288 enables the roller 282, the thrust washer 284, and the tapered raceway 285 to rotate about the input shaft 172. The bearing 288 also maintains the differential speed between the input shaft 172 and the thrust mechanism 280. In one aspect, the tapered raceway 285 has an L-shaped cross section with a radially extending portion 285a and an axially extending portion 285b, wherein the radially extending portion 285a is radially located between the bearing 288 on one side and the thrust roller 282 and the thrust washer 284 on the other side, and the axially extending portion 285b is axially located between the thrust washer 284 and the spherical washer 286. In one aspect, the axially extending portion 285b and the spherical washer 286 have contact surfaces extending at an oblique angle to the longitudinal axis or rotational axis of the thrust mechanism 280, while the spherical washer 286 and the main shaft assembly 180 have contact surfaces extending orthogonally to the rotational axis.

[0123] refer to Fig.18 and 19, showing normal output operation and PTO output operation, respectively. During normal operation, the torques generated from the layshafts 260, 270 are equal and cancel each other, so no net torque is generated at the input head drive gear 200 and the input shaft 172. However, during PTO operation, the single layshaft 270 is loaded, which generates torque on the input head drive gear 200 due to the axial thrust imbalance at the single meshing point. The thrust mechanism 280 advantageously prevents tipping of the head drive gear 200 in the PTO operating mode, thereby reducing mesh misalignment, which helps to improve gear reliability.

[0124] refer to Fig. 20 , it is shown that the spherical washer 286 of the thrust mechanism 280 provides a resting or abutment surface for the main shaft assembly 180. This arrangement makes assembly easier.

[0125] First slip clutch assembly

[0126] refer to Figure 23-24 , various aspects of the sliding clutch assembly 210 will now be described in greater detail.

[0127] In electric vehicle motors, the power and torque characteristic curves require very high low gear utilization, thus challenging the reliability of the gear. The design of a deep high-speed gear reduction ratio (layer 1) will balance the damage accumulation in layer 4 and ensure that the reliability target is met. However, this deep ratio design of layer 1 reduces the root diameter of the head drive gear on the input shaft within a given space (designed center distance). This limits the maximum diameter of the lower spline of the gear and the matching sleeve. At the same time, high motor speeds (e.g., 5000RPM) require a higher thrust area to achieve effective gear PV, and stronger splines are required on layer 2 (due to higher gear steps) to meet the high diameter requirements. Traditional symmetrical sleeve designs will not be able to meet these conflicting requirements, so the disclosed asymmetric sleeve design is proposed to meet these requirements. The disclosed clutch assembly 210 ensures that the gear and the main shaft are fully splined in both rear and front conditions to keep the spline stress within the limit range, and also avoids the sleeve from tilting or misaligning on the main shaft under load conditions (especially under PTO conditions). In addition to the asymmetric design, the disclosed clutch assembly 210 has optimized splines at the mainshaft sleeve interface to help maximize thrust area (reduces deflection and PV value) and radial clearance between the yoke and sleeve (reduces wear and lowers temperatures).

[0128] In one aspect, the clutch assembly 210 includes a shift fork 211 as part of the shift shaft assembly 135 and a sleeve member 212 whose position is controlled by the shift shaft assembly 135. As briefly described above, the clutch member can be operated to fixedly connect the head gear 200 to the main shaft assembly 180 or to fix the gear 230 to the main shaft assembly 180. The sleeve member 212 can also be operated to a neutral position between the gears 200 and 230. As shown, the sleeve member 212 is an annular body extending between a first end 212a and a second end 212b and defining a central opening 212c through which the main shaft assembly 180 extends. In one aspect, the second end 212 defines a thrust area for an internal washer. As shown, the sleeve member 212 defines a first external gear spline 212d adjacent to the first end 212a, the first external gear spline having a plurality of longitudinal splines or teeth, and also defines a spaced apart second external gear spline 212e adjacent to the second end 212b, the second external gear spline having a plurality of longitudinal splines or teeth. The first external gear spline 212d can be characterized as a fourth gear side that engages with corresponding inwardly facing teeth or splines of the head gear 200, while the second external gear spline 212e can be characterized as a third gear side that engages with corresponding inwardly facing teeth or splines of the drive gear 230. A channel 212f is formed between the external gear splines 212d, 212e, which serves as a contact area for the shift fork 211. The sleeve member 212 also defines an internal interface 212g, which includes a plurality of longitudinal splines or teeth. The internal interface 212g meshes with corresponding splines or teeth 182 on the main shaft assembly 180 (see Fig.33 ), so that the sleeve member 212 can slide axially along the length of the main shaft assembly 180 while still being able to transmit torque from the external gear splines 212d, 212e to the main shaft assembly 180. A thrust washer 182 can also be set around the main shaft assembly 180. Fig.33 In the example shown, a thrust washer 184 is provided which provides axial stop for the gear 230 and the sleeve member 212. Fig.29 To facilitate entry of the sleeve 212 into the interior of the head gear 200 and the drive gear 230, the respective ends 212h, 212i of the external gear splines 212d, 212e may be provided with a tapered or chamfered area.

[0129] Continue to refer Fig.31 and 32, showing aspects and dimensions of the head gear 200. In one aspect, the deep head gear ratio enables the head gear 200 to have a root diameter of (114.7 mm). Therefore, the head gear 200 is configured with a minimized internal spline maximum diameter (104.44 mm) to ensure sufficient web thickness (4.5 mm) on the head gear 200. This configuration helps meet the spline strength requirements at the head gear 200 and sleeve member 212 while still being able to package the assembly within a given space between the head gear 200 and the spindle assembly 180. Reference Figures 26 to 29 , the internal spline on the head gear 200 should also be designed to maximize the minimum internal spline diameter (68.5 mm) of the internal interface 212g (configured as spline 212g) of the clutch member 200 to ensure sufficient spline height (2.63 mm) and the maximum possible overlap area between the fork 211 and the sleeve member 212. This configuration reduces the fork deflection and PV value, thereby improving reliability. This maximization further helps to increase the diameter of the fork groove 212f in the sleeve member 212 (80.1 mm) and increase the diameter cross-sectional thickness of the sleeve to 6.36 mm, while still achieving the clearance between the fork 211 and the sleeve member 212.

[0130] refer to Fig.28 , 29 and 34, it should be noted that, since electric vehicle motors rotate at high speeds in excess of 5000 RPM (almost twice the speed of conventional engines), the PV and thrust area of ​​the sleeve member 212 represent key parameters in the design, especially for third gear. If the thrust washer diameter is increased without a corresponding change in the spline diameter, the washer will interfere. Therefore, the spline diameter at the second end 212b of the sleeve member 212 will limit the maximum washer that can be accommodated in the architecture. In order to maximize the thrust area and diameter of the thrust washer 184 between the shaft assembly 180 and the gear 230, the asymmetric sleeve member 212 is designed to have a maximized external spline minor diameter (109.6 mm) on the third gear side (external gear spline 212e). This maximizes the diameter of the thrust washer 184 to 107 mm, thereby effectively reducing the PV between the washer 184 and the gear 230. This design also helps to maximize the overlap area between the fork 211 and the sleeve member 212 and reduce the PV between the fork 211 and the sleeve member 212 .

[0131] In one aspect, the splines 212d, 212e of the sleeve member 212 are designed and optimized to ensure smooth torque transfer and shifting in third and fourth gears. For example, the spline sections 212d, 212e ensure that the shift forces required for third and fourth gears are lower than the XY shifter shift force (240 pounds) under all possible conditions, as shown in Table 1 below.

[0132] Table 1

[0133]

[0134]

[0135] refer to Fig.30 , the splines 212d, 212e of the sleeve member 212 have a reverse taper angle of 2.82° to avoid gear jump-out while ensuring that the disengagement force is not too high and can be easily achieved, as shown in Table 2 below, which shows the pull-out force calculated using this reverse taper angle.

[0136]

[0137] refer to Fig.34 The design of the sleeve member 212 also ensures that even in the engaged condition, sufficient clearance is maintained with the thrust element below the head gear 200. The disclosed design also ensures 100% spline engagement, thereby preventing the sleeve from falling out around the spindle assembly 180 in the fourth gear engaged state.

[0138] Shell sealing

[0139] refer to Fig.43 , the aspects of the enclosure related to sealing are shown in more detail. As shown, a gasket 164 is provided to prevent sealing between the adapter housing 160 and the shallow main housing 150, while an anaerobic sealing joint 158 ​​is provided between the shallow main housing 150 and the rear enclosure portion 102. A gasket 112 is also shown provided between the rear enclosure portion 102 and the rear bearing cover 370. Sealing joints 380a, 390a are also provided for the cover assemblies 380, 390, respectively.

[0140] Other implementations will be apparent to those skilled in the art from consideration of the specification and practice of the examples and teachings presented herein. The specification and examples should be considered exemplary only, with the true scope of the invention being indicated by the following claims.

Claims

1. A transmission assembly, comprising: a) a dual countershaft transmission powertrain gear assembly having an input shaft assembly and an output shaft assembly, the powertrain having at least one mechanism for varying a gear ratio between the input shaft assembly and the output shaft assembly; b) a housing assembly housing the powertrain, the housing assembly comprising a single-piece housing component, the single-piece housing component defining: i) a node mounting structure for mounting the transmission assembly to a vehicle; ii) a mounting device for securing the electronic control unit; and iii) Mounting means for the shifter assembly.

2. The transmission assembly according to claim 1, wherein: The one-piece enclosure member enclosure includes mounting means for supporting a power take-off (PTO) unit.

3. The transmission assembly according to claim 1, wherein: The enclosure assembly includes a modular mounting interface for receiving adapters of different configurations.

4. The transmission assembly according to claim 1, wherein: The enclosure assembly also includes a main housing secured to the open end of the one-piece enclosure member.

5. The transmission assembly according to claim 4, wherein: The main housing supports a pump assembly and includes at least one lubrication passage.

6. The transmission assembly according to claim 5, wherein: The at least one lubrication passage is cast in the shallow main housing.

7. The transmission assembly of claim 1, wherein: The one-piece enclosure member is formed from a metallic material.

8. The transmission assembly of claim 7, wherein: The one-piece enclosure member is formed from aluminum.

9. The transmission assembly of claim 2, wherein: The PTO unit and the output shaft arrangement are located at a first end of the enclosure.

10. The transmission assembly of claim 2, wherein: The PTO unit is directly driven by a layshaft of the powertrain assembly.

11. A transmission assembly comprising: a) an input shaft assembly comprising an input shaft extending between a first end and a second end; b) an output shaft assembly, comprising an output shaft; c) a powertrain gear assembly including at least one mechanism for varying a gear ratio between the input shaft assembly and the output shaft assembly, wherein the powertrain gear assembly includes an overrunning gear directly connected to the input shaft adjacent the first end; and d) a bearing assembly comprising a first bearing assembly supporting the head gear and a second bearing assembly supporting the input shaft adjacent the second end, wherein the second bearing assembly and the second end of the input shaft are located within an inner cavity of the output shaft.

12. The transmission assembly of claim 11, wherein: The head gear has a first connection interface and a second connection interface with the input shaft.

13. The transmission assembly of claim 12, wherein: The first connection interface is a spline connection and the second connection interface is a press-fit interface.

14. A transmission assembly according to claim 11 or 13, wherein: The first bearing assembly is press fit onto the head gear.

15. The transmission assembly of claim 11, further comprising: a) A thrust mechanism for offsetting the opposing axial loads generated between the input shaft and the main shaft.

16. The transmission assembly of claim 15, further comprising: a) a main shaft partially surrounding and coaxially aligned with the input shaft, wherein the thrust mechanism is located between an axial end of the main shaft and an axial surface of one or both of the head gear and the input shaft.

17. The transmission assembly of claim 15, wherein: The thrust mechanism is supported by one or both of the head gear and the input shaft.

18. The transmission assembly of claim 15, wherein: The thrust mechanism is located between the first bearing assembly and the second bearing assembly in the axial direction.

19. The transmission assembly of claim 15, wherein: The thrust mechanism is at least partially disposed in a cavity formed between the head gear and the input shaft.

20. The transmission assembly of claim 11 or 15, further comprising a power take-off (PTO) unit.

21. A transmission assembly comprising: a) an input shaft assembly comprising an input shaft extending between a first end and a second end; b) an output shaft assembly, comprising an output shaft; c) a powertrain gear assembly including at least one mechanism for varying a gear ratio between the input shaft assembly and the output shaft assembly, wherein the powertrain gear assembly includes an overrunning gear directly connected to the input shaft adjacent the first end; and d) a thrust mechanism for offsetting the opposing axial loads generated between the input shaft and the main shaft.

22. The transmission assembly of claim 21, wherein: The thrust mechanism is supported by one or both of the head gear and the input shaft.

23. The transmission assembly of claim 21, wherein: The thrust mechanism is located axially between a first bearing assembly and a second bearing assembly that support the input shaft.

24. The transmission assembly of claim 21, wherein: The thrust mechanism is at least partially disposed in a cavity formed between the head gear and the input shaft.

25. The transmission assembly of claim 21 further comprising a power take off (PTO) unit.

26. The transmission assembly of claim 21, wherein: The thrust mechanism includes a plurality of cylindrical rollers disposed between a pair of thrust washers.

27. A transmission assembly according to claim 21 or 26, wherein: The thrust mechanism includes a bearing located around the input shaft.

28. The transmission assembly of claim 26, wherein: The thrust mechanism includes a tapered raceway adjacent to one of the pair of thrust washers and a spherical washer adjacent to the tapered raceway.

29. The transmission assembly of claim 26, wherein: The thrust mechanism includes a wave spring located between the overhead gear and one of the pair of thrust washers.

30. The transmission assembly of claim 26, wherein: The input shaft assembly is configured to operate at speeds up to 5,000 revolutions per minute.

31. A transmission assembly comprising: a) an input shaft assembly comprising an input shaft extending between a first end and a second end; b) an output shaft assembly, comprising an output shaft; as well as c) a gear train assembly for changing the gear ratio between the input shaft and the output shaft, the gear train assembly comprising: i) a head gear fixed to the input shaft, the head gear intermeshing with the first layshaft gear and defining a first internal drive interface; ii) a drive gear intermeshing with the second countershaft gear and defining a second internal drive interface; iii) a main shaft intermeshing with the output shaft, the main shaft defining a first external drive interface; and iv) a clutch assembly comprising a sleeve member slidably disposed about the main shaft, the sleeve member defining a third internal drive interface engaged with the first external drive interface of the main shaft, the sleeve member defining a first external gear spline for engaging with the first internal drive interface and a second external gear spline for engaging with a second internal drive gear, wherein the first external gear spline has a first diameter and the second external gear spline has a second diameter different from the first diameter.

32. The transmission assembly of claim 31, wherein: The first diameter is smaller than the second diameter.

33. The transmission assembly of claim 31, wherein: The first external gear splines are spaced apart from the second external gear splines to form a channel for receiving a shift fork.

34. The transmission assembly of claim 31, wherein: The first external gear splines are at least partially received within the head gear when the sleeve member is in the first position.

35. The transmission assembly of claim 34, wherein: The second external gear splines are at least partially received within the drive gear when the sleeve member is in the second position.

36. The transmission assembly of claim 35, wherein: When in the second position, the sleeve member abuts a thrust washer.

37. The transmission assembly of claim 31 further comprising: a) A thrust mechanism for offsetting the opposing axial loads generated between the input shaft and the main shaft.

38. The transmission assembly of claim 37, wherein: The thrust mechanism is at least partially received within the sleeve member when the sleeve member is in the first position.

39. The transmission assembly of claim 38, wherein: When the sleeve member is in the first position, the first external gear spline is at least partially received in the head gear.

40. The transmission assembly of claim 31 further comprising a power take off (PTO) unit.

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