TECHNICAL FIELD

[001] The present disclosure relates generally to an automated transmission for an electric vehicle with a valve-operated shifter having a neutral position.

BACKGROUND

[002] Many electric vehicles do not have multi-speed transmissions. Instead they have a single-speed transmission (usually a speed reduction from the electric motor), and simply control the speed of the electric motor to control the speed, acceleration, and a deceleration of the drive shaft, and therefore the vehicle. This provides several advantages. For example, it can reduce the weight of the vehicle and it can simplify the number of parts used in the vehicle.

[003] Reducing the weight of an electric vehicle can reduce the amount of energy required to move the vehicle. Reducing the weight can also improve the energy efficiency of the vehicle. For these reasons, designers avoid using transmissions in electric vehicles.

[004] This arrangement, however, does not work best for all electric vehicles.

Commercial electric vehicles, for example, buses for public transportation and trucks for delivering goods, present especially challenging issues due to their relatively high vehicle and cargo mass. Commercial vehicles sometimes require multiple gear ratios to perform their tasks, especially when carrying heavy loads or traveling up and down inclines. Due to the high mass of these vehicles, the electric motor would need to be very large, powerful, and heavy if the vehicle employed a single-speed transmission.

[005] Commercial vehicles with internal combustion engines as the prime mover use manual, automated, and automatic transmissions. The automatic transmissions for these vehicles use multi-speed transmissions with anywhere from 5 to 18 gear ratios. These multi-speed transmissions provide the appropriate gear ratios for a commercial vehicle, but they can significantly increase the weight of an electric vehicle Therefore, a transmission that optimizes the commercial electric vehicle powertrain is needed that can provide the necessary gear ratios, but minimize weight and size.

SUMMARY

[006] The present disclosure overcomes the above disadvantages and improves the art neutral. The neutral position of the first shifter allows a second shifter to shift positions at zero torque. This arrangement permits a lower weight option for shifting gears.

[007] A transmission assembly comprises a first main shaft. The first main shaft comprises a main-shaft axis; a second main shaft, located along the main-shaft axis; a first main gear, wherein the main-shaft axis passes through the center of the first main gear; a second main gear, wherein the main-shaft axis passes through the center of the second main gear; a third main gear, wherein the main-shaft axis passes through the center of the third main gear; a first counter shaft comprising a first counter gear, a second counter gear, and a third counter gear, wherein the first counter shaft has a first counter-shaft axis parallel to the main-shaft axis; a first shifter comprising a first position, a second position, and a third position along the main-shaft axis, wherein the first shifter engages the first main gear when in the first position, the first shifter engages the second main gear when in the second position, and the first shifter does not engage either the first main gear or the second main gear when in the third position; a second shifter comprising a first position and a second position along the main-shaft axis, wherein the second shifter engages the second main gear when in the first position and the second shifter engages the third main gear when in the second position. Both the first shifter and the second shifter can be a sliding clutch. The sliding clutch can be part of a mechanical synchronizer mechanism.

[008] A method of operating a transmission comprises the step of rotating a first main shaft. The first main shaft comprises an axis. The method also comprises transmitting torque to a second main shaft, wherein the axis passes through the center of the second main shaft; moving a first shifter along the axis to a first position, a second position, and a third position, wherein the first shifter engages a first main gear when in the first position, the first shifter engages a second main gear when in the second position, and the first shifter does not engage either the first main gear or the second main gear when in the third position; and moving a second shifter along the axis to a fourth position and a fifth position, wherein the second shifter engages the second main gear when in the fourth position and the second shifter engages a third main gear when in the fifth position.

[009] Additional objects and advantages will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the disclosure. The objects and advantages will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. [010] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[011] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate principles of the disclosure.

[012] Figure 1 shows a cross-section of a transmission assembly including a countershaft and a valve-operated piston.

[013] Figure 2 shows a cross-section of a transmission assembly including two countershafts.

[014] Figures 3 A - 3D show power paths for a transmission assembly with four different gear ratios.

[015] Figure 4 shows a control system arrangement for a transmission assembly.

[016] Figure 5 shows a flow diagram for selecting a gear.

DETAILED DESCRIPTION

[017] Reference will now be made in detail to the present exemplary embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

Directional references such as "left," "right," "top," and "bottom" are for ease of reference to the figures.

[018] Figure 1 shows a cross-sectional view of a transmission assembly 101 with first housing 120 A and a second housing 120B. The first housing 120 A and the second housing 120B cooperate to enclose the transmission assembly 101 with its affiliated shifters within a cavity. The cavity can be fluid filled with a lubricating fluid or can be filled with air. The transmission assembly 101 can have a first main shaft 102 and a second main shaft 103, where both first main shaft 102 and second main shaft 103 are located along main-shaft axis A. The first main shaft 102 can receive power from a motor (not shown), for example, an electric motor. The electric motor can directly rotate first main shaft 102 or transmit torque to first main shaft 102 via gears or clutches or via a direct spline connection to the motor shaft. Transmission assembly 101 can include a first main gear 113, a second main gear 114, and a third main gear 115. All three of these main gears have a center located along main-shaft axis A. [019] The transmission assembly can have counter shafts 116A and 116B (shown in Figure 2) located parallel to main-shaft axis A. A first counter shaft 116A can have a first counter gear 104A, a second counter gear 105 A, and a third counter gear 106A. All three of these counter gears have a center located along first counter-shaft axis A. Counter shafts 116A and 116B can be identical to each other, improving the stability of the transmission assembly.

[020] The main gears and counter gears can be arranged so transmission assembly 101 comprises four gear ratios, also known as four speeds. This allows transmission assembly 101, and an electric vehicle using transmission assembly 101, to more efficiently transfer power from the electric motor to the vehicle's wheels. Having four gear ratios also allows the electric vehicle to meet the needs of driving conditions requiring both low and high gear ratios. It is also possible to be a two or three speed transmission, as by reducing the number of gear ratios. More or fewer speeds can also be accommodated as by adjusting the number of gears.

[021] When under power, first main shaft 102 can transmit torque through first main gear 113 to first counter gear 104A of first counter shaft 116A (shown in Figure 2). First counter gear 104A and third counter gear 106A can be fixed to first counter shaft 116A so that first counter gear 104A transmits torque to third main gear 115 via third counter gear 106 A. If the transmission assembly has a second counter shaft 116B, as shown in Figure 2, then first main shaft 102 can likewise simultaneously transmit torque through first main gear 113 to first counter gear 104B, which transmits torque to third main gear 115 via second counter shaft 116B. This arrangement represents a first gear ratio. The power path of this first gear ratio is shown in Figure 3A.

[022] First main shaft 102 can transmit torque through second main gear 114 to second counter gear 105 A of first counter shaft 116A (shown in Figure 2). Second counter gear 105 A and third counter gear 106A can be fixed to first counter shaft 116A so that second counter gear 105 A can transmit torque to the third main gear 115 via third counter gear 106A. If the transmission assembly has a second counter shaft 116B, as shown in Figure 2, then first main shaft 102 can likewise simultaneously transmit torque through second main gear 114 to second counter gear 105B, which transmits torque to third main gear 115 via second counter shaft 116B. This arrangement represents a second gear ratio. The power path of this second gear ratio is shown in Figure 3B.

[023] First main shaft 102 can transmit torque through first main gear 113 to first counter gear 104 A of first counter shaft 116A (shown in Figure 2). First counter gear 104 A and second counter gear 105 A can be fixed to first counter shaft 116A so that first counter gear 104A can transmit torque to second main gear 114 via second counter gear 105 A. If the transmission assembly has a second counter shaft 116B, as shown in Figure 2, then first main shaft 102 can likewise simultaneously transmit torque through first main gear 113 to first counter gear 105B, which transmits torque to second main gear 114 via second counter shaft 116B. This

arrangement represents a third gear ratio. The power path of this third gear ratio is shown in Figure 3C.

[024] First main shaft 102 can transmit torque to second main shaft 103 via second main gear such that first main shaft 102 and second main shaft 103 are operatively engaged and rotating at the same speed. This is the fourth gear ratio, or fourth speed. The fourth gear ratio equals one (1.00:1) because the power path does not pass through different sized gears. This is commonly referred to in the transmission industry as Direct-Drive. The power path of fourth gear ratio is shown in Figure 3D.

[025] Main gears 113, 114, and 115 can engage main shafts 102 and 103 via a first shifter and a second shifter. If one of the main gears is not connected to a shifter, then the unconnected main gear can rotate without receiving torque from or transmitting torque to either first main shaft 102 or second main shaft 103. Main gears 113, 114, and 115 can include a bearing that surrounds the main shaft such that the main gear can rotate around the main shaft.

[026] The transmission assembly 101 can control the position of first shifter 108 using valves, for example, three-way pneumatic or hydraulic solenoid valves. The valves can direct compressed air or hydraulic pressure to move piston 110 back and forth along piston axis C. And piston 110 can cause first shifter arm 107 to move first shifter 108 back and forth along main- shaft axis A. As one example, the solenoid valves can have high and low values. A high value causes pressurized fluid PS1, such as air or hydraulic fluid, to enter fluid port 241. Cross-drilling or other porting through valve head 240, piston cap 230, and piston housing 200 provides a fluid pathway in to first cavity 111. A valve "high" command increases the fluid pressure in first cavity 111, while a valve "low" command decreases fluid pressure in first cavity 111. Likewise, fluid port 243 transmits pressurized fluid PS2. A valve "high" command increases the fluid pressure in second cavity 112, while a valve "low" command decreases fluid pressure in second cavity 112. By controlling the pressure in the first and second cavities 111, 112, the piston 110 position along axis C, and hence first (splitter) shifter 108 position, is controlled. By applying a like principle of valve operation to second (range) shifter 109, the shifters are controlled to select various gear ratios and to engage combinations of gears. Table 1 shows one example of solenoid operation for first valve pack 445 and second valve pack 446. TABLE 1

[027] Each "X" indicates which valve receives a command to turn on. For example, when in Gear 1, the "low" valve in first valve pack 445 is on and the "high" valve in first valve pack 445 is off while the "low" valve in the second valve pack 446 is on and the "high" valve in the second valve pack 446 is off.

[028] When in Neutral Gear, both the "low" and "high" valves in first valve pack 445 are on while both the "low" and "high" valves in the second valve pack 446 are off.

[029] In another example (not shown in Table 1) when in Neutral Gear, both the "low" and "high" valves in the first valve pack 445 are on while the "high" valve of the second valve pack 446 is on and the "low" valve of the second valve pack 446 is off. This arrangement allows second shifter 109 to engage a gear during power-down, protecting the gear box.

[030] Returning to Figure 1, pneumatic or hydraulic pressure can move piston 110 back and forth along piston axis C. And piston 110 can cause first shifter arm 107 to move first shifter 108 back and forth along main-shaft axis A. As shown in Figure 1, the piston 110 is seated in a piston housing 200, which can be a sleeve for mounting the piston 110 with respect to the first main shaft 102. Piston seals 201 and 203 cooperate to form first and second cavities 111, 112 about piston baffle 210. O-rings, quad seals, wiper rings or other gasket mechanisms can cooperate with piston seals 201, 203 and piston baffle 210 to assist with a fluid-tight seal between piston housing 200 and piston 110. Piston 110 can include a piston cavity 220. The piston cavity 220 cooperates with a cap cavity 235 in piston cap 230.

[031] It is possible to permit fluid transfer between either the first transmission housing 120 A or the second transmission housing 120B and the cap cavity 235. This can be achieved by permitting fluid transfer between the piston housing 200 and the piston 110. Fluid, which can be air or, in a lubricated transmission, transmission fluid, can communicate with third cavity 224. Cross-drilled hole 222 permits fluid in the third cavity 224 to communicate with piston cavity 220, and then with cap cavity 235. By permitting this fluid transfer, several benefits inure. First, actuation of the piston 110 is faster, because fluid pressure on either side of the piston 110 can be shunted along and within the piston 110. For example, pressure in the cap cavity 235 is relieved to permit easy actuation of the piston 110 as it slides towards the cap 230. A second benefit is the permissive lubrication of the gasket mechanisms surrounding the piston seals 201, 203 and those surrounding piston baffle 210. The lubrication extends the life of the gasket mechanisms and improves performance thereof. When fluid is supplied to first and second cavities 111, 112, that fluid can expel any leaking lubrication fluid as by fluid dynamics of higher versus lower pressure fluids.

[032] As one working example, a solenoid in first valve 241 can actuate to allow pressurized fluid to enter first cavity 111, thereby pushing piston 110 to the right, as oriented in Figure 1 , along piston axis C to a first position. A second solenoid in second valve 243 can actuate to allow pressurized fluid to enter second cavity 112, thereby pushing piston 110 to the left, as oriented in Figure 1 , along piston axis C to a second position. When both first valve and second valve are open, pressurized fluid can enter both first cavity 111 and second cavity 112, causing piston 110 to rest in a third position, in between the first position and the second position along piston axis C, allowing a neutral position of the first shifter 108. It is also possible to permit piston 110 to shift by including settings on valves 241 & 243 to bleed down pressure from first and second cavities 111 & 112. Another example of a piston arrangement that can move a shifter back and forth along an axis is described in U.S. Pat. No. 5,191,804, which is

incorporated herein by reference.

[033] First shifter arm 107 can be connected to piston 110 so that first shifter arm 107 moves first shifter 108 toward first main gear 113 along main-shaft axis A. First shifter 108 can engage first main gear 113 so that first main gear 1 13 rotates at the same speed as first main shaft 102.

[034] First shifter 108 can engage first main gear 113 in a variety of ways. For example, first shifter 108 can be ring shaped and comprise teeth inside an inner ring wall. The teeth of first shifter 108 can engage a complementary set of teeth on first main gear 113 so that first shifter 108 and first main gear 113 rotate together. First shifter 108 can, at the same time, engage with a ring of teeth fixed to first main shaft 102. This way, first main gear 113, first shifter 108, and first main shaft 102 are connected and rotate at the same speed.

[035] Second shifter 109, sometimes called a range shifter, can have two positions: a first position and a second position. Like first shifter 108, second shifter 109 can be controlled by valves. It can move in two opposite directions along second main shaft 103, which is located in line with main-shaft axis A. In the first position, second shifter 109 can engage second main gear 114 while also operatively connected to second main shaft 103. In the second position, second shifter 109 can engage third main gear 115 while also operatively connected to second main shaft 103.

[036] In addition to other known arrangements, both first shifter 108 and second shifter 109 can be arranged like a clutch collar, for example, as described in U.S. Pat. No. 4,584,895, which is incorporated herein by reference. First shifter 108 can be a sliding clutch. Also, both first shifter 108 and second shifter 109 can be arranged like a synchronizer. As such, first shifter 108 and second shifter 109 can move along main-shaft axis A, coupling main gears 113, 114,

115 to first main shaft 102 and second main shaft 103.

[037] Figure 2 shows a cross-section of transmission assembly 101 comprising two counter shafts 116 A, 116B. First counter shaft 116A includes three gears: first counter gear 104A, second counter gear 105 A, and third counter gear 106A, all located along first countershaft axis B. Likewise, second counter shaft 116B includes three gears: first counter gear 104B, second counter gear 105B, and third counter gear 106B, all located along second counter-shaft axis D.

[038] Transmission assembly 101 can have two counter shafts or only one counter shaft. Having two counter shafts makes the arrangement able to transmit up to twice the amount of input torque than with a single counter shaft when the two counter shafts are arranged directly opposite of each other and where main-shaft axis A is located halfway between first countershaft axis B and second counter-shaft axis D.

[039] Figure 2 shows the three main gears 113, 114, 115 engaged with both sets of counter gears. For example first main gear 113 is engaged with first counter gears 104A, 104B. First main gear 113 transmits torque to first counter gears 104A, 104B when first main shaft 102 engages first main gear 113 via first shifter 108, which is moved by first shifter arm 107. Now powered by first main shaft 102, the two counter shafts 116 A, 116B can transmit torque to second main shaft 103 either via second counter gears 105 A, 105B and second main gear 114 or via third counter gears 106A, 106B and third main gear 115, depending on whether second shifter is engaged with second main gear 114 or third main gear 115.

[040] Figure 3 A shows a first power path PI of a first gear ratio flowing from motor 330 to first main shaft 302 through first main gear 313 and first counter gear 304B along second counter shaft 316B through third counter gear 306B and third main gear 315 to second main shaft 303. Arrow Dl shows that first shifter 308 is engaged with first main gear 313. Arrow D2 shows that second shifter 309 is engaged with third main gear 315. [041] Figure 3B shows a second power path P2 of a second gear ratio flowing from motor 330 to first main shaft 302 through second main gear 314 and second counter gear 305B along second counter shaft 316B through third counter gear 306B and third main gear 315 to second main shaft 303. Arrow Dl shows that first shifter 308 is engaged with second main gear 314. Arrow D2 shows that second shifter 309 is engaged with third main gear 315.

[042] Figure 3C shows a third power path P3 of a third gear ratio flowing from motor 330 to first main shaft 302 through first main gear 313 and first counter gear 304B along second counter shaft 316B through second counter gear 305B and second main gear 314 to second main shaft 303. Arrow Dl shows that first shifter 308 is engaged with first main gear 313. Arrow D2 shows that second shifter 309 is engaged with second main gear 314.

[043] Figure 3D shows a fourth power path P4 of a fourth gear ratio flowing from motor 330 to first main shaft 302 to second main shaft 303. Arrow Dl shows that first shifter 308 is engaged with second main gear 314. Arrow D2 shows that second shifter 309 is engaged with second main gear 314. This arrangement couples first main shaft 302 to second main shaft 303 at second main gear 314. The gear ratio in this arrangement is one (1.00: 1).

[044] Figure 4 shows a control unit 441 for a transmission assembly. At a minimum, the control unit 441 comprises a processor 4411 and tangible memory 4412, and the memory stores control programming for execution by the processor 4411. The memory 4412 can receive and store sensed operation conditions as data, and the processor can operate on the received data to determine outputs for controlling actuators within the system. Examples of sensors are as below, and can comprise more or fewer sensors. Examples of actuators include the valves and solenoids mentioned above, and more or fewer actuators can be included.

[045] As one working example, control unit 441 can receive signals from gear speed sensor 442, first main shaft speed sensor 443, and second main shaft speed sensor 444. Gear speed sensor 442 can measure gear position, in addition to or instead of rotational speed.

[046] In another example, control unit 441 can receive signals from a sensor measuring the motor speed (input speed), while also receiving signals from the second main shaft speed sensor 444 measuring the rotational speed of the second main shaft (output speed).

[047] After receiving these signals, control unit 441 can send signals to first shifter valve pack 445 and second shifter valve pack 446. Each valve pack 445, 446 can have two solenoid valves. First shifter valve pack 445 communicates with fluid ports 241, 243 in valve head 240. Second shifter valve pack 446 communicates with actuation mechanisms for second shifter 109. [048] As an example, control unit 441 can send commands to valves in valve packs 445, 446 to open or close, depending on the settings of control unit 441. For example, control unit 441 can send commands to the two valves in first shifter valve pack 445 to open, allowing

pressurized fluid to enter first cavity 111 and second cavity 112 (shown in Figure 1). This puts first shifter 108 in the third position, that is, the neutral position.

[049] First shifter valve pack 445 has three states. The first state, with only one valve open, can put first shifter 108 in a position where first shifter 108 engages first main gear 113. The second state, with a different valve open and the other valve closed, can put first shifter 108 in a position where first shifter 108 engages second main gear 114. The third state has both valves open, putting first shifter 108 in the neutral position.

[050] Second shifter valve pack 446 has two states. The first state, with only one valve open, can put second shifter 109 in a position where second shifter 109 engages second main gear 114. The second state, with a different valve open, can put second shifter 109 in a position where second shifter 109 engages third main gear 115.

[051] Every shift can begin by bringing first shifter 108 to the neutral position. This allows the second shifter 109 to engage either second main gear 114 or third main gear 115 while zero torque is being actively coupled and transmitted from the motor to second main shaft 103. Bringing the torque source through zero in this fashion permits passive torque transmission via freewheeling by the disconnected parts. Active braking can be applied to cease downstream freewheeling of parts.

[052] Ideally, the first main shaft 102 is connected directly to the motor output shaft, or can be also connected via a clutch or other means. The first main shaft 102 and the motor can still be rotating at the desired speed of the motor controller while maintaining zero torque across the transmission. Zero torque does not necessarily mean that either the motor or the main shaft has stopped rotating. Instead, zero torque can exist when the motor is either receiving or transmitting power from a power source, for example, batteries, at just the proper amount to result in zero torque at the main shafts of the transmission. Note that for electric motors, it typically requires some amount of motive power to keep the main shafts rotating at a desired speed even when no torque or power is being transmitted to the transmission or other device that it is driving

[053] Control unit 441 can confirm the shift of second shifter 109 by receiving signals from first main shaft speed sensor 443, second main shaft speed senor 444, or gear speed sensors 442. [054] After second shifter 109 completes its shift, control unit 441 can tell first shifter valve pack 445 to open and close valves in a way that causes first shifter 108 to engage a main gear. Control unit 441 can confirm the shift of first shifter 108 by receiving signals from first main shaft speed sensor 443, second main shaft speed sensor 444, or gear speed sensors 442.

[055] One can also design control unit 441 to use the motor to synchronize shaft speeds and gear speeds during shifting. Control unit 441 can also turn off the valves in second shifter valve pack 446 when first shifter valve pack 445 is in the neutral position.

[056] Control unit 441 can also put valve pack 445 in the neutral position and command second shifter valve pack 446 to move second shifter 109 in a position engaged with a main gear. This can help protect transmission assembly 101 when powering down the motor.

[057] One can design control unit 441 to open valves and move shifters in a manner optimized for transmission assembly 101. The timing of shifting can depend on, among other factors, the size of the gears, the desired output speed of second main shaft 103, the size and power of the motor, energy efficiency concerns, trailering capacity, vehicle weight, and other needs of the vehicle using transmission assembly 101.

[058] By adding a neutral position to piston 110, it is possible to extend the range of possible gear ratios. It also makes the transmission more compact, so as to support electric vehicles and zero-emissions vehicles. The neutral position transmission also applies to range extended electric vehicles. The compact transmissions can be designed with even gear ratio steps, and as 2, 3, or 4 speed transmissions.

[059] A method of operation for the transmission is outlined in Figure 5. The control unit 441 receives a shift command at step S50. The shift command can come through user operation of, for example, a shift lever or other input mechanism. The first shifter valve pack 445 receives commands from the control unit to move the first shifter to neutral in S51. The command can be the result of processing of a stored algorithm. The control unit 441 also brings the torque source through zero, as by reducing or removing the amount of torque coupled to the transmission from the torque source. Torque source can be an electric motor, for example. This reduction or removal of active torque power can be to one or more of the gears 104A, 105 A, 106A. For the example of Figure 5, the gears receive zero torque in step S52.

[060] The system checks whether the first shifter is in neutral in step S 53, as by checking one or more of the position of piston 110, the position of first shifter 108, or the rotational speed of the gears or shafts affiliated with the transmission. Such sensing can be done via gear speed sensors 442, first and second main shaft speed sensors 443, 444, or other like sensor arrangements. If the first shifter is not in neutral, the process returns to commanding the move of the first shifter to neutral. But, if the first shifter is sensed in the neutral position, the process proceeds to step S55 to move the second (range) shifter to select a particular one or more of the gears 104A, 105 A, 106A. Sensing mechanisms are used to check whether the second shifter move is complete in step S57. For example, rotation speeds of first main shaft 102 and second main shaft 103 are checked to confirm that the second (range) shift is complete. If so, the torque source is connected to the selected one or more gears to synchronize their rotation in step S59.

[061] The first shifter is then affirmatively engaged in to the selected gear to maintain the selected gear ratio in step S60. To confirm that the engagement of the gear ratio is complete, sensor data can be analyzed by the control unit 441 to check the motor speed of the torque source. Alternatively or additionally, the output speed of one or both of first main shaft 102 and second main shaft 103 is checked. The method can be reapplied to select a new gear ratio. The method applies equally to the dual counter shaft embodiment so as to select gears 104B, 105B or 106B. When the torque source powers down, the first shifter 108 can shift to neutral and the second shifter 109 can shift to high to protect the gear box. Thus, the three position piston provides a gear-protection function via the neutral position.

[062] The transmission arrangement is not limited to four gear ratios. It could have more or less. One can increase the number of speeds by adding additional gears to the main shafts and counter shafts. For example, one can add an additional gear before first main gear 113 and also place an additional shifter between the additional gear and first main gear 113. Like the first shifter 108, the additional shifter can have three positions, including a neutral position. By adding the additional gear and shifter, and adjusting the counter shafts and gears accordingly, the transmission can have more gear ratios, thus, more speeds.

[063] Also, one can add a gear to second main shaft 103 after third main gear 115 and also add a shifter between third main gear 115 and the additional gear. The number and size of gears can be added to fit the needs of the vehicle. For example, the vehicle might need six speeds to more efficiently operate, while another only needs four.

[064] In the preceding specification, various preferred embodiments have been described with reference to the accompanying drawings. Various other modifications and changes can be made, and additional embodiments can be implemented, without departing from the broader scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.