Compact vehicle transmission

A compact vehicle has a frame and an operating position thereon for at least one rider. An engine having a drive shaft is on the frame, as are a plurality of operational wheels. A transmission operatively couples the engine and the wheels. The transmission is a hydrostatic mechanical transmission with at least 2 operational modes.

BACKGROUND OF THE INVENTION

There are a number of compact vehicles that need to have “automatic” transmissions for ease of driving and for increased utility. These include ATV's, tractors, utility work vehicles and small automobiles. These vehicles are generally in the 25 HP to 50 HP range, and have common requirements for low cost, high efficiency, good controllability and continuous ratio change throughout the entire speed range. These vehicles are small and need transmission packages which are short and narrow and which have inputs and outputs conveniently located.

There can be a wide range in the required transmission ratio spread that varies by vehicle vocation. Further, the transmission configuration varies with the specific vehicle design. Both of these issues can be major determinants of cost. There are some differences in engine speed, which can affect the sizing of the transmission components.

Therefore, a principal object of this invention is to provide a hydrostatic mechanical transmission (HMT) which accommodates the range of vehicle heeds with a basic design approach, and provides for the adapting of different vehicle requirements while retaining many key transmission components across a range of vehicles.

Further objects of the invention are as follows:

1. To provide an HMT with a continuous ratio from full reverse to full forward speed in a compact vehicle. Providing controlled output speed through zero eliminates the need for any clutch between the engine and transmission.

2. To provide controlled output speed which can be configured in either a 2-mode or 3-mode version depending in the application requirement. The third mode is independent in ratio spread from the other two modes.

3. To provide a transmission configuration which has a center housing portion which contains features and location for two hydrostatic units which is common across the range of transmission applications, and two end covers for the center portion which contain the features and location for the mechanical shafts, engine mounting, and PTO drive. The housing split lines are located on the front and rear of the V and F hydrostatic assemblies.

4. To provide for the transmission output shaft location to be below and offset to one side of the input shaft, so as to allow for routing of the driveshaft(s) close to the engine, in either an integrated or non-integrated engine/transmission configuration.

The vehicles intended for application of this transmission have a single seat for the driver who typically sits close to the engine/transmission package and may straddle it. The transmission must be compact and allow routing of the driveshaft below/beside the engine. It is desirable to have a continuous ratio throughout the vehicle speed range in order to allow maximum flexibility for the driver or work to be done. Minimum cost is achieved with no gears between the front and rear driveshafts and with no clutch between the engine and transmission.

Hydromechanical transmissions are characterized by a hydrostatic transmission power path in parallel with a mechanical power transmission path, arranged in a manner to decrease the average power flow through the hydrostatic portion and thereby increase operating efficiency. Typically, the mechanical power path includes a planetary gear set which acts to sum the power flows at either the input or output end of the transmission.

The existence of parallel power paths creates the possibility of reducing the output speed range or torque ratio in order to further reduce transmitted hydrostatic power; this then requires multiple ranges or “modes” to achieve the full torque and speed range of the transmission. The impact of multiple modes is to improve efficiency and sometimes to reduce cost. In addition to efficiency and cost, the magnitude of the output speed range/torque ratio in each mode has an impact on input power capacity relative to the size of the HST. Smaller ratios allow larger input power for the same size hydrostatic units. It is obvious that more modes allow either smaller mode ratios or larger transmission ratios or both. These relationships create the possibility for having a versatile design configuration that accommodates a number of market needs for input power, ratio range and efficiency.

Since a hydrostatic transmission is a part of the unit, one or more of the modes can be hydrostatic, or without parallel power paths. If there is a hydrostatic mode, it is usually the start-up range, or mode1.

Multi-mode HMT's are usually accomplished by reusing the hydrostatic components and clutching to a different mechanical component. The mechanical component will be a planetary if the mode is hydromechanical. Usually the modes are arranged so that there is no ratio change during the mode change in order to have continuous speed or torque delivery. Also, the hydrostatic transmission is usually stroked over center from full positive displacement to full negative displacement in order to fully utilize the installed hydrostatic power. When making a mode change, a planetary element different from any other mode must be used if the speed/torque ratio of the mode is to be independently selected from the other modes.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Vehicle installation: Transverse engine (refer to FIG.1). The engine1crankshaft is positioned transversely to the direction of vehicle motion. The transmission71is mounted directly to the engine, without any clutch, with the output below and to the side of the engine. The engine/transmission interface may be either integrated or nonintegrated. A right-angle gearbox74is connected to the transmission output16with connections to one or both axles70of the vehicle. In this configuration, the driver typically straddles the engine/transmission package so that short transmission length is important.

Longitudinal engine (refer to FIG.2). The engine1crankshaft is positioned parallel to the direction of vehicle motion. The transmission71is mounted directly to the engine, without any clutch, with the output below and to the side of the engine. The engine/transmission interface may be either integrated or non-integrated. The transmission outputs16/12and driveshaft(s) are connected to one or both axles70of the vehicle. In this configuration the driver may straddle the engine/transmission package so that narrow width is important. Short length is important so as to allow operator space in front of the engine.FIG. 2shows a PTO accessory72mounted to the face opposite the engine. This could be an auxiliary pump, a hand starter assembly or other engine connected device.

Description of operation: 2-Mode HMT (Refer toFIGS. 3,4and8). Primary component groups are the hydrostatic transmission51, idler shaft46, input/planetary49and the output assembly50. In the start-up mode, which is hydrostatic, power from engine1travels through shaft38to gear set2/10into the hydrostatic transmission51. The V-unit37starts at zero stroke and no power is transmitted. As the operator and programmed logic commands, a controller strokes swashplate57of V-unit37. As V-unit37is stroked to positive displacement, flow is sent to F-unit36through line43and rotation of gear set9/8starts. Power is delivered to idler shaft46and to gear set17/13. Clutch1is connected, which connects tang24-1with slot22, and power flows to output shaft16and optional output shaft12. As V-unit37is stroked fully, output16/12reaches the maximum forward speed for mode1. Planetary49is inactive in mode1. The stroke control logic for the V-unit37that resides in the controller may be of any type and may be like that described in U.S. Pat. No. 5,560,203.

At the fully stroked position of V-unit37, all elements of output shaft16are at the same nominal speed. A mode change is initiated and clutch1and2are shifted. When clutch2is engaged, tang24-2is connected with slot23and power is delivered to output shaft16through gear set7/11. Note that power is now being delivered to planetary49through gear set18/19to ring5, and through shaft38to sun3, creating parallel power paths. Power is transmitted from both paths to planets4-1,4-2and4-3to carrier6, to gear set7/11and to output50. Because ring5is speed controlled by HST51, a variable speed is controlled at output50. The controller strokes V-unit37from full positive to full negative displacement and output speed delivered through gear set7/11to shaft16reaches maximum for mode2.

After the shift of clutch2, power flows from F-unit36to V-unit37and the pressure in HST51switches to line44. In the second half of mode2, V-unit angle strokes over zero to a negative displacement, the power flow is reversed again and is transmitted from V-unit37to F-unit36. The stroke control logic for V-unit37is consistent with mode1. SeeFIG. 4for an illustration of transmission71output torque, unit36speed and HST51power flow vs. output speed. Note that continuous power is delivered from the engine to the wheels, with continuous ratio change, from full reverse to full forward speed even though the transmission changes modes at about 25% maximum speed.

3-Mode HMT (refer to FIGS.5,6and8). The 3-mode HMT is similar to the 2-mode described above with the addition of planetary/gears150and the clutch3. Note that the numbered elements for the 3-mode are the same configuration as the 2-mode with the addition of 100 (i.e.; HST51for the 2-mode is HST151for the 3-mode). The gear ratios may be different to accommodate different torque/speed ratio spreads. In mode3, clutch3is in engaged that connects carrier135to the output shaft116through tang128to slot127.

At the end of mode2, V-unit137is fully stroked in a negative direction and HST power is flowing from V-unit137to F-unit136in line144. At this condition, all elements of clutch3and output shaft116are at the same nominal speed. The controller initiates a mode change that moves to engage tang128in slot127and to disengage tang124-2from slot123in clutch2. Gear set129/130is driven by the input shaft138, enabling power flow in planetary150through ring132and sun134. As clutch2is disengaged, carrier106no longer drives the output shaft116and turns free, preventing power flow in planetary149. Note that power to planetary150is also delivered through gear sets118/131and109/111from F-unit136to sun134, creating a parallel power path. The controller strokes V-unit137from full negative to full positive displacement, first reducing the speed of F-unit136to zero and then increasing it to full positive speed. This allows variable speed from F-unit136to regulate sun134, and a fixed speed from input138to determine ring132speed, raising output speed to its maximum value.

After the shift of clutch3, the pressure in HST151switches to line143and power flows from F-unit136to V-unit137. When V-unit137angle strokes over zero to a negative displacement, the power flow is reversed and flows from V-unit137to F-unit136. The stroke control logic for V-unit137is consistent with mode1and2. Continuous power is delivered from the engine to the wheels, with continuous ratio change, from full reverse to full forward speed even though the transmission changes modes at about 18% and 54% of maximum speed.

Configuration and Construction: (Refer to FIGS.4,6,7,8,9and10). The hydrostatic transmission51(151) is the same for both the three mode and two mode versions. It is sized to provide adequate power for a low power, low ratio transmission in a 2-mode transmission, and for higher power, higher ratio requirements in a three mode transmission. The speeds and planetary ratios can be adjusted to accommodate the various vehicle requirements, over approximately a 2:1 spread in either variable. When individual mode ratio spreads are reduced, input power capacity increases. When modes are added, transmission ratio spread or input power is increased or both, depending on how the gears ratios and planetary ratios are selected. Note the relationship of ratio spread, input power and hydraulic power, and transmission output torque and speed inFIGS. 4 and 6.

The five main functional groups37(137),36(136),46(146),49(149), and50(150) are all located on a different centerline. In addition to facilitating gear ratio flexibility, this allows the overall transmission length to remain short. Note that moving the gear centerlines to accommodate various vehicle needs for input and output locations may be done with housing141unchanged. The planetary46(146) and150configurations, with the carrier as output, facilitate through drive for the input to PTO and the output for front and rear drive. Having limited functionality on each centerline also facilitates this. Offsetting the output, the V and F units from the input facilitates the output location below and to the side of the engine as well as the short length.

The housing construction supports the ability to alter gear ratios and planetary ratios in a cost efficient manner. (FIGS. 7 and 8) Center housing141which is used for all versions, contains the complex design features for the V-unit137and F-unit136, which are the same for all versions of the transmission. Housing141would also contain the means to stroke swashplate57and for mounting shift sensors. Housing141has space and features for the hydraulic reservoir159. The rear surface160of housing141is flat and accepts mounting of both manifold142and end cover140. This is accomplished by having the split line160in line with the end of units136and137cylinder block face.

Manifold142that contains lines143and144is the same for all versions and is attached to the rear surface160of housing141. Manifold142may also contain other HST circuit elements such as the charge pump charge check valves.

The end covers139and140contain the bearing supports158-1,2, etc. for idler shaft146, input/planetary149, planetary/output150and output shaft116, and are adjusted in location to accommodate different shaft centerline locations as gear ratios change and as output shaft locations change. End cover139is changeable in configuration to accommodate different engine mounting configurations, including integration with the engine housing. Housing portion168may be configured to match with a specific engine housing portion. Split line169is flat by placing it near to but outside the bearing support for V-unit137. In addition to gear ratio differences, end cover140is changeable to accommodate either 2-mode or 3-mode transmissions. End cover140may also be configured to include the mounting flange166for an engine driven PTO172. Both end cover139and140form the ends of reservoir159.