Patent Abstract:
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.

Full Description:
CROSS REFERENCE TO A RELATED APPLICATION 
     This application is a conversion of Provisional Patent Application Ser. No. 60/294,689 filed May 31, 2001. 
    
    
     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&#39;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. 
     Vehicle Background: 
     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. 
     Transmission Background: 
     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 mode  1 . 
     Multi-mode HMT&#39;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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a vehicle using one form of the invention; 
         FIG. 2  is a plan view of a vehicle using another form of the invention; 
         FIG. 3  is a schematic view showing the components of the invention; 
         FIGS. 4A-4C  are three output speed graphs showing output torque, unit speed, and power, respectively, as reflected in two different modes of operation; 
         FIG. 5  is a schematic view similar to that of  FIG. 3  but showing an alternate operational arrangement; 
         FIGS. 6A-6C  are three output torque graphs plotted against output speed, unit speed and power, respectively, as reflected in three different modes of operation; 
         FIGS. 7 and 7A  are partial sectional view of the apparatus of the invention with  FIG. 7  showing a lower portion of the structure of the upper portion shown in  FIG. 7A ; 
         FIG. 8  is a sectional view of the apparatus of the invention; 
         FIG. 9  is a side elevational view thereof; and 
         FIG. 10  is a front elevational view thereof as seen from the righthand side of FIG.  9 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Vehicle installation: Transverse engine (refer to FIG.  1 ). The engine  1  crankshaft is positioned transversely to the direction of vehicle motion. The transmission  71  is 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 gearbox  74  is connected to the transmission output  16  with connections to one or both axles  70  of 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 engine  1  crankshaft is positioned parallel to the direction of vehicle motion. The transmission  71  is 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 outputs  16 / 12  and driveshaft(s) are connected to one or both axles  70  of 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. 2  shows a PTO accessory  72  mounted 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 to  FIGS. 3 ,  4  and  8 ). Primary component groups are the hydrostatic transmission  51 , idler shaft  46 , input/planetary  49  and the output assembly  50 . In the start-up mode, which is hydrostatic, power from engine  1  travels through shaft  38  to gear set  2 / 10  into the hydrostatic transmission  51 . The V-unit  37  starts at zero stroke and no power is transmitted. As the operator and programmed logic commands, a controller strokes swashplate  57  of V-unit  37 . As V-unit  37  is stroked to positive displacement, flow is sent to F-unit  36  through line  43  and rotation of gear set  9 / 8  starts. Power is delivered to idler shaft  46  and to gear set  17 / 13 . Clutch  1  is connected, which connects tang  24 - 1  with slot  22 , and power flows to output shaft  16  and optional output shaft  12 . As V-unit  37  is stroked fully, output  16 / 12  reaches the maximum forward speed for mode  1 . Planetary  49  is inactive in mode  1 . The stroke control logic for the V-unit  37  that 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-unit  37 , all elements of output shaft  16  are at the same nominal speed. A mode change is initiated and clutch  1  and  2  are shifted. When clutch  2  is engaged, tang  24 - 2  is connected with slot  23  and power is delivered to output shaft  16  through gear set  7 / 11 . Note that power is now being delivered to planetary  49  through gear set  18 / 19  to ring  5 , and through shaft  38  to sun  3 , creating parallel power paths. Power is transmitted from both paths to planets  4 - 1 ,  4 - 2  and  4 - 3  to carrier  6 , to gear set  7 / 11  and to output  50 . Because ring  5  is speed controlled by HST  51 , a variable speed is controlled at output  50 . The controller strokes V-unit  37  from full positive to full negative displacement and output speed delivered through gear set  7 / 11  to shaft  16  reaches maximum for mode  2 . 
     After the shift of clutch  2 , power flows from F-unit  36  to V-unit  37  and the pressure in HST  51  switches to line  44 . In the second half of mode  2 , V-unit angle strokes over zero to a negative displacement, the power flow is reversed again and is transmitted from V-unit  37  to F-unit  36 . The stroke control logic for V-unit  37  is consistent with mode  1 . See  FIG. 4  for an illustration of transmission  71  output torque, unit  36  speed and HST  51  power 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 , 6  and  8 ). The 3-mode HMT is similar to the 2-mode described above with the addition of planetary/gears  150  and the clutch  3 . Note that the numbered elements for the 3-mode are the same configuration as the 2-mode with the addition of 100 (i.e.; HST  51  for the 2-mode is HST  151  for the 3-mode). The gear ratios may be different to accommodate different torque/speed ratio spreads. In mode  3 , clutch  3  is in engaged that connects carrier  135  to the output shaft  116  through tang  128  to slot  127 . 
     At the end of mode  2 , V-unit  137  is fully stroked in a negative direction and HST power is flowing from V-unit  137  to F-unit  136  in line  144 . At this condition, all elements of clutch  3  and output shaft  116  are at the same nominal speed. The controller initiates a mode change that moves to engage tang  128  in slot  127  and to disengage tang  124 - 2  from slot  123  in clutch  2 . Gear set  129 / 130  is driven by the input shaft  138 , enabling power flow in planetary  150  through ring  132  and sun  134 . As clutch  2  is disengaged, carrier  106  no longer drives the output shaft  116  and turns free, preventing power flow in planetary  149 . Note that power to planetary  150  is also delivered through gear sets  118 / 131  and  109 / 111  from F-unit  136  to sun  134 , creating a parallel power path. The controller strokes V-unit  137  from full negative to full positive displacement, first reducing the speed of F-unit  136  to zero and then increasing it to full positive speed. This allows variable speed from F-unit  136  to regulate sun  134 , and a fixed speed from input  138  to determine ring  132  speed, raising output speed to its maximum value. 
     After the shift of clutch  3 , the pressure in HST  151  switches to line  143  and power flows from F-unit  136  to V-unit  137 . When V-unit  137  angle strokes over zero to a negative displacement, the power flow is reversed and flows from V-unit  137  to F-unit  136 . The stroke control logic for V-unit  137  is consistent with mode  1  and  2 . 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 , 9  and  10 ). The hydrostatic transmission  51  ( 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 in  FIGS. 4 and 6 . 
     The five main functional groups  37  ( 137 ),  36  ( 136 ),  46  ( 146 ),  49  ( 149 ), and  50  ( 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 housing  141  unchanged. The planetary  46  ( 146 ) and  150  configurations, 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 housing  141  which is used for all versions, contains the complex design features for the V-unit  137  and F-unit  136 , which are the same for all versions of the transmission. Housing  141  would also contain the means to stroke swashplate  57  and for mounting shift sensors. Housing  141  has space and features for the hydraulic reservoir  159 . The rear surface  160  of housing  141  is flat and accepts mounting of both manifold  142  and end cover  140 . This is accomplished by having the split line  160  in line with the end of units  136  and  137  cylinder block face. 
     Manifold  142  that contains lines  143  and  144  is the same for all versions and is attached to the rear surface  160  of housing  141 . Manifold  142  may also contain other HST circuit elements such as the charge pump charge check valves. 
     The end covers  139  and  140  contain the bearing supports  158 - 1 ,  2 , etc. for idler shaft  146 , input/planetary  149 , planetary/output  150  and output shaft  116 , and are adjusted in location to accommodate different shaft centerline locations as gear ratios change and as output shaft locations change. End cover  139  is changeable in configuration to accommodate different engine mounting configurations, including integration with the engine housing. Housing portion  168  may be configured to match with a specific engine housing portion. Split line  169  is flat by placing it near to but outside the bearing support for V-unit  137 . In addition to gear ratio differences, end cover  140  is changeable to accommodate either 2-mode or 3-mode transmissions. End cover  140  may also be configured to include the mounting flange  166  for an engine driven PTO  172 . Both end cover  139  and  140  form the ends of reservoir  159 .

Technology Classification (CPC): 5