Abstract:
A drive mechanism for driving a vehicle, comprising a pair of drive wheels each having a drive shaft, a source of hydraulic oil under pressure on the vehicle and controlled by a control unit for delivering hydraulic oil in two directions, wherein the drive shafts of the pair of wheels are each driven by a high torque, low speed hydraulic motor or pump. The principal components of the motors include a crank shaft mounted in the housing for connection to the drive shafts of the wheels. At least two cylinder and piston assemblies are attached to the crank shaft for rotation of the crank shaft upon movement of the pistons between a minimum and maximum point of travel in the cylinders to thereby impart motion to the wheel drive shaft. A valve assembly provides hydraulic fluid to the cylinders to sequentially move the pistons in the desired direction of piston travel. The two motors are mounted on the vehicle to form a transaxle unit, and controls permit simultaneous or independent operation of the two motors.

Description:
This is a continuation-in-part application of my co-pending application Ser. No. 09/074,642, filed May 7, 1998, now U.S. Pat. No. 6,095,500, issued Aug. 1, 2000, which in turn is a continuation in part of my application having application Ser. No. 08/692,380 filed Aug. 5, 1996, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a transaxle device having a pair of high torque, low speed motors. More particularly the present invention relates to a transaxle and hydraulic motors of greatly improved power to weight design to provide on-road and off-road vehicle power. 
     BACKGROUND OF THE INVENTION 
     Once humanity discovered the wheel and put two of them together with an axle, vehicles have been designed for almost every purpose. Broadly, the development of motors has made vehicles efficient devices for moving persons and objects at faster speeds or with more power than otherwise has been possible. Steam and then internal combustion engines changed history, as persons and objects could be transported faster and farther with less effort than ever before. 
     Whether with internal combustion motors, electric motors, or any such device, power has been derived from rotation of a shaft, such as a crank shaft driven by pistons. The general rule has been the more power that is needed, the faster the revolutions per unit of time of the motor. The only alternative to higher rpms is a larger motor. Hydraulic motors, however, have not been used in many instances as actual drive applications for vehicles, primarily because the requirements of such a motor can&#39;t be met by conventional hydraulic motor designs. The primary drawback is that prior hydraulic motors are designed to drive a shaft, usually in combination with a transmission or gear box. While this would be appropriate for a vehicle using a transmission, such as a lawn mower or other vehicle not requiring much power, hydraulic motors are not as effective over large rpm ranges as the readily available gasoline motors used on such devices. 
     One form of hydraulic motor that has found use in industry is the low speed/high torque hydraulic motor, although it has not been applied to drive vehicles to this date because of certain drawbacks listed below. These low speed and high torque hydraulic motors come in two basic forms and in a variety of designs. The motors either are gear reduction motors or radial piston motors. In the former, high speed motors are reduced using a complicated series of gears to lower the speed and achieve higher torque. In the latter, various schemes for moving fluids around the axis of a crankshaft have been provided. Neither is suitable for use with, for example, a compact design mounted on a small vehicle where high power is needed. My U.S. Pat. No. 5,897,073 illustrates the use of an improved motor for holding extremely large and heavy spools of those cables. Even in that example, the vehicle itself is diesel engine driven. 
     Vane motors employ pressure against a plurality of vanes riding on a ring cam to form sealed chambers that carry fluid through the device, optimally at low pressure. The major disadvantage is that there are too many leakage paths. Rolling-vane motors sequence fluid flow to put high pressure against trailing surfaces and low pressure against leading surfaces, but are limited in displacement 
     There are also a variety of piston motors. Radial piston motors have a wide displacement range and are very efficient in medium or high displacement ranges. Cam type radial piston motors are less efficient and have difficulty at low speed. Axial piston motors are effective and have good starting torque characteristics. Two sources of heavy duty hydraulic motors are Nutron Motor Co., Inc. in Eliot, Me., which produces a radial piston hydraulic motor under the MHA series, and Kawasaki Precision Machinery, Inc. which produces radial piston hydraulic motors at its Staffa facility in Plymouth, England. 
     One of the principle drawbacks to hydraulic motors is that the commercial designs are extremely large for the power that is produced. Both the space or volume taken up by such motors and the weight that is needed are so great as to be seen as drawbacks or handicaps when selection of a motor is being made. In order to have useful torque in industrial applications, such as in heavy equipment, moveable boat and lumber lifts, end loaders, winches, and other hub drive designs, great amounts of power is needed. However, all presently known designs are not capable of effectively using the power of a short stroke, high displacement motor arranged within a compact area or motor volume so as to be adapted to the device of interest. 
     It would be of great advantage if an improved hydraulic motor for use with vehicles could be provided that would deliver the same or greater power using less space and having less weight than conventional motors which have been described. 
     In addition, it would be an advance in the art if high torque, low speed motors could be designed that did not require the use of multiple reducing gears to translate high speed motion into low speed, high torque output. 
     Also, it would be of significant advance if a vehicle could be provided with a hydraulic motor which could drive each of two wheels on an axle independently, such as when using a transaxle. Such a device could be used to drive each wheel separately, or, in another configuration, drive two tracks independently. 
     Finally, it would be an advantage if had the capability of self braking, so that no additional brake device would be needed for the vehicle. In other words, it would be a great advance if the motor could stop at any pre-selected point without the use of additional brake elements. 
     Accordingly, it is an object of the present invention to provide a transaxle device driven by an hydraulic motor capable of operating under high torque and low speed, such motor being suitable for operation in a smaller space than prior art designs. 
     A further object of this invention is to provide a transaxle device and hydraulic motor configuration capable of producing high torque and low speed without the need for multiple reducing gears to translate high speed motion into the resultant high torque and low speed. 
     Yet another object of the present invention is to provide a vehicle having a hydraulic motor having fixed displacement of substantially larger capacity than currently available for transaxle applications, so as to provide orders of magnitude more power in a small enough space to operate on both wheels on the axle. 
     Other objects will appear hereinafter. 
     SUMMARY OF THE INVENTION 
     It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, the present invention provides a transaxle device of reduced size and increased power, capable of operating under high torque and low speed. The device is suitable for operation in a smaller space than prior art designs, so that vehicles can be equipped with a pair of motors to radically increase the power of any given size of vehicle. 
     The present invention comprises a pair of hydraulic motors, described below, which operate using hydraulic fluid under pressure from a source carried on the vehicle. The vehicle frame, a structural bridge or other component, is arranged to mount each motor so that the output shaft is operably connected to a wheel. In one embodiment the wheel is a conventional wheel, perhaps with a rim and tire, or, alternatively with cogs for engagement of a track used in bulldozers and the like. 
     The principal components of the motor or pump include a crank shaft mounted in the housing for connection to a shaft on which a wheel is attached for direct drive. Cylinder and piston assemblies are attached to a crank shaft for rotation upon movement of the pistons in the cylinders to thereby impart motion to the crank shaft and, thus, the wheel shaft or axle. 
     The hydraulic circuit is designed so that the left and right driving wheels on the vehicle are free to seek their own rate of rotation as the vehicle is steered in turns, while continuing to applying full power to each wheel. The motors themselves can be in one common axle assembly or individually mounted to the vehicle, such as on the main frame or some component attached thereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the invention, reference is hereby made to the drawings, in which: 
     FIG. 1 is a schematic view showing the hydraulic flow system utilized in the motor used in this invention. 
     FIG. 2 is a schematic view illustrating a sequence of high and low pressure on both sides of a piston, with three views showing dead center, extending and retracting positions. 
     FIG. 3 is a side elevational view of the preferred embodiment of the present invention, with some moving parts shown in dotted line. 
     FIG. 4 is a plan view showing of the device shown in FIG. 3, again with some moving parts shown in dotted line. 
     FIG. 5 is a schematic view of the valve operation of the device of FIGS. 3 and 4, showing high and low pressure fluid transfer. 
     FIG. 6 is a side elevational view, partially in section along line  6 — 6  of FIG. 7, showing a second embodiment of the present invention, with some moving parts shown in dotted line. 
     FIG. 7 is a plan view of the embodiment shown in FIG. 6, with some moving parts shown in dotted line. 
     FIG. 8 is an end view of the preferred embodiment of the present invention, showing the transaxle having two motors attached thereto to drive the rear wheels of a vehicle. 
     FIG. 9 is a side elevational view of the preferred embodiment of FIG.  8 . 
     FIG. 10 is an end view of an embodiment of the present invention, showing the transaxle having two motors attached thereto, to drive a track assembly for a vehicle. 
     FIG. 11 is a side elevational view of the embodiment of FIG.  10 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in the drawings, the present invention provides a hydraulic motor employing dual action on a piston, so as to push as well as pull the piston with a power stroke. Shown in FIG. 1 is a schematic flow diagram illustrating the way that fluid flows into a pair of pistons to drive a shaft The hydraulic lines route fluid in one end to push the piston to maximum position, then fluid is introduced to the other side of the piston as pressure is released on the first side so that the fluid continues to drive the piston to its minimum position with respect to the crank shaft. 
     Specifically shown in FIG. 1 is a source of hydraulic fluid  11  that is routed under pressure by pump  12 . A return chamber  13  functions to receive the return of fluid under reduced or low pressure and return it to source  11 . Valve  15  transmits high pressure hydraulic fluid from pump  12  and functions as a forward/reverse control, so that the motor operates to rotate in a first or forward direction of rotation or in a second or reverse direction of rotation. 
     Valves  31  and  32  serve to direct the high pressure fluid in one direction for the first cylinder  17  and in the opposite direction for second cylinder  18 . High pressure hydraulic fluid flows through valve  31  via line  19  into first port  21  of cylinder  17 , as shown by the inlet arrow  21   a , pushing piston rod  23  in the direction of arrow  25 . Hydraulic fluid exits cylinder  17  at second port  27  as shown by the outlet arrow  27   a , to be returned via line  29  to return chamber  13  through valve  15 . Valve  31  functions to control flow in lines  19  and  29 . Fluid entering port  21  forces the piston head  23   a  on piston rod  23  to move in the direction of arrow  25  until it reaches its maximum point of travel. 
     At the same time, high pressure hydraulic fluid flows in a second direction via line  30  through valve  32  into second port  28  of cylinder  18 , as shown by the inlet arrow  28   a , pulling piston rod  24  in the direction of arrow  26 . Hydraulic fluid exits cylinder  18  at first port  22  as shown by the outlet arrow  22   a , to be returned via line  20  to return chamber  13  through valve  15 . Valve  32  functions to control flow in lines and  30 . Fluid entering port  28  forces the piston head  24   a  on piston rod  24  to move in the direction of arrow  26  until it reaches its minimum point of travel. 
     When valve  31  senses that piston rod  23  has reached its maximum stroke, as will be shown in several embodiments below, flow in lines  19  and  29  is reversed, so that high pressure fluid enters second port  27  in the opposite direction to arrow  27   a , forcing the piston head  23   a  on piston rod  23  to move in the opposite direction to arrow  25 . Pressure in line  19  is released by valve  31  so that low pressure fluid exits cylinder  17  via first port  21  in the direction opposite to arrow  21   a . Similarly when valve  32  senses that piston rod  24  has reached its minimum stroke, as will be shown in several embodiments below, flow in lines  30  and  20  is reversed, so that high pressure fluid enters first port  22  in the opposite direction to arrow  22   a , forcing the piston head  24   a  on piston rod  24  to move in the opposite direction to arrow  26 . Pressure in line  30  is released by valve  32  so that low pressure fluid exits cylinder  18  via second port  28  in the direction opposite to arrow  28   a . As can be appreciated, both cylinder  17  and cylinder  18  have what is called a null point or dead point when hydraulic pressure is switching from high to low on one side or the other of the piston head  23   a ,  24   a , respectively. For that reason, when two pistons are used, as in FIG.  1  and elsewhere, the piston cycles are offset from each other, preferably by 90°, so that at least one piston is driving in one direction while the other piston is at null as the direction of high pressure flow reverses for that other piston. 
     FIGS. 2 a - 2   f  illustrate the effort applied by two cylinders attached to a crankshaft through one revolution of that shaft FIG. 2 a  illustrates the situation when first cylinder  17   a  is being pushed by high pressure hydraulic fluid (the condition of cylinder  17  shown in FIG. 1) and second cylinder  18   a  is on dwell, providing no effort or movement to the shaft. FIG. 2 b  represents the point in the cycle when both  17   b  and  18   b  are pushing on their respective piston heads  23   a  and  24   a . FIG. 2 c  is the opposite of  2   a , with  18   c  pushing and  17   c  on dwell or null. As the shaft rotates, FIG. 2 d  represents the condition when  18   d  is pushing while cylinder  17   d  is now receiving high pressure hydraulic fluid on the opposite side of the piston head (the condition of cylinder  18  shown in FIG.  1 ). FIG. 2 e  represents the next condition, where  18   e  is on dwell and  17   e  is pulling, with pressure on the rod side of its piston head. Finally, FIG. 2 f  illustrates the condition where both  17   f  and  18   f  are pulling, with pressure as shown for cylinder  18  of FIG.  1 . This completes one revolution of the shaft to which the pistons  17 ,  18  are connected. As can be seen, at all times there is positive hydraulic pressure urging at least one piston to drive the shaft, even when the other piston is at dwell or not exerting power. This not only provides for smoother power transmission, it allows for the motor to always have positive displacement when starting or stopping the motor. 
     FIG. 3 illustrates the preferred embodiment of the present invention, where the motor  33  generally is enclosed in a housing  35 . Cylinders  37  and  38  operate as illustrated in FIG.  2 . Cylinder  37  is receiving high pressure hydraulic fluid on the top of piston head  39 , driving piston rod  41  to its maximum position of extension, thereby rotating crank shaft  43  about axis  44 , as piston rod  41  is attached to crank shaft  43  via crank pin  45 . This corresponds to the schematic condition of cylinder  17  in FIG.  1 . 
     FIG. 3 also illustrates the condition of cylinder  18  in FIG. 1, where cylinder  38  has high pressure hydraulic fluid on the rod side of piston head  40 , thereby moving piston rod  42  to its minimum position and thus rotating crank shaft  43  about axis  44  as piston rod  42  pulls on crank shaft  43  via crank pin  46 . Piston  42  is about to reach its dwell or null point, shown by  2   a  in FIG.  2 . 
     FIG. 4 is a plan view of the device shown in FIG. 3, with the cylinders  37  and  38  in the same point of the motor cycle. FIG. 4 illustrates how hydraulic fluid under pressure is introduced into the cylinders via valve assembly  47 . Valve assembly  47  provides for high pressure hydraulic fluid to flow along valve core  49 , shown in the broken away portion, such that valve assembly  47  oscillates the same as cylinders  37  and  38  from maximum to minimum extension of rods  41  and  42  This travel is determined by the size of crank shaft  43  and the placement of points of attachment of rods  41 ,  42  via crank pins  45 ,  46  respectively. 
     Whatever the orientation of cylinders  37 ,  38 , high pressure oil enters from valve assembly  47  along valve core  49  and communicates with one of two orifices in each cylinder  37  and  38 , depending upon the specific location of the pistons. There is, of course, no flow when a piston is at dwell or null as both orifices are closed during the transfer from one direction of force to the other, such as from push to pull on crank shaft  43 . Cylinder  37  is extending or pushing piston rod  41  as high pressure hydraulic fluid pushes on piston head  39 , flowing from valve assembly  47  along valve core  49  to first orifice  51 . Low pressure hydraulic fluid is also being expelled from behind piston head  39  via second orifice  53  for return in accordance with the flow shown in FIG.  1 . Cylinder  38  is retracting piston rod  42 , thereby pulling crank shaft  43  via crank pin  46 , as high pressure hydraulic fluid flows along core  49  to second orifice  54  as low pressure fluid is expelled via first orifice  52 . 
     FIG. 5 illustrates the flow of hydraulic fluid about valve core  49  as it moves in valve assembly  47  to transfer high pressure H to one orifice and low pressure L return fluid to the other orifice for each piston assembly. Valve assembly  47  moves with respect to valve core  49  as described above as piston heads  39  and  40  cycle between maximum and minimum positions as cylinders  37 ,  38  oscillate. In  5   a , high pressure fluid H enters valve assembly  47  along core  49  and low pressure fluid L exits. As cylinder  37 , for example, rotates, core  49  remains fixed with respect to oscillating assembly  47  in  5   b  to allow high pressure fluid H to enter orifice  51  and low pressure fluid L is removed from behind piston head  39  via orifice  53 . Further travel past a dwell point (similar to  5   a ) shows in  5   c  high pressure fluid H entering orifice  53  and low pressure fluid L exiting orifice  51 . A similar but reverse flow takes place in cylinder  38 , offset by 90° for example, to provide at least one positive force at all times, as shown in FIG.  2 . 
     In an alternative embodiment shown in FIGS. 6 and 7, hydraulic fluid flow is controlled at the opposite end from the device shown in FIGS. 4 and 5, yet the principle of operation is the same. Cylinder  57  oscillates about shaft  59  as piston rod  61  moves about crank shaft  63 . Cylinder  58  also oscillates about shaft  59  as piston rod  62  also moves about crank shaft  63 . For illustration purposes, one cylinder  58  is shown in the dwell location. It should be appreciated that there are only two cylinders in use. In this embodiment, crank shaft  63  includes an outer cam surface  64  and an inner surface  65 , so that valves  67  engage these surfaces via spring biased roller  69 . When roller  69  is on the inner surface  65 , hydraulic fluid flows to port  71  to push piston head  79  and piston rod  61  toward crank shaft  63 . Alternatively when roller  69  is on outer cam surface  64 , hydraulic fluid flows to port  75  to move piston head  80  away from crank shaft  63  so that rod  61  pulls crank shaft  63  to cause further rotation thereof. 
     FIG. 7 illustrates the operation of this two piston embodiment of cylinders  57 ,  58  where first one and then the other piston moves its piston rod  61 ,  62  on the crank shaft  63  as fluid flows in or out of ports  71 ,  75  and  72 ,  76  respectively. In this embodiment as well as that of FIGS. 4 and 5, the two cylinders  57 ,  58  travel through the cycles illustrated in FIG. 2 
     While springs and cams have replaced the valve assembly of FIGS. 4 and 5, operation is still based upon the unique and efficient principle of having hydraulic fluid act alternatively upon both faces of a piston in a cylinder, so that positive force is used to move the piston in both directions. An enormous amount of power is achieved when such motors are used as low speed/high torque hydraulic motors. Working models have been constructed that operates at 3500 psi and has a capability of generating up to 22,000 foot/pounds of torque or more. Tests have shown these motors to operate for 100 hours at full pressure without any leakage or other problems. 
     The motors may be reversed on command, and have a braking function and may be locked solid by control of the fluid pressure flow, or they may move incrementally as desired. As set forth above, the motor functions also as a pump when energy is applied to the crank shaft The housing that supports the motor should be solidly constructed to have high torsional rigidity. The unique push and pull action provides high torque, creating a large displacement motor in a compact package. 
     The device may be used to power a winch, or as a wheel motor for a garden tractor, a large tractor, a boat lift and storage vehicle, an airplane towing vehicle, a crane or lift that can be placed on a truck bed or other vehicle, as a pump, and in many other industrial applications. This hydraulic motor is capable of functioning in most, if not all situations where conventional low speed/high torque hydraulic motors and the like are used, bringing the device of this invention&#39;s unique power and size advantages. While hydraulic fluids such as oil are preferred, the present invention will also function with other fluids such as water, compressible fluids such as inert gases, and the like. The shape of the motor of this invention lends itself to applications where the output of the shaft is at the end of a beam or column, such as in a lifting boom/beam. In one proposed design, the wheels are at the end of stork-like legs that extend down from a platform, such that the motor mechanism is within the leg rather than in the wheel. This provides for increased strength and reliability, among other advantages. 
     Turning now to FIGS. 8 and 9, the preferred embodiment is shown generally by the reference numeral  80 , and includes a vehicle body  81 , a vehicle engine or motor  83 , a variable displacement hydraulic pump  85  which delivers hydraulic oil under pressure from the reservoir  87  through a control unit  89 , which is adapted to provide forward and reverse flow of oil. Hoses  90  and  91  transfer oil under pressure from the control unit  89  as shown by the arrows along a structural bridge  93 , which may be part of the vehicle frame or may be an independent element mounted on the vehicle body  81  as desired. Motors  95  and  97  are also supported on the structural bridge  93  to form the transaxle unit of this invention. Output shafts from motors  95  and  97  drive wheels  99  and  101 , respectively, being attached to said wheels via shafts  100  mounted in hubs and best seen in FIG.  9 . 
     The motors  95  and  97 , as previously described with respect to FIG. 1, for example, are low speed, high torque motors which operate to drive wheels  99  and  101 , providing direct engine power to wheel tractive effort without gears and, of course, without gear reductions. The two motors  95  and  97  have a differential action, such that the right and left wheels  99  and  101  are free to seek their own rate of rotation as the vehicle is steered in turns while maintaining full power applied to each wheel. 
     In an alternative embodiment shown in FIGS. 10 and 11, motors  95  and  97  are adapted to drive a track such as used with bulldozer  103  and other slow moving tracked vehicles normally used off-highway. Two control units  105  and  107  separately control motors  95  and  97  to function as skid steering valves. The bulldozer  103  includes a drive wheels  109  and  111 , driven by motors  95  and  97  respectively through shafts  110  and  112  respectively, wherein drive wheels  109  and  111  have drive sprockets  113  for engagement with tracks  115  and  1   17 , respectively. Control units  105  and  107  function as restricting flow control valves to provide skid steering, as is the normal case with bulldozers and the like. 
     In summary, the present invention of a transaxle device operates using the motor of this invention to produce substantially improved results, using a constant displacement motor for each side of the axle. Motors of this type may operate at speeds of 0 to 20 rpm or more, and have been tested by operation at full pressure for over 100 hours without any hydraulic oil leakage. The cost per unit of motor size, such as cubic centimeters of cylinder size is less than half of that for hydraulic motors using gear reductions, primarily because of the simplicity of design of the motor, but more importantly, the motors of this invention are the first to be positionable to directly drive a pair of wheels, or skids, in a simple, efficient design 
     While particular embodiments of the present invention have been illustrated and described, it is not intended to limit the invention, except as defined by the following claims.