GB2202593A - Hydraulic motors and pumps and vehicle hydrostatic transmission system of wheel motor type - Google Patents

Abstract

A shaft 1 bears an eccentric 20, supported between bearings in a casing 5 and a cover and has separate fluid passages A,A1 connected to respective high and low pressure fluid systems. A cylinder block 14 rotatably mounted on the eccentric 20 has cylinders 14a with pistons 13 whose outer flat end faces 13a are in contact with planar faces 5a in the casing 5. Springs 12 urge the pistons 13 outwards. When the casing 5 turns around the shaft 1, the eccentric 20 urges the pistons 13 to reciprocate in turn in the cylinders 14a. The machine may be of fixed displacement or, as shown, the relative eccentricity of shaft 1 and eccentric 20 may be varied. It is intended for use as a wheel motor to be driven by a pump via a distributing valve. <IMAGE>

Description

Hydraulic Motors and Pumps and Vehicle Hydrostatic Transmission System of Wheel Motor Type This invention relates to a hydrostatic transmission system and hydraulic motors, more particularly to a vehicle hydrostatic transmission of wheel motor type and hydraulic motors therein, as well as hydraulic pumps.

Hydrostatic transmission has many advantages and finds ever increasing applications in recent years. But, due to the poor performance of its major components (especially the hydraulic motor or pump), its application has been very limited.

The application of hydrostatic transmission in vehicle drive systems may bring to it a series of advantages, such as, a genuine continuously variable transmission within its full speed range; equal speeds in forward and reverse; very smooth speed change; the best matching between the engine and the transmission to improve its fuel economy and dynamic performance; easier adaptation to automatic control and its covenient layout on the vehicles etc.

Hydrostatic transmission of wheel motor type is a most ideal power transmission system for most of the vehicles, consisting of a pump driven by an engine, the high pressure oil from the pump being delivered to hydraulic wheel motors in the wheels via control valves, hoses or pipes to generate a driving torque to propel the vehicle. Obviously, this layout could take full advantage of the merits of hydrostatic transmissions and offers following features in addition to those above mentioned.

1) The construction of the transmission system can be significantly simplified especially for those vehicles requiring large speed ratio range or multiple-speed steps or reqired to execute complicate operations.

2) The layout of the vehicle can be realized very conveniently because the engine are connected to the wheel motor by hoses or pipes, with no strict limitation to their relative positions which is valuable in many vehicles, such as, minicar or ultra-minicar, self-propelled agricultural machines, military vehicles, construction machinery etc.

3) Easy realization of interchangeability and series design of the parts and components of transmission system, so the requirements of different vehicles can be met with properly combination of a series of components. Obviously, it will bring great benefits to the manufacturers and users.

Since the hydrostatic transmission of wheel motor type has so many attractive advantages, it has been the target of designers and researchers.

However, limited by the performance of its components (especially the wheel motors), the hydrostatic transmission of wheel motor type can only be used today in some low speed or special purpose vehicles. Therefore, in order to adapt this technology effectively to middle or high speed vehicles, performance and construction of the wheel motors must be overall improved in order to satisty a series of very strict reqiirements as follows 1) It must be direct mounted in the wheels to drive the wheels without any additional speed reducing/increasing gearboses.

2) The hydromotor should has a rather wide speed range to satisfy the speed requirements of the vehicle. For example, for a car it must operate normally in the speed range of 0 to 1000 or more r.p.m. and its efficiency must not decrease significantly with increase of the speed.

The maximum speed of today's wheel motors is about 200-300 r.p.m., falling short of the above reqirement, so its application is limited to low speed (less than 20-30 kilometer-perhour) vehicles.

3) The hydromotor should have high efficiency over a wide speed range. Most vehicles require high tractive forces during starting and climbing, which may be 20-30 times of the relatively light load in normal running. For instance, transportation trucks are running most of the time under light loads at medium to high speeds, just within the low efficiency region of today's hydraulic wheel motors. But fuei economy (overall efficiency) is often the major consideration of this kind of vehicle, which result in very strict demand on the efficiency performance of wheel motors, namely, it must have very high torque efficiency in starting as well as overall efficiency under light loads over wide speed range. It is impossible to meet these requirements with today's hydromotors.

4) The displacement of the hydraulic wheel motor should be variable to meet the requirement of further extending the speed range of the vehicle. Because vehicle speed and load varies over a wide range in its operation and the maximum displacement of the motor is determined by the maximum tractive effort required, therefore, with a fixed displacement motor, the working pressure may fall to 10-30 kg/cm2 during normal running far away from its high efficiency region. Moreover, at high vehicle speeds, the oil flow velocity in the hydraulic system increases proportionally with the vehicle speed, resulting in a high flow loss, further reducing the overall efficiency of the system.If the displacement of the hydraulic motor is made variable, then its displacement can be decreased at above-mentioned working conditions to increase the working pressure and reduce the velocity of the oil flow to improve the overall efficiency of the system.

5) It is necessary to simpli fy the construction, to lower the requirement on material and manufacture technology so that it may more adaptable for mass production to cut down the cost and price. At present, the cost of hydrostatic transmission is often much higher than mechanical transmission, which is one of the main factor limiting its application.

6) The hydraulic wheel motor must accommodate the bad working circumstance which may be encountered in its use, for instance, it should sustain safely the vibration and shock loads in operation, not too sensitive to the working fluid and its filtration, easy for repair maintenance, etc.

To solve the problems above --mentioned, attempts have -been made to improve the construction of hydraulic wheel motor and the vehicle hydraulic transmission system. As an example, S.A.E papers No.790883 "An interesting and informative comparison of mobile hydrostatic wheel hub drives" and S.A.E. 810971, 810974 have systematically described the present state of this art and emphatically compared the performance of the two popular types of hydraulic-wheel- motors today.

First, the axial piston hydraulic motor with a planetary gearbox is widely used in some vehicles, exploiting fully its capability of high speed, high pressure, high efficiency and continuously variable displacement.

However, the disadvantage of complicated construction, high price of axial piston hydraulic motor and planetary gearbox, narrow speed range, low overall efficiency (including the efficiency of the planetary gearbox) and starting torque efficiency and its irregular external shape limits its use in many other applications.

The second type, cam lobe hydromotor has a relatively high starting torque efficiency and mechanical efficiency as well as a wider speed range than the axial piston type. But it is also complicated in construction with its efficiency reduced significantly with increased speed and incapable of containuously variable displacement. Therefore its application is also limited to some low speed (less than 20 kilometer perhour) or special purpose vehicles.

As can be seen from the above, the application of hydrostatic transmission of the wheel motor type is dependent, to a large extent, on the perfection of its performance. There must be a breakthrough in construction and performance of the wheel motor before the hydrostatic transmission of wheel motor type may enjoy wide application. Moreover, a more perfect hydraulic transmission system with further improved overall efficiency and extended speed range must be developed to exploit fully the merits of the wheel motor.

Therefore, my primary object -- is to provide a new design of hydraulic motor or -pump --with -bigh efficiency, -twide -speed range, simple construction and variable displacement. And with this new kind of hydraulic motor or pump, a high efficiency and wide adjustable speed range of a hydrostatic transmission system is developed in which the hydraulic motor is employed to expand its applications. This hydrostatic transmission system can replace not only many current types of - vehicle transmission systems but also find its use in many other machines.

One object is to provide a hydraulic motor or pump having higher starting torque efficiency and mechanical efficiency by rationalizing the layout of the hydraulic motor and optimizing the hydraulic system.

Another object l is to provide means by which the oil churning losses and oil flow losses in the motor or pump can be reduced in order to obtain a hydraulic motor or pump with higher efficiency working region and wide speed range.

Another object is to provide a hydraulic motor or pump with higher rated maximum working speed by reducing the PV rating of its major sliding working surfaces and improved balancing of its rotating parts.

Another object is to provide a continuously variable displacement hydraulic motor or pump to further expand its application in hydrostatic transmission.

Another object is to provide means by which the displacement of the hydraulic motor or pump can be controlled continuously.

Another object is to provide, a hydraulic motor with small size, light weight and symmetrical shape, which can be conveniently mounted in a wheel without any gearboxes.

Another object is to provide a hydraulic motor or pump which has minimum -number of parts and simple in construction, easy to manufacture in order to lower its cost.

Another object : x ! is to provide a hydraulic motor which can sustain reliably the radial and axial shock from the wheel of the vehicle on bad roads.

Another object - is to provide means for the mounting -of hydraulic motor or pump for improving layout and mounting of the wheel motor, pump, pipe lines and displacement control mechanism on a vehicle.

Another object : - is to provide a hydralic transmission system for vehicle in which the working mode of the wheel motor can be controlled spearately to further extend the speed range fo the vehicle.

Another object is to provide a vehicle hydraulic transmission system to accommodate the complicate situations it may encounter in use.

This invention provides a hydraulic motor or pump with a rotating casing and fixed shaft for simplifing the mounting of the wheel motor in a wheel of a vehicle and the flow distribution in the wheel motor.

The hydraulic motor or pump of the invention comprises a casing with a number of planar surface, a cover, bearings installed in said casing and said cover to support an eccentric shaft with a eccentric. A cylinder block with a number of radial cylinders with their center lines perpendicular to the axis of the eccentric shaft mounted on the outer periphery of said eccentric of said eccentric shaft. A piston in each of said cylinders has its outer flat end maintaining constant contact with said plarary surface on said casing under the action of its centrifugal force, a return spring and the oil working pressure. There are two separated groups of oil duct in said ecentric shaft, one for oil inlet and the other for outlet.The eccentric of the eccentric shaft of the hydraulic motor or pump of the invention may be a combined eccentric which is composed of an eccentric shaft and an eccentric sleeve with a cylindrical inner bore and a cylindrical outer surface with an offset being rotably mounted on said eccentric of said eccentric shaft through its bore and with said cylinder block mounted on the outer periphery thereof. The composite eccentric and consequently the piston stroke and displacement may be changed continuously when said eccentric sleeve is rotated on the said eccentric shaft to different positions by an external displacement control means.

A pin is inserted in a hole on the end face of said eccentric sleeve with its rectangular head engaged in the slot on the flange of the displacement control sleeve which is a force fit in the bearing inner race and mounted on said eccentric shaft journal. A displacement control arm mounted on the eccentric shaft journal meshes with the end of said displacement control sleeve as a dog tooth clutch or its internal teeth may engage the external teeth at the end of the displacement control sleeve.

Said displacement control arm may be actuated by a displacement control cylinder or other control means to-rotateSon said eccentric shaft and this .c.

motion will be transmitted through said displacement control sleeve and pin to said eccentric sleeve to rotate on said eccentric shaft to change said composite eccentric or the displacement of said hydraulic motor or pump.

There are two separate oil grooves in said eccentric sleeve in communication with said oil ducks in the eccentric shaft respectively.

A number of safety pins pressed into said casing or said cover each maintaining an appropriate clearance with its adjacent cylinder block wall to allow said cylinder swing freely relative to said casing under normal operation and even at maximum displacement, but when there is a sudden change in roating speed between said casing and said cylinder block, such as the braking of the casing, said safety pin will be in contact with said syclinder wheel wall to limit the amplitude of said relative rotating movement and force said cylinder block to rotate at same speed with said casing to prevent said piston from moving off its seat. A circular oil cushion recess or in the form of radial grooves is machined in the piston end and filled with oil through a throttle hole to form a hydrostatic support.

Based on said variable displacement hydraulic motor or pump, a fixed displacement hydraulic motor or pump can be evolved by replacing said eccentric sleeve and said eccentric shaft with a single eccentric shaft with a fixed eccentric and eliminating said displacement control parts including pin, displacement control sleeve and said displacement control arm.

A spoon-shaped oil duct or ducts can be arranged in said displacement control sleeve or said thrust washer with its inner end communicating with said leakage oil passage in said eccentric shaft and its outer end extending deep down in said casing to scoop and discharge the leakage oil by its inertia and dynamic pressure in running in order to reduce the oil churning loss at high speeds.

For the purpose of adjusting the displacement of said hydraulic motor or pump form outside of the motor, the double-acting piston of the displacement control cylinder actuating the displacement control arm controlled by a control-valve which -may -be manual, automatic or -a combination thereof, in the case of automatically, the automatic control is based on one or several operating parameters, such as the engine torque, r.p.m. intake manifold vacuum, the contents of exhaust gas, the position of accelerator pedal or the oil flow rate or pressure in the hydraulic transmission system.

This invention provide a vehicle hydrostatic transmission system of wheel motor type which comprises an engine or engines, a oil pump or pumps, oil pipe lines, a filter or filter, a vale or valves, a oil tank and a wheel motor or motors, wherein the wheel motors can be mounted on a mounting bracket or othr part of a vehicle which is mounted directly to a vehicle frame or suspension system.

The mounting bracket can facilitate the mounting of said wheel motor or pump. The tapered section of said eccentric shaft of said wheel motor is inserted into a tapered bore on mounting bracket and held in position by a nut with two O-rings to prevent leakage. There are pipe thread holes for pipe fittings in said mounting bracket to communicate with the inlet, outlet and leakage oil passage in said eccentric shaft respectively.

The wheel motor or motors, can either be variable displacement or fixed displacement hydraulic motor or pump. In the case of variable displacement wheel motor, the displacement control cylinder can be mounted on a mounting bracket or other part of the vehicle. The fixed displacement wheel motor can be used in vehicles with a narrow speed in which the displacement control mechanism can be omitted.

The hydraulic system of this invention may provide with a distributing valve to control the working mode (drive or free-wheeling) of said wheel motors to get different drive-system combinations, ranging from one wheel drive to all wheel drive.

The hydraulic transmission system of this invention may be provided with a direction valve for controlling the running direction of the wheel motor; a free-wheeling valve to bypass the oil pumped out from the wheel motor when the vehcileis in free-wheeling; a safety valve arranged between the high pressure line and the low pressure line of the hydraulic system.

The hydraulic transmission system of this invention may be further provide with a oil charge pump driven by the engine and charge valves arranged between the oil pump and the oil tank and a gearbox with a fix ratio arranged between the engine and the oil pump.

Various kinds of pumps can be used in the hydraulic transmission system above mentioned, such as, T-type radial piston pump, axial piston pumps or other kinds of pumps; variable displacement pump or fixed displacement pump; uni-directional variable displacement pump or bi-directional variable displacement pump.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a axial section of a fixed displacement motor or pump; Fig. 2 is a cross section taken from Fig. 1 along line A-A; Fig. 3 is a cross section of a continuously variable displacement motor or pump; Fig. 4 is a cross section taken from Fig. 3 along line C-C; Fig. 5 shows the mounting of a wheel motor; Fig. 6 shows the variable displacement control mechanism of the wheel motor; Fig. 7 shows a hydrostatic transmission system of wheel motor type for a 4x2 drive vehicle; and Fig. 8 shows a comparison of mechanical efficiency of a hydraulic motor according to the invention with those of a axial piston motor with planetary gearbox and a cam lobe hydromotor.

In order to promote a full -understanding of the concept and other aspects of the present invention, it is described by examples with reference to the accompanying drawings.

The hydraulic motor or pump of the invention is a continuously variable displacement or a fixed displacement radial piston type with a fixed shaft and rotating casing. Because the shaft is held stationary, the oil distributing function can be accomplished by the shaft and the cylinder block with the abolition of conventional distributing components and the wheel can be mounted directly to the rotating casing without the conventional hubs and driving parts.

As a result of its unconventional working principle and construction, the hydraulic motor or pump of this invention is simple, compact with high efficiency and wide speed range.

Fig.1 and 2 are schematic illustrations of a fixed displacement hydraulic motor or pump of the invention. It consists of an integral casing 5 with a number of planar surfaces Sa on its inside wall, against which the outer end of pistons maintains constant contact. The integral construction of the casing .5. reduces its deformation under loads and reinforcing ribs may be added on its outside for greater rigidity, if necessary.Cover 7 with a reinforcing flange 7a having a close fit with the casing 5 will help to reduce the deformation of casing under the piston force and oil pressure and to improve the contact between the pistons 13 and piston sets - 5a:. Bearings 4 are installed in casing 5 and cover 7 to support an eccentric shaft 1 with a fixed eccentric ;ia between the bearings :4. The capacity of the bearing 4 is determined by the permissible maximum oil pressure load and is much higher than the static and dynamic wheel loads, ensuring great safety in a road operations under normal working pressure.Two separate oil passagesAAi are provided in eccentric shaf5Afor inlet and A. for outlet, under normal running conditions communicating respectively with oil grooves B and B1 on the eccentric - la;. A star-shaped cylinder block 14; is rotatably mounted on the eccentric la and has a number of radial cylinders 14a machined with their center lines perpendicular to the axis of the eccentric shaft 1..

The cylinder communicates in turn with oil grooves B and .B1 through its oil port 14c;. A piston 13 is installed in each cylinder :14a, with its outer flat end 13a, maintaining constant contact with the planar surface Sa in the casing .5. When the casing 5 performs a rotary motion relative to the eccentric shaft 1, the eccentric la will impart a gyrating motion to the cylinder block causing each piston 13 to reciprocate in its cylinder 14a.This movement, coupled with the oil grooves B and B1 on the eccentric la., creates in each cylinder an intake and exhaust process of the oil necessary for the function of a hydraulic motor or pump.

A preloaded return spring 12 is usually (may be omitted in some cases) installed between the piston 13 and the cylinder 14a to force piston ;13 outwards and maintains constant contact with the planar surface sa: of the casing 5 in conjunction with oil pressure and centrifugal force in operation.

To reduce the friction and wear between piston 13 and the planar surface 5a of the casing 5 , a circular oil cushion recess 13c or in the form of radial grooves is machined in the piston end 13a, and filled with oil through a throttle hole 13e, so that most of the metal to metal piston thrust force will be replaced by the oil pressure. Thrust washers 8 and 11 on both sides of the cylinder block 14 limit its axial movement.

There are several safety pins 10 installed on the side wall of the casing 5 or- the cover .7:, each maintaining an appropriate clearanceKwith its adjacent cylinder (14a) wall to allow some free movement between cylinder block 14 and casing 5 under normal running conditions.

However, when there is a sudden change in rotating speed between the casing 5 and the cylinder block ,14,, such as during the braking of the casing, the safety pin :10. will be in contact with the cylinder block 14 to force it to rotate at same speed with the the casing to prevent piston 13 from moving off its piston seat Sa to guarantee normal operation of the hydraulic pump or motor. The cover (7) or casing (5) may be designed with wheel studs for the direct mounting of wheels. If required, brake disc or drum may be incorporated in seal cover (2) to satisfy the requirement of wheel motors with brakes. The number of pistons (13) and corresponding planar surface (5a) can be any- arbitrary integers, preferably 3, 5, or 7 for the uniformity of the oil flow and convenience of manufacture.

Multi-cylinder banks may also be used to increase the power rating. The tapered section of outer end of the eccentric shaft (1) is mounted in a mounting bracket so that the wheel motor or pump can be mounted at desired position on the vehicle.

When high pressure oil is fed through oil passage (A) and groove (B) in eccentric shaft (1) into the motor, the pistons (13) in the cyliners (14a) communicating with groove (B) will be forced out by oil pressure against the planar surface (Sa) of the casing (5). Because the resultant of the piston forces acting on the surface passes through the center 1 of the eccentric (la) and there is an offset e between center 1 and the center O of the casing (5), it will produce a torque to rotate the casing (5) about its center 0 as a motor. When the cylinder further moves offset line in counterclockwise direction, it will be in communication with the outlet groove (B1) and passage (awl), pistons (13) will be pushed inward by the relative movement of planar surface (5a) and discharge oil through the low pressure outlets.Conversely, if passage (Al) and groove (B1) are connected to high pressure inlet and passage (A) and groove (B) to the low pressure outlet, the motor will turn in the opposite direction; similarly, if the casing (5) is driven by a power source, it will work as a pump.

It should be emphasized that the turning moment of the motor or pump above stated is produced by the offset of the casing (5) to the cylinder block (14) and that the piston (13) is free from overturning moment and lateral force, so the mechanical friction losses are minimized and the piston height can be reduced to make the motor more compact, whereas in most of today's low speed high torque wheel motors the turning moment is accompanied by an overturning moment on the piston resulting in significantly reducing mechanical efficiency, especially at starting, due to the large lateral forces acting between the piston and the cylinder wall.

As tests have shown, the main mechanical losses of the hydraulic motor or pump above stated at high speed comprise oil flow losses in oil passages and oil churning loss produced by the relative movement between the cylinder block (14) and the casing (5) during the operation, so these losses often become the main factors limiting the permissible maximum speed of the motor or pump and will be increased with the operating speed parabolically.To extend the speed range, a spoon-shaped oil duct (lea) is arranged in the thrust washer (11) with its inner end communicating with the leakage oil passage (26) in the eccentric shaft (1) and its outer end extending deeped down into the casing to scoop and discharge the leakage from the casing through the leakage oil passage (26) to an outside reservoir by the dynamic pressure and the inertia of the leakage oil in operation to scavenge the oil leakage accumulated in the casing (5) to reduce the oil churning losses at high speed operation.

Fig.3 and 4 are illustrations of a variable displacement hydraulic motor or pump of the invention. It differs from the fixed displacement hydraulic motor in that the eccentric shaft (1) as shown in Fig.1 and 2 is now replaced by an eccentric shaft (1) and an eccentric sleeve (20) to form a combined eccentric. The eccentric sleeve (20) is rotatably mounted on the eccentric shaft (1) with its inner bore, the outer periphery of the eccentric sleeve (20) parallel to the inner bore and having a offset therebetween.

The combined eccentric and consequently the piston stroke and displacement may be continuously changed when the eccentric sleeve (20) is rotated on the eccentric shaft (1) to different positions, provided a controlling means is available to control continuously the angular position of the eccentric sleeve (20) relative to the eccentric (la).

Such a controlling means is proposed by the invention. A pin hole (20a) is machined in the end face (20f) of the eccentric sleeve (20). A sliding-fit pin (21) is inserted into the pin hole (20a) with its rectangular head (21a) engaged in a slot (22b) in a flange of a displacement control sleeve (22) which is fit tightly against the inner race of bearing (4) and slidly fit (or fit with needle bearing) on the eccentric shaft (1). A displacement control arm (23) mounted on the eccentric shaft (1) meshes the end of the displacement sleeve (22) as a dog tooth clutch (22f) or its internal teeth may engage the external teeth at the end of the displacement control sleeve (22).When the displacement control arm (23) is actuated by a displacement control mechanism to apply a torque in either direction to the displacement control sleeve (22) to rotate it on the eccentric shaft (1), this motion will be transmitted to the eccentric slleve (20) through pin (21) to change the combined eccentricity e. The eccentric sleeve (20) has two separate oil grooves (B) and (B1) in communication with the oil passages (A) and (Al) of eccentric shaft (1). All other parts are the same with the fixed displacement motor or pump above mentioned and illustrated in Fig.1 and 2 to facilitate manufacturing.

The number of cylinders can be any arbitrary integers, preferably 3, 5, or 7. Multi-cylinder banks may also be used to increase the power rating.

As tests have shown, the variable displacement hydraulic motor or pump of the invention can satisfy the vehicle drive requirements. For example, the motor speed ranges from zero to 1500 r.p.m. equivalent to vehicle speeds from zero to 150 kilometer per hour when the wheel is directly driven by the wheel motor. There is a wide high efficiency region with a maximum mechanical efficiency of 0.97 and a slightly lower starting efficiency, so the vehicle can enjoy an overall high efficiency under most working conditions. Employment of variable displacement pump or motor will result in an ideal stepless transmission system with wide adjustable speed ratio and high working efficiency. The wheel motor can sustain safely the dynamic wheel loads under severe running conditions with its large capacity bearings and strong casing and cover construction; it is not sensitive to the temperature, vibration, shock, oil and its filtration, etc.; its manufacturing cost is significantly low as its main components are simple in construction and easy for production.

Fig.8 is a comparison of starting torque efficiency and mechanical efficiency of hydraulic motors of the invention with those of axial piston motor with planetary gearbox (curve 2) and cam lobe motors (curve 1) in SAE pa er 790883. It is obvious that efficiencies of motors of this invention are the highest within a remarkable wider speed range.

The hydraulic motor or pump of the invention has many advantages and the superiority of wheel motor type hydrostatic transmission can be fully exploited in vehicle drive applications, so that its application can be widened remarkably. For example in agricultural and construction machineries, transportation and towing machines, minicars, all terrain vehicles and machine transmission systems, etc. it will benefit them with simplicity in construction, convenience in layout, reduction in cost, stepless speed change, and automatic control.

The method of mounting the wheel motor on the vehicle has great influence on its reliability and the layout of oil pipe lines of the hydrostatic transmission system as well as its related components. Normally, wheel motors with a rotating casing are mounted directly on the vehicle in the cantilever form (through the suspension torque-thrust member or mounted directly to vehicle frame) resulting in following difficulties; the mounted part of the motor will be heavily stressed by dynamic and impact loads acting on the wheel. Loosening or ever breakage will often occur if no proper measure is taken. Since the center distance between the oil inlet and outlet passages in the eccentric shaft is very limited by the journal diameter, the oil pipe connected directly to the end of the shaft will be too small in size and difficult in layout and installation.Under certain conditions, tremendous rigidity will be required where displacement control and/or braking actuation mechanism are connected to the wheel motor. The invention solves these problems by mounting the wheel motor to a mounting bracket.

Fig.5 illustrates the wheel motor mounted on a mounting bracket.

The outer end of the eccentric shaft (1) with a tapered section (ilk) is inserted into the tapered bore (37a) of the mounting bracket (37) and held in position securely by nut (36) with two O-rings (32) to prevent leakage.

There are three pipe thread holes for pipe fittings (33, 34, 35) in the mounting bracket (37) to communicate with the inlet, outlet, and oil leakage passages in the eccentric shaft respectively. The position of the thread holds (33, 34, 35) can be arranged for convenient layout of the oil pipes (in some cases, oil pipe may be installed direct to the oil passages at the end of the shaft). Flange or bolt holes may be provided on the mounting bracket for the mounting of brake or displacement control mechanism. The mounting bracket (37) is in turn mounted directly to the suspension system or frame of the vehicle.

Fig.6 illustrates a displaament control mechanism for the variable displacement motor or pump. A displacement control cylinder (40) with a double-acting piston (42) controlled by control valve (41) is installed on the mounting bracket (37). The piston (42) moves receiprocating by in cylinder (40) to push or pull the displacement control arm (23) to rotate by means of connecting rod (43) around the eccentric shaft (1). This movement will be transmitted through displacement control sleeve (22), pin (21) to rotate eccentric sleeve (20) on the eccentric (la) and to change continuously the combined eccentric or displacement of the motor or pump as required.

The control valve (41) may be manually or automatically operated. In automatic control, control valve (41) may be controlled by one or several operating parameters, such as, the r.p.m. torque, intake manifold vacuum, contents of exhaust gas, position of accelerator pedal of the engine, the oil flow rate and pressure in the hydraulic system, etc. . To accommodate the complicated situations which may be encountered in use, the control valve (41) may be operated by the operator as well as the automatic system.

A closed hydraulic circuit is usually employed in vehicle hydrostatic transmission systems to reduce the weight and size of the oil tank. As an example, Fig.7 shows hydrostatic transmission system in a 4x2 vehicle wheel motor. This hydraulic transmission system can be used in all kinds of drive-system, such as 3x1, 3x2, 3x3, 4x1, 4x2, 4x4, 6x2, 6x4, 6x6, 8x2, 8x4, 8x6, 8x8,etc.

Engine (50), which may be a gasoline or diesel engine or the like may be placed in any part of a vehicle according to its layout requirements.

The output shaft of the engine (50) drives the pump (52) directly or through a fixed ratio gearbox (51) whose ratio is determinated by the rated maximum speeds of the engine and the pump. The pump can be selected from T-type, axial piston type or other high efficiency types and with fixed dispalcement qr variable displacement (either, uni-or bi-directional).

As a example, a unidirectional variable displacement pump in the hydraulic system is shown in Fig.7. Obviously, it is not difficult to deduce a hydraulic system with bi-directional variable displacement pump according to the same principle. The high pressure oil from pump (52) flows through high pressure oil pipe (53a) to direction valve (56) (not reguired when bi-directional pump is used) which controls the running direction of the wheel motor, namely, forward or reverse. The direction valve (56) is similar to a four-port three-position valve in construction. When in its neutral (middle) position, the high pressure oil pipe (53a) is communicated with the return (low pressure) oil pipe (53b); thus the direction valve (56) works as a disengaged clutch or neutral gear, while the motors will run in forward or reverse when it is in the two other positions.

The high pressure oil flows directly from direction valve (56) to wheel motors (58) or via distributing valve (57). One of the functions of the distributing valve (57) is to control the working mode (driving or free-wheeling) of the right and left hand wheel motors. When in the free-wheeling mode the motor inlet oil pipe (59a) will communicates with its outlet oil pipe (59b) with oil circulating freely through the free-wheeling motor. The distributing valve (57) may also create three operating modes in the hydraulic system for the vehicle, namely, right wheels driving only, left wheels driving only, and both wheels driving. The one side wheels driving mode will further extend the speed range. The distr,buting valve (57) has another function equiv alent to a differential lock when the one side wheels are slipping on the ground. The distributing valve (57), in conjuction with appropriate control system, can also be used in multi-axle or multi-wheel drive systems allowing all kinds of driving modes ranging from one axle driving to all axle driving with different combinations.

The distributing valve (57) can also be designed as an automatic distri buting valve (proportional valve) to control the flow to the motors according to displacements of the wheel motors automatically, so that it will limit the oil flow to the wheels slipping on the ground due to low adhesion or load transfer while maintaining the tractive efforts of other driving wheels.

In the closed circuit of hydraulic system, the oil from the wheel motor returns to the direction valve (56) via motor oil outlet pipe (59b) (and distributing valve) and then through return oil pipe (53b) to the intake port of pump (52), forming a closed circuit.

Certain additional oil circuits may be incorporated in the hydraulic system to cope with more complicate vehicle operating conditions 1) Free-wheeling circuit. When the accelerator pedal of the vehicle is suddenly released during the running, the speed of the engine will decrease faster than vehicle deceleration due to the greater inertia of the vehicle. Under such circumstances, the wheel motor will turn to work as a pump and the pump as a motor driving the engine resulting in an engine braking effect on the vehicle. This problem maybesolved by shifting the direction valve (56) into neutral, but it is not convenient for the driver. A free-wheeling valve (54) which is an one-way valve may be arranged between the high pressure oil pipe (53a) and return oil pipe (53b).When the vehicle is coasting, the oil pressure pipe (53b) will be higher than that in pipe (53a) and the valve (54) will be forced to open to bypass most of the oil from the motor (58) thereby eliminating the engine braking to allow the wheel motor free-wheeling while engine idling.

The free-wheeling valve (54) will remain closed in normal vehicle running. If necessary, free-wheeling valve (54) and discharge valve (65) can be manually locked for engine-braking or starting engine by towing the vehicle.

2) Safety or overload protection circuit. When the working pressure in oil pipes (53a) or (53b) exceeds its permissible maximum, safety valve (55) will open and discharges the oil from high pressure to low pressure pipe to protect components in the system from damage. The working pressure difference of safety valve (55) may be manually adjustable so that it may be used by the operator as a clutch.

3) Oil charge circuit. Usually, a closed hydraulic circuit needs a oil charge circuit to replen ish the oil lost due to leakage. As shown in Fig.7, engine (50) drives an oil charge pump (62) which draws oil from oil tank (60) via a coarse filter (61) and pumps it into the return oil pipe (53b) through a fine filter (63) and a one-way replenish oil valve (64) to feed pump (52).

Any excess oil from main hydraulic circuit will pass through the one-way discharge valve (65) and oil cooler (66) before discharged into oil tank (60). Due to the high efficiency of hydraulic motor and the optimization of hydraulic transmission system of this invention, the oil cooler (66) can be omitted on certain transporting vehicles to further simplify the system.

A brake valve (not shown in the drawing) can be incorporated in the hydraulic system, to brake the vehicle by throttling the flow of return oil from the wheel motor and the brake effect can be adjusted by the brake valve.

Claims (20)

Claims:

1. A variable displacement hydraulic motor or pump with rotating casing and fixed shaft, comprising: (a) a casing having a plurality of planar faces on its inner surface; (b) a cover therefor; (c) bearings fitted in the central part of the casing and the cover; (d) an eccentric shaft with an eccentric, supported between the bearings, the eccentric shaft having two separate groups of fluid passages disposed therein and fluid distributing means communicating therewith for conducting a fluid, one group of fluid passages being connected to a high pressure fluid system and the other to a low pressure fluid system; (e) a cylinder block rotatably mounted on the outer periphery of the eccentric, the cylinder block having a plurality of cylinders corresponding to the plurality of planar faces in the casing, radially arranged in a plane perpendicular to the axis of the eccentric shaft;; (f) a sliding piston fitted in each of the cylinders, each piston having an outer flat end contacting with the associated planar face in the casing, whereby when the casing is provided with rotary movement relative to the eccentric shaft, the eccentric will urge the pistons to reciprocatingly slide in the cylinders in turn; and (g) a plurality of return springs positioned between the pistons and the cylinder block urgingly holding the pistons against the planar faces in the casing; wherein the eccentric shaft with the eccentric is a combined eccentric consisting of an eccentric shaft and an eccentric sleeve with a bore and two separate arcuate fluid distributing grooves communicating respectively with the said two separate groups of fluid passages in the eccentric shaft and with the cylinders in the cylinder block in turn to work as a distributing valve, the eccentric sleeve being rotatably mounted on the eccentric shaft through its bore and having the cylinder block mounted on its outer periphery, the dimension of the combined eccentric being adjustable continuously by controlling means arranged to control the relative angular position of the eccentric sleeve to the eccentric shaft, whereby the displacement of the hydraulic motor or pump is continuously adjustable.

2. A motor or pump as claimed in claim 1, wherein the eccentric sleeve has a sliding pin hole in its end face, in which a sliding pin is fitted rotatably, the sliding pin extending to a slide groove in a displacement control sleeve rotatably mounted on the eccentric shaft, the outer periphery of the displacement control sleeve being rigid with an inner ring of the bearing in the casing or cover and having external teeth to connect to an outside displacement control mechanism, whereby a sufficient torque may be applied to the displacement control sleeve to rotate it relative to the eccentric shaft and transmitted via the slide groove and slide pin to the eccentric sleeve, urging the eccentric sleeve to produce a relative rotary movement to the eccentric to adjust the dimension of the combined eccentric continuously.

3. A motor or pump as claimed in claim 2, including a displacement control arm having teeth means to engage with the teeth on the displacement control sleeve and coaxially mounted with a sliding fit on the eccentric shaft externally to the displacement control sleeve and further connected with an external displacement control means to control the displacement of the hydraulic motor or pump.

4. A motor or pump as claimed in claim 3, wherein the displacement control means comprises a displacement control cylinder with a double-acting piston connected to the displacement control arm by a connecting rod, the action of the double-acting piston being controlled by a control valve.

5. A fixed displacement hydraulic motor or pump with rotating casing and fixed shaft, comprising: (a) a casing having a plurality of planar faces on its inner surface; (b) a cover therefor; (c) bearings fitted in the central part of the casing and the cover; (d) an eccentric shaft with an eccentric, supported between the bearings1 the eccentric shaft having two separate groups of fluid passages disposed therein and fluid distributing means communicating therewith for conducting a fluid, one group of fluid passages being connected to a high pressure fluid system and the other a low pressure fluid system; (e) a cylinder block rotatably mounted on the outer periphery of the eccentric, the cylinder block having a plurality of cylinders corresponding to the plurality of planar faces in the casing, radially arranged in a plane perpendicular to the axis of the eccentric shaft;; (f) a sliding piston fitted in each of the cylinders, each piston having an outer flat end face contacting with the associated planar face in the casing, whereby when the casing is provided with rotary movement relative to the eccentric shaft, the eccentric will urge the pistons to reciprocatingly slide in the cylinders in turn; and (g) a plurality of return springs positioned between the pistons and the cylinder block urgingly holding the pistons against the planar faces in the casing.

6. A motor or pump as claimed in any preceding claim, wherein the casing is constructed integrally with a strong, rigid side wall and the cover has a reinforcing ring mounted on the outer periphery of the casing at its open side for restricting deformation of the casing during operation, several safety pins being pressed into the side wall of the casing, the outer end of each safety pin extending into a space between adjacent cylinders of the cylinder block and having a clearance to the cylinder wall to allow the cylinder block to swing freely relative to the casing during normal operation and even at its maximum displacement but at the same time limiting the amplitude of the relative rotating movement and bringing the cylinder block to rotate with the casing to prevent the pistons from moving to arcuate sections of the casing during sudden changes in the relative rotational speed between the casing and the cylinder block.

7. A motor or pump as claimed in any preceding claim, including at least one spoon-like oil duct having an inner end communicating with a leakage oil passage in the eccentric shaft and an outer end extended radially to use the dynamic pressure and the inertia of the leakage oil stored in the casing during its turning to force the leakage oil out.

8. A motor or pump as claimed in any preceding claim, including a reticular fluid groove or recess arranged coaxially in the end face of each piston and communicating with the working fluid through a throttle hole to form a hydrostatic supporter to reduce friction losses, contacting pressure, and wear between the piston and the associated planar face in the casing.

9. A vehicle hydrostatic transmission system of wheel motor type, which comprises: (a) an engine or engines; (b) an oil pump or pumps driven by the engine(s); (c) oil pipe lines including a high pressure line and a low pressure line; (d) a filter or filters; (e) a valve or valves; (f) an oil tank; and (g) a wheel motor or motors, wherein the or each wheel motor is mounted to a mounting bracket which is mounted directly to a vehicle frame or suspension system.

10. A vehicle hydrostatic transmission system as claimed in claim 9, wherein the mounting bracket has a tapered hole into which a tapered section of the outer end of an eccentric shaft of the wheel motor is inserted and has three oil ducts with one end communicated with respective inlet, outlet, and leakage oil passages in the eccentric shaft of the wheel motor and with the other end connected with the oil pipe lines.

11. A vehicle hydrostatic transmission system as claimed in claim 9 or 10, the wheel motor or motors being in accordance with any of claims 1 to 8.

12. A vehicle hydrostatic transmission system as claimed in any of claims 9 to 11, further comprising a direction valve or valves for controlling the running direction of the wheel motor or motors.

13. A vehicle hydrostatic transmission system as claimed in any of claims 9 to 12, further comprising a distributing valve or valves for controlling the working mode of the wheel motors to get different modes of drive-system combination from one wheel driving to all wheels driving.

14. A vehicle hydrostatic transmission system as claimed in any of claims 9 to 13, further comprising a free-wheeling valve which is arranged between the high pressure line and the low pressure line to bypass the oil pumped out from the wheel motor when the vehicle is free wheeling, whereby the engine may run at an idle speed while the wheel motor free wheels with lower loss of fluid flowing.

15. A vehicle hydrostatic transmission system as claimed in any of claims 9 to 14, further comprising a safety valve which is arranged between the high pressure line and the low pressure line.

16. A vehicle hydrostatic transmission system as claimed in any of claims 9 to 15, further comprising a oil charge pump driven by the engine and a charge valve arranged between the oil pump and the oil tank.

17. A vehicle hydrostatic transmission system as claimed in any of claims 9 to 16, further comprising a gearbox with a fixed ratio arranged between the engine and the oil pump.

18. A vehicle hydrostatic transmission system as claimed in any of claims 9 to 17, further comprising anoil cooler.

19. A hydraulic motor or pump substantially as described with reference to, and as shown in, Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.

20. A vehicle hydrostatic transmission system substantially as described with reference to Figure 7 of the accompanying drawings.