Abstract:
A hydraulic machine which can exchange hydraulic fluid pressure with rotational motion of an input/output means, having a radial arrangement of a plurality of hydraulic piston and cylinder assemblies about a crankshaft, the hydraulic cylinder and piston assemblies being longitudinally spaced along the crankshaft; and a means for varying eccentricity of the crankshaft whereby reciprocal motion of the pistons within the respective hydraulic cylinders is consequential to rotational motion of the crankshaft about the longitudinal axis of the crankshaft.

Description:
RELATED APPLICATIONS 
   This application is the U.S. National Phase under 35 U.S.C. § 371 of International Application No. PCT/AU2004/001765, filed on Dec. 15, 2004, which in turn claims the benefit of Australian Application No. 2003906932, filed on Dec. 15, 2003, the disclosures of which Applications are incorporated by reference herein. 
   FIELD OF THE INVENTION 
   This invention relates to hydraulic motors/pumps, otherwise known as hydrostatic drives or hydraulic machines. 
   BACKGROUND TO THE INVENTION 
   Hydraulic pumps/motors have applications in many industries, including the material handling, mining and manufacturing industries. 
   A hydraulic motor/pump can be operated in one of two ways. In one mode of operation, the input medium is pressurised hydraulic fluid, and the output is rotational motion. The process can be reversed such that rotational motion is supplied to the hydraulic motor/pump. In this second mode of operation, the hydraulic fluid is pumped from the motor/pump. 
   An advantage of hydraulic motors/pumps is that they typically have an excellent overall efficiency, among many other desirable characteristics. 
   However, many hydraulic motors/pumps suffer from a distinct disadvantage. There exists a torque-speed trade off, such that as the motor speed increases the output torque decreases, and vice versa. 
   Prior art hydraulic motors/pumps typically have an eccentric disc which is connected to an output shaft. A set of hydraulic cylinder and piston assemblies are positioned in a radial (also known as a “star” or “fan”) arrangement about the axis of rotation of the output shaft. Typically there are five such hydraulic cylinder assemblies. 
   The pistons intermittently exert a force to the edge of the eccentric disc in a coordinated fashion such that the disc is rotated. After exerting a force, the retraction of each piston is effected by the eccentric disc. 
   To vary the torque of the motor (in the driving mode of operation) some such motors have been fitted with a small piston between the output shaft and the centre of the eccentric disc. The eccentricity of the disc is varied by changing the length of small piston. 
   Similarly in a pumping mode of operation, the fluid flow rate and/or the output fluid pressure can be altered by changing the length of the small piston. 
   One disadvantage of such prior art hydraulic motors/pumps is that when the output shaft speed exceeds the fluid flow capabilities of the hydraulic cylinders, the pistons can dissociate from the eccentric disc. This can result in complete failure of the hydraulic motor/pump. 
   A further disadvantage of the prior art devices having a variable eccentric disc is that the possible range of eccentricity is limited. Typically a zero eccentricity situation is not possible. 
   A still further disadvantage is that the small piston can allow small unwanted perturbations of the eccentricity. These perturbations are the result of the fluid properties and the system elasticity. 
   With a high overall efficiency obtainable from hydraulic motors/pumps, there is a need for such a device which can simultaneously produces high torque at high speed. 
   SUMMARY OF THE INVENTION 
   According to the present invention there is provided a hydraulic machine which can exchange hydraulic fluid pressure with rotational motion of an output means, the hydraulic machine having a radial arrangement of a plurality of hydraulic piston and cylinder assemblies about at least one crankshaft coupled to the output means, the hydraulic cylinder and piston assemblies being longitudinally spaced along the crankshaft; and means for varying the eccentricity of the crankshaft. 
   Preferably, each piston is connected to the at least one crankshaft by a connecting rod. 
   Preferably, a spherical bearing is disposed between each connecting rod and the respective crankshaft. 
   Preferably, the eccentricity of the at least one crankshaft can be varied such that the stroke length of the pistons can be varied between zero and the maximum stroke length. 
   Preferably, the means for varying the eccentricity of the at least one crankshaft includes, located at each end of the at least one crankshaft: 
   an inner cylinder with a hollow eccentric cylindrical core within which the respective crankshaft is received such that the longitudinal axes of the inner cylinder and crankshaft are parallel and offset, 
   an outer cylinder with a hollow eccentric cylindrical core within which the inner cylinder is received such that longitudinal axes of the outer cylinder and the inner cylinder are parallel and offset, 
   a cylindrical main bearing with a concentric hollow cylindrical core within which the outer cylinder is received, and 
   a drive means, 
   wherein the drive means can be operated to simultaneously rotate the outer and inner cylinders to change the distance between the longitudinal axes of the main bearing and the crankshaft at both ends of the respective crankshaft. 
   Preferably, the drive means includes, at each end of at least one crankshaft: 
   a ring gear with teeth on both the inner and outer surfaces of the ring, 
   a set of teeth around an end portion of each of the inner and outer cylinders, and 
   a gear train to transfer rotation from the ring gear to the inner and outer cylinders, 
   wherein the ring gear is supported by the respective main bearing, and the main bearing has a cut out portion through which the gear train extends to engage the ring gear. 
   Preferably, the main bearings have teeth on the outer surface, and the ring gears are disposed next to the teeth on the respective main bearing, and the drive means further includes: 
   a shaft with a helix formed on the shaft surface, and pinion gears which engage the teeth on each of the main bearings such that the shaft rotates with the main bearings; 
   at least one nut with an internal helix which engages the helix on the shaft, and at least one projection which is radial with respect to the shaft; 
   at least one hollow cylindrical outer sheath through which the shaft extends, the at least one sheath having two thin pinion gears at each end of the outer sheath, wherein each thin pinion gear engages a ring gear of the drive means, the at least one outer sheath having at least one longitudinal slot through which the at least one projection extends. 
   Preferably, the drive means is operated by moving the nut longitudinally along the shaft, the outer sheath can be rotated with respect to the shaft. 
   More preferably, moving the nut longitudinally advances or retards the ring gears with respect to the main bearings. 
   Preferably, both the inner and outer cylinders each have a counter weight. 
   Preferably, the hydraulic machine further includes at least one lay shaft having, for each of the main bearings, a pinion gear to engage the teeth on the respective main bearing. 
   Thus, the torque applied to each of the main bearings is transferred through the at least one lay shaft rather than being transferred through the crankshafts. 
   Preferably, the heads of the hydraulic cylinder and piston assemblies are supported by the housing such that the hydraulic cylinder and piston assemblies can oscillate as the respective crankshaft rotates. 
   Preferably, the head of each hydraulic cylinder and piston assembly is supported between a pair of thrust blocks which are supported by the housing. 
   Preferably, the heads of the hydraulic cylinder and piston assemblies have, at least partially, a spherical shape. More preferably, each pair of thrust blocks have a complimentary shape to the heads of the hydraulic cylinders. 
   Preferably, there are equal angles between the hydraulic cylinder and piston assemblies attached to each of the at least one crankshaft. 
   More preferably, there are five hydraulic cylinder and piston assemblies disposed at 72° intervals about the at least one crankshaft. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the invention can be more easily understood, an embodiment will now be described, by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1 : is a plan view of the housing of a hydraulic machine according to an embodiment of the present invention; 
       FIG. 2 : is a plan view of the hydraulic machine shown in  FIG. 1  with the housing removed; 
       FIG. 3 : is a view of the hydraulic machine shown in  FIG. 2 ; 
       FIG. 4 : is an end view of the hydraulic machine shown in  FIG. 3  with the output flange removed; 
       FIG. 5 : is a sectional view of the hydraulic machine through the section B-B in  FIG. 1 ; 
       FIG. 6 : is a sectional view of the hydraulic machine through the section A-A in  FIG. 5 ; 
       FIG. 7 : is an axiomatic view of a crankshaft and cylinder unit and thrust block of the hydraulic machine; 
       FIG. 8 : is a side view of the crankshaft and cylinder unit and thrust block of  FIG. 7 ; 
       FIG. 9 : is an end view of the crankshaft, connecting rod, cylinder unit and thrust block of  FIG. 7 ; 
       FIG. 10 : is a sectional view of the crankshaft, connecting rod, cylinder unit and thrust block through the section A-A of  FIG. 8 ; 
       FIG. 11 : is a sectional view of the crankshaft, connecting rod, cylinder unit and thrust block through the section B-B of  FIG. 10 ; 
       FIG. 12 : is an axiomatic view of a crank assembly of the hydraulic machine; 
       FIG. 13 : is a view of the crank assembly of  FIG. 12 , with a pair of lay shafts and a helical shaft; 
       FIG. 14 : is a view of the crank assembly of  FIG. 13 , with outer sheaths; 
       FIG. 15 : is a view of the stroke adjustment assembly in  FIG. 13 ; 
       FIG. 16 : is an end view of the inner and outer eccentrics and gear train of  FIG. 15 ; 
       FIG. 17 : is an exploded view of the inner and outer eccentrics and the gear train of the hydraulic machine; 
       FIG. 18 : is a view of the assembled inner and outer eccentrics and the gear train, of  FIG. 17 ; 
       FIG. 19 : is an end view of the inner eccentric ring; and 
       FIG. 20 : is an end view of the outer eccentric ring. 
   

   DETAILED DESCRIPTION 
     FIGS. 1 to 6  illustrate a hydraulic machine  1  according to an embodiment of the present invention. The hydraulic machine  1  is encased in a housing  10 . The hydraulic machine  1  has an power coupling  5  which can be connected to a complimentary power coupling to transfer rotational motion to or from the machine  1  about an axis of rotation (not shown). 
     FIG. 2  shows the hydraulic machine  1  with the housing  10  removed. The hydraulic machine  1  has two crankshafts  15 , about each of which a bank  20  of five cylinder assemblies  50  are radially arranged. Thus, the hydraulic machine  1  in this embodiment has ten cylinder assemblies  50 . 
   The hydraulic machine  1  can have any integer number of banks  20 . Thus, the total number of cylinder assemblies  50  in a hydraulic machine  1  according to the invention is a multiple of the number of cylinder assemblies  50  per bank  20 ; such as five, ten, fifteen cylinder assemblies. 
     FIGS. 3 to 5  are views of the hydraulic machine  1  as seen looking along the axis of rotation. 
   As can be seen in  FIGS. 3 and 4 , the five cylinder assemblies  50  of each bank  20  are arranged equiangularly about the axis of rotation. Thus when measured with respect to the axis of rotation, the angle between each adjacent pair of cylinder assemblies  50  is 72°. 
     FIGS. 2 and 6  show the hydraulic machine  1  in plan view such that the axis of rotation is in the plane of the page. Each cylinder assembly  50  is directly attached to its respective crankshafts  15  by a connecting rod  55 . As there is a connecting rod  55  for each cylinder assembly  50 , the cylinder assemblies  50  in each bank  20  are longitudinally offset with respect to the axis of rotation. Accordingly, the connecting rods  55  in each bank  20  are arranged in a side-by-side fashion along the respective crankshaft  15 . 
     FIG. 5  shows a sectional view of the hydraulic machine  1  as seen along the line B-B in  FIG. 1 . Thus,  FIG. 5  shows an end view of a bank  20  of a hydraulic machine  1 . 
     FIGS. 7 to 11  show various views of a cylinder assembly  50 , and a crankshaft  15 . The cylinder assembly  50  is one of the five cylinder assemblies in a bank  20 . 
   Each cylinder assembly  50  is supported by an outer thrust block  60 , and an inner thrust block  65 . The thrust blocks  60 ,  65  are attached to the housing  10 . The head  70  of each cylinder assembly  50  has a ball shape. The thrust blocks  60 ;  65  locate the head  70 , while still allowing the cylinder head  70  to oscillate as the crankshaft  15  position changes. 
   A spherical bearing  75  is retained between a connecting rod  55  and the rod cap  56 . The spherical bearing  75  surrounds the crankshaft  15 , providing free relative rotational motion of the crankshaft  15  with respect to the connecting rod  55 . The rod cap  56  is attached to the connecting rod  55  by two big end bolts  80 . 
   By this arrangement, the piston  85  of each cylinder assembly  50  is positively attached to the crankshaft  15  by the connecting rod  55  and rod cap  56  arrangement. Thus, the speed range of the hydraulic motor is limited only by the flow characteristics of the hydraulic fluid. 
   Hydraulic fluid is supplied and removed from the cylinder head  70  via two fluid ports  95 . 
     FIG. 10  shows a cross section through a cylinder assembly  50 . The piston  85  is directly attached to the connecting rod  55 . 
   A gudgeon pin with a sufficient cross sectional area to handle the high forces cannot be arranged within cylinder since the cylinder bore is too narrow. Thus, to provide the angular movement required by the connecting rod  55 , the cylinder head  70  has been designed with a ball shape. 
   The cylinder head  70  is retained between the outer and inner thrust blocks  60 ,  65 . The surfaces  62 ,  67  of the thrust blocks  60 ,  65  are concave to complement the ball shape of the cylinder head  70 . The cylinder head  70  is free to oscillate about an axis parallel to the longitudinal axis of the crankshaft  15 . 
     FIG. 11  shows a cross-section through the crankshaft  15  and the cylinder assembly  50  along the line B-B of  FIG. 9 . Hydraulic fluid is introduced to, and expelled from, the cylinder assembly  50  via fluid ports  95 . 
     FIG. 12  shows an power coupling  5  and a pair of crank assemblies  25 . One crank assembly  25  is provided for each bank  20 . A pair of stroke adjustment mechanisms  100  are also provided for each bank  20 . The pair of stroke adjustment mechanisms  100  operate collaboratively to adjust the throw of the respective crankshaft  15 . By adjusting the throw of the crankshafts  15 , the hydraulic machine is provided with variable displacement. In other words, the swept volume can be increased or decreased by changing the stroke length of the cylinder assemblies  50 . Thus, the hydraulic machine  1  has a stepless ratio transmission throughout the entire speed range. 
   Two main bearings  105  (one at each end of the crankshaft  15 ) contain the stroke adjustment mechanisms  100 . Consequently, the main bearings  105  cannot be used to transmit torque. 
   To transmit output or input torque (depending on the mode of operation of the hydraulic machine  1 ), it is necessary to collect the torque at each main bearing  105 . This is achieved using lay shafts  110  (see  FIG. 13 ). In the preferred embodiment, two lay shafts  110  are used. 
   The lay shafts  110  have pinion gears  115 , each of which engage a bull gear  120  attached to each of the main bearings  105 . The lay shafts  110  collect the torque from the bull gears  120 , and also serve to maintain the synchronisation between the bull gears  120 . 
   In order to control the stroke length of the pistons  85 , a helical shaft  125  is coupled to the bull gears  120 . The helical shaft  125  is not used to transmit torque, but remains in synchronisation with the bull gears  120 . 
   For each bank  20  of cylinder assemblies  50 , a helix  130  is formed on the helical shaft  125 , and a helical nut  135  is fitted. The helical nuts  135  have projections  140 . An outer sheath  145  is also provided for each bank  20  (see  FIG. 14 ). Each outer sheath  145  has a thin pinion gear  150  at each end. The outer sheaths  145  surround the helical shaft  125 . 
   The projections  140  engage slots  155  in the outer sheaths  145 . As a helical nut  135  rotates as it is displaced longitudinally along the helical shaft  125 . Hence, such longitudinal movement of the helical nut  135  causes the associated outer sheath  145  to rotate. 
   Each pinion gears  150  engages a ring gear  160  located adjacent to the bull gears  120 , on the same side as the crankshaft  15 . Each ring gear  160  is rotatable on its main bearing  105 . As the helical nut  135  is moved longitudinally along the helical shaft  125 , the two ring gears  160  of the respective bank  20  are rotated. This mechanism provides means to rotate the ring gears  160  while the hydraulic machine  1  is operating at any speed or load. 
   The ring gears  160  drive the stroke adjustment mechanisms  100 . Thus, longitudinal movement of the helical nuts  135  provide means to drive the stroke adjustment mechanisms  100 . 
   A stroke adjustment mechanism  100  is shown in  FIGS. 15 to 20 . 
   The main bearing  105  is a cylinder with the hollow cylindrical portion eccentrically positioned within the bearing  105 . A pair of eccentric rings  190 ,  195  provide the actual stroke variation. 
   An outer eccentric ring  190  in the shape of a cylinder body with a hollow cylindrical portion. The diameter of the cylinder body of the outer eccentric ring  190  is geometrically dimensioned such that it is rotatably contained within the bore of the hollow portion of the main bearing  105 . 
   A portion of the first end of the outer eccentric ring  190  is provided with a set of gear teeth  195 . The other end is provided with a counter balance  200 . 
   An inner eccentric ring  205  in the shape of a cylinder body with a hollow cylindrical portion. The diameter of the cylinder body of the inner eccentric ring  205  is geometrically dimensioned such that it is rotatably contained within the bore of the hollow portion of the outer eccentric ring  190 . 
   A portion of the first end of the inner eccentric ring  20 S is provided with a set of gear teeth  210 . The other end is provided with a counter balance  215 . 
   Each end of the crankshaft  15  is retained within the hollow portion of an inner eccentric ring  205 . The throw of the crankshaft  15  is varied by moving the crankshaft  15  radially with respect to the respective main bearing  105 . This radial movement is achieved by simultaneously rotating the outer eccentric ring  190  in a first direction and rotating the inner eccentric ring  205  in the opposite direction. The speed of rotation of the eccentric rings  190 ,  205  is the same. 
   There is a set of gear teeth  165  formed on the inner surface of each ring gear  160 . The teeth  165  engage the teeth of the first primary gear  175  of a gear train  170 . The first primary gear  175  engages the teeth  195  on the outer eccentric ring  190 . 
   A second primary gear  180  is attached to the side of the first primary gear  175 . The second primary gear  180  rotates with the first primary gear  175 . A secondary gear  185  is positioned between the second primary gear  180  and the teeth  210  on the inner eccentric ring  205 . 
   A gear train bearing  220  secures the gear train  170  in place. The main bearing  105  has a cut out section  106  through which the gear train  170  extends. 
   To ensure that the stroke adjustment mechanism  100  remains rotationally balanced, the counter balances  200 ,  215  rotate with the respective eccentric rings  190 ,  205 . The counter balances  200 ,  215  cancel themselves out at zero stroke length, and work together at full stroke. The stroke adjustment mechanism  100 , and thus the hydraulic machine  1  are always balanced. 
     FIG. 16  shows a wire frame view of the main bearing  105 , the outer and inner eccentric rings  190 ,  205  and the gear train  170 . The counter balances  200 ,  215  are shown by the broken lines. 
     FIG. 17  is an exploded view of the stroke adjustment mechanism  100 . 
     FIGS. 18 to 20  illustrate the outer and inner eccentric rings  190 ,  205 .  FIG. 18  also shows the gear train  170 . 
   When operating the hydraulic machine  1  as a motor, the five cylinder assemblies  50  in the respective bank  20  sequentially apply a force to the crankshaft  15 , such that rotational motion is imparted to the crankshaft  15 . The rotational motion is transferred through a bull gear  120  to the lay shafts  110 . 
   When operating the hydraulic machine  1  as a pump, the power coupling  5  is rotated. The cylinders assemblies  50  are driven by the rotation of the crankshaft  15 . Thus, hydraulic fluid is pumped from the machine  1 . 
   It will be understood by persons skilled in the art of the invention that many modifications may be made without departing from the scope of the invention. 
   In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.