Abstract:
The invention relates to a variable displacement hydraulic machine, in particular for a motor vehicle, said hydraulic machine comprising a rotating cylinder ( 10 ) including a series of axial pistons ( 12 ) connected to a first plate ( 14 ) axially located on one side of said cylinder within a substantially transverse plane, the slope of which can be controlled, so as to form a first controllable displacement for said machine, wherein said machine is characterized in that the cylinder ( 10 ) further comprises a second series of axial pistons ( 22 ) connected to a second plate ( 24 ), the slope of which is also controllable, said plate being axially located, relative to the first plate ( 14 ), on the other side of said cylinder so as to form a second controllable displacement for said machine.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is the US national stage under 35 U.S.C. §371 of International Application No. PCT/FR2011/052653 having an international filing date of Nov. 16, 2011, which claims the priority of French application 1059752 filed on Nov. 25, 2010. 
     BACKGROUND 
     This invention relates to a variable displacement hydraulic machine capable of working as an engine or as a pump, in particular for a hybrid vehicle, as well as a power train and a hybrid vehicle equipped with such hydraulic machine. 
     Hybrid vehicles comprise in general a combustion engine which provides the main motorization of the vehicle and an additional motorization using energy that can be stored, such as electric or hydraulic energy, to optimize the combustion engine operation. 
     Hybrid vehicles using hydraulic energy, comprise a hydraulic machine connected to drive wheels of the vehicle, capable of operating as a pump to charge the hydraulic pressure accumulators which store energy, or as an engine to deliver mechanical power to the drive wheels while drawing energy stored in the accumulators. 
     In particular, during braking, one can use the hydraulic machine as a pump to recover and store the kinetic energy of the vehicle; this energy is subsequently returned by the hydraulic machine operating as an engine for driving the vehicle. This use of stored hydraulic power enables optimizing the combustion engine operation, and to reduce its fuel consumption and the polluting gas emissions. The hydraulic energy storage also permits driving in hydraulic mode or zero emission mode “ZEV” during which the vehicle does not emit polluting gases, with the combustion engine being shut down. 
     A type of known variable displacement hydraulic machine comprises a rotating cylinder comprising axial pistons distributed as a crown around the axis, which are connected to a plate which is located in a substantially transverse plane. By controlling or adjusting the slope of the plate with respect to the transverse plane, one modifies the stroke of the pistons that can go from a zero stroke with the plate in the transverse plane, resulting in a zero displacement, to a maximum stroke with the strongest plate slope, resulting in the maximum displacement. 
     A known hydraulic machine made according to a variant, shown for example in document WO-A1-2003/058035, comprises a cylinder with a series of axial bores in which floating or free piston rods slide. Axially on each side of the cylinder, there is a tiltable plate that supports bores in which the ends of the piston rods slide, each forming a piston. 
     This way, one obtains a compact hydraulic machine, comprising a single displacement that can be considerable by doubling sets of pistons on each side of the cylinder. 
     However, this type of hydraulic machine comprises a performance that varies greatly on the basis of the displacement actually used, of the speed and the pressure of operation. In that case, one is obligated for an operation on a vehicle that requires varied ranges of use in torque and power, to have at least two hydraulic machines comprising two different displacements, in order to use each of these machines for its optimal operating range. 
     Installing two hydraulic machines creates problems, in particular related to weight, overall dimensions and installation in the vehicle. In addition, this type of machine can produce noise during operation, as well as torque pulsations tied to the number of pistons. 
     SUMMARY 
     In particular, the purpose of this invention is to avoid these inconveniences of the prior art and to propose a compact hydraulic machine with good performance under varied operating conditions, which is suitable in particular for a hybrid vehicle. 
     For that purpose, a variable displacement hydraulic machine, in particular for a motor vehicle, is disclosed, the machine comprising a rotating cylinder comprising a series of axial pistons connected to a first plate situated axially on one side of this cylinder, in a substantially transverse plane for which the slope is controllable or adjustable, to form a first controllable or adjustable displacement of this machine, characterized in that the cylinder also comprises a second series of axial pistons connected to a second plate for which the slope is also controllable or adjustable, which is situated axially with respect to the first plate on the other side of this cylinder, to form a second controllable or adjustable displacement of this machine. 
     An advantage of this hydraulic machine is that one can situate the various bores receiving the two compact piston series on the same cylinder, to form two different pumps for which the different displacements are controlled independently by the adjustment of each of the two tiltable plates. 
     The hydraulic machine can also comprise one or several of the following features, which can be combined between each other. 
     Beneficially, the two plates each comprise an independent adjustment of their slope. 
     Beneficially, the two series of pistons of each displacement, each form a crown centered on the axis and comprising a different radius. 
     According to an embodiment, the hydraulic machine comprises, for each displacement, a hydraulic circuit that comprises a low pressure chamber and a high pressure chamber, separated by two angular sections that are situated at two diametrically opposite points in contact with the outside cylinder contour or wall of the cylinder; it ensures a dynamic seal between these chambers. Each bore of the pistons comprises a communication conduit arranged radially towards the outside to communicate with these chambers. 
     Beneficially, the two displacements of this machine each comprise the same number of pistons, with the pistons of the inside crown being angularly offset with respect to the pistons of the outside crown and the communication conduits of the pistons of the inside crown are inserted angularly between the pistons of the outside crown. 
     The low and high pressure chambers as well as the communication conduits of each hydraulic circuit can be situated on transverse planes axially offset with respect to each other. 
     Optionally, each angular seal section can comprise in its central part, a central channel connected to the outside hydraulic circuit; the width of the communication conduits is provided so that these conduits run out in a certain angular position of the cylinder, at the same time in one of the two pressure chambers, and in this central channel. 
     A transition solenoid valve can be situated between the central channel and the outside hydraulic circuit. 
     A drive train for a hybrid vehicle is proposed comprising a hydraulic traction machine which includes any of the preceding features. 
     In addition, a hybrid vehicle is proposed comprising a drive train with a combustion engine and a hydraulic traction machine, which includes any of the preceding features. 
    
    
     
       DESCRIPTION OF THE FIGURES 
       The invention will be better understood and other features and benefits will appear more clearly upon reading the following description given as an example and without limitation, referenced against the attached drawings where: 
         FIG. 1  is an axial sectional view of a hydraulic machine; 
         FIG. 2  is a transverse sectional view of this hydraulic machine, taken along the sectional plane II of  FIG. 1 ; 
         FIG. 3  is a transverse sectional view of this hydraulic machine, taken along the sectional plane III of  FIG. 1 ; and 
         FIG. 4  is a detailed view of  FIG. 2  comprising a particular angular position of the cylinder. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 to 3  show a hydraulic machine  1  comprising a casing or housing  2 , which is overall cylindrical in form and centered on an axis. The housing defines a cylindrical inner cavity that is axially closed in a sealed manner on one side by a cover  4 . 
     The inner cavity is traversed by an axially situated shaft  6  which is guided during rotation by two bearings  8 , one kept in the housing  2  and the other in the cover  4 . One end of shaft  6  coming out of the hydraulic machine  1  on the cover  4  side, is connected by a transmission (not shown) to the drive wheels of a hybrid vehicle, in the event that this hydraulic machine is provided for this type of vehicle. 
     A rotating cylinder  10  secured to shaft  6  is fitted in the cylindrical cavity of housing  2 . Cylinder  10  comprises a first series of nine axially situated bores, and distributed regularly to form a crown comprising a large radius, situated near the outside contour or surface of the cylinder  10 . 
     As a variant, one can use a different number of bores, preferably an odd number, such as seven or eleven for instance, which modifies the cyclic regularity or the complexity of hydraulic machine  1 . 
     Each bore of this first series of bores receives a piston  12  of which the exiting end on the right side of cylinder  10 , is connected by a ball joint  16  to a friction shoe  17  which is supported on a first plate  14  located in a substantially transverse plane. A slope control or adjustment mechanism comprising an actuator  40  integrated in housing  2 , permits the adjustment of a small slope for this first plate  14  around the transverse plane. 
     In addition, cylinder  10  includes a second series of bores with a same number of bores, nine in this example, arranged axially and distributed in a regular fashion to form a crown of a small radius which is situated radially inside the first series of bores. 
     Each bore of the second series of bores receives a piston  22  for which the exiting end on the opposite or left side of cylinder  10  is connected by a ball joint  26  to a friction shoe  27  which is supported on a second plate  24  situated in a substantially transverse plane. A slope control or adjustment mechanism comprising an actuator  42  integrated in housing  2 , permits to control or adjust the small slope of this second plate  24  around the transverse plane, independently from the adjustment of first plate  14 . 
     Each plate  14 ,  24  is rotationally fixed with respect to the axis of housing  2 , with a slope that is controllable or adjustable with respect to the transverse plane; pistons  12 ,  22  remain in contact with these plates, by sliding on top by means of friction shoes  17 ,  27 . 
     As such, a rotation of cylinder  10  and of pistons  12 ,  22  is obtained which involves at the same time a sliding of each series of pistons according to a back and forth cycle by complete rotation of shaft  6 , according to a stroke adjusted or controlled for each series by the slope of its plate  14 ,  24 . 
     Pistons  12  of the first series of pistons have a larger diameter than the pistons of the second series, thus providing hydraulic machine  1  with a large displacement defined by the diameter and maximum stroke of the first series of pistons, while pistons  22  of the second series have a smaller diameter, thus providing a small displacement also defined by their diameter and their maximum stroke. 
     One will observe that the two displacements, large and small, are each adjustable or controllable independently between a zero volume and a maximum volume. 
     The hydraulic circuit of the large displacement (i.e., of the first series of pistons  12 ) is detailed in  FIG. 2 . 
     In a transverse plane aligned at the bottom of the first series of bores of the large displacement, the inside cavity of housing  2  comprises a low pressure chamber  18  and a high pressure chamber  20 , separated by two angular sections  44  with small width formed by housing  2  which are located at two diametrically opposite points in permanent contact with the outside cylindrical contour or wall of cylinder  10 . The two angular sections  44  form a dynamic seal that isolates the low pressure chamber  18  and high pressure chamber  20  of the large displacement from each other during the rotation of cylinder  10 . 
     Each bore of the first series comprises in the transverse plane pressure chambers  18 ,  20 , a communication conduit  50  turned radially towards the outside, positioning alternatively in communication, the chamber of the first pistons  12  with the low pressure chamber  18  or the high pressure chamber  20 , according to the angular position of this cylinder. 
     The angular position of the two sealing sections  44  is defined to separate both chambers  18 ,  20  in the positions of top or bottom dead center of pistons  12 , so that for each chamber the pistons move in the same direction, while increasing or decreasing the volumes of these chambers. 
     Each low pressure chamber  18  or high pressure chamber  20  is connected by a respectively low pressure  46  or high pressure  48  external channel ( FIG. 4 ), to a supply/feed solenoid valve  56 . 
     The supply/feed solenoid valve  56  includes three positions providing alternatively a direct connection of the two external channels  46 ,  48  between each other, permitting a no-load rotation of the hydraulic machine with very little resistance, with the fluid passing directly from the high pressure chamber  20  to the low pressure chamber  18 , a connection with two outside channels  58  connecting hydraulic machine  1  to pressure accumulators, to receive or send energy towards these accumulators according to whether this machine operates respectively as an engine or as a pump, or a closing of the two external channels  46 ,  48  which blocks the hydraulic machine. 
     By always keeping the same chambers  18 ,  20  for low and high pressure, hydraulic machine  1  turns in one or the other of the two directions of rotation, so as to operate as an engine or as a pump. 
     As a variant, one can invert the links with the hydraulic accumulators to exchange between the low pressure  18  and high pressure  20  chambers, to operate as an engine or as a pump while keeping the same direction of rotation of hydraulic machine  1 . 
     The hydraulic circuit for the small displacement (i.e., of the second series of pistons  22 ) is shown in detail in  FIG. 3 . 
     This hydraulic circuit is similar to the hydraulic circuit for the large displacement. It comprises in the same fashion, with an axial offset to find itself in the transverse plane aligned at the bottom of the second series of bores of the small displacement, a low pressure chamber  28  and a high pressure chamber  30  separated by two angular sections  44 , and in cylinder  10 , communication conduits  70  turned radially towards the outside for each bore of this small displacement. 
     The two displacements (i.e., the large and small displacements) each comprise the same number of pistons, pistons  22  of the internal crown being angularly offset with respect to pistons  12  of the external crown; their communication conduits  70  inserted angularly between each piston  12  of the external crown. 
     The hydraulic circuit of the small displacement also comprises two external channels, for low pressure  66  and for high pressure  68  and a supply/feed solenoid valve  76  connected to the outside conduits  58 . 
     Operation of this second small displacement circuit is similar to the one of the first large displacement circuit, with an independent control or adjustment of its plate  24 , with its reduced displacement delivering lower levels of torque and power, which permit obtaining a better performance in the event that small torque values or small performance values are required, whether as an engine or as a pump. 
     One can also obtain maximum power of hydraulic machine  1  for an operation as an engine or as a pump, by working simultaneously with the two displacements. 
     In addition, as detailed in  FIG. 4 , for each hydraulic circuit with large or small displacement, each angular sealing section  44  comprises in its central part a small radial channel  52  connected to a transition solenoid valve  54  which can operate proportionally or as all or nothing, to alternatively leave this central channel closed or to connect it to one of the two external channels  46 ,  48 . 
     The width of the communication conduits  50 ,  70  of cylinder  10  is provided so that these conduits exit in a given angular position of this cylinder, at the same time in one of the two pressure chambers  18 ,  20  and in central channel  52 , as shown in  FIG. 4 . 
     In particular, for going from the low pressure chamber  18  to the high pressure chamber  20 , central channel  52  is connected by transition solenoid valve  54  to the external high pressure channel  48  and for going from the high pressure chamber  20  to the low pressure chamber  18 , one connects this central channel to external low pressure channel  46 . The flow of the central channel  52  is controlled by its diameter, or by the transition solenoid valve  54  which is proportional. 
     The transition solenoid valves  54  permit a progressive passage from one pressure chamber to the other, so as to avoid hydraulic compressions or cavitation problems, which produce noise and torque pulsations at low rotation speeds. 
     One obtains as such a hydraulic machine  1  comprising two independently adjustable or controllable displacements which is embodied very compactly by using a single cylinder  10  mounted on a shaft  6 , and situated in one and the same housing  2 . In particular, one uses in cylinder  10  a radially available space inside the first series of small diameter pistons  22 , which avoids using a second cylinder, and which provides a light, compact and economical unit with a limited number of components. 
     In addition, with a single rotating cylinder  10 , losses are reduced and the performance of hydraulic machine  1  is improved with respect to other types of machine, achieving two different displacements with two cylinders. 
     As a variant, the hydraulic machine  1  can operate with fewer functions, such as without the supply solenoid valves  56 ,  76  or without transition solenoid valves  54  which can be replaced by calibrated valves to limit the flow. 
     The hydraulic machine can also include common high and low pressure chambers with a common rotating distributor for the two hydraulic small and large displacement circuits, which simplifies the embodiment of this machine, but brings reduced performances. 
     Thanks to its good performance, to its reduced weight and its compactness, which facilitates its incorporation in a vehicle, this hydraulic machine can be used beneficially in a hybrid vehicle.