METHOD OF OPERATING A PUMP/MOTOR
A method of operating a pump/motor includes pumping working fluid into a high-pressure manifold with a first piston/cylinder assembly while the piston in the first piston/cylinder assembly is displaced from a bottom dead center position to a top dead center position, and transferring working fluid from the high-pressure manifold to the cylinder of a second piston/cylinder assembly to displace the piston of the second piston/cylinder assembly from a top dead center position to a bottom dead center position, thereby imparting torque on a cam and an output shaft, within the same complete revolution of the cam and the output shaft in which working fluid is pumped into the high-pressure manifold by the first piston/cylinder assembly.
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The present invention relates to hydraulic pump/motors, and more particularly to hydraulic pump/motors for use in vehicle transmissions, mobile hydraulic applications, and industrial hydraulic applications.
BACKGROUND OF THE INVENTIONMulti-cylinder hydraulic pump/motors are typically utilized in tandem, for example, in a vehicle hydrostatic transmission. A first of the pump/motors is connected to a prime mover (e.g., an engine), while the second pump/motor is connected to the driveline of the vehicle. The first pump/motor is powered by the engine to operate as a pump to supply pressurized hydraulic fluid to the second pump/motor, which operates as a motor to power the driveline. When the second pump/motor is operating as a motor at less than full capacity or displacement (i.e., at low flow fractions), low frequency variations in torque at the output shaft of the second pump/motor often result. Such variations may lead to lugging of a drive train coupled to the output shaft, or undesirable noise, vibration, and harshness generated by the second pump/motor when operating as a motor.
SUMMARY OF THE INVENTIONThe present invention provides, in one aspect, a method of operating a pump/motor in a system including a high-pressure manifold and a low-pressure manifold. The pump/motor includes an output shaft, a plurality of piston/cylinder assemblies, and a cam coupled to the output shaft and disposed between the output shaft and the piston/cylinder assemblies. Each piston/cylinder assembly includes a cylinder and a piston at least partially disposed in the cylinder and engaged with the cam. The method includes displacing the pistons of the respective piston/cylinder assemblies from a bottom dead center position to a top dead center position, and then back to the bottom dead center position, within each revolution of the cam and the output shaft, pumping working fluid into the high-pressure manifold with a first piston/cylinder assembly while the piston in the first piston/cylinder assembly is displaced from the bottom dead center position to the top dead center position, and transferring working fluid from the high-pressure manifold to the cylinder of a second piston/cylinder assembly to displace the piston of the second piston/cylinder assembly from the top dead center position to the bottom dead center position, thereby imparting torque on the cam and the output shaft, within the same complete revolution of the cam and the output shaft in which working fluid is pumped into the high-pressure manifold by the first piston/cylinder assembly.
The present invention provides, in another aspect, a method of operating a pump/motor in a system including a high-pressure manifold and a low-pressure manifold. The pump/motor includes an output shaft, a plurality of piston/cylinder assemblies, and a cam coupled to the output shaft and disposed between the output shaft and the piston/cylinder assemblies. Each piston/cylinder assembly includes a cylinder and a piston at least partially disposed in the cylinder and engaged with the cam, a first valve selectively fluidly communicating the high-pressure manifold and the cylinder, and a second valve selectively fluidly communicating the low-pressure manifold and the cylinder. The method includes opening the first valve of a first group of piston/cylinder assemblies to at least partially fill each of the cylinders within the first group with high-pressure working fluid, thereby displacing the pistons within the respective cylinders in the first group from a top dead center position to a bottom dead center position, rotating the output shaft and the cam with the pistons in the first group, opening the second valve of a second group of piston/cylinder assemblies, driving each of the pistons within the second group, with the rotating cam, from the bottom dead center position to the top dead center position to at least partially exhaust working fluid from each of the cylinders within the second group to the low-pressure manifold, opening the first valve of a first piston/cylinder assembly not in either of the first and second groups while the respective first valves in the first group are opened, and driving the piston in the first piston/cylinder assembly, with the rotating cam, from the bottom dead center position toward the top dead center position to pump working fluid into the high-pressure manifold while the first valve of the first piston/cylinder assembly is opened.
The present invention provides, in yet another aspect, a method of operating a pump/motor in a system including a high-pressure manifold and a low-pressure manifold. The pump/motor includes an output shaft, a plurality of piston/cylinder assemblies, and a cam coupled to the output shaft and disposed between the output shaft and the piston/cylinder assemblies. Each piston/cylinder assembly includes a cylinder and a piston at least partially disposed in the cylinder and engaged with the cam, a first valve selectively fluidly communicating the high-pressure manifold and the cylinder, and a second valve selectively fluidly communicating the low-pressure manifold and the cylinder. The method includes opening the first valve of a first group of piston/cylinder assemblies to fluidly communicate the cylinders in the first group with the high-pressure manifold, rotating the output shaft and the cam, thereby displacing the pistons within the respective cylinders in the first group from a bottom dead center position to a top dead center position to pump working fluid in the respective cylinders in the first group into the high-pressure manifold, opening the second valve of a second group of piston/cylinder assemblies, at least partially filling the respective cylinders within the second group with working fluid from the low-pressure manifold, thereby displacing the pistons within the respective cylinders in the second group from the top dead center position to the bottom dead center position, opening the first valve of a first piston/cylinder assembly not in either of the first and second groups, while the respective first valves in the first group are opened, to at least partially fill the cylinder of the first piston/cylinder assembly with high-pressure working fluid, thereby displacing the piston in the first piston/cylinder assembly from the top dead center position to the bottom dead center position, and imparting a torque on the cam and the output shaft with the piston in the first piston/cylinder assembly as the piston in the first piston/cylinder assembly moves from the top dead center position to the bottom dead center position.
Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.
DETAILED DESCRIPTIONThe pump/motor 14 includes an output shaft 26, a plurality of piston/cylinder assemblies 30, and a cam 34 coupled to the output shaft 26 and disposed between the output shaft 26 and the piston/cylinder assemblies 30. Each piston/cylinder assembly 30 includes a cylinder 38 and a piston 42 at least partially disposed in the cylinder 38 and engaged with the cam 34. In operation, each of the pistons 42 is displaced from a bottom dead center position (see piston 42b) to a top dead center position (see piston 42a), and then back to the bottom dead center position, within each revolution of the cam 34 and the output shaft 26. Although only two piston/cylinder assemblies 30 are shown in
With reference to
Each piston/cylinder assembly 30 of the pump/motor 14 also includes a high-pressure valve 50 operable to selectively fluidly communicate the cylinder 38 with the high-pressure manifold 18. The high-pressure valve 50 is seated outside the cylinder 38, such that the high-pressure valve 50 must be moved in a direction away from the cylinder 38 to unseat or open the high-pressure valve 50 to fluidly communicate the cylinder 38 with the high-pressure manifold 18. In the illustrated construction of the pump/motor 14, the high-pressure valve 50 is actuated to an unseated position by an electromagnetic coil 54, and is biased toward a seated position by a biasing element (e.g., a spring; not shown). Alternatively, other actuators and/or biasing elements may be utilized to move the high-pressure valve 50 between the seated and unseated positions.
The system 10 also includes a controller 58 in communication with each of the actuators (i.e., the electromagnetic coils 48, 54) of the low-pressure valves 46 and the high-pressure valves 50 to control the opening and closing of the valves 46, 50. The controller 58 may communicate with each of the coils 48, 54 of the low-pressure and high-pressure valves 46, 50 using electrical wires 60. Alternatively, any of a number of different wireless protocols may be employed. The system 10 also includes an encoder 62 in communication with the controller 58 to monitor the rotational position of the cam 34 over time (and therefore the rotational speed of the cam 34 and the output shaft 26). Alternatively, other components or devices may be used to permit the controller 58 to monitor the rotational position of the cam 34 during operation of the system 10.
The system 10 may be incorporated, for example, in a vehicle hydrostatic transmission in which the output shaft 26 is coupled to a driveline of the vehicle. Such a vehicle hydrostatic transmission would also include a second pump/motor (not shown) driven by a prime mover (e.g., an engine; also not shown). In operation of the hydrostatic transmission, the engine would drive the second pump/motor as a pump to provide high-pressure working fluid to the high-pressure manifold 18, which would be used to operate the pump/motor 14 shown in
To deliver or impart torque to the cam 34 and the output shaft 26, each of the piston/cylinder assemblies 30 in the pump/motor 14 is actuated through a cycle in which the pistons 42 of the respective assemblies 30 are displaced from the top dead center position to the bottom dead center position, and then back to the top dead center position. Particularly, starting at the top dead center position of the piston 42a, the controller 58 activates the coil 54 of the high-pressure valve 50 to open the valve 50 for a period of time to fluidly communicate the cylinder 38 and the high-pressure manifold 18, causing a transfer of high-pressure working fluid from the high-pressure manifold 18 to the substantially empty cylinder 38 in which the piston 42a is located. The transfer of high-pressure working fluid into the cylinder 38 subsequently displaces the piston 42a toward the cam 34. The cam 34 includes an inclined cam surface 66 which converts the axial motion of the piston 42a to rotational motion of the cam 34 and the output shaft 26. As a result, the linear force exerted on the piston 42a by the high-pressure working fluid transferred into the cylinder 38 is converted to torque on the cam 34 and the output shaft 26 about a rotational axis 70 of the cam 34 and the output shaft 26.
The piston 42a will continue to impart torque to the cam 34 and the output shaft 26 until the piston 42a reaches its bottom dead center position (i.e., the position of the piston 42b in
Shortly before the piston 42a reaches the bottom dead center position, the controller 58 closes the high-pressure valve 50 to cease fluid communication between the cylinder 38 and the high-pressure manifold 18. Continued movement of the piston 42a toward the bottom dead center position reduces the pressure in the cylinder 38 until it is substantially equal to the pressure of the working fluid in the low-pressure manifold 22. After a brief period of time during which the piston 42a dwells near the bottom dead center position, the controller 58 then activates the coil 48 of the low-pressure valve 46 to open the valve 46 to fluidly communicate the cylinder 38 and the low-pressure manifold 22. The rotating cam 34 then drives the piston 42 (e.g., piston 42b) from the bottom dead center position to the top dead center position, during which time the working fluid in the cylinder 38 is exhausted past the low-pressure valve 46 and into the low-pressure manifold 22. The controller 58 closes the low-pressure valve 46 shortly before the piston 42b reaches the top dead center position to permit the remaining working fluid in the cylinder 38 to be pressurized to a value that is substantially equal to the pressure of the working fluid in the high-pressure manifold 18 to permit the high-pressure valve 50 to open for the subsequent cycle of transferring high-pressure working fluid into the cylinder 38.
This process is schematically illustrated in
The piston/cylinder assemblies 30 identified with an “M” are those undergoing the cycle described above in which working fluid from the high-pressure manifold 18 is transferred into the piston/cylinder assemblies 30 to perform work on the cam 34 and the output shaft 26 (i.e., by imparting torque to the cam 34 and the output shaft 26), and subsequently exhausted to the low-pressure manifold 22. This cycle is hereinafter referred to as “motoring,” in which the pump/motor 14 is used as a motor to power the vehicle driveline or other mechanism. The piston/cylinder assemblies 30 used in the motoring cycle (i.e., those marked with an “M”) that are further identified with an “X” as “active” are those in which high-pressure working fluid from the high-pressure manifold 18 is being injected or transferred as described above to impart torque to the cam 34 and the output shaft 26 to rotate the cam 34 and the output shaft 26. The piston/cylinder assemblies 30 used in the motoring cycle in which an “X” is omitted are those in which the pistons 42 are being driven by the cam 34 to exhaust working fluid to the low-pressure manifold 22 as described above.
As shown in
Fewer than the total number of available piston/cylinder assemblies 30 may be utilized at any time when the full capacity or the displacement of the pump/motor 14 (when operating as a motor) is not needed. For example, the pump/motor 14, when operating as a motor, may be operated at less than full displacement when the desired speed of the vehicle driveline (and therefore the speed of the cam 34 and the output shaft 26) is relatively low. To operate the pump/motor 14 at a reduced displacement, a select number of piston/cylinder assemblies 30 in the pump/motor 14 are made inactive. Those inactive piston/cylinder assemblies 30 are interspersed amongst the piston/cylinder assemblies 30 that are motoring. As shown in
With reference to
Particularly, starting at the top dead center position of the piston 42a, the controller 58 activates the coil 48 of the low-pressure valve 46 to open the valve 46 for a period of time to fluidly communicate the cylinder 38 and the low-pressure manifold 22, causing a transfer of low-pressure working fluid from the low-pressure manifold 22 to the substantially empty cylinder 38 in which the piston 42a is located. The transfer of low-pressure working fluid into the cylinder 38 subsequently displaces the piston 42a toward the cam 34. As the pressure of the working fluid in the low-pressure manifold 22 is substantially less than the pressure of the working fluid in the high-pressure manifold 18, any torque imparted on the cam 34 by the piston 42a as it is displaced from the top dead center position to the bottom dead center position is negligible.
The piston 42a will continue to be displaced toward the cam 34 until the piston 42a reaches the bottom dead center position (i.e., the position of the piston 42b in
This process is schematically illustrated in
As shown in
Fewer than the total number of available pump/motor assemblies 30 may be utilized at any time when the full capacity or the displacement of the pump/motor 14 (when operating as a pump) is not needed. For example, the pump/motor 14, when operating as a pump, may be operated at less than full displacement when the speed of the vehicle driveline (and therefore the speed of the cam 34 and the output shaft 26) is relatively low. To operate the pump/motor 14 at a reduced displacement, a select number of piston/cylinder assemblies 30 in the pump/motor 14 are made inactive. Those inactive piston/cylinder assemblies 30 are interspersed amongst the piston/cylinder assemblies 30 that are pumping. As shown in
With respect to the particular manner of operation of the pump/motor shown in
However, the inventors have unexpectedly discovered that the method of
With respect to the particular manner of operation of the pump/motor 14 shown in
The inventors have unexpectedly discovered that the method of
Various features of the invention are set forth in the following claims.
Claims
1. A method of operating a pump/motor in a system including a high-pressure manifold and a low-pressure manifold, the pump/motor including an output shaft, a plurality of piston/cylinder assemblies, and a cam coupled to the output shaft and disposed between the output shaft and the piston/cylinder assemblies, each piston/cylinder assembly including a cylinder and a piston at least partially disposed in the cylinder and engaged with the cam, the method comprising:
- displacing the pistons of the respective piston/cylinder assemblies from a bottom dead center position to a top dead center position, and then back to the bottom dead center position, within each revolution of the cam and the output shaft;
- pumping working fluid into the high-pressure manifold with a first piston/cylinder assembly while the piston in the first piston/cylinder assembly is displaced from the bottom dead center position to the top dead center position; and
- transferring working fluid from the high-pressure manifold to the cylinder of a second piston/cylinder assembly to displace the piston of the second piston/cylinder assembly from the top dead center position to the bottom dead center position, thereby imparting torque on the cam and the output shaft, within the same complete revolution of the cam and the output shaft in which working fluid is pumped into the high-pressure manifold by the first piston/cylinder assembly.
2. The method of claim 1, wherein the second piston/cylinder assembly is included in a group of piston/cylinder assemblies from which the first piston/cylinder assembly is excluded, and wherein the method further includes transferring working fluid from the high-pressure manifold to each of the cylinders of the group to displace the respective pistons in the group from the top dead center position to the bottom dead center position within the same complete revolution of the cam and the output shaft in which working fluid is pumped into the high-pressure manifold by the first piston/cylinder assembly.
3. The method of claim 2, wherein transferring working fluid from the high-pressure manifold to each of the cylinders of the group includes opening a valve in each of the piston/cylinder assemblies of the group to fluidly communicate the respective cylinders of the group with the high-pressure manifold.
4. The method of claim 3, further comprising exhausting working fluid to the low-pressure manifold with each of the piston/cylinder assemblies of the group when the pistons in the group are displaced from the bottom dead center position to the top dead center position within the same complete revolution of the cam and the output shaft in which working fluid is pumped into the high-pressure manifold by the first piston/cylinder assembly.
5. The method of claim 4, wherein exhausting working fluid to the low-pressure manifold includes opening a second valve in each of the piston/cylinder assemblies of the group to fluidly communicate the respective cylinders of the group with the low-pressure manifold.
6. The method of claim 5, further comprising driving each of the pistons of the group with the rotating cam from the bottom dead center position to the top dead center position while the second valve is open to exhaust working fluid from the respective cylinders of the group to the low-pressure manifold.
7. The method of claim 2, further comprising at least partially filling the cylinder of a third piston/cylinder assembly excluded from the group with working fluid from the low-pressure manifold, thereby displacing the piston in the third piston/cylinder assembly from the top dead center position to the bottom dead center position, within the same complete revolution of the cam and the output shaft in which working fluid is pumped into the high-pressure manifold by the first piston/cylinder assembly.
8. The method of claim 7, wherein at least partially filling the cylinder of the third piston/cylinder assembly with working fluid from the low-pressure manifold includes opening a valve in the third piston/cylinder assembly to fluidly communicate the cylinder of the third piston/cylinder assembly with the low-pressure manifold.
9. The method of claim 1, wherein the first piston/cylinder assembly is included in a group of piston/cylinder assemblies from which the second piston/cylinder assembly is excluded, and wherein the method further includes pumping working fluid into the high-pressure manifold with each of the assemblies in the group within the same complete revolution of the cam and the output shaft in which working fluid is transferred from the high-pressure manifold to the second piston/cylinder assembly.
10. The method of claim 9, wherein pumping working fluid into the high-pressure manifold with each of the piston/cylinder assemblies of the group includes opening a valve in each of the piston/cylinder assemblies of the group to fluidly communicate the respective cylinders of the group with the high-pressure manifold.
11. The method of claim 10, further comprising driving each of the pistons of the group with the rotating cam from the bottom dead center position to the top dead center position while the valve is open to pump working fluid from the respective cylinders of the group to the high-pressure manifold.
12. The method of claim 10, further comprising at least partially filling the respective cylinders of the group with low-pressure working fluid from the low-pressure manifold when the pistons in the group are displaced from the top dead center position to the bottom dead center position.
13. The method of claim 12, wherein at least partially filling the respective cylinders of the group with low-pressure working fluid includes opening a second valve in each of the piston/cylinder assemblies of the group to fluidly communicate the respective cylinders of the group with the low-pressure manifold.
14. The method of claim 10, further comprising exhausting low-pressure working fluid from the cylinder of a third piston/cylinder assembly excluded from the group to the low-pressure manifold when the piston of the third piston/cylinder assembly is displaced from the bottom dead center position to the top dead center position within the same complete revolution of the cam and the output shaft in which working fluid is transferred from the high-pressure manifold to the second piston/cylinder assembly.
15. The method of claim 14, wherein exhausting low-pressure working fluid from the cylinder of the third piston/cylinder assembly includes
- opening a second valve in the third piston/cylinder assembly to fluidly communicate the cylinder of the third piston/cylinder assembly with the low-pressure manifold, and
- driving the piston of the third piston/cylinder assembly with the rotating cam from the bottom dead center position to the top dead center position while the second valve is open to exhaust working fluid from the cylinder of the third piston/cylinder assembly to the low-pressure manifold.
16. A method of operating a pump/motor in a system including a high-pressure manifold and a low-pressure manifold, the pump/motor including an output shaft, a plurality of piston/cylinder assemblies, and a cam coupled to the output shaft and disposed between the output shaft and the piston/cylinder assemblies, each piston/cylinder assembly including a cylinder and a piston at least partially disposed in the cylinder and engaged with the cam, a first valve selectively fluidly communicating the high-pressure manifold and the cylinder, and a second valve selectively fluidly communicating the low-pressure manifold and the cylinder, the method comprising:
- opening the first valve of a first group of piston/cylinder assemblies to at least partially fill each of the cylinders within the first group with high-pressure working fluid, thereby displacing the pistons within the respective cylinders in the first group from a top dead center position to a bottom dead center position;
- rotating the output shaft and the cam with the pistons in the first group;
- opening the second valve of a second group of piston/cylinder assemblies;
- driving each of the pistons within the second group, with the rotating cam, from the bottom dead center position to the top dead center position to at least partially exhaust working fluid from each of the cylinders within the second group to the low-pressure manifold;
- opening the first valve of a first piston/cylinder assembly not in either of the first and second groups while the respective first valves in the first group are opened; and
- driving the piston in the first piston/cylinder assembly, with the rotating cam, from the bottom dead center position toward the top dead center position to pump working fluid into the high-pressure manifold while the first valve of the first piston/cylinder assembly is opened.
17. The method of claim 16, wherein driving the piston in the first piston/cylinder assembly, with the rotating cam, from the bottom dead center position toward the top dead center position includes pumping working fluid from the cylinder of the first piston/cylinder assembly, through the first valve of the piston/cylinder assembly, and into the high-pressure manifold.
18. The method of claim 16, wherein the piston/cylinder assemblies are arranged substantially symmetrically about a longitudinal axis of the pump/motor, wherein rotating the output shaft and the cam with the pistons in the first group includes rotating the output shaft and the cam about the longitudinal axis, and wherein opening the first valve of the first piston/cylinder assembly occurs within the same complete revolution of the output shaft and the cam about the longitudinal axis as opening the first valve of the first group of piston/cylinder assemblies.
19. A method of operating a pump/motor in a system including a high-pressure manifold and a low-pressure manifold, the pump/motor including an output shaft, a plurality of piston/cylinder assemblies, and a cam coupled to the output shaft and disposed between the output shaft and the piston/cylinder assemblies, each piston/cylinder assembly including a cylinder and a piston at least partially disposed in the cylinder and engaged with the cam, a first valve selectively fluidly communicating the high-pressure manifold and the cylinder, and a second valve selectively fluidly communicating the low-pressure manifold and the cylinder, the method comprising:
- opening the first valve of a first group of piston/cylinder assemblies to fluidly communicate the cylinders in the first group with the high-pressure manifold;
- rotating the output shaft and the cam, thereby displacing the pistons within the respective cylinders in the first group from a bottom dead center position to a top dead center position to pump working fluid in the respective cylinders in the first group into the high-pressure manifold;
- opening the second valve of a second group of piston/cylinder assemblies;
- at least partially filling the respective cylinders within the second group with working fluid from the low-pressure manifold, thereby displacing the pistons within the respective cylinders in the second group from the top dead center position to the bottom dead center position;
- opening the first valve of a first piston/cylinder assembly not in either of the first and second groups, while the respective first valves in the first group are opened, to at least partially fill the cylinder of the first piston/cylinder assembly with high-pressure working fluid, thereby displacing the piston in the first piston/cylinder assembly from the top dead center position to the bottom dead center position; and
- imparting a torque on the cam and the output shaft with the piston in the first piston/cylinder assembly as the piston in the first piston/cylinder assembly moves from the top dead center position to the bottom dead center position.
20. The method of claim 19, wherein the piston/cylinder assemblies are arranged substantially symmetrically about a longitudinal axis of the pump/motor, wherein rotating the output shaft and the cam includes rotating the output shaft and the cam about the longitudinal axis, and wherein opening the first valve of the first piston/cylinder assembly occurs within the same complete revolution of the output shaft and the cam about the longitudinal axis as opening the first valve of the first group of piston/cylinder assemblies.
Type: Application
Filed: Aug 6, 2010
Publication Date: Feb 9, 2012
Applicant: ROBERT BOSCH GMBH (Stuttgart)
Inventors: Ron Cowan (Rochester Hills, MI), Simon J. Baseley (Ann Arbor, MI)
Application Number: 12/851,959
International Classification: F04B 7/00 (20060101);