Patent Application
20080039262
Both forward and rear traction devices 12, 14 may include one or more wheels located on each side of machine 10 (only one side shown). Alternatively, forward and/or rear traction devices 12, 14 may include tracks, belts, or other traction devices known in the art. Any of forward and rear traction devices 12, 14 may be driven and/or steerable.
Frame 16 may include any structural unit that supports movement of work machine 10. Frame 16 may be, for example, a stationary base frame connecting traction devices 12, 14, power source 18, and transmission 20; a movable frame member of a linkage system; or any other frame known in the art.
Power source 18 may produce a mechanical power output and embody an internal combustion engine such as, for example, a diesel engine, a gasoline engine, a gaseous fuel-powered engine, or any other type of engine apparent to one skilled in the art. Power source 18 may, alternatively, embody a non-combustion source of power such as a furnace, a battery, a fuel cell, a motor, or any other suitable source of power.
As illustrated in
The CVT portion or second power flow path 26 within transmission 20 may include a pump 38 and a motor 40 interconnected by way of a first fluid passageway 42 and a second fluid passageway 44. Pump 38 may be, for example, a variable displacement pump rotated by mechanical output 30 of power source 18 to pressurize fluid. The pressurized fluid may be directed through motor 40 by way of fluid passageways 42 or 44, depending on the travel direction of machine 10. Motor 40, being driven by the pressurized fluid may rotate a portion of gear assembly 32. The direction and speed of this rotation may affect the output ratio of transmission 20. A ratio controller (not shown) may manipulate the displacement of pump 38 with a pump signal to thereby control the rotation of motor 40 and the resulting output ratio of transmission 20. It is contemplated that motor 40 may also be a variable displacement device, if desired. It is to be noted that in an electric CVT configuration, a generator and electric motor may substitute for the fluid pump and motor described above.
Hydraulic assist unit 22 may include components that interact to selectively absorb energy from and release energy to mechanical output 30 of power source 18. Specifically, hydraulic assist unit 22 may include a pump 46, an accumulator 48, a pressure relief valve 50, and a cooler 52. Pump 46 may be fluidly connected to accumulator 48 by way of a fluid passageway 54, and with cooler 52 by way of a fluid passageway 56. Although pressure relief valve 50 illustrated as being disposed between accumulator 48 and cooler 52 within fluid passageway 54, it is contemplated that pressure relief valve 50 may be disposed at any location within hydraulic assist unit 22. It is contemplated that one or more control valves (not shown) may be implemented within hydraulic assist unit 22 such as, for example, within fluid passageways 54 between pump 46 and accumulator 48, within fluid passageway 56, and/or within a drain passageway 60 associated with a lower pressure reservoir 58 to control flow operations within hydraulic assist unit 22, if desired.
Similar to pump 38, pump 46 may also be a variable displacement source of pressurized fluid. During steady state operation of machine 10, the displacement of pump 46 may be set to approximately zero to minimize the friction added by pump 46 to power source 18. However, during situations of excess engine power, the displacement of pump 46 may be increased to pressurize and store pressurized fluid within accumulator 48 for later use. Similarly, during situations of insufficient power, the displacement of pump 46 may be increased and the stored pressurized fluid within accumulator 48 discharged to drive power source 18 by way of pump 46.
Accumulator 48 may embody a pressure vessel filled with a compressible gas that is configured to store pressurized fluid for future use as a source of fluid power. The compressible gas may include, for example, nitrogen or another appropriate compressible gas. As fluid in communication with accumulator 48 exceeds a predetermined pressure, it may flow into accumulator 48. Because the nitrogen gas is compressible, it may act like a spring and compress as the fluid flows into accumulator 48. When the pressure of the fluid within passageways communicated with accumulator 48 drops below a predetermined pressure, the compressed nitrogen within accumulator 48 may expand and urge the fluid from within accumulator 48 to exit accumulator 48. It is contemplated that accumulator 48 may alternatively embody a spring biased type of accumulator, if desired.
Pressure relief valve 50 may fluidly connect the output of pump 46 to low pressure reservoir 58 by way of fluid passageways 56 and 60 to relieve pressure from hydraulic assist unit 22. In particular, pressure relief valve 50 may include a pilot or solenoid operated valve element that is spring-biased toward a closed or fluid-blocking position and movable toward an open or fluid-passing position in response to a pressure within fluid passageway 54 exceeding a predetermined pressure. The predetermined pressure may be variable, if desired, and set or varied according to one or more machine related conditions. Pressure relief valve 50 may maintain system pressure (e.g., the pressure within hydraulic assist unit 22) at the predetermined level by remaining in the fluid-blocking position until the pressure of the fluid acting on pressure relief valve 50 exceeds the biasing spring force and/or the solenoid (not shown) is energized, while simultaneously protecting the system from excessive pressure spikes. The system pressure within hydraulic assist unit 22 may act against the pressurizing work of pump 46, thereby, allowing excess power to be dissipated even when accumulator 48 is filled to capacity. It is contemplated that pressure relief valve 50 may be omitted, if desired.
As pump 46 works the fluid within hydraulic assist unit 22, the dissipated energy may be converted into heat. If left unchecked, this heat could build up and reduce the effectiveness of hydraulic assist unit 22. For this reason, cooler 52 may be utilized to exchange heat with a secondary fluid circuit (not shown). Cooler 52 may embody any type of heat exchanger known in the art such as, for example, a plate-type, tube and fin-type, or shell and tube-type liquid-to-air heat exchanger or a liquid-to-liquid heat exchanger.
The disclosed drivetrain may provide a flexible and robust way to improve vehicle response, regardless of the type of transmission utilized within the vehicle. Specifically, the separate and self-contained hydraulic assist unit of the disclosed drivetrain may selectively provide added power to the primary mover of the vehicle for acceleration and added friction for deceleration. Because this hydraulic assist unit may includes its own source of power and power storage, it can be used in conjunction with a mechanical transmission, an electric transmission, a hydraulic transmission, or any combination of these technologies. The operation of machine 10 will now be described.
Referring to
As transmission 20 changes output gear ratios, particularly stepwise changes in the output ratio, power source 18 may have difficulty immediately supplying the required output torque. As a result, the operation of power source 18 may, in some situations, lag desired performance. In order to accommodate this lag in performance, hydraulic assist unit 22 may selectively supply and absorb the torque difference between demanded torque and engine-available torque. For example, when shifting from a low gear ratio to a high gear ratio, the output torque of power source 18 may lag a desired output torque, causing the speed of the engine to drop undesirably. In this situation, pressurized fluid from accumulator 48 may be directed to drive pump 46 and add torque to mechanical output 30. Conversely, when shifting from a high gear ratio to a low gear ratio, the output torque of power source 18 may be higher than demanded and, because of the lack of friction due to undersizing of power source 18, the output torque decrease of power source 18 may lag a desired torque decrease. In this situation, the excess torque of power source 18 may directed through mechanical output 30 to drive pump 46 and pressurize fluid within hydraulic assist unit 22. By driving pump 46, the friction and, thus, the ability to quickly reduce the torque output of power source 18 may be increased. In addition, the fluid pressurized by pump 46 may be directed to charge accumulator 48 for the next assisting operation. When neither torque addition nor subtraction is necessary and accumulator 48 is filled to capacity, the displacement of pump 46 may be de-stroked such that the efficiency of power source 18 is largely unaffected.
Hydraulic assist unit 22 may selectively add friction to power source 18, even when accumulator 48 is filled to capacity. Specifically, because hydraulic assist unit 22 includes pressure relief valve 50, system pressure, which acts against the rotation of pump 46, may be maintained at a desired predetermined level, regardless of a condition of accumulator 48.
It will be apparent to those skilled in the art that various modifications and variations can be made to the drivetrain of the present disclosure. Other embodiments of the drivetrain will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.
