The present disclosure relates to hydrostatic regenerative braking for efficient use of energy of a vehicle. More particularly, a transmission for coordinating the flow of power between a prime mover, a hydraulic energy storage system and the vehicle wheels is discussed.
Regenerative drive systems including hybrid hydraulic arrangements have been applied to motor vehicles in the past. While conventional vehicle braking systems typically convert a vehicle's kinetic energy into heat energy, hydrostatic regenerative braking systems convert a moving vehicle's kinetic energy into stored hydraulic energy. The hydraulic energy is typically stored in an accumulator for later use to propel the vehicle. At least one hybrid hydraulic drive system includes a hydraulic pump/motor selectively operable to transfer energy from the vehicle driveline to a hydraulic storage device, such as during a braking event, or transfer energy from the hydraulic storage device to the driveline, such as during vehicle acceleration. When the hybrid hydraulic system stores power from the driveline, the hydraulic pump/motor acts as a pump to provide pressurized fluid to the accumulator. When the hybrid hydraulic system transfers power to the driveline, the hydraulic pump/motor acts as a motor driven by the energy stored in the accumulator.
Some vehicles include transmissions for transferring power between the driveline and the hydraulic storage device. At least one transmission cooperates with a hydrostatic regenerative braking system and includes a two gear design with a clutch positioned at an output shaft of the transmission. While this design may provide some benefit, it requires a relatively large diameter driven gear to provide a useful gear reduction ratio. Large packaging volume requirements and high weight are associated with this transmission. Due to the clutch being positioned downstream of the gear reduction mechanism, the clutch is required to transmit a torque approximately three times greater than the pump torque. A relatively large clutch is required to transfer the torque. The size and weight of the transmission are accordingly increased. Furthermore, with the two gear design, only one output drive ratio is available. To provide different versions with different ratios, new sets of gears for each ratio must be provided. Accordingly, a need exists in the art for an improved hydrostatic regenerative braking transmission.