Parallel HHVs

What are Parallel HHVs?
The other type of HHV is a parallel HHV. Unlike series HHVs, parallel HHVs use both the internal combustion engine and the hydraulic motor to power the vehicle and turn the wheels. This is because the hydraulic motor is not a separate system. In the parallel system, the hydraulic motor is fully integrated into the drive shaft of the vehicle. When undergoing a light acceleration, much like the series HHV, the hydraulic motor acts as the engine that powers the vehicle. If the vehicle is undergoing an extended or heavy acceleration, the engine will contribute to the vehicle’s acceleration and will power the vehicle in collaboration with the hydraulic motor. This is to keep the vehicle moving while still being efficient by cutting down on full engine use and ultimately fuel use. When a parallel HHV is cruising, the engine is the only thing that powers the vehicle. A parallel HHV brakes by making the hydraulic motor take the energy from the turning wheels to move fluid from a lower pressure reservoir to the reservoir with higher pressure, the accumulator. This the n slows the vehicle instead of using the friction brakes. The incorporation of the hydraulic motor of an HHV leads to better fuel efficiency than normal hybrids.





 Parallel HHV Light Acceleration


 * 1) Gas pedal is pressed.
 * 2) Pump motor is acctivated as main engine.
 * 3) Pressurized Nitrogen in the high pressure tank/accumulator pushes  hydraulic fluid across the pump motor.
 * 4) Pre ssurized fluid moving across pump motors turns the wheels.
 * 5) Fluid that moved across pump motor is not depressurized.
 * 6) Depressurized fluid moves into low pressure reservoir tank.

​Parallel HHV Heavy Acceleration

 * 1) Gas pedal is pressed.
 * 2) Internal combustion engine is turned on.
 * 3) Engine provides power to the driveshaft.
 * 4) Engine assists the pump motor in turning the vehicle's wheels.

Parallel HHV Cruising

 * 1) Engine is on.
 * 2) Line to the pump motor is bypassed.
 * 3) Engine alone provides power to the wheels,.

Parallel HHV Braking

 * 1) Brake pedal is pressed.
 * 2) The pump motor is activated.
 * 3) Energy from the wheels is used to pump hydraulic fluid from the reservoir to the accumulator.
 * 4) Energy flowing through the pump motor is used to slow the vehicle.

References/Sources
EPA Parallel

Parallel 3D Diagram