New hydraulic hybrid transmission doubles MPG in city driving

Mechanical transmission of power using gears is very energy inefficient. The familiar automotive multi speed gearbox and differential suffers from the friction losses that result is between 20 – 30% of engine power being lost between a cars engine and the wheels. Many technics are being developed to eliminate mechanical transmission including Wheel Motors and Hydraulic transmissions as we have seen being trialed in UPS delivery vans. A Scottish company called Artemis Intelligent Power has developed a new hydraulic hybrid transmission system they say can double a vehicles MPG in city driving.

The heart of the system is a 6 piston radial digital displacement hydraulic pump/motor. This hydraulic motor replaces the port plates and swash plates in conventional hydraulic machines with computer controlled high-speed solenoid valves. These solenoids actively controlled poppet valves that rectify the flow into and out of, each cylinder and are driven by a microprocessor. This hydraulic pump attaches to the flywheel a conventional combustion motor replacing the gearbox. The pump is hydraulically connected to Digital Displacement Motors coupled to the wheels so the only connection between the internal combustion motor and the wheels is the hydraulic system.

In operation the system is conceptually similar to an electric series hybrid but with a pressure accumulator taking the place of the battery. The combustion engine generates hydraulic pressure at a steady rpm that can either drive the wheels with the hydraulic motor coupled to the wheels or that pressure can be added to the accumulator for later use. When the vehicle slows down the wheel coupled motor turns into a pump and regenerates braking energy into hydraulic pressure that is stored in the accumulator. Artemis say Independent tests have confirmed that a prototype car, a BMW 530i, gave double the MPG in city driving compared to the same car with a six speed manual transmission. Overall, including highway driving, the prototype had approximately 30% lower carbon dioxide emissions than it had before the company fitted its energy saving transmission.

The company is working with Bosch Rexroth and Sauer-Danfoss APS to bring this technology to on-highway vehicles and agricultural and handling machinery.