New hydraulic hybrid transmission doubles MPG in city driving
March 2, 2009 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 in 20 – 30% of engine power being lost between a car's engine and the wheels. Many techniques are being developed to eliminate mechanical transmission including Wheel Motors and Hydraulic transmissions that we have seen being trialed in UPS delivery vans. Now in an innovative new approach, Scottish company Artemis Intelligent Power has developed a hydraulic hybrid transmission system it says can double a vehicle's MPG in city driving.
The heart of the system is a six 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. Driven by a microprocessor, these solenoids actively control poppet valves that rectify the flow into and out of each cylinder. The hydraulic pump attaches to the flywheel an conventional combustion motor replacing the gearbox. It 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 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 says 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.