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Powertrain consultancy Integral Powertrain has developed a new stop-start system with a variable ratio drive pulley that it claims brings substantial improvements in cost and CO2 reduction compared with other stop-start technologies.

The belt-integrated starter generator (B-ISG) also allows air-conditioning to be powered while the engine is stopped.

Integral Powertrain technical director Luke Barker said: “Existing B-ISG systems provide refined stop-start operation, but have significant disadvantages. This is mainly due to the requirement to generate very high torque and transmit it through the accessory belt, which impacts cost, packaging, weight and efficiency.

"A further issue is that engine-off comfort is compromised unless an expensive electrical air conditioning pump is fitted.”

At the heart of the new system is the Variable Ratio Pulley, which packages a two-ratio epicyclic gearbox into the belt drive pulley hub.

To start the engine, the high ratio (3.1:1 in the development system) is engaged to substantially reduce the torque requirement, so a medium-sized diesel engine can be cranked without the need for a high belt tension and the associated friction and wear. In tests engine start occurs in less than 0.3 seconds.

When the engine is running, the ancillary drive ratio returns smoothly to 1:1 or can be maintained at the high ratio during low engine speed operation if accessory loading is high. The ability to maintain an efficient drive speed enables lighter, more compact ancillaries resulting in further efficiency improvements.

Integral says the Variable Ratio Crank Pulley also provides cost savings for vehicles with electric drive. When the engine is off, the freewheel facility allows the ancillary drive belt to be powered by the motor, so belt-driven features such as hydraulic power steering, air conditioning and coolant pumps can continue to function.

Traditional systems also need a substantial electrical machine and inverter, with a large battery or costly ultracapacitor system to provide a high current for fast starting in cold conditions.

“Our variable ratio system reduces these costs too,” said Barker. “It also allows the use of efficient, cost-effective permanent magnet machines where previously the combination of high stall torque and high maximum speed has made this type of machine impractical for stop-start. This is particularly significant for mild hybrid applications as it enables increased electrical power and efficiency.”

Integral Powertrain is developing a new high-efficiency permanent magnet motor specifically for this application. With a diameter of 150mm and integrated low-cost, water cooled power electronics, the new machine can directly replace a standard alternator. As well as starting, the machine (rated at 5-10kW) will provide efficient regenerative braking and torque enhancement at a price that will make it affordable in volume sectors.

The stop-start system has completed the first phase of physical testing. Integral expects it to be available for production by 2012.

To run video of start with conventional system click here

To run video of engine start with new VR Pulley system click here