When compared to its two-wheel-drive gasoline-only siblings, two General Motors hybrid sport utility vehicles notch 50% better fuel economy in city driving and an up-to-30% fuel economy up-tick in combined city/highway driving. Among the fuel-smart facilitators is a regenerative braking system.
“Slip control boost (SCB) helps save fuel by being an integral part of the regenerative braking system,” said Dan Milot, Chief Engineer of Advanced Control Systems, North America Brake Engineering, for TRW Automotive. The SCB system replaces traditional boosters, master cylinders, and vacuum pumps with an electrohydraulic control unit and a master-cylinder reservoir device.
The electrohydraulic control unit consists of a motor, pump, high-pressure accumulator, a boost valve, eight slip-control valves, four pressure transducers, and a piston/spring brake-pedal simulator.
“SCB provides the base hydraulic braking function based on inputs from the driver in the form of pedal travel and pedal force,” said Milot. “The system is capable of communicating with the hybrid-electric powertrain to enable the electric motors to deliver the maximum amount of regenerative braking as required in order to maximize energy recovery, and then blend in friction braking as needed”.
The 2008 Chevrolet Tahoe and the GMC Yukon hybrid SUVs use GM’s new electrically variable transmission, a 300-V nickel metal-hydride energy storage system, and a standard Vortec 6.0-L V8 gasoline engine with active fuel management and late intake valve closing technology.
Both the Tahoe and Yukon full-size hybrid SUVs represent the first application of SCB, which has patents pending relating to its system architecture, specific components, and software algorithm features. “SCB is fully compatible with regenerative-braking systems and helps to provide brake blending, which means it supplies the traditional friction brake force needed in addition to the slowing of the vehicle from the energy recovery of the electric motors,” Milot said.
SCB is compatible with vehicle powertrain architectures that have “reduced to no vacuum availability, such as direct-injection engines, diesel engines, and fuel-cell powertrains. SCB is a hydraulic-boost brake system with integrated electronic stability control functionality in one package,” said Milot. To date, TRW has commitments to supply its SCB on four different production platforms.