Vehicle Electrification - November 4, 2010 - 45

November 4, 2010

Helping GM put the brakes on Volt
General Motors tapped TRW’s experience in developing electrohydraulic brake-control technologies for the 2006 T900 hybrid trucks and the Saturn Vue Hybrid and Vue Fuel Cell Vehicle for the Volt program. Dan Milot, Chief Engineer for TRW’s North American Advanced Control Systems group, explains. Q: What specifically did TRW contribute to the 2011 Volt program? Milot: TRW supplies the braking systems actuation and slip controller, the ABS/ESC functionality, to the vehicle. This also encompasses the regenerative braking. It required us to begin working with GM very early in the program. Q: What did your team learn from this program? Milot: Volt’s type of powertrain is different from the GM Two Mode hybrid. The Two Mode has a transmission that’s mated with the two electric motors, but the ICE is the primary engine. Volt is primarily an electric-motordriven vehicle. Its electric drive mode produces scenarios where the vehicle NVH is significantly different than any other car. With Volt’s configuration, the effects of wheel inertia from the traction motor are different than in a vehicle with a conventional powertrain. That includes during ABS and traction control activation, and even the interface with the powertrain for developing torque. We did a lot of work around that to ensure our ABS, ESC, and even the regen blending will quickly generate the actual braking torque for us. Then we determined the friction braking response time to make it all seamless to the driver. Q: What was GM’s brief to TRW for tuning the ‘feel’ of Volt’s braking? Milot: Putting ‘drag torque’ into the regen system is meant to replicate the deceleration feel of a manual transmission. Compared with some electric vehicles that

Dan Milot
have fairly aggressive regen ‘feel’ due to a high calibration, Volt’s braking is tuned to feel more like a conventional vehicle. Lifting off the throttle is not intended to be the primary means of braking; that’s for the brake pedal. The GM engineers provided their own level of what we call ‘base brake’ software, which we integrated into our control module. That had to interface with the powertrain that’s doing the actual brake blending. There was a lot of work to achieve this. We had the powertrain guys and the braking guys working closely together every day to make sure it is a seamless experience for the driver. Q: As an engineer, what did you learn from working with GM on Volt? Milot: A big learning was the car’s NVH, or lack of it. With an EV when you come to a stop, it’s dead silent. If your braking system has to turn a motor on, or if anything comes on, you can hear it. You have to be careful how you control your motors and do your mounting, and pay attention to many other details in these vehicles. We spent a lot of time with GM, including directly with their NVH team, to find solutions to make the system quieter and quieter.

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Chevrolet Volt Special Edition

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Vehicle Electrification - November 4, 2010

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