Hill Hold Moding 2005-01-0786

A typical problem that is encountered by drivers of vehicles with manual transmissions is rollback on an incline. This occurs when the driver is trying to coordinate the release of the brake pedal with the release of the clutch pedal and application of the accelerator all at the same time. If not done in harmony, the vehicle will roll down the incline.

While the Hill Hold function is a highly desirable feature in manual transmission vehicles, it also enhances the driving experience in automatic transmission vehicles equipped with hybrid powertrains. The Hill Hold feature supports the Stop and Go performance associated with a hybrid powertrain by holding the vehicle on an incline and preventing undesired motion.

The objective of this paper is to describe the implementation of the Hill Hold feature using an electric and / or a hydraulic brake control system. The paper describes the moding states in implementing the Hill Hold function at various levels of design complexity. The performance level (basic level, mid-level, up level) varies by the choice of sensors incorporated in the vehicle. The sensors used in the various Hill Hold performance levels described in the paper include a clutch travel sensor, a clutch switch, a gear position sensor, and a longitudinal acceleration sensor. The performance level of the Hill Hold function is dependent on which sensors are used and how they are implemented. The implementation goal is to make the driving experience as comfortable and natural as possible while keeping the system commercially feasible.