Honda HR-V: VSA System Description - Hill Start Assist Control

Overview

The hill start assist control assists drivers by automatically controlling brake pressure when starting a vehicle on a steep hill; this assist prevents the vehicle from rolling on a hill for a few seconds while moving the driver's foot from the brake pedal to the accelerator pedal. The hill assist control may not be activated when the driver does not press the brake strongly enough upon stopping the vehicle or when the driver releases the brake pedal gradually upon starting the vehicle.

Control

The control unit reads the angle of inclination from the yaw rate-acceleration sensor and that all four wheels are stopped, then it calculates the amount of fluid pressure required to keep the vehicle from rolling backward.

This takes place as the control unit sees the brake pressure decrease when the driver lifts their foot off of the brake pedal and moves it onto the accelerator pedal. After the driver transitions to the accelerator pedal and the engine torque is restored to the predetermined level required to start-up the engine, the hill start control will release the brake fluid pressure. The hill start assist control will release the brake fluid pressure if the accelerator pedal is not depressed for a certain period of time after the brake pedal has been released.

VSA SYSTEM DESCRIPTION - OVERVIEW

Control Unit Operation

The VSA system uses the modulator-control unit to actively control the ABS, EBD, TCS, VSA, brake assist, engine drag torque, hill start assist, and automatic brake hold by adjusting the brakes and engine torque as needed by each system.

VSA SYSTEM DESCRIPTION - STEERING ANGLE SENSOR

The absolute angle of the steering wheel is calculated by the rotating angle phase difference of the 2 gears located in the sensor. Its value is sent to the VSA modulator via F-CAN communication.

VSA SYSTEM DESCRIPTION - SYSTEM DIAGRAM

The VSA system controller uses information from wheel sensors, a steering angle sensor, yaw rate-acceleration sensor (insid VSA modulator-control unit), PCM, electric parking brake control unit, back-up light switch (M/T model) and a gauge control module.

VSA SYSTEM DESCRIPTION - TCS CONTROL

Engine TCS Control

If the engine TCS control unit detects the drive wheel slipping during starting, accelerating or cornering, a torque down signal is sent to the PCM. The PCM reduces the amount of torque to the drive wheel to maintain tire traction on the road surface.

Brake TCS Control

During brake TCS control, when wheel slippage is detected, the VSA control unit sends a signal to the modulator unit.

VSA SYSTEM DESCRIPTION - VSA CONTROL

Oversteer Suppression Control

When the vehicle goes into oversteer, the oversteer suppression control outputs a brake pressure signal through the VSA modular-control unit that is optimally distributed between the outside front and rear wheels. This action generates a moment that suppresses the oversteer and stabilizes the vehicle.

Understeer Suppression Control

When the vehicle is experiencing understeer, the understeer suppression control outputs a brake pressure signal through the VSA moular-control unit that is optimally distributed between the inside front and rear wheels. This action generates a moment that suppresses the understeer. Also during acceleration, the PCM outputs an engine torque down signal to increase the drive wheel cornering force to help maintain steerability and improve line traceability.

VSA SYSTEM DESCRIPTION - VSA MODULATOR

The VSA modulator unit consists of the inlet solenoid valve, the outlet solenoid valve, the VSA NO (normally open) solenoid valve, the VSA NC (normally closed) solenoid valve, the reservoir, the pump, and the pump motor. The hydraulic control has three modes of ABS action; pressure intensifying, pressure retaining, and pressure reducing. Pressure intensifying mode (VSA) is a combination of the TCS, VSA, brake assist, and hill start assist control.

VSA SYSTEM DESCRIPTION - VSA OFF MODE

When the VSA OFF switch is pressed, the VSA OFF indicator will illuminate and the VSA will go onto OFF mode.

During VSA OFF mode:

• If the TCS activates, the VSA indicator blinks while the VSA OFF indicator is still on.
• The ability to gain traction on loose sand and deep snow is increased by terminating the TCS function at low speeds.
• During a standing start from varying road surfaces under the left and right side of the vehicle, the TCS function helps gain traction.
• When the vehicle is on a lift while being serviced and its tires are not in contact with any surface, the wheel speed will not exceed 31 mph (50 km/h).
• The TCS function is fully disabled when the VSA maintenance mode is activated.

VSA Maintenance Mode

Enter the VSA maintenance mode when the vehicle is on a lift or two-wheel dynamometer and testing requires wheel speed to reach speeds above 31 mph (50 km/h). Refer to the shop manual Removal and Installation section under "How to enter VSA maintenance mode."

VSA SYSTEM DESCRIPTION - WHEEL SPEED SENSOR

The VSA system uses 4 wheel speed sensors to monitor individual wheel speed. The wheel speed sensor is a semiconductor, Hall effect sensor, installed on the inner sealing surface of each hub and wheel bearing assembly. The frequency of the sensor output signal is proportional to the speed of the wheel and this signal information is sent to the VSA control unit.

VSA SYSTEM DESCRIPTION - YAW RATE-ACCELERATION SENSOR

Yaw Rate-Lateral Sensor (included in the VSA modulator control unit)

The yaw rate-lateral sensor detects changes in sensor element caused by the Coriolis force (lateral motion of the vehicle) and the change in the sensor element increases/decreases the "capacitance" between the electrodes, and then the yaw rate-lateral sensor calculates the acceleration rate based on the change in the capacitance.

Acceleration Sensor (included in the VSA modulator control unit)

The acceleration sensor is a three-axis detection type (longitudinal, lateral, and vertical), so that the acceleration sensor calculates the acceleration rate in each direction (axis) based on the increase/decrease in the capacitance between the electrodes, and the capacitance are given by the changes in the sensor element.

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