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240 Landmarks TopChassis > Vehicle stability control system
 Vehicle stability control system
Usually, many drivers will panic if their vehicle skids, and will not be able to act appropriately to avoid danger. Accidents due to skidding and loss of control are often because drivers fail to spot changes in road conditions, or steer improperly by taking a turn too hard, etc. Conventional ABS technology secures braking stability, and traction control systems (TRC) secure stable acceleration, but neither prevents skidding. VSC is a vehicle stability control system that improves active safety performance when the vehicle skids.
Year manufactured:1995
Manufacturer:Toyota Motor Corporation
Classification:Mass-production system
Current status:In use: on public display
Familiar name:-
Model / Weight
Company name:Toyota Motor Corporation
Location:In use: operational
Installation vehicle:New Toyota Crown Majesta i-Four released in 1995, etc.
Year of manufacture:1995
Structure, type, means, method, etc.:[VSC component]
Yaw rate sensor: The sensor is installed parallel to the vertical axis of the vehicle. It detects only the rotational angular velocity (yaw rate) around the axis.
G sensor: This sensor is set in a horizontal position near the center of gravity of the vehicle. It detects acceleration in the longitudinal and lateral directions.
Steering angle sensor: This sensor is installed on the back of the steering wheel, and directly detects the driver's steering operation.
Brake pressure sensor: This sensor is installed on the VSC hydraulic control unit to detect changes in brake pressure.
Wheel speed sensor: This sensor is set at each wheel to detect each wheel's rotational angular velocity.
Throttle angle sensor: This sensor detects the driver's acceleration pedal operation and the throttle angle when engine output is controlled by VSC.
VSC hydraulic control unit: The TRC and ABS functions work when wheels slip on acceleration and deceleration. The VSC function works when the vehicle skids. The unit supplies hydraulic pressure to control each wheel.
Throttle actuator: It opens and closes the throttle valve when the VSC controls engine output.
Function, effect, etc.:[Driver information]
The driver is notified of possible danger to vehicle and tire grip using visual (indicator) and acoustic (buzzer) information.

[VSC control]
The VSC control consists of a vehicle state calculation portion, a braking force control calculation portion, and a driving force control calculation portion.
(Vehicle state calculation portion) Based on the signals from each sensor, this portion judges the degree of vehicle stability, and computes the state of vehicle behavior (degree of stability and course departure). The computed vehicle state is communicated to the other calculation portions. When the vehicle state becomes unstable, the driver is informed by the slip indicator and buzzer.
(Driving force control calculation portion) This portion computes the target engine output based on the vehicle state, and drives the throttle actuator so that the target output is achieved.
(Braking force control calculation portion) This portion computes the braking force for each wheel to restore the vehicle to a stable state, and calculates driving request values for the brake hydraulic control unit. These request values are sent to the ABS control calculation portion, VSC control requests are then matched with ABS control requests, and the brake hydraulic control unit is activated.

[VSC effect]
The following test was conducted on vehicles with and without VSC: A driver on a straight test course is confronted with a person suddenly running in front of the car. The driver quickly turns the steering wheel to avoid the person before going back to the original lane.
(Vehicle without VSC) The driver lost control of the vehicle due to skidding of the rear wheels caused by sway-back when returning to the original lane. Finally, the vehicle span and left the road.
(Vehicle with VSC)
The vehicle returned to the original lane, maintaining its stability and avoiding the obstacle.
Technical overview:[Basis of VSC motion control]
VSC applies an active braking force independently to the 4 wheels according to the state of the vehicle body and wheel skidding. It controls the turning moment and deceleration force to ensure turning stability and the ability to follow the desired course.
Reference materials:Yamamoto, Vehicle stability control (VSC) system to prevent lateral skid, JSAE Symposium
Advanced Technology of tire-Vehicle System, No.9602 Symposium 1996
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