From the early days, Honda has looked at means to increase active safety in all the cars they built. It was the first to offer a four-wheel anti-lock brake (ABS) system in Japan, and the first in the world to successfully develop a traction control system for front wheel drive vehicles. The Vehicle Stability Assist (VSA) system on the 7th Generation adds side slip control to ABS and TCS systems. This system controls sudden changes in vehicle behaviour giving the driver the time to keep control of the situation. When driving in the rain or on snow, the system stabilizes the vehicle, reducing counter-productive driver tension. The addition of Electronic Throttle Control System (ETCS*) maximizes ABS and VSA function by contributing to a more precise and direct feel. Throttle control in all vehicle speeds, and brake control is expanded from 25 mph on 6th Generation, to 50 mph, which prevents high speed wheel slip. The performance combination between VSA results in climbing and cornering grip improvements in dry and especially in wet conditions. The revised brake system employs ABS and VSA which incorporates a 4-channel modulator and CAN communication capabilities. ETCS* is another name for the throttle body with drive by wire The major components for VSA system are: Left rear wheel sensor Right rear wheel sensor Left front wheel sensor Right front wheel sensor VSA activation indicator ASS Indicator Brake pedal + switch Modulator Steering angle sensor Yaw rate sensor Lateral acceleration sensor Brake fluid level switch VSA main switch How is Side Slip Control detected? On based on the above diagram what does VSA encompass? VSA = ABS+ TCS +Side Slip Control ABS Features When the brake pedal is pressed while driving, the wheels can lock before the vehicle comes to a stop. In such an event, the manoeuvrability of the vehicle is reduced if the front wheels are locked, and the stability of the vehicle is reduced. If the rear wheels are locked creating an extremely unstable condition. The ABS precisely controls the slip rate of the wheels to ensure maximum grip force from the tyres, and it thereby ensures manoeuvrability and stability of the vehicle. The ABS calculates the slip rate of the wheels based on the vehicle speed and the wheel speed, and then it controls the brake fluid pressure to reach the target slip rate. TCS Standing-start Control Although this action does not constitute any type of side-slip control, VSA will engage engine TCS to reduce engine output if the drive wheels begin to spin during a standing start or in any other similar type of situation. In addition if the road conditions at the left and right wheel are different and the wheel on the side of least friction begins to slip, brake TCS will be engaged so that the brakes can be applied to that wheel. At that time, the VSA control unit also sends a traction control signal to reduce engine power. In addition to increasing the degree of wheel grip, this action also ensures that a larger portion of the drive torque can be delivered to the other wheel. Control of Braking during Cornering If high degree of lateral acceleration is detected when braking during cornering, a 3-channel ABS will switch to 4-channel control and will apply a considerably-large braking force to the outer rear wheel. As a result of this action, the stability of the vehicle under this type of driving condition can be increased. Furthermore, the distance required for braking is subsequently reduced. How does the system operates? VSA Oversteer Control: To cope with rear wheel slip which drags the vehicle inward, braking force is delicately applied to the outer wheels. This effects the outward movement of the rear wheels, and at the same time reduces the cornering force of the front wheels. As a result, the inward movement is reduced stabilising the vehicle. VSA Understeer Control: To cope with the driving wheels’ (front wheels) loosing traction and slipping, engine torque is reduced am braking force is delicately applied to the inner rear wheel. This increases tractability by generating inward movement of the front wheels. Steering Angle Sensor The steering angle sensor is used to detect the rotation of the steering shaft and to calculate the steering angle. A disk with evenly spaced slits is positioned between the facing parts of a LED, and a light receiving part (photo transistor). As the disk rotates, it interrupts the light tram the LED. The light which passes through a slit is converted into electric current by the photo transistor, and a waveform is converted by the comparator. This information is fed back to the VSA ECU to make a relation at what position the front wheel are at. How does VSA do it calculations to make the adjustments? It measures the lateral G of car and vehicle speed, all this time the yaw rate sensor is provided real time data of the actual car movements. This is measured to what the target yaw rate pre-set by Honda. If it is determined that any of these signals are deviating from the standards driving conditions and consequently the vehicle is about to become unstable. The VSA ECU kicks in to intervene. The difference of these computations then calculates the understeer, engine control and appropriate brake amount computation.