Brakes "slip/skid" when hitting a bump?

Perhaps the correct term to use is 'Vehicle Stability Control' (VSC).

 

No, no, no, no. It's not Vehicle Stability Control. VSC is an option available on some Prius models. Traction control is standard on all Prius. Traction control deals with loss of traction with the driving wheels, whether used for propulsion or regenerative braking. VSC intervenes when a vehicle fails to respond to driver steering inputs. VSC has steering input sensors and yaw sensors. If you turn the wheel and the car doesn't respond, VSC attempts to correct the problem by reducing power and applying individual brakes as needed. Likewise, if a car skids VSC senses this as uncommanded turning and tries to correct. They both use the brakes, but they are not the same.

Tom

 

Tom,

I'm no expert when it comes to these enhanced vehicle control systems, so I'll defer to your expertise in the matter. If you say it's traction control, then I'll accept that until I see convincing evidence otherwise.

That being said, I'd like to explain my confusion.

For some reason, I thought that the proper description of when wheels failed to maintain traction with the road during braking was "skid caused by locked brakes", and that the advanced control system that compensated for wheels losing traction with the road during braking was the Anti-Lock Brake System (ABS). Since the coefficient of rolling friction is higher than the coefficient of sliding friction, the vehicle can decellerate faster and steer better when traction is maintained. By momentarily releasing the friction brakes (or momentarily releasing the regen braking system), the wheels are allowed to spin freely to match the forward speed of the vehicle and regain traction. The brakes are then re-applied according to the input from the driver through the brake pedal. If the wheels lose traction again, then the brakes are momentarily released and re-applied again. This process repeats until either the vehicle maintains traction or the driver ceases braking. This release/re-apply cycle is the vibration or pumping that the driver feels when the ABS is active.

On the other hand, I thought that the proper description of when the wheels failed to maintain traction while accelerating was "wheelspin", and that the advanced control system that compensated for wheels losing traction with the road during acceleration was the traction control system (TRAC). Since the coefficient of rolling friction is higher than the coefficient of sliding friction, the vehicle can accelerate and steer much better when the wheels have traction. By reducing the power to the wheels they are allowed to spin slower so that the RPM of the wheels matches the forward motion of the vehicle and the tires can regain traction. Power to the wheels is then resumed according to the input from the driver through the accelerator pedal. If the wheels lose traction again, then power is cut and resumed again. This process repeats until either the vehicle maintains traction or the driver ceases accelerating.

I'm not certain about the Prius, but I thought in some vehicles the traction control system was also capable of supplying a bit of braking to one wheel when one wheel is spinning faster than it should for a given vehicle speed. In doing so the differential would transfer more power to the wheel that hasn't yet lost traction with the road.

If you've got the time to explain it, I'd appreciate knowing where my understanding is mistaken.