Brakes - Should I Worry?

[monya]

Told my wife that the brakes on the hybrid Auris that we have, are not linked by wire from the pedal to the wheels and that it's all done by computer. She had a fit and then I wondered if I was talking rubbish anyway. Am I?

[twohats]

In the case of the Prius, I assume the Auris brakes are similar, the brake pedal operates a master cylinder but the pressure generated is prevented from reaching the wheel cylinders by a valve which is held closed as long as the brake system is healthy. The wheel cylinders are operated by a hydraulic pump, electric actuator and a series of valves.

In normal driving, the ECU monitors the pedal pressure and adjusts the motor current and hydraulic brake pressure to produce the desired braking effect. So you are right, its all done by computer.

I am happy to believe the Prius' brakes are reliable. We would have heard about it otherwise.

[Grumpy Cabbie]

But remind her that the plane that flys you on your holidays is probably all fly-by-wire. If she doesn't mind travelling at 500mph at 40,000 feet then 50 mph on the A56 is no different.

[Jan&tone]

But remind her that the plane that flys you on your holidays is probably all fly-by-wire. If she doesn't mind travelling at 500mph at 40,000 feet then 50 mph on the A56 is no different.

Oh grumpy it is vastly different!!!!!!

If you hit something (the ground?) in a fly by wire plane from 500mph at 40k feet - you ain't gonna survive!

You may well do so fro 50mph at ground level :)

I know where I'd rather be in that situation

[monya]

Understood but computers can crash. In the very unlikely event that the cpu shut down whilst driving, would the brakes still function? (not that I'm going to sell the car - it's too good)

[Grumpy Cabbie]

Understood but computers can crash. In the very unlikely event that the cpu shut down whilst driving, would the brakes still function? (not that I'm going to sell the car - it's too good)

I'm going to search the US priuschat forum for more info as I'm sure I've seen a good explanation on how the backup system works. I think the brake system is always on to some degree if all failed in the same way you still get brakes if the servo goes in a normal car.

It might take me a while to find.

[fuel miser]

Understood but computers can crash. In the very unlikely event that the cpu shut down whilst driving, would the brakes still function? (not that I'm going to sell the car - it's too good)

Myth: Prius has an electronically controlled brake system, and I don’t believe it is as reliable as regular hydraulic brakes.

Fact: Prius does have an electronically controlled brake system which is as reliable as hydraulic brakes. This system utilizes both electric motor regenerative braking and hydraulic braking to stop the vehicle. The Prius system is able to recognize a fault in the regenerative braking system, and will send the driver’s brake input to the hydraulic brakes to stop the vehicle. Prius can also detect a fault in the hydraulic brake system booster, and allow all of the driver’s brake force to be directly sent to the two front brake calipers for maximum stopping power under a “no-boost” condition.

Source.........

http://paddocktalk.com/news/html/modules.php?op=modload&name=News&file=article&sid=130298

[monya]

Appreciate your trouble Grumpy

[Grumpy Cabbie]

try this;

http://priuschat.com/forums/gen-ii-prius-main-forum/75877-drive-wire.html

[timberwolf]

In the case of the Prius, I assume the Auris brakes are similar, the brake pedal operates a master cylinder but the pressure generated is prevented from reaching the wheel cylinders by a valve which is held closed as long as the brake system is healthy. The wheel cylinders are operated by a hydraulic pump, electric actuator and a series of valves.

In normal driving, the ECU monitors the pedal pressure and adjusts the motor current and hydraulic brake pressure to produce the desired braking effect. So you are right, its all done by computer.

I am happy to believe the Prius' brakes are reliable. We would have heard about it otherwise.

In other words, the Prius (and hopefully the Auris) has a hydraulic brake fail-safe in case the "brake computer" (ECU) should fail.

Also, if the Auris is like the Prius, it should have a secondary brake power supply, a bank of capacitors, in case the primary 12V power supply fails.