Electro-mechanical Brake Actuator

The drivetrain then has to take braking loads.

I don't mind a chain failure when it's driving the car, but not when it's trying to stop the car.

Very little; a few millimetres.

Doesn't have to... After a lot of googling; I'm glad I didn't have to invent it all:

The trick is reducing the braking force when required; for ABS or simply to allow the car to move. A few SAE references:

2002-01-2582 eBrake(R) - The Mechatronic Wedge Brake 2003-01-3331 Modelling and Validation of the Mechatronic Wedge Brake 980600 Modelling and Control of an Electromechanical Disk Brake 1999-01-0482 Clamping Force Estimation for a Brake-by-Wire Actuator 2003-01-0325 Wheel Slip Control for Antilock Braking Systems Using Brake-by-Wire Actuators 2001-01-2478 Electronic Braking System of EV and HEV - Integration of Regenerative Braking, Automatic Braking Force Control and ABS

The first two papers are available from the eBrake site.

Hopefully the power won't get loused. :-)

The car must not stop immediately. That's a very important safety issue. The car must still be able to stop when all other power is gone, but when the driver wants it to stop.

See paper 2003-01-0325 which is based on experience with the Conti-Teves system.

Aiming for a fixed slip amount appears to be a good strategy. Determining the amount of slip by comparing vehicle speed (given by accelerometers) against the wheel speed produces a slip figure that is the controlled variable.

Apparently not.

Why? You cannot trust all sensors, all the time. Redundant data, even of lower quality can be used to determine if a primary sensor has failed.

Three axis sensing is envisaged; though Conti-Teves seemed to make do with two.

By ignoring the accelerometer and ABS circuits. Pedal position is simply used as a command for brake pad position.

In that respect, it functions like all other ABS.

Independent circuits, yes. Brakes on each wheel for sure. One mechanically actuated by the driver.

Hydraulic lines aren't very tough... Routing signal and power lines so that they aren't exposed to the worst that is dished out is part of sensible design.

The solar car doesn't drive in the rain. There's HIGH VOLTAGE everywhere.

Ahem... last time dwon the centre, we had a brake pad fall out over a stretch of 60 kilometres somewhere North of Alice Springs and the driver had no warning until brakes were required.

Software and electronics are as bad as you make them. If you don't apply Microsoft quality metrics (if it sells, it's good enough) and instead go for paranoid programming only essential functionality in well-defined building block that are tested independently, then software can be boringly reliable.

Just like mechanical systems.

And massive blow-outs leaving bits of rubber on the highway over several hundred metres... not something you can afford to do in a

3-wheeled solar car running on tyres with less rubber than a condom.

Not dual system; independent circuits operating on different wheels. You lose braking ability when one circuit fails.

P.S. Can you please learn to spell "brake"?

In a passive anti wheel lock system, you supply the pressure. The pedal shrinks from your foot a small distance to relieve the excess pressure when a wheel locks. The fluid is returned when the pedal pressure is less than the accumulator pressure and the wheel is spinning again.

Brian W

Weight , energy, and complication seems to be the problems. Would it be possible to run the ABS of a hydraulic accumulator just large enough to power a couple of stops, and charged by a hand pump. The only energy required from the *vehicle* is for the electronics/ valve actuation. The system would need to shut down the ABS if the accumulator emptied... but the driver has a good incentive to keep it pumped up :-).

-- Jonathan

Barnes's theorem; for every foolproof device there is a fool greater than the proof.

To reply remove AT

"Bernd Felsche"

And then to re apply it when the wheel has regained speed

Things do tend to get loused [ up ] , and with brake systems hope is not enough :-).

O.K., but should the system allow the driver to re start the vehicle without repairing the fault, and how about warning the driver, If he is relying on the ABS, and it's not operational.......

This works well, but it's fouled up if you are tracking speed with accelerometers and you spin, ( assume a 360 spin, your record of forward speed is well out ).

For your purposes where a 360 spin would probably shred all your tyres it's maybe not that important.

??? are you agreeing with me, that in the real world you have no chance, or disagreeing with me that there are to many uncontrolled factors to predict the force.

Where are you getting the redundant data from ? what is measured ? A yaw sensor would go a long way to resolving my reservations.

pad position.... will this be related to break force in a consistent way ?

Most ABS systems only monitor wheel speed, and look for the wheel deceleration as the primary trigger for reducing the braking effort.

It's surprising how often common sense is in short supply.

I have seen a hydraulic line on my car rub through to it's braid, if it had been an un-armoured cable it would have gone through to the cores... O.K. so the rubbing should have been picked up earlier, but that is the way life is.

Is the driver in a rubber suit in case of an unexpected shower ?

Yike !! :-(

This assumes you program for all conditions...

Split circuit and mechanical back up....

*Another* post it note on the monitor....:-( Dyslexia rules K.O.

-- Jonathan

Barnes's theorem; for every foolproof device there is a fool greater than the proof.

To reply remove AT

Fluid pressures are not insignificant. Hydraulic valves are usually quite heavy; especially electrically-actuated ones. Special ones may have to be developed ... the ABS control unit in a motor car weighs about 4 kg.

And to carry the valves and accumulator. For 3000km. Form a back of the postage stamp calculation; each kg of mass will take a minimum of 210kJ to move that distance.

Cockpit temperatures in the vicinity of 45 degrees C.

No trick in re-applying. It's the same as applying.

Lack of ABS isn't a safety issue unless the driver doesn't know about it. If the system can figure out that ABS functionality isn't "sane", then it can equally warn the driver of that. That's not rocket science.

Don't spin. :-) _Why_ would you spin?

No; it's not important.

I'm not agreeing with you. And I've given the reason why. Conti-Teves have evidently undertaken significant real-world testing that's published in the cited literature.

If you have some publication to the contrary, then do let me know about it.

Didn't I initially mention a yaw sensor? It was only after reading the literature that I put that idea on the shelf.

The way that standard, "dumb" hydraulic systems work is by the stroke of the piston in the master cylinder resulting in proportional stroke of the slave-piston/piston in the brake.

That is the _simplest_ model for "fail-safe". Attempting to sense or estimate braking force introduces complexity.

The trend is to use total vehicle dynamics for ABS. Especially as this provides "free" stability controls.

Tis a rare quantity indeed.

At 45 degrees C? No way.

The "world" as seen by individual components is constrained by the range of data that's presented at their interface. Out-of-range data, either at the input or at a calculated output, immediately flag an error condition.

The error condition comes up as a system fault and the total system goes into fail-safe mode where the driver is required to exercise more precise control.