[eschaider]

Grubby is right about the Line Loc style devices. They are a normally open hydraulic valve that when activated close off to the hydraulic fluid flow back to the master cylinder creating the locking event.

Because they are normally open they require continuous activation to be used as a parking brake. The continuous activation will draw current from the battery because the car is off. As Grubby has already pointed out, given a long enough activation they could potentially draw a battery down significantly. The continuous activation also heats the energizing coil inside the device used to close off the hydraulic circuit.

The coil inside the Line Lock is designed for periodic, temporary operation. When left on for extended periods of time it can overheat and eventually fail. The overheating is an interesting problem because as it does, the resistance in the coil increases and it draws additional power creating additional heat and, well you can see the problem.

If you could find a valve that would latch and unlatch mechanically with an external coil activated toggle, that type of design should work very nicely. Remember if there is any way for the hydraulic fluid to escape from the closed system over time, after activation, it will and the brake will release.

Historically most auto manufacturers have relied on mechanical mechanisms for the 'parking brake' for just that reason. Some of the newer vehicles use an electrically operated mechanical valve that latches. That valve can be easily built into the anti-skid braking system. If you can find one that is not and is implemented as a stand alone it should work nicely.

The primary design consideration should be the ability to lock the brakes without requiring a continuous draw of power from the car's electrical system.


Ed