Electric application of service and parking brake 1

[harmony]

I am interested in the electric/electronic application of service/secondary braking (including parking brake) of automobiles. I am interested in how they work, how the braking force is applied and what sort of load is placed on the battery. A specific question is, with the engine switched off and the service brakes applied on and off, say 20 times, what effect would this have on the battery? How many applications would you expect to make before the battery could not fully apply the brakes?
I appreciate that the above is a bit of a tall order, but I would appreciate all and any input on this subject.

Thanks

 

[Xtrema]

Can you mechanically actuate the service brake? Or, is the service brake totally hydraulic?

If the service brake is mechanically actuated, the electric actuator must provide the force through whatever mechanical amplifier exists (i.e. a lever). The actuator force can be calculated, then converted to a current draw for each actuation cycle. Based on the amperes required, and the duty cycle of the actuation, one could estimate how long the battery would last.

If you were attempting to provide an electric actuation of the brake, it would seem necessary to make the actuator disengage the brake while the vehicle is running. Only then would the charging system replenish the battery energy required to keep the actuator in its position. Once the vehicle were switched off, the service brake would be automatically actuated. This may not be desirable.

 

[patprimmer]

I would think a service brake must be fail safe, ie apply itself if the battery flattens while parked, especially when parked on a slope. It could be spring loaded to the on position, with the electrical actuator actually being an electrical release, in a similar manner to air over brakes on a large truck.

In my opinion, for the device to be both safe as a parking brake, and as an emergency backup brake, You would need some sort of device limiting automatic application when the electricity fails when the vehicle is traveling at speed, and you would also need some sort of manual overide so the driver could still apply the brake under his complete control in an emergency created by failure of the main brake system

Regards
pat

 

[GregLocock]

I wouldn't do it that way. I'd latch the brake so that once it is applied it stays applied, even if the power fails. This has the disadvantage that you need power to release it, but remember that brake systems are designed to protect against only one failure, so the rules would say if the main brakes have failed then everything else would work normally.

As to the energy required to activate a park brake system. It is actually defined in the ADRs or your vehicle regs, I don't know the exact figure but it would have to be less than 300N by 0.2 m, ie 60 J, ie 12V times 5 amps for 1 second, plus inefficiencies. Much of that goes in friction in the cables rather than in applying the brake. Directly actuating the system at the wheel would be 1/4 of that I guess.







Cheers

Greg Locock

 

[plasgears]

We in the seat actuation business see this as a geared drive with a possible clutch or latch. A sufficiently high gear ratio would not backdrive. A mechanical actuation override looks like a necessary adjunct. It might be a ratchet clutch release.