Torque Shop
Halt! No yanking of an electronic parking brake
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Pulling the EPB switch tells the electric motor to lock the brake disc or drum, preventing the car from rolling.
PHOTO: ST FILE
Shreejit Changaroth
How does the electronic parking brake (EPB) work?
The electronic parking brake (EPB) has been around for a couple of decades, replacing the familiar hand-operated lever, or handbrake.
The handbrake used mechanical steel wires and linkages to apply the brake on a pair of wheels, usually the rear ones. This allowed keen drivers to spin the car on the move, a skill useful for competitive motor gymkhanas.
With an EPB, actuation is handled with a switch. The mechanical bits of a handbrake are replaced by a compact geared motor within the rear brake caliper or drum. This motor pushes a piston that applies pressure on the friction pads, thus locking the wheels.
The gearing arrangement inside the motorised actuator relies on a worm design and nut that is self-locking. This means it is rather like turning a screw and moving the nut along its axis, but the screw cannot be made to turn by pushing the nut.
On many cars these days, EPB is applied automatically when the Park mode is selected. The EPB releases automatically with light pressure on the accelerator pedal while the car is in Drive or Reverse.
The release action is performed by the EPB geared motor.
It is important to know that the geared motor needs electrical power. If the 12-volt battery is totally flat, the EPB will not be able to engage or disengage.
During repairs in a workshop, if the battery is removed before releasing the EPB, the car cannot be pushed.
Similarly, during a breakdown on the road, if somehow the EPB was switched on before the battery went flat, the only way to recover the car is to tow it by raising the parking brake axle. It is not possible to push the car, even if the drive selector is in Neutral.
If you suspect the battery is dead, do not apply the EPB or select Park. Instead, keep the car in Neutral while waiting for help to arrive.
If you are on an incline, get an object like a brick to chock the wheels, or turn the wheels towards the kerbside.
