Locomotive parking brake
A railway vehicle parking brake that can provide the appropriate tension to the braking system using a motor, a brake chain drum interconnected to the motor to take up or release a brake chain, a load arm deflects in response to tension in the brake chain, and a switch that is closed by the load arm when it deflects. A movable sheave interconnects the brake chain and the load arm and is positioned between the brake chain drum and a fixed sheave over which the brake chain is looped. A control method considers the position of the first switch to determine whether to the motor off when applying the brakes and the amount of current being drawn by the motor to determine whether to the motor off because of a system failure.
1. A parking brake, comprising:
a motor;
a brake chain drum interconnected to the motor to take up or release a brake chain when positioned thereon;
a load arm that is deflectable in response to tension in the brake chain;
a first sheave positioned to engage the brake chain and move away from the brake chain into the load arm in response to tension in the brake chain;
a second sheave positioned apart from and in alignment with the brake chain drum to define a section of said brake chain therebetween that will engage the first sheave;
the brake chain extending from a first end over the brake chain drum and between the first and second sheaves to a second end that is configured to be coupled to the brake rigging of a railway vehicle;
a cam coupled to the first end of the brake chain for rotation when the brake chain is taken up or released by the brake chain; and
a switch positioned to be closed when the load arm deflects a predetermined amount in response to tension in the brake chain.
2. The parking brake of claim 1 , further comprising a second switch associated with the cam so that when the brake chain drum drives the brake chain into a fully released position the cam will close the switch.
3. The parking brake of claim 1 , wherein the motor is configured to provide a signal representing an amount of current being used by the motor.