Service braking technique for material handling vehicles

Apparatus for slowing and stopping a material handling vehicle having an electric service motor and a mechanical parking brake, comprising:

• a) processing means for controlling a plugging rate of the electric service motor of a material handling vehicle in order to decelerate said vehicle at a predetermined deceleration rate, said processing means being operatively connected to the mechanical parking brake of said vehicle;
• b) monitoring means, operatively connected to said processing means, for monitoring the actual armature current of said electric service motor and for monitoring the speed of said material handling vehicle;
• and
• c) deadman's switching means, operatively connected to said processing means, for applying a request thereto, whereby said mechanical parking brake is actuated in response to said deadman's switching means request to decelerate said vehicle at a rate of deceleration greater than said predetermined deceleration rate or whereby said mechanical parking brake is actuated when said actual armature current is less than a predetermined value thereof.

A process for plugging an electric service motor of a material handling vehicle for slowing said material handling vehicle to an efficient stop, said material handling vehicle having a mechanical brake and said electric service motor having an armature, the process comprising the steps of:

• a) plugging said electric service motor of a material handling vehicle at a predetermined plug rate to slow said vehicle;
• b) monitoring deceleration of said vehicle, speed of said vehicle, and armature current of said electric motor during plugging and comparing actual deceleration to a predetermined rate of deceleration, comparing actual speed to a predetermined speed, and comparing actual armature current to a predetermined current value, respectively;
• c) ceasing said plugging operation when said actual armature current is less than said predetermined current value, or when said actual speed is less than said predetermined speed, or when said actual deceleration is less than said predetermined rate of deceleration;
• and
• d) engaging said mechanical brake of said material handling vehicle to cause said vehicle to come to a stop.

A process for slowing and stopping a vehicle having an electric service motor, a mechanical parking brake, and a deadman's switch, comprising the steps of:

• a) determining whether said deadman's switch is engaged;
• b) when said deadman's switch is disengaged, plugging said electric service motor at a predetermined plug rate;
• c) monitoring the rate of deceleration of said vehicle and armature current of said electric service motor, and comparing said rate of vehicle deceleration and said armature current, respectively, with a predetermined deceleration rate and predetermined armature current;
• d) ceasing said plugging when said rate of vehicle deceleration is less than said predetermined deceleration rate or when said armature current is less than said predetermined armature current;
• and
• e) engaging said mechanical brake causing said vehicle to come to a stop.