Plugging control

In a system for controlling the power delivered from a source of direct current to a motor having a field and armature connected in series including a main silicon controlled rectifier connected between the motor and said source, a main pulse generator for repeatedly gating the main silicon controlled rectifier into conduction at a controlled rate normally dependent upon the position of an operator-actuated accelerator control, a commutating capacitor, silicon controlled rectifier which when gated into conduction will connect the commutating capacitor across the main silicon controlled rectifier, a commutation pulse generator for normally gating said commutating silicon controlled rectifier into conduction a predetermined time after the main silicon controlled rectifier is gated into conduction, a forward relay having a relay coil and main contacts for connecting the field in one direction to the armature when said forward relay coil is energized to enable said armature to be driven in a forward direction by power from said battery and to enable said motor to function as a generator and produce plug current when said armature is being rotated in a reverse direction, a reverse relay having a relay coil and main contacts for connecting the field in the opposite direction to the armature when said reverse relay coil is energized to enable said armature to be driven in a reverse direction by power from said battery and to enable said motor to function as a generator and produce plug current when said armature is being rotated in a forward direction, means for de-energizing and energizing said relays to effect a reverse-to-forward reversal of the connection of the field during forward rotation of the armature and to effect a forward-to-reverse reversal of the connection of the field to the armature during reverse rotation of said armature, the improvement comprising:

• a. timing means having a time period,
• b. means responsive to a reverse-to-forward reversal of the connection of the field to the armature during forward rotation of the armature and responsive to a forward-to-reverse reversal of the connection of the field to the armature during reverse rotation of the armature for starting said timing means into operation,
• c. means responsive to operation of said timing means and operable during said time period for preventing said main pulse generator from responding normally to the position of said accelerator control during said time period.