Method and means for measuring the torque delivered by an electric motor

In an excavator drive system which is subject to transient loading during digging, said drive system having a d-c motor fed by a d-c generator with the armatures of the generator and motor joined in an armature circuit loop, the combination comprising:

• a control circuit;
• a differentiator having a reactive component and a resistance component for connection across a voltage of the armature circuit loop to develop a signal indicative of acceleration torque;
• a current indicating circuit for connection across a part of the armature circuit loop to develop a signal indicative of motor induced torque;
• and
• circuit connections feeding the acceleration torque signal and induced torque signal to said control circuit.

In a speed control system for a d-c motor fed by a d-c generator with the armatures of the generator and motor connected in an armature circuit loop, and a speed control circuit feeding field windings of the generator with an adjustment for setting a reference signal, the combination therewith of:

• a differentiator circuit having reactive and resistive components connected across a voltage of said armature circuit loop to generate a signal indicative of the first differential of the voltage;
• a current indicating circuit connected across a part of the armature circuit loop to develop a signal indicative of motor armature current;
• a summing component that combines said signals;
• and
• a threshold current limiting element interposed between said summing component and said speed control circuit.