Earth excavator including apparatus for stabilizing performance by compensating for changes in temperature

In an earth excavator of the type whose performance is subject to undesirable variations as a result of wide variations in temperature under which the excavator may be operated, the excavator including a movable earth excavating component and a direct current electric motor for providing motive power for the component, the electric motor having a field winding, the electrical resistance of the motor field winding being a direct function of the temperature of the motor field winding, thereby causing the performance of the motor and thus of the excavator to vary with variations in the current flowing through the motor field winding, and the excavator further including an exciting generator for supplying voltage and current to the motor field winding;

• the improvement wherein said excavator further includes apparatus for stabilizing performance of the excavator by compensating for variations in temperature, said apparatus comprising:
• a. means for sensing output voltage of the direct current exciting generator and for providing a first signal representative thereof;
• b. means for sensing a temperature representative of the temperature of the motor field winding and for providing a second signal representative thereof;
• and
• c. a temperature compensating voltage regulator comprising:
• i. first input means for receiving the first representative signal;
• ii. second input means for receiving the second representative signal;
• iii. means for combining the first and second signals to produce a third signal as an inverse function of the first signal and a direct function of the second signal;
• and
• iv. output means for supplying excitation current to a field winding of the exciting generator in response to the third signal;
• whereby the magnitude of regulated voltage supplied by the exciting generator to the motor field winding is directly related to the temperature of the motor field winding, thereby maintaining current supplied to the motor field winding and therefore the performance of the excavator substantially constant despite variations in the temperature of the said motor field winding.