Redundant DC Gearmotor
This fractional HP Permanent Magnet DC Right Angle Gearmotor functions as an integral part of an automotive transmission system. Specifically, it is a customized design for use in shift‐by‐wire vehicle transmissions that experience a great deal of starting and stopping. The gearmotor works with the vehicle’s automatic transmission to move through the stages of Park‐Reverse‐Neutral‐Drive. Because these vehicles most often carry passengers, failure of the motor is unacceptable. This customized gearmotor design actually incorporates two motors in one integrated gearmotor assembly. With shift‐by‐wire transmissions, there is no mechanical backup, therefore a backup source of motor power is required to perform shifting in the event of a motor failure.
This DC gearmotor’s design features fault tolerance, indication of pending failure, and back‐up power in the event of a motor failure.
The two PMDC motors within a single motor frame operate independently, and it is their combined outputs that drive a common shaft to power the transmission shifting. Under normal operation, their combined output equals X HP. In the event of a motor failure, the second motor is capable of ramping up its output (from ½ X to X) so that the single motor can actuate the transmission shifting.
Because of the intermittent duty of this application, the one remaining operational PMDC motor can adequately provide enough power output to shift the transmission until the vehicle transmission can be serviced, and prevents complete failure.
Under normal operating conditions, the motor provides an output of “1/2 X” power from each of the two motors. The control senses current in both motors. If a motor fails, the control senses an “out‐of‐spec” current reading, indicating that one of the motors has failed, sending a signal to the user that failure is imminent, AND simultaneously the operating motor will draw additional current to provide the required higher output (X).
To our knowledge, there is not a similar product readily available in the market. This design has two independent sets of commutators, windings and dual brushes, and provides continued functionality in the event of a motor failure. It is also designed to IP66 specification and has been “road proven” in mud, salt spray, fog and generally rugged environments.