A brushless DC motor for vehicular AC/heater applications

Abstract

A brushless DC motor is proposed as a potential replacement for DC commutator type motors presently used in almost all automotive applications. A prototype brushless motor has been designed and assembled into the AC blower assembly used on many Ford vehicles in order to evaluate this motor in terms of performance, cost, maintenance, operating problems, size, and weight as compared to the existing commutator motor used in this blower. The new motor operates from the 12-volt vehicle battery through an electronic controller which replaces the lossy resistive controls used on the existing blower system. The new brushless motor is expected to result in the following improvements over the present blower motors: 1. Elimination of the brush-commutator system, which is presently a source of high maintenance and warranty costs on the AC/heaters in vehicles. The motor is maintenance free, except for bearing wear. Data collected by the U.S. Department of Defense for reliability predictions shows that commutator motors have a failure rate of from two to six times that of brushless motors, depending upon operating speed [1]. 2. Simpler construction of the brushless machine in which, besides eliminating the brush-commutator of the DC commutator type, a very simple, stationary, solenoidal electrical coil replaces the complex, rotating, armature winding of the commutator machine. No permanent magnets are used in the field. 3. Improved energy efficiency; the electronic control scheme eliminates the energy loss in resistors presently used to control speed. 4. The electrical winding in the brushless motor is not restricted as to shape or material, but can be adapted to suit the economic and technical restrictions of the time. Material can be copper, aluminum, or high conductivity alloys, and constructed from round, square, strip, or braided conductors. 5. The motor is insensitive to temperature variations compared to PM motors. 6. Due to the simple structure of the motor, the overall volume occupied by the blower assembly is reduced about 25%. 7. A damaged or burned out electrical coil can be quickly and simply replaced without the need for replacing any other motor parts.