The rotor direction is determined by the sequence in which voltage is applied to coil A, B or C and returned to ground through an attached pair. The pairs are A+ and C- B+ and A- C+ and B- ( Fig. Pairs of six switching transistors are forward biased and move the rotor in a clockwise or counterclockwise direction. The brushless bidirectional permanent magnet motor and gear perform the same function as the power cylinder in a hydraulic system. Most applications use a motor worm gear to drive the gear on the steering shaft or rack ( Fig. The brushless motor uses a permanent magnet rotor and three electromagnetic coils to propel the rotor. Other inputs that will affect assist and return are vehicle speed, engine speed and chassis control systems such as ABS and electronic stability control (ESC). The controller processes the steering effort and hand wheel position through a series of algorithms for assist and return to produce the proper amount of polarity and current to the motor.
The torque, speed and position inputs, vehicle speed signal, and other inputs are interpreted in the electronic control module. The steering wheel is referred to as a hand wheel in the service information. Sensors located in the steering column measure two primary driver inputs - torque (steering effort) and steering wheel speed and position. The motor will drive a gear that can be connected to the steering column shaft or the steering rack. 2Ī typical EPS steering application uses a bidirectional brushless motor, sensors and electronic controller to provide steering assist. The system does not drag on the engine from either a power steering pump or alternator because it will not provide assist until required by driver input. The configuration of an EPS system can allow the entire power assist system to be packaged on the rack and pinion steering gear or in the steering column. 1Ī driver unaware of this condition would become concerned if an electrical or electronic failure occurred while the engine was running, as the loss of assist would not be expected.Įlectronic power steering systems eliminate the need for a pump, hoses and a drive belt connected to the engine using variable amounts of power.
This advantage can also be a disadvantage if the system should shut down while the engine is running you lose steering assist. An Electronic Power Steering (EPS) system’s advantage over a hydraulic system is if the engine stalls, you will still have steering assist.
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