Electric Motors

• Free-Spinning Electric Motors - A free-spinning electric motor uses precisely timed opposing magnetic fields to cause an armature shaft to rotate. Free-spinning electric motors can be designed to run on AC or DC current, with brushes or brushless, depending upon their application.

• Stepper Motors - The armature of a stepper motor can be rotated an exact number of turns or just a fraction of a turn. Stepper motors are controlled by a computer to position a mechanical device in an exact location. A typical stepper motor can be positioned to 256 different positions.

The following are examples of free-spinning electric motors used on an automobile.

• Starter Motor - This is a Permanent Magnet-Gear Reduction starter motor. This starter motor comes in a variety of mounting configurations; however, the basic operation is the same for each configuration.

• Starter Solenoid - When the driver of the vehicle requests that the engine be started, the starter solenoid is activated by a computer controlled starter relay. When energized, the spring loaded moveable core of a starter solenoid pulls on a lever which engages the starter drive to rotate the flywheel of an engine. The solenoid also closes some large electrical contacts that allow approximately 150 amps of current from the battery to travel through the brushes to the commutator bars of the armature.

• Brushes - The end cap of the starter motor contains a bushing for the armature shaft and two sets of brushes. Each set of brushed provides a power source (shown on the right side connected to the large wire) and a ground path (shown on the left side connected to the end cap with braided copper straps) to the armature's commutator bars.

• Armature - The armature shown below is a series of very powerful electromagnets. The armature shaft has 24 commutator bars (shown on the right side of the photo below) which are connected to 12 coils of wire (shown with red insulation) positioned between 25 laminated iron core pieces (the shiny metal in the middle). This configuration creates two strong sets of electromagnetic fields positioned 60 degrees apart. The positioning of the commutator bars relative to the brushes, which transfer the current into the bars, allows for precisely timed magnetic fields which are opposed by the magnetic fields of the field magnets in the starter housing. The opposing magnetic fields of the field magnets and the armature's magnetic fields cause the armature shaft to rotate.

• Field Magnets - The armature rotates inside of 6 evenly spaced man-made permanent magnets mounted in the starter housing. The positioning of the permanent magnets allows for 6 sets of north and south magnetic poles which oppose the magnetic fields of the armature shaft causing the armature shaft to rotate.

• Planetary Gear Set - The reduction gear ratio of the armature to the starter drive is 4.77:1; 4.77 turns of the armature to one rotation of the starter drive.

• Starter Drive - When the armature shaft rotates, it turns the sun (center) gear of a planetary gear set which is connected to it. The sun gear turns the three planet gears shown in the photograph below. The planet gears rotate the ring (outer) gear in the opposite direction of the armature. The ring gear rotates the starter drive gear which rotates the flywheel of an engine during cranking. It takes 4.77 turns of the armature shaft to equal one turn of the starter drive.

• Flywheel - The flywheel of the engine this starter came off of has 142 teeth. The reduction gear ratio of the starter drive to the flywheel is 15.78:1; 15.78 turns of the starter drive to one rotation of the flywheel.

• The overall gear reduction of this type of starter motor is 4.77 x 15.78 = 75.27:1; 75.27 turns of the armature to one rotation of the flywheel.

• This starter motor will have an armature speed of 12042 RPM during cranking at 160 engine crankshaft RPM. The typical cranking speed for most engines is between 150 - 200 crankshaft RPM.

• Power Window Motor - Power window motors, and all of the other motors listed below, operate much like the starter motor. They all have an armature shaft and permanent magnets to create precisely timed opposing magnetic fields which rotate the armature. Modern power window motors have built-in over current protection and obstruction detection with window direction reversal.

• Cooling Fan Motor - The cooling fan motor controls the speed of the radiator cooling fan. The fan motors typically have two speeds.

• HVAC Blower Motor - The HVAC blower motor controls the speed of the HVAC system fan. The blower motor typically has four or more speeds.

• HVAC System Door Control Motors - HVAC System Door Control Motors are used to position temperature, air outlet mode (defrost, AC, Heater) and recirculation (inside or outside air) doors.

• Air Injection Reaction (AIR) Pump Motor - The AIR pump is used during the first 240 seconds after a cold engine start. Fresh air is pumped into the exhaust system to help reduce hydrocarbon (HC) emissions, carbon-monoxide (CO) emissions and to help warm up the catalytic converter. The AIR pump is typically relay controlled.

• Electric Fuel Pump Motor - The fuel pump pressurizes the fuel delivered to the engine's fuel injectors.

• Anti-Lock Brake (ABS) Pump Motor - The ABS pump motor can be used to return brake fluid to the master cylinder reservoir during an ABS stop. The ABS pump motor can also used to pressurize brake fluid during an assisted ABS stop or during a traction control event.

The following are examples of stepper motors used on an automobile.

• Idle Air Control (IAC) motor - The end of the armature of this motor is a threaded shaft. An idle air bypass valve is connected to the threaded shaft. As the armature rotates, the valve moves. This action can increase or decrease the engine's idle speed. IAC motors are used on vehicles with throttle cables.

• Throttle Actuator Control (TAC) Motor - TAC motors are used on vehicles without throttle cables. The engine computer reads the accelerator position sensor values and controls the throttle blade opening with the TAC motor.