The first gasoline vehicles had no electric motors. In contrast, today’s cars have tens of “invisible” motors with a range of power levels, sizes, and types.
It’s not news that today’s vehicles, regardless of their motive power source, are packed with what is called “electronics.” Whether it’s for powertrains, advanced driver-assistance systems (ADAS), comfort, entertainment, convenience, navigation, safety, or other uses, the electronics-related content in a vehicle is significant and growing every year (Figure 1).
Yet, there’s a less visible but also highly significant electromechanical content in cars: electric motors. Of course, all-electric vehicles (EVs) and some hybrids (depending on topology) have traction motors for propulsion, while cars with internal combustion engines (ICE) do not. But I’m referring to all the other electric motors in a vehicle.
How many are there? As with most such questions, the answer is simple: “It depends.” A medium-class car currently has an average of ten pumps and compressors and around 40 electric motors in total (again, ignore the traction motors in this count), and this number can double in premium-class cars. Apart from water and fuel pumps, electric motor drives are used for adaptive suspension controls, blowers, compressors, power steering, windshield wipers, and window lifts. (Some of these motors, such as fuel pumps, are not needed in pure EVs.)
Let’s look at one list where a gasoline-powered minivan owner counted over 30 motors and admits he may have missed a few:
- Starter motor
- Radiator-fan motor
- 2nd radiator-fan motor in the cabin
- Driver’s power-window motor
- Diver’s power seat — 3 motors
- Pedal adjustment motor
- Passenger power seat — 3 motors
- Passenger power windows – 3 motors
- Front cabin HVAC — 6 motors, dual climate control (blower, blend, mode, recirculate)
- CD Changer — 3 motors
- Rear HVAC — 2 motors
- Rear vent window — 2 motors
- Sunroof — 2 motors
- Power sliding side doors — 2 motors
- Rear power lift-gate motor
- Power-steering assist motor
- Windshield-wiper motors — front and rear
The owner of an early 1990 coupe had a similar total but with some different specifics (no sliding doors, for example), while the driver of a small hybrid vehicle counted 37 motors, again with some differences… You can see the reality fairly quickly here.
Obviously, the motor for each of these applications is optimized in its type, size, speed/torque, and operation by the location and application. They can be divided into three major categories (Figure 2):
- Performance-related motors
- Comfort related motors
- Volume motors
Clearly, no single motor type can meet all the needs, even if the motor size is scaled to the mechanical output-power requirements. In addition to the various types of traction motors in EVs and HEVs, cars use a combination of motor types, including brushed DC motors, brushless DC motors (BLDC), and induction motors, depending on the load type, duty cycle, available space, and many other factors.
Note that none of these motors are operated “barefoot,” meaning they are connected directly to the car battery with a simple on/off switch. Instead, each has a motion/motor-control IC, usually in conjunction with a discrete-MOSFET power switch and often a position-feedback sensor, to provide management ranging from a basic control-and-driver arrangement to a sophisticated, processor-controlled function.
The abundance and inclusion of smaller electric motors in cars is actually a dramatic tale of evolution. The first gasoline-powered cars around 1900 did not have any motors at all or even a battery. They were hand-cranked to start and used a magneto (a basic, low-efficiency electrical generator with permanent magnets and a moving coil to produce periodic pulses of alternating current) to drive the spark-producing circuit.
The first motor in a car, the electric starter (introduced by Cadillac in 1912 and soon followed by almost all cars), drew on a basic 6-V battery – and that starter was the only electric motor in the car for many years. Then came the addition of features such as in-car AM radio (1930s) power windows in the 1950s and 1960s prompting a necessary increase in the battery rating to 12 V, but the number of motors was still in the single digits. Many functions, such as the air-conditioner compressor and power-steering assist, were not driven by an electric motor but by a power-take-off belt attached to the engine shaft; other functions used air pressure or vacuum derived from the car’s engine.
The proliferation of low-cost, high-performance electric motors in cars, with each tailored to and controlled for a highly localized function, is a testament to the hard work of scientists, researchers, and design and manufacturing engineers across multiple disciplines. Whereas an electric motor was once a large, heavy, inefficient, hard-to-control electricity-to-motion transducer, it has now become a far smaller, lighter, and more efficient unit – to the point where designers don’t have to worry about the validity of using one where it would solve an automotive problem.
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