By Craig Van Batenburg
Why use an all-electric motor when an internal combustion engine (ICE) has been doing a perfectly good job for more than 100 years? There are many reasons to drive electric, but until now, battery technology and costs hadn’t been cheap enough to make it a mainstream vehicle.
The modern hybrid technology that was first mass-marketed by Toyota was great, but it needed an ICE to make up for the range lacked by the batteries of the 1990s lacked. The electric motors were quite advanced back then, but have only gotten better and less expensive to manufacture.
What advantage does a modern electric motor of 150-hp have, if any, over a modern 150-hp gasoline ICE? The electric motor is smaller and lighter, and is less expensive to make, has no emissions, has more available power and torque on demand, is easier to diagnose and simpler to fix (thanks to fewer moving parts), requires sensors and no need for a flammable liquid onboard, increases fuel availability (it can be made at home or work) for less cost, requires no emission inspections or EVAP systems or oil changes or tune-ups or spark plugs or timing belt. Can you think of more? Okay, it makes a really cool exhaust noise at a race track.
It does take support systems to make either a high-voltage electric motor work or an ICE to run. Here are the supporting systems for both an ICE or an electric motor: cooling system(s) and motor mounts.
In addition to that, here is what is added to a pure electric vehicle to support the electric motor: a one-speed gearbox, HV battery (and its support systems), onboard high-voltage charger, DC-DC converter, inverter, cables, relays, sensors and computers.
If you have a modern gasoline 150-hp engine here are the support systems: fuel tank system, injectors, EVAP, oil filtration and filter system, exhaust and catalytic converter, intake and air filter, OBD diagnostics, multi-speed transmission, alternator and more.
As this demonstrates, the advantages of powering a car with electric motors are overwhelming.
There are two parts in each high-voltage electric motor: the “rotor” that rotates and provides power, and the “stator” that produces a three phase rotating electro-magnetic field. The stator consists of electro magnets arranged in a circle. Three HV cables (or bars) attach to the stator to provide power to the stator from the inverter. The inverter gets its power from the high-voltage capacitors that get their power from the high-voltage battery pack.
Modern electric drive vehicles (since model year 1998) use one of two motors.
1. Three Phase Alternating Current (AC) Brushless Interior (or Exterior) Permanent Magnet (PM) Synchronous Motor
2. Three Phase Alternating Current (AC) Brushless Induction Asynchronous Motor
We will call the first motor a “PM Motor,” the second motor an “Induction Motor.” The most popular is the PM motor, so let’s examine each aspect of that one first:
• Three-Phase Alternating Current (AC) — If you were trained by the Honda Motor Company when the Honda Insight Gas/Electric hybrid first came out, the Honda instructors told the technicians that the Honda IMA (integrated motor assist) motor was a DC motor. The motor had three orange cables going to it, and most technicians were confused (as they should be) because Honda was alone in their description of their electric motor; every other OEM at that time (Toyota and more later) described their HV motor(s) as a three-phase AC motor
Who was right? Technically Honda was, but the other OEMs were better understood by their automotive technicians. So the question a hybrid instructor (like myself) must ask is: “Do I want to be technically correct and misunderstood by many, or simplify the answer to be understood by the majority?”
When the time allowed for a class orarticle or lecture is limited, that later answer may be best. (I am writing a college-level text book on hybrids, electric and fuel cell powered vehicles, which will allow the freedom explain both.)
So what is it, a DC motor or a three-phase AC Motor? It depends on what you are sending through the orange cables from the inverter (the inverter is a motor controller of sorts). When a DC battery is suppling power to a three-phase motor, it is sending pulsed DC voltage but alternating current, controlled and managed by the inverter. Honda is correct: In any electric vehicle, when the three-phase motor is driving a shaft (adding torque), it is a DC motor at that time, but when the motor is being driven by that same shaft, it is now a generator and produces pure three-phase alternating current, just like the beloved 12-volt alternator does. But to keep things easy to read and comprehend, we will refer to the motor as a three-phase AC motor.
• Brushless — If I need to explain this we are all in trouble.
• Interior (or Exterior) Permanent Magnet (PM) — The way the PMs are arranged on the rotor (the spinning part that powers the wheels or whatever needs to rotate) determines the name. Most high-voltage electric motors have an interior magnetic rotor because fewer magnets are needed, but there have been exterior rotors that rotate around the outside of the stator in a drum of sorts. This is an expensive part of the motor, so work is constantly being done to reduce costs.
• Synchronous Motor — As you study more about inverters, you will understand how the magnetic fields are created in the stator. The rotational fields can be measured in RPMs, and the speed of the electromagnets in the stator will match the RPM of the rotor. So in a synchronous motor, the speed of the rotating magnetic field equals the speed of the rotor, it is synchronized.
Now, let’s compare that to the “Induction Motor.” Three-Phase Alternating Current (AC). No difference here other than the software will have a different strategy:
• Brushless — Are you serious, you need this explained?
• Induction — Guess what: No magnets. This is the biggest difference. The rotor is sometimes called a “squirrel cage,” and is mostly made of aluminum and copper. The magnetic poles in the rotor are induced by the magnetic fields produced in the stator.
• Asynchronous Motor — The speed of the rotating magnetic field created by the stator is either faster or slower than the rotor. The rotor is excited by the stator, and if the speed of the rotational field matched the rotor, the rotor would stop spinning. When the “Induction” motor is a motor, the rotor is going slower than the rotating magnetic field. If the “Induction” motor is in generator mode, the rotor is going faster.
In another article, we will discuss inverters that power and control the electric motors. •
Craig Van Batenburg is a former repair shop owner who is the CEO of Automotive Career Development Center (www.fixhybrid.com), which offers training and consulting related to electric and hybrid vehicles; he can be reached at Craig@fixhybrid.com.
