Using Electric Drive Motors to Teach Basic Electrical Concepts
We are pleased to share an insightful article written by Curt Ward, Professor at Joliet Junior College. Curt brings a wealth of experience and knowledge in automotive education, and we are confident that you will find his perspectives both valuable and useful.
As I write this article, the fall semester is off to a great start. It is great to see classrooms full of students who are excited to learn. One of the most critical skills our students need to possess when they graduate is a thorough understanding of basic electrical. Sometimes these lessons lack technology that keeps the students engaged and on task. In this article I will highlight several ways an electric drive motor assembly can be used to raise student interest and improve the understanding of basic electrical concepts. The inclusion of the electric drive motor and related lab activities will enhance a basic electrical course or reinforce basic electrical concepts in a stand-alone hybrid and electric vehicle class.
In this article, I am using a Toyota rear axle drive motor assembly. It is used as motor/generator three in the current Toyota on-demand all-wheel drive system. Any permanent magnet drive motor assembly can be used in the classroom and for lab activities. Many times, when we are teaching the concept of magnetism as it relates to energy, we pass a conductive metal rod through a coil of electrical wire, and we show how it generates a small AC voltage reading on a multimeter (See Figure 1- Magnetism). Turning the rotor on the drive motor while measuring the voltage on one of the three phases will produce a more impressive signal because of the arrangement of magnets. The arrangement of the magnets can be seen by holding an inexpensive piece of green magnetic viewing film against the rotor (See Figure 2 - Magnets).
When teaching electrical resistance, a great way to show that a very small difference in resistance makes a big difference in the way a component operates is to use a milli-ohm meter to measure the resistance of the motor windings (See Figure 3- Resistance). The normal resistance of these windings is less than one ohm and cannot be accurately measured with a standard multimeter. The inclusion of the milli-ohm meter allows the instructor to share how temperature will affect resistance and what a Kelvan clamp is and how they must be placed on the circuit to accurately measure the circuit.
When teaching position sensors we typically include hall-effect sensors and permanent magnet sensors. Analog versus digital output of these sensors is one of the key learning outcomes. The resolver is the most commonly used position sensor in a permanent magnet drive motor assembly (See Figure 4 - Resolver). The inclusion of the resolver in the position sensor discussion allows the instructor to cover sine and cosine output signals as well as an excitation signal. The electronic control unit (ECU) responsible for motor operation can detect rotor position, rotational direction, and speed. The position can be determined without turning the rotor.
Most permanent magnet drive motors contain one or more temperature sensors. These thermistors vary in resistance as the temperature
changes much like a coolant temperature sensor or an intake air temperature sensor. The resistance of the sensors can be measured, and the results can be compared to service information to determine the accuracy of the temperature sensor.
The inclusion of the electric drive motor and related lab activities will add excitement to the learning in a basic electrical course. The lab activities will reinforce critical basic electrical concepts in a stand- alone hybrid and electric vehicle class.
I will finish this article with the same offer I make after each of my presentations. If you are interested in getting started in the process of adding hybrid and electric vehicles to your curriculum or want more information, please feel free to reach out. I am more than willing to sit down in-person or online and share my experiences. Are you looking for a classroom textbook? Reach out to Pearson and ask for a review copy of the Electric and Hybrid Electric Vehicle text that Jim Halderman and I co-authored. It is a comprehensive text covering all the latest information on the subject.