This kind of planetary gear set — a compound drive unit — connects the ICE with the MGs to allow a series-parallel operation and the ability to create positive or negative torque, driving the vehicle down the road or charging the battery through regenerative braking
Taking on a hybrid THERE ARE SOME FUNDAMENTALLY DIFFERENT TECHNOLOGIES IN A HYBRID CAR, BUT THEY MUST ALL BOW TO A TRADITIONAL APPROACH TO UNDERSTANDING AND MASTERING AUTOMOTIVE SYSTEMS t’s no secret that the automotive world is changing as governments drive towards lower emissions. We can run, but we can’t hide. Hybrids, plug-in hybrids, and battery-electric vehicles (BEVs) are here to stay, and as carmakers around the world are switching wholesale to the new technology, we all need to get on board with it. It need not be traumatic, and a traditional approach to workshop work can help us navigate this technology, which is also based on well-known and well-understood principles.
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THE THREE-LEGGED STOOL APPROACH Picture an automotive technician perched on a three-legged stool. He or she is supported by three pillars: • fundamental knowledge • reliable service information • proper tooling. The first is developed over years of experience dealing with the components and interactions that make up virtually all systems in almost every vehicle. Experience with how these devices function becomes second nature to us. This must include thorough understanding Ohm’s law, the operation of DC motors, and other inductive devices like
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Auto Channel Issue #38 August 2021
relays and solenoids found in almost everything we see daily. We should have them mastered, and that means we don’t have to research their functionality every time we come across them. Reliable service information includes the wiring diagram — the roadmap for the electric current powering the devices. The wiring diagram allows us to see how any function is carried out on the specific vehicle we are faced with. Equally as important as the wiring diagram is a solid description and theory of operation about the system you are working on and the components that make up the systems. These are both crucial to the successful and efficient diagnosis and repair of the vehicle. Finally, we need proper tooling. Having the tools necessary to evaluate the systems or components is the first step, but understanding the limitations of the tools or tests you are performing is also a must. If we don’t know what to anticipate or learn from the outcome of a test, the data we gather are pointless. This three-legged-stool approach applies to hybrids as well as any other operating system. All three of the stool’s legs must be rigid and supportive to apply this approach. We may be low on some elements of understanding on new systems, and
that is OK. It simply means that we need the training to reinforce the strength of that fundamentalknowledge stool leg.
HYBRID BASICS Let’s fill in some gaps. First we need to acknowledge that a hybrid uses more than one source of propulsion. Some hybrids are configured as parallel hybrids, like that of Honda’s earlier systems (known as ‘Integrated Motor Assist’, or ‘IMA’, systems) in which a three-phase AC-motor stator is confined within the bell housing of the engine and transmission. The motor’s rotor is attached to the crankshaft (where a torque convertor typically rests). The very small displacement internalcombustion engine (ICE) will continue to run as the vehicle is propelled down the road. However, when necessary, the onboard engine control units (ECUs) will allow the IMA motor to produce torque. This allows the vehicle’s small ICE to produce far fewer emissions, yet still require torque output to perform adequately. It’s referred to as a ‘parallel hybrid’ because both propulsion systems (IMA and ICE) operate alongside one another. The IMA motor is also used to start the ICE.
THE SERIES-PARALLEL HYBRID The other configuration of the hybrid is now more common. This ‘series-parallel’ hybrid configuration is used in the Toyota Prius. In this configuration, the ICE serves multiple purposes that will be discussed shortly. The electrified propulsion system has two three-phase AC motor generators (or three, if
