While most of us have a general sense of what a hybrid/electric vehicle is and how it gets power either from an internal combustion engine or electric motors and a battery pack, there's a lot more technology that contributes to the operation of a hybrid vehicle.
Let's see what it really takes to make a hybrid vehicle operate.
It starts with the battery pack -- no pun intended. Current state-of-the-art technology uses lithium ion cells to produce the electrical current. They are smaller, more efficient and can be packaged in better shapes than the nickel metal hydride batteries used previously. Lithium ion batteries are also used in laptops, cellphones and some portable power tools, but these are different than the batteries used in automobiles.
There are hundreds of formulas for constructing a lithium ion cell, and the batteries built for automobiles have to withstand wide temperature variations, severe impacts and vibration, be safe under all conditions and still have a long life. This is one area we will see huge improvements in the future.
To have a long battery life, the state of charge must be carefully controlled. Computers monitor the battery voltage, current and temperature. Fans can be turned on to cool the battery and some use engine coolant or electric heaters to warm the battery in cold weather. Battery charge is typically maintained between 20 and 80 per cent. Trying to charge the battery more than about 80 per cent generates more heat, which shortens battery life.
Auxiliary systems, such as steering, climate control and brakes, are different on hybrid vehicles. The hybrid system will turn off the internal combustion engine under specific conditions to save fuel. Systems normally driven by the engine, such as power-steering pumps, would no longer be effective, so electric systems are used instead. Electric power steering is used on many conventional vehicles now, too, for its fuel-saving capability.
Automatic transmissions need oil pressure to stay in gear when the engine is stopped. Conventional automatics use an engine-driven oil pump. Hybrids may add an electric pump that turns on when the engine stops. Some hybrids use an electric CVT transmission.
To prevent the vehicle from rolling backward on a hill when the driver releases the brake pedal, the brake systems may have a "hill hold" feature that keeps the brakes applied for a couple of seconds as the driver moves their foot to the accelerator pedal. For regular driving, some systems use an electric vacuum pump to provide vacuum for power brake-system operation, while other manufacturers use electric/hydraulic systems to provide power brake operation.
We like our air conditioning, so the A/C compressor, which was previously belt-driven, now is powered by an internal electric motor. Some, such as Honda, use a combination drive, either belt-driven or electric-driven, depending on operating conditions.
With all these "auxiliary" systems using electricity, there needs to be a controller that can manage them. The hybrid system computer will also operate an inverter, which changes voltages from alternating current (AC) to direct current (DC) and back again. The electric motors that drive the vehicle may operate on 280 to 600 volts AC. Other systems can operate on 42 volts and the lights, gauges and entertainment systems will typically still operate on 12 volts DC.
The inverter creates a lot of heat, so some systems use coolant to keep the temperatures under control. Electric pumps, a separate radiator, overflow tank and hoses are often used to provide cooling for the inverter.
Plug-in hybrids are designed to operate more on electric power, so they have a bigger battery capacity and longer range on battery power alone before the internal combustion engine starts up. Electric vehicles are also plugged in and have a range limited by the battery capacity. While these vehicles do use an external "charging station," they also have an internal charger that converts the AC power from your home wiring to DC power to charge the vehicle's battery.
One more item you may not have thought about is a heater. Electric vehicles may use electric heaters for passenger comfort, and so may some plug-in hybrids. Using the internal combustion engine to produce passenger compartment heat is the easiest way, so look for more exhaust system-to-engine coolant heat-exchangers to warm both the engine and the passenger compartment up quickly when you initially start the vehicle.
Jim Kerr is an experienced mechanic, instructor of automotive technology, freelance journalist and member of the Automobile Journalists' Association of Canada.