Because ICE engines and electric motors have very different power-to-energy characteristics each will be used where it is most efficient. The engine will provide constant power source for charging batteries and/or providing power to an electric motor. The electric motor will provide short bursts of power for vehicle acceleration and climbing hills. As shown by the graphs the hybrid of the future will not be required to have a high-horsepower ICE engine. About 50 horsepower would be sufficient for a standard car. The small output ICE engine will be complemented by a 100+ horsepower electric motor, and battery with enough capacity for high energy driving requirements.
Two basic types of hybrid configurations are series and parallel. A series hybrid configuration is like a series electrical circuit, i.e., battery positive, light bulb one, light bulb two and battery ground. In a series hybrid layout energy flows from the fuel tank, to the engine, that drives a generator. From the generator power is directed to either the electric motor, battery or both.
The end of the hybrid series circuit are the drive wheels of the vehicle. The power bus controller is a computer that determines where power is needed depending on driving conditions. During steady-state driving the engine could be turned off to conserve fuel and only the battery used to power the motor. When acceleration is required, and the battery’s energy is used at a high rate, the engine would be started to recharge the battery and power the electric motor. When the brakes are applied the motor would act like a generator and recharge the battery through regenerative braking. For maximum efficiency, energy for the vehicle will be constantly switched between the battery and on-board fuel. When the vehicle is not in use both energy sources are replenished. The battery charged from a stationary power source and the fuel tank filled.
Einstein once said, “Energy cannot be created or destroyed, it can only be changed from one form to another.” and that is the premise of regenerative braking. The average car weighs around 3200 pounds with light trucks adding another 2000 pounds to that figure. To accelerate this mass to 60 miles per hour takes heat energy that comes from fuel or a battery in a hybrid. Conversely to slow down the same amount of mass also takes an equal amount of energy. The braking systems on cars and trucks convert the energy of motion into heat through friction. The heat is dissipated and its potential energy is lost. Regenerative braking can recover much of this heat loss and turn it into work to power a vehicle.
Many current hybrid cars like the Tesla, Toyota Prius, Ford Escape and others use regenerative braking to convert wasted brake heat into electrical energy. The concept is simple. The electric motor used to propel the car can also be used as a generator to charge the battery using the energy of the vehicle slowing down though braking. Using an electric motor as a generator is not a new concept. The starter/generator was installed in Cadillac models in 1912 where it was used to start the engine (a vast improvement over cranking by hand) then once the engine was running it was used as a generator to charge the battery.
Ford Motor Company and the Eaton Corporation are developing Hydraulic Powered Assist (HPA) regenerative braking systems. When the brakes are applied the vehicle’s kinetic energy is used to power a hydraulic pump that forces fluid into a high-pressure accumulator. Pressure (1300 psi or higher) is created by compressing nitrogen gas in the accumulator. When the vehicle is accelerated the high-pressure fluid is used to drive a hydraulic motor that is connected to the powertrain. This translates the kinetic energy of the car into mechanical energy that assists with vehicle acceleration. It is estimated that an HPA system could store up to 80 percent of the vehicle’s inertia lost during braking and turn it back into energy for acceleration. This could reduce fuel consumption by 25 percent or more as this technology matures.
Because of the size of the accumulator, current designs of HPA systems are targeted for large trucks over 10,000 pounds. As the technology is improved HPA designs will be made smaller and can be applied to cars and light trucks. Regenerative braking on hybrid vehicles allows on-board batteries to be used longer without external charging thus extending the range of both hybrid and all-electric vehicles.
Like the series hybrid configuration a parallel layout uses two power sources in separate paths to the vehicle’s drive wheels. The battery powers an electric motor connected to the vehicle’s transmission. The other path of power is the ICE engine, also connected to the transmission. One advantage over series hybrid systems is that no generator required. The electric motor can still act as a generator to charge the battery during braking. The ICE engine could be made smaller as it is directly connected to the transmission. Because the electric motor would have two times, or more the power of the ICE, it could drive the rear wheels during max power requirements while the ICE could drive the front wheels for low-speed driving. With a low-power ICE, the transmission would be less expensive to manufacturer and could be smaller than a standard transmission.
Owning a hybrid of the future will offer several benefits. A hybrid with a large, powerful electric motor will be more fun to drive than a car equipped with only a small fueled engine. All-electrical power accelerates the Tesla Model S from 0-to-60 mph in 3.2 seconds and only a few ICE powered cars can match that acceleration. This is a long way from the image of the “not-a-thrill-to-drive” Toyota Prius with a 0-to-60 time of around 10 seconds. While many future hybrid cars will not reach the acceleration performance of the Tesla S, future hybrids that offer owners a high-performance driving experience will be more common. Consumers will buy efficient vehicles, not to only help the environment, but because they will be fun to drive, and less expensive to own and operate.