Hybrid cars
A hybrid vehicle is one that uses a combination of power sources to achieve greater economy, lower emissions or greater performance - and ideally all three. A schematic diagram of the basic principles can be found on the Honda website's hybrid cars page.
KERS: Performance boost
Technically, many of today's leading Formula One cars are hybrid road cars such as the pioneering Honda Insight because of their Kinetic Energy Recovery System (KERS) performance boost.
KERS captures energy from the engine or brakes and uses it to boost performance, either by using a generator to charge a battery or by capturing kinetic energy by using the braking system to spin a flywheel at up to 80,000rpm. This 'spinning energy' can then be added to the car's normal engine power, giving up to 70hp extra for up to seven seconds.
Integrated Motor Assist
Hybrid road cars such as the pioneering Honda Insight, first introduced in 1999 and now in its fifth generation, use a generator and battery-based system. However, to call it that doesn't do it full justice, for two reasons.
The first is that in Honda's Integrated Motor Assist (IMA) system, the 'electric assist' unit is actually integrated into the basic engineering of the drivetrain, acting as generator, electric drive unit and starter motor. This combination motor/generator acts on the main driveshaft between the engine and transmission.
Honda adopted this system as being light, compact, less complex and less expensive than alternative layouts. The original Insight electric assist unit was only 63.5mm thick and weighed under nine kilograms. The IMA units used in succeeding Civic and Jazz hybrid cars were even lighter and more compact.
Integrated Engineering
There's another reason why thinking of hybrids as generator and battery assisted conventional vehicles doesn't do the concept full justice. It misses the fact that an awful lot more goes into a true Hybrid EV than merely adding an auxiliary electric drive system. Every aspect of the vehicle has to be engineered to save weight, cut aerodynamic drag, reduce rolling resistance and make the most of every last kW of power.
For Honda, a key piece of the puzzle has been the Continuously Variable Transmission (CVT). Whereas a conventional auto transmission uses a fixed set of engine-to-driveshaft ratios, the CVT infinitely varies ratios between low and high limits to match driving conditions and available engine torque. It also meant developing the IPU (Intelligent Power Unit), a small PC-sized computer that controls every aspect of the dynamics and power management. The Honda Jazz tucks the IPU along with the battery pack under the boot floor.
Low drag
It also means minimising the Cd (coefficient of drag) figure that measures how much resistance the hybrid car has to overcome when moving through the air. Since drag builds up exponentially with speed, a low Cd figure is key to allow the hybrid car to combine high fuel economy with good cruising speeds.
The original Honda Insight two-seater achieved a class-leading Cd of 0.25 by using a body that tapered down from just behind the driver's head and a narrower rear axle track for a classic aerodynamic 'tear drop' shape. Remarkably, the Honda Jazz hybrids manage to match this while retaining normal five-seat hatchback dimensions. They also manage to achieve Insight-level fuel economy, partly by minimising weight wherever possible, through meticulous engineering and choice of advanced materials.
Paul McShane - 21 Aug 2013