Toyota

Toyota launched the Prius, the world s first mass-produced hybrid vehicle in 1997, and introduced the

vehicle to the US and Europe in 2000. The Estima and the Crown Mild hybrid vehicle were placed in

the Japanese market following the Prius. Currently, Toyota has over 100,000 hybrid vehicles in the

automotive market. Toyota has developed three different Hybrid systems for the vehicles: THS

(Toyota Hybrid System) for the Prius, THS-C (Toyota Hybrid System

CVT) for the Estima, and

THS-M (Toyota Hybrid System Mild) for the Crown. [2, 3, 4, 5]

Energy Management Principle

Figure 2-3 shows the energy management principle of the Toyota hybrid vehicles. Due to the fact

that the engine has different energy conversion efficiencies at different points in the operating range,

a battery is used to store or supply energy to ensure maximum efficiency is achieved during a typical

drive cycle. When the vehicle accelerates, the additional energy is supplied from the battery, while

the engine runs in the optimum efficiency range to supply the power required by the load. During

cruising of the vehicle, the engine is still operating in the maximum efficiency range, and depending

on the demand, excess energy is stored back in the battery. Energy can be supplied from the battery if

the vehicle needs to operate at a higher load. Finally, during deceleration, the engine is turned off,

and the braking energy is recovered by a generator and is returned to the battery. This state of

operation is often referred to as regenerative braking. Depending on the state of the charge of the

battery, the engine can remain on to charge the battery while still regenerative braking is performed.