Slide 8 – The Toyota Hybrid System – The Engine - 2

Slide 8 The Toyota Hybrid System – The Engine - 3

For the original version for the Japanese market, the power output of the Prius engine was 58 hp at 4000 rpm.

For the North American and European markets, it was increased to 71 hp at 4500 rpm - i.e. by 22 per cent.

The Prius engine has its power peak at only 4500 rpm, because friction losses increase at higher speeds.

This enables lower rates to be used for the valve springs and piston rings, to reduce the friction losses.

The engine block is of aluminium, with thin dry liners of cast iron, giving a wall to wall distance of only 8 mm.

The cylinder axis is offset from the crank axis by 12 mm. This reduces the fuel consumption by 1 to 3 per cent.

In the THS, the engine must be restarted very frequently, so this must be as unobtrusive as possible.

The variable valve timing makes it easier, and direct drive starting by the generator makes it much quieter.

The engine is spun up to about 1000 rpm before the fuel and spark is applied, to minimise wear.