Loud bang when engine switches from hybrid to petrol

[L3xu5 Mum]

My RX450h occasionally makes a loud bang like someone has just hit the car when switching from hybrid to petrol - it only happens when the car is stationary.  Certainly makes me jump! Any ideas on what could be causing this phenomenon please? Car is into dealership for its 50000 service this week. 

[Carl911]

I have had what I would describe as a rather un refined start up on my GS450. Occasionally I push the ignition button and the car jerks as if in gear. This does not happen every time, just now and again.

a similar effect sometimes occurs if the car is stationary in traffic and the hybrid Battery should deplete causing the engine to start.

ive always ignored it but have often wondered why it does this intermittently. 

Carl

[Britprius]

My guess would be a faulty engine or transmission  mounting.

The hybrid cars do not have a starter motor in the conventional manor, but use a motor/generator (MG1) in the transmission. When the car is stationary MG1 is used to turn the engine for starting. This only works in park or in gear, but not in neutral. The engine cannot start in neutral.

Once on the move MG1 is still used to control the starting action, but dependent on vehicle speed may be electrically locked or turned in reverse with the vehicle momentum being used to turn the engine.

There is a clutch mechanism between the engine, and transmission with no method of operating it. This is designed to slip on sudden high loads (torque limiter). There is an outside chance this may be the problem, but the system has been proved to be very reliable, and would be a rare accurance.

John

[rayaans]

A loud rattle is normal.

A loud bang however is not.

Sounds like a loose engine mount