Currently reading: BMW's 'split engine' hybrid plan
Split-engine set-up could link two small capacity engines into one unit

BMW is working on a hybrid system that uses two engines, detailed in a recent patent application.

Described as a ‘hybrid vehicle having a split engine’, the idea is for the car to be driven by one of the engines and the electric motor at low speeds or when power demands are low. When more speed or power is needed, the second engine cuts in.

See BMW split engine patent drawing

The engine is described as “comprising a first internal combustion engine unit… and a second internal combustion engine unit,” suggesting that the two engines will effectively form one unit. The second engine effectively supports and assists the first.

Although the application does not specify the size of the engines, it does mention the possibility of each being a two cylinder unit. It also says that the two engines could be different sizes – so a four-cylinder unit could be supported by a two-cylinder, for example.

The electric motor would automatically generate extra torque to compensate for any loss when the system switches between the two engines. As with BMW’s current hybrids, the electric motor is contained within the transmission.

Dan Stevens

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mybrainaches 9 January 2010

Re: BMW's 'split engine' hybrid plan

the problem with just shitting the cylinders down is that they still pump up because the valves cant be lifted to let air in and out so you get much more than simple frictional losses I wonder if fiat's multiair will solve this. I think that you could package these engines in the same block certainly with the same water jacket, fluids and sump, just a clutch between them. I would probably have a small (1.4-1.6) 4cylinder with a couple of very small turbos and high compression then a 1.5 twin with a big dog turbo and lower compression, with the electric to boost in the transition form 4-6 cylinder. massive power massive economy (M1 supercar engine???)just an idea.

4rephill 9 January 2010

Re: BMW's 'split engine' hybrid plan

theonlydt wrote:
Interesting as Honda has been using "Active Cylinder Management" for a while - instead of two engines it shuts off two or three of the six cylinders in the v6 for when power demand is low. I can imagine that Honda could use a small electric motor to add extra assistance, requiring those extra three or two cylinders to kick in less often. Perhaps because Honda already has the best cylinder management technology patented BMW is looking down this "two engines".... route

Honda aren't the only ones using the ability to shut off cylinders when not required though, Chryslers hemi engined 300c runs on four of it's eight cylinders in normal running and Cadillac's northstar engine had the capability to shut cylinders down back in 1991 (albeit as an emergency get you home measure in the event of coolant loss), so I can't see it being a patent issue stopping BMW from using it.

Dan McNeil v2 9 January 2010

Re: BMW's 'split engine' hybrid plan

Giom37 wrote:
BMW already had the capability to run on half a bank of cylinders back in the late 80s with its 750li.
I think Ford also had a similar set-up back in the '60s. Seem to remember their V8 Galaxie could do this.