cruzinZ

Does anyone have a technical answer why Lexus put in both a FI system & DI into the LS 460?

Doublebase

I have a couple of guesses. One would be fuel economy - perhaps they were having trouble metering the amount of fuel the direct injection system supplied at low speeds. They also may have been trying to reduce carbon buildup problems that are associated with direct injection systems...the intake valves don't get sprayed down with clean fuel in direct injection systems (whereas tuned port injection systems spray and clean intake valves). Direct injection systems have had many many problems with carbon buildup on valves, which lead to expensive repairs.

Those are just a couple of guesses.

robert1408

DI only engines require intake ports and combustion chambers shaped to induce some tumble or swirl to the intake air to limit undesirable charge stratification (non homogenous fuel/air mixture). This induced turbulence somewhat restricts inlet efficiency at high rpm. The addition of port injectors simply allows designers to use freer flowing inlet air path and use port injection to add fuel to prevent unwanted stratified mixtures under various conditions, mainly part throttle operation.


In case anybody is interested, here is somewhat simplified version of what these two systems do at different times.

Cold start: Port injector on intake stroke, Direct injector on compression stroke, creating a stratified rich mixture to quickly light off the cats.

Warm up idle: Port only

Normal idle: Direct only, injects on intake stroke

Normal part throttle: Port and direct, both on intake stroke

Full throttle: Direct only, on intake stroke.

Arvid

A very informative site here, but for the LS 600....still can give some info on the LS460 too:
http://www.ciw.com/example2/engine.htm

NB...push all the tabs You can find for more info :-)
Regards
Arvid

Remi

Check out this thread (which includes research paper PDFs from Toyota):

http://www.ft86club.com/forums/showthread.php?t=3172

Probably more than you wanted to know :-)

Tec80

I notice the switch from port to direct about 10 seconds after a cold start. The nice V8 4th order pulsing sound totally disappears, replaced by a smooth hum.

robert1408

Thanks Arvid and Remi! I love this technical stuff. Remi is right about saving a copy of Toyota tech papers. There was a good one for the 2007 LS 460 on Toyota's Australian pressroom. It's no longer available and I didn't save it. It's description of the D4S system was almost exactly the same as described in both of your links. It said that on shutdown, the electric intake cam retarded to increase valve timing overlap to reduce effective compression for easier cranking on the next start.