Chevrolet Cruze ECO "returnless" variable pressure fuel pump

[MetroMPG]

GM is promoting the crud out of the Cruze ECO these days, with gas prices being near record highs.

Just spotted this tidbit about the car's variable pressure fuel pump, which does away with the need for a fuel return, and reduces load on the engine (through reduced electrical demand):

The microprocessor behind the Electronic Returnless Fuel System electronically manages the delivery of fuel from the fuel tank to the engine. It is controlled by the brain of the Cruze’s fuel system – the fuel system/chassis control module. The control module can raise or lower the pressure in the fuel line by speeding up or slowing down the fuel pump. This allows the system to make more efficient decisions on the amount of fuel provided to the engine compared to vehicles with a standard fuel system whose fuel pump runs at full speed all the time.

The system reduces voltage to a point where the pump doesn’t deliver excess fuel. The lower fuel pump speed results in less power consumption, which reduces the electrical load on the alternator. That reduces the strain on the engine, resulting in increased fuel efficiency.

source: GM - Canada - News & Information

Neato.

[gone-ot]

...they're also touting their Regulated Voltage Control (RVC) system that is effectively an "on-demand only" field regulator system that holds battery voltage at ~ 12.3VDC instead of 14.7VDC all the time.

...instead, it only pumps the voltage up to 14.7VDC right after a heavy load (starting) then backs off to ~12.3VDC while cruising; but, goes back UP in alternator output voltage (if needed) during decelerations and breakings.

...good news for lamps and light bulbs, but not so good on batterys themselves.

[user removed]

Look under the hood of any Ford Focus made in the last 5 or so years and you will see a return less system. Sensor at the front of the fuel rail, sends signal to ECU, which sends a signal to the fuel pump modulator, which controls voltage to the in tank pump.

Smart alternators will eventually go into full charge when engine is in DFCO and AC compressor is not cycling, then if that is not sufficient charging will max during higher vacuum parameters.

Stop start alternators will have much greater capacity to charge quickly and will really pump the juice in a larger capacity battery under forced deceleration.

I still think lower displacement with electric supercharging under high loads will be a factor, especially with start stop alternator-starter systems and higher capacity lightweight batteries.

regards
Mech

[MetroMPG]

Good additional info, guys. Thanks.

[gone-ot]

Originally Posted by Old Mechanic

...Stop start alternators will have much greater capacity to charge quickly and will really pump the juice in a larger capacity battery under forced deceleration.

I still think lower displacement with electric supercharging under high loads will be a factor, especially with start stop alternator-starter systems and higher capacity lightweight batteries.

...augmented by super-capacitors which are great for sudden dumps of current.

[tjts1]

Most new cars have return less fuel system. I remember when GM was promoting the same thing on the LS1 back in the late 90s.

[MetroMPG]

Interesting.

Is returnless automatically the same thing as having a variable output fuel pump? (I don't know.)

[Christ]

Probably not. I'm sure there's some difference, albeit a small one.

[Phantom]

Yes for the most part all returnless systems have variable output fuel pump if not then at higher speeds and loads when demand for fuel is high it would not be able to provide fuel fast enough.

[Blue Angel]

Found this old thread and wanted to add some info.

Traditional return style fuel systems have a vacuum/boost sensitive bypass regulator. The fuel pump's output is constant volume, and the regulator varies fuel pressure based on manifold vacuum/boost. Excess fuel is returned from the engine bay to the tank.

The first returnless designs eliminated the return line and hardware as a cost savings. In this design, the fuel pressure is always constant and is set by an in tank regulator. From an electrical power consumption point of view, this system has the least efficiency as the pump is always pumping enough fuel at pressure to feed the engine at maximum power.

The newer systems like the one in the Cruze use an intelligent driver to manipulate the fuel pump RPM to vary fuel pressure and flow as required. As far as I know, no pressure regulator is used so every bit of gas pumped by the fuel pump is required by the engine. It wouldn't surprise me if lots of vehicles are using this system by now.

Older systems that were less efficient due to pumping losses also heated the fuel in the tank, leading to increased evaporative emissions.