How 2017 Chevy Cruze gets 52 MPG
- Thread starter vwgtiglx
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ssamalin
Veteran Member
Diesel technology of the new Cruze sounds phenomenal. Hooray for GM. Mazda was talking about lower compression diesel to prevent emissions for a while too. Maybe GM will do it. I'd like to hear what the engineers have to say about high pressure multiple injections, variable pressure oil pump, variable nozzle turbo, etc., and how that is new, or catching up, or likely to perform. Anybody?
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GoFaster
Moderator at Large
The GM diesel indeed has a relatively low compression ratio (16:1). Most late model diesels are in this range, VW included, GM larger diesels included.
Multiple injection strategy is also now commonplace in general but I'm sure they have added refinements and worked on the calibration ... a lot. The capability of using multiple injection shots is not new but injectors that can open and close faster and computers that can process signals faster have increased the number of multiple shots that can be given - evidently they are now up to 10. This adds more tuning flexibility (good) but taking advantage of that tuning flexibility in the best manner ... is not easy to figure out.
Variable displacement oil pumps with electronically controlled pressure/volume regulation are in several late model engines (and transmissions), not just this one. In the old days, oil pumps had a fixed displacement and there was a pressure relief valve with a fixed setting and both the displacement and the pressure relief valve setting had to be set to worst-case conditions, but this wastes power because an unnecessary amount of oil is being pumped to an unnecessarily high pressure and a lot of it spilled out of the relief valve. The new oil pumps are an eccentric vane design and in some cases an electrical solenoid valve regulates the pressure that it self-adjusts its displacement in order to achieve. The pump only pumps what it has to and only to the pressure that it has to. There is still a relief valve but the idea is that much less goes through it. This makes a real difference. (Automatic transmissions are starting to use pumps like this, too.)
http://stackpole.com/powertrain-systems-components/systems/
Variable-vane turbochargers are not new, either, but a lot of the trickery is in the control systems and the calibration.
The drag coefficient of the Cruze is 0.28, which helps. (note that the big impressive number is the highway number; the city number isn't anything special)
The GM engine is smaller displacement than the TDI engine that VW sold in North America and smaller than what Mazda is bringing. Less friction, less area for heat transfer in the cylinders - it all helps.
It surprises me that the manual has a highway rating so much better than the automatic does - that's not the norm nowadays. And this is GM's new-fangled 9-speed automatic (which is different from the ZF-derived transmission that Chrysler uses). I don't know much about the GM 9-speed.
Multiple injection strategy is also now commonplace in general but I'm sure they have added refinements and worked on the calibration ... a lot. The capability of using multiple injection shots is not new but injectors that can open and close faster and computers that can process signals faster have increased the number of multiple shots that can be given - evidently they are now up to 10. This adds more tuning flexibility (good) but taking advantage of that tuning flexibility in the best manner ... is not easy to figure out.
Variable displacement oil pumps with electronically controlled pressure/volume regulation are in several late model engines (and transmissions), not just this one. In the old days, oil pumps had a fixed displacement and there was a pressure relief valve with a fixed setting and both the displacement and the pressure relief valve setting had to be set to worst-case conditions, but this wastes power because an unnecessary amount of oil is being pumped to an unnecessarily high pressure and a lot of it spilled out of the relief valve. The new oil pumps are an eccentric vane design and in some cases an electrical solenoid valve regulates the pressure that it self-adjusts its displacement in order to achieve. The pump only pumps what it has to and only to the pressure that it has to. There is still a relief valve but the idea is that much less goes through it. This makes a real difference. (Automatic transmissions are starting to use pumps like this, too.)
http://stackpole.com/powertrain-systems-components/systems/
Variable-vane turbochargers are not new, either, but a lot of the trickery is in the control systems and the calibration.
The drag coefficient of the Cruze is 0.28, which helps. (note that the big impressive number is the highway number; the city number isn't anything special)
The GM engine is smaller displacement than the TDI engine that VW sold in North America and smaller than what Mazda is bringing. Less friction, less area for heat transfer in the cylinders - it all helps.
It surprises me that the manual has a highway rating so much better than the automatic does - that's not the norm nowadays. And this is GM's new-fangled 9-speed automatic (which is different from the ZF-derived transmission that Chrysler uses). I don't know much about the GM 9-speed.
john.jackson9213
Top Post Dawg
Quote below from the GMInsider article linked above:
"A variable-nozzle turbocharger enhances this 1.6-liter unit’s responsiveness at all operating speeds, providing up to 42 psi of boost."
Can this quote be accurate? 42 psi of boost? From atmospheric pressure or is that absolute pressure? i.e. 27 psi over 1 atmospheric pressure of 15 psi?
"A variable-nozzle turbocharger enhances this 1.6-liter unit’s responsiveness at all operating speeds, providing up to 42 psi of boost."
Can this quote be accurate? 42 psi of boost? From atmospheric pressure or is that absolute pressure? i.e. 27 psi over 1 atmospheric pressure of 15 psi?
turbobrick240
Top Post Dawg
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I wonder if the new 1.6 uses piezoelectric or solenoid injectors. I would think The 42 psi of boost is absolute pressure.
Edit: apparently it uses solenoid injectors.
Edit: apparently it uses solenoid injectors.
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ssamalin
Veteran Member
Thanks GoFaster. So these technologies are common among all the diesel brands, but GM has gone smaller displacement (and horsepower?), and has excelled at multiple injection and is quieter. I think the manual being better mpg is a throwback, and may mean the automatic is "too heavy" and not that the manual is more efficient for the small engine. The turbocharger may also be providing high "boost", which I suppose is good. I think 0-60 time should also be expressed "corrected" by dividing by the car weight which I think is a safety indicator. I'm not knocking GM, more like I want to appreciate their achievement. This car sound's like a highly advanced achievement in diesel technology, certainly with this smaller direction they are leading even the Euros.
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