Posted on 12/29/2006 6:44:22 AM PST by Red Badger
Cat’s variable compression ration engine relies on an eccentrically-mounted crankshaft.
The VCR mechanism.
Hydraulic pistons control the cradle
As part of its research and development into HCCI (Homogeneous Charge Compression Ignition) regimes for meeting coming heavy-duty engine emissions requirements, Caterpillar has developed—and filed a patent on—a variable compression ratio (VCR) engine.
A variable compression ratio engine offers the potential to increase combustion efficiency and decrease emissions under varying load and speed conditions.
Caterpillar is part of a Department of Energy-funded research project on high-efficiency, clean combustion along with ExxonMobil (fuels and combustion chemistry), Sandia National Laboratories (optical diagnostics, fuel spray and combustion, fuel effects), and IAV (closed loop control, transient controls, vehicle calibration, sensors). Catvcr2 The VCR mechanism. Click to enlarge.
Benefits of the variable compression ratio engine with an HCCI regime include high-load operation at low-compression ratios; elimination of the cold-start issue with a low-compression ratio; improvement of light-load combustion stability and the emissions of HC/CO; the optimization of load, emissions and fuel economy; and the enabling of engine braking.
The crankshaft in the 15-liter engine is mounted eccentrically in the cradle which sits in the cylinder block. Rotation of the cradle moves the crankshaft which alters the compression ratio. Catvcr3 Hydraulic pistons control the cradle. Click to enlarge.
Hydraulic pistons drive the cradle up and down. As a result, the engine can change its compression ratio from 8 to 15:1.
The VCR engine is by no means a panacea for highly-efficient and clean combustion, but, notes Kevin Duffy from Caterpillar, it is “a valuable development and exploration tool to understand tradeoffs of numerous controls and combustion parameters [with HCCI].”
Caterpillar is not alone in its investigations of variable compression ratio engines.
Many of the earlier initiatives focused on smaller-displacement, light-duty engines. A VCR could enable significant engine downsizing in highly boosted engines, and was seen as a possible solution to bringing gasoline engine efficiency closer to that of diesels.
Among the research and development efforts:
*
In 2000 Saab introduced a prototype VCR engine at the Geneva Auto Show. *
Three European car manufacturers (PSA Peugeot Citroën, Volvo and Renault) two powertrain development companies (FEV Motorentechnik and Le Moteur Moderne) and VKA at Aachen University of Technology worked on VCR engines as part of a 2002 European effort, Project VCR. *
A French development company, MCE-5, is working on a variable compression ratio engine block. *
An earlier DOE project involving Argonne National Laboratory, AVL Powertrain, Computer Systems Management, Envera and Ricardo developed a light-duty variable compression ratio engine prototype in 2001.
Resources:
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Heavy Duty HCCI Development Activities (Caterpillar, DEER 2006) *
Variable Compression Ratio Engine (VCR) *
Project VCR
Rest In Peace, old friend, your work is finished.......
If you want on or off the DIESEL "KNOCK" LIST just FReepmail me........
This is a fairly HIGH VOLUME ping list on some days......
KnOcK!......
I always had trouble aligning the pilot shaft. Now that I get good at it they come up with this. It is a conspiracy, I tell you.
LOL!!!!......It's obviously mades for people just like you! Just stick it in anywhere, it'll work!........
Cool!
Now all they have to do is make the internal gear train and the transmission follow the centerline of the crankshaft. Sounds like a lot of moving parts to me.
I've known a few eccentric cranks though the years...
This seems like a great solution for a combined gasoline/ethanol vehicle.
Increaseing the compression ration would take advantage of ethanol's higher detonation resistance while still allowing the vehicle to run on gasoline.
Caterpillar Ping...
I am struggling through the "Valve Accuator" solenoid campaign with their C-13 engines. Can't wait for HCCI. sarc/.
Just imagine, combine VCR technology with Camless Computer controlled valve timing via actuator solenoids and the digitally controlled piezo electric common rail fuel injectors and Voila! you have the PERFECT engine for all fuel types and load conditions!.................
That would make a good Nom de Plume........
Not necessarily. The centreline of the crankshaft follows a part of a circular arc as it moves. You just need to have a drive gear on the crankshaft the same diameter as the radius of the arc that the crankshaft moves through, and then a driven sprocket of the same diameter, on an output shaft on the same axis as the crankshaft eccentric. As it moved through its arc the crankshaft's axis would always be the same distance from the output shaft's axis
More moving parts in a machine, more problems that can go wrong and wear out.
The resting point will be at the bottom, which translates to low compression at startup. Should save a lot of wear and tear on starters, especially for a diesel.
Or, if you want to visualize a mechanical nightmare, image this combined with a Willys-Knight sleeve-valve design.
Hmmm let me correct myself. Just looked at the diagrams again, and noticed that one half of the crank offset device is a one piece structure. so misalignment problem is overcome.
--More moving parts in a machine, more problems that can go wrong and wear out.--
Back to the wood fired one-lung steamer ...
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