Variable Compression Ratio

ByByS. RoshanS. Roshan

Traditional engine compression ratio What it is How to calculate Disadvantages

Variable compression ratio What it is Advantages Ways to modify CR Design Examples (Saab Tilting Monohead Design, Gomecsys Gen4

VC, MCE-5 VCR Engine Block)Conclusion

Outline

Compression Ratio (CR)What is it?

CR Is the ratio by which the fuel/air mixture is compressed before it is ignited.

It is limited in conventional engines due to the shape of the cylinder and piston.

It determines how efficiently the engine can utilize the energy in the fuel.

How is it calculated?s

b

Because CR cannot vary to fit a wide range of operating conditions:

Power output is reduced.

Fuel efficiency is not optimized.

Pollution from combustion is not minimized.

Disadvantages of Fixed CR

What is it?

The combustion chamber volume, Vc, is altered to meet the power needs to the vehicle.

At low power levels, high CR captures fuel efficiency benefits.

At high power levels, low CR prevents knock.

Variable Compression Ratio (VCR)

Because CR is adjustable to meet power demand (CR’s

range from 7:1 to 21:1) :

Increased fuel efficiency

Claims of up to 30% reduction in fuel consumption

Reduced combustion emissions

VCR - advantages

a) ** Articulated cylinder head(2-part engine block)

b) Variation of piston head height. (hydraulic pistons)

c) ** Eccentrics on bearings

d) Multilink rod-crank mechanisms

e) Variation of combustion chamber volume. Additional piston in cylinder head.

f) ** Gear-based mechanisms

Ways to Modify CR

VCR – Design Examples

Lower Engine Block

Actuator

Upper Engine

Block(monohead)

Pivot Point

Increased Volume

Saab Tilting Monohead Design Articulated cylinder head 2-part engine block allows

cylinder head to be lowered closer to the crankshaft to dynamically alter Vc

CR varied by adjusting the slope of the mono-head in relation to the engine block

Unfortunately, Saab shelved this project due to cost.

Movie

VCR - Saab Tilting Monohead Design

1 2 3

Gomecsys(in English: GoEngine) is a Dutch Engineering company that has developed its own variable compression ratio technology based on a 6mm eccentric on the crankshaft pin.

It has achieved compression ratio change from 8:1 to 18:1

30% reduced fuel consumption and CO2 output without sacrificing full load power.

Movie 1 Movie 2

VCR – Design ExamplesGomecsys Gen4 VC

Eccentric

Internal Ring Gear

One of the big advantages of this system is the simplicity. The complete VCR system is integrated on the crankshaft and every 4-stroke engine can be upgraded by replacing a normal crankshaft with a Gomecsys VCR crankshaft.

Gen4 VC

MCE-5 is a VCR engine which uses a gear-based mechanism to adjust CR.

Up and down movement of control jack results in the displacement of the control rack and ultimately a change in TDC.

Movie

VCR – Design ExamplesMCE-5 VCR Engine Block

MCE-5 VCR Piston Arrangement Change in TDC

placement results in increase or decrease in volume of the combustion chamber and CR.

CR’s adjustable from 7:1 to 20:1.

Movie

Some Advantages :Fast response (<100 ms to move from max CR to min CR) .Electronically controlled sensors allow the engine to quickly tailor itself to the ideal operating conditions.CR can be set for each cylinder separately.

MCE-5 CR ControlPistons

Control jack

Crankshaft

Gear Wheel Control

Rack

MCE-5 Gear and Piston Arrangement

Conventional engines have losses due to contact with the piston skirt.

But the VCR MCE-5 pistons only move up and down, greatly reducing the frictional losses by eliminating radial forces.

MCE-5 Frictional Losses In PistonsDue to the decreased radial forces

between the piston and the skirt, stress and ultimately wear are greatly reduced. Therefore, low piston wear and no “piston slap” lead to a better piston and ring durability.

Variable Compression Ratio engines have great potential to increase engine power and fuel economy.

This technology will likely become commonplace due to increasing energy and environmental concerns and the ease of integration.

Conclusions

Thank You For Your Attention