Variable Compression Ratio (VCR) is a technique to vary the compression ratio of an engine under varying loads. Engine operating at higher loads require lower compression ratio, whereas an engine operating under low loads require higher compression ratio. VCR engines provide the best of both worlds. This adjustment can significantly improve an engine’s fuel efficiency.
Compression ratio is the ratio of total cylinder volume when the piston is at Bottom Dead Centre (BDC) to the clearance volume in the cylinder when piston is at Top Dead Centre (TDC). In order to vary the compression ratio, the clearance volume in the cylinder has to be varied.
Variable compression ratio can be achieved by the following methods:
SAAB Variable Compression (SVC) Engine:
The SAAB Variable compression engine has a cylinder head (also known as monohead) hinged on one end to the crankcase. The cylinder head can be tilted to different angles to achieve variable compression ratios.
Higher compression ratio is achieved at lower loads for higher fuel efficiency and lower compression ratio is required at higher loads to prevent knocking.
The compression ratio varies from 8:1 to 14:1. The engine is employed with a special device known as the eccentric shaft. The eccentric shaft when rotated tilts the monohead (cylinder head) to a certain angle to change the compression ratio. The eccentric shaft is turned with the help of a hydraulic actuator which provided a hydraulic pressure in the range of 60 to 100 bar. The monohead can be tilted to an angle of 4.1 degree.
The SVC is a 1.6 liter 5 cylinder inline engine whose fuel efficiency is 30% better than a conventional gasoline engine. The engine generates 220 hp at 5800 rpm and a maximum torque of 305 Nm at 4000 rpm.
To know more about a different type of VCR engine, Check the following link:
Peugeot MCE-5 VCR Engine
Compression ratio is the ratio of total cylinder volume when the piston is at Bottom Dead Centre (BDC) to the clearance volume in the cylinder when piston is at Top Dead Centre (TDC). In order to vary the compression ratio, the clearance volume in the cylinder has to be varied.
Variable compression ratio can be achieved by the following methods:
- By manufacturing an engine with a cylinder head that can pivot about a point.
- By varying the piston head height.
- By varying the connecting rod length.
SAAB Variable Compression (SVC) Engine:
The SAAB Variable compression engine has a cylinder head (also known as monohead) hinged on one end to the crankcase. The cylinder head can be tilted to different angles to achieve variable compression ratios.
Higher compression ratio is achieved at lower loads for higher fuel efficiency and lower compression ratio is required at higher loads to prevent knocking.
The compression ratio varies from 8:1 to 14:1. The engine is employed with a special device known as the eccentric shaft. The eccentric shaft when rotated tilts the monohead (cylinder head) to a certain angle to change the compression ratio. The eccentric shaft is turned with the help of a hydraulic actuator which provided a hydraulic pressure in the range of 60 to 100 bar. The monohead can be tilted to an angle of 4.1 degree.
The SVC is a 1.6 liter 5 cylinder inline engine whose fuel efficiency is 30% better than a conventional gasoline engine. The engine generates 220 hp at 5800 rpm and a maximum torque of 305 Nm at 4000 rpm.
To know more about a different type of VCR engine, Check the following link:
Peugeot MCE-5 VCR Engine
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