Saab Variable Compression engine
Encyclopedia
The Saab Variable Compression engine was a development project of Saab Automobile
, for which it won an award both in 2000 and 2001.
In a normal internal combustion engine, because cylinder bore diameter, piston stroke length and combustion chamber volume are almost always constant, the compression ratio
(CR) for a given engine is almost always constant.
One exception is the experiment
al Saab Variable Compression (SVC) engine, designed for the Saab 9-5
. This engine uses a technique that dynamically alters the volume of the combustion chamber, thus changing the compression ratio.
To alter the combustion chamber volume, the SVC 'lowers' the cylinder head
closer to the crankshaft
. It does this by replacing the typical one-part engine block with a two-part block, with the crankshaft in the lower block and the cylinders in the upper portion. The two blocks are hinge
d together at one side. By pivoting the upper block around the hinge point, the volume of the combustion chamber can be modified. In practice, the SVC adjusts the upper block through a small range of motion, using a hydraulic actuator.
The SVC project was shelved by General Motors, when it took over Saab Automobile, due to cost.
Saab Automobile
Saab Automobile AB, better known as Saab , is a Swedish car manufacturer owned by Dutch automobile manufacturer Swedish Automobile NV, formerly Spyker Cars NV. It is the exclusive automobile Royal Warrant holder as appointed by the King of Sweden...
, for which it won an award both in 2000 and 2001.
In a normal internal combustion engine, because cylinder bore diameter, piston stroke length and combustion chamber volume are almost always constant, the compression ratio
Compression ratio
The 'compression ratio' of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity...
(CR) for a given engine is almost always constant.
One exception is the experiment
Experiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...
al Saab Variable Compression (SVC) engine, designed for the Saab 9-5
Saab 9-5
The Saab 9-5 is an executive car produced by the Swedish automobile maker Saab. The first generation was introduced in 1997 as the replacement to the Saab 9000 for the 1998 model year. At the time, the car represented a great leap forward for Saab...
. This engine uses a technique that dynamically alters the volume of the combustion chamber, thus changing the compression ratio.
To alter the combustion chamber volume, the SVC 'lowers' the cylinder head
Cylinder head
In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...
closer to the crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...
. It does this by replacing the typical one-part engine block with a two-part block, with the crankshaft in the lower block and the cylinders in the upper portion. The two blocks are hinge
Hinge
A hinge is a type of bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation. Hinges may be made of flexible material or of moving components...
d together at one side. By pivoting the upper block around the hinge point, the volume of the combustion chamber can be modified. In practice, the SVC adjusts the upper block through a small range of motion, using a hydraulic actuator.
The SVC project was shelved by General Motors, when it took over Saab Automobile, due to cost.