Variable compression ratio

Variable compression ratio (VCR) is a technology to adjust the compression ratio of an internal combustion engine while the engine is in operation. This is done to increase fuel efficiency while under varying loads. Variable compression engines allow the volume above the piston at top dead centre to be changed. Higher loads require lower ratios to increase power, while lower loads need higher ratios to increase efficiency, i.e. to lower fuel consumption. For automotive use this needs to be done as the engine is running in response to the load and driving demands. The 2019 Infiniti QX50 is the first commercially available vehicle that uses a variable compression ratio engine.

Variable compression ratio (VCR) is a technology to adjust the compression ratio of an internal combustion engine while the engine is in operation. This is done to increase fuel efficiency while under varying loads. Variable compression engines allow the volume above the piston at top dead centre to be changed. Higher loads require lower ratios to increase power, while lower loads need higher ratios to increase efficiency, i.e. to lower fuel consumption. For automotive use this needs to be done as the engine is running in response to the load and driving demands. The 2019 Infiniti QX50 is the first commercially available vehicle that uses a variable compression ratio engine. ==Engine designs== The first VCR engine built and tested was by Harry Ricardo in the 1920s. This work led to him devising the octane rating system that is still in use today. Many companies have been undertaking their own research into VCR Engines, including Saab, Nissan, Volvo, PSA/Peugeot-Citroën and Renault. The 2019 Infiniti QX50 is available with a production version of the turbocharged variable compression engine. ===Peugeot MCE-5=== The Peugeot design works by varying the effective length of the con-rods connecting the piston to the crank. When the con-rod is shorter, the compression ratio is lower and vice versa. On the left hand-side of the diagram is the conventional piston of an internal combustion engine. On the right is an hydraulic cylinder with double-acting piston. This acts through a rod-crank system with a gear wheel, whose movement adjusts the effective con-rod length and thus the compression ratio in the left cylinder. ===Saab SVC=== SAAB Automobile rekindled interest in variable compression when they introduced their SVC engine to the world at the Geneva motor show in 2000. SAAB had been involved in working with the 'Office of Advanced Automotive Technologies', to produce a modern petrol VCR engine that showed an efficiency comparable with that of a Diesel. The SAAB SVC was an advanced and workable addition to the world of VCR engines, but it never reached production due to the company's bankruptcy in 2016. The design, an implementation of the Larsen VCR engine, consisted of a monobloc head, which contained all of the valve gear, and the crankshaft/crankcase assembly. These parts were connected by a pivot which allowed 4 degrees of movement controlled by a hydraulic actuator. This mechanism allows the distance between the crankshaft centre line and the cylinder crown to be varied. Unlike the Peugeot design, the effective connecting rod length is fixed. A supercharger was chosen in preference to a turbocharger to achieve the necessary response time and high boost pressure. To alter V c , 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 unit, with the crankshaft in the lower block and the cylinders in the upper portion. The two blocks are hinged together at one side (imagine a book, lying flat on a table, with the front cover held an inch or so above the title page). By pivoting the upper block around the hinge point, the V c (imagine the air between the front cover of the book and the title page) can be modified. In practice, the SVC adjusts the upper block through a small range of motion, using a hydraulic actuator. Waulis Patent Application Saab press release Automotive engineering international article Infiniti Introduces the First Production Engine With Variable Compression

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