Constant Displacement Variable Power Engine at a Given RPM

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Issue Addressed: Heavy commercial vehicles like trucks, lorries, earthmovers operate in their lifecycle in two modes corresponding to being empty (only curb weight acting) and loaded (curb weight plus the payload). Usually, the ratio of full load capacity to curb weight of these categories of vehicles ranges from 1.5 to 2.0. Therefore, when the vehicle is running in unloaded mode, the power required is significantly lesser than the loaded mode. However, as the engine volumetric capacity is fixed, power produced is more than what is required at a given engine RPM. This leaves an area of improvement wherein effective engine displacement can be reduced by deactivating cylinders and handling lower displacement in the engine.

Existing Technology: Cylinder deactivation or Displacement-on-Demand is the standard practice, though the entire concept has not been commercially successful. Reputed OEMs have demonstrated cylinder deactivation; however, it is done mechanically by a complex mechanism and the cylinders in the process are subjected to extreme mechanical stresses due to gas pressure.

The Proposed Invention: This invention (an operating procedure) enables multi-cylinder internal combustion engines to operate in two modes corresponding to loaded and unloaded conditions, without the complexity of extant technology. These two modes are herein called the ‘Undifferentiated’ and the ‘Differentiated’ modes, respectively. In this invention, differentiated fuel volume is injected in the firing sequence of the engine cylinders to thermodynamically deactivate a predetermined set of cylinders alternately.

In the Undifferentiated mode, the engine runs as per typical internal combustion engines wherein the volume of fuel injection is controlled by manual throttling by driver/operator (in loaded as well as unloaded operation of the vehicle). In the Differentiated Mode i.e., the unloaded operation of vehicles, a pre-calibrated volume of fuel (say Volume - X) is injected alternately in firing order to deactivate the alternate cylinders thereby achieving effective thermodynamic elimination while being mechanically present.

How is cylinder deactivation achieved? - This is achieved by injection of Volume – X of fuel, which is the volume of fuel required to produce just the amount of power in a cylinder to offset its pumping work and its mechanical presence (frictional losses). This differentiation process is achieved by an ECU program which refers to Graph – X.

Graph – X is simply the graph of ‘Specific Fuel Consumption versus Idle Load Engine RPM’. This idle load condition is achieved when the engine is being run with all its accessories but without any external load on the output shaft equivalent to the motive power required of the vehicle. This is an empirical value determined in an engine test bench.

This operating procedure shall require a flywheel with variable moment of inertia (MI) to arrest any irregularity in peak torque along the firing sequence due to differentiated power generation. There shall be a mechanism to vary the MI of the flywheel as per the mode of operation.

Advantages –Displacement-on-Demand can be achieved without any complex costly physical mechanism or cost and better fuel economy can be achieved.


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  • Name:
    Yengkhom Kamaleshwar Singha
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