Variable compression ratio engine and method of operation

#The present disclosure relates generally to internal combustion engines, and more particularly to a piston assembly that changes length through rotation to change the compression ratio of the engine.

#Engine manufacturers are adapting to the new abundance of natural gas by contemplating engines that can operate utilizing primarily natural gas or primarily distillate diesel fuel, or both. In general, natural gas engines have advantageously been constructed with lower compression ratios than their counterpart diesel engines. A dual fuel engine with a fixed compression ratio may inherently operate less than optimally for at least one of the gaseous or liquid fuels. U.S. Pat. No. 3,417,739 is of interest for teaching a variable compression ratio piston assembly in which a variable volume fluid chamber is defined between a pin carrier and the piston. Changing the volume of fluid in the variable volume chamber changes the distance between the centerline of the pin and the burn surface of the piston, thus changing the compression ratio of the engine.

#The present disclosure as directed toward one or more of the problems set forth above.

#FIG. 1 is a partial schematic view of an internal combustion engine according to the present disclosure;

#FIG. 2 is a perspective internal view of the engine of FIG. 1;

#FIG. 3 is a schematic view of a piston assembly according to the present disclosure;

#Referring initially to FIGS. 1 and 2, an internal combustion engine 10 includes a housing 12 that defines a plurality of cylinders 13. A piston assembly 14 is positioned to reciprocate in each of the cylinders 13 along a cylinder axis 15 between a top dead center and a bottom dead center to define a compression ratio for engine 10. The piston assembly 14 includes a piston 20 rotatably connected to a pin carrier 30 to rotate about the cylinder axis 15. Engine 10 includes a first fuel supply system 40 fluidly connected to each of the cylinders 13, and a second fuel supply system 41 also fluidly to each of the cylinders 13. The first fuel supply system 40 may be a liquid fuel supply system 44 for direct injection of liquid diesel fuel into cylinders 13 in a conventional manner. The second fuel supply system 41 may be a gaseous fuel supply system 43, that may be configured to for port injection of natural gas into cylinders 13 in a conventional manner. Thus, engine 10 may be considered a dual fuel engine capable of burning both natural gas and diesel fuels. In general, piston assembly 14 is configured to transform between a configuration that provides a low compression ratio, maybe less than 15:1 associated more with combustion of natural gas, to a configuration associated with a higher compression ratio, maybe greater than 15:1 more associated with operation of engine 10 in a pure diesel mode.

#Referring now in addition to FIGS. 3-6, the variable compression ratio is accomplished by the piston 20 having a plurality of first wedges 21 respectively contacting a plurality of second wedges 31 of the pin carrier 30 in a hydraulic chamber 33. Each of the first wedges 31 includes a hydraulic surface 22 exposed to fluid pressure in hydraulic chamber 33. Piston 20 rotates from a low compression ratio orientation 18 as shown in FIG. 1 with respect to piston carrier 30 to a high compression ratio orientation 19 as shown in FIG. 3 responsive to an active fluid pressure in the hydraulic chamber 33. Piston 20 rotates from the high compression ratio 19 to the low compression ratio orientation 18 responsive to a passive fluid pressure, which is less than the active fluid pressure, in the hydraulic chamber 33. As expected, the compression ratio at the high compression ratio orientation 19 is greater than the compression ratio at the low compression ratio orientation 18. FIG. 6 is of interest for showing a 180° unrolled side view of hydraulic chamber 33 with the low compression ratio orientation 18 shown with dotted lines and the high compression ratio orientation 19 shown with solid lines. As shown in this view, the hydraulic surface 22, when acted on with active fluid pressure, causes the first wedges 21 to slide along the surface of the second wedges 31 when rotating from the low compression ratio orientation 18 to the high compression ratio orientation 19. In the illustrated embodiment, both the piston 20 and the pin carrier 30 are shown as each including four wedges 21, 31. Nevertheless, those skilled in the art will appreciate that any number of wedges would also fall within the intended scope of the present disclosure.

#Although not necessary, engine 10 may utilize a compression ratio control fluid circuit 55 to control fluid pressure in hydraulic chamber 33, and may utilize engine lubrication oil as the hydraulic medium. In the illustrated embodiment, the compression ratio control fluid circuit 55 is fluidly in parallel with the engine lubrication fluid circuit 60. The compression ratio control fluid circuit 55 may include an electronically controlled pump 57 that is fluidly positioned between a lubrication oil sump 50 and a supply passage 53 that opens into hydraulic chamber 33. Electronically controlled pump 57 may be activated by an operator with a simple switch or may be controlled indirectly by an electronic control module 56 that may receive on/off commands from an operator in a manner well known in the art. Electronically controlled pump 57 may have an output fluid pressure equal to or greater than an active fluid pressure necessary to cause rotation of piston 20 relative to pin carrier 30. Hydraulic chamber 33 may be fluidly connected to lubrication oil sump 50, which is at the passive fluid pressure, through a drain orifice 51 regardless of whether the piston is at the low compression ratio orientation 18 or the high compression ratio orientation 19. Thus, when electronically controlled pump 57 is off or inactive, combustion pressure acting on the top burn surface 25 of piston 20 will cause the hydraulic fluid in hydraulic chamber 33 to drain through drain orifice 51 until the piston 20 passively resumes the low compression ratio orientation 18. When the hydraulic chamber 33 is fluidly connected to a source of lubrication oil 52 at the active pressure, when electronically controlled pump 57 is on or active, the flow rate of fluid into hydraulic chamber 33 from supply passage will exceed the flow rate leaving hydraulic chamber 33 through restricted drain orifice 51, resulting in the piston 20 rotating from its low compression ratio orientation 18 to its high compression ratio orientation 19 as long as the electronically controlled pump 57 continues to operate. A check valve 54 may be positioned in supply passage 53 to prevent the back flow of fluid from hydraulic chamber 33 toward electronically controlled pump 57, such as when high combustion pressures exist during combustion events acting on top burn surface 25 of piston 20. The hydraulic chamber 33 fluid connection to the source of active fluid pressure 52 would be discontinued when the piston 20 is at its low compression ratio orientation 18.