GB2478526A

GB2478526A - Variable compression ratio (VCR) i.c. engine with variable length piston rod or connecting rod

Info

Publication number: GB2478526A
Application number: GB1003756A
Authority: GB
Inventors: Stephen Richard Terry
Original assignee: TCK ENGINES
Current assignee: TCK ENGINES
Priority date: 2010-03-08
Filing date: 2010-03-08
Publication date: 2011-09-14
Anticipated expiration: 2030-03-08
Also published as: GB2478526B; GB201003756D0

Abstract

A variable compression ratio (VCR) mechanism for an internal combustion engine, eg of the crankless type, comprises a part of a connecting rod (piston rod) perpendicularly fixed to the piston 1 and engaged via threads with a further connecting rod part. Rotation of the piston 1 results in change of the length of the combined piston rod. The rod parts 2,3 may engage directly, as in fig.7, or may be engaged by a threaded sleeve (14, figs.3,4). The piston rod part 2 may have external splines 11 that mesh with the internal gear (10, fig.2) of an annulus 9 which is supported by bearings 7 and has an external gear meshing with drive gear 8. The annulus may be spoked to allow the passage of gases.

Description

DESCRIPTION

COMPRESSION RATIO CONTROL FOR INTERNALCOMBUSTION ENGINES

This invention relates to internal combustion engines. In particular, this invention relates to a compression ratio control mechanism for crankless internal combustion engines.

In a conventional internal combustion engine it is necessary to vary the valve timing and compression ratio to optimise engine efficiency at different engine speeds, load and fuel type. For Atkinson Cycle engines ((PCT/GB2009/050858) the optimum Atkinson Ratio (induction stroke/power stroke) would also be dependant compression ratio, engine speed and load conditions. This invention provides for a more efficient system where the compression ratio can be varied. In conventional engines the fixed geometry of the connecting rod and crankshaft, the ignition and exhaust strokes are of equal lengths and the compression ratio is effectively fixed. Maximum efficiency is obtainable only where the exhaust stroke is shorter than the power stroke, and where the compression ratio can be tuned to a particular fuel type. However where the intake is longer than the power stroke the engine becomes self-supercharged. Varying the valve timing by an engine cycle would enable an Atkinson cycle engine to run as a supercharged engine, where the compression ratio would require tuning for each cycle.

Prior art has established that variable compression ratio can improve the efficiency particularly for lean burn', homogenous charge compression ignition (HCCI) direct injection and flexible fuel engines. Internal combustion engines exist which can vary the compression ratio, valve timing, valve duration and actuation. However, these engines are costly to produce due to the complex nature of the internal mechanisms and external electro mechanic, mechatronic and hydraulic/pneumatic systems required.

This invention aims to provide a solution for engines where the connecting rod is perpendicularly fixed to the piston.

According tothefirstaspectofthe invention there is provided an internal combustion engine comprising a cylinder, a piston reciprocally mounted within the cylinder, a connecting rod perpendicularly fixed to the piston at one end the other extending via threads to a further connecting rod for converting reciprocating movement of the piston into rotational movement of an output shaft. As the piston is rotated about the threads the length of the combined connecting rod lengthens or shortens effecting a change in compression ratio. The piston is rotated via splines/gear on the connecting rod which can also serve to hold the piston within the cylinder bore.

According to the second aspect of the invention there is provided an internal combustion engine comprising a cylinder, a piston reciprocally mounted within the cylinder, a piston connecting rod perpendicularly fixed to the piston at one end the other extending via threads into a threaded sleeve. Said threaded sleeve connected to a further cam connecting rod for converting reciprocating movement of the piston into rotational movement of an output shaft. The piston connecting rod and cam connecting rod are rotationally fixed by slidable splines or spindle extending from the cam connecting rod into the piston connecting rod. Rotating the threaded sleeve via splines/gear about the threads of the cam connecting rod and piston connecting rod lengthens or shortens the combined length of said connecting rods effecting a change in compression ratio. This embodiment is suitable for high compression ratio engines having shaped crown pistons where the piston cannot rotate. The splines/gear on the sleeve can also serve to hold the piston within the cylinder bore, with only the piston rings/seals in contact with the cylinder bore. To further reduce friction losses an additional roller can be used on the connecting rod means for the power stroke.

Because the compression ratio is dictated by rotation of the piston or sleeve, it is possible to vary compression ratio in infinitely small increments.

Preferred embodiments of the invention shall now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic side view of the variable compression ratio mechanism; Figure 2 is a partial sectional top view the variable compression ratio adjustment annulus; Figure 3 is a component side view of the connecting rod assembly; Figure 4 is a component partial sectional top view of the connecting rod assembly; Figure 5 is a side view of the connecting rod assembly set at high compression ratio; Figure 6 is a side view of the connecting rod assembly set at low compression ratio; Figure 7 is a schematic side view of the engine with variable compression adjustment, variable valve timing and variable inlet valve adjustment.

For ease of understanding, features common to all embodiments of the invention described herein are identified using identical reference numerals and in general refer to the engine described in patents PCTIGB2009IO5OS5S GB0812891.O.

Figure 1 shows a pistoni rigidly connected to piston connecting rod 2 which has splines or gears 11 extending for the full stroke length S of the piston. Internal threads 5 of piston connecting rod 2 mesh with external threads 4 of cam connecting rod 3 so that as splines/gear 11 rotate the combined length of piston connecting rod 2 and cam connecting rod 3 lengthens or shortens.

Figure 2 shows a top view of a geared annulus 6, 9 supported by bearing 7 and rotated about the piston axis by pinion gear 8. The annulus 9 has internal splines/gears 10 that mesh with piston connecting rod external splines 11 so as the annulus is rotated the piston 1 and piston connecting rod 2 are also rotated. Since the rotation is performed by an annulus there is no net side force on the connecting rods 2, 3; the piston is held within a cylinder bore by the splines/gears. The outer gears of the annulus 9 are rigidly connected to the inner splines/gears 10 by spokes 12 to allow gases to pass through to an expansion chamber or crankcase as the piston operates.

An alternative embodiment is shown in Figure 3 to 6 where a sleeve 18 connects piston rod 2 and cam rod 3 on thread 14 meshing threads 12 and 13 respectively. In operation the annulus 9 rotates the sleeve 18 about the rotationally fixed connecting rods 2, 3 on threads 12, 13 which lengthen or shorten the combined connecting rod length effecting a change in the compression ratio. Extension 16 (hexagonal extension shown) on cam connecting rod 3 slidably engages piston connecting rod 2 and prevents rotational movement of piston 1 as the sleeve 18 rotates. Figure 5 and 6 show the piston 1 adjusted for high compression ration (Figure 5) and low compression ratio (Figure 6). The change in length (d) (Figure 5, 6) effect the compression ratio CR of the engine according to the following equation: jJp2 1.) .) I I CR=4 V +Bd Where: B = cylinder bore diameter S = piston stroke length d = change in connecting rod length V= clearance volume.

The clearance volume of the combustion chamber V is the minimum volume at the end of a compression stroke, i.e. when the piston reaches the maximum top dead centre (TDC). The change in length d varies the TOG of the piston so the compression ratio varies according to the above equation.

Figure 7 shows a schematic of the variable compression ratio mechanism embodied in a crankless engine design (Patent PCT/GB2009/050858 GB0812891.0) where the adjustment shaft 8 is accessible at the cylinder head top. The adjustment can be servo controlled and interfaced to an engine management system.

Claims

CLAIMS1. A variable compression ratio adjustment mechanism for an internal combustion engine comprising a cylinder, a piston reciprocally mounted within the cylinder, a connecting rod perpendicularly fixed to the piston at one end and extending via threads to a further connecting rod for converting reciprocating movement of the piston into rotational movement of an output shaft. As the piston is rotated about the threads the length of the combined connecting rod lengthens or shortens effecting a change in compression ratio.
2. A variable compression ratio adjustment mechanism as claimed in 1 where said connecting rods are connected using a threaded sleeve; said sleeve being rotated to lengthen or shorten the combined length of the connecting rod means.
3. A variable compression ratio adjustment mechanism as claimed in 1, 2 where the piston and connecting rod is guided by an annulus of splines/spurs/gears held in position by a bearing.
4. A variable compression mechanism as claimed in any of claims 1, 3 wherein the rotation of the sleeve is defined by the rotation of an annulus in or on which the sleeve means is slideable.
5. A variable compression mechanism as claimed in any of claims 1, 4 wherein the position of the annulus is held by a bearing in or on which the annulus isrotatable.
6. A variable compression mechanism as claimed in any of claims 1, 5 wherein the annulus has spokes to allow gases to pass said annulus to and from and expansion chamber or crank case during operation of the piston.