GB2376503A

GB2376503A - Automatically variable compression ratio device with adjustable cylinder head portion

Info

Publication number: GB2376503A
Application number: GB0110374A
Authority: GB
Inventors: Martin Leonard Stanley Flint
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-04-27
Filing date: 2001-04-27
Publication date: 2002-12-18
Also published as: GB0110374D0

Abstract

An automatically variable compression device is incorporated into the cylinder head of a four or two-cycle engine. A combined flame plate and injection holder 1 is adjustable hydraulically within the cylinder with respect to fixed piston body 2 to vary the cylinder volume and hence the compression ratio.

Description

AUTOMATIC VARIABLE COMPRESSION DEVICE INCORPORATED INTO A JUNK HEAD OF A TWO OR FOUR CYCLE, OPEN TOP SLEEVE VALVE ENGINE.

This invention relates to an Automatic Variable Compression Device (AVCD) incorporated into a Junk Head of an Open Top Sleeve Valve engine of either the Two or Four Cycle type.

To provide an understanding of how the above mentioned invention can be used in a Two Cycle Double Acting Barrel Cam Engine of the Hermann type using a Uniflow Open Top Sleeve Valve arrangement, is shown in Figure 1. In addition to this invention, the engine design shown in Fig. 1 incorporates many other ideas and mechanisms already tried and tested on more conventional engine types, but not in a Two Cycle Double Acting Barrel Cam Engine of the Hermann type using a Uniflow Sleeve Valve arrangement.

The work of Dr. Mansfield and his colleagues in the 1950's at BICERA, pioneered the Variable Compression Ratio Piston (VCRP). This British invention enabled diesel engines to run at very high boost pressures by automatically lowering the compression ratio to the order of 8: 1 at high load. Conversely, at low load to high compression with ratios of 21: 1 and higher, without increasing peak cylinder pressures.

Early patents held by BICERA showed VCRP designs were for Four Cycle engines, but did include a design for Two Cycle engines. However, it is not known if any were ever built and operated. Ideally, Two Cycle engines permit the simples application for a AVCD when designed into the cylinder head, as in the more simplified case of a manual variable compression device used in model aircraft diesel engines.

The opportunity to locate an AVCD in the cylinder head rather than in a piston, means that the thermal and high acceleration effects on the hydraulic valves experienced in VCRP are virtually eliminated. For instance, the automatic hydraulic load sensing and discharge valves will have a substantially improved durability when AVCD is located in the junk head of an Open Top Sleeve Valve (OTSV) engine.

Benefits selected as significant for a AVCD are :- * Extends the engine load range without requiring to increase the strength of the scantlings or bearing loads by limiting peak pressures.

* Permits higher levels of two stage turbocharging and intercooling to 5 bar and beyond without increasing peak pressures.

* PV diagram becomes wider, but not taller and therefore more area under the curve, as load increases.

* Enables the expansion ratio to increase as the load decreases.

* Greatly improves the part load fuel economy, in some cases by 25%.

* Improves starting in cold weather conditions down to - 30C without aids.

* Allows smooth idling at lower rpm.

The proposed invention provides the same effect, but with improvements that are achieved in a different manner to the BICERA Automatic Variable Compression Piston. For a better understanding of these See GB Patents 762074, 899198 and 2110791 B, US Patent 2742027 and German Patent 1062981.

Referring to Figs. 2,3, 4,5 and 6 the following describes the AVCD.

Fig. 2 is an end view of the concept Two Cycle Barrel engine and shows the high pressure pipework systems for fuel supply to the Fuel Injectors from the Common Rail supply and the supply and return for the AVCD's in the Junk Heads for each cylinder.

Fig. 3 shows the Piston towards the end of the expansion stroke with the Sleeve Valve in the lowest position and the Exhaust Port fully open.

Fig. 4 shows the high load, low compression mode of operation with the Piston in the Top Dead Centre (TDC) position.

Fig 5 shows the Piston at the Top Dead Centre (TDC) position with the AVCD in the low load, high compression mode.

Fig. 6 shows the Piston at BDC with the Inlet Ports fully open and the Exhaust Ports fully closed.

Returning to Fig 3, to show how the AVCD has automatically and hydraulically set itself to low load, high compression mode. This mode is achieved by the Combined Flame Plate and Injector holder (1) at its maximum outward movement with respect to Fixed Piston Body (2) that the Lower Pressure Chamber (6) is also at its maximum volume. The Combined Flame Plate and Injector Holder (1) maintains its maximum outward position by the continuous pressurised hydraulic fluid supply at via Feed Union and Pipe (16 and 17), Check Valve (4) and Feed Orifice (10) to the Lower Pressure Chamber (6). The Lower Pressure Chamber volume (6) is reduced automatically when the engine load increases. As a consequence the fluid pressure in the Lower Pressure Chamber (6) and Channel (11) increases until Pressure Relief Valve (5) reaches a pre-set pressure and it dumps fluid via Drain Union (14) and then via Drain Pipe (15) see Figs. 2 and 3. The hydraulic fluid then returns to the tank. In effect the pre-set pressure in the Pressure Relief Valve (5) limits the maximum cylinder gas pressure. This maximum cylinder pressure is usually determined by the fatigue strength at temperature of the cylinder barrel material. i. e. The generally accepted values of 140 bar for aluminium, 200 bar for Cast Iron and greater than 200 bar if Nodular Iron or Steel is preferred.

At the same time as Lower Pressure Chamber (6) reduces in volume, Upper Pressure Chamber (3) Fig. 4 is increasing in volume, caused by the movement of the Combined Flame Plate and Injector Holder (1) relative to Upper Piston Body (2) rigidly fixed to Head Plate (13). The Upper Pressure Chamber (3) is now filled with fluid under pressure via Feed Pipe and Union (30 and 35) see Fig. 2 through Check Valve (9). The rate of movement of Combined Flame Plate and Injector Holder (1) from low load-high compression mode to high load-low compression mode is controlled by the rate of discharge from the Upper Pressure Chamber (3) via Flow Control Valve (8) and then via Drain Union (31) and Return Pipe (20) see Fig. 2 and back to the tank.

The flow rate through the Flow Control Valve (8) is sized to enable the AVCD to move from high to low compression in approximately 4 to 6 cycles of engine operation when

using diesel fuel. This feature is especially necessary to cater for rapid cylinder pressure increases. When more volatile fuel such as gasoline is used, rapid pressure increases due to detonation can be of limited duration if the Flow Control Valve (8) is sized to go from high to low compression ratio in 2 to 3 cycles.

For Two Cycle Diesel engines of less than 0.5 Lt. per cylinder, an effective compression ratio range of 12: 1 and 30: 1 respectively, is recommended. For cylinders capacities greater than 0. 5 Lt and less than 1.0 Lt. per cylinder, then effective compression ratio range of 10: 1 to 26: 1 is suggested. For cylinder capacity greater than 1.0 Lt. per cyl. 8: 1 to 22: 1 is practical.

As an operating engine is shut down and the engine load is reduced, the Combined Flame Plate and Injector Holder (1) moves to a low load position, and as a result the AVCD sets itself to the high compression mode before stopping. This leaves the engine ready set in the high compression mode for the next start-up. This is a convenient situation especially where cold starts are required. Tests on diesel engines with VCRP's show that cold starting at-30 C is practical without starting aids at all.

When Lower Chamber (6) volume is at a maximum, Upper Chamber (3) is at a minimum and provides a stop with Fixed Piston Body (2). At this position the AVCD is in the high compression mode. See Fig. 5. There is a provision made for a bump gap between the Combined Flame Plate and Injector Holder (1) and the upper surface of Engine Piston (36), see Fig. 5.

Filtered fluid is used as the hydraulic media and is continuously being pumped at pressure into both Upper and Lower Chambers via the two Check Valves (4 and 9) respectively. It is both practical and convenient to use Diesel fuel as the hydraulic media. Hydraulic pressure is supplied via a pressure reducing valve from the Common Rail fuel injection supply.

Fig. 1 Conceptual Low CO2 per kW Engine-longitudinal section.

Fig. 2 View of Cylinder Heads showing Fuel Injection and VCD Pipework.

Fig. 3 Section through Cylinder and VCD-Exhaust Open- Inlet Closed.

Fig. 4 Section through Cylinder and VCD-Low Compression - High Load Mode.

Fig. 5 Section through Cylinder and VCD-High Compression - Low Load Mode Fig. 6 Section through Cylinder and VCD-Inlet Open- Exhaust Closed.

Claims

CLAIMS 1 The replacement of a Junk Head in a Two or Four Cycle Sleeve Valved internal combustion engine, by a "Automatic Variable Compression Device" (AVCD), concentric to the cylinder axis to the designs shown in Fig's 1,2, 4, 5, & 6 to improve :-

* Part and full load Brake Thermal Efficiency (BTE) * Part and full load Brake Mean Effective Pressure (BMEP) * Reduced emissions during cold starting, warm up period and low load through to high load operation.

* Cold starting without aids down to-30 degrees C by high compression mode.

* Scantling and bearing loads controlled by limiting peak cylinder pressure during high load operation.
2 Improvement brought about by invention in Claim 1 to the Brake Thermal Efficiency (BTE) and Brake Mean Effective Pressure (BMEP), whilst achieving higher and smoother torque characteristics, lower exhaust temperatures and lower levels of emissions of a naturally aspirated (NA) and pressure charged and intercooled internal combustion engines of the two or four cycle type.
3 Any internal combustion engine of the type shown in Fig. 1 being fueled by Diesel, DME, Syntrolium, Gasoline, HC Gas or Hydrogen having a plurality of the inventions set forth in anyone of the preceding Claims

1 and 2.