INTERNAL COMBUSTION ENGINE EXHAUST SYSTEM

TECHNICAL FIELD OF INVENTION

The invention relates to an exhaust system for an internal combustion engine, and particularly for use on a four stroke internal combustion engine such as motor vehicle engine, and to a method of exhausting such an engine.

BACKGROUND ART

In the proposed exhaust systems, the energy imparted to the exhaust gases is wasted, as it exhausts to atmosphere.

DISCLOSURE OF THE INVENTION

It is accordingly an object of the invention to seek to mitigate this disadvantage of the prior art.

Accordingly to a. first aspect of the invention there is provided a method of exhausting the gases of combustion from a cylinder of a multi-c linder internal combustion engine including the step of generating a negative pressure by utilising the exhaust gas flow of a fired cylinder to create a negative pressure or partial vacuum at the exhaust port of another cylinder while that cylinder is being exhausted.

According to another aspect of the invention there is provided an exhaust system for an internal combustion engine having a plurality of cylinders, comprising a primary exhaust pipe connected to the exhaust port of each cylinder, and a secondary exhaust pipe connected between a primary exhaust pipe of a first cylinder and that of a second ^" cylinder so that the velocity of exhaust gas from the first cylinder will create a negative pressure or partial vacuum at the exhaust port of the second cylinder during the exhaust stroke of the second cylinder.

Preferably the secondary exhaust pipes may join the primary pipe of one cylinder to that of the next cylinder in the firing order of the engine.

The engine may preferably be a four stroke internal combustion engine.

A four stroke internal combustion engine and an exhaust system therefor embodying the invention are hereinafter described, by way of example, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a diagrammatic view σf an exhaust system according to the invention;

Figure 2 is a fragmentary side elevating of a cylinder head of a four stroke internal combustion engine incorporating the exhaust system of Figure 1 and embodying the invention; and

Figure 3 is a fragmentary sectioned side elevation of a junction of exhaust pipes in the system of Figure 1.

BEST MODE FOR CARRYING OUT THE INVENTION

Figure 1 illustrates a four cylinder four stroke internal combustion engine IQ having a primary exhaust pipe 12,14,16 and 18 connected respectively to the exhaust port of each cylinder of the engine, and a secondary exhaust pipe 20,22,24 and 26 connecte respectively to the primary exhaust pipe of the previous cylinder in the firing sequence or firing order of the engine 10. The firing order of the engine in this embodiment of the invention is 1,2,4,3, therefore pipes 12 and 22,14 and 26, 16 and 20, and 18 and 24 are connected in pairs-

The primary and secondary exhaust pipes of the engine 10 are joined in their respective pairs in respective junction boxes 28

which themselves are joined by further pipes 30 to a main pipe 32.

The secondary pipes 20,22,24 and 26 are joined to the primary pipes 12,14,16 and 18 at the exhaust ports of the engine as illustrated in Figure 2 with the junction apertures between the pipes for example the pipes 12 and 20 shown, being located out of the direct exhaust gas stream from the ports. To further minimise the possibility of exhaust gas entering the secondary pipes under pressure a suitable deflector 34 may be located in the primary pipes* upstream of the junction apertures with the secondary pipes. This deflector 34, in the form of an inclined plate, may be situated closer to the engine, at the position where the primary pipe 12 is connected to the port.

The diameter of the free ends of the primary pipes are narrowed in the junction boxes 28, as shown in Figure 3, to increase the velocity of exhaust gas leaving the pipes. It is important that the configuration of the pipes in the junction boxes 28 be such that little gas turbulence is created at the junctions to minimise back pressure in the primary and secondary pipes.

During operation of the engine, and during the exhaust cycle of cylinder 1 of the engine, exhaust gas under pressure is discharged from the exhaust port of that cylinder 1 through the primary pipe 12 and into the pipes 30 and 32- A very slight gas discharge may occur through the secondary pipe 20 into the junction box 28 of cylinder 3 but this is of no consequence to the operation of the system.

The exhaust gas which leaves the free end of the pipe 12 in the junction ^' box 28 under substantial velocity expands into the pipe 30 and substantially drops the pressure in the secondary pipe 22 to create a negative pressure through the pipe at the exhaust port of cylinder 2. The negative pressure at the exhaust port of cylinder 2 assists in rapidly reducing the pressure in that cylinder as soon as the exhaust valve opens to reduce the pumping load on the piston in the cylinder. The reduced pressure also ensures complete scavaging of the exhaust gasB-ΛOORJGJN

When cylinder 2 is being exhausted a negative pressure is created through the secondary pipe 26 at the exhaust port of the cylinder 4 and so on for the remaining cylinders of the engine.

A further small drop in pressure is created in the system at the junction of the pipes 30 with the pipe 32.

During experiments with the exhaust system of the invention, presumably because of the improved scavaging of the cylinders during the exhaust cycles of the engine full cylinder capacity was made available during the induction cycles of the engine and the performance of the engine to which the system was fitted was considerably improved using smaller carburettor- jets and a leaner fuel mixture than had been used with a conventional exhaust system on the same engine. This result is demonstrated in the following Example.

EXAMPLE

TESTS ON A MERLYN CAR TO DETERMINE THE EFFECT OF AN EXHAUST SYSTEM EMBODYING THE INVENTION

ON EXHAUST EMISSIONS AND FUEL ECONOMY LEVELS.

A Merlyn Formula Ford car was fitted with a standard Ford 1.6 Kent engine together with two competition exhaust systems.

Two series of chassis dynamometer tests comprising 3 tests to measure Exhaust Emissions in accordance to the ECE15—04 procedure for petrol engined vehicles and 4 steady state emission tests at speeds of 40,50,60 and 90 km/hr were carried out. Both Raw and Diluted exhaust emissions were recorded throughout.

TESTWQRK

Testwork conducted to ECE15-04 procedure which requires the use of a constant volume sampler for the collection of the

The chassis dynometer was set up with an inertia setting of 2500 lbs and a road load power setting of 2.4 KW at 50 km/h. This load setting was based upon the values contained in the table of road load power verses inertia contained in ECE15- 03 regulations.

This load and inertia were set to simulate the test conditions of a 1600 cc Ford Cortina.

The first series of tests was carried out on the vehicle as supplied with a tubular 4 into 1 silenced exhaust system.

The second series of tests was carried out using an exhaust system embodying the invention.

No alterations were made to the carburettor or ignition settings for the engine from those used with the first manifold arrangement.

RESULTS

The results obtained from the Merlyn over the ECE 15-04 test cycles and at the steady states are tabulated in Tables 1 and 2, as follows:-

TABLE 2 EXHAUST SYSTEM EMBODYING THE INVENTION

The computed emissions data from the European and Steady s ^' tate tests given in Tables 1 and 2 and include fuel economy levels calculated using a Carbon balance technique.

It may be seen from the results of the European and steady state tests that good repeatability was recorded both with the standard exhaust and with the exhaust system embodying the invention.

The results obtained from the European tests with the exhaust system embodying the invention show reductions in the emission levels of Carbon Monoxide (CO) and Nitrous Oxides (NOx) and a 20% improvement in fuel economy. The steady state tests also showed a reduction in the CO levels and the fuel economy measurements indicated improvements at 60,50 and 40km/h of 9%, 13% and 8% respectively.

It can therefore be seen that .a system embodying the invention improves the power, economy and emissions of an internal combustion engine. The system embodying the invention provides, it will be understood, a "tuned" exhaust system in which pulses and relative pressure levels in dif erent branches of the exhaust system provides improved exhaust and scavaging of the engine