GB2304379A - I.c.engine with cylinder disablement - Google Patents

Abstract

One group of cylinders 4, 5, 6 has the fuel selectively cut-off and 100% exhaust gas recirculation. A non-return valve 24 between intake manifold chambers 12a and 12b is closed when an ON/OFF valve 26a is opened to recirculate exhaust gases. A throttle by pass passage 20a, 20b is opened by the ON/OFF valve 26b when the valve 26a is opened, to increase the charge flow to the operative cylinders.

Description

INTERNAL COMBUSTION ENGINE WITH CYLINDER DISABLEMENT Field of the invention The present invention relates to a multi-cylinder spark ignition internal combustion engine having first and second banks of cylinders supplied with intake air through a common main throttle, and disabling means for selectively disabling the second bank of cylinders, the disabling means including means for cutting off the fuel to the second bank of cylinders, means for isolating the second bank of cylinders from the intake air drawn through the main throttle, and means for recirculating all of the gases discharged by the second bank of cylinders through the second bank of cylinders in order to deactivate the cylinders in the second bank.

Background of the invention Cylinder disablement has been proposed previously, for example in US-A-4,257,372, with the aim of achieving improved fuel economy and reduced emission when the engine is operating at part load. Such systems rely on the fact that spark ignition engines operate less efficiently at low load because of the pumping losses caused by throttling.

Especially in a large engine, it is more efficient to run one bank of cylinder under higher load than two banks under lesser load, while producing the same output power. Simply cutting off the fuel supply to one bank of cylinders would achieve the desired reduction in fuel consumption but if the disabled cylinders are still allowed to pump air, then this would upset the stoichiometry of the exhaust gases and interfere with the operation of the catalytic converter. For this reason, the disabled cylinders only recirculate their own gases, thereby reducing pumping losses without air being added to the exhaust gases flowing through the catalytic converter.

The known systems for cylinder disablement in this manner have been difficult to implement on account of the complexity of the control system required to achieve a changeover between the operating modes of the engine, that is to say with both bank firing and with only one bank firing and the other disabled. Several steps needed to be carried out simultaneously to switch over the gas flows to the second bank of cylinders.

Object of the invention The present invention seeks therefore to provide an engine in which the need to synchronise the operation of several valves during the changeover between operating modes is avoided.

Summary of the invention In accordance with the present invention, an internal combustion engine as set out above is characterised in that the means for isolating the second bank of cylinders comprises a non-return valve arranged between first and second plenum chambers of the intake manifold that lead respectively to the first and second banks of cylinders, and a first ON/OFF valve for supplying gases discharged by the second bank of cylinders to the second plenum chamber, the non-return valve closing automatically in response to the pressure difference between the two plenum chambers in order to prevent the recirculated gases from reaching the first bank of cylinders and to prevent intake air from reaching the second bank of cylinders.

In the present invention, after the ON/OFF valve supplying the recirculated gases to the second bank of cylinders has been opened, the air supply to these cylinders is automatically shut off by the ror.- eturs -.valve, which also ensures that the first bank of cylinders does not receive recirculated gases from this source. The changeover between modes therefore only requires the operation of one ON/OFF valve at the same time as modifying the fuel supply to the cylinders. In the case of an engine having a carburettor or a centre point fuel injection system, the fuel supply to the second bank of cylinders will be shut off automatically at the same time as the air, thereby further simplifying the control system.

If the operation of the first bank of cylinders is unchanged when the second bank is enabled and disabled, then there will be a sudden increase or decrease in engine output power that could prove disconcerting to the driver. It is therefore desirable, as has also been proposed previously, to provide compensating means for supplying a compensation mass air flow to the first bank of working cylinders when the second bank is disabled to avoid sudden changes in engine output power during changeover between engine operating modes.

In a preferred embodiment of the present invention, the latter compensating means comprises a throttle ganged for movement with the main throttle and arranged in a bypass passage that leads from a point upstream of the main throttle to the first plenum chamber, the bypass passage being opened and closed by a second ON/OFF valve ganged for movement with the first ON/OFF valve. In this manner, by the changeover of only one pair of ganged valves, one may ensure that the operation of the first bank of cylinders is modified to achieve a smooth transition between operating modes. In this case, the two ganged throttles should be shaped and dimensioned such that the combined flow through the two throttles is always in a fixed ratio to the flow through the main throttle alone, for all positions of the main throttle.

It is advantageous for the first ON/OFF valve to comprise a cylindrical valve having a housing with diametrically opposed ports leading to the exhaust system and the second plenum chamber, respectively, and a rotatable element having a diametric passage for connecting or isolating the two ports in dependence upon the angular position of the rotatable element within the housing. This makes for a robust and inexpensive construction. It is also possible with such a construction of the ON/OFF valve to provide in the housing a third port communicating with the bypass passage, the third port being connected to the diametric passage of the rotatable element when the latter is in the OFF position in which the first and second ports are isolated from one another, and being shut off by the rotatable element when the valve is in the ON position.By such a construction, one can avoid the risk of exhaust gases leaking past the first ON/OFF valve when the second bank of cylinders is not disabled.

Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which : Figure 1 is schematic view of an internal combustion engine of the invention operating without cylinder disablement, and Figure 2 shows the engine of Figure 1 when the second bank of cylinders is disabled.

Detailed description of the preferred embodiment In the drawings, a six cylinder internal combustion engine 10 is shown having two banks of cylinders, the first bank comprising the cylinders numbered #1 to #3, and the second bank comprising the cylinders nu-.#4 #4 to #6. All the cylinders receive intake air through a common intake manifold 12 which draws ambient air through a mass air flow meter 16 and a main throttle 18. The intake manifold 12 is divided by a non-return valve 24, preferably a reed valve as illustrated, into two plenum chambers 12a and 12b, the first of which leads to the first bank of cylinders and the second leads to the second bank of cylinders.

The exhaust system 14 of the engine is also separated for the two banks of cylinders into two streams 14a and 14b, the stream 14b being recirculated to the second plenum chamber 12b through an EGR pipe 28 and a first ON/OFF valve 26a when the second bank of cylinders is to be disabled.

A compensation passage made up of two pipes 20a and 20b leads from a point between the mass air flow meter 16 and the main throttle 18 to the first plenum chamber 12a, the passage containing a second throttle 22 that is ganged with the main throttle 18 and has a similar geometry. The compensation passage also includes a second ON/OFF valve 26b that is ganged for movement with the first ON/OFF valve 26a.

The ganged valves 26a and 26b are formed in a common housing one above the other, but they are shown side by side for ease of understanding. In the preferred embodiment, the housing is cylindrical and has a rotatable element with two diametric passages that connect or isolate diametrically opposed ports formed in the housing in dependence upon the angular position of the rotatable element. It is preferred that the valve 26a controlling the recirculation should have a third port that is connected to the passage 20a when all the cylinders are firing in the manner shown in Figure 1.

In the position of the first ON/OFF valve 26a shown in Figure 1, the plenum chamber 12b is isolated from the exhaust stream 14b. When one of the cylinders numbered #4, #5 or #6 is in its intake stroke, it crea4sse--a negative pressure in the plenum chamber 12b and air is drawn through the mass air flow meter 16, the main throttle 18 and the forward-biased reed valve 24 to meet the needs of the cylinder. At this time the compensation passage 20a is closed by the second ON/OFF valve 26b and no significant air flow bypasses the main throttle 18. The construction of the valve 26a also avoids any leakage of exhaust gases into the plenum chamber 12b because the third port connected to the compensation passage 20a acts as a buffer.This port will be under ambient pressure when the ON/OFF valves 26a and 26b are closed and there will be little tendency for exhaust gases to leak past the rotatable element because the pressures across it will be balanced. There will be a pressure difference between the third port and the second plenum chamber 12b but this would only result in an air leak which will not affect engine operation as such air leakage will also have passed through the mass air flow meter 16.

To disable or deactivate the second bank of cylinders, the only action required is to rotate the rotatable element of the ON/OFF valves 26a and 26b to the ON position. This will at the same time connect the second plenum chamber 12b to the exhaust stream 14b through the open first ON/OFF valve 26a and establish a connection between the pipes 20a and 20b of the compensation passage through the open second ON/OFF valve 26b. Because the second plenum chamber 12b will now be at exhaust pressure while the first plenum chamber 12a will be under manifold vacuum, the reed valve 24 will automatically shut to isolate the plenum chambers from one another. As shown by the shaded areas in Figure 2, this will now result in 100% recirculation of gases through the second bank of cylinders while the first bank of cylinders continues to fire.This disablement of the second bank of cylinders would, in the absence of the compensation passage, results in a drop in engine output power. However, the opening of the second ON/OFF valve 26b achieves an increased air flow to the ,Cim*s bank of cylinders in order to compensate for this effect. If the two throttles 18 and 22 are correctly matched to one another, then the changeover between operating modes will not be perceived by the driver.

Furthermore because the throttles 18 and 22 are ganged, the correct compensation air flow to the first bank of cylinders would be achieved regardless of the position of the main throttle.

When the air is shut off from the disabled bank of cylinders, it is of course essential also to shut off the fuel supply, and this can either occur automatically if the engine is centrally fuelled upstream of the main throttle, or it may be effected by disabling the individual fuel injectors in a multipoint fuel injection system. The timing of the switching off of the fuel supply is not critical as early shut off will cause recirculation mainly of air whereas late shut off will cause recirculation mainly of burnt gases. In either case, the second bank of cylinders will be deactivated with minimal pumping losses.

It is important that the gases recirculated in the second bank of cylinders should not be drawn from the exhaust gases discharged by the first bank of cylinders and it is for this reason that the exhaust system is divided into separate streams 14a and 14b. This ensures that the recirculated gases do not cause overheating of the disabled cylinders and that the exhaust gases reaching the catalytic converter are not diluted with gases from the disabled cylinders.

To reactivate the second bank of cylinders, the ganged ON/OFF valves 26a and 26b are returned to their OFF position. The reed valve 24 will open automatically to supply intake air to the second bank of cylinders enabling the cylinders to fire once again when supplied with fuel. At the same time, the compensation passage is shut off by the closed second valve 26b to avoid a sudden surge in engine output power.

Claims (6)

1. A multi-cylinder spark ignition internal combustion engine having first and second banks of cylinders supplied with intake air through a common main throttle, and disabling means for selectively disabling the second bank of cylinders, the disabling means including means for cutting off the fuel to the second bank of cylinders, means for isolating the second bank of cylinders from the intake air drawn through the main throttle, and means for recirculating all of the gases discharged by the second bank of cylinders through the second bank of cylinders in order to deactivate the cylinders in the second bank, characterised in that the means for isolating the second bank of cylinders comprises a non-return valve arranged between first and second plenum chambers of the intake manifold that lead respectively to the first and second banks of cylinders, and a first ON/OFF valve for supplying gases discharged by the second bank of cylinders to the second plenum chamber, the non-return valve closing automatically in response to the pressure difference between the two plenum chambers in order to prevent the recirculated gases from reaching the first bank of cylinders and to prevent intake air from reaching the second bank of cylinders.

2. An internal combustion engine as claimed in claim 1, further comprising compensating means for supplying a compensation mass air flow to the first bank of working cylinders when the second bank is disabled to avoid sudden changes in engine output power during changeover between engine operating modes.

3. An internal combustion engine as claimed in claim 2, wherein the compensating means comprises a throttle ganged for movement with the main throttle and arranged in a bypass passa9-e that leads from a point upstream of the main throttle to the first plenum chamber, the bypass passage being opened and closed by a second ON/OFF valve ganged for movement with the first ON/OFF valve.

4. An internal combustion engine as claimed in any preceding claim, wherein the first ON/OFF valve comprises a cylindrical valve comprising a housing with diametrically opposed ports leading to the exhaust system and the second plenum chamber, respectively, and a rotatable element having a diametric passage for connecting or isolating the two ports in dependence upon the angular position of the rotatable element within the housing.

5. An internal combustion engine as claimed in claims 3 and 4, further comprising a third port in the valve housing communicating with the bypass passage, the third port being connected to the diametric passage of the rotatable element when the latter is in the OFF position in which the first and second ports are isolated from one another, and being shut off by the rotatable element when the valve is in the ON position.

6. An internal combustion engine constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.