GB2540929A

GB2540929A - Ignition cut

Info

Publication number: GB2540929A
Application number: GB1511481.2A
Authority: GB
Inventors: Bizzarri Davide; Gentili Maicol
Original assignee: McLaren Automotive Ltd
Current assignee: McLaren Automotive Ltd
Priority date: 2015-06-30
Filing date: 2015-06-30
Publication date: 2017-02-08
Anticipated expiration: 2035-06-30
Also published as: GB201511481D0; GB2540929B

Abstract

A vehicle comprising a spark-ignited internal combustion engine for igniting a combustion mixture, an exhaust system 103 comprising a catalytic converter 105, and an engine control system 113 configured to identify a demand for a reduction in engine torque and in response interrupt sparking of the internal combustion engine for a period of time, the engine control system being configured to limit the sparking interruption so as to maintain the temperature of the catalytic converter below a predetermined temperature by preventing the expulsion of excess amounts of unburnt combustion mixture to the exhaust system, thereby preventing the thermal degradation of the catalytic converter.

Description

IGNITION CUT

This invention relates to the ignition cut of a spark-ignited internal combustion engine of a vehicle. A typical road vehicle comprises an internal combustion engine (ICE) that is spark-ignited to generate an engine torque. An output shaft of the engine can be coupled to a driveshaft of the vehicle (typically through a transmission) to transmit the enginegenerated torque to the driveshaft to drive the wheels of the vehicle. When operating such a vehicle there is often a need to momentarily reduce the engine torque, for example when changing gears, or within a traction control system in order to prevent the engine generating more torque than can be transmitted to the road by the tyres under particular current operating conditions.

One approach to reducing the torque generated by an ICE is to perform an injection cut which is a type of fuel cut to the engine. An injection cut cuts the fuel supply to the combustion chambers of the engine. This may be done, for example, by maintaining the valves of the fuel injectors in a shut, or closed, position so that fuel is not injected into the intake manifold of the vehicle, or into the combustion chamber in the case of direct fuel injection. Although injection cutting is effective at reducing the engine torque, it can have the drawback of suffering from undue delay, or lag from when torque reduction is desired to when the torque is actually reduced. This is because it is typically not possible to interrupt an injection that has already started and thus a requested injection cut may not be able to be implemented (and hence torque reduction cannot occur) until the time of the next injection. This problem may be compounded by the fact that in the case of port fuel injection, the injection phase may be relatively long. Injection cutting may also suffer from a similar problem of undue delay when it is desired to increase the engine torque again. This is because upon resuming the fuel supply, it may take up to an engine cycle, or longer, before the fuel is transferred to the cylinders of the engine from where the injectors supply the fuel. This time delay can make the torque response of the engine slower than desired which may limit the performance of the vehicle.

It would therefore be desirable for there to be an improved way to control the engine torque for a vehicle.

According to one aspect of the present invention there is provided a vehicle comprising: a spark-ignited internal combustion engine for igniting a combustion mixture; an exhaust system arranged to convey exhaust gases and residual combustion mixture from the internal combustion engine, the exhaust system comprising a catalytic converter; and an engine control system configured to identify a demand for a reduction in engine torque and in response interrupt sparking of the internal combustion engine for a period of time, the engine control system being configured to limit the sparking interruption so as to maintain the temperature of the catalytic converter below a predetermined temperature.

The predetermined temperature may be selected in relation to thermal degradation of the catalytic converter.

The predetermined temperature may be such that maintaining the temperature of the catalytic converter thereunder prevents thermal degradation of the catalytic converter.

The internal combustion engine may be configured to, during the sparking interruption, expel unburnt combustion mixture into the exhaust system.

The engine control system may be configured to limit the sparking interruption to a period of time less than a maximum time.

The maximum time may be selected in relation to thermal degradation of the catalytic converter.

The engine control system may be configured to interrupt the sparking of the internal combustion engine for a period of time that is dependent on the richness of the combustion mixture to be ignited.

The engine control system may be configured to interrupt the sparking of the internal combustion engine for a period of time that is dependent on the richness of the combustion mixture to be ignited, up to a maximum time.

The internal combustion engine may comprises at least one combustion chamber configured to receive an injection of combustion mixture, and the maximum time may be calculated in dependence on the volume of the combustion chamber(s) of the internal combustion engine and the flow rate of combustion mixture injected into the combustion chamber(s) during a sparking interruption.

The maximum time may be a predetermined maximum time.

The engine control system may be configured to override interruption of the sparking of the internal combustion engine if, when the demand for reduction in engine torque is identified, the combustion mixture to be ignited has a richness less than a predetermined value.

The vehicle may comprise a transmission coupled to the internal combustion engine, the transmission comprising a plurality of gears, defining a plurality of gear ratios between an output shaft of the internal combustion engine and a driveshaft of the vehicle, and the transmission may configured to select gear ratios for coupling the internal combustion engine to a driveshaft of the vehicle, and the engine control system may be configured to identify a demand for a reduction in engine torque in response to a demand for the transmission to select a gear ratio.

The engine control system may be configured to interrupt the sparking of the internal combustion engine for a period of time sufficient to reduce the engine torque to enable selection of the new gear ratio.

The engine control system may be configured to interrupt the sparking of the internal combustion engine to sufficiently reduce the engine torque to enable selection of the new gear ratio, the spark interruption causing the engine torque to be sufficiently reduced within said period of time that maintains the temperature of the catalytic converter below the predetermined temperature.

The internal combustion engine may be configured to ignite a combustion mixture comprising fuel, the engine control system being further configured to cut injection of fuel into the internal combustion engine in response to identifying a demand for a reduction in engine torque, and to resume injection of fuel prior to the end of the period of time in which sparking of the internal combustion engine is interrupted.

The present disclosure will now be described by way of example with reference to the accompanying drawings. In the drawings:

Figure 1 shows a schematic drawing of components used to drive a vehicle.

Figure 2 shows a schematic illustration of torque response times for spark interruption and injection cutting.

Figure 3 shows a graph of the temperature of a catalytic converter following a series of spark interruptions.

Figure 4 shows a time profile of engine torque for spark interruption and injection cutting.

The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art.

The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

The present disclosure relates to a vehicle comprising an engine control system that is configured to reduce engine torque generated by an internal combustion engine of the vehicle for a given period of time. The vehicle may be an automobile. An internal combustion engine to which the principles described herein apply is not limited in its configuration or fuel type, and could be a straight, flat or V-engine having any number of cylinders and running of any fuel, including petrol, diesel and ethanol. The internal combustion engine may be part of a hybrid drive system for the vehicle where the vehicle comprises one or more electrical machines and an internal combustion engine that can separately and/or in combination drive the vehicle.

Figure 1 shows a schematic diagram of components of a vehicle. The vehicle comprises a spark-ignited internal combustion engine (ICE), indicated generally at 101. The ICE is coupled to an exhaust system indicated generally at 103 that comprises a catalytic converter 105. The exhaust system is arranged to convey exhaust gases and residual combustion mixture from the internal combustion engine to a point exterior of the vehicle.

The ICE is further coupled to a transmission 107 which comprises a plurality of gears (not shown) for coupling a crankshaft 109 of the engine to a driveshaft 111 for driving the wheels of the vehicle. The vehicle further comprises an engine control system 113 and optionally a traction control system 115.

The spark-ignited internal combustion engine comprises a plurality of cylinders 117, each comprising a piston configured to undergo reciprocal motion within a combustion chamber having a volume Vcc. Each piston is coupled at one its ends to the crankshaft 109 via a connecting rod. Each cylinder is connected to an intake port 119 for receiving a combustion mixture to be ignited. In the event the engine is a direct-fuel injection engine, the intake port may receive only air, with the fuel being injected directly into the combustion chamber by a fuel injector. The intake port may be connected to an intake manifold (not shown). The intake manifold is configured to distribute a fuel/air mixture (a combustion mixture) to each cylinder of the engine via the respective intake ports. The intake manifold may be configured to distribute air to each cylinder of the engine in the case of the engine using a type of fuel injection which injects the fuel close to the intake ports of the cylinder. The vehicle may be configured to inject fuel into the intake manifold (known as single point injection or central point injection). The vehicle may alternatively inject fuel into each intake port upstream of an intake valve (known as multi-port injection).

Each cylinder is further connected to an exhaust port 121 to allow the expulsion of exhaust gases and residual combustion mixture from the combustion chamber. In alternative examples each cylinder may be connected to more than one exhaust port. Each exhaust port is connected to an exhaust manifold 123. The exhaust manifold is connected to an exhaust pipe 125. More than one exhaust port may be connected to a single exhaust manifold. In the example shown the exhaust pipe is shown in a Ύ’ arrangement, though it will be understood that other configurations are equally possible. The exhaust pipe is connected to the catalytic converter. The exhaust pipe is configured to channel exhaust gases from the exhaust manifold into the catalytic converter. The vehicle may comprise more than one exhaust manifold and/or exhaust pipe. The vehicle may for example comprise one exhaust manifold and/or exhaust pipe per each bank of cylinders.

The vehicle may comprise more than one catalytic converter. For example, if the cylinders of the engine were arranged into multiple cylinder banks, a V-configuration for example, the vehicle may comprise one catalytic converter per each bank of cylinders. If the vehicle comprises more than one catalytic converter, the vehicle may comprise an exhaust pipe per each converter, and/or per bank of cylinders.

The or each catalytic converter 105 may be further connected to a tail pipe 127. The tail pipe is configured to convey exhaust gases that have passed through the catalytic converter to a point exterior of the vehicle. The vehicle may comprise one or more tail pipes depending on the number of catalytic converters and the cylinder arrangement of the engine. Each of the exhaust port, exhaust manifold, exhaust pipe, catalytic converter and tail pipe may be comprised within the exhaust system 103.

An intake valve (not shown) may be housed within each intake port to control the flow of combustion mixture into the combustion chamber. Similarly, an exhaust valve may be housed within each exhaust port to control the flow of exhaust gases and residual or unburnt combustion mixture out from the combustion chamber through the exhaust system. Each intake port may house more than one intake valve. Each exhaust port may house more than exhaust valve. In alternative examples to that shown in figure 1, each cylinder of the ICE may be connected to more than intake port and/or more than one exhaust port.

When the internal combustion engine is running, the engine may typically perform a four-stroke combustion cycle. The combustion cycle converts the reciprocal motion of each cylinder piston into a rotary motion of an output shaft of the engine. The rotary motion of the engine output shaft can be coupled to the driveshaft of the vehicle via the vehicle’s transmission. The four-stroke combustion cycle is made up of the following strokes: the intake stroke, the compression stroke, the combustion stroke and the exhaust stroke. A description of each stage of the four-stroke combustion cycle will now be made with reference to a single cylinder. The other cylinders operate in a corresponding fashion, generally with an offset in the sequence of the strokes between each of the cylinders. Such an offset may mean that whilst one cylinder is undergoing a combustion stroke another is undergoing an exhaust stroke.

During the intake stroke the intake valve within the intake port is opened to permit the piston to draw fuel into the combustion chamber of the cylinder. When the intake valve is opened the piston may be positioned at or near its highest position within the combustion chamber. The highest position of the piston may be referred to as the top-dead-centre. The piston may then move down within the combustion chamber during the intake stroke to increase the volume of the air-fuel mixture within the chamber. At the end of the intake stroke the intake valve within the intake port is closed to prevent further fuel from being drawn into the cylinder. The intake valve may be closed when the piston is at or near the bottom of the chamber. The valve timings of the intake valve may be altered to affect the performance of the ICE. For example the timing of the intake valve opening can be made earlier or later with respect to the position of the piston within the cylinder. Similarly, the timing of the intake valve closing can be made earlier or later with respect to the position of the piston within the cylinder.

In the compression stroke the piston moves up towards the top of the chamber to compress the combustion mixture within the combustion chamber.

During the combustion stroke the (compressed) combustion mixture is ignited. The ignition of the combustion mixture drives the piston downwards within the combustion chamber. In typical gasoline engines the combustion mixture is ignited by a spark. The use of such a spark to ignite the combustion mixture within the cylinder chambers of the engine is referred to as sparking of the ICE. An ICE that ignites a combustion mixture in this manner may be referred to as a spark-ignited internal combustion engine. Each cylinder of the engine may comprise a spark plug or a glow-plug for producing the spark to ignite the combustion mixture. A spark plug may comprise a central electrode and a lateral electrode spaced from the central electrode. To fire the spark plug a potential difference is applied between the electrodes. When the potential difference exceeds a threshold, the gas between the electrodes becomes ionized and a current flows or arcs between the electrodes. This current flow generates the spark that arcs between the electrodes. The time at which the spark plug generates the spark is referred to as the spark timing. The spark timing for each cylinder may be variably controlled to alter the performance of the ICE. The spark timing may for example be advanced or retarded with respect to the top-dead centre position of the piston. The spark timing is said to be advanced if the spark is generated before the piston reaches top-dead centre and retarded if the spark is generated after the piston reaches top-dead centre.

The engine may be sparked according to a firing order of the engine. For example, for an engine comprising a plurality of cylinders, each cylinder may be sparked at a sequential point in time. Alternatively, pairs of cylinders are sparked at sequential points in time (i.e. cylinders within a given pair have the same spark timing). The firing order is the order in which the engine’s cylinders are sparked. The sparking of each of the engine’s cylinders according to the firing order may be referred to as a firing cycle.

The final stroke in the combustion cycle is the exhaust cycle. During the exhaust cycle the exhaust valve in the exhaust port opens to allow the expulsion of exhaust gases and/or unburnt fuel from the chamber. Exhaust gases and/or unburnt fuel expelled from the chamber are passed through the exhaust manifold and exhaust pipe into the catalytic converter(s) as described above. The exhaust valve may be opened when the piston reaches its lowest position within the chamber (referred to as bottom dead centre) following the combustion stroke. The exhaust valve opening and closing timing may be variably controlled. For example the opening timing may be advanced or retarded with respect to the bottom dead centre position of the piston.

Sparking of the internal combustion engine may be controlled by the engine control system 113. The engine control system may control the spark timing of the engine. The ECS may optionally control the valve timings of the intake valve and/or exhaust valve. The ECS may be configured to determine the fuel/air ratio (i.e. the richness) of the combustion mixture. For example, the ECS may be configured to receive readings from an air-fuel meter such as a lambda sensor. The ECS may be configured to control the injection of fuel into the engine. For example, the ECS may vary the flow-rate of fuel injected in dependence on a reading from the lambda sensor. In certain conditions, the ECS may be configured to cut the injection of fuel into the engine, as will be described in more detail below.

The traction control system (TCS) 115 is configured to attempt to prevent the loss of traction of the vehicle wheels during driving of the vehicle. This may be with the aim of improving the driveability and performance of the vehicle and/or improving the safety of the vehicle. The TCS may be configured to determine if the level of engine torque being generated is on the limit of causing the vehicle’s tyres to slip, or that the current torque has initiated tyre slippage, and if so to limit the power delivery to the vehicle wheels.

The TCS and the ECS may be in the form of electronic control units. They may be programmable. Although the ECS and TCS are shown as discrete components, this is for the purpose of illustration only and both the ECS and TCS may form part of, or be under the control of, a single control unit such as a vehicle management system.

In certain operating conditions of the vehicle there may be a demand to reduce the engine torque generated by the ICE. For example, the TCS may determine that the current level of engine torque exceeds the grip levels afforded by the tyres and is causing, or is on the limit of causing, tyre slippage. The demand for a reduction in engine torque may be in response to a demand for selection of a new gear by the transmission. The demand for a new gear may come from the driver of the vehicle.

The driver may indicate the demand for the selection of a new gear by actuating a gear-selecting mechanism such as a paddle shifter, or button. A gearbox control system may be configured to, in response to the driver actuating the gear-selecting mechanism, generate a control signal that is transmitted to the ECS. This control signal can be indicative of the driver request to change gear. Alternatively, the demand for the selection of a new gear may come from the gearbox control system automatically (i.e. without a direct request from the driver). The gearbox control system may generate the control signal automatically if the transmission were an automatic transmission, or a transmission operating in an automatic mode. As an example, the gearbox control system may transmit a control signal to the ECS automatically in response to the rpm of the engine dropping below a certain value caused by a driver lifting his or her foot off the throttle pedal. The ECS may be configured to identify the demand for the reduction in engine torque from the control signal.

As described herein, the engine control system of the vehicle is configured to identify a demand for a reduction in engine torque, and in response to that demand interrupt sparking of the internal combustion engine for a period of time. During the sparking interruption, combustion mixture present in the cylinders of the engine is not ignited by the spark plug but instead is expelled into the exhaust system. This reduces the torque produced by the ICE. The engine control system is further configured to limit the sparking interruption so as to maintain the temperature of the catalytic converter below a predetermined temperature.

Conventionally, reducing engine torque by spark interruption has been confined to race cars and has not been used in vehicles comprising a catalytic converter. This is because of the damage caused to the catalytic converter known to be caused by expelling unburnt combustion mixture through the exhaust system. The unburnt mixture can be ignited by the temperature of the exhaust which can cause thermal degradation of the catalytic converter. However, the inventors have found that by configuring the engine control system to limit the sparking interruption, the temperature of the catalyst can be maintained below a predetermined temperature that prevents thermal degradation of the catalytic converter.

Interrupting the sparking of the internal combustion engine to reduce the engine torque reduces the time required to cut the engine torque to a demanded lower value compared to using injection cutting alone. It also reduces the time required to increase the engine torque to a target value following a torque cut compared to using injection cutting alone. The time required to reduce the engine torque to a demanded lower value or the time required to increase the torque to a target value following a torque cut may be referred to as a torque-response time. The torque-response time associated with reducing the engine torque may be different from the torque-response time associated with increasing the engine torque following a torque cut.

Figure 2 is a schematic diagram of the spark timing of an ICE with eight cylinders.

In figure 2, time is shown on the x-axis 201. Markings, shown generally at 203, illustrate the spark timings of each of the cylinders of the engine. Each cylinder is labelled with a reference numeral 1-8. In this example the engine is operating at 4000rpm, and so the time interval T between successive spark timings is approximately 3.75ms. Arrows 205 and 207 denote the torque response time following an injection cut and an ignition cut respectively. Each of the ignition cut and injection cut occurred up until time t=0. The response times 205 and 207 denote the time for the engine torque to reach the target engine torque (for the given engine speed of 4000rpm) following the end of an injection cut and ignition cut respectively.

Following a spark interruption, the generation of engine torque can be resumed at the next available spark time by simply resuming sparking of the ICE according to the firing order. Because the fuel supply to the engine was not cut during the spark interruption, the generation of engine torque can be resumed by sparking the next cylinder in the firing order. The response time for spark interruption is therefore approximately bounded by the time interval between successive ignition timings. In the example shown in figure 2, this corresponds to a response time of approximately 3.75ms.

In contrast, following an injection cut the generation of engine torque is not resumed until fuel is re-introduced into the internal combustion engine. The engine rotation during the interval between the end of an injection cut and the resumption of the production of engine torque is referred to as the injection arc. The inventors have found that for an eight-cylinder engine with a speed of 4000rpm, the injection arc is approximately 700 degrees, which corresponds to a time of approximately 30ms. The response time for spark interruption is therefore substantially less than that for injection cutting. The use of spark interruption to reduce engine torque can therefore lead to a vehicle with an improved torque response.

The ECS 113 is configured to limit the spark interruption to maintain the temperature of the catalyst below a predetermined temperature. The predetermined temperature may be programmable. It may be selected in relation to the thermal degradation of the catalytic converter used in the vehicle. For example, the predetermined temperature may correspond to a maximum operating temperature of the catalytic converter. The maximum operating temperature may be a temperature above which thermal damage to the converter can, or is likely to, occur. Alternatively the predetermined temperature may be a safe operating temperature below that of the maximum operating temperature of the catalytic converter. The safe operating temperature may be a temperature at which the working life of the catalytic converter is extended compared to the maximum operating temperature due to the lower temperature. Keeping the temperature of the catalytic converter below the safe operating temperature may further mitigate the risk of damaging the converter. In any event, the predetermined temperature is such that maintaining the temperature of the catalytic converter below the predetermined temperature prevents thermal degradation of the converter.

The ECS may be configured to only interrupt the sparking of the internal combustion engine in response to a demand for a reduction in engine torque if the richness of the combustion mixture is above a predetermined value. That is, the ECS may be configured to only interrupt sparking of the ICE when the vehicle is running under operating conditions such that the engine is running a rich mixture. By limiting the spark interruption to operating conditions of the vehicle in which the combustion mixture is sufficiently rich (i.e. the fuel-to-air ratio is above a predetermined value), the temperature of the catalytic converter can be maintained below the predetermined temperature. This is because a sufficiently rich mixture does not burn as efficiently within the exhaust system (and therefore does not give out as much heat) because of the reduced oxygen content. The fuel itself may also provide a cooling effect within the exhaust system due to the effects of liquid cooling.

If the richness of the combustion mixture is less than the predetermined value, the ECS could override the spark interruption of the engine when a demand for the reduction in engine torque is identified. For example, the ECS could be configured to determine the richness of the combustion mixture upon identifying a demand for a reduction in torque. If the richness is above the predetermined value, the ECS proceeds to interrupt the sparking of the ICE; if the richness is below the predetermined value, the ECS overrides the spark interruption.

The ECS may determine the richness of the combustion mixture from an air-fuel meter such as a lambda sensor. The predetermined richness of the mixture could be selected in dependence on the properties of the catalytic converter. For example, the higher the maximum operating temperature of the converter before it suffers thermal degradation, the lower the predetermined richness value may be. This is because a lower richness mixture may burn more efficiently in the exhaust system due to the increased oxygen content (and thus give out more heat), compared to a richer mixture. Conversely, the lower the maximum operating temperature of the catalytic converter before it suffers thermal degradation, the higher the predetermined richness may be. The predetermined richness of the combustion mixture required for spark interruption may be programmable in the ECS.

The ECS may be configured to determine the period of time for which the sparking of the internal combustion engine is interrupted in dependence on the richness of the combustion mixture. For example, the richer the mixture, the longer the period of time for which sparking of the engine can be interrupted whilst maintaining the temperature of the catalytic converter below the predetermined temperature. This is because a richer mixture will not burn as efficiently (and therefore not give out as much heat) in the exhaust system because of the reduced oxygen content. Conversely, the closer the richness of the mixture is to the predetermined value, the shorter the period of time for which sparking is interrupted. The ECS may determine the period of time of the sparking interruption using a mapping that maps the time duration to various values of combustion mixture richness.

The ECS may be configured to limit the sparking interruption to a period of time less than a maximum time. The maximum time may be programmable. The maximum time may be a predetermined maximum time or it may be calculated by the ECS as a function of operating conditions of the vehicle and/or the vehicle’s parameters. The maximum time could be independent of the richness of the mixture at the time the demand for engine torque reduction was identified. It may for example be a predetermined value. Alternatively the maximum time could be selected in dependence on one more inputs, or parameters, alone or in combination. The maximum time may be selected in relation to thermal degradation of the catalytic converter used in the vehicle. The maximum time may be selected so that limiting the spark interruption to a period of time less than the maximum time maintains the temperature of the catalytic converter below the predetermined temperature. The maximum time may be approximately 100ms, for example.

One input used to select the maximum time may for example be the maximum operating temperature of the catalyst, or the safe operating temperature of the catalyst. Another input may be the richness of the fuel mixture. Thus the maximum time may be calculated in dependence on: i) the safe operating temperature of the catalyst; and ii) the richness of the fuel mixture at the time the demand for torque reduction was identified. Another input could be the volume of the combustion chamber and the injection flow rate of combustion mixture (that is, the flow rate of combustion mixture into the cylinders). The ECS may calculate the maximum time in dependence on the volume of the combustion chamber(s) and the injection flow rate to inhibit, or prevent, damage to the engine, e.g. damage caused by hydraulic lock of the piston. Hydraulic lock of the piston may occur due to the accumulation of combustion mixture within the chamber during the ignition cut. That is, combustion mixture may accrue within the chambers during the period of ignition cut because the mixture is not being fully expelled during the downward stroke of the piston as that stroke is no longer being driven by ignition and/or because the mixture is not being ignited by the engine using a spark. If the volume of mixture within the chamber becomes too great, the compression of the mixture during the compression stroke may damage the engine. The ECS may be configured to calculate the injection flow rate from the pressure of the injection rail/nozzle. Alternatively the ECS may calculate the volume of combustion mixture injected during a sparking interruption and use that value, in combination with the chamber volume, to calculate the maximum time. The volume of mixture may be calculated from the duration of the sparking interruption and from the pressure of the injection rail/nozzle.

The ECS may be configured to, in response to identifying a demand for a reduction in engine torque, interrupt the sparking of the internal combustion engine for a period of time if the richness of the combustion mixture is above a predetermined threshold, and to limit the period of time to be less than or equal to the maximum time. That is, once the ignition has been cut for a period of time equal to the maximum time, the ECS may resume sparking of the engine. The ECS may be configured to identify a demand for a reduction in engine torque by, for example, receiving an input from a TCS or receiving a control signal in response to a driver-requested gear change. The inventors have found that limiting the spark interruption to: i) a period of time less than a maximum time of 100ms; and ii) to operating conditions of the vehicle in which the richness of the combustion mixture is above a predetermined value, is a particularly effective way of controlling the temperature of the catalytic converter. Specifically, it was found during one experiment that limiting the spark interruption to when the air-fuel equivalence ratio λ (which is the ratio of the air-fuel ratio (APR) to the stoichiometric APR for that fuel (APRstoich)) is less than 0.85 and to a time of less than 100ms resulted in a minimal temperature increase of the catalyst.

As an illustration, figure 3 shows the results of an experiment in which the temperature of the catalyst was measured following ignition cuts for a duration of 90ms. The x-axis of the graph indicates time. The left-most y-axis indicates the temperature of the catalyst, measured in degrees Celsius.

Measurement results 301 chart the engine rpm. The periodic spike drops are indicative of respective ignition cuts. In particular, each spike drop is indicative of the complete ignition cut for all cylinders of the engine (in this experiment the engine had eight cylinders). It can be seen from the sharpness of the spikes that controlling the spark interruption enables the engine to have a highly responsive rpm (and thus torque) response. Measurement results 303 and 305 chart the temperature of two catalytic converters coupled to the cylinders in which the ignition is cut. It can be seen that limiting the spark interruption to a period of time of less than 100ms when the ICE is running a rich combustion mixture unexpectedly causes no discernible temperature rise in the catalytic converter. This is particularly unexpected given the conditions of the experiment in which all eight cylinders of the engine were subjected to ignition cut for the duration of 90ms. It is therefore possible to interrupt the sparking of an internal combustion engine without damaging the vehicle’s catalytic converter. This can enhance the vehicle’s torque response compared to other methods of engine torque reduction, such as injection cutting.

The ECS is configured to interrupt the sparking of the ICE in response to identifying a demand for a reduction in engine torque. In one example the ECS is configured to identify a demand for a reduction in engine torque in response to a demand for selection of a new gear by the transmission. The demand for a new gear may be made by the driver of the vehicle, automatically by the transmission or by a gearbox control system, as described above.

In one example, the demand for a reduction in engine torque is in response to a request for selection of a higher gear, i.e. an upshift. It may be desirable to reduce the engine torque in response to a demand for an upshift in order to facilitate rev matching. Rev matching is the process of matching the engine rotation speed with the rotation speed of the driveshaft during a gear change. During an upshift, rev matching requires that the engine rotation speed be reduced. This is because an upshift requires the output shaft of the engine to be coupled to the driveshaft via a larger gear connected to the output shaft of the engine. Since the rotation speed of the driveshaft remains largely constant during the gear change, selecting a larger gear connected to the output shaft of the engine requires that the rotation speed of the output shaft of the engine be reduced. The coupling of the engine to the driveshaft may be via a gearbox which comprises a plurality of gear ratios between the output shaft of the engine and the driveshaft. In this case, an upshift requires the output shaft of the engine to be coupled to the driveshaft using a higher gear ratio than before the upshift. The transmission may comprise at least one clutch disposed between the output shaft of the internal combustion engine and the drive shaft. The at least one clutch may be configured to engage or disengage a torque path via gears of the transmission. The ECS may therefore be configured to interrupt the sparking of the engine to reduce the engine speed to facilitate rev matching in response to a demand for an upshift.

As has been discussed above, the duration of the spark interruption may be limited to maintain the temperature of the catalyst below a predetermined temperature. This may limit the utility of spark interruption as a means of reducing engine torque. However, using spark interruption to reduce engine torque may be particularly useful in facilitating fast gear changes in race cars or high performance road cars, for example during an upshift as described in the above example. Configuring the ECS 113 to interrupt the sparking of the ICE enables the torque to be changed sufficiently quickly (i.e. the torque response times are sufficiently short) to enable a gear change to be completed within the period of time for which the sparking was interrupted. This has the advantage of allowing a gear change to be completed within a period of time that would be difficult to achieve without the use of spark interruption. The use of spark interruption in conjunction with a request for a selection of a new gear may therefore provide a synergistic effect of increased gear change speeds that would be difficult to achieve without the use of spark interruption.

The ECS may be configured to interrupt the sparking of the engine for a period of time dependent on the current gear selected by the transmission and on the requested new gear. In this way the ECS can take account of the different engine-torque reduction requirements for different gear change patterns. For example, a gear change from second gear to fourth gear would require a greater reduction in engine rotation speed (and thus a longer spark interruption) for the purposes of rev matching compared to a change from second gear to third gear.

Alternatively the period of time of the spark interruption may be dependent on: i) the rotation speed of the engine at the time the demand for the reduction in engine torque is identified, and ii) the engine speed associated with the requested new gear. This might enable more accurate rev matching by taking into account the band of possible engine speeds at the time of a demand for selection of a new gear. For example, the driver may request an upshift when the engine is at the rev limit or at a range of engine speeds below the rev limit.

In an alternative embodiment, the ECS may be configured to identify a demand for a reduction in engine torque from a traction control system (TCS) of the vehicle. The TCS could be configured to detect when tyre slippage occurs, or when the vehicle is operating at or near the grip limit afforded by the tyres. Upon detecting this condition, the TCS could send a demand for a reduction in torque to the ECS. In response, the ECS could interrupt the sparking of the engine to reduce the engine torque to thereby prevent the vehicle from losing grip.

In the examples described above the injection of fuel into the ICE is maintained during the spark interruption. However in each of these examples the ECS may be further configured to cut the injection of fuel into the ICE during the period of time in which sparking of the ICE is interrupted. The injection may then be resumed prior to the end of the period of time in which the sparking is interrupted. The use of injection cutting in conjunction with spark interruption may lead in increases in fuel efficiency due to the reduction in the expulsion of unburnt combustion mixture through the exhaust system during the spark interruption. Limiting the expulsion of combustion mixture through the exhaust system may also further minimise the temperature increase of the catalytic converter.

The ECS may resume the fuel injection prior to the end of the spark interruption to conveniently take into account the time lag required to re-introduce fuel into the ICE following an injection cut. In this way, fuel will be reintroduced into the ICE by the time sparking of the engine is resumed, and thus the injection cut will not affect the torque response time of the engine.

Figure 4 is a schematic diagram illustrating how injection cutting may be used in conjunction with spark interruption. Profile 401 shows the engine torque for a spark interruption of 100ms initiated at time Ta. Profile 403 shows the engine torque for an injection cut. The troughs 405 and 407 of profiles 401 and 403 indicate the reduction in engine torque during spark interruption and injection cutting respectively. If the injection cut were also initiated at time Ta or a short time thereafter, the engine torque would be reduced after a time Tb, which corresponds to the time required for the remaining fuel to be passed through the engine. As an example, for an engine with eight cylinders running at 4000rpm, Tb may be approximately 30ms. The sparking of the engine is interrupted until a time Tc. In order for fuel to be injected into the engine by time Tc following the fuel cut, it is necessary to resume fuel injection at a time Td, which is before Tc. For an eight cylinder engine running at 4000rpm, the time delta Tc-Td could be approximately 30ms.

Although the engine torque profiles for spark interruption and injection cutting have been described separately with reference to figure 4, it can be seen from these profiles that performing spark interruption in combination with injection cutting provides a period of time Te (in this example about 40ms) in which no unburnt combustion mixture is expelled from the engine during the spark interruption. It can further be seen that by resuming the fuel injection at a suitable time before the end of the spark interruption (in this example at or before time Td), fuel can be input into the engine in advance of the resumption of engine sparking. Performing the injection cut in combination with the spark interruption in this manner therefore does not adversely affect the torque response of the engine compared to using spark interruption alone, yet may provide advantages in fuel economy.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1. A vehicle comprising: a spark-ignited internal combustion engine for igniting a combustion mixture; an exhaust system arranged to convey exhaust gases and residual combustion mixture from the internal combustion engine, the exhaust system comprising a catalytic converter; and an engine control system configured to identify a demand for a reduction in engine torque and in response interrupt sparking of the internal combustion engine for a period of time, the engine control system being configured to limit the sparking interruption so as to maintain the temperature of the catalytic converter below a predetermined temperature.

2. A vehicle as claimed in claim 1, wherein the predetermined temperature is selected in relation to thermal degradation of the catalytic converter.

3. A vehicle as claimed in claim 2, wherein the predetermined temperature is such that maintaining the temperature of the catalytic converter thereunder prevents thermal degradation of the catalytic converter.

4. A vehicle as claimed in any preceding claim, wherein the internal combustion engine is configured to, during the sparking interruption, expel unburnt combustion mixture into the exhaust system.

5. A vehicle as claimed in any preceding claim, wherein the engine control system is configured to limit the sparking interruption to a period of time less than a maximum time.

6. A vehicle as claimed in claim 5, wherein the maximum time is selected in relation to thermal degradation of the catalytic converter.

7. A vehicle as claimed in any preceding claim, wherein the engine control system is configured to interrupt the sparking of the internal combustion engine for a period of time that is dependent on the richness of the combustion mixture to be ignited.

8. A vehicle as claimed in claim 7, wherein the engine control system is configured to interrupt the sparking of the internal combustion engine for a period of time that is dependent on the richness of the combustion mixture to be ignited, up to a maximum time.

9. A vehicle as claimed in claim any of claims 5 to 8, wherein the internal combustion engine comprises at least one combustion chamber configured to receive an injection of combustion mixture, and wherein the maximum time is calculated in dependence on the volume of the combustion chamber(s) of the internal combustion engine and the flow rate of combustion mixture injected into the combustion chamber(s) during a sparking interruption.

10. A vehicle as claimed in claims 5 to 8, wherein the maximum time is a predetermined maximum time.

11. A vehicle as claimed in any preceding claim, wherein the engine control system is configured to override interruption of the sparking of the internal combustion engine if, when the demand for reduction in engine torque is identified, the combustion mixture to be ignited has a richness less than a predetermined value.

12. A vehicle as claimed in any preceding claim, the vehicle comprising a transmission coupled to the internal combustion engine, the transmission comprising a plurality of gears, defining a plurality of gear ratios between an output shaft of the internal combustion engine and a driveshaft of the vehicle, the transmission being configured to select gear ratios for coupling the internal combustion engine to a driveshaft of the vehicle, and wherein the engine control system is configured to identify a demand for a reduction in engine torque in response to a demand for the transmission to select a gear ratio.

13. A vehicle as claimed in claim 12, wherein the engine control system is configured to interrupt the sparking of the internal combustion engine for a period of time sufficient to reduce the engine torque to enable selection of the new gear ratio.

14. A vehicle as claimed in claim 12 or 13, wherein the engine control system is configured to interrupt the sparking of the internal combustion engine to sufficiently reduce the engine torque to enable selection of the new gear ratio, the spark interruption causing the engine torque to be sufficiently reduced within said period of time that maintains the temperature of the catalytic converter below the predetermined temperature.

15. A vehicle as claimed in any preceding claim, wherein the internal combustion engine is configured to ignite a combustion mixture comprising fuel, the engine control system being further configured to cut injection of fuel into the internal combustion engine in response to identifying a demand for a reduction in engine torque, and to resume injection of fuel prior to the end of the period of time in which sparking of the internal combustion engine is interrupted.

16. A vehicle substantially as described herein with reference to the accompanying drawings.