GB2584427A

GB2584427A - Controller for a vehicle internal combustion engine

Info

Publication number: GB2584427A
Application number: GB1907534.0A
Authority: GB
Inventors: Brockley Nick; Brown Alan; Ross Akister Sigmund
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2019-05-29
Filing date: 2019-05-29
Publication date: 2020-12-09
Anticipated expiration: 2039-05-29
Also published as: GB2584427B; GB201907534D0; DE102020113703A1

Abstract

Disclosed is a controller 14 for a vehicle internal combustion engine 12 operable in a catalyst heating mode. The controller receives in input including a drive torque request, e.g. a driver-demanded drive torque, and a measurement of actual mass airflow into the engine. The controller determines a required engine ignition efficiency value based on the received torque request and actual air mass, and defines an actual engine ignition efficiency value to be the minimum of the required engine ignition efficiency value and a threshold maximum engine ignition efficiency value. The controller determines an ignition timing to be applied to the engine based on the determined actual engine ignition efficiency value, and controls the engine to operate in accordance with the applied engine ignition timing when the engine is operating in the catalyst heating mode. An associated method of controlling an internal combustion engine is also disclosed. The invention ensures that when a high torque demand is present during a catalyst heating event the engine is not so efficient that it cannot provide the required heat to the catalyst.

Description

CONTROLLER FOR A VEHICLE INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a controller for a vehicle internal combustion engine and in particular, but not exclusively, to a controller for a vehicle internal combustion engine operable in a catalyst heating mode. Aspects of the invention relate to a controller, to a vehicle, to a method and to a non-transitory, computer-readable storage medium.

BACKGROUND

In vehicles, e.g. a car, having internal combustion engines it is known to provide a catalytic converter having a catalyst for reducing toxic gases and pollutants in exhaust gas from the engine by catalysing oxidation and reduction reactions. A catalytic converter must be warmed to an operating temperature, typically 400 to 600 degrees Celsius, to be fully effective. This means that, in the event of a cold engine start, there is a period prior to the catalytic converter being heated to its operating temperature in which operation of the catalytic converter is not at its optimal effectiveness, resulting in increased emissions being released to the atmosphere.

During normal operation, an engine is controlled to operate at maximum efficiency. That is, the timing of the engine ignition is set to maximise torque and minimise waste heat produced by the engine. It is known for an engine to be controlled in a catalyst heating mode after a cold start. The engine will operate in catalyst heating mode until the catalyst is fully warmed and typically may take 50 to 60 seconds. In the catalyst heating mode, following an initial flair of high revs to start the engine, the engine will normally settle at an idle speed with the engine being controlled to run inefficiently in order to increase the amount of waste heat to the vehicle exhaust arrangement to reduce the time taken for the catalyst to warm to its operating temperature. The engine is controlled to run inefficiently by retarding engine ignition and having a high air mass flow rate and high fuelling. The engine therefore produces relatively low torque but high catalyst heating via excess fuel combusting in the exhaust when in the catalyst heating mode.

In the catalyst heating mode, when the vehicle is driven relatively gently then the engine ignition efficiency may remain at or near a target catalyst heating efficiency less than the maximum ignition efficiency. When the driver demands a relatively high torque, however, then this is delivered simply by advancing the ignition (towards a point corresponding to optimal ignition efficiency). As there is pre-existing high air mass flow rate and high fuelling then changing the ignition timing in this manner provides a very fast way of delivering higher torque. In fact, the torque response in catalyst heating mode is faster than during normal engine operation where a lag in increasing air mass flow limits the speed of response.

Therefore, a high torque demand during catalyst heating mode results in the engine operating more efficiently, meaning that reduced waste heat is ejected into the exhaust. Hence, this delays the rise in catalyst temperature to its operating temperature, resulting in higher overall emissions.

It is against this background to which the present invention is set.

SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided a controller for a vehicle internal combustion engine operable in a catalyst heating mode. The controller comprises an input configured to receive torque request data indicative of an amount of drive torque requested to be provided by the engine. The input is configured to receive actual air mass data indicative of actual mass airflow into the engine.

The controller comprises a processor configured to determine a required engine ignition efficiency value in dependence on the received torque request data and the actual air mass data. The processor is configured to define an actual engine ignition efficiency value to be a minimum of the required engine ignition efficiency value and a threshold maximum engine ignition efficiency value. The processor is configured to determine an applied engine ignition timing based on the determined actual engine ignition efficiency value.

The controller comprises an output configured to send a control signal to control the engine to operate in accordance with the applied engine ignition timing when the engine is operating in the catalyst heating mode.

The present invention is advantageous in that it caps or guards the engine efficiency to reduce the decrease in heat applied or provided to an exhaust catalyst of the vehicle which would otherwise occur during relatively high torque events when the engine operates in catalyst heating mode. Although this means the torque response provided by the engine will not be quite as fast this will be unnoticed by the vehicle driver, who in normal interaction with the vehicle will subconsciously modulate the demand at the accelerator. In order to meet the torque request while the engine ignition efficiency by the threshold maximum value, the controller will demand more air mass flow. The air mass torque pathway has more lag than simply advancing the ignition timing, thereby causing the slower torque response. The net result is that the driver receives the torque demanded, but the catalyst continues to be heated at a relatively fast rate. In fact, the driver receives the torque request at a rate of delivery that is the same as the response during normal engine operation when the catalyst is fully warmed, i.e. not in the catalyst heating mode. This is because in the warmed (normal) condition, the engine is controlled to run efficiently, i.e. at optimal ignition timing, and so torque demands are normally met by increasing air mass flow. The invention therefore provides a more consistent engine torque response between normal and catalyst heating engine modes.

The present invention leads to reduced variability of toxic and/or polluting engine exhaust emissions, e.g. Real World Tailpipe emissions, because of the more consistent catalyst heating during drive away scenarios, i.e. after a cold engine start, with varying driver demand. In turn, this means that the engine spends less time operating in catalyst heating mode, i.e. it takes less time for the catalyst to heat up to operating temperature. The present invention also reduces variability in engine out emissions (NOx and HC) because of the reduced variability in applied ignition timing during catalyst heating, i.e. when operating in catalyst heating mode. The invention has the potential to reduce the cost of exhaust after-treatment systems or to increase the capability to meet future emission limits.

The present invention is applicable to any spark-ignition engine applications.

The torque request data may comprises acceleration request data indicative of a transient increase in the amount of drive torque requested to be provided by the engine.

The acceleration request data may cause the actual engine ignition efficiency value to be greater than a target engine ignition efficiency value defining a target engine efficiency when the engine operates in the catalyst heating mode.

The processor may be configured to determine the target engine ignition efficiency value in dependence on at least one of the following parameters: vehicle catalyst efficiency; measured catalyst brick temperature; modelled catalyst brick temperature; vehicle engine speed; and, optimal torque relative to engine load.

The processor may be configured to determine the threshold maximum engine ignition efficiency value in dependence on the at least one of the parameters.

The processor may be configured to determine a target air mass value indicative of a target mass airflow into the engine. The target air mass value may be determined in dependence on the received torque request data and the target engine ignition efficiency value. The output may be configured to send the control signal to control the engine to operate in accordance with the target air mass value.

The processor may be configured to determine an optimal air mass value indicative of a mass airflow into the engine that gives rise to optimal engine efficiency. The optimal air mass value may be determined based on the received torque request data. The processor may be configured to determine the target air mass value based on the optimal air mass value.

The processor may be configured to determine the applied engine ignition timing based on an optimal engine ignition timing.

The processor may be configured to determine the optimal engine ignition timing in dependence on the actual air mass data.

The processor may be configured to determine an engine ignition retard value based on the actual engine ignition efficiency value. The processor may be configured to determine the applied engine ignition timing based on the engine ignition retard value.

The processor may be configured to determine a maximum available torque value based on the actual air mass data. The processor may be configured to determine the required engine ignition efficiency value in dependence on the maximum available torque value.

The input may be configured to receive torque intervention data indicative of an amount of torque requested by at least one vehicle subsystem. The processor may be configured to determine a minimum required torque intervention engine ignition efficiency value in dependence on the received torque intervention data. The processor may be configured to define the actual engine ignition efficiency value to be equal to the minimum required torque intervention engine ignition efficiency value if it is greater than the minimum of the required engine ignition efficiency value and the threshold maximum engine ignition efficiency value.

The at least one vehicle subsystem may include at least one of: a windscreen heater system; an air conditioning system; and, a hybrid propulsion system.

The torque request data may be based on an amount of drive torque requested by a driver of the vehicle.

The amount of drive torque requested by the driver may be based on a level of actuation of an acceleration pedal of the vehicle.

The torque request data may be based on an amount of drive torque requested by a driver assistance vehicle of the system.

The one or more driver assistance systems may include at least one of: a traction control system; a transmission control system; and, an idle speed control system.

The torque request data may comprise constant torque request data indicative of the requested amount of drive torque being substantially temporally constant. The actual air mass data may comprise data indicative of the actual mass airflow is a maximum mass airflow. The processor may be configured to determine the threshold maximum engine ignition efficiency value is greater when the requested amount of torque is a maximum requested torque than when the requested amount of torque is a minimum requested torque.

The threshold maximum engine ignition efficiency value may be less than an optimal engine ignition timing when the requested amount of torque is a maximum requested torque.

The threshold maximum engine ignition efficiency value may be dependent on the requested amount of torque when the requested amount of torque is between a lower bound torque greater than the minimum requested torque and the maximum requested torque.

The actual engine ignition efficiency value may equal the required engine ignition efficiency value when the engine is not operating in the catalyst heating mode.

According to another aspect of the present invention there is provided a vehicle comprising a controller as described above.

According to another aspect of the present invention there is provided a method of controlling a vehicle internal combustion engine operable in a catalyst heating mode. The method comprises receiving torque request data indicative of an amount of drive torque requested to be provided by the engine. The method comprises receiving actual air mass data indicative of actual mass airflow into the engine. The method comprises determining a required engine ignition efficiency value in dependence on the received torque request data and the actual air mass data. The method comprises defining an actual engine ignition efficiency value to be a minimum of the required engine ignition efficiency value and a threshold maximum engine ignition efficiency value. The method comprises determining an applied engine ignition timing based on the determined actual engine ignition efficiency value. The method comprises sending a control signal to control the engine to operate in accordance with the applied engine ignition timing when the engine is operating in the catalyst heating mode.

According to another aspect of the present invention there is provided a non-transitory, computer readable storage medium storing instructions thereon that when executed by one or more processors causes the one or more processors to perform the method described above.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of a vehicle having an internal combustion engine and a controller; Figure 2 is a plot of ignition efficiency against ignition retardation for the engine of Figure 1; Figures 3(a) and 3(b) illustrate a control strategy for determining target mass airflow intake and applied ignition timing, respectively, for the engine of Figure 1; Figures 4(a)-4(e) are plots of, respectively, requested versus actual torque; requested versus actual air mass, driver-demanded pedal input, target versus actual efficiency, and exhaust gas temperature for the vehicle and engine of Figure 1; Figure 5 is a plot of ignition efficiency against ignition retardation, and indicating a threshold maximum ignition efficiency for the engine of Figure 1; Figures 6(a) and 6(b) illustrate a control strategy for determining target mass airflow intake and applied ignition timing, respectively, for the engine of Figure 1; Figures 7(a)-7(e) are plots of requested versus actual torque; requested versus actual air mass, driver-demanded pedal input, target versus actual efficiency, and exhaust gas temperature for the vehicle and engine of Figure 1; Figure 8 is a plot of threshold maximum ignition efficiency versus torque at optimal efficiency for the engine of Figure 1; and, Figure 9 shows the steps of a method performed by the controller of Figure 1.

DETAILED DESCRIPTION

Figure 1 is a schematic illustration of a vehicle 10, e.g. an automobile, having an internal combustion engine 12. The vehicle 10 also has an exhaust arrangement (not shown) of suitable, known type for emitting exhaust gases from the engine 12. The exhaust arrangement has a catalyst, or catalytic converter, to reduce the level of pollutants produced by the engine 12 that are emitted from the vehicle 10, in particular by catalysing oxidation and reduction reactions in a known manner. The catalytic converter needs to be heated to a sufficient operating temperature to be fully effective. Specifically, the catalytic converter may include front and rear bricks, e.g. ceramic bricks, which need to be heated to operating temperature.

The vehicle 10 includes a controller 14 for controlling operation of the engine 12, as will be described below. The controller 14 has an input 16, a processor 18, and an output 20. The input 16 is configured to receive data from a plurality of different sensors and systems of the vehicle 10. In particular, the input 16 receives data indicative of an acceleration or torque request from a driver of the vehicle 10 via an acceleration pedal sensor 22 configured to measure a level of actuation of an acceleration pedal of the vehicle 10. The input 16 also receives data indicative of an acceleration or torque request from one or more advanced driver assistance systems (ADAS) 24 of the vehicle 10, e.g. a traction control system, a transmission control system, and an idle speed control system. The input 16 also receives data from an air mass inflow sensor 26 configured to measure the actual mass of air flowing into the engine 12. Furthermore, the input 16 receives data indicative of a torque request from one or more vehicle subsystems 28 where the torque is to power the subsystem 28 rather than to provide traction directly to wheels to the vehicle 10. The vehicle subsystems 28 may include one or more of: a windscreen heater system; an air conditioning system; and, a hybrid propulsion system. In addition, the input 16 receives data indicative of the temperature of the catalytic converter bricks in the exhaust arrangement from one or more temperature sensors 30.

The processor 18 is configured to determine an ignition timing that is to be applied to the engine 12 based on the data received by the input 16, and the output 20 is configured to control the engine 12 to operate in accordance with the determined applied engine ignition timing. In particular, the engine 12 may have one or more actuators 34 that may be adjusted in order that the engine 12 operates in accordance with the ignition timing calculated by the processor 18. This will be described in detail below. The vehicle has a computer-readable memory device 32 that stores instructions for the processor 18 to access so that the processor 18 may determine the applied engine ignition timing.

The ignition timing refers to the timing of the release of a spark in a combustion chamber of the engine 12 near the end of the compression stroke. In particular, the ignition timing is relative to the current position of a piston of the engine 12 and to the angle of a crankshaft of the vehicle 10. During normal running of the engine 12, the ignition timing is set to an optimal value to optimise the power produced by the engine, minimise the waste heat produced and minimise fuel consumption, i.e. to maximise the efficiency of the engine 12. In order to bring the catalytic converter up to operating temperature in a timely manner, the engine 12 operates in a catalyst heating mode during initial start-up of the engine 12. In particular, during the catalyst heating mode the ignition timing is retarded or advanced away from the optimal ignition timing with high air mass flow rate into the engine 12 and high fuelling so that the engine runs inefficiently 12. Operating the engine 12 in this way increases the amount of waste heat that the engine 12 produces and is provided to the exhaust arrangement, which in turn reduces the time taken for the catalytic converter to reach its operating temperature.

Figure 2 shows a plot of engine efficiency (Ign q) 36 against ignition retardation 38 when the engine 12 operates in a known manner. It is seen that the engine 12 operates at or close to maximum efficiency (100% efficiency) for small or zero levels of retardation, that is, the engine 12 operates at, or close to, maximum brake torque (MBT) 40. As the amount of ignition retardation 38 increases, the engine efficiency 36 decreases. In an engine catalyst heating mode for a cold-engine start, when the engine 12 operates at idle speed the engine 12 is controlled in accordance with a target engine efficiency value 42 less than maximum efficiency 40. That is, when the engine 12 is idling the ignition timing is retarded by a specific retardation value 44 from an optimal timing to an ignition timing value that results in the desired or target efficiency 42. The target engine ignition efficiency value may be defined based on one or more of a variety of parameters; for example, vehicle catalyst efficiency, measured catalyst brick temperature, modelled catalyst brick temperature, vehicle engine speed, and optimal torque relative to engine load. The difference 46 between the target and maximum engine efficiency means that there is a torque reserve. This torque reserve may be utilised when torque demand increases above the level required for engine idle speed. For example, when a driver of the vehicle 10 depresses the accelerator pedal to increase the demanded engine torque this transient torque increase is achieved by reducing the level of retardation of the ignition timing which in turn increases the engine efficiency.

Figures 3(a) and 3(b) indicate, respectively, the steps undertaken by the controller 14 to determine the target air mass intake to the engine 12 and the applied ignition timing of the engine 12 when the engine 12 operates in accordance with the map of Figure 2. As part of the control method for normal engine operation, i.e. when the catalyst is heated to operating temperature, the amount of air that is requested for the engine 12 is calculated based on the torque demand and the optimal value of the ignition angle for the particular torque demand. During torque-based engine operation, the ignition angle is set to deliver the requested amount of torque based on an estimate of the actual amount of air entering the engine 12. If the amount of air entering the engine 12 is the minimum amount needed to meet the torque demand then the ignition would be set to the optimal timing value. During catalyst heating mode or operation, the amount of requested air and fuel is increased to provide both the requested amount of torque and additional heat flux for catalyst heating.

Figure 3(a) shows that the target mass of air 50 to be requested for the engine intake is calculated based on torque demand 52 and the target engine efficiency 42. In particular, the indicated or measured torque request 52, e.g. based on a level of actuation of the accelerator pedal by the driver, is received and used to determine the optimal air mass request 54, that is, the minimum amount of air needed to deliver the requested torque, i.e. maximum engine efficiency 40. This optimal air mass 54 is then divided by the target engine efficiency 42 to give the target mass of air 50 to be taken in by the engine 12.

Note that during normal operation, the target engine efficiency 42 is the optimal engine efficiency 40, i.e. equal to one for the present calculation, so that the optimal air mass request 54 is equal to the target air mass request 50. During the catalyst heating mode of the engine 12, however, the target engine efficiency 42 is less than the maximum engine efficiency 40, i.e. less than one for the present calculation, (as shown in Figure 2) so that the target air mass request 50 is greater than the optimal air mass request 54.

Figure 3(b) shows that the ignition timing 60 that is to be applied to the engine 12 is calculated based on actual mass of air 62 received into the engine 12 and the demanded torque 52. In particular, the actual air mass 62 is measured and used to determine the maximum amount of torque 64 that is available, i.e. the maximum amount of torque that can be provided for the given air intake level. The demanded torque level 52 is then divided by the maximum available torque 64 to give the required efficiency 66 at which the engine 12 must operate in order to deliver the requested torque 52 for the given amount of air 62 actually received into the engine 12. The level of ignition timing retardation 38 needed to achieve the required engine efficiency 66 is then determined and then added to the optimal ignition timing 68 (corresponding to maximum engine efficiency) to give the applied ignition timing value 60. Note that when the requested torque 52 is equal to the maximum available torque, then the engine 12 must operate at maximum efficiency 40, i.e. the required engine efficiency 66 is equal to the optimal or maximum engine efficiency 40. When the engine 12 is to operate at maximum efficiency 40 then this corresponds to zero retardation of the ignition timing from the optimal ignition timing 68, meaning that in this case the applied ignition timing 60 is equal to the optimal ignition timing 68.

Figures 4(a) to 4(e) show illustrative plots of various parameters over time when the engine 12 operates in accordance with the map of Figure 2. In particular, Figures 4(a) to 4(e) show parameter plots in the case where the engine 12 operates in a catalyst heating mode and there is a transient increase in driver-demanded torque from the engine 12. Specifically, Figure 4(a) shows requested torque 52 versus actual torque 70, Figure 4(b) shows total requested air mass 50 versus actual air mass 62, Figure 4(c) shows the driver-demanded pedal input 72, i.e. the level of actuation of the accelerator pedal, Figure 4(d) shows the target engine efficiency 42 versus actual engine efficiency 74, and Figure 4(e) shows exhaust gas temperature 76.

It is seen that when there is initial constant driver demanded pedal input, i.e. when the driver does not depress the accelerator pedal or holds the accelerator pedal at a set position (Figure 4(c)), then the requested and actual torque 52, 70 are constant at the same value (Figure 4(a)) and the requested and actual air mass 50, 62 are constant at the same value (Figure 4(b)). In addition, Figure 4(d) shows that the actual engine efficiency 74 is equal to the target engine efficiency 42, which may be any suitable percentage of the maximum engine efficiency 40, e.g. 50% of the maximum engine efficiency 40. Furthermore, Figure 4(e) shows that the exhaust gas temperature 76 is also constant at this point.

It is also seen that when there is a step change increase in the driver demanded pedal input 72, i.e. when the driver depresses the accelerator pedal (Figure 4(c)), there is a step change increase in the requested torque 52 which is substantially matched by the actual torque 70 (Figure 4(a)). The increased requested amount of torque 52 is delivered using the available air mass by adjusting the ignition timing value. In particular, with reference to Figure 2, the ignition retardation value 38 is reduced to make use of the available torque reserve 46 such that there is a step change increase in the actual engine efficiency 74 away from the target efficiency 42 (Figure 4(d)). This increase in engine efficiency means that there is a reduced amount of waste heat provided the exhaust arrangement and so there is a decrease in the exhaust gas temperature 76 (Figure 4(e)). As the requested increase in torque is delivered by adjusting the ignition timing value then the corresponding increase in the actual torque is substantially instantaneous (as shown in Figure 4(a)). In contrast, the actual air mass 62 lags behind the requested air mass 50 (Figure 4(b)) because of the physical constraints of the air path, e.g. actuator delays, time taken to change intake manifold pressure, etc. Figure 4(c) shows that the driver demanded pedal input 72 then remains constant (at a higher value than before) after the step change increase. The actual efficiency 74 gradually returns to the target efficiency 42 (Figure 4(d)) as it compensates for the relatively slow response of the air mass 62. As the actual engine efficiency 74 slowly returns to the target efficiency 42, the exhaust gas temperature 76 slowly increases in a corresponding manner (Figure 4(e)). Clearly, this approach results in reduced exhaust gas temperatures which in turn increases the time taken for the catalyst to heat up to operating temperature. The torque response is faster in the catalyst heating mode than during normal engine operation as it is not dependent on the air path response because of the relatively high torque reserve 46 during catalyst heating mode. The problems of reduced exhaust gas temperatures and increased time taken for catalyst heating are addressed by aspects of the invention provided in the following description and associated Figures.

Figure 5 shows a plot of engine efficiency (Ign q) 36 against ignition retardation 38 when the engine 12 operates according to an example of the invention. Operation is similar to that of the map shown in Figure 2 and like numerals are used for like features. As in the map shown in Figure 2, in Figure 5 when the engine 12 operates in a catalyst heating mode at idle speed, the engine 12 operates in accordance with the target engine efficiency 42 to promote faster catalyst heating through increased waste heat from the engine 12. The differences from the map of Figure 2 are now described. Unlike in the map of Figure 2, in Figure 5 there is a threshold maximum engine ignition efficiency value 80 above which the engine ignition efficiency 36 does not rise when in the catalyst heating mode. For example, the target efficiency 42 may be around 50% of the maximum efficiency 40, and the upper threshold or guard 80 may be around 75% of the maximum efficiency 40; however, any suitable values may be used. The threshold maximum engine ignition efficiency value 80 may be defined based on one or more of a variety of parameters; for example, vehicle catalyst efficiency, measured catalyst brick temperature, modelled catalyst brick temperature, vehicle engine speed, and optimal torque relative to engine load. Like in Figure 2, in Figure 5 when a driver of the vehicle 10 depresses the accelerator pedal to increase the demanded engine torque this transient torque increase is achieved by reducing the level of retardation of the ignition timing which in turn increases the engine efficiency. However, unlike in Figure 2, in Figure 5 the level of retardation of the ignition timing is only permitted to reduce until the ignition efficiency 36 reaches the threshold efficiency 80. If the requested amount of torque still exceeds the torque available at the upper threshold efficiency 80 then this is achieved by an increase in air mass flow into the engine 12. Figure 5 shows that there is a reduced torque reserve 46 available to be used upon a transient increase in requested torque from idle conditions or other steady state condition.

Figures 6(a) and 6(b) indicate, respectively, the steps undertaken by the controller 14 to determine the target air mass intake to the engine 12 and the applied ignition timing of the engine 12 when the engine 12 operates in accordance with the map of Figure 5. The control steps in Figures 6(a) and 6(b) are similar to those in Figures 3(a) and 3(b), and like numerals are used for like features. Figure 6(a) shows the steps performed to determine the target mass of air 50 requested to be taken into the engine 12 when the engine 12 operates in accordance with the map of Figure 5. In fact, it is seen that the target air mass 50 is determined in Figure 6(a) when the upper threshold efficiency 80 is utilised in the same way as in Figure 3(a) when there is not upper threshold efficiency present.

Figure 6(b) shows the steps performed to determine the ignition timing 60 that is to be applied to the engine 12. Like in Figure 3(b), in Figure 6(b) the ignition timing 60 is calculated based on actual mass of air 62 received into the engine 12 and the demanded torque 52. Unlike in Figure 3(b), however, in Figure 6(b) the ignition timing 60 is calculated additionally based on the maximum efficiency limit, i.e. the upper threshold engine efficiency 80. In particular, like in Figure 3(b), in Figure 6(b) the optimal or maximum available torque 64 is determined based on the measured actual air mass 62 into the engine 12, and the required engine efficiency 66 is determined by dividing the requested torque 52 by the maximum available torque 64. However, unlike in Figure 3(b), in Figure 6(b) the required ignition efficiency 66 is not used directly to determine the level of ignition retardation 38 needed. Instead, in Figure 6(b) the controller 14 determines the minimum 82 of the required engine ignition efficiency 66 and the maximum or upper threshold efficiency (for catalyst heating) 80. In the presently described example, a further determination is made prior to determining the required ignition retardation 38 (as described below); however, in some examples this determined minimum 82 is set as the actual engine ignition efficiency value and used to calculate the applied ignition retardation 38 needed to achieve that efficiency, and therefore to calculate the applied ignition timing 60 by summing with the optimal ignition timing 68.

In the example described in Figure 6(b), there is a further step performed by the controller 14 prior to determining the required ignition retardation 38. In particular, the controller 14 only applies the upper threshold ignition efficiency limit 80 to a torque request 52 for providing drive to the vehicle 10. In the present example, the requested torque 52 is based on accelerator pedal actuation by the driver; however, this may alternatively or additionally be based on a torque request from one or more of the advanced driver assistance systems (ADAS) 24 of the vehicle 10. The engine 12 may be required to provide torque to one or more of the other vehicle subsystems 28, e.g. chassis stability control system, transmission speed control, air conditioning system, etc. The torque requested by these subsystems 28 may be referred to as torque interventions, and the controller 14 acts to ensure that the upper threshold ignition efficiency 80 does not prevent the required torque being provided to the subsystems 28 in the event of such torque interventions. In particular, the minimum ignition efficiency 84 needed for the torque interventions is determined and then the actual ignition efficiency is calculated to be the maximum 86 of the minimum ignition efficiency 84 and the minimum 82 (of the required engine ignition efficiency 66 and the maximum or upper threshold efficiency 80). This maximum 86 is then used to determine the level of required ignition retardation 38. The upper limit 80 on ignition efficiency 36 is only applied to driver-demanded or ADAS 24 requested torque and not to increasing torque interventions by way of a selectable option. When active, this option still limits the driver demand to the upper efficiency guard 80 in order to avoid the situation where the driver demand exceeds the increasing intervention request and becomes unguarded while the intervention is active.

Figures 7(a) to 7(e) show illustrative plots of various parameters over time when the engine 12 operates in accordance with the map of Figure 5. Similarly to Figures 4(a) to 4(e), Figure 7(a) shows requested torque 52 versus actual torque 70, Figure 7(b) shows total requested air mass 50 versus actual air mass 62, Figure 7(c) shows the driver-demanded pedal input 72, i.e. the level of actuation of the accelerator pedal, Figure 7(d) shows the target engine efficiency 42 versus actual engine efficiency 74, and Figure 7(e) shows exhaust gas temperature 76.

Like before, when there is a step change increase in the driver demanded pedal input 72 (Figure 7(c)), there is a step change increase in the requested torque 52 which is substantially matched by the actual torque 70 (Figure 7(a)), and results in a step change increase in the actual engine efficiency 74 away from the target efficiency 42 (Figure 7(d)). However, unlike the previous example, when the actual engine efficiency 74 reaches the upper threshold efficiency 80 the ignition may not be advanced any further to meet the torque request 52 (see Figure 5), and the actual ignition efficiency 74 is maintained at the threshold efficiency 80. As seen in Figure 7(b), with the upper threshold efficiency guard 80 in place, during transient operation the lag in the actual air mass 62 relative to the requested air mass 50 remains unchanged from the previous example. However, guarding the maximum engine efficiency in this way restricts the amount of substantially instantaneous torque response that is available. Once the threshold efficiency 80 is reached, it is seen in Figure 7(a) that the actual torque becomes more like normal operation where the engine 12 is operated at maximum efficiency and the torque response 70 follows the response of the air path system (Figure 7(b)). This results in increased exhaust gas temperatures 76 (Figure 7(e)) when compared to an unguarded efficiency (Figure 4(e)), which therefore speeds up the catalyst temperature rise during transient operation. In effect, once the efficiency becomes guarded, priority is given to heating the catalyst rather than to torque demand.

Figure 8 illustrates that the maximum output from the engine 12 may be restricted under steady state conditions, i.e. substantially temporally constant. In particular, Figure 8 illustrates two options as to how the upper threshold ignition efficiency 80 may vary depending on the requested torque at optimal efficiency. Curve A illustrates how the ignition efficiency 36 is limited under transient conditions during catalyst heating to, for example, around 50% of the maximum efficiency 40, but under a full demand condition the ignition efficiency 36 is not limited or restricted under steady conditions at maximum airflow. Curve B has a similar ignition efficiency 36 under transient conditions of increasing airflow as curve A, but at full demand the ignition efficiency 36 is restricted to a threshold value 88 less than the maximum efficiency 40, for example, around 70% of the maximum efficiency 40. A calibration such as this would have the effect of reducing the maximum torque output of the engine 12 but would generate a significant increase to exhaust and catalyst temperature.

Figure 9 summarises the steps of a method 90 (as described above) performed by the controller 14 to control operation of the engine 12. At step 92, the input 16 receives torque request data 52 indicative of an amount of drive torque requested to be provided by the engine 12. This torque request 52 may be driver demanded torque or ADAS demanded torque. At step 94 the input 16 receives actual air mass data 62 indicative of actual mass airflow into the engine 12 from the air mass flow sensor 26. At step 96 the processor 18 determines the required engine ignition efficiency value 66 in dependence on the received torque request data 52 and the actual air mass data 62. At step 98 the processor 18 determines the minimum 82 of the calculated required engine ignition efficiency value 66 and the threshold maximum engine ignition efficiency value 80 and sets this minimum 82 to be the actual engine ignition efficiency value that is to be achieved by the engine 12. At step 100 the processor 18 determines the applied engine ignition timing 60 needed to achieve the actual engine ignition efficiency value, in particular by retarding the ignition timing by a calculated amount from the optimal ignition timing. At step 102, the controller 14 sends a control signal via the output 20 to control the engine to operate in accordance with the applied engine ignition timing 60 when the engine 12 is operating in the catalyst heating mode, e.g. immediately after a cold start of the engine 12 prior to the engine catalyst reaching operating temperature. The engine 12 may switch from catalyst heating mode operation to normal operation once the catalytic converter, specifically the bricks, have been fully warmed to operating temperature.

It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

CLAIMS1. A controller (14) for a vehicle internal combustion engine (12) operable in a catalyst heating mode, the controller (14) comprising: an input (16) configured to receive: torque request data (52) indicative of an amount of drive torque requested to be provided by the engine (12); and, actual air mass data (62) indicative of actual mass airflow into the engine (12); a processor (18) configured to: determine a required engine ignition efficiency value (66) in dependence on the received torque request data (52) and the actual air mass data (62); define an actual engine ignition efficiency value to be a minimum (82) of the required engine ignition efficiency value (66) and a threshold maximum engine ignition efficiency value (80); determine an applied engine ignition timing (60) based on the determined actual engine ignition efficiency value; and, an output (20) configured to send a control signal to control the engine (12) to operate in accordance with the applied engine ignition timing (60) when the engine (12) is operating in the catalyst heating mode.
2. A controller (14) according to Claim 1, wherein the torque request data (52) comprises acceleration request data indicative of a transient increase in the amount of drive torque requested to be provided by the engine (12).
3. A controller (14) according to Claim 2, wherein the acceleration request data causes the actual engine ignition efficiency value to be greater than a target engine ignition efficiency value (42) defining a target engine efficiency when the engine (12) operates in the catalyst heating mode.
4. A controller (14) according to Claim 3, wherein the processor (18) is configured to determine the target engine ignition efficiency value (42) in dependence on at least one of the following parameters: vehicle catalyst efficiency; measured catalyst brick temperature; modelled catalyst brick temperature; vehicle engine speed; and, optimal torque relative to engine load.
5. A controller (14) according to Claim 4, wherein the processor (18) is configured to determine the threshold maximum engine ignition efficiency value (80) in dependence on the at least one of the parameters.
6. A controller (14) according to any of Claims 3 to 5, wherein the processor (18) is configured to determine a target air mass value (50) indicative of a target mass airflow into the engine (12), the target air mass value (50) being determined in dependence on the received torque request data (52) and the target engine ignition efficiency value (42), and wherein the output (20) is configured to send the control signal to control the engine (12) to operate in accordance with the target air mass value (50).
7. A controller (14) according to Claim 6, wherein the processor (18) is configured to determine an optimal air mass value (54) indicative of a mass airflow into the engine (12) that gives rise to optimal engine efficiency, the optimal air mass value (54) being determined based on the received torque request data (52), and wherein the processor (18) is configured to determine the target air mass value (50) based on the optimal air mass value (54).
8. A controller (14) according to any previous claim, wherein the processor (18) is configured to determine the applied engine ignition timing (60) based on an optimal engine ignition timing (68).
9. A controller (14) according to Claim 8, wherein the processor (18) is configured to determine the optimal engine ignition timing (60) in dependence on the actual air mass data (62).
10. A controller (14) according to Claim 8 or Claim 9, wherein the processor (18) is configured to determine an engine ignition retard value (38) based on the actual engine ignition efficiency value, and wherein the processor (18) is configured to determine the applied engine ignition timing (60) based on the engine ignition retard value (38).
11. A controller (14) according to any previous claim, wherein the processor (18) is configured to determine a maximum available torque value (64) based on the actual air mass data (62), and wherein the processor (18) is configured to determine the required engine ignition efficiency value (66) in dependence on the maximum available torque value (64).
12. A controller (14) according to any previous claim, wherein the input (16) configured to receive torque intervention data indicative of an amount of torque requested by at least one vehicle subsystem (28), and wherein the processor (18) is configured to determine a minimum required torque intervention engine ignition efficiency value (84) in dependence on the received torque intervention data, and wherein the (18) processor (18) is configured to define the actual engine ignition efficiency value to be equal to the minimum required torque intervention engine ignition efficiency value (84) if it is greater than the minimum (84) of the required engine ignition efficiency value (66) and the threshold maximum engine ignition efficiency value (80).
13. A controller (14) according to Claim 12, wherein the at least one vehicle subsystem (28) includes at least one of: a windscreen heater system; an air conditioning system; and, a hybrid propulsion system.
14. A controller (14) according to any previous claim, wherein the torque request data (52) is based on an amount of drive torque requested by a driver of the vehicle (10).
15. A controller (14) according to Claim 14, wherein the amount of drive torque requested by the driver is based on a level of actuation of an acceleration pedal of the vehicle (10).
16. A controller (14) according to any previous claim, wherein the torque request data (52) is based on an amount of drive torque requested by one or more driver assistance systems (24) of the vehicle (10).
17. A controller (14) according to Claim 16, wherein the one or more driver assistance systems (24) includes at least one of: a traction control system; a transmission control system; and, an idle speed control system.
18. A controller (14) according to any previous claim, wherein the torque request data (52) comprises constant torque request data indicative of the requested amount of drive torque being substantially temporally constant, wherein the actual air mass data (62) comprises data indicative of the actual mass airflow is a maximum mass airflow, and wherein the processor (18) is configured to determine the threshold maximum engine ignition efficiency value (80) is greater when the requested amount of torque is a maximum requested torque than when the requested amount of torque is a minimum requested torque.
19. A controller (14) according to Claim 18, wherein the threshold maximum engine ignition efficiency value is (80) less than an optimal engine ignition efficiency (40) when the requested amount of torque is a maximum requested torque.
20. A controller (14) according to Claim 18 or Claim 19, wherein the threshold maximum engine ignition efficiency value (80) is dependent on the requested amount of torque when the requested amount of torque is between a lower bound torque greater than the minimum requested torque and the maximum requested torque.
21. A controller (14) according to any previous claim, wherein the actual engine ignition efficiency value equals the required engine ignition efficiency value (66) when the engine (12) is not operating in the catalyst heating mode.
22. A vehicle (10) comprising a controller (14) according to any previous claim.
23. A method (90) of controlling a vehicle internal combustion engine (12) operable in a catalyst heating mode, the method (90) comprising: receiving (92) torque request data (52) indicative of an amount of drive torque requested to be provided by the engine (12); receiving (94) actual air mass data (62) indicative of actual mass airflow into the engine (12); determining (96) a required engine ignition efficiency value (66) in dependence on the received torque request data (52) and the actual air mass data (62); defining (98) an actual engine ignition efficiency value to be a minimum (82) of the required engine ignition efficiency value (66) and a threshold maximum engine ignition efficiency value (80); determining (100) an applied engine ignition timing (60) based on the determined actual engine ignition efficiency value; and, sending (102) a control signal to control the engine to operate in accordance with the applied engine ignition timing when the engine (12) is operating in the catalyst heating mode.
24. A non-transitory, computer readable storage medium (32) storing instructions thereon that when executed by one or more processors (18) causes the one or more processors (18) to perform the method (90) of Claim 23.