Air control signal for a powertrain of a vehicle

Abstract

Disclosed is a control system for controlling a powertrain of a vehicle. The powertrain comprises an internal combustion engine. The system comprises one or more processors configured to receive an in

Description

TECHNICAL FIELD The present disclosure relates to controlling an air control signal for a powertrain of a vehicle. Aspects of the invention relate to a control system, to a system, to a vehicle, to a method, and to computer readable instructions. BACKGROUND It is known for a control system to receive a propulsive torque request, and output control signals to various actuators to control the output torque of an internal combustion engine in dependence on the propulsive torque request. One control signal is an air control signal, which causes control of an inlet air actuator such as an air valve. Another control signal is a combustion control signal, which causes control of a combustion actuator for initiating combustion, such as a fuel injector of a diesel engine, or a spark plug of a gasoline engine. The fuel mass flow rate controlled by the fuel injector, or the spark timing of the spark plug, respond rapidly to changes in the combustion control signal. By contrast, the air mass flow rate controlled by the air actuator responds slowly to the air control signal due to the inertia of the air in the air intake system of the powertrain. It is an aim of the present invention to address one or more disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a control system, to a system, to a vehicle, to a method, and to computer software as claimed in the appended claims. According to an aspect of the present invention there is provided a control system for controlling a powertrain of a vehicle, the powertrain comprising an internal combustion engine, the control system comprising one or more processors collectively configured to: receive an input signal indicative of a propulsive torque request, the input signal comprising a change; determine a lead signal in dependence on the input signal, wherein the lead signal has a greater peak magnitude than the change of the input signal; and output an air control signal to cause control of an inlet air actuator of the powertrain, in dependence on the lead signal, to control the inlet air actuator to cause a magnitude of airflow proportional to the air control signal. An advantage is improving responsiveness, and also emissions control (which in turn minimises emissions) in examples where the internal combustion engine is a diesel engine. Responsiveness is improved because of a lead signal (lead air signal) means, there will be less delay of the change of air mass flow rate into the combustion chambers. This is further improved by causing the lead signal to have a greater peak magnitude than the input signal. Diesel emissions control is improved because the lead signal for the inlet air actuator is advanced relative to the input signal controlling fuel injection timing, creating a separation therebetween. Therefore, the change of air mass flow rate is less likely to fall behind the change of combustion start time and fuel mass flow rate. This helps to minimise unwanted deviations of air-fuel ratio and inappropriate combustion start times during the torque change, and therefore helps to minimise particulate matter production (fuel-rich mixtures) and nitrogen oxide production (fuel-lean mixtures). Further, this helps to maximise a transient capability of a powertrain, In some, but not necessarily all examples, the lead signal in the context of a reactive control scheme relates to the control scheme being configured to boost (e.g., amplify or add an offset) the signal for the inlet air actuator relative to the input signal, and to cause the lead signal for the inlet air 1 actuator to be advanced (leading) relative to a main setpoint signal (e.g., propulsive torque request) or the input signal of the control system. The boosting may cause the lead signal to overtake the input signal in magnitude before the end of the change of the input signal. The control system comprises one or more controllers collectively comprising at least one electronic processor having an electrical input for receiving an input signal; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to at least: receive the input signal; determine the lead signal; and output the air control signal. Optionally, the control system is configured to: determine a setpoint signal in dependence on the input signal; and output a combustion control signal to cause control of a combustion actuator of the internal combustion engine, in dependence on the setpoint signal, wherein the lead signal is advanced relative to the setpoint signal and has a greater peak magnitude than both the setpoint signal and the input signal during the change. Optionally, the combustion control signal comprises the setpoint signal. An advantage is improving responsiveness, maximising a transient capability of a powertrain and improving diesel emissions control if applicable. This is because the lead signal (air control signal) is advanced relative to the setpoint signal (combustion control signal), and has a greater magnitude. The effect is described in the preceding paragraphs. Optionally, determining the setpoint signal comprises applying a first filter to the input signal to determine a first filtered signal, and wherein the setpoint signal comprises the first filtered signal. Therefore, optionally the combustion control signal comprises the first filtered signal. The first filter may comprise a smoothing filter, such as a low pass filter. Optionally, the first filter comprises a proportional low pass filter with a time constant. An advantage of the combustion control signal (setpoint signal) being smoothed relative to the input signal and the lead signal is improved diesel emissions control. Smoothing the setpoint signal helps to provide separation between the lead signal and the setpoint signal. By contrast, relying entirely on boosting the lead signal without smoothing the setpoint signal to create the separation may have diminishing returns because the lead signal can only be boosted so far before the inlet air actuator is unable to increase the airflow any faster. Optionally, the lead signal is dependent on the first filtered signal. Therefore, optionally the lead signal is dependent on the setpoint signal. Therefore, optionally the air control signal is dependent on / proportional to the setpoint signal. An advantage of the lead signal being dependent on the setpoint signal is allowing the separation between the air and combustion control signals to be controlled, whatever the input signal may be. The characteristics of the separation can be predetermined by calibrating a filter parameter (e.g., time constant) of the first filter. Optionally, determining the lead signal comprises applying a filter to the input signal to determine a filtered signal, and determining the lead signal in dependence on the filtered signal. Optionally, the filter is a second filter different than the first filter, and the filtered signal is a second filtered signal different than the first filtered signal. Optionally, the second filter has a different time constant than the first filter. An advantage is that characteristics of the lead signal can be tuned separately than the setpoint signal, because a separate filter with a calibratable parameter (e.g., time constant) is provided for the lead signal determination, different than the first filter for the setpoint signal determination. Optionally, the second filter comprises a proportional low pass filter with a time constant. Optionally, the air control signal is dependent on both the first and second filtered signals. Optionally, the air control signal is boosted in dependence on the second filtered signal. Optionally, the second filter is configured so that the second filtered signal is smoother than the first filtered signal. For example, the second filter may comprise a longer time constant than the first filter. Optionally, the lead signal is dependent on a difference between the input signal and the second filtered signal. Optionally, 2 the difference defines an offset or gain parameter. Optionally, determining the lead signal comprises adding the difference to the setpoint signal to determine the lead signal. Therefore, optionally the air control signal may comprise the sum of the setpoint signal and the difference. This average gradient of the sum (lead signal) may be greater than the average gradient of the input signal during the change, so the lead signal may rise to a greater peak magnitude than the change of the input signal. Therefore, in this manner the lead signal / air control signal is boosted relative to the input signal. An advantage is improving both responsiveness and diesel emissions control. As described earlier, the separation is useful for diesel emissions control, and the boosting is useful for responsiveness. The second filter creates an offset / gain parameter corresponding to the difference / delta between the input signal and the second filtered signal. This offset / gain parameter can be added (or multiplied) to the setpoint signal to determine the boosted lead signal. Unlike a fixed offset or gain, this method of calculating the offset / gain parameter ensures that there is a predetermined separation between the boosted air control signal and the slightly-smoothed combustion control signal, in substantially all operating scenarios. Furthermore, the shape and magnitude of the offset / gain parameter can be predetermined by calibrating a filter parameter (e.g., time constant) of the second filter. By tuning the second filter, the characteristics of the separation between the air and combustion control signals can be optimised. If the separation is not enough, the mass air flow rate may not change quickly enough relative to fuelling or combustion start time, so the air-fuel ratio may be low and soot may be produced. If the separation is too great, excessive intake air may enter the combustion chamber, causing lean running so the engine may produce more nitrogen oxides. Therefore, the second filter when calibrated allows for optimal air-fuel ratios and therefore a minimisation of soot production and nitrogen oxide production. Furthermore, the above manner of calculation ensures that if the first filter is recalibrated, there may be no need to recalibrate the second filter. Optionally, the second filter is configured so that the difference follows a temporal nonlinear profile comprising a peak having a magnitude less than or equal to the input signal at a time step of the peak, and a decay. Optionally, the peak and decay are curved. Optionally, the second filter comprises a proportional low pass filter with a time constant. Optionally, the second filter comprises a PT 1 filter. ‘PT 1 ’ is a term of the art. An advantage is that the difference (also referred to above as the separation / offset parameter) follows a temporal profile that is pre-determined to provide good emissions performance and responsiveness. The temporal nonlinear profile described can be described as the temporal shape of the error (difference) between the second filtered signal and the input signal, the shape being a characteristic of the type of second filter used. Therefore, the type of second filter, and its filter parameter (e.g., time constant) determine the general shape of the temporal nonlinear profile. Optionally, the combustion actuator comprises a fuel injector or a spark plug. For example, if the engine is a diesel engine the combustion actuator may comprise a fuel injector. If the engine is a gasoline engine the combustion actuator may comprise a spark plug. Optionally, the inlet air actuator comprises one or more of: a throttle valve; an exhaust gas recirculation valve; a turbocharger bypass valve; or an active inlet poppet valve. Optionally, the input signal is a reactive arbitrated propulsive torque request, and wherein control system is configured to determine the lead signal reactively. Optionally, the control system comprises a reactive control scheme configured to determine the lead signal and setpoint signal. According to a further aspect of the present invention there is provided a system (e.g., powertrain) comprising the control system and the inlet air actuator. According to a further aspect of the present invention there is provided a vehicle comprising the system or the control system. According to a further aspect of the present invention there is provided a control system for controlling a powertrain of a vehicle, the powertrain comprising an internal combustion engine, the control system comprising one or more processors collectively configured to: 3 receive an input signal indicative of a propulsive torque request; determine a boosted lead signal in dependence on the input signal, boosted to exceed a peak magnitude of a change of the input signal; and output an air control signal to cause control of an inlet air actuator of the powertrain, in dependence on the amplified lead signal. The optional statements defined above also apply to this aspect. As mentioned previously, boosting the lead signal may comprise adding an offset to the setpoint signal, or multiplying the setpoint signal by a gain. According to a further aspect of the present invention there is provided a method of controlling a powertrain of a vehicle, the powertrain comprising an internal combustion engine, the method comprising: receiving an input signal indicative of a propulsive torque request, the input signal comprising a change; determining a lead signal in dependence on the input signal, wherein the lead signal has a greater peak magnitude than the change of the input signal; and outputting an air control signal to cause control of an inlet air actuator of the powertrain, in dependence on the lead signal, to control the inlet air actuator to cause a magnitude of airflow proportional to the air control signal. According to a further aspect of the present invention there is provided computer readable instructions which, when executed by a computer, are arranged to perform the method. According to a further aspect of the invention, there is provided a control system for controlling a powertrain of a vehicle, the powertrain comprising an internal combustion engine, the control system comprising one or more processors collectively configured to: receive an input signal indicative of a propulsive torque request; determine a lead signal in dependence on the input signal; and output an air control signal to cause control of an inlet air actuator of the powertrain, in dependence on the lead signal, to control the inlet air actuator to cause a magnitude of airflow proportional to the air control signal. According to a further aspect of the invention there is provided computer readable instructions which, when executed by a computer, are arranged to perform any one or more of the methods described herein. According to a further aspect of the invention there is provided a non-transitory computer readable medium comprising computer readable instructions that, when executed by one or more electronic processors, causes the one or more electronic processors to carry out any one or more of the methods described herein. 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 falls within the scope of the appended claims. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination that falls within the scope of the appended claims, 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: FIG. 1 illustrates a perspective view illustrating an example of a vehicle; FIG. 2 illustrates a schematic view illustrating an example of a powertrain; FIG. 3 illustrates a schematic view illustrating an example of a control system; FIG. 4 illustrates a schematic view illustrating an example of a non-transitory computer-readable storage medium; FIG. 5 illustrates a flowchart illustrating an example of a method; and FIGS. 6A-6B illustrate graphs depicting example parameter values of the method of FIG. 5. 4 DETAILED DESCRIPTION A vehicle 1 in accordance with an embodiment of the present invention is described herein with reference to the accompanying FIG. 1. In some, but not necessarily all examples, the vehicle 1 is a passenger vehicle, also referred to as a passenger car or as an automobile. In other examples, embodiments of the invention can be implemented for other applications, such as commercial vehicles. FIG. 2 schematically illustrates an example of powertrain 100 of the vehicle 1. The illustrated powertrain 100 comprises an internal combustion engine 102 (“engine” or “ICE”). The invention is not limited to the specific layout shown. The vehicle 1 may be an ICE-only vehicle, or a hybrid electric vehicle (HEV). The control of output torque of the engine depends on the type of engine. If the engine 102 is configured for spark ignition (e.g., gasoline), the control system 300 can vary the ignition timing by controlling spark plug firing timing relative to an engine rotation angle sensed by a crank position sensor. If the engine 102 is configured for compression ignition (e.g., diesel), the control system 300 can vary the ignition timing by controlling fuel injection timing relative to the engine rotation angle. The powertrain 100 comprises a transmission 104 for receiving output torque from the engine 102. The transmission 104 may comprise an automatic vehicle transmission, a manual vehicle transmission, or a semi-automatic vehicle transmission. The linesand boxes represent shafts and differentials connecting the transmission 104 to four driven vehicle wheels FL, FR, RL, RR, therefore indicating that the vehicle 1 is a four-wheel drive vehicle. In other implementations, the vehicle 1 may be a two-wheel drive vehicle or a one-wheel drive vehicle, or other multi-wheel drive vehicle. With reference to FIG. 3, there is illustrated a control system 300 for a vehicle 1. The control system 300 comprises one or more controllers 301. The control system 300 is configured to receive an input signal indicative of a propulsive torque request, from a torque requestor controller in the form of a torque arbitrator 314. The torque arbitrator 314 may be a functional module within the control system 300 or in an external control system. In some, but not necessarily all examples, the input signal is an arbitrated propulsive torque request. The term ‘arbitrated’ means that an upstream torque arbitrator 314 has arbitrated a plurality of torque requests from a plurality of different upstream torque requestor controllers to determine a single torque request. The upstream torque requestor controllers may comprise an accelerator pedal module controller, an automated driving controller, etc. A torque request from an accelerator pedal module controller may depend on accelerator pedal depression and an optional pedal map in the accelerator pedal module controller. A torque request from an automated driving controller may depend on signals from one or more machine vision sensors (e.g., cameras, radar, lidar) mounted to the vehicle 1, or from a cruise control input device, for example. In other examples, the input signal is non-arbitrated, and is received directly from the accelerator pedal module controller or automated driving controller. In some, but not necessarily all examples, the arbitrated propulsive torque request is a raw request, e.g., unshaped. This means that functions associated with the present invention define a first of one or more torque shaping functions. I n other words, the functions associated with the present invention may be lower priority than one or more later torque shaping functions (e.g., stability control intervention functions, etc). The control system 300 may then output an air control signal and a combustion control signal, in dependence on the input signal. The air control signal is sent to a controller of an inlet air actuator 316. The combustion control signal is sent to a controller of a combustion actuator 318 such as a fuel injector or spark plug. The signals may be sent via one or more other torque shaping functions (not shown). The air control signal is sent to a controller of an inlet air actuator 316 to cause control of the inlet air actuator 316 along an air path between an air intake of the vehicle 1 and the combustion chambers 103 of the engine. The air control signal can therefore be referred to as an “air path request”. 5 The air control signal controls the inlet air actuator 316 to cause a magnitude of airflow proportional to the air control signal. It may also be proportional to the input signal. For example, the inlet air actuator 316 may comprise one or more of: a throttle valve; an exhaust gas recirculation valve; a turbocharger bypass valve; or an active inlet poppet valve. A throttle valve, such as a butterfly valve, regulates the volume of air entering the combustion chamber 103, as well as the inlet manifold air pressure. An active inlet poppet valve may perform an equivalent or supplementary function to a throttle valve. For example, a variable-lift valve can regulate the volume of air entering the engine, as well as the start, end, and valve opening duration. A poppet valve controlled by variable cam timing can regulate the start time and / or end time of air aspiration, but not necessarily valve opening duration. An exhaust gas recirculation valve can control the amount of exhaust gas recirculated back into the inlet manifold, so as to regulate the amount of oxygen in the air entering the combustion chamber 103. A turbocharger bypass valve (wastegate) regulates the air pressure generated by the turbocharger, and therefore regulates the volume of air entering the combustion chamber 103. These are just some examples of inlet air actuators 316, along an air path from an air intake of the vehicle 1 to the combustion chambers 103 of the engine. The combustion control signal is sent to a controller of a combustion actuator 318 to cause control of the combustion actuator 318. If the engine 102 is configured for compression ignition (e g., diesel), the combustion control signal may be a fuel injection timing control signal configured to control the fuel injector. The combustion control signal in this context can be referred to as a “fuel path request”. However, if the engine 102 is configured for spark ignition (e.g., gasoline), the combustion control signal may instead be a spark timing control signal configured to control the spark timing of the spark plug(s). Therefore, the signal is referred to more generically as a “combustion control signal”. Either way, the combustion control signal is configured to control the combustion actuator to vary a combustion start timing / fuel injection timing / spark timing proportional to the combustion control signal. The fuel injection timing may also be proportional to the input signal. The air control signal and combustion control signal may be in the same units as the input signal. Therefore, if the input signal is in torque units, the air control signal and combustion control signal may be in units of torque, until they are subsequently converted into actuation signals for controlling the respective actuators. The combustion control signal effectively controls the start time of combustion. Therefore, when the input signal comprises a torque change from a first value to a second value, the combustion control signal causes the engine to output substantially the full torque change, almost immediately. For instance, when the input signal increases, fuel injection may be increased to almost immediately increase torque output, or spark timing may be advanced to almost immediately increase torque output. Therefore, the combustion control signal may be referred to as a setpoint signal, and can also be referred to as an output propulsive torque request. If the control system 300 performs shaping such as filtering, the setpoint signal can be referred to as a shaped / filtered propulsive torque request. The control system 300 as illustrated in FIG. 3 comprises one controller 301, although it will be appreciated that this is merely illustrative. The controller 301 comprises processing means 304 and memory means 306. The processing means 304 may be one or more electronic processing device 304 which operably execute computer-readable instructions. The memory means 306 may be one or more memory device 306. The memory means 306 is electrically coupled to the processing means 304. The memory means 306 is configured to store instructions, and the processing means 304 is configured to access the memory means 306 and execute the instructions stored thereon. The controller 301 comprises an input means 310 and an output means 312. The input means 310 may comprise an electrical input 310 of the controller 301. The output means 312 may comprise an electrical output 312 of the controller 301. The controller 301 may have an interface 302 comprising an electrical input / output I / O 310, 312, or an electrical input 310, or an electrical output 312, for receiving information and interacting with external components. The input 310 is arranged to receive a propulsive torque request (input signal) from a torque requestor controller. The propulsive torque request signal is an electrical signal which is indicative of a magnitude of requested propulsive torque. The output 312 is arranged to output the air control signal and combustion control signal, for controlling the inlet air actuator 316 and combustion actuator 318, respectively. FIG. 4 illustrates a non-transitory computer-readable storage medium 400 comprising the instructions (computer software). FIG. 5 illustrates a method 500 according to an embodiment of the invention. The method 500 is a method of controlling a powertrain 100 of a vehicle 1, such as the vehicle 1 illustrated in FIG. 1. In particular, the method 500 is a method of determining an air control signal and a combustion control signal for the powertrain 100 of the vehicle 1. The method 500 may be performed by the control system 300 illustrated in FIG. 3. In particular, the memory 306 may comprise computer-readable instructions 308 which, when executed by the processor 304, perform the method 500. FIGS. 6A-6B illustrate example values for the parameters of the method 500, and can be read in conjunction with the below description of FIG. 5. The x-axis represents time‘t’, and the y-axis represents the reference units of the control system 300, in this case a propulsive torque demand T. At block 502, the method 500 comprises receiving an input signal T1 indicative of a propulsive torque request. The graph of FIG. 6A illustrates the input signal T1 comprising a change, from a first constant value to a second constant value greater than the first constant value. The change comprises a linear upwards ramp. This represents a simple driving scenario where a constant torque request is increased. The invention is not limited to the scenario shown in FIGS. 6A-6B. The blocks 502-518 of the method 500 define a reactive control scheme. In other words, the output control signals (blocks 508, 518) are reactive to the input signal T1. There is no prediction of future values of the input signal T1. However, in other implementations, the output signals 508, 518 may be dependent on prediction of future values of the input signal T1. The flowchart of FIG. 5 illustrates a first branch (blocks 504,506,508) for determining the combustion control signal (block 508), and a second branch for determining the air control signal (blocks 510, 512, 514, 516,518). The second branch depends on the first branch (see block 516). The first branch is described first, although this does not imply a particular order of execution of the blocks. At blocks 504-506, the method 500 comprises determining a setpoint signal (setpoint torque, ST) by applying a first filter f1 at block 504 to the input signal T1 to determine a first filtered signal 506. Block 506 is labelled ‘ST’ because in this example the setpoint signal ST is equal to the first filtered signal. Therefore, in the following description the first filtered signal 506 and the setpoint signal ST can be referred to interchangeably. In other examples, the setpoint signal ST is dependent on the first filtered signal 506 but not equal. At block 508, the method 500 comprises outputting a combustion control signal to cause control of the combustion actuator 318 of the engine, in dependence on the setpoint signal ST. As shown in FIG. 6A, the first filter f1 of block 504 may comprise a smoothing filter, such as a low pass filter. Therefore, the setpoint signal ST is smoothed relative to the input signal T1. Optionally, the first filter f1 of block 504 comprises a proportional low pass filter with a time constant, such as a PT1 filter. In the present example, the combustion control signal output at block 508 requests an amount of torque which comprises or is equal to the setpoint signal ST, and the setpoint signal ST comprises or is equal to the first filtered signal (block 506) determined by the first filter f 1 of block 504. Therefore, the combustion control signal 508 comprises or is equal to the setpoint signal ST. In examples where they are equal, the line labelled ‘ST’ in FIG. 6A is the same line for each of the combustion control signal 508, the setpoint signal ST, and the first filtered signal 506. In other implementations, additional signal processing may be performed such that the combustion control signal 508 depends on the setpoint signal ST, and the setpoint signal ST may depend on the first filtered signal of block 506, but the signals may be unequal to each other. The second branch for determining the air control signal 518 is now described. At block 510, the method 500 comprises applying a different second filter f2 to the input signal T1 to determine a second filtered signal T2. Block 512 indicates the second filtered signal T2, and the connection from block 510 to 512 indicates the second filtered signal T2 being output by the second filter f2. The second filtered signal T2 is an internal signal of the control system 300, and may not be directly output. As shown in FIG. 6A, the second filtered signal T2 in torque units is smoother than the input signal T1 and has a peak magnitude which is lower than or equal to the second constant value of the input signal T1. This indicates that the second filter f2 of block 510 comprises a smoothing filter, such as a low pass filter. Therefore, the second filtered signal T2 is smoothed relative to the input signal T1. Furthermore, FIG. 6A shows that the second filtered signal T2 is smoother than the setpoint signal ST. This demonstrates that the second filter f2 of block 510 may comprise a longer time constant than the first filter f1 of block 504. Optionally, the second filter f2 of block 510 comprises a proportional low pass filter with a time constant, such as a PT1 filter. The time constant may be different from the time constant of the first filter f1. At blocks 514-516, the method 500 comprises determining a lead signal (lead torque, LT), in dependence on the first and second filtered signals ST, T2. At block 518, the method 500 comprises outputting an air control signal 518 to cause control of the inlet air actuator 316 of the powertrain 100, in dependence on the lead signal LT. The lead signal LT in the context of a reactive control scheme relates to the control system 300 being configured to boost (e.g., amplify or add an offset) the lead signal LT relative to the input signal T1. By contrast, the setpoint signal ST is smoothed relative to the input signal T1. This produces the result shown in FIG. 6A, wherein the lead signal LT is advanced (separated) relative to the setpoint signal ST and has a greater peak magnitude. Furthermore, the lead signal LT dependent on the change of the input signal T1 may reach a peak torque magnitude greater than the changed input signal T1 (i.e., greater than the second constant torque value of the input signal T1). The boosting may in some cases cause the lead signal LT to overshoot / overtake the input signal T1 in magnitude before the end of the change of the input signal T1, in other words before the input signal T1 reaches the second constant torque. Similarly, the peak torque magnitude of the lead signal LT is greater than the peak torque magnitude of the setpoint signal ST. An advantage is improving both responsiveness, and diesel emissions control where the engine 102 is a diesel engine. Responsiveness is improved because the boosted lead signal LT (lead air signal) means there will be less delay of the change of air mass flow rate into the combustion chambers 103. This is further improved by causing the lead signal LT to have a greater peak magnitude than the input signal T1. The diesel emissions control is improved because the lead signal LT for the inlet air actuator 316 is advanced relative to the setpoint signal ST controlling fuel injection and / or spark timing. Therefore, the change of air mass flow rate is less likely to fall behind the change of combustion start time and / or fuel mass flow rate. This helps to minimise unwanted deviations of air-fuel ratio and inappropriate combustion start times during the torque change, and therefore helps to minimise particulate matter production and nitrogen oxide production. Specifically, FIG. 5 shows the lead signal LT being calculated by a subtraction block 514 and an addition block 516. The subtraction block 514 subtracts the second filtered signal T2 from the input signal T1. The output of the subtraction block 514 is the difference (‘delta’, AT), between the two signals T2 and T1. In other words, AT=T2-T 1. The addition block 516 then adds the difference AT to the setpoint signal ST of block 506, to produce the final lead signal LT which is output in block 518 as the air control signal 518. In other words, LT=ST+AT. FIG. 6B illustrates the difference AT with respect to time, on the same axes aligned with FIG. 6A. The difference AT represents the difference between the lines T1 and T3. It also represents the difference between the lines LT and ST. The difference AT follows a temporal nonlinear profile comprising an increasing ramp, a curved peak having a magnitude less than or equal to the input signal T1 at a time step of the peak, and a curved decay. The general shape of the profile AT in FIG. 6B is dependent on the type of second filter f2 of block 510, and the time constant used for the second filter f2 of block 510. The exact magnitude and decay time of the profile AT additionally depend on the input signal T1. If the input signal T1 is constant, the magnitude of AT will be zero. If the input signal T1 comprises a step change, the magnitude of AT will start at a peak which may be equal to T1 (dependent on filter tuning), and will be followed by a decay as the smoothed second filtered signal T2 converges towards the step-changed input signal T1. Therefore, where the second filter f2 is a low pass filter, the peak of the profile AT is greater than zero and is no greater than T1 for a given time step. If the input signal T1 takes a nonzero length of time to reach its changed value as shown in FIG. 6A, the profile AT will comprise an initial ramp leading to the peak. The profile AT shown in FIG. 6B is advantageous. An advantage is that the profile (also referred to above as the difference / separation) has a predetermined shape to provide good diesel emissions performance and responsiveness. The profile AT boosts the magnitude of the lead signal LT relative to the input signal T1 and setpoint signal ST, while also creating a temporal separation between the lead signal LT and setpoint signal ST in the time axis. Therefore, the inlet air actuator 316 is actuated faster and to a position that supplies more air than would be required for producing the changed torque requested by the input signal T1. This will minimise the ‘air delay’ in filling the combustion chambers 103 with oxygen-carrying air. If the second filter f2 has a longer time constant than shown, T2 will beeven smoother relative to T1, so AT=T1-T2 will have a greater area under the curve. Therefore, the lead signal LT=ST+AT will be boosted by a greater degree. This allows the first filter f1 to be tuned with a shorter time constant so that the setpoint signal ST is smoothed / delayed by a lesser degree, to maintain the desired separation AT between the lead signal LT and setpoint signal ST. In some examples, the first filter f1 could even be taken out. Furthermore, if the second filter f2 has a shorter time constant than shown, T2 will be less smooth relative to T1. Therefore AT will have a lower area under the curve. Therefore, the lead signal LT=ST+AT will be boosted by a lesser degree. This means that the first filter f1 should be tuned with a longer time constant so that the setpoint signal ST is smoothed / delayed by a greater degree, to maintain the desired separation AT between the lead signal LT and setpoint signal ST. In FIG. 6A, the second filter f2 has a longer time constant than the first filter f1, as evidenced by T2 being smoother than ST. Consider the situation in which the time constant of the first filter f1 is increased until it is longer than the second filter f2. The setpoint signal ST would be smoother than the second filtered signal T2. As well as the effect of reducing engine responsiveness, this would result in a very large separation AT (FIG. 6B), and a very highly boosted lead signal LT. The very large separation AT could mean that too much inlet air enters the combustion chamber 103 before fuelling / spark changes take effect, resulting in a fuel-lean air-fuel ratio so that nitrogen oxide production increases. This may however be a non-issue for some alternative fuels or engines, which enable lean running without nitrogen oxide production. Consider also the situation in which the time constant of the second filter f2 is decreased until it is shorter than the first filter f1. The second filtered signal T2 would be less smoothed than the setpoint signal ST. This would result in a very small separation AT (FIG. 6B), and less boosting of the lead signal LT. The small separation AT could mean that insufficient inlet air enters the combustion chamber 103 before fuelling / spark changes take effect, resulting in a fuel-rich air-fuel ratio so that soot production increases. This may however be a non-issue for some fuels or engines where soot production is minimal. Therefore, examples of the present invention extend to situations in which the setpoint signal ST is smoother than the second filtered signal T2, depending on the characteristics of the engine and the fuel used. An overall advantage of the approach of FIGS. 5 to 6B is optimisation of both engine responsiveness and diesel emissions. This contrasts from a strategy that focuses only on improving either responsiveness or emissions control. A strategy for diesel engines that only focuses on emissions but not responsiveness may just apply a low pass filter to the input signal T1 to determine the combustion control signal 508. The air control signal 518 may be equal to the input signal T1. Therefore, the combustion start time and / or fuelling is slowed to maintain a desired air-fuel-ratio and combustion start time while the air mass flow rate slowly catches up to the change of input signal T1. In other words, the response of the engine is slowed to optimise emissions. A strategy that focuses only on responsiveness but not diesel emissions would not apply a low pass filter to the input signal T1 to determine the combustion control signal 508. The combustion control signal 508 and air control signal 518 may be equal to the input signal T1. Although the changes to combustion / fuelling would occur substantially immediately in response to the changed input signal T1, the change of air mass flow rate would lag the input signal T1 due to air inertia. The lag would cause temporary deviation of the air-fuel ratio from a desired value until the air mass flow rate ‘catches up’. 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. For example, rather than adding AT to the setpoint signal ST, the setpoint signal ST or input signal T1 may be multiplied by a gain to determine the lead signal LT. The gain may depend on the setpoint signal ST, to achieve at least some of the advantages described herein. It is to be understood that the or each controller 301 can comprise a control unit or computational device having one or more electronic processors (e.g., a microprocessor, a microcontroller, an application specific integrated circuit (ASIC), etc.), and may comprise a single control unit or computational device, or alternatively different functions of the or each controller 301 may be embodied in, or hosted in, different control units or computational devices. As used herein, the term “controller,” “control unit,” or “computational device” will be understood to include a single controller, control unit, or computational device, and a plurality of controllers, control units, or computational devices collectively operating to provide the required control functionality. A set of instructions could be provided which, when executed, cause the controller 301 to implement the control techniques described herein (including some or all of the functionality required for the method(s) described herein). The set of instructions 308 could be embedded in said one or more electronic processors 304 of the controller 301; or alternatively, the set of instructions 308 could be provided as software to be executed in the controller 301. A first controller or control unit may be implemented in software run on one or more processors. One or more other controllers or control units may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller or control unit. Other arrangements are also useful. The, or each, electronic processor 304 may comprise any suitable electronic processor (e.g., a microprocessor, a microcontroller, an ASIC, etc.) that is configured to execute instructions 308. The, or each, electronic memory device 306 may comprise any suitable memory device and may store a variety of data, information, threshold value(s), lookup tables or other data structures, and / or instructions therein or thereon. In an embodiment, the memory device 306 has information and instructions for software, firmware, programs, algorithms, scripts, applications, etc. stored therein or thereon that may govern all or part of the methodology described herein. The processor, or each, electronic processor 304 may access the memory device 306 and execute and / or use that or those instructions and information to carry out or perform some or all of the functionality and methodology described herein. The at least one memory device 306 may comprise a computer-readable storage medium (e.g. a non-transitory or non-transient storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors / computational devices. Examples of the form include, without limitation: a magnetic storage medium (e.g. floppy diskette); optical storage medium (e.g. CD-ROM); magneto optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g. EPROM ad EEPROM); flash memory; or electrical or other types of medium for storing such information / instructions. It will be appreciated that embodiments of the present invention can be realised in any suitable form of hardware, software or a combination of hardware and software. For example, it is contemplated that the present invention is not limited to being implemented by way of programmable processing devices, and that at least some of, and in some embodiments all of, the functionality and or method steps of the present invention may equally be implemented by way of non-programmable hardware, such as by way of non-programmable ASIC, Boolean logic circuitry, etc. The blocks illustrated in FIG. 5 may represent steps in a method and / or sections of code in the computer program 308. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some steps to be omitted. Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Claims

1. A control system for controlling a powertrain of a vehicle, the powertrain comprising an internal combustion engine, the control system comprising one or more processors collectively configured to:receive an input signal indicative of a propulsive torque request, the input signal comprising a change;determine a lead signal in dependence on the input signal, wherein the lead signal has a greater peak magnitude than the change of the input signal; andoutput an air control signal to cause control of an inlet air actuator of the powertrain, in dependence on the lead signal, to control the inlet air actuator to cause a magnitude of airflow proportional to the air control signal.

2. The control system of claim 1, configured to:determine a setpoint signal in dependence on the input signal; andoutput a combustion control signal to cause control of a combustion actuator of the internal combustion engine, in dependence on the setpoint signal,wherein the lead signal is advanced relative to the setpoint signal and has a greater peak magnitude than both the setpoint signal and the input signal during the change.

3. The control system of claim 2, wherein determining the setpoint signal comprises applying a first filter to the input signal to determine a first filtered signal, and wherein the setpoint signal comprises the first filtered signal.

4. The control system of claim 3, wherein the lead signal is dependent on the first filtered signal.

5. The control system of any preceding claim, wherein determining the lead signal comprises applying a filter to the input signal to determinea filtered signal, and comprises determining the lead signal in dependence on the filtered signal.

6. The control system of claim 5 in combination with claim 2 or 3 or 4, wherein the filter is a second filter different than the first filter, andwherein the second filter is configured so that the second filtered signal is smoother than the first filtered signal.

7. The control system of claim 5 or 6, wherein the lead signal is dependent on a difference between the input signal and the filtered signal.

8. The control system of claim 7, wherein determining the lead signal comprises adding the difference to the setpoint signal to determinethe lead signal.

9. The control system of claim 8, wherein the filter is configured so that the difference follows a temporal nonlinear profile comprising apeak having a magnitude less than or equal to the input signal at a time step of the peak, and a decay.

10. The control system of any one of claims 5 to 9, wherein the filter comprises a proportional low pass filter with a time constant.

11. The control system of any preceding claim, wherein the input signal is a reactive arbitrated propulsive torque request, and whereincontrol system is configured to determine the lead signal reactively.

12. A system comprising the control system of any preceding claim and the inlet air actuator.

13. A vehicle comprising the system of claim 12 or the control system of any one of claims 1 to 11.

14. A method of controlling a powertrain of a vehicle, the powertrain comprising an internal combustion engine, the method comprising:12receiving an input signal indicative of a propulsive torque request, the input signal comprising a change;determining a lead signal in dependence on the input signal, wherein the lead signal has a greater peak magnitude than the change of the input signal; andoutputting an air control signal to cause control of an inlet air actuator of the powertrain, in dependence on the lead signal, to control the5 inlet air actuator to cause a magnitude of airflow proportional to the air control signal.

15. Computer readable instructions which, when executed by a computer, are arranged to perform a method according to claim 14.

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