Controlling vehicle traction

Abstract

Aspects and embodiments of the disclosure relate to a method and control system (300) for controlling an internal combustion engine (200) of a vehicle (1). The method comprises: receiving a driver torque signal indicative of a driver torque demand; determining an air control signal (240) configured to control an active tappet (236) to deliver a first air charge to meet driver torque demand; receiving a torque intervention signal from a traction control system (608), the torque intervention signal indicative of a torque intervention by the traction control system (608); and outputting, in dependence on the torque intervention signal, a modified air control signal (242) configured to control the active tappet (236) to deliver a second air charge, the second air charge being a reduced air charge relative to the first air charge.

Description

[0001] CONTROLLING VEHICLE TRACTION

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to controlling vehicle traction. Aspects of the invention relate to a control system, to a system, to a vehicle, to a method, and to computer readable instructions.

[0004] BACKGROUND

[0005] During driving, a vehicle may experience a loss of traction and / or a predicted loss of traction. For example, at least one wheel of the vehicle may slip and / or be predicted to slip. When a loss of traction and / or a predicted loss of traction occurs, torque output by, for example, an internal combustion engine (“engine”) can be changed to enable the vehicle to regain traction and / or prevent loss of traction.

[0006] It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

[0007] SUMMARY OF THE INVENTION

[0008] Aspects and embodiments of the invention provide a control system, a system, a vehicle, a method, and computer readable instructions as claimed in the appended claims.

[0009] 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 internal combustion engine comprising an active tappet to control air charge available for combustion in a combustion chamber of the internal combustion engine, the control system comprising one or more processors collectively configured to:

[0010] receive a driver torque signal indicative of a driver torque demand;

[0011] determine an air control signal configured to control an active tappet to deliver a first air charge to meet driver torque demand; receive a torque intervention signal from a traction control system, the torque intervention signal indicative of a torque intervention by the traction control system; and

[0012] output, in dependence on the torque intervention signal, a modified air control signal configured to control the active tappet to deliver a second air charge, the second air charge being a reduced air charge relative to the first air charge.

[0013] An advantage is torque output from the internal combustion engine is rapidly reduced in response to a fraction control signal.

[0014] 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:

[0015] receive a driver torque signal indicative of a driver torque demand;

[0016] determine an air control signal configured to control an active tappet to deliver a first air charge to meet driver torque demand;

[0017] receive a torque intervention signal from a fraction control system, the torque intervention signal indicative of a torque intervention by the fraction control system; and

[0018] output, in dependence on the torque intervention signal, a modified air control signal configured to control the active tappet to deliver a second air charge, the second air charge being a reduced air charge relative to the first air charge.

[0019] Optionally, the traction control system is operable to monitor and / or predict traction between a road wheel of the vehicle and the driving surface.

[0020] Optionally, the torque intervention signal which is indicative of reduced traction may be generated in response to a wheel slip event. A wheel slip event may be a predicted wheel slip or an occurrence of wheel slip.

[0021] An advantage is torque output from the internal combustion engine is rapidly reduced in response to a fraction control signal, which may be in response to a wheel slip event.Optionally, the control system configured to determine the modified air control signal in dependence on a maximum torque indicated by the torque intervention signal.

[0022] An advantage is torque output from the internal combustion engine is rapidly reduced in response to a maximum indicated in a traction control signal.

[0023] Optionally, determining the modified air control signal comprises converting the maximum torque to an air mass using a look up table to determine the second air charge, and inputting the air mass into a model to determine at least one of valve lift or valve timing for the active tappet to deliver the second air charge.

[0024] An advantage is accuracy of air charge is maintained with use of the second air charge.

[0025] Optionally, the control system is configured to:

[0026] determine that the torque intervention has ended; and

[0027] output in dependence on determining that the torque intervention has ended, an air control signal configured to control the active tappet to deliver the first air charge to meet the driver torque demand.

[0028] An advantage is torque output from the internal combustion engine can be rapidly increased in response to the wheel slip event ending, to meet the driver demanded torque. In some examples, the rate at which the torque output from the internal combustion engine is increased is dependent on the coefficient of friction of the surface that the vehicle is on. In examples, if the surface is slippy (slippery), the torque can be ramped back up carefully to avoid further wheelslip. In examples, if the surface provides good traction, the torque can be increased more quickly. In examples, the rate of reintroduction of torque is dependent on the coefficient of friction of the surface.

[0029] Optionally, determining that the torque intervention has ended is in dependence on the torque intervention signal.

[0030] Optionally, the modified air control signal is configured to control the active tappet to control air intake into an individual combustion chamber of the internal combustion engine to reduce an amount of torque provided by the internal combustion engine.

[0031] An advantage is torque output from the internal combustion engine is rapidly reduced in response to a fraction control signal.

[0032] Optionally, the control system is configured to determine the air control signal using a first method, and to determine the modified air control signal using a second, different method.

[0033] An advantage is air mass accuracy is maintained with use of the first and second air charges.

[0034] Optionally, the first method comprises determining at least one of valve lift or valve timing for the active tappet to deliver the first air charge using a look up table, and wherein the second method comprises determining at least one of valve lift or valve timing for the active tappet to deliver the second air charge using a model.

[0035] An advantage is air mass accuracy is maintained with use of the first and second air charges.

[0036] Optionally, the control system is configured to output, in dependence on the second air charge, a fuel control signal to control an amount of fuel provided to the combustion chamber with the second air charge to maintain a substantially stoichiometric air to fuel ratio for combustion in the combustion chamber.

[0037] An advantage is optimal air / fuel ratio can be maintained, to provide efficient combustion.Optionally, the control system is configured to output, in dependence on the second air charge and the amount of fuel provided to the combustion chamber, an ignition control signal to adjust ignition timing for the combustion chamber to maintain optimal ignition timing for the second air charge and the amount of fuel provided to the combustion chamber.

[0038] An advantage is efficient combustion can be maintained with use of the second air charge.

[0039] Optionally, adjusting ignition timing for the combustion chamber comprises advancing the ignition timing.

[0040] An advantage is efficient combustion can be maintained with use of the second air charge.

[0041] Optionally, the modified air control signal is configured to control at least one of valve lift, valve open duration, or valve timing to deliver the second air charge.

[0042] An advantage is torque output from the internal combustion engine is rapidly reduced in response to a fraction control signal.

[0043] Optionally, the modified air control signal is configured to control the active tappet to deliver the second air charge by at least one of the following:

[0044] changing the lift of the active tappet;

[0045] changing the opening duration of the active tappet;

[0046] changing the timing of opening of the active tappet; and

[0047] changing the timing of closing of the active tappet.

[0048] An advantage is torque output from the internal combustion engine is rapidly reduced in response to a fraction control signal.

[0049] Optionally, the modified air control signal is configured to control a volume of the active tappet to deliver the second air charge.

[0050] An advantage is torque output from the internal combustion engine is rapidly reduced in response to a fraction control signal.

[0051] Optionally, the control system is configured to output, in dependence on the second air charge, a throttle control signal to control a throttle of the internal combustion engine to maintain intake manifold air pressure to the level with the first air charge.

[0052] An advantage is efficient combustion can be maintained with use of the second air charge.

[0053] Optionally, the control system is configured to determine that the torque intervention has lasted longer than a predetermined time period and output, in dependence on determining that the torque intervention has lasted longer than a predetermined time period, at least one actuator control signal configured to control at least one of a throttle, an exhaust phaser, or a camshaft phaser to an optimal setpoint for the traction event torque limit.

[0054] An advantage is setpoints of engine actuators can be changed if it is determined that the torque intervention has lasted longer than a predetermined time period.

[0055] According to another aspect of the invention there is provided a system comprising the control system and the active tappet.

[0056] According to a further aspect of the invention there is provided a vehicle comprising the system or the control system of any aspects of invention discussed herein.According to a further aspect of the invention there is provided a method of controlling a powertrain of a vehicle, the powertrain comprising an internal combustion engine, the internal combustion engine comprising an active tappet to control air charge available for combustion in a combustion chamber of the internal combustion engine, the method comprising:

[0057] receiving a driver torque signal indicative of a driver torque demand;

[0058] determining an air control signal configured to control an active tappet to deliver a first air charge to meet driver torque demand; receiving a torque intervention signal from a traction control system, the torque intervention signal indicative of a torque intervention by the traction control system; and

[0059] outputting, in dependence on the torque intervention signal, a modified air control signal configured to control the active tappet to deliver a second air charge, the second air charge being a reduced air charge relative to the first air charge.

[0060] Optionally, the method comprises determining the modified air control signal in dependence on a maximum torque indicated by the torque intervention signal.

[0061] According to a further aspect of the invention, there is provided computer readable instructions which, when executed by a computer, are arranged to perform the method.

[0062] 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.

[0063] According to another 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 internal combustion engine comprising an active tappet to control air charge available for combustion in a combustion chamber of the internal combustion engine, the control system comprising one or more processors collectively configured to:

[0064] receive a torque intervention signal from a traction control system, the torque intervention signal indicative of a torque intervention by the traction control system; and

[0065] output, in dependence on the torque intervention signal, an air control signal configured to control the active tappet to deliver an air charge that is reduced relative to an air charge for a driver requested torque demand.

[0066] 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.

[0067] BRIEF DESCRIPTION OF THE DRAWINGS

[0068] 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;

[0069] FIGS. 2A and 2B illustrate schematic views illustrating an example of an engine;

[0070] FIG. 3 illustrates a schematic view illustrating an example of a control system;

[0071] FIG. 4 illustrates a flowchart illustrating an example method;

[0072] FIG. 5 illustrates an example method;

[0073] FIG. 6 illustrates another example method; and

[0074] FIG. 7 illustrates a graph illustrating an example of torque, ignition timing, and engine trapped air mass per cycle.DETAILED DESCRIPTION

[0075] 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. 1 also schematically illustrates an internal combustion engine 200 (“engine”) of the vehicle 1.

[0076] FIGS. 2A-2B illustrate an example implementation of a part of the engine 200. FIG. 2A illustrates components associated with a combustion chamber 218 of the engine 200, and FIG. 2B illustrates an inlet arrangement of the engine 200. The components form part of a powertrain 235 of the engine 200.

[0077] The engine 200 is configured to burn fuel such as gasoline, ethanol, hydrogen, or alternative fuels.

[0078] The engine 200 may be configured to operate in a four-stroke cycle, or compatible alternatives thereof.

[0079] The engine 200 can comprise a plurality of combustion chambers 218 arranged in a bank. The engine 200 can comprise one or more banks of combustion chambers 218.

[0080] The illustrated engine 200 is a reciprocating piston engine. Alternatively, the engine 200 may be a different type of internal combustion engine.

[0081] The illustrated engine 200 comprises a reciprocating piston 214 in each combustion chamber 218. The pistons 214 are collectively coupled to a crankshaft by connecting rods. Each piston 214 has a top dead centre (TDC) and bottom dead centre (BDC).

[0082] The illustrated engine 200 comprises one or more inlet ports 208 fluidly coupled to the combustion chamber 218, and one or more exhaust ports 212 fluidly coupled to the combustion chamber 218. Unburnt air is aspirated through the inlet port 208, and exhaust gas is exhausted through the exhaust port 212.

[0083] The illustrated engine 200 comprises an inlet valve 232 for each inlet port 208, and an exhaust valve 233 for each exhaust port 212. Each inlet valve 232 is seated on a respective inlet valve seat 206 when in a closed position. Each exhaust valve 233 is seated on a respective exhaust valve seat 210 when in a closed position. The inlet valve 232 and exhaust valve 233 each comprise a poppet valve, or an equivalent thereof.

[0084] A plurality of engine actuators are also illustrated. These include at least one fuel injector 220, at least one igniter 222, and a variable valve actuation system 234 for each inlet valve 232 and / or for each exhaust valve 233.

[0085] The illustrated fuel injector 220 comprises a direct injection spray nozzle, to spray fuel 246 directly into the combustion chamber 218. Alternatively, or additionally, the fuel injector 220 can comprise an indirect injection spray nozzle, also referred to as a port injector, to spray fuel 246 into the inlet port 208.

[0086] The illustrated igniter 222 comprises a spark plug. In other implementations which do not require variable ignition timing, the igniter 222 may be omitted or replaced with a different type of igniter 222.

[0087] The illustrated engine 200 comprises a throttle 256 located in the inlet port 208 to control the amount of air in the inlet port and consequently the amount of air that can flow into the combustion chamber 218 for combustion.

[0088] Also illustrated in the illustrated example is a control system 300 to control operation of various elements of the engine 200. The illustrated control system 300 is configured to control operation of, at least, the fuel injector 220, the igniter 222, the throttle 256, and the inlet valve 232.The illustrated control system 300 is configured to output actuator control signals 254 to control operation of the fuel injector 220, the igniter 222, the throttle 256, and the inlet valve 232. The illustrated control system 300 is configured to output ignition control signals 248 to control operation of the igniter 222, air control signals 240 and modified air control signals 242 to control operation of the inlet valve 232, fuel control signals 244 to control operation of the fuel injector 220, and throttle control signals 250 to control operation of the throttle 256.

[0089] FIG. 2B illustrates a valvetrain 231 of the engine 200, the valvetrain 231 comprising a camshaft 260 and a variable valve actuation system 234. The engine 200 may comprise a variable inlet valve actuation system 234 for each inlet valve 232.

[0090] The valvetrain 231 may comprise a plurality of variable valve actuation systems 234 configured to be actuated by the same camshaft 260.

[0091] A variable valve actuation system 234 may comprise a variable valve lift actuation system . T raditional valve actuators provide a fixed valve lift profile. The variable valve lift actuation system 234 is distinguished from such valve actuators because it is configured to vary valve timing and / or valve lift.

[0092] FIG. 2B relates to an implementation in which the variable valve lift actuation system 234 comprises an active tappet 236 to control air charge available for combustion in a combustion chamber 218 of the internal combustion engine 200. The active tappet 236 may be an active hydraulic tappet. The variable valve lift actuation system 234 can be described as an electrohydraulic actuation system configured to enable substantially continuously variable valve lift (CWL).

[0093] Illustrated in the example of FIG. 2B is a reciprocating piston 214 and a combustion chamber 218 above the piston 214. An inlet valve 232, in the form of a poppet valve, is configured to be opened to admit air from an inlet port 208. The inlet port 208 is fed from an inlet manifold 258, at the mouth of which is provided a throttle valve 256.

[0094] The inlet valve 232 is closed by a spring (not shown) and is opened by action of a rotatable cam which is provided by a lobe of a camshaft 260. Between the camshaft 260 and the inlet valve 232 is provided an active tappet 236.

[0095] In the schematically illustrated example, the active tappet 236 comprises a hydraulic chamber 237 whose volume is determined according to opening and closing of a bleed valve 264 such as an actively controlled (e g., electrically controlled) switching valve. The bleed valve 264 may be controlled by a solenoid / high-speed solenoid, for example. When open, the bleed valve 264 allows escape of fluid to a reservoir or accumulator (not shown) as indicated by arrow 262. The hydraulic chamber 237 receives a constant supply of oil under pressure, and by varying the timing of opening of the bleed valve 264 with respect to camshaft timing, the volume of oil in the chamber can be changed to affect the lift, duration, and timing of operation of the inlet valve 232. The active tappet 236 may enhance, oppose, or neutralize the effect of the camshaft 260.

[0096] The illustrated active tappet 236 is by way of example and any suitable active tappet can be used. For example, any type of active tappet configured to permit variation of valve lift, duration, and / or timing on a firing event basis can be used. In the illustrated example, valve lift, for example, may be varied at each successive opening of the inlet valve 232, if required, for each cylinder of a multi-cylinder engine 200.

[0097] In the example of FIG. 2B, a control system 300 is configured to control operation of the active tappet 232. The control system 300 is configured to output control signals to, for example, control an amount of oil in the hydraulic chamber 237 to control valve lift, duration, and / or timing.

[0098] Inlet valve lift, duration, and / or timing are controllable based on the amount of oil in the hydraulic chamber 237 throughout a combustion cycle.

[0099] A maximum possible valve lift is possible by maximizing the amount of oil in the hydraulic chamber 237 for the entire duration that the lobe of the camshaft 260 actuates the active tappet 236.A zero or minimum possible valve lift is possible by minimizing the amount of oil in the hydraulic chamber 237 for the entire duration that the lobe of the camshaft 260 actuates the active tappet 236.

[0100] Partial valve lift can be effected by maintaining an amount of oil in the hydraulic chamber 237 that is between the maximum and minimum amount of oil. For example, partial valve lift can be effected by opening the bleed valve 264 after the lobe of the camshaft 260 commences actuating the active tappet 236 and / or by closing the bleed valve 264 before the lobe of the camshaft 260 ceases actuating the active tappet 236.

[0101] The variable valve lift actuation system 234 may be configured to enable the actuation start time and / or actuation end time of the active tappet 236 to be varied on a combustion cycle by combustion cycle basis, separately for each combustion chamber 218 in a bank.

[0102] FIG. 2B is described as a variable inlet valve lift actuation system because the inlet valves 232 primarily control the mass of trapped unburnt air in the combustion chamber 218.

[0103] In some examples, a variable valve actuation system 234 may comprise a variable valve timing system, such as a camshaft phaser for the camshaft for the inlet valves 232 and / or a camshaft phaser (exhaust phaser) for the camshaft for the exhaust valves 233.

[0104] The engine 200 can also comprise various standard engine sensors that are not illustrated.

[0105] 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. Optionally, the control system 300 may be supplied with at least one active tappet as a system 2.

[0106] The control system 300 is configured to receive at least one torque signal, for example a driver torque signal indicative of a driver torque demand from a torque request module 314, and a torque intervention signal from a traction control system 608. The control system 300 is configured to determine at least one control signal to control at least one output vehicle system 316 such as at least one active tappet 236, and / or at least one engine actuator described herein. The control system 300 may then output the at least one control signal to control at least one output vehicle system 316 such as at least one active tappet 236, and / or at least one engine actuator described herein.

[0107] 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.

[0108] 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 torque signal, such as a driver torque signal from the torque request module 314, and a torque intervention signal from the traction control system 608. The torque signal is an electrical signal which is indicative of a torque demand and / or a torque limit. The output 312 is arranged to output at least one control signal, such as an air control signal 240 and / or a modified air control signal 242 indicative of at least one of valve lift or valve timing for an active tappet 236 for controlling an air charge available for combustion in a combustion chamber 218 of an engine 200. The at least one control signal may also comprise a fuel control signal 244 indicative of a required duty cycle of the fuel injector 220 for controlling an injection timing and duration of the fuel injector 220 to inject a calibrated required mass of fuel into the combustion chamber 218. The at least one control signal may also comprise an ignition control signal 248 indicative of a required spark time of the igniter 222 for controlling an ignition time of a fuel air mixture in the combustion chamber 218.The control system 300 may be a control system 300 for controlling a powertrain 235 of a vehicle 1 , the powertrain 235 comprising an internal combustion engine 200, the internal combustion engine 200 comprising an active tappet 236 to control air charge available for combustion in a combustion chamber 218 of the internal combustion engine 200, the control system 300 comprising one or more processors collectively configured to perform at least part of one or more methods described herein.

[0109] FIG. 4 illustrates a method 500 according to an embodiment of the invention. The method 500 is a method of controlling the engine 200 of a vehicle 1 , such as the vehicle 1 illustrated in FIG. 1. In particular, the method 500 is a method of controlling the variable valve actuation system 234 of the engine 200. 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 at least part of the method 500.

[0110] Alternatively, or additionally, the method 500 can be a method of controlling an air charge available for combustion in a combustion chamber 218 of an engine 200 of a vehicle 1.

[0111] Alternatively, or additionally, the method 500 can be a method of controlling an active tappet 236 in an engine 200 of a vehicle 1.

[0112] Alternatively, or additionally, the method 500 can be a method of controlling vehicle traction.

[0113] The method 500 comprises, at block 502, receiving a driver torque signal indicative of a driver torque demand.

[0114] The driver torque signal may be from an automated signal from, for example an advanced driver-assistance (ADAS) system, or from a human driver, for example as a result of a human driver pressing an accelerator pedal of the vehicle 1. A torque request module 314 of FIG. 3 can comprise an ADAS system for automated driving, and a pedal position sensor for human driving.

[0115] A driver torque demand may be indicative of driver requested torque. For example, a driver torque demand may be indicative of an amount of torque to be provided by the engine 200 of the vehicle 1 , to, for example, accelerate the vehicle 1.

[0116] The method comprises, at block 504, determining an air control signal 240 configured to control an active tappet 236 to deliver a first air charge to meet driver torque demand.

[0117] Determining an air control signal 240 may comprise determining an amount of torque to be provided by the engine 200 and converting the determined amount of torque to an air mass of the first air charge to be used to meet the driver torque demand. In examples, determining an air control signal 240 comprises determining an amount of torque to be provided by the engine 200 and converting the determined amount of torque to the first air charge to be used to meet the driver torque demand.

[0118] In examples, an air mass to be used in the combustion chamber 218 of the engine 200 can be determined and an air charge having the determined air mass can be delivered to the combustion chamber 218 of the engine 200.

[0119] In some, but not necessarily all examples, converting the determined amount of torque to an air mass comprises determining a required air mass in dependence on the driver torque demand and at least one additional factor. The at least one additional factor can comprise any factor affecting torque output of the engine 200 for a given air charge in a combustion chamber 218 of the engine 200. For example, the at least one additional factor can comprise at least one of: intake manifold pressure, air to fuel ratio, ignition timing, throttle position, waste gate on turbo and so on.

[0120] Converting the determined amount of torque to an air mass of the first air charge to be used to meet the driver torque demand can comprise using a look-up table, for example, a look-up table determined for optimal efficiency combustion in the combustion chamber 218 of the engine 200.The air control signal 240 may be configured to control the active tappet 236 to deliver the first air charge into the combustion chamber 218 of the engine 200 to meet driver torque demand.

[0121] For example, the air control signal 240 may be configured to control an amount of oil in the hydraulic chamber 237 of the active tappet 236 to control at least one of valve lift and valve timing of the inlet valve 232 of the combustion chamber 218 to control an amount of air allowed to flow into the combustion chamber 218 of the engine 200 to deliver the first air charge to meet driver torque demand.

[0122] The method comprises, at block 506, receiving a torque intervention signal from a traction control system, the torque intervention signal indicative of a torque intervention by the traction control system 608 (FIG. 5).

[0123] The torque intervention signal may be configured to limit an amount of torque to be provided by the engine 200. In examples the torque intervention signal is configured to prevent the amount of torque provided by the engine 200 from exceeding an amount of torque indicated in the torque intervention signal. The torque intervention signal may indicate a maximum torque limit.

[0124] A torque intervention may be an intervention to control an amount of torque provided by the engine 200. In examples, a torque intervention is an intervention to limit an amount of torque provided by the engine 200.

[0125] A torque intervention may be defined as the condition in which the torque limit from the fraction control system is less than the driver torque demand. Therefore, a torque intervention refers to the condition in which the torque output of the engine is reduced relative to driver demand, to reduce wheel slip.

[0126] A fraction control system 608 may be a vehicle system configured to monitor and control traction of the road wheels of the vehicle 1. In examples, the traction control system 608 is configured to monitor and / or predict traction between a road wheel of the vehicle 1 and the driving surface.

[0127] The torque intervention may be due to a current and / or predicted loss of traction, for example wheel slip, of at least one wheel of the vehicle 1. Accordingly, the torque intervention may be received in dependence on the fraction control system 608 determining that loss of fraction has occurred and / or is predicted to occur for at least one wheel of the vehicle 1.

[0128] In some, but not necessarily all, examples there might not have been any actual wheel slip, but wheel slip is expected to occur given what is known of, for example: the driving surface, the attitude of the vehicle 1 (pitch, roll), mass of the vehicle 1 , acceleration of the vehicle 1 , speed of the vehicle 1 , level of driver-demanded torque and so on.

[0129] Accordingly, the torque intervention signal, which is indicative of reduced traction, may be generated, or its torque limit may be reduced, in response to a wheel slip event. A wheel slip event may be a predicted wheel slip or an occurrence of wheel slip.

[0130] Wheel slip may be when wheel speed of a wheel of the vehicle 1 is greater than expected for the speed of the vehicle 1 over the ground. Wheel slip may be determined by a comparison of wheel speed and measured or estimated vehicle speed over the ground.

[0131] The method comprises, at block 508, outputting, in dependence on the torque intervention signal, a modified air control signal 242 configured to control the active tappet 236 to deliver a second air charge. The second air charge being a reduced air charge relative to the first air charge.

[0132] Consequently, FIG. 4 illustrates a method 500 of controlling a powertrain 235 comprising an internal combustion engine 200, the internal combustion engine 200 comprising an active tappet 236 to control air charge available for combustion in a combustion chamber 218 of the internal combustion engine 200, the method 500 comprising:

[0133] at block 502, receiving a driver torque signal indicative of a driver torque demand;

[0134] at block 504, determining an air control signal 240 configured to control an active tappet 236 to deliver a first air charge to meet driver torque demand;at block 506, receiving a torque intervention signal from a traction control system 608, the torque intervention signal indicative of a torque intervention by the traction control system 608; and

[0135] at block 508, outputting, in dependence on the torque intervention signal, a modified air control signal 242 configured to control the active tappet 236 to deliver a second air charge, the second air charge being a reduced air charge relative to the first air charge.

[0136] The method 500 may comprise determining the modified air control signal 242 in dependence on the torque intervention signal.

[0137] In some, but not necessarily all examples, method 500 may comprise determining the modified air control signal 242 in dependence on a maximum torque indicated by the torque intervention signal. Method 500 may comprise determining the modified air control signal 242 to deliver the second air charge to limit torque output by the engine to the maximum torque indicated by the torque intervention signal.

[0138] In some examples, determining the modified air control signal 242 comprises converting the maximum torque to an air mass using a look up table to determine the air mass needed for the second air charge, and inputting the air mass into a model to determine at least one of valve lift or valve timing for the active tappet 236 to deliver the second air charge.

[0139] The air mass may be considered the air mass to be used as the second air charge in the combustion chamber 218 of the engine 200. That is, in examples, the air mass is the air mass to be provided to the combustion chamber 218 of the engine 200 to deliver the second air charge. The air mass may be considered to be the second air charge and therefore method 500 may comprise converting the maximum torque to the second air charge.

[0140] As with determining the air control signal 240, in some, but not necessarily all examples, converting the maximum torque to an air mass comprises determining a required air mass in dependence on the maximum torque and at least one additional factor.

[0141] In examples, the modified air control signal 242 is configured to control the active tappet 236 to control air intake into an individual combustion chamber 218 of the engine 200 to reduce an amount of torque provided by the engine 200 compared to an amount of torque provided by the engine 200 if the first air charge were used in the combustion chamber 218 of the engine 200.

[0142] Method 500 may comprise determining the air control signal 240 using a first method, and determining the modified air control signal 242 using a second, different method.

[0143] In examples, a common method, for example a look-up table, may be used to convert the required torque (for example, driver torque demand or maximum torque from torque intervention) to an air mass. Once the air mass has been determined, a first method may be used to determine the air control signal 240 and a second, different method may be used to determine the modified air control signal 242.

[0144] The first and second methods may comprise methods of determining control signals for the active tappet 236 to deliver the first or second air charge to the combustion chamber 218 of the engine 200. In examples, the first and second methods may comprise methods of determining at least one of valve lift or valve timing for the active tappet 236 to deliver the determined air mass as the first or second air charges.

[0145] In some examples, the first method comprises determining at least one of valve lift or valve timing for the active tappet 236 to deliver the first air charge using a look up table, and the second method comprises determining at least one of valve lift or valve timing for the active tappet 236 to deliver the second air charge using a model.

[0146] In examples, the first air charge is used under normal conditions which enables mapped settings in a look up table to be used, with one or more setpoints for one or more engine actuators determined using one or more look up tables. For example, at least one of valve lift or valve timing for the active tappet 236 may be determined from at least one look up table for normal engine conditions and a given driver torque demand.A look up table may map, in examples, driver demand to engine actuator setpomt(s) for optimal settings. In examples, the look up tables may be determined using at least one model in dependence on known engine operating conditions.

[0147] In examples, the second air charge is used outside of normal conditions which means that the mapped settings in look up tables do not apply. For example, to enable a quick response to a traction event, set points of slower engine actuators, such as a throttle, may be unaffected during a traction event meaning that the engine conditions are no longer applicable to the look up table(s) and mapped settings in the look up table(s) no longer apply.

[0148] In examples, the second air charge is determined using current set points for at least one engine actuator as inputs to a model to determine at least one of valve lift or valve timing for the active tappet 236 to deliver the second air charge.

[0149] This is advantageous as, for example, it enables accuracy of determined air mass to be maintained.

[0150] Method 500 may comprise controlling at least one other actuator of the engine 200 in dependence on the second air charge. For example, method 500 may comprise controlling at least one other actuator of the engine 200 in dependence on the mass of the second air charge. For example, method 500 may comprise controlling at least one other actuator of the engine 200 to maintain substantially optimal combustion efficiency in the combustion chamber 218 of the engine 200.

[0151] In some examples, method 500 may comprise controlling at least one other actuator of the engine 200 to keep combustion efficiency in the engine, for example in the combustion chamber 218, for the second air charge substantially unchanged compared to combustion efficiency for the first air charge. For example, method 500 may comprise controlling at least one other actuator of the engine 200 to substantially maintain combustion efficiency in the combustion chamber 218 unaffected for the second air charge compared to the first air charge.

[0152] In some examples, method 500 may comprise controlling at least one other actuator of the engine 200 to maintain peak combustion efficiency and / or to maintain combustion efficiency in a peak region.

[0153] For example, method 500 may comprise determining, in dependence on the second air charge, a fuel control signal 244 to control an amount of fuel provided to the combustion chamber 218. Method 500 may comprise determining, in dependence on the mass of the second air charge, a fuel control signal 244 to control an amount of fuel provided to the combustion chamber 218.

[0154] In some examples, method 500 may comprise outputting, in dependence on the second air charge, a fuel control signal 244 to control an amount of fuel provided to the combustion chamber 218 with the second air charge to maintain at least one of: a pre-existing target air to fuel ratio (prior to the torque intervention and assuming the same engine speed-load); a substantially stoichiometric air to fuel ratio; a ratio proximal to the stoichiometric ratio. Therefore, advantageously, an efficiency of the air to fuel ratio may be substantially maintained / unaffected in response to a torque intervention signal. The fuel control signal 244 may control the fuel injector 220 to deliver an amount of fuel to the combustion chamber 218 corresponding to the above-described air to fuel ratio.

[0155] This is advantageous as, for example, it allows an optimal air to fuel ratio to be maintained to provide efficient combustion.

[0156] In some, but not necessarily all, examples, method 500 may comprise determining, in dependence on the second air charge and the amount of fuel provided to the combustion chamber 218 an ignition control signal 248 to control ignition timing for the combustion chamber 218. Method 500 may comprise determining, in dependence on the mass of the second air charge and the amount of fuel provided to the combustion chamber 218 an ignition control signal 248 to control ignition timing for the combustion chamber 218.

[0157] In some examples, method 500 may comprise outputting, in dependence on the second air charge and the amount of fuel provided to the combustion chamber 218, an ignition control signal 248 to control ignition timing for the combustion chamber 218 to maintain optimal ignition timing for the secondair charge and the amount of fuel provided to the combustion chamber 218. The ignition control signal 248 may control the igniter 222 to maintain optimal ignition timing for the second air charge and the amount of fuel provided to the combustion chamber.

[0158] In examples, optimal ignition timing means ignition timing to provide at least one of: a pre-existing target ignition timing (prior to the torque intervention and assuming a same engine speed-load); a timing substantially equal to Maximum Brake Torque (MBT); a timing proximal to MBT ; or a timing within 3 degrees crank angle of MBT for a gasoline engine. MBT refers to the spark timing that produces the most torque output.

[0159] A model can be used to determine the optimal ignition timing for the second air charge and the amount of fuel provided to the combustion chamber 218 for a given state of the engine 200.

[0160] This is advantageous as it enables, for example, efficient combustion to be maintained in the combustion chamber 218 of the engine 200, while controlling the torque output by the engine 200.

[0161] In some, but not necessarily all, examples controlling ignition timing for the combustion chamber 218 comprises advancing the ignition timing.

[0162] In examples, the modified air control signal 242 is configured to control at least one of valve lift, valve open duration, or valve timing to deliver the second air charge.

[0163] The modified air control signal 242 may be configured to control the active tappet 236 to deliver the second air charge by at least one of the following: changing lift of the active tappet 236, changing the opening duration of the active tappet 236, changing the timing of opening of the active tappet 236, and changing the timing of closing of the active tappet 236.

[0164] The modified air control signal 242 may be configured to control a volume of the active tappet 236 to deliver the second air charge.

[0165] In some examples, when the second air charge is used, one or more other actuators of the engine 200 are controlled as if a different, higher air charge was being provided to the combustion chamber 218. For example, when the second air charge is used, the one or more actuators may be controlled as if the first air charge were still being provided to the combustion chamber 218. For example, one or more actuators of the engine, such as the throttle, exhaust camshaft phaser, intake camshaft phaser and so on, can be maintained at set points that are determined for use in relation to use of the first air charge even when the second air charge is used instead of the first air charge because of the torque intervention.

[0166] In examples, the one or more actuators of the engine that may be maintained in this way are slower actuators.

[0167] This is advantageous as, for example, maintaining slower actuator(s) of the engine 200 at set points for the first air charge can enable the engine to output the driver demanded torque quickly after the torque intervention has ended.

[0168] In some examples, the throttle 256 may be controlled to maintain inlet manifold pressure to the level the inlet manifold pressure would have been without the torque intervention. That is, the throttle 256 may be controlled to compensate for the reduced airflow into the engine 200 from use of the second air charge by, for example, modulating the throttle 256 if required. At higher loads when the throttle 256 is fully open the turbo charger wastegate can be controlled to similarly maintain inlet manifold pressure.

[0169] Accordingly, method 500 may comprise outputting, in dependence on the second air charge, a throttle control signal 250 to control a throttle of the engine 200 to maintain intake manifold air pressure to the level with the first air charge.

[0170] If the torque intervention lasts for an extended period of time, the one or more actuators may be controlled in dependence on the second air charge. Or, in other words, the one or more actuators may react to the torque intervention signal in dependence on the torque intervention exceeding apredetermined time period. That is, if the torque intervention lasts for longer than a predetermined time period, the one or more slower actuators of the engine 200 may be controlled to be at setpoints that are optimal / targeted for use with the second air charge during the torque intervention.

[0171] Accordingly, in examples, method 500 may comprise determining that the torque intervention has lasted longer than a predetermined time period and outputting, in dependence on determining that the torque intervention has lasted longer than a predetermined time period, at least one actuator control signal 254 configured to control at least one of a throttle 256, an exhaust phaser, or a camshaft phaser to an optimal setpoint for the traction event torque limit.

[0172] The predetermined time period can be a time period in the range 0.5 seconds to 2 seconds. For example, the predetermined time period can be 0.5 seconds, 1 second, 2 seconds and so on.

[0173] In some examples, method 500 may comprise determining that the torque intervention has ended, and outputting in dependence on determining that the torque intervention has ended, an air control signal 240 configured to control the active tappet 236 to deliver the first air charge to meet the driver torque demand.

[0174] In examples, the air charge used in the combustion chamber 218 of the engine 200 can be controlled on a firing event basis, which can, for example, allow a rapid decrease in torque in dependence on the torque intervention and subsequent rapid increase of torque to meet driver demand when the torque intervention has ended. For example, by controlling the air charge in individual combustion chambers 218 of the engine 200, torque can be rapidly decreased to correct a wheel slip event or predicted wheel slip event and then rapidly increased to meet driver torque demand.

[0175] This is advantageous as, for example, decreasing torque output from the engine 200 on a firing event to firing event basis enables fraction of at least one road wheel of the vehicle 1 to be quickly controlled if, for example, it is determined that the at least one wheel is slipping or is predicted to slip.

[0176] This is advantageous as, for example, decreasing torque output from the engine 200 by controlling the air charge used in the combustion chamber 218 of the engine 200 enables traction control while maintaining temperature control of exhaust gas and exhaust components downstream of the engine 200.

[0177] This is advantageous as, for example, rapidly increasing torque output from the engine 200 after the torque intervention has ended enables driver torque demand to be quickly met, allowing the vehicle 1 to correct fraction loss while remaining responsive to driver torque demands.

[0178] The rate at which the torque output from the engine 200 is increased can be dependent on the coefficient of friction of the driving surface. For example, if the driving surface is slippery, the torque can be increased carefully to avoid further wheel slip. For example, if the driving surface provides good fraction, the torque can be increased more quickly. In some examples, the rate of reinfroduction of torque is dependent of the coefficient of friction of the driving surface.

[0179] Further, determining that the torque intervention has ended may be in dependence on the torque intervention signal. For example, the torque intervention signal may cease or may indicate a higher maximum fraction torque limit.

[0180] FIG. 5 illustrates an example of a method 600. FIG. 5 also schematically illustrates operation of a traction control system 608 or fraction controller 608 and an engine controller 618.

[0181] The engine controller 618 can be a control system 300 as described herein. The traction control system 608 can be a control system 300 as described herein. The combination of the fraction control system 608 and the engine controller 618 can be a control system 300 as described herein.

[0182] In the illustrated example, the traction control system 608 receives speed over ground information 614 and wheel speed information 616 and determines if wheel slip is occurring or is predicted to occur for at least one road wheel of the vehicle 1.In examples, the traction control system 608 compares the wheel speed information 616 and the speed over ground information 614 and determines if at least one road wheel of the vehicle 1 is moving faster than appropriate for the indicated speed over ground of the vehicle 1.

[0183] The information 614, 616 can be received from at least one sensor of the vehicle 1 and / or can be estimated in dependence on information from at least one sensor of the vehicle 1.

[0184] In the illustrated example, if the fraction control system determines that wheel slip is occurring or is predicted to occur, the traction control system 608 outputs a torque intervention signal 606 indicating a maximum torque limit. The output of the torque intervention signal 606 can be considered a torque intervention 610.

[0185] In the illustrated example, the torque intervention signal 606 is received by the engine controller 618. The engine controller 618 also receives a driver torque demand 604. The engine controller 618 determines whether the maximum torque limit indicated in the torque intervention signal 606 is lower than the driver torque demand 604 and outputs an air control signal 240 (to meet driver torque demand) or modified air control signal 242 (to meet maximum torque limit indicated in the torque intervention signal 606).

[0186] FIG. 6 schematically illustrates operation of the engine controller 618 in greater detail. FIG. 6 also illustrates a method 700.

[0187] In the illustrated example, the driver torque demand 604 is received and converted, at block 702A, to a driver requested air mass 716A using, for example, a look up table determined for optimal combustion in the engine 200. In examples, the driver requested air mass 716A can be the air mass for the first air charge.

[0188] The driver requested air mass 716A is passed to blocks 704 and 706 where valve lift setpoint (block 704) and intake manifold pressure setpoint (block 706) are determined in dependence on the driver requested air mass 716A. A throttle control signal 250 is output from block 706 in dependence on the intake manifold air pressure set point.

[0189] An air control signal 240 is output from block 704 in dependence on the valve lift setpoint and the air control signal 240 may be output from the engine controller 618 in dependence on the state of switch 710.

[0190] The torque intervention signal 606 indicating the maximum torque limit is received and converted, at block 702B, to a fraction control air mass 716B using, for example, a look up table determined for optimal combustion in the engine 200. In examples, the traction control air mass 716B can be the air mass for the second air charge.

[0191] The traction control air mass 716B is passed to block 714. Information of the status of the engine 200 is also received at block 714. For example, inlet manifold pressure, temperature, intake phase timing, exhaust phase timing and so on can be received at block 714.

[0192] In the illustrated example, at block 714, the received information 716B, 718 is used to determine at least one of valve lift or valve timing. For example, the received information 716B, 718 can be input into a model to determine at least one of valve lift or valve timing.

[0193] A modified air control signal 242 is output from block 714 in dependence on the determined valve lift and / or timing and the modified air control signal 242 may be output from the engine controller 618 in dependence on the state of the switch 710.

[0194] At block 712, if the maximum torque limit is less than the driver torque demand, the switch 710 is set to output the modified air control signal 242 to limit engine torque output to the maximum torque limit. However, if the maximum torque limit is greater than the driver torque demand, the switch 710 is set to output the air control signal 240 to output torque to meet the driver torque demand.FIG. 7 illustrates a graph with time on the x-axis 800 and a plurality of different parameters on the y-axis 801.

[0195] In the illustrated example, maximum traction control torque 606 (torque limit), driver demanded torque 604, engine output torque 804, engine ignition advance crank angle degrees before top dead centre (CA BTDC) 806, and engine air trapped mass 716A / 716B per cycle is illustrated before, during and after a wheel slip event 802.

[0196] Throughout the illustrated time period, the driver demanded torque 604 remains constant. However, the maximum traction control torque drops during the wheel slip event 802, due to a torque intervention.

[0197] The engine trapped air mass is the driver requested air mass 716 A / first air charge before the wheel slip event 802 and reduces to the traction control air mass 716B / second air charge during the wheel slip event 802, which causes the engine output torque 804 to reduce from an initial value prior to the wheel slip event 802 to a value that is less than the maximum traction control torque 606 during the wheel slip event 802.

[0198] When the wheel slip event 802 has ended, the maximum traction control torque 606 is raised and is again greater than the driver demanded torque 604, and consequently the driver requested air mass 716A / first air charge is used and the engine output torque increases to the amount prior to the wheel slip event 802 as the driver demanded torque 604 has not changed.

[0199] The engine ignition advance CA BTDC is advanced during the wheel slip event to maintain optimal ignition efficiency while the traction control air mass 716B / second air charge is used.

[0200] 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.

[0201] 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.

[0202] 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 electronic 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.

[0203] 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 opticalstorage 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.

[0204] 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.

[0205] The blocks illustrated in the FIGS. 4 to 6 may represent steps in a method and / or sections of code in the computer program. 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.

[0206] 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

CLAIMS1. A control system for controlling a powertrain of a vehicle, the powertrain comprising an internal combustion engine, the internal combustion engine comprising an active tappet to control air charge available for combustion in a combustion chamber of the internal combustion engine, the control system comprising one or more processors collectively configured to:receive a driver torque signal indicative of a driver torque demand;determine an air control signal configured to control an active tappet to deliver a first air charge to meet driver torque demand; receive a torque intervention signal from a traction control system, the torque intervention signal indicative of a torque intervention by the traction control system; andoutput, in dependence on the torque intervention signal, a modified air control signal configured to control the active tappet to deliver a second air charge, the second air charge being a reduced air charge relative to the first air charge.

2. The control system of claim 1 , configured to determine the modified air control signal in dependence on a maximum torque indicated by the torque intervention signal.

3. The control system of claim 2, wherein determining the modified air control signal comprises converting the maximum torque to an air mass using a look up table to determine the second air charge, and inputting the air mass into a model to determine at least one of valve lift or valve timing for the active tappet to deliver the second air charge.

4. The control system of any preceding claim, configured to:determine that the torque intervention has ended; andoutput in dependence on determining that the torque intervention has ended, an air control signal configured to control the active tappet to deliver the first air charge to meet the driver torque demand.

5. The control system of any preceding claim, configured to determine the air control signal using a first method, and to determine the modified air control signal using a second, different method.

6. The control system of claim 5, wherein the first method comprises determining at least one of valve lift or valve timing for the active tappet to deliver the first air charge using a look up table, and wherein the second method comprises determining at least one of valve lift or valve timing for the active tappet to deliver the second air charge using a model.

7. The control system of any preceding claim, configured to output, in dependence on the second air charge, a fuel control signal to control an amount of fuel provided to the combustion chamber with the second air charge to maintain a substantially stoichiometric air to fuel ratio for combustion in the combustion chamber.

8. The control system of claim 7, configured to output, in dependence on the second air charge and the amount of fuel provided to the combustion chamber, an ignition control signal to adjust ignition timing for the combustion chamber to maintain optimal ignition timing for the second air charge and the amount of fuel provided to the combustion chamber.

9. The control system of claim 8, wherein adjusting ignition timing for the combustion chamber comprises advancing the ignition timing.

10. The control system of any preceding claim, wherein the modified air control signal is configured to control at least one of valve lift, valve open duration, or valve timing to deliver the second air charge.

11. A system comprising the control system of any preceding claim and the active tappet.

12. A vehicle comprising the system of claim 11 or the control system of any one of claims 1 to 10.

13. A method of controlling a powertrain of a vehicle, the powertrain comprising an internal combustion engine, the internal combustion engine comprising an active tappet to control air charge available for combustion in a combustion chamber of the internal combustion engine, the method comprising:receiving a driver torque signal indicative of a driver torque demand;determining an air control signal configured to control an active tappet to deliver a first air charge to meet driver torque demand; receiving a torque intervention signal from a traction control system, the torque intervention signal indicative of a torque intervention by the traction control system; andoutputting, in dependence on the torque intervention signal, a modified air control signal configured to control the active tappet to deliver a second air charge, the second air charge being a reduced air charge relative to the first air charge.

14. The method of claim 13, comprising determining the modified air control signal in dependence on a maximum torque indicated by the torque intervention signal.

15. Computer readable instructions which, when executed by a computer, are arranged to perform a method according to claim 13 or 14.

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