TECHNICAL FIELD

The present disclosure relates to a vehicle engine soft start control system and method. In particular, but not exclusively it relates to a mild hybrid electric vehicle engine soft start control system and method. Aspects of the invention relate to a control system, a system, a vehicle, a method, and computer software.

BACKGROUND

It is known to use an electric machine to crank (start) an internal combustion engine (‘engine’ herein).

Commonly, the electric machine is a pinion starter. In a hybrid electric vehicle, the electric machine may be a motor-generator. In a P0 mild hybrid electric vehicle, the motor-generator may be a belt- integrated starter generator (BISG) coupled to the engine’s crankshaft via a front end accessory drive (FEAD) belt and at least one pulley.

A movable tensioner arrangement may be provided to optimize the slack position of the belt for a given torque direction. The tensioner arrangement may have a driving position and an overrun position.

The pulley may be coupled to the crankshaft and may comprise a vibration decoupler to partially absorb and damp speed fluctuations encountered from the crankshaft. The vibration decoupler may be in the torque path between the engine and electric machine.

The total torsional stiffness between the electric machine and the crankshaft depends on several factors, which may include: the torsional stiffness of the tensioner arrangement; the position of the tensioner arrangement which depends on the direction of torque between the engine and the electric machine; the torsional stiffness of any vibration decouplers; or slack in the belt which also depends on the direction of torque.

The electric machine initially acts against a low initial torsional stiffness while the tensioner arrangement is moved to its driving position, belt slack is taken up, and the vibration decoupler absorbs the initial belt speed increase. This allows the electric machine to reach a high speed before significant torque is transmitted to the crankshaft.

By the time the torsional stiffness in the FEAD has risen, the electric machine has significant inertia, resulting in a torque spike that is transmitted through the FEAD to the crankshaft.

The torque spike may be even greater when the engine start is commanded during engine overrun (e.g. change of mind event during a stop-start event, or exiting glide mode). This is at least because the tensioner arrangement starts in the overrun position and needs to move to the driving position.

Use of a vibration decoupler significantly increases the torque spike, particularly if the vibration decoupler has variable torsional stiffness (initially soft).

SUMMARY OF THE INVENTION

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

Aspects and embodiments of the invention provide a control system, a system, a vehicle, a method, and computer software as claimed in the appended claims.

According to an aspect of the invention there is provided a control system for controlling starting torque for starting an engine of a vehicle, the control system comprising one or more electronic controllers, the one or more electronic controllers configured to: determine whether a condition is satisfied; and output, to an electric machine, a parameter for controlling starting torque for starting the engine, wherein the parameter is limited to a first value and/or first rate of change in dependence on at least the condition being satisfied, and is not limited to the first value and/or first rate of change when the condition is not satisfied. The limit(s) may be removed once starting torque is no longer required. The parameter may be configured to control an output torque of a belt integrated starter generator. An advantage is an improved engine start.

Satisfaction of the condition may require at least a restart of the engine to be requested for when engine speed is above zero. Satisfaction of the condition may require at least the restart to be requested for when engine speed is falling. The condition may be associated with a change of mind event during implementation of an eco-stop function and/or may be associated with a gliding function or exiting an EV only mode. An advantage is an improved overrunning engine restart.

The first value and/or first rate of change may be configured to be high enough to enable the engine to accelerate to an idling speed in less than a second or two. An advantage is an improved overrunning engine restart.

The parameter may be increased according to a ramp or staircase profile limited to the first rate of change. The first rate of change may control a first derivative of a value of torque. The parameter may be limited to one of the first value and/or first rate of change in dependence on at least the condition being satisfied, and may instead be limited to the other of the first value and/or first rate of change in dependence on at least the condition not being satisfied. The first rate of change and the first value may be configured so that engine start with the parameter limited to the first rate of change is faster than engine start with the parameter limited to the first value, and wherein the parameter may be limited to the first rate of change in dependence on at least the condition being satisfied to enable a faster engine start. An advantage of a rate of change limit compared to a value limit is enabling a faster engine start.

A second value of the parameter may be output for engine start when the condition is not satisfied. A constant value of the parameter may be output for engine start when the condition is not satisfied, having a zero rate of change. An advantage is faster engine start when the condition is not satisfied.

According to another aspect of the invention there is provided a control system for controlling starting torque for starting an engine of a vehicle, the control system comprising one or more electronic controllers, the one or more electronic controllers configured to: output, to a starter- generator electric machine, a parameter for controlling starting torque for starting the engine, wherein the parameter is limited to a first rate of change. An advantage is enabling a faster engine start, as explained above.

According to another aspect of the invention there is provided a system comprising the control system and an electric machine configured to receive the parameter and output the starting torque in dependence on the value of the parameter. The electric machine may be a belt integrated starter generator. An advantage is that the limit(s) may be calibrated in dependence on torque output characteristics of the electric machine.

The system may comprise a component that is elastic or slips under torsional load, wherein the component is arranged to enable the starting torque to flow through the component. The component may be a vibration decoupler. The component may comprise one or more energy dissipating elements that are elastic under torsional load. The energy dissipating elements may comprise coil springs or leaf springs that resiliency deform under torsional load. The energy dissipating elements may comprise coil springs, wherein one or more of the coil springs may resiliency compress in dependence on torsional load in a first direction and resiliency compress in dependence on torsional load in a second direction. An advantage is that the limit(s) may be calibrated in dependence on torque capacity characteristics of the component.

The system may comprise a movable tensioner arrangement arranged to tension a belt to a first side of the electric machine when the electric machine is operated as a generator and to move to tension the belt to a second side of the electric machine when the electric machine is operated as a motor. An advantage is that the limit(s) may be calibrated in dependence on movement characteristics of the tensioner and its effects on rate of change of torque loading.

According to another aspect of the invention there is provided a vehicle comprising the control system or the system.

According to another aspect of the invention there is provided a method for controlling starting torque for starting an engine of a vehicle, the method comprising: determining whether a condition is satisfied; and outputting, to an electric machine, a parameter for controlling starting torque for starting the engine, wherein the parameter is limited to a first value and/or first rate of change in dependence on at least the condition being satisfied, and is not limited to the first value and/or first rate of change when the condition is not satisfied.

According to another aspect of the invention there is provided a method for controlling starting torque for starting an engine of a vehicle, the method comprising: outputting, to a starter- generator electric machine, a parameter for controlling starting torque for starting the engine, wherein the parameter is limited to a first rate of change. According to another aspect of the invention there is provided computer software that, when executed, is arranged to perform one or more of the methods described herein. According to another aspect of the invention there is provide a non-transitory computer readable medium comprising computer readable instructions that, when executed by an electronic processor, cause performance of one or more of the methods described herein.

The one or more electronic controllers may collectively comprise: at least one electronic processor having an electrical input for receiving information associated with determining whether the condition is satisfied; and at least one electronic 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 cause the control system to determine whether the condition is satisfied and to output the parameter.

Although the preceding aspects refer to an engine of a vehicle, in other aspects the engine may be a non-vehicle engine or a non-engine power consumer that needs to be started.

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

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig 1 illustrates an example of a vehicle;

Fig 2A illustrates an example of a control system and Fig 2B illustrates an example of a non- transitory computer readable storage medium;

Fig 3 illustrates an example of a system; Fig 4A illustrates an example of a front-end accessory drive, including a belt integrated starter generator, which is transmitting torque in one direction, and Fig 4B shows torque transmission in the opposite direction;

Fig 5A illustrates a first view of an example component and Fig 5B illustrates a second view of the example component;

Fig 6 illustrates an example of a method; and

Fig 7A, 7B, 7C illustrates graphs of torque limit with respect to time.

DETAILED DESCRIPTION

Fig 1 illustrates an example of a vehicle 10 in which embodiments of the invention can be implemented. In some, but not necessarily all examples, the vehicle 10 is a passenger vehicle, also referred to as a passenger car or as an automobile. Passenger vehicles generally have kerb weights of less than 5000 kg. In other examples, embodiments of the invention can be implemented for other applications, such as industrial vehicles.

The vehicle 10 comprises an internal combustion engine 12. The engine 12 may be a reciprocating piston engine. In some examples, the engine 12 may have four or fewer pistons and/or an inline piston configuration, the balance characteristics of which make use of a vibration decoupler more desirable. However, the engine 12 could take other forms in other examples and may even be non-reciprocating.

The engine 12 may be a petrol engine which may encounter a greater torque spike than a diesel engine. In other examples, the engine 12 is a diesel engine.

The vehicle 10 comprises an electric machine 14. The electric machine 14 is capable of transmitting starting torque to the engine 12 to start the engine 12.

In some examples, the electric machine 14 is also configured to transmit propulsive torque, making the vehicle 10 a hybrid vehicle. In some examples, the electric machine 14 is also configured to act as a generator, for example to provide a regenerative braking function.

The electric machine 14 may be arranged in a parallel hybrid configuration or a series hybrid configuration. The electric machine 14 may be arranged in a mild parallel hybrid configuration. The electric machine 14 may be rated at a nominal 48 volts or another voltage. Typically the electric machine 14 may be rated to increase average crankshaft output torque by between 25Nm to 100Nm, at least for starting the engine 12. The rated output torque may be outside this range in other examples. The torque spike may exceed this average. The torque spike may be higher if the rated average is higher.

A control system 20 is shown in Fig 2A which may implement, at least in part, the functionality of the invention. The control system 20 may comprise means to cause any one or more of the methods described herein to be performed, at least in part.

The control system 20 may comprise one or more (electronic) controllers 22. One controller 22 is shown in Fig 2A.

The controller 22 of Fig 2A includes at least one electronic processor 24; and at least one electronic memory device 26 electrically coupled to the electronic processor 24 and having instructions 28 (e.g. a computer program) stored therein, the at least one electronic memory device 26 and the instructions 28 configured to, with the at least one electronic processor 24, cause any one or more of the methods described herein to be performed.

The control system 20 may be supplied separately from or together with any input devices and any actuators controlled by the control system 20.

Fig 2B illustrates a non-transitory computer-readable storage medium 29 comprising the computer program 28 (computer software).

The control system 20 is configured to output, to the electric machine 14, a parameter for controlling starting torque for starting the engine 12. The parameter may take any appropriate known form that enables the results described herein to be achieved.

If the control system 20 is physically separate from the electric machine 14, the parameter may be communicated via a communication bus of the vehicle 10, such as a CAN(TM) bus, Lin(TM) bus, FlexRay(TM) bus, etc. Fig 3 shows a system 30 comprising the control system 20 of any preceding claim and one or more of: the electric machine 14; the belt 32; the tensioner arrangement 36; the vibration decoupler 34; and the engine 12.

The system 30 of Fig 3 shows a P0 (FEAD BISG) parallel hybrid architecture. In other examples, the architecture may be P2 (belt integrated electric machine 14 between engine 12 and transmission).

In still further examples, the architecture may be P3 (electric machine 14 connected to transmission) or P4 (electric machine 14 connected after transmission), if a torque spike occurs, for example due to lost motion in the transmission and/or a clutch during torque reversal. The torque spike may be highest in the P0 architecture due to the belt 32 and tensioner arrangement 36, however P2-P4 architectures may benefit from aspects of the invention.

Figs 4A and 4B show an example arrangement of an electric machine 14, tensioner arrangement 36, belt 32 and vibration decoupler 34 in a P0 hybrid configuration, with more specific detail shown than Fig 3. An optional further pulley 40 is also shown which could be for air conditioning, power steering or other loads.

The belt 32 may be a V-belt or another suitable type of belt. In some examples, a chain may be provided instead of a belt, or even gears.

The illustrated tensioner arrangement 36 is a decoupling belt tensioner. The illustrated tensioner arrangement 36 is arranged to tension the belt 32 to a first side of the electric machine 14 when the electric machine 14 is operated as a generator (‘regen-mode’ in Fig 4A). This is an overrun position of the tensioner arrangement 36. The other (second) side becomes the slack side of the belt 32.

The illustrated tensioner arrangement 36 is arranged to move to tension the belt 32 to a second side of the electric machine 14 when the electric machine 14 is operated as a motor for engine starting or torque boost (‘start/boost mode’ in Fig 4B). This is a driving position of the tensioner arrangement 36. The first side becomes the slack side of the belt 32. The movement may be rotation as illustrated. The axis of rotation of the tensioner arrangement 36 may be coaxial with an axis of rotation of the electric machine 14. The movement of the tensioner arrangement 36 between the overrun and driving positions may occur automatically when the torque direction in the system 30 changes. When the torque of the BISG 14 reverses the movement of the tensioner arrangement 36 between the overrun and driving positions means there is a period of operation where the torque and speed of the BISG increases in the starting direction before any significant transmission of torque to the crankshaft. The tensioner arrangement 36 may be rotatable sufficiently quickly upon torque reversal and/or its biasing force in a tensioning direction may be sufficiently high, that an overshoot of belt tension may occur due to tensioner flicking which increases the torque spike.

Alternatives to a decoupling belt tensioner include separate tensioner pulleys which move and/or rotate between overrun and driving positions about different axes, a twin tensioner wherein the tensioner pulleys are linked and/or rotate about a common axis, or an active electromechanically actuated tensioner arrangement 36.

The vibration decoupler 34 is now described, with reference to at least Figs 4A-5B. The axis of rotation of the vibration decoupler 34 may be coaxial with the crankshaft axis of rotation, or offset in other examples.

The illustrated vibration decoupler 34 comprises an integrated pulley, however in other examples the pulley may comprise no decoupling means and the vibration decoupler 34 may be provided as a torsional vibration damper or other decoupler. In some examples, more than one vibration decoupler 34 could be provided. In some examples, a vibration decoupler 34 with an integrated pulley could be provided in combination with a coaxial or separate torsional vibration damper (not shown).

The illustrated vibration decoupler 34 is elastic under torsional load. In other examples, the vibration decoupler 34 may slip under torsional load.

The elastic-type vibration decoupler 34 comprises one or more energy dissipating elements

50, 52 that are elastic under torsional load. The illustrated energy dissipating elements are coil springs 50, 52. The illustrated coil springs are arranged as arcs around the axis of rotation of the vibration decoupler 34. However, in other examples the elastic energy dissipating elements may be leaf springs (Geislinger(TM)-type decoupler), or another suitable type. Coil spring decouplers generally have lower rotational stiffness than Geislinger decouplers. Examples of the invention are more desirable when coil springs are used rather than rubber rings or Geislinger leaf springs because it is desirable to prevent coil springs from going coil- bound when subjected to a torque spike, to improve NVH (noise, vibration and harshness).

The energy dissipating elements may decouple a hub of the vibration decoupler 34 from an output (e.g. pulley) of the vibration decoupler 34. When torsional load is received in a first direction, one or more of the energy dissipating elements resiliency deforms in dependence on the torsional load in the first direction. The hub starts to rotate with a delay/lag dependent on the elasticity of the energy dissipating elements. For coil springs, the deformation may be compression. The same principle may apply when torsional load is received in a second direction opposite the first direction, e.g. coil spring compression.

Figs 5A-5B show cross-sections through an example vibration decoupler 34, wherein the viewing axis is parallel to its axis of rotation. The vibration decoupler 34 comprises energy dissipating elements with different dissipation characteristics. At least one energy dissipating element may be less elastic than another energy dissipating element. In the illustration, the energy dissipating elements comprise stiff springs 50 (Fig 5A) and soft springs 52 (Fig 5B). In other examples, the springs may all have the same stiffness. Two stiff springs 50 are visible in Fig 5A and two soft springs 52 are provided in Fig 5B, visible through eight windows. Other numbers of springs 50, 52 could be provided in other examples.

For at least torque in the engine starting direction (towards engine 12), the soft springs start to compress before the stiff springs start to compress. It is desirable that the springs do not become coil bound. For this, it is desirable to inhibit the torque spike. If torque is in the opposite direction, the stiff springs may start to compress first.

Fig 6 illustrates an example method 60 which may be performed by the control system 20. The method 60 determines whether to perform a soft start or a regular start.

At block 62, the method 60 comprises determining whether a condition is satisfied. Satisfaction of the condition may require at least the engine 12 to be in a state at which a torque spike has been found through pre-calibration to be likely and/or over a threshold value. Example conditions are discussed below. At block 64, the method 60 comprises outputting, to the electric machine 14, the parameter for controlling starting torque for starting the engine 12, when the condition is satisfied. The parameter is limited to a first value and/or first rate of change. Therefore, a soft start is provided and the torque spike may be inhibited.

At block 64, the parameter may be output substantially immediately when the condition is satisfied, without first trying to adjust the position of the electric machine 14 into a preferred position before applying starting torque, and without waiting for the engine speed to fall to 0 RPM. This reduces engine start time, and obviates a requirement for position control of the electric machine 14 which requires additional sensors.

At block 66, the method 60 comprises outputting, to the electric machine 14, the parameter for controlling starting torque for starting the engine 12, when the condition is not satisfied. The parameter is not limited to the first value and/or first rate of change. Therefore, a regular start is provided which may provide a faster engine start than the soft start.

The condition of block 62 will now be described in more detail.

The condition may be associated with reversing the direction of the torque flowing through the system 30. As described above, a torque reversal requires additional movement and adjustment in the system 30, such as movement of the tensioner arrangement 36, compared to a normal engine start. The tensioner arrangement 36 may also rapidly flick into its driving position and cause a tension overshoot.

In an example implementation, satisfaction of the condition requires at least a restart of the engine 12 to be requested for when engine speed is above zero. If the engine 12 is still rotating, torque spikes may occur. Further, satisfaction of the condition may require at least the restart to be requested for when engine speed is falling. If engine speed is falling, the torque flow may be from the engine 12 to the electric machine 14, therefore a torque reversal is required for engine restart which can cause a torque spike. Satisfaction of the condition may also require there to be an additional braking torque applied by the electric machine 14 to assist the stopping of the engine. Example scenarios in which the condition may be satisfied include a change of mind event during implementation of an eco-stop function and/or an engine start event for exiting a gliding function or EV only mode. Each of these events involve a potential torque reversal.

An eco-stop function is defined as a function which automatically stops the engine 12 when the vehicle 10 is braked and vehicle speed passes below a threshold or is zero. The engine speed will reach 0 RPM. A change of mind event comprises receiving a driver request for propulsive torque from the engine 12 before the engine speed reaches 0 RPM. The driver may be human or autonomous.

A gliding function is defined as a function which automatically stops the engine 12 and declutches the engine 12 from vehicle wheels, to reduce engine braking. The gliding function may be entered while the engine 12 is overrunning and the vehicle 10 is determined to be maintaining its speed (or would be maintaining its speed once engine braking is removed). There is no requirement of braking or stopping the vehicle 10. The engine speed will reach 0 RPM so it will need restarting. A change of mind event of a gliding function would be defined as receiving the driver request for propulsive torque from the engine 12 before the engine speed reaches 0 RPM.

An EV only mode is defined as a mode in which the engine 12 is not in operation. The electric machine 14 may provide propulsive torque for driving the vehicle 10. In a P2-P4 hybrid architecture, the engine 12 could be declutched enabling the engine speed to fall to 0 RPM. A change of mind may occur before the engine 12 has stopped rotating.

Satisfaction of the condition may be checked by the control system 20 waiting for a signal indicative of the change of mind. The signal may take any appropriate form, such as a change of mind flag received from a separate controller that detects a change of mind. Alternatively, the signal may comprise a restart demand flag or driver request signals (accelerator, brake, clutch, gear), and engine speed, and the control system 20 itself may determine whether they represent a change of mind.

Examples of the torque limits of block 64 (or optionally block 66) will now be described, with reference to Fig 7A-C. Graphs A-C show starting torque on the y-axis and time on the x-axis. The starting torque axis represents either a target (as limited), or an upper limit if torque is permitted to vary below a limit. The starting torque axis could represent the value of the parameter.

The graph of Fig 7A shows the effect of limiting the torque to the first value, as per block 64. In an example, the first value limit is applied (line a) from the start of cranking until the end of cranking. The end of cranking (application of start torque by the electric machine 14) may occur when engine speed reaches a target speed such as a minimum idle speed (e.g. around 400rpm or greater). Thereafter, starting torque may no longer be applied and the first value limit may be removed. In other examples, the first value limit may only be applied for the portion of the engine start during which the torque spike occurs and then removed. The portion may be within the first full crankshaft revolution because force is generally highest on first rotation.

While the value limit is in place, the average or target starting torque must not exceed the value limit. The torque spike above the value limit may still occur, but the value limit may bring its magnitude down to the point where it is less perceptible, compared with the situation in which no limit is applied.

By removing the limit after the engine start, the next engine start will be a regular engine start (block 66) unless/until the condition is next satisfied. The graph of Fig 7C shows starting torque (line c) for a regular engine start (block 66), which is permitted to have a second value greater than the first value. There is no rate of change limit in the graph of Fig 7C.

In various examples, the first value may be from the range approximately 40% to approximately 80% of the second value. In some examples the first value may be from the range 20% to 95%. In an example implementation, the electric machine may be rated at 55Nm, the second value may be 50Nm, and the first value may be from the range 30Nm to 40Nm. Values lower than 30Nm may result in a failed start. The value may be configured to be high enough to enable the engine 12 to accelerate to idling speed within a required time. The required time may be a value from the range 0.5-3 seconds. For example, an engine start taking longer than the required monitored time may be flagged as a failed start. Therefore, the first value may be calibrated so that the engine starts within the required time for 100% (or close to 100%) of attempts. The graph of Fig 7B shows the effect of limiting the torque increase (‘ramp rate’) to the first rate of change, as per block 64. When cranking starts, the starting torque is at a low level, which may or may not be lower than the aforementioned first value.

The starting torque then increases according to the illustrated ramp profile (or a staircase profile), at an average or target rate no higher than the limited first rate of change (line b).

The starting torque then reaches a maximum at or towards the end of cranking the engine 12 which may be greater than the aforementioned first value. The maximum may be the same as or lower than the second value of the graph of Fig 7C (regular starts).

The area under the curve of the graph of Fig 7B during cranking may be greater than the area under the curve of the graph of Fig 7A during cranking, such that the rate of change limit enables a faster engine start than the value limit, without increasing the torque spike. Therefore, in some examples, block 64 may implement the rate of change limit for change of mind events in which a fast restart is important to the driver, while block 66 may implement the first value limit for other engine starts in which speed of restart is less important.

Once the engine speed reaches the target speed or the torque spike portion of the engine start has passed, the first rate of change limit may be removed or the starting torque may reach or have reached the second value of the graph of Fig 7C (regular starts).

In various examples, the first rate of change limit may be from the range approximately 100Nm/s to approximately 500Nm/s. More specifically, the first rate of change limit may be from the range approximately 150Nm/s to approximately 350Nm/s, for a mild hybrid electric vehicle 10 implementation. Although the described rate of change limit applies to the first derivative of instant torque (Nm/s), in various examples the limit may be applied to the second derivative. In some examples, the graph of Fig 7C (regular starts) may have no rate of change (constant value) or may comprise a second rate of change limit (not shown), higher than the first rate of change limit. If a rate of change limit is provided for regular starts, the first rate of change limit may be from approximately 40% to approximately 80% of the second rate of change limit. In the example implementation, the second rate of change limit could be above 350Nm/s, such as around 480Nm/s. The first rate of change limit may be configured to be high enough to enable the engine 12 to accelerate to idling speed within the required time, as mentioned above for the first value limit. In some examples, both the first value limit and the first rate of change limit may be applied for block 64. In other words, the torque may increase at a limited rate to a limited (maximum) value that is less than usual.

The above method 60 of starting the engine may be performed in open loop. The duration of an engine start (less than a second or two, usually a few hundred milliseconds) may not permit accurate closed loop control due to communication latency of receiving sensor signals such as crankshaft position. The limit may therefore be determined from pre-calibration. The limits may be constant for the whole life of the vehicle 10 or may be updatable via software over- the-air updates via a telematics unit associated with the vehicle 10.

The above examples refer to a method 60 that conditionally implements soft start. According to other aspects of the invention, soft start is unconditional. For example, there is provided a method 64 comprising: outputting, to a starter generator electric machine 14, a parameter for controlling starting torque for starting the engine 12, wherein the parameter is limited to a first rate of change. The first rate of change limit may be as described above and as shown in Fig 7 B.

For purposes of this disclosure, it is to be understood that the controller(s) described herein can each comprise a control unit or computational device having one or more electronic processors. A vehicle 10 and/or a control system 20 thereof may comprise a single control unit or electronic controller or alternatively different functions of the controller(s) may be embodied in, or hosted in, different control units or controllers. A set of instructions could be provided which, when executed, cause said controller(s) or control unit(s) to implement the control techniques described herein (including the described method(s)) 60, 64. The set of instructions may be embedded in one or more electronic processors, or alternatively, the set of instructions could be provided as software to be executed by one or more electronic processor(s). For example, a first controller may be implemented in software run on one or more electronic processors, and one or more other controllers may also be implemented in software run on or more electronic processors, optionally the same one or more processors as the first controller. It will be appreciated, however, that other arrangements are also useful, and therefore, the present disclosure is not intended to be limited to any particular arrangement. In any event, the set of instructions described above may be embedded in a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors/computational device, including, 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 various changes and modifications can be made to the present invention without departing from the scope of the present application.

The blocks illustrated in Fig 6 may represent steps in a method and/or sections of code in the computer program 28. 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.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

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.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon. The following numbered clauses define various further aspects and features of the present technique:

1. A control system (20) for controlling starting torque for starting an engine (12) of a vehicle (10), the control system comprising one or more electronic controllers (22), the one or more electronic controllers configured to:

determine (62) whether a condition is satisfied; and

output (64, 66), to an electric machine (14), a parameter for controlling starting torque for starting the engine,

wherein the parameter is limited to a first value (a) and/or first rate of change (b) in dependence on at least the condition being satisfied, and is not limited to the first value and/or first rate of change when the condition is not satisfied.

2. The control system of clause 1 , wherein the one or more electronic controllers collectively comprise:

at least one electronic processor (24) having an electrical input for receiving information associated with determining whether the condition is satisfied; and

at least one electronic memory device (26) electrically coupled to the at least one electronic processor and having instructions (28) 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 cause the control system to determine whether the condition is satisfied and to output the parameter.

3. The control system of clause 1 or 2, wherein satisfaction of the condition requires at least a restart of the engine to be requested for when engine speed is above zero.

4. The control system of clause 3, wherein satisfaction of the condition requires at least the restart to be requested for when engine speed is falling.

5. The control system of any preceding clause, wherein the condition is associated with a change of mind event during implementation of an eco-stop function and/or is associated with a gliding function or exiting an EV mode.

6. The control system of any preceding clause, wherein the limit is removed once starting torque is no longer required. 7. The control system of any preceding clause, wherein the first value and/or first rate of change is configured to be high enough to enable the engine to accelerate to an idling speed in less than a second or two.

8. The control system of any preceding clause, wherein the parameter is increased according to a ramp or staircase profile limited to the first rate of change.

9. The control system of any preceding clause, wherein the first rate of change controls a first derivative of a value of torque.

10. The control system of any preceding clause, wherein the parameter is limited to one of the first value and/or first rate of change in dependence on at least the condition being satisfied, and is instead limited to the other of the first value and/or first rate of change in dependence on at least the condition not being satisfied.

1 1 . The control system of clause 10, wherein the first rate of change and the first value are configured so that engine start with the parameter limited to the first rate of change is faster than engine start with the parameter limited to the first value, and wherein the parameter is limited to the first rate of change in dependence on at least the condition being satisfied to enable a faster engine start.

12. The control system of any preceding clause, wherein a second value (c) of the parameter is output for engine start when the condition is not satisfied.

13. The control system of any preceding clause, wherein a constant value (c) of the parameter is output for engine start when the condition is not satisfied , having a zero rate of change.

14. The control system of any preceding clause, wherein the parameter is configured to control an output torque of a belt integrated starter generator (14).

15. A control system (20) for controlling starting torque for starting an engine (12) of a vehicle (10), the control system comprising one or more electronic controllers (22), the one or more electronic controllers configured to: output (64, 66), to a starter-generator electric machine (14), a parameter for controlling starting torque for starting the engine, wherein the parameter is limited to a first rate of change (b).

16. A system (30) comprising the control system of any preceding clause and the electric machine (14) configured to receive the parameter and output the starting torque in dependence on the value of the parameter.

17. The system of clause 16, comprising a component (34) that is elastic or slips under torsional load, wherein the component is arranged to enable the starting torque to flow through the component.

18. The system of clause 17, wherein the component is a vibration decoupler.

19. The system of clause 17 or 18, wherein the component comprises one or more coil springs (50, 52) or leaf springs that resiliency deform under torsional load.

20. The system of clause 19, wherein the component comprises coil springs, wherein one or more of the coil springs resiliency compresses in dependence on torsional load in a first direction and resiliency compresses in dependence on torsional load in a second direction.

21 . The system of any one of clauses 16 to 20, comprising a movable tensioner arrangement (36) arranged to tension a belt (32) to a first side of the electric machine when the electric machine is operated as a generator and to move to tension the belt to a second side of the electric machine when the electric machine is operated as a motor.

22. A vehicle (10) comprising the control system (20) of any one of clauses 1 to 15 or the system (30) of any one of clauses 16 to 21.

23. A method (60) for controlling starting torque for starting an engine (12) of a vehicle (10), the method comprising:

determining (62) whether a condition is satisfied; and

outputting (64, 66), to an electric machine (14), a parameter for controlling starting torque for starting the engine, wherein the parameter is limited to a first value (a) and/or first rate of change (b) in dependence on at least the condition being satisfied, and is not limited to the first value and/or first rate of change when the condition is not satisfied. 24. A method for controlling starting torque for starting an engine (12) of a vehicle (10), the method comprising:

outputting (64), to a starter generator electric machine (14), a parameter for controlling starting torque for starting the engine, wherein the parameter is limited to a first rate of change (b).

25. Computer software (28) that, when executed, is arranged to perform a method (60, 64) according to clauses 23 or 24.