Control system for a powertrain of a vehicle

Abstract

A control system for controlling a vehicle powertrain comprising an electric machine which can provide torque to a drivetrain, the system configured to: receive an electric machine rotational speed si

Description

TECHNICAL FIELD The present disclosure relates to a control system for controlling a powertrain of a vehicle. Aspects of the invention relate to a control system for controlling a powertrain of a vehicle, to a vehicle including the control system, to a method of controlling the powertrain of the vehicle and to computer readable instructions which, when executed by a computer, are arranged to perform the method. BACKGROUND It is known to provide vehicles with speed sensors and speedometers for allowing a driver of the vehicle to monitor the speed of the vehicle. Speed sensors may also be used to supply data to vehicle control systems, such as cruise control. Known speed sensors measure a rotational speed of a wheel of the vehicle and infer a linear speed of the vehicle from the rotational speed of the wheel. However, the present inventors have observed that this method may lead to inaccuracies in vehicle speed measurement. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a control system for controlling a powertrain of a vehicle, a vehicle including the control system, a method of controlling the powertrain of the vehicle and computer readable instructions which, when executed by a computer, are arranged to perform the method, as claimed in the appended claims. According to an aspect of the present invention there is provided a control system for controlling a powertrain of a vehicle, the powertrain comprising an electric machine and a drivetrain arranged to receive torque from the electric machine, the control system comprising one or more processors collectively configured to: receive an electric machine rotation signal, the electric machine rotation signal comprising information indictive of a rotational speed of the electric machine; receive a drivetrain torque ratio signal, the drivetrain torque ratio signal comprising information indicative of a torque ratio of the drivetrain; and determine a vehicle speed based on the information indicative of the rotational speed of the electric machine and the information indicative of the torque ratio of the drivetrain. By using the electric machine rotational speed to determine the vehicle speed, the vehicle speed may be determined more accurately. In particular, this may be observed at low speeds as wheel speed sensors may cut-out or provide a zero signal at low speed, whereas the higher rotational speed of the electric machine may reduce this effect. The one or more processors may be collectively configured to: determine an electric machine torque requirement based at least partially on the vehicle speed; and output an electric machine torque requirement signal to cause the electric machine to generate a torque based on the electric machine torque requirement. By determining the vehicle speed based on the electric machine rotational speed, the electric machine torque requirement may be determined more accurately, allowing improved control of the vehicle. 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 carry out the functions of the control system defined herein. The one or more processors may be collectively configured to: determine whether the vehicle speed is below a speed determination threshold; and based on a determination that the vehicle speed is below the speed determination threshold, determine the vehicle speed based on the rotational speed of the electric machine and the torque ratio of the drivetrain. By using a speed determination threshold, the electric machine may be used to determine the speed only at low speeds of the vehicle. This may reduce computational requirements in normal use of the vehicle. The one or more processors may be collectively configured to: receive a wheel speed signal indicative of a rotational speed of a wheel of the vehicle; determine whether the vehicle speed is above the speed determination threshold; and based on a determination that the vehicle speed is above the speed determination threshold, determine the vehicle speed based on the rotational speed of the wheel. By using a speed determination threshold, the wheel speed may be used to determine the vehicle speed at high speeds of the vehicle. This may reduce computational requirements when the vehicle is moving quickly. The speed determination threshold may be less than 3 kilometres per hour, preferably less than 2 kilometres per hour, more preferably less than 1 kilometre per hour. By setting the speed determination threshold to these values, the more computationally intensive method of determining speed using the electric machine may be used at the point that wheel speed sensors may become inaccurate. The one or more processors may be collectively configured to: receive a torque demand signal comprising information indicative of a torque demand; determine whether the torque demand is below a torque demand threshold, and based on a determination that the torque demand is below the torque demand threshold, determine the vehicle speed based on the rotational speed of the electric machine and the torque ratio of the drivetrain. The torque demand signal may be generated by a driver input device such as a vehicle pedal or by ADAS. By using the torque demand at least in part to determine how to determine vehicle speed, the vehicle speed may be determined using the electric machine only for bringing the vehicle to rest. The one or more processors may be collectively configured to: determine a vehicle mass and / or a road gradient, and determine the electric machine torque requirement based at least partially on the vehicle mass and / or the road gradient. By determining the vehicle mass and / or the road gradient, the control system may determine the electric machine torque required to drive the vehicle, improving vehicle behaviour. The one or more processors may also be configured to receive an acceleration signal comprising information indicative of a proper acceleration of the vehicle and the vehicle mass and / or road gradient may be estimated based at least partially on the proper acceleration as well as the vehicle speed, and / or on a vehicle acceleration derived from the vehicle speed. The vehicle mass and / or road gradient may also be determined based on the electric machine torque requirement in addition to the proper acceleration and the vehicle speed. Determining the electric machine torque may comprise determining the electric machine torque required to decelerate the vehicle to rest. In this way, the system may bring the vehicle to rest with less driver input. Determining the electric machine torque may comprise determining the electric machine torque required to decelerate the vehicle to rest at a rate of between 2ms‘2 and 7 ms2, preferably between 3ms 2 and 6ms 2, more preferably between 4ms2 and 5ms2. This may provide a more comfortable way to bring a vehicle to rest, improving a passenger experience. According to a further aspect of the invention there is provided a vehicle comprising the control system of the above-described aspect. The vehicle may comprise a battery electric vehicle. The vehicle may be propelled by an electric machine only and may comprise no internal combustion engine. The drivetrain may comprise no torque converter. According to a still further aspect of the invention, there is provided a method for controlling a powertrain of a vehicle, the powertrain comprising an electric machine and a drivetrain arranged to receive torque from the electric machine, the method comprising: receiving an electric machine rotation signal, the electric machine rotation signal comprising information indictive of a rotational speed of the electric machine; receiving a drivetrain torque ratio signal, the drivetrain torque ratio signal comprising information indicative of a torque ratio of the drivetrain; determining a vehicle speed based on the information indicative of the rotational speed ofthe electric machine and the information indicative of the torque ratio of the drivetrain; determining an electric machine torque demand based at least partially on the vehicle speed; and outputting an electric machine torque demand signal to cause an electric machine to generate a torque based on the electric machine torque demand. The method may further comprise measuring the rotational speed of the electric machine with an encoder coupled to an output shaft of the electric machine, and receiving the electric machine rotation signal may comprise receiving the electric machine rotation signal from the encoder. 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. According to a yet stull further aspect of the invention, there is provided computer readable instructions which, when executed by a computer, are arranged to perform a method according to the further aspect. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a vehicle in accordance with all embodiments of the invention; Figure 2 shows a schematic diagram of a vehicle, including a control system and a powertrain, in accordance with an embodiment of the invention; Figure 3a shows a graph of speed against measured speed for a known speed sensor; Figure 3b shows a graph of speed against measured speed for a speed sensor in accordance with the invention; and Figures 4 to 6 show flowcharts illustrating methods in accordance with embodiments of the invention. DETAILED DESCRIPTION Embodiments of this invention relate to the determination of speed of a vehicle and a determination of required torque based on the measured speed. In particular, embodiments of the invention relate to the determination of speed of a vehicle based on measurement of the rotational speed of a power source at low speed. Figure 1 illustrates a vehicle according to an embodiment of the present invention to provide context for the invention. The vehicle 10 includes a control system 110 and a powertrain 120. The control system 110 is arranged to control the powertrain 120. The vehicle 10 may be a hybrid electric vehicle having an electric machine and an internal combustion engine both arranged to drive the wheels of the vehicle or may be a battery electric vehicle powered by an electric machine only. The vehicle 10 may be a mild hybrid electric vehicle (MHEV) or a plugin hybrid electric vehicle (PHEV). Figure 2 shows a schematic diagram of components of the vehicle 10. The vehicle 10 has a control system 110, the control system 110 comprising a plurality of controllers 111, 112, 114, 116. The controllers are collectively configured to receive data from different sensors, systems, and input devices of the vehicle, to process the data and to output commands for controlling the vehicle. The controllers may each or may communally comprise processing means and memory means. The processing means may be one or more electronic processing devices which operably execute computer readable instructions. The memory means may be one or more memory devices. The memory means is electrically coupled to the processing means. The memory means is configured to store instructions, and the processing means is configured to access memory means and to execute the instructions stored thereon. The control system 110 is arranged to control a powertrain 120. The powertrain comprises a power source 122. The power source 122 may be an electric machine and in some cases the powertrain 120 may have two power sources 122 which are an electric machine and an internal combustion engine. The powertrain 120 also comprises a drivetrain 124 that is arranged to receive torque 131 from the power source 122. The drivetrain 124 may be a direct-drive drivetrain and may have a gearbox and a differential for increasing the torque 131 delivered from the power source 122 so that a higher torque 133 may be delivered to the wheels 126 of the vehicle. The power source 122 is controlled by and monitored by a power source control unit 112 of the control system 110. The power source control unit 112 is arranged to output an electric machine torque requirement signal 141 to the power source 122 to cause the power source to generate a required amount of torque 131. The power source control unit 112 is also arranged to receive data 142 from the power source 122. The received data includes a rotational speed of the power source 122 and may include a torque delivered by the power source 122. The drivetrain 124 is controlled by and monitored by a drivetrain control unit 114 of the control system 110. The drivetrain control unit 114 may transmit commands 143 to the drivetrain 124, such as the gear change command to change a torque ratio of the drivetrain 124. The drivetrain control unit 114 may also receive data 144 from the drivetrain 124. The received data 144 may include a rotational speed of one or more components of the drivetrain 124, or an amount of torque received by the drivetrain 124 or output by the drivetrain 124. The torque ratio of the drivetrain may be transmitted from the drivetrain 124 to the drivetrain control unit 114 as part of data 144 or may be stored as a value in the drivetrain control unit 114, as the drivetrain control unit 114 may command the drivetrain 124 in order to control the torque ratio of the drivetrain 124. The control system 110 also includes a wheel speed sensor 116. The wheel speed sensor 116 is arranged to measure a speed 146 of the wheel 126 and may determine a vehicle speed from the wheel speed 146. The control system 110 also contains a central control unit 111. The central control unit 111 is arranged to receive information 151, 153, 155 from the power source control unit 112, the drivetrain control unit 114 and the wheel speed sensor 116. The central control unit 111 may also transmit commands to the power source control unit 112 and the drivetrain control unit 114. For example, the central control unit 111 may transmit a torque demand 152 to the power source control unit 112 to cause the power source 122 to generate a required torque. The central control unit 111 may also transmit a gear change request 154 to the drivetrain control unit 114, to cause the drivetrain 124 to alter a torque ratio of the drivetrain 124. The central control unit 111 may receive a power source speed and / or a power source torque in the data 151 received from the power source control unit 112 and may receive a torque ratio in the data 153 from the drivetrain control unit 114. The central control unit 111 is also arranged to receive further input signals. The control unit 111 is arranged to receive a torque request 103 from a torque input device 102. The torque input device may be a driver's accelerator pedal or may be an autonomous driving system. The control unit 111 is also arranged to receive a proper acceleration value 105 from an inertial measurement unit 104. The proper acceleration may be used to determine a gradient of a road the vehicle is on, and may be used in determination of a mass of the vehicle, in conjunction with a torque value received from the power source 122 and / or the drivetrain 124. The central control unit 111 may also receive a driving mode input value 107 from a driving mode selection switch 106. The driving mode may include information such as a desired driving style, or a terrain over which the vehicle is travelling. It will be understood that the inertial measurement unit 104 and / or the driving mode selection switch 106 may be omitted in some cases. The driving mode selection switch 106 may indicate that a single pedal driving mode is to be effected. In a single pedal driving mode, the control system 110 may instruct the power source 122 to exert a braking torque to decelerate the vehicle based on an input from an accelerator pedal, without any input from a brake pedal. Based on the information 151, 153 received from the power source 122 and the drivetrain 124 via the power source control unit 112 and the drivetrain control unit 114 respectively, the central control unit 111 may determine a speed of the vehicle. In other cases, the control unit 111 may receive a vehicle speed 155 from a wheel speed sensor 116. Based on the determined speed of the vehicle and the torque demand 103, the control unit 111 may output a torque demand 152 to the power source control unit 112 to cause the power source 122 to generate a desired torque. In some cases, a gear change request 154 may be output to the drivetrain control unit 114 to cause the drivetrain 124 to alter the torque ratio of the drivetrain. It will be understood that the control system 110 may be a single, unitary system and signals which are generally described as being received by the control system or output by the control system may be published on a central CAN bus or merely output by one portion of a computer program and received by a further portion of the computer program. Figure 4 shows a flowchart illustrating a method 300 of determining a vehicle speed in accordance with the present invention. The method 300 is a method of controlling a powertrain of a vehicle 10, such as the vehicle 10 illustrated in Figures 1 and 2. The method 300 may be performed by the control system 110 illustrated in Figures 1 and 2. In particular, the control system may comprise a memory, which may comprise computer-readable instructions which, when executed by a processor, perform the method 300 according to an embodiment of the invention. At step 310, the control system 110 receives an electric machine rotation signal 151, which may be received from an encoder arranged to sense a rotational speed of an output shaft of the electric machine 122. At step 315, the control system 110 receives a drivetrain torque ratio signal 153. The signal may indicate a torque ratio of the drivetrain, or a speed ratio of the drivetrain. In some cases, receiving the drivetrain torque ratio signal may be retrieving data stored within the control system indicative of the torque ratio of the drivetrain. At step 320, the control system 110 determines a vehicle speed based on the electric machine rotation signal and the drivetrain torque ratio. The determination may include dividing the electric machine rotation signal by the drivetrain torque ratio, and multiplying the value by a further constant, to convert the rotational speed to a linear vehicle speed. The vehicle may comprise two or more electric machines and electric machine rotation signals comprising information indicative of the rotational speeds of each electric machine may be received by the control system from each of the electric machines. Two or more vehicle speeds may be calculated based on the electric machine rotation signals from the two or more electric machines The vehicle speeds calculated based on the rotational speeds of the separate electric machines may be averaged in order to provide a more reliable value of vehicle speed. Two electric machines may also be used to drive wheels on opposite sides of the vehicle. The electric machines rotating the wheels at different rates may turn the vehicle. Therefore, using an average of the two electric machine rotational speeds or an average of the wheel speeds associated with the respective electric machines may give a more accurate indication of the vehicle speed. The rotational speeds of the electric machines may be compared and a difference between the vehicle speeds calculated based on the rotational speeds of the separate electric machines being above a threshold may result in an error signal being generated. Alternatively, at step 320, the vehicle speed may be determined based on a gearbox output shaft speed and a known torque ratio of the drivetrain downstream of the gearbox, i.e. between the gearbox output shaft and the wheels. At step 330, the control system 110 determines an electric machine torque requirement based on the vehicle speed. The electric machine torque requirement may be calculated in order to change the vehicle speed to a desired speed, and so may be determined based on a torque demand from a user or from ADAS, in combination with the determined vehicle speed. At step 340, the control system 110 outputs a torque requirement signal 152 to cause the power source 122 to generate a required torque. Figure 5 shows a flowchart illustrating a method 350 of determining a vehicle speed in accordance with the present invention. The method 350 may be performed by the control system 110 illustrated in Figures 1 and 2. In particular, the control system may comprise a memory, which may comprise computer-readable instructions which, when executed by a processor, perform the method 350 according to an embodiment of the invention. At the first step 360, a vehicle speed is determined. The vehicle speed may be determined based on either of the electric machine speed or a wheel speed at the first step, and the initial method of determination of vehicle speed may be selected by a designer as required. Generally, a control system may receive data from a wheel speed sensor, from a power source speed sensor and from a drivetrain control unit and may determine a vehicle speed based on either of the vehicle speed determination methods discussed herein initially. At step 370, it is determined whether the vehicle speed is above or below a threshold value. Figure 3A illustrates a graph of vehicle speed S against measured vehicle speed S’ for a known vehicle speed sensor. The graph 200 shows line 210, which illustrates that the measured vehicle speed S’ is a good indication of true vehicle speed S for vehicle speeds above a threshold T. However, below the threshold T the measured vehicle speed S’ may deviate from the true vehicle speed S. The lack of accuracy of the sensor at low speed is due to the speed sensor being based on detecting a rotation of a wheel of the vehicle that is in contact with the road, and at low speeds the wheel rotation rate may be too low to allow the sensor to function correctly. The threshold value may be 3km / h or less, or any threshold at which measured vehicle speed may deviate from true vehicle speed when measured by wheel speed sensors. In the case that it is determined that the vehicle speed determined at step 360 is below the threshold, the method moves to step 380, where the control system determines the vehicle speed based on the electric machine rotation speed and the drivetrain torque ratio. Figure 3B shows a graph 250 of measured vehicle speed S’ against true vehicle speed S for a system in accordance with the present invention where speed is measured based on a rotation speed of an electric machine and a torque ratio of a drivetrain. As the electric machine may rotate more quickly than the vehicle wheels, particularly at low speed where the drivetrain may have a high torque ratio, the measured vehicle speed S’ may be more closely indicative of the true vehicle speed S at low speeds. In this way, the system may determine the vehicle speed more accurately at lower vehicle speeds. However, if the vehicle speed is greater than the threshold, then the vehicle speed may be determined directly from a wheel speed sensor at step 390. At any stage, after the vehicle speed is determined, the determination of how to determine the vehicle speed at step 370 may be repeated, so that the method of determining the vehicle speed may be altered as necessary as the vehicle speed changes. It will be understood that hysteresis may be introduced into the system, so that the threshold may change dynamically depending on the speed determination method used. The threshold may increase when the electric machine is used to determine the speed and may decrease when a wheel speed sensor is used to determine the vehicle speed. This may reduce unnecessary changes between the different schemes for determining the vehicle speed. In some cases, step 370 may be dispensed with, and the speed may be determined using the electric machine rotational speed and the drivetrain torque ratio at all times. Figure 6 illustrates a further method 400 for determining a required electric machine torque. The method 400 may be performed by the control system 110 illustrated in Figures 1 and 2. In particular, the control system may comprise a memory, which may comprise computer-readable instructions which, when executed by a processor, perform the method 400 according to an embodiment of the invention. At step 410 a torque demand is received either from a vehicle user or from an advanced driver assistance system (ADAS). The torque demand 152 may be a request to bring the vehicle to rest. At step 420, the speed of the vehicle is considered and compared to a threshold T, and it is determined whether the vehicle speed is above or below a threshold. If the vehicle speed is above the threshold T, then the vehicle speed is determined at step 430 using a wheel speed sensor. Alternatively, if the vehicle speed is below the threshold, then the vehicle speed may be determined using an electric machine and a torque ratio of a drivetrain at step 440. It will be understood that, in some cases steps 420 and 430 may be omitted and the vehicle speed may be determined using the electric machine speed and a torque ratio of the drivetrain in all cases. At step 450, a vehicle mass and / or a road gradient is determined. The control system 110 may determine the vehicle mass and the road gradient based on one or more vehicle speed measurements taken at different times, a torque output by the power source 122 and the torque ratio of the drivetrain 124, and a proper acceleration measured by an inertial measurement unit. The mass of the vehicle and the road gradient may be determined by a range of different mathematical methods, which are well known to the skilled person based on the received data. For example, a road gradient may be determined directly based on a proper acceleration (with some accounting made for pitching of the vehicle suspension). The vehicle mass may be determined based on a propulsion force that is the resultant of the torque generated by the power source and a weight force due to road gradient divided by a vehicle acceleration calculated based on two or more vehicle speed measurements. At step 460, based on the vehicle speed, the torque demand and / or the road gradient and / or the vehicle mass, a required torque may be determined and a torque requirement signal may be output. The required torque may be determined in order to bring the vehicle to rest at a specific deceleration rate. The required torque may be determined such that the vehicle speed follows a vehicle speed profile, which comprises a plurality of vehicle speeds at different time values. At step 470, the vehicle speed may be measured and compared to the desired vehicle speed profile. In case there is a deviation from the desired vehicle speed profile, the system may re-estimate the vehicle mass and the road gradient such that the required torque may be recalculated at step 460. Alternatively, if the vehicle speed is close to zero, it may be determined that the vehicle is at rest and the method may move to step 480. At step 480, where it is determined that the vehicle is at rest, vehicle foundation brakes may be applied to hold the vehicle in place. In this way, a vehicle may be brought to rest without a driver inputting a brake demand to a brake pedal and 5 without the involvement of ADAS. By using an electric machine speed to determine the vehicle speed, the speed of the vehicle at low speeds as it is brought to rest may be determined more accurately and so the driver experience may be improved. 10 It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

1. A control system for controlling a powertrain of a vehicle, the powertrain comprising an electric machine and a drivetrain arranged to receive torque from the electric machine, the control system comprising one or more processors collectively configured to:receive an electric machine rotation signal, the electric machine rotation signal comprising information indictive of a rotational speed of the electric machine;receive a drivetrain torque ratio signal, the drivetrain torque ratio signal comprising information indicative of a torque ratio of the drivetrain;determine a vehicle speed based on the information indicative of the rotational speed of the electric machine and the information indicative of the torque ratio of the drivetrain;determine an electric machine torque requirement based at least partially on the vehicle speed;andoutput an electric machine torque requirement signal to cause the electric machine to generate a torque based on the electric machine torque requirement.

2. The control system of claim 1, wherein, the one or more processors are collectively configured to: determine whether the vehicle speed is below a speed determination threshold; and based on a determination that the vehicle speed is below the speed determination threshold, determine the vehicle speed based on the rotational speed of the electric machine and the torque ratio of the drivetrain.

3. The control system of claim 1 or 2, wherein the one or more processors are collectively configured to:receive a wheel speed signal indicative of a rotational speed of a wheel of the vehicle; determine whether the vehicle speed is above the speed determination threshold; and based on a determination that the vehicle speed is above the speed determination threshold, determine the vehicle speed based on the rotational speed of the wheel.

4. The control system of claim 2 or 3, wherein the speed determination threshold is less than 3 kilometres per hour.

5. The control system of any preceding claim, wherein, the one or more processors are collectively configured to:receive a torque demand signal including information indicative of a torque demand; determine whether the torque demand is below a torque demand threshold, and based on a determination that the torque demand is below the torque demand threshold, determine the vehicle speed based on the rotational speed of the electric machine and the torque ratio of the drivetrain.

6. The control system of any preceding claim, wherein the one or more processors are collectively configured to:determine a vehicle mass and / or a road gradient, anddetermine the electric machine torque requirement based at least partially on the vehicle mass and / or the road gradient.

7. The control system of any preceding claim, wherein determining the electric machine torque comprises determining the electric machine torque required to decelerate the vehicle to rest.

8. The control system of claim 7, wherein determining the electric machine torque comprises determining the electric machine torque required to decelerate the vehicle to rest at a rate of between 2ms 2 and 7ms2.

9. A vehicle comprising the control system of claims 1 to 8.

10. The vehicle of claim 9, wherein the vehicle is a battery electric vehicle.

11. A method for controlling a powertrain of a vehicle, the powertrain comprising an electric machine and a drivetrain arranged to receive torque from the electric machine, the method comprising:receiving an electric machine rotation signal, the electric machine rotation signal comprising information indictive of a rotational speed of the electric machine;receiving a drivetrain torque ratio signal, the drivetrain torque ratio signal comprising information indicative of a torque ratio of the drivetrain;determining a vehicle speed based on the information indicative of the rotational speed of the electric machine and the information indicative of the torque ratio of the drivetrain;determining an electric machine torque demand based at least partially on the vehicle speed; andoutputting an electric machine torque demand signal to cause an electric machine to generate a torque based on the electric machine torque demand.

12. The method of claim 11, further comprising measuring the rotational speed of the electric machine with an encoder coupled to an output shaft of the electric machine, wherein receiving the electric machine rotation signal comprises receiving the electric machine rotation signal from the encoder.

13. Computer readable instructions which, when executed by a computer, are arranged to perform a method according to claims 11 or 12.13

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