TECHNICAL FIELD

The present disclosure relates to a system for use in the steering apparatus of a vehicle and in particular, but not exclusively, to a system that corrects the configuration of a resistor ladder circuit. Aspects of the invention relate to a vehicle system, to a method for use in a vehicle, and to a vehicle itself.

BACKGROUND

Many aspects of modern vehicles are designed so as to improve user-convenience. One such aspect is to position on the steering wheel of the vehicle electronic controls or buttons to perform electronic functions such as speaker volume up/down, radio station up/down, adaptive cruise control on/off, and hands-free phone call answering. Such steering wheels are referred to as multi-function steering wheels. Positioning of these electronic controls on the multi-function steering wheel rather than in a central portion of the dashboard is advantageous because the user does not require to divert their eyes from the road ahead to locate a specific electronic control and does not require to remove their hand from the steering wheel to select one of the electronic controls, thus improving convenience. As vehicles become more sophisticated, control over a greater number of electronic functions is afforded to the user, and as such, the number of electronic controls on multifunction steering wheels is increasing. Previously, it was known to have several wires (one for each control) on a ribbon cable mounted on a rotary coupler. To minimise propagation delays, rather than making use of a ribbon cable mounted in this way, it is preferable to have a single wire connecting all of the electronic controls via a resistor ladder. However, the greater the number of electronic controls on a particular connection, the narrower the voltage band available to each electronic control, and so the measured output voltage must be more accurate to ensure that the correct electronic control is registered as having been selected. Several factors contribute to lessening the accuracy of the measured output voltage, and therefore increasing the likelihood that an incorrect electronic control is registered. These include ground shift, general electrical noise, resistor tolerances, and lifetime drift of resistor values. In particular, ground shift occurs when the voltage on the ground line is not identically zero because of a current running through the wires; noise may produce random disturbances or fluctuations to an electrical signal; resistor tolerances mean that the actual magnitude of the resistance is different from the stated value within an acceptable error range; and the actual magnitude of the resistance will drift as the resistor ages, particularly in hot and humid climates.

Corrosion can also significantly affect the operation of switches over time. For example, continuous operation of the switches may cause fretting corrosion, whereas prolonged periods of non-operation may lead to the build-up of thin resistive layers on the switch surfaces due to conventional corrosion.

One object of the present invention is to address this issue. Embodiments of the invention may provide a system that is configured to mitigate against the issues described above to ensure that the correct electronic control is registered in a resistor ladder.

SUMMARY OF THE INVENTION

According to an aspect of the invention there is provided a system for use in the steering apparatus of a vehicle, the system comprising a resistor ladder circuit comprising a resistor ladder, the circuit being configured to measure an output across the resistor ladder. The system also comprises a plurality of controls configured to receive a user-input selection into the resistor ladder and a data memory for storing pre-determined output data relating to each of the controls. In addition, the system comprises a processor comprising means configured to receive the output from the resistor ladder circuit, means configured to compare the measured output with the pre-determined output data, and means configured to classify the measured output to a corresponding pre-determined output of the predetermined output data which is indicative of a particular control selection. The processor further comprises means for monitoring and correcting for a difference between the measured output and the corresponding pre-determined output, wherein the pre-determined output data comprises voltage band data relating to a plurality of voltage bands, where each voltage band corresponds to a particular control on the steering apparatus, wherein the voltage band data comprises, for each respective voltage band, an initial bandwidth, an initial value of the centre of each voltage band and an offset value to the initial value of the centre of each voltage band, wherein the processor is configured to correct the offset value by applying a correction value which is determined in dependence on the bandwidth of the associated voltage band.

The correction value may be a pre-determined proportion of the bandwidth of the associated voltage band. The correction value may be about 1 % of the bandwidth of the associated voltage band.

The steering apparatus may include, for example, a multi-function steering wheel or a steering column. Correcting for a difference between the measured output and the corresponding pre-determined output is advantageous to ensure that the correct control is determined even when the measured output is subject to drift over time, or subject to drift for any other reason. The measured output may differ from the corresponding pre-determined output for a number of other reasons. In one embodiment, the plurality of controls form a part of a human machine interface (HMI) on the steering apparatus.

The plurality of electronic controls may typically comprise push button-operated electronic switches. In one embodiment, the system comprises means configured to replace or supplement the pre-determined outputs with updated pre-determined outputs based on user- input selections when the vehicle is in use. This may comprise receiving a user-input selection of a particular electronic control and providing the user-input selection of the particular electronic control to the data memory together with measured output data corresponding to the electronic control to replace or supplement the pre-determined output data. Replacing the pre-determined output data may be desirable if the system has been subject to a significant amount of drift, or if the pre-determined output data contains errors.

The resistor ladder circuit may comprise means configured to de-bounce the measured output. This is of benefit to ensure that the measured output from the circuit accurately represents the user-input selection (for example, a single user-input selection gives a single measured output).

In one embodiment, the measured output takes the form of a measured output voltage. The pre-determined output data may comprise data relating to a plurality of voltage bands, where each voltage band corresponds to a different one of a plurality of electronic controls. The voltage band data may comprise an initial bandwidth for each voltage band, an initial value of the centre of each voltage band, and initial values of the upper and lower boundaries of each voltage band. In one embodiment, the voltage band data further comprises an offset value to the initial value of the centre of each voltage band. In addition, or alternatively, the voltage band data may comprise an offset value to the initial value of one or both of the upper and lower boundaries of each voltage band. In one embodiment, the processor may comprise means configured to correct the offset value corresponding to the voltage band to which the measured output voltage is classified based on the measured output voltage and the initial value of the centre of the voltage band. By way of example, the offset value may be corrected so as to equate to the difference between the measured output voltage and the initial value of the centre of the voltage band.

Where the data comprises a plurality of voltage bands, the processor may comprise means configured to correct the offset value for each of the plurality of voltage bands based on the measured output voltage and the initial value of an associated one of the plurality of voltage bands.

For example, the means configured to correct the offset value may be configured to correct the offset value for each of the plurality of voltage bands so that the offset equates to the difference between the measured output voltage and the initial value of the centre of the associated one of the plurality of voltage bands.

The system may further comprise means configured to compare the difference between the measured output voltage and a current value of the centre of the voltage band to which the measured output voltage is classified, and may be configured to limit the correction to a predetermined proportion of the initial bandwidth in the event that said difference exceeds a predetermined maximum correction value. In another embodiment, the voltage band data may comprise a further offset value to the initial value of one or both of the upper and lower boundaries of each voltage band. The processor may further comprise means configured to correct the further offset value corresponding to the voltage band to which the measured output voltage is classified based on the measured output voltage and the initial value of one or both of the upper and lower boundaries of the voltage band.

The initial bandwidth of each voltage band may depend on a pre-determined expected frequency of use of each electronic control. An electronic control that is used more frequently would expect to be subject to less drift between consecutive measured outputs corresponding to this electronic control, and so the voltage band corresponding to this electronic control could be relatively narrow, thus freeing up bandwidth for less-frequently used electronic controls or for a greater number of electronic controls to be included. In a further embodiment, the system comprises a controller for controlling at least one vehicle subsystem in dependence on to which electronic control the measured output data is classified. According to another aspect of the invention, there is provided a method for use in the steering apparatus of a vehicle, the method comprising; measuring an output across a resistor ladder in a resistor ladder circuit; receiving a user-input selection into the resistor ladder; storing pre-determined output data relating to each of a plurality of controls; and receiving the output from the resistor ladder circuit, comparing the measured output with the pre-determined output data, and classifying the measured output to a corresponding predetermined output of the pre-determined output data indicative of a particular control selection, the method further comprising monitoring and correcting for a difference between the measured output and the corresponding pre-determined output, wherein the predetermined output data comprises voltage band data relating to a plurality of voltage bands, where each voltage band corresponds to a particular control on the steering apparatus, wherein the voltage band data comprises, for each respective voltage band, an initial bandwidth, an initial value of the centre of each voltage band and an offset value to the initial value of the centre of each voltage band, the method further comprising correcting the offset value by applying a correction value which is determined in dependence on the bandwidth of the associated voltage band.

According to another aspect of the invention, there is provided a vehicle comprising a system as described above. In a yet further embodiment, the controller is operable in a diagnostic mode, in which it is operable to receive a measured voltage associated with each of the electronic controls. The controller may then store the measured output voltages, directly to the data memory, as the new centre-of-band values for each of the corresponding electronic controls. For purposes of this disclosure, it is to be understood that the controller described herein can comprise a control unit or computational device having one or more electronic processors.

A vehicle and/or a system thereof may comprise a single control unit or electronic controller or alternatively different functions of the control module may be embodied in, or hosted in, different control units or controllers. As used herein, the term "controller" will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide the required control functionality.

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 method(s) described below). 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 invention 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 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.

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

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures in which: Figure 1 is a diagram of a multi-function steering wheel including a plurality of electronic controls;

Figure 2 is a diagram showing the component parts of a vehicle control system (VCS) for a vehicle having the multi-function steering wheel in Figure 1 , together with the inputs to, and outputs from, the VCS;

Figure 3 is a flow diagram which illustrates a process according to an embodiment of the invention for classifying a particular user-input selection to a particular electronic control, and then correcting the system on the basis of the user-input selection;

Figure 4 is a diagram of a resistor ladder circuit according to an embodiment of the invention which may be employed in the multi-function steering wheel in Figure 1 ; Figure 5 is a schematic diagram of a plurality of voltage bands illustrating a plurality of de- bounced signals for the resistor ladder circuit in Figure 4;

Figure 6 is a flow diagram which illustrates a process according to an embodiment of the invention for classifying a measured output voltage to a particular voltage band for the resistor ladder circuit in Figure 4;

Figure 7 is a flow diagram which illustrates a process according to an embodiment of the invention for correcting the voltage bands on the basis of the measured output voltage for the resistor ladder circuit in Figure 4; and

Figure 8 is a diagram which shows an example of how the voltage bands of the resistor ladder circuit in Figure 4 may be corrected after several user-input selections.

DETAILED DESCRIPTION

Figure 1 shows one embodiment of the multi-function steering wheel 10 of a vehicle, including electronic controls 12 for adjusting the stereo volume 14, changing the radio station 16, activating the adaptive cruise control (ACC) 18, and answering a hands-free phone call 20. Commonly, the electronic controls 12 are positioned such that the user may reach them with their thumb without removing either of their hands from the steering wheel. The electronic controls 12 are connected via a resistor ladder circuit so that a single wire only is required to run through the steering column to the electronic devices in the vehicle. By measuring the output voltage, the particular electronic control that is selected by the user is determined.

Referring to Figure 2, the vehicle includes a vehicle control system (VCS) 30 comprising: a human machine interface (HMI) 32 comprising the plurality of electronic controls or buttons 12 positioned on the steering apparatus of the vehicle, such as the steering wheel 10, and a resistor ladder circuit; a data processor 34; a controller 36 for communicating with various vehicle subsystems 38; and a data memory 40 for storing information regarding to which electronic control each range of voltage values (i.e. each voltage band) corresponds. Specifically, at step 42 the user selects one of the electronic controls 12 on the HMI 32 which closes a particular switch to complete the resistor ladder circuit and, for example, the measured output voltage (or value) is input to the data processor 34. The data processor 34 then classifies the measured output voltage to one of the pre-determined voltage bands in the data memory 40. Each voltage band corresponds to a particular electronic function in a vehicle subsystem 38 (for example, stereo volume up) and so the data processor 34 communicates with the controller 36 which sends a control signal to adjust the relevant vehicle subsystem 38 accordingly (for example, to increase the stereo volume).

In more detail, Figure 3 illustrates a process 50 according to an embodiment of the invention for classifying the measured output voltage to one of the pre-determined voltage bands, and then using the measured output voltage to correct one or more of the voltage bands. The user selects one of the electronic controls 12 at step 42 which closes a particular switch to complete the resistor ladder circuit at step 52. Figure 3 will be referred to further below. Figure 4 shows a resistor ladder circuit 54 with a resistor ladder 56 containing five resistors (with resistance 330, 560, 1200, 2700 and 4700 ohms) according to an embodiment of the invention. The supply voltage is 5 volts and a pull-up resistor 58 with resistance 1000 ohms is also included. The value of the resistance in the circuit 54 varies depending on which of the five switches (Sw1 , Sw2, Sw3, Sw4 and Sw5) is closed. When a switch in the resistor ladder circuit 54 is closed, the input is, in general, not electrically clean, that is, the contacts may bounce or vibrate together and apart upon initial opening or closure to create a plurality of electrical signals for a single user-input selection 42. In particular, the duration of bouncing and the period of each bounce may vary, switches of exactly the same type may bounce differently, and the bounce will differ depending on the force and speed with which the user selects the electronic control 12. When, as is the case here, the switch is being used as an input to a micro-processor 60, then steps must be taken to mitigate against these problems. Specifically, the system must undertake so-called switch de-bouncing, which refers to any kind of hardware device or software that ensures that a single signal only will be acted upon for a single operation of the switch by the user. There is a plurality of approaches to de-bounce a switch; however, by way of example, one approach only is described here, namely a count-based approach using software. Figure 5 shows schematic voltage bands 70 for three switches (Sw1 , Sw2 and Sw3) and a voltage band corresponding to all switches being open ("Not pressed"). A voltage band is the range of measured output voltages over which a particular electronic control 12 is registered as having been selected by the user. Figure 5 also includes "dead bands" 72 between each of the abovementioned voltage bands 70, where a measured output voltage in any of these bands corresponds to an error in the system. One possible problem that could lead to a measurement in a dead band 72 is water in the switch. For a particular switch to be registered as having been closed, a particular number of measurements (in this case, three) are taken at given time intervals, and the measurement at each of these time intervals must be in the same voltage band 70. For example, Figure 5 shows three consecutive readings in the Sw3 voltage band at step 74 and so the switch Sw3 is registered as having been closed. This is followed by three consecutive readings in the "Not pressed" voltage band at step 76 and so all switches are registered as being open.

Next, three consecutive readings in one of the dead bands 72 at step 78 are measured, followed by three consecutive readings in the Sw1 voltage band at step 80; however, the switch Sw1 is not registered as having been closed because, as a precautionary measure in this particular system, a "Not pressed" measurement is required after a dead band 72 measurement before one of the switches may be registered as having been closed. In addition, if fewer than three consecutive measurements in a particular voltage band are registered, for example at step 82 where only two consecutive readings are measured in the Sw3 voltage band, then this switch is not registered as having been closed. The measured output voltage after de-bouncing may, for example, be taken to be the mean of the plurality of measurements or, alternatively, taken to be the final measurement.

Returning to Figure 4, if, for example, switch Sw3 is registered as being closed after debouncing at step 84, the value of the resistance in the circuit 54 is 330 + 560 + 1200 + 1000 = 3090 ohms, which gives a switch current of 5 / 3090 = 0.001618 amps. The output voltage across the resistor ladder is measured by the A/D Micro-controller 60. The resistance across the resistor ladder 56 when switch Sw3 is closed is 330 + 560 + 1200 = 2090, and hence this gives an output voltage of 0.001618 ^* 2090 = 3.3819 volts. If the output voltage is calculated in the same way in each of the cases when one of the five switches Sw1 , Sw2, Sw3, Sw4, Sw5 is closed then the output voltages are 1 .2406, 2.3545, 3.3819, 4.1364, 4.5233 volts, respectively. Voltage bands with a prescribed bandwidth are then defined, where each voltage band includes one of the abovementioned output voltages and corresponds to a particular electronic control 12. Based on the measured value of the output voltage by the A/D Micro-controller 60, the switch that has been closed (and therefore the electronic control 12 that has been selected by the user) is determined at step 86 in Figure 3.

Figure 6 shows the process undertaken by the data processor 34 at the Band Classification step 86 in Figure 3. In particular, the pre-determined value of the output voltage that lies at the centre point between the initial upper and lower boundary voltages (or values) of each voltage band 70 is pre-saved in the data memory 40. These centre-of-band voltages (or values) are retrieved by the data processor 34 from the data memory 40 at step 90. The lowest of these pre-saved values is then selected at step 92. Also saved in the data memory 40 is an offset voltage (or value) to each of the initial centre-of-band values. This offset value corresponding to a particular voltage band is the difference between a measured output voltage and the initial centre-of band value of the voltage band, and is calculated at the Band Correction step 94 in Figure 3. The offset value corresponding to the lowest voltage band 70 is retrieved from the data memory 40 at step 95 and is added to the lowest initial centre-of- band value at step 96 to give the current centre-of-band value for the lowest voltage band. In general, the current centre-of-band value for a particular voltage band 70 is equal to the initial centre-of-band value plus the offset for the particular band. The bandwidth of each voltage band 70 is also pre-saved in the data memory 40 and the bandwidth of the lowest voltage band 70 is retrieved by the data processor 34 at step 98. Half of the bandwidth is added to the current centre-of-band value and half of the bandwidth is subtracted from the current centre-of-band value at step 100 to calculate the current upper and lower boundary values of the lowest voltage band 70. The measured output voltage 101 from the resistor ladder circuit 54 is then compared to the upper and lower boundary values of the lowest voltage band at step 102. If the measured output voltage 101 lies between the two boundary values then this measurement is classified at step 104 to the lowest voltage band 70 and the switch corresponding to this voltage band 70 is registered as having been closed. A signal is then sent to the controller 36 at step 106 to adjust the relevant subsystem 38 accordingly. If, however, at step 104 the measured output voltage 101 does not lie between the two boundary values then this process must be repeated for the next lowest voltage band 70.

At step 108, the processor determines whether the process has already been looped for each voltage band 70 without successfully classifying the measured output voltage 101 to a particular voltage band 70, in which case the measurement is considered invalid 1 10 and no signal is sent to the controller 36. If the highest voltage band 70 is not selected then at step 1 12 the next lowest centre-of-band value is selected and the process starting from step 96 is repeated as described above.

As previously described, the measured output voltage 101 corresponding to a particular switch being closed may drift over time, decreasing the likelihood that the correct switch is determined at the Band Classification step 86. This problem is further exacerbated by an increased number of switches leading to a smaller available bandwidth for each voltage band 70, meaning that measured output voltages 101 must in fact be more accurate to ensure that they are classified to the correct voltage band 70. In fact, using the example of the resistor ladder circuit 54 in Figure 3, the output voltages are 1.2406, 2.3545, 3.3819, 4.1364, 4.5233 volts, and so, by inspection, it is seen that the difference between successive pairs of output voltages monotonically decreases as more resistors are added. This means that the measured output voltage 101 must be more accurate as the number of resistors is increased for the correct electronic control 12 to be registered.

To address this problem, the present invention proposes that the voltage bands 70 are monitored and corrected at step 94 in Figure 3 each time a measured output voltage 101 is classified to a particular voltage band 70. Figure 7 shows a diagram of the process according to one embodiment of the invention that is undertaken by the data processor 34 at step 94 to monitor and correct the voltage bands 70. In particular, once the data processor 34 has completed the Band Classification step 86 as shown in Figure 6 and described above, the measured output voltage 101 is compared with the current centre-of-band value of the voltage band 70 to which the measured output voltage 101 was classified at the Band Classification step 86. Specifically, the measured output voltage 101 is determined to be less than, greater than, or equal to, the current centre-of-band value at step 120.

If the measured output voltage 101 is equal to the current centre-of-band voltage (that is, equal to the initial centre-of-band voltage plus the saved offset value) at step 120, then the offset value does not need to be corrected and the data memory 40 is not updated (that is, the saved offset value is not replaced or supplemented) at step 122 (i.e. the centre-of-band value remains the same). If, however, the measured output voltage 101 differs from the current centre-of-band value then the offset value needs to be corrected and the data memory 40 is updated. Specifically, if the measured output voltage 101 is less than the current centre-of-band value at step 120 then in the present embodiment an additional check is performed at step 124 to ensure that the measured output voltage 101 is greater than a calculated minimum value. The calculated minimum value is defined as the current centre- of-band value minus a pre-determined maximum change value, below which no correction is applied to the offset value, as will be described further below.

Therefore, if the measured output voltage 101 is below [he calculated minimum value then the offset value is not corrected and the data memory 40 is not updated at step 122. If, however, the measured output voltage 101 is above the calculated minimum value then the centre-of-band value is corrected at step 126 and the data memory 40 is updated at step 122. In this embodiment, the correction simply involves the current centre-of-band value being corrected to equal the measured output voltage 101 (that is, the offset value is corrected to equate to the difference between the initial centre-of-band voltage and the measured output voltage). The corrected offset value is then saved to the data memory 40 at step 122 to be used at the next Band Classification step 86.

Similarly, if the measured output voltage 101 is greater than the current centre-of-band value at step 120 then a check is performed at step 128 to ensure that the measured output voltage 101 is less than a calculated maximum value. The calculated maximum value is defined as the current centre-of-band value plus the pre-determined maximum change value, above which no correction is applied to the offset value, as will be described further below.

Therefore, if the measured output voltage 101 is above the calculated maximum value then the offset value is not corrected and the data memory 40 is not updated at step 122. If, however, the measured output voltage 101 is below \ \e calculated maximum value then the current centre-of-band value is corrected at step 130 to equal the measured output voltage 101 and saved to the data memory at step 122.

The additional check to ensure the measured output voltage 101 is above/below the calculated minimum/maximum limit at steps 126, 130 prevents large variations in the current centre-of-band values over small periods of time to minimise the effect of noise and/or spurious readings in the system. This also prevents overlapping of voltage bands 70. The difference between the current centre-of-band value and the calculated maximum/minimum value may be set at a pre-determined proportion of the initial bandwidth of the appropriate band (typically, for example, around 1 %). Note that in other embodiments, other qualifying conditions may be required to be met before a change to the current centre-of-band is permissible.

In an alternative embodiment, a correction may still be applied if the measured output voltage is greater than/less than the calculated minimum/maximum values described above at steps 124, 128, but in this case a maximum correction value is attributed to the amount of the correction. In other words, and in contrast to the method described above, only a small correction is applied to the offset value at steps 126, 130, so that the current centre-of-band value is corrected by the maximum correction value, and not to the measured output voltage. Typically, the maximum correction value may be set at around 1 % of the width of the appropriate band.

Note also that there are several ways that voltage bands 70 may be corrected at steps 126, 130. In the embodiment described above, one centre-of-band value only is corrected at steps 126, 130; however, the system could be configured to, for example, correct the centre- of-band values for each voltage band 70 by the same amount on each occasion one of the values is corrected. Alternatively, rather than correcting the current centre-of-band values for each voltage band 70 by the same amount, any correction could be tapered the greater the difference between the measured output voltage 101 and a particular current centre-of-band value.

Figure 8 shows a schematic diagram of the possible correction of voltage bands with constant bandwidth from their initial positions 140 to their positions 142 after several user- input selections 42. It can be seen that the width of a particular dead band, for example between Sw1 and Sw2 144, can become relatively large after several user-input selections 42. The system may be configured to eliminate these dead bands, for example by expanding the voltage band on each side to take half of the dead band each.

In another embodiment, the VCS may be configured to undertake a diagnostic process whereby the user can reset or correct all of the voltage bands 70. The reset function may involve the user selecting each electronic control 12 in a particular sequence and the measured output voltage 101 for each electronic control 12 being saved directly to the data memory 40 as the centre-of-band value.

The VCS 30 may be configured to output a user command signal to a display means of the HMI device 32, which is configured to display a user command to the user. The user command is representative of an instruction, directing the user to press a steering wheel switch, corresponding to a particular control selection. The VCS 30 is then configured to wait a pre-determined period of time for the user to press the switch and to monitor any output voltage values it receives from the resistor ladder circuit 54. Upon detecting a measured output voltage value, the received value is saved directly to the data memory 40 as the new centre-of-band value, corresponding to the control selection.

The diagnostic process may then be repeated for each of the steering wheel switches until a measured output voltage, corresponding to the activation of each switch, has been classified to a corresponding pre-determined output of the pre-determined output data.

If, after the pre-determined period of time, no output voltage is detected, the VCS 30 resends the user command signal. If a voltage value is not detected after a further pre-determined period of time, the VCS 30 determines that the steering wheel switch is faulty. Upon determining that the switch is faulty, VCS 30 sends a user command signal, indicative of a maintenance notification, display means of the HMI device 32. Thereby notifying the user that maintenance of the steering wheel may be required.

In a further embodiment, the initial bandwidth of each voltage band 70 may be defined according to a pre-determined expected frequency of use of each electronic control 12. In particular, those electronic controls 12 which are more frequently used will be subject to less drift between measurements and so the voltage bands 70 for such electronic controls 12 may be narrower. In one embodiment, the voltage bands 70 of corresponding to frequently- used electronic controls 12 may not be corrected upon every user-input selection 42 of this electronic control 12. In addition to the position or value of the voltage band 70 being corrected, the system could be configured to correct the bandwidth of one or more of the voltage bands to, for example, prevent overlap between neighbouring voltage bands.

Rather than a multi-function steering wheel as described above, the steering apparatus may refer to the steering column in a vehicle. Commonly, controls on a steering column include indicator lights on/off, headlamps on/of, and front and rear wipers on/off. It will be appreciated by a person skilled in the art that the invention could be modified to take many alternative forms without departing from the scope of the appended claims. Further aspects of the present invention are set out in the following numbered Clauses:

Clause 1 . A system for use in the steering apparatus of a vehicle, the system comprising; a resistor ladder circuit comprising a resistor ladder, the circuit being configured to measure an output across the resistor ladder; a plurality of controls configured to receive a user-input selection into the resistor ladder; a data memory for storing pre-determined output data relating to each of the controls; and a processor configured to receive the output from the resistor ladder circuit, to compare the measured output with the pre-determined output data, and to classify the measured output to a corresponding pre-determined output of the predetermined output data which is indicative of a particular control selection, the processor further being configured to monitor and correct for a difference between the measured output and the corresponding pre-determined output.

Clause 2. A system according to Clause 1 , wherein the plurality of controls form a part of a human machine interface (HMI) on the steering apparatus.

Clause 3. A system according to Clause 1 , wherein the processor is configured to replace or supplement the pre-determined outputs with updated pre-determined outputs based on user- input selections when the vehicle is in use. Clause 4. A system according to Clause 3, wherein the processor is further configured to receive a user-input selection of a particular control and to provide the user-input selection of the particular control to the data memory together with measured output data corresponding to the control to replace or supplement the pre-determined output data. Clause 5. A system according to Clause 1 , wherein the resistor ladder circuit comprises a switch configured to de-bounce the measured output.

Clause 6. A system according to Clause 1 , wherein the measured output comprises a measured output voltage. Clause 7. A system according to Clause 1 , wherein the pre-determined output data comprises voltage band data relating to a plurality of voltage bands, where each voltage band corresponds to a particular control on the steering apparatus. Clause 8. A system according to Clause 7, wherein the voltage band data comprises an initial bandwidth, an initial value of the centre of each voltage band, and initial values of upper and lower boundaries of each voltage band.

Clause 9. A system according to Clause 8, wherein the voltage band data further comprises an offset value to the initial value of the centre of each voltage band.

Clause 10. A system according to Clause 9, wherein the processor comprises a correction device configured to correct the offset value corresponding to the voltage band to which the measured output voltage is classified based on the measured output voltage and the initial value of the centre of the voltage band.

Clause 1 1 . A system according to Clause 10, wherein the correction device is configured to correct the offset value so as to equate to the difference between the measured output voltage and the initial value of the centre of the voltage band.

Clause 12. A system according to Clause 9, wherein the processor comprises a correction device configured to correct the offset value for a plurality of voltage bands based on the measured output voltage and the initial value of the centre of each of the plurality of voltage bands.

Clause 13. A system according to Clause 12, wherein the correction device is configured to correct the offset value for each of the plurality of voltage bands so as to equate to the difference between the measured output voltage and the initial value of the centre of the associated one of the plurality of voltage bands.

Clause 14. A system according to Clause 10 or Clause 12, further comprising a comparator configured to compare the difference between the measured output voltage and a current value of the centre of the voltage band to which the measured output voltage is classified, and wherein the correction device is configured to limit the correction to a pre-determined amount in the event that said difference exceeds a pre-determined maximum correction value. Clause 15. A system according to Clause 8, wherein the voltage band data further comprises a further offset value to the initial value of one or both of the upper and lower boundaries of each voltage band.

Clause 16. A system according to Clause 8, wherein the processor comprises means configured to correct the further offset value corresponding to the voltage band to which the measured output voltage is classified based on the measured output voltage and the initial value of one or both of the upper and lower boundaries of the voltage band.

Clause 17. A system according to Clause 8, wherein the initial bandwidth of each voltage band depends on a pre-determined expected frequency of use of each control.

Clause 18. A system according to Clause 1 , comprising a controller for controlling at least one vehicle subsystem in dependence on the control to which the measured output data is classified.

Clause 19. A method for use in the steering apparatus of a vehicle, the method comprising; measuring an output across a resistor ladder in a resistor ladder circuit; receiving a user- input selection into the resistor ladder; storing pre-determined output data relating to each of a plurality of controls; and receiving the output from the resistor ladder circuit, comparing the measured output with the pre-determined output data, and classifying the measured output to a corresponding pre-determined output indicative of a particular control selection, the method further comprising monitoring and correcting for a difference between the measured output and the corresponding pre-determined output.

Clause 20. A data memory device containing a computer readable code for performing the method according to Clause 19.

Clause 21 . A vehicle comprising a system according to Clause 1