GB2513611A

GB2513611A - Control system, vehicle and method

Info

Publication number: GB2513611A
Application number: GB1307864.7A
Authority: GB
Inventors: Katy Holloway; Iain Suffield
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2013-05-01
Filing date: 2013-05-01
Publication date: 2014-11-05
Anticipated expiration: 2033-05-01
Also published as: GB201307864D0; GB2513611B

Abstract

A vehicle diagnostic apparatus and a corresponding method are provided. The apparatus 145, 145S is for a vehicle 100 having an electric propulsion motor 123. The apparatus 145, 145S is operable to receive a signal corresponding to a speed of rotation of the motor 123. The apparatus 145, 145S is configured to generate an audible sound wherein at least one characteristic of the sound is dependent on the signal corresponding to motor speed.

Description

CONTROL SYSTEM, VEHICLE AND METHOD

TECHNICAL FIELD

The present invention relates to apparatus for a motor vehicle, to a vehicle control system, a vehicle and to a method of controlling a vehicle. In particular but not exclusively, embodiments of the present invention relate to apparatus for a vehicle having an electric propulsion motor powered by charge from an energy storage device.

BACKGROUND

It is known to provide an electric vehicle having an electric propulsion motor and a battery for storing charge for powering the motor. The battery may be recharged by connecting the vehicle to a recharging facility.

It is an aim of the present invention to address disadvantages associated with the prior art and to provide an improved electric or hybrid electric vehicle.

SUMMARY OF THE INVENTION

Embodiments of the invention may be understood with reference to the appended claims.

Aspects of the present invention provide an apparatus, a vehicle and a method.

In one aspect of the invention for which protection is sought there is provided an apparatus for a vehicle having an electric propulsion motor, the apparatus being operable to receive a signal corresponding to a speed of rotation of the motor, the apparatus being configured to generate an audible sound wherein at least one characteristic of the sound is dependent on the signal corresponding to motor speed.

Embodiments of the present invention have the advantage that a user may be made aware of a speed at which the electric motor is rotating without having to look at an indicator of motor speed. It is to be understood that motor speed may be directly proportional to vehicle speed in embodiments in which a fixed gear ratio exists between a motor and one or more roadwheels. For example in some vehicles an electric propulsion motor may be mounted in a wheel hub and arranged directly to drive a corresponding wheel of the vehicle.

Some embodiments of the present invention have the advantage that a driver may be provided with reassurance that a propulsion motor is operating even if a driver cannot otherwise hear the motor, due to relatively silent operation thereof.

The apparatus may be operable to commence generation of the audible sound when a user signals starting of the vehicle.

Thus the audible sound may be generated even when the motor is not rotating, the sound subsequently changing in dependence on motor speed.

The user may signal starting of the vehicle by pressing a start' button in some embodiments although other arrangements are also useful.

Alternatively or in addition the apparatus may be operable to commence generation of the audible sound when a user selects a driving mode of the vehicle.

By driving mode is meant a mode or state in which the vehicle may be driven, such as a forward drive mode (typically placarded D' on an automatic transmission selector), or a reverse drive mode (typically placarded R' on an automatic transmission selector).

The apparatus may be configured wherein the at least one characteristic includes a timbre of the sound.

It is to be understood that by the term timbre is meant a form of a variation of amplitude of a sound as a function of frequency, as a function of time. It is to be understood that a timbre of the sound may be changed by changing the form of the spectrum of amplitude as a function of frequency. However, it is to be understood that timbre may be considered to be distinct from the volume or pitch of a sound. Thus, if the volume of a sound is increased, the timbre may remain substantially the same. That is, the relative amplitudes of different respective frequencies making up the sound may remain substantially the same, but the total volume may increase. Similarly, the pitch of a sound may be adjusted by introducing a change in the spectrum of amplitude as a function of frequency relative to a reference spectrum, whilst the timbre of the sound remains substantially unchanged.

In one embodiment, a product function is applied to the frequency spectrum in order to change a characteristic of the sound. Thus, the transformed spectrum corresponds to the original spectrum after application of a factor to each frequency component of the spectrum.

For example in one embodiment frequency doubling (or tripling or some other multiple) may be applied to the original spectrum in which a factor of 2 (or 3 or some other multiple) is applied to each frequency component. Relative amplitudes of frequencies pre-doubling are therefore retained post-doubling, according to the product function.

In some embodiments the relative amplitudes may in addition or instead be modulated by filter means (for example an electrical, electronic or software-driven filter), changing the timbre of the sound. For example, lower frequencies may be more heavily attenuated than higher frequencies, in some embodiments.

The at least one characteristic may include a pitch of the audible sound.

The apparatus may be operable to increase a pitch of the sound with increasing motor speed.

This feature has the advantage that a change in the audible sound may be provided in response to which a user may intuitively perceive that motor speed has increased.

The apparatus may be configured wherein the sound is stored by the apparatus as an audio waveform.

The waveform may be stored as an audio file, for example as a way file, an mp3 file or in any other suitable format.

The apparatus may be operable to vary the pitch by varying a time period over which a prescribed amount of an audible sound file is replayed.

For example, an entire file may be replayed over a period of 1 Os, 8s, 6s, 4s or any other suitable time period, the time period being determined in dependence on motor speed.

The apparatus may be operable to vary a volume of sound generated by the apparatus as a function of motor speed.

The apparatus may be operable to increase the volume of sound generated with increasing motor speed.

The apparatus may be operable to vary at least one characteristic of the sound in dependence on whether a user has selected a boost mode in which operation of the propulsion motor at an increased power level is permitted.

The apparatus may be operable to generate the audible sound whereby the sound may be heard from outside the vehicle.

The apparatus may be operable to generate the audible sound by means of audio transducer means external to a cabin of the vehicle.

The apparatus may be operable to generate the audible sound whereby the sound may be heard from inside the vehicle.

The apparatus may be operable to generate the audible sound by means of audio transducer means internal to the cabin of the vehicle.

In a further aspect of the invention for which protection is sought there is provided a motor vehicle control system comprising apparatus according to the preceding aspect.

In one aspect of the invention for which protection is sought there is provided a motor vehicle comprising apparatus or a system according to a preceding embodiment.

The vehicle may be an electric vehicle. The electric vehicle may comprise energy storage means for powering the motor.

Alternatively the vehicle may be a hybrid vehicle. The hybrid vehicle may comprise energy storage means for powering the motor.

In a still further aspect of the invention for which protection is sought there is provided a method of controlling a vehicle having an electric propulsion motor and energy storage means for powering the motor, the method comprising receiving a signal corresponding to a speed of the motor, and generating an audible sound wherein at least one characteristic of the sound is dependent on the signal corresponding to motor speed.

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. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

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 figures in which: FIGURE 1 is a schematic illustration of a hybrid electric vehicle according to an embodiment of the present invention; FIGURE 2 shows frequency spectra of audio sound generated by apparatus according to an embodiment of the present invention for different states of charge with a fully depressed accelerator pedal control; FIGURE 3 shows frequency spectra of audio sound generated by apparatus according to an embodiment of the present invention for a battery state of charge exceeding 20% for different accelerator pedal control positions; FIGURE 4 shows frequency spectra of audio sound generated by apparatus according to an embodiment of the present invention for a battery state of charge exceeding 20% and a fully depressed accelerator pedal control, with and without boost mode selected; and FIGURE 5 is a flow chart illustrating a method according to an embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 shows a hybrid electric vehicle (HEV) 100 according to an embodiment of the present invention. It is to be understood that embodiments of the present invention are also suitable for use with electric vehicles (EVs), being non-hybrid vehicles.

The vehicle 100 has an internal combustion engine 121 releasably coupled to a crankshaft integrated motor/generator (CIMO) 123 by means of a clutch 122. The CIMO 123 is in turn coupled to an automatic transmission 124. The automatic transmission 124 may be coupled to rear wheels 113, 114 of the vehicle 100 by means of a power transfer unit (PTU) 125 via a rear drive shaft 1 30R. The PTU 125 is also operable to couple the transmission 124 to front wheels 111, 112 of the vehicle 100 via a front drive shaft 1 30F.

A powertrain controller 140 is configured to control the engine 121, clutch 122 and 01MG 123 to provide drive torque to the transmission 124 by means of the engine 121 alone, the CIMG 123 alone or the engine 121 and CIMG 123 in parallel.

It is to be understood that in some embodiments the transmission 124 may be a manual transmission instead of an automatic transmission.

The vehicle 100 has a start button 140S and a driving mode selector dial 124S. The driving mode selector dial 124S is operable to control the transmission 124 to select a forward or reverse driving configuration.

A brake pedal 161 and an accelerator pedal 163 are provided for controlling vehicle speed.

In the embodiment of FIG. 1, the powertrain controller 140 determines an amount by which the brake and accelerator pedals 161, 163 have been depressed by reference to respective pedal position transducers 161T, 163T. The controller 140 outputs a value of a parameter P which provides an indication of the position of the accelerator pedal 163. Parameter P has a value of substantially zero (P=0) if the pedal 163 is substantially undepressed. Parameter F has a value of 1 (P=1) if the pedal 163 is substantially fully depressed. Other arrangements are also useful.

A boost mode button 122B is provided, operable to select a boost mode of the vehicle 100 when pressed. The boost mode may also be referred to as a push to pass' mode. When selected, the boost mode allows the 01MG 123 to generate additional torque to drive the vehicle 100, necessitating a greater rate of drain of charge from the battery 150 than would normally be acceptable. The vehicle 100 is only permitted to operate in the boost mode for a proscribed period of time before the boost mode is cancelled automatically by the powertrain controller 140. Other arrangements are also useful.

The vehicle 100 has a battery 150 connected to an inverter 151 that generates a three-phase electrical supply that is supplied to the 01MG 123 when the 01MG 123 is operated as a motor. The battery 150 is arranged to receive charge from the 01MG 123 via the inverter 151 when the 01MG 123 is operated as a generator.

The battery 150 is also connected to a charging port 1500 that is accessible from an exterior of the vehicle 100. The charging port 1500 allows the battery 150 to be connected to a charging station 160 by means of a charging cable 155 to allow recharging of the battery 150. The vehicle 100 may therefore be described as a HEV of plug-in' type.

The powertrain controller 140 is configured to control operation of the vehicle 100 in an EV mode or hybrid mode. In EV mode, drive torque is provided by the CIMG 123 only. In the hybrid mode, drive torque may be provided in addition or instead by the engine 121.

The vehicle 100 has a vehicle control unit (VCU) 145 operable to place the vehicle in one of a plurality of power modes. The power modes include a parked' power mode (power mode 1, or PM1') in which the controller 140 is prevented from allowing the engine 121 or 01MG 123 to be operated unless a start' button 124S is pressed. The parked mode may be assumed only when the transmission 124 is in the park mode.

If a user exits the vehicle 100 and locks the vehicle, the VCU 145 is operable to place the vehicle in a parked and locked' condition in which vehicle systems are placed in a low power consumption mode. This mode is referred to as power mode 0' or AMO.

The VCU 145 is configured to check that each of four passenger doors and each of two rear payload doors (not shown) are closed before allowing the vehicle to assume mode PMO.

Other checks may also be made before mode PMO may be assumed. For example the VCU may check that one or more controllers such as powertrain controller 140 have shut down before mode PMO may be assumed.

A user may place the vehicle 100 in PMO by means of a key fob 190. The fob 190 has first and second control buttons 191, 192. The first control button 191 is operable to unlock the vehicle 100 whilst the second control button 192 is operable to lock the vehicle 100.

With the vehicle is in mode PMO, if the VCU 145 detects that a user has pressed the first control button 191 of the fob 190, the VCU 145 is configured to control the vehicle 100 to assume power mode FM1 and unlock the doors of the vehicle 100. If the vehicle is in mode PM1 and the VCU 145 detects that a user has pressed the second control button 192 of the fob 190, the VCU 145 is configured to attempt to lock the doors. If the VCU 145 is able to lock the doors, the vehicle is subsequently controlled to assume mode PMO. If the VCU 145 is not able to lock the doors, the vehicle remains in mode PM1. In some embodiments, the yOU 145 may control the vehicle to assume mode PMO from mode PM1 even if the doors are not locked, if the vehicle is stationary for more than a prescribed period of time.

With the vehicle in mode PM1, the VCU 145 monitors the start button 140S. If the user presses the start button 140S the VCU 145 assumes power mode PM2 and the vehicle 100 is made ready to be driven. The VCU 145 may perform one or more further operations, for example by displaying prescribed information on a HMI (human-machine interface) display.

In the embodiment of FIG. 1, the VCU 145 is configured such that if a user subsequently selects a driving mode by means of the driving mode selector 124S, the transmission 124 assumes a corresponding configuration whereby drive torque generated by the engine 121 and/or CIMG 123 is transmitted to the driven wheels.

The VCU 145 is operable to generate audible sound by means of an audio transducer 145S to provide audible feedback to the driver confirming that the vehicle is in mode PM2. The audible sound is generated by repeatedly playing back sound files which may also be described as sonic signatures. In some embodiments, a system other than the VCU 145 may perform this function. In the present embodiment the audio transducer 145S is in the form of a dynamic loudspeaker having a cone-shaped diaphragm and electromagnetic coil driver. Other forms of audio transducer such as contact transducers and bending wave radiators are also useful. Other audio transducers are also useful.

The VCU 145 stores three pairs of sound files for playback when the vehicle is in mode PM2. One pair of files is selected by the VCU 145 at any given moment in time. A first pair of files are selected (employed) when a state of charge of the battery 150 is less than or substantially equal to 20% of the normal allowable range of state of charge. A second pair of files are employed when the state of charge of the battery 150 exceeds 20%. A third pair of files are employed if a user selects operation of the vehicle 100 in the boost mode, by means of boost mode button 122B.

In use, the VCU 145 outputs a sound which is a blend of first and second files of the selected pair of files. The composition of the blend depends on the position of the accelerator pedal 163. If the accelerator pedal 163 is substantially undepressed, indicating that the driver is not demanding positive drive torque, the first file of the appropriate pair is played back at a first volume and the second file of the pair is played back at substantially zero volume. If the accelerator pedal 163 is fully depressed, the second file of the pair is played back at a second volume and the first file is played back at substantially zero volume.

In the present embodiment the first and second volumes are substantially the same. In some alternative embodiments the second volume is greater than the first, although other arrangements are also useful.

For accelerator pedal positions intermediate the undepressed and fully depressed positions, the volume at which the first and second files are played back is blended in proportion to an amount by which the accelerator pedal 163 is advanced. Thus, the volume at which the first file is played back progressively decreases with advancing accelerator pedal position, whilst the volume at which the second file is played back progressively increases with advancing accelerator pedal position.

The first and second files are based on substantially the same sound file, however the first file differs from the second in that a timbre of the sound is different. The first file is generated by applying an attenuating filter to the second sound file to attenuate higher frequencies thereof. This results in a relatively bright, harsher sound when the accelerator pedal 163 is fully depressed, and a relatively dark, softer sound when the accelerator pedal 163 is substantially undepressed. Thus, the first file is essentially a filtered version of the second file.

The first and second pairs of sound files differ from one another also in respect of timbre.

The first pair of sound files are generated by applying an attenuating filter to the second pair of sound files. In particular, in the present embodiment a 6dB attenuation is applied to sounds below 350Hz, and a 12dB attenuation is applied to sounds above 350Hz, with the exception of selected major harmonics.

Application of the attenuating filter in the manner described above results in first and second sound files (forming the first pair of sound files) that produce a more smooth, more closed and more relaxed impression on a user than the corresponding sounds of the second pair of sound files. Thus the first pair of files are intended to provide a user with an indication of tiredness, reflecting the relatively low state of charge of the battery 150. Other methods of modifying the second pair of files to produce the first pair are also useful. In some alternative embodiments the files of the first pair may be derived substantially independently of the second pair.

FIG. 2 illustrates sound pressure level output by transducer 145S as a function of frequency with accelerator pedal 163 substantially fully depressed (P=1) in the situation where the battery Soc is less than 20% (trace Ti) and the situation where the battery soc is greater than 20% (trace T2). Thus, traces Ti and T2 correspond to the second sound files of the first and second pairs, respectively. It can be seen that traces Ti and T2 have a similar variation in sound pressure level as a function of frequency, whilst the signal corresponding to trace

S

Ti is more heavily attenuated than that corresponding to trace T2, at least for sound levels below around 2kHz.

FIG. 3 illustrates sound pressure level output by transducer 145S as a function of frequency with battery SOC greater than 20% with the accelerator pedal 161 fully depressed (P=i) (trace Ti) and fully released (P=0) (trace 12). Trace Ti therefore corresponds to trace 12 of FIG. 2. It can be seen that trace Ti is similar to trace T2 in the lower frequency range illustrated, i.e. the fundamental frequencies (low harmonics) are substantially unchanged.

Higher frequencies, however, are reduced for trace T2, changing the timbre of the sound. i0

The third pair of files are intended to provide a user with an impression of an aggressive mode, and have more high frequency content than the second pair of files. In the present embodiment the sound is generated by simulating playback of the second pair of files through an over-driven amplifier. Thus, the sound is distorted, and has a sense of being is brighter and more crunchy' than the second pair. Other arrangements are also useful.

FIG. 4 illustrates sound pressure level output by transducer 145S as a function of frequency with accelerator pedal 163 substantially fully depressed (P=i) in the situation where the battery SOC is greater than 20% and the vehicle 100 is not operating with the boost mode selected (trace Ti) and the situation whore the vehicle 100 is operating with a similar battery SOC but with the boost mode selected (trace T2).

Thus, traces Ti and 12 correspond to the second sound files of the second and third pairs of sound files, respectively. That is, trace Ti of FIG. 4 corresponds to trace 12 of FIG. 2. It can be seen that traces Ti and T2 have a similar variation in sound pressure level as a function of frequency, whilst the signal corresponding to trace Ti is more heavily attenuated than that corresponding to trace T2.

In some alternative embodiments the files of the third pair may be derived substantially independently of the second pair. Other arrangements are also useful.

The VCU i45, in addition to monitoring battery state of charge and accelerator pedal position, also monitors vehicle road speed and speed of rotation of the 01MG 123.

The VCU i45 is configured repeatedly to play back a blended combination of the first and second files of the first, second or third pair, each playback of the files being completed in a prescribed period of time T which is referred to as the playback period. Thus the playback period is the period of time within which the sound defined by the first and second files is played back from the start of each file to the end of each file in the appropriate blended combination.

The VCU 145 adjusts the playback period T according to the speed at which the CIMG 123 is rotating. The faster the CIMG 123 is rotating, the shorter the selected playback period.

This has the effect that as the speed of rotation of the 01MG 123 increases, a pitch of the sound that is played back increases. This provides a helpful, intuitive feedback to the driver in respect of the speed of the CIMG 123. Thus, if the vehicle 100 is stationary the playback period T is set to a value TO. As CIMO speed increases, the value of I is reduced according to a prescribed functional relationship. The relationship may be linear as in the present embodiment, and in direct proportion to 01MG speed, or any other suitable relationship.

The VCU 145 is provided with data in respect of battery state of charge, accelerator pedal position P, speed of rotation of the CIMG 123 and vehicle speed by means of data transmitted on a controller area network (CAN) bus 170 by one or more other controllers such as the powertrain controller 140.

In the embodiment of FIG. 1 the road speed corresponds to the speed of the wheels 111- 114, which in turn correspond to an output speed of the transmission (corrected if necessary according to a selected gear ratio of the PTU 125, such as a high or low gear ratio). In some embodiments, the VCU 145 may calculate vehicle road speed by reference to a speed of the 01MG 123 and a selected gear of the transmission 124 at a given moment in time.

Conversely, the VCU 145 may in some embodiments calculate 01MG speed by reference to vehicle road speed and the selected gear of the transmission 124.

In some embodiments, when operating in EV mode with the engine 121 switched off, the transmission may be configured to remain in a prescribed gear, for example third gear. In this case, road speed will be directly proportional to motor speed and in the same proportion as long as the transmission 124 remains in the same gear. It is to be understood that the vehicle may operate in a driver selected EV-only mode or a hybrid electric vehicle (HEV) mode. In the driver selected EV-only mode engine starting is prohibited unless driver torque demand exceeds a prescribed value or battery state of charge falls below a prescribed minimum value. That is, the vehicle 100 attempts to remain in EV mode as long as possible, whereby drive torque is provided by means of the 01MG 123 only. Other arrangements are also useful.

In the present embodiment, when operating in the HEV mode the powertrain controller 140 is caused to start and stop the engine 121 according to a prescribed HEV control methodology, and not necessarily only when battery state of charge falls below the prescribed minimum value. Again, other arrangements are also useful.

In some embodiments, the sounds described above are generated at any time when the vehicle 100 is operating in the driver selected EV mode, regardless of whether the 01MG 123 is generating drive torque, and when in the HEV mode and the 01MG 123 is generating drive torque. This feature has the advantage that a user is made aware of the fact that the 01MG 123 is operating, even when the vehicle 100 is operating in the hybrid mode with the engine 121 switched on. In the absence of any other indication that the 01MG 123 is operating as a propulsion motor when the vehicle 100 is in the hybrid mode, it may be difficult for the user to appreciate that the CIMG 123 is in fact operating and providing torque assist to the engine 121 due to quietness of operation of the CIMG 123.

In some embodiments, the VCU 145 may be configured to generate the audible sound by means of the speaker 1455 only when the 01MG 123 is in fact generating drive torque, regardless of vehicle operating mode. Alternatively, the VCU 145 may be configured to generate the sound whenever the vehicle is operating in the driver-selected EV mode or in HEV mode provided the engine 121 is switched off. In some embodiments the VCU 145 may be configured to generate the sound when the vehicle 100 is in HEV mode regardless of whether the engine is switched on or off. Other arrangements are also useful.

FIG. 5 is a flow diagram illustrating a manner in which the VCU 145 controls the audible sound generated via the audio transducer 145S when the vehicle is in mode PM2.

At step SlOl the VCU 145 determines whether the vehicle 100 is in mode PM2. If the vehicle is in mode PM2 the VCU 145 continues at step 5103.

At step S103 the VCU 145 determines whether the SOC of the battery 150 is less than or substantially equal to 20%. If the SOC is less than or equal to 20% the VCU 145 continues at step Si 05, else the VCU 145 continues at step Si 07.

At step SlOS the VOU 145 selects sound file pair A for playback whereas at step S107 the yOU 145 selects sound file pair B. Sound file pairs A and B differ from one another in that respective first and second files of pair B have more high frequency content than the corresponding first and second files of pair A as described above. Pair A are arranged such that first and second files thereof are smoother, more closed and more relaxed than the corresponding first and second files of pair B. In each case the first file of a given pair corresponds to the second file of that pair, but subject to an attenuating filter in which higher frequencies are attenuated in the manner described above.

At step 5109 the VCU 145 determines whether the driver (or user) has selected a boost mode. If the driver has not selected the boost mode the VCU 145 continues at step 5113. If the driver has selected the boost mode the VCU 145 continues at step Sill. At step Sill the VCU 145 selects sound file pair C instead of pair A or B (selected at steps 5105 or Si 07). The VCU 145 then continues at step Si 13.

At step 5113 the VCU 145 checks the value of accelerator pedal position parameter F, which is broadcast on the CAN bus by powertrain controller 140.

At step S115 the VCU 145 determines the volume at which the first sound file Fl is to be played back. The volume at which file Fl is to be played back is determined by multiplying the total sound volume to be generated, V, by (1 -F).

At step 5117 the VCU 145 determines the volume at which the second sound file F2 is to be played back. The volume at which file F2 is to be played back is determined by multiplying the total sound volume to be generated, V, by P. It is to be understood that in some embodiments the total sound volume V may be a function of F, the volume V increasing with F. The increase in V may be linear, non-linear or a combination of linear and non-linear over different respective ranges of P. In some embodiments, in addition or instead the total sound volume V may be a function of vehicle speed, the total volume V increasing with speed.

At step Si 19 the VCU 145 determines the playback period T of the selected pair of sounds by reference to the current speed of rotation of the CIMO 123, also referred to herein as motor speed. In the present embodiment, the playback period T is determined by multiplying a reference period TO by [l-(motor speed/C)], where C is a constant. The value of C is chosen to provide a suitable reduction in playback period T below TO such that at a maximum speed of operation of the CIMG 123 the playback speed is not too short or too long. Suitable values of C may be determined empirically by the skilled person, but may for example be substantially equal to double or triple the value of maximum CIMO speed.

In some alternative embodiments, the period T may have a more complex dependency on 01MG speed. For example the dependency may be non-linear over one or more ranges. The dependency may be linear but with different rates of reduction in T as a function of CIMG speed, in dependence on the value of road speed. Other arrangements are also useful.

In some embodiments the value of C may correspond to a saturation motor speed above which the playback period T is not shortened any further, but rather remains at a minimum saturation value Ts. The VCU 145 may be configured to suspend reducing the playback period below Is if motor speed increases above the saturation motor speed.

At step Si 21 the VCU 145 plays back the appropriate blended combination of file pairs A, B or C with the appropriate playback period determined at step S119.

In the present embodiment, an additional function is implemented in which vehicle roadspeed is monitored and a playback volume of the sound adjusted accordingly. The playback sound may be increased with increasing roadspeed.

Thus, in some embodiments the VCU 145 is configured to increase the playback volume with increasing roadspeed. This feature has the advantage that the sound can still be heard in spite of the presence of the masking effects of wind and road noise.

The functionality may be implemented by a multi-point control loop whereby attenuation at specific control points in respect of speed are defined. Thus in some embodiments, at a speed of substantially Okph a volume of the sound is attenuated by (say) -10dB with respect to a nominal volume, at lokph it is attenuated by (say) -5dB, and at 200kph it is not attenuated (corresponding to an attenuation of 0dB) with respect to the nominal volume. At roadspeeds between specified control points, the volume of the sound is interpolated linearly between the attenuations of the respective control points. Other values of attenuation and other values of roadspeed at which a change in volume is effected (by means of a change in attenuation) are also useful.

Embodiments of the present invention have the advantage that a user may be made aware of the speed of rotation of an electric propulsion motor of the vehicle by means of an audible sound in an intuitive and non-distracting manner. This feature provides a driver with helpful feedback that the motor is operating, and of how fast the motor is operating.

Furthermore, some embodiments of the present invention provide a motor vehicle having an audible sound that varies with pedal position parameter P to provide the driver with intuitive feedback in respect of the amount by which the accelerator pedal 163 is depressed.

Providing an audible indication of the amount by which the accelerator pedal 163 is depressed may provide reassurance to the driver that the VCU 145 has registered a change in torque demand by the driver, in the case that the driver releases or depresses the accelerator pedal 163. In some embodiments of the invention the sound is generated whenever the vehicle is in a driving mode, for example whenever the vehicle is in a mode in which depression of the accelerator pedal will result in application of torque to one or more wheels to propel the vehicle. Other arrangements are also useful.

Embodiments of the present invention may be understood by reference to the following numbered paragraphs: 1. An apparatus for a vehicle having an electric propulsion motor, the apparatus being operable to receive a signal corresponding to a speed of rotation of the motor, the apparatus being configured to generate an audible sound wherein at least one characteristic of the sound is dependent on the signal corresponding to motor speed.

2. An apparatus according to paragraph 1 operable to commence generation of the audible sound when a user signals starting of the vehicle.

3. An apparatus according to paragraph 1 operable to commence generation of the audible sound when a user selects a driving mode of the vehicle.

4. An apparatus according to paragraph 1 wherein the at least one characteristic includes a timbre of the sound.

5. An apparatus according to paragraph 1 wherein the at least one characteristic includes a pitch of the audible sound.

6. An apparatus according to paragraph 5 operable to increase a pitch of the sound with increasing motor speed.

7. An apparatus according to paragraph 1 wherein the sound is stored by the apparatus as an audio waveform.

8. An apparatus according to paragraph 7 operable to increase a pitch of the sound with increasing motor speed, the apparatus being further operable to vary the pitch by varying a time period over which a prescribed amount of an audible sound file is replayed.

9. An apparatus according to paragraph 1 operable to vary a volume of sound generated by the apparatus as a function of motor speed.

10. An apparatus accoiding to paiagraph 9 operable to increase the volume of sound generated with increasing motor speed.

11. An apparatus according to paragraph 1 operable to vary at least one characteristic of the sound in dependence on whether a user has selected a boost mode in which operation of the propulsion motor at an increased power level is permitted.

12. An apparatus according to any paragraph 1 operable to generate the audible Sound whereby the sound may be heard from outside the vehicle.

13. An apparatus according to paragraph 1 operable to generate the audible sound by means of an audio transducer external to a cabin of the vehicle.

14. An apparatus according to paragraph 1 operable to generate the audible sound whereby the sound may be heard from inside the vehicle.

15. An apparatus according to paragraph 1 operable to generate the audible sound by means of an audio transducer internal to the cabin of the vehicle.

16. A motor vehicle control system comprising apparatus according to paragraph 1.

17. A motor vehicle comprising apparatus according to paragraph 1 or a system according to paragraph 16.

18. A vehicle according to paragraph 17 wherein the vehicle is an electric vehicle.

19. A vehicle according to paragraph 17 wherein the vehicle is a hybrid vehicle.

20. A method of controlling a vehicle having an electric propulsion motor, the method comprising receiving a signal corresponding to a speed of the motor, and generating an audible sound wherein at least one characteristic of the sound is dependent on the signal corresponding to motor speed.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

CLAIMS: 1. An apparatus for a vehicle having an electric propulsion motor, the apparatus being operable to receive a signal corresponding to a speed of rotation of the motor and to generate an audible sound wherein at least one characteristic of the sound is dependent on said signal.
2. An apparatus according to claim 1 operable to commence generation of the audible sound when a user signals starting of the vehicle.
3. An apparatus according to claim 1 operable to commence generation of the audible sound when a user selects a driving mode of the vehicle.
4. An apparatus according to any preceding claim wherein the at least one characteristic includes a timbre of the sound.
5. An apparatus according to any preceding claim wherein the at least one characteristic includes a pitch of the audible sound.
6. An apparatus according to claim 5 operable to increase a pitch of the sound with increasing motor speed.
7. An apparatus according to any preceding claim wherein the sound is stored by the apparatus as an audio waveform.
8. An apparatus according to claim 7 as dependent on claim 6 operable to vary the pitch by varying a time period over which a prescribed amount of an audible sound file is replayed.
9. An apparatus according to any preceding claim operable to vary a volume of sound generated by the apparatus as a function of motor speed.
10. An apparatus according to claim 9 operable to increase the volume of sound generated with increasing motor speed.
11. An apparatus according to any preceding claim operable to vary at least one characteristic of the sound in dependence on whether a user has selected a boost mode in which operation of the propulsion motor at an increased power level is permitted.
12. An apparatus according to any preceding claim operable to generate the audible sound whereby the sound may be heard from outside the vehicle.
13. An apparatus according to any preceding claim operable to generate the audible sound by means of audio transducer means external to a cabin of the vehicle.
14. An apparatus according to any preceding claim operable to generate the audible sound whereby the sound may be heard from inside the vehicle.
15. An apparatus according to any preceding claim operable to generate the audible sound by means of audio transducer means internal to the cabin of the vehicle.
16. A motor vehicle control system comprising apparatus according to any preceding claim.
17. A motor vehicle comprising apparatus according to any one of claims 1 to 15 or a system according to claim 16.
18. A vehicle according to claim 17 wherein the vehicle is an electric vehicle.
19. A vehicle according to claim 17 wherein the vehicle is a hybrid vehicle.
20. A method of controlling a vehicle having an electric propulsion motor, the method comprising receiving a signal corresponding to a speed of the motor, and generating an audible sound wherein at least one characteristic of the sound is dependent on the signal corresponding to motor speed.
21. An apparatus, a system, a vehicle or a method substantially as hereinbefore described with reference to the accompanying drawings.