Apparatus and method for audio alert of a vehicle occupant

Abstract

Aspects of the present invention relate to a control system (200) for controlling an exterior audio output device (250) of a vehicle (100). The control system comprises one or more processors (212) co

Description

TECHNICAL FIELD The present disclosure relates to a control system and method for controlling an exterior audio output device of a vehicle. Aspects of the invention relate to a control system, to a system, to a vehicle, to a method, and to computer readable instructions. BACKGROUND If a child, pet, or other occupant is left unattended in a vehicle it can be a problem, for example by the occupant panicking, or potentially suffering ill health through heat stroke. 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, a system, a vehicle, a computer-implemented method, and computer readable instructions as claimed in the appended claims. According to an aspect of the present invention there is provided a control system for controlling an exterior audio output device of a vehicle, the control system comprising one or more processors collectively configured to: when the vehicle is in a park mode, receive an abandoned occupant signal indicative of detection of an occupant left inside the vehicle; and control, in dependence on the abandoned occupant signal, the exterior audio output device to output an audio alert indicative of detection of the occupant inside the vehicle. Advantageously, if an occupant is detected as being abandoned in the vehicle, the exterior audio output device of the vehicle can provide an audio indicator to attract the attention of people nearby the vehicle to the vehicle, and the abandoned occupant can receive assistance. According to an aspect of the present invention there is provided a control system for controlling an exterior audio output device of a vehicle, the control system comprising one or more processors collectively configured to: when the vehicle is in a drive mode, control the exterior audio output device to output a driving audio output exterior to the vehicle; when the vehicle is in a park mode, receive an abandoned occupant signal from an occupant presence sensor, the abandoned occupant signal indicative of detection of an occupant left inside the vehicle; and control, in dependence on the abandoned occupant signal, the exterior audio output device to operate in an occupant alert mode whereby the exterior audio output device outputs an audio alert exterior to the vehicle, the audio alert indicative of detection of the occupant inside the vehicle. Advantageously, if an occupant is detected as being abandoned in the vehicle, the exterior audio output device of the vehicle can provide an audio indicator to attract the attention of people nearby the vehicle to the vehicle, and the abandoned occupant can receive assistance. The exterior audio output device may already be part of the vehicle or a retrofitted part and can operate in a default mode, and is configured as described herein to include an additional mode to provide the occupant alert as well. Therefore additional or new hardware may not be necessary to provide the occupant alert. The “drive mode” may be a mode in which the vehicle is configured to propel itself along the surface on which it is resting, in a forward and / or a reverse gear, i.e. the vehicle is in a forward gear or a reverse gear. The “park mode” may be a mode in which the vehicle is configured to not move along the surface on which it is resting, for example, the hand brake is on, and / or the vehicle is not in a forward or reverse gear (e.g. it may be in a neutral gear or a park gear). Advantageously the control system can provide an audio alert in an appropriate situation, i.e. when the vehicle is parked. The exterior audio output device may be configured to operate in at least a default mode in which the exterior audio output device is configured to output a driving audio output configured to warn external users, for e.g. pedestrians, of the presence of the vehicle at low speeds, and an occupant alert mode in which the exterior audio output device is configured to output an audio alert indicative of detection of an occupant left inside the vehicle. Advantageously the exterior audio output device can be used in different modes for different purposes, and if included originally in a vehicle to operate in a default mode, may be re-purposed to additionally operate in the occupant alert mode. The abandoned occupant signal may be indicative of: an abandoned child, an abandoned animal, or an abandoned adult. The audio alert exterior to the vehicle may comprise an audio signature different to the driving audio output or the default mode audio output. Advantageously, the audio signature can convey information unique to the situation of there being an abandoned occupant, to better attract the attention of passers-by and convey information about the nature of the situation. In some examples the audio alert exterior to the vehicle may be unique to the indication of the occupant, for example, a spoken message to say “child left in vehicle” or “remove pet”. The audio alert may comprise one or more of: a first audio pattern comprising at least two different frequency tones, beeps, or chimes; a second audio pattern comprising one or more of: tones, beeps, or chimes associated only with indication of an abandoned occupant; and / or a spoken message indicative of an abandoned occupant. Advantageously, the audio alert can be customised and can clearly convey information to help attract the attention of the passers-by. By being specific to the situation of the detected abandoned occupant, the alert is less likely to be ignored than a more generic audio alert. For example, a horn sounding may be thought of as an attempt to open the locked door of an empty vehicle, which may be less likely to encourage a passerby to intervene than an alert specifically to indicate an abandoned animal, adult or child. In response to a receipt of one or more of: a door unlocking signal indicative of a vehicle door being unlocked, and a door opening signal indicative of a vehicle door being opened, the control system may be configured to control the exterior audio output device to cease operation in the occupant alert mode. Advantageously, the audio output by the exterior audio output device may be switched off in response to the vehicle being unlocked and / or a door opened, as this is representative of someone returning to the vehicle and accessing it, to assist the abandoned occupant. The control system may be configured to control the exterior audio output device to operate in the occupant alert mode further in dependence on a receipt of a signal indicative of a driver departing the vehicle. Advantageously, the exterior audio output device can operate in the occupant alert mode in response to a signal that the driver has exited the vehicle, as if to leave the occupant unattended. The control system may be configured to control the exterior audio output device to operate in the occupant alert mode further in dependence on receipt of: a journey completion signal transmitted in response to determination of the end of a drive cycle; a driver door use signal indicative of opening and closure of a driver’s door; a driver door closure signal indicative of closure of a driver’s door; a driver door lock signal indicative of locking of a driver’s door; a driver seatbelt operation signal indicate of unbuckling of a driver seatbelt; and an engine-off signal indicative of the engine being turned off at the end of a drive cycle. Advantageously, the exterior audio output device can operate in the occupant alert mode in response to the end of the drive cycle, indicating the end of journey, and the driver’s door being closed, indicating exiting of the driver from the vehicle, as an additional validation that the situation is indicative of the occupant being abandoned in the vehicle. The control system may be configured to control the exterior audio output device to operate in the occupant alert mode further in dependence on expiration of a pause period of a predetermined duration, the pause period commencing on the receipt of the signal indicative of the driver departing the vehicle. Advantageously, the exterior audio output device can operate in the occupant alert mode after a period of time following the end of the drive cycle and the driver exiting the vehicle, for example a period of time to allow the driver to move around to the passenger or backseat and help the occupant to exit the vehicle, so the exterior audio output device is not activated in the occupant alert mode immediately and to give the driver time to assist the occupant to exit the vehicle. The control system may be configured to: receive an abandonment time signal indicative of a time of detection of the occupant being left inside the vehicle; determine an abandonment duration in dependence on the time of detection and a current time; if the abandonment duration is below a predetermined abandonment duration threshold, control the exterior audio output device to operate in a first occupant alert mode, wherein, in the first occupant alert mode, the control system is configured to control the exterior audio output device to output a first audio alert at one or more of: a first volume level, a first frequency, a first tone type, a first spoken message; and if the abandonment duration is at or above the predetermined abandonment duration threshold, control the exterior audio output device to operate in a second occupant alert mode, wherein, in the second occupant alert mode, the control system is configured to control the exterior audio output device to output a second audio alert different from the first audio alert. Advantageously, the nature of the alert can be escalated dependent on the time that the occupant has been detected as being abandoned in different ways. The second audio alert may be at one or more of: a second volume level higher than the first volume level; a second frequency higher than the first frequency, a second tone type different from the first tone type, and a second spoken message different from the first spoken message. Advantageously, the nature of the alert can be escalated dependent on the time that the occupant has been detected as being abandoned. This is in line with the regulations for providing an alert in response to a suspected abandoned child, for example. The exterior audio output device may provide a more noticeable or more urgent warning when operating in the second occupant alert mode when the abandonment duration is above the abandonment time threshold. The control system may be configured to receive an abandonment time signal indicative of a time of detection of the occupant left inside the vehicle; and determine an abandonment duration in dependence on the time of detection and a current time. The abandoned occupant information may comprise a time of detected abandonment. Advantageously, the length of time for which the occupant has been detected as being abandoned may be indicated in the information provided by the exterior audio output device, to assist a passerby in understanding the situation and perform an appropriate response, for example calling out for the driver, or calling the emergency services. In the first occupant alert mode, the control system may be configured to control the exterior audio output device to output a first audio alert sound; and in the second occupant alert mode, the control system may be configured to control the exterior audio output device to project a second audio alert sound different from the first audio alert sound. Advantageously, the nature of the alert can be escalated dependent on the time that the occupant has been detected as being abandoned in different ways, and a second audio alert sound may provide a more urgent or disruptive audio output than the first audio alert sound, to indicate an increased level of urgency of the situation. The control system may be further configured to control, in dependence on the abandoned occupant signal, a further alert element to operate in a further occupant alert mode whereby the further alert element outputs a further alert indicative of detection of the occupant left inside the vehicle. Advantageously, an additional alert mechanism may also be triggered to supplement the audio output by the exterior audio output device. The additional alert mechanism may be of a different nature, such as a light / visible alert, or may be of the same nature but different mechanism of provision, such as sound emitted by the vehicle horn. The further alert element may be one or more of: a light projector, a vehicle light, a vehicle horn, an in-vehicle console, and a remote communication device. The control system may be further configured to: receive a background noise level signal indicative of a background noise level in the environment of the vehicle; determine, in dependence on the background noise level signal, an exterior audio output volume, wherein the exterior audio output device operating at the exterior audio output volume outputs the audio alert indicative of detection of an abandoned occupant inside the vehicle at an audible volume level; and control the exterior audio output device to output the audio alert indicative of detection of the abandoned occupant inside the vehicle at the determined exterior audio output volume. Advantageously, the output audio may be projected at a volume commensurate with the background noise levels, so that an audible alert can be output, while not unnecessarily using more power providing audio at a higher volume than necessary, for example if the environment is quiet. In an aspect of the present invention, there is provided a system comprising: the control system disclosed herein; and an exterior audio output device. Optionally, the system may further comprise an occupant presence sensor. Advantageously, an exterior audio output device may be controlled by the control system as above. The system may also include the occupant presence sensor so that the system is able to detect an abandoned occupant and provide an alert that there is an abandoned occupant. The exterior audio output device of the system may be configured to output the audio alert exterior to the vehicle and indicative of detection of the occupant left inside the vehicle, at a volume up to 75 dB(A). Advantageously, an existing exterior audio output device may be used to provide an audible alert to attract the attention of the driver and / or passer-by to assist the abandoned occupant. In an aspect of the present invention, there is provided a vehicle comprising any control system disclosed herein, or any system disclosed herein. In some examples, the vehicle may be a battery electric vehicle or a hybrid vehicle. In an aspect of the present invention, there is provided a computer-implemented method for controlling an exterior audio output device of a vehicle, the method comprising: when the vehicle is in a drive mode, controlling the exterior audio output device to output a driving audio output exterior to the vehicle; when the vehicle is in a park mode, receiving an abandoned occupant signal from an occupant presence sensor, the abandoned occupant signal indicative of detection of an occupant left inside the vehicle; and controlling, in dependence on the abandoned occupant signal, the exterior audio output device to operate in an occupant alert mode whereby the exterior audio output device outputs an audio alert exterior to the vehicle, the audio alert indicative of detection of the occupant inside the vehicle. In an aspect of the present invention, there are provided computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform any method disclosed herein. In an aspect there is provided a computer readable medium comprising computer readable instructions that, when executed by a processor, cause performance of any method disclosed herein. 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 anyway and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a vehicle according to an embodiment of the invention; Figures 2A and 2E3 show a control system according to an embodiment of the invention; Figure 3 shows a control system configured to account for a pause period according to an embodiment of the invention; Figure 4 shows a control system configured to operate in plural occupant alert modes according to an embodiment of the invention; Figure 5 shows a control system configured to provide alerts by more than one output means according to an embodiment of the invention; Figure 6 shows a control system configured to account for background noise according to an embodiment of the invention; Figure 7 shows a system according to an embodiment of the invention; and Figure 8 shows a method according to an embodiment of the invention. DETAILED DESCRIPTION If a child, pet, or any other occupant is left unattended in a vehicle it can be a problem. An attempt to alert the driver (if nearby the vehicle) or other passer-by by, for example, the vehicle detecting the occupant and sounding the vehicle horn or flashing the vehicle’s hazard lights risks may be ignored as it may be mistaken for an erroneous vehicle security alarm being triggered as if to indicate an attempted unauthorised entry. There is a European New Car Assessment Programme (NCAP) implementation aimed towards improving safety for children who may be left unintentionally in a vehicle, for example by a distracted or tired parent. Even if the child (or in other examples, a pet) is left in a vehicle for a short while, it can cause distress and health issues such as heat-stroke and in extreme cases, death. It is an aim of the present invention to provide an improved system and method of indicating the presence of an occupant left in a vehicle who may be unable to signal for help or exit the vehicle themselves. Examples aim to make use of existing hardware to provide specific audio signalling of the occupant detected within the vehicle and to draw the attention of the driver and / or passers-by in an improved way. For example, providing an audio alert which indicates specifically that a child or pet is left within the vehicle may be more likely to encourage intervention and assisting the occupant to safety than a more generic alert of a sounding horn and / or flashing vehicle hazard lights, for example. A vehicle 100 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figure 1. As shown in Figure 1, the vehicle 100 is a land-going i.e. wheeled vehicle, and the vehicle may be any vehicle in which there may be an occupant other than the driver present and which may have an exterior audio output device 250 (e.g. a speaker or external sounder). It should be noted that the present invention is not limited to the vehicles already having an exterior audio output device and in case the vehicle does not have an in-built exterior audio output device, the exterior audio output device can be retrofitted to the vehicle. The vehicle 100 shown in Figure 1 is a passenger vehicle having a plurality of doors and seats therein, although embodiments of the invention may be used with other types of the vehicle. Figures 2A and 2E3 show a control system 200 according to an embodiment of the invention. The control system 200 is for controlling an exterior audio output device 250 of a vehicle 100. The control system 200 may comprise one or more controllers 210. In the example shown in Figures 2A, 2B, there is one controller 210. The controller 210 as illustrated in Figures 2A and 2B comprises a processing means 212 and a memory means 214. The processing means 212 may be one or more electronic processing device or processors which operably executes computer-readable instructions. The memory means 214 may be one or more memory device or memory. The memory 214 is electrically coupled to the processing means or processor 212. The memory 214 is configured to store instructions, and the processor 212 is configured to access the memory 214 and execute the instructions stored thereon. The memory 214 may also store data for operation by a process executing on the processor 212. It will be understood that the controller 210 may be implemented by more than one processor 212 and memory 214. The controller 210 comprises an input means 216 and an output means 218. The input means 216 may comprise an electrical input 216 of the controller 210. The output means 218 may comprise an electrical output 218 of the controller 210. The control system 200 is for controlling an exterior audio output device 250 of a vehicle. Figure 2A shows the control system 200 operating according to when the vehicle 100 is in a drive mode. The “drive mode” may be a mode in which the vehicle 100 is configured to propel itself along the surface on which is it resting in a forward and / or a reverse gear, i.e. the vehicle is in a forward gear or a reverse gear and able to move. The control system 200 is configured to control the exterior audio output device 250 to output a driving audio output 252 exterior to the vehicle 100. For example, a battery electric vehicle 100 or hybrid vehicle 100 may, when driving, output a driving noise from the exterior audio output device 250 to indicate to pedestrians that the vehicle is present and moving. Electric-powered vehicles typically may not make a noise in the same way an internal combustion engine vehicle (i.e. a fuelled vehicle) does, which can serve as a warning to pedestrians who hear the sound and are alerted to be cautious as there is a moving vehicle nearby. Figure 2B shows the control system 200 operating according to when the vehicle 100 is in a park mode. The “park mode” may be a mode in which the vehicle 100 is configured to not move along the surface on which is it resting. For example, the hand brake is on, the engine is off, and / or the vehicle is not in a forward or reverse gear (e.g. it may be in a neutral gear or a park gear). The control system 200 is configured to receive an abandoned occupant signal 220 from an occupant presence sensor. The abandoned occupant signal 220 is indicative of detection of an occupant left inside the vehicle 100. In Figure 2B, the input 216 is arranged to receive the abandoned occupant signal 220. For example, the driver may inadvertently leave their child, or a pet, inside the vehicle. The occupant presence sensor may comprise a visual sensor such as a camera. There may be an image processor module configured to receive images captured by the visual sensor and image recognition to determine if there is an occupant and, if so, whether the occupant appears to be an adult, a child, an animal, or other occupant. The occupant presence sensor may comprise a pressure sensor, which may be configured to detect a pressure and / or variations in pressure applied to a seat of the vehicle and determine whether there is an occupant present on the seat, and / or whether the occupant is an adult, child, an animal, or any other occupant. The occupant presence sensor may comprise a movement sensor which may detect movement within the vehicle and determine whether there is an occupant present on the seat, and / or whether the occupant is an adult, child, an animal, or other occupant. The occupant presence sensor may comprise an audio sensor, and / or a temperature sensor. Other occupant presence sensors may be envisaged which are able to determine the presence of an abandoned occupant in the vehicle. The abandoned occupant signal may be indicative of an abandoned child, an abandoned animal, or an abandoned adult. The control system 200 is configured to control, in dependence on the abandoned occupant signal 220, the exterior audio output device 250 to operate in an occupant alert mode whereby the exterior audio output device 250 outputs an audio alert 254 exterior to the vehicle 100. The audio alert 254 is indicative of detection of the occupant inside the vehicle. Thus, if an occupant is detected as being abandoned in the vehicle 100, the exterior audio output device 250 of the vehicle 100 can provide an audio indicator 254 to attract the attention of people nearby the vehicle 100, and the abandoned occupant can receive assistance. The control system 200 may output an exterior audio output device signal 230 to cause the exterior audio output device 250 to output the audio alert 254 exterior to the vehicle 100 indicative of detection of the occupant inside the vehicle 100. In Figure 2E3 the output means 218 may be arranged to provide the output signal 230 to the exterior audio output device 250. Advantageously, the exterior audio output device 250 may already be part of the vehicle 100 or a retrofitted part and can operate in a default mode as in Figure 2A, and is configured as described herein to include an additional mode to provide the occupant alert as well, as in Figure 2B. Therefore additional or new hardware is not necessary to provide the occupant alert 254. The exterior audio output device 250 may be configured to output the audio alert exterior to the vehicle 100, and indicative of detection of the occupant inside the vehicle, at a volume up to 75 dB(A) (units of A-weighted decibels), for example, between 0 dB(A) and 75 dB(A), such as between 50 dB(A) and 75 dB(A). Thus the existing exterior audio output device 250 may be used to provide an audible alert to attract the attention of the driver and / or passer-by to assist the abandoned occupant. The abandoned occupant signal 220 may be indicative of: an abandoned child, an abandoned animal, or an abandoned adult, for example. For example, if an in-vehicle camera, as an occupant presence sensor, provides captured images for analysis and it is determined that the occupant is a child, this information can be conveyed in the audio alert 254.The audio alert 254 exterior to the vehicle 100 may comprise an audio signature different to the driving audio output and / or default mode audio output. Advantageously, the audio signature can convey information unique to the situation of there being an abandoned occupant, to better attract the attention of passers-by and convey information about the nature of the situation. In some examples the audio alert 254 exterior to the vehicle may be unique to the indication of the occupant, for example, a spoken message may be output to say “child left in vehicle” or “dog in vehicle”, for example. In some examples the location of the occupant may be detected and indicated, such as “occupant in row 1 footwell”, “child left in row 2”, “animal located on driver side of vehicle” etc. The audio alert 254 may comprise a first audio pattern comprising at least two different frequency tones, beeps, or chimes. The audio alert 254 may comprise a second audio pattern comprising one or more of: tones, beeps, or chimes associated only with indication of an abandoned occupant. The audio alert 254 may comprise a spoken message indicative of an abandoned occupant. Advantageously, the audio alert 254 can be customised and can clearly convey information to help attract the attention of the passers-by in a specific way. An alert stating “child abandoned” is less likely to be ignored than a more generic audio alert such as a horn sounding. The exterior audio output device 250 may be configured to cease operation in the occupant alert mode in response to a door of the vehicle being unlocked, and / or a door of the vehicle being opened. In this way, the exterior audio output device 250 may be switched off in response to the vehicle being unlocked and / or a door opened, as this action is representative of someone returning to the vehicle 100 and accessing it, to assist the abandoned occupant. The control system 100 may be configured to control the exterior audio output device 250 to operate in the occupant alert mode further in dependence on a receipt of a signal indicative of a driver departing the vehicle 100. For example, if the vehicle 100 has stopped after end of a drive cycle and the driver door is detected as being opened, closed, and locked, this may be taken to indicate the driver has left the vehicle and intends to leave it. If an occupant is detected as being present in the vehicle after those actions, the control system 100 may control the exterior audio output device 250 to output an alert. Advantageously, the exterior audio output device can operate in the occupant alert mode in response to a signal that the driver has exited the vehicle, as if to leave the occupant? unattended. In some examples, the control system 100 may be configured to control the exterior audio output device 250 to operate in the occupant alert mode in dependence on: receipt of a journey completion signal transmitted in response to determination of the end of a drive cycle; a driver door use signal indicative of opening and closure of a driver’s door; a driver door closure signal indicative of closure of a driver’s door; a driver door lock signal indicative of locking of a driver’s door; a driver seatbelt operation signal indicate of unbuckling of a driver seatbelt; and / or an engine-off signal indicative of the engine being turned off at the end of a drive cycle. Thus the exterior audio output device 250 can operate in the occupant alert mode in response to the end of the drive cycle, indicating the end of journey, and the driver’s door being closed, indicating exiting of the driver from the vehicle, as an additional validation that the situation is indicative of the occupant being abandoned in the vehicle. The control system 200 may be configured to control the external audio output device 250 to operate in the occupant alert mode further in dependence on receipt of signalling indicating opening and closing of a driver’s door of the vehicle. This may take place in the middle of a journey and without the end of a drive cycle, in some examples. Further, the external audio output device 250 can operate in the occupant alert mode after it is determined that an occupant has entered the vehicle and closed the door as well as after receiving the abandoned occupant signal. For example, a parent may unlock a vehicle in preparation for loading the vehicle before a journey such as a holiday or a day trip, and a child may enter the vehicle without the parent being aware. Accounting for the operation of the vehicle doors as well as receipt of the abandoned occupant signal may be advantageous in determining the presence of an occupant in the vehicle who may need assistance, or who should not be unsupervised in the vehicle, and that the driver or person in charge of the vehicle should be aware of. Figure 3 shows a control system 200 configured to account for a pause period. It may be appropriate to allow the driver a short period of time to assist any occupants out of the vehicle 100 before a determination is made that the occupant has been abandoned. The control system 200 in such examples may be configured to control the exterior audio output device 250 to operate in the occupant alert mode further in dependence on expiration of a pause period 302 of a predetermined duration. The pause period 302 may commence on the receipt of a signal 304 indicative of the driver departing the vehicle. Advantageously, the exterior audio output device 250 can operate in the occupant alert mode after a period of time following the end of the drive cycle and the driver exiting the vehicle, for example after a period of time to allow the driver to move around to the passenger or backseat and help the occupant to exit the vehicle, so the exterior audio output device is not activated in the occupant alert mode immediately and to give the driver time to assist the occupant to exit the vehicle. Figure 4 shows a control system 200 configured to operate in plural occupant alert modes. It may be advantageous to provide different types of alert depending on the context of determining that an occupant has been abandoned in the vehicle 100. For example, the length of time since the occupant has been determined to have been abandoned may be detected and used to cause different audio alerts to be output dependent on the length of time. As another example, the current temperature fore.g. of a vehicle or ambient temperature, may be detected / measured and may be taken into account when controlling the external audio output device, for example to indicate a risk of heat stroke if the temperature is above the threshold temperature. It will be appreciated that other contextual factors may be detected and used to determine what type of audio output is provided by the external audio output device. The control system 200 as shown in Figure 4 is configured to receive an abandonment time signal 402 indicative of a time of detection of the occupant being left inside the vehicle. The abandoned occupant signal 220 is also received as before. In some examples the abandoned occupant signal 220 may comprise the time of detected abandonment 402. The control system 200 can determine (404) an abandonment duration in dependence on the time of detection 402 and a current time. If the abandonment duration is below (408) a predetermined abandonment duration threshold, the control system 200 may control the exterior audio output device 250 to operate in a first occupant alert mode. In the first occupant alert mode, the control system 200 is configured to control the exterior audio output device 250 to output a first audio alert. The first audio alert is output at a first volume level, at a first frequency, at a first tone type, and / or provides a first spoken message, for example. If the abandonment duration is at or above (406) the predetermined abandonment duration threshold, the control system 200 controls the exterior audio output device 250 to operate in a second occupant alert mode. In the second occupant alert mode, the control system 200 is configured to control the exterior audio output device 250 to output a second audio alert different from the first audio alert. Advantageously, the alert can be escalated dependent on the time that the occupant has been detected, and a second audio alert sound may provide a more urgent or disruptive audio output than the first audio alert sound, to indicate an increased level of urgency of the situation. The second audio alert may be output at a second volume level higher than the first volume level; at a second frequency higher than the first frequency, at a second tone type different from the first tone type, and / or may be a second spoken message different from the first spoken message. These variations between the first and second audio alerts are examples and others may be envisaged. Advantageously, the nature of the alert can be escalated dependent on the time that the occupant has been detected as being abandoned. The exterior audio output device 250 may provide a more noticeable or more urgent warning when operating in the second occupant alert mode when the abandonment duration is above the abandonment time threshold. The control system 200 in some examples may be configured to receive an abandonment time signal indicative of a time of detection of the occupant left inside the vehicle. For example a trigger action, such as the driver locking the vehicle, or when all the vehicle doors are closed, may start a detection time counter. In some examples, if a door is subsequently opened (e.g. the driver door), then the counter is stopped. If a later trigger action (e.g. the driver door being closed again), the detection time counter may restart. The control system 200 may determine an abandonment duration in dependence on the time of detection and a current time. The abandoned occupant information conveyed by the external audio output alert may comprise a time of detected abandonment (such as a repeated updated spoken message e.g. “occupant left for 2 minutes...occupant left for 2 minutes and 10 seconds...”). Advantageously, the length of time for which the occupant has been detected as being abandoned may be indicated in the information provided by the exterior audio output device, to assist a passerby in understanding the situation and perform an appropriate response, for example calling out for the driver, or calling the emergency services. Figure 5 shows a control system 200 configured to provide alerts by more than one output means. The control system 200 in this example is configured to control, in dependence on the abandoned occupant signal 220, a further alert element 260 to operate in a further occupant alert mode. The further alert element 260 is configured to output a further alert indicative of detection of the occupant left inside the vehicle. The further alert element 260 may be a light projector, a vehicle light, a vehicle horn, an in-vehicle console, or a remote communication device (e.g. the driver’s smartphone communicatively connected to the control system 200), for example. Advantageously, an additional alert mechanism may also be triggered to supplement the audio output by the exterior audio output device 250. The additional alert mechanism may be of a different nature, such as a light / visible alert, or may be of the same nature but different mechanism of provision, such as sound emitted by the vehicle horn. The further alert element 260 may be operated in the second occupant alert mode for example. The further alert element 260 in some examples may be a driver’s personal electronic device; for example the control system 200 may cause a text message or audio alarm to be provided by the driver’s personal electronic device to alert them of the abandoned occupant. The use of a further alert element 260 may be used to escalate the provided warning in dependence on the length of time of abandonment (or other factor affecting the urgency with which the vehicle should be attended to assist the occupant, such as external temperature). Figure 6 shows a control system 200 configured to account for background noise. The control system 200 in this example is configured to receive a background noise level signal 610 indicative of a background noise level in the environment of the vehicle 100. The control system 200 can then determine (602), in dependence on the background noise level signal 610, an exterior audio output volume. The exterior audio output device 250 operating at the exterior audio output volume outputs the audio alert indicative of detection of an abandoned occupant inside the vehicle at an audible volume level. The control system 200 can then control the exterior audio output device 250 (via a control signal 230) to output the audio alert indicative of detection of the abandoned occupant inside the vehicle at the determined exterior audio output volume. Thus the output audio may be projected at a volume commensurate with the background noise levels, so that an audible alert can be output, while not unnecessarily using more power providing audio at a higher volume than necessary, for example if the environment is quiet. Figure 7 shows a system 700 which comprises any of the control systems 200 disclosed herein, and an exterior audio output device 250. The exterior audio output device 250 is configured to operate in at least a default mode in which the exterior audio output device 250 is configured to output a driving audio output configured to warn external users, for e.g. pedestrians, of the presence of the vehicle at low speeds, and an occupant alert mode in which the exterior audio output device 250 is configured to output an audio alert indicative of detection of an occupant left inside the vehicle. The system 700 may further comprise, as shown, an occupant presence sensor 710, such as a camera, pressure sensor, movement sensor, temperature sensor, or other sensor configured to detect the presence of an occupant. The system 700 may comprise one or more further alert elements 260 as discussed above. Figure 8 illustrates a method 800 according to an embodiment of the invention. The method 800 may be performed by the control system 200 or by the system 700 described above. The method 800 is a method 800 for controlling an exterior audio output device 250 of a vehicle 100. The method 800 comprises at step 802, when the vehicle is in a drive mode, controlling the exterior audio output device to output a driving audio output exterior to the vehicle. At step 804, when the vehicle is in a park mode, receiving an abandoned occupant signal from an occupant presence sensor, the abandoned occupant signal indicative of detection of an occupant left inside the vehicle. At step 806, controlling, in dependence on the abandoned occupant signal, the exterior audio output device to operate in an occupant alert mode whereby the exterior audio output device outputs an audio alert exterior to the vehicle, the audio alert indicative of detection of the occupant inside the vehicle. It will be appreciated that the method stages 802 and 804 need not be performed in a particular order. Also covered in this disclosure are computer readable instructions which, when executed by one or more processors (e.g. the processor 212 of Figure 2A or 2B), cause the one or more processors to perform the method 800 or any method disclosed herein. Also covered in this disclosure is a computer readable medium (e.g. a non-transient medium) comprising computer readable instructions that, when executed by a processor (e.g. the processor 212 of Figure 2A or2B), cause performance of the method 800 or of any method disclosed herein. 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 an exterior audio output device of a vehicle, the control system comprising one or more processors collectively configured to:when the vehicle is in a drive mode, control the exterior audio output device to output a driving audio output exterior to the vehicle;when the vehicle is in a park mode, receive an abandoned occupant signal from an occupant presence sensor, the abandoned occupant signal indicative of detection of an occupant left inside the vehicle; andcontrol, in dependence on the abandoned occupant signal, the exterior audio output device to operate in an occupant alert mode whereby the exterior audio output device outputs an audio alert exterior to the vehicle, the audio alert indicative of detection of the occupant inside the vehicle.

2. The control system of claim 1, wherein the audio alert exterior to the vehicle comprises an audio signature different to the driving audio output.

3. The control system of any preceding claim, wherein the audio alert comprises one or more of: a first audio pattern comprising at least two different frequency tones, beeps, or chimes;a second audio pattern comprising one or more of: tones, beeps, or chimes associated only with indication of an abandoned occupant; anda spoken message indicative of an abandoned occupant.

4. The control system of any preceding claim, wherein the exterior audio output device is configured to cease operation in the occupant alert mode in response to one or more of:a door of the vehicle being unlocked; and a door of the vehicle being opened.

5. The control system of any preceding claim, wherein the control system is configured to control the exterior audio output device to operate in the occupant alert mode further in dependence on a receipt of a signal indicative of a driver departing the vehicle.

6. The control system of claim 5, wherein the control system is configured to control the exterior audio output device to operate in the occupant alert mode further in dependence on expiration of a pause period of a predetermined duration, the pause period commencing on the receipt of the signal indicative of the driver departing the vehicle.

7. The control system of any preceding claim, wherein the control system is configured to:receive an abandonment time signal indicative of a time of detection of the occupant being left inside the vehicle;determine an abandonment duration in dependence on the time of detection and a current time;if the abandonment duration is below a predetermined abandonment duration threshold, control the exterior audio output device to operate in a first occupant alert mode, wherein, in the first occupant alert mode,the control system is configured to control the exterior audio output device to output a first audio alert at one or more of: a first volume level, a first frequency, a first tone type, a first spoken message; andif the abandonment duration is at or above the predetermined abandonment duration threshold, control the exterior audio output device to operate in a second occupant alert mode, wherein, in the second occupant alert mode, the control system is configured to control the exterior audio output device to output a second audio alert different from the first audio alert.

8. The control system of any preceding claim, wherein the control system is further configured to: control, in dependence on the abandoned occupant signal, a further alert element to operate in a further occupant alert mode whereby the further alert element outputs a further alert indicative of detection of the occupant inside the vehicle.

9. The control system of any preceding claim, wherein in response to a receipt of one or more of: a door unlocking signal indicative of a vehicle door being unlocked, and a door opening signal indicative of a vehicle door being opened, the control system is configured to control the exterior audio output device to cease operation in the occupant alert mode.

10. The control system of any preceding claim, further configured to:receive a background noise level signal indicative of a background noise level in the environment of the vehicle;determine, in dependence on the background noise level signal, an exterior audio output volume, wherein the exterior audio output device operating at the exterior audio output volume outputs the audio alert indicative of detection of an abandoned occupant inside the vehicle at an audible volume level; andcontrol the exterior audio output device to output the audio alert indicative of detection of the abandoned occupant inside the vehicle at the determined exterior audio output volume.

11. A system comprising:the control system of any preceding claim; andan exterior audio output device;optionally, wherein the system further comprises an occupant presence sensor.

12. The system of claim 11, wherein the exterior audio output device is configured output the audio alert exteriorto the vehicle and indicative of detection of the occupant inside the vehicle at a volume up to 75 dB(A).

13. A vehicle comprising the control system of any of claims 1 to 10, or the system of claim 11 or claim 12; optionally, wherein the vehicle is a battery electric vehicle or a hybrid vehicle.

14. A computer-implemented method for controlling an exterior audio output device of a vehicle, the method comprising:when the vehicle is in a drive mode, controlling the exterior audio output device to output a driving audio output exteriorto the vehicle;when the vehicle is in a park mode, receiving an abandoned occupant signal from an occupant presence sensor, the abandoned occupant signal indicative of detection of an occupant left inside the vehicle; andcontrolling, in dependence on the abandoned occupant signal, the exterior audio output device to5 operate in an occupant alert mode whereby the exterior audio output device outputs an audio alert exterior to the vehicle, the audio alert indicative of detection of the occupant inside the vehicle.

15. Computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform the method of claim 13.10

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