Technical Field

The present disclosure relates to controlling a heating, ventilation and air conditioning (HVAC) system of a vehicle, and in particular to controlling the HVAC system to regulate a level of carbon dioxide present in a cabin of the vehicle. Aspects of the invention relate to a control system, to a method, to a vehicle, to computer software, and to a non- transitory, computer-readable medium. Background

Heating, ventilation and air conditioning (HVAC) systems in vehicles, such as cars, can be used to control various factors in a cabin of the vehicle. For instance, the vehicle cabin may be heated or cooled by moving air past either a heater core or air conditioning evaporator of the HVAC system before it is introduced into the cabin. A vehicle HVAC system may also include one or more air filters for reducing a level of pollution in the vehicle cabin. In particular, air may be drawn past or through the filters in order to remove pollutants from the air before it is introduced into the vehicle cabin. One type of air filter that may be used in this context is a particulate matter (PM) filter - e.g. a PM2.5 filter - for removing particulate matter contamination from air prior to it entering the cabin.

HVAC systems may utilise vented air, recirculated air, or a combination of both. Vented air refers to air that is drawn into the vehicle cabin from outside of (external to) the vehicle past one or more components of the HVAC system. Recirculated air refers to air in the vehicle cabin that is recirculated past one or more components of the HVAC system before returning to the vehicle cabin.

Typically, an HVAC system includes an inlet door mechanism that may include one or more doors for adjusting the ratio of vented to recirculated air entering the vehicle cabin. In a fully recirculated state of the inlet door mechanism, the HVAC system may be in a recirculation mode in which no air is drawn into the vehicle cabin from outside of the vehicle, with all of the air entering the vehicle cabin being recirculated air. In a fully vented state of the inlet door mechanism, all of the air entering the vehicle cabin may be drawn from outside of the vehicle. The inlet door mechanism may be adjustable to a number of intermediate positions between the fully recirculated and fully vented states. A blower of the HVAC system may also be used to adjust a rate at which air enters the vehicle cabin.

Carbon dioxide levels in the vehicle cabin build up naturally as a result of the occupants of the vehicle breathing out carbon dioxide. High levels of carbon dioxide are known to cause drowsiness, and very high levels of carbon dioxide are known to cause headaches. It is preferable that occupants of the vehicle, and in particular the driver, are not exposed to such levels of carbon dioxide.

It is against this background that the present invention has been devised.

Summary of the Invention

According to an aspect of the present invention there is provided a control system for controlling a heating, ventilation and air conditioning (HVAC) system of a vehicle. The control system comprises one or more controllers and is configured to: receive carbon dioxide (C02) data, from at least one C02 sensor in a cabin of the vehicle, indicative of a level of C02 present in the vehicle cabin; determine, based on the received C02 data, whether to reduce the level of C02 present in the vehicle cabin; and transmit a control signal to control the HVAC system to draw air into the vehicle cabin from external to the vehicle if the processor determines that the level of C02 is to be reduced.

The invention advantageously allows for the level of carbon dioxide in the vehicle cabin to be monitored and reduced if it is determined that the carbon dioxide level is too high. In this way, the carbon dioxide concentration within the vehicle cabin can be prevented from reaching levels that would otherwise have a detrimental impact on occupants of the vehicle. In particular, the carbon dioxide level can be kept below a level at which occupants may begin to feel drowsy, thus avoiding driver and other occupant drowsiness.

The one or more controllers may collectively comprise: at least one electronic processor having an electrical input for receiving the carbon dioxide (C02) data; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein. The at least one electronic processor may be configured to access the at least one memory device and execute the instructions thereon so as to determine whether to reduce the level of C02 present in the vehicle cabin. The control signal may comprise controlling at least one actuatable component of the HVAC system including at least one of: an inlet door mechanism of the HVAC system; and, a blower of the HVAC system.

The control signal may be determined based on a current position of one or more of the actuatable components.

The actuatable components may comprise the inlet door mechanism. The current position of the inlet door mechanism may be; a recirculated air position; a vented or fresh air position or, one of a plurality of intermediate positions. The intermediate positions may define positions of the inlet door mechanism that result in a combination of air from external to the vehicle and recirculated air being drawn into the vehicle cabin.

In some embodiments, the inlet door mechanism may consist of a single door, referred to as a recirculation door, which may be movable between a fully open position and a fully closed position. In that case, the inlet door mechanism may be in the recirculated air position when the recirculation door is in the fully closed position, and may be in the vented air position when the recirculation door is in the fully open position. The recirculation door may be movable or adjustable to a number of intermediate positions between the fully open and fully closed states.

In other embodiments, the inlet door mechanism may comprise a plurality of doors whose positions together define the position of the inlet door mechanism. For example, in one embodiment, the inlet door mechanism may comprise a recirculation door, a partial door and a fresh air door. In that case, the inlet door mechanism may be in the recirculated air position when the recirculation door is in a fully open position, and the partial door and the fresh air door are in fully closed positions. The inlet door mechanism may be in the vented air position when the recirculation door and the partial door are closed, and the fresh air door is open.

The control signal may adjust the position of the inlet door mechanism to increase the amount of air drawn into the vehicle cabin from external to the vehicle. The processor may be configured to: monitor the received C02 data after adjusting the inlet door mechanism to increase the amount of air drawn into the vehicle cabin from external to the vehicle; and determine, based on the monitored C02 data, whether to further reduce the level of C02 present in the vehicle cabin. The control signal may further adjust the position of the inlet door mechanism to further increase the amount of air drawn into the vehicle cabin from external to the vehicle if it is determined to further reduce the level of C02.

The actuatable components may comprise the blower, and the current position of the blower speed may define a speed of the blower. The control signal may be configured to increase a speed of the blower of the HVAC system.

The control signal may be configured to increase the blower speed if adjusting the position of the inlet door mechanism fails to reduce the level of C02 present in the vehicle cabin by a desired level.

The control signal may be determined based on a degree to which the level of C02 is to be reduced.

It may be determined to reduce the level of C02 present in the vehicle cabin if it exceeds a prescribed C02 value. It may be determined to reduce the level of C02 present in the vehicle cabin if it exceeds the prescribed C02 value for a prescribed period of time.

The control signal may continue to control the HVAC system to draw the increased amount of air into the vehicle cabin from external to the vehicle until a stop condition is satisfied. The stop condition may be at least one of: the level of C02 present in the vehicle cabin reduces to a desired level; and a predefined amount of time has elapsed without the level of C02 reaching the desired level.

If the processor determines that a further function controlled by the HVAC system is determined to be active, then the processor may be configured to determine whether to prioritise the further function over reducing the level of C02, and the control signal may control the HVAC system in accordance with the determined prioritisation. The determination of whether to prioritise the further function over reducing the level of C02 may be based on the level of C02 received from the at least one C02 sensor relative to a C02 value.

The further function may be to reduce a level of particulate matter (PM) present in the vehicle cabin. The further function may comprise: the input being configured to receive internal PM data, from at least one PM sensor in the vehicle cabin, indicative of a level of PM present in the vehicle cabin, and configured to receive external PM data, from at least one PM sensor external to the vehicle cabin, indicative of a level of PM external to the vehicle cabin; the processor being configured to determine whether to reduce the level of PM present in the vehicle cabin based on levels of PM present in the vehicle cabin and external to the vehicle cabin indicated in the received internal and external PM data; and, the output being configured to transmit the control signal to increase the amount of air drawn into the HVAC system from the vehicle cabin and recirculated back into the vehicle cabin if it is determined to reduce the level of PM present in the vehicle cabin.

The further function to reduce the level of PM present in the vehicle cabin may be prioritised over reducing the level of C02 present in the vehicle cabin. This prioritisation may occur if the level of PM is deemed to be at a critical level.

The control signal may adjust an inlet door mechanism of the HVAC system to increase the amount of air drawn into the HVAC system from the vehicle cabin and recirculated back into the vehicle cabin if it is determined to reduce the level of PM present in the vehicle cabin.

The C02 sensor and the PM sensor in the vehicle cabin may be part of a single sensor unit.

The further function may be a climate control function to control a temperature in the vehicle cabin.

The controller may be enabled or disabled by a vehicle user to automatically control the HVAC system to control the level of C02 present in the vehicle cabin. The vehicle user may enable or disable the controller via a human-machine interface (HMI) of the vehicle. According to another aspect the invention provides a vehicle comprising a control system, according to any preceding paragraph.

According to another aspect the invention provides a method of controlling a heating, ventilation and air conditioning (HVAC) system of a vehicle. The method comprises: receiving carbon dioxide (C02) data, from at least one C02 sensor in a cabin of the vehicle, indicative of a level of C02 present in the vehicle cabin; determining, based on the received C02 data, whether to reduce the level of C02 present in the vehicle cabin; and, transmitting a control signal to control the HVAC system to draw an increased amount of air into the vehicle cabin from external to the vehicle if a processor determines that the level of C02 is to be reduced.

According to another aspect the invention provides a non-transitory, computer-readable storage medium storing instructions thereon that, when executed by one or more electronic processors, causes the one or more electronic processors to carry out the method according to the preceding paragraph.

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

Brief Description of the Drawings

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

Figure 1 shows a vehicle comprising a controller in accordance with an embodiment of the invention;

Figure 2 is a schematic representation of the controller of Figure 1 ; and Figure 3 illustrates steps of a method undertaken by the controller of Figure 1 . Detailed Description

Figure 1 shows a vehicle 10, in particular a car, that includes a heating, ventilation and air conditioning (HVAC) system (not shown) for controlling the flow of air into a cabin 14 of the vehicle 10.

The HVAC system comprises a vented and recirculation air passages (not shown) that each supply air to a blower 16 of the HVAC system which is illustrated in Figure 2. The vented air passage receives air from outside of the vehicle through a vented air inlet (not shown) and delivers this vented air to the blower 16. Vented air refers to air that is drawn into the cabin 14 from outside of (external to) the vehicle 10. The recirculation passage receives air from inside the vehicle cabin and delivers this recirculated air to the blower 16. The blower 16 delivers vented and recirculated air to the vehicle cabin 14. Recirculated air refers to air in the vehicle cabin 14 that is recirculated past one or more components of the HVAC system before returning to the vehicle cabin 14.

The HVAC system may include one or more filters (not shown) for removing pollutants from air before it enters the vehicle cabin 14. One type of air filter that may be used in this context is a particulate matter (PM) filter - e.g. a PM2.5 filter - for removing particulate matter contamination from air prior to it entering the vehicle cabin 14. Other types of filters that may be included in the HVAC system include but are not limited to carbon layer filters for removing odour, volatile organic compounds, and/or toxic gases from the vehicle cabin 14, an anti-allergen layer for removing one or more allergens from the vehicle cabin, and ionisers for neutralising one or more pathogens from the vehicle cabin.

The blower 16 comprises a fan (not shown) and a motor (not shown) that drives the fan. When the blower 16 is on, the motor drives the fan to rotate in a known manner, and air received from the vented air passage and/or the recirculation passage is delivered to the vehicle cabin 14. The speed at which the fan is driven to rotate, referred to as the blower speed, may be adjusted to control the rate at which air enters the cabin 14, with higher blower speeds drawing more air into the cabin 14 and lower blower speeds drawing less air into the cabin 14. In other words, an increase in blower speed increases the volumetric flow rate of air into the cabin 14. A blower 16 is a well-known component of HVAC systems and as such will not be described in further detail here. The HVAC system further includes an inlet door mechanism 18 for adjusting the ratio of vented air to recirculated air brought into the cabin 14 by the HVAC system. To adjust this ratio of vented air to recirculated air, the inlet door mechanism 18 is adjustable or movable between a recirculated air position and a vented air position, by means of one or more actuators 20.

In the recirculated air position of the inlet door mechanism 18, the vented air passage is closed or blocked to prevent air from outside of the vehicle 10, which may sometimes be referred to as fresh air, from reaching the blower 16. The recirculation passage is open to allow air from the cabin 14 to reach the blower 16. The HVAC system is thus in a recirculation mode in which all of the air entering the vehicle cabin 14 from the HVAC system is recirculated air.

In the vented air position of the inlet door mechanism 18, the recirculation passage is closed or blocked to prevent air from the cabin 14 from reaching the blower 16 via the recirculation passage. The vented air passage is open to allow fresh air from outside of the vehicle 10 to reach the blower 16. The HVAC system is thus in a fresh air mode in which all of the air entering the vehicle cabin from the HVAC system is drawn from outside of the vehicle 10.

The inlet door mechanism 18 is adjustable to a number of intermediate positions between the vented air position and the recirculated air position. In these intermediate positions, a combination of vented air and recirculated air is supplied to the vehicle cabin 14 from the HVAC system, with the ratio of vented air to recirculated air dependent on the intermediate position of the inlet door mechanism 18.

The inlet door mechanism 18 may take a number of different forms.

In one embodiment, the inlet door mechanism 18 may consist of a single door, referred to as a recirculation door, that is movable between a fully open position and a fully closed position. In that case, when the recirculation door is in the fully closed position, the inlet door mechanism 18 is in the recirculated air position such that the HVAC system operates in the recirculation mode. When the recirculation door is in the fully open position, the inlet door mechanism 18 is in the vented air position such that the HVAC system operates in the fresh air mode. The recirculation door may be adjustable to a number of intermediate positions between the fully open and fully closed positions.

In other embodiments, the inlet door mechanism 18 may comprise a plurality of doors whose positions together define the recirculated air position and the vented air position of the inlet door mechanism 18. For example, in one embodiment the inlet door mechanism 18 may comprise a recirculation door provided in the recirculation passage, a vented or fresh air door provided in the vented air passage, and a partial door. In that case, the inlet door mechanism 18 may be in the recirculated air position when the recirculation door is in a fully open position, and the partial door and the fresh air door are in fully closed positions. The inlet door mechanism 18 may be in the vented air position when the recirculation door and the partial door are in fully closed positions, and the fresh air door is in a fully open position. The inlet door mechanism 18 may be in a partially recirculated air position when the recirculation door is fully closed, and the fresh air door and the partial door are in partially open positions.

The HVAC system also includes a carbon dioxide (C0 ₂ ) sensor 22 for monitoring a concentration of carbon dioxide in the cabin 14 of the vehicle 10.

In this embodiment, the carbon dioxide sensor 22 is a nondispersive infrared (NDIR) carbon dioxide sensor that is configured to measure the concentration in parts per million (PPM) of carbon dioxide in the vicinity of the carbon dioxide sensor 22 at one second time intervals. However, in other embodiments of the invention the carbon dioxide sensor 22 may be any other type of sensor suitable for measuring carbon dioxide concentration, and furthermore may be configured to take measurements at different time intervals or substantially continuously.

The carbon dioxide sensor 22 may be mounted on a central console of the vehicle 10. Alternatively, the carbon dioxide sensor 22 could be provided at any other suitable position within the vehicle cabin 14. However, to ensure that a representative sample of the cabin air is monitored, it may be preferable that the carbon dioxide sensor 22 is not arranged at a position within the cabin 14 that is likely to return an artificially high or artificially low carbon dioxide level measurement. If the carbon dioxide sensor 22 is positioned to coincide with the head height of an occupant, for example, this may result in an artificially high level of carbon dioxide being recorded if an occupant is exhaling in the vicinity of the sensor 22. Correspondingly, if the carbon dioxide sensor 22 is positioned in a foot well of the vehicle 10, then this may result in an artificially low carbon dioxide level being recorded by the carbon dioxide sensor 22.

It should also be noted that although a single carbon dioxide sensor 22 is provided in this embodiment, other embodiments may include additional carbon dioxide sensors. In embodiments that utilise additional carbon dioxide sensors 22, some or all may be arranged in different areas of the vehicle to one another, so as to provide measurements of the level of carbon dioxide in different areas of the vehicle 10. These measurements may be combined to provide an average carbon dioxide level value within the cabin 14. Such an average value determined from multiple carbon dioxide sensors 22 positioned in different areas of the cabin 14 may allow for a more representative value of the carbon dioxide level in the cabin 14 to be determined.

The vehicle 10 further includes a control system 23 for controlling the HVAC system. As will be explained in more detail later, the control system 23 is configured to control the HVAC system based on measurements of the level of carbon dioxide in the vehicle cabin 14 provided by the carbon dioxide sensor 22.

Referring to Figure 2, the control system 23 includes one or more controllers 24 that each include an input 26, a processor 28, a memory device 30, and an output 32.

It is to be understood that the or each controller 24 can comprise a control unit or computational device having one or more electronic processors (e.g., a microprocessor, a microcontroller, an application specific integrated circuit (ASIC), etc.), and may comprise a single control unit or computational device, or alternatively different functions of the or each controller 24 may be embodied in, or hosted in, different control units or computational devices. As used herein, the term “controller,” “control unit,” or “computational device” will be understood to include a single controller, control unit, or computational device, and a plurality of controllers, control units, or computational devices collectively operating to provide the required control functionality. A set of instructions could be provided which, when executed, cause the controller 24 to implement the control techniques described herein (including some or all of the functionality required for the method described herein). The set of instructions could be embedded in said one or more electronic processors of the controller 24; or alternatively, the set of instructions could be provided as software to be executed in the controller 24. A first controller or control unit may be implemented in software run on one or more processors. One or more other controllers or control units may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller or control unit. Other arrangements are also useful.

In the example illustrated in Figure 2, the or each controller 24 comprises at least one electronic processor 28 having one or more electrical input(s) for receiving signals related to the control of the level of carbon dioxide in the vehicle cabin, and one or more electrical output(s) for outputting one or more output signal(s). The or each controller 24 further comprises at least one memory device 30 electrically coupled to the at least one electronic processor 28 and having instructions stored therein. The at least one electronic processor 28 is configured to access the at least one memory device 30 and execute the instructions thereon so as to determine whether one or more conditions are satisfied.

The, or each, electronic processor 28 may comprise any suitable electronic processor (e.g., a microprocessor, a microcontroller, an ASIC, etc.) that is configured to execute electronic instructions. The, or each, electronic memory device 30 may comprise any suitable memory device and may store a variety of data, information, limit value(s), lookup tables or other data structures, and/or instructions therein or thereon. In an embodiment, the memory device 30 has information and instructions for software, firmware, programs, algorithms, scripts, applications, etc. stored therein or thereon that may govern all or part of the methodology described herein. The processor 28, or each electronic processor 28 may access the memory device 30 and execute and/or use that or those instructions and information to carry out or perform some or all of the functionality and methodology describe herein.

The at least one memory device 30 may comprise a computer-readable storage medium (e.g. a non-transitory or non-transient storage medium) that may comprise any mechanism for storing information in a form readable by a machine or electronic processors/computational devices, 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 and EEPROM); flash memory; or electrical or other types of medium for storing such information/instructions. Example controllers 24 have been described comprising at least one electronic processor 28 configured to execute electronic instructions stored within at least one memory device 30, which when executed causes the electronic processor(s) 28 to carry out the method as described herein. However, it will be appreciated that embodiments of the present invention can be realised in any suitable form of hardware, software or a combination of hardware and software. For example, it is contemplated that the present invention is not limited to being implemented by way of programmable processing devices, and that at least some of, and in some embodiments all of, the functionality and or method steps of the present invention may equally be implemented by way of non programmable hardware, such as by way of non-programmable ASIC, Boolean logic circuitry, etc.

The input 26 of the controller is configured to receive data from a plurality of sources in this embodiment. Specifically, as will be explained in more detail later, the controller input 26 is configured to receive carbon dioxide data, blower speed data and inlet door mechanism position data.

The carbon dioxide data received by the controller 24 originates from the carbon dioxide sensor 22 and is indicative of a level of carbon dioxide present in the vehicle cabin 14. Specifically, the carbon dioxide data comprises measurements of the concentration of carbon dioxide in the vicinity of the carbon dioxide sensor 22 in parts per million (PPM). In embodiments in which more than one carbon dioxide sensor 22 is provided in the cabin 14, the input may be configured to receive carbon dioxide data from some or all of the carbon dioxide sensors 22.

The blower speed data indicates a blower speed at which the fan of the blower is being driven to rotate. As noted, the blower speed affects the amount of air entering the cabin 14 over a given time period, with higher blower speeds resulting in a higher volumetric flow rate for air entering the cabin 14 and lower blower speeds resulting in a lower volumetric flow rate for air entering the cabin 14.

The inlet door mechanism position data indicates the position of the inlet door mechanism 18 between the vented air position and the full recirculated air position. The inlet door mechanism position value may indicate that the inlet door mechanism 18 is in the recirculated air position, the vented air position, or one of a number of intermediate values therebetween. In this example, the inlet door mechanism position value may take one of twenty position values, xi- ₂₀ , where xi denotes that the inlet door mechanism 18 is in the vented air position and x ₂₀ denotes that the inlet door mechanism 18 is in the recirculated air position. It will be understood that the number of positions of the inlet door mechanism 18 between the vented air position and the recirculated air position may vary in other embodiments, and in some embodiments the inlet door mechanism 18 may take any intermediate position between its vented air and recirculated air positions, rather than one of a plurality of discrete, intermediate positions.

The processor 28 is configured to determine whether to reduce the level of carbon dioxide present in the vehicle cabin 14, based on the carbon dioxide data received from the carbon dioxide sensor 22. The output 32 is configured to transmit a control signal to control the HVAC system to increase the amount of air drawn into the vehicle cabin 14 from external to the vehicle 10 if the processor 28 determines that the level of carbon dioxide in the vehicle cabin 14 should be reduced. As will be explained, the HVAC system is controlled to draw air into the vehicle cabin 14 from external to the vehicle by adjusting at least one of the inlet door mechanism position and the blower speed.

Figure 3 illustrates a method 100 undertaken by the controller 24 to determine and control the level of carbon dioxide in the cabin 14 of the vehicle 10.

At step 102, the controller 24 may determine whether a carbon dioxide control feature or function of the vehicle 10 is enabled. If the controller 24 determines that the carbon dioxide control feature is disabled, then the method may terminate with no further action taken by the controller 24. If the controller 24 determines that the carbon dioxide control feature is enabled, then the method may proceed to step 104.

In this embodiment, the carbon dioxide control feature is enabled in the vehicle 10 by default. However, the carbon dioxide control feature can be manually deactivated (or activated / re-activated) by a user, for instance via a Human-Machine Interface (HMI) or touchscreen of the vehicle 10 if / when desired. The status of the carbon dioxide control feature, i.e. enabled or disabled, is maintained between vehicle ignition cycles in this embodiment. In other embodiments, the status of the carbon dioxide control feature may reset to its default setting at the end of a vehicle ignition cycle. At step 104, the controller 24 receives a measured carbon dioxide value from the carbon dioxide sensor 22 and compares this measured carbon dioxide value with a predefined upper value of carbon dioxide that is stored in the memory device 30 of the controller 24. In embodiments in which the vehicle 10 includes a plurality of carbon dioxide sensors 22, the controller 24 may calculate an average measured carbon dioxide value and compare this average value with the upper value.

The upper value defines a carbon dioxide concentration above which the level of carbon dioxide in the cabin is deemed to be too high. In one example, the default upper value is 5000 parts per million (ppm) of carbon dioxide, but this value may be adjusted by the user, and the default upper value may differ in other embodiments.

If the controller 24 determines that the measured carbon dioxide value is below the upper value, then step 104 may be repeated. As noted already, measured carbon dioxide values are received by the controller 24 at one second intervals in this embodiment, and so step 104 may be carried out at one second intervals to provide continuous monitoring of the carbon dioxide level in the cabin 14.

If the controller 24 determines that the measured carbon dioxide value exceeds the upper value, then the method proceeds to step 106. At step 106, a timer 34 of the controller 24 may be activated for a predetermined time period, t1 . In this example, the duration of the time period, t1 , is sixty seconds, but in other examples this may vary. The controller 24 continues to receive and compare measured carbon dioxide values from the carbon dioxide sensor 22 with the upper value throughout this time period, t1 . At the end of the predetermined time period, t1 , the controller 24 determines if the measured carbon dioxide value still exceeds the upper value.

If the controller 24 determines that the measured carbon dioxide no longer exceeds the upper value at the end of the predetermined time period, t1 , then the method may return to step 104 for continued monitoring of the in-cabin carbon dioxide level.

If the measured carbon dioxide value still exceeds the upper value once the time period, t1 , has elapsed, then the controller 24 determines that the level of carbon dioxide in the vehicle cabin 14 is too high, and that action should be taken to reduce this level. The method proceeds to step 108.

At step 108, the controller 24 determines if adjusting the inlet door mechanism position will be sufficient to reduce the level of carbon dioxide in the cabin 14 back to the upper value within a predetermined time period, t2. For this, the controller 24 receives and compares a current blower speed and a current measured carbon dioxide value with entries of an inlet door mechanism priority matrix stored on the memory device 30 of the controller 24. For a given blower speed and carbon dioxide value, the inlet door mechanism priority matrix indicates an adjusted inlet door mechanism position which it is expected will reduce the level of carbon dioxide in the cabin 14 back to the upper value after the predetermined time period, t2. The adjusted inlet door mechanism position may be any one of the possible inlet door mechanism positions from xi (vented air position) to x ₂₀ (recirculated air position). Flowever, for some combinations of blower speed and carbon dioxide values, there may be no adjusted inlet door mechanism position that is expected to reduce the carbon dioxide level as required, and the inlet door mechanism priority matrix returns a null result.

It should be noted that the controller 24 may request and receive a current blower speed value from the blower 16 at step 108, but may alternatively or additionally receive and store the blower speed value in the memory device 30 of the controller 24 prior to this step. Blower speed values may be sent to the controller 24 at regular intervals, and/or each time the blower speed is adjusted.

If the inlet door mechanism priority matrix returns a null result then the method may proceed to step 120 to determine an adjusted blower speed, as will be explained later.

If the inlet door mechanism priority matrix returns an adjusted inlet door mechanism position for the current carbon dioxide level and blower speed, then the controller may proceed to step 110.

At step 110, the controller 24 transmits a control signal to the FIVAC system to request movement of the inlet door mechanism 18 to the adjusted inlet door mechanism position, and the actuator(s) 20 of the inlet door mechanism 18 is / are controlled to adjust the inlet door mechanism 18 to the adjusted inlet door mechanism position. For this, the controller 24 may use a current inlet door mechanism position value received by the controller 24 to determine how the inlet door mechanism 18 must be adjusted to reach the required adjusted inlet door mechanism position. It will be understood that increasing the amount of vented air entering the vehicle 10 will usually result in a reduction in the concentration of carbon dioxide in the vehicle cabin 14.

In embodiments in which the inlet door mechanism 18 consists of a single, recirculation, door, the adjusted inlet door mechanism position comprises an adjusted recirculation door position. In embodiments in which the inlet door mechanism 18 comprises multiple doors, the adjusted inlet door mechanism position comprises a position value for each door of the inlet door mechanism 18.

The controller 24 may continue to receive carbon dioxide values from the carbon dioxide sensor 22, and use these values to determine the rate at which the carbon dioxide level in the cabin 14 is falling at step 112. If the controller 24 determines that the carbon dioxide level in the cabin 14 is falling at or above a predetermined desired rate of reduction, then no further action is taken until the controller 24 determines at step 114 that the level of carbon dioxide has fallen below a lower value, at which time a control signal is transmitted from the controller 24 to move the inlet door mechanism 18 back to its original position and the method terminates. In this embodiment the lower value is 2000 ppm of carbon dioxide, but in other embodiments this may vary.

If the controller 24 determines that the carbon dioxide level in the cabin 14 is not reducing quickly enough, based on the desired rate of reduction, then the controller 24 transmits a further control signal to the HVAC system to adjust the inlet door mechanism position by an additional increment at step 116. For example, if the current position of the inlet door mechanism 18 is X ₄ , then the inlet door mechanism 18 is adjusted to X ₃ . The controller 24 repeats this process until either the carbon dioxide level is determined to be falling at a sufficient rate, or the inlet door mechanism 18 has reached its vented air position, in which all of the air entering the vehicle 10 is vented air from outside the vehicle 10.

If the carbon dioxide level is determined to be falling at a sufficient rate, then no further action is taken until the controller 24 determines that the level of carbon dioxide has fallen below the lower value, at which time the controller 24 transmits a control signal to move the inlet door mechanism 18 back to its original position at step 118 and the method terminates.

At step 120, the controller 24 determines an adjusted blower speed value. The adjusted blower speed value is the value that it is determined will effectively reduce the carbon dioxide level in the cabin 14 at a current inlet door mechanism position, at the current carbon dioxide level of the cabin 14.

In some embodiments, the controller 24 proceeds to step 120 if the desired rate of reduction of carbon dioxide in the cabin 14 is not achieved with the inlet door mechanism 18 in the vented air position in which all of the air entering the cabin 14 from the HVAC system is from outside of the vehicle 10.

However, a change in blower speed may be requested before the inlet door mechanism 18 reaches the vented air position, in which case the method may proceed to step 120 before the inlet door mechanism 18 reaches the vented air position. In that case, there may be a prescribed inlet door mechanism position above which the system may adjust the blower speed. For example, the system may only adjust the blower speed value if the inlet door mechanism 18 is in a position in which at least half of the air drawn in by the HVAC system is vented air from outside of the vehicle 10. One example of a scenario in which the method may proceed to step 120 before the inlet door mechanism 18 is in the vented air position is when the system is being operated in a hot climate.

Once the adjusted blower speed value has been determined, the controller 24 transmits a control signal to the blower 16 to increase the blower speed to the adjusted blower speed value at step 122. In the case in which the method proceeds directly from step 108 to step 120, the controller 24 also sends a control signal to adjust the inlet door mechanism 18 to its vented air position at step 122.

At step 124 the controller 24 again determines the rate of reduction of carbon dioxide in the cabin 14. If the controller 24 determines that the carbon dioxide level in the vehicle cabin 14 is falling at or above the desired rate of reduction, then no further action is taken until the controller 24 determines that the level of carbon dioxide has fallen below the lower value, at which time the controller 24 transmits control signals to move the inlet door mechanism 18 back to its original position and to adjust the blower 16 back to its original speed at step 126, and the method terminates.

If the controller 24 determines that the carbon dioxide level in the cabin 14 is not reducing quickly enough, based on the desired rate of reduction, then the blower speed is increased incrementally at step 128 until the desired rate of reduction is achieved, or until the blower speed is at its maximum level.

In general, if the carbon dioxide level does not fall below the upper value within a predetermined time window, t3, which in this example is 60 seconds, then the controller 24 sends a request for the inlet door mechanism 18 to revert to its original position and for the blower 16 to revert to its original speed. In this way, the HVAC system reverts to the original settings of the inlet door mechanism 18 and the blower 16 if it is determined that increasing the vented air drawn into the vehicle 10 is not effectively reducing the carbon dioxide level in the cabin 14. Drawing vented air from outside of the vehicle 10 into the cabin 14 may not result in a decrease in carbon dioxide level in the cabin 14 if, for example, the vehicle 10 is in an environment in which the carbon dioxide content of the external air is relatively high, such as in an underground garage for example.

It should be noted that it is possible for the user to adjust the blower speed manually whilst the carbon dioxide control feature is enabled. In that case, the system adjusts the inlet door mechanism position according to this adjusted blower speed value. If it is determined by the controller that the carbon dioxide level in the cabin cannot be controlled with the blower speed at the level requested by the user, then the blower speed may be adjusted by the system as described above. In some embodiments the system may request permission from the user before adjusting the blower speed, and if the request is denied then the carbon control feature may be disabled.

An indication of the carbon dioxide level in the cabin 14 may be displayed on a display (not shown) of the vehicle 10, for example by illuminating an area of the display. A green light may indicate that the carbon dioxide level in the cabin 14 is within acceptable limits, an amber light may indicate that the carbon dioxide level in the cabin 14 is moderate, and a red light may indicate that the carbon dioxide level in the cabin 14 is high. An acceptable level of carbon dioxide may be defined as any value from 0 ppm to 2,000 ppm. A moderate level of carbon dioxide may be defined as any value from 2,001 ppm to 4,999 ppm. A high level of carbon dioxide may be defined as any value from 5,000 ppm to 10,000 ppm. These ranges may vary in different embodiments, and the means with which the carbon dioxide level information is provided to the user may also vary. In some embodiments, for example, the concentration of carbon dioxide in the cabin 14 may be displayed to the user, as well as or instead of the above colour indication. In some embodiments, an audio indication may alert the user if the carbon dioxide level exceeds a predefined value. In some embodiments, an indication may only be provided to the user if the carbon dioxide level exceeds a predefined level, which may be a default value provided by the system, and/or which may be adjustable by the user. In some embodiments, information regarding the current blower speed and the inlet door mechanism position can be provided on the display of the vehicle 10, either by default, on request by the user, or when an adjustment is made to either of these parameters.

In addition to the carbon dioxide control feature, the controller 24 may be configured to implement other control features or functions for controlling various other parameters and/or conditions of the vehicle cabin 14, such as temperature and concentration of particulate matter. For this, the HVAC system and/or the vehicle 10 may include various other sensors in addition to the carbon dioxide sensor 22 that may provide inputs to the controller 24.

For example, in some embodiments the FIVAC system may further comprise one or more particle sensors (not shown) for monitoring a concentration of particulate matter in the cabin 14 of the vehicle 10. The particle sensor may be, for example, a PM2.5 sensor, which can measure the concentration of particles in the air having a diameter of less than or equal to 2.5 microns, but it will be understood that different particulate matter (PM) sensors may be used, e.g. PM1 , PM3, PM10, etc.

In particular, the FIVAC system may include an internal particle sensor within the vehicle cabin 14 for monitoring the concentration of particulate matter inside the vehicle cabin 14, and an external particle sensor arranged to monitor the concentration of particulate matter outside of the vehicle cabin 14 and vehicle 10.

Measurements of the particulate matter concentration inside and outside of the vehicle cabin 14 may be used in a particulate matter control feature implemented by the controller 24. The particulate matter control feature relates to the detection and control of the concentration of particulate matter within the vehicle cabin 14. When activated in the vehicle 10, the controller 24 may be configured to receive measurements from the internal and external particle sensors, and to determine a difference value which indicates the difference between a measured concentration of particulate matter inside the vehicle cabin 14 and a measured concentration of particulate matter outside of the vehicle cabin 14. The controller 24 may be further configured to determine if action should be taken to reduce the concentration of particulate matter in the cabin 14 based on this difference value.

If it is determined by the controller 24 that the concentration of particulate matter in the cabin 14 is too high, then the controller 24 may transmit a signal to adjust the inlet door mechanism 18 by one or more increments so as to reduce fresh air intake, and increase the proportion of recirculated air to vented air introduced into the cabin 14 by the HVAC system. This may help to reduce the amount of particulate matter within the cabin 14 because vented air brought in from outside of the vehicle 10 will tend to have a higher concentration of particulate matter than recirculated air that is repeatedly filtered as it is recirculated through the particulate matter filter of the HVAC system.

Thus, adjusting the inlet door mechanism 18 towards the recirculated air position may result in a fall in the concentration of particulate matter inside the cabin 14. In contrast, adjusting the inlet door mechanism 18 towards the vented air position usually results in a drop in the carbon dioxide level in the cabin 14. Thus, in the event that both the carbon dioxide control feature and the particulate matter control feature are activated, the controller 24 may need to determine which function should take priority. For example, if the controller 24 determines that both the concentration of carbon dioxide and the concentration of particulate matter in the cabin 14 are too high, then the controller 24 may need to decide whether to adjust the inlet door mechanism 18 further to reduce the carbon dioxide level in the cabin 14 or to reduce the particulate matter level in the cabin 14.

For this, an inlet door priority matrix - or other prioritisation look-up table - may be stored in the memory device 30 of the controller 24. The priority matrix may indicate which of the carbon dioxide control feature or the particulate matter control feature should take priority based on the current levels of carbon dioxide and particulate matter in the cabin 14. When priority is given to the carbon dioxide control feature, the controller 24 may prioritise the reduction of carbon dioxide in the cabin 14 over the reduction of particulate matter in the cabin 14. When priority is given to the particulate matter control feature, the controller 24 may prioritise the reduction of particulate matter in the cabin 14 over the reduction of carbon dioxide in the cabin 14.

It will be understood that different embodiments may utilise different priority matrices, such that priority may be given to the different features in dependence on different upper levels of carbon dioxide and particulate matter. For example, the priority matrix may indicate that the particulate matter control feature should take priority over the carbon dioxide feature if the level of particulate matter in the cabin 14 reaches a certain predefined value, unless the carbon dioxide concentration is itself above a certain predefined value.

In some examples, the priority matrix may be defined to balance the requirements of the carbon dioxide control feature and the particulate matter control feature across a range of carbon dioxide values, with neither taking full priority at any time. In that case, the controller 24 may adjust the position of the inlet door mechanism 18 so as to maintain both carbon dioxide and particulate matter levels in the cabin 14 within an acceptable range.

The controller 24 may further be configured to implement a climate control function for controlling the temperature of the cabin 14.

For this, the vehicle 10 may further comprise temperature sensors (not shown) for measuring both the in-cabin temperature and the temperature outside of the vehicle 10. These temperature sensors may transmit this temperature information to the controller 24. If the climate control function is activated, the controller 24 may use this temperature information when determining adjusted blower speed and adjusted inlet door mechanism position values, which values may impact the in-cabin temperature. A priority matrix stored in the memory device 30 may indicate, for example, an upper temperature value above which the climate control function should be prioritised over one or more other activated functions such as the carbon dioxide control feature and the particulate matter control feature, and/or a lower temperature value below which the climate control function should correspondingly be prioritised.

It should also be noted that other operations or functions in the vehicle 10 may override the carbon dioxide control feature in embodiments of the invention. For example, in some embodiments the carbon dioxide control feature is disabled if a maximum air conditioning (AC) setting is selected by the user. In other words, the maximum AC feature may take priority over the carbon dioxide control feature in some embodiments of the invention. Thus, if the maximum AC setting is selected after the carbon dioxide control feature has already been enabled, this may cause the carbon dioxide control feature to cease, and the maximum AC setting to be implemented. If the maximum AC setting is selected before the carbon dioxide control feature is enabled, this may prevent the carbon dioxide control feature from being enabled. 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.