Control method for thermal regulation of a vehicle seat

Conditioned air discharged from a vehicle heating, ventilation and air conditioning (HVAC) unit is further conditioned by a thermoelectric (TE) air conditioning unit and then directed to air passages in a vehicle seat. Activation of the TE air conditioning unit is based on climate control parameters utilized by the HVAC unit, including a set temperature, radiant heating effects, and cabin air temperature. The climate control parameters are utilized to establish a target seat temperature that optimizes occupant comfort and the transient response of the seat cooling effect.

FIELD OF THE INVENTION

The present invention relates to thermal regulation of a vehicle seat for occupant comfort, and more particularly to a method of controlling seat cooling.

BACKGROUND OF THE INVENTION

Occupant comfort in a motor vehicle can be enhanced by regulating the temperature of the seating surfaces in the passenger compartment. For example, the U.S. Pat. No. 5,918,930 discloses a system in which thermally conditioned air discharged from the vehicle's heating, ventilation and air conditioning (HVAC) system is routed through passages in the vehicle seats. And the U.S. Pat. No. Re. 38,128 discloses a system in which Peltier thermoelectric (TE) devices selectively heat or cool cabin air for delivery to seat passages. Alternately, the TE devices can be configured to receive air discharged from the HVAC system for improved transient control of seat temperature.

Ideally, seat temperature regulation in a vehicle should be performed automatically (that is, in a way that does not require the occupant to select a temperature control setting for the seat) and consistent with occupant comfort considerations. The present invention is directed to such a control methodology.

SUMMARY OF THE INVENTION

The present invention provides an improved control methodology for a thermally conditioned vehicle seat in which a TE unit supplies conditioned air to the seat. Preferably, air discharged from the vehicle HVAC unit is further conditioned by the TE unit and then directed to the seat. Activation of the TE unit is automatically controlled based on climate control parameters utilized by the HVAC unit, including a set temperature, radiant heating effects, and cabin air temperature. The climate control parameters are utilized to establish a target seat temperature that optimizes occupant comfort and the transient response of the seat cooling effect.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1, the reference numeral10generally designates a motor vehicle including a cabin20and occupant seats22aand22b. At least one of the seats22ais provided with internal air passages24, including perforated seat and back cushions. Air supplied to the seat22avia the air duct26flows through the air passages24to cool or heat the seating surfaces for enhanced occupant comfort. A heating, ventilation and air conditioning (HVAC) unit28develops conditioned air based on an operator temperature control setting, and supplies the conditioned air to cabin ducts30and one or more seat ducts32. The cabin ducts30convey the conditioned air to cabin vents34and the seat duct32conveys the conditioned air to a thermoelectric (TE) air conditioning unit36. The TE air conditioning unit36further conditions a portion of the air supplied to it via seat duct32; the further conditioned air is supplied to the air passages24of seat22aby the air duct26, and the remaining air is exhausted into the cabin20through the exhaust duct38. A vehicle electrical system including a storage battery40supplies electrical power to the HVAC unit28, which in turn, supplies electrical power to the TE air-conditioning unit36.

Referring toFIG. 2, the TE air-conditioning unit36includes a Peltier TE device42and a pair of heat exchangers44,46. A flow divider48positioned in the seat duct32apportions the inlet air from HVAC unit28between the heat exchangers44and46. Inlet air directed through heat exchanger44is supplied to the seat passages24via air duct26, while air directed through heat exchanger46is exhausted into the cabin20via exhaust duct38. A thermal insulator52disposed between the ducts26and38downstream of the TE device42inhibits the transfer of thermal energy between the ducts26and38.

In operation, the HVAC unit28selectively activates the TE device42to further heat or chill the air flowing through heat exchanger44to provide optimal occupant comfort. In the illustrated embodiment, the control of TE device42is implemented by a microcontroller (uC)28aresident within a control head of HVAC unit28. Referring toFIG. 3, microcontroller28ais responsive to a number of inputs provided by the temperature sensors60-63, the solar sensor64, and optionally by the relative humidity sensor65. The temperature sensors60and61are located in the bottom and back cushions of seat22a, respectively, and produce the seat temperature signals designated as Tseat_bot and Tseat_bk. The temperature sensors62and63are responsive to the temperatures of ambient air and cabin air, respectively, and produce the temperature signals designated as Tamb and Tcabin. The solar sensor64may be a conventional automotive solar radiation sensor, or a mean radiant temperature sensor, and produces a signal designated as SOLAR. The relative humidity sensor65is responsive to the humidity in ambient air, and produces a signal designated as RH. An additional input designated as Tset is supplied by a vehicle occupant through a user interface device66, and represents a desired cabin air temperature. The microcontroller (uC)28aexecutes a number of resident software routines for developing various HVAC-related outputs, including a duty-cycle output DC on line68representing the desired mode (heating or cooling) and activation level of TE air-conditioning unit36. The duty-cycle output is supplied to a thermoelectric power supply (TE PS)70which correspondingly activates the TE device42of TE air-conditioning unit36using battery voltage Vb.

In general, the present invention is directed to a control method carried out by the microcontroller28aduring the air conditioning mode where HVAC unit28supplies chilled air to the cabin and seat ducts30,32in order to satisfy the occupant set temperature Tset. The microcontroller28adevelops a target seat temperature Tseat_tar, and activates TE device42to bring the measured seat temperatures Tseat_bk and Tseat_bot into conformance with Tseat_tar.

To make sure the control is consistent with occupant comfort considerations, the control is based in part on the mean radiant temperature Tmr in cabin20. Technically, Tmr may be defined as the uniform surface temperature of an imaginary enclosure in which an occupant would exchange the same amount of radiant heat as in the actual non-uniform space. The temperature Tmr in ° K can be calculated using the equation:

T_mr=∑n⁢Fp-i⁡(Ti+273)44-273(1)
where Tiis the surface temperature of a surface i, and Fp-iis the view factor between the person and surface, i. In the illustrated embodiment, however, the value of Tmr is determined based on the inputs discussed above in reference toFIG. 3. In cases where the sensor64is a conventional automotive solar sensor, Tmr is calculated as a combined function of SOLAR and Tamb; in cases where the sensor64is responsive to mean radiant temperature, Tmr is obtained directly from SOLAR.

The control is implemented by establishing a reference or threshold cabin temperature Tthr_cabin for comparison with the measured cabin temperature Tcabin. When Tcabin is above Tthr_cabin, the target seat temperature Tseat_tar is determined based on Tset and the mean radiant temperature Tmr of the cabin20to quickly cool the seats as the cabin air is also being cooled by HVAC unit28. When the HVAC unit28has reduced Tcabin to Tthr_cabin, the target seat temperature Tseat_tar is increased based on Tmr and the amount by which Tcabin falls below Tthr_cabin. Additionally, the set temperature Tset may be adjusted based on the measured relative humidity RH since occupant comfort is related to humidity as well as temperature. For example, a humidity-compensated set temperature Tset′ may be calculated based on Tset and RH according to:
Tset′=Tset+[K1*(CAL—RH−RH)]  (2)
where K1is a calibrated gain constant and CAL_RH is a calibrated relative humidity such as 45%.

The threshold cabin temperature Tthr_cabin represents a cabin temperature for optimal occupant comfort, and is computed according to:
Tthr_cabin=(K2*Tset)−(K3*Tmr)  (3)
where the coefficients K2and K3are calibrated constants. In a mechanization of the present invention, K2and K3were assigned values of 1.25 and 0.1825, respectively.

When Tcabin is greater than or equal to Tthr_cabin, the control is in a transient cool-down mode, and the target seat temperature Tseat_tar is computed according to:
Tseat_tar=(K4*Tset)−(K5*Tmr)  (4)
where K4and K5are calibrated constants. For example, K4and K5may be assigned values of 1.0 and 0.1, respectively. The first temperature component (K4*Tset) directly influences Tseat_tar as a function of the occupant-selected set temperature Tset. Using equation (2), the occupant-selected value of Tset can be adjusted downward to compensate for relative humidity readings above CAL_RH % and upward to compensate for relative humidity readings below CAL_RH %. The second temperature component (K5*Tmr) inversely influences Tseat_tar as a function of the mean radiant temperature Tmr which represents the heating effects of solar radiation in cabin20. That is, the target seat temperature is lowered to offset increased solar radiation in cabin20, and vice-versa.

When Tcabin falls below Tthr_cabin, the control transitions from the transient cool-down mode to a steady-state mode in which the target seat temperature Tseat_tar is gradually increased for sustained occupant comfort. This is achieved by defining a steady state modifier SS_MOD and computing Tseat_tar according to:
Tseat_tar=(K4*Tset)−(K5*Tmr)+SS_MOD  (5)
The steady state modifier SS_MOD sustains occupant comfort by bringing the steady-state seat temperature closer to the occupant's body temperature, and its value is scheduled as a function of the mean radiant temperature Tmr to compensate for changes in thermal coupling between the occupant and the seat. A relatively low value of Tmr (18° C., for example) implies the occupant is wearing relatively heavy clothing, resulting in relatively low thermal coupling; in this case the steady state modifier SS_MOD has a relatively low value, say 5-7° C. Conversely, a relatively high value of Tmr (27° C., for example) implies the occupant is wearing relatively light clothing, resulting in relatively high thermal coupling; in this case the steady state modifier SS_MOD has a higher value, say 9-11° C. Intermediate values of SS_MOD can be utilized for intermediate values of Tmr. Of course, the specific ranges of Tmr and SS_MOD can be calibrated to suit a particular application.

As Tcabin falls below the threshold Tthr_cabin, the steady-state modifier SS_MOD is progressively applied to avoid step changes in seat temperature. In the illustrated embodiment, this is achieved by applying the multiplier:
(Tthr_cabin−Tcabin)/3  (6)
to SS_MOD when Tcabin is between Tthr_cabin and (Tthr_cabin−3° C.). As Tcabin falls below Ttrh_cabin, the temperature modification SS_MOD is progressively applied; and is fully applied when Tcabin is three or more degrees below Tthr_cabin. This is graphically illustratedFIG. 4, where the traces72,74,76and78depict Tseat_tar as a function of Tcabin for Tset values of 26.7° C., 23.9° C., 21° C. and 18° C. For the illustration, Tmr is assumed to have a value of 32.2° C. Referring to trace72, for example, Tthr_cabin has a value of 27.5° C. when Tset is 26.7° C. and Tmr is 32.2° C. When Tcabin is higher than Tthr_cabin, Tseat_tar has a value of 23.5° C. When Tcabin falls below Tthr_cabin, Tseat_tar increases due to the operation of the steady-state modifier SS_MOD. And when Tcabin is three or more degrees below Tthr_cabin (i.e., 24.5° C. or lower), the steady-state modifier SS_MOD is fully applied, giving Tseat_tar a value of 32.5° C. If an occupant decreases Tset to lower the cabin temperature, equation (3) proportionately reduces Tthr_cabin, and equations (4)-(6) correspondingly reduce Tseat_tar, and vice-versa. If Tmr increases due to increased solar loading, equation (3) proportionately reduces Tthr_cabin, and equations (4)-(6) correspondingly reduce Tseat_tar, and vice-versa.

The flow diagrams ofFIGS. 5A-5Cand6represent a software routine executed by microcontroller28aduring the cooling mode of HVAC unit28for carrying out the method of the present invention. When seat temperature control is first enabled in a given period of vehicle operation, the blocks90-92configure TE air conditioning unit36for cooling, and activate the TE device42for maximum cooling. The various inputs described above in reference toFIG. 3are sampled at block94, and the blocks96-98are then executed to calculate or otherwise determine the mean radiant temperature Tmr, the humidity-compensated set temperature Tset′, and the actual seat temperature Tseat. As indicated at block98, the actual seat temperature Tseat is calculated as the average of the seat temperature inputs Tseat_bot and Tseat_bk. The block100is then executed to calculate the target seat temperature Tseat_tar.

The block102determines the current mode (heating or cooling) of the TE device42. Initially, the TE device will be configured for cooling due to the operation of block92; in this case, block102is answered in the affirmative, and the blocks104-116ofFIG. 5Bare executed as indicated by the flow connector blocks B. Referring toFIG. 5B, the block104determines if Tseat is within 2° C. of Tseat_tar. If so, the current activation level of TE device42is maintained. If Tseat is not within 2° C. of Tseat_tar, the block106determines if Tseat is greater than Tseat_tar. Thus, block106will be answered in the affirmative if Tseat is above Tseat_tar by at least 2° C., and in the negative if Tseat is below Tseat_tar by at least 2° C. When block106is answered in the affirmative (Tseat too warm), the block108is executed to incrementally increase the activation level of TE device42, if it is not already at the maximum level. When106is answered in the negative (Tseat too cool), the blocks110and112incrementally decrease the activation level of TE device42if activated. If TE device42is not activated, the block114changes the mode of TE device42to heating. So long as seat temperature control continues to be enabled, microcontroller28ais returned to block94ofFIG. 5Aas indicted by the flow connector blocks A; otherwise, the routine is exited.

If the mode of TE device42is changed to heating as described above, the block102ofFIG. 5Awill direct microcontroller28ato execute the blocks118-130ofFIG. 5Cas indicated by the flow connector blocks C. Referring toFIG. 5C, the block118determines if Tseat is within 2° C. of Tseat_tar. If so, the current activation level of TE device42is maintained. If Tseat is not within 2° C. of Tseat_tar, the block120determines if Tseat is greater than Tseat_tar. Thus, block106will be answered in the affirmative if Tseat is above Tseat_tar by at least 2° C., and in the negative if Tseat is below Tseat_tar by at least 2° C. When block106is answered in the negative (Tseat too cool), the block122is executed to incrementally increase the activation level of TE device42, if it is not already at the maximum level. When120is answered in the affirmative (Tseat too warm), the blocks124and126incrementally decrease the activation level of TE device42if activated. If TE device42is not activated, the block128changes the mode of TE device42to cooling. So long as seat temperature control continues to be enabled, microcontroller28ais returned to block94ofFIG. 5Aas indicted by the flow connector blocks A; otherwise, the routine is exited.

The flow diagram ofFIG. 6depicts a routine corresponding to block100ofFIG. 5A: selecting the target seat temperature Tseat_tar. Referring toFIG. 6, the block134calculates the cabin temperature threshold Tthr_cabin based on Tset and Tmr using equation (3). The blocks136,138,140,142and144then schedule the steady-state modifier SS_MOD based on Tmr. Block146determines if Tcabin is greater than or equal to the threshold Tthr_cabin; if so, block148calculates Tseat_tar based on Tset and Tmr using equation (4). Block150determines if Tcabin is between Tthr_cabin and (Tthr_cabin−3); if so, block152calculates Tseat_tar based on Tset, Tmr and SS_MOD using equations (5) and (6). If blocks146and150are both answered in the negative, Tcabin is more than three degrees below Tthr_cabin, and block154calculates Tseat_tar based on Tset, Tmr and SS_MOD using equation (5), completing the routine.

In summary, the present invention provides an easily implemented automatic control method for thermoelectric cooling of a vehicle seat. The control method accounts for ambient and radiant effects, and achieves a desired occupant comfort level without requiring extensive calibration effort. While the present invention has been described with respect to the illustrated embodiment, it is recognized that numerous modifications and variations in addition to those mentioned herein will occur to those skilled in the art. For example, the disclosed control method could be used in a system where the HVAC discharge air or even cabin air is drawn through the TE air conditioning unit36by an auxiliary fan, the steady-state modifier SS_MOD could be phased in based on elapsed time, and so on. Accordingly, it is intended that the invention not be limited to the disclosed embodiment, but that it have the full scope permitted by the language of the following claims.