Abstract:
A method of controlling an electric heating system for a motor vehicle seat, in which a target time (t soll ) for a heating duration is varied as a function of a difference between a measured outside temperature (T A ) and a measured inside temperature (T I ). A control device for a heating mechanism ( 20 ) is also provided having an outside temperature ( 10 ) and an inside temperature sensor or seat temperature sensor ( 12 ), and having a control circuit for preassigning and/or varying a target time (t soll ) for a heat duration, as a function of a difference between a measured outside temperature (T A ) and a measured inside or seat temperature (T I  or T S ).

Description:
TECHNICAL FIELD  
       [0001]     The invention relates to a heating system and a method of controlling a heating system. The heating system may be advantageously used as part of a vehicle seat heating system.  
       BACKGROUND OF THE INVENTION  
       [0002]     There are known methods and systems for controlling electric seat heaters in which the heating mechanism is operated by a control of temperature as a function of a user input. Such control systems are suitable for setting an optimal comfort temperature, but respecting their control they require a comparatively large structural outlay. There are also simpler controls based on a timer function. Here, at the start of seat heating, a target time is assigned, after transgression of which the seat heating is switched off. The disadvantage of such a timer based control is that the timer times are either not variable, or comprise a variability only to the effect that the on-duration depends on the seat temperature.  
         [0003]     DE 101 06 152 A1 discloses a method of controlling a stationary ventilator in a motor vehicle. A timer assigns a target time for an on-duration of the ventilator when the inside temperature exceeds a preassigned limit. The ventilator is switched on and off with an on-duration and an on-frequency so long as the inside temperature is above the preassigned limit. On-duration and on-frequency of the ventilator are determined as a function of the inside temperature of the vehicle.  
         [0004]     DE 100 58 434 A1 describes a method and device for control of the heating of an outside mirror, the heating output being controlled as a function of a variation of the outside temperature per unit time.  
         [0005]     JP 58194612 A, lastly, describes a control device for a vehicle heater that is part of a vehicle air conditioning system. To control the seat heating, various input quantities, such as an outside temperature, a battery voltage and a water temperature of a vehicle cooling system are processed.  
         [0006]     Accordingly, there exists a need for an improved vehicle seat heating system and a control method for the same.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention provides a simple method of controlling a heating mechanism, and a control device of simple structure for a heating mechanism, in which a demand control of the heat output is made possible.  
         [0008]     In one embodiment, a method of controlling a heating mechanism, in particular an electric seat heater for a motor vehicle, provides a variation of a target time for a duration of heating as a function of a difference between a measured outside temperature and a measured inside temperature. The inside temperature may be a measured temperature in or on a seat of a motor vehicle. The method according to this embodiment has the advantage of a very low circuitry and structural outlay, yet a demand control of the heat output is made possible. This is accomplished in that for variation of a target time for an on-duration of the heater, not only is the outside temperature taken into account, but in like manner the inner or seat temperature influences the on-time of the heating. According to measured seat temperatures, a shorter or longer heat duration may be appropriate. The known methods, in contrast, take only an outside temperature to preassign or vary on on-duration or output of the heater.  
         [0009]     The difference of the outside temperature (T A ) and inside temperature (T I ) may in particular be derived by determination of a quantity called the sensory temperature (T E ) and calculated. The sensory temperature may be derived from a function of the outside temperature and the difference between the outside temperature and the seat or inside temperature, and may be represented in principle by the following formula:
 
 T   E   =f[T   A , ( T   A   −T   I )]  (1)
 
 where T E  is the sensory temperature, T A  the outside temperature and T I  is the inside temperature which may be the seat temperature, T S . In this way, the human sensation of temperature differences is better taken into account, so that the measured difference of outside and inside, or seat temperature, is not converted linearly into the variation of target time for the duration of heating. Instead, a function is formed that leads to a demand or sensory variation of the heat duration, as a function of the difference between inside and outside temperatures. 
 
         [0011]     One embodiment of the method according to the invention provides at least two fixedly set heating stages, each with a different target time, referred in each instance to one and the same difference between an inside and an outside temperature, or to the same sensory temperature. Alternatively, however, a plurality of heating stages may be provided. Further, an additional variation of the heat output, stepwise or continuous, may be provided.  
         [0012]     The outside temperature may advantageously be queried and determined by way of a data bus. Normally, in a conventional vehicle outfit, the outside temperature is already available, so that the values of the outside temperature sensor can be queried by way of central control electronics or by way of a data bus in the vehicle (e.g. “CAN-Bus”). The inside temperature, or seat temperature, can then be queried by way of an inside temperature sensor or by way of a seat temperature sensor. For this purpose, in particular, a negative temperature coefficient (NTC) sensor may be used. The inside or seat temperature may be queried likewise by way of an inside temperature sensor used as part of an air conditioning system of the vehicle. The signal for the inside temperature can likewise be made available by way of the same data bus as the outside temperature.  
         [0013]     The preassigned target time for the duration of heat may be converted according to the selected heat stage into a corresponding correction factor, so that for a greater adjusted heating stage, a different correction of the target time for the on-duration of the heating is assigned than for a smaller adjusted heating stage.  
         [0014]     The target times for the heat duration and their corrections may be derived in particular from a vehicle-specific and/or a seat-specific characteristic. For example, the seat may include a fan which may dictate a different heating profile than a non-ventilated seat. In this way, an optimal coordination of various sensory temperatures with corresponding target times for the on-duration can be set up. The heat output for the heating mechanism may in particular be adjusted by variation of voltages and/or by way of a pulse-width modulated signal. The characteristic curves may be stored, according to vehicle type or seat variant, as play-back software in the control unit or in the control circuit. In this way, like control circuits may be employed for the several vehicle and seat variants. The characteristic curves may be played back e.g. by way of so-called “flashes.” Here, the control unit is suitably programmed by playing the correspondingly provided software over programmable memory circuits.  
         [0015]     A heating system according to the invention for a heating mechanism, in particular for an electric heating device of a vehicle seat, provides an outside temperature sensor and an inside or seat temperature sensor as well as a way of preassigning and/or varying a target time for a heating duration as a function of a difference between a measured outside temperature and a measured inside temperature. The heating mechanism may in particular comprise at least two fixedly adjusted heating stages, each with a different target time, referred in each instance to a like difference between inside and outside temperature.  
         [0016]     Other features, embodiments and advantages of the control device according to the invention have already been mentioned in terms of the several variants of the method previously described.  
         [0017]     The present invention itself, together with further objects and attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     For a more complete understanding of this invention reference should now be had to the embodiments illustrated in greater detail in the accompanying figures and described below by way of examples of the invention wherein:  
         [0019]      FIG. 1  shows a schematic diagram of a control device according to one embodiment of the invention;  
         [0020]      FIG. 2  shows an example of a characteristic diagram for controlling a target time as a function of measured temperatures in accordance with an embodiment of the invention;  
         [0021]      FIG. 3  shows a running diagram of a method according to an embodiment the invention; and  
         [0022]      FIG. 4  shows an exemplary environment of the present heating system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     In the following figures, the same reference numerals will be used to refer to the same components. While the present invention is described with respect to an apparatus for a vehicle seat heating system, the present invention may be adapted and applied to various systems including: electrical systems, heating systems, seating systems, vehicle systems, or other systems known in the art.  
         [0024]     In the following description, various operating parameters and components are described for one constructed embodiment. These specific parameters and components are included as examples and are not meant to be limiting.  
         [0025]      FIG. 1  illustrates, in a schematic diagram, the structure of a heat system according to one embodiment of the invention. The outside temperature T A  is acquired by way of an outside temperature sensor  10 . The seat temperature T S  is acquired by way of a seat temperature sensor  12 . The two sensor signals are processed in a control circuit  14  to adapt a target time t soll  in a target time transmitter  16  to the on-time and/or the heat output of the heating mechanism  20 .  
         [0026]     The heating mechanism  20  may be a resistive heating element comprising conductive wires, filaments or fabric. It can be an areal heating element, for example, disposed proximate a vehicle seat cushion surface such as the seating surface or back rest. Other types of heating elements may also be employed.  
         [0027]     The controller  14  may be implemented in hardware or software. For example, it can be a control circuit or it can be implemented in a controller comprising a CPU, inputs, outputs and associated memory. The controller can be stand-alone controller or be part of another vehicle controller such as the HVAC system controller. Also, although the controller  14  and target time transmitter  16  are shown as separate components, they could be integrated into a single unit.  
         [0028]     The outside temperature T A  may be part of an existing vehicle sensor outfit, so that the sensory value is already available in a data bus of the vehicle (for example, CAN-Bus  18 ). For example, many vehicle HVAC systems include or make use of an outside temperature sensor for vehicle interior climate control.  
         [0029]     The seat temperature sensor  12  may in particular be an NTC sensor on or near the seat. For example, it may be located underneath the seating surface to provide a seat surface temperature. It could also be located underneath the seat or near a surface away from the occupant to provide an ambient temperature output. Alternatively, or in addition to seat sensor  12 , an inside temperature sensor  11  may be employed to provide a temperature signal indicative of the ambient vehicle interior temperature (T I ). Again, such inside temperature sensors  11  are typically employed in vehicle HVAC systems. In such a case, its data signal may be made available to the controller  14  by way of a vehicle data bus  18 .  
         [0030]      FIG. 2  shows an example of a characteristic diagram for variation of a target time t soll  for the on-time of the heating as a function of a difference between seat (T S ) or inside (T I ) and outside temperature (T A ). Here, it becomes clear that in a first heating stage (“Low”), a shorter on-time t soll-1  is provided for given temperature difference, whereas on a second heating stage (“High”), a longer on-time is provided for given temperature difference. According to temperature difference or sensory temperature T E , the on-time varies continuously in both stages.  
         [0031]     From the diagram, it becomes clear that with increasing sensory temperature (T E ), a continuous decrease of the on-time of the heating mechanism is provided. This decrease in on-time takes account of the fact that when the seat is already warmer, a shorter heating time of the seat is required to reach a given temperature. For a correspondingly colder seat, a longer heating time is desirable.  
         [0032]     The anterior portion of the curves represents a maximum on-time for both heating stages. The sensory temperature T E-0  is lowest here, and in the example of the sketch is equal to −40° C. The on-time t soll-1  at the lower heating stage (“Low”) may here for example be about 10 minutes. The on-time t soll-2  at the higher heat stage (“High”) may for example be about 20 minutes.  
         [0033]     The intermediate range of the curves represents an intermediate on-time for both heating stages. The sensory temperature T E-1  is located at the so-called working point, and in the embodiment sketched by way of example is 0° C. The on-time t soll-1  at the lower heat stage (“Low”) may here for example be about 4 to 5 minutes. The on-time t soll-2  at the higher heating stage (“High”) may for example be about 8 to 10 minutes.  
         [0034]     The posterior range of the curve represents a minimal on-time for both stages. The sensory temperature T E-2  is here greatest, and in the example of the sketch is about +40° C. The on-time t soll-1  at the lower heat stage (“Low”) may here be about 1 to 2 minutes. The on-time t soll-2  at the higher heat stage (“High”) may here be about 3 to 5 minutes.  
         [0035]     Intermediate values can be determined by continuous shifts of the given values for the temperatures. The characteristic field of  FIG. 2  may be stored in memory within the control circuit  14  or in the target time transmitter  16 . Optionally also, a simplified control may be provided, in which there is no continuous adjustment of target times, but adjustment in a number of steps.  
         [0036]      FIG. 3  shows a flow diagram to illustrate the mode of operation of one method according to the invention. After the start, it is queried in a first step S 1  whether the heating device is switched on or off (On?). If the answer is affirmative (Y), then in a second step S 2  the preassigned heating stage is queried. In the case of two heating stages, these may for example be a “Low” stage and a “High” stage. In a third step S 3 , an outside temperature T A  is queried. As noted above, the outside temperature T A  can be provided by way of the vehicle communication bus  18  from an outside temperature sensor  10 . In a fourth step S 4 , a seat temperature T S  or an inside temperature Ti is queried. These values are provided, for example, from the seat temperature sensor  12  or vehicle interior temperature sensor  11 , and may be communicated directly or by way of the vehicle communication bus  18 . From the two temperature values T A  and T S , or T A  and T I , in a following step S 5  a sensory temperature T E  is computed. From the calculated sensory temperature and the preassigned heat stage, in a following step S 6  a target time t soll  is computed for an on-time of the heating mechanism  20 , and forwarded to the heating controller  14 . This ensures that the heating mechanism  20  is being operated at a preselected heating stage during the calculated time.  
         [0037]     It is contemplated further that a time sequence of a plurality of different heat stages may be provided. For example, with very low outside temperature, this may be first a stage with short, vigorous heating, following by a longer lasting stage with reduced heating. On the other hand, if the outside temperature is not so low, for example a heating stage with intense heating may be followed first by a pause and then by a shorter heating stage with reduced heating compared to the warm-up phase.  
         [0038]      FIG. 4  shows a schematic diagram of one exemplary embodiment of the present heating system and control method in a vehicle seat application. In this example, at least one vehicle seat  24  of the vehicle  22  includes one or more heating elements  20 . The heating elements  20  are shown in both the seat and backrest cushions of the vehicle seat  24 , but could be in one or the other as desired. The controller  14 , as shown, is disposed within the vehicle seat  24 , but could also be located elsewhere in the vehicle as described above. The controller  14  is in electronic communication with the heating elements  20 , either directly or by way of the target time transmitter  16  or vehicle communication bus  18 . The controller  14  receives outside (T A ), inside (T I ) and seat (T S ) temperature values from the respective sensors  10 ,  11 ,  12 , either directly or by way of the communication bus  18 . Also, although both seat sensor  12  and interior sensor  11  are shown, only one or the other may be desired for the particular vehicle application.  
         [0039]     While the invention has been described in connection with one or more embodiments, it is to be understood that the specific mechanisms and techniques which have been described are merely illustrative of the principles of the invention, numerous modifications may be made to the apparatus described without departing from the spirit and scope of the invention as defined by the appended claims.