Abstract:
A device is disclosed for reducing overheating in a passenger compartment of a parked vehicle. The device has a temperature sensor, a temperature comparator, and a control system in electrical communication with the comparator for controlling the actuation and operation of an existing air conditioner fan within the vehicle. The control system incorporates a power supply management arrangement designed to draw energy in pulses from a battery unit of the vehicle to energize the motor when the temperature in the passenger compartment exceeds a predetermined level, and to cease drawing energy when the temperature falls below the predetermined level.

Description:
The present invention relates generally to a vehicle ventilation device, and more particularly to an automatic ventilation device for controlling the internal temperature of a parked vehicle to prevent it from being overheated on hot days. 
     BACKGROUND OF THE INVENTION 
     The operator and passengers of a vehicle often experience considerable discomfort when they enter a vehicle that has been parked under the hot sun or in a non-cooled garage during hot weather. Although air conditioning technology to cool the passenger compartment is well known, it normally takes some time before the air conditioning is effective to reduce the internal temperature of the compartment to a comfortable level and to cool such components as the steering wheel and hand brake to the point that they can be touched without discomfort. In particularly hot conditions the temperature may reach at least 70° C. Such excessively high temperatures not only cause personal discomfort but also may cause damage to interior trim, plastic fixtures and other interior components of the vehicle and to articles that have been left in the vehicle. 
     Many devices have been proposed for overcoming this problem but none have worked effectively or become popular. 
     One form of such device includes a cooling unit consisting of a cooling chamber with at least one insulated wall having on opposite sides, a heat sink and a cooling block having there between a thermoelectric chip. The device also includes an air intake conduit, a cool air conduit, and an exhaust conduit and means for supplying power from the vehicle battery to the cooling unit. 
     A further device is intended to be attached to the side window of the vehicle using an interfacing fixture that is attached between the door frame and the side window. The device includes a housing that has an air outlet port, a DC motor, a centrifugal fan, a voltage polarity switch and a temperature control module. The temperature control module consists of first and second heat exchangers and a Peltier-effect thermoelectric element. Electric power is supplied to the device through a control unit that takes power from the vehicle battery at a pre-selected time. 
     In yet another approach, the device comprises at least one thermal conductor containing a phase-change working substance for cooling the overheated passenger compartment. The thermal conductor has three sections, namely, an evaporator section located in the vehicle compartment, a condenser section located outside the vehicle and an adiabatic section there between. The heat in the vehicle compartment causes evaporation of the working substance in the evaporator section, which draws heat from the compartment. The resulting difference in vapor pressure between the evaporator section and the condenser section drives the vapor-phase working substance from the evaporator section through the adiabatic section to the condenser section where it condenses, thus releasing the latent heat of condensation to the ambient air. The evaporator section is normally attached to the inner surface of the roof panel and the condenser section is mounted on top of the roof panel. 
     All these prior devices are relatively complicated and expensive and, especially for the third approach, require modification of the structure of the vehicle. A further problem associated with the powered devices is that power usage is not particularly efficient, which results in battery drain, especially when the device is directly connected to the battery of the vehicle. 
     An alternative solution to overcome the inconvenience caused by overheating of the passenger compartment of a parked vehicle would therefore be desirable. 
     SUMMARY OF THE INVENTION 
     This invention provides a device for reducing overheating of the passenger compartment of a parked vehicle, which makes use of existing components of the vehicle, for example, the air conditioner fan, its motor and the associated ducting so as to minimize the number of components required and which incorporates a power management system to reduce or eliminate problems of battery drain. 
     According to the invention a device for reducing overheating in the passenger compartment of a parked vehicle comprises a temperature sensor, a temperature comparator and a control means, preferably micro-processor based, in electrical communication with the comparator for controlling the actuation and operation of an existing air conditioner fan of a vehicle; the control means incorporating a power supply management means designed to draw energy in pulses from a battery unit of the vehicle to energise the motor when the temperature in the passenger compartment exceeds a pre-determined level, and to cease drawing energy when the temperature falls below the predetermined level, 
     Preferably, the device incorporates a switch that allows the device to operate only when the ignition of the vehicle is turned off. The switch is preferably designed to operate automatically when the ignition of the vehicle is turned off. 
     Since the device can only operate efficiently when the air conditioner inlet vents are open, when the vehicle has electrically operated air conditioner vents, the control means preferably is designed to open the inlet vents when it is switched on. If the vehicle does not have electrically operated air conditioner vents, the device may be associated with an attachment for converting the inlet ducts to electrical operation. 
     The device is provided with connections, preferably jack connections for connecting it directly or indirectly to the battery of a vehicle and to the motor of the ventilator fan and to by-pass the air conditioner fan speed controller. It preferably also has connections to the inlet vents of the vehicle. 
     The control means preferably employs a pulse width modulation technique to control energy usage from the battery. It is preferred that the pulse frequency of a pulse width modulator is set above the normal audible range and below the RF frequency so as to avoid human discomfort and also to avoid possible frequency related interference to the vehicle including its electronic components and the related devices. It is preferably set at 24 KHz. 
     The use of a pulse width modulation technique by which the device draws power from the battery for a predetermined time and then automatically ceases to draw power for a minimum predetermined time, which may be the same as or different from the first time, if, or until, the temperature again exceeds the predetermined level, allows the device to remain operable over a very much longer period before the battery would be discharged to an unacceptable level at which the vehicle, can no longer be started. 
     The device preferably also incorporates a battery condition monitor whereby operation of the system is halted or prevented if the voltage of the battery unit is, or falls below, below an acceptable level. The battery conditioner monitor is preferably associated with a warning light or other indicator to draw attention to the fact that there may be battery problems. 
     Monitoring battery condition ensures that operation of the device cannot drain the battery to a level below that needed to start the vehicle. Preferably the battery condition monitor prevents operation of the device when the battery voltage drops to a level that is well above the minimum voltage needed to start the vehicle. 
     Preferably the device is programmed to allow only a fixed number of cycles of drawing and ceasing to draw power before it shuts off, regardless of the temperature inside the compartment at that time and is reset when the vehicle is restarted using the ignition switch. 
     The control means may employ analog or, more preferably, digital processing techniques for the temperature comparator and battery monitoring functions of the device. 
     The device of the invention will also normally include a display board or display module which houses the temperature sensor, an on/off switch and an indicator light, preferably an LED, for indicating battery condition. 
     The display board or module is preferably designed to be mounted unobtrusively on the dashboard of the vehicle with the control means being housed in a module that can be mounted beneath the dashboard. 
     The invention thus provides a purely electronic solution to the problem of passenger compartment overheating by “piggy-backing” onto existing components of the vehicle. Moreover, by causing cooler outside air to circulate through the air conditioner ducting, not so much heat will be present in the ducting when the air-conditioner system is subsequently turned on since the air-conditioner evaporator coils will be kept cool by the circulated air. In addition, the humidity of the passenger compartment will tend to equilibrated with the humidity outside the vehicle thus reducing damage to vehicle components and other artifacts that are prone to damage by moisture. 
     The use of the device also produces a deodorizing effect by ensuring that the odours from odiferous vapours are swept out of the vehicle, even when it is parked, and that any odiferous materials that have been accidentally transferred into the vehicle, for example on the shoes of the occupants, and have ceased to smell when they dry do not start to smell again if they are re-moistened by a build-up of humidity in the vehicle. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention will now be described in greater detail, by way of example, with reference to the accompanying drawings in which 
     FIG. 1 is a general flow chart showing the sequence of operations for an automatic vehicle ventilation system incorporating the device of the invention; 
     FIG. 2 is a block diagram of one form of the system: 
     FIG. 3 is a connection block diagram of the system of FIG. 2; 
     FIG. 4 is a circuit diagram of a first embodiment of the device; and 
     FIG. 5 is a circuit diagram of a second embodiment of the device. 
    
    
     As shown in FIGS. 1 and 2, the system of the invention comprises a temperature sensor or thermistor  10  electrically connected in conventional manner to a comparator circuit  16  in a control means  11 . The sensor  10  is disposed within the passenger compartment  5  of a vehicle. The control means also includes a linear voltage regulator  17  for receiving power from a  12  volt battery  13  of the vehicle and converting it to 5 volts, a micro-controller  35 , power switching circuitry  18  and a pulse width modulator  12 . In the control means, voltage regulator  17  is connected to both comparator  16  and micro-controller  35 . Micro-controller  35  is connected to pulse width modulator  12  via switching circuitry  18  and also to the battery  13  by battery condition and/or voltage drop monitoring means (not shown). The pulse width modulator  12  is electrically connected to the existing air conditioner fan motor assembly  14  of the vehicle. Installation of the device and use of the system in no way affects the existing electrical arrangements of the vehicle since the system complements and “piggy backs” on the existing electrical system and is operable only when the other systems are switched off. Normal running of the air-conditioning system is not affected because a relay that automatically disconnects the fan speed controller  59  when the system is operating, operate to reconnects fan speed controller  59  when the system is not operating. 
     As shown in FIG. 1, in operation of the system, when the ignition switch of the vehicle is switched off and the inlet vent or vents to the air conditioner are opened manually or automatically. The device is automatically switched on and the level of the battery is sensed. The temperature inside the vehicle is also sensed and compared to the reference temperature. If the battery level is satisfactory, when the temperature inside the vehicle rises above the reference temperature, the comparator  16  generates a signal that triggers the micro-controller  35  to switch output relays and operate pulse width modulator  12 . This causes the air conditioner fan  14  to operate and draw air from the outside through the open inlet vent  19  into the passenger compartment. The warm air inside the compartment is driven out past the window and door seals and other places that are not completely airtight. After a set period determined by pulse width modulator  12  the output relays are deactivated, power is no longer drawn from the battery  13 , and the fan  14  ceases to operate. After a second set period also determined by pulse width modulator  12 , if the temperature in the vehicle is still below the reference temperature nothing happens but the temperature sensor  10  continues to sense the temperature inside the vehicle until it rises above the reference temperature. If the temperature is above the reference temperature, or when it again rises above the reference temperature, the device again cuts in to operate fan for a further period. 
     Micro-controller  35  is set to operate the fan  14  for a certain period, typically about 60 to 120 seconds. Such sequence of temperature measurement, comparison and fan actuation is repeated as necessary. However, it is generally preferred that the sequences are limited to a maximum of, say, 240 times in one operational cycle until the system is re-set again to avoid battery depletion The system will be re-set again if the ignition switch of the vehicle is turned to its on position, for example during the starting and running of the vehicle when the battery  13  will be recharged. In addition, it is also preferred that the device can only be operated for a maximum of 8 hours in one operational cycle. This feature caters for the possibility of the vehicle being idle for longer periods than normal, for example, while the owner is away from home. 
     The efficiency of the system may be increased even further if the existing ventilation ducting mechanism of the vehicle is also put to use. 
     FIG. 3 shows the connection block diagram of the invention. The system is generally adapted to be assembled in three different modules, i.e., a display board  20 , a control module  21  and a terminal block  22 . The terminal block  22  suitably consists of a 16 Amp, 2-pole terminal for allowing the device to be connected to the existing fan and the air-conditioner control wiring system. As mentioned earlier, the proposed system is intended to “piggy-back” on the existing system and the terminal block allows such connection to be made with ease. The control module  21  encloses the linear regulator  17 , the comparator circuit  16 , micro-controller  35 , power switching circuitry  18  and the power supply management means  12 . Thus, the control module  21  encloses the components of the control means  11 , The display means houses the temperature sensor  10 , an on/off switch  56  and an indicating light or LED  57  along with a biasing resistor  58 . The display means is intended to be mounted on the dashboard of the vehicle using suitable means and the control module  21  may be concealed from view, usually underneath the dashboard. The connections to the battery and ignition system of the vehicle are made on the control module along with suitable grounding. 
     Referring now to FIG. 4, there is shown a circuit diagram of an analog version of the device of the invention. A fast blow fuse  30  is connected to the incoming +12 Volts supply from the vehicle battery  13 . A relay  31  is employed to turn on the system when the ignition switch  32  of the vehicle is turned to its off position. A step-down +5 volt linear regulation method is used to develop a circuit that supplies power to operational amplifiers  33 ,  34  and the micro-controller  35 . A thermistor  10  is placed in series with a resistor  37  at the non-inverting input of the operational amplifier and a reference of 4.1 Volts is obtained using resistors  38 ,  39  and the operational amplifier  33 . A low state trigger output is produced at the output of the operational amplifier  33  if the non-inverting input voltage is less than the reference voltage. The output of operational amplifier  34  is produced at high trigger once the low state trigger at the inverting of operational amplifier  34  is compared with a reference of 4.1 Volts at the non-inverting input of operational amplifier  34 . A resistor  40  is connected between the differential input of operational amplifier  34  to avoid virtual ground effect while in the comparing state. 
     Micro-controller  35  is employed as task monitoring and control unit for the control means  11 . Pins ( 6 ) and ( 7 ) of the micro-controller  35  are connected to a crystal oscillator  41 . The comparison trigger output of operational amplifier  34  is fed into pin ( 2 ) of the micro-controller. Upon receiving the comparison trigger input, the micro-controller  35  cycles through the embedded software and sends out an output signal through pin ( 15 ) of the micro-controller, which is connected to an opto-coupler  42  to drive transistor  43 . Following this, the collector current energizes and turns on output relay  44  that is connected to the fan motor  14 . Relay  45  disconnects fan speed controller  59 . The pulse width modulation to energize the fan motor  14  is accomplished through use of a 555 timer  46  with its associated components, diodes  47 ,  48 , resistors  49 ,  50 ,  51  and capacitors  52 ,  53 ,  54 , generating a continuous pulse with a duty cycle of 48.8% that switches directly through gate resistance  51  to a MOSFET transistor  55  This switching network is utilized to control current drain from the battery  13  and since energy is drawn as pulses, usage of energy from the battery is minimized. This is particularly due to the non-direct connection of the battery terminals to the fan motor  14 . Pin ( 9 ) is employed to detect low battery condition, If for any reason voltage at the battery terminal should fall below 11.9 volts, the system will not be allowed to operate. LED  57  will be lit to indicate such condition. A blinking LED is especially preferred. 
     FIG. 5 shows a digital version of the comparator circuit  16 . This embodiment adopts a much simpler solution by removing the operational amplifiers  33 ,  34  as used in the external comparator shown in FIG.  4 . In this embodiment the device incorporates a built-in comparator within the micro-controller  35 . A number of micro-controllers having such built-in comparators may be found in the market. The micro-controller  35  coupled with the pulse width modulated ramp and the timer is used to implement a single-slope AC/DC conversion to detect the unknown input voltages from the themistor. The input voltage is then read by software in the micro-controller as a digital representation. The output is fed into an RC integrator  60 , which produces a linear ramp. The analog voltages generated from the thermistor  10  are inputted to pin ( 9 ) of the micro-controller. Typically, voltages at these inputs will range between 0 and 5 Volts. When input analog voltage exceeds the pre-determined set level voltage in the software, an interrupt signal in the micro-controller is generated and the blower fan motor will operate as in the device of FIG.  4 . Such a digital technique is generally more preferred since the number of components in the device is reduced. Moreover maintenance work and adjustment may be made through the software with relative ease. 
     As in the analog circuit shown in FIG. 4, low battery voltage detection is also employed. However, in this arrangement, pin ( 8 ) of the micro-controller  35  is used for this purpose.