Microprocessor Based Air Inflation Control System

The present invention pertains to an air inflation control system for adjusting the air pressure within an inflatable device. More particularly, the present invention pertains to a microprocessor based system for monitoring the air pressure within an inflatable device and controlling the supplying of air to and venting of air from the inflatable device, as needed. The system can be implemented in a manner requiring insertion of one or more coins to enable activation, if desired. Further, this system can provide other air-related options, such as a vacuum cleaning capability.

Optimum operation of automobiles and trucks requires that the tires of such vehicles be inflated to a proper level. If the inflation level is lower than it should be, excessive fuel is consumed by the vehicle, and the tires wear out faster. If the inflation level is too high, tire wire is accelerated and the vehicle rides uncomfortably. To permit their customers to adjust their tire pressure, automobile service stations frequently have available for their customers a controlled, pressurized air supply, enabling the customers to add air to or vent air from truck and automobile tires as well as other inflatable devices such as bicycle tires, air mattresses, footballs, basketballs, and other such things. Frequently such air supply consists simply of an adjustable control enabling the customer to set the desired air pressure, and a hose connected to a pressurized air source and terminating in a valve adapted to mate with the air valve of an automobile tire. The accuracy of such air supplies is somewhat low, and the air supply can take an undesirably long time to inflate an inflatable device to a desired air pressure. Additionally, most such air supplies are incapable of automatically venting air from the inflatable device when the actual air pressure in the device is greater than the desired air pressure. Instead, air must be vented manually until the actual air pressure is below the desired air pressure, and then the device must be reinflated to the desired air pressure. Further, such air supplies generally have only one supply rate. Large volume devices, such as automobile or truck tires, are preferably filled at a relatively high rate; however, low volume devices such as bicycle tires and sports equipment are more safely filled at a slower rate to avoid overinflation and possible rupture or other damage.

The provision of such an air supply imposes an expense on the operator of the automobile service station or other establishment. Not only is a capital investment necessary to provide the air supply equipment, but also an operating expense is involved, generally for electricity to run a compressor, and maintenance costs are incurred. In order to more equitably apportion such costs to users, it is desirable that the air supply require payment of a charge to enable its operation, rather than burying the expense of the air supply in the prices of other goods sold by the service station, such as gasoline and motor oil.

The present invention is a microprocessor based system for monitoring the air pressure in an inflatable device and controlling the supplying of air to and the venting of air from such device. In accordance with the present invention, a first input is provided for receipt of an actual air pressure signal indicative of the air pressure in an inflatable device and application of such actual air pressure signal to a system controller. The system controller includes a pressure selector permitting a user to indicate a desired air pressure signal. The system controller is connectable to a numerical indicator for applying to such indicator an air pressure signal to cause the indicator to indicate the air pressure value of the applied air pressure signal. A switch is provided, selectively movable between a first position in which the controller provides the actual air pressure signal for application to the numerical indicator, to cause such numerical indicator to indicate the air pressure value of the actual air pressure signal, and a second position in which the controller provides the desired air pressure signal for application to the numerical indicator, to cause the numerical indicator to indicate the air pressure value of such desired air pressure signal. Control means are provided, selectively movable between a position in which the desired air pressure signal is increased, a position in which the desired air pressure signal remains static, and a position in which the desired air pressure signal is decreased. Thus this control means permits the user to adjust the desired air pressure signal as he wishes.

The system controller is responsive to the desired air pressure signal being less than the actual air pressure signal for providing a vent control signal for application to an air vent control device to cause such air vent control device to vent air from an inflatable device coupled to it. The system controller is also responsive to the desired air pressure signal being greater than the actual air pressure signal for providing a fill control signal for application to an air inflating device to cause such air inflating device to provide air to an inflatable device coupled to it. In addition, the system controller provides a compressor actuation signal for application to an air compressor to activate that air compressor to provide air to the air inflating device as needed, and an intermittent indicator signal for indicating provision of air to the inflatable device or venting of air from the inflatable device. In the preferred embodiment, the system controller is a microcomputer. If desired, the system controller can require the insertion of one or more coins before the air inflation control system is activated. Additional accessory functions can also be included, such as a vacuum for cleaning of car interiors.

These and other aspects and advantages of the present invention are more apparent in the following detailed description and claims, particularly when considered in conjunction with the accompanying drawing in which like parts bear like reference numerals. In the drawings:

FIG. 1 is a perspective view depicting a microprocessor based system for monitoring the air pressure in an inflatable device and controlling the supplying of air to and venting of air from such device in accordance with one embodiment of the present invention;

FIG. 2 is a functional block diagram of an embodiment of the present invention;

FIGS. 3 and 4, when positioned as depicted in FIG. 5, comprise a block diagram of a microprocessor based system for monitoring the air pressure in an inflatable device and controlling the supplying of air to and venting of air from such device, in accordance with a preferred embodiment of the present invention; and

FIG. 6 is a more detailed functional block diagram of the embodiment of FIG. 1.

The microprocessor based system of the present invention, for monitoring air pressure in an inflatable device and controlling the supplying of air to and venting of air from such a device, can be housed within a cabinet 10 as depicted in FIG. 1. An air hose 12 from cabinet 10 provides air to a valve 14 adapted for use in conjunction with the valve of an automobile or truck tire. Air hose 16 brings air from reservoir cylinder 18 to the components within cabinet 10. Compressor 20 provides air to cylinder 18. Power cable 22 permits connection of the electrical components within cabinet 10 to a suitable power source, while power cable 24 permits connection of compressor 20 to such a power source. Cables 22 and 24 could be replaced by a single cable if desired. Cable 26 connects compressor 20 to circuitry within cabinet 10 for control purposes.

The front panel of cabinet 10 includes indicator and control devices. Thus a numerical indicator 28 is provided to indicate air pressure. Switches on cabinet 10 include pressure switch 30 having fill and check positions, fill rate switch 32 having normal and slow positions, accessory switch 34 having off and on positions, increase pressure pushbutton 36, and decrease pressure pushbutton 38. With pressure switch 30 in its check position, indicator 28 indicates the air pressure within an inflatable device connected to valve 14. When pressure switch 30 is in its fill position, indicator 28 indicates the air pressure desired in the inflatable device which is, or is to be, connected to valve 14. Adding of air to and venting of air from the inflatable device can then take place. If the air pressure within an inflatable device connected to valve 14 is less than the desired air pressure set on indictor 28, and the system is enabled to provide air to the inflatable device, fill indicator 40 is energized, and the system opens valves to provide air from cylinder 18 through hoses 16 and 12 and valve 14 to the inflatable device. Compressor 20 is activated as needed to maintain sufficient pressurized air in reservoir cylinder 18. During filling of large volume inflatable devices such as automobile or truck tires, fill rate switch 32 is in its normal position. During filling of low volume inflatable devices, the system is set to supply the air at its slow fill rate, as a result of fill rate switch 32 being set to its slow position, and slow fill indicator 42 is energized in addition to fill indicator 40. If the air pressure within the inflatable device is greater than the desired air pressure set on indicator 28 and the system is enabled to vent air from the inflatable device, vent indicator 44 is energized and the system opens valves to vent air from the inflatable device through valve 14 and hose 12. When accessory switch 34 is in its on position and the system is enable to operate an accessory device, accessory indicator 46 is energized, and the accessory device (not shown) is actuated. Supplying and venting of air cannot take place at such times. Each indicator 40 through 46 can be a light emitting diode, by way of example. When pushbutton 36 is depressed, the desired air pressure is increased, and so the indication of desired air pressure on indicator 28 increases. Conversely, when pushbutton 38 is depressed, the desired air pressure, and the indication on indicator 28, decrease. Coin input slot 48 is provided in housing 10 to permit insertion of coins to activate the system when the system is operating in the mode requiring use of such coins. Loudspeaker 50 is provided in housing 10 for generating intermittent tone or beep indications as air is being applied to or vented from an inflatable device.

FIG. 2 is a functional block diagram of the system of the present invention. Each switch 30, 32, and 34 and each pushbutton 36 and 38 is connected so that in its closed position it grounds an input to system controller 60. Each light emitting diode 40, 42, 44, and 46 has its cathode connected to an output from system controller 60 and its anode coupled through a resistor to ground. Indicator 28 receives signals from system controller 60 to enable it to provide indications of desired air pressure or actual air pressure, depending upon the position of switch 30. Coins inserted through slot 48 are detected by a suitable coin detector which applies a signal on input line 62 to system controller 60. A pressure transducer signal, indicative of the air pressure within an inflatable device to which valve 14 couples hose 12, is applied by line 64 to another input of system controller 60. A signal indicative of the number of coins which must be inserted to activate the system is applied to system controller 60 by line 68. Similarly, a signal indicative of the cycle time for which the system is activated by the receipt of the appropriate number of coins is applied to system controller 60 on input line 70. System controller 60 provides a control signal on output line 72 to components within the system which actuate the appropriate valves to cause air from air line 16 to be applied through air line 12 and valve 14 to an inflatable device. In like manner, output line 74 applies signals from system controller 60 to valves to vent air from the inflatable device through the valve 14 and air line 12. System controller 60 also applies signals on output line 76, which is within cable 26, to activate compressor 20 to apply air to reservoir cylinder 18. Output line 78 applies intermittent tone indications to loudspeaker 50 when air is being applied to an inflatable device. Output line 80 energizes accessory equipment such as a vacuum cleaner or other such device when the system has been enabled by insertion of an appropriate number of coins and accessory switch 34 is in its on position.

When FIGS. 3 and 4 are positioned as depicted in FIG. 5, they form a schematic block digram of a preferred embodiment of the present invention. Power cable 22 applies ac power through step down transformer 88 and full wave rectifier 90 to power supply 91. Output terminal 92 of power supply 91 is connected to the output of rectifier 90 to provide an unregulated 12 to 15 volt output. The output of rectifier 90 is also applied through voltage regulator 94 to regulated 12 volt output terminal 96 and through voltage regulator 98 to regulated 5 volt output terminal 100. Unregulated output terminal 92 is connected to each of the other terminals 92 in FIGS. 3 and 4. Similarly, regulated 12 volt output terminal 96 is connected to each of the other terminals 96 in FIGS. 3 and 4, and regulated 5 volt output terminal 100 is connected to each of the other terminals 100 in FIGS. 3 and 4.

Crystal controlled oscillator 102, having a frequency of 3.579545 megahertz, is coupled to microcomputer 104 to provide timing signals for the system. Microcomputer 104 is preferably an 8748 8-bit microcomputer available from Intel Corporation, although other microcomputers, such as 8048, might be used. If an 8748 or 8048 microcomputer is used, then the pin connections are as indicated in FIG. 3. The coin detector input on line 62 is frequency limited by filter assembly 106 and applied through Schmitt trigger 108 to microcomputer 104. A bypass input signal can be applied through inverter 110 to the microcomputer to make the system operable regardless of whether input line 62 has indicated receipt of the required number of coins.

The pressure transducer input, which is received on input line 64 and which is generally an analog signal, is applied through analog to digital converter assembly 112 to the microcomputer. Preferably analog to digital converter assembly 112 is based on an ACD0831 analog to digital converter 114 wuch as available from National Semiconductor Corporation, and in such case the pin connections are as shown in FIG. 3. The pressure transducer signal can be a one to five volt d.c. signal proportional to the gauge pressure. Analog to digital converter 114 is then referenced to plus one volt d.c. by reference voltage network 116 in order to offset the zero shift of the transducer.

Front panel switches 30, 32, and 34 and pushbuttons 36 and 38 are connected so that when closed they ground associated input ports of microcomputer 104. As shown in FIGS. 3 and 4, two additional input ports can be grounded by jumpers 118 and 120 as desired to permit testing of the system. Cycle time selector switch 122 and coin level selector switch 124 are connected through input/output expander 126 to inputs of the microcomputer. By way of example, expander 126 can be an 8243 input/output expander, in which case the pin connections are as shown in FIG. 4. Cycle time selector switch 122 can permit the setting of a cycle time of, for example, from zero to nine minutes. If zero minutes is selected, the cycle runs continuously. In like manner, coin level selector switch 124 can be set to require insertion of, for example, from zero to nine coins in order to activate the system. If zero coins are required, all of the system functions are free. Normally the display on indicator 28 is in English units, namely, pounds per square inch. However, closing of switch 128, which is coupled through expander 126 to the microcomputer, causes the display to be in metric units, namely kilopascals. Similarly, normal operation requires insertion of a number of coins as determined by the setting of switch 124, but closure of switch 130, which is coupled through expander 126 to the microcomputer, causes all the operation to be free. Closure of switch 132, which is likewise coupled through input/output expander 126 to microcomputer 104, permits testing for maintenance and trouble shooting purposes. When switch 132 is closed, each of the front panel switches is assigned to an output indicator which then can be energized by cosing the associated switch.

An output port of microcomputer 104 is applied through isolating circuit 134 to the fill output line 72 and fill indicator 40. In like manner, another output port from the microcomputer is applied through isolating circuit 136 to vent output line 74 and vent indicator 44. Two further output ports from microcomputer 104 are applied through isolating circuits 138 and 140, to relays 142 and 144 which respectively control the compressor output line 76 and the accessory output line 80. Isolation circuit 140 also controls accessory indicator 46. Slow fill indicator 42 is connected to a port of input/output expander 126. Another output port of the microcomputer is connected through isolating circuit 142 to output line 78 which is connected to loudspeaker 50 to provide an intermittent tone signal while an inflatable device is being inflated.

Two output ports of microcomputer 104 are applied to display driver 146, which by way of example might be a MM5452 display driver having the pin connections shown in FIG. 4. Display driver 146 is connected to liquid crystal display 28 to provide the driving waveforms. Display heater 148 is mounted directly to the rear of the liquid crystal display to permit operation of the display during low ambient temperatures.

When a person wishes to check and adjust the air pressure within an inflatable device, the person first places pressure switch 30 into its check position and then connects valve 14 to the air valve of the inflatable device. Indicator 28 indicates the air pressure within the inflatable device. This might be done without requiring insertion of any coins. To adjust the air pressure within the inflatable device, the person returns pressure switch 30 to its fill position and inserts the requied number of coils. Indicator 28 then indicates a desired air pressure. If that is not the air pressure which the person wants in the inflatable device, the person either increases the desired pressure by pushing pushbutton 36 or decreases the desired pressure by pushing pushbutton 38. Each time pushbutton 36 or 38 is pressed, the indicated desired pressure increases or decreases by one pound per square inch. Pressing and holding pushbutton 36 or 38 for at least one second causes the indicated desired pressure to increase or decrease at a rate of approximately seven pounds per square inch per second. If the indicated desired pressure increases to 70 pounds per square inch, further increasing stops, and pushbutton 36 must be held for at least five seconds before the desired pressure will increase further. This delay is a precaution to prevent accidental setting of an overly high pressure. The desired pressure can not be set above 100 pounds per square inch. If a large volume device is to be inflated, for example an automobile or truck tire, fill rate switch 32 is placed in its normal position. If a small volume device such as a bicycle tire, an air mattress, or an inflated ball is to be filled, then switch 32 is placed in its slow position. Slow fill indicator 42 should then be energized. Valve 14 is then connected to the valve of the inflatable device. A reading of the pressure within the inflatable device is applied to controller 60 by input line 64. If the desired pressure is greater than the actual pressure, then microcomputer 104 applies a signal to indicator 40 and fill output line 72, actuating valves to permit passage of air from reservoir cylinder 18 and air line 16 to air line 12 and valve 14 and then into the inflatable device. Microcomputer 104 also applies a signal to relay 142 to provide a signal on compressor output line 76 as needed to activate compressor 20 to retain an appropriate volume of air in cylinder 18. If the air pressure within the inflatable device is greater than the desired pressure, microcomputer 104 applies a signal to indicator 44 and vent output line 74, actuating valves to permit venting of air from the inflatable device through valve 14 and air line 12. As air is being applied to or vented from the inflatable device, an intermittent signal is applied by microcomputer 104 to tone indicator output line 78 to cause an intermittent beep or tone indication from loudspeaker 50 which ends once the actual air pressure within the inflatable device reashes the desired air pressure, thus alerting the user that the desired air pressure has been reached. At any point during the filling or venting operation, the user may change the position of any of the front panel switches 30, 32, or 34 to read the actual pressure, change the fill rate or activate an accessory device such as a vacuum cleaner, or may activate either of the pushbuttons 36 or 38 to change the desired pressure.

The proprietor of the establishment at which the system of the present invention is installed for operation must set cycle time switch 122 and coil level switch 124, as well as display units switch 128. Either a mechanical coin acceptor or an optical coil acceptor can be utilized, so long as the coin acceptor provides an appropriate signal on line 62 each time a coin is inserted.

On initial turn-on of the system, microcomputer 104 clears its data memory, initializes display driver 146 and analog to digital converter 114, and then checks the input port to which test switch 132 is coupled. If switch 132 is closed to place the system into its test mode, the system undergoes evaluation testing, including activation of the various indicators 40 through 46 in response to actuation of the appropriate switches and pushbuttons 30 through 38.

During normal operation, microcomputer 104 monitors the input from coin level switch 124 to determine the number of coins which must be inserted to cause operation of the system and then monitors the coin input. If insertion of a number of coins is detected equal to the number for which switch 124 is set, microcomputer 104 initiates a paid function and monitors the input from cycle time switch 122 to determine the length of time that the paid cycle is to run. This data is loaded into a cycle time counter and the operation is initiated. Front panel switches and pushbuttons 30 through 38 are monitored and the selected function is initiated. During the pressure check function, microcomputer 104 inhibits its output lines 72 through 80, except that if at the time the pressure check function is initiated, an output is present on compressor output line 76, that output is permitted to continue to prevent the compressor from stalling on turn-on with the air hose pressurized. The pressure transducer input on line 64 is then monitored and converted to the appropriate indication for display on indicator 28.

During the fill operation, a reading of the pressure indicated by the pressure transducer input on line 64 is compared with the desired pressure to determine whether the actual pressure is above or below the desired pressure. If fill switch 32 is in its slow position, microcomputer 104 determines whether the actual pressure is within one pound per square inch of the desired pressure. If it is, the operation is stopped. If the pressure difference is greater than one pound per square inch, an output signal is applied to fill output line 72 or vent output line 74, as appropriate, for a preset interval to increment the actual pressure, and then the cycle is repeated by again monitoring the actual pressure and comparing it with the desired pressure. If fill switch 32 is in its normal position, the measured actual pressure is compared with the target pressure and the result is used to determine whether to provide the fill output signal on line 72 or the vent output signal on line 74 for a preselected period of time. If the pressure difference is less than 20 pounds per square inch, then a fill or vent time ranging from 0.45 seconds to 7.72 seconds is utilized, with the time being related to the pressure difference. If the difference between the desired pressure and the actual pressure is greater than 20 pounds per square inch, then a one second fill or vent time is utilized. This one second fill or vent time for pressure differences greater than 20 pounds per square inch prevents under or over filling of the inflatable device as a result of an erroneous pressure reading as valve 14 is first connected to the inflatable device. The selected vent or fill time is applied to a timer for either the solenoid controlling the valve for filling or the solenoid controlling the valve for venting, and that timer is started and an output provided on tone indicator output line 78. When the timer indicates the selected time has elapsed, the fill or vent signal on line 72 or 74 and the intermittent tone signal on line 78 are terminated, and the pressure within the inflatable device is again read and compared with the desired pressure. If the differences is more than one pound per square inch, the operation repeats. If the difference is less than one pound per square inch, the operation stops until valve 14 is connected to the valve of another tire or other inflatable device to provide a new pressure reading in line 64.

FIG. 6 is a functional block diagram showing pressure selector 160 and pressure sensor 162 applying inputs to comparer 164 which activates valve control 166 or valve control 168, depending upon whether the actual air pressure sensed in the inflatable device is less than or greater than the desired air pressure. Valve control 166 controls inflation valve 170 through which pressurized air from source 172 passes to the inflatable device, while valve control 168 controls vent valve 174 through which air from the inflatable device is vented.

In the preferred embodiment of the present invention, microcomputer 104 is an 8748 single component 8-bit microcomputer from Intel Corporation. Following is the program for the microcomputer. ##SPC1##

Although the present invention has been described with reference to a preferred embodiment, modifications, substitutions, and rearrangements could be made, and still the result would be within the scope of the invention.