Air conditioning system for a vehicle

Abstract: An air conditioning system for a vehicle includes an air supply blower 16, an air chilling device 24, an air heating device 26, speed 53 and power 48 sensing systems for determining the speed and power levels at which the blower 16 is operating, a speed governor 20 for controlling the speed at which the blower 16 is operating, a temperature governor 28, operatively associated with the air chilling 24 and air heating 26 devices, for controlling the temperature of conditioned air supplied by the blower 16 to the interior of the vehicle, and a controller 22 responsive to blower speed and power consumption for operating the temperature governing device 26.

Description: This invention relates to an air conditioning system for a vehicle which offers rapid and precise temperature control notwithstanding varying ram air conditions. The design of vehicular air conditioning systems and controls has presented a variety of problems to the engineer. Not surprisingly, a variety of solutions to specific problems has resulted. One of the problems which has been addressed is the control of the mass flow through a vehicle in terms of not only the total flow through the vehicle but also the direction of the air conditioned mass flow through the vehicle. U.S. Patent 3,403,855 discloses a system for damping an outside air intake port as a function of vehicle speed. U.S. Patent 3,861,282 discloses a system for controlling blower speed as a function of vehicle speed. Japanese Patent 60-78815 discloses a system in which electrical power fed to an air conditioning system blower is reduced when the occupants of the vehicle open a window. None of the systems disclosed in the previously listed patents is capable of controlling the temperature of air processed by the air conditioning system in response to changes in blower speed and power consumption caused by ram air effects. U.S. Patent 4,759,269 discloses a system for maintaining independent air flows to two or more separate segments of the interior of a motor vehicle. The '269 patent does not, however, deal with the problem of maintaining constant system temperature or mass flow during changing environmental conditions. U.K. Patent Application 2,093,233 discloses a system and method for regulating the quantity of air supply to the interior of a vehicle in which variations in the current being supplied to the blower motor are used to damp the air inlet to the vehicle at a location upstream of the blower. The system of the U.K. patent application suffers from a serious fault insofar as the system is incapable of compensating for an operating condition wherein the pressure at the air inlet is less than that of still air. Such a condition could be encountered, for example, when a tailwind having a velocity in excess of the linear velocity of the vehicle impinges upon the vehicle. The system of the U.K. application suffers from additional drawbacks. For example, the outside damper assembly causes added system complexity, cost, package space and reliability concerns. Japanese Patent 57-4418A discloses a system in which an outer air damper is controlled as a function of detection of a gas within the interior of the vehicle. This system, too, is incapable of correcting for ram air impinging upon the vehicle. U.S. Patents 4,382,463 and 4,482,009 deal with distribution of mass flow within the passenger compartment of the vehicle. Each discloses a system for redistributing mass flow within the passenger compartment based upon the occupancy of the passenger compartment. U.S. Patent 4,364,513 discloses a system for controlling discharged air based upon the sensing of occupants within the vehicle. U.S. Patent 4,518,032 discloses an air conditioning system for a motor vehicle having an air supply blower, a heater core, an evaporator and a blend door for controlling the heat flux imported to the air supplied to the interior of the vehicle. In order to prevent excessive heating of the interior of the vehicle the speed of the blower is controlled." This document forms the preamble of claim 1. DE-A-3710470 discloses a system for regulating the air blower in an air conditioner to compensate for fluctuations in ram air. The system includes means for controlling the voltage and current supply and thereby the power consumption to the blower such that a constant airflow is obtained. The present invention seeks to provide an air conditioning system having the capability of responding rapidly to changes in the ram air impinging upon an air inlet of the air conditioning system. This object is achieved by means of the features of the characterizing part of claim 1. It is an advantage of the present air conditioning system that changes in ram air impingement upon the air inlet of the system will be met by adjustment of the blower speed and heat flux of the air conditioning system without the necessity of waiting for the temperature of the interior of the vehicle to change. The temperature governing means used in a system according to the present invention includes a blend door having the capability of directing any fraction of the output of the blower over the heater core. The blend door thus controls the heat flux provided by the temperature governing means so as to compensate for non-programmed blower speed and power changes. Alternatively, the temperature governing means may further comprise means for controlling the flow of engine coolant through the heater core and means for controlling the rate of flow of refrigerant through the evaporator core. A system according to the present invention may include blower speed sensing means comprising means for sensing electromotive force pulses generated by the blower motor and means for converting the pulses into a signal corresponding to the speed of the blower motor. The pulse conversion means may comprise means for transforming the pulses into a square wave having a frequency which is equivalent to the frequency of the pulses and means for counting the frequency of the resultant square wave. The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of a vehicle including a system according to the present invention. Figure 2 is a schematic representation of an air conditioning system according to the present invention. Figure 3 is a block diagram illustrating the motor speed control portion of a system according to the present invention. Figure 4 contains a logic flow block diagram in accordance with an embodiment of this invention. As shown in Figure 1, an air conditioning control system according to the present invention is conveniently employed with a vehicle having an outside air inlet, 12, for conducting ambient air into the air conditioning system. Air passing through the system is conditioned according to the arrangement shown in Figure 2 and distributed to the interior of the vehicle. Turning now to Figure 2, air is drawn into inlet duct 14 and pushed through the balance of the air conditioning system by means of blower wheel 16, which is driven by blower motor 18. The speed of blower motor 18 is controlled by means of blower speed governor 20 in response to commands from control microprocessor 22. It will be appreciated that the microprocessor 22 and its peripheral equipment could be structured according to several different architectures. In a preferred embodiment, however, microprocessor 22 is configured so that control programs are sequentially read for each unit command from a read-only memory (ROM) which stores preset control programs. Unit commands are executed by a central processing unit (CPU). The microprocessor integrally includes input-output control circuits (I/O) for exchanging data with external devices and a random access memory (RAM) for temporarily holding data while the data are being processed. The microprocessor shown in Figure 2 receives inputs from blower speed signal generator 53 and motor power sensor 48, as well as from engine coolant temperature sensor 42, ambient temperature sensor 44, and interior temperature sensor 46. Finally, microprocessor 22 receives input from the operator of the vehicle via driver control panel 40. Those skilled in the art will appreciate in view of this disclosure that a system according to this invention could further include sun load and ambient humidity sensors. The air conditioning system further includes evaporator core 24, through which air being processed by the present system first passes and is chilled. In conventional fashion, the evaporator core may be connected with a compressor, a condenser, an expansion valve, and other control devices. Alternatively, the evaporator may comprise either a conventional heat pipe device or a conventional Peltier effect device or a conventional magnetic flux cooling device, or other type of device suggested by this disclosure. After passing through evaporator core 24, air undergoing the conditioning process passes to the vicinity of heater core 26. The heater core 26 may comprise either a conventional heat exchanger warmed by circulating engine coolant, or a conventional electric resistance heater, or a conventional fuel-burning heater, or any other type of heater suggested by this disclosure. In the event that it is desired to greatly increase the temperature of the air above the discharge temperature from core 24, blend door 28 will be swung completely open so as to allow all of the air passing through the system to pass through heater core 26. If, however, it is not desirable to heat the air passing through the system, at all, blend door 28 will be positioned by microprocessor 22, via actuator 34, in the fully closed position shown in Figure 2. A variety of intermediate positions are available for blend door 28 lying between the fully opened and fully closed positions and such intermediate positions may be employed for governing the temperature of air being discharged from the system. Microprocessor 22 also operates recirculation door 30 and mode door 32. Recirculation door 30, which is operated by microprocessor 22 by means of actuator 38, allows the air conditioning system to utilise either outside air or inside air. The solid lines in Figure 2 representing door 30 depict the door in the outside air mode. A system according to the present invention is intended principally for use when the air conditioning system is operating with air drawn from outside the vehicle, as opposed to recirculated air. Microprocessor 22 operates mode door 32 by means of actuator 36, which serves to shift the flow through the air conditioning system to various registers within the vehicle, such as the defrost or floor or panel registers. Any of the known means for operating various flow control doors may be employed in the various embodiments of this invention. For example, vacuum motor and stepper motor driven linkage mechanisms, or other motor designs or flow control door designs could be employed with this invention. Similarly, different types of blowers, other than the familiar squirrel cage shown in Figure 2, such as axial flow devices, could be employed. As noted above, the system of the preferred embodiment of the present invention relies upon the ability to sense the speed at which the blower is operating. Figure 3 is a block diagram of one such system for sensing blower speed. It is known that many types of electric motors produce extraneous electromotive force impulses when operating. These extraneous electromotive force impulses are sometimes termed "back EMF". If the back EMF is filtered by well known means including band pass filtering, with the filtered signal being passed through a crossing detector, the back EMF may be converted into a square wave suitable for reading into a frequency counter. Accordingly, in Figure 3, blower motor 18 is shown as being operatively connected with filter 52 which removes any objectionable AC or DC noise from the sensed back EMF. The output of filter 52 is then passed to crossing detector 54 which yields a square wave which is ultimately supplied to microprocessor 22, where the speed of the motor is determined by counting the number of square wave pulses over a predetermined time period. Other types of blower speed sensing devices could be employed, such as electro-optical and Hall Effect sensors, to name only two. It will also be appreciated that in the event that an electronically commutated motor is employed in a system according to the present invention, the speed of the motor will be readily calculable from signals produced by the commutation controller. Microprocessor 22 outputs a speed signal to blower speed governor 20 which may comprise any one of numerous suitable and commonly employed devices for controlling the speed of a motor, such as a silicon controlled rectifier, a resistor bank, or other devices. As noted above, the aim of a system according to the preferred embodiment of the present invention is to control the environment of a vehicular passenger compartment in a quick and precise manner. The electronic automatic temperature systems (EATC) used conventionally suffer from a drawback insofar as the flow of ram air through an outside air inlet such as 12 of Figure 1 and then into inlet duct 14 of Figure 2 and then through the balance of the air conditioning system will at least temporarily upset the temperature control of the system. This occurs because the greater mass flow caused by the ram air at a constant heat flux provided by evaporator core 24, heater core 26, and blend door 28 will result in a change in the temperature of the air discharged by the air conditioning system. Conventional systems respond to this type of operating regime by sensing an increase or decrease in the cabin temperature. Waiting for such a perturbation in cabin temperature to occur prior to taking remedial action is not, however, desirable, because the thermal inertia of the vehicle will cause a considerable delay in the restoration of the cabin temperature to the desired set point. If, however, one attempts to control the temperature of the discharged air by merely damping the flow at outside air inlet 12, the results will be unsatisfactory because it is possible under certain operating conditions e.g. with a tailwind impinging on the car, for the flow rate through the air conditioning system to be so low as to negate the effectiveness of a damper in controlling the temperature of the air discharged from the air conditioning system into the interior of the vehicle. To overcome these problems, a system of the preferred embodiment of the invention operates as a subroutine of the main EATC control program according to the flow chart shown in Figure 4. A ram air compensation control program within microprocessor 22 begins at start block 58. Blower speed, S B , and blower power consumption, P B , are sensed at block 60. At block 62, a value for the function f(S B , P B ) is calculated and compared with a preselected value for the function. Several different functions of blower speed and power, as well as other system variables, could be employed for keeping track of the mass flow passed by the blower. One example of such a function could involve taking the quotient comprising blower power consumption divided by blower speed. In any event, the operation at block 62 comprises the detection of non-programmed changes in blower speed and power consumption. Blower power consumption may be determined at any particular time as the product of measured blower motor voltage and current. In general, blower motor power sensor 48 will operate by sensing both the current drawn by motor 18 and the voltage. Knowing these values, the power consumption may be calculated as the product of the current and voltage. Blower current and voltage may be measured according to any of several known methods known in the art and suggested by this disclosure. The results of the comparison at block 62 are used in the following manner. In the event that the calculated function value does not depart from the preselected value by more than an appropriate dead band or hysteresis amount, the microprocessor will know that ram air is not causing a perturbation calling for an adjustment and the program therefore returns to block 60 once again to sense blower speed and power consumption. If, however, the calculated function does differ from the preselected value, the program continues to block 64, wherein adjusted operating points are determined for blower speed and blend door position. The ability to control blend door position in response to ram air changes is important because the blend door controls the heat flux imparted to the air passing through the air conditioning system. Alternatively, the flow of engine coolant through heater core 26, and hence, the flow of heat through the core, could be altered by heater core flow controller 27, and the flow of refrigerant through evaporator core 24 could be altered by means of evaporator flow controller 25. It is desirable to have the capability of controlling not only blower speed and power but also heat flux in response to ram air induced mass flow changes. This conclusion stems from the following considerations. First, with EATC, once a desired temperature operating point has been achieved, blower speed and power will usually be set at a low level. If however, the mass flow through the system increases due to the ram air effect, blower speed will decrease and blower power will increase due to the increased work required to accommodate the increased mass flow. Accordingly, the calculated value of the function f(S B , P B ) will change. Nevertheless, because in this example the blower is already operating at a low speed, the blower will be unable to affect the mass flow through the vehicle greatly, simply because even shutting the blower off will affect the mass flow little for a system designed to have low air-side flow losses. As a result, it will be necessary to maintain the temperature set point by swinging blend door 28 so as to either heat or cool the conditioned air by a greater or lesser extent, thereby changing the heat flux provided by the air conditioning system. Microprocessor 22 will determine the new location for blend door 28 by picking a new location value from a lookup table within the ROM, while using as input variables absolute blower speed, blower speed change, blower power consumption, ambient temperature, cabin temperature, desired temperature, and system operating state (e.g., heating or cooling). As an example, if the blower is operating at three volts out of a total of twelve volts, blower speed will be very low. Accordingly, the microprocessor will know that the position of the blend door must be changed in response to ram air effects. If the air conditioning system is operating in the cooling mode and if the ambient (outside) temperature is 100F, the microprocessor will further know that an increase in ram air should be met by a swing of blend door 28 in the direction such than more of heater core 26 is covered up, such that air passing through evaporator core 24 is not reheated. The lookup table described above could be supplanted by a mathematical formula or algorithm for calculating blend door position and blower program speed. As an alternative to working exclusively with blend door 28 in the example recited above, the same variables and lookup table approach may be employed to alter the operating points of evaporator flow controller 25 and heater core flow controller 27 immediately to either increase or decrease their flow rates, so as to affect the heat flux bearing upon air passing through the air conditioning system. As a further alternative, the blend door could be eliminated, with the heat flux being controlled solely by means of evaporator flow controller 25 and heater core flow controller 27. If for example, it is desired to heat the incoming air to a greater extent, the rate of flow of refrigerant through evaporator core 24 could be reduced while increasing the rate of flow of engine coolant through heater core 26. Conversely, if it is desired to chill the air to a greater extent, the evaporator flow may be increased, while decreasing the heater core flow. In contrast to the situation obtained when the blower is being operated at a low speed, in the event that the vehicle has not reached the specified final interior temperature, as sensed by interior temperature 46, the blower will generally be operating at a high speed. In this case, an increased mass flow through the air conditioning system due to ram air may be compensated for, either wholly, or partially, by a change in blower speed. Accordingly, if blower speed is high and air flow increases, the blower speed will initially decrease and power will increase due to the increased mass flow through the system. The calculated value of the function f(S B , P B ) will change as well. Microprocessor 22 will select a new blower program speed representing a decrease to a new operating point such that the calculated value of f(S B , P B ) is maintained at the preselected value. Because of the nature of the calculations being performed, that it may be necessary to perform the adjustment of blower speed as an iterative process in which the new blower speed is selected by microprocessor 22, the speed is communicated to blower speed governor 20, and the effect of the change noted at block 62 of Figure 4, with further adjustment as required to bring f(S B , P B ) within an acceptable tolerance. In this manner, the mass flow through the air conditioning system and the temperature of air discharged by the system will be maintained at a relatively constant level without the necessity of changing either the blend door position or the operating points of evaporator flow controller 25 or heater core flow controller 27. A system according to the preferred embodiment of the present invention will be useful for maintaining the interior temperature of a vehicle in a situation wherein the vehicle turns from a crosswind into a tailwind. In this type of operating regime, inlet 12 may be subjected to an air pressure which is less than that encountered in still air. As a result, the mass flow through the air conditioning system will decrease. This will be noted at block 60 of Figure 4 as an increase in blower speed and a decrease in blower power consumption. At block 64, microprocessor 22 will determine an increased blower speed, if possible, for increasing the mass flow through the system, so as to maintain the value of f(S B , P B ) constant at a preselected value corresponding to a desired mass flow rate. If it is not possible, however, to increase the blower speed to achieve a constant mass flow rate, blend door 28 will be repositioned to maintain a constant temperature discharge from the air conditioning system. As before, if necessary, evaporator flow controller 25 and heater core flow controller 27 may also give commands so as to affect the heat flux delivered by the system to the incoming mass flow. It is normally preferable to use blend door 28 to accomplish the required changes in heat flux because the blend door is not affected by thermal inertia considerations relevant to evaporator 24 and heater 26.

Claims: An air conditioning system for a vehicle, comprising an air supply blower (16), an evaporator core (24), a heater core (26) and a temperature governing means comprising a blend door (28) operatively associated with said evaporator core (24) and said heater core (26) for controlling the heat flux imported by said evaporator core (24) and said heater core (26) to air supplied by said blower (16) to the interior of said vehicle, characterised by speed sensing means (53) for determining the speed at which said blower (16) is operating and for generating a speed signal corresponding to said blower speed, power sensing means (48) for determining the power being consumed by said blower (16) and for generating a signal corresponding to said power consumption, and control means (22), responsive to said speed signal and said power signal, for operating said blend door (28), comprising means for detecting non-programmed changes in blower speed and blower power consumption; and means for compensating for said non-programmed changes in blower speed and power consumption by changing the position of said blend door (28). An air conditioning system according to Claim 1, also characterised in that said control means (22) further comprises speed governing means (20) for controlling the speed at which said blower (16) is operating and means for compensating for said non-programmed blower speed and power consumption changes by changing the operating point of said speed governing means (20). An air conditioning system according to either Claim 1 or Claim 2, further characterised in that said evaporator (24) contains liquid refrigerant which is vaporised in said core. An air conditioning system according to any preceding claim, further characterised in that said heater core (26) receives engine coolant. An air conditioning system according to any preceding claim further characterised in that said air supply blower (16) comprises an electric motor (18) driving an aerodynamic element. An air conditioning system according to Claim 5, further characterised in that said power sensing means (48) comprises means for sensing the current and voltage applied to said blower motor (18) and means for converting said sensed current and voltage into a signal having a magnitude which is proportional to the power consumption of said blower motor (19). An air conditioning system according to either Claim 5 or 7, further characterised in that said speed sensing means (53) comprises means for sensing electromotive force pulses generated by said blower motor (18) and means for converting said pulses into a signal corresponding to the speed of said blower motor (18). An air conditioning system according to Claim 7, characterised in that said means for converting said pulses into a signal corresponding to the speed of said blower motor (18) comprises means for transforming said pulses into a square wave having a frequency which is equivalent to the frequency of said pulses; and means for counting the frequency of said resultant square wave. An air conditioning system as claimed in Claim 5 further characterised by said heater core (26) is positioned downstream from said evaporator core (24). An air conditioning system as claimed in Claim 5 further characterised in that said temperature governing means further comprises means for controlling the flow of heat through said heater core (26) and the flow of refrigerant through said evaporator core (24).

Inventors: BOLFIK LAWRENCE J, SMITH CALVIN G, BOLFIK, LAWRENCE J., SMITH, CALVIN G.
Applicants: FORD FRANCE, FORD MOTOR CO, FORD WERKE AG, FORD FRANCE S. A., FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1989
Main classification: B60H1
IPC codes: B60H1, G05D23