DEVICE FOR CONTROLLING THE CAPACITY OF A COMPRESSOR

Abstract: A control system for a variable capacity compressor (20) in an automotive air conditioning system is disclosed. The control device includes a first sensor (42) disposed forward of an evaporator (24), a second sensor (43) disposed behind the evaporator and a third sensor (44) disposed at the outside of a compartment. The control device (40) compares the air temperature detected by the sensors with predetermined temperatures, and controls the capacity from the results of these comparisons.

Description: The present invention relates to a device for controlling the capacity of a variable type compressor in an automobile air conditioning system, and more particularly, to a device which controls the capacity of the compressor in accordance with the air conditioning load. Generally, the air conditioning system of an automobile is driven by the vehicle engine through an electromagnetic clutch. The air conditioning system is designed to achieve a predetermined air conditioning performance of a predetermined air conditioning load when the automobile is driven at an average speed. This, when the vehicle engine is idling or is being driven at lower speeds, the rotational speed of the compressor is correspondingly low. Therefore, the performance of the air conditioning system is adversely effected. On the other hand, when the vehicle is driven at high speeds, the rotational speed of the compressor is too high for efficient performance. Thus, electromagnetic clutches are used to control the rotational speed of the compressor under varying drive speeds by intermittently stopping and starting the compressor. However, there are many problems associated with continuously cycling the clutch on and off. For example, when the engine is driven at high speeds and the capacity of the air conditioning system is large, it is necessary for the electromagnetic clutch to be turned on and off frequently. Therefore, large loads sufficient to drive the compressor are intermitently applied to the engine. On the other hand, at low speed or when the vehicle engine is idling, the compressor is not sufficiently driven to maintain the desired temperature in the vehicle. In order to solve the above mentioned problems, a system which controls the capacity of a compressor by detecting the temperature at the outlet side of the air conditioning system evaporator is proposed in published Japanese Application No. JP-A-58-30. In such a system, the performance of the air conditioning system is not directly detected. For example, even though the temperature inside the vehicle may be high, the capacity of the air conditioning system is reduced when the temperature at the outlet side of the evaporator becomes lower than a predetermined temperature. Thus, the capacity of the system is insufficient to cool the vehicle. In addition, when the vehicle is running, the capacity of the air conditioning system is changed frequently, thereby placing great stress and strain on the air conditioning system. It is a primary object of this invention to provide a device for controlling the capacity of a variable type compressor in an automotive air conditioning system in order to provide a more reliable and durable system than those known in the prior art. It is another object of this invention to provide a device for controlling the capacity of a variable type compressor in an automotive air conditioning system wherein the outlet temperature of the air is changed slightly even if the driving condition of the compressor is changed drastically. The above objects of this invention are achieved by providing a control device which includes a first temperature detecting sensor disposed forward of the evaporator for detecting a first air temperature at the inlet side of the evaporator, a second temperature detecting sensor disposed behind the evaporator for detecting a second air temperature at the outlet side of the evaporator, a third temperature detecting sensor for detecting a third air temperature at the outside of a compartment, and a control unit. The control unit compares the detected air temperature with predetermined temperatures and controls the capacity of the compressor in accordance with compared results. Further objects, features and advantages of this invention will be understood from the following detailed description of the preferred embodiments of the invention with reference to the attached drawings. Figure 1 is a block diagram of the air conditioning system; Figure 2 is a graph illustrating the relationship between a medium air conditioning load and a medium vehicle speed; Figure 3 is a graph illustrating the relationship between a low air conditioning load in air mixed mode. Figure 4 is a flow chart illustrating the operation of the control system. Referring to Figure 1, there is shown an automotive air conditioning system which is driven by an engine 30. The air conditioning system comprises a compressor 20, condenser 21, receiver-dryer 22, expansion valve 23 and evaporator 24 connected in series with one another. The compressor 20 is a variable capacity mechanism, the capacity of which can be varied by operating a capacity control mechanism 41 on a signal from a control unit 40. Where the compressor 20 is of the scroll type, the capacity changing mechanism 41 comprises an electromagnetic bypass valve which connects the inlet of the compressor to the intermediate fluid pockets through an intermediate chamber as shown in US-A-4468178. Also, the operation of the compressor 20 is controlled by an electromagnetic clutch 25 mounted on the compressor 20 which operates the signal from the control unit 40. As shown in Figure 1, the evaporator 24 is disposed in a duct 5. A first sensor 42 is disposed at the inlet side of the evaporator 24 and a second sensor 43 is disposed at the outlet side of the evaporator 24. A third sensor 44 is disposed on the exterior of the automobile. The three sensors 42, 43 and 44 are connected to the control unit 40 which compares the detected temperature values with predetermined values and then sends appropriate capacity control signals to the capacity control mechanism 41 to effect a change in the capacity of the compressor 20 or to start or stop the operation of the compressor 20 through the electromagnetic clutch 25. A heater 31 disposed in the duct 5 is connected to the engine 30 and receives coolant from the engine 30 for heating the vehicle when the outside temperature is cold. A damper 32 disposed forward of the heater 31 controls the temperature of the discharged air by control of the angle of its opening. A blower 6 is also disposed forward of the evaporator 24, and the air introduced into the duct 5 is forced by the blower 6 and discharged into the vehicle compartment. With reference to Figure 4, there is shown a flowchart which illustrates the operation of the control unit 40. When the air conditioning system is turned on in step 50 the compressor 20 is operated at a predetermined low capacity (step 51). After the air conditioning system has been operated for a predetermined time T (step 52), control passes to step 53 which sets a comparator mechanism to compare the air temperature C at the outside of the vehicle compartment with a predetermined temperature I. When air temperature C is higher than predetermined temperature I, step 53 proceeds to step 54 which sets the capacity control mechanism 40 to operate the compressor 20 with a large volume. Otherwise, if air temperature C is lower than the predetermined temperature I, step 53 proceeds to step 66 which sets a comparator mechanism to compare the air temperature A at the inlet side of the evaporator 24 with a predetermined temperature Ta. When the air temperature A is higher than the predetermined temperature Ta, step 66 proceeds to step 54, i.e. compressor 20 is operated with a large volume. Otherwise, if temperature A is lower than first predetermined temperature Ta, step 66 proceeds to step 61 which sets the capacity control mechanism 40 to operate the compressor 20 with a small volume. Step 55 sets a comparator mechanism to compare the air temperature A with a second predetermined temperature Tb. When air temperature A is higher than the second predetermined temperature Tb, step 55 proceeds to step 56. Otherwise, if the air temperature A is lower than the second predetermined temperature Tb, step 55 proceeds to step 61 which sets the capacity control mechanism 40 to operate the compressor 20 with a small volume. Step 56 sets a comparator mechanism to compare the air temperature C at the exterior of the vehicle with a comparison predetermined temperature II. When air temperature C is higher than comparison predetermined temperature II, step 56 proceeds to step 57 which sets the values of predetermined temperatures Tc, Td as third and fourth predetermined temperatures. Otherwise, step 56 proceeds to steps 67, 68 which sets values Tc, Td of third and fourth predetermined temperatures. At step 67, values Tc′, Td′ are produced by adding an incremental value ΔT to Tc, Td respectively and, at step 68, the values of Tc, Td are made equal to Tc′ and Td′ as third and fourth predetermined temperatures. Steps 57 and 68 proceed to step 58 which sets the comparator mechanism to compare the air temperature A with the first predetermined temperature Ta. When the air temperature A is higher than the first predetermined temperature Ta, step 58 proceeds to step 62 which sets the comparator mechanism to compare the air temperature B at the outlet side of the evaporator 24 with a fifth predetermined temperature Tf. Otherwise, step 58 proceeds to step 59 which sets the comparator mechanism to compare the air temperature B with the third predetermined temperature Tc, and step 59 proceeds to step 60 which sets the comparator mechanism to compare the air temperature B with the fourth predetermined temperature Td. Otherwise, step 59 proceeds back to step 53. When the air temperature B is higher than the fourth predetermined temperature Td, step 60 proceeds to step 61 which sets the capacity control mechanism 40 to operate the compressor 20 with a small volume. Step 61 proceeds to step 62 which sets the comparator mechanism to compare the air temperature B with the fifth predetermined temperature Tf. When the air temperature B is higher than the fifth predetermined temperature Tf, step 62 proceeds to step 69 which sets a detecting device to detect whether the compressor 20 is operating with a large volume or not. When the compressor 20 is operating with a large volume, step 69 proceeds back to step 53. Otherwise, step 69 proceeds back to step 55. When air temperature B is not higher than the fifth predetermined temperature Tf, step 62 proceeds to step 63 which sets a stop mechanism to stop the operation of the compressor 20. Step 63 proceeds to step 64 which sets the comparator mechanism to compare the air temperature B with a sixth predetermined temperature Te. When the air temperature B is higher than the sixth predetermined temperature Te, step 64 proceeds to step 65 which again drives the compressor 20, and then step 65 proceeds back to step 55. Otherwise, step 64 proceeds back to step 63, and compressor 20 continues to remain stopped until air temperature B exceeds the sixth predetermined temperature Te. In this example, changing the volume of the compressor 20 is not confined to two steps. Although the third predetermined temperature Tc is required to be higher than the fourth predetermined temperature Td and the sixth predetermined temperature Te needs to be higher than the fifth predetermined temperature Tf, the height of each of the third, fourth, fifth and sixth predetermined temperatures does not need to be fixed. Referring to Figure 2, where is shown a graph illustrating the changes in the air temperature B in relation to compressor volume, air temperature A at the inlet side of evaporator 24, and air temperature C at the outside of the compartment. When air temperature A at the inlet side of the evaporator 24 is higher than the first predetermined temperature Ta, the compression volume of the compressor 20 is maintained large. On the other hand, when the air temperature A at the inlet side of the evaporator 24 is below the second predetermined temperature Tb, the compression volume of the compressor 20 is maintained small. Also, when the air temperature A is changed within the range between the first predetermined temperature Ta and the second predetermined temperature Tb, the compression volume of the compressor 20 is changed in accordance with changes of air temperature B at the outlet side of evaporator the 24. The third predetermined temperature Tc is predetermined to be higher than the fourth predetermined temperature Td. When air temperature C at the outside of the compartment changes within the range between the comparison predetermined temperatures I, II, predetermined temperatures Tc, Td for varying the compression volume of the compressor 20 are changed into predetermined temperatures Tc′, Td′, and thus, the proportion of the operation of the compressor with a small compression volume to that with a large volume is increased. Predetermined temperatures Tc, Td are changed into predetermined temperatures Tc′, Td′ by incrementing them by ΔT as described above. Referring to Figure 3, there is shown the condition for variable control when the air conditioning load is low. In this example, an air conditioning system is operated in air mixed mode in which air which is cooled with an evaporator and air which is heated in a heater are mixed in an air duct. Such a mode is mainly used for decreasing humidity for air in a compartment in winter and with circulation of air within the compartment, the air temperature A at the inlet side of evaporator 24 is controlled so as to be higher than the air temperature C. The sixth predetermined temperature Te is predetermined to be higher than the fifth predetermined temperature Tf. In such a condition, when air temperature C at the outside of a compartment is lower than the comparison predetermined temperature I and the air temperature A at the inlet side of the evaporator 24 is lower than the first predetermined temperature Ta, the compression volume of compressor 20 is maintained small. When the air temperature A at the outlet side of the evaporator 24 is below the fifth predetermined temperature Tf, an electromagnetic clutch 25 mounted on the compressor 20 stops operation. When the air temperature B is higher than the sixth predetermined temperature Te, the electromagnetic clutch 25 is turned on, and compressor 20 is started, for operation with a small compression volume.

Claims: 1. A device for controlling the capacity of a variable capacity compressor (20) having an evaporator (24) and a compressor capacity changing means (41), the device comprising; first temperature detecting means (43) adjacent the evaporator inlet for detecting a first air temperature (B) at an outlet side of the evaporator; second temperature detecting means (42) for detecting a second air temperature (A) at an outlet side of the evaporator; third temperature detecting means (44) disposed for detecting a third air temperature (C) at the outside of a compartment; and control means (40) for controlling the capacity changing means (41), the control means including first comparison means (53) for comparing a first predetermined comparison temperature (I) with the third air temperature (C) and providing a first control signal when the third air temperature (C) is higher than the first predetermined comparison temperature (I), the capacity changing means (41) changing the capacity of the compressor to a large capacity (54) in response to the first control signal, second comparison means (66) for comparing a first predetermined temperature (Ta) with the second air temperature (A) in response to the comparison by the first comparison means (53) and the absence of the first control signal, the second comparison means (66) providing a second control signal when the second air temperature (A) is higher than the first predetermined temperature (Ta), in response to the second control signal the capacity changing means (41) changing the capacity of the compressor to a large capacity (54) and in the absence of the second control signal the capacity changing means (41) changing the capacity of said compressor to a small capacity (61), third comparison means (55) for comparing a second predetermined temperature (Tb) with the second air temperature (A) and providing a third control signal when the second air temperature (A) is higher than the second predetermined temperature (Tb), the capacity changing means (41) changing the capacity of the compressor to a small capacity (61) in the absence of the third control signal, fourth comparison means (56) for comparing a second predetermined comparison temperature (II) with the third air temperature (C) in response to the comparison by the third comparison means (55) and the presence of the third control signal and providing a fourth control signal when the third air temperature (C) is higher than the second predetermined comparison temperature (II), in response to the fourth control signal third (Tc) and fourth (Td) predetermined temperatures are set and in the absence of the fourth control signal a fifth predetermined temperature (Tc′) is set which is an incremented value of the third predetermined temperature (Tc) and a sixth predetermined temperature (Td′) is set which is an incremented value of the fourth predetermined temperature (Td), fifth comparison means (58) for comparing the first predetermined temperature (Ta) with the second air temperature (A) and providing a fifth control signal when the second air temperature (A) is higher than the first predetermined temperature (Ta), sixth comparison means (59) for comparing the third predetermined temperature (Tc) with the first air temperature (B) in response to the comparison by the fifth comparison means (58) and the absence of the fifth control signal, the sixth comparison means (59) providing a sixth control signal when the third predetermined temperature (Tc) is higher than the first air temperature (B), seventh comparison means (60) for comparing the fourth predetermined temperature (Td) with the first air temperature (B) in response to the comparison by the sixth comparison means (59) and the presence of the sixth control signal, the seventh comparison means (60) providing a seventh control signal when the first air temperature (B) is higher than the fourth predetermined temperature (Td), the capacity changing means (41) changing the capacity of the compressor to a small capacity (61) in the absence of the seventh control signal, eighth comparison means (62) comparing an eighth predetermined temperature (Tf) with the first air temperature (B) and providing an eighth control signal when the first air temperature (B) is higher than the eighth predetermined temperature (Tf), the compressor (20) being turned off in the absence of the eighth control signal, and ninth comparison means (64) comparing a seventh predetermined temperature (Te) with the first air temperature (B) in response to the comparison by the eighth comparison means (64) and the absence of the eighth control signal, the ninth comparison means (64) providing a ninth control signal when the first air temperature (B) is higher than the seventh predetermined temperature (Te), in the presence of the ninth control signal the compressor (20) being turned on and in the absence of the ninth control signal the compressor (20) being turned off. 2. The device of claim 1, wherein the control means further includes determination means (69) for determining whether the compressor (20) is operating with a small capacity in response to the comparison by the eighth comparison means (63) and the presence of the eighth control signal, the determination means providing a tenth control signal when the compressor (20) is operating with a small capacity. 3. The device of claim 2, wherein in response to the determination by the determination means (69) and the presence of the tenth control signal, the first comparison means (53) is controlled to make the comparison between the first predetermined comparison temperature (I) and the third air temperature (C). 4. The device of claim 2, wherein in response to the determination by the determination means (69) and the absence of the tenth control signal, the third comparison means (55) is controlled to make the comparison between the second predetermined temperature (Tb) and the second air temperature (A). 5. The device of claim 1, wherein in response to the comparison by the fifth comparison means (58) and the presence of the fifth control signal, the eighth comparison means (62) is controlled to make the comparison between the eighth predetermined temperature (Tf) and the first air temperature (B). 6. The device of claim 1, wherein in response to the comparison by the sixth comparison means (59) and the absence of the sixth control signal, the first comparison means (53) is controlled to make the comparison between the first predetermined comparison temperature (I) and the third air temperature (C). 7. The device of claim 1, wherein in response to the comparison by the seventh comparison means (60) and the presence of the seventh control signal, the third comparison means (55) is controlled to make the comparison between the second predetermined temperature (Tb) and the second air temperature (A). 8. The device of claim 1, wherein in response to the comparison by the ninth comparison means (64) and the presence of the ninth control signal, the third comparison means (55) is controlled to make the comparison between the second predetermined temperature (Tb) and the second air temperature (A). 9. A method of controlling the capacity of a variable capacity compressor (20) having an evaporator (24) and a compressor capacity changing means (41), using a device according to claim 1, the method comprising: comparing in the first comparison means (53) a first predetermined comparison temperature (I) with the third air temperature (C) and providing a first control signal when the third air temperature (C) is higher than the first predetermined comparison temperature (I), the capacity changing means (41) changing the capacity of the compressor to a large capacity (54) in response to the first control signal, comparing in the second comparison means (66) a first predetermined temperature (Ta) with the second air temperature (A) in response to the comparison by the first comparison means (53) and the absence of the first control signal, the second comparison means (66) providing a second control signal when the second air temperature (A) is higher than the first predetermined temperature (Ta), in response to the second control signal the capacity changing means (41) changing the capacity of the compressor to a large capacity (54) and in the absence of the second control signal the capacity changing means (41) changing the capacity of said compressor to a small capacity (61), comparing in the third comparison means (55) a second predetermined temperature (Tb) with the second air temperature (A) and providing a third control signal when the second air temperature (A) is higher than the second predetermined temperature (Tb), the capacity changing means (41) changing the capacity of the compressor to a small capacity (61) in the absence of the third control signal, comparing in the fourth comparison means (56) a second predetermined comparison temperature (II) with the third air temperature (C) in response to the comparison by the third comparison means (55) and the presence of the third control signal and providing a fourth control signal when the third air temperature (C) is higher than the second predetermined comparison temperature (II), in response to the fourth control signal third (Tc) and fourth (Td) predetermined temperatures are set and in the absence of the fourth control signal a fifth predetermined temperature (Tc′) is set which is an incremented value of the third predetermined temperature (Tc) and a sixth predetermined temperature (Td′) is set which is an incremented value of the fourth predetermined temperature (Td), comparing in the fifth comparison means (58) the first predetermined temperature (Ta) with the second air temperature (A) and providing a fifth control signal when the second air temperature (A) is higher than the first predetermined temperature (Ta), comparing in the sixth comparison means (59) the third predetermined temperature (Tc) with the first air temperature (B) in response to the comparison by the fifth comparison means (58) and the absence of the fifth control signal, the sixth comparison means (59) providing a sixth control signal when the third predetermined temperature (Tc) is higher than the first air temperature (B), comparing in the seventh comparison means (60) the fourth predetermined temperature (Td) with the first air temperature (B) in response to the comparison by the sixth comparison means (59) and the presence of the sixth control signal, the seventh comparison means (60) providing a seventh control signal when the first air temperature (B) is higher than the fourth predetermined temperature (Td), the capacity changing means (41) changing the capacity of the compressor to a small capacity (61) in the absence of the seventh control signal, comparing in the eighth comparison means (62) an eighth predetermined temperature (Tf) with the first air temperature (B) and providing an eighth control signal when the first air temperature (B) is higher than the eighth predetermined temperature (Tf), the compressor (20) being turned off in the absence of the eighth control signal, and comparing in the ninth comparison means (64) a seventh predetermined temperature (Te) with the first air temperature (B) in response to the comparison by the eighth comparison means (64) and the absence of the eighth control signal, the ninth comparison means (64) providing a ninth control signal when the first air temperature (B) is higher than the seventh predetermined temperature (Te), in the presence of the ninth control signal the compressor (20) being turned on and in the absence of the ninth control signal the compressor (20) being turned off.

Inventors: SATO, MOTOHARU
Applicants: SANDEN CORPORATION
Application year: 1987
Main classification: G05D23
IPC codes: F25B49, F24F11, G05D23, B60H1