Method for controlling a fixed displacement compressor of a cooling system of a combustion motor vehicle

Abstract

The invention relates to a method for controlling a fixed displacement compressor (3) of an air conditioning system (1) of a combustion motor vehicle, said compressor (3) being connected to the engine (M) of the motor vehicle by means of a controllable clutch (30), the air conditioning system (1) also comprising an evaporator (6) intended for the passage of an internal air flow (200) through it, the control method comprising a step of determining the temperature of the internal air flow (200) at the outlet of the evaporator (6), - if the temperature of the internal air flow (200) at the outlet of the evaporator (6) is lower than a first threshold value (T1) and the controllable clutch (30) is engaged, the controllable clutch (30) is disengaged so that the compressor (3) no longer rotates, - if the temperature of the internal air flow (200) at the outlet of the evaporator (6) is higher than a second threshold value (T2) and the controllable clutch (30) is disengaged, the controllable clutch (30) is engaged so that the compressor (3) rotates, the temperature value of the first threshold value (T1) being higher than the temperature value of the second threshold value (T2).

Description

[0001] This invention relates to the field of methods for controlling cooling systems of motor vehicles. More particularly, this invention relates to a method for controlling a constant displacement compressor of an air conditioning system for a combustion-type motor vehicle.

[0002] Typically, in combustion-powered motor vehicles, the air conditioning system's compressor is directly driven to rotate by the combustion engine. The compressor's rotation is usually controlled by a controllable clutch to engage or disengage it from the combustion engine. The air conditioning system includes an evaporator, typically located within the heating, ventilation, and air conditioning (HVAC) unit, to cool the interior airflow intended for use inside the vehicle.

[0003] The temperature of the internal airflow at the evaporator outlet is measured and controlled to ensure that the internal airflow reaches a target temperature determined by the user. This control of the air temperature at the evaporator outlet is typically achieved through a cycle of engagement and disengagement of a controllable clutch to set the compressor to run or not run. When the temperature of the internal airflow at the evaporator outlet drops and reaches a minimum threshold, the controllable clutch disengages to stop the compressor and limit the temperature drop. When the temperature of the internal airflow at the evaporator outlet rises and reaches a maximum threshold, the controllable clutch engages to start the compressor and limit the temperature rise. The minimum temperature threshold is lower than the maximum temperature threshold.

[0004] Due to the inertia of the air conditioning system, this control of the minimum and maximum temperature thresholds of the internal airflow at the evaporator outlet causes a considerable variation in the temperature of the internal airflow at the evaporator outlet, for example, ±3 degrees.

[0005] To ensure user comfort, this change is typically compensated for by a heater located within the ventilation and air conditioning system, downstream of the evaporator in the internal airflow. This heater (e.g., an electric heater or a radiator in which the heat transfer fluid of a heat engine's cooling circuit circulates) heats the internal airflow to eliminate its temperature variation and redistribute it within the vehicle interior at a target temperature.

[0006] However, this method of controlling the temperature of the internal airflow at the evaporator outlet is unsatisfactory when the heater is unusable (e.g., in the event of a malfunction, or if the heater is absent, such as in a simple ventilation and air conditioning system).

[0007] Therefore, one of the objectives of this invention is to overcome at least part of the shortcomings of the prior art and to propose an improved control method.

[0008] Therefore, the present invention relates to a method for controlling a constant displacement compressor of an air conditioning system in a combustion engine vehicle, the compressor being connected to the engine of the vehicle for being driven to rotate, the connection having a controllable clutch.

[0009] The air conditioning system also features an evaporator through which internal airflow is directed.

[0010] The air conditioning system has a temperature sensor located at the evaporator to determine the temperature of the internal airflow at the evaporator outlet.

[0011] The control method includes a step of determining the temperature of the internal airflow at the evaporator outlet.

[0012] If the temperature of the internal airflow at the evaporator outlet is below a first threshold, and if the controllable clutch is engaged, then the controllable clutch disengages, causing the compressor to stop rotating.

[0013] If the temperature of the internal airflow at the evaporator outlet is higher than the second threshold, and if the controllable clutch disengages, then the controllable clutch engages, causing the compressor to be driven to rotate.

[0014] The temperature value of the first threshold is higher than the temperature value of the second threshold.

[0015] According to one aspect of the invention, the control method has a first disengagement period and a second engagement period, such that:

[0016] If the temperature of the internal airflow at the evaporator outlet is below a first threshold, if the controllable clutch engages and if a second engagement period has passed, then the controllable clutch disengages, causing the compressor to stop rotating, and the first disengagement period begins.

[0017] If the temperature of the internal airflow at the evaporator outlet is higher than the second threshold, if the controllable clutch disengages and if the first disengagement period has passed, then the controllable clutch engages, causing the compressor to be driven to rotate and initiating the second engagement period.

[0018] According to another aspect of the invention, the first time period and the second time period are determined based on parameters such as the following:

[0019] -Around air temperature,

[0020] - Target temperature of the internal airflow inside the vehicle

[0021] -Compressor rotation speed,

[0022] - The flow rate of the internal airflow.

[0023] - The capacity, size, and performance of different components of the air conditioning system.

[0024] According to another aspect of the invention, the total time of the first disengagement period and the second engagement period is determined such that the frequency of the engagement / disengagement cycle of the controllable clutch is below the limiting frequency.

[0025] According to another aspect of the invention, the first disengagement period is longer than the second engagement period.

[0026] According to another aspect of the invention, a first temperature threshold and a second temperature threshold for the temperature of the internal airflow at the outlet of the evaporator are determined based on parameters such as the following:

[0027] -Around air temperature,

[0028] - Target temperature of the internal airflow inside the vehicle

[0029] - Compressor rotation speed, and

[0030] - The flow rate of the internal airflow.

[0031] According to another aspect of the invention, the controllable clutch is an electromagnetic clutch.

[0032] According to another aspect of the invention, the temperature sensor is disposed against the fins inside the evaporator, and the temperature of the internal airflow at the outlet of the evaporator is determined based on the following:

[0033] - The temperature measured by the temperature sensor

[0034] -Outside air temperature, and

[0035] - The flow rate of the internal airflow.

[0036] According to another aspect of the invention, the temperature sensor is disposed downstream of the evaporator in the internal airflow.

[0037] According to another aspect of the invention, the evaporator is disposed within a ventilation and air conditioning unit, which has no heater downstream of the evaporator in the internal airflow.

[0038] Further features and advantages of the invention will become clearer from the following description, given in a non-limiting manner and with reference to the accompanying drawings, in which:

[0039] Figure 1 A schematic diagram of the air conditioning system is shown.

[0040] Figure 2 A schematic diagram of a heating, ventilation, and air conditioning (HVAC) unit is shown.

[0041] Figure 3A schematic diagram of a ventilation and air conditioning unit is shown.

[0042] Figure 4 A graph showing the change and control of the air temperature at the outlet of the evaporator according to an embodiment of the prior art is presented.

[0043] Figure 5 A graph showing the change and control of the air temperature at the outlet of the evaporator according to the present invention over time is shown.

[0044] In these figures, the same elements are referred to by the same reference numerals.

[0045] The following embodiments are examples. Although the specification relates to one or more embodiments, this does not necessarily mean that every reference numeral refers to the same embodiment, or that these features are applicable only to one embodiment. Individual features of different embodiments may also be combined and / or interchanged to provide other embodiments.

[0046] In this specification, certain elements or parameters may be indexed, such as first element or second element, first parameter and second parameter, or first standard and second standard, etc. In this context, this is merely an index used to distinguish and indicate similar but not identical elements, parameters, or standards. Such indexing does not imply that one element, parameter, or standard takes precedence over another, and such representations are readily interchangeable without departing from the scope of this specification. Nor does such indexing imply any temporal order, for example, when evaluating any given standard.

[0047] In this specification, "upstream" should be understood as relative to the direction of fluid circulation, where one element is placed before another. In contrast, "downstream" should be understood as relative to the direction of fluid circulation, where one element is positioned after another.

[0048] Figure 1 A simplified air conditioning system 1 for a motor vehicle having a combustion engine M is shown. The air conditioning system 1 has the following characteristics in the direction of refrigerant fluid circulation:

[0049] -Compressor 3,

[0050] - Condenser 4, specifically, through which external airflow is intended, and which is located, for example, at the front surface of a motor vehicle.

[0051] -Expansion device 5, such as an expansion valve, and

[0052] - Evaporator 6, internal airflow 200 is designed to pass through the evaporator.

[0053] The air conditioning system 1 may also have a phase separation device 7, such as a storage device, which is located upstream of the compressor 3, between the evaporator 6 and the compressor 3.

[0054] Compressor 3 is a fixed displacement compressor, meaning its displacement is not variable and cannot be adjusted according to cooling capacity requirements. Compressor 3 is connected to the engine M of the motor vehicle, such that engine M drives compressor 3 to rotate. More specifically, compressor 3 is connected to a first pulley 30 via a connecting shaft, and engine M has a second pulley 32, which is typically fixed to the crankshaft. The first pulley 31 and the second pulley 32 are connected by a belt 33 (referred to as an accessory belt). Alternatives with sprockets and chains are also conceivable. The connection between compressor 3 and engine M also includes a controllable clutch 30. More specifically, this clutch can be located on the connecting shaft connecting the first pulley 31 and compressor 3. This controllable clutch 30 can be, for example, an electromagnetic clutch electrically connected to a computer (not shown) that implements the management method.

[0055] Still based on Figure 1 The air conditioning system 1 also has a temperature sensor 20, which is located at the evaporator 6 to determine the temperature of the internal airflow 200 at the outlet of the evaporator 6.

[0056] According to the first embodiment, the temperature sensor 20 can be positioned against the fins inside the evaporator 6. The temperature of the internal airflow 200 at the outlet of the evaporator 6 is then determined based on the following:

[0057] - The temperature measured by the temperature sensor 20,

[0058] - Ambient air temperature, which is typically measured by a dedicated temperature sensor.

[0059] - The rotational speed of compressor 3, and

[0060] - The flow rate of the internal airflow 200, which is typically determined based on the vehicle's travel speed and / or the rotational speed of the fan 101 as described below in this specification.

[0061] In this first embodiment, because the sensor is in direct contact with the evaporator 6, the measured temperature does not directly correspond to the temperature of the internal airflow 200 at the outlet of the evaporator 6. These parameters allow the temperature of the internal airflow 200 at the outlet of the evaporator 6 to be determined by means of a conversion table experimentally established for the evaporator 6. This first embodiment is particularly useful for providing an evaporator 6 with an integrated sensor 20, thereby facilitating assembly and integration.

[0062] According to the second embodiment, the temperature sensor 20 is disposed downstream of the evaporator 6 in the internal airflow 200. This second embodiment allows for direct measurement of the temperature of the internal airflow 200 at the outlet of the evaporator 6.

[0063] Without departing from the scope of the invention, other more complex architectures of the air conditioning system 1 can be contemplated, provided that such architectures include a temperature sensor 20 and an evaporator 6 through which the internal airflow 200 is intended to pass, the temperature sensor being located at the evaporator 6 to determine the temperature of the internal airflow 200 at the outlet of the evaporator 6. The air conditioning system 1 may, for example, be reversible to operate in heat pump mode, thereby heating the internal airflow.

[0064] Figure 2 A heating, ventilation, and air conditioning (HVAC) unit 100 is shown. This HVAC unit 100 has a fan 101 or blower for generating internal airflow. An evaporator 6 is disposed within the HVAC unit 100 to allow internal airflow 200 to pass through it. According to the second embodiment described above, a temperature sensor 20 may be integrated into the HVAC unit 100 downstream of the evaporator 6. Downstream of the evaporator 6, the HVAC unit 100 has a heater 110, such as an electric heater, for heating the internal airflow 200. Still downstream of the evaporator 6, the HVAC unit 100 also has a distribution chamber 102 for redistributing the airflow 200 in ducts 103a, 103b, and 103c. More specifically, these ducts 103a, 103b, and 103c may each have a flap 104 to allow or disallow the passage of internal airflow 200. These ducts 103a, 103b, and 103c can specifically feed the upper portion of the vehicle interior under the windshield, the vehicle interior itself, and the lower portion of the vehicle interior in the direction of the user's feet, respectively. The HVAC unit 100 may also have a mixing flap 105 to redirect the internal airflow 200 at the outlet of the evaporator 6 toward the distribution chamber 102, the heater 110, or both simultaneously.

[0065] Figure 3 A ventilation and air conditioning (VAC) unit 100' is shown. This VAC unit 100' is identical to the heating, ventilation, and air conditioning (HVAC) unit 100, except that there is no heater 110 downstream of the evaporator 6 in the interior airflow 200. This VAC unit 100' is specifically designed for vehicles operating in hot climates where heating of the interior airflow 200 is not required. Furthermore, this VAC unit 100' is more economical because it lacks a heater 110 or a distribution flap 105.

[0066] When the heater 110 is not in operation or when the vehicle is equipped with a ventilation and air conditioning system 100', the target temperature of the internal airflow 200 inside the vehicle can only be controlled by controlling the temperature of the internal airflow 200 at the outlet of the evaporator 6.

[0067] The method for controlling the temperature of the internal airflow 200 includes the step of determining the temperature of the internal airflow 200 at the outlet of the evaporator 6. This determination of the temperature at the outlet of the evaporator 6 is performed by means of a temperature sensor 20. Depending on the location of the temperature sensor 20, it can be performed by direct measurement or by calculation based on different parameters as described above.

[0068] If the temperature of the internal airflow 200 at the outlet of the evaporator 6 is lower than the first threshold T1 (referred to as the disengagement threshold), and if the controllable clutch 30 is engaged, then the controllable clutch 30 disengages, causing the compressor 3 to no longer be driven to rotate.

[0069] If the temperature of the internal airflow 200 at the outlet of the evaporator 6 is higher than the second threshold T2 (referred to as the engagement threshold), and if the controllable clutch 30 disengages, then the controllable clutch 30 engages, causing the compressor 3 to be driven to rotate.

[0070] Figure 4 A graph showing the temperature change over time of the internal airflow 200 at the outlet of the evaporator 6 when the temperature value of the first threshold T1 is lower than the temperature value of the second threshold T2 is shown. Figure 4 In the example shown, the outside air temperature is approximately 25°C, and the target temperature Ttarg at the outlet of evaporator 6 is 10°C. The temperature of the first threshold T1 is 8°C, and the temperature of the second threshold T2 is 8.4°C. The curve showing the temperature change of the internal airflow 200 illustrates a cyclical temperature change of approximately 6°C between the minimum and maximum temperatures.

[0071] First, because the air conditioning system 1 is operating, the temperature of the internal airflow 200 decreases, which means that the controllable clutch 30 engages, and therefore the compressor 3 is rotating. Next, the temperature of the internal airflow 200 reaches a first threshold T1, and the controllable clutch 30 disengages.

[0072] Between the first threshold T1 and the second threshold T2, a curve showing the temperature change of the internal airflow 200 is formed. Figure 4Part A is marked in the diagram. In the first part of this part A, due to the thermal inertia of the air conditioning system 1, the temperature of the internal airflow 200 continues to decrease. The temperature of the internal airflow 200 reaches a minimum value below the first threshold T1. Then, due to the disengagement of the controllable clutch 30 and the stopping of the compressor 3, the temperature of the internal airflow 200 rises until it reaches the second threshold T2. Then, the controllable clutch 30 engages to set the compressor 3 to rotate again and restart the air conditioning system 1.

[0073] Between the second threshold T2 and the first threshold T1, a curve showing the temperature change of the internal airflow 200 is formed. Figure 4 Part B is marked in the diagram. In the first part of this part B, due to the thermal inertia of the air conditioning system 1 and the restart of the air conditioning system 1, the temperature of the internal airflow 200 continues to rise. The temperature of the internal airflow 200 reaches a maximum value higher than the second threshold T2. Then, due to the engagement of the controllable clutch 30 and the restart of the compressor 3, the temperature of the internal airflow 200 drops again until it reaches the first threshold T1 again.

[0074] Figure 5 It also shows a graph of the temperature change of the internal airflow 200 at the outlet of the evaporator 6 over time when the temperature value of the first threshold T1 is higher than the temperature value of the second threshold T2. The curve of the temperature change of the internal airflow 200 at the outlet of the evaporator 6 has a similar shape to... Figure 4 The outline of the curve is shown. However, because the temperature value of the first threshold T1 is higher than the temperature value of the second temperature threshold T2, the curve showing the temperature change of the internal airflow 200 shows a temperature cycle of approximately 4°C between the lowest and highest temperatures. These changes are less than... Figure 4 The changes in temperature circulation result in a more constant airflow within the vehicle, thus improving comfort. This reduction in temperature cyclical variation is due to the inertia of the air conditioning system 1 being anticipated and compensated for.

[0075] The first temperature threshold T1 and the second temperature threshold T2 of the internal airflow 200 at the outlet of the evaporator 6 are preferably variable and determined according to parameters such as the following:

[0076] -Around air temperature,

[0077] - The target temperature of the internal airflow inside the vehicle is 200.

[0078] - The rotational speed of compressor 3, and

[0079] - Internal airflow rate of 200.

[0080] The external air temperature, the rotational speed of compressor 3, and the flow rate of internal airflow 200 allow for characterization of the cooling capacity of air conditioning system 1. Next, a first threshold T1 and a second threshold T2 are determined according to experimental tables to achieve the target temperature of the internal airflow 200 inside the vehicle. Figure 5 In the example shown, the first threshold T1 is approximately 9.5°C, and the second threshold T2 is approximately 8.5°C.

[0081] In addition, when determining the first threshold T1 and the second threshold T2, parameters such as the capacity, size and performance of different components of the air conditioning system can also be considered.

[0082] To limit the frequency of engagement / disengagement cycles of the controllable clutch 30 and thus maintain the service life of the controllable clutch 30 and the compressor 3, the control method can have a first disengagement period D1 during which the controllable clutch 30 cannot re-engage and a second engagement period D2 during which the controllable clutch 30 can disengage. This can be achieved... Figure 5 The first time period D1 and the second time period D2 can be seen in the data.

[0083] Therefore, if the temperature of the internal airflow 200 at the outlet of the evaporator 6 is lower than the first threshold T1, if the controllable clutch 30 engages and if the second engagement period D2 has passed, then the controllable clutch 30 disengages, causing the compressor 3 to no longer be driven to rotate, and the first disengagement period D1 begins.

[0084] Similarly, if the temperature of the internal airflow 200 at the outlet of the evaporator 6 is higher than the second threshold T2, if the controllable clutch 30 disengages and if the first disengagement period D1 has passed, then the controllable clutch 30 engages, causing the compressor 3 to be driven to rotate and the second engagement period D2 to begin.

[0085] In the same manner as the first threshold T1 and the second threshold T2, the first time period D1 and the second time period D2 can be determined based on parameters such as the following:

[0086] -Around air temperature,

[0087] - The target temperature of the internal airflow inside the vehicle is 200.

[0088] - The rotational speed of compressor 3, and

[0089] - Internal airflow rate of 200.

[0090] In addition, when determining the first time period D1 and the second time period D2, parameters such as the capacity, size and performance of different components of the air conditioning system can also be considered.

[0091] The external air temperature, the rotational speed of the compressor 3, and the flow rate of the internal airflow 200 allow the cooling capacity of the air conditioning system 1 to be characterized. Next, a first time period D1 and a second time period D2 are determined according to the experimental table to achieve the target temperature of the internal airflow 200 inside the vehicle.

[0092] Furthermore, the total time of the first disengagement period D1 and the second engagement period D2 can be determined such that the frequency of the engagement / disengagement cycle of the controllable clutch 30 is below the limit frequency. This makes it particularly possible to meet the manufacturer's requirements regarding the frequency of these cycles. For example, the maximum cycle frequency could be approximately four or five cycles per minute.

[0093] Preferably, the first disengagement period D1 is longer than the second engagement period D2. Specifically, the disengagement time of the controllable clutch 30 and the stopping of the compressor 3 (partly due to the inertia of the air conditioning system 1) are longer than the engagement time of the controllable clutch 30 and the restarting of the compressor 3 (also partly due to the inertia of the air conditioning system 1). Therefore, for example, for... Figure 5 The experimental conditions are the same as those in the experiment, that is, an external temperature of 25°C and a target temperature Ttarg of 10°C at the outlet of evaporator 6. The first time interval D1 can be about 7 seconds, and the second time interval D2 can be about 5 seconds. The first time interval D1 and the second time interval D2 enable a cycle frequency of less than 5 cycles per minute.

[0094] Therefore, it is clear that the fact that the temperature value of the first threshold T1 is higher than the temperature value of the second threshold T2 makes it possible to limit the magnitude of temperature variation in the method used to control the temperature of the internal airflow 200 at the outlet of the evaporator 6, and thus this allows for a higher level of comfort inside the vehicle, and the temperature of the internal airflow 200 is perceived as more constant.

Claims

1. A method for controlling a constant displacement compressor (3) of an air conditioning system (1) of a combustion-type motor vehicle, the compressor (3) being connected to an engine (M) of the motor vehicle for being driven to rotate, the connection having a controllable clutch (30). The air conditioning system (1) also has an evaporator (6), through which the internal airflow (200) is intended to pass. The air conditioning system (1) has a temperature sensor (20) located at the evaporator (6) to determine the temperature of the internal airflow (200) at the outlet of the evaporator (6). The control method includes the step of determining the temperature of the internal airflow (200) at the outlet of the evaporator (6). - If the temperature of the internal airflow (200) at the outlet of the evaporator (6) is lower than a first threshold (T1), and if the controllable clutch (30) is engaged, then the controllable clutch (30) disengages, causing the compressor (3) to no longer be driven to rotate. - If the temperature of the internal airflow (200) at the outlet of the evaporator (6) is higher than the second threshold (T2), and if the controllable clutch (30) disengages, then the controllable clutch (30) engages, causing the compressor (3) to be driven to rotate. The temperature value of the first threshold (T1) is higher than the temperature value of the second threshold (T2).

2. The control method as described in the preceding claim, characterized in that, The control method has a first disengagement period (D1) and a second engagement period (D2), such that: - If the temperature of the internal airflow (200) at the outlet of the evaporator (6) is lower than the first threshold (T1), if the controllable clutch (30) engages and if the second engagement period (D2) has passed, then the controllable clutch (30) disengages, so that the compressor (3) is no longer driven to rotate, and the first disengagement period (D1) begins. - If the temperature of the internal airflow (200) at the outlet of the evaporator (6) is higher than the second threshold (T2), if the controllable clutch (30) disengages and if the first disengagement period (D1) has passed, then the controllable clutch (30) engages, causing the compressor (3) to be driven to rotate and the second engagement period (D2) to begin.

3. The control method as described in the preceding claim, characterized in that, The first disengagement period (D1) and the second engagement period (D2) are determined based on the following parameters: - Ambient air temperature, - The target temperature of the internal airflow (200) inside the vehicle. - The rotational speed of the compressor (3), and - The flow rate of the internal airflow (200).

4. The control method as described in any one of claims 2 and 3, characterized in that, The total time of the first disengagement period (D1) and the second engagement period (D2) is determined such that the frequency of the engagement / disengagement cycle of the controllable clutch (30) is below the limit frequency.

5. The control method as described in claim 2, characterized in that, The first disengagement period (D1) is longer than the second engagement period (D2).

6. The control method according to claim 1, characterized in that, The first temperature threshold (T1) and the second temperature threshold (T2) of the internal airflow (200) at the outlet of the evaporator (6) are determined according to the following parameters: - Ambient air temperature, - The target temperature of the internal airflow (200) inside the vehicle. - The rotational speed of the compressor (3), and - The flow rate of the internal airflow (200).

7. The control method according to claim 1, characterized in that, The controllable clutch (30) is an electromagnetic clutch.

8. The control method as described in claim 1, characterized in that, The temperature sensor (20) is disposed against the fins inside the evaporator (6), and the temperature of the internal airflow (200) at the outlet of the evaporator (6) is determined according to the following: - The temperature measured by the temperature sensor (20), - Ambient air temperature, and - The flow rate of the internal airflow (200).

9. The control method as described in claim 1, characterized in that, The temperature sensor (20) is located downstream of the evaporator (6) in the internal airflow (200).

10. The control method according to claim 1, characterized in that, The evaporator (6) is located within a ventilation and air conditioning unit (100'), which does not have a heater (110) downstream of the evaporator (6) in the internal airflow (200).

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