Abstract:
An internal combustion engine has an engine shut-down system that automatically interrupts engine operation when vehicle operation indicates that no torque is required from the engine. An air conditioner compressor operates to cool a passenger compartment of the vehicle and is actuated in a first phase time, and is not actuated in a second phase time. An override system compares the time the compressor is in the enabled first phase time to the time the compressor is in the disabled second phase time. The override system disables the engine shut-down system unless it is determined that a ratio of the disabled second phase time to the enabled first phase time has a low rate of change, that the ratio is greater than a predetermined value, and that the time the compressor is in the disabled second phase is greater than a predetermined value.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an engine system in a vehicle that overrides an engine shut-down system based upon the operation of the air conditioner compressor of the vehicle. 
     2. Background 
     Full hybrid vehicles are vehicles that are equipped with a battery-powered motor that is capable of propelling the vehicle without assistance from an internal combustion engine. Mild hybrid and other “Stop/Start” vehicle system configurations are vehicles that enable engine to be turned off whenever the vehicle is coasting, braking, and/or stopped, yet restarted quickly when required. When the driver presses the gas pedal to accelerate the vehicle, the engine is required to restart quickly to accelerate the vehicle. As opposed to a full hybrid, mild hybrids do not have an exclusive electric-only mode of propulsion and therefore rely on the quick restart of the combustion engine to accelerate the vehicle on demand. 
     Conventional air conditioners are driven by the engine in a mild hybrid vehicle. During the time that the engine is in a shut-down mode, the compressor of the air conditioner is no longer powered by the engine, and therefore does not work to compress fluid in the air conditioning system. Therefore, air conditioning systems in mild hybrid vehicles lose effectiveness while the engine is temporarily shut down. 
     It is necessary to maintain passenger comfort while the engine of a mild hybrid is in shut-down mode. One way to maintain passenger comfort includes the use of a system that restarts the engine whenever the air in the vehicle cabin becomes too warm. One problem with this approach is that the engine may frequently stop and restart to reach and maintain an optimal cabin temperature. Frequent engine stopping and restarting may be referred to as “on/off busyness” that is objectionable to vehicle occupants. Another way to maintain passenger comfort includes the use of temperature sensors, humidity sensors, and sun load sensors to predict when the shut-down mode would be undesirable. These sensors are typically expensive and therefore undesirable in some vehicles. Algorithms are typically used in combination with these sensors to maintain passenger comfort. 
     There is currently a need for a cost effective system by eliminating or minimizing the use of sensors while assuring the comfort of vehicle occupants without unwanted turning off and restarting of the engine. 
     SUMMARY 
     According to one aspect of the present disclosure, an engine system for a vehicle is provided. The engine system includes an internal combustion engine that has an engine automatic shut-down system. The engine shut-down system automatically interrupts engine operation when vehicle operation indicates that no torque is required from the engine. For example, the engine shut-down system may conserve energy and shut the engine down if the vehicle is coasting, braking, or stopped. An air conditioner compressor operates to cool a passenger compartment of the vehicle. The compressor is actuated in a first phase time, and is not actuated in a second phase time. An override system compares the time the compressor is in the enabled first phase time to the time the compressor is in the disabled second phase time. The override system disables the engine shut-down system unless it is determined that a ratio of the disabled second phase time to the enabled first phase time has a low rate of change, that the ratio is greater than a predetermined value, and that the time the compressor is in the disabled second phase is greater than a predetermined value. 
     In another aspect of the present disclosure, an engine system includes an engine and an air conditioner that cools a passenger compartment of the vehicle. The air conditioner includes a clutch that engages and disengages a compressor in a duty cycle. The engine shut-down system automatically interrupts engine operation when vehicle operation indicates that no torque is required from the engine. An override system monitors the duty cycle of the clutch and decides whether or not to disable the engine shut-down system. The override system disables the engine shut-down system unless the duty cycle has a rate of change of approximately zero, is greater than a predetermined ratio, and the compressor is disengaged for at least a predetermined time. 
     According to another aspect of the present disclosure, an air conditioning system is provided for a vehicle that has an engine and an engine shut-down system that automatically stops the engine. The air conditioning system includes a compressor and a clutch that engages and disengages the compressor in an activated phase and a deactivated phase, respectively. A clutch status signal generator generates a clutch status signal, indicating that the clutch is either in the activated phase or in the deactivated phase. A control module monitors the clutch status signal, and according to the signal either enables or disables the engine stop system. The control module may determine the ratio of the time the clutch is in the deactivated time to the time the clutch is in the activated time. The control module enables the engine stop system if this ratio has a rate of change that is approximately zero, if the ratio is greater than a predetermined ratio, and if the deactivated phase time is greater than a predetermined time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing the structure of an engine system for a vehicle according to at least one embodiment of the present disclosure; 
         FIG. 2  is a flow chart showing an override system that overrides an engine shut-down system according to one embodiment of the present disclosure; 
         FIG. 3  is a flow chart showing an override system that overrides an engine shut-down system according to an alternative embodiment of the present disclosure; 
         FIG. 4  is a flow chart showing an override system that overrides an engine shut-down system according to another alternative embodiment of the present disclosure; 
         FIG. 5  is a graph showing an example of the compressor state, the cabin temperature, and the evaporator temperature as the cabin temperature is pulled down and stabilized; and 
         FIG. 6  is graph showing an example of the compressor state, the cabin temperature, and the evaporator temperature while the cabin temperature is stabilized. 
     
    
    
     DETAILED DESCRIPTION 
     Detailed embodiments of the present disclosure are disclosed, but it should be understood that the disclosed embodiments may be embodied in various and alternative forms. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. Specific structural and functional details disclosed by Applicant are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art how to practice the present disclosure. 
     Referring to  FIG. 1 , a vehicle system  10  is shown that has an engine  12  and an engine shut-down system  14 . The engine shut-down system shuts down the engine  12  to conserve fuel when vehicle operation indicates that no torque is required from the engine (e.g. when the vehicle is coasting, braking, and/or stopped). The engine load must be below a predetermined value in order to trigger the engine shut-down system  14  to shut down the engine  12 . An air conditioner compressor  16  is actuated by a clutch  18  and power is transmitted from the engine  12 , through a belt  20  and to the clutch  18  that actuates the compressor  16 . When the compressor  16  is actuated by the clutch  18 , cool air may be provided to vehicle occupants from an air conditioning system. Air conditioning systems art known in the art and may include a condenser  21  to condense refrigerant fluid, an expansion valve  22 , or expansion device, to expand the refrigerant fluid, an evaporator  23  that cools air by absorbing heat from ambient air. The system may also include a fan  24  that blows the cooler air into the cabin of the vehicle. A pressure switch  25 , or thermister, may indicate when the refrigerant pressure provided to the compressor  16  is too low for compressor operation. The clutch  18  can also be in a deactivated phase in which the clutch  18  does not actuate the compressor  16 . In the deactivated phase the compressor  16  does not compress fluid in the air conditioning system. 
     A control module  26  includes a clutch status sensor  28  that senses when the clutch  18  engages the compressor  16  in an activated phase, and senses when the clutch  18  disengages the compressor  16  in a deactivated phase. It should be understood that the status of the clutch may be determined by a clutch status signal generator, and the sensor or signal generator may be located in any location such that the engagement or disengagement of the clutch can be determined. The control module  26  compares the time that the compressor is in an activated phase with the time the compressor is in a deactivated phase to override and disable the engine shut-down system  14 , preventing the engine  12  from shutting down. 
     In an automatic climate control system, the control module  26  may also include a sun load sensor  30  that senses the amount of sun load entering the vehicle, a humidity sensor  32  that senses the humidity in the vehicle, and a cabin temperature sensor  34  that senses the temperature of the air in the cabin of the vehicle. The evaporator low temperature sensor or low pressure cycling switch  25  indicates when refrigerant pressure entering the compressor  16  is too low for compressor operation. The control module  26  decides whether or not the compressor  16  should work the air conditioning system to provide cooler air to the cabin of the vehicle based upon the data provided by the sensors  30 ,  32 ,  34  and the switch  25  that is provided to the input  36  for the control module  26 . 
     In a manual climate control system, a vehicle occupant can increase amount of time that the compressor  16  is actuated by decreasing the desired temperature on a vehicle user interface or by increasing the quantity of air passing over the evaporator by increasing the fan  24  speed. In the manual climate control system sensors  30 ,  32 ,  34  may not be present, in which case compressor control could be strictly determined by the state of the low pressure cycling switch input. It should be understood that control module  26  may also be part of the powertrain control module of a vehicle. It should further be understood that sensors  30 ,  32 ,  34  may communicate with the same control module  26  that the clutch status sensor  28  communicates with, or the sensors  30 ,  32 ,  34  may communicate with a separate air conditioning control module. It should also be understood that the clutch status sensor may, or may not be a physical device. It may be just the result of calculations made within the control module used to determine clutch actuation. 
     Referring to  FIGS. 1 and 2 , one embodiment of an override system  40  is disclosed. The override system  40  includes input from the clutch status sensor  28  in which the time the clutch activates the compressor (t on ) is measured, and the time the clutch does not activate the compressor (t off ) is measured. The air conditioning system may use refrigerant pressure, evaporator temperature, or air temperature to modulate the air conditioner clutch  18  on and off to prevent freezing of the evaporator. The clutch status sensor  28  senses the time the clutch  18  is on and off, and uses this as feedback to the control module  26  and to the override system  40 . 
     The override system  40  begins at Key On Engine Running (KOER)  42 , in which a vehicle occupant has turned a key or otherwise started the engine. A ratio determination is made at  44  as to the ratio of t off  to t on , and whether or not the rate of change of this ratio is approximately zero. The rate of change  44  may be calculated over any predetermined range or may be calculated as an instantaneous rate of change, but preferably the rate of change is calculated over the previous 5 to 10 clutch cycles. The rate of change determination  44  may infer whether or not the temperature of the air in the cabin is stable. It should be noted that the rate of change being “approximately zero” means that the rate of change of the ratio of t off  to t on  is within a predetermined de minimis range or threshold that is sufficient to assure passenger comfort. 
     If the rate of change determination at  44  is not approximately zero (“No”), the engine shut-down system  14  is disabled. However, if the rate of change determination at  44  is approximately zero (“Yes”), then a ratio determination is calculated at  46 . A determination is made as to whether the ratio of t off  to t on  of the clutch  18  is greater than a predetermined ratio. Again, this determination may be calculated over any predetermined range, but preferably the ratio is calculated over the previous 5 to 10 clutch cycles. The predetermined ratio “X” may be set as any value, but preferably the predetermined ratio “X” is between 0.2 and 2.0, and more preferably the predetermined ratio “X” is 0.9. The ratio determination  46  may infer whether or not the temperature of the air in the cabin is at a comfortable level as set by the vehicle occupants. 
     If the ratio determination at  46  is not greater than the predetermined value (“No”), the engine shut-down system  14  is disabled. However, if the ratio determination at  46  is greater than the predetermined ratio (“Yes”), then a compressor off time is evaluated at  48 . The clutch status sensor senses the time that the compressor is off (t off ), and the control module compares t off  with a predetermined time “C”. The predetermined time “C” may be any predetermined time, but preferably more than 10 seconds. If the compressor off time is not above a threshold time (“No”), the engine shut-down system is disabled. However, if the compressor off time is above a threshold time (“Yes”), the engine shut-down system  14  is enabled at  50 . 
     If any one of the rate of change determination  44 , ratio determination  46 , or t off  comparison  48  yield an output of “No”, this means that either the cabin temperature is not stable, is not comfortable, or a threshold t off  is not reached, respectively. In any “No” result, the control module  26  disables the engine shut-down system  14 . This prevents the engine  12  from shutting down in a situation where a restart of the engine  12  would quickly be necessary to keep the air conditioning system effective in cooling the air in the vehicle cabin. This provides a vehicle system  10  that assures a comfort level to vehicle occupants without unwanted turning off and restarting of the engine. 
     Referring to  FIG. 3 , another embodiment of an override system  40  is disclosed. Once KOER  42  is determined, the rate of change determination  44  and the ratio determination  46  are made similar to the embodiment in  FIG. 2 . If the calculations yield “Yes” for both, the engine shut-down system  14  is enabled, but if either determination  46 ,  48  yields “No,” the engine shut-down system  14  is disabled. 
     Referring to  FIG. 4 , yet another embodiment of an override system  40  is disclosed. Once KOER  42  is determined, the rate of change is determined at  44  and the compressor off time is evaluated at  48 . As shown in both  FIGS. 3 and 4 , it is preferred that the rate of change determination  44  is present in the override system  40 . This determination  44  is important because it indicates that the air conditioner has pulled the vehicle cabin temperature down to a stabilized temperature. This is an important factor in deciding that the engine  12  will not need to restart quickly after shutting down in order to keep the cabin air at a desired temperature. 
     It should be understood that any or all of the rate of change determination  44 , ratio determination  26 , and clutch off time determination  48  may be used in the override system  40 , and in any order.  FIGS. 2-4  are mere examples of combinations of the three determinations  44 ,  46 , and  48 . 
     Referring to  FIGS. 1 and 5 , the compressor state  54  is shown in an actuated phase and a non-actuated phase. A duty cycle includes t on  when the clutch status sensor  28  indicates that the compressor  16  is actuated, and t off  when the clutch status sensor  28  indicates that the compressor  16  is not actuated. Changes in t on  and t off  correspond to the change in cabin temperature  60 . The compressor is actuated  56  much more than it is not actuated  58  in order to pull the cabin temperature down to a stabilized temperature that is desirable to the vehicle occupants. Once the temperature has stabilized, the compressor  16  does not need to be actuated as frequently as it did during the initial cabin temperature pull down. 
     The evaporator temperature  62  is also shown in  FIG. 5 . The clutch  18  is modulated on and off by the control module  26  to keep the evaporator from freezing. As the clutch  18  does not actuate the compressor  16  during t off , a spike in the evaporator temperature  62  is shown, indicating a temperature rise preventing freezing. The amount of time t on  and t off  is then input into the override system  40  shown in  FIGS. 2-4 . 
     Referring to  FIG. 6 , the compressor state  54  is shown during a time when the cabin temperature  60  is stable. The compressor state  54  remains mostly on, but is off at intervals to prevent the evaporator temperature  62  from remaining low and possibly causing the evaporator to freeze. 
     Referring to  FIGS. 1-5 , as the cabin temperature  60  is pulled down, the rate of change of the ratio of t off  to t on  is not approximately zero. Therefore, according to the override system  40 , the engine shut-down system  14  would be disabled such that the engine continues to provide power to the compressor  16  through the clutch  18  and belt  20 . However, once the temperature reaches a stabilized temperature exemplified in  FIG. 6 , the rate of change of the ratio of t off  to t on  is approximately zero. Therefore, the override system  40  does not disable the engine shut-down system upon the condition that the ratio is greater than a predetermined ratio at  46 , and the time the compressor is off is greater than a predetermined time at  48 . 
     Referring to  FIGS. 1-6 , it should be understood that a variable capacity air conditioner compressor may be used in the vehicle system  10 . Sensors may be used to determine when the variable capacity compressor is operating at maximum and minimum capacity, as well as when the compressor is off. The control module may then compare the time the compressor is operating at maximum to the time the compressor is operating at minimum. This comparison may then be used in an override system as described in regards to  FIGS. 2-4 , and the engine shut-down system  14  may be disabled. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the disclosure. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the disclosure.