Abstract:
Methods and devices that use an engine load condition of a vehicle, for example, the vehicle&#39;s engine intake manifold or plenum vacuum, to promote the efficiency of the engine. The methods and devices are operable to control the compressor of the vehicle&#39;s air-conditioning system, enabling the compressor to be shut off when the vehicle is under relatively high loads. The methods and devices operate by sensing a parameter indicative of an engine load condition of the vehicle, determining a difference between a reading of the parameter and an average based on multiple readings of the parameter, and then engaging and disengaging the compressor clutch depending on whether the reading of the parameter is above or below the average of the parameter. The compressor clutch is engaged if the engine operates under a high load for a duration that is dependent on the average of the parameter.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/380,650, filed Sep. 7, 2010, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to air-conditioning systems, and more particularly to automotive air-conditioning systems configured to disengage the compressor of the system when the vehicle is under relatively high loads. 
     The efficiency of an automotive engine&#39;s operation can be increased by engaging the compressor of its air-conditioning system to operate the system only when the engine is not loaded or only lightly loaded. As a result, various methods have been proposed for interrupting the operation of air-conditioning systems for the purpose of reducing the load on a vehicle under certain conditions, for example, during acceleration and when operating on an incline. As an example, certain systems have been proposed that engage and disengage a clutch through which power is delivered to the compressor based on one or more parameters that are indicative of the load on the engine. 
     Engine intake manifold vacuum is a good indicator of engine loading, and therefore air-conditioning systems have been proposed that utilize the engine intake manifold or plenum vacuum level as a parameter for controlling the operation of the compressor. Engine intake manifold vacuum and engine loading are inversely proportional, such that a high manifold vacuum level (in other words, a low manifold absolute pressure relative to ambient atmospheric pressure) corresponds to a low engine load and lower manifold vacuum levels (in other words, manifold absolute pressures relatively closer to ambient atmospheric pressure) correspond to higher engine loads. Therefore, the compressor clutch is disengaged if the manifold pressure level rises above a predetermined threshold indicative of a high engine load, for example, during acceleration, and allowed to re-engage once the manifold pressure level has dropped below a predetermined threshold, for example, after the desired vehicle speed is attained and during vehicle coasting. In this manner, the system operates to override the heating, ventilating, and air-conditioning (HVAC) computer of a vehicle and its control of the compressor. 
     A complicating factor in the incorporation of systems of the type described above occurs if a vehicle is operated for prolonged periods at high engine loads, for example, when a long incline is encountered. Aside from the annoyance of the passenger compartment becoming warmer than desired, safety issues can arise if weather conditions require that the vehicle&#39;s HVAC controls are set to defrost. As a possible remedy, U.S. Pat. No. 5,228,305 proposed means by which the threshold at which an air-conditioning compressor is disengaged can be manually adjusted by the vehicle&#39;s operator. However, the necessity for the operator to know how to make such manual adjustments can be burdensome and potentially dangerous. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention provides methods and devices that use an indicator for the engine load of a vehicle, for example, the vehicle&#39;s engine intake manifold or plenum vacuum, to promote the efficiency of the engine. The methods and devices are operable to control the compressor of the vehicle&#39;s air-conditioning system, enabling the compressor to be shut off when the vehicle is under relatively high loads, for example, during acceleration or when operating on an incline. 
     According to a first aspect of the invention, such a device ( 10 ) includes means (X 1 ) for sensing a parameter indicative of an engine load condition of the vehicle, means (Q 1 ) for determining a difference between a reading of the parameter sensed by the sensing means (X 1 ) and an average based on multiple readings of the parameter sensed by the sensing means (X 1 ), and means (Q 2 ) for engaging and disengaging the compressor clutch depending on whether the reading of the parameter is above or below the average of the parameter. The engaging/disengaging means (Q 2 ) engages the compressor clutch if the engine operates under a high load for a duration that is dependent on the average of the parameter. 
     According to a second aspect of the invention, a method is provided that uses a device ( 10 ) comprising the elements described above to promote the efficiency of the vehicle engine. 
     According to another aspect of the invention, a method of promoting the efficiency of the vehicle engine includes sensing a parameter indicative of an engine load condition of the vehicle, determining a difference between a reading of the parameter and an average based on multiple readings of the parameter, and engaging and disengaging the compressor clutch depending on whether the reading of the parameter is above or below the average of the parameter. The compressor clutch is engaged if the engine operates under a high load for a duration that is dependent on the average of the parameter. 
     A technical effect of the invention is the ability to automatically disengage an air-conditioning compressor of a vehicle operating at high engine loads, yet also automatically avoid the compressor being disengaged over prolonged periods, for example, when a long incline is encountered. This capability avoids potential safety issues that can arise if weather conditions require the operation of the defrost to maintain visibility through the vehicle&#39;s windshield, as well as addresses comfort issues for occupants of the vehicle. 
     Other aspects and advantages of this invention will be better appreciated from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically represents a switching circuit connected to an electrical circuit for operating a compressor clutch of a vehicle air-conditioning (AC) system, wherein the switching circuit is adapted to disengage the compressor clutch if the vehicle is operated at a sufficiently high engine load. 
         FIG. 2  is a graph representing a preferred functional aspect of the switching circuit of  FIG. 1 . 
         FIGS. 3A and 3B  schematically represent an electrical circuit for use as the switching circuit of  FIG. 1  in accordance with a preferred embodiment of this invention. 
         FIGS. 4 and 5  represent front and top views of a module into which the switching circuit of  FIGS. 1 ,  3 A and  3 B can be incorporated in accordance with a preferred aspect of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As previously noted, engine intake manifold vacuum is a good indicator of engine loading, and therefore engine intake manifold or plenum vacuum level can be used as a parameter for limiting the operation of a compressor of an automotive engine&#39;s air-conditioning system when the engine is operating under high loading conditions (other indications of engine load, for example, the throttle position signal of the Engine Control Module (ECM), could be used and are therefore also within the scope of the invention). Because engine intake manifold vacuum and engine loading are inversely proportional, a relatively low manifold vacuum level (in other words, a manifold absolute pressure relatively close to ambient atmospheric pressure) corresponds to a relatively high engine load, whereas higher manifold vacuum levels (in other words, lower manifold absolute pressures relative to ambient atmospheric pressure) correspond to lower engine loads, the present invention can monitor engine intake manifold or plenum pressure levels to disengage the compressor clutch if the manifold pressure level rises above a threshold indicative of a high engine load, for example, during acceleration and long inclines, and then re-engage the clutch once the manifold pressure level has dropped below a threshold, for example, after the desired vehicle speed is attained and during vehicle coasting. In this manner, the system operates to override the heating, ventilating, and air-conditioning (HVAC) computer of a vehicle and its control of the compressor. As discussed below, the threshold at which the clutch disengages and re-engages is not a constant, but a variable that changes as a result of the operating conditions of the vehicle. 
     Preferred aspects of the invention can be accomplished using a switching circuit  10  represented in  FIG. 1  as being installed in an electrical circuit  12  for a compressor clutch  14  of a vehicle air-conditioning (AC) system to interrupt and resume electrical power to a coil  16  that operates the clutch  14 . The circuit  10  includes a pressure sensor  18  by which intake manifold pressure (or vacuum) can be used as an input parameter to the circuit  10 . The sensor  18  generates an electrical voltage that corresponds to the sensed intake manifold pressure, for example, proportional to the pressure. The electrical voltage serves as an input to a processing circuit  20 , such as a microprocessor or other device having a switching capability. As discussed in more detail below, the switching circuit  10  is also operable to maintain a running average of the intake manifold pressure. The average intake manifold pressure can be calculated from multiple pressure readings taken over any suitable time period, though in the preferred embodiment the average is based on readings that are continuously monitored whenever the engine is operating. The processing circuit  20  compares the calculated average to the instantaneous intake manifold pressure reading sensed by the pressure sensor  18  and, as illustrated in  FIG. 2 , interrupts power to switch the clutch coil  16  “off” if the instantaneous pressure reading rises above the average pressure or, more preferably, above the average pressure plus a predetermined offset (“OFFSET”). A suitable offset, for example, about 4.5 inches Hg (about 0.15 bar), avoids a shutdown of the compressor if the intake manifold pressure rises due to fluctuations that may occur during engine operation or otherwise do not indicate a sufficiently high engine load condition that warrants shutdown of the compressor. In this manner, a sufficient rise in intake manifold pressure is recognized by the circuit  10  that acceleration of the vehicle has begun or the vehicle is otherwise under an increased load condition and shutdown of the compressor is desirable to promote the operating efficiency of the engine. Any resulting fuel economy savings will depend on the use of the vehicle&#39;s air-conditioning system and the driving habits of the vehicle&#39;s operator. 
       FIG. 2  further indicates that the circuit  10  also operates to switch the compressor “on” if, due to sustained high engine loading conditions, the average pressure (plus any offset) rises above the instantaneous pressure reading. Logically, a similar result occurs if the instantaneous pressure reading were to drop, for example, if the vehicle were no longer accelerating or on an incline. 
     By the comparison of the average pressure (plus any offset) to the instantaneous pressure reading, the circuit  10  is capable of being adapted to essentially any vehicle and/or engine combination, as well as prolonged periods of high engine load. The latter is useful as a safety feature because, even while the vehicle is operating under a high engine load, the circuit  10  is adapted to eventually switch the compressor “on” if the vehicle&#39;s HVAC controls are set to defrost. As such, the comparison of average to instantaneous pressure readings is compatible with the vehicle&#39;s entire HVAC system, such as when the air-conditioning system is engaged and the air-conditioning compressor is required to operate, for example, when operation of the windshield defroster is required for safety issues. 
     The averaging time constant can be adjustable and based on “under hood” or ambient temperatures. For example, a longer time constant can be provided on cooler days while a shorter time constant may be preferred on hotter days, which results in the compressor being off for longer periods of time on cooler days and off for shorter periods of time on hotter days. 
     The circuit  10  can also be configured such that the compressor is switched off for a predetermined minimum amount of time, such as about two seconds (shorter and longer times are foreseeable), so as to prevent the clutch from rapid on/off cycling of the compressor, which could occur if the vehicle were accelerating and decelerating quickly. 
     This switching circuit  10  can be incorporated into the ECM of new vehicles, since intake manifold vacuum is already an input to the ECM. The ECM would then perform the algorithm for stopping and starting the compressor. Alternatively, the circuit  10  can be configured as a module that can be separately installed during vehicle assembly as well as in the aftermarket. To illustrate,  FIGS. 3A and 3B  (showing portions of the same switching circuit  10  connected by the lines labeled as OR, WT and BK) represent an electrical schematic for the switching circuit  10  in accordance with what is believed to be a preferred embodiment of the invention. The circuit  10  can be incorporated into a module  22  represented in  FIGS. 4 and 5 . As illustrated, the module  22  has terminal blades  24  that enable the module  22  to replace an existing AC compressor relay, such that the module  22  can be separately installed during vehicle assembly or anytime thereafter. An inlet port fitting  26  allows a tube (not shown) to connect the module  22  to a source of the intake manifold pressure, such that the pressure sensor  18  can be located within the module  22 , along with the processing circuit  20 . 
     As represented in  FIGS. 3A and 3B , the circuit  10  includes a pressure sensor X 1  by which intake manifold pressure (or vacuum) is used as an input parameter to the circuit  10 . In the embodiment of  FIGS. 3A and 3B , the sensor X 1  measures pressure and its voltage output is proportional to the sensed pressure reading (and therefore inversely proportional to vacuum level). The voltage output of the sensor X 1  is used as the base voltage of a PNP transistor Q 1 , which acts as a buffer/diode to the raw signal from the sensor X 1 . As the sensed pressure decreases, resulting in a lower voltage at the base of the transistor Q 1 , a capacitor C 1  is discharged from the current draw through the emitter of the transistor Q 1 . Inherent to the design of the transistor Q 1 , a voltage drop (V be ) exists between its base and emitter, for example, a voltage drop of about 0.6+/−0.1 volt. The emitter current of the transistor Q 1 , which is used to discharge a second capacitor C 2 , is approximately the voltage from the base of the transistor Q 1  (+V be ) to ground, divided by the collector resistance (R 4 +R 5 ), and multiplied by the beta of the transistor Q 1  according to the following.
 
Emitter current=( V   base /( R 4 +R 5))*50
 
     Assuming a beta value of about +/−30%, an attack time constant can be calculated as follows.
 
 t =( V   base   +V   be )* C 2/(Emitter current)
 
where C 2  is the capacitance of the second capacitor C 2 . The attack time constant is calculated as long as the collector to emitter voltage of transistor Q 1  remains above 0.2 volt. If the change in vacuum is great enough to cause the collector to emitter voltage of the transistor Q 1  to drop to less than 0.2 volt, the transistor Q 1  acts as a diode and beta becomes 1.
 
     As the pressure increases (vacuum decreases), the transistor Q 1  turns off and the decay time constant is initiated whose value is calculated as follows
 
 t =( RT 1 +R 3)* C 2
 
wherein RT 1  is the resistance of a thermistor. RT 1  varies inversely to the ambient air temperature, so that a higher ambient air temperature results in a lower resistance RT 1 . As a result, a higher ambient air temperature reduces the time constant, which reduces the compressor “off” time. On the other hand, a lower ambient air temperature increases the time constant, which increases the compressor “off” time.
 
     If the intake manifold pressure sensed by the sensor X 1  is constant (steady-state), the input to a comparator U 2 E is such that the pin  11  of the comparator U 2 E (U 2 E- 11 ) is greater by an offset value of at least V be  compared to the pin  10  of the comparator U 2 E (U 2 E- 10 ) when a threshold pot (“THRESHOLD”) is set to a minimum value. As noted above, this offset value (the OFFSET of  FIG. 2 ) may relate to about 4.5 inches Hg (about 0.15 bar) of pressure, with the result that the intake manifold pressure can rise about 0.15 bar (corresponding to a vacuum drop of about 0.15 bar) without having any effect on the compressor due to such fluctuations being mathematically attributed to “normal” driving. As represented in  FIG. 3A , the threshold pot can preferably be increased, for example, to a value of over 20 inches Hg (about 0.68 bar). However, threshold pot levels of this level could lower the absolute trigger threshold to the extent that the function of the circuit  10  would be largely disabled. 
     When accelerating, the higher intake manifold pressure causes the instantaneous voltage at U 2 E- 10  to rise above the average voltage at U 2 E- 11 , triggering a low voltage condition at the U 2 E- 13  pin. This causes the input to a pin  4  of a second comparator U 2 A (U 2 A- 4 ) to drop to zero volts. The input to a pin  5  of the comparator U 2 A (U 2 A- 5 ) is the AC control command from the vehicle&#39;s ECM, which if “on” is higher than U 2 A- 4  to trigger a high output on pin  2  of the U 2 A comparator (U 2 A- 2 ). This condition causes a gate of a MOSFET transistor Q 2  to turn power off to the coil for the compressor clutch (“AC CLUTCH”). 
     The decay time constant determines the slope of the increasing voltage at U 2 E- 11  (corresponding to the average pressure level, i.e., the output of the sensor X 1  plus any offset value). With continuing higher readings from the sensor X 1 , the voltage at U 2 E- 11  eventually surpasses the voltage at U 2 E- 10  (corresponding to the instantaneous pressure level) and U 2 E- 13  is triggered high to cause U 2 A- 4  to rise above U 2 A- 5 . If the ECM AC command is on, U 2 A- 2  is triggered low, causing the gate of the MOSFET transistor Q 2  to return power to the AC Clutch. On the other hand, if the ECM AC Command is off, U 2 A- 2  will remain high to keep the AC Clutch off. 
     While the invention has been described in terms of specific embodiments, it is apparent that other forms could be adopted by one skilled in the art. For example, the scope of the invention also extends to the use of electrical signals from a vehicle&#39;s ECM and/or manifold vacuum transmitter to electrically monitor manifold vacuum levels, instead of directly monitoring manifold pressure, as the input for controlling the engagement and disengagement of the compressor clutch. Furthermore, as was noted above, other indications of engine load, for example, the throttle position signal of the ECM, could be used as the input parameter to the circuit  10 , and the use of such alternative parameters is also within the scope of the invention. Therefore, the scope of the invention is to be limited only by the following claims.