Patent Publication Number: US-7913669-B2

Title: Method for controlling cylinder deactivation

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of a co-pending patent application to Luken et al., U.S. patent application Ser. No. 12/123,912 filed on May 20, 2008, and published as Publication number 2009/029439 published Nov. 26, 2009, the disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to motor vehicles and in particular to a method for controlling cylinder deactivation. 
     2. Description of Related Art 
     Methods for controlling cylinder deactivation have been previously proposed. Bolander (U.S. Pat. No. 2006/0130814) is directed to a method of regulating a displacement on demand (DOD) engine. The Bolander method teaches adjusting activation of a first cylinder to partially achieve the desired engine displacement and subsequently adjusting activation of a second cylinder to fully achieve the desired engine displacement. In other words, instead of activating multiple cylinders simultaneously, a first cylinder is activated, followed by a second cylinder being activated. During a first step before partial deactivation, the control device determines whether the displacement on demand system should be disabled. The displacement on demand system is disabled whenever the vehicle is in a situation where activation of the DOD system would be inappropriate. Such conditions include that the vehicle is in a transmission mode other than drive (i.e. park, reverse or low range). Other situations include the presence of engine controller faults, cold engine, improper voltage levels and improper fuel and/or oil pressure levels. 
     Foster (U.S. Pat. No. 6,904,752) is directed to an engine cylinder deactivation system that improves the performance of the exhaust emission control systems. The Foster design discloses a cylinder deactivation system to control temperature and air/fuel ratio of an exhaust gas feed-stream going into an after-treatment device. Foster teaches cylinder deactivation for controlling temperature of the exhaust gas continues as long as the operating point of the engine remains below a predetermined level, or the coolant temperature is below the operating range of 82-91 degrees C., or the exhaust gas temperature is below an optimal operating temperature of the after-treatment device, e.g. 250 degrees C. In other words, the Foster device uses a single threshold limit for the engine operating level, the coolant temperature and the exhaust gas temperature. 
     Donozo (U.S. Pat. No. 4,409,936) is directed to a split type internal combustion engine. In the Donozo design, the internal combustion engine comprises a first and second cylinder unit, each including at least one cylinder, a sensor means for providing a signal indicative of engine vibration and a control means for disabling the first cylinder unit when the engine load is below a predetermined value. The controller means is adapted to hold the first cylinder unit active, regardless of engine load conditions, when the engine vibration indicator signal exceeds a predetermined value indicating unstable engine operation. In the Dozono design, cylinder deactivation may occur during low load conditions any time the measured vibrations are below a particular threshold value. Dozono does not teach a method where cylinder deactivation is stopped for low load conditions based on engine speed. 
     Wakashiro (U.S. Pat. No. 6,943,460) is directed to a control device for a hybrid vehicle. The Wakashiro design teaches a method for determining if cylinder deactivation should be used and a separate method for determining if the engine is in a permitted cylinder deactivation operation zone. The factors used to determine if the engine is in a permitted cylinder deactivation zone are the temperature of the engine cooling water, the vehicle speed, the engine revolution rate, and the depression amount of the accelerator pedal. In each case, these factors are evaluated based on a single predetermined threshold. In other words, if each of these factors is determined to be above or below (depending on the factor) a predetermined threshold, the cylinder deactivation operation is prevented. 
     While the prior art makes use of several parameters in order to determine if cylinder deactivation should be stopped, there are shortcomings. The prior art teaches only threshold limits above which cylinder deactivation can continue and below which cylinder deactivation should be stopped. Also, the prior art does not teach the use of stop deactivation dependent on various parameters including engine speed, vehicle speed, transmission ratio, or engine load. There is a need in the art for a system and method that addresses these problems. 
     SUMMARY OF THE INVENTION 
     A method for controlling cylinder deactivation is disclosed. Generally, these methods can be used in connection with an engine of a motor vehicle. The invention can be used in connection with a motor vehicle. The term “motor vehicle” as used throughout the specification and claims refers to any moving vehicle that is capable of carrying one or more human occupants and is powered by any form of energy. The term motor vehicle includes, but is not limited to cars, trucks, vans, minivans, SUV&#39;s, motorcycles, scooters, boats, personal watercraft, and aircraft. 
     In some cases, the motor vehicle includes one or more engines. The term “engine” as used throughout the specification and claims refers to any device or machine that is capable of converting energy. In some cases, potential energy is converted to kinetic energy. For example, energy conversion can include a situation where the chemical potential energy of a fuel or fuel cell is converted into rotational kinetic energy or where electrical potential energy is converted into rotational kinetic energy. Engines can also include provisions for converting kinetic energy into potential energy, for example, some engines include regenerative braking systems where kinetic energy from a drivetrain is converted into potential energy. Engines can also include devices that convert solar or nuclear energy into another form of energy. Some examples of engines include, but are not limited to: internal combustion engines, electric motors, solar energy converters, turbines, nuclear power plants, and hybrid systems that combine two or more different types of energy conversion processes. 
     In one aspect, the invention provides a method for controlling cylinder deactivation in a motor vehicle comprising the steps of: determining the availability of a cylinder deactivation mode; receiving information related to a parameter associated with an operating condition of the motor vehicle; comparing the parameter with a predetermined prohibited range, the predetermined prohibited range having a lower limit and an upper limit; and prohibiting cylinder deactivation when the parameter is within the predetermined prohibited range. 
     In another aspect, the parameter is engine speed. 
     In another aspect, the parameter is vehicle speed. 
     In another aspect, the parameter is transmission condition. 
     In another aspect, the parameter is engine load. 
     In another aspect, the invention provides a method for controlling cylinder deactivation in a motor vehicle comprising the steps of: receiving information related to a parameter associated with an operating condition of the motor vehicle; comparing the parameter with a predetermined prohibited range, the predetermined prohibited range having a lower limit and an upper limit; permitting cylinder deactivation when a value of the parameter is below the lower limit of the predetermined prohibited range; prohibiting cylinder deactivation when the parameter is within the predetermined prohibited range; permitting cylinder deactivation when the value of the parameter is above the upper limit of the predetermined prohibited range; and where the lower limit has a value that is less than the upper limit. 
     In another aspect, the parameter is engine speed. 
     In another aspect, the parameter is vehicle speed. 
     In another aspect, the parameter is transmission condition. 
     In another aspect, the parameter is engine load. 
     In another aspect, there are multiple deactivated cylinder modes. 
     In another aspect, the invention provides a method for controlling cylinder deactivation in a motor vehicle including an engine having a plurality of cylinders comprising the steps of: establishing a maximum cylinder mode wherein all of the plurality of cylinders is operated; establishing a minimum cylinder mode wherein a minimum number of cylinders is operated, wherein the minimum number is less than the maximum number; establishing an intermediate cylinder mode wherein an intermediate number of cylinders is operated, wherein the intermediate number is less than the maximum number but greater than the minimum number; receiving information related to a parameter associated with an operating condition of the motor vehicle; comparing the parameter with a predetermined prohibited range; prohibiting cylinder deactivation to the minimum number of cylinders when the parameter is within the predetermined prohibited range, but permitting cylinder deactivation to the intermediate number of cylinders. 
     In another aspect, the maximum number of cylinders is six. 
     In another aspect, the maximum number of cylinders is eight. 
     In another aspect, the maximum number of cylinders is ten. 
     In another aspect, the maximum number of cylinders is twelve. 
     In another aspect, the maximum number of cylinders is six, the minimum number is three and the intermediate number is four. 
     In another aspect, the maximum number of cylinders is eight, the minimum number is four and the intermediate number is six. 
     In another aspect, the maximum number of cylinders is ten, the minimum number is five and the intermediate number is six. 
     In another aspect, the maximum number of cylinders is twelve, the minimum number is six and the intermediate number is eight. 
     In another aspect, the invention provides a method for controlling cylinder deactivation in a motor vehicle comprising the steps of: determining the availability of a cylinder deactivation mode; receiving information related to a parameter associated with an operating condition of the motor vehicle; comparing the parameter with a first predetermined prohibited range and a second predetermined prohibited range, the first predetermined prohibited range having a first lower limit and a first upper limit and the second predetermined prohibited range having a second lower limit and a second upper limit; the second lower limit being greater than the first upper limit; and prohibiting cylinder deactivation when the parameter is within either the first predetermined prohibited range or the second predetermined prohibited range. 
     In another aspect, the parameter is engine speed. 
     In another aspect, the parameter is vehicle speed. 
     In another aspect, the parameter is engine load. 
     In another aspect, the parameter is transmission condition. 
     In another aspect, the invention provides a method for controlling cylinder deactivation in a motor vehicle comprising the steps of: receiving information related to a parameter associated with an operating condition of the motor vehicle; comparing the parameter with a first predetermined prohibited range, the first predetermined prohibited range having a first lower limit and a first upper limit greater than the first lower limit; comparing the parameter with a second predetermined prohibited range, the second predetermined prohibited range having a second lower limit and a second upper limit, the second lower limit being less than the second upper limit and greater than the first upper limit; permitting cylinder deactivation when a value of the parameter is below the first lower limit of the first predetermined prohibited range; prohibiting cylinder deactivation when the parameter is within the first predetermined prohibited range; permitting cylinder deactivation when the value of the parameter is above the first upper limit of the first predetermined prohibited range and below the second lower limit of the second predetermined prohibited range; prohibiting cylinder deactivation when the parameter is within the second predetermined prohibited range; and permitting cylinder deactivation when the value of the parameter is above the second upper limit of the second predetermined prohibited range. 
     In another aspect, the parameter is engine speed. 
     In another aspect, the parameter is vehicle speed. 
     In another aspect, the parameter is transmission condition. 
     In another aspect, the parameter is engine load. 
     Other systems, methods, features and advantages of the invention will be, or will become, apparent to one of ordinary skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description and this summary, be within the scope of the invention, and be protected by the following claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. 
         FIG. 1  is a schematic view of a preferred embodiment of a cylinder deactivation system; 
         FIG. 2  is a schematic view of a preferred embodiment of several configurations for cylinder deactivation; 
         FIG. 3  is a preferred embodiment of a relationship showing prohibited noise regions; 
         FIG. 4  is a preferred embodiment of a relationship showing multiple prohibited noise regions; 
         FIG. 5  is a preferred embodiment of a process for controlling cylinder deactivation; 
         FIG. 6  is a preferred embodiment of a process for switching between deactivated cylinder modes; 
         FIG. 7  is a preferred embodiment of a relationship showing prohibited noise regions; 
         FIG. 8  is a preferred embodiment of a process for controlling cylinder deactivation; 
         FIG. 9  is a preferred embodiment of a relationship showing prohibited noise regions; 
         FIG. 10  is a preferred embodiment of a relationship showing prohibited noise regions; 
         FIG. 11  is a preferred embodiment of a process for controlling cylinder deactivation 
         FIG. 12  is a preferred embodiment of a process for controlling cylinder deactivation; 
         FIG. 13  is a preferred embodiment of a relationship showing prohibited noise regions; 
         FIG. 14  is a preferred embodiment of a process for controlling cylinder deactivation; and 
         FIG. 15  is a preferred embodiment of a step of a process for controlling cylinder deactivation. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a schematic view of a preferred embodiment of cylinder deactivation system  100 . Preferably, cylinder deactivation system  100  may comprise engine  102 , control unit  104  and sensor system  106 . In some embodiments, cylinder deactivation system  100  could include additional components, such as multiple engines and/or multiple sensor systems. In a preferred embodiment, cylinder deactivation system  100  may be part of a motor vehicle of some kind. 
     In the current embodiment, engine  102  includes first cylinder  111 , second cylinder  112 , third cylinder  113 , fourth cylinder  114 , fifth cylinder  115  and sixth cylinder  116 . For purposes of clarity, engine  102  is shown in  FIG. 1  as a six cylinder engine. In other embodiments, engine  102  may include more or less than six cylinders. For example, other preferred embodiments of engine  102  could include three cylinders, four cylinders, eight cylinders, nine cylinders, ten cylinders or twelve cylinders. Generally, engine  102  could include any desired number of cylinders. 
     In the preferred embodiment, sensor system  106  may comprise multiple sensors. Preferably, sensor system  106  includes one or more of the following sensors: engine speed sensor  121 , vehicle speed sensor  122 , intake manifold sensor  123 , throttle angle sensor  124 , airflow sensor  125  and transmission sensor  126 . In other embodiments, sensor system  106  may include additional sensors. In a preferred embodiment, sensor system  106  includes each of the sensors  121 - 126 . 
     In some embodiments, cylinder deactivation system  100  may also include control unit  104 . Preferably, control unit  104  may be an electronic device or may include a computer of some type configured to communicate with engine  102  and sensor system  106 . Control unit  104  may also be configured to communicate with and/or control other devices or systems within a motor vehicle. 
     Generally, control unit  104  may communicate with engine  102  and sensor system  106  using any type of connection, including both wired and/or wireless connections. In some embodiments, control unit  104  may communicate with engine  102  via first connection  141 . Additionally, control unit  104  may communicate with engine speed sensor  121 , vehicle speed sensor  122 , intake manifold sensor  123 , throttle angle sensor  124 , airflow sensor  125  and transmission sensor  126  via second connection  142 , third connection  143 , fourth connection  144 , fifth connection  145 , sixth connection  146  and seventh connection  147 . With this preferred configuration, control unit  104  may function to control engine  102 , especially in response to various operating conditions of the motor vehicle as measured or determined by sensor system  106 . 
     Preferably, control unit  104  may include provisions for cylinder deactivation in order to modify the engine displacement and thereby increase fuel efficiency in situations where load demands do not require all cylinders to be operating. Cylinder deactivation occurs whenever one or more cylinders within engine  102  are not used. In some embodiments, there may be more than one mode of cylinder deactivation. Referring to  FIG. 2 , engine  102  may be operated in maximum cylinder mode  202 , intermediate cylinder mode  204  or minimum cylinder mode  206 . Preferably, maximum cylinder mode  202  operates using the maximum number of cylinders, minimum cylinder mode  206  operates using some number of cylinders less than the maximum number, and intermediate cylinder mode  204  operates using some number of cylinders between the maximum and minimum number of cylinders. Any cylinder mode using less than the maximum number of cylinders may be referred to as a ‘deactivated cylinder mode’. 
     In the preferred embodiment, during maximum cylinder mode  202 , cylinders  111 - 116  are all preferably operating. During intermediate cylinder mode  204 , first cylinder  111 , third cylinder  113 , fourth cylinder  114  and sixth cylinder  116  remain operating, while second cylinder  112  and fifth cylinder  115  are deactivated. Finally, during minimum cylinder mode  206 , first cylinder  111 , third cylinder  113  and fifth cylinder  115  remain operating while second cylinder  112 , fourth cylinder  114  and sixth cylinder  116  are deactivated. In other words, in the preferred embodiment, maximum cylinder mode  202  is a six cylinder mode, intermediate cylinder mode is a four cylinder mode and minimum cylinder mode is a three cylinder mode. However, in other embodiments, each cylinder mode may use a different number of cylinders during operation. 
     In different embodiments, each cylinder mode can be achieved by deactivating different cylinders. Generally, any combination of cylinders may be deactivated in order to achieve a deactivated cylinder mode. In embodiments including an intermediate, or four cylinder, mode, any combination of two cylinders can be deactivated to achieve the intermediate mode. For example, in another embodiment, intermediate cylinder mode  204  can be achieved by deactivating first cylinder  111  and sixth cylinder  116  and allowing the other cylinders to remain activated. In still another embodiment, intermediate cylinder mode  204  can be achieved by deactivating fifth cylinder  115  and sixth cylinder  116 . In still other embodiments, any other two cylinders can be deactivated. Likewise, in embodiments including a minimum, or low cylinder, mode any combination of three cylinders can be deactivated to achieve the minimum mode. For example, in another embodiment, first cylinder  111 , third cylinder  113  and fifth cylinder  115  may be deactivated and second cylinder  112 , fourth cylinder  114  and sixth cylinder  116  may remain activated to achieve minimum cylinder mode  206 . 
     Generally, engine  102  may switch between maximum, intermediate and minimum (in this case six, four and three) cylinder modes according to current power demands. For high power demands, engine  102  may be operated in maximum cylinder mode  202 . For low power demands, engine  102  may be operated in minimum cylinder mode  206 . For intermediate power demands, engine  102  may be operated in intermediate cylinder mode  204 . In some cases, control unit  104  or another device may monitor current power demands and facilitate switching engine  102  between the minimum, intermediate and maximum cylinder modes  206 ,  204  and  202 , according to these power demands. 
     The configurations described here for cylinder deactivation are the preferred configurations. In particular, both intermediate cylinder mode  204  and minimum cylinder mode  206  include configurations of cylinders that are symmetric. These symmetric configurations will decrease the tendency of engine  102  to be unbalanced during operation. When engines with more than six cylinders are used, various other configurations of cylinder deactivation could also be accommodated. 
     Sometimes, problems may occur during cylinder deactivation. Under certain operating conditions, when an engine is in a deactivated cylinder mode, the engine mounts and exhaust system must operate under increased vibrations and exhaust flow pulsations. Additionally, drivetrain components can also introduce additional vibrations. In some cases, unacceptable levels of noise vibration and harshness (NVH) may occur and negatively impact the comfort of the driver and/or passengers within a motor vehicle. 
     Preferably, cylinder deactivation system  100  includes provisions for reducing or eliminating occurrences of unacceptable NVH within a motor vehicle due to cylinder deactivation. In some embodiments, cylinder deactivation may be prohibited under certain operating conditions of the motor vehicle, even when the current engine load does not require the use of all six cylinders  111 - 116 . In a preferred embodiment, control unit  104  may be configured to prohibit or stop cylinder deactivation when various operating parameters measured using sensor system  106  lie within discrete prohibited ranges. 
     Referring to  FIG. 3 , discrete ranges of engine speed may be associated with unacceptable levels of noise whenever engine  102  is in a deactivated cylinder mode. Relationship  302  is a preferred embodiment of noise vs. engine speed for various engine displacement modes. The noise, as used here, could be NVH in particular, as experienced by a driver or passenger in the cabin of the motor vehicle. In particular, minimum cylinder line  304 , intermediate cylinder line  306  and maximum cylinder line  308  are illustrated and represent the value of noise as a function of engine speed for minimum cylinder mode  206 , intermediate cylinder mode  204  and maximum cylinder mode  202  of engine  102  (see  FIG. 2 ), respectively. Noise limit  310  represents the upper limit on acceptable noise. 
     As seen in  FIG. 3 , minimum cylinder line  304  includes first peak  312 , disposed above noise limit  310 . Also, intermediate cylinder line  306  includes second peak  314 , disposed above noise limit  310 . Finally, it is clear that maximum cylinder line  308  is disposed below noise limit  310  for all speeds. This is to be expected since, presumably, engine  102  (see  FIG. 1 ) is tuned to limit noise for maximum cylinder mode  202  (see  FIG. 2 ) at all engine speeds. 
     In this preferred embodiment, first peak  312  of minimum cylinder line  304  corresponds to a range of engine speeds within first engine speed range  322 . First engine speed range  322  preferably includes the entire range of possible engine speeds for engine  102 . In particular, first peak  312  of minimum cylinder line  304  corresponds to first prohibited range  320 . First prohibited range  320  may be limited below by first lower limit L 1  and bounded above by first upper limit L 2 . In this embodiment, if the current engine speed has a value that lies within first prohibited range  320 , undesired noise may occur when the engine is operating in minimum cylinder mode  206 . 
     Second peak  314  of intermediate cylinder line  306  also preferably corresponds to a range of engine speeds within second engine speed range  324 . Second engine speed range  324  is preferably identical to first engine speed range  322 , including the entire range of possible engine speeds for engine  102 . In this embodiment, second peak  314  of intermediate cylinder line  306  corresponds to second prohibited range  326 . Second prohibited range  326  may be limited below by second lower limit L 3  and bounded above second upper limit L 4 . In this embodiment, if the current engine speed has a value that lies within the second prohibited range  326 , undesired noise may occur when the engine is operating in intermediate cylinder mode  204 . 
     Prohibited ranges  320  and  326  are only meant to be illustrative of possible ranges of engine speed where undesirable noise may occur. In other embodiments, prohibited ranges  320  and  326  may be any ranges, as determined by various empirical or theoretical considerations. In the preferred embodiment, control unit  104  may be configured to include these predetermined prohibited ranges that may be used in controlling cylinder deactivation. Furthermore, all prohibited ranges discussed throughout this detailed description are only meant to illustrate possible prohibited ranges, including prohibited ranges of various types of parameters associated with varying levels of noise. In other embodiments, each prohibited range may vary. 
     In other embodiments, each cylinder mode  204  and  206  may include multiple prohibited ranges for engine speed.  FIG. 4  is a preferred embodiment of prohibited ranges  400  of third engine speed range  402  and fourth engine speed range  404 , corresponding to the possible range of engine speeds for minimum cylinder mode  206  and intermediate cylinder mode  204 , respectively. In this embodiment, third engine speed range  402  includes third prohibited range  406  and fourth prohibited range  408 . Third prohibited range  406  is preferably bounded below by third lower limit L 5  and bounded above by third upper limit L 6 . Fourth prohibited range  408  is preferably bounded below by fourth lower limit L 7  and bounded above by fourth upper limit L 8 . In this embodiment, if the current engine speed has a value that lies within third prohibited range  406  or fourth prohibited range  408 , undesired noise may occur when the engine is operating in minimum cylinder mode  206 . 
     In addition, fourth engine speed range  404  preferably includes fifth prohibited range  410  and sixth prohibited range  412 . Fifth prohibited range  410  is preferably bounded below by fifth lower limit L 9  and bounded above by fifth upper limit L 10 . Sixth prohibited range  412  is preferably bounded below by sixth lower limit L 11  and bounded above by sixth upper limit L 12 . In this embodiment, if the current engine speed has a value that lies within fifth prohibited range  410  or sixth prohibited range  412 , undesired noise may occur when the engine is operating in intermediate cylinder mode  204 . 
     Preferably, cylinder deactivation system  100  includes provisions for prohibiting cylinder deactivation when the current engine speed lies within one of these prohibited ranges in order to reduce or eliminate unwanted levels of noise. In some embodiments, control unit  104  may prohibit or stop cylinder deactivation in response to information received by sensors. In a preferred embodiment, control unit  104  may prohibit or stop cylinder deactivation in response to information received by engine speed sensor  121 . 
       FIG. 5  is a preferred embodiment of method  500  of a process for controlling cylinder deactivation between maximum cylinder mode  202  and minimum cylinder mode  206 . For purposes of clarity, intermediate cylinder mode  204  is not available for engine  102  in the current embodiment. In other words, in the current embodiment, the only available deactivated cylinder mode is minimum cylinder mode  206 . In other embodiments, a similar process could also be used to control cylinder deactivation between maximum cylinder mode  202  and intermediate cylinder mode  204 . 
     The following steps are preferably performed by control unit  104 . However, in some embodiments, some of the steps may be performed outside of control unit  104 . 
     During a first step  502 , control unit  104  preferably determines if cylinder deactivation is available. In other words, control unit  104  determines if engine  102  is currently in a deactivated mode or if engine  102  may switch to a cylinder deactivation mode soon. Preferably, the availability of cylinder deactivation is determined by current power demands on the engine, as previously discussed. In particular, the switching or continued running of engine  102  in minimum cylinder mode  206  is preferably determined according to current power demands. 
     If the engine is required to operate in maximum cylinder mode according to the current power demands, cylinder deactivation is not available, and control unit  104  may proceed to step  504 . During step  504  control unit  104  waits for the availability of cylinder deactivation. If, during step  502 , cylinder deactivation is available, in other words the engine may soon be or is operating in minimum cylinder mode  206 , control unit  104  proceeds to step  506 . 
     Once control unit  104  proceeds to step  506 , control unit  104  preferably receives information from one or more sensors. In the current embodiment, control unit  104  preferably receives information from engine speed sensor  121 . In other embodiments, control unit  104  could receive information from additional sensors as well. 
     Next, during step  508 , control unit  104  determines if the current engine speed, as determined during the previous step  506 , lies in a prohibited range associated with minimum cylinder mode  206 . In the current embodiment, first prohibited range  320  (see  FIG. 3 ) is the prohibited range associated with minimum cylinder mode  206 . In other embodiments, however, any prohibited range could be used. If, during step  508 , the current engine speed is determined to be within first prohibited range  320  associated with minimum cylinder mode  206 , control unit  104  preferably proceeds to step  510 . During step  510 , control unit  104  stops or prohibits cylinder deactivation. 
     On the other hand, if, during step  508 , the current engine speed is determined to be outside of first prohibited range  320  associated with minimum cylinder mode  206 , control unit  104  preferably proceeds to step  512 . In this embodiment, the current engine speed could lie outside first prohibited range  320  if it is either below first lower limit L 1  or above first upper limit L 2 . During step  512 , control unit  104  preferably continues, or permits, cylinder deactivation. 
     For the purposes of clarity, a single prohibited range was considered for each cylinder mode in the previous embodiment (see  FIG. 3 ). However, in other embodiments, multiple prohibited regions could also be used. For example, returning to step  508  of the previous embodiment, control unit  104  may compare the current engine speed with the prohibited ranges  406  and  408  (see  FIG. 4 ), associated with minimum cylinder mode  206 . Whenever the current engine speed is below lower limit L 5  of third prohibited range  406  or above upper limit L 8  of fourth prohibited range  408 , control unit  104  may proceed to step  512  to permit or continue cylinder deactivation. Likewise, whenever the current engine speed is between upper limit L 6  and lower limit L 7 , control unit  104  may proceed to step  512  to permit or continue cylinder deactivation. Alternatively, whenever the current speed is between lower limit L 5  and upper limit L 6  of the third prohibited range  406  or between lower limit L 7  and upper limit L 8  of the fourth prohibited range  408 , control unit  104  may proceed to step  510  to stop or prohibit cylinder deactivation. A similar process could also be applied to prohibit intermediate cylinder mode  204 , using prohibited ranges  410  and  412 . 
     By using this single or multiple prohibited range configuration, the range of engine speeds over which cylinder deactivation is prohibited can be confined to smaller discrete ranges, rather than a single large range that includes all of the speeds associated with unacceptable noise. In previous designs, a single threshold value for a parameter such as engine speed has been used to determine if cylinder deactivation should be prohibited or stopped. Such designs limit, the use of cylinder deactivation with speeds above (for example) the threshold value, even though the prohibited region may only include a small range of engine speeds associated with unacceptable noise. By increasing the range of engine speeds where cylinder deactivation is allowed, greater fuel efficiency can be achieved over other systems that use a single threshold value. 
     In the previous embodiment, the cylinder mode of the engine was assumed to be predetermined by power demands. In particular, either one deactivation mode (minimum deactivation mode  206  or intermediate deactivation mode  204 ) was available to engine  102 , according to power demands, or engine  102  was operated in maximum cylinder mode  202 . In some cases, the available cylinder mode as determined by power demands may not be allowed due to prohibited values of engine speed, however another deactivated mode may be allowed for the same engine speed. For example, the current engine speed could lie within a prohibited range associated with minimum cylinder mode  206  and prevents engine  102  from switching to or continuing to operate in minimum cylinder mode  206 . However, if the current engine speed does not lie in a prohibited region for operating engine  102  in intermediate cylinder mode  204 , control unit  104  could switch engine  102  to intermediate cylinder mode  204 , rather than completely stopping or prohibiting cylinder deactivation. 
       FIG. 6  is a preferred embodiment of method  600  of a process for controlling cylinder deactivation system  100 . In this embodiment, two cylinder deactivation modes are assumed to be available, including minimum cylinder mode  206  and intermediate cylinder mode  204 , according to the current power demands. In other words, engine  102  is either currently operating in, or about to switch to, one of these two deactivated cylinder modes. In particular, the current power demands would allow for engine  102  to operate in either cylinder mode  204  or  206 . Throughout the current embodiment, the prohibited ranges or unacceptable noise ranges associated with each of these cylinder modes  204  and  206  are the same as for the previous embodiment, which may be found in  FIG. 3 . 
     Starting at step  602 , control unit  104  preferably receives information from at least one sensor. In a preferred embodiment, control unit  104  may receive information from vehicle speed sensor  121 . In another embodiment, control unit  104  may receive information from additional sensors as well. Following this step  602 , control unit  104  may proceed to step  604 . 
     During step  604 , control unit  104  may determine if engine  102  is operating in first prohibited range  320 , associated with minimum cylinder mode  206 . Because both minimum cylinder mode  206  and intermediate cylinder mode  204  are assumed to be available, control unit  104  is configured to start by checking to see if engine  102  could run in minimum cylinder mode  206 , since typically the smallest engine displacement is preferred whenever more than one deactivated cylinder mode is available. If control unit  104  determines that the current engine speed does not lie within first prohibited range  320 , control unit  104  preferably proceeds to step  606 . During step  606 , control unit  104  preferably switches engine  102  to, or allows engine  102  to continue in, minimum cylinder mode  206 . 
     If, during step  604 , control unit  104  determines that the current engine speed is within first prohibited range  320 , control unit  104  preferably proceeds to step  608 . During step  608 , control unit  104  determines if the current engine speed is within second prohibited range  326  associated with intermediate cylinder mode  204 . If the current engine speed is within second prohibited range  326 , control unit  104  preferably proceeds to step  610 . In the current embodiment, first prohibited region  320  and second prohibited region  326  do not overlap, and therefore the current engine speed could not be in both prohibited ranges. However, in embodiments where the prohibited regions do overlap, control unit  104  would proceed to step  610 . During step  610 , control unit  104  preferably stops or prohibits cylinder deactivation, since the current engine speed lies within both the first and second prohibited ranges. In this case, engine  102  is configured to operate in maximum cylinder mode  202 . 
     If, during step  608 , control unit  104  determines that the current engine speed is outside of second prohibited range  326 , control unit  104  preferably proceeds to step  612 . During step  612 , engine  102  is preferably configured to operate in intermediate cylinder mode  204 . 
     Using this method, engine  102  may be operated in any deactivated cylinder mode where the current engine speed is not within a prohibited range of speeds associated with the deactivated cylinder mode and the deactivated cylinder mode is available according to current power demands. This configuration allows increased fuel efficiency, since engine  102  may operate in a deactivated cylinder mode by switching between two or more deactivated cylinder modes when the current engine speed falls within the prohibited range of one deactivation mode, but not within a prohibited range of the other deactivated mode. 
     Although the current embodiment includes two deactivated cylinder modes, in other embodiments, additional deactivated cylinder modes could be used. Furthermore, throughout the remainder of this detailed description, wherever a method or process is given for controlling cylinder deactivation system  100 , it should be understood that the method or process could be modified for switching between any available deactivated cylinder modes. 
     The current embodiment is only intended to illustrate a method for controlling cylinder deactivation according to engine speed. In other embodiments, other parameters may be associated with unacceptable levels of noise for certain values of those parameters. Using a process or method similar to the method used for controlling cylinder deactivation according to engine speed, control unit  104  could be configured to control cylinder deactivation according to these other parameters. 
     In another embodiment, vehicle speed could be used to control cylinder deactivation. Vehicle speed is important because it may be associated with various driveline vibrations that can lead to unacceptable noise whenever engine  102  is in a deactivated cylinder mode. As with the previous embodiment, one or more discrete ranges of vehicle speeds associated with unacceptable noise could be identified and control unit  104  could prohibit cylinder deactivation whenever the current vehicle speed is within one of these prohibited ranges. 
     Referring to  FIG. 7 , discrete ranges of vehicle speed could be associated with unacceptable levels of noise whenever engine  102  is in a deactivated cylinder mode. Relationship  702  is a preferred embodiment of noise vs. vehicle speed for various engine displacement modes. In particular, minimum cylinder line  704 , intermediate cylinder line  706  and maximum cylinder line  708  are illustrated and represent the value of noise as a function of vehicle speed for minimum cylinder mode  206 , intermediate cylinder mode  204  and maximum cylinder mode  202  (see  FIG. 2 ), respectively. Noise limit  710  represents the upper limit on acceptable noise. As seen in  FIG. 7 , minimum cylinder line  704  includes third peak  712 , disposed above noise limit  710 . Also, intermediate cylinder line  706  includes fourth peak  714 , disposed above noise limit  710 . Finally, it is clear that maximum cylinder line  708  is disposed below noise limit  710  for all speeds. This is to be expected since, presumably, engine  102  (see  FIG. 1 ) is tuned to limit noise for maximum cylinder mode  206  (see  FIG. 2 ) at all vehicle speeds. 
     In this preferred embodiment, third peak  712  of minimum cylinder line  704  corresponds to a range of vehicle speeds within first vehicle speed range  722 . First vehicle speed range  722  preferably includes the entire range of possible vehicle speeds for the motor vehicle associated with engine  102 . In particular, third peak  712  of minimum cylinder line  704  corresponds to first prohibited range  720 . First prohibited range  720  may be limited below by first lower limit T 1  and bounded above by first upper limit T 2 . In this embodiment, if the vehicle speed has a value that lies within first prohibited range  720 , undesired noise may occur when the engine is operating in minimum cylinder mode  206 . 
     Fourth peak  714  of intermediate cylinder line  706  also preferably corresponds to a range of vehicle speeds within second vehicle speed range  724 . Second vehicle speed range  724  is preferably identical to first vehicle speed range  722 , including the entire range of possible vehicle speeds for the motor vehicle associated with engine  102 . In particular, fourth peak  714  of intermediate cylinder line  706  corresponds to second prohibited range  726 . Second prohibited range  726  may be limited below by second lower limit T 3  and bounded above second upper limit T 4 . In this embodiment, if the vehicle speed has a value that lies within the second prohibited range  726 , undesired noise may occur when the engine is operating in intermediate cylinder mode  204 . 
     As with the previous embodiment, each deactivated cylinder mode  204  and  206 , may include multiple prohibited ranges for vehicle speed. These multiple prohibited ranges of vehicle speed may vary for different embodiments. 
     Preferably, cylinder deactivation system  100  includes provisions for prohibiting cylinder deactivation when the vehicle speed lies within one of these prohibited ranges in order to reduce or eliminate unwanted levels of noise. In some embodiments, control unit  104  may prohibit or stop cylinder deactivation in response to information received by sensors. In a preferred embodiment, control unit  104  may prohibit or stop cylinder deactivation in response to information received by vehicle speed sensor  122 . 
       FIG. 8  is a preferred embodiment of method  800  of a process for controlling cylinder deactivation between maximum cylinder mode  202  and minimum cylinder mode  206 . For purposes of clarity, intermediate cylinder mode  204  is not available for engine  102  in the current embodiment. In other words, in the current embodiment, the only available deactivated cylinder mode is minimum cylinder mode  206 . In other embodiments, a similar process could also be used to control cylinder deactivation between maximum cylinder mode  202  and intermediate cylinder mode  204 . The following steps are preferably performed by control unit  104 . However, in some embodiments, some of the steps may be performed outside of control unit  104 . 
     During a first step  802 , control unit  104  preferably determines if cylinder deactivation is available. In other words, control unit  104  determines if engine  102  is currently in a deactivated mode or if engine  102  may switch to a cylinder deactivation mode soon. Preferably, the availability of cylinder deactivation is determined by current power demands on the engine, as previously discussed. In particular, the switching or continued running of engine  102  in minimum cylinder mode  206  is preferably determined according to current power demands. 
     If the engine is required to operate in maximum cylinder mode according to the current power demands, cylinder deactivation is not available, and control unit  104  may proceed to step  804 . During step  804  control unit  104  waits for the availability of cylinder deactivation. If, during step  802 , cylinder deactivation is available, in other words the engine may soon be or is operating in minimum cylinder mode  206 , control unit  104  proceeds to step  806 . 
     Once control unit  104  proceeds to step  806 , control unit  104  preferably receives information from one or more sensors. In the current embodiment, control unit  104  preferably receives information from vehicle speed sensor  122 . In other embodiments, control unit  104  could receive information from additional sensors as well. 
     Next, during step  808 , control unit  104  determines if the current vehicle speed, as determined during the previous step  806 , lies in a prohibited range associated with minimum cylinder mode  206 . In the current embodiment, first prohibited range  720  (see  FIG. 7 ) is the prohibited range associated with minimum cylinder mode  206 . In other embodiments, however, any prohibited range could be used. If, during step  808 , the current vehicle speed is determined to be within first prohibited range  720  associated with minimum cylinder mode  206 , control unit  104  preferably proceeds to step  810 . During step  810 , control unit  104  stops or prohibits cylinder deactivation. 
     On the other hand, if, during step  808 , the current vehicle speed is determined to be outside of first prohibited range  720  associated with minimum cylinder mode  206 , control unit  104  preferably proceeds to step  812 . In this embodiment, the current vehicle speed could lie outside first prohibited range  720  if it is either below first lower limit T 1  or above first upper limit LT. During step  812 , control unit  104  preferably continues, or permits, cylinder deactivation. 
     As with the previous embodiment, multiple prohibited ranges could also be used during step  808 . In this case, cylinder deactivation would be prohibited if the current vehicle speed was determined to be within any of the multiple prohibited ranges associated with minimum cylinder mode  206 . 
     By using this single or multiple prohibited range configuration, the range of vehicle speeds over which cylinder deactivation is prohibited can be confined to smaller discrete ranges, rather than a single large range that includes all of the vehicle speeds associated with unacceptable noise. By increasing the range of vehicle speeds over which cylinder deactivation is allowed, greater fuel efficiency can be achieved over other systems that use a single threshold value. 
     Another cause of noise during deactivated cylinder modes is driveline vibrations that vary with different gears. In another embodiment, transmission conditions could be used to determine if cylinder deactivation should be prohibited due to undesired levels of noise associated with particular gears, or discrete ranges of gears. 
     Generally, prohibited regions could be defined by one or more gears that are associated with undesired noise during deactivated cylinder modes.  FIG. 9  is a preferred embodiment of prohibited gears associated with minimum cylinder mode  206  and intermediate cylinder mode  204 . In this embodiment, gear  902  and gear  904  are preferably associated with high levels of noise when engine  102  is in minimum cylinder mode  206  (associated with first gear range  920 ). Likewise, in this embodiment, gear  906  and gear  908  are associated with high levels of noise when engine  102  is in intermediate cylinder mode  204  (associated with second gear range  922 ). 
     In some cases, a motor vehicle may include a continuously variable transmission (CVT), rather than a standard transmission with fixed gear ratios. Under these circumstances, undesired NVH may occur within ranges of transmission conditions. The term ‘transmission condition’ refers to a particular state of the CVT system, corresponding to some value for the input/output ratio of the rotational shafts. As with previously discussed parameters such as vehicle speed and engine speed, the transmission condition of a CVT may take on any value within some predefined range. 
       FIG. 10  is a preferred embodiment of prohibited transmission conditions for an engine operating in minimum cylinder mode  206  and an engine operating in intermediate cylinder mode  204 . In this embodiment, first prohibited region  1002  of first transmission condition range  1004  is bounded below by first lower value V 1  and bounded above by first upper value V 2 . Second prohibited region  1006  of second transmission condition range  1008  in bounded below by second lower value V 3  and bounded above by second upper value V 4 . As with the previous embodiment, each cylinder mode  204  and  206  may include multiple prohibited ranges for transmission conditions. 
     Preferably, cylinder deactivation system  100  includes provisions for prohibiting cylinder deactivation when the current transmission condition lies within one of these prohibited ranges in order to reduce or eliminate unwanted levels of noise. In some embodiments, control unit  104  may prohibit or stop cylinder deactivation in response to information received by sensors. In a preferred embodiment, control unit  104  may prohibit or stop cylinder deactivation in response to information received by transmission sensor  126 . 
       FIG. 11  is a preferred embodiment of method  1100  of a process for controlling cylinder deactivation between maximum cylinder mode  202  and minimum cylinder mode  206 . For purposes of clarity, intermediate cylinder mode  204  is not available for engine  102  in the current embodiment. In other words, in the current embodiment, the only available deactivated cylinder mode is minimum cylinder mode  206 . In other embodiments, a similar process could also be used to control cylinder deactivation between maximum cylinder mode  202  and intermediate cylinder mode  204 . The following steps are preferably performed by control unit  104 . However, in some embodiments, some of the steps may be performed outside of control unit  104 . 
     During a first step  1102 , control unit  104  preferably determines if cylinder deactivation is available. In other words, control unit  104  determines if engine  102  is currently in a deactivated mode or if engine  102  may switch to a cylinder deactivation mode soon. Preferably, the availability of cylinder deactivation is determined by, current power demands on the engine, as previously discussed. In particular, the switching or continued running of engine  102  in minimum cylinder mode  206  is preferably determined according to current power demands. 
     If the engine is required to operate in maximum cylinder mode  202  according to the current power demands, cylinder deactivation is not available, and control unit  104  may proceed to step  1104 . During step  1104  control unit  104  waits for the availability of cylinder deactivation. If, during step  502 , cylinder deactivation is available, in other words the engine may soon be or is operating in minimum cylinder mode  206 , control unit  104  proceeds to step  1106 . 
     Once control unit  104  proceeds to step  1106 , control unit  104  preferably receives information from one or more sensors. In the current embodiment, control unit  104  preferably receives information from transmission sensor  126 . In other embodiments, control unit  104  could receive information from additional sensors as well. 
     Next, during step  1108 , control unit  104  determines if the current transmission condition, as determined during the previous step  1106 , lies in a prohibited range associated with minimum cylinder mode  206 . In the current embodiment, first prohibited range  1002  (see  FIG. 10 ) is the prohibited range associated with minimum cylinder mode  206 . In other embodiments, however, any prohibited range could be used. If, during step  1108 , the transmission condition is determined to be within first prohibited range  1002  associated with minimum cylinder mode  206 , control unit  104  preferably proceeds to step  1110 . During step  1110 , control unit  104  stops or prohibits cylinder deactivation. 
     On the other hand, if, during step  1108 , the current transmission condition is determined to be outside of first prohibited range  1002  associated with minimum cylinder mode  206 , control unit  104  preferably proceeds to step  1112 . In this embodiment, the current transmission ratio could lie outside first prohibited range  1002  if it is either below first lower limit V 1  or above first upper limit V 2 . During step  1112 , control unit  104  preferably continues, or permits, cylinder deactivation. 
     Alternatively, during step  1108 , multiple prohibited ranges could be used. 
     By using this single or multiple prohibited range configuration, the range of transmission conditions over which cylinder deactivation is prohibited can be confined to smaller discrete ranges, rather than a single large range that includes all of the transmission conditions associated with unacceptable noise. By increasing the range of transmission conditions over which cylinder deactivation is allowed, greater fuel efficiency can be achieved over other systems that use a single threshold value. 
     In another embodiment, engine load conditions at a given engine speed could be used to determine if cylinder deactivation should be prohibited due to undesired levels of noise. In this embodiment, it may be important to know both the current engine speed and the current engine load in order to determine if the engine is operating within a prohibited region associated with unacceptable noise. 
       FIG. 12  is a preferred embodiment of method  1200  of a process for controlling cylinder deactivation according to engine speed and engine load. In the current embodiment, it is assumed that control unit  104  has already determined that engine  102  is in a deactivated mode. During a first step  1202 , control unit  104  preferably receives information from multiple sensors. Preferably, control unit  104  receives information from sensors associated with engine load conditions. In the current embodiment, control unit  104  may receive information from engine speed sensor  121 , intake manifold sensor  123 , throttle angle sensor  124  and/or airflow sensor  125 . Next, during step  1204 , control unit  104  may determine the current engine speed and engine load. In particular, using measurements made by one or more of sensors  123 - 125 , control unit  104  could calculate or determine the current engine load and determine the current engine speed directly from engine speed sensor  121 . 
     Following step  1204 , control unit  104  preferably proceeds to step  1206 . During step  1206 , control unit  104  may determine if the engine is operating in a prohibited region, according to a predetermined prohibited region.  FIG. 13  is a preferred embodiment of relationship  1300  illustrating possible prohibited regions for minimum cylinder mode and intermediate cylinder mode. In particular, first prohibited region  1302  is preferably associated with minimum cylinder mode  206  and second prohibited mode  1304  is preferably associated with intermediate cylinder mode  204 . Using relationship  1300 , or a similar table, control unit  104  can determine if the current engine speed and engine load lie within the first prohibited region  1302  when the engine is operating in minimum cylinder mode  206  or within the second prohibited region when the engine is operating in intermediate cylinder mode  204 . If the engine speed and engine load are associated with a point on relationship  1300  within the prohibited region associated with the available cylinder mode, control unit  104  may proceed to step  1208 . During step  1208 , control unit  104  preferably prohibits or stops cylinder deactivation. Otherwise control unit  104  may proceed to step  1210 . During step  1210 , control unit  104  preferably continues cylinder deactivation. 
       FIGS. 14 and 15  refer to a preferred embodiment of a general method for controlling cylinder deactivation using any parameters where predetermined prohibited ranges of the parameters (associated with undesired noise) are available. These parameters may be any of the parameters discussed previously, as well as other parameters for which discrete ranges of the parameters are associated with undesired noise. 
     During a first step  1402 , control unit  104  may receive information from multiple sensors. In some embodiments, control unit  104  preferably receives information from engine speed sensor  121 , vehicle speed sensor  122 , intake manifold sensor  123 , throttle angle sensor  124 , airflow sensor  125  and transmission sensor  126 . Additionally, in some embodiments, control unit  104  may receive information from a linear airflow sensor, an S02 sensor, a knock sensor, an oil pressure sensor, a crank position sensor, a transmission temperature sensor, a transmission speed sensor, a VCM solenoid sensor, an active mount sensor, as well as other types of sensors associated with a motor vehicle. Furthermore, in some embodiments, control unit  104  can receive information from one or more systems, including, but not limited to a drive-by-wire system and an active noise cancellation system, as well as other systems. It should be understood that in other embodiments, control unit  104  can receive information from any sensor or system associated with a motor vehicle. 
     Following step  1402 , control unit  104  may proceed to step  1404 . During step  1404 , control unit  104  may determine the parameters relevant to controlling cylinder deactivation.  FIG. 15  is a preferred embodiment of an exemplary list of the parameters referred to in step  1404 . Generally, any sensed values or any values calculated by a control unit can be used to determine a region of limited cylinder deactivation activity. In some embodiments, these parameters may include, but are not limited to the engine speed, the vehicle speed, the transmission condition and the engine load. Additionally, these parameters can include airflow, SO2 levels, manifold pressure, knock levels, oil pressure, crank position, transmission temperature, transmission speed, VCM solenoid values, active mount information and active noise information. In still other embodiments, additional parameters can be used according to information received from any sensors as well as any calculated values determined by the control unit. 
     Next, control unit  104  preferably proceeds from step  1404  to step  1406 , where control unit  104  may compare the parameters from the previous step  1404  with prohibited operating ranges for these parameters. Preferably, these prohibited operating ranges are predetermined operating ranges that are currently available to control unit  104 . If the parameters are determined to be within the prohibited ranges associated with the operating parameters, control unit  104  preferably proceeds to step  1408 , where control unit  104  prohibits or stops cylinder deactivation. Otherwise, control unit  104  may proceed to step  1410 , where control unit  104  continues cylinder deactivation. 
     As previously discussed, the current embodiment could be modified to incorporate additional deactivated cylinder modes, as well as provisions for switching between various deactivated cylinder modes. Also, the prohibited ranges discussed here could be determined by any method, including empirical or theoretical considerations. In particular, there may be multiple prohibited ranges for any given parameter. 
     While various embodiments of the invention have been described, the description is intended to be exemplary, rather than limiting and it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents. Also, various modifications and changes may be made within the scope of the attached claims.