Patent Publication Number: US-6209520-B1

Title: Method and apparatus for cylinder balancing

Description:
FIELD OF THE INVENTION 
     This invention relates to a method and to an apparatus for cylinder balancing and more particularly to a method and to an apparatus for balancing the cylinders of an automobile engine effective to cause each of these cylinders to produce a substantially equal torque. 
     BACKGROUND OF THE INVENTION 
     Automobile engine combustion cylinders typically include a movable piston which is connected to a crankshaft. Particularly, air and gasoline are selectively and mixably combusted within the chambers causing the respectively contained pistons to move within the cylinders and against the crankshaft, thereby cooperatively causing the crankshaft to rotate. The selectively moving pistons therefore cooperatively and individually create a torque which is applied to the crankshaft and which causes the automobile to be selectively movable. 
     Due to structural variances of each of the respective cylinders, variations in the amount of air introduced into each of the cylinders, and/or variations associated with the fuel injection assemblies utilized by each of the cylinders, the torque produced by each of the cylinders is not substantially equal, thereby causing the cylinders to be “out of balance”. This imbalance causes or creates an undesirable crankshaft oscillation and drive train resonance which reduces the operating life of the drive train and increases gasoline consumption and the generation of undesirable combustion created emissions. It is therefore desirable to have the torque produced by each of the cylinders be substantially equal and to have the cylinders “balanced.” 
     Existing cylinder balancing methodologies using individual peak cylinder pressure values or crankshaft acceleration measurements are highly susceptible to noise type error and provide relatively unreliable and inaccurate balancing corrections. There is therefore a need for a new and improved balancer assembly. 
     SUMMARY OF THE INVENTION 
     It is a first object of this invention to provide a method and an apparatus for balancing the combustion cylinders of an automobile effective to cause the torque produced by each of the cylinders to be substantially equal. 
     It is a second object of this invention to provide a method and an apparatus for balancing the combustion cylinders of an automobile by use of pressure sensors, each of which is resident within a unique one of each of the cylinders. 
     It is a third object of this invention to provide a method and an apparatus for balancing the combustion cylinders of an automobile by the use of a pressure sensor resident within an exhaust manifold. 
     According to a first aspect of the present invention a cylinder balancing assembly is provided for use with an automobile engine having several combustion cylinders which each contain a movable piston. The engine further includes a movable crankshaft, several conrods which each connect a unique one of the pistons to the crankshaft, and several fuel injectors which are each adapted to receive a quantity of fuel and to selectively inject the fuel into a unique one of the cylinders, the injected fuel being selectively combined with air and combusted within each of the cylinders effective to create a certain respective pressure which cycles each of the respective pistons between a first extended position and a second crankshaft rotation position in which each cylinder produces a torque by having its respective piston rotate the crankshaft and then completing a movement cycle by returning to the respective first position. The cylinder balancing assembly includes several sensors which respectively sense the pressure of a unique one of the cylinders and which respectively provide an output signal representing the respectively sensed pressure; and a controller which is coupled to the several sensors and to the several fuel injectors. The controller receives the output signals from each of the several sensors, uses the output signals to calculate the total amount of torque produced by each of the moving pistons during each of their respective movement cycles, and based upon the calculation regulates the amount of fuel entering each of the fuel injectors effective to cause each of the produced torques to be substantially equal, thereby balancing the cylinders. 
     According to a second aspect of the present invention a method is provided to cause the torque produced by each of the cylinders of an automobile engine to be substantially equal. The method includes the steps of calculating the torque produced by each of the cylinders during certain respective intervals of time, thereby creating a plurality of torque values; averaging the calculated torque values; and regulating the amount of fuel injected into each of the cylinders, effective to cause each of the respective torques produced by each of the cylinders to be substantially equal to the average torque value. 
    
    
     Further objects, features, and advantages of the present invention will become apparent from a consideration of the following description when taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmented and block diagrammatic view of an automobile combustion cylinder assembly made in accordance with the teachings of the preferred embodiment of the invention; 
     FIG. 2 is a diagram similar to FIG.  1  and illustrating the movement of the pistons; 
     FIG. 3 is a fragmented and block diagrammatic view of an automobile combustion cylinder assembly made in accordance with the teachings of an alternate embodiment of the invention; and 
     FIG. 4 is a data table utilized by each of the assemblies shown in FIGS.  1  and  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
     Referring now to FIG. 1, there is shown an automobile engine combustion cylinder assembly  10  made in accordance with the teachings of the preferred embodiment of the invention. As shown, assembly  10  includes several combustion cylinders or chambers  12 ,  14 , each of which movably and respectively contains a unique piston  16 ,  18  which are respectively coupled to integrally formed projections  22 ,  24  of rotatable crankshaft  20  by connecting rods or “conrods”  26 ,  28 . While two piston-containing chambers  12 ,  14  are shown, it should be appreciated that additional and substantially identical combustion cylinders may be included within a typical automobile engine and that the foregoing invention is equally and substantially identically applicable to these other cylinder arrangements. 
     As further shown in FIG. 1, each chamber  12 ,  14  respectively communicates with a conventional and commercially available fuel injector assembly  30 ,  32 . Particularly, each injector  30 ,  32  is communicatively and selectively coupled to a source of gasoline or fuel  34  and selectively and controllably receives and injects fuel into the respective cylinders  12 ,  14 . The injected fuel is typically mixed with a certain amount of ambient air, selectively traversing through the intake manifold  35 , and this mixture is selectively combusted by use of a spark plug or other types of combustion assemblies (not shown), thereby selectively creating a certain pressure within each of the cylinders  12 ,  14  before being exhausted into the exhaust manifold  33 . 
     Particularly, this selectively created combustion pressure causes the respectively contained pistons  16 ,  18  to cycle or move from a first extended position, in close proximity to one of the fuel injectors  30 ,  32 , to a second crankshaft rotation position (shown in FIG. 2) in which the pistons  16 ,  18  respectively move away from the injectors  30 ,  32  and cause the respective and substantially identical conrods  26 ,  28  to create a torque which rotates the crankshaft  20  in the direction of arrow  21 . The selectively rotating crankshaft  20 , which is normally deployed within a “crank case”  23 , transfers the created rotational torque or force to the automobile drive train  29 , thereby allowing the automobile to be selectively moved or driven. A piston movement cycle is then completed when the pistons  16 ,  18  return to their respective first position. Typically, each of the cylinders  12 ,  14  provides one piston movement cycle within a certain designated time interval corresponding to a single engine rotation cycle or a single “firing” caused by the selective energization of each of the spark plugs contained within the automobile&#39;s spark plug assembly or by the selective increase in compression pressure, such as that occurring within a diesel engine. 
     As further shown in FIG. 1, assembly  10  includes a controller  36  which is operating under stored program control, which is controllably and communicatively coupled to the fuel injectors  30 ,  32 , and which is effective to selectively control the amount of fuel injected into each of the cylinders  12  and  14 . Controller  36  may comprise a conventional and commercially available microprocessor and the communication between controller  36  and the fuel injectors  30 ,  32  may occur by use of bus  37 . Moreover, in one embodiment of this invention, controller  36  is adapted to receive signals corresponding to the instantaneous speed of the engine, such signals being available, by way of example and without limitation, by use of a conventional tachometer bus (not shown) which is typically present within the automobile engine. These received signals also enable controller  36  to determine whether the vehicle is being accelerated or whether the transmission is selectively “shifting” or providing a new gearing arrangement. Controller  36  is also coupled, by bus  47 , to conventional and commercially available sensors  41 ,  43  which respectively measure and provide controller  36  with the pressure within crankcase  23  and the crank angle which will be described later. 
     Assembly  10  further includes pressure sensors  38 ,  40  which are respectively resident within each of the combustion cylinders  12 ,  14  and which each sense the pressure respectively and combustably created in each of the cylinders  12 ,  14  at substantially small and substantially regular intervals of time. These sensors  38 ,  40  create and communicate respective signals, representative of the respectively sensed pressures within the cylinders  12 ,  14 , to the controller  36  by use of bus  39 . Sensors  38 ,  40  may comprise conventional and commercially available piezoelectric sensors or optical sensors. Non-limiting examples of such sensors  38 ,  40  include the sensor commonly referred to by “model number 6125” which is produced by and is available from the Kistler Corporation and those optical sensors which are produced by and are available from Bookham Technologies, Inc. 
     In operation, controller  36  separately calculates the total amount of torque produced by each of the cylinders  12 ,  14  during each engine cycle. This is accomplished by mathematically integrating, during each engine cycle, a certain functional relationship existing between the instantaneous torque produced by each cylinder  12 ,  14  and certain measurable parameters or values, such as the values associated with the signals produced by each of the sensors  38 ,  40 ,  41 , and  43 . Particularly, in one embodiment of the invention, this functional relationship, which may be selectively and separately evaluated for each cylinder  12 ,  14  at an instant or interval of time, is expressed by “equation 1” below:                      Instantaneous                 torque     =                    τ   ^     i          (       p   cyl     ,   θ     )                   =                  (       p   cyl     -     p   a       )     ·   A   ·   r   ·                              (       sin                 θ     +       r                 sin                 θcos                 θ           l   2     -         r   2     ·     sin   2          θ             )                   (equation 1)                         
     The variables resident within equation 1 are as follows: 
     “P cyl ” represents the value of the signals produced by one of the sensors  38 ,  40 ; “θ” represents the “crank angle” which may be defined as the angle between one of the projections  22 ,  24  and the substantially vertical axis  25  passing through center  27  of crankshaft  20  and which is selectively measured and transmitted by sensor  43 . Of course, other angles may selectively be used. 
     “P α ” represents the pressure within the crankcase which may be approximated by the ambient pressure and which is selectively measured and transmitted by sensor  41 . “A” represents the cross-sectional area of each substantially identical piston  16 ,  18 ; “r” represents the crank radius shown as radius  50 ; and “l” represents the length of each of the substantially identical conrods  26 ,  28 . Some of these variables may change during each instant or interval of time over which the functional relationship is being evaluated. 
     In the preferred embodiment of the invention, this instantaneous torque function is mathematically integrated, by controller  36 , for each respective piston movement cycle of each cylinder  12 ,  14 , as shown more clearly in Equation 2 below:                  τ   i     =         ∫   0   upperimitvalue                τ   ^     i          (       p   cyl     ,   θ     )               θ                   for                 i       =   1       ,     …                 n             (equation 2)                         
     where i=a unique one of the engine&#39;s combustion cylinders and where the “upper limit value” equals 720° for a four stroke engine and 360° for a two stroke engine. 
     In the preferred embodiment of the invention, the foregoing total torque integral expression is separately evaluated for each cylinder  12 ,  14  during each engine rotation cycle in order to ensure that all of the torque produced by each of the cylinders  12 ,  14 , in their respective piston movement cycles, is accounted for and utilized in the balancing methodology. Importantly, the foregoing methodology provides a relatively accurate and reliable measure of the total torques produced by each of the respective cylinders  12 ,  14  and allows for relatively accurate cylinder balancing to be selectively accomplished in a superior manner to prior balancing techniques. 
     In this manner and for each engine cycle, the total torque produced by each cylinder  12 ,  14  is separately calculated by and stored within controller  36 . For each engine cycle, a mathematical average is produced. Particularly, each mathematical average is calculated by use of the total torque cylinder values occurring within a particular engine rotation cycle, according to equation 3 below: 
     Average of the cylinder torque values occurring within an                engine                 cycle     =       τ   d     =       1   4          ∑     τ   i                   (equation 3)                         
     For each engine cycle, controller  36 , in the preferred embodiment of the invention, subtracts the foregoing calculated average value “τ d ” from each of the previously calculated individual cylinder torque values used within the average calculation and occurring within that particular engine cycle, thereby producing or creating an imbalance value for each cylinder  12 ,  14 . 
     Particularly, these imbalance values represent the amount by which each of the torques, provided by each of the respective cylinders  12 ,  14 , in an engine cycle, respectively differ from the “average” torque value “τ d ”. Moreover, these imbalance values represent the amount of “correction” needed to be applied to each respective cylinder  12 ,  14  in order to cause each of the cylinders  12 ,  14  to provide substantially equal torques; each of the respective and corrected cylinder provided torques being substantially equal to this calculated average value “τ d ”. Alternatively, “τ d ” may represent the measured torque value of one of the cylinders  12 ,  14 , thereby obviating the need to calculate the foregoing “average value”. 
     For each engine cycle, each of these individual imbalance values are then stored within controller  36  and separately multiplied by an adaptive correction and/or control factor which is typically a fractional value and which selectively reduces each of the respective cylinder correction values, thereby forming respective “adaptive correction and/or adaptive control” values for each of the cylinders  12 ,  14 . These adaptive correction or control values allow the controller  36  to correct the calculated cylinder imbalances relatively slowly and in a “stepwise” manner. 
     This “slow or stepwise correction” is highly desirable since many of the factors, which cause cylinder imbalance, such as variations in the cylinder or fuel injectors which may be caused by a “build up” of soot, occur relatively slowly. Hence, the perceived or calculated “need” for a rather large instantaneous correction is probably due to some transient error. Rather than apply this errant and rather large correction, thereby risking inadvertently creating a relatively large and undesirable cylinder imbalance, the use of these adaptive control values allows a smaller “stepwise” correction to be made and allows the system  10  to later “re-calculate” the imbalances, during other engine cycles, to determine whether the large imbalance still remains and whether additional and perhaps larger “stepwise” corrections are necessary. 
     In an alternate embodiment of the invention, controller  36  contains a certain limit correction value which defines the largest possible correction (e.g., the largest amount of fuel) which may be “made” within system  10  and applied to any of the cylinders  12 ,  14  during a single correction interval. In this embodiment, each adaptive control value is compared with this limit and the correction is made only if the limit is not exceeded. If the limit is exceeded, only the correction defined by the limit is made. 
     In yet another embodiment of the invention, the average value “τ d ” is updated for each rotation of crankshaft  20  corresponding to and/or equaling about 180°. That is, each cylinder  12 ,  14  produces a total torque for each respective rotation of the crankshaft  20  equaling about 180°. Hence, as these new total torque values become available, in this embodiment, they are immediately used to update the average value “τ d ” and to allow adaptive control values to be generated during each such 180° rotation of the crankshaft  20  and to thereafter be employed by system  10  in the foregoing manner. 
     In the preferred embodiment of the invention, the very first adaptive control values (“the initial adaptive control valves”), each being respectively associated with a unique one of the cylinders  12 ,  14 , are applied to the respective cylinders  12 ,  14  and are later stored within a separate table  200  contained within controller  36  and shown, for example and without limitation in FIG.  3 . In the preferred embodiment of the invention, each cylinder  12 ,  14  is uniquely associated with a separate and distinct table  200  and each table  200  contains only the data which is associated with one unique cylinder  12 ,  14  and which is stored within controller  36 . 
     Particularly, each table  200  initially contains a unique one of the initial adaptive correction values  202 . Each value  202  is referenced within the table  200  which corresponds to the very same cylinder  12 ,  14  that the value  202  corresponds to. Each value  202  is referenced within the table  200  by the engine speed  208  and amount of injected fuel  206  occurring and measured when value  202  was calculated. 
     Each new adaptive correction value, which is calculated when the engine is at the same or substantially the same engine speed  208  and the amount of fuel being injected into the respective cylinder  12 ,  14  is equal or substantially equal to fuel value  206 , is simply added to the previously stored correction value  202 , thereby creating an updated correction value. The previous correction value  202  is replaced by this updated correction value within the table  200  and the fuel correction defined by the updated correction value is made within assembly  10 . If no previous correction value  202  for a particular engine speed and fuel injection value exists within the table  200 , the current adaptive correction value along with the current engine speed and the amount of fuel being injected into the corresponding cylinder  12 ,  14  is insertably stored within the table  202  and its specified correction is applied to the respective and corresponding cylinder  12 ,  14 . 
     In the foregoing manner, controller  36  automatically contains the respective corrected fuel amount necessary to balance the cylinders  12 ,  14  at a particular sensed engine speed and fuel injection level. Hence, controller  36  automatically ensures that the historically required fuel corrections are made at every engine speed and fuel injection level which is referenced within each table  200 , thereby automatically achieving an approximate cylinder balancing condition based upon historical data. The imbalance associated with this historically generated condition is then measured and modified in the manner described above, such modifications being placed within table  200  and forming the updated “historical data” which may be later utilized by controller  36 . Each table  200  remains stored within controller  36  even after the automobile ceases to be operated or to “run”. In another alternate embodiment, each updated correction value is reduced by a value equal to the arithmetic mean of all of the previous correction values in order to reduce and/or correct for non-zero biasing. In yet another alternate embodiment of the invention, balancing assembly  10  is made inoperable during vehicle accelerations or transmission gear shifting in order to reduce the probability of noise generated error. 
     Referring now to FIG. 2 there is shown an assembly  100  which is made in accordance with the teachings of a second embodiment of the invention and which differs from the embodiment described with respect to FIG. 1 by the use of a single sensor  102  which is selectively positioned within the exhaust manifold  104  in place of the individual cylinder sensors  38 ,  40 . 
     Particularly, the combusted gas emanating from each respective cylinder  12 ,  14  is exhaustibly communicated to manifold  104 , thereby creating a respective exhaust pressure within the manifold  104  at unique intervals of time. Each respective cylinder provided exhaust pressure is sensed or measured at relatively small intervals of time by sensor  102 , which may be a commercially available piezoelectric sensor, and the measurement is included within a signal transmitted to the controller  36  along bus  103 . 
     Applicant has discovered that there exists a direct relationship between the torque produced by a cylinder  12 ,  14  and the respective exhaust pressures created within the exhaust manifold  104  by that cylinders  12 ,  14 . The second embodiment utilizes this relationship to selectively measure the various cylinder-produced torques and to selectively provide cylinder balance. 
     Particularly, in this second embodiment of the invention, controller  36  separately calculates or measures, for each exhaust manifold  104 , the total exhaust pressure produced by each of the cylinders  12 ,  14  communicating with each respective manifold  104 , according to the following equation 4.                      p   _     i     =       ∫     φ   1     φ2              p   x          (   θ   )               θ           ;                     i   =     1                 total                 number                 of                 cylinders                 for                 each                                  respective                 exhaust                 manifold             (equation 4)                         
     Where the variables are as follows: “P x ” is the manifold pressure; “i” denotes a cylinder; “θ” is the “crankangle” and where “φ 1 ” and “φ 2 ” are respective offset angles. 
     Particularly, in this non-limiting single manifold example, each of the cylinders  12 ,  14  has a respective manifold exhaust pressure which is evaluated for every portion of the engine rotation cycle for which they respectively produce or exhausts gas into the manifold  104  (e.g., the first cylinder exhausts gas between the angles of “φ 1 ” and “φ 2 ” It of the crankshaft). These angles (“φ 1 ”, “φ 2 ”) therefore become the integral limits used by controller  36  in evaluating the integral equation 4 and they equal different angular values depending upon the identity of the cylinder  12 ,  14  whose exhaust pressure is being evaluated and/or measured (e.g., they respectively equal the lowest and highest “crankangle” associated with the production of exhaust gases by that cylinder). In the preferred embodiment of the invention, each angle “φ 1 ” and “φ 2 ” is respectively increased by a certain offset angle in order to account for the transport delay associated with the communication of the cylinder produced exhaust gasses into the manifold  104 . 
     Each of these individual exhaust pressure values is then multiplied with a first correction factor which accounts for bias associated with the placement of the sensor  102  within the manifold  104 , thereby creating respective first imbalance values for each cylinder  12 ,  14 . That is, the closer that the sensor  102  is placed within the exhaust manifold  104  to a particular and respective cylinder  12 ,  14  exhaust output, the greater will be its “reading” or “measurement” of the exhaust pressure of that cylinder  12 ,  14 . Moreover, the “measurement” of the respective exhaust pressures from the remaining cylinders  12 ,  14  will concomitantly be unduly minimized or restricted since the pressures from these other cylinders  12 ,  14  will have been reduced within the manifold  104  before “reaching” or being sensed by pressure sensor  102 . 
     Accordingly, in one embodiment of the invention, the distance from the exhaust manifold contained sensor  102  to the center of each of the respective interface ports  108 ,  110  is measured and averaged (e.g., interface port  108  is associated with and/or used by cylinder  12  to exhaust combusted products while port  110  is similarly used by cylinder  14 ). A correction factor, for each cylinder  12 ,  14 , is created and, in one non-limiting embodiment, is respectively defined by a numerator equaling the distance between the center of the respectively associated interface port  108 ,  110  and the sensor  102  and a denominator equally the average distance between the sensor  102  and the center of each respective port  108 ,  110 . The respective first cylinder imbalance values “γ i ” are then averaged according to equation 5 below:                γ   d     =     ∑       γ   i     ·     1   4                 (equation 5)                         
     These values are subtracted from each of the measured pressures to obtain a respective initial correction value which is then multiplied by an adaptive correction factor resulting in the creation of separate adaptive correction and control values, for each cylinder, which allow controller  36  to correct for calculated cylinder imbalances relatively slowly and in a “stepwise” manner. The correction factor may be substantially similar to the correction factor used within the first embodiment of the invention. The resulting adaptive correction factors may thereafter be used in a substantially similar manner to those factors which have been previously described with respect to the first embodiment of the invention. In yet another embodiment of the invention, a separate sensor  102  is employed in each exhaust manifold of a multi-exhaust manifold engine, thereby allowing each of the cylinders  12 ,  14  to be selectively balanced in a desired manner. 
     It should be understood that this invention is not to be limited to the exact construction or embodiment described above but that various changes may be made without departing from the spirit or the scope of the invention.