Patent Publication Number: US-10330007-B2

Title: Systems and methods for a crankshaft of a piston engine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of U.S. patent application Ser. No. 15/415,772 entitled, “SYSTEMS AND METHODS FOR A CRANKSHAFT OF A PISTON ENGINE,” filed on Jan. 25, 2017. U.S. patent application Ser. No. 15/415,772 claims priority to German Patent Application No. 102016201469.2, filed on Feb. 1, 2016. The entire contents of the above-referenced applications are hereby incorporated by reference in their entirety for all purposes. 
    
    
     FIELD 
     The current description relates to the design and structure of a crankshaft for a piston internal combustion engine or piston engine. 
     BACKGROUND\SUMMARY 
     The crank webs of a crankshaft are usually formed to be symmetric with respect to a longitudinal center axis which intersects the axis of rotation of the crankshaft, since the mass balancing of the countershafts must compensate for the rotating and translating parts of the connecting rods, bearings, and journals, and this mass balancing is calculable only when the center of gravity of the masses involved is known. A symmetric crank web is desirable when the centrifugal forces occurring during operation act perfectly symmetrically on an individual crankshaft portion consisting of two webs, two counterweights, two main bearings, and a crankpin. 
     However, the inventors herein have recognized potential issues with symmetric crank webs. As one example, combustion gas pressure does not act symmetrically on the crank webs, because it usually exerts the greatest force on the piston, connecting rod, and crankpin, only after top dead center. Specifically, the mixture injected into the cylinder combusts with a certain delay, and the highest gas pressure occurs close to the so-called CA50 point, which represents the crankshaft angle of rotation at which approximately 50% of the quantity of injected fuel has been combusted in the cylinder. The CA50 point may lie in a range from approximately 10° to 15°, or even up to 30°, after the top dead center of the piston. 
     In one example, the issues described above may be at least partially addressed by a crankshaft for a piston internal combustion engine, the crankshaft comprising a crankshaft throw, the crankshaft throw comprising crank webs that are formed asymmetrically in a region of a crankpin with respect to a plane intersecting an axis of rotation of the crankshaft and a center axis of the crankpin, such that the breaking strength of the crankshaft throw is increased at a crankshaft angle of rotation which differs from the top dead center and at which the highest combustion-induced force acts on the crankpin. By constructing the crankshaft webs to be asymmetric, the crankshaft can be subjected to equal or greater loading than a crankshaft of a larger or equal inherent weight having symmetric crankshaft webs. 
     In another example, a method for producing a crankshaft comprises generating a first crankshaft design which comprises a crankshaft with symmetrically formed crank webs; determining a distribution of loads in the crank webs which occur when a piston driving rotation of the crank webs exerts a maximum force on the crank webs; generating a second crankshaft design based on the first crankshaft design and the distribution of loads in the crank webs, where points of the crank webs which are more loaded at the maximum force are reinforced by the addition of crank web material; and manufacturing the crankshaft based on the second crankshaft design. 
     As yet another example, a crankshaft for an internal combustion engine comprises a crankpin, and a first crank web coupled to the crankpin, where a center of mass of the crank web is offset from a central axis of the crank web, and where the center of mass is more proximate a leading rotational edge and top of the crank web than a trailing rotational edge and bottom of the crank web. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic diagram of an example engine system, in accordance with an embodiment of the present disclosure. 
         FIG. 2  shows a front isometric view of an example crankshaft of an engine system, such as the engine system of  FIG. 1 , in accordance with an embodiment of the present disclosure. 
         FIG. 3  shows a side isometric view of the example crankshaft of  FIG. 2 , including crank webs with asymmetric mass distributions, in accordance with an embodiment of the present disclosure. 
         FIG. 4  shows a front isometric view of the example crankshaft of  FIG. 3 , in accordance with an embodiment of the present disclosure. 
         FIG. 5  shows a flow chart of an example method for designing and manufacturing a crankshaft, such as the example crankshaft of  FIGS. 2-4 , in accordance with an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description relates to systems and methods for constructing a crankshaft of an internal combustion engine. An example internal combustion engine system is shown in  FIG. 1 . The crankshaft, an example of which is shown in  FIGS. 2-4 , includes webs that couple the crankpins to the main bearing journal of the crankshaft. In particular, the combination of crankpin and two connecting webs are commonly referred to as a crankshaft throw. The crankshaft may comprise one or more crankshaft throws, depending on the number of cylinders of the internal combustion engine, where the crankpin of each crankshaft throw is coupled to a reciprocating piston of the combustion engine by, for example, a connecting rod. Thus, each crankshaft throw may comprise a crankpin and two connecting webs, where the two connecting webs couple the crankpin to the main bearing journal of the crankshaft at a position offset from a central axis of the main bearing journals and crankshaft. That is, the crankpins may not share a common central axis with the main bearing journals of the crankshaft. However, the crankpins do circle around the same central rotational axis as the main bearing journals, via the coupling to the main bearing journals provided by the crank webs. Thus, each crankpin is driven by a reciprocating piston, and as each piston reciprocates between top dead center (TDC) and bottom dead center (BDC), the crankpins circle around the central axis of the crankshaft, driving rotation of the main bearing journals, and thereby converting the reciprocating motion of the piston into rotational motion of the crankshaft. 
     However, the peak force provided by combusting gasses in a cylinder of the internal combustion engine may not occur until after the piston reaches TDC. Thus, the maximum force output by the combusting gasses may occur during the power stroke while the piston is in-between TDC and BDC, and reciprocating towards BDC and away from TDC. Thus, as shown in the example  FIGS. 2-4 , the crank webs may be constructed such that the mass distribution of the crank webs is asymmetric with respect to a central axis of the crank webs (more heavily weighted towards one side of the crank webs than the other side). In this way, the crankshaft with asymmetric crank webs may withstand larger forces from the driving pistons when the combusting gasses within the combustion chambers exert their maximum force on the crankpins, for example, between 10° and 30° after TDC, than crankshafts including symmetric crank webs. As such, crankshaft durability and longevity may be increased relative to crankshafts including symmetric crank webs. As described in the example method of  FIG. 5 , the crank webs may be designed such that their mass distributions are not symmetric. That is, the crank webs may be designed and manufactured such that they are more heavily weighted towards a leading edge, such that their center of mass is offset from a central axis of the crank web. 
     Referring to  FIG. 1 , a schematic diagram showing one cylinder of multi-cylinder engine  10 , which may be included in a propulsion system of an automobile, is illustrated. Engine  10  may be controlled at least partially by a control system including controller  20  and by input from a vehicle operator  132  via an input device  130 . In this example, input device  130  includes an accelerator pedal and a pedal position sensor  134  for generating a proportional pedal position signal PP. Combustion chamber (i.e., cylinder)  71  of engine  10  may include combustion chamber walls  72  with piston  76  positioned therein. Piston  76  may be coupled to crankshaft  80  so that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Crankshaft  80  may be coupled to at least one drive wheel of a vehicle via an intermediate transmission system. Further, a starter motor may be coupled to crankshaft  80  via a flywheel to enable a starting operation of engine  10 . The piston  76  may be coupled to a crankpin included within the crankshaft  80 , and may drive the crankpin to circle around a central axis of the crankshaft  80 , as described in greater detail below with reference to  FIG. 2 . Thus, the piston  76  exerts a force on a crankpin. The crankpin in turn, revolves around main journals of the crankshaft, and converts reciprocating motion of the piston  76  into rotational motion of the crankshaft  80 . 
     Combustion chamber  71  may receive intake air from intake manifold  44  via intake passage  42  and may exhaust combustion gases via exhaust passage  48 . Intake manifold  44  and exhaust passage  48  can selectively communicate with combustion chamber  71  via respective intake valve  52  and exhaust valve  54 . In some embodiments, combustion chamber  71  may include two or more intake valves and/or two or more exhaust valves. 
     In this example, intake valve  52  and exhaust valves  54  may be controlled by cam actuation via respective cam actuation systems  51  and  53 . Cam actuation systems  51  and  53  may each include one or more cams and may utilize one or more of cam profile switching (CPS), variable cam timing (VCT), variable valve timing (VVT) and/or variable valve lift (VVL) systems that may be operated by controller  20  to vary valve operation. The position of intake valve  52  and exhaust valve  54  may be determined by position sensors  55  and  57 , respectively. In alternative embodiments, intake valve  52  and/or exhaust valve  54  may be controlled by electric valve actuation. For example, cylinder  71  may alternatively include an intake valve controlled via electric valve actuation and an exhaust valve controlled via cam actuation including CPS and/or VCT systems. 
     Fuel injector  66  is shown arranged in intake manifold  44  in a configuration that provides what is known as port injection of fuel into the intake port upstream of combustion chamber  71 . Fuel injector  66  may inject fuel in proportion to the pulse width of signal FPW received from controller  20  via electronic driver  68 . Fuel may be delivered to fuel injector  66  by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. In some embodiments, combustion chamber  71  may alternatively or additionally include a fuel injector coupled directly to combustion chamber  71  for injecting fuel directly therein, in a manner known as direct injection. 
     Intake passage  42  may include a throttle  62  having a throttle plate  64 . In this particular example, the position of throttle plate  64  may be varied by controller  20  via a signal provided to an electric motor or actuator included with throttle  62 , a configuration that is commonly referred to as electronic throttle control (ETC). In this manner, throttle  62  may be operated to vary the intake air provided to combustion chamber  71  among other engine cylinders. The position of throttle plate  64  may be provided to controller  20  by throttle position signal TP. Intake passage  42  may include a mass air flow sensor  120  and a manifold air pressure sensor  122  for providing respective signals MAF and MAP to controller  20 . 
     Ignition system  88  can provide an ignition spark to combustion chamber  71  via spark plug  92  in response to spark advance signal SA from controller  20 , under select operating modes. Though spark ignition components are shown, in some embodiments, combustion chamber  71  or one or more other combustion chambers of engine  10  may be operated in a compression ignition mode, with or without an ignition spark. 
     Exhaust gas sensor  126  is shown coupled to exhaust passage  48  upstream of emission control device  70 . Sensor  126  may be any suitable sensor for providing an indication of exhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor. Emission control device  70  is shown arranged along exhaust passage  48  downstream of exhaust gas sensor  126 . Device  70  may be a three way catalyst (TWC), NOx trap, various other emission control devices, or combinations thereof. In some embodiments, during operation of engine  10 , emission control device  70  may be periodically reset by operating at least one cylinder of the engine within a particular air/fuel ratio. 
     Controller  20  is shown in  FIG. 1  as a microcomputer, including microprocessor unit  102 , input/output ports  21 , an electronic storage medium for executable programs and calibration values shown as read only memory chip  106  in this particular example, random access memory  108 , keep alive memory  110 , and a data bus. Controller  20  may receive various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including measurement of inducted mass air flow (MAF) from mass air flow sensor  120 ; engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114 ; a profile ignition pickup signal (PIP) from Hall effect sensor  118  (or other type) coupled to crankshaft  80 ; throttle position (TP) from a throttle position sensor; and absolute manifold pressure signal, MAP, from sensor  122 . Engine speed signal, RPM, may be generated by controller  20  from signal PIP. Manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum, or pressure, in the intake manifold. Note that various combinations of the above sensors may be used, such as a MAF sensor without a MAP sensor, or vice versa. During stoichiometric operation, the MAP sensor can give an indication of engine torque. Further, this sensor, along with the detected engine speed, can provide an estimate of charge (including air) inducted into the cylinder. In one example, sensor  118 , which is also used as an engine speed sensor, may produce a predetermined number of equally spaced pulses every revolution of the crankshaft. 
     Storage medium read-only memory chip  106  can be programmed with computer readable data representing instructions executable by processor  20  for performing the methods described below as well as other variants that are anticipated but not specifically listed. 
     As described above,  FIG. 1  shows only one cylinder of a multi-cylinder engine, and that each cylinder may similarly include its own set of intake/exhaust valves, fuel injector, spark plug, etc. 
     Continuing to  FIGS. 2-4 , they show an example crankshaft  200  that may be included in an internal combustion engine, such as the engine  10  described above with reference to  FIG. 1 . Thus, crankshaft  200  may be the same or similar to crankshaft  80  described above with reference to  FIG. 1 . 
       FIGS. 2-4  are drawn approximately to scale and show the relative sizes and positioning of the components of the crankshaft  200 . Further,  FIGS. 2-4  show an axis system  250  including a vertical axis  252 , a horizontal axis  254 , and a lateral or longitudinal axis  256 . The axis system  250  may be used to reference the relative positioning of components of the crankshaft  200 . For example, components may be referred to as “above” or “below” one another with respect to the vertical axis  252 , where for example, a first component said to be positioned “above” a second component, is positioned further along the positive direction of the vertical axis  252  than the second component. As another example, components may be referred to as “to the left of” and “to the right of” one another with respect to the horizontal axis  254 . As another example, components may be referred to as “in front of” or “behind” one another with respect to the lateral axis  256 . For example, a first component said to be positioned “behind” a second component, is positioned further along the positive direction of the lateral axis  256  than the second component. 
     Further,  FIGS. 2-4  show example configurations with relative positioning of the various components of the crankshaft  200 . If shown directly contacting each other, or directly coupled, then such elements may be referred to as directly contacting or directly coupled, respectively, at least in one example. Similarly, elements shown contiguous or adjacent to one another may be contiguous or adjacent to each other, respectively, at least in one example. As an example, components laying in face-sharing contact with each other may be referred to as in face-sharing contact. As another example, elements positioned apart from each other with only a space there-between and no other components may be referred to as such, in at least one example. As yet another example, elements shown above/below one another, at opposite sides to one another, or to the left/right of one another may be referred to as such, relative to one another. Further, as shown in the figures, a topmost element or point of element may be referred to as a “top” of the component and a bottommost element or point of the element may be referred to as a “bottom” of the component, in at least one example. As used herein, top/bottom, upper/lower, above/below, may be relative to a vertical axis of the figures and used to describe positioning of elements of the figures relative to one another. As such, elements shown above other elements are positioned vertically above the other elements, in one example. As yet another example, shapes of the elements depicted within the figures may be referred to as having those shapes (e.g., such as being circular, straight, planar, curved, rounded, chamfered, angled, or the like). Further, elements shown intersecting one another may be referred to as intersecting elements or intersecting one another, in at least one example. Further still, an element shown within another element or shown outside of another element may be referred as such, in one example. 
     Focusing first on  FIG. 2 , it shows a front isometric view of a portion of the crankshaft  200 . The crankshaft  200  includes a shaft journal  201  which extends along a crankshaft central axis of rotation  202 , which is indicated by the dotted line in  FIG. 2 , and a crankshaft throw  204  which comprises a first crank web  206 , a crankpin  208  and a second crank web  210 . Thus, the shaft journal  201  and crankshaft  200  share a common central axis (e.g., are coaxial), around which they both rotate. Both shaft journal  201  and crankshaft  200  therefore rotate around the central axis of rotation  202 . Shaft journal  201  may comprise a crankshaft main bearing journal and as such may also be referred to herein as crankshaft main bearing journal  201 . 
     At the periphery of the shaft journal  201 , first crank web  206 , and crankpin  208  there is indicated a partially interrupted line  6  which forms a longitudinal center line of the crankshaft throw  204  and which extends in a plane which intersects both the crankshaft axis of rotation  202  and the center axis of the crankpin  208 . 
     In the example of  FIG. 2 , the crankshaft throw  204  is shown at an angle of rotation which is situated approximately 10° to 15° after the top dead center of the associated piston (e.g., 10° to 15° from TDC, while the piston is reciprocating towards BDC and away from TDC) and at which a maximum combustion-induced force “K” acts on the crankpin  208  during a combustion cycle, which force is situated at an inclined angle to the plane which intersects the crankshaft central axis of rotation  202  and the center axis of the crankpin  208 . 
     Since the force K acts asymmetrically on the crankshaft throw, the halves of the webs  206  and  210  situated to the right of the line  212  in the example of  FIG. 2  are partially loaded more greatly with pressure in the region of the crankpin  208  than the halves of the webs  206  and  210  situated to the left of the line  212 . 
     The two differently loaded halves of the first crank web  206  are indicated in the figure as two hatched web regions  206   a  and  206   b . Portions, or all of second web region  206   b  which is loaded more greatly with pressure at the piston position shown in the example of  FIG. 2  than portions or all of the first web region  206   a , are configured to be sturdier than portions or all of the web region  206   a . The first web region  206   a  can thus accordingly be configured to be weaker such that material from the first web region  206   a  can be redistributed to the second web region  206   b.    
     In view of all this, it must of course also be taken into consideration that the web region  206   a  is also loaded slightly in tension at the indicated angle of rotation of the crankshaft and, in order to deal with the tensile loading which occurs, a certain material redistribution can be effected within the web region  206   a . Thus, the second web region  206   b  may be weighted more heavily. In some examples, the second web region  206   b  may have a higher density than the first web region  206   a  to achieve a greater weight than the first web region  206   a . In other examples, the second web region  206  may comprise the same density, but may comprise more mass and therefore a greater volume than the first web region  206   a  to achieve a greater weight than the first web region  206   a.    
     In some examples, as described in greater detail below with reference to  FIG. 5 , the web regions  206   a  and  206   b  may initially be designed to be the same weight and density (e.g., web  206  is designed to be symmetric about the line  6 ). Then, the symmetric webs and crankshaft may be coupled to an internal combustion engine and undergo testing to determine the loading on the webs. The webs can then be redesigned to shift mass and weight around in the webs. Thus, mass may be redistributed in the webs to make the webs stronger when the webs are rotated away from TDC, and the piston exerts a maximum force on the crankpin and webs. In this way, the center of mass of the web  206  may be shifted away from the line  6 , and towards the right in the example of  FIG. 2 . 
     The unbalances which occur in the web regions  206   a  and  206   b  as a result of these material redistributions are balanced by suitable material redistributions in the radially opposite counterweights. 
     Turning to  FIG. 3 , it shows a side isometric view of the crankshaft  200  including crank web supports  302 ,  304 , and  306 . First crank web support  302  is coupled to the first crank web  206  on a front-facing surface  303  of the crank web  206 , opposite a rear-facing surface  305  of the crank web  206 , to which the crankpin  208  is coupled. The first crank web support  302  may extend downwards from a top of the web  206  and/or between the crankpin  208  and the central axis of rotation  202 . In particular, the first crank web support  302  may extend along a portion of the front-facing surface  303  in an area approximately similar to the surface area of the rear-facing surface  305  which the crankpin  208  interfaces with. Thus, the support  302 , may be diametrically opposed from the interface of the crankpin  208  and rear-facing surface  305 . Second crank web support may be coupled to the front-facing surface  303 , below the first crank web support  302 , between the first crank web support  302  and the central axis of rotation  202 . Third crank web support  306  may be coupled to a rear-facing surface  307  of the second crank web  210 , opposite a front-facing surface  309  of the second crank web  210 , to which the crankpin  208  is coupled. 
     The crank web supports  302 ,  304 , and  306  may comprise the same or similar material to the crank webs  206  and  210 , and may comprise one or more of the same density, elasticity, strength, hardness, etc. However, in other examples, the crank web supports  302 ,  304 , and  306  may comprise different materials and/or different densities, elasticities, strengths, harnesses, etc., than the crank webs  206  and  210 . In some examples, the first and third crank web supports  302  and  306 , respectively, may be approximately the same or similar. 
     Further, in some examples, the crank web supports  302 ,  304 , and  306  may be integrally formed with the crank webs  206  and  210 . That is, the crank web supports  302 ,  304 , and  306  may be formed at the same time with the crank webs  206  and  210 , and the crank web supports  302  and  304  and the first crank web  206  may form a single continuous piece, and the crank web support  306  and the second crank web  210  may form a single continuous piece. That is, the crank web supports  302 ,  304 , and  306  may generated during a design phase of the crankshaft  200 . Therefore, the supports  302 ,  304 , and  306  may be shown in  FIGS. 3 and 4  as distinct elements from the webs  206  and  210 , merely to show how the webs  206  and  210  may be adjusted from a symmetric design, and be redesigned to be asymmetric. Thus, in some examples, the crank web supports  302 ,  304 , and  306  may not be formed separately from the crankshaft. Further, the web supports  302 ,  304 , and  306  may not comprise adjustments made to the crankshaft  200  post production. Thus, the webs may be designed to by asymmetric, and may not be physically manipulated after they are constructed to redistribute mass. That is, a symmetric web design may be adjusted to an asymmetric web design, and then asymmetric webs may be manufactured. 
     However, in other examples, the crank web supports  302 ,  304 , and  306  may be formed separately from the crank webs  206  and  210 , and may then be coupled to the crank webs  206  and  210  via one or more of adhesives, fasteners, etc. In yet further examples, the second crank web  210  may additionally include a fourth crank web (not shown in  FIG. 3 ) that may be the same or similar to second crank web support  304 , and may be positioned on the rear-facing surface  307 , below the third crank web support  306 , between the third crank web support  306  and the central axis of rotation  202 . 
     In yet further examples, the crank web supports  302 ,  304 , and  306  may be formed by physically redistributing mass in already constructed webs  206  and  210 . Thus, the webs  206  and  210  may in some examples be constructed to be symmetric, and then may be machined and/or physically manipulated afterwards to redistribute weight. 
     Continuing to  FIG. 4 , it shows a front isometric view of the crankshaft  200 , similar to the view of the crankshaft  200  shown above in  FIG. 2 . In  FIG. 4 , a central axis  402  of the crank web  206  is shown which is orthogonal to the central axis of rotation  202  of the crankshaft  200 . The central axis  402  of the crank web  206  passes through the central axis of rotation  202  of the crankshaft  200  and may divide the crank web  206  in half. A top dead center position of the crank web  206  is shown by dotted line  404 . Thus, when the piston to which the crankpin  208  is coupled (e.g., piston  76  described above in  FIG. 1 ) is at its top dead center position, the central axis  402  of the crank web  206  may be in the orientation depicted by the dotted line  404 . Thus, when the piston is at its top dead center position, the web  206  may be orientated straight with respect to the vertical axis  252 , such that its central axis  402  is parallel to the vertical axis  252 . Further, a top  408  of the web  206  is vertically above a bottom  210  of the web  206  at the top dead center position of the piston. In the example of  FIG. 2 , the web  206  and crankshaft  200  are shown rotated clockwise from the top dead center position by an angle, θ. 
     The angle θ may correspond to an angle at which the combustion gasses in the combustion chamber including the piston (e.g., combustion chamber  71  described above in  FIG. 1 ) exert a maximum force on the piston and crankpin  208 . In particular angle θ may correspond to an angle at which approximately 50% of the injected fuel during a single combustion cycle has combusted. Angle θ may be an angle in a range of angles between 10° and 30° from top dead center. In the example of  FIG. 4 , the crankshaft  200  rotates in the clockwise direction, such that the top  408  of the web  206  is vertically above the bottom  410  of the web  206  at the top dead center position, and the bottom  410  of the web  206  is vertically above the top  408  of the web  206  at the bottom dead center position. Thus, in the position shown in the example of  FIG. 4 , the piston is between top dead center and bottom dead center, and is reciprocating towards the bottom dead center position, and away from the top dead center position. 
     A leading edge  412  of the web  206  is positioned opposite a trailing edge  414  of the web  206 , and the leading edge  412  is rotationally ahead or in front of the trailing edge  414 . In particular, as the crankshaft  200  and web  206  rotate clockwise in the example of  FIG. 4 , the leading edge  412  is ahead of the trailing edge  414  relative to the position of the piston. For example, as the piston reciprocates from top dead center to bottom dead center, the leading edge  412  will reach the bottom of its circular trajectory before the trailing edge  414 . In the example of  FIG. 4 , the leading edge  412  is positioned to the right of the trailing edge  414 . 
     As shown in the example of  FIG. 4 , the crank support  302  may not be symmetric about the central axis  402 . In particular, the crank support  302  may be weighted more heavily towards the leading edge  412 , and away from trailing edge  414 . Thus, the crank support  302  may include more mass to the right of the central axis  402  than to the left, in the example of  FIG. 4 . In some examples, the crank support  302  may not comprise a symmetric shape, but may be positioned approximately equidistant from the trailing and leading edges  414  and  412 , respectively. In other examples the crank support may not comprise a symmetric shape and may be positioned more proximate the leading edge  412  than the trailing edge  414 . In example where the crank support  302  is asymmetric, the crank support  302  may be thicker (wider along the longitudinal axis  256 ) more proximate the leading edge  412  than the trailing edge  414 . 
     In other examples, the crank support  302  may be symmetric. In examples where the crank support  302  is symmetric and is positioned equidistantly from the leading and trailing edges  412  and  414 , the crank support  302  may be more dense more proximate the leading edge  412 , and less dense more proximate the trailing edge  414 . In other examples, where the crank support  302  is symmetric and is positioned more proximate the leading edge  412  than the trailing edge  414 , the crank support may comprise a uniform density. 
     In all of the above examples, the crank support  302  is configured to have a center of mass that is shifted towards the leading edge  412  away from the trailing edge  414 . That is, the center of mass of the crank support  302  is more proximate the leading edge  412  than the trailing edge  414  and thus is to the right of the central axis  402  in the example of  FIG. 4 . 
     Thus, the center of mass of the crank web  206  may also be shifted towards the leading edge  412 , away from the trailing edge  414 . Further, mass may be shifted towards the top  408  and away from the bottom  410  of the crank web  206 . That is, the center of mass of the crank web  206  may be more proximate the leading edge  412  than the trailing edge  414  and thus is to the right of the central axis  402  in the example of  FIG. 4 . 
     In the example of  FIG. 4 , the crank web  206  may be more loaded by the force of the piston and combustion gasses at positions of the crank web  206  more proximate the leading edge  412  than the trailing edge  414  as shown by the force vector “K” in  FIG. 2 . Thus, points of the crank web  206  which are lesser loaded at the maximum force of the combustion gasses (e.g., more proximate the trailing edge  414 ) may be weakened by removal of crank web material. Further crank web material may be added to the more loaded points of the crank web  206 , more proximate the leading edge  412  of the crank web  206 . Thus, the web  206  may first be designed to be symmetric, and then mass may be added to the more loaded points of the crank web  206  that exist when the combustion gasses are exerting their maximum or close to their maximum force on the piston and crankpin  208  (between 10° and 30° after top dead center). The amount of crank web material used for reinforcement at the more loaded portions of the web  206  may be approximately equal to an amount of material removed from lesser loaded points. In other examples the amount of crank web material used for reinforcement may be less than an amount of material removed from lesser loaded points. 
     Turning to  FIG. 5 , it shows a flow chart of an example method  500  for designing and manufacturing a crankshaft (e.g., crankshaft  200  described above with reference to  FIGS. 2-4 ) and crank web (e.g., crank web  206  described above with reference to  FIGS. 2-4 ). In particular a symmetrical crank web has points which are lesser loaded at the CA50 point than corresponding points on the opposite side of its longitudinal center axis which, for their part, are more greatly loaded. Therefore, the more greatly loaded points can be reinforced with additional material without this having to be done on the opposite side, where, moreover, material can be saved at lesser loaded points. 
     In other words, in the case of the crankshaft according to the invention, at the angle of rotation of the force maximum for which the crankshaft throw is formed asymmetrically in a strength-increasing manner, the breaking strength of the crankshaft throw is higher than that of a corresponding crankshaft throw having crank webs which are formed symmetrically with the same amount of material. Thus, the crankshaft can either be made lighter without durability losses or made more durable with the same weight. 
     What the invention thus teaches is not to design crank webs in such a way that, in addition to the centrifugal forces which occur, they also withstand the highest pressure forces which, for the sake of simplicity, were previously assumed as acting at the top dead center, but with consideration to the fact that the crank webs experience the highest pressure forces only more or less far behind the top dead center. 
     The asymmetry of the crank webs and the associated asymmetrical distribution of the crank web material lie in particular in geometric deviations from a mirror symmetry with respect to the plane which passes through the axis of rotation of the crankshaft and the axis of rotation of the crankpin. 
     Method  500  begins at  502  which comprises constructing a crankshaft and generating a first crankshaft design with symmetrically formed crank webs. In some examples, the crankshaft may be designed such that it is rigid enough to withstand all loads occurring during its service life. 
     Method  500  then continues from  502  to  504  which comprises, on the basis of the first crankshaft design, an actual crankshaft can be produced and installed in an internal combustion engine and the crankshaft angle of rotation at which the highest combustion-induced force acts on the crankpin (e.g., crankpin  208  described above with reference to  FIGS. 2-4 ) can be determined by means of dynamometer tests. The distribution of the loads in the crank webs which occur at the force maximum can also be determined experimentally, for example by means of expansion and compression sensors. 
     Alternatively, the method  500  at  504  may comprise determining the angle of rotation of the computationally designed crankshaft at which the highest combustion-induced force acts on the crankpin by the use of empirical values, and it is then possible, on the basis of the design data of the crankshaft having symmetrically formed crank webs, to calculate the spatial distribution of the loads in the crank webs which occur at the force maximum. 
     After the distribution of the loads in the crank webs which occur at the force maximum has been determined experimentally and/or computationally, method  500  continues from  504  to  506  which comprises modifying the crankshaft and/or generating a second crankshaft design based on the first crankshaft design and the determined load distributions. In particular, the method  500  at  506  may comprise redesigned the first crankshaft design, with points of the crank webs which are more greatly loaded at the force maximum being reinforced by the addition of crank web material, and actual crankshafts can then be produced on the basis of the design data thus obtained. 
     The steps of determining load distributions and of locally adding crank web material can be carried out repeatedly in order to carry out fine tuning and to gradually give the crankshaft its final form. 
     Method  500  may then continue to  508  from  506  which comprises constructing the crankshaft based on the second crankshaft design. 
     Here, it is possible not only for crank web material to be added but it is also possible for points of the crank webs which are lesser loaded at the force maximum to be weakened by removal of crank web material, with it being possible for the amount of material used for reinforcement to be substantially equal to or less than the amount of material removed from lesser loaded points. 
     Moreover, asymmetric addition or redistribution of crank web material first creates an unbalance, but this is compensated for by an appropriate redesign of the counterweights. 
     In one representation, a crankshaft for a piston internal combustion engine, may comprise a crankshaft throw, the crankshaft throw including crank webs formed asymmetrically in a region of a crankpin with respect to a plane intersecting an axis of rotation of the crankshaft and a center axis of the crankpin, such that the breaking strength of the crankshaft throw is increased at a crankshaft angle of rotation which is different than top dead center and at which the highest combustion-induced force acts on the crankpin. In a first example, the crankshaft the breaking strength of the crankshaft throw at the highest combustion-induced force is higher than that of a corresponding crankshaft throw having crank webs which are formed symmetrically with the same amount of material. A second example of the crankshaft optionally includes the first example and further includes that the asymmetry of the crank webs lies in geometric deviations from a mirror symmetry with respect to the plane which passes through the axis of rotation of the crankshaft and the axis of rotation of the crankpin. A third example of the crankshaft optionally includes the first and/or second example, and further includes that the angle of rotation for which the crankshaft throw is formed asymmetrically in a strength-increasing manner corresponds to an angle of rotation at which approximately 50% of a quantity of fuel injected into a combustion chamber including a piston coupled to the crankpin has been combusted and a maximum combustion gas pressure acts on the piston. A fourth example of the crankshaft optionally includes one or more of the first through third example, and further includes that the angle of rotation for which the crankshaft throw is formed asymmetrically in a strength-increasing manner lies in a range from approximately 10° to 30° after top dead center piston position. 
     In another representation, a method for producing a crankshaft comprises generating a first crankshaft design which comprises a crankshaft with symmetrically formed crank webs; determining a distribution of loads in the crank webs which occur when a piston driving rotation of the crank webs exerts a maximum force on the crank webs; generating a second crankshaft design based on the first crankshaft design and the distribution of loads in the crank webs, where points of the crank webs which are more loaded at the maximum force are reinforced by the addition of crank web material; and manufacturing the crankshaft based on the second crankshaft design. In a first example of the method, the method may optionally include that the generating the first crankshaft design, determining the distribution of loads, and generating the second crankshaft design are carried out repeatedly in a loop, where the load distribution in the second crankshaft design is recalculated. A second example of the method optionally includes the first example and further includes that points of the crank webs which are lesser loaded at the maximum force are weakened by removal of crank web material. A third example of the method optionally includes the first and/or second examples and further includes that wherein the amount of crank web material used for reinforcement is substantially equal to an amount of material removed from lesser loaded points. A fourth example of the method optionally includes one or more of the first through third examples, and further includes that wherein the amount of crank web material used for reinforcement is less than an amount of material removed from lesser loaded points. 
     In another representation, a crankshaft for an internal combustion engine comprises a crankpin, and a first crank web coupled to the crankpin, where a center of mass of the crank web is more proximate a leading rotational edge of the crank web than a trailing rotational edge of the crank web. A first example of the crankshaft optionally includes that the leading rotational edge of the crank web is in front of the trailing rotational edge of the crank web relative to a direction of rotation of the crankshaft and a piston to which the crankpin is coupled. A second example of the crankshaft optionally includes the first example and further includes that the crank web is symmetric in shape but not in density, where the density of the crank web is greater more proximate the leading rotational edge of the crank web than the trailing rotational edge of the crank web. A third example of the crankshaft optionally includes one or more of the first and second examples, and further includes that the crank web is asymmetric in shape, where the crank web is thicker more proximate the leading rotational edge of the crank web than the trailing rotational edge of the crank web. A fourth example of the crankshaft optionally includes one or more of the first through third examples, and further comprises a first web support coupled to the crank web to shift the center of mass of the crank web towards the leading rotational edge of the crank web and away from the trailing rotational edge. A fifth example of the crankshaft optionally includes one or more of the first through fourth examples and further includes that the web support is coupled to the crank web on a surface of the crank web opposite the crankpin, between the crankpin and a central axis of the crankshaft. A sixth example of the crankshaft optionally includes one or more of the first through fifth examples and further includes a second web support coupled to the crank web on the surface of the crank web opposite the crankpin, between the first web support and the central axis of the crankshaft. A seventh example of the crankshaft optionally includes one or more of the first through sixth examples, and further includes that the web support is positioned more proximate the leading rotational edge of the crank web than the trailing rotational edge of the crank web. An eighth example of the crankshaft optionally includes one or more of the first through seventh examples, and further includes that the web support is positioned approximately equidistant between the leading rotational edge and the trailing rotational edge of the crank web, but is more heavily weighted towards the leading rotational edge than the trailing rotational edge. A ninth example of the crankshaft optionally includes one or more of the first through eighth examples and further comprises a second crank web coupled to the crankpin on a side of the crankpin opposite the first crank web, where a center of mass of the second crank web is more proximate a leading rotational edge of the second crank web than a trailing rotational edge of the second crank web. 
     In this way, by shifting the center of mass towards the leading edge of the crank web, a technical effect of increasing crankshaft strength, durability, and longevity is achieved. In particular, the amount of force at which the crankshaft will break is increased at a piston angle where a maximum amount of force is exerted on the piston by the combustion gasses for a combustion cycle. Thus, since the maximum force exerted by the piston during a combustion cycle may be during the power stroke, after the piston has reached top dead center and is reciprocating towards bottom dead center, an asymmetric mass distribution for the crank web increases the load that the crankshaft can tolerate without breaking. 
     It will be appreciated by those skilled in the art that although the present application has been described by way of example and with reference to the one or more examples above, it is not limited to the disclosed examples and that alternative examples could be constructed without departing from the scope of the present application as defined by the appended claims. 
     Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described actions, operations and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the engine control system. 
     It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.