Patent Publication Number: US-2023139667-A1

Title: Inferred Engine Cylinder Pressure System and Method

Description:
TECHNICAL FIELD 
     This patent disclosure relates generally to internal combustion engines and, more specifically, to systems and methods of measurement or estimation of engine operating parameters. 
     BACKGROUND 
     Internal combustion engines operate based on a controlled burning of an air and fuel mixture within one or more engine cylinders. Expanding gas trapped within the cylinder, and the pressure it produces, pushes onto a piston disposed in a bore, which in turn provides the work necessary to turn a crankshaft of the engine to produce power. Gas pressure within the engine cylinders is sometimes used to monitor the air/fuel burning progress to better control engine operation. This monitoring is especially useful when the chemical properties of the fuel provided to operate the engine is not known or uniform. For example, engines operating generators (gensets) in an environment where natural gas is used as a fuel to operate the engine may experience unreliable operation if the chemical makeup of the natural gas changes. 
     To ensure proper engine operation, various solutions have been proposed in the past for devices that can measure cylinder pressure in an operating engine. Some solutions propose use of pressure transducers placed directly in contact with the cylinder gases, but such solutions expose these sensors to extreme operating conditions and are generally unreliable or expensive to implement reliably. Indirect cylinder pressure measurements have also been proposed. For example, U.S. Pat. No. 7,623,955 to Rackmil et al. discusses a method for inferring Indicated Mean Effective Pressure (IMEP) in an engine by monitoring crankshaft rotation. The method disclosed in Rackmil includes acquiring at least one crankshaft time stamp for use in determining a cylinder-specific engine velocity; calculating an incremental change in engine kinetic energy from the previously fired cylinder (j-1st) to the currently fired (jth) cylinder using the cylinder-specific engine velocity; equating the incremental change in engine kinetic energy to a change in energy-averaged cylinder torque (IMEP) from the previously-fired (j-1st) to a currently-fired (jth) cylinder; summing a plurality of the incremental changes in engine kinetic energy over time to determine a value of the transient component of indicated torque; determining a value of the quasi-steady indicated engine torque; and adding the value of transient component of indicated torque to the value of quasi-steady indicated engine torque to yield the Indicated Mean Effective Pressure. However, Rackmil&#39;s method, while at least partially effective in estimating cylinder pressure, can also be susceptible to inaccuracy and depends on the rotation of the crankshaft, which is typically connected to a transmission and other rotating structures in a vehicle or machine, which can further introduce inaccuracies in the measurement method. 
     SUMMARY 
     The disclosure describes, in one aspect, a drive arrangement between a driver and a driven system. The drive arrangement includes a rotatable driver component having first and second sensors associated therewith, the first sensor rigidly mounted relative to the rotatable driver component and configured to provide a first signal indicative of a rotation of the rotatable driver component. The arrangement further includes a rotatable driven component and a flexible coupler disposed between the rotatable driver component and the rotatable driven component. The second sensor is configured to provide a second signal indicative of a rotation of the rotatable driven component. A controller is disposed to receive the first signal and the second signal. The controller is configured to calculate a difference between the first signal and the second signal, and infer a torque variation between the rotatable driver component and the rotatable drive component based primarily on the difference between the first signal and the second signal. 
     In another aspect, the disclosure describes a genset that includes an engine having a plurality of cylinders, and a generator. Each of the plurality of cylinders of the engine is connected to and configured to drive a flywheel during operation of the engine. A first timing sensor is associated with the engine and provides an input signal indicative of rotation of the flywheel. A flexible coupling has an input side connected to the flywheel and an output side connected to an input shaft of a generator. The input shaft of the generator includes a tone ring. A second timing sensor is rigidly connected relative to the engine and is configured to provide an output signal indicative of a rotation of the tone ring. A controller is associated with the engine. The controller is disposed to receive the input signal and the output signal. The controller is programmed to calculate a difference between the input signal and the output signal, and infer a cylinder pressure in each of the plurality of cylinders based on the difference. 
     In yet another aspect, the disclosure describes a method for measuring a torque variation across a flexible coupler disposed between a rotatable driver component and a rotatable driven component. The method includes providing the flexible coupler between the rotatable driver and driven components, the flexible coupler having a driver side connected to the rotatable driver component and a driven side connected to the rotatable driven component. First and second sensors are provided and rigidly mounted relative to the driver side of the flexible coupler. Rotation of the rotatable driver component is sensed using the first sensor to provide a first signal. Rotation of the rotatable driven component is sensed using the second sensor to provide a second signal. A difference between the first signal and the second signal is calculated using a controller to infer a torque variation across the flexible coupler based on the difference between the first signal and the second signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an outline view of a genset in accordance with the disclosure. 
         FIG.  2    is a partial section view of the genset shown in  FIG.  1   , and  FIG.  3    is an enlarged detail view thereof. 
         FIG.  4    is a front plan view of a portion of an engine around a flywheel ring gear in accordance with the disclosure. 
         FIG.  5    is a chart in accordance with the disclosure. 
         FIGS.  6  and  7    are detail views of a portion of an engine in accordance with the disclosure. 
         FIG.  8    is a flowchart for a method in accordance with the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure relates to management of engine systems and, more particularly, to systems and methods for the indirect measurement or, stated differently, the inference of cylinder pressure within combustion cylinders of an engine by use of external sensors. 
     More specifically, in an exemplary embodiment, a genset  100  is shown in an outline view in  FIG.  1   . The genset  100  generally includes an engine  102 , which in this embodiment is a gas or natural gas, spark ignition engine having 12 combustion cylinders  106  arranged in two rows in what&#39;s commonly referred to a Vee configuration along or within a cylinder case  104 . The engine  102  can be any type of internal combustion engine including compression ignition engines operating with a single fuel, two fuels, a combination of diesel and a gaseous fuel, and the like in the known fashion. The engine  102  includes a cooling arrangement  103 , for example, an intercooler, radiator, and the like, and internal to the cylinder case  104  includes a crankshaft (not shown) that is connected to pistons reciprocally disposed within the cylinders  106  and configured to rotate about an axis  108  during engine operation as the cylinders carry out a combustion cycle, for example, a  4  stroke cycle that includes an intake stroke, a compression stroke, a power stroke that provides power to turn the crankshaft, and an exhaust stroke, as is known. 
     The crankshaft is connected to a flywheel  212  ( FIG.  2   ) disposed within a coupling guard  110 , which in turn is connected to a transmission  112 . The transmission  112 , which can also be omitted, is connected to and drives an electrical power generator  114  which converts mechanical energy from the engine to electrical power. The electrical power from the generator  114  can be used in many electrical or hybrid power applications. In one example, the genset  100  may be operating at an oil and gas facility either onshore or offshore such that excess gas byproducts can be used as a fuel, alone or in combination with another fuel, to operate the engine  102 . The electrical power from the generator is used to operate equipment, provide motive power to propulsion systems, or a combination of the two. A switchgear  116  is connected to the generator  114  and operates to control and distribute the electrical power produced thereby. A controller  118  is configured to monitor and control the operation of the engine  102  and the generator  114  to optimal levels during service. 
     In the illustrated embodiment, the controller  118  is further configured to tune operation of the engine, for example, in terms of fuel quantity, ignition timing, power output and the like, based on the electrical needs of an electrical consumer system connected to the switchgear  116  and also based on changes of engine operation that are caused by differences in the chemical makeup of the natural gas used to fuel the engine  102 . For example, a higher concentration of compounds having a lower octane rating may require retarding of engine ignition and injection timing, and correspondingly a lower quality fuel may require advancement of engine ignition and timing to avoid engine knocking during operation of the engine  102 . Engine knocking, as is known, can cause inefficient engine operation because it involves uncontrolled burning of the air/fuel mixture provided to the cylinders  106 , and can also increase stresses in engine components, which can increase wear and reduce component service life. To accomplish this, the controller  118  receives signals from sensors that are indicative of cylinder pressure within the cylinders of the engine. This cylinder pressure is measured indirectly based on rotational or angular differences or variations present at the engine to generator connection. 
     A partial section view through a portion of the engine  102  around a connection end of the flywheel  212  of the engine  102  with the generator  114  is shown in  FIGS.  2  and  3   . In reference to these figures, the flywheel  212  is connected through a coupling hub  206  to an input shaft  200  of the generator  114 . The input shaft is supported by bearings  201  so it can rotate within a chassis, body or stator of the generator  114 . At its end, the input shaft  200  of the illustrated embodiment includes a generator input flange  202  that is connected to a tone ring  204  and to a coupling hub  206 , which in general has considerable mass and smooths rotational vibrations at the input of the generator  114 . 
     The coupling hub  206  is elastically connected to an engine output flange  210  via elastomeric elements  208 . The engine output flange  210  is connected to the flywheel  212  and is rotated thereby. Rotation of the flywheel  212  causes the output flange  210  to rotate, and the rotation is transferred to the coupling hub  206  connected to the generator input shaft  200  via elastomeric elements  208 . The elastomeric elements  208 , in a typical configuration, include compressible or stretchable elements in sections that can elastically deform peripherally around the coupling hub  206  and are retained in place by paddles  209  that extend radially or perpendicularly relative to the axis  108  between the coupling hub  206  and the engine output flange  210 . Vibrations produced by bursts of power of a particular cylinder firing, or drains of power when another cylinder compresses cause continuous micro stretching and micro compressive stresses in the elastomeric elements  208  in a rotational or angular direction during engine operation. The elastomeric elements  208  also take up any minor axial misalignments between the flywheel  212  and the generator input shaft  200 . A protective cover  214  is placed over and around the various rotating components, i.e., the tone ring  204 , the flywheel coupling hub  206 , the elastomeric elements  208 , the engine output flange  210 , and any other components that may be present in this area in this and other implementations. 
     The engine  102  further includes a timing gear formed peripherally around an outer portion of the flywheel  212  having teeth  402  ( FIGS.  2  and  7   ) extending peripherally around the flywheel  212 . The timing gear teeth  402  excite a crankshaft sensor or first timing sensor  406  that is mounted on the engine  102 . Although the timing gear is shown mounted on the flywheel  212  it should be appreciated that it may be placed elsewhere in the engine, for example, on a camshaft or another structure that rotates without slipping along with the crankshaft while the engine is operating. During engine operation, the first timing sensor  406  provides information to the controller  118  that is indicative of the position and rotational speed of the crankshaft and flywheel  212  for use in controlling engine operation in the typical fashion. 
     As can be seen in the enlarged detail view of  FIG.  3   , the tone ring  204  can be sandwiched between the generator input flange  202  and the coupling hub  206  by use of a spacer ring  302 , within an annular notch  304  formed in the generator input shaft  200 , thus enabling installation of the tone ring  204  as a retrofit onto existing engines without increasing a distance, D, between an end face  216  of the generator input shaft  200  and an interface plane  218  of the flywheel  212  with the engine crankshaft (not shown). 
     An outline view of the tone ring  204  as installed on the generator  114  is shown in  FIG.  4   . In this view, it can be seen that the tone ring  204  is generally circular and includes a plurality of teeth  401  along an outer periphery region  404  thereof. The protective cover  214  includes a flange  407  that is mountable onto the cylinder case of the engine around an area of the flywheel  212  ( FIG.  2   ). A bracket  408  is connected to the flange  407  and supports a second timing sensor  410  thereon. The second timing sensor  410  is disposed to measure rotation of the tone ring  204  by sensing the location of the teeth  401  disposed along the tone ring  204  but, importantly, the second timing sensor  410  is mounted on the engine and the tone ring  204  is mounted on the coupling hub  206  opposite the elastomeric elements  208  such that the second timing sensor  410  can measure rotational variations of the elastomeric elements  208  present during engine operation compared to the engine and the flywheel  212 . Stated differently, any rotational or angular deflection one way or the other of the elastomeric elements  208  causes a corresponding effect in the tone ring  204  and consequently in the readings of the second timing sensor  410  by creating a difference between the measurement of the flywheel rotation via the first timing sensor  406  measuring the teeth  402  on the flywheel  212  and the measurement of the tone ring  204  rotation via the second timing sensor  410  measuring the teeth  401  on the tone ring  204 . This difference in measurement is proportional to the rotational or angular deflection of the elastomeric elements  208 , which results from variations in the engine output torque caused by the various combustion strokes of the engine cylinders. In other words, when there is no rotational or angular deflection between the flywheel  212  and the tone ring  204 , the measurements of the first timing sensor  406  and the second timing sensor  410  are substantially identical. These two measurements will diverge one way or the other (advanced or retarded relative to one another) depending on the direction of rotational or angular deflection of the elastomeric elements one way (compression) or the other (extension). 
     To illustrate, the sensor readings of the first timing sensor  406  on the engine and the second timing sensor  410  would or should be identical if there was a solid connection between the engine and the generator, i.e., if there were no elastomeric elements  208  used between the flywheel  212  and the generator input shaft  200 . However, since the elastomeric elements  208  are present, their minute rotational or angular compression or stretching during engine operation caused by successive torque spikes or delays caused by cylinder operation will cause differences in the readings between the first and second timing sensors  406  and  410 , which can also be referred to as an input sensor (the first timing sensor  406 ) to the flexible coupling between the engine and generator, and an output sensor (the second timing sensor  410 ). The terms input and output in this context refer to the input and output signal changes of any torque variations provided from the engine to the generator via the flexible coupling that includes the elastomeric elements  208 . 
     The signals from both the input sensor  406  and the output sensor  410  are provided to the controller  118 . The controller  118  monitors an input signal from the input sensor  406  and an output signal from the output sensor  410 , calculates a difference between the two, and based on the difference between the input and output signals calculates or infers a cylinder pressure that is present concurrently with the measurements within the cylinders of the engine. 
     More specifically, a graph of the difference between the input and output signals over time for a single cylinder operating on the engine  102  is shown in  FIG.  5   . The curve  500  represents the value of the difference between the input signal provided by the input sensor or the first timing sensor  406 , and the output signal provided by the output sensor or the second timing sensor  410 . In essence, the magnitude of the vertical dimension of the curve  500  indicates the extent of rotational or angular deformation of the elastomeric elements  208  at any point in time, which time is plotted against the horizontal axis. The horizontal axis also represents a zero deflection of the elastomeric elements  208 , so the direction of the curve  500  above or below the horizontal axis also indicates the direction of rotational or angular deflection of the elastomeric elements  208 , with positive (above axis  502 ) indicating stretching of the elements  208 , and negative (below the axis  502 ) indicating compression of the elements  208 . As previously discussed, rotational or angular stretching of the elements  208  occurs when power or torque is input to the crankshaft in a rotational or angular direction tending to accelerate the flywheel  212  during a cylinder firing event or stroke, and rotational or angular compression of the elements  208  occurs when power or torque is stolen from the flywheel in a rotational or angular direction tending to decelerate the flywheel during a cylinder compression event. 
     In reference to  FIG.  5   , the trace of the input/output sensor signal difference is shown for a single cylinder and for a period between two successive power strokes. At a point  1  the cylinder is at peak cylinder pressure during a power stroke. Segment  2  represents a lowering of cylinder pressure during an expansion stroke after peak pressure. At segment  3  the cylinder continues expanding until point  4 , and then begins compressing the exhaust gas during segment  5  until the cylinder exhaust valve(s) open at point  6 . Exhaust gas is pushed out of the cylinder during a segment  7 , and at point  8  the cylinder is at top dead center (TDC), the exhaust valves close, and the cylinder consumes work over a segment  99  until the intake valves open at point  10 . The air or air and fuel mixture are pulled into the cylinder over segment  11  and consume work until the intake valves close at  12  and a compression stroke begins at segment  13 . The compression stroke over segment  14  continues and combustion starts to increase cylinder pressure during the power stroke, which stretches the elements  208  and pulls the curve  500  towards the positive side, providing work and torque to the crankshaft until peak pressure is reached at a second point  1 , and the cycle repeats. 
     It has been determined that the curve  500 , or a parameter representing the difference between measurements taken by the first and second timing sensors  406  and  410  is a very accurate and reliable indicator of cylinder pressure. The difference parameter tracks cylinder pressure as well as a pressure sensor that is placed within the cylinder, but without requiring sophisticated sensor technologies such as piezo sensors that are configured to operate in the harsh in-cylinder environment. A reliable cylinder pressure determination can be made by using the outputs of the first and second timing sensors  406  and  410 , one being the crankshaft sensor that is typically found on engines, and the other being a second sensor that is placed on the engine and measures rotation of a tone ring placed opposite the elastomeric elements  208 . 
     Illustrations of an exemplary embodiment for the placement of the second timing sensor  410  on an engine are shown in the detail views provided in  FIGS.  6  and  7   . As can be seen in these figures, the bracket  408  is mounted using fasteners  600  onto the engine cylinder case along the cover  214  such that the bracket  408  and, thus, the second timing sensor  410  supported thereby, are rigidly mounted onto the engine  102 . The tone ring  204  is rigidly mounted on the input shaft  200  of the generator  114  and its teeth  401  excite the second timing sensor  410  so that the readings of the second timing sensor  410  will be affected by any compression or stretching of the elastomeric elements  208  when compared with corresponding readings of the teeth  402  on the flywheel  212  excite the first timing sensor  406 . A cover plate  604  is placed over the exposed face of the tone ring  204 . A conductor  602  can receive the signals from the second timing sensor  410  and communicate them to the controller  118 . 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is applicable to internal combustion engines of any type that include a flexible coupling or connection between an engine output shaft and an input shaft of a driven system. A flowchart of a method of indirectly measuring cylinder pressure is provided in  FIG.  8   . In accordance with an embodiment, a flexible coupler is provided between a driver, such as an engine, and a driven component such as a generator at  802 . The flexible coupler, for example, may include any type of flexible couplers including elastomeric elements placed between rotatable flanges that can compress or stretch depending on torque variations present between the rotating flanges. 
     A first sensor configured to sense rotation of a driver component is mounted on one side of the coupler that is rigidly associated with the driver component or system at  804 . A second sensor is mounted on the same side of the coupler that is rigidly associated with the driver side of the system at  806 . The second sensor is also configured to sense rotation of a tone ring mounted on the driven side of the coupler, or across the coupler, such that variations in the angular position of the coupler between the driver and driven components will affect the measurement of the second sensor relative to the first sensor. The difference between the first and second sensor signals is calculated at  808 , and a rotational or angular deflection of the coupler is inferred at  810  based on the magnitude and direction of the difference. In one embodiment, the driver is an engine, the driven component is a transmission or generator, and the difference is indicative of cylinder pressure in the engine. 
     As can be appreciated, in an exemplary engine installation having rubber elastomeric couplings, the rotational or angular deflection of the measurement can be about 10 degrees. The controller can be programmed to calibrate the sensor difference at each startup, for example, when the engine is not carrying appreciable load, to account for various differences in the system that may affect measurements such as temperature, the hardness from weathering of the elastomeric elements, and the like. By measuring cylinder pressure during engine operation, the controller can control fuel and ignition timing, if applicable, when ignition requires delay or advancement as indicated by the cylinder pressure on the fly in the event engine operation changes, for example, due to inconsistent fuel quality. By measuring cylinder pressure in this fashion, other parameters such as burn duration, cylinder pressure rise rate, peak pressure, ignition timing and other parameters can also be calculated and used to optimize engine operation. 
     The tone ring  204 , in one embodiment for an engine having 20 cylinders, can be arranged with 183 teeth. In such embodiment, the controller can effectively and accurately sense specific cylinder firings per engine revolution, or a trace that measures the location of about 18 teeth per firing, which provides sufficient resolution to infer the desired engine operating and cylinder firing parameters. 
     As can be appreciated, in the embodiment described herein two sensors are mounted onto the input side of a flexible coupling (the engine) and measure timing signals of two timing gears, one timing gear being disposed on the input side of the flexible coupling (the engine flywheel) and the other timing gear being disposed on the output side of the flexible coupling (the tone ring). In an alternative embodiment, the sensors may also be mounted onto the output side of the flexible coupling (the generator). 
     It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated. 
     Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.