Patent Publication Number: US-7913545-B2

Title: Time and angle based cylinder pressure data collection

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/049,045, filed on Apr. 30, 2008. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to engine systems, and more specifically to systems and methods for evaluating a cylinder pressure. 
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Some vehicles include an internal combustion engine that generates drive torque. More specifically, the engine draws in air and mixes the air with fuel to form a combustion mixture. The combustion mixture is compressed and ignited to drive pistons that are disposed within the cylinders. The pistons drive a crankshaft that transfers drive torque to a transmission and wheels. 
     A crankshaft position signal is generated based on the rotation of the crankshaft and a cylinder pressure signal is generated based on the pressure in the cylinder. A control module determines an engine position and an engine speed from the crankshaft signal and a cylinder pressure from the cylinder pressure signal. Cylinder pressure is used to control one or more subsystems within the vehicle. Errors in the cylinder pressure measurement can cause inaccurate cylinder pressure computations and therefore may cause one or more vehicle subsystems to operate inefficiently. 
     Cylinder pressure signals generated in the time and angle domains are used to control spark knock and combustion in the engine, respectively. A control module that determines cylinder pressure from cylinder pressure signals generated in the time and angle domains requires at least two analog-to-digital (A/D) converters, one A/D converter to sample cylinder pressure generated in the time domain and another A/D converter to sample cylinder pressure generated in the angle domain. 
     Cylinder pressure generated in the angle domain is typically sampled at each degree of rotation of the crankshaft. The location of each degree is predicted based on the engine position and engine speed. Variations in the engine speed may cause errors in the predicted location of each degree, which may cause errors in cylinder pressure sampled in the angle domain. 
     SUMMARY 
     A control module comprising a crankshaft position determination module that determines a first crankshaft position in an engine at a first time, a time-based cylinder pressure determination module that determines N time-based cylinder pressures in the engine at N times, wherein N is an integer greater than one, and an angle-based cylinder pressure determination module that determines an angle-based cylinder pressure at the first crankshaft position based on the first time, the N time-based cylinder pressures, and the N times. 
     A method comprising determining a first crankshaft position in an engine at a first time, determining N time-based cylinder pressures in the engine at N times, wherein N is an integer greater than one, and determining an angle-based cylinder pressure at the first crankshaft position based on the first time, the N time-based cylinder pressures, and the N times. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a schematic illustration of a vehicle according to the present disclosure; 
         FIG. 2  is a functional block diagram of the control module shown in  FIG. 1 ; 
         FIG. 3  is a flow chart illustrating a method of determining cylinder pressure according to the present disclosure; and 
         FIG. 4  is a graphical representation of the relationship between time-based cylinder pressure and angle-based cylinder pressure according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     Referring now to  FIG. 1 , an exemplary vehicle  10  is schematically illustrated. The vehicle  10  includes an engine  12  and a control module  14 . The engine  12  may be a spark ignition internal combustion engine or a diesel engine. The engine  12  includes a plurality of cylinders  16  having a plurality of pistons  18  disposed for reciprocating motion therein and drivingly engaged with a crankshaft  20  by a series of connecting rods  22 . 
     Cylinder pressure sensors  24  are in communication with cylinders  16  and measure pressures within cylinders  16 . Cylinder pressure sensors  24  are in communication with the control module  14 . While each cylinder  16  is shown having a cylinder pressure sensor  24  in communication therewith, it is understood that a single one of cylinders  16  may have cylinder pressure sensor  24  in communication therewith and the remainder of cylinders  16  may not, as discussed below. For simplicity, the discussion below will relate to a single cylinder  16  and a single cylinder pressure sensor  24 . 
     The cylinder pressure sensor  24  provides a signal indicative of a pressure within the cylinder  16  to the control module  14 . A crankshaft position sensor  26  provides a signal indicative of the position of the crankshaft  20  to the control module  14 . The control module  14  determines a pressure in the cylinder  16  at a degree of rotation of the crankshaft  20  based on the pressure within the cylinder  16  and the position of the crankshaft  20 . 
     Referring now to  FIG. 2 , the control module  14  includes a crankshaft position determination module  28 , a time-based cylinder pressure determination module  30 , a buffer  32 , and an angle-based cylinder pressure determination module  34 . The crankshaft position determination module  28  is in communication with the angle-based cylinder pressure determination module  34 . The crankshaft position determination module  28  determines a crankshaft position occurring at a corresponding time based on the crankshaft position signal provided by the crankshaft position sensor  26 . The crankshaft position determination module  28  provides a signal indicative of the determined crankshaft position and the corresponding time to the angle-based cylinder pressure determination module  34 . 
     The time-based cylinder pressure determination module  30  is in communication with the buffer  32 . The time-based cylinder pressure determination module  30  determines a cylinder pressure based on the signal indicative of cylinder pressure from the cylinder pressure sensor  24 . The time-based cylinder pressure determination module  30  may include a filter (not shown) that filters the signal indicative of cylinder pressure to improve the accuracy of the determined cylinder pressure. The time-based cylinder pressure determination module  30  may also include an analog-to-digital (A/D) converter (not shown) that samples a signal indicative of the cylinder pressure at a predetermined rate that enables oversampling. The time-based cylinder pressure determination module  30  provides a signal indicative of the determined cylinder pressure and a corresponding time to the buffer  32 . 
     The buffer  32  is in communication with the angle-based cylinder pressure determination module  34  and an output of the control module  14 . The buffer  32  stores a plurality of cylinder pressures occurring at a plurality of times based on the signal indicative of the determined cylinder pressure and the corresponding time from the time-based cylinder pressure determination module  30 . The buffer  32  has sufficient memory to store the plurality of cylinder pressures and the corresponding plurality of times with a range of the plurality of times including two times that correspond to crankshaft positions determined at the lowest speed of the engine  12 . The buffer  32  provides a signal indicative of the plurality of cylinder pressures and the corresponding plurality of times to the angle-based cylinder pressure determination module  34  and the output of the control module  14 , which may be used to control spark knock in the engine  12 . 
     The angle-based cylinder pressure determination module  34  is in communication with the output of the control module  14 . The angle-based cylinder pressure determination module  34  determines a cylinder pressure at a degree of crankshaft rotation based on the signal indicative of the determined crankshaft position and the corresponding time from the crankshaft position determination module  28  and the signal indicative of the plurality of cylinder pressures and the corresponding plurality of times from the buffer  32 . Since the pressure at a degree of crankshaft rotation is determined based on a time-based cylinder pressure signal, only a single A/D converter is required to determine a time-based cylinder pressure and an angle-based cylinder pressure. The angle-based cylinder pressure determination module  34  provides a signal indicative of the pressure corresponding to a degree of crankshaft rotation to the output of the control module  14 , which may be used to control combustion in the engine  12 . 
     Referring to  FIG. 3 , exemplary steps executed by the control module  14  to determine a time-based pressure and an angle-based pressure in the cylinder  16  will be described in detail. In step  36 , control determines first and second crankshaft positions (θ 1 , θ 2 ) corresponding to first and second times (t 1 , t 2 ). Crankshaft position may be determined in degrees of rotation of the crankshaft  20  relative to a reference point, such as a position of the piston  18  within the cylinder  16 . In step  38 , control determines a plurality of cylinder pressures (P t ) at a plurality of times (t P ) corresponding to a predetermined sampling rate, or inversely, a predetermined sampling period (T). 
     In step  40 , control determines a time at a degree of crankshaft rotation (t D ) between said first and second crankshaft positions (θ 1 , θ 2 ) based on the first and second crankshaft positions (θ 1 , θ 2 ) and the first and second times (t θ1 , t θ2 ). In this manner, control is back-calculating a location of each degree based on engine position rather than predicting the location of each degree based on engine position and engine speed, which avoids errors in the location of each degree due to variations in engine speed. 
     In step  42 , control compares the time at a degree of crankshaft rotation (t D ) to the plurality of times (t P ). In step  44 , when the time at a degree of crankshaft rotation (t D ) is equal to one of the plurality of times (t P ), control sets a cylinder pressure at a degree of crankshaft rotation (P D ) equal to one of the plurality of cylinder pressures (P t ) occurring at the equivalent one of the plurality of times (t P ). 
     In step  46 , when the time at a degree of crankshaft rotation (t D ) is not equal to one of the plurality of times (t P ), control determines the cylinder pressure at a degree of crankshaft rotation (P D ) based on the time at a degree of crankshaft rotation (t D ), two of the plurality of times (t P ) nearest in magnitude to the time at a degree of crankshaft rotation (t D ), and two of the plurality of cylinder pressures (P t ) occurring at the two of the plurality of times (t P ). 
     Referring now to  FIG. 4 , a graphical representation of the relationship between time-based cylinder pressure and angle-based cylinder pressure may be used to describe exemplary steps of the control module  14  in greater detail. Control determines the plurality of cylinder pressures (P t ) at the plurality of times (t P ) corresponding to the predetermined sampling period (T), represented by the top row of solid vertical lines. Control may set the predetermined sampling period (T) equal to 10 μs. Control determines the first and second crankshaft positions (θ 1 , θ 2 ) and the corresponding first and second times (t θ1 , t θ2 ) at negative-sloped edges of a signal provided by the crankshaft position sensor  26 , represented by a stepped line located below the top row of solid vertical lines. 
     Control determines a time at a degree of crankshaft rotation (t D ) by multiplying a time per degree by a difference between the degree and one of the first and second crankshaft positions (θ 1 , θ 2 ) and adding the product to one of the first and second times (t θ1 , t θ2 ), respectively. The time at a degree of crankshaft rotation (t D ) is represented by the vertical dashed lines. Control determines the time per degree by dividing the difference between first and second times (t θ1 , t θ2 ) by the difference between the first and second crankshaft positions (θ 1 , θ 2 ). Control determines a number of samples per degree by dividing the time per degree by the predetermined sampling period (T). Control uses the number of samples per degree as a pointer to the plurality of cylinder pressures relative to a degree of crankshaft rotation. 
     Control determines the cylinder pressure at a degree of crankshaft rotation (P D ) based on the corresponding time at the degree of crankshaft rotation (t D ), the plurality of cylinder pressures (P t ), and the plurality of times (t P ). The cylinder pressure at a degree of crankshaft rotation (P D ) is represented by the bottom solid vertical lines. When the time at a degree of crankshaft rotation (t D ) is equal to one of the plurality of times (t P ), control sets the pressure at the degree of rotation (P D ) equal to the one of the plurality of cylinder pressures (P t ) occurring at the equivalent predetermined time (t P ). When the time at a degree of crankshaft rotation (t D ) is not equal to one of the plurality of times (t P ), as shown in  FIG. 4 , control use interpolation to determine the cylinder pressure at the degree of crankshaft rotation (P D ) based on the time at the degree of crankshaft rotation (t D ), two of the plurality of times immediately lower and higher than the time at the degree of crankshaft rotation (t Pl , t Ph ) and two of the plurality of cylinder pressures corresponding to the two plurality of times (P tl , P th ). For example, control may determine a cylinder pressure at a degree of crankshaft rotation (P D ) using the following equation: 
     
       
         
           
             
               P 
               D 
             
             = 
             
               
                 P 
                 tl 
               
               + 
               
                 
                   [ 
                   
                     
                       
                         t 
                         D 
                       
                       - 
                       
                         t 
                         Pl 
                       
                     
                     
                       
                         t 
                         Ph 
                       
                       - 
                       
                         t 
                         Pl 
                       
                     
                   
                   ] 
                 
                 ⁢ 
                 
                   ( 
                   
                     
                       P 
                       th 
                     
                     - 
                     
                       P 
                       tl 
                     
                   
                   ) 
                 
               
             
           
         
       
     
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.