Patent Publication Number: US-7712441-B2

Title: Predicted engine oil pressure

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/015,358, filed on Dec. 20, 2007. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to engine oil pressure prediction, and more specifically to engine oil supply pressure prediction based on a downstream oil pressure measurement. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Engines typically include an oil supply pressure sensor to monitor oil pressure supplied to a lubricated portion of the engine, such as the main bearings. With additional hydraulically actuated components such as cam phasers and multi-step lifters being incorporated into engines, additional oil pressure sensors may be needed at locations downstream of an oil supply pressure sensor. Additional oil pressure sensors may add additional cost and complexity to engines. 
     SUMMARY 
     A method may include opening an oil control valve (OCV) in an engine to provide an oil flow that actuates a cam phaser, measuring a first engine oil pressure at a location between the OCV and the cam phaser when the OCV is open, and determining a second engine oil pressure at a location between the OCV and an oil pump outlet location based on said first engine oil pressure. 
     A control module may include a cam phaser control module, a cam phaser oil pressure determination module, and a system oil pressure prediction module. The cam phaser control module may control an oil control valve (OCV) to control an oil flow to a cam phaser. The cam phaser oil pressure determination module may be in communication with the cam phaser control module and may determine a first engine oil pressure at a location between the OCV and the cam phaser when the OCV is in an open position. The system oil pressure prediction module may determine a second engine oil pressure at a location between the OCV and an oil pump outlet based on the first engine oil pressure. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic illustration of a vehicle according to the present disclosure; 
         FIG. 2  is a schematic illustration of an engine oil system of the vehicle of  FIG. 1 ; 
         FIG. 3  is a control block diagram of the control module shown in  FIG. 1 ; and 
         FIG. 4  is a flow diagram illustrating steps for oil pressure prediction for the vehicle of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, 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 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, or other suitable components that provide the described functionality. 
     Referring now to  FIG. 1 , an exemplary vehicle  10  is schematically illustrated. Vehicle  10  may include an engine  12  in communication with an intake system  14  and a control module  15 . Engine  12  may include a plurality of cylinders  16  having pistons  18  disposed therein. Engine  12  may further include a fuel injector  20 , a spark plug  22 , an intake valve  24 , an exhaust valve  26 , an intake valve lifter  28 , and an exhaust valve lifter  30  for each cylinder  16 , as well as intake and exhaust camshafts  32 ,  34 , and intake and exhaust cam phaser systems  36 ,  38 . 
     Intake system  14  may include an intake manifold  40  and a throttle  42  in communication with an electronic throttle control (ETC)  44 . Throttle  42  and intake valves  24  may control an air flow into engine  12 . Fuel injector  20  may control a fuel flow into engine  12  and spark plug  22  may ignite the air/fuel mixture provided to engine  12  by intake system  14  and fuel injector  20 . Intake and/or exhaust valve lifters  28 ,  30  may include multi-step lifters, such as two-step lifters. 
     With additional reference to  FIG. 2 , engine  12  may include an oil system  46  that includes an oil pump  48 , a cam bearing and lifter gallery  50 , a main bearing gallery  52 , and a cam phaser oil feed  54  in fluid communication with the intake and exhaust cam phaser systems  36 ,  38 . Intake cam phaser system  36  may include an oil control valve (OCV)  56 , a cam phaser  58 , and a pressure sensor  60  located between OCV  56  and cam phaser  58 . Pressure sensor  60  may be in communication with control module  15  and may provide a signal to control module  15  indicative of an oil pressure between OCV  56  and cam phaser  58 . Exhaust cam phaser system  38  may include an OCV  62  and a cam phaser  64 . While oil pressure sensor  60  is shown located between OCV  56  and cam phaser  58 , it is understood that oil pressure sensor  60  may alternatively be located between OCV  62  and cam phaser  64 . 
     Control module  15  may be in communication with engine  12  and may receive a signal from engine  12  indicative of a current engine speed. Control module  15  may additionally be in communication with intake and exhaust cam phaser systems  36 ,  38  and ETC  40 . More specifically, in the present example control module  15  may be in communication with OCV  56  and intake phaser  58  to control opening of OCV  56  and to determine phasing rate and location of cam phaser  58 . With reference to  FIG. 3 , control module  15  may include a cam phaser control module  66 , a cam phaser oil pressure determination module  68 , and a system oil pressure prediction module  70 . 
     Cam phaser control module  66  may control the opening of OCV  56  and therefore the phasing rate and displacement of cam phaser  58 . Cam phaser oil pressure determination module  68  may be in communication with and receive a signal from cam phaser control module  66  that indicates a position of OCV  56  and a phasing rate of cam phaser  58 . Cam phaser oil pressure determination module  68  may determine the oil pressure at a location between OCV  56  and cam phaser  58 . The determined oil pressure may be used for evaluation of the intake and/or exhaust valve lifters  28 ,  30  when multi-step lifters are incorporated into engine  12 . The determined oil pressure may additionally be used to estimate or predict an oil supply pressure. The oil supply pressure may include an oil pressure at a location in oil system  46  between oil pump  48  and OCV  56 , and more specifically an oil pressure at main bearing gallery  52 . 
     System oil pressure prediction module  70  may be in communication with cam phaser oil pressure determination module  68  and may receive the determined oil pressure. System oil pressure prediction module  70  may estimate a system oil flow rate and predict the oil supply pressure. 
     With reference to  FIG. 4 , control logic  100  generally illustrates a method of predicting the oil supply pressure discussed above. Control logic  100  may begin at block  102  where OCV  56  is opened to actuate cam phaser  58 . Control logic  100  may then proceed to block  104  where oil pressure (P d ) is determined at a location between OCV  56  and cam phaser  58  using pressure sensor  60  while OCV  56  is open. Control logic  100  may then proceed to block  106  where the oil supply pressure (P s ) is predicted. Control logic  100  may terminate once the oil supply pressure is determined. 
     Prediction of the oil supply pressure (P s ) using the determined oil pressure (P d ) may include a calculation of the oil supply pressure based on the following equations: 
                         P   s     =       P   d     +             V   .     2     ⁢   ρ       2   ⁢     C   d   2     ⁢     A   d   2         ⁢     (     1   -       (       A   s       A   d       )     2       )       +     g   ⁢           ⁢   ρ   ⁢           ⁢   h         ;     ⁢     
     ⁢   and           (   1   )                   C   d     =     f   ⁡     (       V   .     ,   ρ   ,   v     )         ;           (   2   )               
where P s  is the oil supply pressure, P d  is the determined oil pressure (a downstream oil pressure between OCV  56  and cam phaser  58  in the present example), {dot over (V)} is an estimated system volumetric oil flow rate, ρ is oil density, ν is oil viscosity, C d  is a discharge coefficient, A s  is a supply side reference area, A d  is a downstream side reference area, g is the gravitational constant (9.81 m/s 2 ), and h is the height of the location of P d  relative to P s .
 
     A matrix of discharge coefficients (C d ) may be determined for a variety of engine operating conditions. The discharge coefficients (C d ) may be determined from component level testing and may be a function of volumetric oil flow rate ({dot over (V)}), oil density (ρ), and oil viscosity (ν), as shown in equation (2) above. More specifically, the discharge coefficients (C d ) may be calculated based on the component level testing. 
     For example, a known volumetric oil flow rate ({dot over (V)}) may be supplied to the engine  12  at a location corresponding to an oil pump outlet. A range of volumetric oil flow rates ({dot over (V)} 1 , {dot over (V)} 2 , . . . , {dot over (V)} n ) may be supplied for a variety of engine conditions including oil temperatures (which accounts for oil density (ρ) and oil viscosity (ν)) as well operating conditions of cam phasers  58 ,  64 . A first oil pressure measurement (P 1 ) that generally corresponds to determined oil pressure (P d ) may be taken at pressure sensor  60  and a second oil pressure measurement (P 2 ) that generally corresponds to oil supply pressure (P s ) may be taken upstream of first oil pressure measurement (P 1 ). For example, second oil pressure measurement (P 2 ) may be taken at main bearing gallery  52 . A range of first oil pressures (P 1   1 , P 1   2 , . . . , P 1   n ) and second oil pressures (P 2   1 , P 2   2 , . . . , P 2   n ) may be collected that correspond to the range of volumetric oil flow rates ({dot over (V)} 1 , {dot over (V)} 2 , . . . , {dot over (V)} n ). 
     Equation (1) may be manipulated to solve for discharge coefficient (C d ) using the first and second oil pressure measurements (P 1 , P 2 ) as seen below in equation (3): 
                     C   d     =       V   .       (       A   d     ⁢             2   ρ     ⁢     (       P   ⁢           ⁢   2     -     P   ⁢           ⁢   1       )       -     2   ⁢   gh         1   -       (       A   d       A   s       )     2             )               (   3   )               
A range of discharge coefficients (C d1 , C d2 , . . . , C dn ) may be calculated that correspond to the range of volumetric oil flow rates ({dot over (V)} 1 , {dot over (V)} 2 , . . . , {dot over (V)} n ) first oil pressures (P 1   1 , P 1   2 , . . . , P 1   n ) and second oil pressures (P 2   1 , P 2   2 , . . . , P 2   n ). Supply and discharge side reference areas (A s , A d ) may be selected, where A s  is not equal to A d . Supply and discharge side reference areas (A s , A d ) may be selected in a relatively arbitrary manner, as long as the same supply and discharge side reference areas (A s , A d ) are used for the calculation of each of discharge coefficients (C d1 , C d2 , . . . , C dn ) and for the calculation of the supply pressure (P s ).
 
     The range of discharge coefficients (C d1 , C d2 , . . . , C dn ) may form a matrix of discharge coefficients for use in the calculation of the supply pressure (P s ). The values for the range of discharge coefficients may form a regression-based function or may be incorporated into a look-up table. Therefore, based on estimated system oil flow rate ({dot over (V)}), the supply pressure (P s ) may be predicted based on the determined oil pressure (P d ) from pressure sensor  60 . 
     Alternatively, oil supply pressure (P s ) may be determined from a purely empirical regression equation shown in equation (4) below:
 
 P   s   =f ( P   d ,RPM, T,{dot over (φ)}   I ,{dot over (φ)} E );  (4)
 
where P d  is the determined oil pressure, as discussed above, RPM is engine speed (revolutions/minute), T is oil temperature, {dot over (φ)} I  is intake phaser phasing rate, and {dot over (φ)} E  is exhaust phaser phasing rate. Equation (4) may be derived experimentally from engine testing. Engine speed (RPM) may be used where oil pump  48  is driven by a mechanical component of engine  12  such as the crankshaft. Engine speed (RPM) may be disregarded where oil pump  48  is driven independently from engine  12 , such as by an electric motor.
 
     In either oil supply pressure (P s ) determination method, pressure sensor  60  may generally provide for the estimation of a system supply pressure, eliminating the need for an additional oil pressure sensor.