Cam Phase Actuator Control Systems and Methods

Abstract

The systems and methods described herein provide an approach for cam phase angle control where an axial or rotational position of an actuator of a cam phaser has a direct relationship to the phase angle of the cam shaft, allowing for accurate cam phasing without the need for cam shaft or crank shaft position sensors. Providing phase angle adjustability without the need for crank shaft or cam shaft position sensors enables control of phase angle solely by sensing the axial or rotational position of the actuator of the cam phaser.

We claim: 
     
         1 . A cam phasing control system for varying a rotational relationship between a crank shaft and a cam shaft, the cam phasing control system comprising:
 a cam phaser including a first component configured to be coupled to a cam shaft and a second component configured to be coupled to a crank shaft;   an actuator configured to adjust a rotational position of the first component relative to the second component;   an actuator position sensor configured to detect an actuation position of the actuator; and   a controller including a processor and a memory, the processor configured to:
 receive a phase angle command; 
 determine a required actuation position of the actuator based on the phase angle command and a predetermined relationship between an actuation position of the actuator and cam phase angle; and 
 command the actuator to displace from a first fixed position to a second fixed position, wherein a magnitude of the displacement between the first fixed position and the second fixed position corresponds with a proportional rotational displacement between the first component and the second component. 
   
     
     
         2 . The system of  claim 1 , wherein the predetermined relationship between the actuation position of the actuator and the cam phase angle is linear. 
     
     
         3 . The system of  claim 1 , wherein the determination of the required actuation position is done without a cam shaft position sensor and a crank shaft position sensor. 
     
     
         4 . The system of  claim 1 , wherein the predetermined relationship between the actuation position of the actuator and the cam phase angle is defined by a helical feature arranged between an input shaft of the cam phaser and one of the first component or the second component. 
     
     
         5 . The system of  claim 4 , wherein the actuator is configured to axially displace the input shaft of the cam phaser. 
     
     
         6 . The system of  claim 1 , wherein the predetermined relationship between the actuation position of the actuator and the cam phase angle is defined by a gear ratio of a planetary gear train arranged between an input shaft of the cam phaser and one of the first component or the second component. 
     
     
         7 . The system of  claim 6 , wherein the actuator is configured to rotationally displace the input shaft of the cam phaser. 
     
     
         8 . The system of  claim 1 , wherein the predetermined relationship is governed by the following equation:
   θ=β( a−a   1 )+θ 1  
   
       wherein a is the actuation position, θ is the cam phase angle, β is a coefficient defined by one of a helical feature or a gear ratio of a planetary gear train arranged between an input shaft of the cam phaser and one of the first component or the second component, and a 1 , θ 1  are coefficients representative of a known operating point for a known actuation position and a corresponding known cam phase angle, respectively. 
     
     
         9 . The system of  claim 1 , further comprising a crank shaft position sensor configured to detect a crank shaft position and a cam shaft position sensor configured to detect a cam shaft position;
 wherein the processor is configured to measure a cam phase angle based on the crank shaft position and the cam shaft position.   
     
     
         10 . The system of  claim 9 , wherein the predetermined relationship is stored in the memory of the controller as a two-dimensional look up table;
 wherein the processor is configured to update the two-dimensional look up table based on the measured cam phase angle and the actuation position of the actuator.   
     
     
         11 . The system of  claim 10 , wherein the processor is further configured to execute a calibration procedure, the processor configured to:
 command the actuator to an end position;   determine the cam phase angle based on the crank shaft position and the cam shaft position; and   generate the two-dimensional look up table based on the determined cam phase angle and a coefficient defined by one of a helical feature or a gear ratio of a planetary gear train arranged between an input shaft of the cam phaser and one of the first component or the second component.   
     
     
         12 . The system of  claim 9 , wherein the processor is further configured to operate in an open loop mode and a closed loop mode, the processor configured to:
 detect an actuator error between a commanded actuator position and a sensed actuator position of the actuator; and   determine if the actuator error is within a predetermined range;   wherein when the actuator error is outside of the predetermined range, the processor is configured to operate the cam phasing control system in an open loop mode;   wherein when the actuator error is within the predetermined range, the processor is configured to determine if a measured cam phase angle detected by the cam shaft position sensor and the crank shaft position sensor is accurate; and   wherein when the phase angle reading is determined to be accurate, the processor is configured to operate the cam phasing control system in a closed loop mode.   
     
     
         13 . The system of  claim 12 , wherein when the cam phasing control system is in the closed loop mode, the processor is configured to:
 receive a phase angle command;   determine an estimated actuation position of the actuator based on the phase angle command and the predetermined relationship between the actuation position of the actuator and the cam phase angle;   determine a phase angle error between the commanded phase angle and an actual cam phase angle; and   command the actuator to an actuator position based on the phase angle error and the estimated actuation position.   
     
     
         14 . A method of open loop control of a cam phasing system for varying a rotational relationship between a crank shaft and a cam shaft, the method comprising:
 receiving a phase angle command;   determining a required actuation position of a cam phaser actuator based on the phase angle command and a predetermined relationship between actuation positions of the cam phaser actuator and cam phase angles; and   commanding the cam phaser actuator to the required actuation position.   
     
     
         15 . The method of  claim 14 , wherein the predetermined relationship between the actuation positions of the cam phaser actuator and the cam phase angles is linear. 
     
     
         16 . The method of  claim 14 , wherein the determination of the required actuation position is done without a cam shaft position sensor and a crank shaft position sensor. 
     
     
         17 . The method of  claim 14 , wherein commanding the cam phaser actuator to the required actuation position includes displacing the cam phaser actuator from a first fixed position corresponding to a first phase angle to a second fixed position corresponding to a second phase angle. 
     
     
         18 . The method of  claim 17 , wherein a magnitude of the displacement between the first fixed position and the second fixed position corresponds with a proportional rotational displacement between a first component and a second component of a cam phaser. 
     
     
         19 . The method of  claim 17 , wherein the first fixed position and the second fixed position are a first axial position and a second axial position for the cam phaser actuator, the second axial position being distinct from the first axial position; or
 wherein the first fixed position and the second fixed position are a first rotational position and a second rotational position for the cam phaser actuator, the second rotational position being distinct from the first rotational position.   
     
     
         20 . The method of  claim 14 , wherein determining the required actuation position of the cam phaser actuator includes executing the following equation:
   θ=β( a−a   1 )+θ 1  
   wherein a is the required actuation position, θ is the commanded phase angle, β is a coefficient defined by one of a helical feature or a gear ratio of a planetary gear train internal to a cam phaser, and a 1 , θ 1  are coefficients representative of a known operating point for a known actuation position and a corresponding known cam phase angle, respectively.