METHOD OF CALIBRATION

FIELD OF THE INVENTION

[0001] The invention relates to sensing a position of a camshaft in an internal combustion engine which includes an electric variable cam phaser, and more particularly to a positional control system for an actuator shaft of an electrically operated cam phaser with a feedback loop and a method of calibration.

BACKGROUND

[0002] The operation of an electric phaser for a cam phasing system is such that a sun gear or planet gear carrier is stationary, and a ring gear and other member rotates with a camshaft, which is driven by a crank through a gear, belt or chain system. One method of control is to use a first position sensor mounted on the crankshaft and a second position sensor mounted on the camshaft. After the cam is rotating, the angular position of the cam can be calculated by an electronic control unit (ECU) and a signal can be sent to move the stationary member to adjust the phaser angle of the cam, for example, see U. S. Patent No. 5,680,837. Other control systems can be seen in U.S. Patent No. 7,640,907; and U.S. Patent No. 7,243,627.

[0003] U.S. Published Patent Application No. 2012/0053817 discloses a method for sensing the position of a camshaft in an internal combustion engine having a camshaft phaser for controllably varying the phase relationship between a crankshaft of the internal combustion engine and the camshaft, where the camshaft phaser is actuated by an electric motor and includes a gear reduction mechanism with a predetermined gear reduction ratio and rotational position means for determining the rotational position of the electric motor. The method includes generating a rotational position signal indicative of the rotational position of the electric motor by using the rotational position means to determine the rotational position of the electric motor, and calculating the position of the camshaft based on the rotational position signal and the gear reduction ratio of the gear reduction mechanism. The rotational position means includes three Hall Effect sensors, one sensor disposed between each of the three electrical windings in the stator of the motor, for generating a rotational position signal indicative of the rotational position of the rotor. The published application asserts that this method can also be used to detect the position of the rotor even at zero revolutions per minute (RPM) as long as the engine control module (ECM) is still powered on. The disclosure further asserts that using Hall Effect sensors to determine the position of the camshaft, through the mathematical equations corresponding to the attached harmonic gear drive unit, eliminates the need for a separate sensor for determining the position of the camshaft. While the disclosed configuration may be suitable for the intended purpose, the complexity of the sensor configuration increases cost of the motor and potentially raises issues regarding the simplicity of assembly and/or initialization of the assembled motor system.

SUMMARY

[0004] It would be desirable to know the position of a stationary member of a gear reduction drive train, or an actuator shaft of the stationary member, prior to initial cranking of an internal combustion engine. It would be desirable to be able to determine the position of a stationary member of a gear reduction drive train, or an actuator shaft of the stationary member, with a low cost, simple assembly interacting with a stationary member of a gear reduction drive train, or an actuator shaft of the stationary member, of a cam phaser. It would be desirable to move the cam to a new position prior to the engine spinning for varying conditions of the engine and vehicle for improved start (time and harshness) and reduced emissions. As such, knowing the position of the stationary camshaft member allows repositioning of the cam accurately prior to initial engine cranking.

[0005] An apparatus and method for controlling an angular position of a camshaft in an internal combustion engine having a camshaft phaser for controllably varying the phase relationship between a crankshaft of the internal combustion engine and the camshaft. The camshaft phaser can be actuated by an electric motor having an actuator shaft operating through a gear reduction drive train having a stationary adjusting member which rotates when a phase change adjustment is desired. A sensor can generate a signal corresponding to an angular position of the stationary adjusting member of the gear reduction drive train. An engine control unit can adjust a position of the camshaft through operation of the electric motor for rotating the stationary adjusting member based on the generated signal corresponding to the angular position of the stationary adjusting member.

[0006] A method can control an angular position of a camshaft in an internal combustion engine having a camshaft phaser for controllably varying the phase relationship between a crankshaft of the internal combustion engine and the camshaft. The camshaft phaser can be actuated by an electric motor having an actuator shaft operating through a gear reduction drive train having a stationary adjusting member which rotates when a phase change adjustment is desired. A signal can be generated corresponding to an angular position of the stationary adjusting member of the gear reduction drive train with a sensor, and a position of the camshaft can be adjusted through operation of the electric motor for rotating the stationary adjusting member based on the generated signal corresponding to the angular position of the stationary adjusting member with an engine control unit.

[0007] A method can control an angular position of a camshaft in an internal combustion engine having a camshaft phaser for controllably varying the phase relationship between a crankshaft of the internal combustion engine and the camshaft. The camshaft phaser can be actuated by an electric motor having an actuator shaft operating through a gear reduction drive train having a stationary adjusting member which rotates when a phase change adjustment is desired. A position of the stationary member can be controlled while running the internal combustion engine by commanding the stationary member to move toward a position in response to a cam phase adjustment signal, adjusting the stationary member position toward the commanded position, receiving a stationary member position sensor signal, and determining if the stationary member is in the commanded position. If not in the commanded position, the method can continue movement toward the commanded position. If in the commanded position, the method can receive a camshaft position sensor signal and a crankshaft position sensor signal, and determine if the stationary member position sensor signal, camshaft position sensor signal, and crankshaft position sensor signal are consistent with one another. If consistent with one another, the method can wait for another cam phase adjustment command. If not consistent with one another, the method can recalibrate the stationary member position and continuing movement of the stationary member toward the commanded position.

[0008] Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:

[0010] Figure 1 is a schematic view of an electric phaser controller diagram with actuator position loop for a stationary member of a gear reduction drive train in a phaser positional control system and a method of calibration;

[0011] Figure 2 is a simplified cross sectional view of a positional control system for an actuator shaft of an electric phaser;

[0012] Figures 3 A is a simplified schematic view of a gear reduction drive train having a stationary member with a sensor generating a signal corresponding to a position of the stationary member to an electronic control unit for controlling the electric motor connected to the stationary member for adjustment of a camshaft phase position, wherein the stationary member is a sun gear;

[0013] Figures 3B is a simplified schematic view of a gear reduction drive train having a stationary member with a sensor generating a signal corresponding to a position of the stationary member to an electronic control unit for controlling the electric motor connected to the stationary member for adjustment of a camshaft phase position, wherein the stationary member is a planet gear carrier;

[0014] Figures 3C is a simplified schematic view of a gear reduction drive train having a stationary member with a sensor generating a signal corresponding to a position of the stationary member to an electronic control unit for controlling the electric motor connected to the stationary member for adjustment of a camshaft phase position, wherein the stationary member is a ring gear; [0015] Figure 4 is a simplified control diagram for driving the stationary member of the gear reduction drive train toward a commanded position with a position feedback signals from the stationary member;

[0016] Figure 5 is a simplified control diagram for calibrating the stationary member of the gear reduction drive train without running the internal combustion engine;

[0017] Figure 6 is a simplified control diagram for calibrating the stationary member of the gear reduction drive train while running the internal combustion engine; and

[0018] Figure 7 is a simplified control diagram for driving the stationary member of the gear reduction drive train toward a commanded position with a position feedback signal from the stationary member defining an internal control loop, and feedback signals from a camshaft sensor and a crankshaft sensor defining an external control loop for calibrating a position of the stationary member while the internal combustion engine is running.

DETAILED DESCRIPTION

[0019] Referring now to Figures 1-3C, a device and method is illustrated for controlling an angular position of a camshaft 12 in an internal combustion engine having a camshaft phaser 14 for controllably varying the phase relationship between a crankshaft of the internal combustion engine and the camshaft. The camshaft phaser 14 can be actuated by an electric motor 16 having an actuator shaft 18 operating through a gear reduction drive train 20 with a stationary adjusting member 22 which rotates when a phase change adjustment is desired. The method can include generating a signal corresponding to an angular position of the stationary adjusting member 22 of the gear reduction drive train 20 with a sensor 30, and adjusting a position of the camshaft 12 through operation of the electric motor 16 for rotating the stationary adjusting member 22 based on the generated signal corresponding to the angular position of the stationary adjusting member 22 with an engine control unit 40. As illustrated in Figure 2, the actuator shaft 18 can be driven by an electric motor 16. The actuator shaft 18 can include a magnet 24 interacting with a sensor 26 in communication with a printed circuit board (PCB) 28 for signaling an angular position of the actuator shaft 18.

[0020] Referring now to Figure 3A, the gear reduction drive train 20 can include an assembly of a planetary gear system or assembly 50 having a sun gear 52, a plurality of planet gears 54 rotationally engaging the sun gear 52 and supported for synchronized rotation about the sun gear 52 with a carrier 56. A ring gear 58 can rotationally engage the plurality of planet gears 54 and can have an axis of rotation coaxial with the sun gear 52 and carrier 56. The sun gear 52 in this configuration can define the stationary adjusting member 22.

[0021] Referring now to Figure 3B, the gear reduction drive train 20 can include an assembly of a planetary gear system or assembly 50 having a sun gear 52, a plurality of planet gears 54 rotationally engaging the sun gear 52 and supported for synchronized rotation about the sun gear 52 with a carrier 56. A ring gear 58 can rotationally engage the plurality of planet gears 54 and can have an axis of rotation coaxial with the sun gear 52 and carrier 56. The carrier 56 in this configuration can define the stationary adjusting member 22.

[0022] Referring now to Figure 3C, the gear reduction drive train 20 can include an assembly of a planetary gear system or assembly 50 having a sun gear 52, a plurality of planet gears 54 rotationally engaging the sun gear 52 and supported for synchronized rotation about the sun gear 52 with a carrier 56. A ring gear 58 can rotationally engage the plurality of planet gears 54 and can have an axis of rotation coaxial with the sun gear 52 and carrier 56. The ring gear 58 in this configuration can define the stationary adjusting member 22.

[0023] Referring now to Figure 4, a method or control program for controlling 400 a position of the stationary adjusting member 22 can include determining 402 a position to command the stationary adjusting member 22 to move toward in response to a cam phase adjustment signal. The stationary adjusting member 22 can be adjusted 404 toward the commanded position. A position sensor 30 for the stationary adjusting member 22 generates a signal that can be received 406. Query 408 determines if the stationary adjusting member 22 is in the commanded position. If the stationary adjusting member 22 is not in the commanded position, movement toward the commanded position is continued in step 410. If the stationary adjusting member 22 is in the commanded position, the method returns to the beginning and waits 412 for the next cam phase adjustment signal to be received.

[0024] Referring now to Figure 5, a calibration program 500 is illustrated for calibrating a position of the stationary adjusting member 22 without running the internal combustion engine. The calibration program 500 can including moving 502 the electric motor 16 to a first stop position. The electric motor 16 is then moved 504 to a second stop position. A range of the electric motor movement is recorded 506. The calibration program 500 then sets 508 a output of the position sensor 30 to first and second direct current voltage values corresponding to the first and second stop positions.

[0025] Referring now to Figure 6, a calibration program 600 is illustrated for calibrating a position of the stationary adjusting member 22 while running the internal combustion engine. The calibration program 600 can include receiving 602 a signal from a position sensor 30 associated with stationary adjusting member 22. A signal can be received 604 from a camshaft position sensor 32. A signal can also be received 606 from a crankshaft position sensor 34. Query 608 can determine if the signaled positions are consistent with one another. If the signaled positions are consistent with one another, the calibration program waits 610 for another cam phase adjustment command. If the signaled positions are not consistent with one another, the calibration program recalibrates 612 the stationary adjusting member 22 position and rechecks the signals from position sensors 30, 32, 34 for consistency.

[0026] Referring now to Figure 7, a method or control program is illustrated for controlling an angular position of a camshaft 12 in an internal combustion engine having a camshaft phaser 14 for controllably varying the phase relationship between a crankshaft of the internal combustion engine and the camshaft. The camshaft phaser 14 can be actuated by an electric motor 16 having an actuator shaft 18 operating through a gear reduction drive train 20 with a stationary adjusting member 22 which rotates when a phase change adjustment is desired. The method or control program can include controlling 700 a position of the stationary adjusting member 22 while running the internal combustion engine. The method can involve moving 702 the stationary adjusting member 22 toward a commanded position in response to a cam phase adjustment signal. A signal is received 704 from a stationary adjusting member 22 position sensor 30 signal. The control program or method determines 706 if the stationary adjusting member 22 is in the commanded position. If the stationary adjusting member 22 is not in the commanded position, the control program or method continues 708 movement of the stationary adjusting member 22 toward the commanded position. If the stationary adjusting member 22 is in the commanded position, the control program or method receives 710, 712 a camshaft position sensor 32 signal and a crankshaft position sensor 34 signal. The control program or method determines 714 if the stationary member position sensor 30 signal, camshaft position sensor 32 signal, and crankshaft position sensor 34 signal are consistent with one another. If the signals from the sensors 30, 32, 34 are consistent with one another, the control program or method waits 716 for another cam phase adjustment command. If the signals form the sensors 30, 32, 34 are not consistent with one another, the control program or method recalibrates 718 the stationary adjusting member 22 position and continues movement of the stationary adjusting member 22 toward the commanded position.

[0027] The operation of an electric phaser for a cam phasing system is such that a sun gear or planet gear carrier is stationary, and a ring gear and other member rotates with a camshaft, which is driven by a crank through a gear, belt or chain system. One method of control is to use a first position sensor mounted on the crankshaft and a second position sensor mounted on the camshaft. After the cam is rotating, the angular position of the cam can be calculated by an electronic control unit (ECU) and a signal can be sent to move the stationary member to adjust the phaser angle of the cam.

[0028] An improvement is provided by mounting an angular position sensor with respect to the stationary member of the gear reduction drive train, such that an output signal corresponds to the position of the stationary member. The angular position sensor can be mounted on the stationary member, or on an actuator -shaft that moves the stationary member. Accordingly, the position of a stationary member of a gear reduction drive train, or an actuator shaft of the stationary member, can be known prior to initial cranking of an internal combustion engine. The position of a stationary member of a gear reduction drive train, or an actuator shaft of the stationary member, can be determined with a low cost, simple assembly interacting with a stationary member of a gear reduction drive train, or an actuator shaft of the stationary member, of a cam phaser. As a result of knowing the current position of the stationary member of a gear reduction train drive, or an actuator shaft of the stationary member, the cam can be moved to a new position prior to the engine spinning for varying conditions of the engine and vehicle for improved start (time and harshness) and reduced emissions. Accordingly, knowledge regarding the position of the stationary camshaft member allows repositioning of the cam accurately prior to initial engine cranking.

[0029] By way of example and not limitation, a Hall Effect sensor can be located across from an end of a worm gear motor actuator shaft and a magnet can be mounted to the end of the actuator shaft. This will give an output to the Electronic Control Unit (ECU), or Proportional-Integral-Derivative (PID) controller, to control the position of the shaft. Other sensors known in the industry can be used if desired, by way of example and not limitation, such as non-contact analog position sensor. The actuator position loop allows the actuator to move in response to the setpoint change and then fine tune the cam phaser angle by determining the phaser position by using the cam position sensor and crank position sensor.

[0030] Due to tolerance stack up the angular position sensor can have a slight error with respect to the actual position of the shaft. A calibration procedure can be performed for improved accuracy of the angular position of the shaft. One such calibration is to move the motor to the stops, record the range and set the output to 0.5VDC to 0.45 VDC. This range is selected so that if the output signal is at either OVDC or 5 VDC a fault signal will be sent to the engine controller.

[0031] Once the actuator is mounted in the engine and the engine is running a second calibration can be performed similar to the above mentioned calibration only this time the phase angle of the cam and crank position signal can be used to calibrate the position of the actuator shaft. This would help reduce any inaccuracies in the fixed member and other gear train members. [0032] For the control of the phaser position there will be an inner control loop used for feed forward to adjust the position of the actuator to the commanded position quickly and then have an outer control loop using the cam and crank position sensor to finely adjust the phaser position. This will improve the phaser response allowing the phaser to have quick response and accurate positional control.

[0033] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.