CN115704328A

CN115704328A - Cam phase actuator control system and method

Info

Publication number: CN115704328A
Application number: CN202210965565.8A
Authority: CN
Inventors: M·库杰克; T·沃伦伯格; P·海瑟夫; D·瓦德勒
Original assignee: Husco Automotive Holdings LLC
Current assignee: Husco Automotive Holdings LLC
Priority date: 2021-08-12
Filing date: 2022-08-12
Publication date: 2023-02-17
Also published as: EP4134526A1; JP2023026407A; US20230050408A1

Abstract

The present invention relates to a cam phasing control system in which the axial or rotational position of the actuator of the cam phaser has a direct relationship with the phase angle of the camshaft, allowing accurate cam phasing without the need for a camshaft or crankshaft position sensor. Phase angle adjustability is provided without the need for a crankshaft or camshaft position sensor to be able to control the phase angle by simply sensing the axial or rotational position of the cam phaser actuator. The invention also relates to an open-loop control method for a cam phasing system for varying the rotational relationship between a crankshaft and a camshaft.

Description

Cam phase actuator control system and method

Cross Reference to Related Applications

This application is based on U.S. provisional patent application No. 63/232,495, entitled Cam Phase Actuator Control Systems and Methods, filed on 12/8/2021, which is hereby incorporated by reference in its entirety for all purposes.

Background

Typically, cam phasing systems include a rotary actuator or phaser configured to adjust the rotational position of a camshaft relative to the crankshaft of an internal combustion engine.

Disclosure of Invention

According to one aspect, the present disclosure provides a cam phasing control system for varying a rotational relationship between a crankshaft and a camshaft. The cam phasing system includes a cam phaser including a first component configured to be coupled to a camshaft and a second component configured to be coupled to a crankshaft; 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 actuator position of the actuator; and a controller including a processor and a memory. The processor is configured to receive the phase angle command, and determine a desired actuation position of the actuator based on the phase angle command and a predetermined relationship between the actuation position of the actuator and the cam phase angle. The processor is further configured to instruct the actuator to displace from a first fixed position to a second fixed position, wherein a magnitude of displacement between the first fixed position and the second fixed position corresponds to a proportional rotational displacement between the first component and the second component.

According to some aspects, the desired actuation position is determined without a camshaft position sensor and a crankshaft position sensor.

According to another aspect, the present disclosure provides an open-loop control method for a cam phasing system for varying a rotational relationship between a crankshaft and a camshaft. The method includes receiving a phase angle command, determining a desired actuation position of the cam phaser actuator based on the phase angle command and a predetermined relationship between the actuation position of the cam phaser actuator and the cam phase angle, and commanding the actuator to the desired actuation position.

According to another aspect, the present disclosure provides a method of calibrating a cam phasing control system. The method includes commanding the cam phaser actuator to an end position, detecting a camshaft position and a crankshaft position, determining a phase angle of the camshaft relative to the crankshaft based on the camshaft position and the crankshaft position, and defining a proportional relationship between an actuated position of the cam phaser actuator and a phase angle of the camshaft based on the determined phase angle and a predetermined relationship between the actuated position of the cam phaser actuator and the resulting phase angle.

According to another aspect, the present disclosure provides a method of controlling a cam phasing system for varying a rotational relationship between a crankshaft and a camshaft. The method includes detecting an error between a commanded actuator position and a sensed actuator position of a cam phaser actuator, and determining whether the error is within a predetermined range. When the error is outside a predetermined range, the cam phasing system operates in an open loop mode. When the error is within a predetermined range, it is determined whether the phase angle reading sensed by the camshaft position sensor is accurate. When the phase angle reading is determined to be accurate, the cam phasing system operates in a closed loop mode.

According to another aspect, the present disclosure provides a cam phasing control system operable in an open loop mode and a closed loop mode. The cam phasing control system includes a cam phaser including a first component configured to be coupled to a camshaft and a second component configured to be coupled to a crankshaft; an actuator configured to adjust a rotational position of the first component relative to the second component; and a controller in communication with an actuator position sensor configured to detect an actuation position of the actuator, a crankshaft position sensor configured to detect a crankshaft position, and a camshaft position sensor configured to detect a camshaft position. When the controller is in the open-loop mode, the controller is configured to receive a phase angle command, determine a desired actuation position of the actuator based on the phase angle command and a predetermined relationship between the actuation position of the actuator and the cam phase angle, and command the actuator to displace to the desired actuation position. When the controller is in the closed-loop mode, the controller is configured to receive a phase angle command, determine an estimated actuated position of the actuator based on the phase angle command and a predetermined relationship between the actuated position of the actuator and a cam phase angle, determine an error between the commanded phase angle and an actual cam phase angle detected by the camshaft position sensor and the crankshaft position sensor, and command the actuator to shift to an actuator position based on the error and the estimated actuated position.

Drawings

Fig. 1 is a schematic diagram of a cam phasing control system, according to one aspect of the disclosure;

FIG. 2 is a schematic diagram of an open loop control method according to one aspect of the present disclosure;

FIG. 3 is a graphical illustration of a proportional relationship between actuator position and cam phase angle according to one aspect of the present disclosure;

fig. 4 is a schematic diagram of a method of calibrating the lookup table of fig. 3.

FIG. 5 is a schematic diagram of a modified closed-loop-control method according to one aspect of the present disclosure;

fig. 6 is an algorithmic diagram for determining an operating mode of a cam phasing control system, according to one aspect of the disclosure;

FIG. 7 is a schematic diagram of an algorithm for determining the accuracy of a camshaft or crankshaft position sensor reading, according to one aspect of the present disclosure;

FIG. 8 is a graph of measured actuator angle, measured phase angle, and engine speed over time;

FIG. 9 shows one non-limiting example of a cam phasing system utilizing an axial displacement actuator; and

fig. 10 shows one non-limiting example of a cam phasing system utilizing a rotary displacement actuator.

Detailed Description

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, "connected" and "coupled" are not restricted to physical or mechanical connections or couplings.

The following discussion is presented to enable a person skilled in the art to make and use embodiments of the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein may be applied to other embodiments and applications without departing from embodiments of the invention. Thus, the embodiments of the invention are not intended to be limited to the embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description should be read with reference to the drawings, in which like elements in different drawings have like reference numerals. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of embodiments of the invention. Those skilled in the art will recognize that the examples provided herein have many useful alternatives and that they fall within the scope of embodiments of the present invention.

Currently, cam phasers may be hydraulically, electronically, or mechanically actuated. Typically, a mechanically actuated phaser collects cam torque pulses to enable the phaser to rotate. In most cases, the system can only control whether the system is allowed to rotate in the desired direction, with little control over speed or final position. The rotational speed of the phaser and the stop position of the phaser after the cam torque pulse has ended are functions of the magnitude/direction of the cam torque pulse and the engine speed, among other things. Because the damping of cam torque pulses relative to mechanical cam phasing systems can be large, the phaser can easily overshoot or undershoot the desired amount of rotation. For effective control, these systems rely on camshaft and crankshaft position sensors read by an engine controller ("ECU") and require very fast control or continuous cycling on and off. That is, in a mechanical system, one component may lock or unlock the rotation between two components. However, the two components in the locked or unlocked state are independent of the phase angle. Instead, the components in the locked or unlocked states only determine whether to allow the phaser to advance or retard the camshaft relative to the crankshaft. Thus, the individual actuators cannot command the phaser to drive to a predetermined, predictable position.

Hydraulically actuated phasers typically utilize an oil control solenoid to control oil pressure to enable the phaser to rotate. While this operation may allow for bi-directional control of the phaser, hydraulically actuated phasers rely on camshaft and crankshaft position sensors read by an engine controller ("ECU") for active control. That is, the position of the spool in the oil control solenoid is independent of the phase angle. Rather, the position of the spool only determines whether the phaser is actuated to advance or retard the camshaft relative to the crankshaft. Thus, the individual actuators cannot command the phaser to drive to a predetermined, predictable position. Hydraulic phasers are also sensitive to the oil pressure, viscosity and quality of the oil inside the internal combustion engine, which is susceptible to deterioration over time.

Electronically actuated phasers (also known as "electronic phasers") typically utilize an electric rotary actuator to effect rotation of the phaser. In this operation, the rotary actuator must rotate faster or slower than the phaser (e.g., faster or slower than the cam speed) to actuate the phaser. Like hydraulically actuated phasers, electronically actuated phasers rely on camshaft and crankshaft position sensors read by an engine controller ("ECU") for active control. That is, the rotational position of the electric rotary actuator in these conventional electronic phasers is independent of the phase angle. Instead, the speed of the rotary actuator merely determines whether the phaser is driven to advance or retard the camshaft relative to the crankshaft. Thus, the individual actuators cannot command the phaser to drive to a predetermined, predictable position. Further, these electronically actuated phasers typically require the system to return to a "home position" when the engine is shut down to know the position of the phaser.

Due to the deficiencies of these cam phasing systems, it would be desirable to have a cam phasing system that is capable of changing the relationship between the camshaft and the crankshaft on an internal combustion engine independently of the magnitude and direction of the cam torque pulses and the engine speed.

The systems and methods described herein are capable of changing the rotational relationship between a camshaft and a crankshaft on an internal combustion engine (i.e., cam phasing), regardless of engine speed and amplitude of cam torque pulses, where the position of the cam phaser actuator has a direct relationship to the phase angle of the camshaft relative to the crankshaft. As will be described, the systems and methods provide a method in which the axial or rotational position of the cam phaser actuator alone has a direct relationship with the phase angle of the camshaft, allowing for accurate cam phasing without the need for a camshaft or crankshaft position sensor. Phase angle adjustability is provided without requiring a crankshaft or camshaft position sensor to be able to control the phase angle by simply sensing the axial or rotational position of the cam phaser actuator.

As used herein, a camshaft position sensor refers to a sensor that detects the actual rotational position of a camshaft. This is typically accomplished by the camshaft position sensor detecting a geometric/structural feature that specifies a zero position for the camshaft (e.g., a feature that specifies the start of a new rotation). Similarly, the crank shaft position sensor means a sensor that detects an actual rotational position of the crank shaft. This is also typically done by the crankshaft position sensor detecting geometric/structural features that specify a zero position for the crankshaft. In conventional cam phasing systems, as described above, signals from camshaft and crankshaft position sensors are used to determine the phase angle of the camshaft relative to the crankshaft to determine how to control the cam phaser or its actuator.

Fig. 1 illustrates a cam phasing system 10 configured to control a phase angle of a camshaft 14 relative to a crankshaft 16 in open-loop and closed-loop modes. The cam phasing system 10 may include a cam phaser 12 configured to be coupled between a camshaft 14 and a crankshaft 16 of an internal combustion engine (not shown). The cam phaser 12 may include a first component 18 (e.g., a carrier rotor) coupled to the camshaft 14 and a second component 20 (e.g., a sprocket hub) coupled to the crankshaft 16. The first member 18 may drive the camshaft 14 via its coupling with the camshaft 14, such as via one or more fasteners. The second member 20 may be driven by the crank shaft 16, for example via a belt, chain or gear train assembly. This can drive the second member 20 to rotate at a speed proportional to the crankshaft speed (e.g., half the crankshaft speed). One of ordinary skill in the art will appreciate that alternative configurations for the relative coupling of the first member 18, the second member 20, the camshaft 14, and the crankshaft 16 are possible. For example, in one embodiment, the crankshaft 16 may be coupled to the first component 18 and the camshaft 14 may be coupled to the second component 20.

The cam phasing system 10 can include an actuator 22 configured to engage the cam phaser 12 to adjust a rotational position of the first member 18 relative to the second member 20. As will be described herein, in some non-limiting examples, the actuator 22 may be configured to directly or indirectly engage an intermediate member (e.g., a star rotor, see fig. 9 and 10) of the cam phaser 12 for precisely controlling the rotational position of the intermediate member with a mechanism that causes the first member 18 to follow the rotational position of the intermediate member to change the rotational relationship between the camshaft 14 and the crankshaft 16 on the internal combustion engine.

The actuator 22 may be configured to provide an axial or rotational input to the cam phaser 12. For example, the actuator 22 may be a linear actuator or a solenoid configured to axially displace in response to an electrical current. The actuator 22 may also be a mechanical linkage, a hydraulically actuated actuation element, or other mechanism capable of providing an axial force and/or displacement to the cam phaser 12. According to another example, the actuator 22 may be a rotary actuator and may include a stator and a rotor electromagnetically coupled to the stator. An electrical current may be applied to the rotary actuator that may cause a rotary output to be provided by the rotary actuator in a desired direction with a desired force. In some non-limiting examples, the rotary actuator may be in the form of a brushless direct current (BLDC) motor.

The cam phasing system may include a controller 24 that includes a processor 26 and a memory 28. The memory 28 may be a non-transitory computer readable medium or other form of storage, such as flash memory or other type of memory, containing programs, software, or instructions executable by the processor 26. According to some non-limiting examples, controller 24 may be integrated in an engine control unit of an internal combustion engine. As other non-limiting examples, controller 24 may be separate from the engine control unit. For example, the controller 24 may be integrated into the body of the actuator 22.

In the non-limiting example shown, the controller 24 may be in electrical communication with the actuator 22 to provide actuation command signals to the actuator 22. The controller 24 may also be in electrical communication with an actuator position sensor 30 configured to measure/sense the actuation position of the actuator 22. According to some non-limiting examples, the controller 24 may also be in electrical communication with a camshaft position sensor 32 and a crankshaft position sensor 34 configured to detect rotational positions of the camshaft 14 and the crankshaft 16, respectively. It should be understood that camshaft and crankshaft speeds and accelerations may also be derived from the camshaft position sensor 32 and the crankshaft position sensor 34.

Open loop mode

The cam phasing system 10 of fig. 1 can operate in both open loop and modified closed loop modes. FIG. 2 shows a non-limiting example of an open loop operating method 100. Referring to fig. 1 and 2, the process may begin by receiving or generating a phase angle instruction at block 102. The phase angle command may be received by controller 24, for example from an engine control unit. According to one non-limiting example, the phase angle command may be generated by controller 24 based on an operating parameter of the internal combustion engine (e.g., engine speed, engine load, etc.). Controller 24 may then determine a desired actuation position of actuator 22 based on the phase angle command and a predetermined relationship between the actuation position of actuator 22 and the resulting cam phase angle at block 104 (see fig. 3).

After determining the desired actuation position, the controller 24 may command the actuator 22 (e.g., via a signal or current provided to the actuator 22) to the desired actuation position at block 106. That is, the controller 24 may instruct the actuator 22 to axially or rotationally displace the actuating element to engage or otherwise displace an intermediate component, such as a star rotor (see fig. 9 and 10), from a first fixed position associated with a first phase angle (e.g., a stationary actuating element position) toward a second fixed position associated with a second phase angle, where the first fixed position and the second fixed position are different positions and the first phase angle and the second phase angle are different phase angles. The actuator 22 will continue to advance toward the second fixed position until the actuation position sensor 30 detects that the actuator 22 or an actuation element controlled by the actuator 22 is in the second fixed position. As will be described, the magnitude of the actuating element displacement of the actuator 22 between the first and second fixed positions corresponds to a proportional rotational displacement between the first and

second components

18, 20 of the cam phaser 12, thereby proportionally adjusting the phase angle of the camshaft 14 relative to the crankshaft 16 based on the position of the actuating element of the actuator 22.

During open loop operation, controller 24 controls cam phaser 12 to achieve the desired phase angle using only the predetermined relationship between the actuation position of actuation position sensor 30 and actuator 22 and the resulting cam phase angle. That is, the camshaft position sensor 32 and the crankshaft position sensor 34 are not needed or utilized during open loop operation. Utilizing the actuation position sensor 30 and the predetermined relationship that relates actuation position to cam phase angle may allow for rapid and large phase angle changes. This open-loop operation can also be more robust than closed-loop operation because it is independent of the camshaft and crankshaft trigger wheel (i.e., the encoder), which can be susceptible to encoder faults, such as false readings (e.g., "false zeros" or "false missing teeth" are detected) that may occur during large, rapid phase angle changes. Open loop operation may also reduce settling time without increasing overshoot by enabling large, rapid phase angle changes via utilizing a predetermined relationship between actuation position and resulting cam phase angle, rather than operating in a closed loop feedback mode.

Referring now to fig. 1 and 3, the actuator 22 is configured to provide an axial or rotational input to the cam phaser 12 that corresponds to a known desired rotational displacement between the first and

second components

18, 20 of the cam phaser 12. As a result, a known amount of displacement of the actuating element of actuator 22 may result in a known amount (also referred to as phase angle) of clockwise or counterclockwise rotation of camshaft 14 relative to crankshaft 16, depending on whether it is desired to advance or retard the timing of valve opening/closing events controlled by camshaft 14.

Fig. 3 shows one example of a predetermined proportional relationship 206 between the fixed actuator position 202 and the resulting phase angle 204. In the non-limiting example shown, each different position of the actuator 22, e.g., the axial/linear or rotational position of its actuating element, results in a different phase angle 204. The resulting phase angle 204 is proportional to the actuator position 202. In one particular non-limiting example of operation, the actuator position 202 may be at a first fixed position associated with the first phase angle 204. The controller 24 may instruct the actuator 22 to displace from the first fixed position toward the second fixed position until the actuation position sensor 30 detects that the actuator 22 is in the second fixed position. When the actuator 22 is in the second fixed position, the resulting phase angle is the second phase angle. In this non-limiting example, each of the first and second fixed positions and the first and second phase angles decrease along the proportional relationship 206 shown in FIG. 3.

In the non-limiting example shown, the resulting phase angle is linearly proportional to the actuator position, but other proportional relationships are possible. For example, the relationship may be substantially linear, where the relationship between the phase angle and the actuator position may deviate slightly from perfect linearity at one or more actuator positions. According to another example, the relationship between the phase angle and the actuator position may be inversely proportional. As will be described, the ratio between actuator position and phase angle may be defined by the geometry or configuration of components of the cam phaser. According to some non-limiting examples, the ratio is defined by a helical feature inside the cam phaser (see, e.g., fig. 9). According to other non-limiting examples, the ratio is defined by the gear ratio of a gear train inside the cam phaser (see, e.g., fig. 10).

Calibration

Referring now to fig. 1, 3 and 4, controller 24 may execute a calibration procedure 300 configured to define the predetermined relationship previously described. According to some non-limiting examples, the calibration process may utilize a predetermined relationship between actuator position and phase angle to generate a two-dimensional look-up table for use during open-loop cam phaser operation. The following equation illustrates one non-limiting example of an equation representing a predetermined relationship between actuator position (a) and resulting phase angle (θ).

θ＝β(a-a ₁ )+θ ₁ (1)

In the above equation, β is a coefficient representing the slope of the relationship shown in fig. 3, and (a) ₁ ，θ ₁ ) Are coefficients representing known operating points. As will be described, the beta factor may be defined by known geometric features or configurations of the cam phaser, and a known operating point may be determined during the calibration process.

The calibration process 300 may begin at block 302 by the controller 24 commanding the actuator 22 to a first end position 208 (e.g., a maximum position in a first direction) or a second end position 210 (e.g., a maximum position in a second direction) of an operating range of the actuator 22 (see fig. 3). For example, for an axial actuator, the actuator may be commanded to a first end position or a second end position. In another example, for a rotary actuator, the actuator may be commanded to a maximum clockwise or counterclockwise position.

The controller 24 may then detect the actuator position via the actuation position sensor 30. The controller 24 may then sense or measure the camshaft position via the camshaft position sensor 32 and the crankshaft position via the crankshaft position sensor 34 at block 304. Next, controller 24 may determine a cam phase angle based on the sensed camshaft and crankshaft positions at block 306 to learn the phase angle of camshaft 14 at maximum retarded position 212 or maximum advanced position 214 at first end position 208 or second end position 210, respectively.

Once at least one operating point (e.g., one cam phase angle and corresponding actuator position) is known, controller 24 may use equation (1) above in conjunction with the known operating points to define a relationship between actuator position and resulting cam phase angle for the entire actuation range of actuator 22, as well as a predetermined proportional relationship between actuator position and phase angle (i.e., slope 206, β) defined by the geometry or configuration of the components of cam phaser 12. The predetermined relationship (e.g., slope or linear function) may be known by the controller 24, for example, by being stored in the memory 28 (see fig. 1).

According to some non-limiting examples, controller 24 may instruct actuator 22 to tilt between first end position 208 and second end position 210 and at a plurality of different intermediate positions and determine a phase angle for each of the plurality of intermediate positions using camshaft position sensor 32 and crank shaft position sensor 34 to generate the relationship shown in fig. 3. In this particular non-limiting example, the controller 24 can be interposed between a plurality of different locations. A proportional relationship between actuator position and phase angle (e.g., slope 206) may then be calculated or derived from the plurality of data points. According to another non-limiting example, the controller 24 may command the actuator 22 to one of the first end position 208 and the second end position 210, determine a phase angle at that position using the camshaft position sensor 32 and the crankshaft position sensor 34, then command the actuator 22 to the other of the first end position 208 and the second end position 210, and again determine the phase angle. Controller 24 may then use the two known positions to generate the relationship shown in fig. 3 and insert a proportional relationship (e.g., linear or non-linear) between the two known positions.

The calibration instructions and information may be stored in the memory 28 of the controller 24. According to one non-limiting example, the calibration process 300 may be performed at the factory while the vehicle is at or off the assembly line. According to other non-limiting examples, the calibration process 300 may be performed at engine start-up.

By defining the predetermined relationship, controller 24 may utilize the predetermined relationship (e.g., fig. 3/equation 1) and actuate position sensor 30 during both open-loop and closed-loop control of cam phasing system 10. For example, controller 24 may implement the predetermined relationship as a two-dimensional lookup table at block 308. According to some non-limiting examples, controller 24 may continuously update the look-up table based on the measurement data during closed loop operation, for example, by utilizing actuation position sensor 30, camshaft position sensor 32, and crankshaft position sensor 34. This measurement data may cause the look-up table to have portions that deviate from perfect proportions (e.g., perfect linearity or not falling directly on the line defined by equation 1), among other factors, primarily due to differences between manufactured cam phasers, tolerances, and friction between components.

Modified closed loop mode

The cam phasing system 10 of fig. 1 can also operate in a modified closed-loop mode. During closed loop operation, the controller may use readings from the camshaft position sensor 32 and the crankshaft position sensor 34 to determine an actual cam phase angle relative to a commanded phase angle to determine a phase angle error. This phase angle error may then be used in a feedback loop to command the actuator 22 to adjust the cam phaser 12 to correct the error between the actual cam phase angle relative to the commanded phase angle. In addition, this modified closed loop mode utilizes the predetermined relationship shown in FIG. 3 as a feed forward mechanism. That is, as shown in FIG. 5, the controller 24 may be integrated into a modified closed-loop-control algorithm 350 using the method described above with respect to FIG. 2.

The algorithm 350 may begin by receiving or generating a phase angle instruction at block 352. Controller 24 may then determine an estimated actuation position of actuator 22 based on the phase angle command and a predetermined relationship between the actuation position of actuator 22 and the resulting cam phase angle at block 354 (see fig. 3 and equation 1). The controller 24 may then sense or measure the camshaft position via the camshaft position sensor 32 and the crankshaft position via the crankshaft position sensor 34 to determine an actual cam phase angle based on the sensed camshaft and crankshaft positions. The controller 24 may then determine a phase angle error at block 356 by comparing the actual cam phase angle with respect to the commanded phase angle. Controller 24 may then command actuator 22 to the actuator position based on the estimated actuation position and phase angle error at block 358. According to some non-limiting examples, the phase angle error is delivered by a PID controller.

Selecting open-loop or closed-loop modes

In general, open loop control may be particularly beneficial when large phase angle changes are desired, as the cam phasing system may respond more quickly. For example, conventional closed loop control may result in the end of the error, resulting in a slow response time. The modified closed loop mode described herein may be beneficial once the current phase angle approaches the commanded phase angle, or for small phase angle changes, because closed loop control allows for precise fine tuning. Furthermore, if either the camshaft position sensor 32 or the crankshaft position sensor 34 fails or provides inaccurate readings, the cam phasing system 10 described herein allows the cam phasing operation to continue in an open loop mode, thereby providing a more robust and adaptive system.

Referring now to fig. 1 and 6, controller 24 may execute an algorithm 400 configured to determine whether cam phasing system 10 should operate in an open-loop mode or a modified closed-loop mode. Algorithm 400 may begin at block 402, where controller 24 may detect an actuator error and determine whether the actuator error is within a predetermined range. The actuator error may be defined by the difference between the current phase angle and the commanded phase angle as derived from the camshaft position sensor 32 and the crankshaft position sensor 34, or as derived from the actuation position sensor 30 and a predetermined relationship between actuator position and phase angle. In the event that controller 24 maintains the phase angle under given engine conditions (e.g., at idle, or while maintaining some engine speed at cruise), the actuator error may be small because the current phase angle closely matches the commanded phase angle. Conversely, in the event that the phase angle just commanded changes, the actuator error may be large because the newly commanded phase angle is different from the current phase angle.

According to some non-limiting examples, the predetermined range may be defined by a percentage. For example, the predetermined range may be defined by a percentage relative to the current phase angle (e.g., within 10%, 15%, 25%, etc. of the current phase angle). According to other non-limiting examples, the predetermined range may be defined by a phase angle. For example, the predetermined range may be defined by the phase angle relative to the current phase angle (e.g., within 10 °, 15 °, 25 °, etc. of the current phase angle).

If controller 24 determines at block 402 that the actuator error is outside of the predetermined range (i.e., not within the range), controller 24 uses the open-loop control mode described with respect to FIG. 2 at block 404. In some non-limiting examples, if controller 24 determines at block 402 that the actuator error is within a predetermined range, controller 24 may proceed to block 408 to utilize the modified closed-loop-control mode. Alternatively, if the controller 24 determines at block 402 that the actuator error is within the predetermined range, the controller 24 may proceed to block 406 where the controller may determine whether the phase angle measurements from the camshaft position sensor 32 and the crank shaft position sensor 34 are accurate. If the controller 24 determines at block 406 that the phase angle measurements are inaccurate, the controller 24 uses the open loop control mode described with respect to FIG. 2 at block 404. If the controller 24 determines that the phase angle measurement is accurate, the controller 24 uses the modified closed-loop-control mode at block 408. It should be appreciated that algorithm 400 may be repeated continuously during engine operation, and controller 24 may switch between open-loop and closed-loop operation multiple times at any given time depending on actuator error.

Fig. 7 illustrates one particular and non-limiting example of a method 500 of determining the accuracy of phase angle measurements. As previously described, the camshaft position sensor 32 and the crankshaft position sensor 34 may sense or detect geometric features that specify a zero position for the camshaft and crankshaft (e.g., features that specify the start of a new rotation). According to some non-limiting examples, the geometric feature may be a gap on the trigger wheel. According to another non-limiting example, the geometric feature may be a protrusion on the trigger wheel. According to one non-limiting example, the geometric feature may be a "tooth" of the trigger wheel (i.e., the encoding wheel), which may have one missing "tooth". The detection of this missing tooth may define a geometric feature that specifies a "zero" position and may be used to determine the crank angle relative to the missing tooth. That is, the missing tooth is considered to be a "zero" or starting point (e.g., 0 ° point) for the crankshaft or camshaft rotation. The signals from the camshaft position sensor 32 and the crankshaft position sensor 34 may thus resemble sinusoidal signals, where the falling edge of the sinusoidal signal may be correlated with the passage of teeth. A sufficiently large gap between the detections of adjacent teeth may indicate a zero signature of the camshaft or crankshaft. It should be appreciated that the following description may be used with respect to a crankshaft or a camshaft to determine whether their respective position measurements are accurate. If either position measurement is inaccurate, the resulting phase angle calculation is also inaccurate and controller 24 may switch to open loop operation. It should also be understood that the following description describes one particular and non-limiting example of determining the accuracy of the measured phase angle sensed by the crank and cam position sensors, and that the description may be applied to various other geometric features or trigger wheels, such as those described above.

Method 500 may begin at block 502 when controller 24 detects a falling edge of a tooth. Controller 24 may then determine at block 504 whether a geometric feature specifying "zero" is detected, e.g., whether a sufficiently large gap is detected in the signal from the previous peak caused by the previous tooth. If the controller 24 does not detect a signal condition indicating zero, the controller increases the number of teeth and returns to the starting point at block 506. For example, if the current number of teeth detected by the controller 24 via the crank/cam position sensor is some number "n", the controller 24 increases the number of teeth to "n +1".

If the controller 24 detects a signal condition indicative of zero, the controller proceeds to block 508 and determines if the current tooth number "n" is equal to a predetermined total number of teeth (e.g., 50) of the crank or cam activation wheel, which may be stored in the memory 28 of the controller 24. If the controller 24 determines that the current tooth number "n" is equal to the predetermined tooth number, the controller 24 detects the exact zero (i.e., missing tooth) of the trigger wheel and knows the position of the camshaft 14 or crankshaft 16 (block 510). Controller 24 may then proceed to block 512 by resetting the current tooth number "n" to equal one, and the process may return to the starting point. Upon determining that the crankshaft and camshaft positions are accurate, the controller 24 may switch to modified closed loop operation.

If the controller 24 determines that the current tooth number "n" is not equal to the predetermined tooth number, the controller 24 detects a "false" zero (i.e., a gap between teeth, rather than a missing tooth) for the trigger wheel and the position of the camshaft 14 or crankshaft 16 is unknown (block 514). Controller 24 may then proceed to block 512 by resetting the current tooth number "n" equal to one, and the process may return to the starting point. Upon determining that the crankshaft and camshaft positions are inaccurate, the controller 24 may switch to open loop operation. According to some non-limiting examples, controller 24 claims to open loop operation.

As described above, a "false" zero may be caused by a rapid change in phase angle or an error in the signal from the camshaft position sensor 32 or the crankshaft position sensor 34. For example, during phasing, camshaft speed may vary (e.g., increase or decrease) depending on the direction of phasing. In some specific and non-limiting examples, the camshaft speed may slow to the point where the camshaft position sensor 32 detects an abnormally large gap between the teeth of the trigger wheel, which may result in a signal state that is indicated as zero. That is, detecting the gap between adjacent teeth during phasing operation may be large enough to resemble the geometric feature of a given zero position (i.e., missing tooth), resulting in erroneous readings.

Fig. 8 shows one non-limiting example of cam phasing at startup using the cam phasing system 10 described herein. As shown, during engine start-up, controller 24 may control the phase angle in open loop operation without the need for proper or accurate phase angle measurements. That is, the camshaft or crankshaft may not have rotated enough time during startup to determine whether the signal from the camshaft position sensor 32 or the crankshaft position sensor 34 is accurate (see FIG. 1).

Cam phaser examples

As previously described herein, the ratio between actuator position and phase angle may be defined by the geometry or configuration of components of the cam phaser. For example, a geometric feature or component of the cam phaser may be disposed between the input shaft and one of the first and second components of the cam phaser to couple to the camshaft and the crankshaft, respectively. According to some non-limiting examples, the ratio is defined by helical features internal to a Cam phaser, such as the Cam phaser described in U.S. patent No. 10,072,537 to Schmitt et al, entitled "Mechanical Cam Phasing Systems and Methods," which is incorporated herein by reference in its entirety. According to other non-limiting examples, the ratio is defined by the gear ratio of a gear train inside a cam phaser, such as the cam phaser described in U.S. patent application No. 2020/031346 to Van Weelden et al, entitled Systems and Methods for Controlled Relative Rotational Motion, the entirety of which is incorporated herein by reference.

As shown in fig. 9, a helical feature inside the cam phaser may define a relationship between rotational position and actuation position between the rotating components. Fig. 9 illustrates a cam phasing system 1000 configured to be coupled to a camshaft (not shown) of an internal combustion engine (not shown). As shown in fig. 9, cam phasing system 1000 can include a carrier rotor 1018 (e.g., a first component) configured to couple to a camshaft, a sprocket hub 1020 (e.g., a second component) configured to couple to a crankshaft, a star rotor 1006, an input shaft configured as a screw 1008, and an end plate 1010. The sprocket hub 1020, the carrier rotor 1018, the star rotor 1006, the screw rod 1008, and the end plate 1010 may all share a common central axis 1011 when assembled. The sprocket hub 1020 may include a gear 1012 and the gear 1012 may be connected to an outer diameter of the sprocket hub 1020, and the gear 1012 may be coupled to a crankshaft (not shown) of the internal combustion engine. This can drive the sprocket hub 1020 to rotate at a speed proportional to the speed of the crankshaft.

The actuator 1022 may be configured to engage the screw stem 1008. The actuator 1022 may be configured to apply an axial force to the screw rod 1008 in a direction parallel to or along the central axis 1011. The actuator 1022 may be a linear actuator, a mechanical linkage, a hydraulically actuated actuation element, or any other mechanism capable of providing an axial force and/or displacement to the screw stem 1008. That is, the actuator 1022 may be configured to axially displace the screw rod 1008 to a known position that corresponds to a desired rotational displacement of the star rotor 1006. The actuator 1022 may be controlled and powered by a controller (e.g., controller 24 of fig. 1).

The screw shaft 1008 includes a helical portion 1082 that is configured to be received within the helical feature 1056 of the star rotor 1006. The interaction between the helical portion 1082 of the screw shaft 1008 and the helical feature 1056 of the star rotor 1006 enables the star rotor 1006 to rotate relative to the sprocket hub 1020 in response to the axial displacement exerted on the screw shaft 1008 by the actuator 1022. When assembled, as shown in fig. 9, the star rotor 1006 may be constrained such that it cannot displace axially. Thus, in response to the axial displacement exerted on the screw rod 1008 by the actuator 1022, the star rotor 1006 is forced to rotate clockwise or counterclockwise by a known amount, depending on whether it is desired to advance or retard a valve event controlled by the camshaft. That is, due to the interaction between the helical portion 1082 of the screw shaft 1008 and the helical feature 1056 of the star rotor 1006, the star rotor 1006 will rotate relative to the sprocket hub 1020.

In operation, when it is desired to change the rotational relationship between a camshaft secured to the carrier rotor 1018 and a crankshaft coupled to the sprocket hub 1020, a controller (e.g., controller 24 of fig. 1) can command the actuator 1022 to provide axial displacement to the screw rod 1008 from a first fixed axial position to a second fixed axial position. When a signal is sent to axially displace the screw rod 1008, the cam phasing system 1000 can transition from a locked state, in which the rotational relationship between the carrier rotor 1018 and the sprocket hub 1020 is locked, to an actuated state. Due to the interaction between the helical portion 1082 of the screw rod 1008 and the helical feature 1056 of the star rotor 1006, the star rotor 1006 may rotate clockwise or counterclockwise depending on the direction of the axial displacement in response to the axial displacement applied to the screw rod 1008. Rotation of the star rotor 1006 may cause the star rotor 1006 to engage a locking feature (not separately labeled) to place the cam phasing system 1000 in an actuated state. When the cam phasing system 1000 is in an actuated state, the carrier rotor 1018 rotationally follows the star rotor 1006 in the same direction as the star rotor 1006 rotates (e.g., by collecting cam torque pulses applied to the carrier rotor 1018). The carriage rotor 1018 will continue to rotate until the carriage rotor 1018 is rotationally displaced to a rotational position related to the magnitude of the axial displacement of the screw shaft 1008 and the angle of the screw feature 1056.

In general, the design of cam phasing system 1000 requires an input force from actuator 1022 to screw rod 1008 only when relative rotation is desired (e.g., actuator 1022 is displaced between fixed positions, and these fixed positions are related to a known phase angle between the camshaft and the crankshaft).

As shown in fig. 10, the gear ratio of the planetary gear train of the cam phaser may define the relationship between the rotational position and the actuated position between the rotational components. Fig. 10 shows a non-limiting example of a cam phasing system 2000 including a planetary actuator 2001. In the non-limiting example shown, the mechanical cam phasing system 2000 includes a carrier rotor 2018 (e.g., a first component) configured to be coupled to a camshaft, a sprocket hub 2020 (e.g., a second component) configured to be coupled to a crankshaft, the carrier rotor 2018, a bearing cage or star rotor 2008, a plurality of locking assemblies 2010, and a planetary actuator 2001. The planetary actuator 2001, sprocket hub 2020, carrier rotor 2018, and bearing holder 2008 may all share a common central axis C when assembled.

In the non-limiting example shown, the mechanical cam phasing system 2000 includes an actuator 2022 configured as a rotary actuator. In some non-limiting examples, the rotary actuator 2022 can include a stator and a rotor electromagnetically coupled to the stator. A current may be applied to the rotary actuator 2022 that may cause a rotary output to be provided by the rotary actuator 2022 in a desired direction with a desired force. In some non-limiting examples, the rotary actuator 2022 may be in the form of a brushless direct current (BLDC) motor.

The planetary actuator 2001 includes a first ring gear 2200, a first sun gear 2202, a carrier assembly 2204, a second ring gear 2206, a second sun gear 2208, and an input shaft 2021. The planet carrier assembly member 2204 includes a first set of planet gears 2222, a second set of planet gears 2224 and a planet carrier plate 2226. The first set of planet gears 2222 and the second set of planet gears 2224 can be arranged on axially opposite sides of the planet carrier plate 2226. In the non-limiting example shown, the first set of planet gears 2222 mesh with the first sun gear 2202, while the second set of planet gears 2224 mesh with the second sun gear 2208.

The first ring gear 2200 may be selectively rotatable in a desired direction relative to the second ring gear 2206. To facilitate rotation of the first gear ring 2200 relative to the second gear ring 206, the input shaft 2021, which is rotatably coupled to the rotary actuator 2022, may be rotated in a first direction. Rotation of the input shaft 2021 in a first direction causes rotation of the first sun gear 2202 in the first direction. Rotation of the first sun gear 2202 in a first direction causes the planet gears of the first set of planet gears 2222 to rotate in a second direction, opposite the first direction, which causes the first ring gear 2200 to rotate in a second direction. With the second sun gear 2208 rotationally fixed, this selective rotation of the first sun gear 2202, and thus the first ring gear 2200, allows the first ring gear 2200 to rotate relative to the second ring gear 2206 in the second direction. If the input shaft is rotated in the second direction, and vice versa.

The sprocket hub 2020 can include a gear 2011 disposed on an outer diameter thereof, which can be coupled to a crankshaft (not shown) of an internal combustion engine (not shown), for example, via a belt, chain, or gear train assembly. The carrier rotor 2018 may be configured to be attached to a camshaft (not shown) of an internal combustion engine via bolts 2034. Generally, the carriage rotor 2018 may be engaged with the locking assembly 2010.

In the non-limiting example shown, the input shaft 2021 may be coupled to a rotary actuator 2022 such that the rotary output provided by the rotary actuator 2022 is rotationally transferred to the input shaft 2021. The second sun gear 2208 is rotationally fixed to the rotary actuator 2022 and is prevented from rotating. The rotary actuator 2022 is rotationally coupled to the first sun gear 2202 and controls rotation thereof. Generally, the second ring gear 2206 may be configured to be rotationally coupled to the sprocket hub 2020 such that the second ring gear 2206 rotates with the sprocket hub 2020.

In operation, the rotary actuator 2022 may be configured to apply a rotational displacement/torque to the first sun gear 2202 to achieve a known rotational displacement of the first ring gear 2200, which corresponds to a known desired rotational displacement of the bearing cage 2008, based on the gear ratio of the planetary actuator 2001. The rotary actuator 2022 may be controlled and powered by a controller (e.g., controller 24 of fig. 1).

During operation, the sprocket hub 2020 can be coupled to a crankshaft of an internal combustion engine. The camshaft of the internal combustion engine may be fastened to the carrier rotor 2018. Thus, the camshaft and crankshaft may be coupled for rotation together via the mechanical cam phasing system 2000, with the rotational speed of the camshaft being one-half of the rotational speed of the crankshaft. When the engine is running and rotational adjustment of the camshaft is not desired, the mechanical cam phasing system 2000 can be in a locked state to lock the rotational relationship between the sprocket hub 2020 and the carrier rotor 2018, thereby locking the rotational relationship between the camshaft and the crankshaft. In this locked state, the rotary actuator 2022 does not provide a rotary output to the input shaft 2021 of the planetary actuator 2001, and the first and second gear rings 2200, 2206 rotate in unison with the sprocket hub 2020. Accordingly, the bearing holder 2008 does not rotate relative to the sprocket hub 2020, and the locking assembly 2010 locks relative rotation between the carrier rotor 2018 and the sprocket hub 2020. Thus, when the mechanical cam phasing system 2000 is in a locked state, the rotational relationship between the camshaft 14 and the crankshaft 12 is unchanged.

If it is desired to advance or retard the camshaft relative to the crankshaft, the rotary actuator 2022 may be commanded by the controller 24 to provide rotational displacement/torque to the input shaft 2021 of the planetary actuator 2001. That is, the controller 24 may instruct the actuator 2022 to provide a rotational displacement to the input shaft 2021 from a first fixed rotational position to a second fixed rotational position. The direction and magnitude of rotation of the input shaft 2021 may be related to the known rotation of the first ring gear 2200 relative to the second ring gear 2206. Since the second gear ring 2206 is rotationally coupled to the sprocket hub 2020, the first gear ring 2200 can rotate relative to the sprocket hub 2020. The desired magnitude and direction of relative rotation imparted to the first ring gear 2200 may be rotationally transferred to the bearing cage 2008 via the coupling therebetween. The coupling is configured to maintain the force applied to the bearing cage 2008 until the carrier rotor 2018 reaches a desired rotational position relative to the sprocket hub 2020, which is determined by the rotational input displacement/force provided by the rotary actuator 2022 and the gear ratio of the planetary actuator 2001. Rotation of the bearing cage 2008 may engage the locking assembly 2010 and place the cam phasing system 2000 in an actuated state.

In the actuated state, the carrier rotor 2018 rotates in the same rotational direction as the bearing holder 2008 rotates. For example, in a non-limiting example in which first ring gear 2200 rotationally offsets bearing cage 2008 clockwise, carrier rotor 2018 may be rotationally displaced in a clockwise direction. Generally, in response to a given rotational input displacement/force applied to the bearing holder 2008 by the planetary actuator 2001, the carrier rotor 2018 rotationally follows the bearing holder 2008 based on the magnitude of the rotational input of the input shaft 2021 and the gear ratio of the planetary actuator 2001 and ultimately reaches a predetermined final rotational position of the bearing holder 2008.

Rotation of the carrier rotor 2018 relative to the sprocket hub 2020, which occurs during this phasing process, can change the rotational relationship between the camshaft and the sprocket hub 2020, which simultaneously changes the rotational relationship between the camshaft and the crankshaft. As described above, for a given rotational input displacement/torque provided by the rotary actuator 2022, the amount of rotation achieved by the bearing cage 2008 may be known based on the gear transmission between the first sun gear 2202 and the first ring gear 2200 and the resulting gear ratio defined therebetween. Furthermore, the design of the mechanical cam phasing system 2000 can allow the carrier rotor 2018 to only be allowed to rotate in the same direction as the bearing cage 2008. Thus, during engine operation, the mechanical cam phasing system 2000 can vary the rotational relationship between the camshaft and the crankshaft.

In general, the design of the cam phasing system 2000 requires input torque/displacement provided to the input shaft 2021 from the rotary actuator 2022 only when relative rotation is desired (e.g., the actuator 2022 is displaced between fixed positions, and these fixed positions are related to a known phase angle between the camshaft and the crankshaft).

It should be understood by those skilled in the art that while the present invention has been described above in conjunction with specific embodiments and examples, the invention is not necessarily so limited, and that various other embodiments, examples, uses, modifications and alterations to the embodiments, examples and uses are intended to be encompassed by the appended claims. The entire disclosure of each patent and publication cited herein is incorporated by reference as if each patent or publication were individually incorporated by reference.

Various features and advantages of the invention are set forth in the following claims.

Claims

1. A cam phasing control system for varying a rotational relationship between a crankshaft and a camshaft, the cam phasing control system comprising:

a cam phaser including a first component configured to be coupled to a camshaft and a second component configured to be coupled to a crankshaft;

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 comprising a processor and a memory, the processor configured to:

receiving a phase angle instruction;

determining a desired actuation position of the actuator based on the phase angle command and a predetermined relationship between the actuation position of the actuator and a cam phase angle; and

commanding displacement of the actuator from a first fixed position to a second fixed position, wherein a magnitude of displacement between the first fixed position and the second fixed position corresponds to a proportional rotational displacement between the first component and the second component.

2. The system of claim 1, wherein the predetermined relationship between the actuated position of the actuator and the cam phase angle is linear.

3. The system of claim 1, wherein the desired actuation position is determined without a camshaft position sensor and a crankshaft position sensor.

4. The system of claim 1, wherein the predetermined relationship between the actuated position of the actuator and the cam phase angle is defined by a helical feature disposed 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 actuated position of the actuator and the cam phase angle is defined by a gear ratio of a planetary gear train disposed 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 controlled by the equation:

θ＝β(a-a ₁ )+θ ₁

wherein a is the actuated position, θ is the cam phase angle, β is a coefficient defined by one of a helical feature disposed between an input shaft of the cam phaser and one of the first or second components or a gear ratio of a planetary gear train, and a ₁ 、θ ₁ Respectively, coefficients representing a known operating point for a known actuation position and a corresponding known cam phase angle.

9. The system of claim 1, further comprising a crankshaft position sensor configured to detect a crankshaft position and a camshaft position sensor configured to detect a camshaft position;

wherein the processor is configured to measure a cam phase angle based on the crank shaft position and the camshaft position.

10. The system of claim 9, wherein the predetermined relationship is stored as a two-dimensional look-up table in the memory of the controller;

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:

commanding the actuator to an end position;

determining the cam phase angle based on the crankshaft position and the camshaft position; and

generating the two-dimensional look-up table based on the determined cam phase angle and a coefficient defined by one of a helical characteristic disposed between an input shaft of the cam phaser and one of the first component or the second component or a gear ratio of a planetary gear train.

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:

detecting an actuator error between a commanded actuator position and a sensed actuator position of the actuator; and

determining whether the actuator error is within a predetermined range;

wherein when the actuator error is outside 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 whether the measured cam phase angles detected by the camshaft position sensor and the crankshaft position sensor are accurate; and

wherein, when it is determined that the phase angle reading is 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:

receiving a phase angle instruction;

determining an estimated actuation position of the actuator based on the phase angle command and a predetermined relationship between the actuation position of the actuator and the cam phase angle;

determining a phase angle error between the commanded phase angle and the actual cam phase angle; and

commanding the actuator to an actuator position based on the phase angle error and the estimated actuation position.

14. An open-loop control method for a cam phasing system for varying a rotational relationship between a crankshaft and a camshaft, the method comprising:

receiving a phase angle instruction;

determining a desired actuation position of a cam phaser actuator based on the phase angle command and a predetermined relationship between actuation position and cam phase angle of the cam phaser actuator; and

commanding the cam phaser actuator to the desired actuation position.

15. The method of claim 14, wherein the predetermined relationship between the actuated position of the cam phaser actuator and the cam phase angle is linear.

16. The method of claim 14, wherein the desired actuation position is determined without a camshaft position sensor and a crankshaft position sensor.

17. The method of claim 14, wherein commanding the cam phaser actuator to the desired actuation position comprises shifting 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 to 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 and second fixed positions are first and second axial positions of the cam phaser actuator, the second axial position being different from the first axial position; or

Wherein the first and second fixed positions are first and second rotational positions of the cam phaser actuator, the second rotational position being different from the first rotational position.

20. The method of claim 14, wherein determining the desired actuation position of the cam phaser actuator comprises performing the equation:

θ＝β(a-a ₁ )+θ ₁

where a is the desired actuation position, θ is the commanded phase angle, β is a coefficient defined by one of a helical feature inside the cam phaser or a gear ratio of the planetary gear train, and a ₁ 、θ ₁ Respectively, coefficients representing a known operating point for a known actuation position and a corresponding known cam phase angle.