Control Structure For Electro-mechanical Camshaft Phase Shifting Device

Abstract

A camshaft phase shifting device (30) includes a coaxially arranged three-shaft gear system, having an input shaft (16), an output shaft (14), and a control shaft (34) for adjusting the phase angle between the input and output shafts (16, 14). The control structure is a torque-based control structure. The dynamic response of the gear system and thus the desired phase angle of a camshaft (12) associated with the output shaft (16) is controlled and adjusted by a controller (40) which produces a torque command based on received signals. These signals include, but are not limited to, cam shaft phase angle error signal, torque load, and/or angular position signal of the camshaft (12), and relative speed signal between the input and output shafts (16, 14). The torque command is converted by an electric machine (32) into an electro-magnetic torque exerting on the control shaft (34) of the camshaft phase shifting device (30), and includes two parts, a feed forward part to compensate for the known disturbances in system torques and a feedback part to compensate for unknown disturbances.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is related to, and claims priority from, U.S. Provisional Patent Application Ser. No. 60/868,644 filed on Dec. 5, 2006, and which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention is related generally to a camshaft adjustment mechanism for use in an internal combustion engine, and in particular, to a control structure for an electro-mechanical camshaft phase shifting device.

[0003] Camshaft phase shifting devices are used more often in gasoline engines to vary valve timing for benefits of improving fuel consumption and exhaust gas quality. There are many types of cam shaft phase shifting devices. Hydraulic adjusters are commonly seen in many current applications. The major challenges for hydraulic adjusters includes improving slew rate in slow-speed operation, maintaining accurate camshaft angular position, and extending the operating temperature range. In addition, to reduce high pollutant emissions, it is highly desirable to adjust the cam phase angle before or during engine startup. This requires the camshaft phase shifting device to be controlled prior to or during engine startup. These challenges can only be met by electro-mechanical camshaft phase shifting devices.

[0004] In co-pending WO International Application No. PCT/US2007/078755 (Continuous Camshaft Phase Shifting Apparatus) filed on Sep. 18, 2007 and herein incorporated by reference, an electro-mechanic camshaft phase shifting device (eCPS) is disclosed. The eCPS device includes a three-shaft gear unit and an electric machine. According to the demand from engine electronic control unit (ECU), the electric machine is operated in one of three available modes, the neutral operating mode, the motoring mode, and the generating mode, to achieve desired performance objectives. The present invention discloses a control structure that provides a concrete means for an eCPS device to realize these operation modes. The disclosed control structure may additionally be applied to regulate the operation of other similar electro-mechanical camshaft phase shifting devices.

BRIEF SUMMARY OF THE INVENTION

[0005] Briefly stated, the present disclosure provides a control structure for electro-mechanic camshaft phase shifting devices in general and a control structure for an electro-mechanic camshaft phase shifting device with a self-locking mechanism in particular.

[0006] In an embodiment of the present disclosure, the camshaft phase shifting device includes a coaxially arranged three-shaft gear system, having an input shaft, an output shaft, and a control shaft for adjusting the phase angle between the input and output shafts. The control structure is a torque-based control structure. The dynamic response of the gear system and thus the desired phase angle of camshaft is controlled and adjusted by a controller (or compensator) which produces a torque command based on received signals. These signals include, but are not limited to, cam shaft phase angle error signal (deviation of cam phase shift angle from the reference value), torque load, and/or angular position signal of the cam shaft, and relative speed signal between the input and output shafts. This torque command (a voltage signal for example) is then converted by an electric machine into an electro-magnetic torque exerting on the control shaft of the camshaft phase shifting device. The torque command includes two parts, a feed forward part to compensate for the known disturbances in system torques and a feedback part to clear up unknown disturbances and to track reference change. Optionally, the controller may include an on-and-off switch to turn off the torque command for energy savings when self-locking mechanism is determined active.

[0007] The foregoing features, and advantages set forth in the present disclosure as well as presently preferred embodiments will become more apparent from the reading of the following description in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0008] In the accompanying drawings which form part of the specification:

[0009] FIG. 1 illustrates a block diagram of a preferred control structure for controlling an electro-mechanical cam phase shifting device of the present invention;

[0010] FIG. 2 is a sectional view of an electro-magnetic cam phase shifting device;

[0011] FIG. 3 is an input-output diagram for the control structure of FIG. 1;

[0012] FIG. 4 illustrates a block diagram of an alternate control structure for controlling an electro-mechanical cam phase shifting device of the present invention.

[0013] Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings. It is to be understood that the drawings are for illustrating the concepts set forth in the present disclosure and are not to scale.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0014] The following detailed description illustrates the invention by way of example and not by way of limitation. The description enables one skilled in the art to make and use the present disclosure, and describes several embodiments, adaptations, variations, alternatives, and uses of the present disclosure, including what is presently believed to be the best mode of carrying out the present disclosure.

[0015] Turning to the figures, and to FIG. 1 in particular, a preferred control structure for controlling an electro-mechanical cam phase shifting device is shown generally. The system shown in FIG. 1 is comprised of an engine 10, an engine control unit (ECU) 20, a phase shifting device 30, and a controller (or compensator) 40. The phase shifting device 30 is a three-shaft, positive differential gear drive, having three co-axially arranged rotate-able shafts, as is depicted in FIG. 2. The input shaft 16 is connected through sprocket 18 and a chain drive (not shown) to engine crank shaft. The output shaft 14 is connected to engine cam shaft 12. The control shaft 34 is coupled to the rotor of an electric machine 32.

[0016] The phase shifting device has a built-in frictional self-locking mechanism, which enables the output shaft 14 to lock-up with the input shaft 16, and therefore to transmit torque between the two shafts with a 1:1 speed ratio. Under this condition, there will be no phase shift between input shaft 16 and output shaft 14. Frictional locking between the input shaft 16 and the output shaft 14 can only be unlocked by applying an adequate toque to the control shaft 34. The required torque is generated by the electric machine 32 coupled to the shaft 34 in response to a torque command received by the electric machine. When the phase shifting device is unlocked, there may be a slight difference between the input and output shaft speeds. This allows the cam shaft connected to the output shaft 14 to shift in angular position with respect to the input shaft 16.

[0017] The controller (or compensator) 40 generates the torque command, which can be in the form of a voltage signal or any other suitable signal form, based on information received by the controller (or compensator) 40. The received information may include, but is not limited to, a cam shaft phase shift set point (reference), or an actual cam shaft phase shift measured and/or computed from one or more angular position sensor signals. The actual cam phase shift angle is compared to a reference value to generate a differential (error) signal. The differential or error signal is then communicated to a PID compensator 42 to generate a feedback torque (torque adjustment) command. This feedback torque command in turn is used to direct the electric machine for controlling and adjusting the cam phase angle to reduce the error signal to the input of the PID compensator 42. In doing so, the desired cam phase shift is archived. For a torque based control structure, the PID compensator is primarily a proportional-and-derivative controller (PD).

[0018] In engine applications, there may be disturbances to the control system. Shaft torque varies as a function of cam phase angle during valve lift events. To improve the system response to a reference input and the ability of the system to identify and/or reject disturbances, it often is desirable to use a feed-forward scheme to compensate any known disturbances. Therefore, controller (or compensator) 40 may further include a feed-forward branch (or a unit) 44 for processing and computing the anticipated torque disturbances within the system. The resulting signal is fed forward to, and combined with, the output signal of the PID controller, forming the torque command signal. The anticipated torque disturbance, also referred to as feed-forward torque, is determined from two components, T.sub.rq.sub.--.sub.static and T.sub.rq.sub.--.sub.friction. T.sub.rq.sub.--.sub.static is calculated from the frictionless static equilibrium condition of the three-shaft gear drive, while T.sub.rq.sub.--.sub.friction represents the component required to overcome the frictional torque for a current cam shaft torque load. The sign of T.sub.rq.sub.--.sub.friction is determined by the relative speed between the control shaft 34 and the input shaft 16 (or the output shaft 14). For the disclosed configuration of phase shifting device shown in FIG. 2, the feed-forward torque is calculated as

T.sub.ffwd=T.sub.rq.sub.--.sub.static+T.sub.rq.sub.--.sub.friction=(1-SR- .sub.0)T.sub.cam+sgn(v)f(T.sub.cam)

[0019] where T.sub.cam is the cam shaft torque load, which is a function of cam phase angle and which can be expressed by an analytical equation or by a look-up table. The value sgn(v) represents sign of relative speed v between the control shaft 34 and the input shaft 16, while the function f(T.sub.cam) represent the magnitude of the frictional torque T.sub.rq.sub.--.sub.friction.

[0020] SR.sub.0 is the base speed ratio of output shaft 14 to the input shaft 16, given by following equation

SR 0 = N S 1 N S 2 N P 2 N P 1 ##EQU00001##

[0021] where N denotes the number of gear teeth with its subscripts .sub.S1, S2, P1, and .sub.P2 representing the first sun gear 31 coupled to the input shaft 16, the second sun gear 33 coupled to the output shaft 14, the first planet gear 35 engaging the first sun gear 31, and the second planet gear 37 engaging the second sun gear 33, respectively. As shown in FIG. 2, the first and second planet gears 35, 37 are integrally formed with, and carried on a common planet assembly 39 which is supported by, and rotates with, the control shaft 34.

[0022] Since, as described before, the phase shaft device features a self-locking mechanism, it is possible to turn the controller and the electric machine off for energy savings when the actual cam phase shift angle is in a close proximity to the desired value (a reference value or a set point). This is done, for example, by commanding a zero torque to the electric machine. FIG. 3 illustrates an alternate implementation of the controller 40 in simulation, where a power-on logic and power switch are shown in separate blocks.

[0023] Optionally, the derivative portion of the PID compensator may be moved to the feedback path to reduce the effects of impulses (sudden changes) in reference input. FIG. 4 shows the corresponding control structure for this optional configuration.

[0024] It is also possible to use other type of compensators with alternative control laws, such as model predictive controller (MPC), to replace the PID compensator 42, and the current invention may include other embodiments that can be derived from the current torque based control structure.

[0025] The present disclosure can be embodied in-part the form of computer-implemented processes and apparatuses for practicing those processes. The present disclosure can also be embodied in-part the form of computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or an other computer readable storage medium, wherein, when the computer program code is loaded into, and executed by, an electronic device such as a computer, micro-processor or logic circuit, the device becomes an apparatus for practicing the present disclosure.

[0026] The present disclosure can also be embodied in-part the form of computer program code, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the present disclosure. When implemented in a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits.

[0027] As various changes could be made in the above constructions without departing from the scope of the disclosure, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

1. A camshaft phase shifting device comprising: a coaxially arranged three-shaft gear system, having an input shaft, an output shaft, and a control shaft, said control shaft configured to adjust a phase angle between said input shaft and said output shaft; a friction self-locking mechanism responsive to said control shaft to selectively phase-lock said input shaft and said output shaft; and a controller operatively coupled to said control shaft, said controller responsive to at least one input signal to regulate a source of an applied electro-magnetic torque to said control shaft to control said friction self-locking mechanism to unlock the phase angle of said input shaft relative to said output shaft.

2. The camshaft phase shifting device of claim 1 wherein said controller operates with a torque-based control structure.

3. The camshaft phase shifting device of claim 1 wherein said controller is configured to generate a torque command to said source of applied electro-magnetic torque in response to said at least one plurality of input signal.

4. The camshaft phase shifting device of claim 1 wherein said at least one input signal is selected from a set of input signals including, but not limited to, a cam shaft phase angle error signal, a torque load signal, an angular position signal of the cam shaft, and relative speed signal between the input and output shafts.

5. The camshaft phase shifting device of claim 1 wherein said source of applied electro-magnetic torque is an electric machine configured to exert said electro-magnetic torque on said control shaft, said electric machine regulated by a torque command from said controller.

6. The camshaft phase shifting device of claim 5 wherein said torque command includes at least a feed-forward component to compensate for known disturbances in system torques, and at least a feedback component to compensate for unknown disturbances and to track reference input.

7. The camshaft phase shifting device of claim 6 wherein said feed-forward component of said torque command is calculated as: T.sub.ffwd=T.sub.rq.sub.--.sub.static+T.sub.rq.sub.--.sub.friction=(1-SR.- sub.0)T.sub.cam+sgn(v)f(T.sub.cam) where T.sub.rq.sub.--.sub.static is the torque load reflected on the control shaft based on frictionless static equilibrium condition of the phase shifting device; T.sub.rq.sub.--.sub.friction is the force required to overcome the frictional torque corresponding to the current control shaft torque load; SR.sub.0 is the base speed ratio of the output shaft relative to the input shaft; T.sub.cam is the cam shaft torque load; sgn(v) represents the sign of a relative speed v between the control shaft and the input shaft; and f(T.sub.cam) represent the magnitude of the frictional torque T.sub.rq.sub.--.sub.function.

8. The camshaft phase shifting device of claim 7 wherein SR.sub.0 is calculated according to: SR 0 = N S 1 N S 2 N P 2 N P 1 ##EQU00002## where N denotes the number of gear teeth with its subscripts .sub.S1, S2, P1, and .sub.P2 representing a first sun gear coupled to the input shaft, a second sun gear coupled to the output shaft, a first planet gear engaged with the first sun gear, and a second planet gear engaged with the second sun gear, respectively; and wherein said first and second planet gears are integral with a common planet carrier coupled to said control shaft.

9. The camshaft phase shifting device of claim 1 wherein said frictional self-locking mechanism is configured for transmitting torque from said input shaft to said output shaft; and wherein an application of torque to said control shaft controls said frictional self-locking mechanism to selectively unlock the phase angle of said input shaft relative to said output shaft.

10. A method for altering a camshaft phase angle for a camshaft driven though a camshaft phase shifting device including coaxially aligned input, output and control shafts, wherein the input shaft and the output shaft are frictionally phase-locked by said control shaft, comprising: regulating a torque applied to said control shaft, wherein an application of torque to said control shaft releases said frictional self-locking of said input shaft and said output shaft to unlock said input shaft phase from phase-lock with said output shaft phase.

11. The method of claim 10 for altering a camshaft phase angle wherein said step of regulating said torque applied to said control shaft is responsive to at least one input signal selected from a set of input signals including, but not limited to, a cam shaft phase angle error signal, a torque load signal, an angular position signal of the cam shaft, and relative speed signal between the input and output shafts.

12. The method of claim 10 for altering a camshaft phase angle wherein said step of regulating said torque applied to said control shaft includes controlling an electric machine configured to exert an electro-magnetic torque on said control shaft.