CONTROL STRUCTURE FOR ELECTRO-MECHANICAL CAMSHAFT PHASE SHIFTING DEVICE
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.
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 ffwd =T rq — static +T rq — friction =(1 −SR 0 )· T cam +sgn ( v )· f ( T cam )
where
T rq — static is the torque load reflected on the control shaft based on frictionless static equilibrium condition of the phase shifting device;
T rq — friction is the force required to overcome the frictional torque corresponding to the current control shaft torque load;
SR 0 is the base speed ratio of the output shaft relative to the input shaft;
T 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 cam ) represent the magnitude of the frictional torque T rq — function .
8 . The camshaft phase shifting device of claim 7 wherein SR 0 is calculated according to:
SR
0
=
N
S
1
N
S
2
·
N
P
2
N
P
1
where
N denotes the number of gear teeth with its subscripts S1, S2, P1, and 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.