IV。 GEAR SHIFTING CONTROL FOR   DCTS

A。 Basic Concept and Motivation

0 0。2 0。4 0。6 0。8 1 1。2 1。4 1。6 1。8 2

Time [s]

Fig。 4。    Open-loop based control for gear shifting (1-2    upshift)

normal force to be decreased or held。 Thus, it  does  not allow the clutch to put it back into the direction of the initial position once the clutch is started。 It is possible for the clutch to complete the engagement more quickly while avoiding some actuator nonlinearities such as dead zone, saturation, and etc。 Here, one issue may arise: How does one make a feedback signal including negative rate control input? This question can be answered by using the physical peculiarity of DCTs。 Since DCTs can employ two clutches as control inputs, it is extremely useful to complement each other during clutch control。 The feed-forward control is given as a baseline controller for gearshift operation。 It is based on two smoothed profiles for engagement of the oncoming clutch and disengagement of the off-going clutch, respectively。 The details are illustrated in the  following。

1) Oncoming clutch: When the decreasing normal force trajectory is applied on the oncoming clutch, the output of the controlled input is limited as hold status since the normal force rate is non-negatively constrained。 At this moment, if the off-going clutch is also to be held, the oncoming clutch can obtain the effect that its force is decreasing。

2) Off-coming clutch: When the increasing normal force trajectory is applied on the off-going clutch, it remains held without positive rate。 At this moment, if the on- going clutch is also to be held, this is equivalent to negative rate force of the off-coming  clutch。

Although this control strategy restricts the negative rate of the normal force of an on-going clutch, it can be realized incorporating an off-going clutch as another actuator。 As a result, clutch is engaged as fast as possible without clutch tie-up and backward power circulation。

B。 Control Strategy

Let x(t, x0, u) ∈ Rn denote the trajectory dynamic model of a DCT driveline system corr an initial state x0 ∈ Rn and a control input u = [u R2。 uon and uof f denote the oncoming and t clutch torque, respectively。 In our synthesis, t assumptions can be made on the  system。

A1) The vector valued function u of the    c is continuously differentiable and sati

umin(x, x˙) ≤ u(x, x˙) ≤ umax(x, A2) The time derivative of u(t)  is

|u˙ |≤ f (x, x˙) ∀t ≥ tc

The control strategy described in the

is defined in the discrete time domain as   follow

uon[(i + 1)ΔT ]

⎧  uon(iΔT ) if u˙of f  > 0, ∀t ∈ [tc, ts]

= ⎨  uon,ci(iΔT )   if u˙of f  ≤ 0, ∀t ∈ [tc, ti]

⎩  uon,is(iΔT )   if u˙of f  ≤ 0, ∀t ∈ [ti, ts]

uon,ci(iΔT )= uonFF (iΔT )

uon,is(iΔT )= uon,FF (iΔT )+ uon,FB(iΔT )

¸ (i+1)ΔT