Direct clutch control for dual clutch transmissions

A control system for controlling clutches of a dual clutch transmission includes an internal model based force control algorithm that converts a desired clutch force to a pressure control signal, a pressure control valve that receives the pressure control signal, a hydraulic actuator to which the pressure control valve applies a pressure related to the pressure control signal, and a clutch assembly with a spring lever and a plurality of clutch plates. The hydraulic actuator applies a desired force corresponding to the pressure control signal to a distal end of the spring lever such that the desired force to the distal end of the spring lever imparts an actual clutch force to the clutch plates.

FIELD

The present invention relates to a system for controlling clutches in a motor vehicle transmission. More specifically, the present invention relates to a direct clutch force control system for dual clutch transmissions.

BACKGROUND

A typical dual clutch transmission includes a pair of operating clutches which drive a pair of input shafts. The input shafts may be located on opposite sides of an output shaft or may be located concentrically between spaced-apart output shafts. A plurality of synchronizers selectively couple rotatable gears associated with the shafts to achieve forward and reverse gear ratios. Further, solenoid and valve assemblies actuate the clutches and synchronizers to achieve the forward and reverse gear ratios. Typically an electronically controlled hydraulic circuit or system is employed to control the solenoids and valve assemblies. As the clutch plates of the clutches wear, compensating for variations between the desired clutch force and the force actually applied to the clutch becomes more difficult for these electronically controlled circuits.

Accordingly, there is a need for an improved control system for dual clutch transmissions.

SUMMARY

A control system for controlling clutches of a dual clutch transmission includes an internal model based force control algorithm that converts a desired clutch force to a pressure control signal, a pressure control valve that receives the pressure control signal, a hydraulic actuator to which the pressure control valve applies a pressure related to the pressure control signal, and a clutch assembly with a spring lever and a plurality of clutch plates. The hydraulic actuator applies a desired force corresponding to the pressure control signal to a distal end of the spring lever such that the desired force to the distal end of the spring lever imparts an actual clutch force to the clutch plates.

DETAILED DESCRIPTION

Referring now to the drawings, a clutch control system embodying the principles of the present invention is illustrated inFIGS. 2 through 4and designated at100, and, for the sake of comparison, a conventional clutch control system is illustrated inFIG. 1and designated at10. These clutch control systems are associated with motor vehicle powertrains, particularly dual clutch transmissions

The conventional clutch control system10includes a hydraulic actuator12and a clutch assembly17. The clutch assembly17includes a set of clutch plates17A,17B, and17C and a diaphragm spring lever16. The diaphragm spring lever16is in contact with the clutch plate17A and is coupled to the hydraulic actuator12with an applied bearing15near or at the distal end of the diaphragm spring lever16.

The system10also includes a force-to-position convertor18, a closed loop position control algorithm20, a flow control valve22, a pressure control valve21, and a position transducer14. During the operation of a dual clutch transmission, the clutch assembly17is controlled by a microprocessor. The microprocessor sends a signal, Fd, which is the desired clutch force, to the force-to-position convertor18, which, in turn, converts the desired clutch force, Fd, to a hydraulic actuator position command, Xc. The force-to-position convertor18sends the position command, Xc, information to the position control algorithm20, which generates a control signal, Q, for the flow control valve22. The flow control valve22receives the control signal, Q, as well as signals from the pressure control valve21, to adjust the position of the hydraulic actuator12coupled to the applied bearing15, such that there is approximately a one-to-one correspondence between the position, d, of the applied bearing15, and hence the deflection of the distal end of the diaphragm spring lever16, and the actual force applied to the clutch plates17A,17B, and17C of the clutch assembly17.

Note that the position transducer14receives a signal13associated with the position, d, of the applied bearing15and transmits the measured position, Xm, of the hydraulic actuator position (and hence the deflection of the spring lever16) as feedback to the control algorithm20to form a closed loop control system. In general, the position transducer14is expensive, and as the clutch plates17A,17B, and17C wear, compensating for variations between the position, d, and the actual force applied to the clutch plates becomes difficult for the system10.

Referring now toFIG. 2, in accordance with principles of the present invention, the clutch control system100includes a clutch assembly109and a hydraulic actuator110. The clutch assembly109includes a set of clutch plates109A,109B, and109C and a diaphragm spring lever108. The diaphragm spring lever108is in contact with the clutch plate109A and is coupled to the hydraulic actuator110with an applied bearing115near or at the distal end of the diaphragm spring lever108. The diaphragm spring lever108is significantly stiffer than the conventional spring lever16to minimize the deflection at the distal end of the spring lever108when a force is applied to it. For example, in certain implementations the distal end of the spring lever108has a deflection from about 2 mm to about 5 mm, whereas the distal end of the conventional lever spring16described previously typically has a deflection of about 15 mm.

The system100also includes an internal model based force control algorithm102and a pressure control valve106. During the operation of an associated dual clutch transmission, the clutch assembly109is controlled by a microprocessor. The microprocessor sends a signal, Fd, which is the desired clutch apply force, to the internal model based force control algorithm102, which, in turn, converts the desired clutch apply force, Fd, to a control signal, P, for the pressure control valve106. With the control signal, P, the pressure control valve applies pressure to the hydraulic actuator110such that the hydraulic actuator applies a desired force to the applied bearing115and hence the distal end of the spring lever108. Accordingly, there is approximately a one-to-one correspondence between the pressure applied to the hydraulic actuator110and the force applied to the clutch plates109A,1098, and109C.

Referring now toFIG. 3, the internal model based force control algorithm102includes an internal plant model114and a feed-forward/feedback control112for the internal plant model. The internal plant model114is a model of the actual plant104: the pressure control valve106, the hydraulic actuator110, the spring lever108, and the clutch plates109A,109B, and109C stored in the microprocessor. Specifically, the internal plant model114includes the dynamics of the pressure control valve106, the hydraulic actuator110, the spring lever108, the clutch plates109A,109B, and1090, and the nonlinearities and hysteresis of the system100.

During the operation of the dual clutch transmission, the aforementioned microprocessor sends the desired clutch force signal, Fd, to the feed-forward/feedback control of the internal model102, which, in turn, converts the desired clutch force, Fd, to the control signal, P. The pressure control signal, P, is sent to the pressure control valve106as well as the internal plant model114. The internal plant model114then takes into account the actual plant dynamics along with the pressure control valve information, P, and transmits a signal116that is added or subtracted from the desired clutch force, Fd, at118. T to form a closed loop control system. The modified desired clutch force, Fd, is then sent to the feed-forward/feedback control112so that there is direct control of the pressure signal, P, sent to the pressure control valve106. The feed-forward/feedback control112allows the clutch force in the internal plant model114follow the clutch force, Fd, signal from the microprocessor in a desired manner.

A particular implementation of the internal model102is shown inFIG. 4. The internal model102includes a gain120, an integrator126, a first function122(F1), and a second function124(F2). The integrator126is a typical mathematical integrator, the gain120generates a gain signal, k, which determines the response speed of the internal model102, the first function122maps the steady-state actual clutch force to the hydraulic pressure in the hydraulic actuator110, and the second function124models the equivalent linear damping and friction characteristics of the actual plant104. Each of the functions122and124can be a proportional gain function, a look-up table, or a non-linear relationship.

When the internal model102is in operation, the integrator126integrates the signal from the gain120and sends the integrated output to the first function122and as a feedback signal that is added or subtracted from the desired clutch force, Fd, at118to form the closed loop control system. The information from118is fed into the gain120which in addition to feeding information to the integrator126sends information to the second function124. The signal from the first function122and the signal from the second function124are added together at128to form the control signal, P, for the pressure control valve106of the actual plant104.