Abstract:
A method and unit for controlling a clutch powered by a hydraulic actuator having a work chamber connected to a solenoid valve; a target value of the pressure of the fluid inside the work chamber is generated, an actual value of the pressure of the fluid inside the work chamber is measured, and a control signal for controlling the solenoid valve is calculated using feedback control of the pressure of the fluid inside the work chamber; and the target value of the pressure of the fluid is generated on the basis of an actual value of the position of the hydraulic actuator, and of a target value of the position of the hydraulic actuator.

Description:
This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). BO02003A 000002 filed in ITALY on Jan. 2, 2003, the entire contents of which are hereby incorporated by reference. 
   The present invention relates to a method of controlling a clutch powered by a hydraulic actuator. 
   BACKGROUND OF THE INVENTION 
   The internal combustion engine of a vehicle transmits power to the vehicle via a transmission train comprising a gearbox and a clutch, which are normally operated by the driver of the vehicle. Power-assisted manual shifts, however, are becoming increasingly popular, and which are structurally similar to a conventional manual shift, except that the driver-operated control pedals and levers are replaced by corresponding electric or hydraulic servocontrols. Using a power-assisted manual shift, the driver simply sends an up- or downshift command to a central control unit, which automatically shifts gears by acting on the various servocontrols. 
   When a gear shift is commanded by the driver, a clutch servocontrol releases the clutch, a shift servocontrol makes the desired gear shift, and the clutch servocontrol re-engages the clutch. The servocontrols are obviously controlled and operated using sensors for real-time determining the values of various reference quantities of the gearbox-clutch system. 
   A power-assisted manual gearshift is typically expected to provide for both dynamic performance and passenger comfort, which call for fast gear shifting with no passenger-perceptible oscillations. To achieve this, correct clutch position control is essential, in that both shift time and any oscillations produced are determined by operation of the clutch. Currently marketed hydraulic-actuator-powered clutches, however, fail to provide for correct clutch position control in all operating conditions. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a method of controlling a clutch powered by a hydraulic actuator, which is cheap and easy to implement, and which at the same time provides for eliminating the aforementioned drawbacks. 
   According to the present invention, there is provided a method of controlling a clutch powered by a hydraulic actuator, as claimed in claim  1 . 
   The present invention also relates to a unit for controlling a clutch powered by a hydraulic actuator. 
   According to the present invention, there is provided a control unit for controlling a clutch powered by a hydraulic actuator, as claimed in claim  10 . 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
       FIG. 1  shows a schematic view of a vehicle featuring a power clutch controlled by the control unit according to the present invention; 
       FIG. 2  shows an operating diagram of a hydraulic actuator of the  FIG. 1  clutch; 
       FIG. 3  shows a block diagram of the control unit controlling the power clutch in FIG.  1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Number  1  in  FIG. 1  indicates a vehicle comprising a front internal combustion engine  2 , which comprises a drive shaft  3  and two rows  4  of four cylinders  5  each. In actual use, engine  2  produces on drive shaft  3  a drive torque which is transmitted to the road surface by a transmission train  6  to move vehicle  1 . 
   Transmission train  6  comprises a power clutch  7 , which is housed in a housing  8  integral with engine  2 , and connects drive shaft  3  to a propeller shaft  9  terminating in a mechanical power-assisted gearbox  10  at the rear axle. A differential  11  is cascade-connected to gearbox  10 , and from which extend two axle shafts  12 , each integral with a respective rear drive wheel  13 . 
   Clutch  7  comprises two disks  14  respectively integral with drive shaft  3  and propeller shaft  9 , and which are movable with respect to each, by a known hydraulic actuator  15 , between a closed position (clutch engaged), in which the two disks  14  contact to transmit the drive torque from drive shaft  3  to propeller shaft  9 , and an open position (clutch released), in which the two disks  14  are detached to disconnect drive shaft  3  and propeller shaft  9 . 
   Gearbox  10  has a hydraulic actuator  16  for varying, in known manner, the gear ratio of gearbox  10  by varying the position of a secondary shaft (not shown), angularly integral with differential  11 , with respect to the position of a primary shaft (not shown) angularly integral with propeller shaft  9 . 
   Hydraulic actuators  15  and  16  are both controlled by the same central control unit  17  by means of a series of solenoid valves (not shown in detail in FIG.  1 ). To perform its control function, central control unit  17  is connected to a series of sensors (not shown in detail in  FIG. 1 ) to acquire both driver commands and the values of various system reference quantities. 
   As shown in  FIG. 2 , hydraulic actuator  15  controlling clutch  7  is controlled by central control unit  17  by means of a hydraulic circuit  18 , which is also partly used to control hydraulic actuator  16  and for this reason is substantially located at the rear axle and fitted to gearbox  10 . 
   Hydraulic circuit  18  is filled with oil, and comprises an atmospheric-pressure oil tank  19 , from which extends a pipe  20  fitted with a pump  21  and a non-return valve  22  to supply pressurized oil to a hydraulic accumulator  23 ; and hydraulic accumulator  23  is connected by a pipe  24  to an inlet of a proportional solenoid valve  25 , from which extend a pipe  26  terminating in tank  19 , and a pipe  27  terminating in a work chamber  28  of hydraulic actuator  15 . More specifically, solenoid valve  25  is designed to isolate pipe  27 , and therefore work chamber  28 , from pipes  24  and  26  to keep hydraulic actuator  15  in a given position; is designed to connect pipe  27 , and therefore work chamber  28 , to pipe  24  to feed pressurized oil to work chamber  28  and move hydraulic actuator  15  in a direction  29 ; and is designed to connect pipe  27 , and therefore work chamber  28 , to conduit  26  to draw pressurized oil from work chamber  28  and move hydraulic actuator  15  in a direction  30  opposite direction  29 . 
   Tank  19 , hydraulic accumulator  23 , and solenoid valve  25  are located at the rear axle and fitted to gearbox  10 ; and pipe  27  extends from the rear axle and terminates in work chamber  28  of hydraulic actuator  15 , which is housed inside housing  8  of clutch  7 . More specifically, pipe  27  is defined by a flexible portion  31  connecting solenoid valve  25  to a connecting block  32  integral with housing  8  of clutch  7 , and by a rigid portion  33  connecting block  32  to work chamber  28 . 
   Hydraulic accumulator  23  is fitted with a sensor  34  connected to central control unit  17  and for real-time determining the actual value Pp of the oil pressure inside hydraulic accumulator  23 ; and connecting block  32  is fitted with a sensor  35  connected to central control unit  17  and for real-time determining the actual value Put of the oil pressure inside rigid portion  33  of pipe  27 . It should be pointed out that, given the short length (roughly 25-35 cm) of rigid portion  33 , the value of the oil pressure inside rigid portion  33  practically equals the value of the oil pressure inside work chamber  28  of hydraulic actuator  15 . Finally, hydraulic actuator  15  is fitted with a potentiometer  36  connected to central control unit  17  and for real-time determining the position of hydraulic actuator  15  (and therefore of clutch  7 , which is mechanically integral with hydraulic actuator  15 ). 
   As shown in  FIG. 3 , central control unit  17  employs a reference generator  37 , which generates a target value Pos* of the position of hydraulic actuator  15 , a target value Vel* of the speed of hydraulic actuator  15  (i.e. the derivative prior to target value Pos*, and a target value Acc* of the acceleration of hydraulic actuator  15  (i.e. the derivative prior to target value Pos*). More specifically, reference generator  37  generates the desired values according to known control methods and as a function of both drive-entered commands and the operating conditions of vehicle  1 . 
   Target value Vel* of the speed of hydraulic actuator  15 , and target value Acc* of the acceleration of hydraulic actuator  15  are supplied by reference generator  37  to a computing block  38 , which also receives the actual value Pos of the position of hydraulic actuator  15  (and therefore of clutch  7  mechanically integral with hydraulic actuator  15 ) determined in real time by potentiometer  36 . And, on the basis of the Pos, Vel* and Acc* values, computing block  38  calculates a forecast value P 1  predicting the future value Put of the oil pressure inside work chamber  28 . 
   Central control unit  17  also employs a differential block  39 , which calculates the value Err of the error in the position of hydraulic actuator  15  (i.e. the difference between the target value Pos* and the actual value Pos of the position of hydraulic actuator  15 ). 
   The forecast value P 1 , the target value Pos* of the position of hydraulic actuator  15 , and the actual value Pos of the position of hydraulic actuator  15  are supplied to a Bode regulator  40 , which, on the basis of values P 1 , Pos* and Pos, determines a target value Put* of the oil pressure inside work chamber  28 . In other words, Bode regulator  40  determines the target value Put* of the oil pressure inside work chamber  28  required for the actual value Pos of the position of hydraulic actuator  15  to match the target value Pos* of the position of hydraulic actuator  15 . 
   Finally, central control unit  17  employs a controller  41  for generating the target value I* of the current circulating in the electric actuator (not shown in detail) of solenoid valve  25 . More specifically, the electric actuator of solenoid valve  25  implements feedback control of the current circulating through the electric actuator itself. 
   Controller  41  receives the target value Put* of the oil pressure inside work chamber  28 , the value Err of the error in the position of hydraulic actuator  15 , the target value Vel* of the speed of hydraulic actuator  15 , the actual value Put of the oil pressure inside work chamber  28 , as determined by sensor  35 , the actual value Pp of the oil pressure inside hydraulic accumulator  23 , as determined by sensor  34 , and the actual value Pt of the oil pressure inside tank  19  (not sensor-detected, but considered substantially constant and equal to atmospheric pressure). It is important to note that the actual oil pressure value Pp is the pressure value of the oil supplied to work chamber  28 , while oil pressure value Pt is the pressure value of the oil drained from work chamber  28 . 
   As will be clear from the foregoing description, three feedback control loops are employed to control the position of hydraulic actuator  15  (i.e. of clutch  7 ), i.e. to control the actual value Pos of the position of hydraulic actuator  15 . A first feedback control loop is controlled by Bode regulator  40 , employs the actual value Pos of the position of hydraulic actuator  15  as the feedback variable, and supplies the target value Put* of the oil pressure inside work chamber  28 . A second feedback control loop is controlled by controller  41 , employs the actual value Put of the oil pressure inside work chamber  28  as the feedback variable, and supplies the target value I* of the current circulating in the electric actuator of solenoid valve  25 . And a third feedback control loop is controlled by the actuator of solenoid valve  25 , and employs the measured current circulating through the actuator as the feedback variable. 
   Tests have shown that, by virtue of sensor  35  for determining the actual value Put of the oil pressure inside work chamber  28 , central control unit  17  is capable of ensuring optimum control of the position of clutch  7  in any operating condition.