Abstract:
A transmission clutch pressure control apparatus is suitable for a configuration that includes a pilot valve and a pressure regulating valve working in tandem. The pilot valve produces a pilot pressure that varies in accordance with a pilot valve drive signal. The pressure regulating valve provides fluid to a clutch at an output clutch pressure that is in turn variable based on the pilot pressure. The apparatus includes a pilot pressure sensor in fluid communication with the pilot valve output and generates a pilot pressure signal. The apparatus also includes a control arrangement having a pilot valve pressure estimation block configured to produce a pilot pressure command in response to a clutch pressure command. The estimation block is configured to reflect the relationship between the clutch pressure and the pilot pressure. The control arrangement also includes a summer that produces an error signal based on the difference between the commanded and sensed pilot pressure. The control arrangement also includes additional control blocks implementing a control strategy that ultimately develops and output the pilot valve drive signal all based on the pilot pressure command and the pilot pressure error signal.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to improvements in clutch pressure controls in a vehicle automatic transmission and more particularly to a transmission clutch pressure control via pilot pressure feedback. 
       BACKGROUND OF THE INVENTION 
       [0002]    Hydraulic fluid controls can be found in a variety of automotive applications such as automatic speed change transmissions as well as others. In these applications, it is often desirable to control the pressure of the hydraulic fluid, as seen by reference to U.S. Pat. No. 6,308,725 entitled “APPARATUS FOR CONTROLLING HYDRAULIC FLUID PRESSURE” issued to Lawlyes et al., assigned to the common assignee of the present invention. Lawlyes et al. disclose a smart actuator including a solenoid element and a pressure sensor element, both of which are in electrical communication with a remote control through a wire harness. Lawlyes et al. provide for remote pressure sensing of a solenoid output. 
         [0003]    In the specific context of an automatic speed change power transmission, it is known to use transmission control units that are configured to generate electrical signals that control actuators/solenoids resulting in the control of fluid flow as well as the pressure in a hydraulic fluid line. As known, the pressure of a hydraulic fluid line can be used to control various other elements in an automatic transmission system including for example the engagement of individual gears. By engaging various combinations of gears (e.g., planetary gears in a planetary gear transmission), an automatic transmission system accomplishes the same task as the shifting of gears in a manual transmission. Hydraulically-actuated clutches are also found in transmissions and are typically used for engaging a pair of gears (e.g., a pair of rotating members, or alternatively, one rotating member and one non-rotating member) together such that when the clutch is applied torque can be transmitted from one shaft to the other. Shift changes may also include switching three or more clutches on occasion for certain types of shifts, and herein references to two clutch type shifts could also include the multiple shifts. 
         [0004]    An important operating aspect of a hydraulically operated clutch relates to the pressure of the applied hydraulic fluid. In general, such applied pressure is sought to be controlled and varied to achieve a predetermined fluid flow to the clutch in order to obtain a desired engagement characteristic, principally with respect to timing and smoothness. It should be appreciated that if the timing of the engagement of one gear with the disengagement of another gear is not coordinately properly, overall shift performance may suffer. It is thus desirable and known in the art to control the pressure of the hydraulic fluid being supplied to such clutch. However, in some configurations, the hydraulically-actuated clutch needs such a relatively large volume of hydraulic fluid that a combination of a pilot valve and a larger flow, pilot operated valve are used in tandem to control the clutch pressure. In this arrangement, the pilot valve is controlled by a controller or the like to produce a variable pilot pressure output which in turn is supplied to and operates the pilot-operated, larger flow valve. The pilot operated valve, in response, provides a variable output pressure, which is supplied to the hydraulically actuated clutch. 
         [0005]    One approach for controlling the clutch pressure in this configuration involves using a pressure sensor disposed to sense the clutch pressure and to generate a clutch pressure signal that is fed back to a controller. However, in some configurations, it is difficult to mount a pressure sensor in the clutch chamber due to various physical constraints. 
         [0006]    There is therefore a need for a hydraulic clutch pressure control system that minimizes or eliminates one or more of the problems set forth above. 
       SUMMARY OF THE INVENTION 
       [0007]    One advantage of the present invention is that it provides a pressure control having the benefits of a direct measure clutch pressure closed-loop system without the difficulties associated with mounting a pressure sensor in the clutch chamber. 
         [0008]    An apparatus for hydraulic clutch pressure control includes a pilot valve, a pilot pressure sensor, a pressure regulating valve and a control arrangement. The pilot valve has an outlet that is configured to provide hydraulic fluid at a pilot pressure that is variable based on a pilot valve drive signal. The pilot pressure sensor is configured to sense the pilot pressure and generate a pilot pressure signal indicative of the sensed pilot pressure. The pressure regulating valve has an output configured for connection to the clutch and to provide hydraulic fluid at an output pressure that is variable based on the pilot pressure. Finally, the control arrangement is configured to generate the pilot valve drive signal in response to (i) a clutch pressure command signal indicative of a desired output pressure to be provided to the clutch (“clutch pressure”), and (ii) the pilot pressure signal (as a feedback) indicative of the sensed pilot pressure. 
         [0009]    In a preferred embodiment, the control arrangement includes (i) a feed forward control block configured to generate an open loop pilot valve control signal; (ii) a closed loop controller responsive to a pilot pressure error (difference) signal configured to generated a closed loop pilot valve control signal; and (iii) a summer responsive to both the open loop pilot valve control signal and the closed loop pilot valve control signal and configured to produce an output pilot valve control signal. The control arrangement further includes a translation block that converts the output pilot valve control signal into a pilot valve drive signal suitable for the type of pilot valve being used. 
         [0010]    Other features and aspects of the invention are also presented. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention will now be described by way of example, with reference to the accompanying drawings: 
           [0012]      FIG. 1  is a block diagram of an apparatus for hydraulic clutch pressure control in accordance with the invention. 
           [0013]      FIG. 2  is a block diagram showing, in greater detail, a control arrangement portion of the apparatus of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    Referring now to the drawings wherein like reference numerals are used to identify identical components in the various views,  FIG. 1  is a simplified block diagram of an apparatus  10  for controlling hydraulic fluid clutch pressure. The apparatus  10  provides the benefits of direct measure clutch pressure closed loop control without the difficulty of mounting a pressure sensor in the clutch chamber. In an illustrated embodiment,  FIG. 1  shows a hydraulic fluid supply  12 , a pilot valve  14 , a pressure regulating valve  16 , a hydraulically-actuated clutch  18 , a pair of rotating members  20 ,  22 , a pilot pressure sensor  24 , an optional feed or supply fluid pressure sensor  26  and a control arrangement  28 . It should be understood that the pair of rotating members in the illustrated embodiment is exemplary only and not limiting in nature. For example, in alternate embodiments, one of the members  20 ,  22  may comprise a non-rotating member, as described in the Background. 
         [0015]    The illustrated embodiment of apparatus  10  may be suitably employed in an automatic speed change power transmission of the type described in the Background. That is, a transmission of the type having hydraulic fluid actuated clutches, such as clutch  18 , configured such that when applied are operative to engage first and second members (e.g., planetary gears, or other rotating members in one embodiment, or one rotating and one non-rotating member in an alternate embodiment) together so that rotating torque may be transmitted from one member to the other. As also described in the Background, controlling and varying the hydraulic fluid pressure supplied to clutch  18  materially affects the operating characteristic of the clutch and in turn the resulting engagement of gears. 
         [0016]    With continued reference to  FIG. 1 , hydraulic fluid supply  12  includes an outlet that supplies hydraulic fluid through line  30  to pilot valve  14 , pressure regulating valve  16  and optionally pressure sensor  26 . Fluid supply  12  may comprise conventional components known to those of ordinary skill in the art, for example, pumps, pressure regulating devices, valves and the like. Fluid supply  12  provides hydraulic fluid at a nominal feed pressure (P F ) in accordance with the design requirements of any particular constructed embodiment. 
         [0017]    Pilot valve  14  includes (i) an inlet to receive the supply of hydraulic fluid at the feed pressure, which in the  FIG. 1  is designated Pf, via line  30  as well as (ii) an outlet coupled to a line  32 . Pilot valve  14  is configured to provide hydraulic fluid at a pilot pressure (P P ) that is variable in accordance with a pilot valve drive signal  34 . Pilot valve  14  may comprise conventional components known to those of ordinary skill in the art. In one embodiment, pilot valve  14  may comprise a pressure control solenoid (for example a variable bleed solenoid, or variable flow solenoid), a current controlled device that produces an output pressure as a function of an applied current (i.e., pilot valve drive signal  34 ). In an alternate embodiment, pilot valve  14  may comprise a pulse-width modulated (PWM) actuator that produces an output pressure corresponding to the duty cycle of an input drive signal. It should be understood that the present invention is not limited to these two embodiments, which are merely exemplary and not limiting in nature. 
         [0018]    Pressure regulating valve  16  is provided with (i) an inlet for receiving a supply of hydraulic fluid as well as (ii) an output configured for connection to clutch  18  via line  36 . Valve  16  is configured to provide fluid on line  36  at an output pressure (P C ) to the clutch that is variable in accordance with the pilot pressure (P P ). Pressure regulating valve  16  is configured to provide flow at a greater level than available with pilot valve  14 , in accordance with the requirements of clutch  18  (e.g., 5-6 liters per minute). Valve  16  may comprise conventional components known in the art, for example, in one embodiment, valve  16  may comprise a pilot operated spool valve. 
         [0019]    Pilot pressure sensor  24  is in fluid communication with line  32  and is configured to sense the pilot pressure (P P ) and generate a pilot pressure signal  38  indicative of the sensed pilot pressure. Pressure sensor  24  may comprise conventional components known in the art. 
         [0020]    Feed pressure sensor  26  may be optionally included in apparatus  10 . Sensor  26  (if provided) is in fluid communication with supply line  30  and is configured to sense the feed pressure (P F ) and generate a feed pressure signal  40  indicative of the sensed feed pressure. Feed pressure sensor  26  may comprise conventional components known in the art. In an alternate embodiment, pressure sensor  26  is omitted and is substituted with means  26 ′ for generating a feed pressure estimation parameter  40 ′ that is indicative of the feed pressure. In this alternative embodiment, pressure estimation parameter  40 ′ is provided to control arrangement in lieu of pressure signal  40 . 
         [0021]    An estimated feed pressure (e.g., the pressure estimation parameter  40 ′) may be achieved by a mathematical model describing the relationship of the commanded supply pressure and the output supply pressure. Such model can have various forms, such as mathematical equations, empirical data and a combination of both. The developed model can be executed in control software running inside the transmission control unit (not shown in  FIG. 1 ), and can use various known control methodologies, including Proportional-Integral (P-I) type control, and Proportional-Integral-Differential (P-I-D) type control. 
         [0022]    Control arrangement  28  is configured to generate pilot valve drive signal  34  in response to (i) a clutch pressure command signal  42  indicative of a desired output pressure (“clutch pressure”) and (ii) pilot pressure signal  38  (as a feedback signal) indicative of the sensed pilot pressure. The principle of the present invention is that there is a relationship between clutch pressure (P C ) and pilot pressure (P P ) that can be characterized with sufficient definiteness to implement in control arrangement  28 . Therefore, “closed loop” clutch pressure control can be achieved, effectively, by way of closed loop pilot pressure control. In one embodiment, the relationship may be characterized in terms of a mathematical model describing the relationship between the clutch pressure and the pilot pressure. The developed model can be executed in control arrangement  28 , as described in greater detail below. The present invention provides the benefits of direct clutch pressure measurement as feedback without the complications of trying to overcome the physical limitations involved in mounting a pressure sensor in the clutch chamber. 
         [0023]    With continued reference to  FIG. 1 , in basic operation, in an automotive automatic transmission system, a desired clutch pressure command  42  is generated by a transmission control unit (TCU—not shown) or the like. As understood in the art, the desired clutch pressure may be based on a variety of factors such as engine rpm, vehicle speed and other driving conditions. Control arrangement  28 , configured with the intelligence linking the relationship between clutch pressure and pilot pressure, as described above, internally develops what the desired pilot pressure should be in order to achieve the commanded clutch pressure per the overall transmission control strategy. Control arrangement  28  is further configured to compare the internally developed target pilot pressure with the sensed pilot pressure and produce an error signal representing the difference. The control arrangement uses this error signal in a feedback loop to alter the pilot valve drive signal to reduce the error. Through the foregoing, effective “closed loop” control of the clutch pressure through pilot pressure feedback can be achieved. 
         [0024]      FIG. 2  is a simplified block diagram showing, in greater detail, control arrangement  28  of  FIG. 1 . Control arrangement  28  includes a pilot pressure estimation block  44 . Estimation block  44  is responsive to clutch pressure command signal  42  and is configured to generate a pilot pressure command signal  46  indicative of a desired pilot pressure needed to obtain the commanded (i.e., commanded by clutch pressure command signal  42 ) clutch pressure (P C ). Estimation block  44  is configured to implement the mathematical model describing the relationship between the clutch pressure and the pilot pressure, as described above. In this regard, it should be understood that estimation block  44  may be implemented in hardware, software, firmware, or any combination thereof. 
         [0025]    More specifically, the mathematical model describing the relationship between the clutch pressure and the pilot pressure for block  44  can be derived based on the design of the hydraulic circuit using physical laws. Such representation can have various forms, such as force balance equations, Bernoulli and Euler equations, and other physical equations that represent the responses (pressure and time) that the system should see. Because the system is highly complex, models which are based on empirical data, by measuring actual responses of the system in the early development stages, and then modeling the system response via look-up tables and higher order polynomials, is also possible means to model the system. It is also possible to do a combination of the two. 
         [0026]    Control arrangement  28  further includes a feed forward control block  48  producing an open loop pilot valve control signal  50 , a summer  52  producing an output pilot valve control signal  54 , a translation block  56 , another summer  58  and a closed loop controller  60 . 
         [0027]    Feed forward control block  48  is responsive to pilot pressure command signal  46  and feed pressure signal  40  (or estimation parameter  40 ′) for generating control signal  50 . In the illustrated embodiment, control signal  50  is shown as i_sol_OL, which is applicable when pilot valve  14  is implemented using a current controlled valve, as described above. It should be understood, however, that block  48  is not so limited, and may be configured to generate control signal  50  applicable for a PWM duty cycle controlled pilot valve, also as described above. 
         [0028]    Summer  58  is configured to generate a pilot pressure error signal  62  indicative of a difference between the commanded and sensed pilot pressures. In this regard, summer  58  is responsive to pilot valve command signal  46  and pilot pressure signal  38  (at the inverting input) in generating the error signal  62 . 
         [0029]    Closed loop controller  60  is responsive to the generated error signal  62  and a temperature signal  64  produced by a temperature sensor  66  or other available source of temperature to generate a closed loop pilot valve control signal  68 . Temperature signal  64  via temperature sensor  66  is typically available in automotive applications via a Controller Area Network (CAN), for example. 
         [0030]    Summer  52  is configured to sum and generate output pilot valve control signal  54  based on and responsive to (i) open loop pilot valve control signal  50  and (ii) closed loop pilot valve control signal  68 . Output control signal  54  is provided to translation block  56 . 
         [0031]    It should be understood that feed forward block  48 , closed loop controller  60  and summers  52 ,  58  may be configured to interact and cooperate with each other all in accordance with conventional control principles to generate the output control signal  54 . For example, the foregoing components may implement proportional integral (PI) control, proportional integral derivative (PID) and any other suitable, conventional control strategy. Other variations are possible in accordance with that known to one of ordinary skill. 
         [0032]    Translation block  56  is configured generally to convert or translate output pilot valve control signal  54  to pilot valve drive signal  34 . In an embodiment where the pilot valve is a current controlled pilot valve (as described above), the translation block may take the form of a current controller, as shown, which may include pressure-to-current conversion facilities implemented in software, firmware, hardware or a combination thereof. In an alternate embodiment where pilot valve  14  comprises a PWM duty cycle controlled valve, the translation block  56  may comprise pressure-to-PWM conversion facilities including a PWM duty cycle controller. One of ordinary skill in the art will recognize that variations are possible, depending on the type of pilot valve used, that remain within the spirit and scope of the invention. 
         [0033]    With continued reference to  FIG. 2 , block  56  outputs pilot valve drive signal  34  (also shown in  FIG. 1 ), which is applied to pilot valve  14  causing it to output hydraulic fluid at the driven pilot pressure. It should be appreciated that temperature can also influence the operation and performance of pilot valve  14 —this temperature influence is shown in block form and is designated “ 70 ” in  FIG. 2 . The pilot pressure (P P ) is then fed back via pressure sensor  24 , all as described above. 
         [0034]    In accordance with the invention, a new and improved hydraulic clutch pressure control system is provided which obtains the benefit of direct measure clutch pressure feedback without the difficulties associated with mounting a pressure sensor in a clutch chamber. 
         [0035]    While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.