Abstract:
A method of operating a control system to move an EGR valve ( 24 ) toward its seat ( 32 ), in which the control system includes an actuator ( 16 ) operable in response to an electrical position command signal ( 84, 86 ). The method comprises the steps of determining ( 102 ) if the valve is being commanded toward a closed position, and determining ( 106 ) if the valve is still at least a predetermined distance (X) from a Stage 1 Position. If both answers are affirmative, the valve is commanded toward the Stage 1 Position, then the logic determines when the valve is within a predetermined tolerance (T) of the Stage 1 Position, and when it is, the logic provides a position command signal corresponding to an unchanging position of the valve for a predetermined period of time (Y), while any overshoot of the valve position settles out, and the valve position stabilizes before the logic proceeds with the rest of the closing operations. The result is greatly reduced stress on the valve ( 24 ) and the gear train which drives the valve.

Description:
BACKGROUND OF THE DISCLOSURE 
     The present invention relates to control systems for moving objects rapidly toward engagement with some sort of stop, and more particularly, to an improved method for operating such a control system. 
     Although the method of the present invention may be used for operating control systems to move various types of objects toward engagement with various types of stops, the present invention is especially suited for use in operating a control system for an exhaust gas recirculation (EGR) valve as it moves toward its valve seat, and will be described in connection therewith. 
     EGR systems are employed in automotive vehicles in order to help reduce engine emissions. Such EGR systems typically utilize an EGR poppet valve that is disposed between the engine exhaust manifold and the engine intake manifold and is operable, when in an open position, to permit recirculation of exhaust gas from the exhaust manifold back into the intake manifold. 
     An actuator is employed for moving the EGR valve between its open and closed positions, because the recirculation of exhaust gasses is appropriate and helpful only at certain times, as is well know to those skilled in the EGR art, and therefore will not be discussed in greater detail hereinafter. EGR valves of the type with which the present invention may be utilized are illustrated and described in U.S. Pat. Nos. 5,937,835 and 6,102,016, both of which are assigned to the assignee of the present invention and incorporated herein by reference. 
     Electrically actuated EGR valve systems preferably employ software-implemented control logic such that the EGR valve is operating under closed loop control when the EGR valve is being moved from a closed position to an open position and when the EGR valve is being moved from an open position to a closed position. As used herein, the term “closed loop” in regard to the control of the EGR valve will be understood to mean that the control logic is constantly “reading” the position of the EGR valve and utilizing the position of the EGR valve as part of the feedback to the control logic. The closed loop control logic controls electrical current to an electric motor which serves as the actuator to control the position of the EGR valve. In such systems, the control logic may generate pulse width modulated (PWM) signals to power the actuator motor and modulate the acceleration and deceleration of the EGR valve, as it moves from one position to another. 
     For purposes of the present invention, the portion of the total operating cycle of an EGR valve which is of greatest concern is whenever the EGR valve is being moved from an open position to a closed position, in which the EGR valve engages its “stop”. Typically, an EGR valve is a poppet valve of the same general configuration and construction as an engine intake or exhaust poppet valve, in which case the “stop” is a valve seat of the conventional type. Moving the EGR valve to a closed position is of concern for several reasons, and as is typical, involves a tradeoff. On the one hand, when the control logic commands the actuator to close the EGR valve, it is desirable to close the EGR valve quickly, thus stopping the flow of EGR gasses from the exhaust manifold back into the intake manifold. On the other hand, if the EGR valve is closed too quickly (too high a current to the actuator motor), one likely result would be a dynamic engagement of the EGR valve with its valve seat, thus inducing stresses in the EGR valve itself, and also in the linkage between the electric motor and the EGR valve. 
     Among the known closing logic arrangements is that illustrated and described in U.S. Pat. No. 6,012,437, assigned to the assignee of the present invention and incorporated herein by reference. The incorporated patent teaches the concept of controlling an EGR valve, during the closing mode, by first controlling the EGR valve under closed loop control until the valve reaches a predetermined distance from the valve seat, and then subsequently, operating the EGR valve under open loop control until the valve engages the valve seat. As used herein, “open loop” control will be understood to refer to a control mode in which the logic does not utilize valve position as a feedback to the logic. The purpose of the logic of the above-incorporated patent is to close the valve and hold it closed (sealed relative to its seat) with a known current which remains fairly constant, and within a “safe” range for the particular application. 
     It has been observed by the assignee of the present invention, in the course of developing EGR valves and control systems for commercial use, that impact engagement of the EGR valve with its valve seat may occur much more frequently than is desirable. In addition, such impact engagements may involve excessive impact force and stress on the gear train driving the EGR valve. 
     BRIEF SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improved method for operating a control system to move an object rapidly toward engagement with a stop, in which the improved method overcomes the disadvantages of the generally known prior art. 
     It is a more specific object of the present invention to provide a method of operating an electrical control system to move an EGR valve rapidly toward engagement with its valve seat, but with almost no likelihood of a premature impact engagement of the EGR valve and its valve seat. 
     The above and other objects of the invention are accomplished by the provision of an improved method of operating a control system to move an object rapidly toward engagement with a stop, the control system including an actuator operable in response to an electrical position command signal to move the object toward the engagement with the stop. 
     The improved method of operating the control system comprises the steps of determining if the object is being commanded toward a position within a predetermined distance of the stop. The next step is determining if the object is still at least a predetermined distance from a first position. If the answer to the first step is affirmative and the answer to the second step is affirmative, the next step is commanding the object to the first position, and then determining if the object is within a predetermined tolerance of the first position, and when it is, providing a position command signal corresponding to a substantially unchanging position of the object for a predetermined time period. After the predetermined time period, the next step is continuing the move of the object from the first position toward the engagement with the stop. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a transverse cross-section of an exhaust gas recirculation valve and control system therefor. 
     FIG. 2 is an electrical block diagram of an EGR valve control system of the type with which the present invention may be utilized. 
     FIG. 3 is a logic flow chart for the control logic of the present invention. 
     FIG. 3A is an enlarged graph of EGR valve position, as a function of time, illustrating one important aspect of the present invention. 
     FIGS. 4 and 5 are graphs of EGR valve position and linkage stress, as a function of time, for the prior art and the present invention, respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, which are not intended to limit the invention, FIG. 1 illustrates an electrically-actuated EGR valve control system, generally designated  10 . The control system  10  is an EGR valve control system of the type illustrated and described in greater detail in the above-incorporated U.S. Pat. No. 5,937,835. As is well know to those skilled in the art, the EGR system  10  includes a manifold portion  12 , a heat transfer (cooling) portion  14 , and an actuator portion  16 . 
     The manifold portion  12  includes a manifold housing  18  that defines a flow passage  20 . At the upstream end of the flow passage  20 , the manifold portion  12  is connected to an exhaust passage E, and, at the downstream end of the flow passage  20 , the manifold portion  12  is connected to an intake passage  1 . The manifold housing  18  also defines a bore  22  within which a valve assembly, generally designated  24 , is reciprocally supported for axial movement therein. Valve assembly  24  includes a valve stem  26  that is integrally formed with a poppet valve  28 , and an input stem portion  30  that is coupled to the valve stem  26  by means of a coupling arrangement  31 , such that the input stem portion  30  and the valve stem  26  have common axial movement. It should be understood, however, that such a coupling arrangement is not an essential feature of the invention. The manifold housing  18  further includes a valve seat  32  against which the poppet valve  28  seats or engages when the valve assembly  24  is closed, such that the valve seat  32  serves as a “stop” for the closed position of the valve assembly  24 . It should be noted that in FIG. 1, the valve assembly  24  is shown in its open position. 
     Actuator portion  16  includes an actuator housing  34  to which is attached a housing cover  36  by means of bolts  38  or any other suitable means. Attached to the exterior of the housing cover  36  is the casing of an electric motor, generally designated  40 . Although the particular construction and specification of the electric motor  40  are not essential features of the present invention, the motor  40  preferably is of the relatively high speed, continuously rotating type, and is preferably one with a high torque-to-inertia ratio, such as a permanent magnet DC commutator motor. As is described in greater detail below, control logic controls the functioning of the electric motor  40  by means of electrical connections  84  and  86 . 
     The electric motor  40  of the actuator portion  16  provides a low torque, high speed rotary output at a motor output shaft  42  which drives a gear train, generally designated  44 . The gear train  44  translates the relatively low torque, high speed rotary output of the motor  40  into a relatively high torque, low speed rotary output. The output, as described above, of the gear train  44  is then converted by means of a linkage, not shown herein, into axial movement of the input stem portion  30 , and of the entire valve assembly  24 . In view of the fact that the present invention is not limited specifically to an EGR valve control system, it should be even more apparent that the invention is not limited to any particular configuration of EGR valve, gear train, actuator, etc. 
     Attached to the actuator housing  34  is a sensor assembly, generally designated  48 , the function of which is to sense the axial position of the valve assembly  24 . The sensor assembly  48  converts the sensed position into an appropriate electrical signal that is transmitted as an input to control logic (to be described hereinafter) that controls the functioning of the electric motor  40 . In the preferred embodiment, the sensor assembly  48  is a resistive position sensor of the type typically used in the vehicle industry for throttle position measurements. 
     Referring now primarily to FIG. 2, there is illustrated an electrical block diagram of a control  60  for controlling the EGR valve control system  10 . Included in the control  60  is a controller  70 , a drive circuit  72 , the EGR actuator portion  16  (including the electric motor  40 ), and the sensor assembly  48 . In the preferred embodiment, the controller  70  is a microprocessor-based controller which has been appropriately modified and protected to be able to withstand the under-the-hood environment, in terms of vibration, heat, etc. The control logic included within the controller  70  controls the functioning of the electric motor  40 , and is described in greater detail below. The controller  70  and the drive circuit  72  are electrically coupled by means of electrical connections  78 ,  80  and  82 . The controller  70  provides a motor-actuating signal and a direction signal to the drive circuit  72  by means of the electrical connections  78  and  80 , respectively. In the preferred embodiment, the motor-actuating signal  78  is a PWM (pulse-width modulated) signal, of the general type which is known to those skilled in the art, although other types of signals, such as analog signals, may also be utilized. 
     The direction signal  80  indicates whether the valve assembly  24  is to be moved toward a closed position (with the poppet valve  28  engaging the valve seat  32 ) or is to be moved toward the open position shown in FIG. 1, with either a clockwise or counter-clockwise rotation of the motor  40  providing the appropriate axial movement to the valve assembly  24 . The drive circuit  72  provides a current feedback signal to the controller  70  by means of the electrical connection  82  and by means of this feedback signal  82 , the controller  70  can detect if over-current conditions are present in the motor  40 , so that electrical power to the motor  40  can be discontinued. The controller  70  receives a position signal from the sensor assembly  48  by means of an electrical connection  88 , with the position signal being indicative of the axial position of the valve assembly  24 , as was mentioned previously. In the preferred embodiment, the controller  70  and the drive circuit  72  are located within the engine compartment of the vehicle, preferably in close proximity to the EGR valve control system  10 . 
     The drive circuit  72  receives input from the controller  70  by means of the electrical connections  78  and  80 , as described previously, and in response thereto, drives the electric motor  40  of the EGR actuator portion  16 . Operating as a “power amplifier” with respect to the PWM signal  78 , the drive circuit  72  supplies a bi-directional current to the electric motor  40  by means of the electrical connections  84  and  86 . The drive circuit  72  receives power from a power source  76  by means of electrical connections  92  and  94  and supplies a +5 Volt regulated DC operating voltage to the position sensor  48  by means of an electrical connection  90 . A variety of generally satisfactory drive circuits are well know to those skilled in the art and therefore, the drive circuit  72  will not be described in detail hereinafter, a preferred embodiment thereof being illustrated and described in the above-incorporated U.S. Pat. No. 6,012,437. 
     Referring now primarily to FIGS. 3 and 3A, there is illustrated a logic flow chart illustrating several important aspects of the present invention. The control logic illustrated in the flow chart of FIG. 3 is implemented in the controller  70 , and by means of the electrical connections  84  and  86 , controls the electric motor  40  and therefore, the position of the valve assembly  24 . The control logic begins at a block  100  and proceeds, after any number of standard start-up operations (not shown), to a decision block  102 . In the decision block  102 , the logic determines if the valve assembly  24  has been commanded to be either fully closed or fully opened, as opposed to being only partially closed or partially opened. Those skilled in the art of EGR valve systems will understand that, at any given point in time, the decision to open or close the valve, and to do so fully or partially, is determined in connection with a number of engine and vehicle operating parameters, a discussions of which would be beyond the scope of the present invention, and therefore will not be discussed herein in detail. 
     In describing the control logic shown in FIG. 3, reference will also be made to the graph of EGR valve position, as a function of time, in FIG. 3A, and at various locations on the graph there are certain reference numerals (between  102  and  118 ) located on the graph to indicate, by way of example only, the position (or in some cases, one possible position) of the valve assembly  24  when the particular logic step from FIG. 3 is to be performed. If the result of the decision block  102  is negative (“No”), the control logic proceeds to an operation block  104 , under which the logic performs in a normal closed loop mode, whether the valve assembly  24  is being opened or closed. If the result of the decision block  102  is positive (“Yes”), the logic then proceeds to another decision block  106  which determines whether or not the valve assembly  24  is, at that point in time, positioned at or above a predetermined minimum distance “X” from a so-called “Stage 1 Position”. 
     If the result of the decision block  106  is negative (“No”), indicating that the valve  24  is already separated from the Stage 1 Position by less than the predetermined minimum distance X, the control logic then proceeds to the operation block  104 , as was described previously. On the other hand, if the result of the decision block  106  is positive (“Yes”), the control logic then proceeds to an operation block  108 , under which the control logic generates the appropriate command signals, and transmits those signals by means of the electrical connections  84  and  86 , to command the valve to the Stage 1 Position (see FIG.  3 A). It is an important aspect of the present invention that the Stage 1 Position be selected, for the particular object being moved, such that commanding the object to the Stage 1 Position will move the object close to its stop but, taking into account any potential over-travel or overshoot, the object will not engage its stop at this stage of the control process, as a result of such overshoot. 
     After the operation block  108 , the control logic then proceeds to a decision block  110 , in which the control logic determines if the valve  24  is at the Stage 1 Position (plus or minus some predetermined tolerance T). If the result of the decision block  110  is negative, the control logic then proceeds to an operation block  112  which merely performs a “waiting” operation i.e., as the logic timer is incremented, the operation block  112  senses that the timer has been incremented and permits the control logic to loop back, as shown in FIG. 3, to a location upstream of the decision block  110 . When, eventually, the result of the decision block  110  is positive, the logic then proceeds to an operation block  114 . 
     In the operation block  114 , the control logic again performs a “waiting” operation in which the control logic now recognizes the likelihood that the position of the valve  24  has engaged in “overshoot” of its intended position (i.e., the Stage 1 Position) and the logic simply waits for the overshoot to “settle” (i.e., for the position of the valve  24  to become equal to the Stage 1 Position, and remain (stabilize) at that position for some predetermined period of time Y (see FIG.  3 A). 
     The control logic then proceeds to an operation block  116  in which the control logic generates an appropriate command signal to command the valve  24  to its fully closed position, in engagement with its stop (the valve seat  32 ). It should be understood by those skilled in the art, and it may be seen in FIG. 3A, that the rate at which the valve is closed, under operation block  116 , is substantially less than the rate it was closing under the operation block  108 , thus the more gradual slope in that portion of the valve position curve in FIG.  5 . It should be noted in the graph of FIG. 5, that the overshoot shown in the graph of FIG. 3A is not included, primarily for ease of illustration, recognizing that the graph of FIG. 3A is greatly enlarged relative to that of FIG.  5 . 
     It should also be understood that under the operation block  116 , the control logic is still moving the valve  24  in a closed loop mode, as that term was defined hereinabove. After the operation block  116 , the control logic then proceeds to an operation block  118 , under which the control logic operates to accomplish a Mode Transition in accordance with the teachings of the above-incorporated U.S. Pat. No. 6,012,437. Therefore, under the operation block  118 , the control logic continues to move the valve  24  toward its stop in a closed loop mode, until the valve  24  is at a predetermined distance Z from the stop (see FIG.  3 A), after which the logic moves the valve the remainder of the distance to the stop, but operates now in an open loop mode, thus the reference numeral “118” appears in FIG. 3A both above and below the line referenced “Z”. As was mentioned previously, one primary difference, for a control system of this type, between the closed loop and open loop modes of operation is that the electrical current to the electric motor  40  will, in the open loop mode, be defined to be relatively constant and within a safe range, and preferably, will be approximately equal to that which is required simply as a “holding” current, i.e., a level of electrical current required to hold (maintain) the valve  24  in its closed position. By way of contrast, in the closed loop mode of operation, the current to the electric motor  40  may vary greatly, as the logic attempts to compensate for the sensed position of the valve  24 . 
     Referring now primarily to FIGS. 4 and 5, the present invention will be compared to the prior art. What is most significant about the graphs of FIGS. 4 and 5 is that, just as the valve position reaches zero (closed) in the prior art, there is a substantial spike in the “Link Stress”, i.e., in the stress induced in the linkage between the gear train  44  and the input stem portion  30 . Although graphically, the stress is represented as a negative quantity, those skilled in the art will understand that the spike in the stress level, as shown in FIG. 4, is very undesirable. By way of contrast, using the logic of the present invention, just after the valve position reaches zero, there is a small increase in Link Stress, on the order of about one-third of the stress which occurred with the prior art arrangement. The substantial decrease in the Link Stress is the direct result of the fact that, with the present invention, the valve  24  engages its stop with much less energy than in the case of the prior art (without the logic of the invention). 
     It should be understood by those skilled in the art that, if desirable, the present invention may be utilized in several stages, i.e., instead of achieving a Stage 1 Position, and then going into the Mode Transition logic, the logic could achieve Stage 1 Position, then repeat the same series of logic steps to achieve a Stage 2 Position (not illustrated herein), then a Stage 3 Position, etc., before going to the Mode Transition logic. At each successive stage, the valve  24  would be closer to the stop, and preferably would be moving somewhat slower, thus reducing the anticipated overshoot. 
     The invention has been described in great detail in the foregoing specification, and it is believed that various alterations and modifications of the invention will become apparent to those skilled in the art from a reading and understanding of the specification. It is intended that all such alterations and modifications are included in the invention, insofar as they come within the scope of the appended claims.