Patent Publication Number: US-2009229583-A1

Title: Motor poppet valve and an egr device for an internal combustion engine using the same

Description:
TECHNICAL FIELD 
     The present invention relates to a motor poppet valve and an EGR device for an internal combustion engine using the motor poppet valve. 
     BACKGROUND ART 
     An internal combustion engine, whether it be a gasoline engine or a diesel engine, has a tendency to employ an EGR device (exhaust gas recirculation device) that recirculates a portion of exhaust gases to the intake system mainly for reducing NOx. 
     In general, an EGR passage is provided with an EGR valve, which allows and prohibits the communication of EGR gas and regulates the amount of communication. 
     Particularly, an important feature of the EGR valve is its high sealability exhibited when blocking the communication of EGR gas. In order to secure a stable sealability even in the situation where there is a great differential pressure between the upstream side and the downstream side of the EGR valve, a poppet valve that is constantly closed by the biasing force of a contracted spring is generally utilized. The poppet valve is opened by being pressed, resisting the biasing force of the spring. By so doing, a flow rate of EGR gas is regulated. One example of means for pressing the poppet valve is an air-driven type using a solenoid. In addition, another type that uses the driving force of an electric motor (step motor, for example) (motor poppet valve) has recently been developed for its high controllability. 
     As a flow rate change of a poppet valve is great when the valve is in its small opening position, it is required to regulate the flow rate of EGR gas with accuracy when the valve is in its small opening position. 
     There generates a great differential pressure in EGR gas between the upstream side (exhaust side) and the downstream side (intake side) of the EGR valve. This differential pressure fluctuates according to operation conditions of the internal combustion engine. If such a differential pressure is produced and also fluctuates, and if the EGR valve is a poppet valve, a force corresponding to the differential pressure acts on a valve element of the poppet valve and has an effect on the operation of the poppet valve. 
     A device has been developed, in which, for example, a drive rate of an electric motor is controlled to change according to a fluctuating differential pressure if a motor poppet valve is utilized as an EGR valve. The device is disclosed, for example, in Japanese Patent Application Publication No. 11-351075 (hereinafter, referred to as patent document). 
     When a poppet valve that is biased by a spring into its constantly closed position is utilized as mentioned above, it is required to resist the biasing force of the contracted spring in order to open the poppet valve. 
     However, for instance, in the case of a motor poppet valve that performs general PID control, a motor torque is gradually increased from zero when the electric motor is activated. Therefore, at least before the motor torque reaches the biasing force of the spring (spring set force), the poppet valve is not activated. Accordingly, there is the problem that response is delayed until the poppet valve is actually opened, and the technology disclosed in the above patent document is not an exception. 
     The smaller the desired opening of the poppet valve is (low valve lift), and the lower the drive rate of the motor is, that is, the slower the start-up of the motor torque is, the more noticeable the above-mentioned problem grows, as illustrated in  FIG. 4  showing, with variations of desired opening, the motor torque of the motor poppet valve and the change of valve opening with time when general PID control is implemented. 
     Such a response delay in the opening of the poppet valve is undesirable because control accuracy is drastically deteriorated especially in slight opening of the poppet valve, for a reason that opening timing is not stabilized, and the like. 
     DISCLOSURE OF THE INVENTION 
     The present invention has been made to solve the above-mentioned problem. It is an object of the present invention to provide a motor poppet valve that can be controlled into its open position with accuracy and without response delay, and an EGR device for an internal combustion engine using such a motor poppet valve. 
     In order to achieve the object, the motor poppet valve of the present invention has a poppet-valve body including a valve element interposed in a fluid passage and a stem portion extending through an outer shell of the fluid passage to protrude outside the fluid passage, in which the valve element is brought into contact with a valve seat formed in the outer shell to block a flow of fluid running through the fluid passage, and the valve element is detached from the valve seat to allow communication of the fluid; a spring cap that is fitted on a stem head portion of the poppet-valve body; a spring that is disposed in between the spring cap and the outer shell of the fluid passage in a contracted position and biases the valve element so that the valve element contacts the valve seat; a shaft that is disposed coaxially with the axis of the stem portion of the poppet-valve body and moves in the axial direction to press the stem head portion; an electric motor that has a rotor screwed onto the shaft and reciprocates the shaft by rotating the rotor forward and backward; and motor control means for controlling the operation of the electric motor. The motor poppet valve is characterized in that the motor control means has initial motor torque setting means for setting an initial motor torque of the electric motor so that the initial motor torque equals a torque corresponding to a force biasing the valve element toward the valve seat or a value proximate thereto, and drives the electric motor so as to obtain the initial motor torque that is set by the initial motor torque setting means when driving the electric motor in order to press the stem head portion by means of the shaft and to detach the valve element from the valve seat. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view showing a schematic configuration of an EGR device for an internal combustion engine using a motor poppet valve according to the present invention; 
         FIG. 2  is a time chart showing opening of an EGR valve formed of the motor poppet valve and change of a motor torque with time during a time period between start and stop of an engine and is also a view for explaining a method of estimating a spring set force; 
         FIG. 3  is a time chart showing motor torques and change of valve opening with time in comparison between the present invention in which initial motor torque is in consideration (b) and conventional art in which initial motor torque is not in consideration (a); and 
         FIG. 4  is a view showing, with variations of desired opening, motor torque of the motor poppet valve and change of the valve opening with time when general PID control is implemented. 
     
    
    
     BEST MODE OF CARRYING OUT THE INVENTION 
     An embodiment of the present invention will be described below with reference to the attached drawings. 
       FIG. 1  shows a sectional view of a schematic configuration of an EGR device for an internal combustion engine using a motor poppet valve according to the present invention. Hereinafter, a configuration of the motor poppet valve according to the present invention and that of the EGR device for an internal combustion engine using the motor poppet valve will be described below with reference to  FIG. 1 . 
     As illustrated in  FIG. 1 , an EGR valve  20  formed of a motor poppet valve is interposed in an EGR duct  10  that is installed in an engine (internal combustion engine, not shown) and recirculates EGR gas (fluid) that is a portion of exhaust gases to an intake system. 
     The EGR valve  20  is roughly made up of a poppet valve  30  and a motor portion  40 . 
     The poppet valve  30  is formed of a poppet-valve body  32  consisting chiefly of a valve element  33  and a stem  34 , and a spring  38 . 
     More specifically, the valve element  33  of the poppet-valve body  32  is disposed within the EGR duct  10 . A valve seat  12  is formed in the inner circumference of the EGR duct  10 . The poppet-valve body  32  is constructed so that the valve element  33  blocks off an EGR passage  11  in the EGR duct  10  by bringing the circumferential edge thereof into contact with the valve seat  12 , and opens the EGR passage  11  by detaching the circumferential edge thereof from the valve seat  12 . In other words, the poppet valve  30  is driven to a closed position when the valve element  33  of the poppet-valve body  32  contacts the valve seat  12 , whereas the poppet valve  30  is driven to an open position when the valve element  33  moves away from the valve seat  12 . 
     The stem  34  of the poppet-valve body  32  extends through the EGR duct  10  to protrude outside. A spring cap  36  is fitted on a stem head  35  at the end of the stem  34 . The spring  38  is disposed in a contracted position in between the spring cap  36  and a valve case  14  formed integrally with the EGR conduct  10 . Accordingly, the valve element  33  of the poppet-valve body  32  is usually in contact with the valve seat  12  due to a biasing force of the spring  38 , so that the poppet valve  30  functions as a normally-closed valve. 
     The motor portion  40  consists chiefly of an electromagnetic coil  42 , a rotor  44 , and a shaft  46 . 
     To be concrete, the rotor  44  is supported by a bearing  45 , and is rotated (autorotated) when being excited by the electromagnetic coil  42 . The rotor  44  also has a hollow form. The shaft  46  is interfitted in the hollow portion. 
     The shaft  46  is located coaxially with the axis of the stem  34  of the poppet-valve body  32 . The stem head  35  of the poppet-valve body  32  can be pressed by the shaft  46  moving in the axial direction. 
     A screw  47  is formed in the outer circumference of the shaft  46 . A screw projection  48  is formed in the inner circumference of the rotor  44  so as to be engaged with the screw  47 . As a result, when the rotor  44  is excited by the electromagnetic coil  42  to be rotated (rotated forward and backward), the screw projection  48  moves along the screw  47 , and the shaft  46  can reciprocate (appear and hide) in the axial direction of the stem  34 . 
     Stated differently, the EGR valve  20  is constructed so that when the rotor  44  is rotated forward to move the shaft  46  to an appear side, the poppet-valve body  32  is pressed by the shaft  46 , and the valve element  33  is detached from the valve seat  12  to move to the open position, and when the rotor  44  is rotated backward to move the shaft  46  to a hide side, the poppet-valve body  32  is returned by the biasing force of the spring  38 , and the valve element  33  is brought into contact with the valve seat  12  to move to the closed position. 
     The EGR valve  20  is provided with a position sensor  49  for detecting a move amount of the shaft  46 , and accordingly, actual opening of the EGR valve  20 , by detecting a rotation angle of the rotor  44 . A pressure sensor  16  and a pressure sensor  18  are interposed in the EGR duct  10  in the upstream side (exhaust system side) and in the downstream side (intake system side) of the valve element  33 , respectively, for the purpose of detecting pressure of the EGR gas. 
     The EGR valve  20  is electrically connected to an ECU (electric control unit, motor control means)  50 . 
     Concretely, the pressure sensors  16  and  18 , the position sensor  49 , and the like, and a battery, not shown, are connected to an input side of the ECU  50 . Connected to an output side of the ECU  50  are the electromagnetic coil  42  and the like. 
     As illustrated by a block diagram in  FIG. 1 , the ECU  50  is provided with a desired opening setting section  52 , a PID compensator  53 , an initial torque (electric current) calculator (initial motor torque setting means)  54 , a spring set force estimator  55 , and a differential pressure detector (differential pressure detection means)  56 . 
     The desired opening setting section  52  has a function of setting a desired EGR amount, namely desired opening of the EGR valve  20  based upon operation conditions of the engine and the like, and of outputting a desired opening signal corresponding to the desired opening. The PID compensator  53  is formed of a proportional controller, an integral controller, and a differential controller. The PID compensator  53  has a function of regulating a motor torque to be applied to the motor portion  40 , that is, an electric current value to be supplied to the electromagnetic coil  42 , while conducting the PID control based upon feedback deviation between the desired opening signal and an actual opening signal of the EGR valve  20 , which is detected by the position sensor  49 , and of outputting the electric current value to the electromagnetic coil  42 . 
     The initial torque (electric current) calculator  54  has a function of calculating an initial motor torque to be applied to the motor portion  40 , namely an initial electric current value to be supplied to the electromagnetic coil  42 , and of outputting the initial electric current value to the electromagnetic coil  42  together with the electric current value regulated according to the desired opening signal. 
     To be specific, the initial torque (electric current) calculator  54  is inputted with spring set force information that is estimated by the spring set force estimator  55 , or biasing force information of the contracted spring  38  of the poppet valve  30 , and is also inputted with differential pressure information of the EGR gas between the upstream side (exhaust system side) and the downstream side (intake system side) of the valve element  33 , which are detected on the basis of information from the pressure sensors  16  and  18  in the differential pressure detector  56 . In the initial torque (electric current) calculator  54 , the initial motor torque, or initial electric current value, is calculated on the basis of the spring set force information and the differential pressure information of the EGR gas. 
     The spring set force estimator  55  may measure the biasing force of the contracted spring  38  beforehand. In this specification, however, in consideration of change with time and the like, for instance, as illustrated in a time chart in  FIG. 2  showing the opening of the EGR valve  20  and change of the motor torque with time during a time period between start (power ON) and stop (power OFF) of the engine, and as shown by circular broken lines in  FIG. 2 , the electromagnetic coil  42  is supplied with electric current to continuously apply motor torques by force in a prescribed period A immediately after the start of the engine (immediately after the power is turned ON) in such a condition that exhaust pressure does not act on the valve element  33  and in a prescribed period B immediately after the stop of the engine (immediately after the power is turned OFF). A motor torque at a time point when the EGR valve  20  starts to open is estimated as a spring set force. 
     In practice, the motor torque at the time point when the EGR valve  20  starts to open is not always fixed due to temperature change, property change of the spring  38 , control fluctuation, and the like. Therefore, the spring set force estimator  55  sets and outputs as the spring set force a value that is a little smaller than an estimated value (proximate value) of the motor torque so that the EGR valve  20  is not opened only by applying the estimated value of the motor torque. 
     The differential pressure detector  56  obtains an EGR gas pressure which acts on the valve element  33  by multiplying the detected differential pressure of the EGR gas by a projected area of the valve element  33 , to thereby output the EGR gas pressure. 
     In the initial torque (electric current) calculator  54 , a torque corresponding to a force obtained by adding the EGR gas pressure to the spring set force is calculated as the initial motor torque. The initial electric current value corresponding to the initial motor torque is outputted to the electromagnetic coil  42 . 
     Hereinafter, operations of the motor poppet valve according to the present invention thus constructed and the EGR device for an internal combustion engine using the motor poppet valve will be described. 
     When it is required to recirculate the EGR gas to the intake system according to operation conditions of the engine, and the ECU  50  outputs an open-valve command for the EGR valve  20 , the desired opening is determined by the desired opening setting section  52 . At the same time, based upon the feedback deviation between the desired opening signal and the actual opening signal of the EGR valve  20 , the electric current value to be supplied to the electromagnetic coil  42  is regulated by the PID compensator  53 , and the electric current value is outputted to the electromagnetic coil  42 . 
     To put it briefly, by using the PID compensator  53 , the electric current value is outputted to the electromagnetic coil  42  while being gradually increased toward an electric current value corresponding to the desired opening through the PID control. 
     At the same time with the output of the open-valve command of the EGR valve  20 , the initial torque (electric current) calculator  54  calculates as the initial motor torque the torque corresponding to the force obtained by adding the EGR gas pressure to the spring set force, and the initial electric current value corresponding to the initial motor torque is outputted to the electromagnetic coil  42 . 
     When the initial electric current value corresponding to the initial motor torque is outputted to the electromagnetic coil  42 , for example, if there is no initial electric current value, the electric current value from the PID compensator  53 , or motor torque, is gradually increased by the PID control. The EGR valve  20  is not opened until the motor torque reaches a torque capable of opening the EGR valve  20 , that is, the torque corresponding to the force obtained by adding the EGR gas pressure corresponding to the differential pressure between before and after the EGR valve  20  to the biasing force of the spring  38 . As a result, there generates response delay during this period. However, the motor portion  40  is immediately activated in order to obtain the initial motor torque, so that the response delay is solved, and the EGR valve  20  serving as a motor poppet valve is instantaneously opened with good response. 
       FIG. 3  shows the motor torque of the EGR valve  20  serving as a motor poppet valve and change of valve opening with time in the form of a time chart in comparison between conventional art in which the initial motor torque is not in consideration (a) and the present invention in which the initial motor torque is in consideration (b). As illustrated in  FIG. 3 , the response delay of the EGR valve  20  as in conventional art is solved by applying the initial motor torque. Therefore, the motor torque at once reaches the torque corresponding to the force obtained by adding the EGR gas pressure to the spring set force substantially at the same time with the output of the open-valve command for the EGR valve  20 . Accordingly, the EGR valve  20  quickly starts moving to the open position. Thereafter, the EGR valve  20  is satisfactorily controlled into the open position by stages toward the desired opening by feedback control and the PID control. 
     If the EGR valve  20  is a motor poppet valve, the smaller the desired opening of the EGR valve  20  is (low valve lift), that is, the slower the start up of the motor torque is, the greater the response delay tends to be (see  FIG. 4 ). However, by doing as described above, it is possible to enhance the response of the EGR valve  20  regardless of the desired opening and to improve control accuracy especially in slight opening of the EGR valve  20 . 
     The embodiment of the present invention has been described here, but an aspect is not limited to the above-mentioned embodiment. 
     For instance, in the embodiment, the spring set force estimator  55  estimates the spring set force in the prescribed period A immediately after the start of the engine (immediately after the power is turned ON) and in the prescribed period B immediately after the stop of the engine (immediately after the power is turned OFF). However, the spring set force may be estimated in either one of the prescribed periods A and B. 
     According to the embodiment, the initial torque (electric current) calculator  54  calculates as the initial motor torque the torque corresponding to the force obtained by adding the EGR gas pressure to the spring set force, and outputs the initial electric current value corresponding to the initial motor torque to the electromagnetic coil  42 . However, since most of the force biasing the valve element  33  toward the valve seat  12  is the biasing force of the contracted spring  38 , the initial motor torque, namely the initial electric current value, may be set based only upon the torque corresponding to the spring set force. In short, the pressure sensors  16  and  18  and the differential pressure detector  56  may be omitted. In this manner, too, it is possible to properly set the initial motor torque, and accordingly, the initial electric current value, and to gain full advantage. Needless to say, however, if the EGR gas pressure is applied as in the embodiment, the initial motor torque can be more properly determined regardless of operation conditions of the engine. 
     Although the embodiment has been described with reference to the example in which the motor poppet valve is employed as the EGR valve  20 , the present invention is not limited to this example. It is a matter of course that the present invention is applicable to all kinds of motor poppet valves regardless of their uses.