Abstract:
The invention relates to an engine control valve ( 1 ) which comprises a rotatable actuator ( 7 ), a valve ( 5 ), and a movement transformation device ( 9 ) suitable for transforming the rotation of the actuator ( 7 ) into translation of the valve ( 5 ). The movement transmission device ( 9 ) comprises a helical link with uniform pitch for translating the valve ( 5 ).

Description:
The invention relates to the field of automotive vehicles. 
     It relates more specifically to an engine control valve designed to manage the flow of a fluid in a pipe connected to the engine of the vehicle. 
     BACKGROUND OF THE INVENTION 
     Engine control valves which are actuated by a rotary motor and designed to bring about a translational movement of a valve shutter arranged in a pipe and which are able to control the passage of a fluid through this pipe are known. These valves comprise an electric motor associated with a gearset allowing a cam system to be rotated. The translational movement generated allows the valve shutter to be driven in a rectilinear movement. 
     OBJECT OF THE INVENTION 
     It is an object of the invention to improve this type of valve by proposing an engine control valve the control of which is easier and more robust. 
     BRIEF DESCRIPTION OF THE INVENTION 
     To this end, the invention is aimed at an engine control valve comprising a rotary actuator, a valve shutter and a movement conversion device designed to convert the rotational movement of the actuator into a translational movement of the valve shutter, characterized in that the movement conversion device comprises a constant-pitch helical connection for driving the translational movement of the valve shutter. 
     Thanks to this configuration, the translational drive of the valve shutter by the movement conversion device is according to a substantially linear law, which means to say that the axial force exerted on the valve shutter in order to open it varies, according to the valve lift and therefore according to the rotation of the actuator, and these variations can be represented by a substantially straight line. This does not allow a significant stepping down of the force applied to the valve shutter from the start of the valve lift phase (when the forces that have to be overcome are the greatest), as is commonly performed in valves of the prior art in which the force decreases rapidly after the start of valve lift (see  FIG. 4 , curve drawn in dotted line) in a connection the pitch of which is not constant, or even which has a double slope. 
     The valve according to the invention for its part enjoys a conversion device that behaves in a linear manner and is therefore easier to control. 
     At the very start of valve lift, the pressure forces of the fluid flowing through the valve are the greatest. As the magnitude of the forces to be overcome in order to cause valve lift is directly dependent on the initial position of the valve shutter, not concentrating the application of force at the start of valve lift runs counter to common wisdom which is to distribute this force according to the apparent need, which means to say concentrated at the start and then dropping off rapidly. 
     This valve may further comprise the following features, alone or in combination:
         the helical connection comprises a camway of constant pitch;   the movement conversion device comprises a tubular wall in which the camway is formed;   the camway comprises two tracks arranged facing one another on the tubular wall;   the valve comprises at least one follower attached to the valve shutter and designed to collaborate with the camway;   said at least one follower is mounted to rotate on a bar attached to the valve shutter, the bar being arranged in the volume delimited by the tubular wall so as to collaborate with an input wheel which is driven by the rotary actuator and which is designed to rotate the bar; the input wheel can be driven directly or indirectly by the rotary actuator;   the input wheel is mounted to rotate on the tubular wall;   the input wheel is mounted to rotate on the tubular wall via a rolling bearing;   a position sensor that senses the position of the valve shutter is positioned in the space delimited by the tubular wall;   the position sensor is a linear-displacement transducer. The use of a linear-displacement transducer is more advantageous than the use of a rotary sensor because it directly measures the displacement of the valve shutter. This sensor here in fact behaves in a substantially linear manner because it is directly associated with the element (the valve shutter) the position of which is to be determined, without any stepping down or conversion of movement. In valves of the prior art, rotary sensors are generally used to determine the angular position of a cam that acts on the valve shutter and indirectly therefrom deduce the position of the valve shutter by taking the shape of said cam into consideration. In these valves, a linear-displacement transducer would in fact behave in a nonlinear manner. What is meant by “behave in a substantially linear manner” is, for an element of the valve, to behave physically like a linear system theoretical model, within the meaning that this has in the fields of automation and signal processing;   the rotary actuator comprises an electric motor that behaves in a substantially linear manner;   this motor is a DC motor;   the rotary actuator is connected to the movement conversion device by transmission means which behave in a substantially linear manner;   the valve comprises return means that return the valve shutter to the closed position, these return means behaving in a substantially linear manner;   the elastic return means comprise a helical torsion spring;   the drive train from the rotary actuator to the valve shutter is made up of elements that behave in a substantially linear manner.       

     Another aspect of the invention targets an assembly of such a valve shutter with control means programmed to a linear model. 
     The control means may comprise conventional electronic devices such as an engine control unit (or ECU). 
     They are programmed to a linear model, which means that the transfer function of the model which describes the position of the valve shutter as a function of the input command is a linear function. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood in the light of the description which follows of one preferred and nonlimiting embodiment, which description is given with reference to the attached drawings, among which: 
         FIG. 1  is a perspective view of a valve according to the invention; 
         FIG. 2  is an exploded view of the valve of  FIG. 1 ; 
         FIG. 3  is a perspective view of the movement conversion device of the valve of  FIG. 1 ; 
         FIG. 4  is a graph showing the axial force applied to the valve shutter as a function of its valve lift travel in the valve of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  depicts an engine control valve  1  which in this example is an exhaust gas recirculation valve commonly known as an EGR valve. The various elements that make up the valve  1  are visible separately in the exploded view of  FIG. 2 . 
     The valve  1  comprises a fluid inlet  2  and a fluid outlet  3  between which the head  4  of a valve shutter  5  is positioned. In the way that is conventional for an EGR valve, when the valve shutter  5  is in the closed position it shuts off the flow of fluid entering via the inlet  2  and leaving via the outlet  3 . By contrast, when the valve shutter  5  is wide open it allows this fluid to flow freely, whereas when the valve shutter  5  is in an intermediate position it meters the fluid. 
     The valve  1  comprises a mount  6  on which there are mounted an actuator, here consisting of an electric motor or rotary actuator  7 , a movement conversion device  9  and a transmission wheel  8  which allows the motor  7  to drive the movement conversion device  9 , the latter converting the rotary movement of the transmission wheel  8  into a rectilinear movement of the valve shutter  5 . 
     The movement conversion device  9  has a tubular overall shape and at one of its ends comprises a valve seat  10  and at the other of its ends comprises a camway or constant pitch helical connection  11 . As an alternative, the valve may have no valve seat. In this example, the camway  11  comprises two tracks made in a tubular wall  12  of the movement conversion device  9 . A bar  13  fixed to the valve shutter  5  and equipped with followers  14  is designed to follow the camway  11 . 
     The movement conversion device  9  collaborates with an input wheel  15  comprising a toothed portion  16  attached to a tubular portion  17  mounted to rotate on the movement conversion device  9  via a rolling bearing  18 . 
     Elastic return means  19  are provided here in the form of a helical torsion spring to return the input wheel  15  to one of its extreme angular positions corresponding, in this example, to the closed position of the valve shutter  5 . 
     The motor  7  is therefore in this instance operated against the action of the return means  19  in order to open the valve shutter  5 . 
     A position sensor  20  additionally allows the position of the valve shutter  5  along its axial travel to be measured at any moment, and does so via a feeler  21  kept in contact with the bar  13  by means of a spring (not depicted). The sensor  20  therefore behaves in a linear manner in so far as the feeler  21  [lacuna]. 
     A protective cap  22  (see  FIG. 2 ) mounted on the support  6  protects the rotary parts of the valve  1 . 
     The motor  7  is powered and driven with inbuilt control in a way that is conventional to computation means (not depicted). 
     When the motor  7  is made to rotate, it drives the rotation of the transmission wheel  8  (and any other gearset that might be provided) which in turn turns the input wheel  15 . The latter also drives the rotation of the bar  13  through complementary shapes (see  FIG. 1 ), while leaving it free to effect axial translational movement. That causes the followers  14  to roll along the camway  11  (which is fixed, the movement conversion device  9  being fixed to the support  6 ) and therefore causes the joint translational movement of the bar  13  and of the valve shutter  5  in the axial direction, causing the valve shutter  5  to open or to close. 
     With reference to  FIG. 4 , the movement conversion device  9  is depicted outside the valve  1  here. In this figure, the input wheel  15  is in an angular position which:
         corresponds to an angular position of the bar  13 ;   corresponds to a position of the followers  14  in the camway  11  (at the end of the track);   corresponds to a position of the valve shutter (the closed position).       

     The camway  11  is configured so that the force exerted on the valve shutter  5  as it opens is substantially linear. 
     The movement conversion device  9  thus behaves in a way very similar to that of a linear system. A linear system is a system model which applies a linear (first order) operator to an input signal. A linear system typically displays characteristics and properties that are far simpler than the general non-linear case. 
     These linear properties improve the controllability of the system. 
     The axial force applied to the valve shutter varies in a linear or near-linear manner along the axial travel of the valve shutter  5 . The curve  23  indicative of the axial force applied to the valve shutter  5  as a function of its axial travel (valve lift) is therefore substantially a straight line. In  FIG. 4 , this curve  23  is depicted in solid line whereas a conventional curve  24  relating to valves of the prior art is shown in dotted line. 
     For the same rotation of the motor  7 , corresponding directly to a variation in angle of the bar  13 , the variation in axial force applied to the valve shutter  5  thanks to collaboration between the camway  11  and the followers  14  is therefore substantially constant and is identical over the entire working rotational range of the motor  7 . 
     In the example of  FIG. 4 , the variation in the axial force applied to the valve shutter  5  is not only constant but very small. By way of example, the force at the start of valve lift (point  25  in  FIG. 4 ) may be 420 N while the force at the end of valve lift (point  26  in  FIG. 4 ) may be 380 N, which represents a variation in force of around 10% over the entire valve lift travel of the valve shutter  5 . By way of comparison, the order of magnitude of the variation in force for valves of the prior art is 1000% (see  FIG. 4 ). 
     The curve  23  is therefore not only a straight line here but also nearly horizontal. 
     The camway  11  is, in the present example, made up of two tracks arranged face to face (diametrically opposite each other) on the tubular wall  12 , each of these tracks being formed here of an open slot made in the tubular wall  12 . The shape of the slot is a helicoid extending along the tubular wall  12 . To obtain an axial valve lift force with constant variation, this helicoid in this example has a constant helix pitch (see  FIG. 3 ). 
     Thus, by virtue of the movement conversion device  9 , the way in which the valve  1  behaves when opened is substantially linear in the sense that a rotation of the motor  7  through a given angle will produce substantially the same variation in force on the valve shutter  5  whatever the position of the valve shutter  5 . Because this variation is also reduced to a minimum here, rotating the motor  7  through a given angle will cause substantially the same force to be applied to the valve shutter  5 , regardless of the position of the valve shutter  5 . 
     Moreover, the substantially linear way in which the movement conversion device  9  behaves may be supplemented by other components of the drive train extending from the motor  7  to the valve shutter  5  and which likewise advantageously behave in a substantially linear manner. 
     The embodiment of the present example, which is particularly advantageous, contains in this drive train only elements which behave in a substantially linear manner. This drive train can therefore be modeled as a linear model with satisfactory results. This linear model is embedded in the electronic device selected to control the valve. 
     The motor  7  first of all in this instance is a DC motor, which means that it behaves in a substantially linear manner. 
     All the gearing that transmits the rotation of the motor  7  to the input wheel  15  also behaves in a substantially linear manner, which means to say that the teeth of the gearwheels (in this instance the wheels  8  and  15 ) are evenly distributed about the working circumference of said wheels. 
     Friction is also a source of non-linearity. The rolling bearing  18  here reduces this friction so that the system behaves even more like a linear system. 
     The helical torsion spring that makes up the return means  19  also here behaves in a substantially linear manner, which means to say that the rotation of the input wheel  15  is directly proportional to the torque that has caused this rotation (the torque applied by the transmission wheel). This manner of behaving is obtained by choosing a spring with a substantially constant spring rate. 
     The entire drive train from the motor  7  to the valve shutter  5  thus behaves in a substantially linear manner, thus making it more controllable. 
     The workload on the computation means (not depicted) for controlling the motor  7  is reduced here because, in order to get from a position instruction for the valve shutter  5  to the corresponding command for the motor  7 , the computation means have linear equations to handle, which requires less computing power, better responsiveness and greater robustness. The control of the motor  7  is therefore linear in this instance, which means to say performed to a first-order linear model. 
     Other features of the valve  1  can be conceived of without thereby departing from the scope of the invention. In particular, the gearset from the motor  7  to the input wheel  15  may contain any number of gears or pinions. 
     The valve shutter can be any component that controls the flow (opens, closes and/or meters) using a member that undergoes a translational movement.