FR3075305A1 - ACTUATING DEVICE HAVING A STAINLESS STEEL RING - Google Patents

Abstract

 The present invention relates to an actuating device (20) for an engine control valve, comprising:  - an outer ring (1) movable along an axis (D1),  - an inner ring (2) movable along the axis (D1),  a set of balls (3) kinematically connecting the outer ring (1) and the inner ring (2), the balls (3) being arranged to circulate in a helical track (4) formed at least partially on the rings (1, 2)  the actuator (20) being characterized in that the outer ring (1) is made of stainless steel.

Description

Actuation device comprising a stainless steel ring

The present invention relates to an actuating device. This actuation device can be integrated into an engine control valve, such as a valve for controlling the flow of recirculated exhaust gases at the intake of an automobile heat engine.

It is well known to use globe valves for applications as a metering valve for the flow of recirculated exhaust gases between the exhaust and the intake of a heat engine, in particular of an automobile.

The valve has a valve movable in translation disposed in the gas circulation conduit, and the valve is set in motion by an electric motor driving a control mechanism.

In order to obtain a low level of friction, it is known to integrate a ball screw in the movement transformation mechanism of the rotational movement of the electric motor in translational movement of the valve. Such an example is described for example in patent application FR3040746.

Ball screws are conventionally made of steel with high hardness, allowing good resistance to wear and a low level of friction.

Gases flowing through the valve circulation duct can enter the valve control mechanism.

In applications in which the gases passing through the valve contain engine exhaust gases, these gases are corrosive.

The various elements of the ball screw can thus oxidize.

Oxidation can create defects on the surface of the parts in contact, and these defects create hard spots in the mechanism.

The progression of the oxidation phenomenon can lead in the long term to blocking and therefore the failure of the valve control mechanism.

The object of the invention is to provide a valve whose ball screw mechanism does not oxidize, even in the presence of corrosive gases. The reliability of the control mechanism, and therefore of the valve itself, is thus improved.

To this end, the invention provides an actuating device for an engine control valve, comprising:

- an outer ring movable along an axis,

- an inner ring movable along the axis,

- A set of balls kinematically connecting the outer ring and the inner ring, the balls being arranged to circulate in a helical track formed at least partially on the rings, the actuating device being characterized in that the outer ring is made of stainless steel . The outer ring thus resists oxidation. The part of the helical track produced in the outer ring does not undergo any deterioration in its surface condition.

According to a preferred embodiment, the inner ring is made of stainless steel.

Likewise, the inner ring does not undergo degradation due to corrosion.

According to an exemplary implementation of the invention, the balls are made of stainless steel.

As for the other parts, the stability of the dimensions and the surface condition is ensured.

Advantageously, the inner ring is of cylindrical shape and has an external lateral surface.

Preferably, the helical track is formed at least partially on the external lateral surface of the inner ring.

In other words, part of the helical track used to circulate the balls is made in the thickness of the wall of the inner ring.

Advantageously, the outer ring has the general shape of a hollow cylinder and has an internal lateral surface.

Preferably, the helical track is formed at least partially on the internal lateral surface of the outer ring.

In other words, part of the helical track used to circulate the balls is made in the thickness of the wall of the outer ring.

According to one embodiment, the inner ring is made of type 304L steel.

This steel grade provides corrosion resistance for most applications.

According to another embodiment, the inner ring is made of type 316L steel.

This steel grade provides superior resistance to oxidation and is used for applications where the environment is particularly corrosive. This can be the case in the case of gases containing sulfur for example.

According to one embodiment, the outer ring is of type 304L steel. The outer ring can also be made of type 316L steel.

According to another embodiment, the balls are made of type 304L steel. The balls can also be made of type 316L steel.

According to the applications, all combinations of materials of the three elements which are the outer ring, the inner ring and the balls can be produced.

According to a preferred embodiment, the internal lateral surface of the outer ring comprises a surface layer hardened by a hardening treatment.

The hardening treatment improves the mechanical strength of stainless steel, which is lower than that of conventional rolling steel. The nature of the steel used ensures corrosion resistance and the hardening of the surface makes it possible to maintain mechanical properties compatible with the forces present in a ball screw.

In a variant where, in a complementary manner, the external lateral surface of the inner ring comprises a surface layer hardened by a hardening treatment.

In a variant where, in a complementary manner, the balls comprise a surface layer hardened by a hardening treatment.

The hardening treatment can be applied to one or more of the different elements in contact.

Advantageously, the hardening treatment is a treatment for the diffusion of chemical elements.

This type of treatment provides good mechanical resistance and is achievable for all shapes of parts.

According to one embodiment, the hardening treatment is a carbonitriding.

This treatment makes it possible to obtain a very high surface hardness and is not likely to undergo corrosion itself.

Preferably, the thickness of the hardened surface layer is between 0.03 mm and 0.2 mm.

Advantageously, the outer ring has a recirculation path for recirculating the balls from one end to the other of the helical track.

The recirculation of the balls during the rotation of the ring relative to the screw makes it possible to have an unlimited amplitude of rotation.

Preferably, the helical track has a bottom having a cross section in an arc.

The helical track thus has, in the zone of contact with the balls, a shape complementary to that of the balls. This allows good ball guidance and a low level of friction.

The invention also relates to a fluid circulation valve, comprising:

- A body defining a fluid circulation conduit,

- An actuating device as described above,

- A movable shutter between an open position allowing the passage of the fluid in the duct and a closed position preventing the passage of the fluid in the duct, the shutter comprising a cylindrical shaft secured to the inner ring.

Thanks to the corrosion resistance of the actuating device, the reliability of the valve is improved. It is not necessary to provide a specific sealing system in order to isolate the control mechanism from a corrosive atmosphere.

Advantageously, the inner ring surrounds the shaft.

According to one embodiment, the shaft is welded to the inner ring.

This fixing means is quick to produce and offers good mechanical resistance.

According to another embodiment, the shaft is brazed to the inner ring.

According to yet another embodiment of the valve, the shaft is crimped to the inner ring.

This fixing means is achievable with inexpensive tools.

According to one embodiment, the outer ring being fixed in translation and free in rotation, the inner ring being fixed in rotation and free in translation.

Advantageously, the valve comprises an electric motor arranged to drive the outer ring in rotation.

According to one embodiment, the axis of the electric motor is perpendicular to the axis of the outer ring.

This arrangement makes it possible to limit the height of the valve and to obtain a compact valve.

Alternatively, the axis of the electric motor is parallel to the axis of the outer ring.

This arrangement allows easy assembly of the main elements of the valve control mechanism.

Advantageously, the valve comprises a toothed wheel secured to the outer ring, the electric motor being arranged to mesh with the toothed wheel, the movable shutter comprising an anti-rotation device.

According to one embodiment, the outer ring is held in an inner cage of a bearing.

Preferably, an outer cage of the bearing is maintained in the valve body.

The use of a bearing for positioning and guiding the ring of the ball screw allows good precision and a low level of friction.

According to one embodiment, the fluid circulating in the conduit contains exhaust gases from a heat engine.

The use of a stainless steel ball screw is particularly suitable for use with exhaust gases, which are corrosive.

According to an exemplary implementation of the invention, the valve is an exhaust gas recirculation valve between an exhaust circuit and an intake circuit of a heat engine. The conditions encountered in an exhaust gas recirculation circuit are particularly demanding, in particular because of the sulfur present in the fuel and of the condensation which may occur when the engine is started.

According to one embodiment, the recirculated exhaust gases are recirculated in the intake circuit downstream of a compressor of a device for supercharging the heat engine. In other words, the valve is used according to the so-called “high pressure” architecture. This type of valve is well suited to this application, in particular because of its low level of leaks.

Other characteristics and advantages of the invention will appear on reading the detailed description of the embodiments given by way of nonlimiting examples, accompanied by the figures below:

FIG. 1 represents a sectional view of an exhaust gas recirculation valve incorporating an actuating device according to the invention,

FIG. 2 is a partial sectional view of the device for actuating the valve of FIG. 1.

In the various figures, similar elements are designated by identical reference numerals. In order to facilitate the reading of the figures, the various elements are not necessarily shown to scale.

FIG. 1 shows a valve 30 for circulating fluid, comprising:

A body 10 defining a fluid circulation conduit 11,

- An actuating device 20,

- A shutter 12 movable between an open position allowing the passage of the fluid in the duct 11 and a closed position preventing the passage of the fluid in the duct 11, the shutter 12 comprising a cylindrical shaft 14 integral with the inner ring 2 .

According to the example of Figure 1, the valve is an exhaust gas recirculation valve between an exhaust circuit and an intake circuit of a heat engine.

The valve 30 can be used according to the so-called “high pressure” architecture. In other words, the recirculated exhaust gases are recirculated in the intake circuit downstream of a compressor of a device for supercharging the heat engine. The recirculated exhaust gases are taken from the engine exhaust system upstream of the turbine.

The valve body 10 receives the main elements of the valve. The valve has a cover 22 enabling the valve body 10 to be closed hermetically from solid and liquid bodies.

The mobile shutter 12 is, in the example shown, a valve. The movable obturator 12 comprises a shaft 14, also called a valve stem, and a valve head 9. The movable obturator 12 slides in a guide 26 inserted in the valve body 10.

The shutter 12 is movable in translation between a position for closing the duct 11 in which the valve head 9 rests on a seat 23, as shown in FIG. 1, and a position of maximum lift where the distance between the valve head 9 and seat 23 is maximum. When the valve head 9 of the shutter 12 rests on its seat 23, the gas flow in the duct is zero. By zero flow is meant that there is no gas flow, with the exception of the inevitable parasitic leaks.

When the shutter 12 is in the maximum lifting position, the gas passage section in the conduit 11 is maximum.

The actuation device 20 converts a rotational movement into a translational movement of the shaft 14.

FIG. 2 details the structure of the actuating device 20.

The actuating device 20 comprises:

an outer ring 1 movable along an axis Dl,

an inner ring 2 movable along the axis Dl,

- A set of balls 3 kinematically connecting the outer ring 1 and the inner ring 2, the balls 3 being arranged to circulate in a helical track 4 formed at least partially on the rings 1,2.

The set of balls 3 is arranged radially between the outer ring 1 and the inner ring 2 and circulates in the helical track 4 during a rotation of the outer ring 1 relative to the inner ring 2.

The outer ring 1 has a recirculation path 7 enabling the balls 3 to be recirculated from one end to the other of the helical track 4.

The recirculation of the balls during the rotation of the outer ring 1 relative to the inner ring 2 makes it possible to have an unlimited amplitude of rotation.

According to the state of the art, the outer ring 1, the inner ring 2 and the balls 3 are made of so-called rolling steel, having a high hardness in order to resist wear. For example, the steel designated by 100 C6 according to the AFNOR standard, or 100Cr6 according to the NF A 35-590 standard, is commonly used.

The inner ring 2 surrounds the shaft 14.

The shaft 14 is fixed to the inner ring 2 of the actuating device 20.

In the example shown in FIG. 2, the shaft 14 is welded to the inner ring 2.

The inner ring 2 is cylindrical in shape and has an outer lateral surface 5.

The helical track 4 is formed at least partially on the external lateral surface 5 of the inner ring 2.

The outer ring 1 has the general shape of a hollow cylinder and has an internal lateral surface 6.

The helical track 4 is formed at least partially on the internal lateral surface 6 of the outer ring 1.

In other words, part of the helical track used to circulate the balls is made in the thickness of the wall of the inner ring, as well as in the thickness of the wall of the outer ring.

The helical track 4 has a bottom 8 having a cross section in an arc.

The helical track thus has, in the zone of contact with the balls, a shape complementary to that of the balls. This allows good ball guidance and a low level of friction.

The outer ring 1 is fixed in translation and free in rotation, the inner ring 2 being fixed in rotation and free in translation.

The outer ring 1 is held in an inner cage 19 of a bearing 18.

The outer ring 1 can for example be fitted into the inner cage 19 of the bearing

18.

The outer cage 21 of the bearing 18 is held in the valve body 10.

The bearing 18 is arranged in a bore of the body 10, the bore ensuring the radial retention. The axial maintenance of the bearing 18 is ensured by two screws, not shown. The screws are supported on a lateral surface of the outer cage 21 and press the bearing 18 against the bottom wall of the bore.

The use of a bearing for positioning and guiding the ring of the ball screw allows good precision and a low level of friction.

Thus, the outer ring 1 is fixed in translation and free in rotation about the axis Dl.

The shaft 14, linked to the inner cage 19, is free in translation along the axis Dl and fixed in rotation.

The valve 30 comprises an electric motor 15 arranged to drive the outer ring 1 in rotation.

More specifically, the valve 30 comprises a toothed wheel 16 secured to the outer ring 1, the electric motor 15 being arranged to mesh with the toothed wheel, the movable shutter 12 comprising an anti-rotation device 17.

The pinion 25 of the electric motor 15 meshes with the toothed wheel 16 which is integral with the outer ring 1.

The electric motor 15 is here a DC motor.

The axis D2 of the electric motor 15 is perpendicular to the axis Dl of the outer ring 1.

The anti-rotation device 17 is fixed to the shaft 14 and bears on a part rigidly connected to the valve body 10. The shaft 14 can thus move in translation but is locked in rotation.

An electronic control unit, for example that controlling the operation of the heat engine, controls the supply current of the electric motor 15 of the valve 30, in order to ensure the desired degree of opening of the shutter 12. The flow rate of recirculated exhaust gas can thus be regulated to its set value, and can vary continuously.

The electronic control unit has not been shown. The connector 24 located on the cover 22 allows the electrical connection between the valve 30 and the electronic control unit.

During the passage of the gases in the conduit 11, the gases are present between the guide 26 and the shaft 14. Despite the presence of the seal 27, part of the gases can join the part of the valve body in which the device is placed. actuation 20.

The various elements of the actuating device 20 can therefore be in contact with the gases.

When the gases are corrosive, the various elements are subjected to the chemical effect of the gases and can oxidize. Thus, the surfaces of the outer ring 1, of the inner ring 2, and of the balls 3 are liable to oxidize.

Oxidation creates defects on the surface of the parts in contact, and these defects can create hard spots in the mechanism.

The progression of the oxidation phenomenon can lead in the long term to blocking and therefore the failure of the valve control mechanism.

The proposed device aims to solve this drawback.

To this end, the actuating device 20 comprises:

an outer ring 1 movable along an axis Dl,

an inner ring 2 movable along the axis Dl,

a set of balls 3 kinematically linking the outer ring 1 and the inner ring 2, the balls 3 being arranged to circulate in a helical track 4 formed at least partially on the rings, the actuating device 20 being characterized in that the outer ring 1 is made of stainless steel.

The outer ring 1 thus resists oxidation. The portion of helical track 4 produced in the outer ring 1 does not undergo degradation of its surface condition, which makes it possible to maintain a circulation of the balls 3 without hard point.

Likewise, the inner ring 2 is made of stainless steel.

Likewise, the inner ring 2 does not undergo degradation due to corrosion.

The balls 3 are made of stainless steel.

As for the other parts, the stability of the dimensions and the surface condition is ensured.

Various grades of stainless steel are of course usable.

According to one embodiment, the inner ring 2 is made of type 304L steel. The outer ring 1 is made of type 304L steel. The balls 3 are made of type 304L steel.

This steel grade provides corrosion resistance for most applications.

According to another embodiment, the inner ring 2 is made of 316L type steel. The outer ring 1 can also be made of type 316L steel. The balls 3 can also be made of type 316L steel.

This steel grade provides superior resistance to oxidation and is used for applications where the environment is particularly corrosive. This may be the case in applications where the gases contain a high sulfur content and contain moisture.

The terms 304L and 316L refer to the AISI standard. These designations are equivalent, respectively, to designations 1.4307 and 1.4404 of the EN euronorm standard.

According to the applications, all the combinations of materials of the three elements that are the outer ring 1, the inner ring 2 and the balls 3 can be produced.

In the example shown, the outer ring 1 and the inner ring 2 are made of 316L stainless steel, and the balls are made of 100Cr6 bearing steel.

Since stainless steel has a lower hardness than rolling steel, the stainless steel elements are hardened by surface treatment. This maintains good resistance to wear and a low coefficient of friction, while benefiting from the anti-corrosion properties provided by the nature of the base material.

Thus, the internal lateral surface 6 of the outer ring 1 has a surface layer hardened by a hardening treatment.

The hardening treatment improves the mechanical strength of stainless steel, which is lower than that of conventional rolling steel. The nature of the steel used ensures corrosion resistance and the hardening of the surface makes it possible to maintain mechanical properties compatible with the forces present in a ball screw.

Likewise, the outer lateral surface 5 of the inner ring 2 has a surface layer hardened by a hardening treatment.

Also, the balls 3 comprise a surface layer hardened by a hardening treatment.

The hardening treatment can be applied to one or more of the three elements

The hardening treatment is here a treatment for the diffusion of chemical elements.

More specifically, the hardening treatment is carbonitriding.

This treatment makes it possible to obtain a very high surface hardness and is not likely to undergo corrosion itself.

The thickness of the hardened surface layer is between 0.03 millimeter and 0.2 millimeter.

The example described is that of an exhaust gas recirculation valve, which is often subjected to particularly demanding conditions, in particular because of the sulfur present in the fuel and of the condensation which may occur when the engine is started.

Other embodiments corresponding to other applications are of course possible.

According to embodiments not shown, the actuating device as well as the fluid circulation valve integrating this device can also include one or more of the characteristics below, considered individually or combined with each other:

The shaft 14 can be brazed to the inner ring 2,

The shaft 14 can be crimped to the inner ring 2,

The axis D2 of the electric motor 15 can be parallel to the axis DI of the outer ring 1.

Of course, the invention is in no way limited to the embodiments described and illustrated, which have been given only by way of examples.

Claims (9)

1. Actuating device (20) for engine control valve (30), comprising: - an outer ring (1) movable along an axis (Dl), - an inner ring (2) movable along the axis (Dl), a set of balls (3) kinematically connecting the outer ring (1) and the inner ring (2), the balls (3) being arranged to circulate in a helical track (4) formed at least partially on the rings (1, 2), the actuating device (20) being characterized in that the outer ring (1) is made of stainless steel. 2. Actuating device (20) according to the preceding claim, wherein the inner ring (2) is made of stainless steel. 3. Actuating device (20) according to claim 1 or 2, wherein the balls (3) are made of stainless steel. 4. actuation device (20) according to one of the preceding claims, in which the outer ring (1) has the general shape of a hollow cylinder and has an internal lateral surface (6), the internal lateral surface (6) of the outer ring (1) comprising a surface layer hardened by a hardening treatment. 5. Actuating device (20) according to one of the preceding claims, in which the inner ring (2) is cylindrical in shape and has an external lateral surface (5), the external lateral surface (5) of the internal ring (2) having a surface layer hardened by a hardening treatment. 6. Actuating device (20) according to one of the preceding claims, in which the balls (3) comprise a surface layer hardened by a hardening treatment. 7. An actuating device (20) according to one of claims 4 to 6, in which the hardening treatment is a treatment for the diffusion of chemical elements. 8. An actuating device (20) according to the preceding claim, in which the hardening treatment is carbonitriding. 9. Fluid circulation valve (30), comprising: - A body (10) defining a conduit (11) for fluid circulation, - An actuating device (20) according to one of the preceding claims,