EP0042900B1 - Device for feeding a liquid-fuel burner - Google Patents

Abstract

1. A device for feeding a liquid-fuel burner, comprising a pump with a rotary piston (20) provided with a cut-away portion (22) and accommodated in a pressure tight manner in a housing (10) itself provided with an inlet port (11) and a delivery port (12) adapted to communicate periodically and alternately during rotation of the piston with the cut-away portion there of, and a cam mechanism (13, 14, 23) interposed between the housing (10) and the rotary piston (20), and defining internally of the housing (10) a variable volume of space communicating with the cut-away portion of the piston, and a motor (27) for driving the piston in rotation, characterized by the fact that the piston (20) is constituted by the motor shaft, on which the housing (10) is slidingly mounted, whilst being resiliently urged towards the motor shaft (20) by a weak return spring (15), whilst flexible connections (11a, 12a) connect the inlet and delivery ports of the body, substantially rotationally held, to fixed parts.

Description

The present invention relates to a device which applies in particular to the supply of fuel to burners for domestic boilers.

Various factors, in particular the improvement in the insulation of buildings, mean that today the average flow rate required from a liquid fuel supply pump for a domestic boiler burner tends to decrease to less than 2.5 liters / hour.

Conventional gear pumps, suitable for higher flow rates, require too high motor torque at low flow rates and are excessively costly.

It is known to use pumps for conveying fluids called axial piston pumps capable of providing low flow rates proportional to the speed of rotation. Because the axial translation of the piston must be controlled by an additional rotary piston or, in the case where the axial piston is driven by a combined movement of translation and rotation, by gears with long teeth, the known pumps are complicated , expensive and not easy to dismantle.

Liquid supply devices are also known, comprising a rotary piston pump provided with a light and housed in a sealed manner in a casing itself provided with a suction port and a discharge port capable of communicate periodically and alternately during the rotation of the piston with the light thereof, and a cam mechanism interposed between the housing and the rotary piston, and defining within the housing a cavity of variable volume communicating with the light of the piston , as well as a motor to drive the piston in rotation.

Devices of this kind are known from patent FR-A-1,510,351 for supplying lubricating oil and from patent FR-A-1,416,519 for supplying a domestic heating burner.

The pumps of these known devices, in which the piston is driven by a combined movement of translation and rotation, have the drawbacks mentioned above.

The invention relates to a device for supplying a burner with liquid fuel comprising a pump of simple, light and inexpensive design, well suited to low liquid flow rates.

The proposed device comprises a rotary piston pump of the aforementioned type.

According to the invention, the piston consists of the motor shaft, on which the housing is slidably mounted, while being elastically urged towards the motor shaft by a weak return spring, while hoses connect the orifices of suction and discharge of the casing, substantially immobilized in rotation, at the fixed parts.

The invention is correlative to the fact that, for this pump intended to operate at low pressures, it suffices to use an extremely light casing; this therefore generates low axial dynamic forces, and can be associated with a weak return spring, so that the dynamic and return forces remain without undesirable repercussions on the cam mechanism and on the rotary piston. The mobile casing is easily removable to allow control or replacement of the cam mechanism. In addition, it facilitates rapid stopping of the pump.

The cam mechanism can advantageously be formed by machining the end of the motor shaft. The pump according to the invention thus took advantage of the excellent tolerances of the drive shafts.

The cam mechanism may include a stop associated with the piston and a cooperating cam surface associated with the housing.

The movable casing of the pump can be made of a metallic material or preferably plastic. It may have a tapered configuration on the side of the rotary piston so as to have a thinned end, endowed with radial elasticity, if necessary carrying an annular necking piece, and capable of causing the sealed application of said end on the piston. .

The sealing thus produced in a simple manner makes it possible to further reduce the weight of the casing and correspondingly to reduce the force of the return spring or to increase the stroke of the casing and consequently the flow rate of the pump. In addition, the radial elasticity of the end of the casing allows it to self-center more easily on the motor shaft.

The pump drive motor can be of the type with axial translation of the rotor when starting and stopping, which allows a frank operation and interruption of pumping without the need for a special solenoid valve.

When the motor shaft also drives an air supply fan, the fan can produce on the shaft at start and stop an axial thrust sufficient to produce a decoupling translation of the piston relative to the casing.

• Les Figures 1 et 2 sont des vues en coupe longitudinale partielle d'un premier mode de réalisation du dispositif d'alimentation à pompe simplifiée selon l'invention ;
• Les Figures 1A et 2A étant des coupes transversales correspondantes :
• Les Figures 3 et 3A sont des coupes longitudinales partielles montrant comment on peut régler le débit de la pompe par action sur la butée réglable 13 ;
• Les Figures 4 et 4A montrent un dispositif d'alimentation pour brûleur, dans lequel la mise en oeuvre et l'interruption franches du pompage sont assurées par effets électromagnétiques dans le moteur ;
• Les Figures 5 et 5A sont des vues en coupe longitudinale partielle et en coupe transversale d'un second mode de réalisation de l'invention ; et
• La Figure 6 est une vue en coupe d'une variante du carter.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, given with reference to the appended drawings, given solely to illustrate, without limitation, various embodiments of the invention, and in which:

• Figures 1 and 2 are views in partial longitudinal section of a first embodiment of the simplified pump supply device according to the invention;
• Figures 1A and 2A being corresponding cross sections:
• Figures 3 and 3A are partial longitudinal sections showing how the flow rate of the pump can be adjusted by action on the adjustable stop 13;
• Figures 4 and 4A show a burner supply device, in which placing in operation and the frank interruption of pumping is ensured by electromagnetic effects in the engine;
• Figures 5 and 5A are views in partial longitudinal section and in cross section of a second embodiment of the invention; and
• Figure 6 is a sectional view of a variant of the housing.

In the first embodiment of the invention (FIGS. 1, 1 A, 2 and 2A), the low-flow pump of the device for supplying liquid fuel comprises a casing 10 disposed axially movable on a rotary piston 20.

Provided with a suction orifice 11 from a reservoir and a discharge orifice 12 towards a spraying member, the casing 10 has a cylindrical cavity 10a open on the left and closed on the right on a blind bottom 10b. The blind bottom is equipped with a flow adjustment piece, for example an eccentric screw 13 which is mounted in leaktight manner and which bears offset at its end situated in the cavity 10 has a support, for example constituted by a ball joint ball 14. Made of a light, metallic or preferably plastic material with a low coefficient of friction, the casing cooperates by its bottom 10b with a helical or conical return spring 15, producing a relatively weak axial effect.

The suction and discharge conduits 11a, 12a connected to the orifices 11, 12, are constituted by hoses preventing any significant rotation of the casing while, in addition to its return function, the spring 15 contributes to preventing such rotation due to the fact that one of its ends 15a associated with the casing is immobilized by abutment or embedding on the bottom 10b while its other end 15b is associated with an element 16 of the frame of the device.

It goes without saying that the spring can be constituted by a leaf spring or an elastomer support element.

The casing 10 is slidably and sealingly mounted on the rotary piston 20. The sealing is carried out by means of an elastomeric lip seal with radial contact 19 or with tangential contact of a type customary for shaft seals rotating or by means of an O-ring supporting the inner ring in "Teflon". The rotary piston 20 is directly machined on the shaft of an electric motor 27 driving on the side opposite the pump a fan 40 for supplying combustion air.

The head 21 of the piston 20 has a lumen 22 in the form of a ring segment of less than 180 ° and an oblique face 23 forming a cam surface inclined at an angle a on a plane perpendicular to the axis of rotation of the piston.

The ball 14 of the adjustable stop 13 normally comes to bear on the cam surface 23 under the effect of the return spring 15.

The pump illustrated in Figures 1 and 2 operates as follows. In the position of Figure 1, the chamber 25 defined between the housing and the piston has its maximum volume; the rotation of the piston in the direction indicated cuts the communication between the light 22 and the suction port 11 and prepares to open the communication between the light and the discharge port 12 (FIG. 1A), while the surface cam tends to cause the translation of the housing 10 to its position of Figure 2. In this position, the chamber 25 takes its minimum volume and the communication between the light 22 and the orifice 12 is cut (Figure 2A). When the piston continues to rotate, the light is again open on the orifice 11 and the fuel is sucked into the chamber 25 until one returns to the position of FIG. 1.

Figures 3 and 3A show how the screw 13 and the ball 14 allow manual adjustment of the flow rate. In Figure 3, the ball 14 is applied to the cam surface 23 at a point defining a maximum stroke C1 between the housing 10 and the piston 20; in the position of Figure 3A which is obtained by simple rotation of a half-turn of the screw 13, the ball 14 is applied to the surface 23 at a point defining a course C2 much shorter. The stop contact remains effective between the ball 14 and the surface 23 regardless of the adjustment position.

In addition to the manual adjustment of the flow rate by means of the screw 13, it is possible to operate a proportional regulation of the flow rate of the pump by acting directly on the speed of rotation of the motor.

Due to the fact that the described pump operates at low flow rate and therefore with a reduced crankcase stroke, the alternating stresses of the flexible hoses for connection of the orifices 11 and 12 with the suction and the discharge only cause reduced stresses which are not detrimental to the longevity of the whole.

FIGS. 4 and 4A show a supply device with operation and frank interruption of the pumping so as to avoid the dripping of the fuel out of the spraying member between the moment when the stop order is given to the engine and the moment when the rotor 29 of the motor 27 stops definitively. The motor comprises a stator 28 and the motor shaft comprises on the side opposite the pump two shoulders 30, 31 for limiting the stroke cooperating with a stop 32 integral with the frame. A spring 35 mounted between a stop 33 and the drive shaft or the rotor 29 urges the shoulder 31 at rest against a stop 32 (Figure 4) so that the rotor 29 is offset axially relative to the stator 28. A shoulder 10c of the casing 10 of the pump is applied at rest by the return spring 15 against a stop 18 secured to the stator (Figure 4) or to the frame (Figure 4A). It goes without saying that the stops described, in particular the stop 18, can be axially adjustable.

When the engine is started, the field produced by the stator 28 attracts the rotor 29 and the latter compresses the decoupling spring 35, the cam surface 23 being therefore applied against the adjustable stop 14, so that the pump is implemented.

When the engine stops the rotor 29 continues to turn, but suddenly back to the left until the shoulder 31 is applied against the stop 32. The piston 20 is decoupled from the stop 14, which immediately stops the operation of the pump and the supply to the burner. At the same time, the torque transmitted by the piston 20 to the casing 10 disappears and the springs 15 and 35 relax to return to the rest position of FIG. 4.

In a simple variant, the axial translation of the rotor when starting and stopping is obtained by means of the fan 40 by the simple use of the axial force of aeraulic origin exerted on the blades and therefore on the fan shaft.

It goes without saying that the translation of the motor rotor must be greater than the stroke of the pump housing, a return spring or equivalent means having to bring the piston to rest in its decoupling position.

Due to the lack of linearity produced at low speeds in motors with axial rotor shift, it may be desirable for certain applications to realize the quick stop function of the pump by means of a stop solenoid valve placed on the line. liquid delivery. In this case, the pressure which forms in the chamber 25 as soon as the solenoid valve is closed causes an automatic decoupling of the casing from the piston under the effect of the compression of the weak spring 15.

When it is desired to obtain a delayed start-up of the pump relative to the start-up of the motor, it is preferable to resort to axial translation of the rotor by means of the fan, since the latter produces an axial effect greater than that of the spring only for a specified number of engine revolutions. It is advantageous to combine the offset forces under the effect of the motor and under the effect of the fan so as to obtain a delayed pump start with respect to the rotor start and a pump stop before the rotor stops.

The cam surface 23 or 42a can be of treated steel. The ball may be a steel ball 14 or 43 trapped in a cell of its support so as to be able to pivot freely and / or provided with a flat wear area so as to avoid punctual contact. The ball can also be simply crimped onto the end of the screw 13 or of an equivalent adjustment part or even onto the blind bottom of the casing.

The embodiment illustrated in FIGS. 5 and 5A comprises a washer 42, one face 42b of which is in abutment against a ball 43 crimped or pivotally mounted in the end of the rotary piston 20. The other face of the washer is in abutment against two stops associated with the blind bottom of the casing; one of the stops 41 constitutes the adjustable stop which makes it possible to vary by action on the screw 13 the angle of inclination a 'of the face 42a relative to the axis of the piston 20; the other stop 44 serves as a point or preferably linear support in order to define for the washer a pivot axis contained in a plane perpendicular to the piston axis.

In the embodiment of FIG. 6, the wall of the casing is thinned at 10c on the side of the motor 27 so as to provide at the end of the casing an elastic annular zone 10d applied with self-centering on the piston 20. On the zone 10d is mounted a clamping ring 50 possibly retained by a stop 51. Constituted for example by an O-ring, a ring or an annular spring, the ring 50 tightly seals the area 10d of the housing on the piston 20. The housing thus lightened makes it possible to use an even weaker spring 15 or, for the same spring, to increase the useful axial stroke. A seal 52 is associated with the adjustable stop screw or finger 13.

In certain cases, the radial elasticity of the zone 10d is sufficient to produce the desired seal by pinching the piston 20 and the constriction means 50 can therefore be eliminated.

Claims (9)

1. A device for feeding a liquid-fuel burner, comprising a pump with a rotary piston (20) provided with a cut-away portion (22) and accommodated in a pressure tight manner in a housing (10) itself provided with an inlet port (11) and a delivery port (12) adapted to communicate periodically and alternately during rotation of the piston with the cut-away portion there of, and a cam mechanism (13, 14, 23) interposed between the housing (10) and the rotary piston (20), and defining internally of the housing (10) a variable volume of space communicating with the cut-away portion of the piston, and a motor (27) for driving the piston in rotation, characterised by the fact that the piston (20) is constituted by the motor shaft, on which the housing (10) is slidingly mounted, whilst being resiliently urged towards the motor shaft (20) by a weak return spring (15), whilst flexible connections (11a, 12a) connect the inlet and delivery ports of the body, substantially irrotationally held, to fixed parts.

2. A device according to claim 1, characterised by the fact that the cam mechanism (13, 14, 23 ; 43, 42, 41) is formed in part by machining (23, 43) of the end of the motor shaft.

3. A device according to either of claims 1 and 2, characterised by the fact that the irrotational holding of the body is essentially achieved by the flexible connections (11a, 12a).

4. A device according to any one of claims 1 to 3, characterised by the fact that the cam mechanism comprises an abutment (43) associated with the piston and a cooperating cam surface (42) associated with the housing.

5. A device according to any one of claims 1 to 3, characterised by the fact that the cam mechanism comprises an abutment (13, 14) associated with the housing and a cooperating cam surface (23) associated with the piston.

6. A device according to any one of claims 1 to 5, characterised by the fact that the cam surface (23 ; 43) is constitued by a surface oblique with respect to a plane perpendicular to the axis of rotation of the piston.

7. A device according to any one of claims 1 to 6, characterised by the fact that the motor is an electric motor (27) of the type having a rotor axially movable between running and stopping, the axial movement being greater than the maximum stroke of the body for permitting uncoupling of it with respect to the piston.

8. A device according to any one of claims 1 to 7, including a combustion air feed impeller by the motor shaft (27), characterised by the fact that the impeller produces an axial movement of the shaft for a predetermined number of turns of the motor.

9. A device according to any one of claims 1 to 8, characterised by the fact that it comprises a stop electrovalve arranged in the delivery line connected to the delivery port of the pump, closing of the electro-valve occurring when turning of the motor creates in the pump space a pressure provoking uncoupling of the housing from the piston under the compression effect of the return spring.

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