PUMP FOR SUPPLYING AN APPLICATION SYSTEM OF A LIQUID COVERING PRODUCT

Abstract

A pump supplying an application system of a liquid covering product including a motor actuating at least two pistons, a drum rotated by the motor, the drum including an outer cylindrical surface having a cam profile, each piston being secured to a rod on which a roller is fastened rolling over the cam profile such that the roller connected to each piston via one of the rods is translated along the translation axis of the corresponding piston under the action of the rotation of the drum, each roller being in contact with the cam profile in an angularly offset position relative to the other rollers such that one of the pistons is moving when the other piston reaches an inversion point of its movement direction, and the pump including compensating means suitable for accelerating one of the pistons when another piston reaches an inversion point of its movement direction.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 USC §119 of French Patent Application No. 15 61346 filed on Nov. 25, 2015.

FIELD OF THE INVENTION

The invention relates to a pump for supplying an application system of a liquid covering product.

BACKGROUND OF THE INVENTION

Pumps for supplying application systems for liquid covering products such as paints are generally made up of an electric or pneumatic motor, a hydraulic pump and a coupling means connecting the motor to the pump. Electric pump will refer to a supply pump having an electric motor and pneumatic pump, a pump having a pneumatic motor. Electric pumps are preferably used due to their better performance and lower usage cost. The issue lies in converting the movement between the electric motor, which has a rotating movement, and the hydraulic pump, which has an alternating linear movement. When its movement direction is inverted, the piston of the hydraulic pump reaches a zero speed, which causes a drop in the pressure at the outlet of the pump. Electric pumps must therefore be provided to offset these inversions.

Pumps comprising a single piston actuated by a connecting rod-crank system are known. In these pumps, the rotation speed of the electric motor is controlled to obtain a constant flow rate. Pumps comprising a single piston actuated by a rack are known from US-A-2015/219819. The inversions are done on different teeth of the rack to reduce its wear. None of these systems make it possible to avoid a pressure drop at the outlet of the pump.

It is also known to use a pump with two diametrically opposite pistons, i.e., phase-shifted by Pi radians, the movements of which are caused by the rotation of a heart-shaped cam, the profile and associated mechanism of which are adapted so that, during the inversion of the movement of one of the pistons, the other piston is not completely at the end of its travel. However, such a system is not fully satisfactory inasmuch as it involves the continuous variation of the torque to be provided by the motor. Furthermore, given the design of the known heart-shaped cam, the latter has only one means for pushing the piston of the hydraulic pump; thus, to achieve the travel of the piston in the opposite direction, a return mechanism is needed.

SUMMARY OF THE DESCRIPTION

The invention aims to resolve these drawbacks by proposing a new pump for supplying an application system of a liquid covering product, allowing more effective compensation of the inversions of the pistons of the pump.

To that end, the invention relates to a pump for supplying an application system of a liquid covering product, comprising a motor actuating at least two pistons. This pump is characterized in that it comprises a drum rotated by the motor, the drum comprising an outer cylindrical surface having a cam profile, in that each of the pistons is secured to a rod on which a roller is fastened rolling over the cam profile such that the roller connected to each of the pistons via one of the rods is translated along the translation axis of the corresponding piston under the action of the rotation of the drum, in that each of the rollers is in contact with the cam profile in an angularly offset position relative to the position of the other rollers such that one of the pistons is moving when the other piston reaches an inversion point of the movement direction, and in that it comprises compensating means suitable for accelerating one of the pistons when another piston reaches an inversion point of its movement direction.

Owing to the invention, the acceleration of one of the pistons during the inversion of another piston allows an effective compensation of the pressure drop. The pressure obtained at the outlet of the pump is globally constant.

According to advantageous but optional aspects of the invention, such a pump may incorporate one or more of the following features, considered in any technically allowable combination:

The compensating means comprise means for accelerating the rotation speed of the drum during a predetermined length of time before and after the passage of one of the pistons by its inversion point: in this embodiment, at the time of the inversions, the rotation speed of the motor increases, while the torque decreases, such that the power requested from the motor remains constant.

The acceleration means comprise a control unit of the motor.

The compensating means comprise a pressure sensor placed downstream from the pistons, and the acceleration means are suitable for increasing the rotation speed of the drum as a function of a pressure value measured by the pressure sensor.

The compensating means are formed by two angular sectors of the cam profile having an incline angle, relative to a plane perpendicular to the rotation axis of the drum, larger than an incline angle of a remaining angular sector of the cam profile. In this embodiment, the compensation is done while retaining a constant speed and motor torque.

The incline angle of the angular sectors of the cam profile forming the compensating means is twice the incline angle of the remaining angular sector of the cam profile.

The pump comprises two pistons angularly offset by 90°.

The cam profile comprises two helical slots each extending over half the circumference of the drum, and symmetrical relative to a plane passing through the rotation axis of the drum.

The rollers are angularly offset by an angle comprised between 70° and 100°.

The offset angle of the rollers is 90°.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood, and other advantages thereof will appear more clearly, in light of the following description of a supply pump according to its principle, provided as a non-limiting example in reference to the appended drawings, in which:

FIG. 1 is a perspective view of a pump according to a first embodiment of the invention;

FIG. 2 is an enlarged view of detail II in FIG. 1;

FIG. 3 is a top view of the pump of FIGS. 1 and 2;

FIG. 4 is a sectional view along plane IV-IV in FIG. 3;

FIG. 5 is a curve showing the variation of the rotational speed as a function of the annular position of a motor of the pump of FIGS. 1-4;

FIG. 6 is a view similar to that of FIG. 4 and enlarged of a pump according to a second embodiment of the invention, in which only a drum and rollers of the pump are shown; and

FIG. 7 is a view similar to FIG. 1 of a pump according to a third embodiment of the invention.

DETAILED DESCRIPTION

FIGS. 1-5 show a pump 1 for supplying an application system of a liquid covering product, not shown. The pump 1 comprises an electric motor 3 with rotation axis X-X′.

The motor actuates two pistons 5 and 6 each mounted in a chamber 8 with the possibility of sliding along respective axes X5 and X6 parallel to the axis X-X′. The movement of the pistons 5 and 6 in the chambers 8 makes it possible to deliver a pressurized liquid covering product, such as a paint.

The motor 3 actuates the pistons 5 and 6 via a transmission system comprising a drum 9 rotated by the motor 3 around the axis X-X′. The transmission of the rotation from the motor 3 to the drum 9 can be direct or indirect, via a gear reduction system, not shown.

The drum 9 comprises an outer cylindrical surface 90 centered on the axis X-X′. The outer surface 90 has a cam profile 92. Each of the pistons 5 and 6 is respectively secured to a first rod 51 and a second rod 61 on which a first roller 53 and a second roller 63 are fastened, each of the rollers 53 and 63 rolling over the cam profile 92 such that each of the rollers 53 and 63 connected to each of the pistons 5 and 6 via the rod 51 and 61 is translated parallel to the axis X-X′ under the action of the rotation of the drum 9.

In the illustrated example, the cam profile 92 is formed by a continuous slot comprising two helical slots 94 and 95 each extending over half the circumference of the drum 9, and symmetrical relative to a plane P1 passing through the rotation axis X-X′ of the drum. The slots 94 and 95 each comprise a respective cylindrical bottom 94a and 95a, upper helical walls 94b and 95b and lower helical walls 94c and 95c. The rollers 53 and 63 are selectively in contact with one of the upper 94b and 95b or lower 94c and 95c helical walls, along contact lines perpendicular to the axis X-X′.

In FIG. 4, the motor 3, the drum 9 and the rollers 53 and 63 appear twice due to the geometry of the cutting plane IV-IV. When the drum 9 rotates on itself around the axis X-X′, the contact between the helical walls 94b, 95b, 94c, 95c and the rollers 53 and 63 causes the translation of the rods 51 and 61, which is transmitted to the pistons 5 and 6, which makes it possible to alternately obtain the aspiration of the covering product, then its pressurized expulsion at the outlet of the pump 1.

Each of the pistons 5 and 6 has a top dead center and a bottom dead center corresponding to the inversion points of its translational movement direction. During these inversions, the linear speed of the pistons 5 and 6 decreases, then passes by a zero value, which causes a cut in the pressure at the outlet of the pump. It is therefore necessary to offset the slowing of the speed of one of the pistons 5 and 6 when it reaches its inversion point with the movement of the other piston. Thus, according to the invention, the contact point of one of the rollers 53 and 63 with the cam profile 92 is in an angularly offset position relative to the position of the contact point of the other rollers such that one of the pistons 5 and 6 is moving when the other piston is at an inversion point of its movement direction. Advantageously, the respective positioning of the rollers 53 and 63 makes it possible, as shown in FIG. 4, for the roller 53 to reach its top inversion point while the roller 63 is approximately midway through its upward movement. This makes it possible to partially offset the pressure drop due to the inversion of a piston.

The offset angle A of the rollers 53 and 63 is preferably comprised between 70° and 100°. Preferably, the offset angle A of the rollers is 90°. This angle A is also the angle formed by the axes X5 and X6 relative to the axis X-X′. The offset may not be 180°, since the pistons 5 and 6 would reach their inversion point at the same time and could not offset one another.

Thus, as shown in FIG. 3, the rollers 53 and 63 are offset by a quarter revolution of the drum 9, which means that the roller 53 reaches the boundary between the slots 94 and 95 while the roller 63 reaches the central part of the slot 95, which corresponds to half of the travel of the piston 6.

In order to more effectively compensate the inversion of the pistons, according to the invention, the pump 1 comprises compensating means suitable for accelerating one of the pistons 5 and 6 while the other piston reaches its inversion point.

According to a first embodiment of the invention, the compensating means comprise means for accelerating the rotation speed of the drum 9 formed by a control unit 10 shown diagrammatically in FIG. 1, during a predetermined length of time before and after the passage of one of the pistons 5 and 6 by its inversion point. Thus, during the entire period where one of the pistons slows down, passes by zero speed, then again accelerates, the rotation speed of the drum 9 is accelerated by the control unit 10 so that the translation speed of the other piston is also accelerated, so as to allow the compensation of the slowing of the first piston. This method is shown by the curve illustrated in FIG. 5, which shows the evolution of the rotation speed V of the drum 9 as a function of the angular position of the drum 9. The speed profile is transmitted to the motor 3 by the control unit 10 in the form of an electrical signal S10. Upon each quarter revolution of the drum 9, corresponding to a rotation of Pi/2 radians, an inversion of a piston 5 or 6 occurs, which leads to a compensation by the increase of the speed V around this angular position.

As an example, the rotation speed of the drum 9 can be increased from 5 to 10 revolutions per minute.

The control unit 10 is preferably an electronic unit performing an enslaved control of the rotation speed of the motor 3.

As an example, the angle interval before and after the passage of the piston by the inversion point during which the speed of the drum 9 is increased, may be comprised between 0.14 and 0.28 radians.

A second embodiment of the invention is shown in FIG. 6. In this embodiment, the elements shared with the first embodiment bear the same references and operate in the same manner. Only the differences with respect to the first embodiment are outlined below.

In FIG. 6, only the drum 9, in its two positions of the sectional view of FIG. 4, and the rollers 53 and 63 are shown out of a concern for clarity.

In the embodiment shown in FIG. 6, the compensating means may comprise, to replace the means for accelerating the rotation speed of the drum 6 or concomitantly, two angular sectors 97 of the cam profile 92 whereof the incline angle A97, measured relative to a plane P2 perpendicular to the rotation axis X-X′, is larger than the incline angle A92, called nominal, of a remaining angular sector of the cam profile 92. The remaining angular sector is defined as the portion of the cam profile 92 extending outside the angular sectors 97. An angular sector 97 with an accentuated incline is arranged on a central part of each of the slots 94 and 95. Thus, the rollers 53 and 63 being offset by 90°, the roller 53 reaches an inversion point, as shown on the left in FIG. 6, while the roller 63 is in contact with the angular sector 97, as shown on the right in FIG. 6. In this way, the translation speed along the axis X-X′ of the roller 63 is therefore increased owing to the increase in the slope of the walls 94b, 95b, 94c and 95c. The acceleration of the piston 6 secured to the roller 63 therefore offsets the slowing and passage by the zero speed of the piston 5. This makes it possible for the fact that one of the pistons 5 and 6 has reached its inversion point to cause only a relatively small variation in the output pressure of the pump 1.

According to one advantageous, but optional aspect of the invention, the value of the incline angle A97 is preferably twice the value of the incline angle A92.

Of course, the position of the angular sectors 97 at the center of the slots 94 to 95 is related to the orientation of the rollers 53 and 63 at 90°.

According to a third embodiment, the pump 1 may also comprise a pressure sensor 100 situated downstream from two hydraulic outlet conduits C1 and C2 of the pistons 5 and 6, making it possible to measure the pressure at the outlet of the pump 1 and to measure the pressure drop following the approach of one of the pistons to an inversion point. The pressure sensor 100, which is comprised in the compensating means, is connected to the control unit 10, or to any other means suitable for increasing the rotation speed of the drum 9 as a function of the pressure value, measured by the pressure sensor 10 and sent to the control unit 10 in the form of an electrical signal SP. To that end, the triggering of the acceleration of the speed of the drum 9 may be subject to the passage, by the value of the outlet pressure, below a threshold value, for example equal to 15 bars.

According to one embodiment of the invention that is not shown, the pump 1 may comprise more than two pistons.

The features of the embodiments and alternatives described above may be combined to form new embodiments of the invention.

Claims

1. A pump for supplying an application system of a liquid covering product, comprising a motor actuating at least two pistons, wherein it comprises a drum rotated by the motor, the drum comprising an outer cylindrical surface having a cam profile, wherein each of the pistons is secured to a rod on which a roller is fastened rolling over the cam profile such that the roller connected to each of the pistons via one of the rods is translated along the translation axis of the corresponding piston under the action of the rotation of the drum, and wherein each of the rollers is in contact with the cam profile in an angularly offset position relative to the position of the other rollers such that one of the pistons is moving when the other piston reaches an inversion point of the movement direction, and wherein it comprises compensating means suitable for accelerating one of the pistons when another piston reaches an inversion point of its movement direction.

2. The pump according to claim 1, wherein the compensating means comprise means for accelerating the rotation speed of the drum during a predetermined length of time before and after the passage of one of the pistons by its inversion point.

3. The pump according to claim 2, wherein the acceleration means comprise a control unit of the motor.

4. The pump according to claim 2, wherein the compensating means comprise a pressure sensor placed downstream from the pistons, and the acceleration means are suitable for increasing the rotation speed of the drum as a function of a pressure value measured by the pressure sensor.

5. The pump according to claim 1, wherein the compensating means are formed by two angular sectors of the cam profile having an incline angle, relative to a plane perpendicular to the rotation axis of the drum, larger than an incline angle of a remaining angular sector of the cam profile.

6. The pump according to claim 5, wherein the incline angle of the angular sectors of the cam profile forming the compensating means is twice the incline angle of the remaining angular sector of the cam profile.

7. The pump according to claim 1, wherein it comprises two pistons angularly offset by 90°.

8. The pump according to claim 1, wherein the cam profile comprises two helical slots each extending over half the circumference of the drum, and symmetrical relative to a plane passing through the rotation axis of the drum.

9. The pump according to claim 1, wherein the rollers are angularly offset by an angle comprised between 70° and 100°.

10. The pump according to claim 1, wherein the offset angle of the rollers is 90°.