PUMP FOR MEASURING OUT A FLUID

The present invention relates to the field of systems for mixing exhaust gas with reagents, for example for reducing the emissions of substances which are harmful for the environment and for the health of people, and in particular the present invention relates to a pump for measuring out a fluid. It is known that exhaust gases of internal combustion engines contain a high quantity of harmful elements that can damage both the environment and the health of people who may breathe the polluted air.

In order to reduce the environmental impact of these devices over the years, attempts have been made to develop systems which are able to improve the combustion process, so as to have a smaller quantity of waste products, and to treat / filter the exhaust gases before being released into the atmosphere.

In particular, a class of compounds contained in the exhaust gases which are particularly dangerous for the environment and for people is that of the NOx compounds, i.e. nitrogen oxides and their mixtures.

These compounds contribute to the production of ozone, nitrates and nitrogen dioxide, which, as is known, can also cause serious respiratory problems when inhaled, as well as contribute to the creation of acid rain.

It is therefore evident that a strongly felt need in the field of internal combustion engines is to find solutions capable of reducing the quantity of polluting compounds emitted into the atmosphere.

In particular, a technique is known which allows to obtain a reduction of the NOx compounds present in the exhaust gases called Selective Catalytic Reduction (SCR).

According to the SCR technique, a reducing chemical is added, in the liquid or gaseous state, to the exhaust gases in the presence of a catalyst. The reducing element, in particular it is known the use of mixtures of water and urea, tends to bind with oxygen, thus preventing the production of NOx within the exhaust gas, thus favouring the emission of nitrogen (N2). However, systems and devices exploiting the SCR technique have some critical aspects.

For example, this type of systems requires a very high precision while measuring out the reducing chemical, since the introduction into the exhaust gas of a too low quantity of reducing element would cause a reduction in the efficiency of the system and the incorrect elimination of pollutants.

The same effect would be to introduce an excessively high quantity of reducing element which would settle on the catalyst, thus decreasing the surface useful for the catalysis reaction, yet risking damaging the catalyst itself at a structural level.

In this context, the technical task underlying the present invention is to propose a pump for measuring out a fluid that overcomes at least some of the drawbacks of the known art mentioned above.

In particular, it is an object of the present invention to provide a pump for measuring out a fluid capable of guaranteeing a high level of precision and efficiency even for high volumes to be pumped.

The mentioned technical task and the specified aims are substantially achieved by a pump for measuring out a fluid, including the technical specifications set out in one or more of the appended claims.

According to the present invention, a pump for measuring out a fluid is shown comprising: a first pumping chamber having an inlet opening suitable for being placed in fluid communication with a feeding device and an outlet opening; a second pumping chamber having an outlet opening, suitable for being placed in fluid communication with a using device and an inlet opening; a transfer valve, interposed between the outlet opening of the first pumping chamber and the inlet opening of the second pumping chamber, which is movable between an opened configuration and a closed configuration for permitting or preventing the flow of a fluid, respectively.

The inlet opening of the first pumping chamber comprises an inlet valve and the outlet opening of the second pumping chamber comprises an outlet valve, these valves being movable between an open configuration and a closed configuration for allowing or preventing the flow of a fluid, respectively.

The pump further comprises an actuator group configured to mediate the passage of each valve from the closed configuration to the open configuration and to promote a pumping of the fluid from the first to the second pumping chamber.

Another method of the present invention is a method for pumping a fluid comprising the steps of:

A) preparing a pump to measure out a fluid according to the present invention;

B) pumping a quantity of fluid to be supplied from a feeding device to the first pumping chamber;

C) activating the actuator group by promoting the movement of the transfer valve from the closed configuration to the open configuration;

D) pumping the quantity of fluid to be supplied from the first pumping chamber to the second pumping chamber;

E) deactivating the actuator group by promoting the movement of the transfer valve from the open configuration to the closed configuration;

F) pumping the quantity of fluid to be supplied from the second pumping chamber to the using device.

Further features and advantages of the present invention will become more apparent from the description of an exemplary, but not exclusive, and therefore non-limiting preferred embodiment of a pump for measuring out, as illustrated in the appended figures, wherein:

- figure 1 shows a sectional view of a particular configuration of a pump for measuring out a fluid according to the present invention;

- figure 1b shows a sectional view of a further particular configuration of a pump for measuring out a fluid according to the present invention;

- figure 2 shows a sectional view of one of a detail of a pump for measuring out a fluid;

- figure 3 shows a sectional view of one of a further detail of a pump for measuring out a fluid;

- figure 4 shows a sectional view of a further detail of a pump for measuring out a fluid.

In the accompanying figures, in general, number 10 indicates a pump for the dosage of a fluid according to the present invention.

The pump 10 is particularly suitable for pumping a reducing element in a Selective Catalyst Reduction system for reducing the polluting emissions in diesel-cycle internal combustion engines.

This type of system usually uses compressed air devices to atomize a reducing element, such as a mixture of water and urea, inside a portion of the exhaust of a diesel-cycle internal combustion engine, dedicated to the development of a process of hydrolysis by which the nitric oxide cleaves into nitrogen and oxygen.

In particular, the pump 10 includes a first pumping chamber 11 and a second pumping chamber 12.

The first pumping chamber 11 has an outlet opening suitable for being placed in fluid communication with a feeding device of a fluid and an outlet opening.

The feeding device may be a container for a reducing element which must be atomized inside the exhaust of an internal combustion engine so as to catalyse a reduction reaction of the pollutants contained in the exhaust gases, products of the combustion process of the engine, so as to promote its degradation into inert compounds or in any case not harmful or dangerous for the environment and for people.

The inlet opening of the first pumping chamber 11 further comprises an inlet valve 13 being movable between an open configuration, wherein the feeding device is in fluid communication with the first pumping chamber 11 and a closed configuration wherein the feeding device is not in fluid communication with the first pumping chamber 11. In other words, the inlet valve 13 is configured to permit or prevent the unidirectional passage of a fluid from the feeding device to the first pumping chamber 11.

Operationally, as will be described in greater detail below, the inlet valve 13 will be open when it will be necessary to fill the first pumping chamber

11 and will instead be closed during an emptying step of the first pumping chamber 11 so as to guarantee that no fluid flows can occur from the first pumping chamber 11 towards the feeding device.

The second pumping chamber 12 has an inlet opening suitable for being placed in fluid communication with a using device of a fluid and an inlet opening.

The using device may be, for example, an exhaust of a diesel-cycle internal combustion engine.

The outlet opening of the second pumping chamber 12 further comprises an outlet valve 14 being movable between an open configuration wherein the second pumping chamber 12 is in fluid communication with the using device and a closed configuration wherein the second pumping chamber

12 is not in fluid communication with the using device.

In other words, the outlet valve 14 is configured to permit or prevent the unidirectional passage of a fluid from the second pumping chamber 12 to a using device.

Operationally, the inlet valve 14 will be closed when it will be necessary to fill the second pumping chamber 12 and will instead be open during an emptying step of the first pumping chamber 12 so as to guarantee that no fluid flows can occur from the using device towards the second pumping chamber 12.

The pump 10 further comprises a transfer valve 15, interposed between the outlet opening of the first pumping chamber 11 and the inlet opening of the second pumping chamber 12.

The transfer valve is movable between an open configuration, wherein the first pumping chamber 11 is in fluid communication with the second pumping chamber 12 and a closed configuration wherein the first pumping chamber 11 is not in fluid communication with the second pumping chamber 12.

Operationally, the transfer valve 15 will be closed when it will be necessary to fill the first pumping chamber 11 and to empty the second pumping chamber 12 and will instead be open when it will be necessary to promote the passage of a fluid from the first pumping chamber 11 to the second pumping chamber 12.

The transfer valve 15 also ensures that no fluid flows can occur from the second pumping chamber 12 towards the first pumping chamber 11.

Preferably, the valves 13, 14, 15 consist of an alumina 99% precision ball and a conical seat made using the same material.

The pump 10 further comprises an actuator group 16 configured to mediate the passage of each valve 13, 14, 15 from the closed configuration to the open configuration and to promote a pumping of the fluid from the first pumping chamber 11 to the second pumping chamber 12.

It is furthermore observed that the actuator group 16, by means of the opening / closing action of the valves, in particular those of inlet 13 and outlet 14, is further configured to recall a quantity of fluid to be supplied from the feeding device to the first pumping chamber 11 through the inlet valve 13 and to promote an ejection of the quantity of fluid to be supplied from the second pumping chamber 12 wards to the using device through the outlet valve 14.

In particular, the actuator group 16 comprises a piston 17 having a first end 17a, at least partially inserted in the first pumping chamber 11 , and a second end 17b, at least partially inserted in the second pumping chamber 12 and a bush 20 capable of preventing undesirable fluid flows from one pumping chamber to the other and itself constituting the passage opening between the transfer valve 15 and the second pumping chamber 12.

According to a possible embodiment, the piston 17 has a substantially cylindrical shape, arranged along a main development direction "X".

The piston 17 is movable between a first position, shown in detail in Fig. 1a, wherein the piston 17 is inserted into the first pumping chamber 11 , occupying a volume equal to a quantity of fluid to be supplied and a second position, shown in detail in Fig. 1b, wherein the piston is inserted into the second pumping chamber 12, occupying a volume equal to the quantity of fluid to be supplied.

In detail, when the piston 17 passes into the first position, the inlet valve 13 and the outlet valve 14 are in the closed configuration, whereas the transfer valve 15 is in the open configuration and when the piston 17 passes into the second configuration, the inlet valve 13 and the outlet valve 14 are in the open configuration, whereas the transfer valve 15 is in the closed configuration.

The actuator group 16 further comprises activation means 18, preferably of the electromagnetic type, suitable to promote the passage of the piston from the first to the second position and the elastic return means 19 suitable to promote the movement of the piston from the second to the first position.

According to a preferred embodiment, shown by way of non-limiting example in the accompanying figures, the activation means is a solenoid, whereas the elastic return means consist of a spring.

In other words, the activation means 18 can be activated by promoting the displacement of the piston 17 by overcoming the force of the elastic return means 19, thus compressing the fluid present in the first pumping chamber 11.

The inlet valve 13 is closed as the transfer valve 15 is being opened.

At the same time, in the second pumping chamber 12 the volume of the piston 17 entering the first pumping chamber 11 is missing.

The outlet valve 14 is closed and the fluid is transferred from the first pumping chamber 11 to the second pumping chamber 12 by the combined effect of the compression in the first pumping chamber 11 and of the depression in the second pumping chamber 12 which was generated due to the displacement of the piston 17.

When, on the other hand, the activation means 18 is deactivated, the force exerted by the elastic return means 19 is no longer balanced and overcome by the action of the activation device 18, and the piston 17 is brought back from the first to the second position.

During the step of returning to the second position of the piston 17, the transfer valve 15 is closed, in the first pumping chamber 11 a depression is created due to the increase in the available volume given by the outflow of the piston 17.

The inlet valve 13 opens and the difference in volume is balanced by the fluid recalled by the feeding device.

At the same time, in the second pumping chamber 12 the volume of the piston 17 which had penetrated into the first pumping chamber 11 is re transferred into the second pumping chamber 12, compressing the fluid therein.

As a result of this compression, the outlet valve 14 is opened and the fluid is transmitted in the direction of the using device, the return to the pumping chamber 11 being prevented by the transfer valve 15 in the closed condition and by the hydraulic seal between the bush 20 and the piston 17.

The pump 10 for measuring out a fluid according to the present invention advantageously presents a series of further expedients which are particularly suitable to improve the efficiency of the device, thus guaranteeing optimal precisions even in case of prolonged use over time, for example up to supplies of the reducing element in the order of 60000 litres.

To ensure the correct movement of the piston 17 from the first to the second position, the pump 10 comprises a bush 20 suitable to constrain the piston 17 to slide along a correct axial direction coinciding with the main development direction "X" of the piston 17 itself and simultaneously to perform the hydraulic sealing function to separate the two pumping chambers. The pump 10 further comprises a piston guide 31 suitable to prevent the occurrence of radial loads and vibrations during the working step of the activation device 18 which could compromise the correct operation of the pump 10.

In order to guarantee a constant and equal piston 17 stroke for all the produced pumps 10 without which the required measuring out accuracy could not be achieved, the pump 10 further comprises an upper end- stroke device 21 and a lower end-stroke device 22 suitable to define a maximum stroke of the piston 17 between the first and the second position.

In other words, when the piston 17, by means of the action of the actuator group 16, passes from the second to the first position, it is guided by the guides 20 and 31 and stopped by the upper end-stroke device 21 once the first position is reached, thus ensuring the correct operation of the device.

In the same way, when the actuator group 16 is deactivated, the piston 17 passes from the first to the second position and is stopped in its movement by the lower end-stroke device 22.

Preferably, the upper end-stroke device 21 and the lower end-stroke device 22 are made of rubber, in particular rubber having a hardness between 80 and 100 shores.

In order to guarantee an accurate measuring out of the fluid even in the presence of possible errors due to the geometrical constructional tolerances of the components of the pump 10, there is also an adjusting device 23, shown in detail in Fig. 2, which allows the lower end-stroke device 22 to be moved so as to vary the length, increasing or decreasing it, of the maximum stroke of the piston 17 between the first and the second position.

In particular, the adjusting device 23 can be provided by means of a screw-nut screw coupling which allows the lower end-stroke device 22 to be brought closer or further away from the upper end-stroke device 21. It is furthermore noted that, when in the second position, the piston 17 defines, in combination with the lower end-stroke device 22, a closing element of the outlet opening of the second pumping chamber 12.

In fact, it would otherwise be impossible to guarantee a perfect seal of the fluid for long periods of pump stop and with line pressures according to the specifications required for the correct operation of this type of device.

The applied solution is therefore that of completely closing the outlet opening of the second pumping chamber 12 with the second end 17b of the piston 17 which is in contact with the lower end-stroke device 22 and, thanks to the thrust provided by the elastic return means 19 acts as an additional valve for closing the pump 10.

However, whenever the piston 17 ends its stroke and abuts against the lower end-stroke device 22, between the latter and the outlet valve 14 it is possible to create a sealed chamber which could generate a suction effect which would slow down or prevent the starting of the piston 17 once the actuator group 16 has been activated.

Normally, the fluid present between the second portion 17b of the piston 17 and the outlet valve 14 should be pressurized when, in order to exit from the pump, it must exceed the opening pressure of the outlet valve 14, ensuring that no suction effect will occur.

As a further safeguard mechanism, to prevent the occurrence of the suction effect, according to a possible embodiment shown in detail in Fig. 3, the pump 10 comprises a valve-opening device 24 configured to abut on one part of the outlet valve 14 when the piston 17 is in its second position by contributing to maintain the open configuration of the outlet valve 14 so as to guarantee that no suction effect occurs.

According to a further aspect, the pump 10 according to the present invention is particularly suitable for operating in a particularly wide range of temperatures, preferably between -40°C and 85°C without being damaged or having its performance altered.

Within this range, it is therefore necessary to provide that the pump being stopped, the volume of the fluid contained in the pumping chambers 11 , 12 may change in phase.

The freezing of the fluid generates an expansion of its volume, thus generating a pressure which will stress the structure of the pump 10 up to the point of causing a probable rupture.

To avoid this possibility, as shown in detail in Fig. 4, the pump 10 according to the present invention comprises: a pump body 25 suitable to contain at least partially the actuator group 16; a valve body 26 suitable to contain the transfer valve 15 and a suction body 27 suitable to contain the inlet valve 13.

The pump body 25, the valve body 26 and the suction body 27 are respectively movable, preferably along the main development direction "X" of the piston 17.

During the freezing of a fluid contained in the pumping chambers 11 , 12, the bodies 25, 26, 27 are thrusted away from each other by the mutual increase of the volume due to freezing of the fluid present in the pump 10. In order to allow the return to a correct operating position of the various parts of the pump 10, following to the defrosting the fluid, the pump 10 comprises at least a second elastic return means suitable for promoting the repositioning of the bodies 25, 26, 27 and to cushion the movement of the pump body 25, the valve body 26 and the suction body 27, respectively, thus preventing an abrupt passage of the fluid inside the pump 10 to the solid phase from damaging the same.

With this system, the pumping chambers 11 , 12 therefore have the possibility of being able to expand when necessary, not constraining the parts to each other and of always guaranteeing the same length of the stroke of the piston 17 when the pump 10 starts to operate, i.e. when the fluid inside the pump is completely defrosted.

Advantageously, the load of the second elastic return means 28 is sized to a value such that no movements are allowed to the moving parts of the pump 10 when this is operating within the above-specified operating range.

Preferably, to guarantee an optimum movement of the parts of the pump 10, the second return means is made of a spring 28. To provide a good seal of the device even after the exposure to bad weather and potentially damaging atmospheric conditions, the pump 10 is provided preferably with a bellows seal 29, preferably made of elastomeric material.

In particular, the bellows seal 29 is associated to a coupling portion of the suction body 27 with a containment body 30 of the pump 10 and suitable to prevent dirt from entering inside the pump 10 from the external environment.

In other words, the presence of the bellows seal 29 allows to ensure that no entering of fluid or dust, in general impurities, occurs from the external environment towards the inside of the pump 10 itself, especially in the portion of the pump 10 wherein the suction body 27 is coupled to the containment body 30 which has the function of enclosing the components of the pump 10 and isolating them from the external environment.

The pump 10 further comprises a bush 20, preferably made of polyetherketone loaded with mineral additives which increase its tribological properties, acting as a piston guide and distributing the fluid flow from a pumping chamber to the other as well as having a function of sealing, guaranteed exclusively by a precise coupling between its internal diameter and the external diameter of the piston 17, and a second piston guide 31 , preferably made of the same material as the bush 20, which only performs the function of guiding the piston avoiding harmful radial loads during the working step of the activation means 18.

The second piston guide 31 have to guarantee the passage of the fluid not effectively pumped, as otherwise there would be the risk to prevent the fluid from flowing outwards, the passage section of the bush is therefore preferably equal to at least 1.5 times the smallest passage section crossed by the fluid exiting the second pumping chamber 12.

It is also an object of the present invention method for pumping which is particularly suitable for being actuated by a pump 10 according to the above description.

The pumping method comprises the steps of:

A) preparing a pump to measure out a fluid according to the above;

B) pumping a quantity of fluid to be supplied from a feeding device to the first pumping chamber 11 ;

C) activating the actuator group 16 by promoting the movement of the transfer valve 15 from the closed configuration to the open configuration;

D) pumping the quantity of fluid to be supplied from the first pumping chamber 11 to the second pumping chamber 12;

E) deactivating the actuator group 16 by promoting the movement of the transfer valve 15 from the open configuration to the closed configuration;

F) pumping the quantity of fluid to be supplied from the second pumping chamber 12 to the using device.

In other words, the pumping of the fluid from the feeding device to the using device takes place through the movement, by the actuator group 16, of the piston 17 from the first to the second position, directly causing the opening and closing of the inlet valves 13, valve of output 14 and transfer valve 15.

By way of example, consider an initial pump stop situation wherein the actuator group 16 is deactivated, the piston 17 is in the second position and there is a quantity of fluid to be supplied inside the first pumping chamber 11.

Once the actuator group 16 has been activated, the activation means 18 is energized causing the piston 17 to pass from the second position to the first position, overcoming the force exerted by the elastic return means 19. The fluid present in the first pumping chamber 11 is compressed, thereby exerting a pressure on the inlet valve 13, ensuring its closure, while the transfer valve 15 is being opened.

At the same time, in the second pumping chamber 12 the volume of the piston 17 entering the first pumping chamber 11 is missing, thus creating a depression which ensures the closure of the outlet valve 14.

The combined action exerted by the pressure piston 17 on the first pumping chamber 11 and of depression on the second pumping chamber 12 due to the volume displacement thereof, equal and equivalent to the volume of the quantity of fluid to be supplied, from a chamber to the other, promotes the pumping of the quantity of fluid to be supplied through the transfer valve 15.

When the piston 17 reaches the upper end-stroke device 21 , going to completely obstruct the fluid passage opening from the first pumping chamber to the second one, a sharp increase of the pressure in the direction of the first pumping chamber 11 instantly closes the transfer valve 15, completely isolating the two chambers 11 , 12.

This operation ensures a high hydraulic efficiency as well as preventing any hammering due to rapid fluid displacements from creating pressure imbalances between one chamber and the other, thus avoiding the occurrence of over-pumping or overdosing phenomena or, vice versa, uncontrolled losses of hydraulic efficiency.

The pressure increase in the first pumping chamber 11 also avoids the occurrence of bonding phenomena due to the suction effect between the piston 17 and the upper end-stroke device 21 and counteracts phenomena of magnetic resorption due to the magnetic hysteresis of the materials constituting the pump 10.

Subsequently, the actuator group 16 is deactivated, interrupting the energization of the activation means 18.

The piston 17 then passes from the first position to the second position due to the force exerted by the elastic return means 19, no longer opposed by the force exerted on the piston 17 by the activation means 18. The fluid present in the second pumping chamber 12 is compressed, thereby simultaneously exerting a pressure on the outlet valve 14, ensuring its opening and therefore the passage of the fluid towards a using device, while the transfer valve 15 remains closed, thus preventing the return of the fluid in the first pumping chamber 11.

At the same time, in the first pumping chamber 11 the volume of the piston 17 which is penetrating into the second pumping chamber 12 is missing, creating a depression which guarantees the opening of the inlet valve 13 thus allowing to recall a quantity of fluid which is equal to the quantity of fluid to be supplied in the first pumping chamber 11 from the feeding device.

It is therefore evident that step B) and the step F) occur simultaneously.

In other words, during the activation of the actuator group 16, the quantity of fluid to be supplied passes from the first pumping chamber 11 to the second pumping chamber 12, whereas when the actuator group 16 is deactivated, the quantity of fluid to be supplied is pumped from the second pumping chamber 12 to the using device, and the same quantity of fluid is restored in the first pumping chamber 11.

In order to allow the correct operation of the device it is therefore evident that, due to the effect of the actuator group 16, by moving the piston 17 during the phase step F) the transfer valve 15 is in the closed configuration while the inlet 13 and closing 14 valves are in open configuration.

Likewise, during the step D) the transfer valve 15 is in its open configuration, whereas the inlet 13 and outlet 14 valves are in closed configuration.

However, it may happen that due to defects, malfunctions or other, following the step B), in the first pumping chamber 11 there is a quantity of fluid which is lower than the quantity of fluid to be supplied.

In the case just described, i.e. if the volume of the piston 17 which is missing in the second pumping chamber 12 is not balanced by the same quantity of fluid volume coming from the first pumping chamber 11 , during the step D), in the second pumping chamber 12, a vacuum is created so as to allow the inlet valve 13 to be sufficiently opened to rebalance the pressure by feeding other fluid from the feeding device into the pump 10 until the correct achievement of the second pumping chamber 12 of the quantity of fluid to be supplied.

In the case just described, it is evident that a configuration could occur during step D) wherein transfer valve 15 and the inlet valve 13 are in open configuration, whereas the closing valve 14 is in closed configuration.

In these systems, it is essential that the quantity of the reducing element injected is extremely accurate and proportional to the quantity of nitrogen oxide to be reduced at any time.

In particular, the pump 10 for measuring out of the present invention, and the relating method allow to obtain precision levels with errors lower than 5% over the entire range of the required flow rates, of the entre supply voltage range and of the entire range of admissible pressures both on delivery and in suction.

Even more particularly, the present invention allows to obtain precision levels with errors lower than 2%.

Advantageously, the present invention provides a pump 10 for measuring out a fluid capable of guaranteeing high levels of precision and high operating efficiency even after a considerable number of drives, for example for a pump with a maximum displacement of 0.0625 cc even after the 60000 L of supply equal to about 1 billion complete strokes of the piston 17.

The presence of the double pumping chamber ensures the high precision of the quantity of fluid supplied by the pump 10.

The presence of the adjusting device 23 ensures the correct operation of the pump 10 independently of any defects / differences in the single components of the pumps 10.

The modularity generated by the subdivision of the various components in the bodies 25, 26, 27, and their respective mobility ensures the correct operation of the pump also following a freezing event of the fluid contained therein.

Finally, the presence of the valve-opening device 24 ensures, in particular during the periods of pump stop, wherein it is necessary to ensure the correct closure of the outlet opening of the second pumping chamber 12, the non-occurrence of suction effects which could cause a delay in the activation of the piston 17 movement.