CH703969A1 - volumetric liquid pump comprising a cartridge heater. - Google Patents

Abstract

Volumetric liquid pump (1) comprising: - a cylinder (24) - a liquid inlet valve in said cylinder (24) - a liquid expulsion valve out of said cylinder (24) - a piston (52) actuated by a transmission tube (51) and sliding in said cylinder (24) so as to suck said liquid into said cylinder (24), then to expel it from said cylinder (24), characterized in that said cylinder (24) comprises at least one heating cartridge (41) for heating the liquid in said cylinder (24). The device and method of the invention can be used for example for a hot drink dispenser, in particular a coffee machine. The liquid pump of the invention can also be used when the positon slides in a horizontal direction.

Description

Technical area

The present invention relates to a volumetric liquid pump comprising a heating cartridge. This pump is used to pump liquid, heat it and also measure volume.

State of the art

[0002] Numerous examples of liquid pumps operating according to different principles are known. There are also different types of water heaters. Many coffee machines use a tank in which the water is preheated before being pumped through the coffee powder and then poured into the cups. These devices require preheating a larger volume of water than that which will ultimately be used, which causes energy waste. Conversely, when a volume of coffee is required that is greater than the capacity of the tank, it is necessary to wait after filling until the newly introduced water has been heated.

Also known are continuous liquid heating devices in which the water is heated during its passage through a tube or pipe. Such devices are described for example in the patent application EP-A1-1380243 (Nestec SA), which illustrates a liquid heating module comprising a hollow tube coated with at least two heating resistors, for example wires or inks conductors deposited on a substrate. A similar solution is also described in EP-A1-1 097 663.

The solutions of the prior art generally require a pump to circulate the water in a heating tube or a thermoblock, and a flow meter to control the amount of water supplied. The complete device therefore comprises many discrete discrete parts, complex to combine, and whose assembly requires a large volume. Moreover, the temperature of the water depends both on the electric current in the heating module and the flow rate of the water in the tube, which requires rather complex regulation.

The patent application FR 2 780 262 discloses a coffee machine comprising a hollow piston pump driven by an electromagnetic motor. The hollow piston traversed by the liquid is difficult to clean; in addition, it does not allow to move a constant volume of water with each actuation. A flowmeter is therefore required, formed in this case of a crazy wheel with blades rotated by the flow of liquid.

Other examples of a hot drink dispenser comprising a piston pump are described in US Pat. Nos. 2,654,505 and 2,012,636.

The patent application EP-A1-496 939 discloses another pump for a coffee machine comprising a piston sliding in a cylinder actuated by a motor and an actuator. The stroke of the piston, which determines the volume of liquid sucked and then rejected in the cylinder, is controlled using micro-connectors or an encoder connected to the engine. The signals from the microswitches or the encoder are processed by electronics that generate control signals for the motor. The volume of water in the cylinder is heated using a resistive wire wound around the outer surface of the cylinder and traversed by an electric current.

This arrangement makes it possible to heat the liquid directly inside the pump, so that an additional heating tube is not required. Moreover, the use of a piston pump makes it possible to easily control the volume of liquid aspirated, simply by modifying the stroke of the piston. However, the time it takes to get a cup of hot coffee is important for several reasons:

First, the tube is heated using a discrete wire wound around the cylinder. Only a part of the heat emitted by the wire is transmitted to the cylinder and then to the liquid; the rest is dissipated in the air. The thermal resistance between the wire and the cylinder is indeed important, unless expensive measurements, for example the use of an electrically conductive paste, are implemented.

On the other hand, the heating of the cylinder begins only when it is full of liquid. The significant thermal inertia of the heating wire and the cylinder slows the heat transfer and increases the time required to heat the volume of liquid sucked. This inertia also makes it difficult to precisely maintain a constant temperature of the liquid; the reaction time of the system is too important, especially when the external conditions change, for example during the evacuation of the liquid. Moreover, because of the high thermal inertia and the thermal resistance between the wire and the cylinder, the system remains hot for a relatively long time even when the electric current is interrupted.

Finally, the heat of the resistance is transmitted over the entire length of the cylinder, even when a small amount of liquid must be heated for an espresso for example. The turns of the resistance above the piston, in the empty zone of liquid, provide a heat which is scarcely used and which is transmitted to the environment at a loss. If the wastage of electric current that results can be tolerated in a plant powered by the mains electricity, this is not the case in the case of a machine intended to be powered by a power source. autonomous, for example a car battery.

WO2009 / 087 203 discloses a liquid pump comprising an electric circuit for heating the cylinder with at least two branches to electrically heat the liquid in the cylinder, the branches being made in the form of electrically conductive thin track deposited on or in the wall of the cylinder and occupying different longitudinal portions along said cylinder, to control the longitudinal portion of the heated cylinder by selecting the branches traversed by a current depending on the volume of heated liquid to be produced.

This pump therefore allows to deliver a controlled volume of water, at a controlled flow rate, and with a constant temperature throughout the flow. It is known that the quality of a coffee depends greatly on the temperature of the water passing through the powder; a precisely controlled and constant temperature throughout the flow through the powder can significantly improve the quality of coffee obtained. Indeed, a temperature too low does not allow the water to carry all the aromas of the coffee, while a too high temperature burns some aromas, or even produces vapor bubbles which simply pass through the coffee powder without take the taste.

With this pump it is possible to choose the longitudinal portion of the cylinder which is heated at each moment by selecting the branches supplied with current. Thus, a number of branches will be fed depending on the amount of volume to be heated, so as to avoid dissipating heat over large portions of the cylinder above the upper stroke limit of the piston. In one example, only the bottom half of the cylinder is heated with a branch when it is desired to produce a half volume of hot water cylinder.

This pump, however, has various disadvantages. First of all, the industrial manufacture of conductive tracks on a cylinder proves, unexpectedly, delicate and expensive.

On the other hand, in the case of an installation with the cylinder in a horizontal position, that is to say when the piston slides in a horizontal direction, and that the cylinder contains little liquid, steam that is formed above the liquid in the cylinder can destroy or detach the resistive branches. Such a horizontal installation is however useful for certain configurations of coffee machine, for example in the case of use in a car, a caravan, a truck or any electrically autonomous vehicle.

The horizontal position of the pump is also advantageous for reducing the temperature gradient of the liquid, which improves the quality of coffee produced and reduces energy waste.

Such horizontal use of the pump described in WO2009 / 087 203 is however not indicated, since its correct operation is guaranteed only in the case where its piston slides in a vertical direction.

Furthermore, in WO2009 / 087 203 a temperature sensor measures the temperature of the liquid output to interrupt or modify the electric current branches depending on the temperature of the liquid, for example 94 ° C. However, if the environment where the pump is placed is cold, at the beginning the temperature measured by the probe does not correspond to the temperature of the liquid, since this temperature also depends on the external temperature.

There is therefore a need for a liquid pump that allows to deliver a volume of controlled water with a constant temperature throughout the flow as the pump of WO2009 / 087 203, but which can also be used when the piston slides in a horizontal direction.

There is also a need for a liquid pump that allows a more effective measurement of the temperature of the heated liquid.

Brief summary of the invention

An object of the present invention is to avoid or mitigate one or more disadvantages mentioned above.

According to the invention, these objects are achieved in particular by means of a liquid pump according to claim 1 and a method for heating a determined volume of liquid of a cylinder according to claim 15.

The pump according to the invention comprises a cylinder, a cylinder head in which there is an intake valve and a valve for expelling the liquid, a piston actuated by a transmission tube. The piston slides in the cylinder so as to suck and / or expel the liquid in respectively out of the cylinder. At least one heating cartridge is present in the chamber to heat the liquid present. Advantageously, the transmission tube slides around the heating cartridge of which at least a portion is immersed in the liquid, especially when the piston is recessed so as to allow the filling of the cylinder. The heat transfer from the cartridge to the liquid is thus optimal.

Heating cartridges are in themselves known in fields far removed from the field of liquid pumps for coffee machine, for example in the field of metallurgy or the production of plastic. The use of such a heating cartridge within a volumetric liquid pump, for example for a hot drink dispenser, especially a coffee machine, including a coffee machine for car or caravan etc., is completely new and solves the problems mentioned, including the problem of using a pump in which the piston slides in the horizontal direction only.

This cartridge may comprise one or more heating zones, corresponding to one or more electrical circuits. In another variant it may comprise a progressive heating zone, corresponding to a non-regularly wound resistance. In this way it is possible not only to obtain the same effects of "ad hoc" heating of the liquid according to its volume, thereby reducing the energy waste, but also to use the pump when the piston slides in a horizontal direction, this which allows a more homogeneous distribution of the temperature in the liquid to be heated thus making it possible to better adapt to the use of such a pump in a car or a caravan for example.

In a variant, the pump according to the invention comprises several resistors in parallel in the same heating cartridge, or several heating cartridges, to heat more quickly a larger amount of liquid. In this way it is thus possible to turn on a coffee machine comprising such a pump and to obtain almost instantaneous heating. For example, it is possible to mount three heating cartridges angularly spaced 120 °, or four heating cartridges spaced 90 °, in a single volume of water or in several independent volumes of water, or crossed successively by the same portion of water. liquid.

In another variant each heating cartridge comprises a temperature sensor for measuring the temperature of the liquid: unlike known solutions, this measurement is effective and accurate, since it is performed in the center of the volume of heated liquid.

In another variant the pump comprises a position sensor, for example an angular sensor arranged to cooperate with the teeth of a driving pulley which rotates through an electric motor a thrust screw for moving the piston, in order to measure the position of the piston and, therefore, how much liquid has been sucked up and / or expelled. A light barrier and / or a switch may advantageously be provided on the transmission tube to determine the zero point of the stroke of the piston.

The sealing of the piston is guaranteed by means of at least one seal, for example of the X-ring type. In a preferred embodiment two seals are used, one between the piston and the transmission tube, the other between the piston and the cylinder. The "X" shaped section of the preferential seal avoids possible twisting movements. Other geometries of joints are possible.

Brief description of the figures

Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which: <tb> Fig. 1 <sep> illustrates an overview of an embodiment of the pump according to the invention. <tb> Fig. 2 <sep> illustrates an exploded view of the pump of FIG. 1. <tb> Fig. 3 <sep> illustrates an exploded view of an embodiment of the third part or transmission part of the pump according to the invention. <tb> Fig. 4 <sep> illustrates an exploded view of an embodiment of the first piece of the complete pump or cylinder head (valve, seal and cartridge assembly). <tb> Fig. <Sep> illustrates an exploded view of one embodiment of the complete piston (transmission tube assembly, piston and seals). <tb> Fig. 6 <sep> illustrates an embodiment of the heating cartridge, comprising two electrical circuits. <tb> Fig. 7 <sep> illustrates another embodiment of the heating cartridge, comprising a non-regularly wound resistor.

Example (s) of embodiment of the invention

FIG. 1 illustrates an overview of one embodiment of the pump according to the invention: it comprises a first part 4 or complete breech, exploded in FIG. 4, a second part 2 which comprises all the mounting accessories of the pump and a third part 3 or transmission, exploded in FIG. 3.

As illustrated in FIG. 2, the first piece 4 or complete breech, which is integral with at least one heating cartridge 41, is inserted into the part 5, detailed in FIG. 5: in particular the cartridge 41 is inserted into a longitudinal hole through the piston 52 and into the transmission tube 51. The piston 52 is actuated by the movable transmission tube 51. The latter is inserted in a guide 22 of anti-rotation square section which engages the endless thrust screw 31 of the part 3. The rotation of this screw 31 determines the displacement of the piston 52 of the pump; its direction of rotation determines the direction of movement. A portion of the heating cartridge 41 is thus housed in the tube 51 while the upper portion of this cartridge is directly immersed in the liquid to be heated. The depth of immersion of the cartridge in the hole of the tube 51 depends on the longitudinal position of this tube.

As detailed in FIG. 3, the screw 31 is rotated by a motor 32 through a driving pulley 37, a driven pulley 36 and a belt 35, for example a toothed belt. Each pulley may be provided with a clipping washer 38, for example a Starlock washer, for a quick and efficient assembly on the shaft of the electric motor 32. The two pulleys and the belt make it possible to reduce the speed and an increase in the torque transmitted by the motor 32 to the screw 31. Other types of gearless motors, for example gear reducers, can be used. Similarly it is possible to mount the motor or gear motor directly online without using a reference.

The motor 32 is preferably a linear electric cylinder capable of moving alternately in one direction and then in the other when an electric current is provided. According to a preferred feature of the invention, the motor can be powered at 12 or 24 volts, or at a lower voltage, which allows it to be used in an automobile with the current produced by a battery. Other DC or alternating voltage sources are also conceivable within the scope of the invention. Rotary motors with a worm, cam, connecting rod or toothed belt system for converting rotation into a translation, or pneumatic cylinders can also be employed.

In a preferred embodiment the motor 32 comprises a geared motor to change the speed ratio or / and torque provided.

The pulleys 36, 37, the belt 35 and the washers are engaged in a housing 33 through screws 34, for example screws of the tapered Torx type. This housing cooperates with the motor 32 and, through the nut 312 and the bearing 310, with the thrust screw 31.

The third transmission part 3 in a variant may comprise a position sensor 39 arranged to cooperate with the driving pulley 37 to measure the position of the piston 52 in the cylinder 24 and, therefore, how much liquid has been sucked and / or expelled. In a preferred embodiment, this circuit 39 comprises an angular encoder which, according to the number of turns made by the screw 31 during its rotation, determines the position of the piston 52 during its stroke.

In another variant this position sensor 39 is replaced by any other position sensor, for example a Hall sensor, placed in the cylinder 24. Angular position sensors mounted on other rotating elements of the geared motor or the device, or linear position sensors directly measuring the position of the piston, can also be employed.

In a variant, the transmission tube 51 comprises a light barrier and / or a switch or any other means adapted to determine the zero point of the piston stroke.

In a preferred embodiment, the stroke of the piston 52 can be controlled to vary the amount of liquid aspirated by the valve 42 and expelled via the valve 43. The stroke is preferably controlled by a microcontroller not shown by modifying the duration of supply of the motor 32. The control can be carried out in open circuit, that is to say by applying a pulse duration which depends solely on the set value chosen for the stroke and the volume, or preferably in a closed circuit with a feedback loop taking into account a measurement value supplied by the circuit or the position sensor 39.

FIG. 2 further illustrates a second part 2 of the pump, which includes its mounting accessories. These accessories comprise a cylinder 24, intended to contain liquid, fixed through a square spacer 23 to a cover 20 through screws 21. The cylinder 24 is surrounded by one or more traction rods, which cooperate with screws 26, to ensure stability at the pump and maintain its parts.

FIG. 4 illustrates an exploded view of an embodiment of the first part of the pump or complete cylinder head (assembly valves, seals and cartridge): the cylinder head 40 has two holes for respectively engaging the intake valve 42 and the valve of expulsion 43 of the liquid. In a preferred embodiment these valves 42, 43 are non-return valves.

The yoke 40 cooperates through an inner seal 46, for example an O-ring, with at least one heating cartridge 41 and, through an outer seal 47, for example an O-ring, with the cylinder 24 to guarantee the tightness.

In a variant, the heating cartridge 41, detailed in FIG. 6, may comprise one or more heating zones, corresponding to one or more electrical circuits 410, 411, for example resistive circuits. In another variant, illustrated in FIG. 7, it may comprise a progressive zone of heating, corresponding to a resistor 412 resistivity variable along its length. In both cases it is possible to obtain an "ad hoc" heating of the liquid according to its volume, thereby reducing the energy waste: for example if the pump according to the invention is used in a hot drink dispenser and after the control of a cappuccino an espresso is controlled, the heating cartridge 41 can heat only a reduced portion of the cylinder, lower than the heated portion for the cappuccino. It is also possible to reduce the heating of the cartridge portion inserted into the transmission tube 51, and further heat the cartridge portion immersed in the liquid to be heated. The portion of heated cartridge, and the current flowing in this cartridge, may further vary during the movement of the piston.

The heating cartridge 41 includes a thermocouple which can be integrated into the cartridge itself. In one variant, such a cartridge 41 may comprise an unillustrated temperature sensor for measuring the temperature of the liquid. The temperature measurement thus carried out is precise and effective, since it is carried out in the center of the volume of liquid, avoiding that the temperature of the environment can modify it in a wrong way.

The choice of the number of heating zones to be supplied with current may also depend on the temperature of the desired liquid. In general, the heating power, and therefore the time required to obtain a given liquid temperature, can be controlled by acting on one or more of the following parameters: Number of electrical circuits 410, 411 supplied with current Connection of electrical circuits 410, 411 to each other (series, parallel, etc.) Duration of Current in Electrical Circuits 410, 411. Some electrical circuits 410, 411 may be powered longer, or differently, than others. Intensity of current in each electrical circuit 410, 411 or resistor 412, or modulation of this intensity as a function of time.

The choice of the above parameters depends on the volume of liquid to be heated and the set temperature introduced with a control circuit 12 not shown, and possibly the initial temperature of the cylinder if it is known. The temperature sensor of the cartridge 41 or an external temperature sensor may furthermore be used to measure the temperature of the liquid, in order to interrupt or modify the electric current as a function of the measured temperature and thus to carry out a control in closed loop.

The external dimensions of the cartridge 41 can be defined very precisely and adapted to the pump: for example in a variant its outer diameter can be normalized and even rectified, hence a simplification of the seal with the piston .

In a variant, the pump according to the invention may comprise several heating cartridges 41 in parallel, either to heat more liquid or to heat the same amount of liquid in a lower time.

The presence of such a cartridge also makes the pump safer, since the source of heat is internal to the transmission tube 51 and is not directly accessible by a user, which reduces the risk of burns.

Advantageously, the pump comprises an electronic circuit 8 not shown, for example a microcontroller controlled by a computer program or an FPGA circuit, which preferably controls the following events: Opening and closing valves 42, 43. Motor supply 32 so as to cause the displacement of the piston 52 Control of the different heating zones 410, 411, 412 of the heating cartridge 41 Taking into account the signals provided by the position sensor 39 of the piston, by the temperature sensor, and by a not shown control circuit for entering set values for the volume to be heated and / or the temperature to be obtained.

FIG. 5 illustrates an exploded view of an embodiment of the part 5 of the pump according to the invention, comprising the transmission tube 51, in which at least one heating cartridge 41 is engaged, which at one end cooperates with a nut. 50 which prevents its rotation, and at the other end with the piston 52. An inner ring 53 in the form of a ring ensures the seal between the piston 52 and the transmission tube 51. An outer seal 54 ensures sealing between the piston 52 and the cylinder 24, Advantageously the section of these seals 53, 54 may be shaped "X" - it is therefore "X-ring" joints - to avoid torsional movements.

In another variant the pump may comprise two or more pistons advantageously working out of phase to transfer and heat several times controlled amounts of liquid. This makes it possible to supply a hot liquid continuously without any dead point when filling the piston. Moreover, by modifying the number of pistons actually used, it is possible to control the volume of heated and transferred liquid. The number of pistons used can be modified using numerical controls to control the valves that must be opened or closed during each cycle, and possibly the pistons that need to be moved. The different pistons can be driven by the same engine or cylinder, or by individual cylinders. The race of the different postons can be identical, or different.

It is also possible to use a double-acting piston, which sucks and represses the liquid continuously to reduce the pulling time. In this case the pump will include two cylinder heads, two intake valves and two expulsion valves.

In an advantageous embodiment, the pressure of the liquid ejected from the cylinder is also controlled by means of a reaction loop, in order to use a pressure of the liquid through the beverage powder adapted to the type of liquid. desired drink. The pressure of the liquid directly influences the quality of the coffee or drink. For this purpose, the device of the invention advantageously comprises a pressure sensor downstream of the cylinder, not shown, providing a measurement value used by a control circuit to control the current applied to the piston translation system and thus obtain a constant liquid pressure during the evacuation and close to the set point depending on the desired beverage.

We will now describe the process used to produce a desired amount of hot liquid. In a first step, at least one heating zone 140, 141, 142 is activated in order to circulate an electric current in the heating cartridge 41, so as to preheat the cylinder. The heat generated by the heating cartridge 41 is transmitted to the corresponding portion of the walls of the cylinder 24. Simultaneously, or shortly before or after, the inlet valve 42 is opened while the expulsion valve 43 is closed, by electromechanically under the control of an electronic control circuit, or mechanically, for example by means of springs.

The piston 52 is then raised under the action of the motor 32, so as to suck the liquid inside the cylinder 24 and through the intake valve 42. The heating of the cylinder is preferably continued at course of aspiration. The stroke of the piston 52 is preferably regulated to correspond to the volume of liquid to be produced using the open loop control or closed feedback loop discussed above.

When the piston 52 has reached the end in stroke or at the height corresponding to the desired volume of liquid, it is preferably maintained at this position for the time necessary for heating the liquid to the desired temperature. This time can be determined according to the volume of liquid, or preferably interrupted when the cartridge temperature probe or an external probe indicates that the liquid has reached the desired temperature, for example 94 ° C for the coffee.

The electric current injected into the circuit, as well as the number of electrical circuits traversed by a current, can be regulated depending on the volume of liquid to be heated and / or the target temperature to be reached. The inlet valve 42 is preferably closed as soon as the piston 52 has reached its maximum height, in order to prevent the heated liquid from leaving the intake channel or the heat escaping by convection or mixture of liquid.

The expulsion valve 43 is then opened, and the piston 52 descended so as to expel the heated liquid. The heating of the cylinder can be maintained and regulated during this expulsion phase so as to ensure a constant temperature of the liquid throughout the expulsion. In a preferred embodiment, the heating is interrupted, or at least reduced by decreasing the electric current, before the complete expulsion of the liquid out of the cylinder. This exploits the thermal inertia of the cylinder and it avoids transmitting heat to the cylinder which will not have time to be communicated to the liquid. In one variant, the speeds during aspiration or expulsion may be variable to allow the desired modulation of the pressure / depression as well as the flow rates of the liquid.

The interruption or the rapid reduction of the heating also makes it possible to avoid excessive temperature differences between the last drops of the liquid expelled and those leaving the cylinder first, which allows for example to avoid production. unnecessary vapor by evaporation of the last drops of liquid. It is also possible to modify the electrical connections of the heating circuit during the displacement of the piston, and for example to interrupt more quickly the supply of printed tracks which cover the bottom of the emptied cylinder first.

The device and method of the invention can be used for example for a hot drink dispenser, including a coffee machine, including a coffee machine for car or caravan or mobile home, or all electrically autonomous vehicles such as planes, taxi, trains, boats, etc. A similar pump can also be used for the dosing of heated liquid, in the food industry, for gluing with a heated glue, for the evacuation of condensates, etc.

Reference numbers used in the figures

[0064] <Tb> 1 <September> Pump <tb> 2 <sep> Second piece or set of mounting accessories <Tb> 20 <September> Cover <tb> 21 <sep> Screw for the lid <tb> 22 <sep> Square element with guide <tb> 23 <sep> Square Spacer <tb> 24 <sep> Traction cylinder <tb> 25 <sep> Traction rod (s) <tb> 26 <sep> Screws for pull rods <tb> 3 <sep> Third part or part of transmission <tb> 31 <sep> Thrust screws <Tb> 310 <September> Bowling <Tb> 312 <September> Nut <Tb> 32 <September> Motor <Tb> 33 <September> Carter <tb> 34 <sep> Crankcase screw <Tb> 35 <September> Belt <tb> 36 <sep> Led pulley <tb> 37 <sep> Pulley leading <Tb> 38 <September> Washer <tb> 39 <sep> Position sensor <tb> 4 <sep> First piece or complete breech (set of valves, seals and cartridge) <Tb> 40 <September> Cylinder Head <tb> 41 <sep> Heating cartridge <tb> 410 <sep> First electric circuit <tb> 411 <sep> Second electrical circuit <tb> 412 <sep> Non-regular wound resistance <tb> 42 <sep> Intake valve <tb> 43 <sep> Deportation valve <tb> 46 <sep> O-ring internal cylinder head gasket <tb> 47 <sep> O-ring external cylinder head gasket <tb> 5 <sep> Complete piston (transmission tube assembly, piston and seals) <tb> 50 <sep> Anti-rotation nut <tb> 51 <sep> Transmission tube <Tb> 52 <September> Piston <tb> 53 <sep> Internal piston ring X-ring <tb> 54 <sep> External piston seal X-ring

Claims (17)

1. Volumetric liquid pump (1) comprising: a cylinder (24) An inlet valve (42) for liquid in said cylinder (24) An expulsion valve (43) for the liquid out of said cylinder (24) A piston (52) actuated by a transmission tube (51) and sliding in said cylinder (24) so as to suck said liquid into said cylinder (24) and then expel it from said cylinder (24) characterized in that said transmission tube (51) slides along at least one heating cartridge (41) to heat the liquid in said cylinder (24). 2. The pump of claim 1, said heating cartridge (41) comprising one or more heating zones. 3. The pump according to claim 2, said one or more zones corresponding to one or more electrical circuits (410; 411) controllable individually to circulate electric currents therein. 4. The pump of claim 1, said heating cartridge (41) having a resistor (412) whose resistivity varies along the length of the cartridge. 5. The pump according to one of the preceding claims, said pump comprising at least two heating cartridges (41) in parallel. 6. The pump according to one of the preceding claims, said heating cartridge (41) comprising a temperature sensor for measuring the temperature of said liquid. 7. The pump according to one of the preceding claims, said heating cartridge (41) being contained in a transmission tube (51) around which said piston (52) slides. 8. The pump according to one of the preceding claims, said piston (52) being actuated by an electric motor (32), the stroke of the piston being adjustable depending on the volume of heated liquid to be produced. 9. The pump according to the preceding claim, comprising at least one driving pulley (37), a driven pulley (36), a belt (35) and a thrust screw (31) which cooperate with said electric motor (32). 10. The pump according to the preceding claim, comprising a position sensor (39) arranged to cooperate with said driving pulley (37) to measure the position of said piston (52) and how much liquid has been sucked and / or expelled. 11. The pump according to the preceding claim, said transmission tube (51) comprising a light barrier and / or a switch for determining the zero point of the stroke of said piston (52). The pump according to one of claims 7 to 11, comprising an X-ring seal (53) between said piston (52) and said transmission tube (51) and an X-ring seal (54) between said piston ( 52) and said cylinder (24). 13. The pump according to one of claims 10 to 12, comprising an electronic circuit which controls at least one of the following events: - Opening and closing said intake valves (42) and expulsion (43) Powering said motor (32) so as to cause the displacement of said piston (42) Controlling said zones (410, 411, 412) of said heating cartridge (41) - Taking into account the signals provided by said position sensor (39) of said piston (52), by said temperature sensor, and by a control circuit for entering set values for the volume to be heated and / or the temperature to obtain. 14. The pump according to one of the preceding claims, said piston (52) being a double-acting piston. A method of heating a predetermined volume of liquid of a cylinder (24), comprising the steps of: - Heating at least a portion of at least one heating cartridge (41) in said cylinder (24) to heat said liquid - Opening a liquid inlet valve (42) to allow liquid to enter said cylinder (24), Longitudinal displacement in a first direction of a piston (52) in said cylinder (24), so as to suck said determined volume of liquid into said cylinder (24), Closing said inlet valve (42) and opening an expulsion valve (43), - Longitudinal displacement in a second direction opposite to said first direction of said piston (52) in said cylinder (24), so as to expel the heated liquid out of said cylinder. 16. The method according to the preceding claim, said heating of at least a portion of at least one heating cartridge comprising the circulation of an electric current in one or more electrical circuits (410, 411) of said heating cartridge (41). . The method of claim 15, said heating of at least a portion of at least one heating cartridge comprises circulating an electric current in a variable resistivity resistor (412) in said cartridge (41).