WO2023038529A2

WO2023038529A2 - Engine for a liquid dispensing device and liquid dispensing device including such engine

Info

Publication number: WO2023038529A2
Application number: PCT/NL2022/050516
Authority: WO
Inventors: Paulo Nervo; Lukas Jacob Willem VAN DEN HEUVEL
Original assignee: Dispensing Technologies BV
Current assignee: Dispensing Technologies BV
Priority date: 2021-09-13
Filing date: 2022-09-13
Publication date: 2023-03-16
Anticipated expiration: 2024-03-13
Also published as: NL2029181B1; WO2023038529A3; CN219651843U

Abstract

The invention relates to an engine for a liquid dispensing device, comprising: a frame; a pump chamber arranged in the frame; a piston movably arranged in the pump chamber; a trigger movably connected to the frame and operatively coupled with the piston; a nozzle; an outlet channel arranged in the frame and connecting the pump chamber to the nozzle; an outlet valve operatively connected with the outlet channel; and a pair of springs mounted or mountable on opposite sides of the frame and engaging or engageable with the trigger; wherein the springs are connected to each other by a bridge piece extending between the opposite sides of the frame and configured for securing the outlet valve to the frame. The invention further relates to a method of assembling an engine for a liquid dispensing device, comprising the steps of: providing a frame including a pump chamber and an outlet channel arranged therein; movably arranging a piston in the pump chamber; movably connecting a trigger to the frame and operatively coupling the trigger with the piston; operatively connecting an outlet valve with the outlet channel; and mounting a pair of springs on opposite sides of the frame and engaging the springs with the trigger; wherein the outlet valve is secured to the frame by means of a bridge piece which connects the springs to each other and which extends between the opposite sides of the frame.

Description

ENGINE FOR A LIQUID DISPENSING DEVICE AND LIQUID DISPENSING DEVICE INCLUDING SUCH ENGINE

The invention relates to an engine for a liquid dispensing device, comprising a frame, a pump chamber arranged in the frame, a piston movably arranged in the pump chamber, a trigger movably connected to the frame and operatively coupled with the piston, a nozzle, an outlet channel arranged in the frame and connecting the pump chamber to the nozzle, an outlet valve operatively connected with the outlet channel, and a pair of springs mounted or mountable on opposite sides of the frame and engaging or engageable with the trigger. Such an engine for a liquid dispensing device, also called a “trigger sprayer”, is disclosed in WO 2006/073307 Al.

In this prior art engine, the outlet valve is arranged in a valve chamber in the frame of the engine, and is locked in that valve chamber by an end wall that is part of a shroud. This requires the shroud to be designed to withstand structural loads, which affects the required wall thickness and consequently the amount of material that is used for the shroud. Moreover, this means that the valve is only secured in the very last step of the assembly process, when the shroud is placed on the engine. Furthermore, the springs of this prior art engine are integrally formed with the trigger. As a result, the trigger and the springs are made of the same material, which is not optimal, since the requirements in terms of strength and stiffness differ greatly for the trigger and the springs.

The invention has for its object to provide an engine for a liquid dispensing device of the type discussed above, in which these drawbacks are obviated or at least minimized. In particular, it is an object of the invention to provide such an engine which may be constructed using only a minimum amount of virgin plastics material and with a maximum number of parts made of recycled plastics material..

In accordance with a first aspect of the invention, this is achieved in that the springs are connected to each other by a bridge piece extending between the opposite sides of the frame and configured for securing the outlet valve to the frame. In this way the outlet valve, which may be a pre-compression valve, no longer needs to be locked in place by a shroud, and may be secured much earlier in the assembly process. Moreover, the design and material of the shroud is no longer dictated by the requirement of securing the valve, so that a thinner and more lightweight shroud may be used, having a minimum number of structural features. This allows the shroud, which constitutes an important part of the engine, to be made of recycled plastics material, which may not have the same structural properties as virgin plastics material. Alternatively, if the shroud is still made from virgin plastics material, this feature allows the required amount of that material to be minimized.

In an embodiment of the engine, the bridge piece is further configured for securing the springs to the frame. In this way the bridge piece performs a double function, thus reducing the complexity and the parts count of the engine. Moreover, by using the bridge piece, rather than the trigger, to secure the springs, the springs may be made from a different type of material than the trigger. Since the springs are continuously loaded, they will normally be made from virgin plastics material. However, the trigger is only loaded during dispensing, and includes a relatively larger amount of material than the springs, so that structural requirements are less severe and allow the use of recycled plastics material. And finally, by using the bridge piece to secure the springs, they may initially be mounted on the frame without yet having to be pre -tensioned. This allows the engine to be functionally tested on the assembly line by activating the trigger and piston without stressing the springs. Plastic springs require natural aging and relaxation prior to being stressed, which will increase their operational lifetime.

In a further embodiment, the outlet valve may be arranged in a valve chamber in the frame, and the bridge piece may comprise a wall part for locking the outlet valve in the valve chamber. This allows the outlet valve to be securely locked in place.

The wall part may be secured to an outer edge of the valve chamber, e.g. by being snapped over a protruding ridge or by means of lugs being received in openings.

In order to securely lock the valve in the valve chamber when pressure is being built up by the pump, the wall part may be reinforced. For instance, the wall part may have external ribs to prevent it from being deformed by the pressure in the valve chamber.

In an embodiment of the engine, the bridge piece may comprise arms connecting the wall part with each of the springs, and each arm may have a stiffness that is substantially smaller than that of the corresponding spring. In this way interaction between the springs and the wall part may be prevented, even though these parts are integrally made. The very flexible arms neither affect the action of the springs, nor do they exert any forces that might dislodge the wall part. Instead, the arms merely keep the springs and the wall part together before and during assembly of the engine.

In order to further minimize the influence of the arms on the action of the springs, the bridge piece may be connected to each of the springs at or near an end thereof that is mounted or mountable on the frame. In this way the main part of each spring is safeguarded against possible loading by the arms.

When each spring has a forward end engaging or engageable with the trigger and a rear end received or receivable in a recess of the frame, the entire length of the spring, which may be a flexure spring, may be used for generating a biasing force to act on the trigger. Moreover, mounting the spring by arranging one end in a recess of the frame is relatively simple.

According to another aspect of the invention, an engine for a liquid dispensing device is provided, which further comprises a reinforcing member arranged at a top of the frame and extending in a lengthwise direction of the frame. Such a reinforcing member may provide support for a shroud, which may therefore be made as a thin-walled and lightweight part. Providing such support is especially important in view of the rapid growth of e-commerce, which leads to products like liquid dispensing devices increasingly being shipped individually to consumers. Such individual shipping requires the liquid dispensing device to be sufficiently sturdy to withstand transport loads. The reinforcing member may have a flat top side for cooperation with the shroud. The reinforcing member may have a cross-sectional profile which provides resistance against deformation, e.g. a T-shape or an inverted U-shape.

In order to achieve maximum reinforcement while adding only a minimum amount of material to the structure of the frame, the reinforcing member may be elongate and may be attached to the frame at least near its front and rear ends. In this way the reinforcing member protrudes from the top of the frame like a resilient bumper or crash structure, which may absorb transport loads before they can damage the dispensing device proper.

In accordance with a further aspect, the invention provides an engine for a liquid dispensing device, wherein the trigger has a front surface facing away from the piston and including at least one concave part for engagement by a user’ s finger, and wherein the concave part is spaced from the nozzle when the trigger is in a position of rest. In this way there is no risk of a user’ s finger being pinched between the trigger and the nozzle during operation of the liquid dispensing device. In the prior art engine of WO 2006/073307 Al the entire trigger is provided with concave parts separated by convex parts, which lead to the formation of a very narrow region between the nozzle and the top of the trigger, where a user’s finger may easily be caught. By providing space between the finger engagement part of the trigger and the nozzle, the formation of a narrow region is prevented.

The risk of pinching may be further reduced when the front surface of the trigger includes a flat part adjacent the nozzle when the trigger is in a position of rest. This flat part, which may extend below the nozzle, provides an even greater space between the finger engagement part of the trigger and the nozzle.

According to yet another aspect of the invention, an engine for a liquid dispensing device is provided, in which the trigger has an at least partially spherical socket facing the piston, while the piston has an at least partially spherical connector facing the trigger, the at least partially spherical socket being configured for receiving the at least partially spherical connector. This type of connection between the trigger and the piston is more compact than the one disclosed in WO 2006/073307 Al, where the trigger has transverse lugs which are snapped into apertures of the piston. Due to the compact connection mechanism, the piston can be shorter and the trigger can be kept closer to the frame, so that a user does not have to extend his finger(s) as far as with the earlier device.

In an embodiment, the engine further comprises a shroud arranged over the frame and extending from the nozzle towards an end of the frame that is configured to be connected to a container for a liquid to be dispensed. Such a shroud conceals the inner structure of the engine and can be used e.g. for branding. The various features discussed above allow the shroud to be thinwalled and substantially free from structural features, so that it can be made from recycled plastics material, if so desired.

In a further embodiment of the engine, at least the frame and the trigger are made of recycled plastics material. By making such major components of the engine from recycled material, the use of virgin plastics material is further limited, thus improving the sustainability of the production of the engine. In addition, the shroud and/or the nozzle may also be made of recycled plastics material, thus further limiting the amount of virgin plastics material that is used. And if the engine is provided with a separate threaded closure for connecting the engine to a container, that closure may also be made of recycled plastics material, as may the piston.

The invention further relates to a liquid dispensing device which comprises a container for a liquid to be dispensed and an engine of the type discussed above connected to the container.

And finally, the invention relates to a method of assembling an engine for a liquid dispensing device. A conventional assembly method, e.g. the method disclosed in WO 2006/073307 Al, comprises the steps of: a) providing a frame including a pump chamber and an outlet channel arranged therein; b) movably arranging a piston in the pump chamber; c) movably connecting a trigger to the frame and operatively coupling the trigger with the piston; d) operatively connecting an outlet valve with the outlet channel; and e) mounting a pair of springs on opposite sides of the frame and engaging the springs with the trigger.

The method of the present invention is distinguished from the known method by the step of: f) securing the outlet valve to the frame by means of a bridge piece which connects the springs to each other and which extends between the opposite sides of the frame. As discussed above, this allows the valve to be secured early in the assembly process, well before a shroud is placed on the engine. Moreover, this allows various functional tests to be performed on the engine without the springs being stressed. And finally, this allows the shroud to be made either from a lower grade recycled plastics material or from a minimum of virgin plastics material.

In an embodiment of the method, step e) may include the substep of: el) securing the springs to the frame by means of the bridge piece. This allows the springs to be easily mounted as one.

In another embodiment of the method, step d) may include the substep of: dl) arranging the outlet valve in a valve chamber in the frame; and substep el) may include the substep of: el a) securing a wall part of the bridge piece to an outer edge of the valve chamber. This allows the outlet valve to be securely locked in place and tested in-line prior to final assembly of all parts, thus saving parts and material in the event of rejection due to a functional failure.

In a further embodiment of the method, step e) may further include the subsequent substep of: e2) arranging a rear end of each spring in a corresponding recess of the frame and bringing a forward end of each spring into engagement with the trigger.

In another embodiment of the method, functional tests are performed on the engine after step el), and step e2) is performed only if results of the functional tests are satisfactory. As the springs are already securely connected to the frame after step el), the functionality of the engine may be tested while the forward and rear end of the springs are still disengaged. Step e2) of tensioning the springs between the trigger and the frame may be performed at a relatively late stage of manufacturing, thus prolonging the life of the springs.

And finally, as discussed above, in an embodiment of the method, at least the frame and the trigger may be made of recycled plastics material to reduce the amount of virgin material used and improve sustainability of the engine and circularity of its production.

The invention will now be elucidated by means of an exemplary embodiment thereof, with reference being made to the annexed drawings, in which:

Fig. 1 is a rear perspective view of an engine for a liquid dispensing device in accordance with the invention, with a shroud being shown in phantom for improved clarity;

Fig. 2 is a side view of the engine of Fig. 1 during assembly and testing, with the trigger in an operative position and with the shroud removed for reasons of clarity;

Fig. 3 is a longitudinal sectional view of the engine of Figs. 1 and 2, with the shroud again shown in phantom, and with the spring(s) tensioned between the frame and the trigger;

Fig. 4 is a view corresponding with Fig. 2, but showing the trigger in its position of rest and the spring(s) engaged between the frame and the trigger, while the shroud is shown in phantom;

Fig. 5 is a view corresponding with Fig. 3, but showing the trigger in its position of rest;

Fig. 6 is a quarter front view of the engine of Figs. 1-5;

Fig. 7 is a collection of views of the frame of the engine of Figs. 1-6;

Fig. 8 is a perspective view of the springs and bridge piece of the engine; and

Fig. 9 is a side view of the springs and bridge piece of Fig. 8.

An engine 1 for a liquid dispensing device comprises a frame 2 in which a pump chamber 3 is arranged (Fig. 1). A piston 4 is movably arranged in the pump chamber 3 (Fig. 3). A trigger 5 is movably connected to the frame 2 and is operatively coupled with the piston 4. In this embodiment the trigger 5 is pivotably mounted in a cylindrical opening 27 in the frame 2 by means of inwardly extending stubs (not shown).

A nozzle 6 is arranged at a forward end of the frame 2. An outlet channel 7 which is arranged in the frame 2 connects the pump chamber 3 to the nozzle 6. The engine 1 further comprises an outlet valve 8 which is operatively connected with the outlet channel 7.

A pair of springs 9 is mounted on opposite sides 2L, 2R of the frame 2 and engages with the trigger 5. These springs 9 are connected to each other by a bridge piece 10 which extends between the opposite sides 2L, 2R of the frame 2. In the illustrated embodiment the springs 9 and the bridge piece are integrally made from a plastics material, e.g. by injection molding (Figs. 8, 9).

In the illustrated embodiment the bridge piece 10 has two functions. It secures the outlet valve 8 to the frame 2 and it further secures the springs 9 to the frame 2.

In this embodiment the outlet valve 8 is arranged in a valve chamber 11 which is located between an outlet 12 of the pump chamber 3 and the outlet channel 7. The outlet valve 8 here has the form of a dome, which is integrally molded with a sleeve 13.The dome valve 8 sealingly engages a valve seat 14 surrounding an entry of the outlet channel 7. The sleeve 13 carries two annular sealing flaps 15, 16.

The bridge piece 10 in this example comprises a wall part 17 for locking the outlet valve 8 in the valve chamber 11. The wall part 17 has a bent edge 18 which is secured to a ridge 19 protruding from an outer edge of the valve chamber 11. As shown here, the wall part 17 is reinforced by two orthogonal protruding ribs 20, 21.

In the illustrated embodiment the bridge piece 10 further comprises two arms 22, each of which connects the wall part 17 with one of the springs 9. Each of these arms 22 has a stiffness that is substantially smaller than the stiffness of the corresponding spring 9, so that the bridge piece does 10 not transfer any loads to the springs 9, and does not affect their biasing function. As shown here, the bridge piece 10 is connected to each of the springs 9 at or near an end 23 of each spring that is mounted on the frame 2.

In the illustrated embodiment each spring 9 has a forward end 24 that is configured to engage with the trigger 5 when the engine 1 is fully assembled and operational, as well as a rear end 23 that can be received in a recess 25 of the frame 2. The forward end 24 is shown to be substantially triangular, for fitting engagement in a pocket of the trigger 5, and has a protruding part 26 with which the forward end 24 of the spring 9 may be locked in the trigger 5. The rear end 23 of the spring 9 is shown to be cylindrical, so as to allow a slight pivoting movement in the recess 25, which is cylindrical as well. In the shown embodiment the springs 9 have an inverted U- shaped cross section, consisting of two webs 48 and a top flange 49. The inverted U-shape results in a very efficient distribution of material in locations where it provides an optimum contribution to resilience and stress resistance of each spring 9. As stated above, the springs 9 are initially secured to the frame 2 by means of the bridge piece 10. When the wall part 17 of the bridge piece 10 is snapped over the outer edge of the valve chamber 11, the springs 9 are connected to the frame 2, even if their ends 23 are not yet received in the recesses 25 - as shown in circle R in Fig. 2. This arrangement, in which the forward ends 24 of the springs 9 are not yet connected to the trigger 5 - as shown in circle F in Fig. 2 - allows the engine to undergo some functional testing during assembly, without applying any load or stress to the springs 9. Only after the forward ends 24 of the springs 9 have been brought into engagement with the trigger 5, and the rear ends 23 have been introduced into the recesses 24 - shown in circles F and R, respectively, in Fig. 3 - will the springs 9 be subject to any loads and stresses.

In the illustrated embodiment the engine 1 further comprises a reinforcing member 28 arranged at a top of the frame 2 and extending in a lengthwise direction of the frame 2. The reinforcing member 28 is shown to be elongate here and is attached to the frame 2 near its front end 29 and near its rear end 30. In this embodiment there is also a third attachment 31 near the rear end 30. The elongate reinforcing member 28 serves as a support for an upper part 50 of a shroud 32. It is resiliently deformable, and can bend downward in the direction of the frame 2 when subjected to a load from the top, as illustrated by the dashed line 28’ in Fig. 4.

In this example of the engine 1, a front surface 33 of the trigger 5, which faces away from the piston 4, includes a concave part 33 A for engagement by a user’s finger. When the trigger 5 is in a position of rest (Figs. 4, 6), the concave part 33A is spaced from the nozzle 6. To this end, the front surface 33 may include a flat part 33B, which is arranged such that it is adjacent the nozzle 6 when the trigger 5 is in a position of rest. In this way the risk of a user’ s finger being pinched between the trigger 5 and the nozzle 6 may be reduced.

As stated above, the trigger 5 is operatively coupled with the piston 4. In the illustrated embodiment, the trigger 5 has a partially spherical socket 34 facing the piston 4 and the piston 4 has a partially spherical connector 35 facing the trigger 5 (Fig. 3). The partially spherical socket 34 is configured for receiving the partially spherical connector 35. This connector 35 is integrally formed with a piston rod 36, which in turn is integrally formed with the piston 4. The partially spherical socket 34 defines an inscribed angle of more than 180D, so that its edge 37 defines an opening that is smaller than the maximum diameter of the spherical part of the connector 35. This allows the connector 35 to be snapped into the socket 34 and securely held. In this way the connector 35 and socket 34 act as a ball joint for converting the pivoting motion of the trigger 5 into a linear motion of the piston 4.

In the illustrated embodiment, the engine 1 further comprises a shroud 32. As shown here, the shroud 32 is arranged over the frame 2 to cover the various parts of the engine 1. On the one hand this protects these parts from outside influences, while on the other hand the parts are hidden from sight to create an aesthetically pleasing exterior. The shroud 32 is shown to extend from the nozzle 6 towards an end 38 of the frame 2 that is configured to be connected to a container 39 for a liquid to be dispensed.

In the shown embodiment the shroud 32 is made as a single piece, but it may be assembled from more than one piece. The various novel features of the engine 1 discussed above allow the shroud to be a thin-walled and lightweight part without any structural support features. Since the shroud 32 is so thin, it is supported at the top of the frame 2 by the reinforcing member 28. Because the shroud 32 does not have to perform any load bearing functions, it can be made of a relatively low-grade material like e.g. recycled plastics material. Alternatively, the shroud 32 could be made from virgin plastics material, precisely because it is so thin and lightweight.

The shroud 32 is wrapped closely around the engine 1 so as to minimize the amount of material required. The only exception is at the rear of the engine 1, where the shroud has a protruding part 40 that comes to rest on a user’ s hand when the engine 1 is used, so as to enable a strong and stable grip.

The end 38 of the frame 2 that is to be connected to the dispenser 39 is shown to include a conventional annular closure 41 having internal threading 42 for cooperation with external threading on a neck of the container 39. The engine 1 further includes a gasket 43 arranged around a plug-type lower edge 44 of the engine 1 , which is configured to be fittingly inserted into the container neck. When connected, the engine 1 and container 39 form a liquid dispensing device. It should be noted that instead of a threaded connection between the closure of the engine and the neck of the container other connection mechanisms are also conceivable, like e.g. a bayonet connection or a snap connection. In those cases the closure 41 will be provided with internal bayonet or snap features like e.g. lugs or hooks.

The engine 1 is further shown to include a dip tube 45 which extends into the container 39 and debouches in an opening 46 in the frame 2, which is surrounded by the annular sealing flaps 15, 16. Local deformation of the sealing flap 15 will bring the opening 46 into fluid communication with an inlet 47 of the pump chamber 3, so that liquid from the container 39 may be drawn into the pump chamber 3.

The design and structure of the engine 1 allow many parts to be made from recycled plastics material, thus reducing the carbon footprint of the liquid dispensing device in which it is used. At least the frame 2 and the trigger 5, but preferably also the shroud 32, the nozzle 6, the piston 4 and the closure 41 are made from recycled plastics material, e.g. polyethylene (PE) like LDPE or HDPE, polypropylene (PP) or polyethylene terephthalate (PET). Only the springs 9, which are relatively highly stressed during use, will have to be made from a virgin plastics material like PE, PP or PET.

Although the invention has been disclosed by reference to a specific embodiment thereof, it will be clear that it is not limited to this embodiment and can be varied in many ways. For instance, the shapes and dimensions of the various parts could be modified, depending on the requirements of a specific case, as could be the materials used to manufacture these parts. The scope of the invention is defined solely by the appended claims.

Claims

1. An engine for a liquid dispensing device, comprising:

- a frame;

- a pump chamber arranged in the frame;

- a piston movably arranged in the pump chamber;

- a trigger movably connected to the frame and operatively coupled with the piston;

- a nozzle;

- an outlet channel arranged in the frame and connecting the pump chamber to the nozzle;

- an outlet valve operatively connected with the outlet channel; and

- a pair of springs mounted or mountable on opposite sides of the frame and engaging or engageable with the trigger; characterized in that the springs are connected to each other by a bridge piece extending between the opposite sides of the frame and configured for securing the outlet valve to the frame.

2. The engine of claim 1 , wherein the bridge piece is further configured for securing the springs to the frame.

3. The engine of claim 1 or 2, wherein the outlet valve is arranged in a valve chamber in the frame, and the bridge piece comprises a wall part for locking the outlet valve in the valve chamber.

4. The engine of claim 3, wherein the wall part is secured to an outer edge of the valve chamber.

5. The engine of claim 3 or 4, wherein the wall part is reinforced.

6. The engine of any one of claims 3-5, wherein the bridge piece comprises arms connecting the wall part with each of the springs, each arm having a stiffness that is substantially smaller than that of the corresponding spring.

7. The engine of any one of the preceding claims, wherein the bridge piece is connected to each of the springs at or near an end thereof that is mounted or mountable on the frame.

8. The engine of any one of the preceding claims, wherein each spring has a forward end engaging or engageable with the trigger and a rear end received or receivable in a recess of the frame.

9. The engine of any one of the preceding claims or of the preamble of claim 1, further comprising a reinforcing member arranged at a top of the frame and extending in a lengthwise direction of the frame.

10. The engine of claim 9, wherein the reinforcing member is elongate and is attached to the frame at least near its front and rear ends.

11. The engine of any one of the preceding claims or of the preamble of claim 1 , wherein the trigger has a front surface facing away from the piston and including at least one concave part for engagement by a user’s finger, wherein the concave part is spaced from the nozzle when the trigger is in a position of rest.

12. The engine of claim 11, wherein the front surface of the trigger includes a flat part adjacent the nozzle when the trigger is in a position of rest.

13. The engine of any one of the preceding claims or of the preamble of claim 1, wherein the trigger has an at least partially spherical socket facing the piston and wherein the piston has an at least partially spherical connector facing the trigger, the at least partially spherical socket being configured for receiving the at least partially spherical connector.

14. The engine of any one of the preceding claims, further comprising a shroud arranged over the frame and extending from the nozzle towards an end of the frame that is configured to be connected to a container for a liquid to be dispensed.

15. The engine of any one of the preceding claims, wherein at least the frame and the trigger are made of recycled plastics material.

16. A liquid dispensing device, comprising a container for a liquid to be dispensed and an engine of any one of the preceding claims connected to the container.

17. A method of assembling an engine for a liquid dispensing device, comprising the steps of: a) providing a frame including a pump chamber and an outlet channel arranged therein; b) movably arranging a piston in the pump chamber; c) movably connecting a trigger to the frame and operatively coupling the trigger with the piston; d) operatively connecting an outlet valve with the outlet channel; and e) mounting a pair of springs on opposite sides of the frame and engaging the springs with the trigger; characterized by the step of: f) securing the outlet valve to the frame by means of a bridge piece which connects the springs to each other and which extends between the opposite sides of the frame. The method of claim 17, wherein step e) includes the substep of: el) securing the springs to the frame by means of the bridge piece. The method of claim 18, wherein step d) includes the substep of: dl) arranging the outlet valve in a valve chamber in the frame; and wherein substep el) includes the substep of: el a) securing a wall part of the bridge piece to an outer edge of the valve chamber. The method of claim 18 or 19, wherein step e) further includes the subsequent substep of: e2) arranging a rear end of each spring in a corresponding recess of the frame and bringing a forward end of each spring into engagement with the trigger. The method of claim 20, wherein functional tests are performed on the engine after step el), and wherein step e2) is performed only if results of the functional tests are satisfactory. The method of any one of claims 17-21, wherein at least the frame and the trigger are made of recycled plastics material.