WO2020067888A1

WO2020067888A1 - Underwater propulsion means which is attachable to the human body

Info

Publication number: WO2020067888A1
Application number: PCT/NL2019/050638
Authority: WO
Inventors: Rudolf Petrus MULDER; Jacques Leopold Catharina ROMPEN
Original assignee: Columbus Design B.V.
Priority date: 2018-09-28
Filing date: 2019-09-24
Publication date: 2020-04-02
Also published as: NL2021731B1

Abstract

The invention relates to an underwater propulsion means which is attachable to the human body, comprising a frame provided with attachment means for attaching the propulsion means directly to the human body, an electric motor connected to the frame and an impeller which is coupled to an output shaft of the electric motor via a toothed belt transmission and which is provided on a peripheral side with an external toothing for engagement with the toothed belt. The invention also relates to a system of two such underwater propulsion means.

Description

Underwater propulsion means which is attachable to the human body

The invention relates to an underwater propulsion means which is attachable to the human body, comprising a frame provided with attachment means for attaching the propulsion means directly to the human body, an electric motor connected to the frame, and an impeller which is coupled to an output shaft of the electric motor via a drive belt transmission, in particular a toothed belt transmission. The invention also relates to a system of at least two such underwater propulsion means.

The concept of a propulsion system which is attachable to the body for underwater use is already known from the prior art. Such systems are designed to be used in the diving sector as underwater propulsion means for individual divers. An advantage of propulsion systems which are attachable to the body, is the fact that they permit the user a large degree of freedom of movement because the user does not have to hold on to anything and does not have to sit on anything or support himself on anything.

However, the abovementioned propulsion systems also face several technical challenges, as a result of which their practical application has hitherto not materialized. Thus, the propulsion means has to be able to provide sufficient thrust to the user thereof, so that the user is able to move forward at a sufficiently high speed under various circumstances. However, the ability to provide sufficient thrust should not be to the detriment of the system dimensions. After all, it is essential for a system which is attachable to the body that the total dimensions of the system are kept as small as possible in order to keep the system manageable. The reason for this is that the user has to be able to wear the system both in the water and, to a limited degree, also outside the water and has to be able to move with the system. For the same reason, the amount of thrust to be delivered should not be to the detriment of the total mass of the system which, by reason of the ease of handling, has to be low. However, with underwater applications, the buoyancy of the user also plays a part. Thus, a compressed air diver will, usually, balance himself out in such a way that he has a neutral buoyancy on the water surface. In this case, a low total mass of the system makes it possible to easily compensate for changes in buoyancy caused by the system. Finally, the desired amount of available thrust will have to go hand in hand with a useful operating range and/or operating time, in which case the duration of an average compressed air dive may be used as a starting point. In this case, the streamlining of the system will also play a defining role. It is therefore an object of the present invention to provide a practically usable underwater propulsion means for attaching to the human body which is sufficiently efficient in terms of the generated thrust and/or streamlining plotted against the power used, the mass and the volume of the system. To this end, the invention provides an underwater propulsion means which is attachable to the human body, comprising a frame provided with attachment means for attaching the propulsion means directly to the human body, an electric motor connected to the frame, and an impeller which is coupled to an output shaft of the electric motor via a drive belt transmission, in particular a toothed belt transmission, characterized in that a peripheral side of the impeller is adapted to cooperate with the drive belt. In case the drive belt is formed by a toothed belt, the peripheral side of the impeller is preferably provided with an external toothing for engagement with the toothed belt. The peripheral side of the impeller is preferably adapted to accommodate a part of the drive belt. In this case, it is conceivable for the peripheral side of the impeller to be provided with at least one, generally groove shaped, accommodation space for accommodating a part of the drive belt. With such an embodiment, it is preferred if (the cross section of) at least one

accommodation space which is formed on the peripheral side of the impeller is designed to be substantially complementary to (the cross section of) the drive belt. Such a complementary design generally improves the mutual cooperation between the drive belt, in particular the toothed belt, and the impeller, in particular the impeller provided with a toothing. It is also possible to use drive belts which differ from a toothed belt, such as a V belt, a hexagonal belt and/or a pulley. The abovementioned drive belts may optionally be provided with a toothing, as a result of which these in this case also qualify as toothed belts. Drive belts operate relatively quietly and are relatively durable. In addition, drive belts do not have to be lubricated and they continue to function in a reliable and smooth manner, even at relatively high rotary speeds and when they come into contact with water and/or are submerged. An additional advantage of a toothed belt is the fact that the toothed belt is provided with an internal tooth profile, optionally provided with a, preferably wear-resistant tooth coating which is generally made of nylon, as a result of which slip between the toothed belt on the one hand and the electric motor and/or the impeller on the other hand can be prevented. Below, various variant embodiments will be described, with the toothed belt often being described explicitly as the preferred embodiment. However, in the variant embodiments mentioned below, it is conceivable for the toothed belt to be replaced by a different kind of drive belt. In case a (untoothed or toothless) drive belt is used, the impeller does not have to be provided with a toothing on the peripheral side. In this case, possible attachment means include all kinds of belts and strips which can attach the frame directly to the body. Clamps or pieces of clothing connected to the frame may also serve as suitable attachment means. Often, the frame will be in contact with a part of the body, in which case the shape of the frame advantageously corresponds to the shape of the body part at the location where it contacts the body. This

correspondence generally benefits the streamlining of the underwater propulsion means significantly, as a result of which less motor output is required in order to be able to propel a person, as a result of which the underwater propulsion means may be of a relatively compact design, further benefitting the streamlining. The impeller is responsible for the water displacement, with the energy which the electric motor transfers to the impeller subsequently being transferred to the water. In the context of the present invention, the name“impeller” has to be interpreted broadly, with each part which is able to produce an increase in speed or pressure downstream of the aforementioned part by means of a rotating movement being deemed to fall under the definition of “impeller”. Thus, names such as“fan”,“ducted fan”,“water wheel”,“propeller”, or“screw” have to be deemed to be exchangeable with the name“impeller” within the context of the present invention. The impeller is driven by the electric motor via a toothed belt transmission. The toothed belt transmission uses a toothed belt provided with an internal toothing which prevents the belt from slipping. Commonly, the toothed belt is made of a fibre-reinforced plastic which gives the toothed belt both the required tensile strength and flexibility. The use of a toothed belt transmission has the advantage that it does not require lubrication in order to function well, as a result of which a lubricating system can be omitted. In addition, a toothed belt transmission is wear-resistant and suitable for high rotary speeds. By means of its toothing, the toothed belt engages with, on the one hand, an output shaft of the electric motor which is commonly directly connected to the rotor of the electric motor. A gear wheel or pulley with external toothing may to this end be arranged on the output shaft with the toothed belt being arranged on top.

On the other hand, the toothed belt engages with the impeller which is to this end provided with external toothing on a peripheral side. The blades of the impeller which extend in a radial direction from a rotation axle are to this end connected to a peripheral wall at an end which faces away from the rotation axle. Where appropriate, the impeller comprises at least one blade, preferably 1 , 2, 3, 4, or 5 blades. As a result thereof, a strong connection between the peripheral wall and the rotation axle may be formed. The outer side (peripheral side) of the peripheral wall is in this case preferably provided with the abovementioned toothing over which the toothed belt is arranged. Preferably, adjacent blades of the impeller overlap one another in the longitudinal direction of the impeller. In this way, it is possible to improve the water displacement. It is preferred if the blades of the impeller are oriented standardly with respect to the axle of the impeller, as a result of which a balanced propulsion may be achieved which aids a balanced load of the impeller, the drive belt, and the electric motor. The one or several blades of the impeller preferably have a curved geometry in order to be able to pass water through the impeller as efficiently as possible. In this case, the peripheral side of a blade preferably extends from a supply side of the impeller to a discharge side of the impeller. As a result thereof, the blade may be provided with a desired gauge. Preferably, the distance between the abovementioned supply side and discharge side of the impeller is at least 25 mm.

The underwater propulsion means is adapted to displace water, as a result of which a propelling force is generated. Therefore, the underwater propulsion means, or at least the impeller, will be situated at least partly underwater during normal use in order to be able to achieve the desired water displacement. During this normal use, the person who is connected to the underwater propulsion means will generally be, at least partly or even completely underwater. However, it is also conceivable for this person to be substantially or even completely above water during normal use, with only the underwater propulsion means being situated at least partly

underwater, and with the person for example possibly being located on a surfboard (bodyboard) or any other floating body.

The specific design of the impeller in which the toothing is incorporated on the peripheral side is crucial in order to make it possible to achieve a compact and lightweight embodiment of the underwater propulsion means. By means of the impeller with toothing, the water displacement function and the transmission function are accommodated in a single component, which is beneficial both with regard to the weight and the dimensions of the propulsion means. In addition, the peripheral wall provided with teeth gives additional reinforcement to the impeller, as a result of which the impeller can be of a lighter design and is also able to withstand relatively large forces which are due to high rotary speeds. By means of the combination of this impeller with a toothed belt transmission and an electric motor, an efficient, compact and lightweight underwater propulsion means is obtained which is eminently suitable for direct attachment to the body in the light of the requirements which are placed on a propulsion system which is attachable to the body.

In an advantageous variant embodiment of the propulsion means according to the invention, the transmission ratio between the output shaft of the electric motor and the impeller is greater than 1 , with the output shaft of the electric motor performing more than a full rotation for every full rotation of the impeller. In order to provide the impeller with a sufficiently large torque and to ensure maximum efficiency of the electric motor, with the aim of achieving an electric motor having relatively good streamlining, a relatively low mass, and a relatively limited volume, it was found that the output shaft of the electric motor has to rotate at a higher speed than the impeller. In this case, empirical tests have found that a transmission ratio of the electric motor on the impeller of between 2:1 and 20:1 , and of 3:1 is particularly desirable. Due to the fact that the toothing - if used - by means of which the toothed belt has to engage with the impeller is provided on the peripheral side of the impeller, the toothed belt engages with the impeller at a location which is as far removed from the rotation axle of the impeller as possible. A similar situation applies if other types of drive belts are used. As a result thereof, it becomes possible to achieve large transmission ratios without using further parts.

In a further possible embodiment of the propulsion means according to the invention, the impeller is substantially entirely surrounded by a jet pipe. The jet pipe which, where appropriate, is designed as a substantially closed cylindrical wall, performs a few advantageous functions in the underwater propulsion means.

Firstly, the jet pipe at least partly protects the impeller, as a result of which the rotating impeller cannot come into contact with external objects or body parts, or does so less easily. In order still to make the coupling with the toothed belt possible, the jet pipe may in this case be provided with two through-holes for passing through the toothed belt. The jet pipe may also serve as an attachment surface for other parts of the propulsion means with which it may form part of the frame or may be directly connected to the frame. Where appropriate, the electric motor may be attached to an outer side of the jet pipe by means of an attaching support. The distance between the electric motor and the impeller, and thus the distance to be bridged by the toothed belt is in this case effectively minimized, which benefits the compactness of the propulsion means.

In order to control the outflow of water emanating from the impeller, the jet pipe may comprise a rear part which extends downstream of the impeller in a direction facing away from the impeller. By obtaining control of the direction of outflow of the water propelled by the impeller, it is possible to prevent thrust being lost due to the water not being propelled in a uniform direction. Commonly, the jet pipe will be adapted to guide the water propelled by the impeller in an axial direction of the impeller, for which reason the jet pipe is generally axially aligned with the impeller.

It is also conceivable for the rear part of the jet pipe to be movable with respect to the impeller, in such a way that the direction of the outflowing water flow may be influenced. By means thereof, the direction of propulsion of the underwater propulsion means can be controlled, which may serve as a control mechanism. It is also conceivable for the jet pipe to be provided with a separate control part or a jet- reversing mechanism, such as a baffle by means of which the propulsion jet can be directed in a desired direction or can even be reversed. The rear part of the jet pipe which extends behind the impeller furthermore ensures that the impeller is protected from a rear side of the propulsion means.

The diameter of the rear part of the jet pipe may decrease in a direction facing away from the impeller, and in particular taper. A decrease in the diameter of the jet pipe in a downstream direction results in an acceleration of the outflowing propulsion flow, leading to an increase in thrust. This makes it possible to increase the efficiency of the propulsion means to a greater degree. It is also conceivable for the rear part of the jet pipe to have a substantially constant diameter. As another possible measure for increasing the thrust of the propulsion means, the rear part of the jet pipe may comprise one or several stator blades. The stator blades ensure that the rotation which the rotating impeller imparts to the propulsion flow is reduced, as a result of which the radial speed component of the propulsion flow decreases and the axial flow component of the propulsion flow increases. For the sake of a uniform flow profile, the stator blades are preferably positioned in the jet pipe so as to be rotationally symmetrical. Where appropriate, the stator blades extend from a central axis of the jet pipe in a radial direction up to an inner side of the jet pipe, as a result of which the outflowing propulsion flow will flow entirely along the stator blades. Also, the stator blades in this case have a positive effect on the strength of the jet pipe construction. Furthermore, the stator blades may extend in an axial direction up to an end of the rear part of the jet pipe facing away from the impeller. In this case, the propulsion flow is passed along the entire length of the rear part of the jet pipe along the stator blades, as a result of which a maximum effect can be exerted on the direction of outflow of the propulsion flow.

In order to protect the impeller on the front side, the jet pipe may comprise a front part which extends upstream of the impeller in a direction facing away from the impeller. This front part of the jet pipe may also contribute to the efficiency of the impeller due to the front part of the jet pipe improving the inflow of water to the impeller. Usually, the diameter of the front part of the jet pipe will decrease in the (upstream) direction facing the impeller, and in particular taper. It is also

conceivable for the diameter of the front part of the jet pipe to be substantially constant.

In order to increase the protective function of the front part of the jet pipe, the front part of the jet pipe may comprise several spacers, wherein the spacers extend from a central axis of the jet pipe in a radial direction up to an inner side of the jet pipe. The abovementioned spacers compartmentalize the inflow opening of the jet pipe, thus effectively limiting the size of the objects which are able to reach the impeller via the spacers. In addition, the spacers support the jet pipe wall, which benefits the sturdiness of the jet pipe. The spacers are usually fixedly connected to the inner side of the jet pipe. Also, the spacers are preferably arranged so as to be rotationally symmetrical. Where appropriate, the jet pipe may comprise a metal and may, in particular, be made of a metal or metal alloy. A metal or metal alloy may give the jet pipe the desired strength properties. In this case, metals have a relatively high thermal conduction coefficient, as a result of which the jet pipe may also serve as a cooling body for heat-generating components of the propulsion means, such as the electric motor and its (electronic) control means.

In a possible embodiment of the propulsion means according to the invention, the electric motor is a brushless DC motor. A significant advantage of the brushless DC motor is the absence of a mechanical commutator and the associated carbon brushes, which assembly is not only subject to significant wear, but also negatively impacts on the efficiency of the electric motor. In this case, a brushless DC motor is able to achieve high rotary speeds and deliver a large maximum power in proportion to the weight and the dimensions of the electric motor. It has been found that, for use in an underwater propulsion means according to the invention, it is advantageous if the electric motor performs at least 10,000 revolutions per minute.

It is also conceivable for the electric motor to run at rotary speeds greater than 10,000, such as for example 15,000, 16,000, 20,000 and 25,000. By means of the toothed belt transmission, the rotary speed of the impeller can then be lowered, in which case the torque of the impeller increases.

In order to be able to provide commutation in the electric motor and regulate the motor output, the electric motor is usually connected to an electronic speed regulator. Where appropriate, the electronic speed regulator is formed by an electronic circuit which is capable of regulating the speed of the electric motor. For the purpose of cooling the electronic speed regulator, the electronic speed regulator may be in direct and/or indirect heat-exchanging contact with the jet pipe, with the jet pipe functioning as a cooling body. Since the jet pipe has a relatively large surface area and is in direct heat-exchanging contact with the water flowing past, the jet pipe is particularly suitable to be used as a cooling body. The jet pipe may also serve as a cooling body for the electric motor, with the stator coils or magnets often being in direct and/or indirect thermally conductive contact with the jet pipe. As has already been mentioned above, it is advantageous, if the jet pipe acts as a cooling body, if at least a part of the jet pipe is made from a material having a high thermal conduction coefficient. Metals or metal alloys are eminently suitable for this purpose, but thermally conductive foils, such as graphite foils or graphene foils, may also be used for this purpose.

The electric motor may be supplied with power by a battery pack which is likewise directly attachable to the human body. This battery pack usually consists of several batteries which are connected in series and/or in parallel in order to be able to provide the electric motor with sufficient power. Due to the high energy density, lithium batteries are highly suitable for use in such a battery pack. It is possible for the battery pack to be attached to the frame of the propulsion means, thus producing a single compact propulsion module. However, due to a possible lack of space on the body at the location of the attached propulsion means and for the sake of a more even weight distribution and/or better streamlining, it is also possible for the battery pack, optionally together with the electronic speed regulator, to be adapted such that it can be attached to a different part of the body than the part of the body to which the assembly of electric motor, transmission, impeller and/or optionally the electronic speed regulator, is attached. In the latter case, the battery pack may be connected to the electric motor and/or the electronic speed regulator by means of a cable. In yet a further embodiment of the underwater propulsion means according to the invention, the propulsion means is adapted for attaching to the lower leg, and in particular the ankle. Because the lower leg will generally always be under the water surface, even when moving forward on the water surface, the underwater propulsion means will also always be underwater when it is attached to the lower leg. In addition, the lower leg is not usually an attaching location for standard diving equipment, as a result of which an underwater propulsion means which is attachable to the lower leg can be used in combination with standard diving equipment without any problem. The propulsion means may furthermore comprise an operating member for actuating the propulsion means, the operating member being adapted for operation by means of the foot. To this end, the operating member may comprise a foot- retaining element for attaching to the foot. As such an operating member makes operation by foot possible, the hands of the operator are free to perform other tasks. In a specific embodiment, the operating member may be adapted for increasing the thrust delivered by the electric motor by means of a plantar flexion of the foot and for decreasing the thrust delivered by the electric motor by means of a dorsal flexion of the foot. Due to its similarity to a standard accelerator pedal, the operator of the propulsion means finds this way of regulating the motor power very intuitive. Also, this way of regulating causes minimal drag in the water at maximum thrust and maximum drag at minimal thrust. Furthermore, the aforementioned operating member may be used as a separate device in underwater propulsion means whose powertrain differs from that of the underwater propulsion means according to Claim 1. In this case, the advantages of the operating member regarding the practical, intuitive and efficient operation of the propulsion means are maintained. In addition, the aforementioned operating member may be used in underwater propulsion means which are not adapted to be (directly) attached to the human body. In addition, the invention relates to a system of at least two underwater propulsion means according to the invention, in which at least two underwater propulsion means are preferably connected to the same battery and/or the same battery pack. In this case, it is also conceivable for at least two underwater propulsion means to be connected to different batteries or different battery packs. A system of at least two underwater propulsion means which are each attached to the body in a different location may be beneficial for the control and the stability of the propulsion means during use. By controlling the thrust of the propulsion means separately from one another, it is possible for the user to perform a rotating movement, as a result of which the travelling direction of the user may be chosen and corrected. In one possible arrangement, each of the underwater propulsion means is attached to a different lower leg of the user and the battery pack is attached to the body of the user at a different location, such as an upper leg, the stomach or the back. With the system according to the invention, it is conceivable for at least two underwater propulsion means to be physically coupled to one another, these underwater propulsion means preferably comprising a common frame.

The invention will be explained by means of non-limiting exemplary embodiments illustrated in the following figures. Similar elements in the figures are denoted by identical reference numerals. In the figures: - Fig. 1 shows a cut-away perspective view of an underwater propulsion means according to the present invention,

- Fig. 2 shows a cross section in the longitudinal direction of the underwater propulsion means as illustrated in Fig. 1 ,

- Fig. 3 shows a cross section in the longitudinal direction of an alternative embodiment of an underwater propulsion means according to the present invention,

- Fig. 4 shows a side view of a system of underwater propulsion means

according to the invention in a position attached to a user,

- Fig. 5 shows a top view of a system of underwater propulsion means such as illustrated in Fig. 4, again in a position attached to a user, and

- Fig. 6 shows a detail view of the attachment to the leg of the system of

underwater propulsion means as illustrated in Figs. 4 and 5.

Figs. 1 and 2 respectively show a cut-away perspective view and a cross section in the longitudinal direction of an underwater propulsion means 1 according to the present invention. The underwater propulsion means 1 comprises an electric motor 2 whose output shaft 3 is in contact with an impeller 5 by means of a toothed belt 4. To this end, the toothed belt 4 engages with, on the one hand, a gear wheel 6 which is placed on the output shaft 3 of the electric motor 2. On the other hand, the toothed belt 4 engages with a peripheral side of the impeller 5 which is, to this end, provided with an external toothing 7. By choosing a gear wheel 6 on the output shaft 3 with a circumference which is smaller than the circumference of the impeller 5, the transmission ratio between the output shaft 3 of the electric motor 2 and the impeller 5 is greater than 1. The impeller 5 is virtually completely surrounded by a jet pipe 8, which jet pipe 8 is provided with two through-holes 9 (of which only one is shown in Fig. 1 ) for passing through the toothed belt 4. The jet pipe 8 and the electric motor 2 are coupled to each other by means of a frame, for which purpose the frame in the illustrated embodiment comprises two attaching supports 10a, 10b. The attaching supports 10a, 10b also serve to suspend the rotatable impeller 5 in the jet pipe 8 in a secured way. The jet pipe 8 comprises a rear part 1 1 which extends downstream of the impeller 5 in a direction facing away from the impeller 5 and in this case tapers, so that the diameter of the rear part 1 1 of the jet pipe 8 decreases in the downstream direction. In addition, the rear part 1 1 of the jet pipe 8 comprises several stator blades 12 which are positioned in the jet pipe 8 so as to be rotationally symmetrical and extend in the radial direction up to the inner side of the jet pipe 8, as a result of which de facto several ducts are created for the outflowing water flow. In the illustrated variant embodiment, the stator blades 12 also extend in the axial direction up to an end of the rear part 1 1 of the jet pipe 8 facing away from the impeller 5. The jet pipe 8 also comprises a front part 13 which extends upstream of the impeller 5 in a direction facing away from the impeller 5. Several spacers 14 are provided in this front part 13 of the jet pipe 8 which extend from a central axis of the jet pipe 8 in a radial direction up to an inner side of the jet pipe 8 and simultaneously serve as a protection for the impeller 5. Fig. 3 shows a cross section in the longitudinal direction of an alternative

embodiment of an underwater propulsion means 30 according to the present invention, in which the underwater propulsion means 30 is partly illustrated in perspective. In the illustrated embodiment, the underwater propulsion means 30 is surrounded by a housing 31 which protects the mechanics of the underwater propulsion means 30 - comprising the electric motor 2 with output shaft 3, the impeller 5 which is in contact with the gear wheel 6 placed on the output shaft 3 by means of the toothed belt 4 and the rear part 1 1 of the jet pipe 8 - against the user. In this case, the housing 31 forms part of the frame and also forms the engagement point for attachment means 32 by means of which the underwater propulsion means 30 can be attached to the user 33. In addition, the housing 31 functions as a front part 34 of the jet pipe 8, namely guiding the flow of water in the direction of the impeller 5.

Figs. 4 and 5 respectively show a side view and a top view of a system 40 of underwater propulsion means 41 according to the invention in a position attached to a user 42. The illustrated system 40 comprises two underwater propulsion means 41 which are provided with attachment means for attachment to the body. The attachment means are formed by a number of belts 44 attached to the housings 43 of the underwater propulsion means 41 by means of which each of the underwater propulsion means 41 is attached to a leg 47 of the user 42 at the location of the lower leg 45 and the ankle 46. It is also conceivable for attachment means other than belts 44 to be used. In addition, the attachment location on the body may differ from the positions illustrated here. The underwater propulsion means 41 are electrically coupled to a battery pack 49 by means of cables 48 which supply power to the electric motors 2 of the underwater propulsion means 41 . The battery pack 49 is also attached to the body of the user 42, in this case by means of a waist belt 50 which may be connected to a (diving) jacket 51 worn by the user 42. However, it is possible in this case as well for the battery pack 49 to be connected to the body in an alternative location. In addition, it is conceivable that each of the underwater propulsion means 41 is supplied with power by a dedicated instead of a central battery pack 49, in which case the different battery packs are worn on other parts of the body. Furthermore, each of the underwater propulsion means 41 in the illustrated embodiment is provided with an operating member 52 which is adapted to be operated by means of the foot 53. This operating member 52 is explained in more detail with reference to Fig. 6.

Fig. 6 shows a detail view of the attachment of the system 40 of underwater propulsion means 41 such as illustrated in Figs. 4 and 5 to the leg. By means of belts 44 which are connected to the housings 43 in which the electric motor 2, the impeller 5 with toothed belt transmission 4 and the rear part 1 1 of the jet pipe 8 of the underwater propulsion means 41 are accommodated, the underwater propulsion means 41 are to be attached to the body of the user 42 at the location of the ankles 46 and the lower legs 45. In addition thereto, each of the underwater propulsion means 41 is provided with a foot-retaining element 60 which engages around the foot 53 and is connected to an operating member 52 of the respective underwater propulsion means 41. This operating member 52 is adapted to actuate the electric motor 2 of the underwater propulsion means 41 and is also adapted, by means of the use of the aforementioned foot-retaining element 60, to be operated by means of the foot 53. In the illustrated embodiment of the system 40 of underwater propulsion means 41 , actuation of the electric motor 2 takes place by means of a rotation of the operating member 52. This rotation is made possible by a rotation of the foot-retaining element 60 coupled to the operating member 52. In particular, it is preferred if the control means of the electric motor 2 which are coupled to the turning direction of the operating member 52 are chosen such that a rotation caused by a plantar flexion 61 of the foot 53 leads to an increase of the thrust delivered by the electric motor 2 and a rotation caused by a dorsal flexion 62 of the foot 53 leads to a decrease or even a reversal of the thrust delivered by the electric motor 2. It will be clear that the invention is not limited to the exemplary embodiments illustrated and described here, but that numerous variants are possible without departing from the scope of the attached claims which are obvious to the person skilled in the art. In this case, it is conceivable that different inventive concepts and/or technical measures of the above-described variant embodiments can be combined in part or in their entirety without departing from the inventive idea described in the attached claims.

Claims

1. Underwater propulsion means which is attachable to the human body, comprising:

- a frame provided with attachment means for attaching the propulsion means directly to the human body,

- an electric motor connected to the frame, and

- an impeller which is coupled to an output shaft of the electric motor via a toothed belt transmission,

characterized in that

a peripheral side of the impeller is provided with an external toothing for

engagement with the toothed belt.

2. Underwater propulsion means according to claim 1 , characterized in that the transmission ratio between the output shaft of the electric motor and the impeller is greater than 1 , with the output shaft of the electric motor performing more than a full rotation for every full rotation of the impeller.

3. Underwater propulsion means according to claim 1 or 2, characterized in that the impeller is substantially entirely surrounded by a jet pipe.

4. Underwater propulsion means according to claim 3, characterized in that the jet pipe is provided with two through-holes for passing through the toothed belt.

5. Underwater propulsion means according to claim 3 or 4, characterized in that the electric motor is attached to an outer side of the jet pipe by means of an attaching support.

6. Underwater propulsion means according to one of claims 3 - 5,

characterized in that the jet pipe comprises a rear part which extends downstream of the impeller in a direction facing away from the impeller.

7. Underwater propulsion means according to claim 6, characterized in that the rear part of the jet pipe decreases in diameter in a direction facing away from the impeller, and in particular tapers.

8. Underwater propulsion means according to claim 6 or 7, characterized in that the rear part of the jet pipe comprises several stator blades, wherein the stator blades are preferably positioned in the jet pipe so as to be rotationally symmetrical.

9. Underwater propulsion means according to claim 8, characterized in that the stator blades extend from a central axis of the jet pipe in a radial direction up to an inner side of the jet pipe.

10. Underwater propulsion means according to claim 8 or 9, characterized in that the stator blades extend in an axial direction up to an end of the rear part of the jet pipe facing away from the impeller.

1 1 . Underwater propulsion means according to one of claims 3 - 10,

characterized in that the jet pipe comprises a front part which extends upstream of the impeller in a direction facing away from the impeller.

12. Underwater propulsion means according to claim 1 1 , characterized in that the front part of the jet pipe comprises several spacers, wherein the spacers extend from a central axis of the jet pipe in a radial direction up to an inner side of the jet pipe.

13. Underwater propulsion means according to one of claims 3 - 12,

characterized in that the jet pipe comprises a metal and, in particular, is made of a metal or metal alloy.

14. Underwater propulsion means according to one of the preceding claims, characterized in that the electric motor is a brushless direct current motor.

15. Underwater propulsion means according to one of the preceding claims, characterized in that the electric motor is connected to an electronic speed regulator.

16. Underwater propulsion means according to claim 15 and one of claims 3 - 13, characterized in that the electronic speed regulator and/or the electric motor are in direct and/or indirect heat-exchanging contact with the jet pipe.

17. Underwater propulsion means according to one of the preceding claims, characterized in that the electric motor is supplied with power by a battery pack which is likewise directly attachable to the human body.

18. Underwater propulsion means according to one of the preceding claims, characterized in that the propulsion means is adapted for attaching to the lower leg, and in particular the ankle.

19. Underwater propulsion means according to claim 18, characterized in that the propulsion means comprises an operating member for actuating the propulsion means, the operating member being adapted for operation by means of the foot.

20. Underwater propulsion means according to claim 19, characterized in that the operating member comprises a foot-retaining element for attaching to the foot.

21 . Underwater propulsion means according to claim 19 or 20, characterized in that the operating member is adapted for increasing the thrust delivered by the electric motor by means of a plantar flexion of the foot and for decreasing the thrust delivered by the electric motor by means of a dorsal flexion of the foot.

22. System of at least two underwater propulsion means according to one of the preceding claims, characterized in that at least two underwater propulsion means are connected to the same battery and/or to the same battery pack.