RELATED APPLICATION DATA

This application claims the benefit of Swedish Patent Application No. 1851398-6, filed on Nov. 9, 2018, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The invention considers a dumbbell with a rotating grip.

BACKGROUND ART

Different kinds of dumbbells with a rotating grip or rotating weights are known, but they have a number of drawbacks.

One solution is presented in document KR20120005422U, which describes a dumbbell with rotatable weights. The dumbbell has a grip inside which a rotatable shaft extends, and the weights are attached to the rotatable shaft. The object of the invention is to provide vibrations in the dumbbell, which vibrations affects muscles in the body. The vibrations are achieved by that the weights rotates while the handle is moved to the right and left respectively forwards and backwards. The problem solved by this solution is another than the present invention solves, and the solution is complicated.

Another solution is presented in CN206660427U, which discloses a dumbbell with a rotatable shaft, arranged inside a grip. The ends of the shaft are connected to the dumbbell heads by threaded connection, and a plurality of bearings are arranged along the outside of the shaft to connect the outside of the shaft with the inside of the grip, whereby the shaft is rotatable inside the grip. Further, a gasket is provided between the grip and the dumbbell heads. The purpose of the invention is to avoid injuries on the human wrist and elbow joint. This solution is not a premium solution and will have problems over time due to a design affected by external shock forces and the like.

There are a number of other solutions on the market, with or without patent protection. Some problems of prior art solutions concern the life time of the dumbbell, especially with remained high-end feeling of the rotating grip. The rotating grip is normally negatively affected by shock forces and the like, which is common in the daily use of dumbbells, since prior art solutions often are designed with contact between the shaft and the rotating grip, like the Korean patent presented above. One problem with prior art solutions related to this is that the grip, especially in the premium segment of dumbbells, is made rather thick, to take care of the shock forces, and this together with the constructional design of the rotating grip makes the total cross-section of the grip part large. A thin grip fits all users, but it is a problem in prior art to provide such solutions which also is useable for all weights from light weights to heavy weights. Another problem is that the rotating grip in many prior art solutions has a play between the grip and the shaft, which makes the impression or “feeling” of the product as a product with poor quality. Especially dumbbells with slide bearings tend to get worn over time, which is a problem. Thus, it is a problem in prior art to provide a premium dumbbell with a “premium-feel”, and with a thin grip design and which fits all weights from light weights up to heavy weights, and which is not impaired over time due to the normal handling during daily use.

SUMMARY OF THE INVENTION

It is an object of the invention to address at least some of the problems and issues outlined above. It is possible to achieve these objects and others by a dumbbell as defined in the attached independent claims.

According to an aspect of the invention, a dumbbell with a rotating grip is disclosed. The dumbbell comprises a shaft which extends along a longitudinal axis and which has a cross-sectional dimension. Further, a first dumbbell head is fixedly connected to a first end of the shaft and centered around the longitudinal axis of the shaft, and a second dumbbell head is fixedly connected to a second end of the shaft and also centered around the longitudinal axis of the shaft. The first dumbbell head comprises an inner side facing the second dumbbell head and an opposite outer side facing away from the second dumbbell head. The second dumbbell head comprises an inner side facing the first dumbbell head and an opposite outer side facing away from the first dumbbell head. Further, a tube-shaped hollow grip is arranged around the shaft and is centered around the longitudinal axis of the shaft. The grip has a first end and an opposite second end and an inner diameter and an outer diameter. The inner diameter of the grip is greater than the outer cross-sectional dimension of the shaft such as there is no contact between the grip and the shaft. A first ball bearing is centered around the longitudinal axis of the shaft, and an outer ring of the first ball bearing is connected to the first dumbbell head, and an inner ring of the first ball bearing is fixedly arranged to the first end of the hollow grip. Further, a second ball bearing is centered around the longitudinal axis of the shaft, and an outer ring of the second ball bearing is connected to the second dumbbell head, and an inner ring of the second ball bearing is fixedly arranged to the second end of the hollow grip.

By such an arrangement, a high end dumbbell with an ergonomic and user friendly design is achieved. The grip is as mentioned above, rotatable relative to the shaft and the dumbbell heads, and thereby the design of the dumbbell is gentle to the wrist. The overall design enables the use of a thinner grip, which fits most users and is able to use for all weights from light weights to heavy weights. Since the shaft is fixedly connected to the dumbbell heads, any shock force hitting the dumbbell, for example by a sudden drop of the dumbbell, only affects the dumbbell heads and the shaft, but hardly not at all, the rotating grip. This is far better than existing dumbbells and enables a longer life time of the dumbbell, and with remained high end feeling of the rotating grip. The rotating grip of prior art dumbbells is normally negatively affected by shock forces and the like, which is normal in the daily use of dumbbells, since there normally is contact between the shaft and the rotating grip in known solutions. Since the rotating grip is fixedly arranged to the inner rings of the ball bearings in the present solution, and the shaft is fixedly arranged to the dumbbell heads, the shaft as well as the grip may be rather thin, preferably with only a minimum of space between inside of the grip and the outside of the shaft. Thereby, the outside diameter of the grip may be for example 38 mm, and thereby fit most users. Prior art premium solutions, designed for use at all kinds of weights from say 5 kg up to 68 kg, have grips with outer diameter of about 50 mm, since the design is made such as the bearing is arranged between the grip and the shaft and sometimes with a rather thick shaft. In some prior art solutions with thin shaft design, the rotating grip is fitted around the shaft with a slide bearing between the grip and the shaft. Such solutions do not provide a premium feel and tends to be impaired over time since the slide bearing is worn out. With the inventive rotating, thin-grip design of the present dumbbell, the premium feel is not impaired over time and fits all dumbbells from low weights to high weights, even up to 68 kg which is not at hand in prior art dumbbells.

According to an embodiment, the inner ring of the first ball bearing and the inner ring of the second ball bearing respectively has an inner diameter which substantially corresponds with the outer diameter of the grip, such as the grip is fixedly arranged with its first end inside the inner ring of the first ball bearing and with its second end inside the inner ring of the second ball bearing. By the corresponding dimensions of the inner diameter of the ball bearings and the outer diameter of the grip, it is possible to get a robust fixation of the grip inside the bearings. And by fixedly fitting the ends of the grip inside the inner rings of the ball bearings and by that the inner diameter of the grip is slightly greater than the outer diameter of the shaft, the grip is not in contact with the shaft. Thereby, shock forces from a sudden drop of the dumbbell or a careless handling of the same, are taken care of by the dumbbell heads and the shaft and is not affecting the rotating grip that much. This is a far better solution compared to prior art.

According to an embodiment, the inner side of the first dumbbell head comprises a first cavity, which is centered around the longitudinal axis of the shaft. In the same way, the inner side of the second dumbbell head comprises a second cavity, which also is centered around the longitudinal axis of the shaft. The first cavity has an outer diameter which substantially corresponds with an outer diameter of the first ball bearing and the second cavity has an outer diameter which substantially corresponds with an outer diameter of the second ball bearing. This enables that the first ball bearing may be arranged in the first cavity and the second ball bearing may be arranged in the second cavity. To arrange the ball bearings into cavities in the dumbbell heads makes a smooth and nice design which doesn't impact on the grip and the space available for the hand.

According to an embodiment, the first dumbbell head is fixedly connected to the first end of the shaft by press fitting, and the second dumbbell head is fixedly connected to the second end of the shaft by press fitting. Thereby, a robust fixation of the dumbbell heads to the shaft is achieved, which gains power absorption from hits and shock forces and thus enables a longer life time compared to prior art.

According to an alternative embodiment, compared to fit the inner rings to the grip by any simple method as discussed above and which may be enough, the inner ring of the first ball bearing may be fixedly arranged to the first end of the hollow grip by press fitting, and the inner ring of the second ball bearing may fixedly arranged to the second end of the hollow grip by press fitting.

According to an embodiment, the first ball bearing is arranged in the first cavity by slip fitting, and the second ball bearing is arranged in the second cavity by slip fitting. This means that the ball bearing is precisely guided and fitted into the cavity and that there is contact between the walls of the cavity and the ball bearing. But the outer rings of the ball bearings are not pressed with high force into the cavity to make a totally solid or totally robust engagement between the outer ring of the ball bearing and the cavity walls. One reason for this is to avoid that the rings of the ball bearings are displaced during the assembly of the dumbbell, which might be a problem since the grip is fixedly fitted to the inner rings. Another reason to use slip fitting instead of for example press fitting when attaching the dumbbell heads to the outer rings of the ball bearing is to avoid a possible shock force transportation to the ball bearings and the grip from the dumbbell heads. But there is as said enough contact between the walls of the cavity and the outer ring, to make the grip rotate relative the dumbbell heads, but with no play and with remained premium-feel.

In a preferred embodiment, a first wave washer is arranged in the first cavity between a bottom of the first cavity and the first ball bearing and centered around the longitudinal axis of the shaft. In the same way, a second wave washer is arranged in the second cavity between a bottom of the second cavity and the second ball bearing and centered around the longitudinal axis of the shaft. Depending on tolerances in production of the dumbbell heads and its cavity as well as the tolerances of the ball bearings, a play may occur between the ball bearing and the cavity. To ensure that the eventual play between the cavity and the ball bearing is eliminated, the wave washer is arranged in the cavity.

According to an embodiment of the inventive dumbbell, the outer side of the first dumbbell head comprises a third cavity and the outer side of the second dumbbell head comprises a fourth cavity. Further, the first end of the shaft comprises an outer portion with a thread wherein the outer portion protrudes in the third cavity, and the second end of the shaft comprises an outer portion with a thread wherein the outer portion protrudes in the fourth cavity. By this, the first dumbbell head may be further secured to the first end of the shaft by a first nut engaged with the thread of the first end of the shaft, and in the same way, the second dumbbell head may be further secured to the second end of the shaft by a second nut engaged with the thread of the second end of the shaft.

According to an embodiment, the shaft is made of steel with a yield strength between 800-1000 N/mm2and a tensile strength of 1000-1400 N/mm2. By using a high strength steel, the shaft may be designed with a small cross-section with remained strength suitable for all actual weights, but still with a grip with a thin cross-section.

According to an embodiment, the ball bearings are sealed low friction ball bearings. Thereby, the rotation of the grip is very easy, and the impact of the wrist is minimized. At the same time, the seal prevents dirt from entering into the ball bearing, which facilitates a simple and cost effective design where the ball bearing may have an exposed side facing the grip, without any cover plate or the like, thanks to the seal.

According to an embodiment, the first dumbbell head is fixedly connected to the first end of the shaft by a press fitting force of at least 100 kN, and the second dumbbell head is fixedly connected to the second end of the shaft by a press fitting force of at least 100 kN.

Further possible features and benefits of this solution will become apparent from the detailed description below.

