EP1880621B1

EP1880621B1 - Improvement in a helmet visor

Info

Publication number: EP1880621B1
Application number: EP07103674A
Authority: EP
Inventors: Roberto c/o Mavet S.r.l. Parissenti
Original assignee: Dainese SpA
Current assignee: Dainese SpA
Priority date: 2006-03-09
Filing date: 2007-03-07
Publication date: 2010-01-27
Anticipated expiration: 2027-03-07
Also published as: EP1880621A2; ITRM20060124A1; ATE456314T1; EP1880621B9; EP1880621A3; DE602007004534D1

Abstract

A visor (1) for helmet (100) is characterised in that it has at least one portion (10) concave with respect to a surface (101) defined by the development of said helmet (100).

Description

The present invention refers to a helmet visor for sporting activities, in particular motorcycling.
As it is known, motorcycling helmets use a visor to protect a wearer's eyes both from the air flow impinging on the helmet during motion and from any small thing, e.g. sand or insects, which may hit the helmet during travel.
Said visors are generally made by means of the use of variously cut and shaped sheets of see-through plastics material (classically polycarbonate). Alternatively, visor making may occur by injection moulding.
Visor shape is substantially analogous for all types of existing helmets and, in particular, it is initially carried out by means of the cutting to size of a pane (so that the curvature of the visor appears present according to a sole radius) whose curvature is subsequently changed.
Such curvatures, having a radius that may reach 4 cm, generate a particular geometry allowing the visor to be integral part of the geometry of the helmet itself, so as to limit the aerodynamic effects it creates, see for example GB 1 586 377 .
Moreover, jet-type helmets devoid of the chin-rest are widespread, where the length of the visor is such as to at least partially cover also the chin.
In these helmets the visors, though having no structural function, are made so as to limit undesired aerodynamic effects of flow recirculation inside of the padding and the visor itself.
For this reason, some of the helmets made according to the known art exhibit a high downward extension allowing to limit, as much as possible, the entity of the flow lapping the wearer's face.
Likewise, also on "integral"-type helmets, in which the cap comprises also a chin-rest for chin protection, the visor is a component formally having no structural functions and mounted so as to open in case of need, generally by means of a rotation about an axis.
As it is easily conceivable, the hereto-described embodiment allows a simple production with high features of scale economy and simplicity of production, besides an easy implementation of tear off protection systems, allowing to easily make a cleaning system on competition helmets.
However, visors made according to the known art entail the drawback of having scarce aerodynamic features, with the entailed general decrease in performances and wearer's comfort.
More precisely, owing to the geometry used, and to purely aerodynamic reasons, the stress to which the visor is subjected substantially translates into static pressure acting on a point, called stagnation point, approximately located in the central zone of the visor itself.
This action generates a gradient of pressure and velocity such that onto the air flow impinging on the helmet there appears the so-called boundary layer detachment phenomena, often followed by re-attachment. This phenomenon entails the presence of areas exhibiting flow recirculation bubbles, of variable dimensions, which overall create conditions useful to the generation of an oscillating flow.
This condition creates a series of problems that limit internal comfort, owing to the increase of the overall drag of the helmet, the pressure range variability and the instability of the internal and external flow.
Hence, the technical problem underlying the present invention is to provide a helmet with a visor overcoming the drawbacks hereto mentioned with reference to the known art.
Such a problem is solved by a visor according to claim 1 and a helmet comprising the same according to claim 5.
The present invention provides several relevant advantages. The main advantage lies in that the visor according to the present invention allows to create a particularly even pressure field, thereby ensuring a high comfort to the wearer.
Moreover, unlike the known art, the visor according to the present invention modifies the overall aerodynamic behaviour of the helmet, introducing advantageously exploitable induced flows.
Other advantages, features and the operation modes of the present invention will be made apparent from the following detailed description of some embodiments thereof, given by way of example and not for limitative purposes. Reference will be made to the figures of the annexed drawings, wherein:

Fig. 1 is a side exploded view of a helmet comprising a visor made according to the present invention;
Fig. 2 is a partially sectional side view of a helmet with visor made according to the known art;
Fig. 3 is a partially sectional side view of the helmet with visor of Fig. 1;
Fig. 4 is a partially sectional top plan view, illustrating a detail of the helmet and visor of Fig. 3;
Fig. 5 is a top plan view of the helmet with visor of Fig. 3;
Fig. 6 is a sectional and partial front view, showing a detail of the helmet and visor of Fig. 5;
Figgs. 7A and 7B are schematic illustrations depicting pressure distribution on the surface of a helmet comprising a visor made according to the known art and a visor according to the present invention, respectively;
Figgs. 8A and 8B are schematic illustrations depicting flow velocity distribution on the surface of a helmet comprising a visor made according to the known art and a visor according to the present invention, respectively; and
Fig. 9 is a graph illustrating the pattern of the drag load depending on flow velocity in helmets comprising a visor made according to the known art and a visor according to the present invention, respectively.

Referring initially to Fig. 1, a visor 1 according to the present invention is fixed, analogously to known visors, to a cap 102 of helmet 100, so as to provide protection in correspondence of an opening 103 typically present on the cap 102. In the present embodiment, the helmet is of integral type, i.e., the cap also comprises a chin-rest; however, as it will be made apparent hereinafter, the same considerations will apply to other helmet types.
Therefore, referring to Fig. 3, the visor according to the present invention is characterised in that it has at least one portion 10 concave with respect to a surface 101 defined by the development of the helmet 100. Therefore, it may be observed that at said opening 103 the visor does not follow the shape of said surface 101.
In particular, the visor has a curvature facing inwards the helmet, unlike helmets made according to the known art in which, as illustrated in Fig. 2, the visor substantially follows the pattern of the helmet cap.
Referring to Figgs. 1 and 3, the visor 1 extends substantially along a contour 105 defining the opening 103, so as to prevent entry of air into the helmet. To improve the closure provided, there are also utilized sealing elements 104 fixed on the cap, or alternatively on the visor itself.
Therefore, the visor 10 may be arranged substantially according to a closed configuration that, as hereto-described, protects the wearer's face during helmet use, or the former may be raised, allowing access to face, through the opening 103. Such a raised configuration is not described in figure, since it is well-known to a person skilled in the art.
However, in order to place the visor in the two aforedescribed configurations, the latter is fixed to the cap 102 by means of suitable connecting means 2, allowing a combined motion of rotation and translation of the visor. In fact, the shape of the visor is such that a mere rotation would be hindered by the contour 105.
The connecting means 2 may, e.g., be formed by the combination of a guide and a hinge, not illustrated in figure since this constructive solution is known to a person skilled in the art and, therefore, it will not be further detailed hereinafter.
Referring again to Fig. 3, the visor has an extension substantially defined by the region delimited by the contour 105, and develops along a curved surface whose center of curvature 11 is positioned externally to the volume defined by the helmet. In helmets made according to the known art, the center of curvature of the visor substantially matches the center of curvature 106 of the surface 101 and therefore lies inside said volume, as it is shown in Fig. 2.
Hence, referring to Figgs. 4 and 5, note also that the hereto-described curvature is not constant along the extension of the visor 1; instead, the concavity is less pronounced in the neighbourhood of the connecting means 2.
In fact, it should be understood that generally the radius of curvature of the development surface of the visor is not constant and, accordingly, also the position of the center of curvature 11 varies depending on the visor shape. However, at the concave portion 10, the center of curvature 11 appears anyhow as mentioned above, outside of the volume circumscribed by the helmet.
Moreover, at the connecting means 2, the shape of the visor substantially matches that defined by the cap 102.
On the other hand, evidently the portion 10, at which the visor 1 has a concave shape, may not extend to the connecting means 2, but be of smaller dimensions with respect to the overall development of the visor.
Note also that the making of the visor according to the present invention substantially provides to invert the curvature direction with respect to what is made according to the known art.
Such a feature provides an effective channelling of the air flow impinging on the visor, substantially forming channels, defined by its development, allowing to ensure to the flow an effective acceleration in the horizontal direction, along a plane substantially perpendicular to what in aerodynamic jargon is called "stagnation point", identifiable by a good approximation on the center of gravity of the visor itself.
This fluid-dynamic behaviour, related to the hereto-described geometry, entails substantial advantages in terms of sensitivity to turbulent wake.
Experimental tests performed by the Applicant highlighted that such a sensitivity is limited of about the 17% in terms of turbulent kinetic energy (TKE), generating appreciable advantages both in terms of noise, the latter directly depending on the turbulent kinetic energy, of buffeting frequencies (instability due, again, to effects related to the turbulent wake) and also of drag, since the present solution substantially decreases its induced part, though a slight increase of the so-called "form drag" is observed.
However, analyses highlighted that induced drag decrease is far greater than form drag increase, so that ultimately the end balance is anyhow positive.
Moreover, the flow channelling effect is particularly advantageous since it can be exploited to improve the performances of suitable dynamic ventilation and/or extraction and/or forced ventilation means, not illustrated in figure, and arranged in a zone 12 immediately adjacent to the connecting means 2 of the visor 1, illustrated in Fig. 1, or, alternatively, directly onto the cap. The ventilation means may comprise, e.g., an array of dynamic air intakes, both inlet and outlet ones.
In fact, in this zone channelled flows are implemented which, thanks to the presence of a negative pressure gradient, markedly accelerate the flow, without however diffusing on the entire helmet cap.
Hence, their specific flow rate is extremely high; according to the relationship defined by Bernoulli's theorem, said zone will be characterised by a low static pressure.
Hence, the dynamic pressure can be well exploited by a dynamic air intake, or by an extraction air intake, which, thanks to the high pressure difference generated between the inside and the outside of the visor, ensures an excellent extraction flow rate.
This feature proves very advantageous, as it substantially allows to eliminate any visor fogging problem.
The relative motion between helmet and fluid (generally air) occurring during motorcycling practice, and generally in every sporting activity requiring helmet use, generates a flow that starts with a laminar characterization in the immediate neighbourhood of the stagnation point, whereas, when departing from this point, it is characterised by an increase of the thickness of the boundary layer, i.e. of the velocity profile immediately near to the helmet surface, until getting to a turbulent transition.
The applicant has experimentally observed that the phenomenon of transition to a turbulent regimen occurs at <100 mm linear distances onto the helmet surface, already at velocities higher than 10 m/s.
Subsequently, owing to the tangential efforts internal to the boundary layer, a detachment of the boundary layer occurs, which in turn feeds the turbulent wake behind the helmet.
Moreover, note that the geometry of the visor described hereto allows to exploit an accumulation effect of the generated fluid threads, as those tend to remain internal to the zone corresponding to the visor, without perturbing the external flow.
With reference to this latter feature, in Fig. 7A it is depicted the pressure distribution on a helmet comprising a visor according to the present invention, compared in Fig. 7B with that obtained in a helmet according to the known art.
From a comparison of the two figures, it may be seen that in helmets with a traditional visor there is a greater presence of low-pressure zones; their presence being indicated by a lighter colour, in which there is an entailed greater possibility of detachment.
However, at a local level and externally to the visor zone, a set of pressure gradients are created, organized so as to be positive with respect to in-visor values that, by being actually channelled, tend to locally have a pressure lower than the external one. Unlike from what occurs with a convex visor, i.e. a visor of traditional shape, this feature allows to attain a high thickening of the fluid threads so as to ensure a high energizing internally to the boundary layer.
Accordingly, the flow transits in a delayed manner, as it may be observed in Figgs. 8A and 8B, where flow transition zones with the visor according to the present invention or with a traditional visor are compared.
Lastly, in Fig. 9 it is disclosed the result of an aerodynamic simulation of the present invention, illustrating the drag load pattern on the helmet as a function of flow velocity, in which it may be observed that, drag loads being equal, the visor according to the present invention allows to have a lower flow velocity with respect to traditional visors.
Incidentally, said aspects were also observed by the Applicant in tests, performed in wind tunnels, demonstrating that the visor according to the present invention ensures a correct transition from laminar to turbulent flow and keeps the flow under acceleration on limited zones, with no diffusion thereof being created. Ultimately, such features allow to keep a correct motion field, with ample improvements both under the standpoint of the aerodynamic behaviour and of the phonometric one.
Lastly, note that the curvature of the visor will be selected and sized depending on the helmet geometry and on the fluid-dynamic features that are to be enhanced more.
These design choices are anyhow within the reach of a person skilled in the art and, e.g., attainable by means of numerical simulations, and therefore will not be further detailed hereinafter.
The present invention has hereto been described with reference to preferred embodiments thereof. It is understood that there might be other embodiments referable to the same inventive kernel, all falling within the protective scope of the claims hereinafter.

Claims

A visor (1) for helmet (100), characterised in that it has at least one portion (10) concave with respect to a surface (101) defined by the development of said helmet (100).
The visor (1) for helmet (100) according to claim 1, wherein said concave portion (10) is apt to define channels apt to carry out an acceleration of a fluid impinging on said helmet (100) in a horizontal direction, along to a plane substantially perpendicular to the stagnation point of said flow.
The visor (1) for helmet (100) according to one of the preceding claims, wherein said concave portion (10) has a development along a surface having respective centers of curvature (11) positioned externally to the volume defined by said helmet (100).
The visor (1) according to one of the preceding claims, comprising dynamic ventilation and/or extraction and/or forced ventilation means arranged near a side portion (12) of said visor.
A helmet (100), in particular for sporting activities, characterised in that it comprises a visor (1) according to one of the claims 1 to 4.
The helmet (100) according to claim 5, wherein said visor (1) extends substantially at a surface whose extension is defined by a contour (105) delimiting an opening (103) made on said helmet (100).
The helmet (100) according to one of claims 5 or 6, wherein said visor (1) is connected to said helmet (100) by means of suitable connecting means (2) apt to carry out a combined motion of rotation and translation of said visor (100).