Patent Description:
Safety helmets, such as open face helmets and full face helmets for example, are conventionally known as helmets that riders of motorcycles, for example, put on to protect their heads. Such conventional helmets are mainly configured from an outer shell and, disposed inside the shell, a shock absorbing liner, a right and left pair of chin straps, and internal padding for improving the comfort of the wearer. Furthermore, through holes for ventilation are provided at the upper portion of a facial opening provided in the front face of the helmet to ensure a field of view for the wearer.

When a region of part of the outer shell is impacted, the shell functions to disperse the impact to a wider region and absorb the impact energy through deformation. Furthermore, the shock absorbing liner functions to absorb, through a reduction in its thickness (i.e., compression), the impact energy propagated from the outer shell and delay the propagation of the impact energy to the wearer's head to thereby reduce the maximum acceleration resulting from the impact. Here, "maximum acceleration" means the maximum value of acceleration obtained by an "impact absorption test" of the helmet.

To verify the protection of a safety helmet, conventionally an "impact absorption test" is performed. In the "impact absorption test," a model head made of metal is used as a model of the helmet wearer's head. The impact applied to the helmet in the "impact absorption test" is absorbed as described above, and maximum acceleration is measured by an accelerometer disposed inside the model head made of metal as the impact force that finally propagated to the head. The method of the "impact absorption test" and the standard value for maximum acceleration are respectively determined by respective countries.

To enhance the protection performance of a safety helmet, it is necessary to reduce the maximum acceleration produced by an impact. For this purpose, conventionally, measures that increase the thickness of the outer shell and/or the shock absorbing liner have been adopted.

However, because a helmet has a substantially spherical shape, the rigidity of the top portion is inevitably greater than that of the other portions and makes it difficult to absorb an impact. Thus, a structure called an insert liner was invented.

<CIT> discloses a helmet according to the preamble of claim <NUM>. <CIT> discloses a structure where a cavity portion is provided in the top portion of the inside of a shock absorbing liner and a separate member is inserted into the cavity portion. The inserted member (called an insert liner) has a smaller density, that is, is softer than the shock absorbing liner, so it can reduce the rigidity of the top portion. In this way, the impact absorbability of the top portion can be maintained.

Traffic accidents of late include cases the rider suffers a diffuse axonal injury to the head. Diffuse axonal injury is an injury where axons in the brain become sheared and trauma develops as a result of the brain being violently shaken. The mechanism by which a diffuse axonal injury occurs in the head of a rider is described as follows.

For example, when the right side of the helmet receives an external force caused by an impact, the helmet moves leftward. The cervical spine and trunk of the wearer similarly move even a little leftward because they are not anchored. For that reason, the direction in which the force of impact acts is largely a direction perpendicular to the outer surface of the helmet. The impact acceleration (called "translational acceleration") that occurs because of the external force acting in the perpendicular direction is measured by the "impact absorption test. " Conventional insert liner structures have mainly been measures for the translational acceleration of an impact.

However, when an impact is delivered above the helmet in the vicinity of the top portion, the point of impact is higher than the center of gravity of the helmet, so the helmet tries to rotate leftward about the center of gravity. In this way, a force that causes the helmet to rotate, that is, rotational acceleration is produced by the impact. The rotation of the helmet is stopped as a result of the lower end of the helmet hitting the neck of the wearer or because of friction between the helmet and a road surface.

However, the rotational acceleration produced by the impact propagates to the wearer's head. Here, if the wearer has firmly tightened the chin straps, the wearer's head also stops rotating at the same time as the helmet. Moreover, when the rotational acceleration propagates to the inside of the wearer's head, inside the cranium, rotational force acts on the brain floating in the cerebrospinal fluid, and axons interconnecting the brain and the interior of the cranium become sheared.

In consideration of the above circumstances, it is an object of the present invention to obtain a helmet that can effectively reduce the rotational acceleration of an impact and at the same time also effectively reduce translational acceleration.

Accordingly, an impact to the outer shell is absorbed by the shock absorbing liner disposed inside the outer shell becoming deformed. Furthermore, the insert liner is fitted into the recessed portion of the main body liner. The central support member becomes compressively deformed by the impact, and the insert liner tilts. That is, the insert liner moves with respect to the main body liner. At this time, the wearer's head in close contact with the insert liner also moves together with the insert liner, so rotational acceleration does not propagate to the inside of the head. Moreover, in the recessed portion of the main body liner, there is a space in addition to the insert liner and the central support member. That is, volume of the insert liner is reduced rather than density being reduced as in the insert liner of the conventional example, so the same effects as those of the conventional insert liner are obtained. In this way, not only rotational acceleration of the wearer's head but also translational acceleration can be effectively reduced.

The shock absorbing liner has three other support members disposed around the central support member.

By providing the three support members, even when the wearer's head compresses the insert liner when the wearer tightens the chin straps, the support members support the insert liner together with the central support member, so the helmet can be worn in a stable state without the insert liner tilting and the helmet wobbling.

The central support member may be molded integrally with the insert liner, so the number of constituent parts of the helmet can be inhibited from increasing.

The cross-sectional area of respective distal end of the three other support members may be smaller than the cross-sectional area of a distal end of the central support member, and the central support member and the three other support members may be molded integrally with the insert liner.

The central support member and the three other support members may be molded integrally with the insert liner, so the number of constituent parts of the helmet can be inhibited from increasing. Furthermore, when the force of impact travels from the bottom surface of the recessed portion to the central support member and the three other support members, the three other support members with the smaller contact area become deformed or break first, so the central support member can be prevented from being completely destroyed by the impact. In this way, tilting of the insert liner by the central support member can be reliably carried out.

Outside air taken in through the air inlet at the front face of the helmet is guided to the recessed portion of the main body liner and reaches the air outlet at the back side from the recessed portion. Because of this flow of air, heat emanating from the wearer's head is guided from the inner surface of the main body liner through the ventilation passage of the insert liner to the recessed portion. Furthermore, the outside air in the recessed portion goes to the inner surface of the main body liner. In this way, ventilation in the helmet can be excellently carried out.

The air inlet may be provided at an edge-rolled member disposed at an open portion of a front face of the helmet, so works for providing the air inlet that runs through the shell can be saved and the number of constituent parts of the helmet can be inhibited from increasing.

The helmet pertaining to the invention has the excellent effect that it can effectively reduce the rotational acceleration of an impact and at the same time also effectively reduce translational acceleration.

When a helmet <NUM> receives an impact F2 at a position lower than its center of gravity (G) as shown in <FIG>, the neck of the wearer and the trunk supporting the neck move as shown in <FIG>. Because of this, a force that pushes the helmet <NUM> sideways acts. That is, translational acceleration occurs. However, when the helmet <NUM> receives an impact F1 at a position higher than its center of gravity (G), a force that tries to rotate the helmet <NUM> acts as shown in <FIG>. If the line interconnecting the point of impact and the center of gravity (G) forms a <NUM>-degree to <NUM>-degree angle with the line interconnecting the center of gravity (G) and the top of the helmet <NUM>, both rotational acceleration and translational acceleration occur, but the translational acceleration is greater. Consequently, the force of impact can be mitigated by conventional measures for translational acceleration.

As the angle becomes smaller than <NUM> degrees, rotational acceleration gradually increases and reaches a maximum at <NUM> degrees. Thus, in the present invention, it is deemed preferable to provide in a main body liner <NUM> a recessed portion <NUM> described later (see <FIG>) in a position of <NUM> degrees to <NUM> degrees with respect to the line connecting the top to the center of gravity (G). Furthermore, it is deemed more preferable to provide the recessed portion <NUM> in a position of <NUM> degrees to <NUM> degrees.

First, the configuration of the helmet <NUM> pertaining to an embodiment of the present invention will be described using <FIG>. It will be noted that arrow FR indicates a forward direction in a front and rear direction as seen from the perspective of a wearer currently using the helmet, arrow RH and arrow LH indicate a rightward direction and a leftward direction, respectively, and arrow UP indicates an upward direction in an up and down direction. Furthermore, when the directions of front/rear, right/left, and upper/lower are simply used in the following description, these will be understood to mean front/rear, right/left, and upper/lower as seen from the perspective of the wearer currently wearing the helmet.

As shown in <FIG>, the helmet <NUM> of the present embodiment has an outer shell <NUM> formed with a hard material such as fiber-reinforced plastic and a shock absorbing liner <NUM> disposed inside the shell <NUM> and joined to an inner surface of the shell <NUM>.

As shown in <FIG>, the shock absorbing liner <NUM> has a main body liner <NUM> and an insert liner <NUM> attached to the main body liner <NUM>. Moreover, the main body liner <NUM> has a recessed portion <NUM> for fitting the insert liner <NUM> therein.

As shown in <FIG>, the main body liner <NUM> is formed using synthetic resin foam, and the main body liner <NUM> is formed in the shape of a dome (a recessed shape) in which one side thereof is open. Specifically, the main body liner <NUM> has a left liner portion <NUM> and a right liner portion <NUM> that are disposed along the side portions of the user's head, a rear liner portion <NUM> that is disposed along the rear portion of the user's head, and a front liner portion <NUM> that is disposed along the front portion of the user's head. Furthermore, the main body liner <NUM> has an upper liner portion <NUM> that is disposed opposing the top portion of the user's head. When seen from the underside of the main body liner <NUM>, the upper liner portion <NUM> has an elliptical shape whose longitudinal direction coincides with the front and rear direction and whose transverse direction coincides with the right and left direction, and the recessed portion <NUM> into which the insert liner <NUM> described later (see <FIG>) is fitted is formed in the upper liner portion <NUM>. Ventilation holes <NUM> that communicate with an air inlet at a front side of the helmet <NUM> and ventilation holes <NUM> that communicate with an air outlet at the back side of the helmet <NUM> are formed in the recessed portion <NUM>. Furthermore, a central recessed portion <NUM>, whose edge portion is circular as seen from below and with which a central raised portion <NUM> (see <FIG>) of the insert liner <NUM> described later mates, is formed in the right and left direction and front and rear direction center portion of the recessed portion <NUM>. Moreover, three peripheral recessed portions <NUM>, with which three peripheral raised portions <NUM> (see <FIG>) of the insert liner <NUM> described later mate, are formed around the central recessed portion <NUM>. In the present embodiment, two peripheral recessed portions <NUM> disposed an interval apart from each other in the right and left direction are formed at the front side of the central recessed portion <NUM>, and one peripheral recessed portion <NUM> is formed in the right and left direction center portion at the rear side of the central recessed portion <NUM>.

The position of the recessed portion <NUM> in the main body liner <NUM> is preferably within an elliptical shape formed by the intersection of the surface of the outer shell of the helmet <NUM> with a cone drawn when the line interconnecting the position of the center of gravity of the helmet <NUM> and the top of the helmet <NUM> (see <FIG>) is tilted <NUM> degrees around the helmet <NUM>, and more preferably within a <NUM>-degree cone. Furthermore, the original thickness of the main body liner <NUM> when it is supposed that the recessed portion <NUM> is not provided is preferably <NUM> to <NUM> and more preferably <NUM> to <NUM>. At this time, the depth of the recessed portion <NUM> is preferably <NUM> or less and more preferably <NUM> or less.

As shown in <FIG>, the insert liner <NUM> is formed using synthetic resin foam like the main body liner <NUM>. Specifically, the insert liner <NUM> has an insert liner main body portion <NUM>, which is formed in the shape of a shallow bowl (a recessed shape) in which one side thereof is open, and the central raised portion <NUM> serving as a central support member and the three peripheral raised portions <NUM> serving as other support members, which project upward from the surface on the upper side of the insert liner main body portion <NUM>. The surface on the underside of the insert liner main body portion <NUM> curves in a shape following the top portion of the user's head, and plural grooves <NUM> for ventilation are formed therein. Furthermore, a thin-walled portion <NUM> is disposed at the end portion of an outer periphery <NUM> of the insert liner main body portion <NUM>. The thin-walled portion <NUM> has a thinner wall thickness than the insert liner main body portion <NUM>, and plural cutout portions <NUM> serving as communicating portions that are continuous with the plural grooves <NUM> and whose edge portions are substantially U-shaped as seen from below are formed in the thin-wall portion <NUM>. In this way, the surface on the underside of the insert liner <NUM> (the surface that contacts the wearer's head) has a shape that is longitudinally and bilaterally symmetrical. To industrially manufacture the insert line <NUM>, it is preferably circular or elliptical in shape. Furthermore, the central raised portion <NUM> is formed substantially in the shape of a solid cylinder and projects upward from the front and rear direction center portion and the right and left direction center portion of the surface on the upper side of the insert liner main body portion <NUM>. Furthermore, the three peripheral raised portions <NUM> are each formed substantially in the shape of a circular truncated cone with a smaller outer diameter than the central raised portion <NUM>. In the present embodiment, two peripheral raised portions <NUM> disposed an interval apart from each other in the right and left direction are formed at the front side of the central raised portion <NUM>, and one peripheral raised portion <NUM> is formed in the right and left direction center portion at the rear side of the central raised portion <NUM>.

The insert liner <NUM> preferably has a thickness of <NUM> or more from its surface on the underside (the surface facing the wearer's head) to the bottom surface of the recessed portion <NUM> of the main body liner <NUM>, and more preferably has a thickness of <NUM> to <NUM>. Moreover, the central raised portion <NUM> and the peripheral raised portions <NUM> prevent the insert liner <NUM> from being pushed by the wearer's head and wobbling when the helmet is put on. However, when a region in the vicinity of the top portion of the helmet receives an impact, first, the peripheral raised portions <NUM> become deformed, bent, or cracked by the impact force, but because the central raised portion <NUM> supports the insert liner <NUM> in its center position, a phenomenon occurs where part of the insert liner <NUM> sinks into the recessed portion <NUM> and the part on the opposite side comes up. That is, the insert liner <NUM> tilts with respect to the main body liner <NUM>. Next, the sunk-in peripheral raised portion <NUM> comes up because of repulsive force from the bottom surface of the recessed portion <NUM> (the surface of the upper liner portion <NUM>), and then the central raised portion and the other peripheral raised portions <NUM> to which the impact has propagated after that become deformed, bent, or crack and sink into the recessed portions. In this way, the insert liner <NUM> swings (oscillates). It will be noted that the peripheral raised portions <NUM> may also have conical distal ends as shown in <FIG>, or may also be shaped like walls (mountain ridgelines) such as the Great Wall of China, for example, as shown in <FIG>, so that their area of contact with the bottom surface of the recessed portion <NUM> becomes smaller. Furthermore, the cross section of each of the central raised portion <NUM> and the peripheral raised portions <NUM> at the surface on the upper side of the insert liner is preferably circular or elliptical in shape with a diameter of <NUM> or less and more preferably with a diameter or <NUM> or less.

As shown in <FIG> and <FIG>, the insert liner <NUM> described above is attached (secured) to the main body liner <NUM> in a state in which the insert liner <NUM> has been fitted into the recessed portion <NUM> of the main body liner <NUM>. Specifically, the insert liner <NUM> is secured to the main body liner <NUM> in a state in which the central raised portion <NUM> and the three peripheral raised portions <NUM> are engaged with the central recessed portion <NUM> and the three peripheral recessed portions <NUM> of the main body liner <NUM>. It will be noted that in the present embodiment an adhesive is interposed between the central raised portion <NUM> of the insert liner <NUM> and the central recessed portion <NUM> of the main body liner <NUM> so that the insert liner <NUM> does not come away from the main body liner <NUM> even when the helmet is taken off.

Furthermore, in a state in which the insert liner <NUM> is secured to the main body liner <NUM>, a gap is formed between the surface on the upper side of the insert liner main body portion <NUM> of the insert liner <NUM> and the main body liner <NUM>. In order for the insert liner <NUM> to swing (oscillate and move with respect to the main body liner), a gap formed between the outer periphery <NUM> of the insert liner <NUM> and the inner wall of the recessed portion <NUM> is preferably <NUM> or less and more preferably <NUM> to <NUM>. Moreover, it is possible for the central raised portion <NUM> and the three peripheral raised portions <NUM> of the insert liner <NUM> to be members separate from the insert liner <NUM> and the main body liner <NUM>, and to industrially manufacture them, the central raised portion <NUM> and the three peripheral raised portions <NUM> may be integrally molded on the upper surface of the insert liner <NUM>.

Furthermore, the thin-walled portion <NUM> covers and hides the space between the outer periphery <NUM> of the insert liner <NUM> and the inner wall of the recessed portion <NUM>; however, when the insert liner <NUM> swings, the thin-walled portion <NUM> becomes pushed against the inner wall of the recessed portion <NUM> and easily becomes deformed or broken, so it does not obstruct the swinging.

Next, the action and effects of the embodiment will be described.

As shown in <FIG>, and <FIG>, according to the helmet <NUM> described above, an impact to the outer shell <NUM> is absorbed as a result of the shock absorbing liner <NUM> disposed inside the outer shell <NUM> becoming deformed. Furthermore, as shown in <FIG>, <FIG>, and <FIG>, the insert liner <NUM> is fitted into the recessed portion <NUM> of the main body liner <NUM>. Additionally, the central raised portion <NUM> and the three peripheral raised portions <NUM> become deformed, thereby reducing translational acceleration, and the insert liner is moved (swings) with respect to the main body liner <NUM>, whereby rotational acceleration of the head of the user wearing the helmet <NUM> can be effectively reduced.

Specifically, a gap is provided between the insert liner <NUM> and the recessed portion <NUM>, so as soon as the impact travels to the insert liner <NUM>, instantaneously the phenomenon of rising and sinking occurs (i.e., the insert liner <NUM> swings). Because the insert liner <NUM> swings in this way, the wearer's head in close contact with the insert liner <NUM> also swings and rocks together with the insert liner <NUM>. That is, even if the rotation of the helmet <NUM> is stopped after rotational force has occurred in the helmet <NUM> because of an impact, the wearer's head inside the helmet <NUM> continues to move, so the rotational acceleration caused by the impact does not propagate to the inside of the head or can be reduced.

In order to maximize the rocking effect resulting from the rising and sinking (swinging) of the insert liner <NUM>, it is necessary for the insert liner <NUM> to tilt centering on the center point of the insert liner <NUM>. The central raised portion <NUM> is provided in the center point of the upper surface of the insert liner <NUM> the peripheral raised portions <NUM> are disposed therearound. Furthermore, by giving the peripheral raised portions <NUM> a shape that becomes deformed more easily than the central raised portion <NUM>, deformation occurs starting at the peripheral raised portions <NUM> because of an impact, so the tilting of the insert liner <NUM> centered on the central raised portion <NUM> can be promoted.

Here, test results of an impact test of the helmet <NUM> will be described.

The helmet <NUM> was put on a model head and dropped on top of a steel anvil from a height of <NUM>, and the rotational force produced by the impact at that time was measured by an angular velocimeter. It will be noted that the places of impact were the three points of the vicinity of the top portion of the helmet <NUM>, the front portion in a case where the helmet <NUM> was tilted <NUM> degrees forward, and the left side portion in a case where the helmet was tilted <NUM> degrees leftward.

As will be apparent from table <NUM>, when the swinging insert liner <NUM> was used as in the helmet <NUM> of the embodiment, rotational acceleration was clearly reduced compared to the conventional insert liner. It will be noted that the conventional insert liner is a type where the insert liner does not swing with respect to the main body liner.

Furthermore, in the helmet <NUM> of the embodiment, as shown in <FIG>, <FIG>, and <FIG>, the insert liner <NUM> can be maintained in a stable state by providing the three peripheral raised portions <NUM> in addition to the central raised portion <NUM>.

Furthermore, if only the central raised portion <NUM> is provided, the insert liner <NUM> is unstable just with the wearer putting on the helmet <NUM> (the insert liner <NUM> easily tilt's with respect to the main body liner <NUM>), so comfort is poor. Furthermore, if the translational acceleration of the impact is too large, it is expected that the central raised portion <NUM> will not be able to support the wearer's head and be easily crushed, resulting in the insert liner <NUM> caving in substantially parallel to the recessed portion <NUM>. That is, in this case, the rising and sinking phenomenon of the insert liner <NUM> does not occur. Thus, by providing, in addition to the central raised portion <NUM>, the three peripheral raised portions <NUM> in which the cross-sectional area of their distal ends is smaller than that of the central raised portion <NUM>, the force with which the insert liner <NUM> is supported can be reinforced. Additionally, translational acceleration can be buffered as a result of any of the three peripheral raised portions <NUM> being deformed or bent, and rotational acceleration can also be buffered as a result of the insert liner <NUM> producing the rising and sinking phenomenon.

Moreover, in this embodiment, as shown in <FIG>, <FIG>, and <FIG>, the ventilation holes <NUM>, <NUM> serving as ventilation passages that communicate with the air inlet at the front side of the helmet <NUM> and the air outlet at the back side of the helmet <NUM> are provided, and the cutout portions <NUM> that communicate the recessed portion <NUM> with the wearer's head region are provided at the insert liner <NUM>. An air flow arises wherein outside air taken in through the air inlet in the front face of the helmet <NUM> is introduced through the ventilation holes <NUM> formed in the recessed portion <NUM> of the main body liner <NUM> to the inside of the recessed portion <NUM> and is then discharged via the ventilation holes <NUM> through the air outlet. For that reason, heat emanating from the wearer's head is guided through the cutout portions <NUM> (communicating portions) to the recessed portion of the main body liner. Moreover, some of the outside air introduced to the recessed portion <NUM> reaches the wearer's head through the cutout portions <NUM> (communicating portions). In this way, the ventilation performance inside the helmet <NUM> can be enhanced. That is, heat inside the helmet <NUM> is discharged so that comfort can be provided to the wearer. Furthermore, by providing, in the top portion including the recessed portion <NUM>, the ventilation holes <NUM>, <NUM> that communicate with the front side and back side of the helmet <NUM>, the main body liner <NUM> more easily absorbs translational acceleration caused by an impact. It will be noted that although in the present embodiment the cutout portions <NUM> are provided as the communicating portions for communicating the wearer's head region with the recessed portion <NUM>, the communicating portions are not limited to this, and plural communicating holes that run through the insert liner <NUM> may also be provided.

Furthermore, in the insert liner <NUM> of the present embodiment, the thin-walled portion <NUM> whose thickness is thinner compared to the thickness of a center portion <NUM> is disposed at the end portion of the outer periphery <NUM> of the insert liner main body portion <NUM>. In addition to this, the plural cutout portions <NUM> are formed in the thin-walled portion <NUM>. The rigidity of the thin-walled portion <NUM> is reduced because of the cutout portions <NUM>. Because of this, when the helmet <NUM> is impacted, the thin-walled portion <NUM> is easily deformed or broken, so the thin-walled portion <NUM> does not obstruct the moving (swinging) of the insert liner. Additionally, in the present embodiment, the insert liner <NUM> is reinforced by disposing the plural peripheral raised portions <NUM> around the central raised portion <NUM> so that the central raised portion <NUM> does not become crushed and the insert liner <NUM> swings without collapsing into the recessed portion <NUM>.

Furthermore, in the present embodiment, as shown in <FIG> and <FIG>, the air inlet is provided at an edge-rolled member <NUM> in the open portion of the front face of the helmet, and outside air that has been taken in is divided in two, with one flow traveling over the outer surface of the main body liner <NUM> and reaching the recessed portion <NUM> through the ventilation holes <NUM> and the other flow traveling over the inner surface of the main body liner <NUM> and being guided to the ventilation grooves <NUM> provided at the underside of the insert liner <NUM>. In this way, the number of parts for the air inlet can be reduced and the number of manhours for assembly can be reduced.

Claim 1:
A helmet (<NUM>), comprising an outer shell (<NUM>) configured by a hard material, and a shock absorbing liner (<NUM>) formed using synthetic resin foam, disposed inside the outer shell (<NUM>),
wherein the shock absorbing liner (<NUM>) comprises a main body liner (<NUM>), a recessed portion (<NUM>) provided at an inner surface of the main body liner (<NUM>), an insert liner (<NUM>) fitted into the recessed portion (<NUM>), and a central support member (<NUM>) and three other support members (<NUM>) disposed between a bottom surface of the recessed portion (<NUM>) and an upper surface of the insert liner (<NUM>), the three other support members (<NUM>) disposed around the central support member,
a ventilation passage (<NUM>) that communicates with an air inlet at a front side of the helmet (<NUM>) is provided at the recessed portion (<NUM>), and
a ventilation passage (<NUM>) that communicates the recessed portion (<NUM>) with an inner surface of an insert liner main body portion (<NUM>) is provided at the insert liner (<NUM>), the inner surface being configured to contact a head region of a wearer, wherein:
the central support member (<NUM>) is formed substantially in the shape of a solid cylinder and projects upward from a front and rear direction center portion and a right and left direction center portion of the surface on the upper side of the insert liner main body portion (<NUM>),
characterized in
that a gap is formed between the surface on the upper side of the insert liner main body portion (<NUM>) and the main body liner (<NUM>),
that the central support member (<NUM>) is engaged with a central recessed portion (<NUM>) formed at the recessed portion (<NUM>) of the main body liner (<NUM>), and three other support members (<NUM>) are mated with three peripheral recessed portions (<NUM>) formed around the central recessed portion (<NUM>) of the main body liner (<NUM>), and
that a ventilation passage (<NUM>) that communicates with an air outlet at a back side of the helmet (<NUM>) is provided at the recessed portion (<NUM>).