DESC:TECHNICAL FIELD

[001] The present subject matter described herein relates to a head safety systems, and more particularly relates to a motorcycle helmet.

BACKGROUND

[002] A helmet is a form of protective gear worn to protect the head from injuries. For helmet to work properly it must be tightened properly and should not become loose during an accident. The retention system performs these tasks and holds the helmet on head. A good retention system is therefore a must for the helmet to work effectively in preventing injuries and providing safety. A retention system must also be easy to use and not cause any discomfort to the user. Many researchers have developed systems and mechanisms for retaining a helmet on the head which would optimize both safety and comfort of the user. Most of these retention systems include an adjustment mechanism which permits the wearer to tighten or loosen the strap while the helmet is on the wearer’s head. Such adjustment mechanism comprises usually a knob or another shape which provides grip to the wearer to adjust the tension on his head.

[003] According to the U.S. Patent No. 5,027,479, the inventors used some adjustable flaps which would help to tighten the strap according to the desired change in head size. The major drawback with these adjustable flaps is that the helmet can be used only for three (limited) head sizes. Another step towards developing a new retention system is given by U.S. Patent No. 6,425,142 (‘142). The patent ‘142 addresses the problem and suggests a retention system which comprises an adjustment mechanism for adjusting the size, an elastic element or a spring for positioning the dome against the occipital region of the wearer’s head to stabilize the helmet against the wearer’s head. The drawback with the system disclosed in the ‘142 is that the spring pushes the adjustment mechanism against the occipital region of the wearer’s head which may result in asymmetric tightening and unequal pressure distribution along the head.

[004] According to the U.S. Patent No. 7,178,175, the inventors have provided one extra strap along with the usual strap which has been used for tightening the helmet to the occipital region of the wearer’s head. One of the ends of both these straps has been connected with the help of slide/coupling mechanism which is used for adjusting the tightness of the straps. This coupling mechanism tightens both the straps by means of friction. However, the straps may slip during a sudden impact and may lead to the loosening of strap therefore the retention system is not reliable.

[005] Some people have also developed the retention system which has a shape like the dome which can be fitted inside the helmet. As stated in U.S. Patent No. 9,066,551, the retention system for a helmet includes a front head belt, a rear basket and a tensioning device for tensioning the front head belt and a rear basket along the wearer’s head. The tensioning device includes a spring and a cable which is attached to the front head belt. This self- adjusting retention system is attached to the dome.

[006] The drawbacks of the retention system as mentioned above is that it can slip from the head during the fatal accidents because of this dome shape and the absence of the main strap also enhances the slipping. As prior literatures mainly focused on the self adjusting part of the retention system but has ignored the fact that locking is also important, if not considered more important, than self adjustment. In U.S. Patent No. 9,101,176 (‘176) the inventors have developed a retention system for the helmet which introduces the locking with the help of cutting the teeth on the surface of plastic straps in opposite directions so when the straps are mated, they form a locking. According to the ‘176, a special pin has been designed to adjust the length of the straps. They made the plastic strap in the curved form. The major drawback with this retention system is that the curved shape strap is not feasible because the shape of the chin of the wearer may be different so that it may not adjust with all the wearers.

[007] Literature indicates that among helmet users, 15% suffer critical injuries owing to the negligence in fastening chinstrap of their helmets. In countries like India, it is observed that most of the people do not bother to tighten the strap of helmet. This is because of ignorance of significance of the strapping, laziness in tying the strap, or due to mechanism deteriorating over a period of time and not functioning properly. A helmet is often used by multiple users with different sized heads and there is reluctance to change the setting of the strap each time a different person wears the helmet. As a result people either hesitate to use the available strap mechanisms in motorcycle helmet or use it without applying proper locking. According to the available literature, most of the existing strap mechanisms have manual locking, which always has some functional failure like slipping. A loose strap is dangerous as the helmet can wobble on the rider`s head during driving and come off from the head during an accident leading to serious head injury. Apart from this, there is a problem of location of strap mechanism because the buckle for locking is made of plastic which touches the lower part of the chin and causes irritation.

[008] Thus, it may be understood from the above that the helmet retention system should have minimal manual intervention for adjusting and locking the strap and the mechanism should be so located that it will not cause any irritation to the rider. One such location is the inside of helmet shell itself. The strap mechanism should be reliable and maintain its quality over usage time.

[009] Without a reliable strap mechanism, the motorcycle helmet is useless and will not perform its function of providing safety to the head during an accident. Strap mechanism which is specifically designed to keep the helmet on the head during an impact must function correctly for the purpose it is designed.

[0010] The above-described deficiencies of the retention systems of the helmets are merely intended to provide an overview of some of the problems of existing systems, and are not intended to be exhaustive. Other problems with conventional systems and corresponding benefits of the various non-limiting embodiments described herein may become further apparent upon review of the following description

SUMMARY OF THE INVENTION

[0011] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

[0012] An objective of the present invention is to solve the problems associated with manual strap adjustment and locking by providing a self tightening strap mechanism for a motorcycle helmet.

[0013] Another objective of the present invention is to provide a retention system that is simple to use and ensures that the helmet is worn properly. The strap in the present invention can be rolled on a roller and does not hang freely. Further, a single button is provided to tighten the strap in a comfortable locking position.

[0014] Another objective of the present invention is to provide a retention system that is light in weight as well as small in size.

[0015] Yet another objective of the present invention is to provide a retention system that has an auto - adjustable feature so that the user will not have to adjust it again and again.

[0016] Still another objective of the present invention is to provide a helmet having a retention system that is reliable.

[0017] It is noted that, the helmets presently available in the market have manually operated strap tightening mechanism with non-efficient locking, which affects the basic protection provided by the helmet. In countries like India, among helmet riders, 15% suffer critical injuries owing to the negligence in fastening chinstrap of their helmets according to the survey.

[0018] Accordingly, the present subject matter provides an automated strap tightening mechanism for a motorcycle helmet ensuring that the helmet does not fly off from the head during an accident thereby preventing fatal injuries during motorcycle accidents. It is auto-adjustable and self-locking capabilities. The strap mechanism ensures that the strap is adjusted automatically at the chin rest and also ensures that the helmet will be retained on the head during an accident.

[0019] In one implementation, according to the present invention, the rider has to just press a switch for automatic tightening of strap, so it will overcome the problem of adjustment of strap again and again. This is achieved due to the spiral spring coupled with the switch. It is to be noted that, in working condition, the wearer first of all releases the strap and during releasing the strap the spiral spring stores energy. This energy will be released when the switch is the strap rewinds and adjusts to chinrest. It may be also understood by the person skilled in the art that, pressing the switch is manual but adjusting the strap below chinrest is automatic.

[0020] In one implementation, according to the present invention, the helmet will be retained on the head during an accident. To achieve this feature, the ratchet and pawl locking mechanism has been used. A ratchet is a mechanical device that allows continuous rotary motion only in one direction while preventing motion in the opposite direction. In the present strap mechanism, pawl is connected with a torsion spring and it can operate like a lever or button. When the rider will press the button, the mechanism will unlock which means that there is no contact between pawl and ratchet and at this point, the strap can be pulled out from roller. In default condition, the button will be engaged with pawl means locking condition. In locking condition, the mechanism will not allow the strap to pull out from roller. After manufacturing the mechanism (for testing), various tests specified by the Snell Foundation have been done to check proper performance of the locking as well as complete mechanism. Because the mechanism successfully passed these tests, it is ensured that the strap mechanism work correctly and helmets will not fly off from head during the accident.

[0021] As compared to the prior-art head safety mechanisms, the present invention provides an auto-adjustability feature wherein the rider has to just press a lever or a switch for automatic tightening of strap, so it will overcome the problem of adjustment of strap again and again. In order to achieve this, a new design of the head system comprises a spiral spring connected in between a fixed point and wound upon a shaft at the other end.

[0022] Although there are various types of locking mechanisms available but due to the space constraint, ratchet and pawl mechanism were found to provide perfect locking. A ratchet is a mechanical device that allows continuous rotary motion in one direction only while preventing motion in the opposite direction.

[0023] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0024] The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0025] Figure 1 illustrates an inner view of the helmet attached with strap mechanism, in accordance with an embodiment of the present invention.

[0026] Figure 2 illustrates an outer view of the helmet attached with strap mechanism, in accordance with an embodiment of the present invention.

[0027] Figure 3 illustrates an assembled view of the strap mechanism, in accordance with an embodiment of the present invention.

[0028] Figure 4 illustrates an exploded view of the strap mechanism, in accordance with an embodiment of the present invention.

[0029] Figure 5 illustrates a roller, in accordance with an embodiment of the present invention.

[0030] Figure 6 illustrates a pawl, in accordance with an embodiment of the present invention.

[0031] Figure 7 illustrates a locking collar, in accordance with an embodiment of the present invention.

[0032] Figure 8 illustrates a spring collar, in accordance with an embodiment of the present invention.

[0033] Figure 9 illustrates a casing, in accordance with an embodiment of the present invention.

[0034] Figure 10 illustrates a square ended rod, in accordance with an embodiment of the present invention.

[0035] Figure 11 illustrates a switch, in accordance with an embodiment of the present invention.

[0036] Figure 12 illustrates a guide way for switch movement, in accordance with an embodiment of the present invention.

[0037] Figure 13 illustrates a stopper, in accordance with an embodiment of the present invention.

[0038] Figure 14 illustrates a spiral spring, in accordance with an embodiment of the present invention.

[0039] Figure 15 illustrates torsion spring, in accordance with an embodiment of the present invention.

[0040] Figure 16 illustrates a strap, in accordance with an embodiment of the present invention.

[0041] Figure 17 illustrates a hinge, in accordance with an embodiment of the present invention.

[0042] Figure 18 illustrates a ratchet and pawl mechanism, in accordance with an embodiment of the present invention.

[0043] Figure 19 (a-g) illustrates various test conducted on the product of the present invention, in accordance with an embodiment of the present invention.

[0044] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0045] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0046] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0047] The terms and words used in the following description are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention.

[0048] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0049] By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0050] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0051] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0052] The components given in the figures are individually numbered where the numbers refer to the following:

1 Helmet
2 Strap mechanism
3 Strap
4 Rivet
5 Switch mechanism
6 Roller
7 Pawl
8 Locking collar
9 Spring collar
5 Casing
11 Rod
12 Switch
13 Guide way for switch movement
14 Switch stopper
15 Spiral spring
16 Torsion spring
17 Hinge
18 Ratchet wheel. This end is connected to the left side collar at ‘13’
19 Space for winding the strap. This side connected to the roller at ‘4’,’5’
20 Slot to fix strap
21 Slot to lock the one end of spiral spring
22 Slot to fix the one end of spring
23 Hole for hinge
24 Space to fix one end of torsion spring
25 Locking teeth
26 Projection to guide the pawl
27 Hole for hinge
28 Square hole to constraint the rotation degree of freedom
29 Space to fix the one end of torsion spring
30 Grooves to limit the motion of pawl
31 Slots to lock the one end of spiral spring
32 Step for connecting the casing
33 Square slot for the rod
34 Slot for guiding the strap
35 Slots to attach the mechanism with helmet

[0053] Helmets are widely used by two wheeler riders to protect their head during the accidents or falls. However, with more motor cycle riders involved in accidents and with everyday use, the weak points of today’s helmet designs are revealed. One such weak point has been proved to be the hazard of chin strap malfunctioning or not being tied properly. The purpose of a chin strap is to keep the helmet on the wearer’s head (especially during accidents). Presently in helmets, there is a chance that the wearer does not tie the strap or keeps it loose. In some cases, it can lead to fatal accident or severe injury, though he wears the helmet. That is either due to lack of any locking or at a certain level the strap does not get tightened properly. Apart from that, available strap mechanism has many more problems like an uncomfortable location, absence of auto-adjustment and imperfect locking capabilities. Therefore, there is a need to fill this gap by designing a strap mechanism in such a way that will tackle the above mentioned difficulties. Therefore, the main aim of this study is to enhance the effectiveness of the helmet.

[0054] Accordingly, the present subject matter provides an automated strap tightening mechanism for a motorcycle helmet ensuring that the helmet does not fly off from the head during an accident. The strap mechanism is very useful to secure the head from the fatal injuries during motorcycle accidents. It has auto-adjustable and self-locking capabilities. The strap mechanism ensures that the strap is adjusted automatically at the chin rest and also ensures that the helmet will be retained on the head during an accident.

[0055] Working of Strap mechanism: The working of the automatic strap mechanism consists of two stages as explained below:

[0056] Stage 1: Releasing the Strap: Initially the strap 3 is fully rolled over the roller 6. The pawl 7 is disengaged from the ratchet wheel 18 by sliding the switch 12 in upward direction as shown in the figure 2. While the switch moves upward, the ratchet will become free so that the roller 6 can rotate on the stationary shaft. In this condition, the strap 3 is pulled out by the wearer to wear the helmet. Since the roller 6 is attached to one end of the spiral spring 15, the spiral spring 15 stores the energy when the wearer pulls the strap. In this state wearer can put on the helmet 1.

[0057] Stage 2: Tightening the Strap: The stored energy, due to pulling the strap 3, helps to regain the locking position after wearing the helmet just by pressing the switch 12. At this instant, the strap will be in tight condition and the rotation of the roller 6 will be locked because of the engagement of ratchet and pawl 7. Now, the helmet will not release until rider will not use the switch.

[0058] It may be understood by the person skilled in the art that, the strap is permanently fixed at a point (say point 4 as shown in figure 1), the wearer will releasing the strap by pulling action. Pressing the switch is manual but adjusting the strap below chinrest is automatic.

[0059] Some advantages of the strap mechanism according to the present subject matter are as providedbelow:
i. The mechanism is very easy to use because it operates with a single slide type switch (i.e. pawl). So that the users can put on and take off their helmet many times in a day easily.
ii. The use of the strap mechanism in the helmet is such that it does not allow the user to use the helmet without using the strap.
iii. The efficient locking mechanism fully ensures that the helmet will not fly off from the head in case of an accident which makes it reliable to use.
iv. The strap mechanism weight is 45 gm, so after attaching with the helmet it will not increase the weight of helmet significantly.
v. The optimum size of the strap mechanism allows attachment to the existing helmet shell.
vi. Multiple users, i.e. different people can use the helmet without having to manually adjust the strap to fit different sized head.

[0060] Referring now to the components as shown in the respective figures:

[0061] Roller: This is a very important part of the strap mechanism 2 on which the strap 3 will be wrapped. It rotates on the stationary shaft. The main uses of roller are as follows:
i. It provides the space for winding the strap marked as ‘19’ (figure 5).
ii. The space for accommodating the spiral spring. The other end of the spring is connected inside the roller shown at ‘21’ (figure 5), so when the roller is rotating over the rod, the spring will wind up.
iii. Roller also consists of the ratchet wheel marked as ‘18’ (figure 5) by which locking will takes place.
iv. The slot at ‘20’ (figure 5) is provided to fix the one end of the strap.
v. The thin slot at position ‘22’ (figure 5) is provided to avoid the disturbance of spiral spring locked end.

[0062] Pawl: The pawl works like a button which locks the mechanism by engaging or disengaging with the ratchet (i.e. roller). It is connected with the spring, so it will always be engaged with the ratchet in free condition. It will disengage from the ratchet while pressing it. The hole at ‘23’ (figure 6) is provided for making the pin joint connection with the hole marked as ‘27’ (figure 7) in the locking collar.

[0063] Locking Collar 8: The locking collar is directly connected to one side of the casing 5. The centre square hole is also provided in this collar to connect the steel rod. The purpose of this collar is to make a rigid connection between casing 5 and rod 11, which makes the whole assembly stationary apart from the roller 6. It provides the provision to connect the pawl with a pin joint marked as ‘27’ (figure 7), so that the pawl can rotate and engage with ratchet with the help of a spring. One end of the torsion spring is connected to this collar at ‘29’ (figure 7) and another will be in the pawl at ‘24’ (figure 6) to control the pawl movement.

[0064] Spring Collar 9: The spring collar is connected to the casing and it is also attached to a square ended rod by providing a press fit in a square hole. Spring collar also provides a rigid connection between the casing and the rod. Figure 8 shows the spring collar.

[0065] Casing: The casing has the following purposes-
i. To cover-up the whole assembly.
ii. It helps to guide the strap in slot provided at ‘34’ (figure 9)
iii. To make the rod stationary with the help of spring and locking collars.
iv. To attach the mechanism with the helmet.

[0066] Rod: The square ended rod (figure 10) is used to support all parts of the mechanism in the assembled condition. The rod ends are square in shape to resist the rotation of spring and locking collar. The roller is free to rotate on this rod.

[0067] Switch: Figure 11 shows the switch to operate the locking mechanism in the helmet. This switch is attached to the end portion of the pawl. So when the switch will slide in the upward direction, the roller will be free to rotate.

[0068] Guide way: The guide way is provided to guide the switch movement smoothly shown in figure 12.

[0069] Stopper: The stopper is fixed at one end of the guide way after inserting the switch. It helps to constrain the stroke of the switch, so that the switch will not come out from the guide way during the working. The stopper is shown in figure 13.

[0070] Spiral Spring: A flat spiral spring (figure 14) is used to provide a restoring torque to a roller when it is rotated through an angular displacement. It is generally rectangular in cross-section. One end of the spring is connected to the slot in spring collar at ‘31’ (figure 8) and the other end is connected to the roller at ‘21’ (figure 5).

[0071] Torsion Spring: The torsion spring (figure 4-15) is used to control the pawl motion. One end of the spring is fixed to the locking collar at ‘29’ (figure 7) and the other end is connected to the pawl at ‘24’ (figure 6).

[0072] Strap: The purpose of strap is to fasten the helmet on the head and prevent it from rolling off. Helmet straps are generally made of nylon. The length and the width of the used strap are taken as 400-500 mm and 20 mm respectively. Figure 16 shows the strap.

[0073] Hinge: The hinge is fixed the one end of the strap to the outer shell of the helmet. Figure 17 shows the hinge.

[0074] Figure 1 illustrates an inner view of the helmet attached with strap mechanism, in accordance with an embodiment of the present invention.

[0075] Figure 2 illustrates an outer view of the helmet attached with strap mechanism, in accordance with an embodiment of the present invention.

[0076] Figure 3 illustrates an assembled view of the strap mechanism, in accordance with an embodiment of the present invention.

[0077] Figure 4 illustrates an exploded view of the strap mechanism, in accordance with an embodiment of the present invention.

[0078] Figure 5 illustrates a roller, in accordance with an embodiment of the present invention.

[0079] Figure 6 illustrates a pawl, in accordance with an embodiment of the present invention.

[0080] Figure 7 illustrates a locking collar, in accordance with an embodiment of the present invention.

[0081] Figure 8 illustrates a spring collar, in accordance with an embodiment of the present invention.

[0082] Figure 9 illustrates a casing, in accordance with an embodiment of the present invention.

[0083] Figure 10 illustrates a square ended rod, in accordance with an embodiment of the present invention.

[0084] Figure 11 illustrates a switch, in accordance with an embodiment of the present invention.

[0085] Figure 12 illustrates a guide way for switch movement, in accordance with an embodiment of the present invention.

[0086] Figure 13 illustrates a stopper, in accordance with an embodiment of the present invention.

[0087] Figure 14 illustrates a spiral spring, in accordance with an embodiment of the present invention.

[0088] Figure 15 illustrates torsion spring, in accordance with an embodiment of the present invention.

[0089] Figure 16 illustrates a strap, in accordance with an embodiment of the present invention.

[0090] Figure 17 illustrates a hinge, in accordance with an embodiment of the present invention.

[0091] Figure 18 illustrates a ratchet and pawl mechanism, in accordance with an embodiment of the present invention.

[0092] In an exemplary embodiment, the table below shows the material used for parts and their manufacturing methods:

Part No. Part Name Material Manufacturing Method
1. Roller Cast nylon Lathe, Shaping, CNC milling
2. Pawl ABS 3D Printing
3. Locking Collar ABS 3D Printing
4. Spring Collar ABS 3D Printing
5. Casing ABS 3D Printing
6. Rod MS Facing, Turning, Grinding
7. Switch ABS 3D Printing
8. Guide-way for Switch movement ABS 3D Printing
9 Stopper ABS 3D Printing
Table: Exemplary material used for parts and their manufacturing methods

[0093] In an exemplary embodiment, the table below shows the list of procured parts used in strap mechanism.

Part No. Part Name Description Material
10. Spiral Spring Flat spiral spring with rectangular cross-section Spring steel
11. Torsion Spring 5 mm outer diameter Stainless steel
12. Strap 20 mm width and 1mm thickness Nylon
Table: List of procured parts used in strap mechanism

[0094] Experimental Analysis: Figure 19 (a-g) illustrates various test conducted on the product of the present invention, in accordance with an embodiment of the present invention.

[0095] Position Stability Test: When a two wheeler undergoes a collision with another object the rider may be unseated from the vehicle and/or his head may undergo considerable movement. In such a situation, unless tied properly, the helmets come/lift off due to movement of the head. The present mechanism ensures that the straps are tied properly and the helmet does not lift off. The test is performed on the Instron impact testing machine to determine the response of strap mechanism at the time of impact. To perform this test, the retention system is fixed at the left side of the helmet and the right side of the helmet has been exposed to impact. The helmet was placed over the rigid dummy head form and tightened with the designed retention system. The side impact test has been performed at a velocity of 7.5 m/s. The experimental setup for the test is shown in figure 19 (a).
Result: The position stability test was performed to check the stability of strap mechanism during side impact at a velocity of 7.5 m/s. After performing the test, it was observed that the helmet did not move from its initial position during the impact. It shows that the newly designed retention system is effective in locking and capable of retaining the position of the helmet over the head during sudden impact. It also shows that the mechanism or its mechanical parts did not malfunction during the impact test.

[0096] Dynamic Retention Test: The dynamic retention test is used to ensure appropriate strength, design of the restraint system and compatibility with the helmet to which it is fitted. In this test, the helmet was placed on a head form and fastened by designed strap mechanism just below the chin rest. The strap which is on the chin rest was loaded with a mass of 23 kg for approximately one minute. After that 23 kg mass was removed and 38 kg mass was applied simultaneously in an abrupt guided fall from a height of 120 mm. The strap mechanism fails if it cannot support the mechanical loads or if the maximum instantaneous deflection (stretch) of the strap exceeds 30 mm. The experimental setup for the test is shown in figure 19 (b). In this test, the helmet was fixed on a fixture with the help of strings. Figure 19 (b) shows the weights used to perform the dynamic retention test. These weights were supported with the help of a rod, one end of which had a supporting plate for the weights, and the other end had a hook to hang the rod to the strap. Figure 19 (c) shows the bottom portion of the helmet with the strap.
Results: Initially, the static test was performed in which 23 kg mass was applied to the strap for at least one minute. The strap mechanism was able to sustain the weight. Next the dynamic test (38 kg mass freely falls from a height of 120 mm on the strap) was performed on the same mechanism. The strap mechanism was able to lock the strap without the teeth of the ratchet getting damaged. The tests were repeated on the two new strap mechanisms.

[0097] Torsion spring fatigue/ life cycle test: The torsion spring is used for controlling the motion of pawl which maintains the locking in the designed mechanism in default condition. Since locking-unlocking is a cyclic process, there is a need to find out life cycles of the spring before failure. A fatigue test of spring was performed in the designed experiment setup as shown in figure 19 (e). In figure 19 (e), a pin firmly attached between the teeth of a spur gear with the help of a hose clamp. The spur gear mounted on a shaft of a D.C. motor running at 60 RPM. The direction of pawl movement is shown in the figure 19 (g) with the help of an arrow. The spring loaded button is rigidly fixed with the fixture in such a manner that only pawl can rotate about z-axis as shown in figure 19 (f).
[0098] Result: The pawl was able to withstand 60,000 cycles before failing.

[0099] Apart from what is disclosed above, the present invention has below mentioned additional advantages:
i. The mechanism (strap mechanism) of the present invention is very easy to use because it operates with a single slide type switch (i.e. pawl) So that the users can put on and take off their helmet many times in a day easily.
ii. The optimum size of the strap mechanism allows attachment to the existing helmet shell.

[00100] Although automatic strap mechanism for motorcycle helmet is disclosed, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or methods or devices described. Rather, the specific features are disclosed as examples of implementations of the automatic strap mechanism for motorcycle helmet.
,CLAIMS:1. A strap mechanism 2 for head safety systems 1 comprising:
a roller 6 adapted to rotate on a stationary shaft and having at least one strap 3 wrapped over, the strap 3 fixed between a shaft and at least one fixed point 4 is adapted to automatically fasten the head safety systems 1 on the head and thereby prevents the head safety systems 1 from rolling off by using the strap 3; and
a pawl 7 adapted to lock the strap mechanism 2 by engaging or disengaging the roller 6 to automatically fasten or loosen the strap 3 by using a switch 12.
2. The strap mechanism 2 as claimed in claim 1, wherein the pawl 7 is connected with a casing 5 at one end and is connected to a locking collar 8 at the other end, the locking collar 8 is adapted to couple with the roller 6 and, to make a rigid connection between the casing 5 and a rod 11 passing through the roller 6, to engage or disengage the roller 6.
3. The strap mechanism 2 as claimed in claim 2, wherein the casing 5 comprises a guide way 13 for a movement of the switch 12 between a switch stoppers 14, thereby coupling the pawl 7 and the switch 12.
4. The strap mechanism 2 as claimed in claim 1, comprises at least one torsion spring 16 is adapted to engage with the locking collar 8 at one end and with the pawl 7 at other end to control the pawl movement.
5. The strap mechanism 2 as claimed in any of the preceding claims, wherein the pawl 7 is connected with the torsion spring 16 is adapted to be engaged with the roller 6 in free condition and be disengaged from the roller 6 while pressing the pawl 7.
6. The strap mechanism 2 as claimed in any of the preceding claims, comprises at least one spiral spring 15 adapted to provide a restoring torque to the roller 6 when the roller 6 is rotated through an angular displacement, wherein one end of the spiral spring 15 is connected to a spring collar 9 and the other end is connected to the roller 6.
7. The strap mechanism 2 as claimed in any of the preceding claims, wherein the torsion spring 16 is adapted to control a motion of the pawl 7.
8. The strap mechanism 2 as claimed in any of the preceding claims, wherein the roller 6 comprises a space for accommodating a spiral spring 15, one of the spiral spring 15 is connected at a slot 21 provided on the roller 6 such that when the roller 6 is rotating over the rod 11, the spiral spring 15 is adapted to wind up.
9. The strap mechanism 2 as claimed in any of the preceding claims, wherein the roller 6 consists of a ratchet wheel 18 adapted to provide the engaging or disengaging of the roller 6.
10. The strap mechanism 2 as claimed in any of the preceding claims, wherein the roller 6 comprises a slot 20 adapted to fix a one end of the strap.
11. The strap mechanism 2 as claimed in any of the preceding claims, wherein the strap mechanism 2 is auto-adjustable at a chin rest of a user and also ensures that the head safety systems 1 is retained on the head of the user.
12. The strap mechanism 2 as claimed in any of the preceding claims, wherein the strap mechanism 2 comprises a self-locking capability.
13. The strap mechanism 2 as claimed in any of the preceding claims, wherein the pawl 7 is connected with the torsion spring 16 adapted to be always engaged with the roller 6 in free condition and disengaged from the roller 6 on pressing the torsion spring 16.