Patent Publication Number: US-2023157402-A1

Title: Helmet

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims the benefit of priority from Chinese Patent Application No. 202122942401.7, filed on 25 Nov. 2021, the entirety of which is incorporated by reference herein. 
     TECHNICAL FIELD 
     The disclosure relates to the technical field of human body safety protection appliances, and more particularly, to a helmet. 
     BACKGROUND 
     Workers who work in many special occasions, such as a spraying workshop, fire-fighting, disaster-relief, anti-terrorism and anti-riot occasions, underground tunnel operation environments including mining, coal mining and tunnelling, and driving environments in a motor vehicle, a racing car and an aircraft, must wear helmets to protect their heads. A typical helmet generally includes a helmet shell body, a shield and a jaw guard, wherein the shield and the jaw guard are both mounted on the helmet body, and the shield may be lifted or lowered relative to the helmet body according to the needs. The shield is made of a transparent material, which can prevent harmful particles such as dust, rain and smoke from invading, and can especially prevent branches, flying stones and even explosives from harming eyelids. The jaw guard can effectively protect important organs such as a chin, a nose, a mouth and cheeks of a wearer in the case of collision or other events. 
     In fact, during wearing and using of the helmet, it is often necessary to lift the shield every now and then, so as to communicate with the outside world, or to dissipate water mist generated by breathing of a driver and accumulated inside the helmet. For those helmets with a variable jaw guard, there is another meaning for lifting the shield, which is to prevent the shield from colliding with the jaw guard, that is, the lifting of the shield must be matched and correlated with an operating state of the jaw guard. In other words, when a state of the jaw guard is switched between a full helmet structure and a half helmet structure, the shield must be located at a lifted position at a right time, so as to avoid the jaw guard from colliding with the shield in a lowered state to be damaged when returning to a full helmet position. 
     In the related technology, existing helmets can be switched between the full helmet and the half helmet, but for most of the helmets, the shield and the jaw guard rotate around a fixed axis. In order to ensure that the jaw guard can be rotated to a rear side of the helmet, a space should be reserved between the jaw guard and the shield, which requires that the helmet should be manufactured in a large size, resulting in the helmet being bulky as a whole. During rotation, due to a small space reserved between the jaw guard and the shield, the jaw guard and the shield are easy to get stuck when the helmet is switched between the full helmet and the half helmet. 
     SUMMARY 
     The disclosure aims to solve at least one of the technical problems in the existing technology. Therefore, the disclosure provides a helmet, which can reduce a size of a jaw guard, and can be better switched between the full helmet and the half helmet. 
     The disclosure also provides another helmet. 
     A helmet according to an embodiment in a first aspect of the disclosure includes: 
     a helmet body; 
     a jaw guard, wherein the jaw guard is provided with two fork handles, the jaw guard is mounted on the helmet body through the two fork handles and is rotatable around a fixed axis relative to the helmet body, and the jaw guard is movable between a closed position in front of the helmet body and an open position behind the helmet body and beyond a vertex of the helmet body; 
     a shield assembly movably mounted on the helmet body, wherein the shield assembly is movable between a lowered position and a raised position relative to the helmet body, and the shield assembly includes a shield and brackets arranged at two sides of the shield; and 
     a lifting mechanism, wherein the lifting mechanism includes:
         a guide plate, wherein the guide plate is mounted on the helmet body, or the guide plate and the helmet body are manufactured in an integrated structure, the guide plate is configured for guiding and limiting movement of the shield assembly, and the guide plate and the bracket are provided with respective guide assemblies which are matched with each other;   a gearwheel, wherein the gearwheel is mounted on one of the fork handles of the jaw guard, or the gearwheel and the fork handle on the jaw guard are manufactured in an integrated structure, and the gearwheel is rotatable with the jaw guard; and   a pinion engaged with the gearwheel, wherein the pinion is provided with a trigger, and the trigger is located beside the bracket of the shield assembly at the lowered position no matter the jaw guard is located at the closed position or the open position;       

     wherein, at an initial movement stage of switching the jaw guard from the closed position to the open position or switching the jaw guard from the open position to the closed position, the gearwheel drives the pinion to rotate, and the trigger is capable of touching the bracket of the shield assembly at the lowered position and raising the shield assembly from the lowered position. 
     The helmet according to the embodiment of the disclosure at least has the following beneficial effects. 
     The helmet includes the helmet body, the jaw guard, the shield assembly and the lifting mechanism, wherein the jaw guard is provided with two fork handles, the two fork handles are respectively mounted at two sides of the helmet body, and the jaw guard is mounted on the helmet body through the two fork handles and is rotatable around a fixed axis relative to the helmet body, so that the jaw guard is movable between the closed position in front of the helmet body and the open position behind the helmet body and beyond the vertex of the helmet body; the shield assembly includes the shield and the brackets arranged at two sides of the shield, the shield assembly is movably mounted on the helmet body, and the shield assembly is movable between the lowered position and the raised position relative to the helmet body; and the lifting mechanism includes the guide plate, the gearwheel and the pinion, wherein the guide plate is mounted on the helmet body, or the guide plate and the helmet body are manufactured in the integrated structure, the guide plate is configured for guiding and limiting the movement of the shield assembly, and the guide plate and the bracket are provided with the respective guide assemblies which are matched with each other, so that the whole shield assembly is movable along a designed path of the guide plate; the gearwheel is mounted on the fork handle of the jaw guard, the jaw guard is fixedly connected with the gearwheel, or the gearwheel and the fork handle on the jaw guard are manufactured in the integrated structure, and the gearwheel is rotatable with the jaw guard; the pinion is engaged with the gearwheel, so that rotation of the gearwheel drives rotation of the pinion, the pinion is provided with the trigger, and the trigger is located beside the bracket of the shield assembly at the lowered position no matter the jaw guard is located at the closed position or the open position; at the initial movement stage of switching the jaw guard from the closed position to the open position and switching the jaw guard from the open position to the closed position, the gearwheel drives the pinion to rotate, and the trigger is capable of touching the bracket of the shield assembly at the lowered position and raising the shield assembly from the lowered position, so that the shield assembly rotates along a fixed path, and the jaw guard rotates around a fixed axis, thus avoiding interference between the shield assembly and the jaw guard during rotation, and switching the helmet from the full helmet to the half helmet. 
     In some embodiments of the disclosure, the gearwheel and the pinion are internally engaged. 
     In some embodiments of the disclosure, the gearwheel and the pinion are externally engaged. 
     In some embodiments of the disclosure, the gearwheel and the pinion are both rotatable around a fixed axis relative to the helmet body. 
     In some embodiments of the disclosure, when the jaw guard is switched from the closed position to the open position, a forward rotation angle of the pinion is greater than or equal to 270°; and when the jaw guard is switched from the open position to the closed position, a reverse rotation angle of the pinion is greater than or equal to 270°. 
     In some embodiments of the disclosure, the trigger is at least one deflector rod. 
     In some embodiments of the disclosure, the guide assembly includes a guide post and a guide groove matched with each other, and the guide post and the guide groove are respectively mounted on the guide plate and the bracket. 
     In some embodiments of the disclosure, the guide plate and the bracket located at the same side of the helmet body are provided with two sets of guide assemblies. 
     In some embodiments of the disclosure, the guide groove of at least one set of guide assemblies is set as V-shaped groove or arc-shaped groove. 
     In some embodiments of the disclosure, the lifting mechanism further includes an elastic element, one end of the elastic element is connected with the bracket, and the elastic element is configured to make the shield assembly continue to move to the raised position after the shield assembly leaves the lowered position. 
     In some embodiments of the disclosure, the elastic element is a tension spring. 
     In some embodiments of the disclosure, the bracket is provided with a draw hook for hooking the tension spring. 
     In some embodiments of the disclosure, the gearwheel is arranged on a turntable, and the turntable is fixedly mounted on the fork handle. 
     In some embodiments of the disclosure, the lifting mechanism further includes a chassis cover for covering the lifting mechanism, and the chassis cover is fixedly connected with the fork handle. 
     In some embodiments of the disclosure, the jaw guard is provided with a first limiting portion, the helmet body is provided with a second limiting portion, and the second limiting portion is matched with the first limiting portion for limiting a rotation position of the jaw guard relative to the helmet body. 
     In some embodiments of the disclosure, the first limiting portion is one of a bulge and a groove, and the second limiting portion is the other of the bulge and the groove. 
     A helmet according to an embodiment in a second aspect of the disclosure includes: 
     a helmet body; 
     a jaw guard, wherein the jaw guard is provided with two fork handles, the jaw guard is mounted on the helmet body through the two fork handles and is rotatable around a fixed axis relative to the helmet body, and the jaw guard is movable between a closed position in front of the helmet body and an open position behind the helmet body and beyond a vertex of the helmet body; 
     a shield assembly, wherein the shield assembly includes a shield and brackets arranged at two sides of the shield, an end portion of the bracket far away from the shield is hinged on the helmet body, the shield assembly is rotatable around a hinged position, and the shield assembly is movable between a lowered position and a raised position relative to the helmet body; and 
     a lifting mechanism, wherein the lifting mechanism includes a trigger, and the trigger is located beside the bracket of the shield assembly at the lowered position no matter the jaw guard is located at the closed position or the open position; 
     wherein, at an initial movement stage of switching the jaw guard from the closed position to the open position or switching the jaw guard from the open position to the closed position, the trigger is capable of touching the bracket of the shield assembly at the lowered position and raising the shield assembly from the lowered position. 
     The helmet according to the embodiment of the disclosure at least has the following beneficial effects. 
     The helmet includes the helmet body, the jaw guard, the shield assembly and the lifting mechanism, wherein the jaw guard is provided with two fork handles, the two fork handles are respectively mounted at two sides of the helmet body, the jaw guard is mounted on the helmet body through the two fork handles and is rotatable around a fixed axis relative to the helmet body, so that the jaw guard is movable between the closed position in front of the helmet body and the open position behind the helmet body and beyond the vertex of the helmet body; the shield assembly includes the shield and the brackets arranged at two sides of the shield, the end portion of the bracket far away from the shield is hinged on the helmet body, the shield assembly is rotatable around the hinged position, and the shield assembly moves between the lowered position and the raised position relative to the helmet body; and the lifting mechanism includes the trigger, and the trigger is located beside the bracket of the shield assembly at the lowered position no matter the jaw guard is located at the closed position or the open position; at the initial movement stage of switching the jaw guard from the closed position to the open position and switching the jaw guard from the open position to the closed position, the trigger is capable of touching the bracket of the shield assembly at the lowered position and raising the shield assembly from the lowered position, thus switching the helmet from the full helmet to the half helmet. 
     In some embodiments of the disclosure, the trigger is a deflector rod. 
     In some embodiments of the disclosure, the lifting mechanism further includes an elastic element, one end of the elastic element is connected with the bracket, and the elastic element is configured to make the shield assembly continue to move to the raised position after the shield assembly leaves the lowered position. 
     In some embodiments of the disclosure, the elastic element is a tension spring. 
     In some embodiments of the disclosure, the bracket is provided with a draw hook for hooking the tension spring. 
     The additional aspects and advantages of the disclosure will be partially provided in the following description, and will partially be apparent in the following description, or learned by practice of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is further described hereinafter with reference to the drawings and the embodiments, wherein: 
         FIG.  1    is a schematic structural diagram of a helmet according to an embodiment of the disclosure; 
         FIG.  2    is a partial exploded view of the helmet in  FIG.  1   ; 
         FIG.  3    is an exploded view of a lifting mechanism of the helmet according to an embodiment of the disclosure; 
         FIG.  4    is a schematic diagram of matching of a bracket, a pinion and a guide plate according to an embodiment of the disclosure; 
         FIG.  5    is an exploded view of the matching of the bracket, the pinion and the guide plate in  FIG.  4   ; 
         FIG.  6    is a schematic diagram of the guide plate according to an embodiment of the disclosure; 
         FIG.  7    is a schematic diagram of the pinion according to an embodiment of the disclosure; 
         FIG.  8    is a schematic diagram of the bracket according to an embodiment of the disclosure; 
         FIG.  9    is a schematic diagram of matching between a jaw guard and a gearwheel according to an embodiment of the disclosure; 
         FIG.  10    is a schematic diagram of a matching relationship between the jaw guard and a shield in a full helmet state according to an embodiment of the disclosure; 
         FIG.  11    is a schematic diagram of a matching relationship between the jaw guard and the shield in a state of switching from the full helmet to the half helmet according to an embodiment of the disclosure; 
         FIG.  12    is a schematic diagram of the matching relationship between the jaw guard and the shield in the state of switching from the full helmet to the half helmet according to an embodiment of the disclosure; 
         FIG.  13    is a schematic diagram of the helmet in a half helmet state according to an embodiment of the disclosure; 
         FIG.  14    is a locally enlarged view of a part A in  FIG.  13   ; 
         FIGS.  15 A- 15 E  are schematic diagram of switching from the full helmet to the half helmet according to an embodiment of the disclosure; and 
         FIGS.  16 A- 16 E  are schematic diagram of switching from the half helmet to the full helmet according to an embodiment of the disclosure. 
     
    
    
     REFERENCE NUMERALS 
       100  refers to helmet; 
       110  refers to helmet body;  120  refers to jaw guard;  121  refers to fork handle;  130  refers to shield assembly;  131  refers to shield;  132  refers to bracket;  140  refers to lifting mechanism;  141  refers to guide plate;  142  refers to gearwheel;  143  refers to pinion;  1431  refers to trigger;  1411  refers to first guide post;  1412  refers to second guide post;  1413  refers to first guide groove;  1414  refers to second guide groove;  144  refers to elastic element;  1441  refers to draw hook;  1421  refers to turntable;  145  refers to chassis cover;  1201  refers to first limiting portion; and  1101  refers to second limiting portion. 
     DETAILED DESCRIPTION 
     The embodiments of the disclosure are described in detail hereinafter, and examples of the embodiments are shown in the drawings, wherein the same or similar reference numerals throughout the drawings denote the same or similar elements or elements having the same or similar functions. The embodiments described hereinafter with reference to the drawings are exemplary, and are only used to explain the disclosure, but should not be understood as limiting the disclosure. 
     In the description of the disclosure, it should be understood that the orientations or positional relationships indicated by the terms such as “upper”, “lower” and the like, refer to the orientations or positional relationships shown in the drawings, which are only intended to facilitate describing the disclosure and simplifying the description, and do not indicate or imply that the indicated devices or elements must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the disclosure. 
     In the description of the disclosure, the term “a plurality of” refers to being two or more. If there are descriptions of “first” and “second”, it is only for the purpose of distinguishing between technical features, and should not be understood as indicating or implying relative importance, implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features. 
     In the description of the disclosure, the terms “arrangement”, “installation”, “connection” and the like should be understood in broad sense unless otherwise specified and defined. The specific meanings of the above terms in the disclosure may be reasonably determined according to specific contents of the technical solutions by those of ordinary skills in the art. 
     With reference to  FIG.  1    and  FIG.  2   , an embodiment in a first aspect of the disclosure provides a helmet  100 , which includes: a helmet body  110 , a jaw guard  120 , a shield assembly  130  and a lifting mechanism  140 . The jaw guard  120  is provided with two fork handles  121 , the two fork handles  121  are respectively mounted at two sides of the helmet body  110 , and the jaw guard  120  is mounted on the helmet body  110  through the two fork handles  121  and is rotatable around a fixed axis relative to the helmet body  110 , so that the jaw guard  120  is movable between a closed position in front of the helmet body  110  and an open position behind the helmet body  110  and beyond a vertex of the helmet body  110 . The shield assembly  130  includes a shield  131  and brackets  132  arranged at two sides of the shield  131 . It should be noted that the shield  131  herein is made of a transparent material, and can prevent rainwater and dust from invading into the helmet body  110  in the case of driving. The shield assembly  130  is movably mounted on the helmet body  110 , and the shield assembly  130  is movable between a lowered position and a raised position relative to the helmet body  110 . The lifting mechanism  140  includes a guide plate  141 , a gearwheel  142  and a pinion  143 . The guide plate  141  is mounted on the helmet body  110 , the guide plate  141  is configured for guiding and limiting movement of the shield assembly  130 , and the guide plate  141  and the bracket  132  are provided with respective guide assemblies which are matched with each other, so that the whole shield assembly  130  is movable along a designed path of the guide plate  141 . The gearwheel  142  is mounted on the fork handle  121  of the jaw guard  120 , the jaw guard  120  is fixedly connected with the gearwheel  142 , and the gearwheel  142  rotates with the jaw guard  120 . The pinion  143  is engaged with the gearwheel  142 , so that rotation of the gearwheel  142  drives rotation of the pinion  143 , the pinion  143  is provided with a trigger  1431 , and the trigger  1431  is located beside the bracket  132  of the shield assembly  130  at the lowered position no matter the jaw guard  120  is located at the closed position or the open position. At an initial movement stage of switching the jaw guard  120  from the closed position to the open position or switching the jaw guard  120  from the open position to the closed position, the gearwheel  142  drives the pinion  143  to rotate, and the trigger  1431  is capable of touching the bracket  132  of the shield assembly  130  at the lowered position and raising the shield assembly  130  from the lowered position, so that the shield assembly  130  rotates along a fixed path, and the jaw guard  120  rotates around a fixed axis, thus avoiding interference between the shield assembly  130  and the jaw guard  120  during rotation, and switching the helmet  100  from the full helmet to the half helmet. 
     The gearwheel  142  and the fork handle  121  may also be manufactured in an integrated structure, so that when the fork handle  121  is rotated, the gearwheel  142  is rotatable with the fork handle  121 , so as to ensure that the fork handle  121  is capable of driving the gearwheel  142  to rotate in time during rotation. Similarly, the guide plate  141  and the helmet body  110  may be manufactured in an integrated structure, so that fixation between the guide plate  141  and the helmet body  110  is better. 
     In an embodiment of the disclosure, with reference to  FIG.  10    to  FIG.  13   , the gearwheel  142  and the pinion  143  are internally engaged with each other. With gear transmission, movement can be transmitted more reliably, which has wide ranges of applicable load and speed, high use efficiency, long service life, compact structure, and small external size. The internal engagement can better reduce a volume of the helmet  100 , so that transmission is compact, wearing is small, and a service life is long. The gearwheel  142  and the pinion  143  may also be externally engaged with each other, which can also implement the transmission, and is not limited herein. 
     In an embodiment of the disclosure, with reference to  FIG.  10    to  FIG.  12   , when the jaw guard  120  is switched from the closed position to the open position, a forward rotation angle of the pinion  143  driven by the gearwheel  142  is greater than or equal to 270°; and when the jaw guard  120  is switched from the open position to the closed position, a reverse rotation angle of the pinion  143  driven by the gearwheel  142  is greater than or equal to 270°. Whether switching from the closed position to the open position or switching from the open position to the closed position, the rotation angle of the pinion may be 270°, 300°, 330°, 360° and the like, for example, when the jaw guard  120  is switched from the closed position to the open position, the gearwheel  142  drives the pinion  143  to rotate by a turn in a forward direction; and when the jaw guard  120  is switched from the open position to the closed position, the gearwheel  142  drives the pinion  143  to rotate by a turn in a reverse direction. The transmission is simple, reliable and easy to implement, the gearwheel  142  drives the pinion  143  to rotate, the pinion  143  drives the bracket  132  to rotate, and the bracket  132  is fixedly connected with the shield  131 , so that the shield  131  is movable according to a defined path of the guide plate  141 , thus avoiding the jaw guard  120  from colliding with the shield  131 . 
     In an embodiment of the disclosure, with reference to  FIG.  7   , the trigger  1431  is at least one deflector rod. The pinion  143  is provided with the trigger  1431 , and the trigger  1431  may be one deflector rod or two deflector rods, which is not limited herein. The rotation of the pinion  143  drives rotation of the deflector rod, and the deflector rod is contacted with the bracket  132 , so that the deflector rod moves the bracket  132  during rotation. The bracket  132  moves along a specified path of the guide plate  141  due to limitation of the guide plate  141 . The deflector rod is simple in structure and reliable in force transmission. 
     In an embodiment of the disclosure, with reference to  FIG.  4    to  FIG.  8   , the guide assembly includes a guide post and a guide groove matched with each other, and the guide post and the guide groove are respectively mounted on the guide plate  141  and the bracket  132 . The guide post and the guide groove are matched with each other, so that the bracket  132  is movable along the specified path of the guide groove. 
     The guide plate  141  and the bracket  132  located at the same side of the helmet body  110  are provided with two sets of guide assemblies. One set of guide assemblies is configured for limiting a moving path of the shield  131 , and the other set of guide assemblies is configured for preventing the bracket  132  from being unstable and deviating when the shield  131  moves. With reference to  FIG.  4    to  FIG.  8   , the guide plate  141  is provided with a first guide groove  1413  and a first guide post  1411 , and the bracket  132  is provided with a second guide groove  1414  and a second guide post  1412 . The first guide groove  1413  is movably matched with the second guide post  1412 , and the second guide groove  1414  is movably matched with the first guide post  1411 . The first guide groove  1413  is movably matched with the second guide post  1412 , which ensures that the bracket  132  is movable along a designed direction of the first guide groove  1413 . It should be noted that a designed path of the first guide groove  1413  refers to a path taken by the shield  131  moving from the lowered position to the raised position, and that is to say, the path referred in this embodiment is to move forward and upward relative to the helmet body  110  first to reach a highest point, and then to move backward and downward. This path is not limited herein, and may be subjected to various changes according to different sizes of the helmet  100  or various needs. The second guide groove  1414  is movably matched with the first guide post  1411 , which ensures that the bracket  132  moves stably without deviation, and ensures that the bracket  132  can drive the shield  131  to move stably. The guide post is slidably matched with the guide groove, so that the guide post is movable along the guide groove. 
     The guide groove of at least one set of guide assemblies is set as V-shaped groove or arc-shaped groove. With reference to  FIG.  10    to  FIG.  12    and  FIGS.  15 A- 15 E , in a full helmet state, when the jaw guard  120  is driven to rotate backward, the gearwheel  142  is driven to rotate, the gearwheel  142  drives the pinion  143  to rotate in a forward direction, and the pinion  143  makes the bracket  132  move. The bracket  132  drives the shield  131  to move along the specified path of the first guide groove  1413 , which is to move upward and forward first to reach the highest point, and then to move downward and backward to be close to the helmet body  110 , so that the shield  131  is close to the helmet body  110  and far away from the jaw guard  120 . Therefore, a certain gap is generated between the shield  131  and the jaw guard  120 , and the jaw guard  120  rotates around a fixed axis, and can smoothly rotate over the shield  131 , thus switching the helmet from the full helmet to the half helmet. With reference to  FIG.  10    to  FIG.  12    and  FIGS.  16 A- 16 E , in a half helmet state, when the shield  131  is driven to rotate forward, the gearwheel  142  is driven to rotate, the gearwheel  142  drives the pinion  143  to rotate in a reverse direction, and the pinion  143  makes the bracket  132  move. The bracket  132  drives the shield  131  to move upward and forward first to reach the highest point, and then to move downward and backward to be close to the helmet body  110 , so that the shield  131  is close to the helmet body  110  and far away from the jaw guard  120 . Therefore, a certain gap is generated between the shield  131  and the jaw guard  120 , and the jaw guard  120  rotates around a fixed axis, and can smoothly rotate over the shield  131 , thus switching the helmet from the half helmet to the full helmet. 
     In an embodiment of the disclosure, with reference to  FIG.  10    to  FIG.  12   , the lifting mechanism  140  further includes an elastic element  144 , one end of the elastic element  144  is connected with the bracket  132 , and the elastic element  144  is configured to make the shield assembly  130  continue to move to the raised position after the shield assembly  130  leaves the lowered position. The elastic element  144  provides an elastic force for the movement of the bracket  132 , which makes the bracket  132  rotate faster, and makes the bracket  132  continue to move to the raised position along a specified direction of the guide plate  141  after being separated from the pinion  143  at the same time, thus switching the bracket from the lowered position to the raised position. The elastic element may be a spring, a tension spring and the like, with a simple structure and a high stability. 
     In an embodiment of the disclosure, as shown in  FIG.  8   , the bracket  132  is provided with a draw hook  1441  for hooking the tension spring, which facilitates connection of the bracket  132  with the tension spring, and also facilitates replacement or disassembly of the tension spring after being damaged. 
     In an embodiment of the disclosure, as shown in  FIG.  9   , the gearwheel  142  is arranged on a turntable  1421 , and the turntable  1421  is fixedly mounted on the fork handle  121 . The gearwheel  142  is provided with the turntable  1421 , and the turntable  1421  is fixedly connected with the fork handle  121 , so that the gearwheel  142  is fixedly connected with the turntable  1421 , the structure is easy to implement, the manufacturing is simple and reasonable, and the fork handle  121  or the gearwheel  142  can also be replaced or disassembled. 
     In an embodiment of the disclosure, as shown in  FIG.  2   , the lifting mechanism  140  further includes a chassis cover  145  for covering the lifting mechanism  140 , and the chassis cover  145  is fixedly connected with the fork handle  121 , thus avoiding dust, rainwater and other pollutants from entering the helmet  100  to damage the lifting mechanism  140 , better protecting the lifting mechanism  140 , and prolonging a service life of the helmet  100 . 
     In an embodiment of the disclosure, as shown in  FIG.  13    and  FIG.  14   , the jaw guard  120  is provided with a first limiting portion  1201 , the helmet body  110  is provided with a second limiting portion  1101 , and the second limiting portion  1101  is matched with the first limiting portion  1201  for limiting a rotation position of the jaw guard  120  relative to the helmet body  110 . Therefore, the rotation angle of the jaw guard  120  is better limited, thus avoiding excessive rotation of the jaw guard  120  due to overexertion to damage the helmet  100 . Meanwhile, the jaw guard  120  can also be well fixed, so that the jaw guard  120  is stationary relative to the helmet body  110  in the half helmet state, thus being safer. 
     The first limiting portion  1201  is one of a bulge and a groove, and the second limiting portion  1101  is the other of the bulge and the groove. The groove and the bulge are simple in structure and convenient to manufacture, and meanwhile, the bulge is in snap fit with the groove, thus being convenient for a user to use. 
     With reference to  FIG.  1    to  FIG.  3   , an embodiment in a second aspect of the disclosure also provides another helmet  100 . The helmet  100  includes a helmet body  110 , a jaw guard  120 , a shield assembly  130  and a lifting mechanism  140 . The jaw guard  120  is provided with two fork handles  121 , the two fork handles  121  are respectively mounted at two sides of the helmet body  110 , the jaw guard  120  is mounted on the helmet body  110  through the two fork handles  121  and is rotatable around a fixed axis relative to the helmet body  110 , so that the jaw guard  120  is movable between a closed position in front of the helmet body  110  and an open position behind the helmet body  110  and beyond a vertex of the helmet body  110 . The shield assembly  130  includes a shield  131  and brackets  132  arranged at two sides of the shield  131 , an end portion of the bracket  132  far away from the shield  131  is hinged on the helmet body  110 , the shield assembly  130  is rotatable around a hinged position, and is movable between a lowered position and a raised position relative to the helmet body  110 . The lifting mechanism  140  includes a trigger  1431 , and the trigger  1431  is located beside the bracket  132  of the shield assembly  130  at the lowered position no matter the jaw guard  120  is located at the closed position or the open position. At an initial movement stage of switching the jaw guard  120  from the closed position to the open position or switching the jaw guard  120  from the open position to the closed position, the trigger  1431  is capable of touching the bracket  132  of the shield assembly  130  at the lowered position and raising the shield assembly  130  from the lowered position, thus switching the helmet  100  from the full helmet to the half helmet. 
     In an embodiment of the disclosure, with reference to  FIG.  4   ,  FIG.  5    and  FIG.  7   , the trigger  1431  is a deflector rod. The deflector rod has a simple structure, the lifting mechanism  140  drives the deflector rod to rotate during rotation, and the deflector rod pushes the bracket  132  to move, so that the shield assembly  130  is movable from the lowered position to the raised position. 
     In an embodiment of the disclosure, with reference to  FIG.  10    to  FIG.  12   , the lifting mechanism  140  further includes an elastic element  144 , one end of the elastic element  144  is connected with the bracket  132 , and the elastic element  144  is configured to make the shield assembly  130  continue to move to the raised position after the shield assembly  130  leaves the lowered position. The elastic element  144  provides an elastic force for the movement of the bracket  132 , which makes the bracket  132  rotate faster, and makes the bracket  132  continue to move to the raised position along a specified direction of the guide plate  141  after being separated from the pinion  143  at the same time, thus switching the bracket from the lowered position to the raised position. 
     The elastic element may be a spring, a tension spring and the like, with a simple structure and a high stability. 
     In an embodiment of the disclosure, as shown in  FIG.  8   , the bracket  132  is provided with a draw hook  1441  for hooking the tension spring, which facilitates connection of the bracket  132  with the tension spring, and also facilitates replacement or disassembly of the tension spring after being damaged. 
     In a specific embodiment, with reference to  FIGS.  15 A- 15 E , from  FIG.  15 A  to  FIG.  15 B , the jaw guard  120  is opened and starts to be driven to rotate. Since a size of the pinion  143  is smaller than that of the gearwheel  142 , it is ensured that the jaw guard  120  does not move beyond the shield  131 , i.e., the jaw guard  120  moves behind the shield  131 , before the shield  131  is close to the helmet body  110 . From  FIG.  15 B  to  FIG.  15 C , the jaw guard  120  rotates, and the gearwheel  142  rotates with the jaw guard  120  at the same time as the jaw guard  120  is fixedly connected with the gearwheel  142 . Rotation of the gearwheel  142  causes rotation of the pinion  143  by means of gear transmission. The pinion  143  is provided with the deflector rod, and the bracket  132  fixedly connected with the shield  131  is movably matched with the pinion  143 , and is also matched with the deflector rod at the same time. The rotation of the pinion  143  drives the rotation of the deflector rod, and the deflector rod pushes the bracket  132  to move. However, since the second guide post  1412  of the bracket  132  is movably matched with the first guide groove  1413  of the guide plate  141 , the bracket  132  moves in the designed direction of the first guide groove  1413 , which is to move upward and forward first to reach the highest point, and then to move downward and backward to be close to the helmet body  110 . From  FIG.  15 C  to  FIG.  15 D , the jaw guard  120  rotates over the shield  131 , and then continues to rotate, with reference to  FIG.  15 E , until the first limiting portion  1201  of the jaw guard  120  is connected with the second limiting portion  1101  of the helmet body  110 , and the jaw guard  120  is fixed on the helmet body  110 , thus switching the helmet from the full helmet to the half helmet. At the moment, if the shield  131  is needed, the shield  131  may be deflected down manually. With reference to  FIGS.  16 A- 16 E , from  FIG.  16 A  to  FIG.  16 B , in the half helmet state, the first limiting portion  1201  and the second limiting portion  1101  are opened in a fixed connection state, the jaw guard  120  starts to be driven to rotate. From  FIG.  16 B  to  FIG.  16 C , the jaw guard  120  rotates, and the gearwheel  142  rotates with the jaw guard  120  at the same time as the jaw guard  120  is fixedly connected with the gearwheel  142 . Rotation of the gearwheel  142  causes rotation of the pinion  143  by means of gear transmission. The pinion  143  is provided with the deflector rod, and the bracket  132  fixedly connected with the shield  131  is movably matched with the pinion  143 , and is also matched with the deflector rod at the same time. The rotation of the pinion  143  drives the rotation of the deflector rod, and the deflector rod pushes the bracket  132  to move. However, since the second guide post  1412  of the bracket  132  is movably matched with the first guide groove  1413  of the guide plate  141 , the guide plate  141  is fixed on the chassis cover  145 , and the chassis cover  145  is fixed on the helmet body  110 , the bracket  132  will move in the designed direction of the first guide groove  1413 , which is to move upward and forward first to reach the highest point, and then to move downward and backward to be close to the helmet body  110 . From  FIG.  16 C  to  FIG.  16 D , the shield  131  rotates over the helmet body  110 , and then continues to rotate to return to a position in which the helmet is in the full helmet state, and then the shield  131  is deflected down, thus switching the helmet from the half helmet to the full helmet. 
     The embodiments of the disclosure are described in detail with reference to the drawings above, but the disclosure is not limited to the above embodiments, and various changes may also be made within the knowledge scope of those of ordinary skills in the art without departing from the purpose of the disclosure.