Patent Publication Number: US-2009223360-A1

Title: Actuator

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an actuator for use in automotive safety equipment and more particularly to, for example, an actuator for use in an operation such as one for raising a hood panel of an automobile when receiving a pedestrian as an object to be protected by the hood panel. 
     2. Related Art 
     Conventionally, as actuators for safety equipment mounted on motor vehicles, there have been actuators for raising a rear end of a hood panel so as to receive a pedestrian by the hood panel itself by making use of energy absorption taking place when the hood panel is plastically deformed (for example, refer to JP-A2004-330913). 
     As the actuators for raising the hood panel, there have been actuators which were configured as actuators of a piston cylinder type in which gas generated when a gas generator was activated was used as a drive source, so as to be put into operation quickly. In the actuators so configured, gas generated as working fluid when the gas generator was activated was filled within the cylinder so as to raise the piston rod housed in the cylinder, so that the hood panel connected to an upper end of the piston rod could be raised. In addition, the piston rod was constructed into something like one in which the piston was integrated with a support rod which extended from the piston so as to support the hood panel. In addition, in the actuator configured as the piston cylinder type, a lock mechanism was built therein so as to restrict a descending movement of the piston rod that had once been raised relative to the cylinder so as to prevent the descending movement of the hood panel after the hood panel had once been raised by gas from the gas generator being filled within the cylinder. 
     In addition, as the gas generator, a micro gas generator was used in which gunpowder or gas generating chemicals were ignited by an activation signal being inputted thereinto, and in the gas generator like this, gas generated by burning of gunpowder or chemical reaction of gas generating chemicals (reaction such as oxidation or oxidative combustion) was used to move the piston rod. 
     However, in the conventional actuators, as the construction of the lock mechanism, the construction was adopted in which the annular elastic element such as a snap ring which is elastically deformed in a diametrically contracting direction was provided on the inner circumferential surface side of the cylinder, the outer circumferential surface side of the piston rod was made to slide relative to the inner circumferential surface of the cylinder over substantially the full length thereof, and the groove into which the annular elastic element was to be fitted was provided in the position on the outer circumferential surface of the piston rod where the piston rod was desired to be locked. 
     In the conventional actuators that were configured in the way described above, since the outer circumferential surface of the piston rod was constructed in such a manner as to slide, over substantially the full length thereof, on the inner circumferential surface of the cylinder, the annular elastic element provided on the inner circumferential surface side of the cylinder was caused to press against the outer circumferential surface of the piston rod in the diametrically contracting direction at all times while the piston rod was moving upwards. Since this pressure acted as sliding resistance to the ascending piston rod, the smooth forwarding movement (ascending movement) of the piston rod was interrupted. 
     SUMMARY OF THE INVENTION 
     The invention has been made with a view to solving the problem, and an object thereof is to provide an actuator which can allow a piston rod to move forwards as smoothly as possible although a configuration is adopted in which an annular elastic element is used in a lock mechanism. 
     With a view to achieving the object, according to an aspect of the invention, there is provided an actuator for use in automotive safety equipment, including a cylinder, a piston rod disposed so as to be able to move forwards within the cylinder, and a lock mechanism for restricting a backward movement of the piston rod that has once moved forwards, 
     the piston rod including: 
     a piston portion which moves forwards when in operation; and 
     a support rod portion extended from the piston portion in a forward direction, so as to project from a distal end wall portion of the cylinder to support a receiving member for receiving an object to be protected, 
     the lock mechanism including: 
     an annular elastic element provided in a position on an inner circumferential surface side of the cylinder where the piston rod is disposed after the piston rod has moved forwards such that an inner circumferential edge is made to project further than an inner circumferential surface of the cylinder and adapted to expand diametrically in a restorable manner; and 
     a groove provided along an outer circumferential surface of the piston portion so that the annular elastic element is allowed to be fitted therein so as to restrict a backward movement of the piston rod that has once moved forwards, wherein 
     the support rod portion includes: 
     a rod main body portion having a smaller diameter than an inside diametrical dimension of the annular elastic element and adapted to project from the distal end wall portion of the cylinder when the piston rod moves forwards; and 
     a tapered portion provided at a piston portion side end portion of the support rod portion and having a taper surface which is gradually expanded diametrically towards the piston portion until an outside diametrical dimension of the piston portion is reached. 
     In the actuator according to the aspect of the invention, since the outside diameter of the rod main body portion which projects from the distal end wall portion of the cylinder when the piston rod moves forwards is made to be smaller than the inside diameter of the annular elastic element, when the actuator is activated so that the piston portion of the piston rod disposed within the cylinder moves forwards, the outer circumferential surface of the rod main body portion of the support rod portion which extends from the piston portion is not brought into press contact with the inner circumferential surface of the annular elastic element. Namely, since there is no situation in which the rod main body portion is pressed against by the elastic force in the diametrically contracting direction that is possessed or applied by the annular elastic element when the piston rod moves forwards, the piston rod can move forwards in a smooth fashion. 
     Thereafter, since the tapered portion of the support rod portion expands gradually the inside diameter of the annular elastic element to the outside diametrical dimension of the piston portion when the tapered portion passes through the position where the annular elastic element is provided, the annular elastic element comes to have a biasing force in a diametrically contracting direction for it to fit into the groove in the piston portion. Following this, when the piston rod has completed its forward movement, the annular elastic element is restored in the diametrically contracting direction and fits in the groove in the piston portion, thereby making it possible to restrict a backward movement of the piston rod. Then, the expanded portion does not have to be provided along the full length of the support rod portion as long as the tapered portion has the taper surface tapered at such an angle to diametrically expand the annular elastic element smoothly to the outside diameter of the piston portion, and hence, the tapered portion can be configured in a short length dimension. Because of this, in proportion to the reduction in length of the tapered portion, the piston rod can move forwards more quickly until the support rod portion brings the tapered portion into contact with the annular elastic element. 
     Consequently, in the actuator according to the aspect of the invention, even though the configuration is adopted in which the annular elastic element is used in the lock mechanism, the piston rod can be made to move forwards as smoothly as possible. 
     In addition, a snap ring made of a spring steel can be raised as an example for use for the annular elastic element of the invention of the subject patent application. Additionally, the object to be protected is not limited to a pedestrian or an occupant of a vehicle but can include, for example, a body component such as a bumper. 
     In addition, the pressure of an operating fluid such as oil, water and gas like air, the suction force of a solenoid, and the biasing force (restoring force) of a compressed spring can be used as a drive source for moving the piston rod. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a vehicle which is equipped with a pedestrian protection system to which an actuator of an embodiment of the invention is applied. 
         FIG. 2  is a plan view of an enlarged portion of the vehicle equipped with the pedestrian protection system to which the actuator of the embodiment is applied. 
         FIG. 3  is a schematic vertical sectional view of the pedestrian protection system of the embodiment taken along a longitudinal direction of the vehicle, which corresponds to a portion indicated by the line III-III in  FIG. 2 . 
         FIG. 4  is a schematic vertical sectional view showing the pedestrian protection system of the embodiment which is being activated. 
         FIG. 5  is a schematic diagram showing a state in which a support rod portion of the actuator of the embodiment is plastically deformed. 
         FIGS. 6A and 6B  are schematic vertical sectional views of the actuator of the embodiment showing states resulting before the actuator is activated and when the actuation has been completed. 
         FIGS. 7A to 7C  are vertical sectional views of an enlarged portion of the actuator of the embodiment showing a process from diametric expansion of an annular elastic element to fitment thereof in a groove. 
         FIGS. 8A and 8B  are schematic horizontal sectional views of a portion of the actuator of the embodiment where the annular elastic element making up a lock mechanism is disposed showing states resulting before the actuator is activated and when the actuator has been completely activated, the portion corresponding to the portion indicated by the line III-III in  FIGS. 6A and 6B . 
         FIGS. 9A and 9B  are diagrams showing a modified example to the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, an embodiment of the invention will be described based on accompanying drawings. As is shown in  FIGS. 1 to 4 , an actuator  31  of the embodiment is an actuator for use in a hood lift-up apparatus (hereinafter, referred to simply as a lift-up apparatus) FU in a pedestrian protection system M 1  as automotive safety equipment mounted on a vehicle V. This lift-up apparatus FU raises a rear end  15   c  of a hood panel  15  when the actuator  31  is activated to operate. In addition, such actuators  31  of the embodiment are provided underneath the hood panel  15  of the vehicle V in positions which lie in the vicinity of side edges, a left-hand edge  15   d  and a right-hand edge  15   e , and in the vicinity of the rear end  15   c  of the hood panel  15 , respectively. The pedestrian protection system M 1  includes the lift-up apparatus FU for raising the rear end  15   c  of the hood panel  15  functioning as a receiving member for receiving a pedestrian and an air bag apparatus AB having an air bag  10  which protects a pedestrian from a front pillar  4 . 
     In addition, as is shown in  FIG. 1 , sensors  6 , adapted to detect or predict a collision with a pedestrian as an object to be protected, are provided in a front bumper  5  of the vehicle V. In this construction, signals from the sensors  6  are inputted into an activation circuit, not shown, and this activation circuit is made to activate an inflator  11  (refer to  FIG. 4 ) of the air bag apparatus AB and a gas generator  48  (refer to  FIGS. 6A and 6B ) functioning as a drive source in the actuator  31  of the lift-up apparatus FU when a collision of the vehicle V with a pedestrian is detected or predicted based on the signals from the sensors  6 . 
     In addition, when used in this specification, front-rear or longitudinal and up-down or vertical directions are understood as coinciding, respectively, with longitudinal and vertical directions of the vehicle V 1 , and directions denoted by left and right are understood as coinciding, respectively, with the left and right of the vehicle V when the vehicle V is seen from the front towards the rear thereof. 
     As is shown in  FIGS. 1 to 4 , the hood panel  15  is such as to be provided to cover an engine room ER of the vehicle V from thereabove and is connected to a body  1  of the vehicle V by hinge portions  16  which are disposed, respectively, on the left-hand and right-hand edges in positions lying in the vicinity of the rear end  15   c  in such a manner as to be opened and closed at a front end thereof. The hood panel  15  is made of a sheet metal made of aluminum (aluminum alloy) and includes an outer panel  15   a  which lies on an upper surface side and an inner panel  15   b  which lies on a lower surface side of the hood panel  15  and whose strength is increased more than that of the outer panel  15   a . The hood panel  15  is such as to be plastically deformed so as to absorb the kinetic energy of a pedestrian when the hood panel  15  receives the pedestrian. In addition, when a pedestrian collides with the vehicle V, the rear end  15   c  is raised by activating the actuators  31  of the lift-up apparatuses FU for the purpose of providing a large space above the engine room ER so that the amount of deformation of the hood panel  15  is increased. In addition, the lift-up apparatus FU of the embodiment functions to provide a large space s (refer to  FIG. 4 ) between a cowl  7  and the rear end  15   c  of the hood panel  15  through which the air bag  10  is allowed to project outwards. 
     The hinge portions  16  are provided, respectively, on the left-hand edge  15   d  and the right-hand edge  15   e  in the positions lying on the rear end  15   c  side of the hood panel  15  (refer to  FIG. 1 ) and each includes a hinge base  17  which is fixed to a mounting bracket  2   a  connected to a hood ridge reinforcement  2  on the body  1  side, a mounting bracket  20  which is fixed to the hood panel  15  side and a hinge arm  19  which is connected to the hinge base  17  and the mounting bracket  20  (refer to  FIG. 3 ). As is shown in  FIGS. 2 ,  3 , each hinge arm  19  is configured to have a substantially semi-arcuate shape by curving an angle material made of a sheet metal in such a manner as to project downwardly or be concave upwardly. The hinge arm  19  is connected rotatably to the hinge base  17  at a hinge base  17  side proximal end  19   a  thereof by making use of a support shaft  18  and is connected to the mounting bracket  20  by making use of welding or the like at a distal end  19   b  which is spaced apart from the proximal end  19   a . Each support shaft  18  is provided with its axis made to extend along the transverse direction of the vehicle V. Because of this, when opening the hood panel  15 , a front end  15   f  side of the hood panel  15  (refer to  FIG. 1 ) as well as the distal end  19  sides of the respective hinge arms  19  are raised so that the hood panel  15  is rotated upwards about the respective support shafts  18  as a rotating center so as to be opened at the front end  15   f  from a position indicated by solid lines to a position indicated by chain double-dashed lines in  FIG. 3 . 
     In addition, a portion of the hinge arm  19  lying in the vicinity of the distal end  19   b  is made into a plastic deformation portion  19   c  which is plastically deformed when the rear end  15   c  of the hood panel  15  is pushed up by support rod portions  55  when the actuators  31  are activated (refer to  FIG. 4 ). Incidentally, a latch mechanism for locking a hood lock striker which is not shown but is disposed at the front end  15   f  of the hood panel  15  is provided at the front end  15   f  side of the hood panel  15  for normally closing the hood panel, and the front end  15   f  side of the hood panel  15  is prevented from being disengaged from the body  1  side by the latch mechanism which locks the hood lock striker, not shown, even when the rear end  15   c  of the hood panel  15  is raised. 
     As is shown in  FIGS. 3 ,  4 , the air bag apparatuses AB includes the air bag  10 , the inflator  11  for supplying an inflation gas into the air bag  10 , a case  12  which houses the air bag  10  and the inflator  11  and an air bag cover  13  for covering the case  12  which houses the air bag  10  and the inflator  11  in such a way as to allow the opening of the case  12 . Such air bag apparatuses  10  are equipped in locations on the cowl  7  which lie below the positions on the left-hand edge  15   d  and the right-hand edge  15   e  at the rear end  15   c  of the hood panel  15 . In the air bag apparatuses AB that are configured and equipped as described above, when the lift-up apparatuses FU are activated to raise the rear end  15   c  of the hood panel  15 , the inflators  11  are activated to operate to supply the inflation gas into the corresponding air bags  10 , which are folded, so that the folded air bags  10  are distended to project through the space S defined between the rear end  15   c  of the hood panel  15  and the cowl  7 . Then, when the inflation gas is caused to flow thereinto, the air bags  10  push open door portions  13   a  of the air bag covers  13  which have covered openings  12   a  at rear end portion sides of the cases  12  and are then deployed to be distended to cover front sides of left and right front pillars  4 ,  4  (refer to  FIG. 1 ). 
     As is shown in  FIG. 3 , the cowl  7  includes a metallic cowl panel  7   a  (made of a sheet metal) which lies on the body  1  side and has high rigidity and a cowl bar  7   b  lying above the cowl panel  7   a . The cowl bar  7   b  is made of a synthetic resin and is provided to continue to a lower portion  3   a  of a windshield  3  at a rear end portion thereof. As is shown in  FIG. 1 ,  2 , the front pillars  4 ,  4  are provided on left and right sides of the windshield  3 . 
     In addition, in the case of the embodiment, the cases  12  of the air bag apparatuses AB are attached to the cowl panel  7   a . In addition, the cowl bar  7   b  is fabricated by the air bag covers  13  and actuator covers  24  which cover the actuators  31  from thereabove being molded integrally with other general portions. The actuator covers  24  are disposed above the left and right actuators  31 , respectively, and include door portions  26  which are provided in areas surrounded by cylindrical sleeve portions  25  and are adapted to be push opened by head portions  56  of the support rod portions  55  of the actuators  31  when the actuators  31  are activated. The cowl bar  7   b  is molded with portions having different pliabilities provided therein and includes hard portions  8  and soft portions  9  which are more pliable than the hard portions  8 . The soft portions  9  constitute the aforesaid air bag covers  13  and portions lying in the vicinity of the sleeve portions  25  including the door portions  26  in the actuator covers  24 . 
     As is shown in  FIGS. 3 to 5 , the lift-up apparatus FU includes the actuator  31  and a receiving seat  22  which is provided on the hood panel  15  side. As is shown  FIG. 1 , the actuators  31  are provided below the positions lying on the left- and right-hand edges at the rear end  15   c  of the hood panel  15  in such a manner as to correspond to the two locations on the hood panel  15  where the left and right hinge portions  16  are disposed. As is shown in  FIGS. 6A and 6B , each actuator  31  is configured as an actuator of piston cylinder type which utilizes as a drive source an operating gas G which is generated when the gas generator  48  is activated, and a piston rod  50  is housed within a cylinder  32 . The receiving seat  22  is attached to a portion of a lower surface of the rear end  15   c  of the hood panel  15  where the mounting bracket  20  is provided, and a lower surface  22   a  of the receiving seat  22  is made to receive the head portion  56  at the distal end of the support rod portion  55  of the actuator  31  which moves upwards. 
     As is shown in  FIGS. 3 to 5 , the actuators  31  of the embodiment are held by mounting brackets  28  having a U-shaped cross section which are fastened to mounting flanges  2   b  connected to the hood ridge reinforcements  2  with bolts  29  and are provided below the positions on the hood panel  15  which lie on the left- and right-hand edges at the rear end  15   c  thereof. In addition, as is shown in  FIGS. 6A to 7C , each actuator  31  includes the cylinder  32 , the piston rod  50  which is housed slidably within the cylinder  32  and a lock mechanism  61  for restricting a backward movement (a descending movement in the case of the embodiment) of the piston rod  50  which has moved forwards (an ascending movement in the case of the embodiment). 
     As is shown in  FIGS. 6A to 8B , the cylinder  32  includes a substantially cylindrical circumferential wall  33 , and an upper cap  36  and a lower cap  44  which are fixed respectively to upper and lower ends of the circumferential wall  33 . A recessed portion  33   c  is formed on an upper end inner circumferential surface of the circumferential wall  33  in such a manner as to be recessed along the full circumference of the circumferential wall  33  in a circumferential direction, and a bottom surface side of the recessed portion  33   c  is formed into an annular shape, so as to form a disposition stepped portion  34  where to dispose an annular elastic element  62 . The disposition stepped portion  34  is provided in a position which substantially coincides with a position of a groove  51   a  in a piston portion  51  of the piston rod  50  which results after the piston rod  50  has completed its upward movement, whereby the annular elastic element  62  is supported by an upper surface  34   a  of the disposition stepped portion  34 . 
     The annular elastic element  62  fits in the groove  51   a  of the piston portion  51  after the piston rod  50  has moved forwards (moved upwards in this embodiment), so as to make up the lock mechanism  61  for restricting a backward movement (a descending movement in this embodiment) of the piston rod  50 . The annular elastic element  62  is disposed in the disposition stepped portion  34  in such a state that the annular elastic element  62  can be expanded to an outside diametrical dimension of the piston portion  51  in a restorable manner with an inner circumferential edge  62   a  made to project further radially inwards than an inner circumferential surface  33   d  of the circumferential wall  33  of the cylinder  32 . In addition, in the case of this embodiment, the annular elastic element  62  is made up of a snap ring (a C ring) which is made of a spring steel. 
     The upper cap  36  on the upper end of the circumferential wall  33  includes a distal end wall portion  37  having a head portion accommodating recessed portion  37   a  which accommodates the head portion  56  of the support rod portion  55  of the piston rod  50  before it starts to operate and a substantially cylindrical inner wall portion  38  which is made to extend downwards with its outside diametrical dimension made smaller than the distal end wall portion  37  and which makes up an upper end inner circumferential surface of the cylinder  32 . The inner wall portion  38  has an insertion hole  39  which is opened vertically throughout the upper cap  36  for a rod main body portion  57  of the support rod portion  55  to be inserted thereinto and a tapered portion accommodating recessed portion  40  which is disposed underneath the insertion hole  39  for accommodation of a tapered portion  58  of the piston rod  50  when the piston rod  50  moves upwards. 
     In addition, the inner wall portion  38  of the upper cap  36  includes on an outer circumferential surface  38   b  thereof an external thread  38   a  which screws in an internal thread  33   a  cut in an upper end inner circumference of the circumferential wall  33  of the cylinder  33 . Additionally, the upper cap  36  is attached to the circumferential wall  33  with the rod main body portion  57  of the support rod portion  55  inserted into the insertion hole  39  and the external thread  38   a  on the inner wall portion  38  made to screw in the internal thread  33   a  on the circumferential wall  33 . The annular elastic element  62  making up the lock mechanism  61  is held between a lower end face  38   c  of the inner wall portion  38  and the upper face  34   a  o the disposition stepped portion  34  while being permitted to be deformed in diametrically expanding and contracting directions in such a state that the inner circumferential edge  62   a  is made to project further radially inwards than the inner circumferential surface  33   d  of the circumferential wall  33  of the cylinder  32 . 
     In addition, an O ring  41 , which is brought into press contact with the head portion  56  of the support rod portion  55  is disposed on an inner circumferential surface of the head portion accommodating recessed portion  37   a . By this configuration, the airtightness within the cylinder  32  is ensured and the looseness of the head portion  56  of the support rod portion  55  is prevented. 
     The lower cap  44  on the lower end of the circumferential wall  33  includes a distal end wall portion  45  which is disposed in such a manner as to close a lower end of the circumferential wall  33  and a substantially cylindrical circumferential wall portion  46  which extends upwards from an outer circumferential edge of the proximal end wall portion  45 . The gas generator  48  is attached to the proximal end wall portion  45  by making use of a circumferential edge of an insertion hole  45   a  which is opened vertically throughout the lower cap  44 . An internal thread  46   a  is cut in an inner circumferential surface of the circumferential wall portion  46  in such a manner as to screw on an external thread  33   b  which is provided on a lower end outer circumference of the circumferential wall  33  of the cylinder  32 . In addition, the lower cap  44  is attached to the circumferential wall  33  by the internal thread  46   a  screwing on the external thread  33   b  in such a state that the gas generator  48  is attached to the proximal end wall portion  45 . 
     A micro gas generator is used for the gas generator  48 , and a lead wire  49  is connected to a lower end face of the gas generator  48  so that an electric signal from a control circuit, not shown, is inputted into the gas generator  48  therethrough. When an electric signal from the control circuit, not shown, is inputted into the gas generator  48 , gunpowder incorporated in the gas generator  48  is ignited, and gas generating chemicals are then burned by the ignition of the gunpowder so as to generate a gas. The gas so generated is supplied to a lower surface  51   b  side of the piston portion  51  within the cylinder  32  as an operating gas G. 
     The piston rod  50  includes the piston portion  51  which is caused to move forwards by the operating gas G that is caused to flow into the cylinder  32  when the actuator  31  is activated and the support rod portion  55  which is made to extend coaxially in the forward direction (in the upward or ascending direction in the embodiment) from the piston portion  51  to such an extent that it projects from the distal end wall portion  37  of the cylinder  32  so as to support the hood panel  15  functioning as a receiving member for receiving an object to be protected. 
     The piston portion  51  has a disk shape and has the groove  51   a  which is recessed along the full circumference of an outer circumferential surface in a circumferential direction. The groove  51   a  fits on the annular elastic element  62  disposed in the disposition stepped portion  34  on the circumferential wall  33  of the cylinder  32  when the piston rod  50  completes a forward movement (an ascending movement in the embodiment) and thus, makes up the locking mechanism  61  for restricting a backward movement (a descending movement in the embodiment) of the piston rod  50 . In addition, a piston ring  52 , which is brought into press contact with the inner circumferential surface  33   d  of the circumferential wall  33  of the cylinder  32 , is disposed on the outer circumferential surface of the piston portion  51  in a position lying further downwards than the groove  51   a , so as to ensure airtightness between the piston portion  51  and the gas generator  48 . 
     The support rod portion  55  includes the rod main body portion  57  which projects from the distal end wall portion  37  of the cylinder  32  when the support rod portion  55  moves forwards (ascends in the embodiment) and the tapered portion  58  which is disposed at a piston portion  51  side end portion and is adapted to expand diametrically the annular elastic element  62 . In addition, the support rod portion  55  includes at an upper end of the rod main body portion  57  the cylindrical head portion  56  which is brought into abutment with the receiving seat  22  provided on the mounting bracket  20  at the rear end  15   c  of the hood panel  15  when the support rod portion  55  ascends, so as to push up the rear end  15   c  of the hood panel  15 . 
     The rod main body portion  57  is formed into a vertically long cylinder and projects from the distal end wall portion  37  when the actuator  31  is activated to operate so as to ensure a raising stroke of the rear end  15   c  of the hood panel  15 . As is shown in  FIG. 5 , the rod main body portion  57  is made of a metallic material such as steel so as to be plastically deformed. In addition, an outside diametrical dimension D 0  of the rod main body portion  57  is made smaller than an inside diametrical dimension d of the annular elastic element  62  so that an outer circumferential surface of the rod main body portion  57  is brought into press contact with an inner circumferential surface of the annular elastic element  62  (refer to  FIG. 8A ). 
     The tapered portion  58  is substantially trapezoidal in vertical section and has a tapered outer circumferential surface (hereinafter, referred to as a “taper surface”)  58   a  which gradually expands diametrically from a lower end outer circumference of the rod main body portion  57  towards an upper end outer circumferential edge of the piston portion  51  until an outside diametrical dimension D 1  (refer to  FIG. 8B ) of the piston portion  51  is reached. As is shown in  FIGS. 7A to 7C , when the piston rod  50  ascends, the taper surface  58   a  starts to press contact the inner circumferential surface of the annular elastic element  62  after the rod main body portion  57  of the support rod portion  55  has passed through the annular elastic element  62 . Thereafter, as the piston rod ascends, the tapered portion  58  expands gradually the inside diametrical dimension d of the annular elastic element  62  to the outside diametrical dimension D 1  of the piston portion  51 . 
     In addition, as is shown in  FIGS. 6A to 7C , when an upper portion of the taper surface  58   a  of the tapered portion  58  is brought into abutment with an upper edge side inner circumferential edge of the tapered portion accommodating recessed portion  40  to thereby stop the ascending movement of the piston rod  50 , the annular elastic element  62  which is being expanded diametrically fits in the groove  51   a  on the piston portion  51  by an elastic deformation made by an elastic force generated in the annual elastic element  62  itself in such a state, so as to restrict a backward movement of the piston rod  50 . Namely, the annular elastic element  62  making up the lock mechanism  61  is restored from an outside diametrical dimension D 2  resulting when it is diametrically expanded to become an outside diametrical dimension D 3  (refer to  FIG. 8B ) which extends between the groove  51   a  of the piston portion  51  and the disposition stepped portion  34  in the circumferential wall  33  of the cylinder  32 , so as to fit in the groove  51   a  making up the locking mechanism  61 , whereby a backward movement of the piston rod  50  is restricted in that position. 
     In addition, as is indicated by chain double-dashed lines in  FIG. 6A , an inner circumferential surface  40   b  making up the tapered portion accommodating portion  40  in the upper cap  36  of the cylinder may have a taper shape which is parallel to the taper surface  58   a  of the tapered portion  58  of the piston rod  50 . As this occurs, since the substantially whole surface of the taper surface  58   a  of the tapered portion  58  is brought into abutment with the inner circumferential surface (the taper surface)  40   b  to thereby complete the ascending movement of the piston rod  50 , the ascending movement of the piston rod  50  can be completed in a stable fashion. 
     In addition, while in the embodiment, the piston portion  51 , the tapered portion  58  and the rod main body portion  57  are configured into the integral unit, they may, of course, be formed as separate members. In the event that the piston portion  51 , the tapered portion  58  and the rod main body portion  57  are configured as separate members, the support rod portion can be built into the piston portion in a replaceable fashion by, for example, the support rod portion being screwed into and out of a threaded hole. In addition, in the event that the kinetic energy absorption amount of a pedestrian by the plastic deformation of the support rod portion is increased or decreased, the support rod portion may be replaced by a support rod portion in which the rod main body portion is made thicker so as to increase the bending rigidity of the support rod portion or a support rod portion in which the rod main body portion is thinner so as to decrease the bending rigidity. In addition, the material of the support rod portion may be changed in order to adjust the plastic deformation stress of the support rod portion. 
     In the pedestrian protection system M 1  of the embodiment, when detecting or predicting a collision of the vehicle V with a pedestrian based on electric signals from the sensors  6 , the activation circuit, not shown, activates the gas generator  48  in the actuator  31  of each lift-up apparatus FU and also activates the inflator  11  in each air bag apparatus AB. 
     Then, in the event that the gas generator  48  of the actuator  31  is activated, as shown in  FIGS. 3 ,  4 ,  6 A and  6 B, the operating gas G generated by the gas generator  48  acts to push up the piston portion  51  within the circumferential wall  33  of the cylinder  32 , the head portion  56  at the upper end of the support rod portion  55  which extends from the piston portion  51  push opens the door portion  26  of the actuator cover  24  to thereby be brought into abutment with the receiving seat  22 . Further, the head portion  56  raises the rear end  15   c  of the hood panel  15  to thereby define the space S between the hood panel  15  and the cowl  7  on the rear end  15   c  side. In addition, in the event that the inflator  11  of the air bag apparatus AB is activated, as is indicated by chain double-dashed lines in  FIGS. 1 and 2  and is shown in  FIG. 4 , the inflation gas generated by the inflator  11  is caused to flow into the air bag  10 , which is folded and accommodated, and then, the air bag  10  is deployed to push open the door portion  13   a  of the air bag cover  13  so as to project to an upper side of the windshield  3 . Furthermore, the air bag  10  passes through the space S so as to be inflated. Then, when having been completely inflated, the air bag  10  covers the front side of the front pillar  4 . 
     In addition, in the actuator  31  of the embodiment, since the outside diametrical dimension D 0  of the rod main body portion  57  which projects from the distal end wall portion  37  of the cylinder  32  when the rod main body portion  57  moves forwards is made to be smaller than the inside diametrical dimension d of the annular elastic element  62 , when the actuator  31  is activated to operate, causing the piston rod portion  51  of the piston rod  50  disposed within the cylinder  32  to move forwards, the outer circumferential surface of the rod main body portion  57  of the support rod portion  55  which extends from the piston portion  51  is prevented from being brought into press contact with the inner circumferential surface of the annular elastic element  62 . Namely, since when the piston rod  50  moves forwards, the rod main body portion  57  is not pressed against by the elastic force generated in the annular elastic element  62  in the diametrically contracting direction, the piston rod  50  can move forwards in a smooth fashion. 
     Thereafter, when the tapered portion  58  of the support rod portion  55  passes through the position where the annular elastic element  62  is provided, since the tapered portion  58  gradually expands the inside diameter of the annular elastic element  62  to the outside diametrical dimension D 0  of the piston portion  51 , the annular elastic element  62  is put into the state in which it holds the biasing force that attempts to act in the diametrically contracting direction so as to allow the annular elastic element  62  to fit into the groove  51   a  on the piston portion  51 . Following this, when the piston rod  50  has completed its forward movement, the annular elastic element  62  is restored in the diametrically contracting direction to thereby fit into the groove  51   a  on the piston portion  51 , thereby making it possible to restrict the backward movement of the piston rod  50 . In addition, in the event that the tapered portion  58  includes the taper surface  58   a  having the angle a (refer to  FIG. 6A ) which causes the annular elastic element  62  to be diametrically expanded smoothly to the outside diametrical dimension D 0  of the piston portion  51 , such a tapered portion does not have to be provided along the full length of the support rod portion  55 . Because of this, in proportion to reduction in length of the tapered portion  58 , the piston rod  50  can move forwards more quickly until the tapered portion  58  of the support rod portion  55  is brought into contact with the annular elastic element  62 . In addition, the tapered portion  58  is desirably configured to have a length dimension which is in a range of about one third or less the stroke distance resulting when the support rod portion  55  moves forwards (this stroke distance being made to be about one eighth in this embodiment). In addition, the angle of the taper surface  58   a  is desirably set to the angle a which ranges from 30 degrees to 45 degrees (30 degrees in the embodiment) based on the moving direction of the support rod portion  55  so that the annular elastic element  62  can be expanded diametrically in a smooth fashion and that the length dimension of the tapered portion  58  can be kept decreased. 
     Consequently, in the actuator  31  of the embodiment, even though the configuration is adopted in which the annular elastic element  62  is used in the lock mechanism  61 , the piston rod  50  can be caused to move forwards as smoothly as possible. 
     In addition, according to the embodiment, when the hood panel  15 , which functions as the receiving member, receives a pedestrian, which constitutes an object to be protected, the hood panel  15  is plastically deformed and absorbs the kinetic energy of the pedestrian so as to receive the pedestrian while mitigating impact generated then. Further, as is shown in  FIG. 5 , since the rod main body portion  57  of the support rod portion  55  is also plastically deformed as being bending deformed so as to absorb the kinetic energy of the pedestrian, the pedestrian can be received in such a state that the impact is mitigated further by the deformation of the support rod portion  55  in addition to the deformation of the hood panel  15 . 
     In addition, in the actuator  31  of the embodiment, while the forward movement is described as the ascending movement and the backward movement as the descending movement, the operating directions are not limited thereto. For example, the actuator of the invention may be applied to an application where it operates in a horizontal direction, and the automotive safety equipment in which the actuator of the invention is used may be applied to safety equipment other than the pedestrian protection system M 1 . For example, as is shown in  FIGS. 9A and 9B , the actuator  31  may be applied to a knee protection system M 2  as automotive safety equipment for receiving safely the knees of the driver by a knee panel. 
     This knee protection system M 2  is such as to protect the knees K of the driver DR by receiving the knees K, an object to be protected, of the driver DR. When the vehicle is involved in a frontal collision, the actuator  31  is activated so as to push out a knee receiving material  72  disposed in an instrument panel  71  to the rear. Then, when the knees K move forwards to collide with the knee receiving material  72 , the rod main body portion  57  of the support rod portion is bent to be plastically deformed so as to absorb the kinetic energy of the driver DR while receiving the knees. In addition, the knee receiving member  72  is supported rotatably at a hinge portion  73  attached to the instrument panel  71  at a lower end  72   b  side, so that an upper end  72   a  is pushed to the rear about the hinge portion  76  functioning as a rotating center when the actuator  31  is activated to operate. 
     In addition, in the actuator  31  of the embodiment, while the operating gas G generated by the gas generator  48  is used as the drive source for moving the piston rod  50  forwards, water, oil and air may, of course, be used as an operating fluid, so that their water pressure, oil pressure and air pressure may be made use of as the drive source. 
     Further, as the drive source for moving the piston rod forwards, the suction force of a solenoid and the biasing force (restoring force) of a compressed spring can be used. For example, in the case of the suction force of a solenoid being used, a movable iron core is disposed within the cylinder as a piston rod. When exciting coils disposed around the circumference of the movable iron core in the cylinder are energized, the piston can be caused to move forwards. In addition, in the case of a spring being used, the piston rod is connected to a free end of a compressed coil spring, and a distal end of the piston rod or the compression coil spring is locked by a stopper which is made up of a solenoid in such a manner as to be pulled in. Then, in the event that the stopper so configured is made to be pulled in so as to cancel the locking, the piston rod moves forwards by the restoring force of the compression coil spring.