Actuator for Hood Lifting Device

Abstract

To provide an actuator for a hood lifting device that regulates the retraction of a piston rod when a load from a hood is a predetermined value or less after the piston rod projects out, and can retract the piston rod when the load from the hood exceeds the predetermined value.SOLUTION: An actuator 1 for a hood lifting device moves a piston rod 3 disposed in a cylinder 2 by gas pressure, thereby lifting a hood of a vehicle. The actuator 1 is equipped with a holding mechanism 12 that is fixed on an inner peripheral surface of a tip end portion of the cylinder 2 and holds the piston rod 3 to prevent retraction after the piston rod 3 projects out. The holding mechanism 12 prevents the retraction of the piston rod 3 while being fixed on the inner peripheral surface of the cylinder 2 when a load on the piston rod 3 from the hood is a predetermined value or less, and is separated from the inner peripheral surface of the cylinder 2 to retract in the cylinder 2 along with the piston rod 3 when the load exceeds the predetermined value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an actuator for a hood lifting device that raises the hood (bonnet hood) of a motor vehicle when a collision with a pedestrian or the like is detected or predicted.

Background Art

[0002] As an actuator used in a hood lifting device of a motor vehicle, there is one including a gas generating device, a cylinder, and a piston rod. In this actuator, when the gas generating device operates, the piston rod protrudes from the cylinder to lift the hood.

[0003] Patent Document 1 discloses an actuator having a lock mechanism built therein that prevents the retraction of the protruding piston rod so as not to lower the hood after lifting the hood.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide an actuator for a hood lifting device that restricts the retraction of a piston rod when the load from the hood is below a predetermined value after the piston rod protrudes, and allows the piston rod to retract when the load from the hood exceeds the predetermined value.

Means for Solving the Problems

[0006] The actuator for the hood lifting device of the present invention is an actuator for a hood lifting device that moves a piston rod disposed in a cylinder by gas pressure to lift the hood of a vehicle, and is fixed to the inner peripheral surface of the tip of the cylinder. After the piston rod protrudes, it is provided with a holding mechanism that holds the piston rod and prevents retraction. When the load from the hood to the piston rod is equal to or less than a predetermined value, the holding mechanism prevents the piston rod from retracting while remaining fixed to the inner peripheral surface of the cylinder. When the load exceeds the predetermined value, it disengages from the inner peripheral surface of the cylinder and retracts in the cylinder together with the piston rod.

[0007] In one aspect of the present invention, a groove is provided around the base end side of the piston rod, and the holding mechanism has a locking ring that is biased in the diameter-reducing direction and abuts against the outer peripheral surface of the piston rod. When the piston rod protrudes, the locking ring enters the groove.

[0008] In one aspect of the present invention, the holding mechanism has a tapered surface whose distance from the inner peripheral surface of the cylinder decreases downward and a groove portion located above the tapered surface. A locking ring biased in the diameter-expanding direction is disposed on the base end side of the piston rod. When the piston rod protrudes, the locking ring moves upward while reducing its diameter along the tapered surface, expands from the diameter-reduced state to restore when it exceeds the tapered surface, and enters the groove portion.

[0009] The actuator for a hood lifting device of the present invention is an actuator for a hood lifting device that moves a piston rod disposed in a cylinder by gas pressure to lift the hood of a vehicle. A holding mechanism is fixed to the outer peripheral surface of the base end portion of the piston rod, moves upward when the piston rod projects, holds the piston rod at the tip end portion of the cylinder, and prevents retraction. When the load from the hood to the piston rod is equal to or less than a predetermined value, the holding mechanism remains fixed to the outer peripheral surface of the piston rod and prevents retraction of the piston rod. When the load exceeds the predetermined value, the holding mechanism disengages from the outer peripheral surface of the piston rod, and the piston rod retracts within the cylinder while leaving the holding mechanism at the tip end portion of the cylinder.

[0010] In one aspect of the present invention, the holding mechanism has a tapered surface whose distance from the outer peripheral surface of the piston rod decreases upward, and a groove portion located below the tapered surface. At the tip end portion of the cylinder, a locking ring that is biased in the direction of reducing the diameter and abuts against the outer peripheral surface of the piston rod is disposed. When the piston rod projects, the locking ring moves relatively downward with respect to the piston rod while expanding in diameter along the tapered surface, and when it exceeds the tapered surface, it contracts in diameter so as to return from the expanded state and enters the groove portion.

[0011] In one aspect of the present invention, the holding mechanism has a locking ring biased in the direction of expanding the diameter, and a groove is provided on the inner peripheral surface of the tip end portion of the cylinder. When the piston rod projects, the locking ring enters the groove.

Advantages of the Invention

[0012] According to the present invention, after the piston rod projects, when the load from the hood is equal to or less than a predetermined value, retraction of the piston rod is restricted, and when the load from the hood exceeds the predetermined value, the piston rod can be retracted.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0015] Figure 1 shows an actuator 1 for a hood lifting device according to an embodiment. This hood lifting device is for lifting the hood to mitigate the impact on a pedestrian when the vehicle collides with the pedestrian.

[0016] In the following description, the end in the protruding direction of the piston rod is referred to as the upper end or the tip, and the end in the direction opposite to the protruding direction is referred to as the lower end or the rear end.

[0017] This actuator 1 is a linear actuator having a cylinder 2 and a piston rod 3. A gas generator 4 is provided at the rear end of the cylinder 2. The gas generator 4 is connected to an ECU (electronic control unit) (not shown), operates based on the commands of the ECU, and generates high-pressure gas. This high-pressure gas pushes up the piston rod 3 and causes it to protrude from the cylinder 2.

[0018] On the tip side of the cylinder 2, a flange-shaped end member 5 having a hole in the center is fixedly installed. The inner peripheral edge side of the end member 5 protrudes more toward the center than the inner peripheral edge of the cylinder 2.

[0019] The tip side of the piston rod 3 protrudes upward through the central hole of the end member 5. Grooves are provided around the inner peripheral surface of the end member 5, and a stopper ring 6 is engaged with these grooves.

[0020] Although not shown, claw pieces project radially from the outer peripheral edge of the stopper ring 6. A plurality of claw pieces are provided at intervals in the circumferential direction of the stopper ring 6.

[0021] The stopper ring 6 prevents the piston rod 3 from protruding upward during normal operation (when the gas generator is not operating). A cover cap 7 is attached to the tip of the piston rod 3.

[0022] The rear end portion of the piston rod 3 forms a piston portion 8. A groove 9 is provided around the outer peripheral surface of the piston portion 8. An O-ring 10 is disposed in the groove 9 and is in airtight and slidable contact with the inner peripheral surface of the cylinder 2.

[0023] A groove 11 is provided around the outer peripheral surface of the rear end portion (base end portion) of the piston rod 3 above the piston portion 8. The groove 11 has a bottom surface 11a, an upper surface 11b extending from the upper end of the bottom surface 11a so as to be orthogonal to the piston rod axial direction, and a lower surface 11c extending from the lower end of the bottom surface 11a so as to be orthogonal to the piston rod axial direction. The groove 11 is a storage groove in which a locking ring 13 described later is stored when preventing the retraction of the piston rod 3.

[0024] The tip side of the cylinder 2 is closed by a tip wall portion 2a, and an insertion hole through which the piston rod 3 is inserted is provided at the central portion of the tip wall portion 2a.

[0025] At the tip of the cylinder 2, a holding mechanism 12 for holding the piston rod 3 and preventing retraction is provided between the inner peripheral surface of the cylinder and the piston rod 3. As shown in FIG. 2, the holding mechanism 12 has a substantially cylindrical side wall portion 12a, a tip wall portion 12c extending from the tip of the side wall portion 12a toward the piston rod axis side so as to be orthogonal to the piston rod axial direction, and a rear end wall portion 12e extending from the rear end of the side wall portion 12a toward the piston rod axis side. An insertion hole through which the piston rod 3 is inserted is provided at the central portion of the tip wall portion 12c.

[0026] An insertion hole 12g through which the piston rod 3 is inserted is provided at the central portion of the rear end wall portion 12e. The diameter of this insertion hole 12g is smaller than that of the piston portion 8, and the piston portion 8 cannot pass through. Also, the diameter of the insertion hole 12g is such that the locking ring 13 housed in the groove 11 cannot pass through the insertion hole 12g. In other words, the diameter of the insertion hole 12g is smaller than the sum of the diameter (thickness) of the piston rod 3 in the groove 11 portion and twice the thickness of the locking ring 13.

[0027] On the upper surface side of the rear end wall portion 12e, that is, the stepped surface at the boundary between the inner peripheral surface 12b of the side wall portion 12a and the rear end wall portion 12e, is a tapered surface 12f with a smaller distance from the outer peripheral surface of the piston rod toward the bottom. A locking ring 13 is disposed in the region surrounded by the inner peripheral surface 12b of the side wall portion 12a, the flat surface 12d below the tip wall portion 12c, the tapered surface 12f, and the outer peripheral surface of the piston rod. The locking ring 13 is biased in the diameter-reducing direction and normally abuts against the outer peripheral surface of the piston rod.

[0028] Internal threads are formed on the inner peripheral surface at the tip of the cylinder 3. External threads are formed on the outer peripheral surface of the side wall portion 12a of the holding mechanism 12. By screwing the internal threads on the inner peripheral surface of the cylinder into the external threads on the outer peripheral surface of the holding mechanism 12, the holding mechanism 12 can be attached to the cylinder 3.

[0029] Next, the operation of this actuator 1 will be described with reference to FIGS. 3A to 3E. FIGS. 3A to 3E illustrate the function of preventing the retraction of the protruding piston rod 3, and the illustration of the gas generator 4, the cover cap 7, etc. is omitted.

[0030] When a collision between the vehicle and a pedestrian is detected or predicted by the detection system, the gas generator 4 operates based on a command from the ECU to generate high-pressure gas. As shown in FIGS. 3A and 3B, the high-pressure gas is supplied into the cylinder 2 to move the piston rod 3 upward.

[0031] The piston rod 3 deforms the claw piece of the stopper ring 6 and protrudes upward to push up the bonnet hood. The piston rod 3 moves upward until the piston portion 8 hits the holding mechanism 12.

[0032] When the piston rod 3 moves upward until the piston portion 8 hits the holding mechanism 12, the locking ring 13 enters the groove 11. The locking ring 13 biased in the diameter-reducing direction abuts against the bottom surface 11a of the groove 11.

[0033] When a load is applied from the raised bonnet hood and the piston rod 3 tries to retract (descend), as shown in Fig. 3C, the locking ring 13 is engaged between the upper surface 11b of the groove 11 and the tapered surface 12f of the holding mechanism 12, restricting the retraction of the piston rod 3.

[0034] When the load from the bonnet hood exceeds a predetermined value, the engagement between the internal thread on the inner peripheral surface of the cylinder and the external thread on the outer peripheral surface of the holding mechanism 12 disengages, and as shown in Figs. 3D and 3E, the piston rod 3 retracts within the cylinder 2 together with the holding mechanism 12. Thereby, the impact is absorbed.

[0035] Fig. 4 shows an actuator 1A according to another embodiment. In this actuator 1A, a first large-diameter portion 21 and a second large-diameter portion 23 are provided below the piston rod 3 (above the piston portion 8), and a groove portion 22 is formed between the first large-diameter portion 21 and the second large-diameter portion 22.

[0036] The upper surface of the first large-diameter portion 21 is a tapered surface 21a with a smaller interval from the inner peripheral surface of the cylinder towards the lower side. The lower surface of the second large-diameter portion 23 is a tapered surface 23a with a smaller interval from the inner peripheral surface of the cylinder towards the upper side.

[0037] A locking ring 24 that abuts against the lower end of the tapered surface 21a of the first large-diameter portion 21 and the inner peripheral surface of the cylinder and is biased in the diameter-expanding direction is arranged.

[0038] The diameter of the second large-diameter portion 23 is such that it cannot pass through the piston rod insertion hole provided in the central portion of the tip wall portion 2a of the cylinder 2.

[0039] At the tip of the cylinder 2, a holding mechanism 25 for holding the piston rod 3 and preventing its retraction is provided between the inner peripheral surface of the cylinder and the piston rod 3. The holding mechanism 25 has a substantially cylindrical side wall portion 25a, a tip wall portion 25c that extends towards the center orthogonally to the piston rod axial direction from the tip of the side wall portion 25a, and a rear end wall portion 25e that projects towards the piston rod axis side from the rear end of the side wall portion 25a.

[0040] An opening slightly larger than the diameter of the second large-diameter portion 23 is provided at the central portion of the tip wall portion 25c. The lower surface of the tip wall portion 25c is a flat surface 25d orthogonal to the piston rod axis direction.

[0041] On the upper surface side of the rear end wall portion 25e, that is, the stepped surface at the boundary between the inner peripheral surface 25b of the side wall portion 25a and the rear end wall portion 25e, is a flat surface 25f orthogonal to the piston rod axis direction. The width of the flat surface 25f is smaller than the thickness of the locking ring 24. The lower surface side of the rear end wall portion 25e is a tapered surface 25g whose distance from the inner peripheral surface of the cylinder becomes smaller toward the lower side. The flat surface 25f and the tapered surface 25g are connected at their ends.

[0042] Internal threads are formed on the inner peripheral surface of the tip portion of the cylinder 3. External threads are formed on the outer peripheral surface of the side wall portion 25a of the holding mechanism 25. By screwing the internal threads on the inner peripheral surface of the cylinder into the external threads on the outer peripheral surface of the holding mechanism 25, the holding mechanism 25 can be attached to the cylinder 3.

[0043] When this actuator 1A operates and the piston rod 3 moves upward, as shown in FIG. 5A, the locking ring 24 moves upward while reducing its diameter along the tapered surface 21a and the tapered surface 25g.

[0044] As shown in FIG. 5B, when the piston rod 3 moves upward until the second large-diameter portion 23 hits the tip wall portion 2a of the cylinder 2, the locking ring 24 exceeds the upper end of the tapered surface 25g and expands from the reduced-diameter state to restore its diameter, and enters the region (groove portion) surrounded by the flat surface 25d on the lower surface side of the tip wall portion 25c, the inner peripheral surface 25b of the side wall portion 25a, and the flat surface 25f on the upper surface side of the rear end wall portion 25e, and abuts against the inner peripheral surface 25b.

[0045] When a load is applied to the raised bonnet hood by a pedestrian or the like and the bonnet hood and the piston rod 3 tend to retract (descend), as shown in Fig. 5C, the locking ring 24 is engaged between the tapered surface 23a of the second large-diameter portion 23 and the flat surface 25f of the holding mechanism 25, restricting the retraction of the piston rod 3.

[0046] When the load from the bonnet hood exceeds a predetermined value, the engagement between the internal thread on the inner peripheral surface of the cylinder and the external thread on the outer peripheral surface of the holding mechanism 25 disengages, and as shown in Figs. 5D and 5E, the piston rod 3 retracts inside the cylinder 2 together with the holding mechanism 25. Thereby, the impact is absorbed.

[0047] Fig. 6 shows an actuator 1B according to another embodiment. In this actuator 1B, a holding mechanism 30 is attached to the lower part of the piston rod 3 (above the piston portion 8).

[0048] The holding mechanism 30 is cylindrical, and the central part is an insertion hole for the piston rod 3. The lower surface of the flange portion 34 on the proximal end side (rear end side) of the holding mechanism 30 abuts against the upper surface of the piston portion 8 (or the upper surface of the large-diameter portion 82 in Fig. 10 described later). The outer diameter of the flange portion 34 is slightly smaller than the inner diameter of the cylinder 2. An intermediate cylinder portion 33 is provided above the flange portion 34, and the flange portion 34 projects radially from the lower end of the intermediate cylinder portion 33. The upper surface of the flange portion 34, that is, the stepped surface at the boundary between the outer peripheral surface 33a of the intermediate cylinder portion 33 and the flange portion 34, is a flat surface 34a extending in the radial direction.

[0049] The side surface of the tip portion 31 of the holding mechanism 30 is a tapered surface 31a whose distance from the outer peripheral surface of the piston rod becomes smaller toward the upper side. The tapered surface 31a and the inner peripheral surface of the tip portion 31 are connected at their upper ends.

[0050] Between the tip portion 31 and the intermediate cylindrical portion 33 is a groove portion 32. The step surface at the boundary between the lower surface of the tip portion 31, that is, the bottom surface of the groove portion 32 and the tip portion 31, is a flat surface 31b extending in the radial direction. Also, the upper surface of the intermediate cylindrical portion 33, that is, the step surface at the boundary between the bottom surface of the groove portion 32 and the intermediate cylindrical portion 33, is a flat surface 33b extending in the radial direction.

[0051] On the inner peripheral surface of the holding mechanism 30, an internal thread is formed. On the outer peripheral surface of the lower portion of the piston rod 3, an external thread is formed. By screwing the internal thread on the inner peripheral surface of the holding mechanism 30 onto the external thread on the outer peripheral surface of the piston rod 3, the holding mechanism 30 can be attached to the piston rod 3.

[0052] The tip side of the cylinder 2 is a thick portion, and a first overhanging portion 35 and a second overhanging portion 36 that project inward are provided. The first overhanging portion 35 is connected to the tip wall portion 2a. The lower surface of the first overhanging portion 35 is a flat surface 35a extending in a direction orthogonal to the piston rod axial direction. The inner diameter of the first overhanging portion 35 is approximately the same as the maximum outer diameter of the tip portion 31 of the holding mechanism 30.

[0053] Below the first overhanging portion 35, a second overhanging portion 36 is provided. The upper surface of the second overhanging portion 36 is a tapered surface 36a whose distance from the outer peripheral surface of the piston rod becomes smaller downward. The lower surface of the second overhanging portion 36 is a flat surface 36b extending in a direction orthogonal to the piston rod axial direction.

[0054] A locking ring 37 is disposed between the first overhanging portion 35 and the second overhanging portion 36. The thickness of the locking ring 37 is larger than the distance between the inner peripheral surface of the first overhanging portion 35 and the outer peripheral surface of the piston rod, so that the locking ring 37 cannot enter between the inner peripheral surface of the first overhanging portion 35 and the outer peripheral surface of the piston rod.

[0055] Also, the thickness of the locking ring 37 is larger than the distance between the lower end portion of the tapered surface 36a of the second overhanging portion 36 and the outer peripheral surface of the piston rod, so that the locking ring 37 cannot move downward in the cylinder 2 beyond the second overhanging portion 35.

[0056] The locking ring 37 is biased in the direction of diameter reduction and is in contact with the outer peripheral surface of the piston rod before the actuator 1B operates.

[0057] When this actuator 1B operates, as shown in Fig. 7A, the piston rod 3 moves upward until the flat surface 34a on the upper surface side of the flange portion 34 contacts the flat surface 36b on the lower surface side of the second overhanging portion 36. When the piston rod 3 rises, the tip portion 31 of the holding mechanism 30 enters between the locking ring 37 and the outer peripheral surface of the piston rod.

[0058] The locking ring 37 moves relatively downward with respect to the piston rod 3 while expanding in diameter along the tapered surface 31a, and when it exceeds the tapered surface 31a, it enters the groove portion 32. The locking ring 37 contracts so as to be restored from the expanded diameter state and contacts the bottom surface of the groove portion 32.

[0059] When a load is applied to the pushed-up bonnet hood from a pedestrian or the like and the bonnet hood and the piston rod 3 tend to move backward (descend), as shown in Fig. 7B, the locking ring 37 is engaged between the flat surface 31b on the lower surface side of the tip portion 31 and the tapered surface 36a on the upper surface side of the second overhanging portion 36, and the backward movement of the piston rod 3 is restricted.

[0060] When the load from the bonnet hood exceeds a predetermined value, the engagement between the female thread on the inner peripheral surface of the holding mechanism 30 and the male thread on the outer peripheral surface of the piston rod is disengaged. As shown in Figs. 7C and 7D, the piston rod 3 is disengaged from the holding mechanism 30 and moves backward in the cylinder 2. The holding mechanism 30 remains at the tip side of the cylinder 2.

[0061] Fig. 8 shows an actuator 1C according to another embodiment. In this actuator 1C, a holding mechanism 40 is attached to the lower part of the piston rod 3 (above the piston portion 8).

[0062] The holding mechanism 40 is cylindrical, and the central part is an insertion hole for the piston rod 3. The lower surface of the flange portion 43 on the proximal end side of the holding mechanism 40 is in contact with the upper surface of the piston portion 8 (or the upper surface of the large-diameter portion 82 in FIG. 10 to be described later). The outer diameter of the flange portion 43 is slightly smaller than the inner diameter of the cylinder 2. The upper surface of the flange portion 43 is a flat surface 43a extending in a direction orthogonal to the piston rod axial direction.

[0063] The upper surface of the tip portion 41 of the holding mechanism 40 is a flat surface 41a extending in a direction orthogonal to the piston rod axial direction. The lower surface of the tip portion 41 is a tapered surface 41b with a smaller gap from the inner peripheral surface of the cylinder toward the upper side.

[0064] A locking ring 44 biased in the diameter-expanding direction is disposed in the groove portion 42 between the tip portion 41 and the flange portion 43. The locking ring 44 is slidable within the cylinder 2 and is in contact with the inner peripheral surface of the cylinder.

[0065] Internal threads are formed on the inner peripheral surface of the holding mechanism 40. External threads are formed on the outer peripheral surface of the lower portion of the piston rod 3. By screwing the internal threads on the inner peripheral surface of the holding mechanism 40 onto the external threads on the outer peripheral surface of the piston rod 3, the holding mechanism 40 can be attached to the piston rod 3.

[0066] The tip side of the cylinder 2 protrudes in the radial direction (outer peripheral side), and the inner diameter and outer diameter are larger than those other than the tip portion. A groove portion 45 (recess) is formed on the inner peripheral surface of the cylinder tip side. The groove portion 45 has a bottom surface 45a, an upper side surface 45b extending from the upper end of the bottom surface 45a toward the cylinder center side, and a lower side surface 45c extending from the lower end of the bottom surface 45a toward the cylinder center side. The depth of the groove portion 45 is smaller than the thickness of the locking ring 44. The width of the groove portion 45 is larger than the thickness of the locking ring 44.

[0067] When this actuator 1C operates and the piston rod 3 moves upward, as shown in FIG. 9A, the enlarged-diameter locking ring 44 enters the groove portion 45. The locking ring 44 abuts against the bottom surface of the groove portion 45. The piston rod 3 moves upward until the flat surface 41a on the upper surface side of the tip portion 41 hits the tip wall portion 2a of the cylinder 2.

[0068] When a load is applied to the pushed-up bonnet hood by a pedestrian or the like and the bonnet hood and the piston rod 3 tend to move backward (downward), as shown in FIG. 9B, the locking ring 44 is caught between the tapered surface 41b on the lower surface side of the tip portion 41 and the lower side surface 45c of the groove portion 45, restricting the backward movement of the piston rod 3.

[0069] When the load from the bonnet hood exceeds a predetermined value, the engagement between the female thread on the inner peripheral surface of the holding mechanism 40 and the male thread on the outer peripheral surface of the piston rod disengages, and as shown in FIGS. 9C and 9D, the piston rod 3 disengages from the holding mechanism 40 and moves backward within the cylinder 2. The holding mechanism 40 remains at the tip side of the cylinder 2.

[0070] In the above embodiment, an example in which the holding mechanisms 12, 25, 30, 40 and the cylinder 2 and the piston rod 3 are fixed by screw fastening has been described, but the two may be fixed by different methods such as pin insertion, dowel attachment, caulking, and press-fitting.

[0071] The actuators 1, 1A, 1B, 1C may be provided with a mechanism that applies a reaction force to the bonnet hood when the piston rod 3 moves backward. For example, a small-diameter portion 81 and a large-diameter portion 82 as shown in FIG. 10 may be provided in the region between the groove 11 of the piston rod 3 of the actuator 1 and the piston portion 8. The diameter of the large-diameter portion 82 is slightly smaller than the inner diameter of the cylinder 2.

[0072] The small-diameter portion 81 has a substantially inverted truncated cone shape. The side circumferential surface of the small-diameter portion 81 is a tapered surface 83 whose distance from the inner circumferential surface of the cylinder becomes smaller upward. A plurality of intervening bodies 85 such as balls or rings are arranged between the tapered surface 83 and the inner circumferential surface of the cylinder. The distance between the upper end portion of the small-diameter portion 81 and the inner circumferential surface of the cylinder is smaller than the diameter of the ball or the thickness of the ring.

[0073] A holding ring 86 is arranged so as to surround the small-diameter portion 81 on the lower side of the intervening body 85. The holding ring 86 is arranged in contact with the stepped surface on the small-diameter portion 81 side of the piston portion 8.

[0074] The stepped surface on the lower surface side of the large-diameter portion 82, that is, the boundary portion between the tapered surface 83 and the large-diameter portion 82, is a regulating surface 84 formed of a plane extending in the radial direction.

[0075] In the normal state before the actuator 1 operates, the intervening body 85 is in contact with the upper surface of the holding ring 86. Also, in this state, the intervening body 85 is in slidable contact with the inner circumferential surface of the cylinder or there is a slight gap between the two.

[0076] While the actuator 1 operates and the piston rod 3 moves upward, the intervening body 85 is in contact with the upper surface of the holding ring 86 and does not restrain the movement of the piston rod 3.

[0077] After the piston rod 3 is held by the holding mechanism 12, when the load from the bonnet hood exceeds a predetermined value and the piston rod 3 tries to retract, the intervening body 85 is in a state of being wedged between the inner circumferential surface of the cylinder 2 and the tapered surface 83. Due to the downward load applied to the piston rod 3, the intervening body 85 receives a component force in the radial direction from the tapered surface 83, is pressed against the inner circumferential surface of the cylinder, and bites into the inner circumferential surface of the cylinder. The intervening body 85 that has bitten into the inner circumferential surface of the cylinder moves upward relative to the piston rod 3, comes into contact with the regulating surface 84, and then moves downward integrally with the piston rod 3.

[0078] By providing a small-diameter portion 81, a large-diameter portion 82, an intervening body 85, etc., a reaction force can be applied to the bonnet hood.

[0079] The above embodiment is an example of the present invention, and the present invention may be in other forms than the above.

Explanation of Reference Signs

[0080] 1, 1A, 1B, 1C Actuator 2 Cylinder 3 Piston Rod 4 Gas Generator 8 Piston Portion 12, 25, 30, 40 Holding Mechanism

Claims

1. An actuator for a hood lifting device that moves a piston rod disposed within a cylinder by gas pressure to lift the hood of a vehicle, comprising a holding mechanism fixed to the inner peripheral surface of the tip of the cylinder, and configured to hold the piston rod and prevent retraction after the piston rod protrudes, wherein when the load from the hood to the piston rod is below a predetermined value, the holding mechanism remains fixed to the inner peripheral surface of the cylinder and prevents the piston rod from retracting, and when the load exceeds the predetermined value, the holding mechanism disengages from the inner peripheral surface of the cylinder and retracts within the cylinder together with the piston rod, a groove is provided around the base end side of the piston rod, the holding mechanism has a locking ring biased in the diameter-reducing direction and contacting the outer peripheral surface of the piston rod, and when the piston rod protrudes, the locking ring enters the groove, an actuator for a hood lifting device.

2. An actuator for a hood lifting device that moves a piston rod disposed within a cylinder by gas pressure to lift the hood of a vehicle, comprising a holding mechanism fixed to the inner peripheral surface of the tip of the cylinder, and configured to hold the piston rod and prevent retraction after the piston rod protrudes, wherein when the load from the hood to the piston rod is below a predetermined value, the holding mechanism remains fixed to the inner peripheral surface of the cylinder and prevents the piston rod from retracting, and when the load exceeds the predetermined value, the holding mechanism disengages from the inner peripheral surface of the cylinder and retracts within the cylinder together with the piston rod, the holding mechanism has a tapered surface with a smaller interval from the inner peripheral surface of the cylinder downward, and a groove portion located above the tapered surface, a locking ring biased in the diameter-expanding direction is disposed on the base end side of the piston rod, and when the piston rod protrudes, the locking ring moves upward while reducing its diameter along the tapered surface, expands from the diameter-reduced state to restore when it exceeds the tapered surface, and enters the groove portion, an actuator for a hood lifting device.

3. An actuator for a hood lifting device that moves a piston rod disposed within a cylinder by gas pressure to lift the hood of a vehicle, comprising a holding mechanism fixed to the outer peripheral surface of the base end portion of the piston rod, moving upward when the piston rod protrudes, and configured to hold the piston rod at the tip of the cylinder and prevent retraction. When the load from the hood to the piston rod is equal to or less than a predetermined value, the holding mechanism prevents the piston rod from retracting while being fixed to the outer peripheral surface of the piston rod. When the load exceeds the predetermined value, the holding mechanism disengages from the outer peripheral surface of the piston rod, and the piston rod retracts within the cylinder while leaving the holding mechanism at the tip of the cylinder. An actuator for a hood lifting device. **Claim 4** The holding mechanism has a tapered surface whose distance from the outer peripheral surface of the piston rod decreases upward and a groove portion located below the tapered surface. A locking ring that is biased in the direction of reducing the diameter and abuts against the outer peripheral surface of the piston rod is disposed at the tip of the cylinder. The locking ring moves downward relative to the piston rod while expanding in diameter along the tapered surface when the piston rod protrudes, and contracts in diameter so as to return from the expanded state when it exceeds the tapered surface and enters the groove portion. The actuator for a hood lifting device according to claim 3. **Claim 5** The holding mechanism has a locking ring biased in the diameter-expanding direction. A groove is provided in the inner peripheral surface at the tip of the cylinder. When the piston rod protrudes, the locking ring enters the groove. The actuator for a hood lifting device according to claim 3.

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