US3853199A

US3853199A - Collision sensor for fender bumper operated vehicle safety device

Info

Publication number: US3853199A
Application number: US00310943A
Authority: US
Inventors: Y Hayakawa; K Hirashima; S Matsui
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1971-11-30
Filing date: 1972-11-30
Publication date: 1974-12-10
Anticipated expiration: 1991-12-10
Also published as: GB1403597A; FR2182429A5; AU4927072A; DE2258772C2; AU458138B2; DE2258772A1; CA1000384A

Abstract

An impact-responsive switch mounted on a shock-absorbing bumper and having a housing for a bore. An elongate retractable member is axially slidably mounted in the bore to retract to open or close two contacts provided therein when subjected to a collision impact. The elongate retractable member has attached thereto a permanent magnet which, in the retracted position, applies an attractive or repulsive force tending to close or open the two contacts which are hermetically sealed within an evacuated glass tube to prevent degeneration of the contacts. The impactresponsive switch is so positioned on the bumper that the elongate member is subjected to the collision impact upon compression of a resilient member which is interposed between a back plate of a buffer bar and an end plate of a piston rod forming a part of the bumper mechanism.

Description

United States Patent [191 Hirashima et a1.

[11] 3,853,199 [4 Dec. 10, 1974 COLLISION SENSOR FOR FENDER BUMPER OPERATED VEHICLE SAFETY DEVICE [75] Inventors: Kenzo Hirashima; Shunji Matsui,

both of Yokohama; Yoshikazu Hayakawa, Yokosuka, all of Japan [73] Assignee: Nissan Motor Company, Limited,

' Yokohama City, Japan [22] Filed: Nov. 30, 1972 [21] Appl. No.: 310,943

301 Foreign Application Priority Data Nov. 30, 1971 Japan 46-111870 Apr. 28, 1972 Japan 47-49731 [52] US. Cl. 180/91, 180/103, 200/61.08,'

200/61.44, ZOO/61.45 R, ZOO/61.51, 293/4 [51] Int. Cl B60r 21/00, l-lOlh 3/16 [58] Field of Search 200/61.45 R, 61.53, 6,

200/16 A, 61.08, 159 A, 166C, 166 BA;

Koepke 335/205 3,495,675 2/1970 Hass et a1 ZOO/61.45 R X 3,654,412 4/1972 l-Iaruna et a1. 180/91 X 3,668,355 6/1972 Campbell et a1... 200/166 C 3,673,358 6/1972 Harmon 335/206 X 3,699,276 10/1972 Atakkaan 200/16 A 3,704,514 12/1972 Fuchs et al 200/166 C X 3,718,877 2/1973 Matsushima... 335/205 3,744,588 7/1973 Nave, Sr. 180/103 X 3,778,572 12/1973 Matsui et a1. ZOO/61.5 X 3,793,498 2/1974 Matsui ct a1. ZOO/61.45 R

FOREIGN PATENTS OR APPLICATIONS 507,283 12/1951 Belgium 293/4 Primary Examiner.1ames R. Scott [5 7] ABSTRACT elongate retractable member is axially' slidably mounted in the bore to retract to open or close two contacts provided therein when subjected to a collision impact. The elongate retractable member has attached thereto a permanent magnet which, in the retracted position, applies an attractive or repulsive force tending to close or open the two contacts-which are hermetically sealed within an evacuated glass tube to prevent degeneration of the contacts. The impactresponsive switch is so positioned on the bumper that the elongate member is subjected to the collision impact upon compression of a resilient member which is interposed between aback plate of a buffer barand an end plate of a piston rod forming a part of the bumper mechanism. a

15 Claims, 16 Drawing Figures COLLISION SENSOR FOR FENDER BUMPER OPERATED VEHICLE SAFETY DEVICE This invention relates generally to motor vehicle safety devices and more particularly to an improved switch mechanism of the impact-responsive type to be mounted on a shock-absorbing bumper of a motor vehicle.

Heretofore, many safety devices and collision sensors have been developed for use on motor vehicles. Such collision sensor usually comprises a switch mechanism which is adapted to be closed or opened upon sensing a collision condition. It has been found in the art that in order to successfully protect occupants from injuries the switch is required to be closed or opened within one or two milliseconds after a collision begins. Another requirement to be satisfied by the switch mechanism of this kind is that it cannot be readily actuated by anything else than a collision.

It is an object of the present invention to provide an improved switch mechanism for a motor vehicle safety device that meets the above-stated requirements for successfully protecting occupants from injuries at the time of a collision.

Another object of the present invention is to provide an improved switch mechanism which is adapted for use on a shock-absorbing bumper of amotor vehicle to sense an impact upon the bumper resulting from a collision of the vehicle. I

It is a further object of the present invention to provide an improved switch mechanism which is adapted for use with an inertia switch of a known type to insure a reliable detection of a collision of the vehicle.

It is still another object'of the present invention to provide an improved switch mechanism-which is simple in construction, inexpensive to manufacture and durable in use.

These and other objects will be readily apparent from the following description of the invention taken in conjunction with accompanying drawings, in which: I

FIG. 1 is a side elevation, partly in section, of a shock-absorbing bumper of a motor vehicle on which a switch mechanism according to the invention is mounted; I v

FIG. 2 is an enlarged sectional view of the connection between a buffer bar and a piston rod of the bumper mechanism the switch mechanismv of the invention being shown as mounted on an end plate of the piston rod;

FIG. '3 is a perspective view. with a schematic diagram of theassociated electrical circuit, of a shockabsorbing' bumper according to the invention;

FIG. 4 is a longitudinal sectional view ofa typical switch mechanism according to the invention;

FIG. 5 is a view showing the manner in which the switch mechanism of the invention is mounted on the buffer bar of the bumper mechanism;

FIG. 6 is a view of a modification of the switch mechanism of FIG. 4;

FIG. 7 is an illustration of a further embodiment of the switch mechanism according to the invention;

FIG. 8 is a view of a typical hermetically sealed' an inertia switch employed in combination with the switch mechanism of the invention.

A simplified schematic diagram illustrating a preferred overall arrangement of a shock-absorbing bumper to which the sensor or switch mechanism of the invention is applied is shown in FIG. 1. The bumper comprises an impact member, such as a buffer bar 10 extending crosswise and horizontally of the vehicle in front of the front wheels or in the back of the rear wheels. The buffer bar 10 is of profiled steel type having a web portion 10a and upper and lower inwardly directed flanges 10b. Affixed on the outer surface of the web portion 10a is an elongate plate-like member 13 of urethan foam or other suitable material that serves to lessen impacts upon pedestrians which could otherwise cause critical physical damages to them at the time of a collision. A back plate or impact receiving member 15 is provided which extends between the upper and lower flanges 10b of the buffer plate 10, the upper and lower ends of the back plate 15 being secured to the inner surfaces of the upper and lower flanges 10b, respectively. by welding or other suitable method. The back plate 15 has one or more openings 17 formed therein (see FIG. 2) for securing thereto a piston 'rod which forms part of a shock absorbing mounting 21.

The shock absorbing mounting 21 is preferably of the hydraulic cushion type and comprises a cylinder 23, a

piston (not shown) axially movable within the cylinder 23, and the piston rod 25 extending from the piston toward the buffer bar 10. The cylinder 23 is secured-on a longitudinally disposed frame portion or a side bar 27 of a vehicle chassis by means of bracket members 29.

As is best seen in FIG. 2, thepiston rod 25 has mounted thereon or integrally formed therewith an end plate 31 which is secured to the back plate 15 by a bolt and nut assembly 33 with a resilient plate member 35 interposed therebetween. The resilient member 35 is made of foam rubber or any other suitable material that is sufficiently resilient to absorb shearing stresses as well as compression stresses. The opening 17 in the back plate 15, and its

corresponding openings

37 and 39 formed in the end plate 31 and the resilient member 35, respectively, are so arranged as to have same diameters which are somewhat larger than the outer diameter of a bolt 33a so as to provide slight lateral movement or play of the back plate 15 relative to the end plate 31.

The sensor or switch mechanism according to the invention is generally designated by and is mounted on the end plate 31 of the piston rod 25 to sense an impact upon the buffer bar 10 at the time of a collision. A typical example of the switch mechanism is shown in FIG. 4, which comprises a casing or housing 52 having a chamber 54 formed therein and an axial bore 56 extending from the chamber 54. An elongate retractable member 58 is mounted in the axial bore 56 slidably movable therein. The elongate member 58 has secured at its inner end a plate 60 of electrically conductive material for normally providing an electric path between two contacts 62 and 63 provided in the chamber 54 on both sides of the axial bore 56. The chamber 54 is also provided with a spring seat 65 for receiving a coil or helical spring 67 which acts to apply a force on the end plate 60 to urge the elongate retractable member 58 to its fully extended position shown in FIG. 4. Connections to the contacts 62 and 63 are made by wires 72 and 73, respectively, which are connected to a vehicle safety device (not shown).

As seen in FIG. 2, the resilient member 35 and the end plate 31 of the piston rod 25 have formed therein aligned openings 75 and 76, respectively, which are of identical diameter somewhat larger than the outer diameter of the elongate retractable member 58. The sensor or switch mechanism 50 is secured to the surface of the end plate 31 opposite to the resilient member 35 by suitable means (not shown), with the elongate retractable member 58 extending through the aligned openings 75 and 76. It should be noted that the length of the elongate member 58 is such that there is a gap left between the tip of the elongate member 58 and the surface of the back plate 15 under normal conditions.

In the operation of the arrangement shown in FIGS. 1, 2, 3and 4, when the buffer bar is subjected to a strong impact due to a violent collision of the vehicle against'another one or a stationary structure in the path of advance, the buffer bar 10 is deformed instantly inwardly, causing the resilient member 35 to be compressed. Even if a collision other than a headon one is encountered by the vehicle, the resilient member 35 is compressed by the back plate of the buffer bar 10,

.since the plate 15 is connected with the end plate 31 permitting a slight lateral movement relative to each other. as described above. When this occurs, the elongate member 58 is urged into the housing 52 by the back plate 15, so that the end plate 60 of the elongated member 58 is moved in a right-hand direction as viewed in FIG. 4 against the action of the spring 67.

This will disconnect the contacts 62 and 63 from each FIG. 6 illustrates another preferred embodiment of the sensor or switch mechanism according to the invention which is different from that of FIG. 4 in that a leaf spring 85 is employed in place of the coil or helical spring 67. The leaf spring 85 is preloaded so as to normally urge the elongate member 58' to its fully extended position through a protuberance 87 provided on the end plate 60'. The leaf spring 85 is made of electrically conductive material and is normally kept in contact with afixed contact 89 provided in the housing 52. When the elongate member 58 is caused to retract into the housing 52' due to an impact thereon resulting from a collision of the vehicle, the leaf spring is moved away from the fixed contact 89 resulting in actuation of the vehicle safety device.

FIG. 7 illustrates a further embodiment of the switch mechanism according to the invention which includes a permanent magnet 90 for magnetically actuating a hermetically sealed switch 92. As illustrated, the sensor or switch mechanism also includes a casing or housing 94 having a chamber 96 formed therein and an axial bore 98 extending from the chamber 96. An elongate retractable member 100 is axially slidably mounted in the axial bore 98 and is normally biased to its fully extended position by means of a spring 102. The permanent magnet 90 is mounted at the inner end of the elongate member 100 and, when the elongate member 100 is moved to its retracted position, the magnet 90 is placed in a position immediately above the hermetically sealed switch 92, where it actuates the switch 92. The switch 92 is disposed within the chamber 96 longitudinally of the housing 94 to extend along the spring 102.

The switch 92, as best seen in FIG. 8, comprises an elongate hollow tube 106 of electrically insulating material such as glass, containing inert gas. Alternatively, the hollow tube 106 may be evacuated to prevent degeneration of contacts provided therein. A contact 108 extends into the interior of the tube 106 from the left exterior side thereof and is preferably made of nonmagnetic material such as aluminum or copper. Another contact 110 is made of resilient and magnetic material and extends into the tube 106 from the right exterior side thereof toward the contact 108. The contact 110 is preloaded so that the tip thereof is normally held in contact with the lower surface of the contact 108. When the permanent magnet 90 is moved from the position indicated by the solid line 90a to that indicated by the broken line 90b in response to a collision, the tip of the contact 110 is moved downwards away from the contact 108 due to a repulsive force applied thereto by the magnet 90.

FIG. 9 illustrates the sensor or switch mechanism according to the invention which includes a cover mounted on the housing 52 to enclose the elongate retractable member 58. The cover 120 serves to prevent the entrance of dirt, water or other foreign matter into the axial bore 56 (not identified) which would otherwise cause corrosion of contacts or lead to malfunction of the switch mechanism.

FIG. 10 illustrates a further preferred embodiment of the sensor or switch mechanism according to the invention which sensor is generally of the pneumatically actuated type. A casing or housing has formed therein a chamber 132 which is divided into two axial compartments 132a and 1321; by a partition member 134 provided in the chamber 132. A piston 136 is axially slidably mounted within the compartment 132a and has a piston rod 138 extending externally therefrom through an opening formed in the housing 130. The partition member 134 is formed in the center thereof with an opening 140 which communicates with the interior of a bellows member 142 provided within the compartment 132a on the partition member 134. The bellows member 142 is secured to a plate member 144 through which the bellows member 142 is normally compressed to its contracted condition by means of a spring 146 provided between the partition member 134 and the plate member 144. The plate member 144 is of electrically conductive material and is normally engaging a contact 148 leading to a'terminal 150. A fixed contact 152 is provided between the partition member 134 and the plate member 144 and is normally held in abutting engagement with the conductive plate member 144. Another terminal 154 is provided leading to the fixed contact 152. When a collision takes place, the piston rod 138 is urged into the housing to move the piston 136 in a right-hand direction as viewed in FIG. 10, thereby causing the bellows member 142 to expand. Expansion of the bellows member 142 moves the plate member 144 away from the fixed contact 152 against the action of the spring 146, so that an electric circuit between the terminals and 154 is opened.

FIG. 11 illustrates still another preferred embodiment of the sensor or switch mechanism according to the invention which is similar to that shown in FIG. 4 except that the elongate retractable member 58 is normally held in its fullyextended position by means of a magnet instead of the spring 67'(see FIG. 4). The magnet 160 may be a permanent magnet or an electromagnet which is capable of holding the elongate member 58 in the-position shown without being affected by rather light impacts not resulting from a collision of the vehicle.

FIG. .12 illustrates a still .further preferred embodiment of the sensor or switch mechanism accordingto the invention which is also similar to that shown in FIG. 4 except that the contacts 62 and 63 are replaced by a tubular contact member 165. As is best seen in FIG. 13, the tubular contact member comprises two elongate portions 165a and l65b which are made of glass or other suitable material having thereon a coating of electrically conductivemate'rial. When a collision takes place, the portions 165:: and 16512 shatter, interrupting an electric path between terminals connected thereto.

'The contact member 165 may be formed of carbon,

and further, it may be formed in a circular fashion as seenin FIGQM. I

The switch mechanisms as shown and described 7 above are employed separately or in combination with other collision-sensitive switch types in order to insure a reliable sensing of a collision condition which could possibly cause critical physical injuries to the vehicle occupants.

FIG. 15 illustrates a typical arrangement of the inertia switch which is of the sensitivity-modulating type. The switch 170 includes a weight 174 of magnetic material which is suspended by a conductive wire 176 leading to a terminal 178. The weight 174 is normally held in abutting engagement with a permanent magnet I80 and an electromagnet 182 which is energized by a battery 184 through the switch mechanism 50 of the invention. Since, in normal condition. the weight 174 is held in the position shown with two forces exerted by the permanent magnet I80 and the electromagnet 182, it will be appreciated that even a rapid acceleration or deceleration of the vehicle during normal driving cannot cause movement of the weightl74 away from the magnets and 182. However, when a collision occurs, the switch mechanism 50 is opened, reducing to zero the force exerted on the weight 174 by the electromagnet 182, so that the weight 174 is moved into contact with a fixed contact 186 with a decreased force of inertia applied to the weight 174. It will be appreciated that with this arrangement it is possible to keep at a relatively low value the'magnitude of deceleration above which the inertia switch 17 is actuated at the time of a collision.

FIG. 16 illustrates another arrangement of the inertia switch 170' which is adapted for use with the sensor or switch mechanism of the invention. The inertia switch 170 comprises a tubular member or housing 190 having an internal cylindrical bore 192 f0 formed therein within which a weight in the form of a sphere 194 is disposed. The weight 194 is normally held against one end wall of the cylidrical bore 192 by a contact member 196 which in turn is urged in a left-hand direction as viewed in FIG. 16 by a spring 198 provided within the cylindrical bore 192. Extending inwardly from the other end wall of the bore 192 toward the contact member 196 is another contact member 200 which leads to a terminal 202. The spring 198 is of electrically conductive material, connecting the contact member 196 to a terminal 204. The inertia switch 170' also includes an electromagnet 206 provided in the left end portion of the tubular member 190 adjacent the spherical weight 194. The electromagnet 206 is connected in series with the switch mechanism 50 of the present inmembers it should be understood that the invention is not restricted to either one of the two types. It would be possible to readily modify the switch mechanism from a closed-open to open-closed or from open-closed to closed-open type. In this connection, it should be noted that the switch mechanism which is opened when a collision takes place is characterized by a quick response in that even a slight movement of the movable contact causes itself to be disconnected fromthe fixed contact.

Furthermore, it should be noted that with the employment of the hermetically sealed switch 92 shown in FIG. 8, the switch mechanism of the invention has an increased durability in use since the internally mounted contacts 108 and 110 are prevented from exposure to the air.

Still furthermore, it should be noted that since the piston rod 25 of the shock absorbing mounting 21 is connected with the back plate 15 of the buffer bar 10 in a manner to permit slight lateral movement relative to each other, the sensor or switch mechanism of the invention is responsive toa collision other than a headon collision as well.

What is claimed is: l. In a motor vehicle having a safety device actuable in response to a collision signal, at least one shock absorbing bumper, which bumper includes an impact receiving member extending crosswise horizontally of the vehicle, a cylinder disposed longitudinally of the vehicle and secured to the vehicle's body, a piston axially slidable in a bore of the cylinder, a piston rod extending externally from the piston and having one end secured to the impact receiving member, the piston rod being adapted to be withdrawn into the cylinder when said impact receiving member deforms upon collision against a solid obstacle, and a resilient member disapparatus comprising, in

means defining aligned niches in said one end of said piston rodand said resilient member and lying adjacent said insulated housing,

an elongate actuating member axially slidably mounted in the cavity and extending externally of said housing, said elongated actuating member being arranged to normally extend through said niche in said one end of said piston rod into said niche formed in said'resilient member but to be withdrawn into said housingupon compression of the resilient member resulting from the collision,

a fixed contact disposed in said cavity, and

a movable contact which is associated with said elongate actuating member, disposed in said cavity and normally held in contact with the fixed contact, the

movable contact being movable to disengage from the fixed contact in response to the withdrawal movement of said elongate actuating member to open said first electric circuit;

anda normally open, inertia responsive switch forming part of a second electric circuit connected with the safety'device for producing the collision signal upon closure thereof, said inertia responsive switch including,

an insulated housing mounted on the vehicle body adjacent 'to said impact receiving member, the housing defining a cavity therein,

an inertia-responsive magnetic weight located in said cavity for movement in a longitudinal direction of the vehicle body in response to the inertia applied to the body during the collision,

a movable contact disposed on said inertia weight,

a fixed contact disposed in said housing adjacent to the movable contact, the fixed contact being positioned in a path of the inertia responsive movement of said inertia weight,

means applying a force to usually hold said movable contact apart from said fixed contact, the force being overcome by the inertia force at a predeterv mined degree, and electromagnetic means mounted in the cavity of said inertia responsive switch housing and situated adjaonly by overcoming the force of said force applying means to close said second electric circuit.

2. An apparatus according to claim 1, in which said movable contact of the deformation responsive switch is disposed on the inner end of said elongate actuating member.

3. An apparatus according to claim 2, further comprising means to keep said elongate actuating member at its extended position.

4. An apparatus according to claim 3, in which said means to keep said elongate actuating member at its extended position is a spiral spring disposed between a wall of said cavity and said elongate actuating member and preloaded to urge the actuating member toward the extended position.

5. An apparatus according to claim 3, in which said means to keep said elongate actuating member at its extended position is plate spring having one end fixed to a wall of said cavity and preloaded to urge the actuating member toward the extended position.

6. An apparatus according to claim 3, in which said means to keep said elongate actuating member at its extended position is a permanent magnet disposed on said housing to exert an attractive force upon said movable contact on said actuating member to urge it toward the extended position.

7. An apparatus according to claim 2, in which said fixed contact of the deformation responsive switch is a tubular member of glass coated thereon with an electrically conductive material and disposed in contact with said movable contact, said tubular member being adapted to be broken by said actuating member when said actuating member is withdrawn thereby cutting off the electric connection of said movable contact with said fixed contact.

8. An apparatus according to claim 1, in which said deformation responsive switch further comprises a permanent magnet provided on said elongate actuating member.

9. An apparatus according to claim 8, in which said movable contact and said fixed contact of the deformation responsive switch form a reed enclosed in a fluidtight tube disposed adjacent to said permanent magnet.

10. An apparatus according to claim 1, in which said cavity of said housing of said deformation responsive switch is divided into a first compartment and a second compartment by a partition member, and accommodates therein a piston secured to the inner end of said elongate actuating member, said piston being axially slidable in the first compartment, and a bellows member provided within the second compartment and communicating with the first compartment through an opening formed in the partition member, and in which said movable contact is disposed on the bellows member for movement therewith and said fixed contact is provided in the second compartment normally in contact with said fixed contact by a tension spring, whereby upon compression of said bellows member, said movable contact is removed from said fixed contact.

11. An apparatus according to claim 1, in which said inertia weight of the inertia responsive switch is of a pendent type hanging from the top wall of the housing by a flexible wire.

12. An apparatus according to claim 11, in which said force applying means is a permanent magnet disposed adjacent to said inertia weight on the side site to the position of said fixed contact.

13. An apparatus according to claim 1, in which said force applying means is a spring within said cavity ex-- tending in. the longitudinal direction of the vehicle and having one end anchored to the movable contact on said inertia weight to urge ittoward the electromagnetic means.

14. An apparatus according to claim 13, in which said inertia weight is a spherical member held in position by said spring.

15. A collision sensor for sensing a collision condition of a motor vehicle to actuate a safety device mounted thereon, said collision sensor being mounted on a shock-absorbing bumper which includes an impact receiving member extending crosswise horizontally of the vehicle, a cylinder extending longitudinally of the vehicle and secured to the vehicle's body, a piston axially slidable in the cylinder, a piston rod extending externally from the piston and connected with the impact receiving member, and a resilient member provided on the impact receiving member to partially absorb an impact resulting from a collision, said collision sensor comprising: a housing having a bore formed therein; an elongate actuating member axially and slidably mounted in the bore and extending externally of said oppohousing, said elongate actuating member being arranged to normally extend into a niche formed in the resilient member but to be retracted into said housing upon compression of the resilient member resulting from a collision; biasing means for normally biasing said elongate actuating member to its extended position; switch means provided in said housing for actuating the safety device when said elongate actuating member is forcibly moved to its retracted position, said housing having a chamber divided into first and second compartments by a partition member; and said elon gate actuating member has a piston secured to the inner end thereof, the piston being axially slidable in the first axial compartment; and a bellows member is provided within the second compartment and communicates with the first compartment through an opening formed in the partition member; and said switch means comprises a movable contact secured to the bellows member for movement therewith, and a fixed contact provided in the second compartment; and said biasing means comprises a spring provided between the partition member and the movable contact to normally keep the bellows member in a contracted condition, the movable contact being kept in contact with the fixed contact when the bellows member is contracted.

Claims

1. In a motor vehicle having a safety device actuable in response to a collision signal, at least one shock absorbing bumper, which bumper includes an impact receiving member extending crosswise horizontally of the vehicle, a cylinder disposed longitudinally of the vehicle and secured to the vehicle''s body, a piston axially slidable in a bore of the cylinder, a piston rod extending externally from the piston and having one end secured to the impact receiving member, the piston rod being adapted to be withdrawn into the cylinder when said impact receiving member deforms upon collision against a solid obstacle, and a resilient member disposed between the impact receiving member and the piston rod to partially absorb an impact resulting from a collision, a collision signal producing apparatus comprising, in combination, a normally closed, vehicle deformation responsive switch forming part of a first electric circuit, said deformation responsive switch including an insulated housing mounted adjacent said resilient member and disposed on said one end of the piston rod, the housing defining a cavity formed therein, means defining aligned niches in said one end of said piston rod and said resilient member and lying adjacent said insulated housing, an elongate actuating member axially slidably mounted in the cavity and extending externally of said housing, said elongated actuating member being arranged to normally extend through said niche in said one end of said piston rod into said niche formed in said resilient member but to be withdrawn into said housing upon compression of the resilient member resulting from the collision, a fixed contact disposed in said cavity, and a movable contact which is associated with said elongate actuating member, disposed in said cavity and normally held in contact with the fixed contact, the movable contact being movable to disengage from the fixed contact in response to the withdrawal movement of said elongate actuating member to open said first electric circuit; and a normally open, inertia responsive switch forming part of a second electric circuit connected with the safety device for producing the collision signal upon closure thereof, said inertia responsive switch including, an insulated housing mounted on the vehicle body adjacent to said impact receiving member, the housing defining a cavity therein, an inertia-responsive magnetic weight located in said cavity for movement in a longitudinal direction of the vehicle body in response to the inertia applied to the body during the collision, a movable contact disposed on said inertia weight, a fixed contact disposed in said housing adjacent to the movable contact, the fixed contact being positioned in a path of the inertia responsive movement of said inertia weight, means applying a force to usually hold said movable contact apart from said fixed contact, the force being overcome by the inertia force at a predetermined degree, and electromagnetic means mounted in the cavity of said inertia responsive switch housing and situated adjacent to the inertia weight on the side opposite to the position of said fixed contact to exert, upon energization thereof, an attractive force upon said inertia weight to hold the movable contact apart from said fixed contact, said electromagnetic means being connected with the first electric circuit and adapted to be deenergized upon opening of said first electric circuit; whereby said movable contact of the inertia weight is allowed to engage with the fixed contact at a predetermined degree of collision which is enough to open said vehicle deformation responsive switch, only by overcoming the force of said force applying means to close said second electric circuit.

9. An apparatus according to claim 8, in which said movable contact and said fixed contact of the deformation responsive switch form a reed enclosed in a fluid-tight tube disposed adjacent to said permanent magnet.

12. An apparatus according to claim 11, in which said force applying means is a permanent magnet disposed adjacent to said inertia weight on the side opposite to the position of said fixed contact.

13. An apparatus according to claim 1, in which said force applying means is a spring within said cavity extending in the longitudinal direction of the vehicle and having one end anchored to the movable contact on said inertia weight to urge it toward the electromagnetic means.

15. A collision sensor for sensing a collision condition of a motor vehicle to actuate a safety device mounted thereon, said collision sensor being mounted on a shock-absorbing bumper which includes an impact receiving member extending crosswise horizontally of the vehicle, a cylinder extending longitudinally of the vehicle and secured to the vehicle''s body, a piston axially slidable in the cylinder, a piston rod extending externally from the piston and connected with the impact receiving member, and a resilient member provided on the impact receiving member to partially absorb an impact resulting from a collision, said collision sensor comprising: a housing having a bore formed therein; an elongate actuating member axially and slidably mounted in the bore and extending externally of said housing, said elongate actuating member being arranged to normally extend into a niche formed in the resilient member but to be retracted into said housing upon compression of the resilient member resulting from a collision; biasing means for normally biasing said elongate actuating member to its extended position; switch means provided in said housing for actuating the safety device when said elongate actuating member is forcibly moved to its retracted position, said housing having a chamber divided into first and second compartments by a partition member; and said elongate actuating member has a piston secured to the inner end thereof, the piston being axially slidable in the first axial compartment; and a bellows member is provided within the second compartment and communicates with the first compartment through an opening formed in the partition member; and said switch means comprises a movable contact secured to the bellows member for movement therewith, and a fixed contact provided in the second compartment; and said biasing means comprises a spring provided between the partition member and the movable contact to normally keep the bellows member in a contracted condition, the movable contact being kept in contact with the fixed contact when the bellows member is contracted.