Abstract:
Disclosed is a collision energy absorbing structure of a vehicle capable of relieving impact by using a tubular pipe member having equally-sized rectangular cross section and equal plate thickness and including no inside ribs and by adding a suitable trigger, and being easily manufactured at a low cost. By forming a cutout portion on the left side of the front end portion of the collision energy absorbing structure, the deformation starting portion is provided. The cutout portion is formed at parts of three flat plate portions comprised of one of the four flat plate portions and corresponding opposite portions thereof. The general portion, which follows the deformation starting portion, is tubular with rectangular cross section and has a closed cross-section structure.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a collision energy absorbing structure of a vehicle which is used for absorbing a collision energy generated by a collision of vehicles such as railroad vehicles by bellows-like deformation (plastic deformation) of a tubular energy absorbing member with rectangular cross section to relieve impact when collision occurs. 
   2. Description of the Related Art 
   In general, it is known that a pipe member can be used as an energy absorbing member for absorbing a collision energy by bellows-like deformation, because the pipe member is plastically deformed like bellows while suppressing deformation of the Euler buckling when a compression force is axially applied to the pipe member by suitably selecting a dimension or a thickness thereof. Since such bellows-like deformation is capable of stably absorbing the collision energy, conventionally, the collision energy absorbing structure using the pipe member has been widely used. 
   By the way, since a high reaction force is generated in triggering the bellows-like deformation when such pipe member is used to form the collision energy absorbing structure, the impact acting on passengers is increased in an initial stage of collision. Accordingly, the following structure has been proposed as a structure for reducing the maximum force in the initial stage of collision.
     (1) By way of example, in a structure disclosed in Japanese Patent No. 2650527 in which ribs are longitudinally formed integrally with the inside of a member body extruded to have closed cross section and provided in the longitudinal direction of the vehicle to define a plurality of parts in the member body, the ribs have inclined portions at end portions thereof which are extending from points connecting the ribs to peripheral portions of the member body toward the inside of the body. In this structure, since the inclined portions are thus formed in the ribs at end face portion of the member body and the corresponding rib cross-sectional areas are extremely small, the member body tends to be axially deformed by buckling upon application of an axial collision force to the end portion of the member body in collision of the vehicle. Consequently, an initial reaction force can be reduced.   (2) As another example, as disclosed in Japanese Patent No. 2882243, a plurality of arc-shaped grooves inwardly recessed and axially extending from the front end are formed circumferentially and at substantially equal intervals at the front end portion of a tubular chassis frame provided in the longitudinal direction of the vehicle. In this structure, upon application of impact to the front end portion from front, the arc-shaped groove portions and the portions without the grooves are continuously and axially deformed by buckling while being deformed alternately and inwardly or outwardly from the front end, so that plastic deformation is stabilized with bellows being close to one other.   (3) As a further example, as disclosed in Publication of Examined Patent Application No. Hei. 11-5564, a side member of a vehicle formed to have a hollow shaft by extruding aluminum is provided with at least one rib in the longitudinal direction thereof and the thickness of the rib and the thickness of the side member are gradually increased from the end portion toward a vehicle chamber side in the longitudinal direction of the vehicle. Because of such a gradual increase in the thickness, this structure is capable of reducing an initial maximum force while keeping a collision energy absorbing ability large as the whole.   (4) As a still further example, as disclosed in Publications of Examined Patent Applications Nos. Hei. 9-277953, 9-277954, in an energy absorbing member capable of absorbing a collision energy by bellows-like bucking deformation, a cross section of a buckling deformation starting end is a polygon-shaped closed cross section with angles more than 4 and a cross section of the other end is a polygon-shaped closed cross section having sides more than those of the cross section of the starting end, between which the cross section gradually varies. These structures enable the increasing of the buckling force and the reducing of the initial impact force by utilizing the polygon-shaped cross section or a tapered shape with varying cross section to suppress the initial impact force or stabilize the first buckling deformation.   

   However, the structures of (1)-(4) suffer from the following drawbacks.
     (A) In the structure disclosed in Japanese Patent No. 2650527, since the inclined portions are formed at the ribs inside of the member body, its structure is complicated. In addition, this structure is only applicable to the structure having inside ribs (e.g., extruded aluminum).   (B) The structure disclosed in Japanese Patent No. 2882243 is applicable only to the cylindrical frame. Since the bellows-like deformation tends to be unstable in the cylindrical frame as compared to the tubular frame with rectangular cross section, a stable energy absorbing characteristic is difficult to obtain.   (C) In the structures disclosed in Publications of Examined Patent Applications Nos. Hei. 11-5564, 9-277953, 9-277954, since the pipe member (side member or energy absorbing member) has a structure with the cross section varying in the axial direction thereof, a special and complicated process is needed.   

   SUMMARY OF THE INVENTION 
   The present invention addresses the above-described condition, and an object of the present invention is to provide a collision energy absorbing structure of a vehicle capable of absorbing impact by using a tubular pipe member having an equally-sized rectangular cross section and an equal plate thickness and including no inside ribs and by adding a suitable trigger, and being easily manufactured at a low cost. 
   To achieve the above object, according to the present invention, there is provided a collision energy absorbing structure of a vehicle comprising: a tubular energy absorbing member with rectangular cross section, provided in the longitudinal direction of the vehicle and having four flat plate portions, the tubular energy absorbing member being adapted to receive a collision force in the longitudinal direction of the vehicle and deformed like bellows by buckling, so as to absorb a collision energy; and a deformation starting portion provided by forming a cutout portion in one of right and left sides or one of upper and lower sides of a front end portion of the energy absorbing member. 
   According to the present invention, the strength of the deformation staring portion is lower than the strength of the other part of the energy absorbing member and the initial impact force can be reduced. In addition, since the deformation starting portion is provided by reducing the size of part of the tubular energy absorbing member with rectangular cross section, the structure can be simplified. 
   In the collision energy absorbing structure, the deformation starting portion may be provided by forming a cutout portion in one end of right and left sides or one of upper and lower sides of a front end portion of the energy absorbing member. Also, the cutout portion may be formed in parts of three flat plate portions comprised of one of the four flat plate portions and flat plate portions located on both sides thereof. By increasing/reducing the number of the energy absorbing members, the amount of absorbed energy can be adjusted in the whole structure. The tubular member needs to have four flat plate portions and may have square or rectangular cross section. The energy absorbing member may be manufactured by forming the cutout portion at the front end portion of the tubular member with rectangular cross section (closed cross section structure), or otherwise, by opposing open sides of two channel members having different lengths because of the cutout portion to each other and bonding flanges thereof together. 
   The tubular energy absorbing member may have a portion extended from part of the front end portion so as to be substantially channel shaped. The provision of the cutout portion at the front end portion of the energy absorbing member is equivalent to the provision of the extended portion at the front end portion. 
   In this constitution, upon application of the force in the longitudinal direction of the vehicle when collision occurs, since the front end portion is provided with the cutout portion and has the open cross section, i.e., provided with the extended portion, the initial force peak for generating the bellows-like deformation can be reduced as compared to the case where the tubular portion (closed cross section structure) is deformed like bellows without the cutout portion. 
   Since the front end portion (extended portion) has already started to be deformed, the following tubular portion starts to be deformed like bellows naturally. More specifically, the deformation sequentially occurs in the front end portion (extended portion) and the portion continuous with the front end portion, while the portion provided with the cutout portion starts to be newly deformed like bellows after the bellows-like deformation of the front end portion, so that the force peak for generating the new bellows-like deformation is reduced and the bellows-like deformation naturally takes place. Consequently, the collision energy can be efficiently absorbed. 
   Further, since the tubular pipe with rectangular cross section is provided with the cutout portion, that is, the channel-shaped extended portion, the energy absorbing member can be manufactured easily and at a low cost. In particular, since the front end portion is provided with the cutout portion, i.e., the extended portion so as to be vertically or laterally asymmetric, the reaction force in the initial stage of collision can be reduced with such simple structure. Also, since the bellows-like deformation has already started in part (asymmetric portion) of the front end portion, the reaction force at the start of deformation of the other portion is reduced to be substantially equal to the reaction force in the initial stage of the collision (see FIG.  2 ), thereby keeping a constant reaction force. Consequently, the impact acting on the passengers can be relieved without a rapid rise in the impact force. 
   Also, a plurality of impact absorbing members may be provided so as to be vertically or laterally symmetric. 
   In this constitution, since the plurality of energy absorbing members are vertically or laterally symmetric, the impact in the traveling direction is evenly applied to the front end portions (extended portions) of these energy absorbing members, so that the bellows-like deformation occurs naturally without falling the energy absorbing members. 
   The collision energy absorbing structure may further comprise: a rubber damper connected to a coupler of the vehicle, for absorbing and relieving impact generated between vehicles, and a front end portion of the energy absorbing member may be connected to a rear end portion of the rubber damper and a rear end portion of the energy absorbing member may be connected to a draft stop mounted to a vehicle body frame. 
   With this constitution, the small collision energy can be absorbed by the rubber damper and the great collision energy can be absorbed by bellows-like deformation of the energy absorbing member. 
   In the collision energy absorbing structure, the energy absorbing member may be provided behind a rail guard board for eliminating obstacles on a rail during traveling and a rear end portion of the energy absorbing member may be connected to a support device mounted to a vehicle body frame. 
   With this constitution, when the excessive collision energy is applied to the rail guard board for eliminating obstacles on the rail during traveling, this collision energy is absorbed by the bellows-like deformation of the energy absorbing member. 
   The collision energy absorbing structure, may further comprise: a support device mounted to a vehicle body frame, provided behind a coupler and extending forwardly of a rail guard board, and in this structure, a rear end portion of the energy absorbing member may be connected to a front end portion of the support device, and the energy absorbing member may extend forwardly of the coupler. 
   In this constitution, since the energy absorbing member extending forwardly of the coupler in the front vehicle is provided with the collision member at the front end thereof, the collision member is collided and the collision energy is absorbed by the bellows-like deformation of the energy absorbing members. Consequently, the impact acting on the passengers can be relieved. 
   The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE BRIEF DRAWINGS 
       FIG. 1  is a perspective view showing a front end portion of an energy absorbing member used in a collision energy absorbing structure of a vehicle according to the present invention; 
       FIG. 2  is a view showing a result of a computer simulation analysis of the relationship between displacement and force applied to the energy absorbing member according to the present invention; 
       FIG. 3  is an explanatory view schematically showing a first stage of a deformation mode of the front end portion of the energy absorbing member according to the present invention; 
       FIG. 4  is an explanatory view schematically showing a second stage of the deformation mode of the front end portion of the energy absorbing member according to the present invention; 
       FIG. 5  is an explanatory view schematically showing a third stage of the deformation mode of the front end portion of the energy absorbing member according to the present invention; 
       FIG. 6  is an explanatory view schematically showing a fourth stage of the deformation mode of the front end portion of the energy absorbing member according to the present invention; 
       FIG. 7  is an explanatory view schematically showing a fifth stage of the deformation mode of the front end portion of the energy absorbing member according to the present invention; 
       FIG. 8  is an explanatory view schematically showing a sixth stage of the deformation mode of the front end portion of the energy absorbing member according to the present invention; 
       FIG. 9  is an explanatory view schematically showing a seventh stage of the deformation mode of the front end portion of the energy absorbing member according to the present invention; 
       FIG. 10  is an explanatory view schematically showing an eighth stage of the deformation mode of the front end portion of the energy absorbing member according to the present invention; 
       FIG. 11  is an explanatory view schematically showing a ninth stage of the deformation mode of the front end portion of the energy absorbing member according to the present invention; 
     FIG.  12 (A) is a graph showing the relationship between a first peak force generated in an initial stage of collision and a size of a deformation stating portion; 
     FIG.  12 (B) is a graph showing the relationship between a second peak force generated in a middle stage of collision and a size of the deformation staring portion; 
     FIG.  12 (C) is a graph showing the relationship between a ratio between the first peak force and the second peak force and a size of the deformation starting portion; 
       FIG. 13  is a side view showing an example in which a collision energy absorbing structure of a vehicle according to the present invention is applied to a coupler of a railroad vehicle; 
       FIG. 14  is a plan view showing the collision energy absorbing structure of the vehicle of  FIG. 13 ; 
       FIG. 15  is a side view showing an example in which the collision energy absorbing structure of the vehicle according to the present invention is applied to a rail guard of a front vehicle of the railroad vehicle; 
       FIG. 16  is a plan view showing a collision energy absorbing structure of the vehicle of  FIG. 15 ; 
       FIG. 17  is a side view showing an example in which the collision energy absorbing structure of the vehicle according to the present invention is mounted to a front portion of a front vehicle of the railroad vehicle; and 
       FIG. 18  is a plan view showing the collision energy absorbing structure of the vehicle of FIG.  17 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Hereinafter, a preferred embodiment of the present invention will be described with reference to drawings. 
     FIG. 1  is a perspective view showing an energy absorbing member used in a collision energy absorbing structure of a vehicle according to the present invention. 
   Referring now to  FIG. 1 , there is shown a tubular energy absorbing pipe member  1  (energy absorbing member) with rectangular cross section. The energy absorbing pipe member  1  is provided with a cutout portion  1   a  having an axial dimension L and a width dimension B on the left side of a front end portion S 1  which corresponds to a deformation starting portion that has channel-shaped open cross section and is laterally asymmetrical. Here, the width dimension B of the cutout portion  1   a  is equal to substantially ½ of a width W of the member  1 . 
   The energy absorbing pipe member  1  has a closed cross-section structure having four flat plate portions  1 A,  1 B,  1 C,  1 D and the cutout portion  1   a  is formed by the flat plate portion  1 A and parts of the flat plate portions  1 B,  1 C connected to both sides of the flat plate portion  1 A at the front end portion (deformation starting portion) S 1 . The front end portion S 1  provided with the cutout portion  1   a  functions as a trigger portion for triggering bellows-like deformation for energy absorption and has the channel-shaped open cross section. While corner portions of the cutout portion  1   a  have certain degrees, for example, 90 degrees in  FIG. 1 , they may be curved. 
   In other words, the channel-shaped deformation starting portion (extended portion) S 1  is extended from the whole width of the flat plate portion  1 A, and part of the flat plate portion  1 B and part of the flat plate portion  1 C. The extended portion S 1  has a length L as shown in FIG.  1 . 
   When the axial force is evenly applied to the front end face of the tubular energy absorbing pipe member  1  with rectangular cross section, deformation (bellows-like deformation) that is laterally asymmetric starts from the deformation starting portion S 1  corresponding to the extended portion having low strength. In brief, the deformation starting portion S 1  is deformed in the initial stage of collision, which deformation triggers the bellows-like deformation mentioned later. 
   In the bellows-like deformation (buckling deformation) of the deformation starting portion S 1  (trigger portion) in the initial stage of collision, since the deformation starting portion S 1  is laterally asymmetrical and has the open cross section because of the cutout portion  1   a  and initial force necessary for generating the bellows-like deformation as the result of collision is therefore small, the peak of the initial force in the collision is considerably reduced as compared to the case where the tubular pipe member  1  with rectangular cross section is deformed like bellows without the cutout portion  1   a.    
   Then, the bellows-like deformation (buckling deformation) of the deformation starting portion S 1  (right-half portion) of the energy absorbing pipe member  1  gradually progresses and reaches a general portion S 2  as the closed cross section. Since the asymmetric bellows-like deformation has been already generated, new bellows-like deformation does not occur in the entire general portion S 2 , but occurs in the left half portion of the general portion S 2 . So, there is a difference between the time when the initial force (force peak) at the start of the buckling deformation of the deformation starting portion S 1  is generated and the time when the initial force at the start of the buckling deformation of the general portion S 2  is generated. For this reason, the force necessary for causing the bellows-like deformation in the energy absorbing pipe member  1  is divided into the force at the start of the bellows-like deformation of the deformation starting portion S 1  and the force for the start of the bellows-like deformation of the general portion S 2 . As a result, the peak force in the initial stage of collision is reduced and a constant reaction force is kept. Therefore, the impact acting on the passengers is relieved without a rapid rise in the impact force. 
   Thus, the bellows-like deformation of the deformation starting portion S 1  triggers the bellows-like deformation of the general portion S 2 . Once the bellows-like deformation occurs in the general portion S 2 , stable bellows-like deformation continues thereafter. In this case, since the axial (longitudinal) force applied to the energy absorbing pipe member  1  is considerably higher than the force orthogonal to the axial force, transitions of the bellows-like deformation from the deformation starting portion S 1  to the general portion S 2  smoothly takes place. 
     FIG. 2  shows a result of computer simulation analysis of the relationship between the force and displacement of this deformation.  FIGS. 3 through 11  are views schematically showing change occurring when the collision force is applied to a contact plate  2  provided at the front end of the energy absorbing pipe member  1 . In the state of  FIG. 3  before collision, no force is applied and the forces in the states of  FIGS. 4 through 11  correspond to the forces at force peak points P 1 -P 8  in FIG.  2 . As shown in  FIGS. 3 through 11 , the contact plate  2  is provided on the deformation starting portion S 1  of the energy absorbing pipe member  1 . In these cases, the cutout portion  1   a  is formed at the upper half portion of the front end portion (see FIGS.  4  through  11 ). In other words, the deformation starting portion (extended portion) S 1  is extended from the lower half portion of the front end of the energy absorbing pipe member  1 . 
   The state before collision is shown in FIG.  3 . Once the collision occurs and the axial collision force (dynamic force) is applied through the contact plate  2 , first, the deformation starting portion S 1  corresponding to the lower half portion of the energy absorbing pipe member  1  starts to be deformed by buckling. Then, as shown in  FIG. 5 , the upper flat plate portion of the upper half portion of the closed cross-section structure of the energy absorbing pipe member  1  starts to be deformed by buckling, and then, as shown in  FIG. 6 , right and left flat plate portions of the closed cross-section structure starts to be deformed by buckling. In this case, a force peak point P 1  corresponding to  FIG. 4  at which the deformation starting portion S 1  starts bellows-like deformation is substantially equal to a force peak point P 2  corresponding to  FIG. 5  at which the general portion S 2  starts bellows-like deformation, although the force peak point P 2  is slightly greater than the force peak point P 1 , thus keeping a constant reaction force. 
   Once the bellows-like deformation starts, the buckling deformation of the upper and lower flat plate portions (see  FIGS. 7 ,  9 , and  11 ) and the buckling deformation of the right and left flat plate portions (see  FIGS. 8 ,  10 ) are alternately repeated. Also, in these cases, the constant reaction force can be maintained without significant force fluctuation. 
   The reason why the reaction force in the initial stage of the collision decreases as shown in  FIG. 2 , is that there is a difference between the time when the buckling deformation of the upper flat plate portion starts and the time when the buckling deformation of the lower flat plate portion starts in the states of  FIGS. 4 ,  5 , and in the state of FIG.  6  and thereafter, the deformation in its previous stage facilitates the buckling deformation. 
   Also, the deformation in the initial stage is asymmetric (see  FIGS. 4 through 6 ) and then becomes symmetric. This is because the buckling deformation of the right and left flat plate portions starts from deformation oblique with respect to the axial direction in the state of  FIG. 7 , and with a progress, this deformation gradually changes into deformation in the direction orthogonal to the axial direction. 
   Subsequently, simulation analysis results of how the size of the cutout portion  1   a  affects the initial force will be explained with reference to FIGS.  12 (A), (B), (C). In FIGS.  12 (A),  12 (B),  12 (C), B denotes a width of the cutout portion  1   a , L denotes an axial length of the cutout portion  1   a , and Ac, As respectively denote the cross-sectional area of the deformation starting portion S 1  and the cross-sectional area of the general portion S 2 . 
   As can be seen from FIG.  12 (A), the first peak force generated just after the collision tends to decrease with an increase in the size of the cutout portion  1   a  i.e., with an increase in Ac/As, whereas, as can be seen from FIG.  12 (B), the following second peak force tends to increase with the increase in the cutout portion  1   a.    
   Since it is desirable that there is no great difference between the first and second peak forces and the force fluctuates evenly, judging from FIG.  12 (C), the ratio Ac/As between the cross-sectional area of the deformation starting portion S 1  and the cross-sectional area of the general portion S 2  is preferably approximately 0.5. It is confirmed that the similar tendency and results are obtained in the tubular member with square cross section and the tubular member with rectangular cross section. 
   EXAMPLE 1 
   In this example, the energy absorbing member is applied to a coupler of a railroad vehicle. 
   Referring to  FIGS. 13 ,  14 , a rubber damper  11  comprises a draft stop  12  having a front support portion  12   a  and a rear support portion  12   b , front and rear impact absorbing rubbers  13   a ,  13   b  respectively provided in the front support portion  12   a  and the rear support portion  12   b  of the draft stop  12 , a pair of connecting rod members  14 R,  14 L for respectively connecting and fixing the impact absorbing rubbers  13   a ,  13   b  (rubber plates) to the draft stop  12 , and flange members  15   a ,  15   b  respectively mounted to a front portion of the connecting rod member  14 R and a rear portion of the connecting rod member  14 L and interposing the impact absorbing rubbers  13   a ,  13   b  in the draft stop  12 . The front end portions of the connecting rod members  14 L,  14 R are connected to a front support frame  16 F, which is connected to a rear end portion of a coupler  18  with an intermediate member  17  interposed therebetween. 
   Front end portions of a pair of energy absorbing pipe members  19 L,  19 R are connected to the rear flange member  15   b  and rear end portions of the energy absorbing pipe members  19 L,  19 R are connected to a rear support frame  21  supported by a vehicle body frame  20 . The energy absorbing pipe members  19 L,  19 R are laterally symmetric such that cutout portions  19   a ,  19   b  are inwardly opposed for enabling the well-balanced reception of impact force. In other words, the energy absorbing pipe members  19 L,  19 R are placed to allow the deformation staring portions  19   c ,  19   d  respectively provided at front ends of the energy absorbing pipe members  19 L,  19 R to be located outerly. 
   With this constitution, by supporting the rubber damper  11  by means of the energy absorbing pipe members  19 L,  19 R (energy absorbing members), the collision energy remaining partially unabsorbed as the result of deformation by the rubber damper  11  is absorbed by the bellows-like deformation (plastic deformation) of the energy absorbing pipe members  19 L,  19 R. In a case where a railroad vehicle comprised of a plurality of vehicles collides with another vehicle, the energy absorbing ability of the energy absorbing pipe members  19 L,  19 R complements the energy absorbing ability of the rubber damper  11  when insufficient, and the event that the vehicle is severely damaged or significant impact acts on passengers can be avoided. 
   EXAMPLE 2 
   In this example, the energy absorbing member is applied to a rail guard of a front vehicle of a railroad vehicle. 
   Referring to  FIGS. 15 ,  16 , a rail guard board  31  for eliminating obstacles is bent like horseshoe and mounted and fixed to a vehicle body frame  32 . Two energy absorbing pipe members  33  are placed behind the rail guard board  31  so as to be spaced apart therefrom. These energy absorbing pipe members  33  are coupled by means of a coupling member  33   b  and supported by a support device  34 . More specifically, the flat-plate shaped coupling member  33   b  is connected to tip ends of the respective energy absorbing pipe members  33  and rear ends of the members  33  are fixed to the support device  34 . An upper end portion of the support device  34  is fixed to the vehicle body frame  32 . In this case, the cutout portions  33   a  of the respective energy absorbing pipe members  33  are opened outwardly (or inwardly) and laterally symmetric as shown in FIG.  16 . In other words, the energy absorbing pipe members  33  are laterally symmetric to allow deformation staring portions  33   c  provided at front ends of the energy absorbing pipe members  33  to be inwardly located. Reference numeral  50  denotes a rail. 
   With this constitution, the energy, which remains partially unabsorbed as the result of the deformation of the rail guard board  31 , is absorbed by the energy absorbing pipe members  33 , thereby relieving the impact on the vehicle body frame  32 . 
   In addition, lightweight is achieved. Specifically, although the energy remaining partially unabsorbed as the result of the deformation of the rail guard board has been conventionally absorbed by the energy absorbing plate composed of flat springs and provided behind the front side of the rail guard board, and the weight is correspondingly increased, the use of the energy absorbing pipe members  33  provides significant lightweight. 
   EXAMPLE 3 
   In this example, the impact absorbing member is mounted to the front portion of the front vehicle of the railroad vehicle to absorb the collision energy when front vehicles head-on collide. 
   Referring to  FIGS. 17 ,  18 , an energy absorbing pipe member  43  is provided between a coupler  41  located on an upper side and a rail guard plate  42  located on a lower side in the vertical direction. A support pipe member  45  is provided so as to extend in the longitudinal direction of the vehicle from a support device  44  and a rear end portion of the energy absorbing pipe member  43  provided with a tip member  46  is connected to a tip end portion of the support pipe member  45 . 
   The support pipe member  45  extends forwardly of the rail guard board  42  and has a length so as to be located behind the coupler  41 . When the vehicle is not used as the front vehicle, the energy absorbing pipe member  43  is removed from the vehicle to allow vehicles to be interconnected by means of the coupler  41 . Reference numeral  48  denotes a vehicle body frame. At a portion where the energy absorbing pipe member  43  is connected to the tip member  46 , the cutout portion  43   a  is provided at a lower portion thereof and laterally symmetric. In other words, the energy absorbing pipe member  43  is placed so that a deformation starting portion  43   b  extended from the tip end of the energy absorbing pipe member  43  is located on the upper side. The tip member  46  is located in a cover  47  on the tip side. Similarly to the examples, 1, 2, it is needless to say that two energy absorbing pipe members symmetrically placed may support a collision member. 
   With this constitution, when the front vehicles collide with each other, the tip member  46  collides with the tip member  46  of the opposed vehicle, thereby causing the energy absorbing pipe member  43  to be deformed by buckling to absorb the collision energy. Consequently, damage to the other parts can be avoided. Similarly, the opposed vehicle is provided with the energy absorbing pipe member and the tip member. 
   The present invention is carried out as described above and has the following advantages. 
   In the collision energy absorbing structure according to the present invention, to deal with the collision in which the force in the longitudinal direction of the vehicle is applied, the cutout portion with the open cross section is formed at the front end portion of the energy absorbing member, and from the front end portion, the deformation starts. In other words, the substantially channel-shaped deformation starting portion is extended from part of the front end of the energy absorbing member. This constitution facilitates the deformation of the front end portion and reduces the initial force peak for generating the bellows-like deformation, and also makes the deformation of the front end portion trigger the following bellows-like deformation and reduces the corresponding force peak. Thereby, the bellows-like deformation occurs naturally and the collision energy can be efficiently absorbed. In other words, since the force peak in the initial stage of collision and the following force peak can be made small and substantially equal and the constant reaction force can be maintained, the impact acting on the passengers can be relieved without a rapid rise in the impact force. In particular, since the cutout portion is provided at the tubular energy absorbing pipe member with rectangular cross section as the energy absorbing member, having equal cross-section dimension and plate thickness and including no inside ribs, the member can be manufactured easily and at a low cost. 
   In addition, since the plurality of impact absorbing members are vertically or laterally symmetric, the impact force in the traveling direction can be evenly applied to the front end portion of the energy absorbing member so as to cause the bellows-like deformation without falling the energy absorbing member. 
   Further, since the rubber damper is connected to the vehicle coupler, for relieving the impact generated between the vehicles, the front end portion of the energy absorbing member is connected to the rear end portion of the rubber damper, and the rear end portion of the energy absorbing member is connected to the draft stop mounted to the vehicle body frame, the small collision energy can be absorbed by the rubber damper and the great collision energy can be absorbed by bellows-like deformation of the energy absorbing member. 
   Still further, by providing the energy absorbing member behind the rail guard board for eliminating obstacles on the rail during traveling and connecting the rear end portion of the energy absorbing member to the vehicle body frame by means of the support device, the excessive collision energy applied to the rail guard board can be absorbed by the bellows-like deformation of the energy absorbing member. 
   Moreover, by connecting the rear end portion of the energy absorbing member extending forwardly of the coupler and provided with the collision member at the front end to the front end portion of the support device (support pipe member) mounted to the vehicle body frame, provided behind the coupler, and extending forwardly of the rail guard board, the collision energy can be absorbed by the bellows-like deformation of the energy absorbing member and the impact acting on the passengers can be relieved. 
   As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within meters and bounds of the claims, or equivalence of such meters and bounds thereof are therefore intended to be embodied by the claims.