Abstract:
Disclosed is a vibration source attachment structure equipped with a vibration isolation device. In the vibration source attachment structure, the vibration source ( 41 ) of an engine, or the like, is attached via the vibration isolation device ( 50 ) to a subframe ( 30 ) that has been attached in a downward position with respect to a vehicle body frame ( 20 ). The vibration isolation device ( 50 ) is provided with a first attachment ( 51 ) that attaches to the vibration source ( 41 ), a second attachment ( 52 ) that attaches to the subframe ( 30 ), and an elastic body ( 53 ) that connects the first and second attachments ( 51, 52 ). The subframe ( 30 ) is provided with fitting holes ( 31 ) that are formed in the vertical direction of said subframe. The second attachment ( 52 ) is detachably attached to the fitting holes ( 31 ) by means of press fitting.

Description:
TECHNICAL FIELD 
     The present invention relates to a vibration source attachment structure for mounting a vibration source to a subframe of a vehicle. 
     BACKGROUND ART 
     Vibration isolation devices in vibration source attachment structures prevent vibrations produced by an engine or other vibration source from being transmitted to the subframe by absorbing these vibrations. Such vibration source attachment devices are known, as proposed, for example, in Patent Literature 1. 
     The vibration source attachment structure disclosed in Patent Document 1 has a vehicle body frame extending in a longitudinal or front-rear direction of the vehicle body, a subframe disposed below the vehicle body frame, and an engine attached to the subframe via a vibration isolation device. A flange (engine mount bracket) of the vibration isolation device is disposed on an attachment base provided on the subframe, and the vibration isolation device is attached to the subframe by bolting the flange to the attachment base. 
     Because of such a structure, more time is required to install and dismantle the subframe on the vehicle body frame as part of the maintenance operation involved in servicing, inspecting, and replacing the vibration isolation device, and improvements are therefore required in terms of the ease of maintenance. 
     In addition, due to the presence of the attachment base and the flange, the subframe and the vibration isolation device are therefore proportionally heavier, and result in a disadvantage in terms of minimizing the subframe resonance caused by the vibrations of the vibration source. The vibrations transmitted from the subframe to the vehicle body frame are transmitted to the inside of the vehicle passenger compartment. It is preferable that the vibrations and sound transmitted to the inside of the vehicle passenger compartment be minimized as much as possible in order to increase the riding enjoyment and comfort of the passenger. 
     PRIOR ART DOCUMENTS 
     Patent Literature 
     
         
         Patent Document 1; Japanese Patent Application Laid-Open Publication No. 2006-52740 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     An object of the present invention is to provide a technique capable of improving the efficiency in maintaining a vibration isolation device and suppressing the resonance and vibrational amplification of a subframe and its periphery. 
     Solution to Problem 
     According to one aspect of the present invention, there is provided a vibration source attachment structure comprising a vehicle body frame, a subframe disposed below the vehicle body frame and attached to the vehicle body frame, and an engine or other vibration source attached to the subframe via a vibration isolation device, characterized in that the vibration isolation device has a first attachment part attached to the vibration source, a second attachment part attached to the subframe, and an elastic body connecting the first attachment part and the second attachment part; the subframe has a fitting hole formed in a vertical direction of the subframe; and the second attachment part is attached to the fitting hole by detachable press-fitting. 
     The second attachment part preferably has a positioning stopper for positioning the press-fitting direction relative to the subframe during press-fitting into the fitting hole. 
     The subframe preferably has a detachable retaining stopper for preventing the second attachment part press-fitted into the fitting hole from falling off in a direction opposite to the press-fitting direction. 
     Advantageous Effects of Invention 
     In the vibration isolation device of the vibration source attachment structure according to the present invention, the second attachment part for attachment to the subframe is attached to the fitting hole, which is formed in a vertical direction of the subframe, by detachable press-fitting from above or below. In this way, the second attachment part is merely attached to the fitting hole of the subframe by direct press-fitting, and less time is therefore required to install and dismantle the subframe on the vehicle body frame as part of the maintenance operation involved in servicing, inspecting, and replacing the vibration isolation device. As a result, the vibration isolation device can be maintained in good condition with greater ease. 
     Moreover, an attachment base for attaching the vibration isolation device to the subframe is unnecessary because the second attachment part is merely attached to the fitting hole of the subframe by direct press-fitting. Nor is it necessary for the second attachment part to have a flange for attaching the device (bracket for mounting the vibration source) to the attachment base by bolting. The subframe and the vibration isolation device can be made proportionally more lightweight. 
     In addition, the attachment base and the flange are thus dispensed with, and hence these members cannot cause resonance or vibrational amplification. Accordingly, the resonance and vibrational amplification of the subframe and its periphery can be minimized for the vibrations generated by the vibration source. 
     The positioning stopper comes into contact with the subframe when the second attachment part is press-fitted into the fitting hole up to a preset constant position. As a result, the press-fitting direction of the second attachment part can be positioned relative to the subframe. The operator need not pay attention to the position of the press-fitting direction relative to the subframe when the second attachment part is press-fitted into the fitting hole. The vibration isolation device can therefore be maintained in good condition with greater ease. 
     The second attachment part is prevented from falling off in a direction opposite to the press-fitting direction relative to the fitting hole by the retaining stopper. The second attachment part is therefore prevented from being caused to fall off from the fitting hole by the vibrations generated by the vibration source and the vibrations generated during the running of the vehicle. The state of attachment of the vibration isolation device to the subframe can be maintained for a longer period of time. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of the front part of a vehicle having a vibration isolation device according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view of the vibration isolation device shown in  FIG. 1 ; 
         FIG. 3  is an enlarged cross-sectional view taken along line  3 - 3  of  FIG. 2 ; and 
         FIG. 4  is a cross-sectional view of the periphery of a vibration isolation device according to a second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Certain preferred embodiments of the present invention are described below with reference to the accompanying sheets of drawings. 
     First Embodiment 
     A front part of a vehicle body  11  in a vehicle  10  is formed from a vehicle body frame  20 , and a subframe  30  attached to a front part of the vehicle body frame  20 , as shown in  FIG. 1 . 
     The front part of the vehicle body frame  20  includes left and right front side frames  21 ,  21  extending in a longitudinal or front-rear direction of the vehicle body on both sides of the front part of the vehicle body, left and right upper frames  22 ,  22  extending to the front and back of the vehicle body above and to the outside, in the vehicle width direction, of the front side frames  21 ,  21 , left and right damper housings  23 ,  23  spanning between the front side frames  21 ,  21  and the upper frames  22 ,  22 , and a front bulkhead  24  joined to the front part of the left and right front side frames  21 ,  21  and the front part of the left and right upper frames  22 ,  22 . The front part of the vehicle body is a monocoque body. 
     Such a vehicle body frame  20  has a structure in which the subframe  30  is suspended via four front/back/left/right vibration isolation elastic bushings (not shown) from the front part of the left and right front side frames  21 ,  21 , and a front end part of left and right floor frames  25 ,  25  (shown only on the left side) extending rearward from the back end of the front side frames  21 ,  21 . Specifically, the subframe  30  is attached so as to be suspended from the vehicle body frame  20 . 
     The subframe  30  is formed from a frame having an approximately square shape in a plan view. A longitudinal mounted engine  41  (power source  41 ) is mounted on a front-half part of the subframe  30 , and a transmission  42  is mounted on a back-half part. The engine  41  and the transmission  42  are attached on the subframe  30  via a plurality of vibration isolation devices  50  (only one is shown). The engine  41  and the transmission  42  are one kind of vibration source. 
     A mount  30   a  to which the vibration isolation device  50  is attached is integrally formed with a side part of the subframe  30 , as shown in  FIG. 2 . The mount  30   a  is a part of the subframe  30 , and therefore the mount  30   a  is included when the “subframe  30 ” is referenced. The vibration isolation device  50  is attached to the mount  30   a . An engine bracket  41   a  of the engine  41  is attached to an upper end part of the vibration isolation device  50 . The engine bracket  41   a  is integrally formed on the engine  41 , or attached as a separate member. Hereinafter, the engine bracket  41   a  is included when the engine  41  is referenced. 
     The vibration isolation device  50  has a first attachment part  51  attached to the engine  41 , a second attachment part  52  attached to the subframe  30 , and an elastic body  53  connecting the first attachment part  51  and the second attachment part  52 , as shown in  FIG. 3 . The first and second attachment parts  51 ,  52  and the elastic body  53  are arranged on the vertical axis CL (center) in the vibration isolation device  50 . 
     The structure of the vibration isolation device  50  is described in detail below. 
     The first attachment part  51  is attached to the engine bracket  41   a  of the engine  41 . The second attachment part  52  is a cylindrical member to which the elastic body  53  is connected. The first and second attachment parts  51 ,  52  are formed from steel, aluminum alloy, or other metal material. The elastic body  53  is a rubber block, which is elastically deformable to absorb vibrations transmitted between the first attachment part  51  and the second attachment part  52 , and which is formed in a cup shape that is mostly open at the bottom. 
     A liquid seal structure  60 , for example, is provided in a space formed in a lower part of the vibration isolation device  50  by the second attachment part  52  and the elastic body  53 . The liquid seal structure  60  may be a well-known construction, and one example is given in the following. Specifically, the liquid seal structure  60  is formed from a diaphragm  61  for blocking the opening at the lower end of the second attachment part  52 , a liquid chamber  62  divided into compartments by the elastic body  53  and the diaphragm  61 , a dividing member  63  for dividing the liquid chamber  62  into two upper and lower chambers of a main liquid chamber  62   a  on the side near the elastic body  53  and an auxiliary liquid chamber  62   b  on the side near the diaphragm  61 , an orifice passage  64  provided in the dividing member  63  so that the auxiliary liquid chamber  62   b  is in communication with the main liquid chamber  62   a , and an elastic movable membrane  65  provided on the dividing member  63  and used for absorbing fluctuations in liquid pressure. An operating liquid Lq is sealed in the main liquid chamber  62   a  and the auxiliary liquid chamber  62   b.    
     The structure for attaching the engine  41  to the subframe  30  via the vibration isolation device  50  is described in detail below. 
     The subframe  30  has a fitting hole  31  at the position at which the vibration isolation device  50  is attached. The fitting hole  31  passes through the subframe  30  in the vertical direction. 
     The fitting hole  31  is constructed of a large-diameter hole  31   a  formed in the lower side of the subframe  30  and a small-diameter hole  31   b  formed in the upper side of the subframe  30 . The diameter of the large-diameter hole  31   a  is larger than the diameter of the small-diameter hole  31   b . A step  31   c  therefore exists at the border between the large-diameter hole  31   a  and the small-diameter hole  31   b . Hereinafter, the step  31   c  is referred to as the positioning step  31   c . The insertion depth of the second attachment part  52  is determined by the positioning step  31   c . The position (depth) of the positioning step  31   c  relative to a lower surface  32  of the subframe  30  is preset. 
     The second attachment part  52  is attached to the fitting hole  31  by detachable press-fitting. Specifically, the second attachment part  52  is press-fitted to the large-diameter hole  31   a  in the fitting hole  31  from below the subframe  30 . 
     Here, “attached by detachable press-fitting” refers to attaching and fitting the second attachment part  52  to the fitting hole  31  to a detachable extent using a tool. Specifically, this refers to fitting to an extent at which self-holding is possible without the second attachment part  52  dropping out from the fitting hole  31  at a vibration extent transmitted from the outer part to the subframe  30 . In this way, the load for attaching the second attachment part  52  to the fitting hole  31  by press-fitting is a load applied to the extent at which the second attachment part  52  can be detached from the fitting hole  31 . 
     The second attachment part  52  has a positioning stopper  52   a  on the upper end. The positioning stopper  52   a  is used to position the press-fitting direction (upward direction) relative to the subframe  30  when the second attachment part  52  is press-fitted into the fitting hole  31 , and is integrally formed, for example, on the upper edge of the second attachment part  52 . The attaching position of the second attachment part  52  relative to the subframe  30  is determined by the positioning stopper  52   a  coming into contact with the positioning step  31   c.    
     The subframe  30  has a cover  35  capable of blocking the lower opening of the fitting hole  31  and the entire lower end of the vibration isolation device  50 . The cover  35  is a substantially plate-shaped member detachably attached to the lower surface  32  of the subframe  30  by a plurality of bolts  36 . The inner surface of the cover  35  attached to the subframe  30  is adjacent to the lower end of the second attachment part  52 . Such a cover  35  is referred to as the “retaining stopper  35 ” below, where the second attachment part  52  press-fitted into the fitting hole  31  is retained in the direction (downward direction) opposite to the press-fitting direction by the cover  35 . 
     In this way, falling off of the second attachment part  52  in a direction opposite to the press-fitting direction relative to the fitting hole  31  is prevented by the retaining stopper  35 . The second attachment part  52  is therefore prevented from falling off from the fitting hole  31  by the vibrations generated by the engine  41  and the vibrations generated during the running of the vehicle  10 . Accordingly, the state of attachment of the vibration isolation device  50  to the subframe  30  can be maintained for a longer period of time. 
     The first attachment part  51  protrudes above the subframe  30 , and one end part of a stud bolt  54  is embedded in the upper end surface of the attachment part. The stud bolt  54  is positioned on the axis CL of the vibration isolation device  50 , and extends upward. The engine  41  (more specifically, the engine bracket  41   a ) stacked on the first attachment part  51  is detachably attached to the first attachment part  51  by the stud bolt  54  and a nut  55 . 
     In  FIG. 3 , the member  38  indicated by an imaginary line is a lateral-runout stopper for the first attachment part  51 . The lateral-runout stopper  38  is used to restrict the amount of displacement by which the first attachment part  51  is displaced in the horizontal direction when the vehicle  10  ( FIG. 1 ) quickly accelerates and decelerates, and is attached, for example, above the subframe  30 . 
     An example of a maintenance procedure for the vibration isolation device  50  is described below. 
     The subframe  30  is in a state in which the engine  41  is mounted via the vibration isolation device  50 , as shown in  FIG. 3 . To maintain the vibration isolation device  50  in this state in good condition, the nut  55  is first separated from the stud bolt  54 , and the lateral-runout stopper  38  is separated from the subframe  30 . The retaining stopper  35  is then separated from the subframe  30 , and the second attachment part  52  is extracted downward from the fitting hole  31 . As a result, the vibration isolation device  50  can be detached from the fitting hole  31 . 
     After the vibration isolation device  50  has been serviced and inspected, the device is again returned to the fitting hole  31  or replaced with a new vibration isolation device  50 . The specific procedure involves first inserting the vibration isolation device  50  into the fitting hole  31  from below the subframe  30 , and press-fitting the second attachment part  52  to the large-diameter hole  31   a . The positioning stopper  52   a  comes into close contact with the positioning step  31   c  of the subframe  30  when the second attachment part  52  is press-fitted to the fitting hole  31  up to a certain preset position. As a result, the press-fitting direction of the second attachment part  52  is positioned relative to the subframe  30 , as shown in  FIG. 3 . The operator need not pay attention to the position of the press-fitting direction relative to the subframe  30  when the second attachment part  52  is press-fitted into the fitting hole  31 . The vibration isolation device  50  can therefore be made easier to maintain in good condition. 
     The position of the engine  41  is not changed from the original position relative to the subframe  30 . The upper end part of the stud bolt  54  therefore fits in a bolt hole of the engine bracket  41   a  when the press-fitting direction of the second attachment part  52  is positioned relative to the subframe  30 . The lateral-runout stopper  38  is subsequently attached to the subframe  30 , and the engine bracket  41   a  is attached to the first attachment part  51  by screwing the nut  55  onto the stud bold  54 . The retaining stopper  35  is then attached to the subframe  30  to complete the series of maintenance operations. 
     The following is a summary of the above explanation. 
     The second attachment part  52 , which is used to attach the vibration isolation device  50  to the subframe  30 , is attached to the fitting hole  31 , which is formed in a vertical direction of the subframe  30 , by press-fitting with a detachable load from below. In this way, the second attachment part  52  is merely attached to the fitting hole  31  of the subframe  30  by direct press-fitting, and less time is therefore required to install and dismantle the subframe  30  on the vehicle body frame  20  as part of the maintenance operation involved in servicing, inspecting, and replacing the vibration isolation device  50 . As a result, the vibration isolation device  50  can be maintained in good condition with greater ease. 
     Moreover, an attachment base for attaching the vibration isolation device  50  to the subframe  30  is unnecessary because the second attachment part  52  is merely attached to the fitting hole  31  of the subframe  30  by direct press-fitting. Nor is it necessary for the second attachment part  52  to have a flange for attaching the device (bracket for mounting the vibration source) to the attachment base by bolting. The subframe  30  and the vibration isolation device  50  can be made proportionally more lightweight. In addition, the attachment base and the flange are thus dispensed with, and hence these members cannot cause resonance or vibrational amplification. Accordingly, the resonance and vibrational amplification of the subframe  30  and its periphery can be minimized for the vibrations generated by the engine  41  (vibration source). 
     The engine  41  can be greatly displaced in the vertical direction, that is, the direction along the axis CL of the vibration isolation device  50 , during quick acceleration or deceleration of the vehicle  10  ( FIG. 1 ). The lower surface of the engine bracket  41   a  can strike the upper surface of the vibration isolation device  50  when the amount of displacement is excessive. A downward load from the engine bracket  41   a  acts on the vibration isolation device  50  when the device is struck. This downward load is a force acting in a direction in which the vibration isolation device  50  is caused to fall downward off from the fitting hole  31  of the subframe  30 . 
     In response to this, a cushioning member  39  is preferably disposed with a constant gap δ between the upper surface of the lateral-runout stopper  38  and the lower surface of the engine bracket  41   a , as shown in  FIG. 3 . The cushioning member  39  is formed from a rubber attached to, for example, the upper surface of the lateral-runout stopper  38 . The cushioning member  39  may also be a structure disposed between the upper surface of the subframe  30  and the lower surface of the engine bracket  41   a.    
     The size of the gap δ and the thickness of the cushioning member  39  are set according to the downward load so that the downward load can be stopped by the cushioning member  39  without the lower surface of the engine bracket  41   a  striking the upper surface of the vibration isolation device  50 . The downward load is therefore mitigated by the cushioning member  39  and is stopped by the lateral-runout stopper  38  or the subframe  30 . Accordingly, in cases in which the engine  41  is greatly displaced toward the vibration isolation device  50 , the downward load is prevented from acting on the upper surface of the vibration isolation device  50  by the engine bracket  41   a  striking the upper surface of the cushioning member  39 . The vibration isolation device  50  is prevented from falling downward off from the fitting hole  31  of the subframe  30 . The state of attachment of the vibration isolation device  50  to the subframe  30  can be maintained over a longer period of time. 
     Second Embodiment 
     A second embodiment is described below with reference to  FIG. 4 . These parts that are the same as those in the first embodiment are marked with the same reference characters, and the descriptions thereof are omitted.  FIG. 4  shows an area surrounding a vibration isolation device (second embodiment) according to the present invention and provides a depiction that corresponds to the aforementioned  FIG. 3 . However, the lateral-runout stopper  38 , the engine bracket  41   a , and the nut  55  shown in  FIG. 3  are omitted. 
     The second embodiment is substantially the same structure as the first embodiment, but the following aspects are different. Specifically, the first embodiment shown in  FIG. 3  is a structure in which the second attachment part  52  is attached to the fitting hole  31  “from below.” In contrast, the second embodiment shown in  FIG. 4  is different in the aspect of having a structure in which a second attachment part  52 A is attached to a fitting hole  31 A by press-fitting a detachable load “from above.” The differences are described in detail below. 
     The fitting hole  31 A of the second embodiment shown in  FIG. 4  corresponds to the fitting hole  31  of the first embodiment shown in  FIG. 3 . The fitting hole  31  of the first embodiment is a stepwise hole formed from the large-diameter hole  31   a , the small-diameter hole  31   b , and the step  31   c . In contrast, the fitting hole  31 A of the second embodiment is a through-hole vertically passing through in a stepless straight shape. The diameter of the fitting hole  31 A is set to the same diameter as that of the large-diameter hole  31   a  of the first embodiment. 
     Moreover, the second attachment part  52 A of the second embodiment shown in  FIG. 4  corresponds to the second attachment part  52  of the first embodiment shown in  FIG. 3 . The outside diameter of the second attachment part  52 A is set to the same outside diameter as that of the second attachment part  52  of the first embodiment. 
     In the first embodiment, the positioning stopper  52   a  provided on the second attachment part  52  determines the attachment position of the second attachment part  52  relative to the subframe  30  by coming into contact with the positioning step  31   c  of the fitting hole  31 . The outside diameter of the positioning stopper  52   a  is slightly smaller than the diameter of the large-diameter hole  31   a.    
     In contrast, in the second embodiment, the positioning stopper  52   a  provided at an upper end of the second attachment part  52 A determines the attachment position of the second attachment part  52 A relative to the subframe  30  by coming into contact with the upper surface  33  of the subframe  30 . The outside diameter of the positioning stopper  52   a  of the second embodiment is set larger than the diameter of the fitting hole  31 A. 
     The positioning stopper  52   a  thus comes into contact with the upper surface  33  of the subframe  30  when the second attachment part  52 A is press-fitted into the fitting hole  31 A in the downward direction from above up to a preset constant position. As a result, the second attachment part  52 A can be positioned in the press-fitting direction (downward direction) relative to the subframe  30 , as shown in  FIG. 4 . The operator need not pay attention to the position of the press-fitting direction relative to the subframe  30  when the second attachment part  52 A is press-fitted into the fitting hole  31 A. The vibration isolation device  50  can therefore be maintained in good condition with greater ease. 
     The positioning stopper  52   a  of the second embodiment has the dual role as a retaining stopper for preventing the attachment part from dropping out of the subframe  30 . Because the positioning stopper  52   a  comes into contact with the upper surface  33  of the subframe  30 , the second attachment part  52 A can be restricted more securely in its tendency to drop down from the fitting hole  31 A. The retaining stopper  35  shown in  FIG. 3  can therefore be dispensed with. 
     As described above, in the vibration isolation device  50  of the second embodiment, the second attachment part  52 A for attaching the device to the subframe  30  is attached, by detachable press-fitting from above, to the fitting hole  31 A formed in a vertical direction of the subframe  30 . The second attachment part  52 A is thus merely attached to the fitting hole  31 A of the subframe  30  by direct press-fitting, and less time is therefore required to install and dismantle the subframe  30  on the vehicle body frame  20  as part of the maintenance operation involved in servicing, inspecting, and replacing the vibration isolation device  50 . As a result, the vibration isolation device  50  can be maintained in good condition with greater ease. 
     Moreover, an attachment base for attaching the vibration isolation device  50  to the subframe  30  is unnecessary because the second attachment part  52 A is merely attached to the fitting hole  31 A of the subframe  30  by direct press-fitting. Nor is it necessary for the second attachment part  52 A to have a flange for attaching the device (bracket for mounting the vibration source) to the attachment base by bolting. The subframe  30  and the vibration isolation device  50  can be made proportionally more lightweight. In addition, the attachment base and the flange are thus dispensed with, and hence these members cannot cause resonance or vibrational amplification. Accordingly, the resonance and vibrational amplification of the subframe  30  and its periphery can be minimized for the vibrations generated by the engine  41  (vibration source). 
     In the present invention, the vehicle body  11  may also be a structure in which the subframe  30  is attached to the back part of the vehicle body frame  20 . 
     The vibration source may be any source producing motive power for propulsion, and may also be, for example, an electric motor in addition to the engine  41  or the transmission  42 . 
     INDUSTRIAL APPLICABILITY 
     The vibration source attachment structure of the present invention can be used in an automobile in which an engine  41  or other vibration source is attached via a vibration isolation device  50  to a subframe  30  attached to a vehicle body frame  20  from below. 
     REFERENCE SIGNS LIST 
     
         
           10  Vehicle 
           20  Vehicle body frame 
           30  Subframe 
           31 ,  31 A Fitting hole 
           31   c  Positioning step 
           32  Lower surface 
           33  Upper surface 
           35  Retaining stopper 
           41  Vibration source (engine) 
           41   a  Engine bracket 
           50  Vibration isolation device 
           51  First attachment part 
           52 ,  52 A Second attachment part 
           52   a  Positioning stopper 
           53  Elastic body 
         Up, Dw Press-fitting direction