Patent Publication Number: US-2023137698-A1

Title: Power transmission device for helicopter

Description:
CROSS REFERENCE TO THE RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 16/722,354, filed Dec. 20, 2019, which is a continuation application, under 35 U.S.C. § 111(a) of international patent application No. PCT/JP2018/024132, filed Jun. 26, 2018, which claims priority to Japanese patent application No. 2017-124892, filed Jun. 27, 2017, the entire disclosures of all of which are herein incorporated by reference as a part of this application. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a transmission device (transmission) for a helicopter. 
     Description of Related Art 
     Transmission devices for helicopters include a casing for accommodating a rotating member, such as a transmission gear, the casing being provided with an oil sump for retaining oil. The oil in the oil sump is injected to the rotating member through a lubrication passage. A part of the injected oil remains as oil mist in an inner space of the casing. The rest of the oil is collected in the oil sump. For the reasons of, e.g., necessity of cooling the oil by heat radiation and matters in installation space within the casing, a part of the lubrication passage is disposed outside the casing. 
     In such a transmission device for a helicopter, there is a demand for a dry-run capability that allows the helicopter to operate even in a state where oil supply is interrupted. Although current technology ensures a necessary dry-run capability, further enhancement in the dry-run capability is desired because of recent trends, such as increasing occasions of over water flights. As current measure against dry running, reserving emergency oil for continuing the supply in case of emergency has been known (for example, Patent Document 1). 
     RELATED DOCUMENT 
     Patent Document 
     
         
         [Patent Document 1] JP Laid-open Patent Publication No. 2007-008461 
       
    
     Although there are various causes of dry running (oil interruption), it is difficult to take measures against, among others, a situation where an oil leak out of a casing occurs from a conduit because of e.g. a failure or a fall of a component of a lubrication passage and the oil is discharged out of the casing due to discharge pressure of a lubrication pump. If this situation continues, even the oil mist inside the casing may possibly be discharged outside the casing. In Patent Document 1 listed below, it is possible to secure emergency oil, but not to prevent oil from flowing out of a casing. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a transmission device capable of preventing oil from flowing out of a casing during dry-run time. 
     In order to achieve the above object, a transmission device for a helicopter according to a first aspect of the present invention includes: a casing accommodating a rotating member and having an oil sump configured to retain oil in a liquid form; a lubrication pump configured to suck and discharge the oil from the oil sump; a supply port configured to inject the oil from the lubrication pump to the rotating member; a lubrication passage connecting the lubrication pump and the supply port; a connection portion provided in a part of the lubrication passage, which part is disposed outside the casing; and a direction control valve provided downstream of the lubrication pump and upstream of the connection portion in the lubrication passage with respect to a flow direction of the oil. An inner space of the casing contains oil in a mist form. The lubrication pump, the supply port and the direction control valve are provided in the inner space of the casing. The direction control valve is configured to open the lubrication passage when a hydraulic pressure in the lubrication passage exceeds a predetermined value and to close the lubrication passage when the hydraulic pressure is equal to or lower than the predetermined value. 
     The expression “part of the lubrication passage, which part is disposed outside the casing” used herein means a part where the oil leaks out of the casing when a failure occurs. That is, in the rest part of the lubrication passage excluding the “part which is disposed outside the casing,” the oil leaks within the casing when a failure, such as a fall of a component, occurs. The hydraulic pressure becomes the predetermined value or lower, for example, when the helicopter comes into a dry-run state. The direction control valve is, for example, a check valve configured to open the lubrication passage when a pressure upstream of the check valve exceeds the predetermined value. 
     When the oil flows out of the casing because a failure occurs in the connection portion disposed outside the casing or because the connection portion falls off, the pressure within the lubrication passage decreases. According to this configuration, when the hydraulic pressure in the lubrication passage becomes a predetermined value or lower, the direction control valve closes the lubrication passage. This makes it possible to prevent the discharge pressure of the lubrication pump from being applied to the lubrication passage, thereby to prevent the oil from further flowing out of the casing. 
     Where the direction control valve is a check valve, the transmission device may further include a discharge passage that is branched at a location between the lubrication pump and the check valve in the lubrication passage and is configured to discharge the oil upstream of the check valve in the lubrication passage into the inner space of the casing. According to this configuration, since the pressure upstream of the check valve is lowered due to the discharge passage, it is possible to make the check valve smaller because a force for preventing backflow is reduced, and also, to suppress pressure loss during normal operation because the pressure at which the check valve operates to open can be lowered. 
     Where the discharge passage is provided, the discharge passage may have a restriction part. According to this configuration, the restriction part makes it possible to adjust the pressure upstream of the check valve. In such a case, the restriction part may generate a predetermined set pressure within the discharge passage, and the predetermined set pressure may be lower than the predetermined value at which the direction control valve closes. According to this configuration, the restriction part suppresses a pressure decrease in the lubrication passage during normal operation. 
     In the first aspect of the present invention, the connection portion may be, for example, an oil cooler configured to cool the oil in the lubrication passage. The oil cooler has better heat exchanging efficiency when provided outside the casing. Thus, even where a part of the lubrication passage is disposed outside the casing, the oil does not flow out of the casing from the oil cooler because, according to the above aspect, the oil is not supplied to the oil cooler during dry-run time, thanks to the direction control valve. 
     In the first aspect of the present invention, the lubrication passage may include: an oil reservoir provided upstream of the supply port; and an opening provided upstream of an outlet of the oil reservoir and above the outlet of the oil reservoir. According to this configuration, when the hydraulic pressure in the lubrication passage is decreased because of a failure in the lubrication passage, air is taken into the lubrication passage through the opening. Thus, the oil in the oil reservoir is dripped to a lubrication target located downstream of the oil reservoir. This configuration makes it possible to perform both of oil lubrication during normal time and dripping lubrication during dry-run time, without providing a dedicated tank for dry-run time. Thus, it is possible to suppress a decrease in the oil mist in the inner space of the casing while continuing the oil supply by dripping lubrication during dry-run time. 
     A transmission device for a helicopter according to a second aspect of the present invention includes: a casing accommodating a rotating member and having an oil sump configured to retain oil in a liquid form; a lubrication pump configured to suck and discharge the oil from the oil sump; a supply port configured to inject the oil from the lubrication pump to the rotating member; a lubrication passage connecting the lubrication pump and the supply port; and a direction control valve provided in the lubrication passage. An inner space of the casing contains oil in a mist form. The lubrication pump, the supply port and the direction control valve are provided in the inner space of the casing. The lubrication passage includes: an external passage part disposed outside the casing; a first internal passage part disposed inside the casing and located downstream of the lubrication pump and upstream of the external passage part with respect to a flow direction of the oil; and a second internal passage part disposed inside the casing and located downstream of the external passage part and upstream of the supply port. The direction control valve is provided in the first internal passage part and is configured to open the lubrication passage when a hydraulic pressure in the first internal passage part exceeds a predetermined value and to close the first internal passage part when the hydraulic pressure is equal to or lower than the predetermined value. 
     The second aspect makes it possible to prevent the oil from flowing out of the casing, as in the first aspect described above. 
     The present invention encompasses any combination of at least two features disclosed in the claims and/or the specification and/or the drawings. In particular, any combination of two or more of the appended claims should be equally construed as included within the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more clearly understood from the following description of preferred embodiments thereof, when taken in conjunction with the accompanying drawings. However, the embodiments and the drawings are given only for the purpose of illustration and explanation, and are not to be taken as limiting the scope of the present invention in any way whatsoever, which scope is to be determined by the appended claims. In the accompanying drawings, like reference numerals are used to denote like parts throughout the several views. 
         FIG.  1    is a system diagram of a lubrication system of a transmission device according to a first embodiment of the present invention; 
         FIG.  2    is a simplified system diagram of the lubrication system of the transmission device; 
         FIG.  3    is a system diagram of a lubrication system of a transmission device according to a second embodiment of the present invention; and 
         FIG.  4    is a simplified system diagram illustrating a state of the lubrication system during dry-run time. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be explained with reference to the drawings. In the following description, the term “normal time” refers to a period of time when a helicopter operates in a state where lubrication oil is normally supplied and circulated in a transmission device (transmission) of the helicopter. The term “dry-run time” refers to a period of time when a helicopter operates in a state where lubrication oil contained in a transmission device of the helicopter is leaking. 
       FIG.  1    shows a lubrication system diagram of a transmission device  1  for a helicopter according to a first embodiment of the present invention. The transmission  1  includes a casing  2  and a transmission gear  4 . The casing  2  forms an outer structure or outer shell of the transmission device  1 . The casing  2  is formed with an oil sump  6 . The oil sump  6  retains liquid oil OL for lubrication. In this embodiment, the oil sump  6  is formed by a part (central part) of a bottom wall of the casing  2 , which part is recessed downward. In this embodiment, the oil sump  6  is integrally formed with the casing  2 . The oil sump  6 , however, is not limited to this configuration. For example, the oil sump  6  may be formed as a recess provided in a part of a side wall of the casing  2 . 
     The transmission gear  4  is accommodated in the casing  2 . The transmission gear  4  constitutes a rotating member of the transmission device  1 . The transmission gear  4  is configured to change a speed of rotation of an engine (not illustrated) to transmit the rotation to a main rotor (not illustrated) and a tail rotor (not illustrated). 
     A lubrication target T of this embodiment is a rotating member of the transmission  1  of the helicopter. Specifically, the lubrication target T is the transmission gear  4  or a bearing part of a rotation shaft to which a gear is provided. In particular, where the lubrication target T is the transmission gear  4 , the oil OL is preferably supplied to an engagement part of the gear. 
     The transmission device  1  further includes a lubrication pump  8 , a lubrication passage  10 , and a supply port  12 . The lubrication pump  8  sucks and discharges the oil OL from the oil sump  6 . The lubrication pump  8  is disposed within the oil sump  6 . The lubrication pump  8  as a whole, however, is not necessarily provided within the oil sump  6 , as long as a suction port of the pump or a conduit connected to the suction port is disposed within the oil sump  6 . The lubrication pump  8  is not particularly limited and may be, for example, a gear pump. The oil OL discharged from the lubrication pump  8  passes through the lubrication passage  10  and is supplied to the lubrication target T. 
     The oil OL having passed the lubrication passage  10  is supplied to the lubrication target T through the supply port  12 . The supply port  12  is formed in an inner space SP of the casing  2 . The supply port  12  may be, for example, a jet nozzle. The supply port  12 , however, is not limited to this configuration. For example, the supply port  12  may be a through-hole defined in a conduit constituting the lubrication passage  10 . A part of the oil OL injected from the supply port  12  remains as oil mist M in a mist form in the inner space SP of the casing  2 . That is, the inner space SP of the casing  2  contains the oil mist M. The rest of the oil OL is collected in the oil sump  6 . 
     The lubrication passage  10  is a passage for supplying the oil OL which extends from the lubrication pump  8  to the supply port  12  for the lubrication target T. The lubrication passage  10  is provided with various devices therein and is mainly constituted of conduits. The lubrication passage  10  may include an internal passage that is integrally formed with a wall of the casing  2 . 
     The lubrication passage  10  includes an external passage part  22 , a first internal passage part  24 , and a second internal passage part  26 . The external passage part  22  is disposed outside the casing  2 . The first internal passage part  24  is disposed inside the casing  2 . Specifically, the first internal passage part  24  is located downstream of the lubrication pump  8  and upstream of the external passage part  22 , with respect to a flow direction of the oil. The second internal passage part  26  is also disposed inside the casing  2 . Specifically, the second internal passage part  26  is located downstream of the external passage part  22  and upstream of the supply port  12 . 
     In this embodiment, the external passage part  22  and the first internal passage part  24  are communicated with each other via a first through part  28 . The external passage part  22  and the second internal passage part  26  are also communicated with each other via a second through part  30 . The first and second through parts  28 ,  30  are portions that pass through the walls of the casing  2 . That is, in this embodiment, the part of the lubrication passage  10 , which part is between the lubrication pump  8  and the first through part  28 , forms the first internal passage part  24 . The part between the first through part  28  and the second through part  30  forms the external passage part  22 . Further, the part downstream of the second through part  30  forms the second internal passage part  26 . It should be noted that as described later, the through parts  28 ,  30  are not necessarily provided between the external passage part  22  and the internal passage parts  24 ,  26 . 
     The transmission device  1  further includes a direction control valve  14 . The direction control valve  14  controls a flow direction of a fluid within a passage. The direction control valve  14  will be described later in detail. The transmission device  1  also includes an oil filter  16  and an oil cooler  18 . The direction control valve  14  is provided downstream of the lubrication pump  8 , with respect to the flow direction of the oil. The oil filter  16  filters the oil OL. The oil filter  16  is provided downstream of the direction control valve  14 . The oil cooler  18  cools the oil OL. The oil cooler  18  is provided downstream of the oil filter  16 . The oil filter  16  and/or the oil cooler  18  may be omitted in accordance with use condition. 
     In this embodiment, the oil filter  16  and the oil cooler  18  are provided in a part of the lubrication passage  10 , which part is disposed outside the casing  2 . On the other hand, the lubrication pump  8 , the direction control valve  14  and the supply port  12  are disposed inside the casing  2 . That is, the passage part between the lubrication pump  8  and the direction control valve  14  is also disposed inside the casing  2 . 
     The expression “part of the lubrication passage  10 , which part is disposed outside the casing  2 ” used herein means a part where the oil OL leaks out of the casing  2  when a failure occurs. That is, in the rest part of the lubrication passage excluding the “part which is disposed outside the casing  2 ,” the oil leaks within the casing  2  when a failure, such as a fall of a component, occurs. The external passage part  22  includes the “part of the lubrication passage  10 , which part is disposed outside the casing  2 .” For example, where the lubrication passage  10  is integrally formed with a side wall of the casing  2 , if a component, such as a sensor or a gauge, is attached to the lubrication passage  10  from the outside of the casing  2 , this passage part corresponds to a “part disposed outside the casing  2 ,” i.e., to the external passage part  22 . In such a case, there may be no through part between the external passage part  22  and the internal passage parts  24 ,  26 . 
     In this embodiment, a connection portion  32  is disposed outside the casing  2 . Specifically, the connection portion  32  is provided in the part of the lubrication passage  10 , which part is disposed outside the casing  2 , i.e., the external passage part  22 . In this embodiment, each of the oil filter  16  and the oil cooler  18  constitutes the connection portion  32 . The connection portion  32 , for example, may include a device interposed in the passage, or an instrument attached through an opened part of the passage, or a part that connects conduits constituting the passage. The device interposed in the passage may include, for example, the oil filter  16  and the oil cooler  18  of this embodiment. The instrument attached through an opened part of the passage may include, for example, an oil jet (nozzle), a pressure sensor, a temperature sensor, and a conduit window for viewing flow of the oil, all of which are provided in the external passage part  22 . The part that connects conduits may include, for example, a flange for connecting conduits and a coupling (joint). It should be noted that these are mere examples, and that the connection portion  32  is not limited to these components. 
     The direction control valve  14  is provided upstream of the connection portion  32 , with respect to the flow direction of the oil. Specifically, the direction control valve  14  is provided in the first internal passage part  24  within the casing  2 . In operation of the helicopter, the direction control valve  14  opens the lubrication passage  10  when a hydraulic pressure P 1  in the lubrication passage  10  (first internal passage part  24 ) exceeds a predetermined value V 1 . In operation of the helicopter, the direction control valve  14  closes the lubrication passage  10  (first internal passage part  24 ) when the hydraulic pressure P 1  in the lubrication passage  10  is equal to or lower than the predetermined value V 1 . The hydraulic pressure P 1  becomes the predetermined value V 1  or lower, for example, when the helicopter shifts from normal time to dry-run time. An example of dry running may include a situation where the oil discharged from the lubrication pump  8  leaks out to cause the oil surface in the oil sump  6  to be lowered, resulting in a decrease in the discharge pressure of the lubrication pump  8 . 
     In this embodiment, the direction control valve  14  is a check valve. That is, the direction control valve (check valve)  14  opens the lubrication passage  10  when the pressure upstream the valve exceeds the predetermined value V 1 . The check valve  14  includes a valve body  14   a  and a closing-force application member  14   b  as shown in  FIG.  2   . The closing-force application member  14   b  presses the valve body  14   a  in the valve closing direction. The closing-force application member  14   b  is, for example, a spring. The direction control valve  14 , however, is not limited to a check valve. As long as the direction control valve  14  is operable to control a flow direction of the oil OL, it may be, for example, an electromagnetic switching valve. 
       FIG.  2    shows the lubrication system of the lubrication passage  10  in a simplified manner. In this embodiment, the transmission device  1  further includes a discharge passage  34 . The discharge passage  34  is branched at a location between the lubrication pump  8  and the direction control valve  14  in the lubrication passage  10 . The discharge passage  34  discharges the oil OL upstream of the direction control valve  14  in the lubrication passage  10  into the inside of the casing  2 . The discharge passage  34 , however, may be omitted. 
     As shown by a double dotted line in  FIG.  2   , a restriction part or choke part  36  may be provided in the discharge passage  34 . The restriction part  36  generates a predetermined set pressure V 2  within the discharge passage  34 . The restriction part  36  is, for example, an orifice. The set pressure V 2  of the restriction part  36  is set to be smaller than the predetermined value V 1  of the direction control valve  14 . Where the restriction part  36  is provided in the discharge passage  34 , the pressure upstream of the check valve (direction control valve)  14  can be adjusted to be higher than the predetermined value V 1 . 
     Moreover, the set pressure V 2  of the restriction part  36  is set to be smaller than the predetermined value V 1  of the direction control valve  14 , so as to suppress a pressure decrease during normal operation. The increased pressure of the oil OL by the lubrication pump  8  is quickly raised to the set pressure V 2 , without a pressure decrease. When the pressure of the oil OL exceeds the set pressure V 2 , a part of the oil OL passes through the restriction part  36  to be discharged into the casing  2  from the discharge passage  34 . When the pressure of the oil OL exceeds the predetermined value V 1 , the check valve  14  opens. The restriction part  36 , however, may be omitted. 
     The flow of the oil OL in the transmission device  1  of this embodiment will be described in detail. During normal time, the oil OL in the oil sump  6  is sucked and discharged by the lubrication pump  8 . At such a time, when the pressure of the oil OL reaches the set pressure V 2 , a part of the oil OL is discharged into the casing  2  from the discharge passage  34 . Thus, the pressure at the inlet of the check valve  14  is prevented from increasing excessively. The oil OL discharged from the discharge passage  34  is collected in the oil sump  6 . Until the pressure of the oil OL reaches the predetermined value V 1 , the oil OL is blocked by the direction control valve  14 . When the pressure of the oil OL exceeds the predetermined value V 1 , the oil OL passes through the direction control valve  14  and is, after having been filtered through the oil filter  16  outside the casing  2 , cooled by the oil cooler  18 . 
     The oil OL cooled by the oil cooler  18  then returns to the inside of the casing  2  and is supplied to the lubrication target T (transmission gear  4 ) through the supply port  12 . The oil OL supplied through the supply port  12  lubricates the lubrication target T and is then collected in the oil sump  6 . A part of the oil OL is injected through the supply port  12  into the inner space SP of the casing  2  and remains in the inner space SP as the oil mist M. 
     For example, as shown by a double dotted line in  FIG.  2   , where an oil leak occurs from the oil cooler  18  outside the casing  2 , the hydraulic pressure P 1  in the lubrication passage  10  decreases to bring the device to a dry-run state. When the hydraulic pressure P 1  in the lubrication passage  10  decreases to the predetermined value V 1  in this state, the direction control valve  14  closes. Thus, the oil supply from the lubrication pump  8  to the lubrication passage  10  is blocked by the direction control valve  14 , thereby making it possible to prevent the oil OL from flowing out of the casing  2 . Consequently, outflow of the oil OL in the oil sump  6  and the oil mist M in the inner space SP is suppressed. Therefore, the dry-run capability can be enhanced (i.e., duration of continuous flight can be increased). 
     In addition, the discharge passage  34  allows the pressure upstream of the check valve (direction control valve)  14  to be lowered. Thus, the check valve  14  can have a smaller closing-force application member  14   b , thereby making it possible to compactly configure the check valve  14  as a whole. Further, the pressure V 1  at which the check valve  14  operates can be lowered. Therefore, the pressure loss during normal operation can be suppressed. 
     The oil cooler  18  has difficulty in being disposed inside the casing  2  due to space constraints and has higher heat exchange efficiency when disposed outside the casing  2 . Thus, according to the above configuration, even when a part of the lubrication passage  10  is disposed outside the casing  2 , the direction control valve  14  is closed during dry-run time, and therefore, the oil OL is not supplied to the outside of the casing  2 . As a result, the oil OL does not flow out of the casing  2 . 
       FIG.  3    is a system diagram illustrating, in a simplified manner, a lubrication system of a transmission device  1 A according to a second embodiment of the present invention. The transmission device  1 A of the second embodiment differs from the transmission device  1  of the first embodiment in that the lubrication passage  10  is provided with an oil reservoir  38  and an opening  40  as described later. Hereinafter, description of these elements will be made in detail. Features corresponding to those of the first embodiment are denoted with like reference numerals, and description thereof is omitted. 
     The lubrication target T of the second embodiment is illustrated in a divided manner as a first lubrication target  42  and a second lubrication target  44 . It should be noted the number of the lubrication target T is not limited to this. For example, the second lubrication target  44  may be omitted. Alternatively, the number of the lubrication target T may be 3 or more. In this embodiment, the first lubrication target  42  rotates at a higher speed than that of the second lubrication target  44 . In particular, the first lubrication target  42  is preferably a part of the transmission gear  4  which rotates at highest speed. For example, the first lubrication target  42  preferably includes a gear to which rotation of an engine (not illustrated) is inputted and a bearing for the gear. 
     The supply ports  12  of the second embodiment include a first supply port  46  for supplying the oil OL to the first lubrication target  42  and a second supply port  48  for supplying the oil OL to the second lubrication target  44 . It should be noted that the number of the supply ports  12  is not limited to this. For example, where the second lubrication target  44  is omitted, the second supply port  48  may also be omitted. Alternatively, where the number of the lubrication target T is 3 or more, there may be 3 or more supply ports  12 . The first supply port  46  is provided right above the first lubrication target  42 . The expression “provided right above” used herein mean that the first supply port  46  is provided above the first lubrication target  42  and within a range where the oil OL dripped from the first supply port  46  under the influence of gravity during dry-run time reaches the first lubrication target  42 . That is, the expression “right above” includes horizontal deviation in the range where the oil OL dripped by gravity reaches the first lubrication target  42 . In the second embodiment, the first supply port  46  is configured to drip the oil OL to the first lubrication target  42  during dry-run time. 
     The oil reservoir  38  is disposed upstream of the first supply port  46  in the lubrication passage  10 . Specifically, the oil reservoir  38  is disposed upstream of the first supply port  46  and downstream of the second supply port  48  in the lubrication passage  10 . The oil reservoir  38  is disposed inside the casing  2 . Specifically, the oil reservoir  38  is provided in the second internal passage part  26 . During normal time, the oil reservoir  38  retains the oil OL thereinside. During dry-run time, the oil OL retained in the oil reservoir  38  is dripped to the first lubrication target  42  through the first supply port  46 . The volume of the oil reservoir  38  may be suitably selected in accordance with a required dry-run capability. 
     In the second embodiment, the oil reservoir  38  is configured as a box-like tank. The oil reservoir  38 , however, is not limited to this configuration. For example, the oil reservoir  38  may be formed by increasing the diameter of the conduit(s) constituting the lubrication passage  10 . Thus, the oil reservoir  38  has a larger passage area (cross-sectional area) than those of the conduits located upstream and downstream of the oil reservoir  38 , and has a greater amount of the oil OL storage per a unit length (the same length) than those of the conduits located upstream and downstream of the oil reservoir. Alternatively, the oil reservoir  38  may be integrally provided with a side wall or an upper wall of the casing  2 . 
     In the second embodiment, the box-like oil reservoir  38  is formed with an inlet  37  in an upper wall  38   a  thereof and with an outlet  39  in a lower wall  38   b  thereof. That is, the lubrication passage  10  leading to the opening  40  is connected to the upper wall  38   a  of the oil reservoir  38 , and the lubrication passage  10  leading to the first supply port  46  is connected to the lower wall  38   b  of the oil reservoir  38 . The oil reservoir  38 , however, is not limited to this configuration. For example, the outlet  39  of the reservoir  38  may be provided in a lower portion of a side wall  38   c , instead of the lower wall  38   b.    
     The opening  40  is provided upstream of the outlet  39  of the oil reservoir  38  and above the outlet  39  of the oil reservoir  38  in the lubrication passage  10 . In the present embodiment, the opening  40  is provided upstream of the oil reservoir  38  and above the oil reservoir  38  in the lubrication passage  10 . The opening  40  is disposed inside the casing  2 . Specifically, the opening  40  is defined within the inner space SP. As long as the opening  40  is located above the outlet  39  of the oil reservoir  38 , the opening  40  may be provided in the oil reservoir  38  per se. Even where the opening  40  is provided upstream of the oil reservoir  38  in the lubrication passage  10 , as in this embodiment, the opening  40  is not necessarily located right above the oil reservoir  38 . That is, the expression “above” used herein means above (i.e. at a higher location) in the vertical direction, and the oil reservoir  38  and the opening  40  may be offset from each other in the horizontal direction. In the second embodiment, the opening  40  is provided downstream of the oil cooler  18  and between the second supply port  48  and the oil reservoir  38 . 
     The opening  40  is configured to inject the oil OL during normal time. Therefore, when the lubrication target T is disposed downstream of the opening  40 , the lubrication target T is lubricated during normal time. On the other hand, the opening  40  is configured such that, when the hydraulic pressure P 1  in the lubrication passage  10  decreases, specifically, when the hydraulic pressure P 1  in the lubrication passage  10  decreases to a pressure P 2  in the oil sump  6  (inner space SP), air is taken into the lubrication passage  10  through the opening  40 . In the second embodiment, the opening  40  is a through hole provided in a conduit constituting the lubrication passage  10 . The opening  40 , however, is not limited to this configuration and may be a projected nozzle hole provided in the conduit. Where the opening  40  is configured as a nozzle, a part of the oil can be precisely supplied to the lubrication target T from the opening  40  during normal time. 
     The oil reservoir  38  and the opening  40  are accommodated in the casing  2  of the transmission device  1 A. The opening  40  is provided at least above an underside (lower wall  38   b ) of the oil reservoir  38  and above the first supply port  46 . The opening  40  may preferably be provided above a topside (upper wall  38   a ) of the oil reservoir  38 . Thus, all the oil OL in the oil reservoir  38  can be supplied to the first lubrication target  42  during dry-run time. The lubrication passage  10  between the opening  40  and the oil reservoir  38  may be partially located above the opening  40 . In such a case, however, a part of the oil OL that is located above the opening  40  in the lubrication passage  10  moves reversely and flows out from the opening  40  during dry-run time. Therefore, the lubrication passage  10  between the opening  40  and the oil reservoir  38  is preferably provided below the opening  40 . 
     The first supply port  46  is provided at least below the topside (upper wall  38   a ) of the oil reservoir  38  and below the opening  40 . The term “below” used herein refers to a lower location in the vertical direction, regardless of horizontal locations. If, however, the first supply port  46  is provided above the underside (lower wall  38   b ) of the oil reservoir  38 , the oil OL that is retained below the first supply port  46  in the oil reservoir  38  is not supplied to the first lubrication target  42  during dry-run time. Therefore, the first supply port  46  is preferably provided below the underside (lower wall  38   b ) of the oil reservoir  38 . For the above reasons, the opening  40  is preferably provided above the topside of the oil reservoir  38 , and the first supply port  46  is preferably provided below the underside of the oil reservoir  38 . Thus, all the oil OL in the oil reservoir  38  can be supplied to the first lubrication target  42  during dry-run time. The discharge passage  34  of the second embodiment may be provided with a restriction part  36 , as in the first embodiment. 
     Referring to  FIG.  3    and  FIG.  4   , the operation of the transmission device  1 A in the second embodiment will be described.  FIG.  3    shows flow of the oil OL during normal time, and  FIG.  4    shows flow of the oil OL during dry-run time. During the normal time as shown in  FIG.  3   , the oil OL in the oil sump  6  is sucked and discharged by the lubrication pump  8 . The oil OL discharged by the lubrication pump  8  passes through the lubrication passage  10  to be supplied to the lubrication target T. 
     The flow of the oil OL during normal time in this embodiment will be described in detail. The oil OL discharged by lubrication pump  8  is filtered by the oil filter  16  outside the casing  2  and is then cooled by the oil cooler  18 . The oil OL cooled by the oil cooler  18  is returned into the casing  2 , and a part of the oil is supplied to the second lubrication target  44  from the second supply port  48 . During normal time, the oil OL is injected from the second supply port  48  under the hydraulic pressure in the lubrication passage  10 . 
     The oil OL further flows within the lubrication passage  10 , and a part of the oil OL is injected from the opening  40  into the inner space SP of the casing  2 . The rest of the oil OL further flows within the lubrication passage  10  to reach the oil reservoir  38 . A predetermined amount of the oil OL is retained in the oil reservoir  38 . The oil OL having passed the oil reservoir  38  is supplied to the first lubrication target  42  from the first supply port  46 . During normal time, the oil OL is injected from the first supply port  46  under the hydraulic pressure in the lubrication passage  10 . The oil OL supplied from the first and second supply ports  46 ,  48  lubricates the first lubrication target  42  and the second lubrication target  44 , and then, are collected in the oil sump  6 . A part of the oil OL is injected into the inner space SP from the supply ports  46 ,  48  and the opening  40 , and remains in the inner space SP as the oil mist M. 
     As shown in  FIG.  4   , when an oil leak occurs from the oil cooler  18  outside the casing  2 , the hydraulic pressure P 1  in the lubrication passage  10  decreases. When the hydraulic pressure P 1  in the lubrication passage  10  decreases to the predetermined value V 1 , the direction control valve  14  closes. Thus, the oil supply from the lubrication pump  8  is stopped or halted, thereby preventing the oil OL from further flowing out of the casing  2 . 
     Further, when the hydraulic pressure P 1  in the lubrication passage  10  decrease to the pressure P 2  in the oil sump  6  (inner space SP), air A is taken into the lubrication passage  10  through the opening  40 . Thus, the oil OL downstream of the opening  40  in the lubrication passage  10  flows into the oil reservoir  38  under the influence of gravity. The oil OL in the oil reservoir  38  is then dripped from the first supply port  46  to the first lubrication target  42  under the influence of gravity. Since a hydraulic pressure P 3  in the oil reservoir  38  is maintained at the same pressure as the pressure P 2  in the oil sump  6  (inner space SP) through the opening  40 , stable dripping lubrication is achieved. 
     The second embodiment provides the same advantage as that of the first embodiment described above. Furthermore, according to the second embodiment, during the normal time as in  FIG.  3   , the oil OL in the lubrication passage  10  is supplied to the first lubrication target  42  from the first supply port  46  through the oil reservoir  38 . During normal time, a predetermined amount of the oil OL is retained in the oil reservoir  38 . During the dry-run time as in  FIG.  4   , air A is taken into the lubrication passage  10  through the opening  40 . Then, the oil OL in the oil reservoir  38  as well as the oil OL located between the opening  40  and the oil reservoir  38  in the lubrication passage  10  are dripped to the first lubrication target  42  from the first supply port  46  under the influence of gravity. Thus, the common oil reservoir  38  can be used for the oil lubrication during normal time as well as dripping lubrication during dry-run time. Therefore, the dry-run capability can be enhanced with a simple configuration. 
     That is, the second embodiment makes it possible to suppress outflow of the oil OL in the oil sump  6  and the oil mist M in the inner space SP to the outside of the casing  2  by closing the direction control valve  14  during dry-run time as well as to perform dripping lubrication of the first lubrication target  42  with the oil OL in the oil reservoir  38 . Thus, the dry-run capability can be enhanced. It should be noted that the dripping lubrication by use of the oil reservoir  38  is performed in the same manner in the case of not only an oil leak occurring outside, but also an oil leak occurring inside the casing. 
     The oil sump  6 , the lubrication pump  8 , the lubrication target T and the oil reservoir  38  are accommodated in the casing  2 , and the opening  40  is provided inside the casing  2 . Thus, during the normal time as in  FIG.  3   , the oil OL injected from the opening  40  can be supplied to the lubrication target T disposed in the inner space SP of the casing  2 . 
     The opening  40  of the lubrication passage  10  is provided downstream of the oil cooler  18  disposed outside the casing  2 . This makes it possible to supply the oil OL, after cooling by oil cooler  18 , to the first lubrication target  42  and to supply the oil OL after cooling to the second lubrication target  44  from a location between the oil cooler  18  and the oil reservoir  38  in the lubrication passage  10 , during normal time. 
     The second supply port  48  for supplying the oil OL to the second lubrication target  44  is provided upstream of the oil reservoir  38  in the lubrication passage  10 , and the opening  40  is provided between the second supply port  48  and the oil reservoir  38 . This makes it possible to effectively lubricate the first lubrication target  42  of high lubrication priority, during dry-run time. 
     The first lubrication target  42  and the second lubrication target  44  are rotating members (transmission gear  4 ) of the transmission device  1 A, and a high-speed rotating member that rotates at a higher speed than that of the second lubrication target  44  is made the first lubrication target  42 . This makes it possible to concentratedly lubricate, in particular, the high-speed rotating member of high lubrication priority during dry-run time. 
     The lubrication pump  8  and the direction control valve  14  are provided between the oil sump  6  and the second supply port  48 , and the opening  40  is provided between the second supply port  48  and the oil reservoir  38 . Therefore, the second supply port  48  arranged below the opening  40  can lubricate the second lubrication target  44  with the returning oil OL during dry-run time. 
     Although in the second embodiment as shown in  FIG.  3    and  FIG.  4   , the opening  40  is provided upstream of the oil reservoir  38  in the lubrication passage  10 , the opening  40  may be defined in the topside (upper wall  38   a ) of the oil reservoir  38 . Further, the opening  40  may be defined in the topside of the side wall  38   c  of the oil reservoir  38 , preferably in above a position at ⅔ of the height of the oil reservoir  38 . 
     The present invention is not limited to the embodiments described above, and various additions, modifications, or deletions may be made without departing from the scope of the invention. Accordingly, such variants are included within the scope of the present invention. 
     REFERENCE NUMERALS 
     
         
         
           
               1 ,  1 A . . . Transmission device 
               2  . . . Casing 
               4  . . . Transmission gear (rotating member) 
               6  . . . Oil sump 
               8  . . . Lubrication pump 
               10  . . . Lubrication passage 
               12  . . . Supply port 
               14  . . . Direction control valve (check valve) 
               18  . . . Oil cooler 
               22  . . . External passage part 
               24  . . . First internal passage part 
               26  . . . Second internal passage part 
               32  . . . Connection portion 
               34  . . . Discharge passage 
               36  . . . Restriction part 
               38  . . . Oil reservoir 
               39  . . . Outlet of the oil reservoir 
               40  . . . Opening 
               42  . . . First lubrication target 
               44  . . . Second lubrication target 
               46  . . . First supply port 
               48  . . . Second supply port 
             M . . . Oil mist (mist-like oil) 
             OL . . . Liquid oil 
             P 1  . . . Hydraulic pressure in the lubrication passage 
             SP . . . Inner space 
             V 1  . . . Predetermined value