Abstract:
Provision of a new gear parking brake of a power transmission device that enables the simple achievement of in-gear parking.  
     A gear parking brake ( 31 ) of a power transmission device has a fluid coupling ( 4 ) positioned on the engine side and a friction clutch ( 5 ) positioned on the transmission ( 2 ) side, arranged in series. This gear parking brake ( 31 ) is provided with a brake mechanism on an input shaft ( 3 ) of the transmission ( 2 ), which activates at the time of parking. Even though the friction clutch ( 5 ) becomes disengaged, the rotation of the input shaft ( 3 ) of the transmission ( 2 ) is restricted, thereby enabling in-gear parking.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a power transmission device for transmitting power from the engine of heavy motor vehicles such as trucks and buses to the transmission, comprising a fluid coupling and a friction clutch, and more particularly to a gear parking brake enabling in-gear parking.  
           [0003]    2. Description of the Related Art  
           [0004]    Conventionally, a power transmission device that uses a fluid coupling in combination with a wet multiplate friction clutch has been proposed as a power transmission device for transmitting power from the engine of heavy motor vehicles such as trucks and buses to the transmission.  
           [0005]    As shown in FIG. 5, this power transmission device has a fluid coupling  4  and a wet multiplate friction clutch  5  joined between the engine&#39;s crankshaft  1  and input shaft  3  of the transmission  2 , so as to be able to connect and disconnect. This enables smooth gear change and reliable power transmission to be achieved without it being necessary for the driver to operate the clutch.  
           [0006]    The basic structure and application of a conventional power transmission device having this kind of structure will be described below.  
           [0007]    First, in the same way as a well-known conventional fluid coupling, the fluid coupling  4  mainly consists of a pump shell  7  fixed to the engine&#39;s crankshaft  1  through a casing  6 , a turbine shell  8  positioned opposite the pump shell  7 , and a stator  9  fixed therebetween. The torque of the crankshaft  1  is delivered from the pump shell  7  through the fluid filled therein to the turbine shell  8 , and the torque of the turbine shell  8  is transmitted to an output shaft  11  that is connected to the wet multiplate friction clutch  5 , through a hub  10 . Further, a lock-up mechanism  13  (to be described later) activated by a fluid-activated mechanism  12  is formed between the casing  6  and the turbine shell  8 , and when the engine speed reaches a prescribed speed, the crankshaft  1  and output shaft  11  are directly linked through the above mechanisms and efficient power transmission is achieved.  
           [0008]    Next, the wet multiplate friction clutch  5  comprises a clutch outer  14  spline fitted to the output shaft  11 , and a clutch center  15  mounted to the input shaft  3  of the transmission  2 . In the same way as in a conventional wet multiplate friction clutch, a plurality of friction plates  16  formed on the inside of the clutch outer  14  and a plurality of friction plates  17  formed on the outside of the clutch center  15  are made to come into contact with each other, thereby transmitting the power of the output shaft  11  to the input shaft  3  of the transmission  2 . Further, this wet multiplate friction clutch  5  contains a connection and disconnection mechanism  18  activated by a fluid-activated mechanism  12 , which will be described later, and when the engine is started or the gears are changed, the clutch outer  14  and the clutch center  15  disengage and the power between the output shaft  11  and the input shaft  3  is cut off.  
           [0009]    Further, the fluid-activated mechanism  12  that operates this lock-up mechanism  13  of the fluid coupling  4  and the connection and disconnection mechanism  18  of the wet multiplate friction clutch  5  mainly consists of a hydraulic pump  21  formed inside an intermediate wall  20  of a joint housing  19  that contains the above-mentioned fluid coupling  4  and wet multiplate friction clutch  5 ; a lock-up mechanism control valve  22  and a connection and disconnection mechanism control valve  23  activated by the operating oil discharged from the hydraulic pump  21  as shown in FIG. 6; and electromagnetic selector valves  24  and  25  to control the activation and shutoff of these control valves  22  and  23 . As shown in FIG. 5, this hydraulic pump  21  operates the whole time that the engine is running, accompanying the rotation of the pump shell  7  of the fluid coupling  4 , and it sucks in the operating oil that is pooled in the operating oil retention space  26  at the bottom of the joint housing  19  through a suction passage  27 . The operating oil is sent to the above-mentioned lock-up mechanism control valve  22  and the clutch connection and disconnection mechanism control valve  23  and either activates these valves or after passing through is returned back into the operating oil retention space  26  in a cycle. Further, the electromagnetic selector valves  24  and  25  that activate the lock-up mechanism valve  22  and the connection and disconnection mechanism control valve  23  are each controlled by control signals from a controller consisting for example of a micro-computer (not shown in the drawings).  
           [0010]    In a power transmission device having this kind of construction, first, when the engine starts up, the lock-up mechanism  13  of the fluid coupling  4  and the connection and disconnection mechanism  18  of the wet multiplate friction clutch  5  are both turned to a disconnected (OFF) state. Therefore, in the fluid coupling  4  a state of so-called creep occurs, the power from the engine&#39;s crankshaft  1  is cut off by the wet multiplate friction clutch  5 , and is not transmitted to the input shaft  3  of the transmission  2 . Next, from this state when the driver shifts the transmission  2  into gear to move the vehicle, the controller, which receives this signal, activates the electromagnetic selector valve  25  and the clutch connection and disconnection mechanism control valve  23 . Accordingly the connection and disconnection mechanism  18  is activated by the operating oil discharged from the hydraulic pump  21 , and by connecting the wet multiplate friction clutch  5 , the power from the output shaft  11  is transmitted to the transmission  2  through the input shaft  3  and the vehicle begins to move. In such a way, the engine&#39;s power is transmitted to the transmission  2  and the vehicle starts moving, and when a prescribed speed is reached, the driver then operates a shift lever  28  to shift the transmission  2  up to second gear, third gear and so on in order to further increase the speed of the vehicle. However, each time the driver shifts up to a higher gear, it is automatically controlled so that the instant that the driver operates the shift lever  28  this is detected by the controller and the wet multiplate friction clutch  5  is momentarily cut off. Then, after the shift to the next gear has been completed the wet multiplate friction clutch  5  is automatically reconnected, and thus smooth upshift is achieved. Further, at the same time, when the vehicle has reached a prescribed speed, the lock-up mechanism  13  of the fluid coupling  4  is activated by an electromagnetic control valve  24 , which is also activated by the controller. By directly connecting the crankshaft  1  and the output shaft  11 , power from the engine&#39;s crankshaft  1  is transmitted to the transmission  2  without loss.  
           [0011]    However, in a vehicle with a power transmission device having this kind of construction, so-called in-gear parking cannot be achieved. In other words, when the engine  1  is stopped in order to park, the hydraulic pump  21  for engaging the wet multiplate friction clutch  5  is inactivated and the wet multiplate friction clutch  5  is automatically disengaged. Therefore, whatever gear the transmission  2  is put into, the wet multiplate friction clutch  5  just runs idle and the engine brake does not work, meaning that the vehicle cannot be put into a definite stop.  
           [0012]    Further, the side brake that is ordinarily used when parking a motor vehicle is not always able to be used and is prone to certain inconveniences, for example the brake wire may freeze in cold temperatures and not be able to be unfrozen, or the wire that activates it may snap.  
           [0013]    For these reasons, methods such as forming a multiplate disc-type countershaft brake on the end of the countershaft  29  of the transmission  2 , and restricting the torque of the countershaft  29  so as to enable in-gear parking, have been considered. However, under this method a linking hole linking to the wet multiplate friction clutch  5  is opened to the casing  30  of the transmission  2  and it is necessary to extend the end of the countershaft  29  to the wet multiplate friction clutch  5 . Therefore, certain disadvantages arise, for example gear oil inside the transmission  2  may leak out from the linking hole, and it is also necessary to secure a space in which to form the multiplate disc-type countershaft brake on the wet multiplate friction clutch  5 . In addition, when a gear parking brake function is imposed on the countershaft brake, due to the relationship between the transmission&#39;s reduction gears it is necessary to ensure that the brake power is greater than the reduction gears (about 1.8 times), and this requires countershaft brakes to be larger and take up a greater space.  
         SUMMARY OF THE INVENTION  
         [0014]    Therefore, the present invention was designed to effectively resolve these sorts of problems. An object of the present invention is to provide a new gear parking brake of a power transmission device that enables in-gear parking to be easily achieved.  
           [0015]    In order to resolve the above-mentioned problems, as shown in claim 1, the present invention is a gear parking brake of a power transmission device having a fluid coupling positioned on the engine side and a friction clutch positioned on the transmission side, arranged in series, comprising a brake mechanism on an input shaft of the above-mentioned transmission, which activates at the time of parking. Accordingly, even though the friction clutch becomes disengaged when the engine is stopped, the torque of the transmission&#39;s input shaft at the time of parking can be restricted, thereby enabling so-called in-gear parking.  
           [0016]    More specifically, as shown in claim 2, the above-mentioned brake mechanism comprises: a friction plate that revolves together with the input shaft; a pressure plate provided on the transmission housing so as to move towards and away from the friction plate; and a pressure piston provided on the transmission housing side so as to pressure weld the friction plate to the pressure plate. In other words, when the friction clutch becomes disengaged when the engine stops, the friction plate and the pressure plate are welded together by the pressure piston and the torque of the transmission&#39;s input shaft is restricted, thereby enabling in-gear parking when the transmission has been put into any gear.  
           [0017]    Further, as shown in claim 3, the brake mechanism may comprise a brake drum integrally formed on the transmission&#39;s input shaft; a brake band provided so as to be able to expand and contract, and to encircle the circumference of the brake drum; and a tightening mechanism to shorten the diameter of the brake band and tighten the brake drum. In other words, when the engine is stopped, the transmission&#39;s input shaft is tightened by the brake band and the rotation is controlled, thereby enabling in-gear parking when the transmission has been put into any gear.  
           [0018]    Further, as shown in claim 4, if the brake drum is integrally formed in the clutch center of the friction clutch, which is formed on the input shaft of the transmission, it can be easily mounted without requiring a particularly large amount of space.  
           [0019]    Further, as shown in claim 3, when one end of the brake band is attached to the clutch housing of the friction clutch and the other end is positioned on the brake drum, simply by pressing that end to the brake drum using the tightening mechanism, the brake band&#39;s diameter can easily be shortened and the brake drum can be securely tightened.  
           [0020]    Further, as shown in claim 4, by forming this tightening mechanism from a hydraulic pump that is activated by the engine&#39;s power and a piston that is moved up and down by the oil pressure of this hydraulic pump and shortens the brake band&#39;s diameter, at the time that the engine is stopped and the oil pressure drops, the piston projects out so as to shorten the diameter of the brake band, thereby enabling automatic activation of the mechanism simultaneous with the engine stopping, without requiring any special operation.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is a sectional view showing the first embodiment of a gear parking brake of a power transmission device according to the present invention;  
         [0022]    [0022]FIG. 2 is a compositional view showing the first embodiment of a gear parking brake according to the present invention;  
         [0023]    [0023]FIG. 3 is a hydraulic circuit view showing the operation of a gear parking brake according to the present invention;  
         [0024]    [0024]FIG. 4 is a sectional view showing the second embodiment of a gear parking brake according to the present invention;  
         [0025]    [0025]FIG. 5 is a sectional view showing one example of a conventional power transmission device; and  
         [0026]    [0026]FIG. 6 is a hydraulic circuit view of a conventional power transmission device. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    Next, a preferred embodiment of the present invention will be described with reference to the attached drawings.  
         [0028]    [0028]FIG. 1 and FIG. 2 show the first embodiment of a gear parking brake  31  of a power transmission device, according to the present invention. In FIG. 1, reference numeral  4  depicts the fluid coupling positioned on the engine&#39;s crankshaft  1  as described above, and reference numeral  5  depicts the wet multiplate friction clutch positioned on the input shaft  3  of the transmission  2 .  
         [0029]    As shown in the drawings, this gear parking brake  31  is formed proximate to the wet multiplate friction clutch  5 , and comprises a brake drum  32  formed on the input shaft  3  of the transmission  2  on the same axis; a brake band  33  formed so as to encircle the circumference of the brake drum  32 ; and a tightening mechanism  34  to shorten the diameter of the brake band  33  and tighten the brake drum  32 .  
         [0030]    This brake drum  32  is a cylinder integrally formed in a clutch center  15  of the wet multiplate friction clutch  5  that is spline fitted to the input shaft  3  of the transmission  2 , so as to protrude therefrom into the transmission  2 . The brake drum  32  accompanies the revolution of the clutch center  15  and revolves together with the input shaft  3 .  
         [0031]    The brake band  33  consists of a metal band that is able to expand and contract, and one end thereof is joined to a dividing wall  35  that divides the wet multiplate friction clutch  5  from the transmission  2 . In other words, it is pin-joined by a mounting bolt  38  to the mounting part  37  of a clutch housing  36  enclosing the wet multiplate friction clutch  5 . Further, as shown in FIG. 2, the other end of this brake band  33  is freely positioned on the brake drum  32 , and an engaging projection  39  formed on the tip of this brake band  33  is engaged by the tip of a plunger  40  of a hydraulic piston  41  of the tightening mechanism  34  to be described next.  
         [0032]    As described before, this tightening mechanism  34  consists of a hydraulic pump  21  activated by the engine&#39;s power and the hydraulic piston  41  activated by the hydraulic pump  21 . By projecting out the plunger  40 , which is engaged with the engaging projection  39  of the released end of the brake band  33 , tangentially to the brake drum  32 , the brake band  33  is pressed onto the brake drum  32  so as to tighten the brake drum  32 .  
         [0033]    More specifically, this hydraulic piston  41  contains a piston  43  integrated with the plunger  40  inside a cylinder  42  mounted to the clutch housing  36 , and a coil spring  44  that impels the piston  43  in the direction of the brake band  33 . The hydraulic piston  41  injects operating oil from the hydraulic pump  21  into this cylinder  42  and by moving the piston  43  in the opposite direction to the brake band  33  (to the left in the drawing), the brake band  33  is loosened. Conversely, when the pressure of the operating oil in the cylinder  42  is released, the piston  43  is moved in the direction of the brake band  33  (to the right in the drawing) by the force of the coil spring  44  and the brake band  33  goes into a tightened state.  
         [0034]    [0034]FIG. 3 shows the relationship between the gear parking brake  31  of the present invention and the hydraulic pump  21 . In the present invention, as described before, the operating oil line L 1  that is connected to the lock-up mechanism control valve  22  and the connection and disconnection control valve  23  connects to a branch line L 2 . By sending one portion of the operating oil to the hydraulic piston  41  of the tightening mechanism  34  through the branch line L 2 , the hydraulic piston  41  becomes activated.  
         [0035]    Further, in the gear parking brake  31  of the present invention having this kind of structure, when the engine starts up, the piston  43  of the hydraulic piston  41  is pushed back by the oil pressure from the hydraulic pump  21  that is being driven continuously. Since the piston  43  loses its ability to press the brake band  33  onto the brake drum  32 , the brake drum  32  revolves smoothly together with the clutch center  15  of the multiplate friction clutch  5 , without there being friction between the brake band  33  and the brake drum  32 . Therefore power transmission from the clutch center  15  to the input shaft  3  of the transmission  2  can be achieved without loss.  
         [0036]    On the other hand, from this state, when the engine is stopped the hydraulic pump  21  also stops and the oil pressure to the pressure piston  41  drops. Since the piston  43  is pushed out by the force of the coil spring  44 , the brake band  33  is pressed onto the brake drum  32 , and acts to tighten the brake drum  32 , resulting in the occurrence of a strong frictional force between the brake band  33  and the brake drum  32 , and the torque of the brake drum  32  is restricted.  
         [0037]    Accordingly, since the torque of the input shaft  3  of the transmission  2  is also restricted, at the time of parking, if the engine is stopped while the transmission  2  is in gear, the torque of the drive source downstream thereof is restricted and so-called in-gear parking is enabled.  
         [0038]    More specifically, the gear parking brake  31  according to the present invention uses one portion of oil pressure from the hydraulic pump  21  that is in constant activation together with the engine drive, and loosens the brake band  33 . When the engine stops and the oil pressure from the hydraulic pump  21  is no longer applied, since the brake band  33  naturally tightens due to the force of the coil spring  44 , compared to using a conventional multiplate disc-type countershaft brake, the present invention has a simple construction and is able to exert a reliable gear brake function. Further, since it is no longer necessary to extend the end of the countershaft  29  through the clutch housing  36  to the wet multiplate friction clutch  5 , the seal of the dividing wall  35  is maintained. In addition, a smaller amount of force can be used to restrict the torque than that used to restrict the torque of the countershaft  29  from the relationship between the gear ratios, for example, thereby enabling a more reliable in-gear parking.  
         [0039]    Note that if a vehicle is being towed when the engine is stopped, if the gear of the transmission  2  is put into neutral, even though the rotation of the input shaft  3  is restricted by the brake band  33 , since the power transmission in the transmission  2  between the input shaft  3  and the vehicle axle is cut off, smooth towing can be achieved without any problems arising.  
         [0040]    Next, FIG. 4 shows a gear parking brake  31  of a power transmission device according to the second embodiment of the present invention.  
         [0041]    As shown in the drawing, the present embodiment comprises two friction plates  45  and  45  on the input shaft  3  of the transmission  2  described before, which to be more specific, are formed on a clutch center  15  of the wet multiplate friction clutch  5  formed on the input shaft  3 . The present embodiment also comprises three pressure plates  46 ,  46  and  46  positioned between and to the front and back of these friction plates  45  and  45 , and a pressure piston  47  to pressure weld the friction plates  45  and  45  and the pressure plates  46 ,  46  and  46  to each other.  
         [0042]    These friction plates  45  and  45  are each spline fitted to a drum  48  that extends from the clutch center  15  to the transmission  2  in the same way as a friction plate  17  that forms one part of the wet multiplate friction clutch  5 . They revolve together with the drum  48  and are able to be moved along same in the axial direction.  
         [0043]    Further, these pressure plates  46 ,  46  and  46  are positioned so as to overlap the front and back of the area where the friction plates  45  and  45  are moved, in the same way as the one friction plate  16  which comprises a part of the wet multiplate friction clutch  5 . They are also spline fitted to the inside of a mounting drum  49  formed on the dividing wall  35  of the clutch housing  36 . In relation to the axial direction of the input shaft  3 , they are able to move towards and away from the friction plates  45  and  45 , however their rotation is restricted by the mounting drum  49 .  
         [0044]    Meanwhile, a pressure piston  47  on the dividing wall  35  of the clutch housing  36  is formed in the mounting drum  49 , and by protruding from the surface of the dividing wall  35  towards the wet multiplate friction clutch  5  due to the force of a coil spring  51 , it pressure welds the friction plates  45  and  45  and the pressure plates  46 ,  46  and  46  to each other. Conversely when the pressure piston  47  retracts inside the dividing wall  35 , due to operating oil supplied from an operating oil passage  50  formed in the same dividing wall  35 , the friction plates  45  and  45  and the pressure plates  46 ,  46  and  46  disengage from each other. Note that the operating oil supplied from the operating oil passage  50  is supplied from the hydraulic pump  21  that works together with the engine, in the same way as in the above embodiment.  
         [0045]    Therefore, in the gear parking brake  31  according to the present embodiment having this kind of structure, when the engine is running, the pressure piston  47  is pulled back into the dividing wall  35  of the clutch housing  36  by operating oil supplied from the hydraulic pump  21 , and since the friction plates  45  and  45  mounted to the input shaft  3  and the pressure plates  46 ,  46  and  46  mounted to the dividing wall  35  are in a free state in relation to each other, the rotation of the input shaft  3  is not restricted by these, and power transmission from the wet multiplate friction clutch  5  through the input shaft  3  to the transmission  2  can be achieved smoothly.  
         [0046]    On the other hand, at the time the vehicle is being parked, the driver disengages the wet multiplate friction clutch  5 , and when the engine is turned off in an in-gear state, (in other words with one of the gears of the transmission  2  in gear), the supply of operating oil from the hydraulic pump  21  also stops, and there is no force to pull the pressure piston  47  back into the dividing wall  35 . Therefore the pressure piston  47  protrudes out in the direction of the wet multiplate friction clutch  5  because of the stretching force of the coil spring  51  formed in the dividing wall  35 , and acts to pressure weld the friction plates  45  and  45  and the pressure plates  46 ,  46  and  46  to each other.  
         [0047]    Consequently, the rotation of the input shaft  3  is restricted and even though the wet multiplate friction clutch  5  is disengaged, the input shaft  3  stops revolving and in-gear parking is enabled in the same way as the above embodiment.  
         [0048]    Accordingly, in the present embodiment, in the same way as the above embodiment, compared to using a conventional multiplate disc-type countershaft brake, the present invention has a simple construction and is able to exert a reliable gear brake function. Further, the seal of the dividing wall  35  can be maintained and a smaller amount of force can be used to restrict the rotation, thereby enabling more reliable in-gear parking.  
         [0049]    In addition, for its lubrication, since the gear parking brake  31  according to the present invention is formed in the moist chamber containing the wet multiplate friction clutch  5 , the ATF oil used for the wet multiplate friction clutch  5  and the fluid coupling  4  can be used in that state for lubrication, and this can prevent reduction of the brake power created by lubricative defects.  
         [0050]    In summary, the present invention can produce the superior effects described below.  
         [0051]    1. A brake drum is formed on the input shaft of the transmission, and this brake drum is automatically tightened by a brake band when the engine stops, thereby enabling in-gear parking when the transmission has been put into gear, even though the engine has stopped and the friction clutch is disengaged, because the rotation of the input shaft is restricted.  
         [0052]    2. Further, in comparison to a conventional multiplate disc-type countershaft brake, the structure is comparatively simple, and since for example the sealability of the transmission is maintained, the present invention contributes to improving the reliability of the whole power transmission device as well as the reliability of the parking brake.  
         [0053]    3. In addition, since the gear parking brake according to the present invention is formed as a whole in the moist chamber containing the wet multiplate friction clutch, the ATF oil used for the wet multiplate friction clutch and the fluid coupling can also be used for lubrication of the gear parking brake; this can prevent reduction of the brake power created by lubricative defects.