Abstract:
There is provided a power transmission system which is capable of positively preventing a driver from having a feeling of inertia travel due to torque transmission interruption during an up-shifting operation, simply by using synchromeshes alone and without increasing the axial length of a transmission. This power transmission system includes first to third gear pairs each having an input gear arranged on an input shaft and an output gear arranged on an output shaft, and first to third synchromeshes each capable of performing disconnecting operation for disconnecting a corresponding one of the first to third gear pairs from the input shaft or the output shaft, baulking operation for power transmission until rotations of the corresponding one of the gear pairs and the input shaft or the output shaft are synchronized, and connecting operation for connecting between the corresponding one of the gear pairs and the input shaft or the output shaft by meshed engagement. When the speed position of the transmission is shifted from the M-th speed position to the L-th speed position, the third synchromesh is caused to move toward the third gear pair by a first predetermined amount which is not large enough to cause the third synchromesh to engage with the third gear pair, to thereby transmit the driving force of the input shaft to the output shaft.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a power transmission system for transmitting a driving force of a prime mover to driving wheels via a stepped transmission.  
           [0003]    2. Description of the Prior Art  
           [0004]    Conventionally, a power transmission system of the above-mentioned kind has been proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 2000-65199. The power transmission system includes a five-forward-speed transmission having first to fifth speed input gears arranged on an input shaft thereof which is connected to an engine, in the mentioned order from the engine side, and first to fifth speed output gears arranged on an output shaft thereof, in constant mesh with the respective first to fifth speed input gears. These first to fifth speed input and output gears form first to fifth speed gear pairs, respectively. Further, the first and second speed output gears are rotatably supported on the output shaft, and a synchromesh is arranged on the output shaft between the two gears. The synchromesh is selectively put into meshing engagement with and disengagement from one of the first and second speed output gears, to connect and disconnect the one of the output gears to and from the output shaft, whereby the speed position of the transmission is set to the first speed position or the second speed position. Similarly, the third and fourth speed input gears are rotatably supported on the input shaft, and another synchromesh is arranged on the input shaft between the two gears. The synchromesh selectively connects and disconnects one of the third and fourth speed input gears to the input shaft, whereby the speed position of the transmission is set to the third speed position or the fourth speed position.  
           [0005]    On the other hand, the fifth speed input gear is rotatably supported on the input gear, and connected/disconnected to and from the input shaft by a shift clutch. The shift clutch is of a hydraulic type the engagement force of which is controllable. The shift clutch is arranged on an end portion of the input shaft on a side remote from the engine, and further, a shift cylinder for controlling the shift clutch is arranged at a location outward of the shift clutch. When the speed position of the transmission is set to the fifth speed position, the hydraulic pressure of the shift cylinder is maximized, whereby the shift clutch is completely engaged. On the other hand, in conducting up-shifting operations within a shift range up to the fourth speed by using the synchromeshes, the hydraulic pressure of the shift cylinder is reduced to a smaller value to allow the shift clutch to slide, whereby part of engine torque is transmitted and supplied to the output shaft as supplemental or compensating torque. In general, in torque transmission by a synchromesh alone, the transmitted torque is reduced to zero or a value close to zero during a time period from completion of synchronization of the synchromesh to establishment of complete meshing engagement thereof. The above control operation for the shift clutch is conducted to prevent this phenomenon of “torque transmission interruption” from giving the driver a feeling of inertia travel which is peculiar to the synchromesh.  
           [0006]    However, in the conventional power transmission system, it is necessary to arrange the hydraulic shift clutch and the shift cylinder for actuating the same on the input shaft along the same in addition to the synchromeshes so as to prevent the driver from having the inertia travel feeling during an up-shifting operation, which increases the length of the transmission in a direction along the input shaft and hence makes it impossible to make the transmission and the power transmission system including the same compact in size.  
         SUMMARY OF THE INVENTION  
         [0007]    It is an object of the invention to provide a power transmission system which is capable of positively preventing a feeling of inertia travel from being caused by torque transmission interruption which might occur during a time period between completion of synchronization of a synchromesh and establishment of meshing engagement of the same in an up-shifting operation, simply by using synchromeshes alone and without increasing the axial length of a transmission.  
           [0008]    To attain the above object, the present invention provides a power transmission system for transmitting a driving force of a prime mover to driving wheels via a stepped transmission,  
           [0009]    the stepped transmission comprising:  
           [0010]    an input shaft connected to the prime mover;  
           [0011]    an output shaft connected to the driving wheels;  
           [0012]    a first gear pair for an L-th speed position, a second gear pair for an M-th speed position higher than the L-th speed position, and a third gear pair for a speed position other than and higher than the L-th speed position and the M-th speed position, each of the gear pairs having an input gear arranged on the input shaft, and an output gear arranged on the output shaft and in mesh with the input gear, with one gear of the input gear and the output gear being rotatably supported on the input shaft or the output shaft;  
           [0013]    first to third synchromeshes for transmitting the driving force of the prime mover from the input shaft to the output shaft via the gear pairs; and  
           [0014]    synchromesh control means for controlling respective operations of the first to third synchromeshes,  
           [0015]    wherein when a speed position of the transmission is shifted from the L-th speed position to the M-th speed position, the synchromesh control means causes the third synchromesh to move toward the third gear pair by a first predetermined amount which is not large enough to bring the third synchromesh into meshing engagement with the third gear pair, to thereby transmit the driving force of the input shaft to the output shaft.  
           [0016]    According to this power transmission system, a first gear pair for an L-th speed position, a second gear pair for an M-th speed position, and a third gear pair for a speed position other than and higher than the L-th and M-th speed positions are formed by respective input gears arranged on the input shaft connected to the prime mover and respective output gears arranged on the output shaft and in mesh with the respective input gears, and there are provided first to third synchromeshes for transmitting the driving force of the prime mover from the input shaft to the output shaft via the gear pairs. When the speed position of the transmission is shifted from the L-th speed position to the M-th speed position, the synchromesh control means causes the third synchromesh to move toward the third gear pair by a first predetermined amount which is not large enough to bring the third synchromesh into meshing engagement with the third gear pair, to thereby transmit the driving force of the input shaft to the output shaft.  
           [0017]    As described above, in the power transmission system, in the up-shifting operation for shifting the speed position of the transmission from the L-th speed position to the M-th speed position, the third synchromesh is moved toward the third gear pair by the first predetermined amount which is not large enough to bring the third synchromesh into meshing engagement with the third gear pair, whereby during this time period, the driving force of the input shaft is transmitted via the third gear pair to the output shaft as a supplemental (i.e. compensating) driving force. As a result, the second synchromesh can be put into complete meshing engagement under the condition of the supplemental driving force being thus supplied, which makes it possible to positively prevent the transmitted driving force (torque) from being reduced to zero or a value close to zero during the up-shifting operation, thereby preventing the operation of the synchromesh from causing the feeling of inertia travel peculiar thereto. Further, since the supplemental driving force can be supplied by utilizing the third gear pair and the third synchromesh for speed positions other than the ones directly involved in the up-shifting operation from the L-th speed position to the M-th speed position, it is unnecessary to add any special component parts so as to carry out the operation for supplying the supplemental driving force. Thus, it is possible to positively prevent the driver from having the inertia travel feeling, simply by using the existing synchromeshes alone and without increasing the axial length of the transmission.  
           [0018]    Preferably, the first to third synchromeshes are each capable of performing disconnecting operation for disconnecting the one gear of the input gear and the output gear of a corresponding one of the first to third gear pairs from the input shaft or the output shaft rotatably supporting the one gear, baulking operation by the first predetermined amount of motion thereof, for power transmission until rotations of the one gear and the input shaft or the output shaft rotatably supporting the one gear are made synchronous, and connecting operation by a second predetermined amount of motion thereof, for connecting the one gear with the input shaft or the output shaft through the meshing engagement, and each for transmitting the driving force of the prime mover from the input shaft to the output shaft via a connected one of the gear pairs including the connected one gear, and when the speed position of the transmission is shifted from the L-th speed position to the M-th speed position, the synchromesh control means causes the second synchromesh to perform the baulking operation, and causes the third synchromesh to perform the baulking operation at least during a time period after the second gear pair is made synchronous by the baulking operation of the second synchromesh and before the synchromesh control means causes the second synchromesh to start the connecting operation.  
           [0019]    According to the preferred embodiment, each synchromesh performs the disconnecting operation, the baulking operation, and the connecting operation for a corresponding one of the first to third gear pairs. When the speed position of the transmission is shifted from the L-th speed position to the M-th speed position, the third synchromesh is caused to perform the baulking operation at least during the time period from completion of the synchronization of the second gear pair by the baulking operation of the second synchromesh and the start of the connecting operation of the same, and hence during this time period, the driving force of the prime mover is transmitted from the input shaft to the output shaft via the third gear pair to supply a supplemental (i.e. compensating) driving force. As a result, the second synchromesh is put into complete meshing engagement through its connecting operation under the condition of the supplemental driving force being thus supplied, which makes it possible to positively prevent the transmitted driving force (torque) from being reduced to zero or a value close to zero during the time period from completion of the synchronization of the second synchromesh to the complete meshing engagement of the same, thereby preventing the operation of the synchromesh from causing the feeling of inertia travel peculiar thereto.  
           [0020]    More preferably, when the speed position of the transmission is shifted from the L-th speed position to the M-th speed position, the synchromesh control means causes, on or after starting to cause the second synchromesh to perform the baulking operation, the third synchromesh to perform the baulking operation and the first synchromesh to perform the disconnecting operation, and then after completion of the synchronization of the second gear pair by the baulking operation of the second synchromesh, causes the second synchromesh to perform the connecting operation.  
           [0021]    According to this preferred embodiment, in shifting the speed position of the transmission from the L-th speed position to the M-th speed position, the synchromesh control means causes, on or after starting to cause the second synchromesh to perform the baulking operation, the third synchromesh to perform the baulking operation and the first synchromesh to perform the disconnecting operation, and then after termination of the baulking operation of the second synchromesh, causes the second synchromesh to perform the connecting operation. Therefore, the driving force of the prime mover can be positively supplied to the output shaft via the third gear pair over the time period from the completion of the synchronization of the second synchromesh to the start of the connecting operation of the same, which makes it possible to positively prevent the driver from having the inertia travel feeling during execution of the up-shifting operation.  
           [0022]    Further preferably, when the speed position of the transmission is shifted from the L-th speed position to the M-th speed position, the synchromesh control means starts to cause the third synchromesh to perform the baulking operation simultaneously with starting to cause the second synchromesh to perform the baulking operation.  
           [0023]    According to this preferred embodiment, when the speed position of the transmission is shifted from the L-th speed position to the M-th speed position, the baulking operation is performed by the third synchromesh simultaneously with the baulking operation of the second synchromesh, and hence the driving force of the prime mover is supplied to the output shaft via the third gear pair as the supplemental driving force from the start of the up-shifting operation. Therefore, torque load applied to the second synchromesh can be reduced by the amount of the torque transmitted via the third synchromesh, which makes it possible to reduce the torque capacity of the second synchromesh and suppress wear of the same.  
           [0024]    Preferably, the first gear pair and the third gear pair are arranged adjacent to each other, and the first and third synchromeshes are formed by a unitary synchromesh arranged between the first gear pair and the third gear pair.  
           [0025]    According to this preferred embodiment, the operation for disconnection of the first gear pair for the up-shift and the operation for supply of the supplemental driving force via the third gear pair can be carried out by using the unitary synchromesh. This reduces the number of synchromeshes to be controlled, and hence makes it possible to simplify control operations for the up-shifting operation and the supply of the supplemental driving force.  
           [0026]    More preferably, when the speed position of the transmission is shifted from the L-th speed position to the M-th speed position, the synchromesh control means causes the third synchromesh to perform the baulking operation, then causes the first synchromesh to perform the disconnecting operation and subsequently the second synchromesh to perform the baulking operation, and further after completion of the synchronization of the second gear pair by the baulking operation of the second synchromesh, causes the second synchromesh to perform the connecting operation.  
           [0027]    According to this preferred embodiment, in shifting the speed position of the transmission from the L-th speed position to the M-th speed position, the synchromesh control means first causes the third synchromesh to perform the baulking operation, and then causes the first synchromesh to perform the disconnecting operation and subsequently the second synchromesh to perform the baulking operation. Further, after termination of the baulking operation of the second synchromesh, causes the second synchromesh to perform the connecting operation. Therefore, in this preferred embodiment as well, the driving force of the prime mover can be positively supplied via the third gear as the supplemental driving force over a time period from the completion of the synchronization of the second synchromesh to the start of the connecting operation of the same, which makes it possible to positively prevent the driver from having the inertia travel feeling during execution of the up-shifting operation. Further, since the second synchromesh is caused to perform the baulking operation after the disconnecting operation of the first synchromesh, the first and second gear pairs arranged adjacent to each other can be connected/disconnected by using the unitary synchromesh, and hence the present invention can be applied to a conventional transmission having a plurality of gear pairs arranged in order of speed positions, without changing the layout of the gear pairs.  
           [0028]    Preferably, the M-th speed position is one speed position higher than the L-th speed position.  
           [0029]    The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    [0030]FIG. 1 is a view schematically showing the arrangement of a power transmission system to which the invention is applied and a vehicle incorporating the same;  
         [0031]    [0031]FIG. 2 is a flowchart of a supplemental torque supply process of a first embodiment of the invention, which is executed by the FIG. 1 power transmission system;  
         [0032]    [0032]FIG. 3 is a timing chart showing an example of operations carried out according to the FIG. 2 supplemental torque supply process;  
         [0033]    [0033]FIG. 4 is a diagram showing the relationship between each speed position up-shift, and a synchromesh and a gear pair to be used for supplemental torque supply in the FIG. 1 power transmission system;  
         [0034]    [0034]FIG. 5 is a flowchart of a supplemental torque supply process of a second embodiment of the invention;  
         [0035]    [0035]FIG. 6 is a timing chart showing an example of operations carried out according to the FIG. 5 supplemental torque supply process;  
         [0036]    [0036]FIG. 7 is a view schematically showing the arrangement of another power transmission system to which the FIG. 2 supplemental torque supply process is applied and a vehicle incorporating the same;  
         [0037]    [0037]FIG. 8 is a diagram showing the relationship between each speed position up-shift, and a synchromesh and a gear pair to be used for supplemental torque supply in the FIG. 7 power transmission system;  
         [0038]    [0038]FIG. 9 is a flowchart of a supplemental torque supply process of a third embodiment of the invention;  
         [0039]    [0039]FIG. 10 is a timing chart showing an example of operations carried out according to the FIG. 9 supplemental torque supply process;  
         [0040]    [0040]FIG. 11 is a view schematically showing the arrangement of still another power transmission system to which the FIG. 9 supplemental torque supply process is applied and a vehicle incorporating the same;  
         [0041]    [0041]FIG. 12 is a partial cross-sectional view showing the construction of a synchromesh; and  
         [0042]    [0042]FIGS. 13A to  13 D are views useful in explaining operations of the synchromesh. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0043]    The invention will now be described in detail with reference to the drawings showing preferred embodiments thereof. Referring first to FIG. 1, there is schematically shown the arrangement of a power transmission system to which the present invention is applied and a vehicle incorporating the same. The power transmission system  1  transmits a driving force (torque) from the engine  2  as a prime mover to driving wheels W, W while changing the rotational speed, and includes a stepped transmission  4 , a starting clutch  5  for connecting/disconnecting between the engine  2  and the transmission  4 , and an ECU  6  controlling operations of devices including the transmission  4  and the clutch  5 .  
         [0044]    The clutch  5  includes a friction disk  7 , a pressure disk  8 , and a diaphragm spring  9 , which are arranged in the mentioned order between a flywheel  2   b  connected to a crankshaft  2   a  of the engine  2  and the transmission  4 . The friction disk  7  is slidably supported on one end of an input shaft  14  of the transmission  4 . The diaphragm spring  9  has a central portion thereof supported by a clutch cover  10  and an inner periphery thereof connected to a release bearing  11  slidably mounted on the input shaft  14 . Further, the diaphragm spring  9  has an outer periphery thereof held in contact with the pressure disk  8  for urging the same toward the friction disk  7 . Connected to the release bearing  11  is one end of a release fork  12  which has an intermediate portion thereof pivotally supported by a fulcrum  12   a  and the other end thereof connected to a starting actuator  13 .  
         [0045]    Due to the construction described above, when the starting actuator  13  is not in operation, the friction disk  7  is held in a state firmly sandwiched between the pressure disk  8  and the flywheel  2   b  by the urging force of the diaphragm spring  9 . As a result, the input shaft  14  of the transmission  4  is connected to the crankshaft  2   a  of the engine  2  via the friction disk  7  and the flywheel  2   b , whereby the clutch  5  is held in an engaged state. On the other hand, when the starting actuator  13  operates, the release fork  12  is pivotally moved about the fulcrum  12   a  in a clockwise direction, as viewed in the figure, to press the release bearing  11  against the diaphragm spring  9 . As a result, the diaphragm spring  9  is resiliently deformed to move in a direction away from the pressure disk  8 , so that the friction disk  7  is released from the sandwiched state, whereby the input shaft  14  of the transmission  4  and the crankshaft  2   a  of the engine  2  are disconnected from each other to bring the clutch  5  into a disengaged state.  
         [0046]    The starting actuator  13  is of a hydraulic type or an electric type, and the operation thereof is controlled by a control signal from the ECU  6 . The starting actuator  13  is actuated only at the start of the vehicle, whereby the clutch  5  is sequentially controlled to the engaged state, then to the disengaged state, and again to the engaged state, during the start of the vehicle. The clutch  5  is held in the engaged state at the other times.  
         [0047]    The transmission  4  is of an automatic type in which shifting operation is controlled by the ECU  6  according to the shift position of a shift lever  21 , etc. The transmission  4  includes the input shaft  14  as a main shaft, an output shaft  15  as a counter shaft, first to seventh speed gear pairs GP 1  to GP 7  (hereinafter generically referred to as “the gear pairs GP”) for forward drive of the vehicle, a reverse gear shaft  16 , and a reverse gear train GRT. The input shaft  14 , the output shaft  15 , and the reverse gear shaft  16  extend in parallel with each other.  
         [0048]    The first to seventh speed gear pairs GP 1  to GP 7  are comprised of first to seventh speed input gears GI 1  to GI 7  arranged on the input shaft  14 , and first to seventh speed output gears GO 1  to GO 7  arranged on the output shaft  15 , which form pairs with the first to seventh speed input gears GIl to GI 7 , and in constant mesh therewith, respectively. The gear ratios of the respective gear pairs GP 1  to GP 7  are set such that as a gear pair is of a higher speed position, the gear ratio thereof is smaller.  
         [0049]    The gear pairs GP and the reverse gear train GRT are arranged from the engine side in the order of the reverse gear strain GRT the first speed gear pair GP 1  the second speed gear pair GP 2  the fifth speed gear pair GP 5  the third speed gear pair GP 3  the sixth speed gear pair GP 6  the fourth speed gear pair GP 4  the seventh speed gear pair GP 7 . In the following, description will be given following this order.  
         [0050]    The reverse gear train GRT is comprised of a reverse input gear GIR integrally formed with the input shaft  14 , a reverse intermediate gear GMR integrally formed with the reverse shaft  16 , and a reverse output gear GOR rotatably fitted on the output shaft  15 . Further, the first speed input gear GI 1  of the first speed gear pair GP 1  is integrally formed with the input shaft  14 , while the first speed output gear GO 1  is rotatably fitted on the output shaft  15 . Between the first speed output gear GO 1  and the reverse output gear GOR, there is arranged a reverse/first speed synchromesh SR 1  (first synchromesh) for selectively switching the speed position of the transmission  4  to a reverse speed position and a first speed position.  
         [0051]    This reverse/first speed synchromesh SR 1  has a known construction. The construction and operation thereof will be described hereafter with reference to FIGS. 12 and 13A to  13 D. It should be noted that the reverse/first speed synchromesh SR 1  has its right and left halves constructed symmetrically between the first speed output gear GO 1  and the reverse output gear GOR, and hence the following description will be basically given by taking the first speed output gear-side half as an example.  
         [0052]    As shown in FIG. 12, the reverse/first speed synchromesh SR 1  includes a hub  51  splined to the output shaft  15  and having lots of spline teeth  51   a  axially extending on an outer peripheral surface thereof, an annular sleeve  52  having an inner peripheral surface thereof formed with lots of spline teeth  52   a , and axially slidable along the hub  51  by meshing engagement between the spline teeth  51   a  and  52   a , a blocking ring  53  received in a recess  51   b  formed in an axial end face of the hub  51 , and a synchro-spring  54  arranged on the outer peripheral surface of the blocking ring  53 .  
         [0053]    A shift fork  55  is fitted on the outer peripheral surface of the sleeve  52 . The shift fork  55  is actuated by a shift actuator  17  (see FIG. 1) connected thereto, to actuate the sleeve  52  in the axial direction with respect to the hub  51 . The spline teeth  52   a  as portions of the sleeve  52  are each formed with a protrusion  52   b  protruding radially inward from an axial end thereof. Each protrusion  52 b has a radially inner surface thereof continuously formed with first and second slopes  52   c ,  52   d  in the mentioned order from the axial end face of the sleeve  52 .  
         [0054]    The blocking ring  53  is comprised of an outer ring  56  arranged at a location radially outward, an inner ring  57  arranged at a location radially inward, and a tapered cone  58  interposed between the two rings  56 ,  57 . The outer ring  56  and the inner ring  57  are formed with locking pieces  56   a ,  57   a , respectively, and locked to each other by engagement between the locking pieces  56   a ,  57   a  inhibiting relative rotation of the two rings  56 ,  57 . The tapered cone  58  has outer and inner peripheral surfaces formed as tapered surfaces  58   a ,  58   b , respectively. The inner peripheral surface of the outer ring  56  is slidably held in contact with the tapered surface  58   a , while the outer peripheral surface of the inner ring  57  is slidably held in contact with the tapered surface  58   b.    
         [0055]    The outer ring  56  has an axial end portion thereof formed with lots of dog teeth  56 b (see FIGS. 13A to  13 D) each projecting radially outward, while the first speed output gear GO 1  opposed to the dog teeth  56   b  also has an end portion thereof formed with lots of dog teeth  59   a  (see FIGS. 13A to  13 D). These dog teeth  56   b ,  59   a  are formed in a manner meshable with the spline teeth  52   a  of the sleeve  52 . Further, as shown in FIGS. 13A to  13 D, the spline teeth  52   a  of the sleeve  52  each have an end formed with an inclined surface portion  52   e , while each dog tooth  56   b  of the outer ring  56  and each dog tooth  59   a  of the first speed output gear GO 1  have respective ends thereof formed with inclined surface portions  56   c  and  59   b  with which the inclined surface portion  52   e  can be brought into contact. The tapered cone  58  is formed with protrusions  58   c  protruding outward in the axial direction. The protrusions  58   c  are loosely fitted in respective recesses  59   c  formed in the first speed output gear GO 1 .  
         [0056]    The synchro-spring  54  is supported by a plurality of spring supporting portions, not shown, formed at circumferentially spaced intervals on the outer peripheral surface of the outer ring  56 . As shown in FIG. 12, when the sleeve  52  is in a neutral position, the synchro-spring  54  is surrounded by the dog teeth  56   b  of the outer ring  56 , the axial end face of the hub  51 , and the axial end portions of the respective spline teeth  52   a  of the sleeve  52 .  
         [0057]    According to the construction described above, when the sleeve  52  is in the neutral position as shown in FIG. 12, the respective protrusions  52   b  of its spline teeth  52   a  are not in contact with the synchro-spring  54 , and hence the urging force of the synchro-spring  54  does not act on the outer ring  56 . Consequently, the outer and inner rings  56  and  57  of the blocking ring  53  are in a state relatively rotatable with respect to the tapered cone  58  of the same. Therefore, while the outer ring  56  and the inner ring  57  rotate in unison with each other, the tapered cone  58  rotates in unison with the first speed output gear GO 1 , so that baulking action does not occur between the sleeve  52 , hence the output shaft  15 , and the first speed output gear GO 1  (see FIG. 13A).  
         [0058]    When the sleeves  52  is slid from the above position toward the first speed output gear GO 1  by the shift fork  55  actuated by the shift actuator  17 , the first slope  52   c  of the sleeve  52  urges the outer ring  56  of the blocking ring  53  via the synchro-spring  54  toward the first speed output gear GO 1 . Further, the inclined surface portion  52   e  of each spline tooth  52   a  of the sleeve  52  is brought into a state pressed by the inclined surface portion  56   c  of the corresponding dog tooth  56   b  of the outer ring  56  (see FIG. 13B), whereby a large frictional force is generated between the outer and inner rings  56  and  57  of the blocking ring  53  and the tapered cone  58  of the same. In this state, baulking operation is performed between the output shaft  15  and the first speed output gear GO 1 .  
         [0059]    Then, when the baulking operation is completed, the difference in rotational speed between the output shaft  15  and the first speed output gear GO 1  is reduced to zero, so that rotations of the output shaft  15  and the first speed output gear GO 1  are made synchronous with each other, whereupon the resistance of the blocking ring  53  to the movement of the sleeve  52  is reduced or disappears. As a result, the spline teeth  52   a  of the sleeve  52  are each fitted between dog teeth  56   b ,  56   b  of the outer ring  56  (see broken lines in FIG. 13B). Further, each spline tooth  52   a  is brought into abutment on the inclined surface portion  59   c  of the corresponding dog tooth  59   a  of the first speed output gear GO 1  (see FIG. 13C), and then fitted between the dog tooth  59   a  and an adjacent dog tooth  59   a  (see FIG. 13D). This causes the first speed output gear GO 1  and the output shaft  15  to be completely united with each other, whereby the first speed gear pair GP 1  is placed in the connected state, which establishes the first speed position of the transmission  4 . It should be noted that during a time period from completion of the synchronization between the blocking ring  53  and the first speed output gear GO 1  to the time point the spline teeth  52   a  of the sleeve  52  are each brought into abutment on the inclined surface portion  59   c  of the corresponding dog tooth  59   a  of the first speed output gear GO 1  (i.e. between the state indicated by the broken lines in FIG. 13B and the state shown in FIG. 13C), a frictional force between the blocking ring  53  and the first speed output gear GO 1  is reduced or disappears, and hence torque transmitted to the output shaft  15  is reduced to zero or a value close to zero.  
         [0060]    Although not shown, when the sleeve  52  is slid toward the reverse output gear GOR, in quite the same manner as the above operation, the spline teeth  52   a  of the sleeve  52  are brought into engagement with the dog teeth  59   a  of the reverse output gear GOR after completion of synchronization between the blocking ring  53  and the reverse output gear GOR. This causes the reverse output gear GOR and the output shaft  15  to be completely united with each other, whereby the reverse gear train GRT is placed in the connected state. In this case, the transmission  4  is set to the reverse speed position due to existence of the reverse intermediate gear GMR interposed between the reverse output gear GOR and the reverse input gear GIR. Further, when the sleeve  52  is held in the neutral position, the first speed gear pair GP 1  and the reverse gear train GRT are both held in the disconnected state.  
         [0061]    It should be noted that the shift actuator  17  (synchromesh control means) for actuating the sleeve  52  is of a hydraulic or electric type, and the operation thereof is controlled by the ECU  6 . Further, during the baulking operation in which the spline teeth  52   a  of the sleeve  52  are pressed against the respective dog teeth  56   b  of the blocking ring  53  for the synchronization, the pressing load can be controlled to control the amount of torque to be transmitted from the input shaft  14  to the output shaft  15  via the reverse/first speed synchromesh SR 1 . This pressing load is also controlled by the ECU  6  via the shift actuator  17 . Other synchromeshes S 25 , S 36  and S 47 , referred to hereinafter, are each similar in construction and operation to the reverse/first speed synchromesh SR 1 . These synchromeshes will be generically referred to as “the synchromeshes S”.  
         [0062]    The second and fifth speed gear pairs GP 2  and GP 5  located next to the reverse gear train GRT and the first speed gear pair GP 1  have a second speed input gear GI 2  and a fifth speed input gear GI 5 , respectively, each of which is integrally formed with the input shaft  14 , and a second speed output gear GO 2  and a fifth speed output gear GO 5 , respectively, each of which is rotatably fitted on the output shaft  15 . The above-mentioned second/fifth speed synchromesh S 25  (second synchromesh) similar in construction to the reverse/first speed synchromesh SR 1  is arranged between the second and fifth speed output gears GO 2  and GO 5 . Accordingly, similarly to the synchromesh SR 1 , the second/fifth speed synchromesh S 25  selectively connects one of the second speed output gear GO 2  and the fifth speed output gear GO 5  to the output shaft  15  or disconnects them from the output shaft  15  simultaneously. Thus, the input shaft  14  and the output shaft  15  are connected/disconnected to and from each other via the second speed gear pair GP 2  or the fifth speed gear pair GP 5 , whereby the transmission  4  is set to the second or fifth speed position.  
         [0063]    On the other hand, the third and sixth speed gear pairs GP 3  and GP 6  located next to the gear pairs GP 2  and GP 5  have a third speed input gear GI 3  and a sixth speed input gear GI 6 , respectively, each of which is rotatably fitted on the input shaft  14 , and a third speed output gear GO 3  and a sixth speed output gear GO 6 , respectively, each of which is integrally formed with the output shaft  15 . The third/sixth speed synchromesh S 36  (third synchromesh) similar in construction to the above speed synchromeshes SRI and S 25  is arranged between the third and sixth speed input gears GI 3  and GI 6 . Accordingly, the third/sixth speed synchromesh S 36  selectively connects one of the third speed input gear GI 3  and the sixth speed input gear GI 6  to the input shaft  14  or disconnects them from the same simultaneously. Thus, the input shaft  14  and the output shaft  15  are connected/disconnected to and from each other via the third speed gear pair GP 3  or the sixth speed gear pair GP 6 , whereby the transmission  4  is set to the third or sixth speed position.  
         [0064]    Similarly, the fourth and seventh speed gear pairs GP 4  and GP 7  located next to the gear pairs GP 3  and GP 6  have a fourth speed input gear GI 4  and a seventh speed input gear GI 7 , respectively, each of which is rotatably fitted on the input shaft  14 , and a fourth speed output gear GO 4  and a seventh speed output gear GO 7 , respectively, each of which is integrally formed with the output shaft  15 . The fourth/seventh speed synchromesh S 47  is arranged between the fourth and seventh speed input gears GI 4  and GI 7 . Accordingly, the fourth/seventh speed synchromesh S 47  selectively connects one of the fourth speed input gear GI 4  and the seventh speed input gear GI 7  to the input shaft  14  or disconnects them from the same simultaneously. Thus, the input shaft  14  and the output shaft  15  are connected/disconnected to and from each other via the fourth speed gear pair GP 4  or the seventh speed gear pair GP 7 , whereby the transmission  4  is set to the fourth or seventh speed position.  
         [0065]    The output shaft  15  is integrally formed with a connection gear  18 , which is in constant mesh with a gear  19   a  of a differential  19 . Accordingly, the driving force of the engine  2  is transmitted to the output shaft  15  at a transmission gear ratio corresponding to the established speed position of the transmission  4 , and then transmitted to the driving wheels W, W via the differential  19 , to drive the driving wheels W, W for rotation.  
         [0066]    The ECU  6  forms synchromesh control means, and is implemented by a microcomputer comprised of a RAM, a ROM, a CPU and an input/output interface (none of which is shown). The ECU  6  drives the starting actuator  13  and the shift actuator  17  e.g. according to the shift position of the shift lever  21 , which is detected by a shift position sensor  22 , to thereby control the operations of the clutch  5  and the transmission  4 . Further, the ECU  6  also performs torque control of the engine  2  required for control of the transmission  4 .  
         [0067]    Next, a supplemental torque supply process according to a first embodiment of the invention, which is executed by the ECU  6 , will be described with reference to FIGS. 2 and 3. The supplemental torque supply process is carried out so as to prevent the inertia travel feeling from being caused by torque transmission interruption occurring when a synchromesh comes into an engaged state during up-shifting of the speed position of the transmission  4 . FIGS. 2 and 3 show a case of the speed position of the transmission  4  being up-shifted from the first speed position to the second speed position. First, it is determined in a step  1  (in the figures, shown as “S1”, the other steps being also shown in the same manner) whether or not a shift signal has been delivered which instructs that the transmission  4  should be up-shifted from the first speed position (1st) in which the first speed gear pair GP 1  is connected to the output shaft  15  by the reverse/first speed synchromesh SR 1  to the second speed position (2nd).  
         [0068]    If the answer to the question is affirmative (YES), the program proceeds to a step  2 , wherein baulking operation of the second/fifth speed synchromesh S 25  on the second speed gear pair GP 2  is started (time t 1  in FIG. 3). More specifically, the sleeve  52  of the second/fifth speed synchromesh S 25  is actuated to shift toward the second speed gear pair GP 2  for baulking operation. As a result, the sleeve  52  is pressed against the blocking ring  53 , whereby torque (driving force) of the engine  2  is transmitted to the output shaft  15  via the second/fifth speed synchromesh S 25 . As the torque transmitted to the output shaft  15  via the second/fifth speed synchromesh S 25  is progressively increased, torque transmitted via the reverse/first speed synchromesh SR 1  is reduced by the amount of the increased torque transmission via the second/fifth speed synchromesh S 25 .  
         [0069]    Then, it is determined in a step  3  whether or not the torque transmitted via the second/fifth speed synchromesh S 25  has become approximately equal to the torque of the engine  2 . If the answer to the question is affirmative (YES), i.e. the former has become approximately equal to the latter (time t 2 ), pulling load applied to the sleeve  52  of the reverse/first speed synchromesh SR 1  for pulling the sleeve  52  from the first speed output gear GO 1  is increased in a step  4  so as to disconnect the first speed gear pair GP 1  from the output shaft  15 . Then, it is determined in a step  5  whether or not the sleeve  52  has been completely pulled off the first speed output gear GO 1 . If the sleeve  52  has been completely pulled off (time t 3 ), the program proceeds to a step  6 , wherein the torque of the engine  2  is reduced, and baulking operation of the third/sixth speed synchromesh S 36  on the third speed gear pair GP 3  is started while reducing pressing load applied to the blocking ring  53  by the sleeve  52  of the second/fifth speed synchromesh S 25 . As a result, transmission of torque via the third/sixth speed synchromesh S 36  is started, and as this transmitted torque is progressively increased, the torque transmitted to the output shaft  15  via the second/fifth speed synchromesh S 25  is reduced by the amount of the increased torque transmission via the third/sixth speed synchromesh S 36 .  
         [0070]    Then, it is determined in a step  7  whether or not synchronization of the second/fifth speed synchromesh S 25  has been completed. If the synchronization has been completed (time t 4 ), the torque of the engine  2  is increased in a step  8 . When the synchronization is completed, the torque transmitted via the second/fifth speed synchromesh S 25  is reduced to zero or a value close to zero. Then, in a step  9 , it is determined whether or not the torque transmitted via the third/sixth speed synchromesh S 36  has become approximately equal to the torque of the engine  2 . When the former has become approximately equal to the latter (time t 5 ), the pressing load by the sleeve  52  of the second/fifth speed synchromesh S 25  is increased in a step  10 . As a result, the spline teeth  52   a  of the sleeve  52  of the second/fifth speed synchromesh S 25  are each fitted between dog teeth  59   a ,  59   a  of the second speed output gear GO 2 , whereby the shift of the speed position of the transmission  4  to the second speed position is completed.  
         [0071]    During the time period from the completion of the synchronization of the second/fifth speed synchromesh S 25  to the meshing engagement of the same with the second speed output gear GO 2 , the torque transmitted via the second/fifth speed synchromesh S 25  is reduced to zero or a value close to zero. However, at this time, the torque transmitted via the third/sixth speed synchromesh S 36  as supplemental (or compensating) torque has been increased to a value approximately equal to the torque of the engine  2 , so that the driver cannot sense torque transmission interruption. Thus, a feeling of inertia travel can be positively prevented from being given to the driver.  
         [0072]    Then, it is determined in a step  11  whether or not the shift to the second speed position has been completed. If the shift has been completed (time t 6 ), the sleeve  52  of the third/sixth speed synchromesh S 36  is moved in a direction of being pulled off to thereby bring the synchromesh S 36  into a disengaged state in a step  12 , followed by terminating the program.  
         [0073]    As described above, in the up-shifting operation from the first speed position to the second speed position, the third/sixth speed synchromesh S 36  is caused to perform the baulking operation, whereby torque is transmitted and supplied as supplemental torque to the output shaft  15  via the same. This prevents momentary interruption of torque transmission during the time period from the completion of the synchronization of the second/fifth speed synchromesh S 25  to the meshing engagement of the same with the second speed output gear GO 2 , and hence makes it possible to positively prevent the driver from having the inertia travel feeling due to the torque transmission interruption. Further, since the supplemental torque is supplied by utilizing the third/sixth speed synchromesh S 36  other than the reverse/first speed synchromesh SR 1  and the second/fifth speed synchromesh S 25  directly involved in the present up-shifting operation, it is possible to carry out the operation of the third/sixth speed synchromesh S 36  for the supplemental torque supply separately from the up-shifting operation and without interfering with the same. Further, it is not required to add any special component parts to carry out the operation for the supplemental torque supply. Thus, it is possible to positively prevent the driver from having the inertia travel feeling, simply by using the existing synchromeshes S alone and without increasing the axial length of the transmission  4 .  
         [0074]    Although in the above example, description is given of the case where supplemental torque is supplied during the up-shifting operation from the first speed position to the second speed position, similar operations for supplemental torque supply are carried out during respective up-shifting operations between other speed positions. FIG. 4 illustrates an example of the relationship between each speed position up-shift and the corresponding synchromesh S and gear pair GP driven for supplemental torque supply. This example shows that supplemental torque is supplied via a gear pair GP for a speed position one speed position higher than a speed position as a shift destination. More specifically, in up-shifting operation from the second speed position to the third speed position, supplemental torque is supplied via the fourth speed gear pair GP 4  by baulking operation of the fourth/seventh speed synchromesh S 47 ; in an up-shifting operation from the third speed position to the fourth speed position, supplemental torque is supplied via the fifth speed gear pair GP 5  by baulking operation of the second/fifth speed synchromesh S 25 ; in an up-shifting operation from the fourth speed position to the fifth speed position, supplemental torque is supplied via the sixth speed gear pair GP 6  by baulking operation of the third/sixth speed synchromesh S 36 ; and in an up-shifting operation from the fifth speed position to the sixth speed position, supplemental torque is supplied via the seventh speed gear pair GP 7  by baulking operation of the fourth/seventh speed synchromesh S 47 . It should be noted that in the above example, supplemental torque supply in the up-shifting operation from the sixth speed position to the seventh speed position is omitted because the driver is hardly given the inertia travel feeling due to torque transmission interruption in the up-shifting operation between these high speed positions.  
         [0075]    According to the above control method, since supplemental torque is supplied during each of the up-shifting operations except the one between the sixth speed position and the seventh speed position, it is possible to positively prevent torque transmission interruption from causing an inertia travel feeling. Further, in each case, supplemental torque is supplied by using a synchromesh other than ones directly involved in an up-shifting operation being carried out, so that it is possible to carry out the operation for supplemental torque supply without interfering with the up-shifting operation and without adding any special component parts.  
         [0076]    Next, a supplemental torque supply process according to a second embodiment of the invention will be described with reference to FIGS. 5 and 6 by taking an up-shifting operation from the first speed position to the second speed position as an example. It should be noted that the present supplemental torque supply process is similar to the FIG. 2 process except for a few steps, so that steps similar to those of the FIG. 2 process are designated by the same step numbers, and the following description is given mainly on different points. The present process is basically distinguished from the FIG. 2 process in that when a shift signal instructing that the speed position of the transmission should be shifted from the first speed position to the second speed position is delivered (YES to step  1 ), the third/sixth speed synchromesh S 36  starts baulking operation thereof simultaneously with the start of baulking operation of the second/fifth speed synchromesh S 25  in a step  22 . Further, in the present process, when the sleeve  52  is completely pulled off the first speed output gear GO 1  (YES to step  5 ), pressing load by the third/sixth speed synchromesh S 36  is increased in a step  26 .  
         [0077]    According to the present process, in response to the shift signal, torque of the engine  2  is supplied as supplemental torque to the output shaft  15  via the third speed gear pair GP 3  from the start of the up-shifting operation from the first speed position to the second speed position (from time t 1  in FIG. 6), so that torque load applied to the second/fifth speed synchromesh S 25  can be reduced by the amount of the supplemental torque, which makes it possible to reduce the torque capacity of the synchromesh S 25  and suppress wear of the same.  
         [0078]    [0078]FIG. 7 shows another power transmission system to which the present invention is applied. This power transmission system  31  is distinguished from the power transmission system  1  of the first embodiment by a transmission  4  having five forward speed positions and the layout or arrangement of gear pairs GP and a reverse gear train GRT on an input shaft  14  and an output shaft  15 . More specifically, the power transmission system  31  has the first speed gear pair GP 1 , the third speed gear pair GP 3 , the second speed gear pair GP 2 , the fourth speed gear pair GP 4 , the fifth speed gear pair GP 5 , and the reverse gear train GRT arranged on the input and output shafts  14 ,  15  in the mentioned order from the engine side. Further, there are arranged a first/third speed synchromesh S 13  between respective rotatable first and third speed output gears GO 1  and GO 3  of the first and third speed gear pairs GP 1  and GP 3 , a second/fourth speed synchromesh S 24  between respective rotatable second and fourth speed input gears GI 2  and GI 4  of the second and fourth speed gear pairs GP 2  and GP 4 , and a fifth speed/reverse synchromesh S 5 R between a rotatable fifth speed input gear GI 5  of the fifth speed gear pair GP 5  and a rotatable reverse input gear GIR of the reverse gear train GRT.  
         [0079]    [0079]FIG. 8 illustrates an example of the relationship between each speed position up-shift and the corresponding synchromesh S and gear pair GP driven for supplemental torque supply. Similarly to the FIG. 4 example, the present example shows that supplemental torque is supplied via a gear pair GP for a speed position one speed position higher than a speed position as a shift destination. More specifically, in an up-shifting operation from the first speed position to the second speed position, supplemental torque is supplied via the third speed gear pair GP 3  by baulking operation of the first/third speed synchromesh S 13 ; in an up-shifting operation from the second speed position to the third speed position, supplemental torque is supplied via the fourth speed gear pair GP 4  by baulking operation of the second/fourth speed synchromesh S 24 ; and in an up-shifting operation from the third speed position to the fourth speed position, supplemental torque is supplied via the fifth speed gear pair GP 5  by baulking operation of the fifth speed/reverse synchromesh S 5 R. It should be noted that similarly to the first embodiment, supplemental torque supply in an up-shifting operation from the fourth speed position to the fifth speed position is omitted because the driver is hardly given the inertia travel feeling in the up-shifting operation between these highest speed positions.  
         [0080]    Further, since the gear pairs GP and the synchromeshes S are arranged as above, e.g. in the up-shifting operation from the first speed position to the second speed position, the operation for disconnection of the first speed gear pair GP 1  for the up-shift and the operation for supplemental torque supply via the third speed gear pair GP 3  are carried out by using the common first/third speed synchromesh S 13 . Thus, the up-shifting operations and the operations for supplemental torque supply can be performed simply by operating the two synchromeshes S 13 , S 24 , which makes it possible to simplify control operation for the synchromeshes S, compared with the power transmission system  1  of the first embodiment, in which it is necessary to operate three synchromeshes S. In the present embodiment, since supplemental torque is supplied via the third speed gear pair GP 3  after disconnection of the first speed gear pair GP 1 , the FIG. 2 process can be employed for the supplemental torque supply.  
         [0081]    The relationship between a synchromesh S and a gear pair GP driven for supplemental torque supply in the up-shifting operation from the second speed position to the third speed position is similar to that in the up-shifting operation from the first speed position to the second speed position. More specifically, in the up-shifting operation from the second speed position to the third speed position, respective operations for disconnection of the second speed gear pair GP 2  and the supplemental torque supply via the fourth speed gear pair GP 4  can be carried out by using the common second/fourth speed synchromesh S 24 , which makes it possible to simplify control operation for the synchromeshes S.  
         [0082]    Next, a supplemental torque supply process according to a third embodiment will be described with reference to FIGS. 9 and 10 by taking an up-shifting operation from the first speed position to the second speed position as an example. It should be noted that the present supplemental torque supply process is similar to the FIG. 2 process except for a few steps, so that steps similar to those of the FIG. 2 process are designated by the same step numbers, and the following description is given mainly on different points. The present process is basically distinguished from the FIG. 2 process in that when a shift signal instructing that the speed position of the transmission should be shifted from the first speed position to the second speed position is delivered (YES to step  1 ), not the second/fifth speed synchromesh but the third/sixth speed synchromesh S 36  is first started to be operated in a step  32 ,, and then, only after the sleeve  52  is completely pulled off the first speed output gear GO 1  (YES to step  5 ; time t 3 ), the second/fifth speed synchromesh S 25  is caused to start baulking operation. Accordingly, during the above process, when torque transmitted via the third/sixth speed synchromesh S 36  has become approximately equal to torque of the engine  2  (YES to step  33 ; time t 2  in FIG. 10), pulling load for pulling the sleeve  52  off the first speed output gear GO 1  is increased in a step  4 . Steps subsequent to the step  36  are the same as the step  7  et seq. in the FIG. 2 process.  
         [0083]    According to the present process, baulking operation of the second speed gear pair GP 2  is started after completion of the operation for disconnection of the first speed gear pair GP 1  as described above, it is possible to use the common synchromesh S for engagement/disengagement of the first and second speed gear pairs GP 1 , GP 2  adjacent to each other. Therefore, the present embodiment can be applied to ordinary transmissions having a plurality of gear pairs GP arranged in order of speed positions. FIG. 11 shows a power transmission system using a transmission  4  with the ordinary layout of gear pairs GP. The power transmission system  61  has first to fifth speed gear pairs GP 1  to GP 5  and a reverse gear train GRT arranged in the mentioned order from the engine side. Further, there are arranged a first/second speed synchromesh S 12  between the first speed and second speed gear pairs GP 1  and GP 3 , a third/fourth speed synchromesh S 34  between the third speed and fourth speed gear pairs GP 3  and GP 4 , and a fifth speed/reverse synchromesh S 5 R between the fifth speed gear pair GP 5  and the reverse gear train GRT. Therefore, if the supplemental torque supply process of the third embodiment is employed, the present invention can be applied to the conventional transmission  4  without changing the layout of the gear pairs.  
         [0084]    It should be noted that the invention is not limited to the embodiments described above, but can be practiced in various forms. For instance, although in the above embodiments, supplemental torque is supplied during each of the up-shifting operations except that between the highest speed positions, this is not limitative, but since the feeling of inertia travel is conspicuous particularly in low-speed travel, supplemental torque may be supplied only in up-shifting operations between low/middle speed positions, e.g. from the first speed position to the second speed position and from the second speed position to the third speed position. Further, although in the above embodiments, supplemental torque is supplied via a gear pair GP for a speed position one speed position higher than a speed position as a shift destination, supplemental torque may be supplied via a plurality of gear pairs GP other than the gear pair of the shift destination. For instance, if supplemental torque is supplied via the third and fourth speed gear pairs GP 3 , GP 4  in the up-shifting operation from the first speed position to the second speed position, it is possible to further reduce torque load applied to the synchromeshes.  
         [0085]    It is further understood by those skilled in the art that the foregoing are preferred embodiments of the invention, and that various changes and modifications may be made without departing from the spirit and scope thereof.