1 Description Title of Invention: CONTROL SYSTEM OF MECHANICAL AUTOMATIC TRANSMISSION 5 Technical Field [0001] The present invention relates to a control system of a mechanical automatic transmission, particularly to clutch control during gear shifting. 10 Background Art [0002] As a transmission for a vehicle, some mechanical automatic transmissions enable automatic gear shifting by actuating the operation (select and shift) of a gear shift 15 box, and the engagement/disengagement of a clutch in a manual transmission by an actuator (Patent Literature 1). In the automatic transmission, when the clutch is disengaged during gear shifting, a shock may occur due to an abrupt shutdown of engine power. 20 [0003] Therefore, in an automatic transmission, a shock during gear shifting is reduced by reducing the torque fluctuation due to a disconnection of engine power at the time of clutch disengagement, for example, such as by disengaging the clutch while the engine torque is brought 25 into no-load condition as in Patent Literature 1, by changing the speed at which the clutch is disengaged according to the engine torque as in Patent Literature 2, and by disengaging the clutch after the engine torque is controlled such that the acceleration of the vehicle 30 becomes zero as in Patent Literature 3. Citation List 6882249_1 (GHMatters) P95528.AU MELC 2 Patent Literature [0004] Patent Literature 1: Japanese Patent Laid-Open No. 2004-270812 Patent Literature 2: Japanese Patent Laid-Open No. 5 2007-211945 Patent Literature 3: Japanese Patent No. 3752959 Patent Literature 4: Japanese Patent No. 3417823 Summary of Invention 10 Technical Problem [0005] In the automatic transmissions of the above described patent literatures, however, the disengagement of the clutch is controlled based on engine torque, and load acting on the drive train components from the clutch to 15 drive wheels is not taken into consideration. [0006] Therefore, as a result of a disengagement of the clutch, the inertia of the engine side which acts on drive train components after the clutch is abruptly eliminated, and thereby the load acting on the drive train components 20 is abruptly released leading to a significant disturbance in the rotation of the drive train components (for example, a rotational frequency of the clutch), by extension to a shock during gear shifting, which is unfavorable. [0007] Moreover, for example, when the clutch is 25 disengaged in association with a gear shift in the technique of the above described Patent Literature 1, first the clutch is operated in the disengaging direction at a predetermined speed, and thereafter the operating speed of the clutch is increased to complete the disengagement at a 30 predetermined timing when the clutch torque (the torque transferred via the clutch) is sufficiently lowered and the risk of causing a shock is eliminated. 6882249_1 (GHMatters) P95528.AU MELC 3 [0008] That is, since only a fixed operating speed is applied without alternatives from the start of disengaging operation of the clutch to the predetermined timing, decreasing the clutch operating speed for the suppression 5 of shock will lead to a prolongation of the gear shift time, and increasing the clutch operating speed for the shortening of gear shift time will result in a shock. Therefore, the suppression of the shock induced during clutch disengagement and the shortening of the gear shift 10 time are in a trade-off relationship so that it is not possible to satisfy both of them at the same time. [0009] The present invention has been made to address such problems and provides the advantages of a control system of a mechanical automatic transmission which enables 15 the reduction of shock during gear shifting. Solution to Problem [0010] To achieve the above described advantage, a control system of a mechanical automatic transmission of 20 the present invention comprises: gear shift means being mounted on a vehicle and including an input shaft to which power from an internal combustion engine is inputted via a clutch, an output shaft for outputting power to driving wheels of the vehicle, a plurality of gear trains provided 25 on the input shaft and the output shaft, and a plurality of switching means for switching an engagement state of the plurality of gear trains, the gear shift means adapted to actuate the plurality of switching means to output the power, which is inputted from the internal combustion 30 engine, in an accelerated or decelerated condition; and control means for controlling the actuation of the clutch and the plurality of switching means, wherein the control 6882249_1 (GHMatters) P95528.AU MELC 4 means is adapted to disengage the clutch when a drive train load which is a load acting on the clutch is zero, when switching the engagement state of the gear trains. [0011] In another embodiment, the control system of a 5 mechanical automatic transmission may comprise driving condition detection means for detecting a driving condition of the internal combustion engine, wherein the control means is adapted to calculate the drive train load based on an output torque of the internal combustion engine to be 10 detected in the driving condition detection means, a preset inertia moment of the internal combustion engine, and a rotational-speed change amount of the internal combustion engine to be detected in the driving condition detection means. 15 [0012] In a further embodiment, the control system of a mechanical automatic transmission may comprise running condition detection means for detecting a running condition of the vehicle, wherein the control means is adapted to monitor on a map a relationship between the drive train 20 load and a clutch stroke, correct the map based on the running condition of the vehicle to be detected in the running condition detection means, and calculate the clutch stroke based on the map after the. [0013] Furthermore, in another embodiment of the 25 invention the control system of a mechanical automatic transmission, the control means may comprise: clutch-slip indicator calculation means for calculating a slip indicator in correlation with a slip state of the clutch based on input and output rotational speeds of the clutch; 30 partially-applied clutch state determination means for determining whether or not the clutch has come into a partially-applied clutch state in which a slip has occurred 6882249_1 (GHMatters) P95528.AU MELC 5 based on the slip indicator calculated by the clutch-slip indicator calculation means during operation in a disengaging direction of the clutch; and clutch operating speed control means for increasing the operating speed of 5 the clutch when a determination that the clutch is in a partially-applied clutch state is made by the partially applied clutch state determination means [0014] In another embodiment of the control system of a mechanical automatic transmission, the clutch operating 10 speed control means may be adapted to continuously increase the operating speed of the clutch at a predetermined change rate, when a determination is made that the clutch is in a partially-applied clutch state 15 Advantageous Effects of Invention [0015] According to a control system of a mechanical automatic transmission of the present invention, clutch operation is performed such that upon switching an engagement state of the gear trains, the clutch is 20 disengaged when a drive train load is zero. In this way, by performing clutch operation when the drive train load is zero, it is possible to prevent an abrupt decrease in the force (inertia force, etc.) transferred from the internal combustion engine side, which 25 acts on drive train components located on the driving wheel side of the clutch in association with a disengagement of the clutch when the internal combustion engine is under no load, and prevent the load on the drive train components from being abruptly released. 30 [0016] Thus, since it is possible to prevent the rotation of the drive train components (for example, a rotational frequency of the clutch) from being significantly disturbed, 6882249_1 (GHMatters) P95528.AU MELC 6 the occurrence of a shock during gear shifting can be prevented (claim 1). Moreover, since the drive train load is calculated based on the output torque of the internal combustion 5 engine, the inertia moment of the internal combustion engine, and the rotational-speed change amount of the internal combustion engine, and there is no need of providing sensors for detecting the drive train load, it is possible to accurately calculate the drive train load while 10 suppressing an increase of cost (claim 2). [0017] Moreover, a clutch stroke amount is calculated from a map of the drive train load and the clutch stroke, which is corrected based on the running condition of the vehicle to be detected in the running condition detection 15 means, so that it is possible to accurately calculate the clutch stroke by taking a deterioration of the clutch into consideration even in a case in which for example, the travel distance of the vehicle has increased and the clutch has deteriorated (claim 3). 20 [0018] Moreover, a slip indicator in correlation with a slip state of the clutch is calculated based on input and output rotational speeds of the clutch during operation in the disengaging direction of the clutch to determine whether or not the clutch has come into a partially-applied 25 clutch state based on this slip indicator, and when a determination is made that the clutch is in a partially applied clutch state, the operating speed of the clutch is increased, so that when the clutch is in a partially applied clutch state, no significant shock will occur even 30 if the operating speed in the disengaging direction is increased, and on the other hand, increase of the operating speed makes it possible to significantly move up the timing 6882249_1 (GHMatters) P95528.AU MELC 7 of the completion of disengagement of the clutch. Thus, since both the shock suppression during clutch disengagement and the shortening of the gear shift time can be achieved at the same time, it is possible to improve 5 gear shift feeling (claim 4). [0019] Moreover, since when a determination is made that the clutch is in a partially-applied clutch state, the operating speed of the clutch is continuously increased at a predetermined change rate, both the shock suppression and 10 the shortening of the gear shift time can be simultaneously achieved at a higher level (claim 5). Brief Description of Drawings [0020] 15 [Figure 1] Figure 1 is a schematic configuration diagram of a control system of a mechanical automatic transmission relating to a first example of the present invention. [Figure 2] Figure 2 is a control block diagram showing a clutch actuation control procedure of a control system of a 20 mechanical automatic transmission relating to the first example of the present invention. [Figure 3] Figure 3 shows a clutch control state in time series during gear shift operation of a control system of a mechanical automatic transmission relating to the first 25 example of the present invention. [Figure 4] Figure 4 is a map showing the relationship between the clutch torque and the clutch stroke of a control system of a mechanical automatic transmission relating to the first example of the present invention. 30 [Figure 5] Figure 5 is a control block diagram showing a clutch actuation control procedure of a control system of a 6882249_1 (GHMatters) P95528.AU MELC 8 mechanical automatic transmission relating to a second example of the present invention. [Figure 6] Figure 6 shows a clutch control state in time series during gear shift operation of a control system of a 5 mechanical automatic transmission relating to the second example of the present invention. [Figure 7] Figure 7 shows a clutch controlled state in time series during gear shift operation in another embodiment. 10 Description of Embodiments [0021] Hereafter, embodiments of the present invention will be described based on the drawings. First, a control system of a mechanical automatic transmission relating to a first example of the present 15 invention will be described. [First Example] Figure 1 is a schematic configuration diagram of a control system of a mechanical automatic transmission relating to a first example of the present invention. 20 Hereafter, the configuration of the control system of a mechanical automatic transmission will be described. [0022] As shown in Figure 1, the control system of a mechanical automatic transmission is mounted on a vehicle not shown, and is generally made up of an engine (internal 25 combustion engine) 10, a mechanical automatic transmission (gear shift means) 20, and an electronic control unit (hereafter, referred to as an ECU) (control means) 30. Note that respective components are electrically connected. [0023] The engine 10 generates power according to the 30 amount operation of a throttle pedal, which is not shown, by a driver. Moreover, the engine 10 is provided with a crank angle sensor (driving condition detection means) 11 6882249_1 (GHMatters) P95528.AU MELC 9 for detecting a rotational speed of the engine 10, that is, a rotational speed on the input side of a clutch 21, an airflow sensor (driving condition detection means) 12 for detecting an intake air amount of the engine 10, and a fuel 5 injection valve (driving condition detection means) 13 for injecting fuel to adjust the output of the engine 10. [0024] The mechanical automatic transmission 20 is for actuating a plurality of gear shift units (switching means) not shown and switching the engagement state of the gear 10 trains to shift and amplify the power generated at the engine 10 according to the vehicle speed, and transferring the power to tires not shown. Moreover, the mechanical automatic transmission 20 comprises a clutch 21, an input shaft 22, an output shaft 23, a propeller shaft 24, a 15 clutch operating unit 25, an output shaft rotation sensor (running condition detection means) 26, and a clutch rotational speed sensor 27. [0025] The clutch 21 is interposed between the engine 10 and the input shaft 22 and is for transferring or shutting 20 down the power generated at the engine 10 to or from the input shaft 22. The propeller shaft 24 is connected to the output shaft 23 and is for transferring a shifted power to tires. [0026] The clutch operating unit 25, which is made up of 25 an actuator and the like, performs the engagement and disengagement of the clutch 21. Moreover, the clutch operating unit 25 has a built-in stroke sensor for detecting a stroke amount of the clutch 21. The output shaft rotation sensor 26, which is 30 primarily for detecting a rotational speed of the output shaft 23, makes it possible to calculate the speed of the vehicle based on a detection signal of the concerned sensor, 6882249_1 (GHMatters) P95528.AU MELC 10 a gear ratio after the output shaft 23 (final reduction ratio), and a perimeter of the tire. [0027] The clutch rotational speed sensor 27, which is primarily for detecting a rotational speed of the output 5 side of the clutch 21, makes it possible to calculate a rotational speed difference between the input and the output of the clutch 21 based on a detection signal of the concerned sensor, and a detection signal of the crank angle sensor 11 for detecting the rotational speed of the engine 10 10. Note that the input rotational speed of the clutch is the rotational speed of the engine 1, and the output rotational speed of the clutch 21 is the rotational speed of the clutch 21. [0028] The ECU 30 is a control apparatus for performing 15 comprehensive control of a vehicle and is configured to include an input/output device, a storage device (ROM, RAM, non-volatile RAM, and the like), and a central processing unit (CPU). Sensors such as the crank angle sensor 11, the 20 airflow sensor 12, the fuel injection valve 13, the clutch operating unit 25, and the clutch rotational speed sensor 27 are electrically connected to the input side of the ECU 30, and detection information from these various sensors are inputted thereto. 25 [0029] On the other hand, the clutch operating unit 25 is electrically connected to the output side of the ECU 30. The ECU 30 calculates running conditions of the vehicle such as a vehicle speed, and driving conditions of the engine 10 such as engine torque from detection 30 information detected by these various sensors. Moreover, the ECU 30 discriminates those running conditions, driving conditions, and operating states of the shift operating 6882249_1 (GHMatters) P95528.AU MELC 11 unit not shown of the driver, and controls the clutch operating unit 25 and the gear shift unit to perform gear shifting of the mechanical automatic transmission 20. [0030] Hereafter, the actuation control of the clutch 21 5 in the ECU 30 of the thus configured control system of the mechanical automatic transmission relating to the first example of the present invention will be described. Figure 2 is a control block diagram showing a clutch actuation control procedure of a control system of a 10 mechanical automatic transmission relating to the first example of the present invention. [0031] Moreover, Figure 3 shows a clutch control state in time series during gear shift operation in the ECU 30 of the control system of a mechanical automatic transmission 15 relating to the first example of the present invention, in which a thick broken line in the figure indicates an engine torque Teg which is a torque outputted by the engine 10, a thick solid line indicates a clutch torque (driving load) Tcl which is a torque applied to the clutch 21, a thin 20 broken line indicates a fully engaged position in which the clutch 21 is fully engaged, a chain line indicates a partially-applied clutch start position at which the clutch 21 starts the transfer of power, and a two-dot chain line indicates a fully disengaged position at which the clutch 25 21 is fully disengaged, respectively. [0032] Further, Figure 4 is a map showing the relationship between the clutch torque Tcl and the clutch stroke Scl, in which a broken line in the figure indicates "before correction", and a solid line indicates "after 30 correction", respectively. The term "before correction" indicates a transferable clutch torque Tcl with respect to a clutch stroke Scl when the clutch 21 is a new article. 6882249_1 (GHMatters) P95528.AU MELC 12 Moreover, the term "after correction" indicates a transferable clutch torque Tcl with respect to a clutch stroke Scl for which a degree of deterioration of the clutch 21 due to running conditions such as the vehicle 5 speed and travel distance of the vehicle is taken into consideration. Furthermore, the concerned map is set such that the clutch stroke Scl comes into a partially-applied clutch position when the clutch torque Tcl = 0. [0033] As shown in Figure 3, when the operating state of 10 the shift operating unit by the driver, the vehicle speed of the vehicle, and the like are discriminated and gear shifting is started, the ECU 30 actuates the clutch operating unit 25 to cause the clutch stroke Scl to be changed in a direction in which the clutch 21 is disengaged 15 ("a" in Figure 3). [0034] Next, when the clutch stroke Scl becomes a first predetermined value as shown by "b" in Figure 3, the clutch stroke control thereafter is performed based on the clutch torque Tcl at that time such that the clutch stroke Scl is 20 in a partially-applied clutch position at the clutch torque Tcl = 0, that is, the clutch 21 is unable to transfer power at the clutch torque Tcl = 0. For example, as shown in Figure 3, after the clutch stroke Scl becomes the first predetermined value, the clutch stroke Scl is caused to 25 change at a smaller gradient than that of the clutch stroke Scl before the first predetermined value. [0035] For further details, as shown in Figure 2, the engine torque Teg which is a torque generated by the engine 10 is calculated in an engine torque calculation unit 31 30 based on the rotational speed of the engine 10 which is detected by the crank angle sensor 11, the intake air amount of the engine 10 which is detected by the airflow 6882249_1 (GHMatters) P95528.AU MELC 13 sensor 12, the fuel injection amount which is calculated based on a working state of the fuel injection valve 13 for supplying fuel to the engine 10. Moreover, in a rotational change amount calculation unit 32, the rotational speed of 5 the engine 10, which is detected by the crank angle sensor 11, is differentiated by time to calculate a rotational speed change amount aeg. [0036] Then, in a clutch torque calculation unit 33, a clutch torque Tcl is calculated based on the engine torque 10 Teg calculated in the engine torque calculation unit 31, the rotational-speed change amount aeg calculated in the rotational change amount calculation unit 32, an engine inertia moment Ieg of the engine 10 which is pre-stored in the ECU 30, and the following Formula (1) which is 15 determined from the equation of motion. [0037] Tcl = Teg - Ieg x aeg ... (1) Next, in a clutch stroke calculation unit 34, a clutch stroke Scl is calculated based on the clutch torque Tcl calculated in the clutch torque calculation unit 33, 20 and the map representing the relationship between the clutch torque Tcl and the clutch stroke Scl in Figure 4, which takes into consideration the deterioration of the clutch 21 due to the vehicle speed and travel distance of the vehicle, etc. Note that the concerned map is set such 25 that the clutch stroke Scl comes into a partially-applied clutch start position when the clutch torque Tcl = 0. As shown by "c" in Figure 3, the clutch stroke Scl comes into the partially-applied clutch start position when the clutch torque Tcl = 0. 30 [0038] Then, the clutch operating unit 25 is actuated such that the clutch stroke Scl calculated in the clutch stroke calculation unit 34 is achieved. 6882249_1 (GHMatters) P95528.AU MELC 14 Then, when the clutch stroke Scl becomes a second predetermined value after passing the partially-applied clutch start position, the clutch operating unit 25 is actuated such that the clutch stroke Scl changes by a 5 predetermined clutch stroke Scl per a predetermined time period as in before the first predetermined value, that is, such that the clutch stroke Scl changes at a predetermined gradient, thereby moving the clutch 21 in the disengaging direction up to a fully disengaged position ("d" in Figure 10 3). [0039] In this way, according to the control system of a mechanical automatic transmission relating to the first example of the present invention, configuration is made such that during gear shifting, when the clutch torque Tcl 15 calculated from the above described Formula (1) is zero, the clutch operating unit 25 is actuated such that the clutch stroke Scl comes into a partially-applied clutch start position, that is, a position where the clutch 21 becomes unable to transfer power. 20 [0040] This makes it possible to prevent that as a result of the clutch 21 being disengaged when the engine 10 is under no-load, force (inertia force etc.) which is transferred from the engine 10 side and acting on drive train components located after the clutch 21, such as the 25 input shaft 22, the output shaft 23, the propeller shaft 24, etc. is abruptly decreased, and thereby the load acting on the drive train components is abruptly released. Thus, since it is possible to prevent the rotation of the drive train components from being significantly 30 disturbed, the occurrence of a shock during gear shifting can be prevented. 6882249_1 (GHMatters) P95528.AU MELC 15 [0041] Moreover, since as shown by the above described Formula (1), the clutch torque Tcl is calculated based on the engine torque Teg, the clutch torque Tcl changes corresponding to the fluctuation of the engine torque Teg 5 during the control of the clutch 21 so that slipping of the clutch 21 and unnecessary rise of the engine rotational speed are suppressed, thereby allowing smooth gear shifting. Particularly, since clutch slip can be suppressed, it is possible to prevent wear of the clutch 21 due to frequent 10 uses of partially-applied clutch during gear shifting, and to avoid stalling due to slipping of the clutch 21 when a shift-up is performed during hill climbing under the condition of a large vehicle weight. [0042] Moreover, since the clutch torque Tcl is 15 calculated based on the above described Formula (1), and there is no need of providing sensors for detecting the clutch torque Tcl, it is possible to accurately calculate the clutch torque Tcl while suppressing the rise of cost. [0043] Moreover, the configuration is made such that the 20 clutch stroke Scl is calculated from a map of the clutch torque Tcl and the clutch stroke Scl, which is to be corrected based on running conditions of the vehicle such as a vehicle speed and a travel distance so that even when the travel distance of the vehicle increases and the clutch 25 21 deteriorates, it is possible to accurately calculate the clutch stroke Scl by taking into consideration the deterioration of the clutch 21. [0044] Further, in a situation in which the clutch cannot be appropriately disengaged if control according to Formula 30 (1) is performed, such as in which the engine rotational speed is relatively low during gear shifting and, to avoid engine stopping, the engine torque cannot be lowered, the 6882249_1 (GHMatters) P95528.AU MELC 16 control may be performed such that the clutch is disengaged at a constant speed so as to avoid engine stopping and vehicle dashing out (runaway), until the control according to Formula (1) becomes possible. 5 [0045] Further, in between "a" and "b" of Figure 3, it is also possible to disengage the clutch 21 so as to satisfy Formula (1) as in between "b" and "c" of Figure 3, and for example a technique may be adopted in which the clutch 21 is disengaged so as to satisfy Formula (1) while decreasing 10 the engine torque at a different gradient in each of several divided sections in between "a" and "c" of Figure 3. [Second Example] Hereafter, a control system of a mechanical automatic transmission relating to a second example of the 15 present invention will be described. [0046] In the second example, the actuation control of the clutch after the clutch stroke Scl of "c" of Figure 3 passes the partially-applied clutch start position is different in comparison with in the above described first 20 example, and the differences from the above described first example will be described below. Figure 5 is a control block diagram showing a clutch actuation control procedure of a control system of a mechanical automatic transmission relating to the second 25 example of the present invention. Moreover, Figure 6 shows a clutch control state in time series during gear shift operation in an ECU 30 of a control system of a mechanical automatic transmission relating to the second example of the present invention, in which a thick broken line in the 30 figure indicates an engine torque Teg which is a torque outputted by the engine 10 or an engine rotational speed Ne which is a rotational speed to be outputted, a thick solid 6882249_1 (GHMatters) P95528.AU MELC 17 line indicates a clutch torque (driving load) Tcl which is a torque applied to the clutch 21, or a clutch rotational speed Nc which is the rotational speed of the clutch 21, a thin broken line indicates a fully engaged position in 5 which the clutch 21 is fully engaged, a chain line indicates a partially-applied clutch start position at which the clutch 21 starts the transfer of power, and a two-dot chain line indicates a fully disengaged position at which the clutch 21 is fully disengaged, respectively. 10 Moreover, a rotational speed difference AN in the figure indicates the difference between the engine rotational speed Ne and the clutch rotational speed Nc, and a clutch operating speed indicates a working speed of clutch by the clutch operating unit 25. 15 [0047] As shown in Figure 6, as the clutch stroke Scl increases, slip between the clutch input and output occurs at any time point ("b" in Figure 6) so that a rotational speed difference AN (slip indicator) occurs between the engine rotational speed Ne which is the rotational speed of 20 the input side of the clutch 21 and the clutch rotational speed Nc which is the rotational speed of the output side of the clutch 21. The rotational speed difference AN gradually increases along with the clutch slip, and the rotational speed difference AN at this time is successively 25 calculated by a clutch-slip indicator calculation unit (clutch-slip indicator calculation means) 35 of the ECU 30. [0048] Then, when the rotational speed difference AN exceeds a predetermined determination value ANO ("c" in Figure 6), a partially-applied clutch state determination 30 unit (partially-applied clutch state determination means) 36 of the ECU 21 regards that the clutch 21 comes into a partially-applied clutch state, and the operating speed of 6882249_1 (GHMatters) P95528.AU MELC 18 the clutch 21 is switched from al to a2 (>al) by a clutch operating speed control unit (clutch operating speed control means) 37 of the ECU 30. Note that the determination value ANO is set as a value slightly larger 5 than zero to reliably determine that slip has occurred in the clutch 21. [0049] Note that although the rotational speed difference AN between the clutch input and output was used as the slip indicator which is in correlation with clutch slip in the 10 present example, this is not limiting. For example, a ratio between the engine rotational speed Ne and the clutch rotational speed Nc may be used. The operating speed of the clutch 21 by the clutch operating unit 25 increases, and the clutch 21 becomes 15 operated in the disengaging direction more rapidly. [0050] Then, a predetermined timing is preset as a point in time immediately after the clutch torque Tc decreases to zero, and it is regarded that the predetermined timing is reached, for example, at a point in time when the clutch 20 stroke increases to a predetermined determination value STO ("d" in Figure 6), and the operating speed of the clutch 21 is switched from a2 to a3 (>a2) . Since there is no need of considering the suppression of shock thereafter, the operating speed a3 is set to a sufficiently large value. 25 For this reason, the clutch 21 becomes operated further rapidly toward the disengaging side, eventually being fully disengaged ("e" in Figure 6). [0051] Note that the timing to increase the operating speed of the clutch 21 to a3 will not be limited to the one 30 described above, and for example, the operating speed may be increased to a3 by regarding that a point in time when 6882249_1 (GHMatters) P95528.AU MELC 19 the clutch torque decreases to zero is the predetermined timing. [0052] Thus, according to the control system of a mechanical automatic transmission relating to the second 5 example of the present invention, the operating speed of the clutch 21 by the clutch operating unit 25 is increased from al to a2 when the rotational speed difference AN between the input and the output exceeds the predetermined determination value ANO after the disengagement of the 10 clutch 21 is started. Then, since the clutch 21 at this point in time is in a partially-applied clutch state, no significant shock will occur even if the operating speed is increased, and on other hand, increase of the operating speed makes it possible to significantly move up the timing 15 of the completion of disengagement of the clutch 21. Thus, since both the shock suppression during clutch disengagement and the shortening of the gear shift time can be achieved at the same time, it is possible to improve gear shift feeling. 20 [0053] Although description of embodiments of the present invention is finished so far, the present invention will not be limited to the embodiments. For example, although the present embodiments are configured such that in the rotational change amount 25 calculation unit 32, the rotational speed of the engine 10 to be detected by the crank angle sensor 11 is differentiated by time to calculate the rotational-speed change amount aeg, this is not limiting and for example, the calculation may be performed by differentiating the 30 vehicle speed and using a tire diameter and an overall gear ratio. In this way, by calculating the rotational-speed change amount aeg based on a vehicle speed which has 6882249_1 (GHMatters) P95528.AU MELC 20 relatively less fluctuation than the rotational speed of the engine 10, it is possible to achieve smoother gear shifting. [0054] Moreover, although the second example of the 5 present invention is configured such that the clutch operating speed is increased from al to a2 in a stepwise manner at a point in time when the rotational speed difference AN between the input and output of the clutch 21 exceeds the determination value ANO, the present invention 10 will not be limited to this, and as shown in Figure 7, for example, the clutch operating speed may be continuously reset toward the increasing side in response to an increase in the rotational speed difference AN. [0055] It is to be understood that, if any prior art 15 publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. [0056] In the claims which follow and in the preceding 20 description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not 25 to preclude the presence or addition of further features in various embodiments of the invention. Reference Signs List [0057] 10 Engine (internal combustion engine) 30 11 Crank angle sensor (driving condition detection means) 6882249_1 (GHMatters) P95528.AU MELC 21 12 Airflow sensor (driving condition detection means) 13 Fuel injection valve (driving condition detection means) 5 20 Mechanical automatic transmission 21 Clutch 25 Clutch operating unit 26 Output shaft rotation sensor (running condition detection means) 10 30 ECU (control means, clutch-slip indicator calculation means, partially-applied clutch state determination means, clutch operating speed control means) 6882249_1 (GHMatters) P95528.AU MELC