METHOD AND APPARATUS FOR CONTROLLING A TRANSMISSION SYSTEM

Abstract: In a construction wherein an electronic pressure regulating valve (31 ∼ 36) is connected individually to each clutch of a two-stage transmission, i.e. main transmission (1st, 2nd, R, 4th, 3rd) and subtransmission (L H) and each clutch can be controlled independently by a controller (10), the present invention cuts off the supply of an oil pressure to a transmission clutch for a present speed stage on the basis of a transmission instruction when the present speed stage is shifted down to the next stage at the time of power-ON, operates the pressure regulating valve so as to start the supply of the oil pressure to this transmission clutch at the point of time when the relative number of rotations at the transmission clutch for the next stage transmission becomes zero, then increases gradually the supply oil pressure after confirmation of the end of filling time to this transmission clutch, and thus prevents offensive feeling due to the speed change shock applied to an operator in whichever state the acceleration operation quantity and the brake operation state may be. In the shift-down operation involving the operations of the transmission clutches of both main and sub-clutches, a torque-OFF time is not provided to the sub-transmission clutch but the supply of the oil pressure to the clutch for the next stage transmission is started immediately so as to make the gradually increasing supply of the oil pressure. After this clutch is meshed, the gradually increasing supply of the oil pressure to the main transmission clutch is made after the filling time described above is over, and offensive feeling due to the transmission shock is prevented.

Description: The present invention relates to controlling a transmission system. In recent years, a demand for reducing a speed-change shock in a construction machine such as a dump truck has been expressed by operators (users). As is well known, by the speed-change shock referred to herein is meant a shock which is produced when the acceleration in the longitudinal direction of a vehicle changes within a short period of time due to the fact that the driving-side torque does not match the load-side torque at the time of a speed change. Particularly in cases where a downshift is effected with power on such as when a vehicle including a construction machine or the like travels from a flat road to a sloping road, the following speed-change shock is produced. Namely, as shown in Fig. 21(c), in cases where the oil pressure of a speed-changing clutch currently being engaged (hereinafter referred to as the pre-speed-changing clutch) is set to zero upon the issuance of a speed-change command, the supply of pressure oil to a speed-change clutch to be engaged next (hereinafter referred to as the post-speed-changing clutch) is simultaneously commenced, and an oil pressure modulation is subsequently executed in such a manner as to gradually increase the pressure of the post-speed-change clutch, then sudden torque fluctuations extending over both positive and negative sides, as shown in the part (a) of the drawing, occur at the output shaft. In particular, such sudden torque fluctuations extending over the positive and negative sides impart discomfort to the operator. The mechanism of the aforementioned speed-change shock is generally explained as follows. That is, as for the numbers of revolutions of the rotating bodies of the post-speed-change clutch, since a downshift is effected, the number of revolutions of the output side of the transmission is higher than the number of revolutions of the input side (the relative number of revolutions is negative, see the part (b) of Fig. 21). For this reason, the clutch-engaging torque becomes negative until the two sides come to rotate in a matched manner during engagement of the clutch, and this causes the speed-change shock. Here, it is assumed that the relative number of revolutions is expressed as one in which the number of revolutions of the output-side rotating body is subtracted from the number of revolutions of the input-side rotating body. Accordingly, in order to reduce the aforementioned speed-change shock, the present inventors have made an attempt in which a time lag (this time will be referred to as the torque off time) is deliberately provided from the point of time when the oil pressure of the pre-speed-change clutch has become zero until the point of time when a gradual increase in the oil pressure of the post-speed-change clutch is commenced, and the clutch is engaged after the relative number of revolutions of the post-speed-change clutch is synchronized with zero. In addition, in a transmission system having a two-stage configuration composed of a sub transmission and a main transmission, at the time of a downshift with power on for which speed-changing clutches on both sides need to be engaged, the following control is carried out on the basis of the technique of providing the aforementioned torque off time. Namely, as shown in the parts (f) and (g) of Fig. 22, the oil pressure of respective pre-speed-change clutches of the sub transmission-side speed-changing clutch (hereinafter referred to as the sub transmission clutch) and the main transmission-side speed-changing clutch (hereinafter referred to as the main transmission clutch) is set to zero simultaneously, and a gradual increase in the oil pressure of the two post-speed-change clutches is simultaneously commenced after a lapse of the torque off time from that point of time. When this control is effected, a long time is required until the relative numbers of revolutions of the two post-speed-change clutches become synchronous, as shown in the part (e) of the drawing, and it can be seen that particularly the main transmission clutch still shows a negative value even after the point of time when a gradual increase in the clutch pressure for that clutch is commenced. For this reason, since negative torque is produced at the output shaft during engagement of the main transmission clutch, as shown in the part (a) of the drawing, fluctuations extending over the positive and negative sides occur at the output shaft, which imparts discomfort to the operator. In addition, as a conventional technique for reducing a speed-change shock, for instance, one shown in Fig. 23 is known. In this technique, control is effected in such a manner that the filling time of a speed-changing clutch to be engaged next (hereinafter referred to as the post-speed-change clutch) is completed before the oil pressure acting on a speed-changing clutch being presently engaged (hereinafter referred to as the pre-speed-change clutch) is set to zero. At the same time, a holding pressure P₁ of the pre-speed-change clutch and an initial pressure P₂ of the post-speed-change clutch are controlled so as to be variable in correspondence with an amount of the accelerator pedal pressed (corresponding to engine load), thereby eliminating the discontinuity of torque. For instance, in terms of the initial pressure P₂, when the amount of pressing is large, P₂ is set to a high level, while when the amount of pressing is small, P₂ is set to a low level. With this conventional technique, although the initial pressure of the post-speed-change clutch is made variable in response to the amount of the accelerator pedal pressed, an increase rate dp/dt for gradually increasing oil pressure for the post-speed-change clutch is constantly fixed. In cases where the increase rate dp/dt is uniformly set in the above-described manner, the following problem occurs. Generally, the speed-change shock is quantitized by a jerk value J, i.e., a rate of change in the acceleration of the vehicle, and this rate of change is proportional to the increase rate dp/dt of the clutch pressure. In addition, if the speed-change shock is considered as the operator's sensitivity evaluation value, even if the rate of change in the acceleration of the vehicle (i.e., this meaning the aforementioned increase rate dp/dt) is the same, the aforementioned evaluation value differs according to the state of the amount of the accelerator pedal pressed. In other words, in the state with the accelerator pedal is pressed (power on), the operator has the intention to accelerate the speed, even if a speed-change shock occurs, the operator does not feel it as appreciable discomfort, and in some cases he or she would even feel the speed-change shock as being fraught with a sense of acceleration and as a good feeling (comfort) derived from sufficient torque. On the other hand, in the state in which the accelerator pedal is not pressed (power off), since the output shaft torque is small, even if relatively small torque fluctuations occur at the output shaft, the operator may feel them as a large speed-change shock. Accordingly, in cases where the oil pressure increase rate dp/dt of the post-speed-change clutch is set to a uniform level as in the case of the prior art, when the amount of the accelerator pedal pressed is large, the operator does not feel the torque fluctuations, such as those shown at the arrow F in Fig. 23, as a speed-change shock, but when the amount of the accelerator pedal pressed is small, he or she would in some cases feel the similar torque fluctuations as a speed-change sock. Thus, with the conventional technique, it has been impossible to completely overcome the discomfort imparted to the operator as a result of the speed-change shock. In addition, when the oil pressure increase rate dp/dt is considered from the viewpoint of the durability of the speed-changing clutches, at the time of a high load (when the amount of the accelerator operated is large), it is desirable to engage the post-speed-change clutch speedily, thereby preventing damage caused by the thermal load acting on the clutch. Accordingly, it is necessary to set the oil pressure increase rate dp/dt to a high level. Conversely, in cases where the post-speed-change clutch is engaged at a low oil pressure increase rate dp/dt at the time of a high load, a long time is required in engagement, and there is the possibility of appreciably impairing the durability of the clutch. Furthermore, at the time when a brake is being operated, since an excessively large negative torque is applied to the engine side, the engine is placed under a high load. If a speed change is effected at this point of time, the durability of the post-speed-change clutch is appreciably impaired in a similar manner. Accordingly, it is necessary to increase the oil pressure increase rate dp/dt in order to avoid this. The present invention has been devised in view of the above-described circumstances, and has as its primary object to substantially prevent discomfort imparted to an operator by preventing negative torque from being produced at the output shaft when a down shift is effected with power on, and has as a second object to substantially prevent discomfort attributable to a speed-change shock in whatever state an amount of the accelerator operated and the state of operation of the brake are, and at the same time to improve the durability of speed-changing clutches. As prior art there may also be mentioned US-A-4 653 351 which discloses a method for controlling a transmission system which includes a plurality of speed-changing clutches for selecting a speed-change stage and pressure control valves respectively connected to the speed-changing clutches, wherein the control valves are controlled when a present speed stage is shifted down to a next speed stage with power on, the method comprising the steps of: turning off the pressure control valve pertaining to the speed-changing clutch in the present speed stage upon the issuance of a speed-change command; actuating the pressure control valve corresponding to the speed-changing clutch in the next speed stage at an operation start timing when a filling time of the speed-changing clutch is completed, at a point of time when the relative number of revolutions of the speed-changing clutch becomes zero, so as to supply pressure oil to the speed-changing clutch; and confirming the completion of the filling time of the speed-changing clutch, and subsequently controlling the pressure control valve pertaining to the speed-changing clutch in such a manner as to gradually increase the oil pressure of the speed-changing clutch. According to the present invention from one aspect, there is provided a method for controlling a transmission system which includes a plurality of sub transmission clutches in a first stage from an input shaft of a transmission, a plurality of main transmission clutches in a second stage and pressure control valves respectively connected to said sub transmission clutches and said main transmission clutches, said transmission system being adapted to select a speed stage through a combination of said sub transmission clutches and said main transmission clutches, wherein said pressure control valves are controlled when said clutches to be engaged are both a sub transmission clutch and a main transmission clutch at the time when a present speed stage is shifted down to a next speed stage with power on, the method comprising the steps of: a) turning off respectively the pressure control valves pertaining to the sub transmission clutch and the main transmission clutch in the present speed stage upon the issuance of a speed-change command; b) starting the supply of pressure oil to the sub transmission clutch in the next speed stage at a point of time when the pressure control valve pertaining to the sub transmission clutch in the present speed stage is turned off, and subsequently controlling the pressure control valve pertaining to the sub transmission clutch in such a manner as to gradually increase the pressure of the sub transmission clutch; c) actuating the pressure control valve corresponding to the main transmission clutch in the next speed stage at an operation start timing when a filling time of the main transmission clutch is completed, at a point of time when the relative number of revolutions of the main transmission clutch becomes zero, so as to supply pressure oil to the main transmission clutch; and d) confirming the completion of the filling time of the main transmission clutch, and subsequently controlling the pressure control valve pertaining to the main transmission clutch in such a manner as to gradually increase the oil pressure of the main transmission clutch. According to the present invention from another aspect, there is provided a transmission system which includes a plurality of sub transmission clutches in a first stage from an input shaft of a transmission, a plurality of main transmission clutches in a second stage, and pressure control valves respectively connected to said sub transmission clutches and said main transmission clutches, said transmission system being adapted to select a speed stage through a combination of said sub transmission clutches and said main transmission clutches, wherein the system includes control means for controlling the pressure control valves when said clutches to be engaged are both a sub transmission clutch and a main transmission clutch at the time when a present speed stage is shifted down to a next speed stage with power on, the control means comprising: a) means for turning off respectively the pressure control valves pertaining to the sub transmission clutch and the main transmission clutch in the present speed stage upon the issuance of a speed-change command; b) means for starting the supply of pressure oil to the sub transmission clutch in the next speed stage at a point of time when the pressure control valve pertaining to the sub transmission clutch in the present speed stage is turned off, and subsequently controlling the pressure control valve pertaining to the sub transmission clutch in such a manner as to gradually increase the pressure of the sub transmission clutch; c) means for actuating the pressure control valve corresponding to the main transmission clutch in the next speed stage at an operation start timing when a filling time of the main transmission clutch is completed, at a point of time when the relative number of revolutions of the main transmission clutch becomes zero, so as to supply pressure oil to the main transmission clutch; and d) means for confirming the completion of said filling time of the main transmission clutch, and subsequently controlling the pressure control valve pertaining to the main transmission clutch in such a manner as to gradually increase the oil pressure of the main transmission clutch. Namely, in the control of this invention, torque off time is provided for the main transmission side alone, while the torque off time is not provided for the speed change on the sub transmission side. The speed change of the sub transmission side is completed during the torque off time of the main transmission side, and control is carried out for the main transmission side to reduce a speed-change shock. That is, the oil pressure of both the sub transmission clutch and the main transmission clutch in the present speed stage becomes zero simultaneously with the start of speed change. At this juncture, torque off time is not provided for the sub transmission clutch in the next speed stage, pressure oil is supplied immediately thereto, and the oil pressure is subsequently gradually increased before the completion of engagement of that sub transmission clutch. Torque fluctuations occurring at this juncture do not appear at the output shaft of the transmission as torque fluctuations since the main transmission side is in the torque off time. In due course of time, control is conducted with respect to the main transmission clutch in the next speed stage and negative-side torque does not occur at the output shaft of the transmission. Accordingly, it is possible to reduce the uncomfortable speed-change shock at the time of downshift with power on, thereby substantially alleviating the operator's fatigue. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a block diagram conceptually illustrating a transmission system using a method in accordance with an example of the present invention; Figs. 2 to 5 are flowcharts illustrating processing procedures that are executed within a controller shown in Fig. 1; Fig. 6 is a timing chart illustrating the manner of changes in various elements of a transmission system in a case where the flowchart shown in Fig. 3 is executed; Fig. 7 is a timing chart illustrating the manner of changes in various elements of a transmission system in a case where the flowchart shown in Fig. 4 is executed; Figs. 8 and 9 are timing charts illustrating another mode of operation of the system; Fig. 10 is a hydraulic circuit diagram illustrating an internal configuration of a clutch oil pressure supplying device in the apparatus shown in Fig. 1; Fig. 11 is a cross-sectional view illustrating an internal configuration of a clutch oil pressure controlling valve; Fig. 12 is a timing chart explaining the operation of the clutch oil pressure controlling valve; Fig. 13 is a diagram used for explaining the judgement of a timing for effecting an automatic speed change; Fig. 14 is a graph conceptually illustrating the relationships between an amount of an accelerator operated, a jerk value J, and an operator sensitivity evaluation value; Fig. 15 is a diagram illustrating amounts of a accelerator pedal pressed which is shown in Fig. 1; Fig. 16 is a diagram conceptually illustrating contents that are stored in a memory inside the controller shown in Fig. 1; Fig. 17 is a timing chart illustrating the manner in which the pressure of a speed-changing clutch undergoes a change accompanying the execution of the flowchart shown in Fig. 5; Fig. 18 is a timing chart illustrating the manner in which the clutch pressure is gradually increased after a speed change with gradually increasing patterns stored in the memory shown in Fig. 16; Figs. 19 and 20 are timing charts illustrating the manner in which elements of the transmission system undergo changes when the flowchart shown in Fig. 5 is executed; and Figs. 21 to 23 are timing charts illustrating the manner in which the elements of the transmission system undergo changes when the prior art control of a transmission system is executed. Fig. 1 is a block diagram conceptually illustrating a transmission system using a method in accordance with an example of the present invention. It should be noted that in this embodiment a case is assumed in which the aforementioned apparatus is mounted on a construction vehicle such as a dump truck or the like. In Fig. 1, an output of an engine 1 is transmitted to a transmission 3 via a torque converter 2, and an output of the transmission 3 is transmitted to drive wheels 5 via a differential gear/final reducing gear 4. Interposed between input and output shafts of the torque converter 2 is a lock-up clutch 6 for directly coupling these shafts. Revolution sensors 7, 8, and 9 respectively outputting signals representative of values corresponding to the numbers of revolutions n₁, n₂, n₃ of an input shaft of the transmission 3, an intermediate shaft disposed between a sub transmission and a main transmission, which will be described later, and an output shaft of the transmission 3 are provided for the transmission 3. Outputs of these sensors are applied to a controller 10. A throttle amount sensor 11 is provided on an accelerator pedal 11a, and the sensor 11 is adapted to detect an amount of the throttle pedal 11a pressed and input a signal S (S1 - S5, see Fig. 15) representative of this amount of pressing to the controller 10. A brake sensor 12 is provided on a brake pedal 12a, and the sensor 12 detects whether or nor the brake has been actuated and inputs the detected value to the controller 10. A shift selector 13 inputs to the controller 10 a signal representative of a shift position (R, N, D, 1, ...) selected by a shift lever 14. The controller 10 determines a speed stage for automatically effecting a speed change on the basis of a shift position signal inputted from the shift selector 13, and shifts up or down the speed of the transmission 3 one stage at a time via a clutch oil pressure supplying device 20 for controlling the pressure of a speed-changing clutch corresponding to the speed stage of the transmission 3 on the basis of a signal representative of the number of revolutions (n₁) of the input shaft and the throttle signal S respectively inputted from the revolution sensor 7 and the throttle amount sensor 11 in such a manner that an optimum speed stage will be obtained among the aforementioned speed stages in which the automatic speed change is possible. When the shift position D has been selected by the shift lever 14, if it is assumed that automatic speed change is possible for the speed stages of Forward 1st to Forward 7th, the speed change of an upshift or downshift in these speed stages is effected with patterns shown in Fig. 13 in correspondence with the number of revolutions n₁ of the input shaft and the throttle signal S. In other words, in cases where the throttle signal is S₃ (see Fig. 15), when the number of revolutions n₁ of the input shaft becomes r₄ or more, a downshift is effected by one speed. In addition, a downshift with power on, which is a subject of the present invention, is a downshift at the time when a driving force is being transmitted to a traveling system, and this power on downshift is valid when the throttle pedal 11a is pressed when traveling with the number of revolutions of the input shaft at r₃ or less and when the throttle signal is S4, S5. The transmission 3 comprises sub transmission clutches L (Low) and H (High) in the first stage that are connected to the output shaft of the torque converter 2 as well as main transmission clutches 1st, 2nd, 3rd, 4th and R in the second stage that are connected to the output shaft of the transmission 3. As shown in Table 1 below, through a combination the sub transmission side clutches H, L and the main transmission side clutches 1st, 2nd, 3rd, 4th, and R (those marked with a circle in the table), a speed stage is selected from among Rev (Reverse), Neu (Neutral), F1 (Forward 1st), F2 (Forward 2nd), F3 (Forward 3rd), F4 (Forward 4th), F5 (Forward 5th), F6 (Forward 6th), and F7 (Forward 7th). As shown in Fig. 10, the clutch pressure oil supplying device 20 for supplying pressure oil to these clutches comprises an oil pressure pressure oil 21 and a relief valve 22, as well as clutch oil pressure control valves 31, 32, 33, 34, 35, 36, and 37 adapted to apply oil pressure to the clutches L, H, 1st, 2nd, R, 4th, and 3rd, respectively, and provided separately for the respective clutches. In addition, the lock-up clutch 6 also has an electronically operated pressure-proportional control valve (not shown) for applying oil pressure to said clutch. These valves 31 - 37 are independently actuated by means of electric commands i₁ - i₇ from the controller 10. It should be noted that the oil pressure control valves 31 - 37 which will be described below are respectively provided with filling sensors for detecting each completion of filling, the filling sensors being adapted to input detection signals e₁ - e₇ to the controller 10. Fig. 11 illustrates a configuration of the aforementioned clutch oil pressure control valves 31 - 37, and these clutch oil pressure control valves 31 - 37 are respectively composed of a pressure control valve 301 for controlling clutch oil pressure, a flow-rate detection valve 302, and a sensor element 303 for detecting the completion of filling, as shown in Fig. 10 as well. The pressure control valve 301 is controlled by the controller 10, while a detection signal of each of the sensor elements 303 is inputted to the controller 10. Each of the clutch oil pressure control valves 31 - 37 allows oil from the pump 21 to flow in via an input port 310 and supplies the oil to each clutch via an output port 311. A port 312 is closed, while ports 313, 314 are drain ports. The electronically operated pressure control valve 301 has a spool 315, a right-hand end of the spool 315 abuts against a plunger 317 of a proportional solenoid 316, and a spring 318 being provided at a left-hand end thereof. Pressure oil of an oil passage 322 is fed back to an oil chamber 320 defined by the spool 315 and a piston 319 via an oil chamber 321 formed in the spool 315. The flow-rate detection valve 302 has a spool 325, which defines coil chambers 326, 327, and 328. An orifice 330 is formed between the oil chambers 327, 328 of this spool 325. The spool 325 is arranged to have three different pressure-receiving areas A₁, A₂, and A₃ which are provided with relationships of A₁ + A₃ > A₂ and A₂ > A₃. A spring 331 is disposed on a left end of the spool 325, and a spring 332 is disposed on a right end thereof. The spool 325 is arranged to maintain its neutral position shown in Fig. 10 with the springs 331, 332 set at the positions of their free lengths when the pressure is not built up in the oil chambers 327, 328. That is, in this case, the spring 331 acts as a return spring for the spool 325, while the spring 332 acts as a pressure-setting spring for detecting the oil pressure of the clutch. A metallic detecting pin 334 is disposed on the right-hand side of an upper portion of a valve body 333, and this detecting pin 334 detects that the spool 325 has moved from its neutral position shown in Fig. 10 to the right against a spring force of the spring 332. This detection pin 334 is fixed to the body 333 via an insulating sheet 336 by means of a cover 335, and a lead wire 337 is led from the detection pin 334. This lead wire 337 is connected to a point a between resistors R₁ and R₂ that are connected in series. A predetermined DC voltage V (e.g., 12V) is applied across these resistors R₁, R₂, and the body 333 is grounded. Referring now to the timing chart shown in Fig. 12, a description will be given of the operation of the valves 31 - 37 thus arranged. In Fig. 12, the part (a) shows a command current I from the controller 10, the part (b) the oil pressure (clutch pressure) of the oil chamber 328, and the part (c) an output of the sensor 303. When an attempt is made to engage the clutch, the controller 10 inputs a trigger command to the solenoid 316 of a relevant clutch oil pressure control valve, and the command current I is then made to drop to a predetermined initial pressure command current corresponding to the initial pressure of the clutch oil pressure. In this state, the operation is set in a standby state until completion of the filling (see the part (a) of Fig. 12). Upon receiving the aforementioned trigger command, the spool 315 of the pressure control valve 301 moves leftward, and the oil from the pump flows into the oil chamber 327 of the flow-rate detection valve 302 via the input port 310 and the oil passage 322. The oil which has entered the oil chamber 327 flows into the oil chamber 328 via the orifice 330 and then flows into the clutch via the output port 311. At this time, since differential pressure occurs between the oil chambers 327 and 328 by means of the orifice, the spool 325 moves leftward. As a result, the flow-rate detection valve 302 is opened, and the oil from the pump which has entered an oil passage 329 flows into the oil chamber 327 via the oil chamber 326 and then flows into the clutch via the orifice 330, the oil chamber 328, and the output port 311. The flow of oil continues until the clutch pack is filled with the oil. Here, when the spool 325 is in its neutral position shown in Fig. 10, and the spool 325 is in the period of a filling time t f when it is moved leftward from the neutral position, the spool 325 is spaced apart from the detecting pin 334. For this reason, in this state, the potential at the point a is one in which the voltage V is divided by the resistors R₁, R₂, as shown in the part (c) of Fig. 12. When the clutch pack is filled with oil, the filling is completed, and the oil no longer flows to it, so that the differential pressure on opposite sides of the orifice 330 disappears. Accordingly, the spool 325 moves rightward by means of a force in which a force attributable to a difference in the pressure-receiving areas of the spool 325 ( A₁ + A₃ - A₂ ) is added to the returning force of the spring 331. At the time when the spool 325 returns, the oil pressure from the pump is applied to the clutch oil pressure via the oil passage 329, the oil chamber 327, the orifice 330, the oil chamber 328, and the like. As a result, an overshoot pressure such as the one shown in the part (b) of Fig. 12 is produced. Here, the spring constant of the spring 332 has been set to a pressure Th smaller than the aforementioned overshoot pressure, as shown in the part (b) of Fig. 12. Accordingly, during this returning operation, after moving rightward to its neutral position, as shown in Fig. 11, the spool 325 further moves rightward by overcoming the urging force of the spring 332 by means of the shoot pressure, with the result that its right end face abuts against the pin 334. Consequently, the detection pin 334 is made conductive with the body 333 grounded via the spool 325, so that the potential at the point a drops to zero, as shown in the part (c) of Fig. 12, and no voltage appears at the point a . This potential at the point a has been input to the controller 10, so that the controller 10 determines the completion of filling on the basis of the fall of the potential at the point a . Immediately upon determining the completion of filling, the controller 10 gradually increases the command current I with respect to the relevant clutch from the value of the initial pressure command current (the part (a) of Fig. 12). As a result, as shown in the part (b) of Fig. 12, after the pressure of that clutch has fallen from the value of the aforementioned overshoot pressure to the initial pressure, the clutch pressure is increased gradually. Hence, the spool 325 moves temporarily leftward toward the neutral position from the state in which it abuts against the pin 334. Subsequently, since the clutch pressure is increased gradually, the clutch pressure exceeds the set pressure Th of the spring 332 at a certain point of time. As a result, the spool 325 moves rightward again by overcoming the urging force of the spring 332, and its right end face abuts against the detection pin 334. Hence, the potential at the point a falls again to zero and this zero level is subsequently maintained. In other words, since the potential at the point a is set to zero when a pressure exceeding the set pressure Th is built in the clutch, while that potential is set to a predetermined voltage value when the clutch pressure is less than the set pressure Th, by monitoring this potential at the point a the controller 10 is capable of not only detecting the completion of filling but also ascertaining the presence or absence of the clutch pressure, i.e., the state of engagement of the clutch. Referring now to the flowcharts shown in Figs. 2 to 4, a description will be given of the speed change control by the controller 10 having the above-described configuration. As described before, the controller 10 determines on the basis of outputs of the revolution sensor 7 and the throttle amount sensor 11 whether or not a speed change is to be effected. Thus the controller 10 discriminates whether a downshift is to be effected (Step 101), and whether the present state is that of power on (Step 102). As for this discrimination, the state of power on is discriminated when, for instance, the throttle signal is more than a reference value. Then, when the state for effecting a downshift with power on is detected, a determination is made (Step 103) as to whether or not both the main transmission and the sub transmission have been changed over as the speed change. If only either one of the main transmission and the sub transmission has been changed over, a first subroutine for transmission control shown in Fig. 3 is executed (Step 105). Meanwhile, if both have been changed over, a second subroutine for transmission control shown in Fig. 4 is executed (Step 106). Parenthetically, if it is determined in the aforementioned Step 101 that it is the case of an upshift, or if it is determined in the aforementioned Step 102 that it is not the power on state, i.e., if it is determined that it is not a downshift with power on, then an ordinary routine for transmission control, which is different from the purport of the present invention, is executed, and the speed change is completed (Step 104). Now, if it is determined in Step 103 that only either one of the main transmission and the sub transmission has been changed over, it is assumed that, for instance, the sub transmission clutch L and the main transmission clutch 2nd are presently being engaged and the speed stage F2 has been selected, and the case of a downshift from F2 to F1 is assumed. At the speed stage F1, the main transmission clutch 1st is engaged (refer to the aforementioned Table 1). In this case, the first subroutine for transmission control is executed. As shown in Fig. 3, upon the starting of the speed change, the controller 10 first executes processing for turning off the valve 34 connected to the main transmission clutch 2nd being then engaged (at a timing t₀ in Fig. 6, Step 201). Then, processing for reading from an unillustrated memory in the controller 10 a time T₀ from the timing t₀ until a timing t₁ when the supply of pressure oil to the valve 33 of the main transmission clutch 1st to be engaged next is commenced. Here, a description will be given of the time T₀ stored in the memory. In a case where the supply of pressure oil to the post-speed-change clutch 1st is commenced at the timing t₁ at which the time T₀ has elapsed from the timing t₀ when the load on the oil pressure at the pre-speed-changing clutch 2nd has zero, then this time T₀ is a time which is set so that the relative number of revolutions, Vc, of the post-speed-change clutch 1st becomes zero at a timing t₂ when a filling time T₁ has elapsed. More specifically, optimum set times T₀, ..., ..., (= t₁ - t₀) at which the relative number of revolutions becomes zero upon the completion of the filling time are determined in advance through simulations and experiments (actual vehicle tests etc.) by using various speed stages and engine power (throttle openings) as parameters. These set times T₀, ..., ... are stored in the aforementioned memory in the controller 10 in the form of a map. Accordingly, at the time of a speed change, when the set time T₀ corresponding to the output of the throttle amount sensor 11 and the speed stage of the present case is read from this memory, and when a pressure control valve concerning a clutch to be engaged next is actuated to supply the pressure oil at the timing t₁ when this set time T₀ has elapsed, then the relative number of revolutions of the clutch to be engaged next becomes zero at the point of time when the filing time T₁ (= t₂ - t₁) has elapsed (this fact has been confirmed through the aforementioned simulations and the like). It should be noted that the output of the throttle amount sensor 11 may be used for the detection of engine power, and in cases where the output shaft torque of the engine can be detected with a torque sensor or the like, the detection value may be used. Thus when the st time T₀ corresponding to the speed change (F2 → F1) of the present case and the output of the throttle amount sensor 11 is read from the memory (Step 202), a determination is consecutively made by an unillustrated timer as to whether or not the set time T₀ has elapsed (Step 203). Then, the supply of pressure oil to the pressure control valve 33 of the main transmission clutch 1st to be engaged next is commenced at the timing t₁ when the aforementioned time T₀ has elapsed (see the part (d) of Fig. 6, Step 204). Subsequently, the controller 10 confirms the completion of filling on the basis of an output e₃ of the filling detection sensor 303 of the valve 33 connected to the aforementioned main transmission clutch 1st (Step 205), and executes the following two items of control (a) and (b) at the point of time (at the timing t₂ in Fig. 6) when the aforementioned filling completion detection signal is inputted from the sensor 303. a) The pressure control valve of the lock-up clutch 6 is turned off (the part (e) of Fig. 6, Step 206). b) The oil pressure of the main transmission clutch 1st for which the aforementioned completion of filling has been detected is gradually increased with a predetermined buildup rate (the part (d) of Fig. 6, Step 207). Upon completion of this control, at a timing t₃ when a predetermined time (hereinafter referred to as the lock-up clutch delay time) T₃ has elapsed from the timing t₂ (Step 208), the controller 10 starts to build up the oil pressure of the lock-up clutch 6. When the above-described speed-change control is effected, the relative number of revolutions, Vc, of the post-speed-changing clutch 1st becomes zero at the timing t₂ when the torque off time T₂ of that clutch 1st has elapsed, as shown in the part (b) of Fig. 6. Subsequently, as for the clutch 1st, engagement is effected in a state in which the numbers of revolutions of the two rotating bodies are synchronized, so that negative torque due to the engagement load is not produced, as shown in the part (a) of the drawing. Accordingly, the operator does not feel a sense of deceleration (discomfort) due to it. Meanwhile, if it is determined in the aforementioned Step 103 that both the main transmission and the sub transmission have been changed over, it is assumed that, for instance, the sub transmission clutch L and the main transmission clutch 3rd are being engaged and the speed stage F4 has been selected, and the case of a downshift from F4 to F3 is assumed. At the speed stage F3, the sub transmission clutch H and the main transmission clutch 2nd are engaged (refer to the aforementioned Table 1). In this case, the second subroutine for transmission control is executed. As shown in Fig. 4, upon the starting of the speed change, the controller 10 first executes processing for turning off the valves 31, 37 respectively connected to the sub transmission clutch L and the main transmission clutch 3rd being then engaged (at a timing t₀' in Fig. 7, Step 401). Then, at this timing t₀', the supply of pressure oil to the valve 32 of the clutch H to be engaged next is commenced with respect to the sub transmission side only (Step 402). Subsequently, at the point of time when the completion of filling is confirmed on the basis of an output e₂ of the filling detection sensor 303 of the valve 32 of the post-speed-changing clutch H (Step 403), the oil pressure of the post-speed-changing clutch H is gradually increased with a predetermined buildup rate (the part (f) of Fig. 7, Step 404). Then, processing similar to that of Steps 202 - 209 of the aforementioned first subroutine for transmission control is executed with respect to the main transmission-side clutch 2nd to be engaged next (and with respect to the lock-up clutch 6). That is, an appropriate set time T₀' corresponding to the output of the throttle amount sensor 11 and the speed stage of the present case is read from the memory in the controller 10 (Step 202), and at a timing t i ' when that set time T₀' has elapsed as shown in Fig. 7 (Step 203) the valve 34 of the main transmission clutch 2nd to be engaged next is actuated so as to supply pressure oil thereto (Step 204). Upon confirming the completion of a filling time T₁' (t₂' - t₁') for the main transmission clutch 2nd (Step 205), at the timing t₂' when a filling completion detection signal e₄ is inputted, the lock-up clutch 6 is set to off (Step 206), and the oil pressure of the main transmission clutch 2nd is gradually increased with a predetermined buildup rate (Step 207). Subsequently, at a timing t₃' when the lock-up clutch delay time T₃' has elapsed from that timing t₂' (Step 208), the buildup of the oil pressure of the lock-up clutch 6 is commenced (Step 209). In this second subroutine for transmission control, with respect to a sub transmission clutch, at the point of time when the oil pressure of the pre-speed-change clutch L is set to zero (clutch released), pressure oil is supplied immediately to the post-speed-change clutch H, and the engagement of the post-speed-changing clutch H is completed within the torque off time T₂' of the main transmission clutch. During the engagement of the sub transmission H, torque fluctuations due to engagement load occur in the clutch H. At the time of the occurrence of these torque fluctuations, however, they do not appear at the output shaft of the transmission in which the main transmission side is in the period of torque off period. Moreover, at a timing t₄ (see the part (e) of Fig. 7) when the relative number of revolutions of the sub transmission clutch H has become zero, the state becomes similar to that of the timing t₀ shown in Fig. 6, i.e., the state becomes one in which the engagement is to be effected with respect to the main transmission-side post-speed-changing clutch (2nd) only. For this reason, if a similar procedure to that of the first subroutine for transmission control is subsequently executed for the post-speed-changing clutch 2nd, and if the supply of pressure oil to the clutch 2nd is commenced at the timing (timing t₁') of completion of the filling time at the point of time when the relative number of revolutions of the post-speed-changing clutch 2nd becomes zero, then negative torque is not produced at the output shaft of the transmission in a similar manner. In the embodiment, as shown in Fig. 6 or 7, the lock-up clutch 6 is set in an engaged state during the period of the torque off time T₂ or T₂'. Thus, as the input end shaft of the transmission is directly coupled with the output shaft of the engine, the number of revolutions of a turbine of the torque converter 2 increases sharply, i.e., the rotating-side rotating body on the input side of the post-speed-changing clutch increases quickly. Accordingly, an effect is obtained in that the timing for setting the relative number of revolutions of the post-speed-changing clutch to zero can be quickened. In addition, in accordance with the embodiment, at the time of engagement of the post-speed-changing clutch, an arrangement is provided for alleviating load on clutch engagement by providing the lock-up clutch delay time T₃ or T₃' with respect to the lock-up clutch 6. It should be noted that when the oil pressure of the post-speed-changing clutch is gradually increased subsequent to the point of time when the filling time was completed, if the relative number of revolutions of that clutch is zero at that point of time, the initial pressure and the rate of gradual increase of oil pressure subsequent to the filling time may be fixed. In practice, however, there are cases where the relative number of revolutions deviates from zero at the completion of the filling time. For that reason, in implementing the embodiment, the aforementioned initial value and the rate of gradual increase of oil pressure may be varied in correspondence with the throttle amount and the speed stage of the present case in the same way as the aforementioned set time T₀ or T₀' in order to alleviate a speed-change shock caused by that deviation. In addition, it is effective to set the initial pressure of the post-speed-changing clutch at a low level in reducing the speed-change shock, since the torque of the output shaft of the transmission needs to rise from zero. In this embodiment, the supply of pressure oil to the post-speed-changing clutch is commenced at the point of time when a set time obtained in advance through simulations and the like has elapsed, but it is possible to implement the embodiment as follows: A set relative number of revolutions, Vco, is read from the memory. By the relative number of revolutions, Vco, is meant a value which is obtained in advance as an optimum one through simulations and the like, and it is a number of revolutions in which the relative number of revolutions becomes zero at the completion of the filling time in cases where the supply of pressure oil to the post-speed-changing clutch is commenced at the point of time when the relative number of revolutions of the post-speed-changing clutch has reached the relative number of revolutions, Vco. Set relative numbers of revolutions, Vco, ..., ... are also stored in the memory in the form of a map in correspondence with each speed stage and engine power in the same way as the aforementioned set times T₀, ..., .... Accordingly, the set relative number of revolutions, Vco, corresponding to the output of the throttle amount sensor 11 and the speed stage of the present case is read from the memory (Step 202'). The relative number of revolutions of the post-speed-changing clutch is consecutively detected, and a determination is made as to whether or not the relative number of revolutions detected has reached the set relative number of revolutions, Vco, read (Step 203'). Then, at a timing t₁'' when the relative number of revolutions detected has reached the set relative number of revolutions, Vco, as shown in Fig. 8, pressure oil is supplied to the post-speed-changing clutch (Step 204), and the oil pressure of the post-speed-changing clutch is gradually increased at a timing t₂'' of completion of the filling time (Steps 205, 207). With respect to the lock-up clutch 6 as well, processing (Steps 206, 208, 209) similar to the above-described one is executed. When the above-described control is effected, it is possible to obtain a similar effect to that of the above-described embodiment. Furthermore, in accordance with this modification, an advantage is obtained in that the timing when the relative number of revolutions of the post-speed-changing clutch and the timing of completion of the filling time of that clutch can be made to coincide with each other with good accuracy. It should be noted that in the foregoing embodiment, during the lock-up clutch delay time, the oil pressure of the lock-up clutch 6 is completely set to zero, with the result that, at the completion of engagement of that clutch 6, a speed-change shock occurs as shown in the part (a) of Fig. 6, the part (a) of Fig. 7, and the part (a) of Fig. 8. Accordingly, in order to reduce the shock occurring at the time of engagement of the lock-up clutch 6, it is possible to implement the embodiment such that, during engagement of the post-speed-changing clutch, the oil pressure of the lock-up clutch 6 is not completely set to zero but is maintained at a pressure level slightly higher than the internal pressure of the torque converter 2, as shown in the part (e) of Fig. 9. In cases where a predetermined oil pressure is thus maintained while the oil pressure of the lock-up clutch 6 is lowered, the engagement of the clutch 6 is completed with the transmitting torque of the lock-up clutch 6 lowered, so that it is possible to reduce or overcome the shock at the time of engagement, as shown in the part (a) of Fig. 9. Moreover, at the same time, it is possible to reduce the engagement load acting on the post-speed-changing clutch. It should be noted that although in the embodiment a plurality of set times or set relative numbers of revolutions both corresponding to each speed stage and engine power are prepared, it is possible to uniformly set a set time or a set relative number of revolutions regardless of the speed stage or engine power and use the same in an actual implementation. Although in the first subroutine for transmission control of the embodiment a description has been given of the case of F2 → F1, a similar effect can be obtained with respect to the cases of F3 → F2, F5 → F4, and F7 → F6 for effecting a speed change for one side of the transmission by carrying out similar processing. In addition, with respect to the second subroutine for transmission control as well, a similar effect can be obtained in the case of not only F4 → F3 but F6 → F5 by carrying out similar processing to that of the embodiment. Next, a description will be given of a second mode of operation of the apparatus of Fig. 1. The speed - change shock of a gear transmission is evaluated by a jerk value J which is defined by the following formula: J = dα dt = K G I · (µ dp dt + P dµ dt ) (1) Where J: jerk value α: acceleration of the vehicle K: coefficient of transformation G: constant of the reduction ratio I: vehicle total weight (body weight + cargo weight) µ: coefficient of friction of the clutch disk P: oil pressure of the clutch The aforementioned constant of the reduction ratio, G, is determined on the basis of each reduction speed stage, but also includes a coefficient suggesting the number of laminated layers of a clutch plate and its area in each speed stage. Accordingly, the value of this constant G varies slightly depending on the speed stage. It goes without saying that G becomes the reduction ratio itself in cases where the numbers of the laminated layers of the clutch plates and their areas are equal for the respective speed stages. The second term in the parentheses of the aforementioned Formula (1) is an expression having a bearing when the difference between static friction and dynamic friction is large, and its effect appears at the completion of engagement of the clutch. In cases where there is no difference between the two, it can be ignored. In the below, a description will be given on an assumption that the first term is valid. The jerk value J in the above Formula (1) can be expressed as J = K G I µ dp dt (1)' Here, if it is assumed that K' = K · G I · µ (2) then the above Formula (1)' is expressed as dp dt = J K' (3) Thus, an oil pressure increase rate dp/dt of the clutch is determined by K' and the jerk value J (a rate of change in acceleration) that are determined by the conditions at the time of the speed change. Here, since the parameters K, G of K' are determined by the various conditions of the clutch and the reduction ratio, if the vehicle total weight I and the coefficient of dynamic friction µ are assumed to be constant, K' can be determined unconditionally from the manner of speed change, i.e., the difference between the upshift and downshift and the speed stage at the time of the speed change. If the parameter of an amount of an accelerator operated is added to the operator's sensitivity evaluation value, the relationship between the amount of accelerator operated, the jerk value J, and the sensitivity evaluation value becomes such as the one shown in Fig. 14. As is apparent from the drawing, in cases where a targeted jerk value J p is set uniformly without taking the magnitude of the amount of the accelerator operated, and a speed-changing clutch is engaged at a corresponding pressure increase rate dp/dt, then the operator feels "comfortable" in the section I (where the amount of the accelerator operated is partial), but feels "the speed-change shock is large" in the section M (where the amount of the accelerator operator is small). In addition, the operator feels a "sense of reduced acceleration" in the section Q, and in conjunction with it there occurs the drawback of a reduction in the durability of speed-changing clutches. For that reason, in this apparatus, when the amount of the accelerator operated, S, is a low value S L , the jerk value J is set to a small targeted jerk value J PL , while when the amount of the accelerator operated, S, is a low value S H , the jerk value J is set to a high targeted jerk value J PH . That is, by setting the pressure increase rate dp/dt corresponding to the amount of the accelerator operated such that the greater the amount of the accelerator operated, the greater the targeted jerk value, i.e., the rate of change in the vehicle acceleration becomes, an attempt is made to constantly obtain the sensitivity evaluation value of "comfortable", and the durability of clutches improves. It should be noted that K' in the above Formula (2) has the following tendency: The higher the speed stage after the speed change, the smaller the value K becomes. Hence, according to the above Formula (3), it suffices if the higher the speed stage after the speed change, the higher the oil pressure increase rate dp/dt is set. At the time of operation of the brake, the engine is placed under a high load, so that there is the possibility of the clutches being damaged by thermal load at the time when the speed-changing clutch is engaged. To obviate this, in this apparatus, when the brake is being operated, the speed-changing clutch is engaged during a speed change by setting the pressure increase rate at a high level (at the level of a pressure increase rate corresponding to a substantially maximum value of the amount of the accelerator operated (slightly lower than the maximum value)). That is, at the time when the brake is being operated, the clutch is engaged with a high pressure increase rate dp/dt regardless of the amount of the accelerator operated. To execute the above-described control of the gradual increase of oil pressure, patterns of an optimum gradual increase in the clutch oil pressure are stored in the memory (not shown) inside the controller 10 shown in Fig. 1 in correspondence with the amount of the accelerator operated and a combination of the state of operation of the brake and various speed-change modes, as shown in Fig. 16. More specifically, an explanation will be given by citing the case of one speed-change mode "upshift, F1 → F2". Patterns of a gradual increase in oil pressure, PT1, PT2, PT3, PT4, PT5, in which the greater the amount of pressing, the higher the oil pressure gradual increase rate dp/dt are stored in correspondence with detection values S1 - S5 of the throttle amount sensor 11 (see Fig. 15). In addition, also stored is a pattern of a gradual increase in oil pressure, PT6, for engaging the clutch at an oil pressure increase rate dp/dt which is slightly lower than an oil pressure increase rate dp/dt corresponding to a full-throttle state (S5) in correspondence with a case where the operation of the brake is detected by the brake sensor 12 (brake on). These patterns of a gradual increase in oil pressure which vary according to the magnitude of the amount of the accelerator operated are stored in the memory so that the clutch will be engaged at a higher oil pressure increase rate dp/dt at a higher speed stage with respect to each speed change mode. Referring now to the flowchart shown in Fig. 5 and the timing chart shown in Fig. 17, a description will be given of the speed change control by the controller 10 having the above-described configuration. The controller 10 determines on the basis of outputs of the revolution sensor 7 and the throttle amount sensor 11 whether or not a speed change is to be effected. Simultaneously with this determination, a discrimination is made between an upshift and a downshift (Step 501). Now, it is assumed that the clutch L and the clutch 1st are being engaged and the speed stage F1 (Forward 1st) has been selected, and that an upshift from F1 (Forward 1st) to F2 (Forward 2nd) is to be carried out. In the speed stage F2, the clutch 2nd is engaged (see the Table 1 above). Upon starting of the speed change, the controller 10 first commences the supply of pressure oil to the clutch oil pressure control valve 34 of the speed-changing clutch 2nd (Step 102, timing t₀ in Fig. 6). Subsequently, on the basis of an output of the filling detection sensor attached the valve 34 connected to the post-speed-changing clutch 2nd, the controller 10 confirms the completion of filling (Step 105), and executes the following control at the timing (timing t₁ in Fig. 17) when the filling completion detection signal e₄ is inputted from this sensor: The valve 33 of the pre-speed-changing clutch 1st being engaged is turned off (Step 507, part (a) of Fig. 17). The oil pressure of the post-speed-changing clutch 2nd for which the filling completion has been detected is gradually increased with an oil pressure gradual pattern PT which will be described later (Step 511, part (b) of Fig. 17). Here, in the control of the aforementioned Steps 507, 511, an attempt is made to prevent a speed-change shock by setting to appropriate values the oil pressure P₁ (see the part (a) of Fig. 17) of the clutch 1st to be set to off and the oil pressure P₂ (see the part (b) of Fig. 17) of the clutch 2nd to be set to on so that the output shaft torque of the transmission 3 will become equal immediately before the speed change and upon completion of the filling. That is, the speed-change shock occurs due to a difference in the output torque of the transmission 3 immediately before and after the speed change. For this reason, the speed-change shock can be prevented if the speed change is effected in such a manner that this torque difference disappears. The numbers of revolutions n₀, n₁ of the input and output shafts of the torque converter 2 shown in Fig. 1 are respectively detected by the sensors. Accordingly, by determining a ratio between these numbers of revolutions, e = n₁/n₀ , it is possible to calculate a primary coefficient (STP) and a torque ratio (ST) indicating the performance of the torque converter 2. In addition, since the input torque T p of the torque converter can be expressed as T p = STP·(n₀/1000) (4) and since the output torque T t of the torque converter can be expressed as T t = T p ·ST (5) the value of the output torque T t of the torque converter can be calculated on the basis of these formulae and the aforementioned coefficient (STP) and torque ratio (ST). Thus, by determining the output torque T t of the torque converter at the timing t₀ when the aforementioned speed-change command is issued, it is possible to determine the torque T B of the output shaft of the transmission 3 at that timing t₀ on the basis of the following formula: T B = G·T t (6) where G: gear ratio of the transmission 3 as a whole Meanwhile, the frictional torque T C of the clutch at the filling completion timing t₁ of the clutch 2nd can be expressed as T C = K C ·µ·P (7) where K C : clutch coefficient at timing t₁ µ: frictional coefficient of the clutch at timing t₁, and this is a function of the relative rotational speed V of the clutch disk P: clutch oil pressure In addition, this frictional torque T C can be converted into the output shaft torque T A of the transmission 3 at the timing t₁ on the basis of the following Formula (8): where G': gear ratio between the engaged clutch and the output shaft of the transmission at timing t₁ In order to prevent fluctuations of the torque during speed change, it suffices if the transmission output shaft torque T B at the timing t₀ shown in Formula (6) and that torque T A at the timing t₁ shown in Formula (8) become equal. The oil pressure of the engaged clutch which satisfies this condition T B = T A can be expressed as follows on the basis of Formula (6) and (8): P = (G·T t ) / (K C ·µ·G') (9) It should be noted that since the frictional coefficient µ of the clutch shown in Formula (9) above is a function of the relative number of revolutions of the clutch disk, it is impossible to ascertain the frictional coefficient µ in advance. However, it is possible to obtain the frictional coefficient µ since the relative number of revolutions of the disk at the time of the start of speed change can be determined from the number of revolutions n₁ detected by the sensor 7, the gear ratio of the transmission 3 before and after the speed change, and the number of revolutions of the output shaft detected by the sensor 9. Accordingly, the controller 10 calculates the oil pressure P₂ to be applied to the post-speed-changing clutch 2nd on the basis of the aforementioned Formula (9) (step 503), and causes this oil pressure value P₂ to act on the 2nd clutch at the timing t₁ of completion of the filling time of the clutch 2nd (Step 506). It should be noted that it suffices if the oil pressure P₁ to be applied to the 1st clutch is a value which is capable of maintaining the output torque value during the filling time t₀ - t₁, and this oil pressure value P₁ can also be determined in accordance with the aforementioned Formulae (6) and (8). This oil pressure P₁ is applied to the clutch 1st during the period of the filling time (Step 504). Upon completion of the filling time, as for the post-speed-changing clutch 2nd, the initial pressure P₂ is applied to that clutch 2nd, and its oil pressure is then gradually increased in accordance with the oil pressure gradual pattern PT. In this embodiment, an attempt is made to engage the clutch 2nd so that the operator will not feel a speed-change shock in terms of his or her sense and with an optimum pattern of a gradual increase in oil pressure for improving the durability of the clutches. Namely, in Step 508 shown in Fig. 5, when it is determined on the basis of an output of the sensor 12 that the brake is being operated, the oil pressure gradual increase pattern PT6 is read from the memory incorporated in the controller 10 (Step 512), and the control valve 34 for the post-speed-changing clutch 2nd is actuated by a current command signal according to this pattern. As a result, the oil pressure of the clutch 2nd is gradually increased at the timing t₁ of completion of the filling time (Step 513), as shown at PT6 in Fig. 18. Meanwhile, in Step 508, when it is determined that the brake is not being operated, on the basis of an output of the throttle amount sensor 11 (Step 509), processing is effected in which an oil pressure gradual increase pattern (PT1 - PT5) corresponding to the detection value (S1 - S5) of the sensor 11 is selected and read from the memory (Step 510). Thus the control valve 34 concerning the speed-changing clutch 2nd is actuated by a current command signal according to the pattern selected. As a result, the oil pressure of the clutch 2nd is gradually increased at the timing t₁ of completion of the filling time in correspondence with the patterns PT1 - PT5 selected, as shown at PT1 - PT5 in Fig. 18 (Step 511). The parts (a) and (b) of Fig. 19 are timing charts respectively illustrating the manner of changes in the torque of the output shaft of the transmission 3 and the pressure of the pre- and post-speed-changing clutches (clutches 1st and 2nd) in cases where the amount of the accelerator operated is large, e.g., where a throttle signal S5 is being outputted from the throttle amount detection sensor 11. The parts (a) and (b) of Fig. 20 are timing charts respectively illustrating the manner of changes in the torque of the output shaft of the transmission 3 and the pressure of the pre- and post-speed-changing clutches (clutches 1st and 2nd) in cases where the amount of the accelerator operated is small, e.g., where a throttle signal S1 is being outputted from the throttle amount detection sensor 11. As shown in the part (b) of Fig. 19, in cases where the amount of the accelerator operated is large (throttle amount S5), the gradual increase pattern PT5 with a high increase rate is selected, and the post-speed-changing clutch 2nd is engaged with a very short time of engagement in accordance with this pattern PT5. Parenthetically, in this case, when the amount of the accelerator operated is large, the initial pressure P₂ is set to a relatively large value, as shown in Fig. 19. On the other hand, in cases where the amount of the accelerator operated is small (throttle amount S1), as shown in the part (b) of Fig. 20, the gradual increase pattern PT1 with a low increase rate is selected, and the post-speed-changing clutch 2nd is engaged for a sufficiently long time in accordance with this pattern PT1. As shown in this Fig. 20, when the amount of the accelerator operated is small, the initial pressure P₂' is set to a relatively small value. In a situation where the brake is being engaged, thermal load acting on the clutch 2nd becomes very large during a speed change regardless of the magnitude of the amount of the accelerator operated. However, since the gradual increase pattern PT6 whose increase rate is slightly lower than that of the gradual increase pattern PT5 with a high increase rate is selected, and the clutch 2nd is engaged for a very short time, the damage caused to the clutch 2nd can be checked to a substantially small level. As described above, in whatever state the amount of the accelerator operated, the state of operation of the brake, and the speed change mode may be, the operator is constantly able to avoid feeling a speed-change shock in terms of his or her sense, and it is possible to improve the durability of speed-changing clutches. It should be noted that in the second mode the arrangement provided is such that a determination is made as to whether or not the brake is being operated, and if it is determined that the brake is being operated, the post-speed-changing clutch is subjected to a gradual increase in accordance with the gradual increase pattern PT6. However, it is naturally possible to provide an arrangement in which the amount of operation of the brake is detected as an analog value or a multiple value, a plurality of gradual increase patterns are set within the range of an oil increase rate corresponding to a case in which the amount of the accelerator operated is large, as illustrated at PT6' in Fig. 18, and a gradual increase pattern with a higher oil pressure increase rate is selected from among the plurality of patterns as the amount of operation of the brake increases, thereby engaging the post-speed-changing clutch with the pattern thus selected. Incidentally, the state of operation of the brake can be determined by detecting the amount of the brake pedal pressed, the pressure of a master cylinder, or the like. In addition, although in the second mode the amount of the accelerator operated is detected on the basis of the amount of the accelerator pedal pressed, instead the pressure within the intake manifold of the engine may be detected, or a rotating angle of a lever of the governor may be detected. In addition, although in the second mode a description has been given of the case where the vehicle weight I is fixed, instead the weight I may be detected, and K' shown in Formula (2) determined in correspondence with a detection value, whereby the gradual increase pattern is set so as to obtain an optimum targeted jerk value corresponding to the K' thus obtained. Furthermore, although gradual increase patterns are stored in advance in the memory and one of them is read when a speed-change command has been given, this operation may be effected by an arithmetic operation. It goes without saying that the present invention is applicable not only to an automatic transmission vehicle but also to a manual transmission vehicle. The present invention is applicable to speed change control of a transmission of a construction vehicle such as a dump truck, a wheel loader, or the like, or a passenger car, and particularly provides a control method and apparatus suitable for reducing a speed-change shock.

Claims: A method for controlling a transmission system which includes a plurality of sub transmission clutches (L,H) in a first stage from an input shaft of a transmission (3), a plurality of main transmission clutches (1st,2nd. 3rd,4th,R) in a second stage and pressure control valves (31,32,33,34,37,36,35) respectively connected to said sub transmission clutches and said main transmission clutches, said transmission system being adapted to select a speed stage through a combination of said sub transmission clutches and said main transmission clutches, wherein said pressure control valves are controlled when said clutches to be engaged are both a sub transmission clutch and a main transmission clutch at the time when a present speed stage is shifted down to a next speed stage with power on, the method comprising the steps of: a) turning off respectively the pressure control valves pertaining to the sub transmission clutch and the main transmission clutch in the present speed stage upon the issuance of a speed-change command; b) starting the supply of pressure oil to the sub transmission clutch in the next speed stage at a point of time when the pressure control valve pertaining to the sub transmission clutch in the present speed stage is turned off, and subsequently controlling the pressure control valve pertaining to the sub transmission clutch in such a manner as to gradually increase the pressure of the sub transmission clutch; c) actuating the pressure control valve corresponding to the main transmission clutch in the next speed stage at an operation start timing when a filling time of the main transmission clutch is completed, at a point of time when the relative number of revolutions of the main transmission clutch becomes zero, so as to supply pressure oil to the main transmission clutch; and d) confirming the completion of the filling time of the main transmission clutch, and subsequently controlling the pressure control valve pertaining to the main transmission clutch in such a manner as to gradually increase the oil pressure of the main transmission clutch. A transmission system which includes a plurality of sub transmission clutches (L,H) in a first stage from an input shaft of a transmission (3), a plurality of main transmission clutches (1st,2nd,3rd,4th,R) in a second stage, and pressure control valves (31,32,33,34,37,36,35) respectively connected to said sub transmission clutches and said main transmission clutches, said transmission system being adapted to select a speed stage through a combination of said sub transmission clutches and said main transmission clutches, wherein the system includes control means (10) for controlling the pressure control valves when said clutches to be engaged are both a sub transmission clutch and a main transmission clutch at the time when a present speed stage is shifted down to a next speed stage with power on, the control means comprising: a) means for turning off respectively the pressure control valves pertaining to the sub transmission clutch and the main transmission clutch in the present speed stage upon the issuance of a speed-change command; b) means for starting the supply of pressure oil to the sub transmission clutch in the next speed stage at a point of time when the pressure control valve pertaining to the sub transmission clutch in the present speed stage is turned off, and subsequently controlling the pressure control valve pertaining to the sub transmission clutch in such a manner as to gradually increase the pressure of the sub transmission clutch; c) means for actuating the pressure control valve corresponding to the main transmission clutch in the next speed stage at an operation start timing when a filling time of the main transmission clutch is completed, at a point of time when the relative number of revolutions of the main transmission clutch becomes zero, so as to supply pressure oil to the main transmission clutch; and d) means for confirming the completion of said filling time of the main transmission clutch, and subsequently controlling the pressure control valve pertaining to the main transmission clutch in such a manner as to gradually increase the oil pressure of the main transmission clutch.

Inventors: OKURA Y KABUSHIKI KAISHA KOMAT, OKURA, Y. KABUSHIKI KAISHA KOMATSU SEISAKUSHO
Applicants: KOMATSU MFG CO LTD, KABUSHIKI KAISHA KOMATSU SEISAKUSHO
Application year: 1989
Main classification: F16H61
IPC codes: F16H61, F16H59, F16H63