Automatic transmission control system

Abstract: In an automatic transmission control system provided for an internal combustion engine (M4) having an automatic transmission system equipped with a traction control system in which a throttle valve (M2) is adjusted towards a closed state from a throttle position corresponding to an operation of an accelerator pedal (M1) when wheel slippage occurs, a detection unit (M6) detects a degree of operation of the accelerator pedal. A shift point changing unit (M6) changes a shift point so that gear shifting occurs on the basis of the degree of operation of the accelerator pedal in a normal state and gear shifting occurs at an engine speed lower than a predetermined engine speed at which gear shifting normally occurs when the degree of operation of the accelerator pedal is equal to or greater than a predetermined value.

Description: BACKGROUND OF THE INVENTION The present invention deals with an automatic transmission control system as shown in the closest prior art according to the US-A-5,047,940. This known system has a traction control system comprising a throttle valve whose degree of opening is set in response to the actuation of an accelerator pedal and which is adjusted in the closed state if the control system detects a slip at one of the wheels. Furthermore the known automatic transmission control systems offers the possibility of changing the shift point in case the traction control system is activated such that a shifting from a lower to a higher gear is already effected at a speed which is lower than that in the case of an inactive transmission control system. In column 2, lines 35 to 40 of the above-mentioned US-A-5047940 it is in this connection described that the known shift characteristic changing means effects the change of the shift point in such a manner that said first shift characteristic is used at the time of ordinary running when no slip control is carried out by said slip control means and that said second shift characteristic is used when slip control is carried out by said slip control means. That is to say that the normal shift point is automatically changed independent of the accelerator pedal position when the slip control means is operated. According to the US-A-5,047,940 the shift point is thus maintained at a lower speed during the whole time of operation of the slip control means so that in the case of these control conditions a maximum acceleration of the vehicle is no longer possible. In view of this state of the art it is the object of the present invention to provide an automatic transmission control system capable of suppressing wheel slippage that occurs when gear shifting is performed and which at the same time renders a maximum acceleration of the vehicle possible. According to the invention, this object is achieved by means of the features of claim 1. Accordingly, the invention has to be seen in that the shift point is changed as claimed in the enclosed claim 1 when the degree of operation of the accelerator pedal is equal to or greater than a predetermined value and when the traction control system is ON. According to this claim 1, the shift point is changed when the degree of operation- of the accelerator pedal is large (equal to or greater than the predetermined value). Hence, even during traction control operation, the shift point is not changed if the degree of operation of the accelerator pedal is small. Thus, according to the claimed invention it is even during traction control possible to maintain the acceleration response which can be obtained during the normal accelerator pedal operation and it is also possible to prevent the occurrence of slippage which may be caused when the accelerator pedal is operated greatly and the engine speed is increased. BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings, in which: Fig. 1 is a block diagram illustrating an overview of the present invention; Fig. 2 is a diagram illustrating the entire structure of a vehicle to which an automatic transmission control system according to an embodiment of the present invention is applied; Figs. 3 and 4 are flowcharts of a basic control process of a traction control; Fig. 5 is a flowchart of a process for setting a main throttle valve opening ratio executed by an EFI unit of a control unit shown in Fig. 2; Fig. 6 is a block diagram of a process for setting the main throttle valve opening ratio; Fig. 7 is a graph showing how up-shifting is performed with respect to the throttle valve opening ratio and the vehicle speed; Fig. 8 is a flowchart of a gear shifting process executed by an ECT unit of the control unit shown in Fig. 2; and Fig. 9 is a flowchart of a variation of the process for setting the main throttle valve opening ratio executed by the EFI unit. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 illustrates an overview of the present invention. An automatic transmission control system that controls an automatic transmission M5 includes an accelerator pedal M1, a throttle valve M2, a valve control unit M3, and a shift point change unit M6. M4 denotes an internal combustion engine. The shift point change unit M6 changes the shift point towards a low engine speed when the quantity of depression (degree of operation or setting) of the accelerator pedal M1 becomes equal to or greater than a threshold value. Hence, wheel slippage can be prevented when the accelerator pedal M1 is deeply depressed. The automatic transmission performs shift control on the basis of the opening ratio of the throttle valve M2 and the vehicle speed. It will now be assumed that the vehicle is traveling on a slippery road (low-µ road) like an iced road while the traction control (TRC) is ON and the throttle valve M2 is maintained in the closed state. When the driver depresses the accelerator pedal M1, the engine speed increases but the driving force is not transferred to the road because of wheel slippage. Hence, the vehicle speed does not increase. Since gear shifting is based on the opening ratio of the throttle valve and the vehicle speed, the engine speed increases to a high value until the vehicle speed reaches the shift point while the vehicle is traveling on the slippery (low-µ) road. When up-shifting occurs in the above state, the engine speed greatly decreases to the speed defined by a gear selected by the up-shifting. Hence, the driving wheels slip a great deal on the road and the behavior of the vehicle becomes extremely unstable. According to the present invention, the shift point change unit M6 changes the shift point towards a low engine speed when the amount of operation of the accelerator pedal M1 becomes equal to or greater than the threshold value. Hence, the gear shifting occurs before the engine speed reaches a value causing a large amount of wheel slippage. Hence, wheel slippage because of gear shifting, particularly when the vehicle is traveling on a slippery road, can be prevented, and stable driving can be obtained. A description will now be given of an embodiment of the present invention with reference to Fig. 2 which illustrates the entire structure of a vehicle equipped with a control system for an automatic transmission. An internal combustion engine 10 is mounted on a vehicle 1. Driving wheels 3a and 3b are driven by the engine 10 through an automatic transmission 5 and a drive shaft 26. The vehicle 1 also has idler wheels 4a and 4b. Wheel speed sensors 22a, 22b, 24a and 24b for respectively detecting wheel speeds of the driving wheels 3a and 3b and the idler wheels 4a and 4b are provided for these wheels. A main throttle valve 14 responding to a driver's operation of an accelerator pedal 12 is provided in an air intake passage of the internal combustion engine 10. A sub-throttle valve 16 is fastened to the intake air passage and located on the upstream side of the main throttle valve 14. The sub-throttle valve 16 is driven by a stepping motor 18. A control unit 30 includes two integrated digital computers. One of the two digital computers functions as an electronic fuel injection (EFI) unit, and the other digital computer functions as an automatic transmission control (ECT) unit. The EFI unit performs fuel injection control and ignition timing control. The ECT unit performs shifting control of the automatic transmission 5. The control unit 30 receives, as the EFI unit, a sensor output signal of an engine speed sensor 32, a sensor output signal of a main throttle valve opening ratio sensor 34, and a sensor output signal of a sub-throttle valve opening ratio sensor 36. Further, the control unit 30 receives desired sensor output signals of other sensors necessary for engine control as in the case of conventional engines. The control unit 30 is connected to a fuel injection valve 38 and an igniter 40. The control unit 30 controls the quantity of fuel injection and the ignition timing via the fuel injection valve 38 and the igniter 40. The control unit 30 controls, as the ECT unit, the shift point most suitable for the current driving conditions on the basis of a sensor output signal of a vehicle speed sensor 35 and data indicating a main throttle valve opening ratio  MG from the EFI unit. The system shown in Fig. 2 includes an acceleration slip control unit (traction control unit: TRC unit) 50. The TRC unit 50 is formed with a digital computer, and is supplied with the sensor output signal of the engine speed sensor 32 and the sensor output signals of the main and sub-throttle valve opening ratio sensors 34 and 36 in order to perform the traction control. Further, the TRC unit 50 controls the opening ratio of the sub-throttle valve 16. Furthermore, the TRC unit 50 is connected to the control unit 30, and outputs a signal FS, a fuel cut signal and an ignition timing delay angle signal to the control unit 30. The FS signal indicates whether or not the TRC is being performed. The present embodiment carries out driving torque control by controlling the opening ratio of the sub-throttle valve 16 on the basis of slippage of the driving wheels 3a and 3b. The sub-throttle valve opening ratio  s(n) is controlled based on a slip quantity ΔV of the driving wheels 3a and 3b, and is written as follows:  s(n) =  s(n-1) + (d s /dt) x T 0 (d s /dt) = K 1 x ΔV + K 2 x K 3 x ΔG where  s(n-1) denotes the sub-throttle opening ratio used in the previous computation, and T 0 denotes a computation executing period. Further, K 1 , K 2 and K 3 are respectively positive constants, and ΔV is the difference between a target driving wheel speed V S obtained from a vehicle speed (idler wheel speed) V B , and the actual driving wheel speed V D . In the present embodiment, the slip quantity ΔV is defined as V S - V D . In equation (2), ΔG is the difference between the ratio of variation of the vehicle speed V R and the rate of variation of the driving wheel speed V D , that is, |(dV R /dt) - (dV D /dt)|. A description will now be given, with reference to Figs. 3 and 4, of a basic operation of the traction control according to the embodiment of the present invention. Figs. 3 and 4 show a basic routine of the traction control performed by the TRC unit 50. The basic routine is repeatedly executed with a repetition period of, for example, 12msec. In step 100, the TRC unit 50 determines whether or not a TRC execution condition is satisfied. In the embodiment of the present invention, the main throttle valve is not completely closed and the sensors operate normally when the TRC execution condition is satisfied. When it is determined, in step 100, that the TRC execution condition is not satisfied, the TRC unit 50 executes step 154, in which step all flags are reset and  smax (full throttle) is set as the sub-throttle valve opening ratio  s . Then, the TRC unit 50 ends execution of the routine. When it is determined, in step 100, that the TRC execution condition is satisfied, the TRC unit 50 computes the vehicle speed V R as follows: V R = (1/2)(V FR + V FL ) where V FR and V FL respectively denote the wheel speeds of the idler wheels 4a and 4b. In step 104, the TRC unit 50 calculates the target driving wheel speed V S in the following manner: [1] V S = V R + 2.4km/h when V R ≤ 30km/h [2] V S = (V R x 1.08)km/h when 30km/h < V R ≤ 100km/h [3] V S = MIN[(V R x 1.08)km/h, (V R + 10)km/h] when 100km/h < V R where MIN[x, y] is equal to x when x < y and is equal to y when y < x. The target driving wheel speed V S is selected so that it is always greater than the vehicle speed V R and a predetermined slip occurs in the driving wheels. It can be seen from the above [1] - [3] that a target slip ratio (V S - V R )/V R is set to a large value and the acceleration characteristic can be improved when the vehicle speed is low. When the vehicle speed is high, V S = V R + 10km/h and the slip ratio is set low, so that the straight line stability can be improved. In step 106, the TRC unit 50 sets a control starting speed V TB of the traction control. The control starting speed V TB is calculated as follows: V TB = V S + β where β is a constant for making the control starting speed greater than the target driving wheel speed V S by β in order to prevent frequent TRC control. More particularly, the constant β is set between 2.0km/h and 4km/h on the basis of the road surface condition. In step 108, the TRC unit 50 calculates the driving wheel speed V D by the following equation: V D = (1/2)(V DR + V DL ) where V DR and V DL respectively denote the wheel speeds of the driving wheels 3a and 3b. After determining the speed parameters in steps 102 - 108, the TRC unit 50 determines whether or not the flag FS is equal to 1. When FS = 0, the traction control is not started. In this case, the TRC unit 50 executes step 112 in which step it is determined whether V D > V TB in order to determine whether or not the traction control might be needed. When it is determined, in step 112, that the control starting speed V TB is equal to or higher than the driving wheel speed V D , the TRC unit 50 determines that the traction control is not needed and executes step 154 (Fig. 4) in which flags FS, FFBS and CEND are reset to zero, and the aforementioned  smax (full throttle) is set as the sub-throttle valve opening ratio  s . When it is determined, in step 112 that the driving wheel speed V D is higher than the control starting speed V TB , the TRC unit 50 sets the flag FS to 1 in step 114. Then, the TRC unit 50 sets the subthrottle valve opening ratio  s to an initial target opening ratio f (NE) in step 116, and resets the flag FFBS to zero in step 118, the flag FFBS being an initial feedback control inhibit flag. Then, the TRC unit 50 ends execution of the routine. The initial target opening ratio f (NE) of the sub-throttle valve 16 is selected on the basis of the engine speed NE and the road surface conditions. The sub-throttle valve 16 is maintained in the full-throttle state when the traction control is not performed. Hence, when feedback control is started in the full-throttle state of the sub-throttle valve 16, it takes a long time to respond to a variation in the sub-throttle valve opening ratio. With the above in mind, in step 116, the sub-throttle valve 16 is closed up to an opening ratio ( s ) at which a response appears, at the same time as the traction control is started, and then the feedback control is started. The initial feedback control inhibit flag FFBS is set to 1 when a predetermined requirement is satisfied after the traction control is started. When steps 112 - 118 have been executed until the previous execution of the routine, that is, until FS = 1, the TRC unit 50 executes step 132 in which step it is determined, on the basis of the signal from the sub-throttle valve opening ratio sensor 36, whether or not the sub-throttle valve 16 has been closed to the initial target opening ratio  s . When the result of step 132 is negative, the TRC 50 ends execution of the routine. When the result of step 132 is YES, the TRC unit 50 executes step 134 in which step a feedback control inhibit flag FFBI is set to 1. In step 136 (Fig. 4), the TRC unit 50 determines whether or not the feedback inhibit flag FFBI is equal to 1. When the result of step 136 is YES, the TRC unit 50 ends execution of the routine. The feedback inhibit flag FFBI is a flag set in a shift-up control performed by the ECT unit of the control unit 30. More particularly, the feedback inhibit flag FFBI is set to 1 at the time of shift control by the ECT unit. When the ECT unit performs the shift-up control by the step-136 process, execution of the basic control routine (feedback control after step 140) with respect to the sub-throttle valve 16 is inhibited. In step 138, the TRC unit 50 determines whether or not the initial feedback control inhibit flag FFBS is equal to 1. The feedback control from step 140 controls the sub-throttle valve opening ratio  s . When the result of step 138 is NO, the TRC unit 0 ends execution of the routine without executing steps 140 - 154. When the result of step 138 is YES, the TRC unit 50 executes step 140 from which step the feedback control of the sub-throttle valve opening ratio  s is started. When it is determined, in step 138, that FFBS = 1, the TRC unit 50 determines a control quantity Δ s with respect to the sub-throttle opening ratio. In step 142, the TRC unit 50 determines the target sub-throttle valve opening ratio  s by  s =  s(n-1) + Δ s , and outputs a signal corresponding to the determined valve opening ratio  s to the stepping motor 18 for driving the sub-throttle valve 16. The traction control is continued while a condition remains satisfied and as long as a predetermined time has not elapsed. The above condition is such that the sub-throttle valve opening ratio  s is greater than the main throttle valve opening ratio  M (step 144), and the absolute value of the slip quantity |V S - V D | is less than a predetermined value d (step 146). The above-mentioned predetermined time is measured by using a parameter CEND, which is incremented by 1 in step 148. In step 150, the TRC unit 50 determines whether or not the value of the parameter CEND is greater than D where D is the above-mentioned predetermined time. When it is determined, in step 150, that the traction control should be terminated (when the result of step 150 is affirmative), the flags FS, FFBS and CEND are reset to zero, and the sub-throttle valve opening ratio  s is set to  smax (full-throttle state) in step 154. The control unit 30 is informed of the value of the flag FS set in step 114 (Fig. 3). A description will now be given of a setting process for the main throttle valve opening ratio  M carried out by the EFI unit of the control unit 30, by referring to Fig. 5. As has been described previously, the EFI unit of the control unit 30 is supplied with information indicating the engine speed NE, the main throttle valve opening ratio  M , and the sub-throttle valve opening ratio  s and other sensor signals necessary for engine control. The control unit 30 performs the fuel injection control and the ignition timing control using the above information and sensor signals. The ECT unit of the control unit 30 controls the shift point most suitable for the current driving conditions on the basis of the vehicle speed SPD indicated by the vehicle sensor 35 and a coded stepwise main throttle valve opening ratio  MG . The process shown in Fig. 5 is carried out in synchronism with the basic control routine of the traction control shown in Figs. 3 and 4 with a period of 12msec. In step 200, the control unit 30 obtains the main throttle valve opening ratio  M from the output signal of the main throttle valve opening ratio sensor 34, and carries out a Gray code conversion operation on the valve opening ratio  M , so that the coded main throttle valve opening ratio  MG can be obtained. For the sake of simplicity, the main throttle valve opening ratio (0% - 100%) is converted into one of nine steps between  0 (0%) and  8 (100%). After calculating the current coded main throttle valve opening ratio  MG , the control unit 30 determines, in step 202, whether or not the traction control is being performed. This determination is performed by referring to the traction control execution flag FS (step 114 shown in Fig. 3) controlled by the TRC unit 50. When it is determined, in step 202, that the traction control is not being performed, the EFI unit of the control unit 30 executes step 208 and informs the ECT unit thereof of the coded main throttle valve opening ratio  MG calculated in step 200. When it is determined, in step 202, that the traction control is not being performed, the EFI unit of the control unit 30 executes step 208 in which step the ECT unit of the control unit 30 is informed of the main throttle valve opening ratio  MG . When it is determined, in step 204, that the current main throttle valve opening ratio  MG is equal to a valve opening ratio at which slip because of gear shifting may occur, in other words, it is determined that  MG is an upper guard value A%, the control unit 30 executes step 206 in which step a main throttle valve opening ratio  MG-1 lower than the actual main throttle valve opening ratio  MG by one step is determined as the current main throttle valve opening ratio  MG . The above process will be described in detail with reference to Fig. 6. It will be assumed that the coded actual main throttle valve opening ratio  MG obtained in step 200 is  7 and the upper guard value A% is determined as shown in Fig. 6. It can be seen from Fig. 6 that the actual main throttle valve opening ratio  7 is greater than the upper guard value A%. Hence, in step 206, the main throttle valve opening ratio  6 lower than the main throttle valve opening ratio  7 by one step is set as the main throttle valve opening ratio  MG . In step 208, the ECT unit is informed of the main throttle valve opening ratio  MG determined in the above manner. When the result of step 204 is negative, that is, when it is determined that the current main throttle valve opening ratio  MG does not cause wheel slippage due to gear shifting, the steps 204 and 206 are not executed, and the ECT unit is informed of the read main throttle valve opening ratio  MG . The gear shifting process carried out by the ECT unit will be described with reference to Figs. 7 and 8. Fig. 7 shows up-shifting as a function of the throttle valve opening ratio and the vehicle speed. The ECT unit of the control unit 30 performs the gear shifting process on the basis of the diagram of Fig. 7. Fig. 8 is a flowchart of the gear shifting process performed by the ECT unit 30. The flowchart of Fig. 8 relates to a case where the gear is shifted from the first gear to the second rear. When the gear shifting process shown in Fig. 8 is started, the ECT unit of the control unit 30 is informed of the main throttle valve opening ratio  MG sent from the EFI thereof in step 300. As has been described previously, the main throttle valve opening ratio  MG input in step 300 is equal to the main throttle valve opening ratio lower than the actual main throttle valve opening ratio by one step when the actual main throttle valve opening ratio is higher than the upper guard value A%. Further, the main throttle valve opening ratio  MG input in step 300 is equal to the actual main throttle valve opening ratio when it is not higher than the upper guard value A%. In the following description, the following will be assumed. The main throttle valve opening ratio  MG input in step 300 is equal to  7 , which is higher than the upper guard value A%. Hence, by the process of steps 204 and 206, the main throttle valve opening ratio  MG is set equal to  6 . In step 302, the ECT unit of the control unit 30 determines whether or not the vehicle speed SPD indicated by the sensor output signal of the speed sensor 35 is equal to or greater than a threshold vehicle speed V 1 . When the vehicle speed is equal to or greater than the threshold speed V 1 , the ECT unit executes step 304 in which step it is determined that the current gear shift position is at the first gear. When it is determined that the current shift position is at the first gear, the ECT unit executes step 306 in which step the ECT unit performs the up-shifting process from the first gear to the second gear. As has been described previously, the ECT unit performs the gear shifting process on the basis of the main throttle valve opening ratio  MG sent from the EFI. More particularly, in the setting process of the main throttle valve opening ratio  MG by the EFI unit, when the actual main throttle valve opening ratio  MG is higher than the upper guard value A%, data indicating the main throttle valve opening ratio  MG-1 lower than the actual one by one step is sent to the ECT unit. By way of example, in the ECT gear shifting process shown in Fig. 8, if the actual main throttle valve opening ratio  7 is used without any change, up-shifting from the first gear to the second gear is performed when the vehicle speed SPD is equal to a speed V 2 , as shown in Fig. 7. On the other hand, according to the present embodiment, the main throttle valve opening ratio  6 lower than the actual main throttle valve opening ratio  7 is used instead of the actual main throttle valve opening ratio  7 . Hence, up-shifting from the first gear to the second gear is performed when the vehicle speed SPD is equal to V 1 (V 2 > V 1 ). Hence, according to the present embodiment, up-shifting is made at an engine speed which is lower than the conventional engine speed (corresponding to V 2 ) by an engine speed corresponding to the difference between the vehicle speeds V1 and V2. The above up-shifting process is equivalent to a process in which the shifting point is changed towards the low-engine-speed side. As described above, according to the present embodiment, the shift point of the up-shifting process is changed to the low-engine-speed side when the degree of depression of the accelerator pedal 12 is equal to or greater than the threshold value and the main throttle valve opening ratio  MG is higher than the upper guard value A%. Hence, the engine speed can be reduced when up-shifting is made, and the unstable behavior of the vehicle due to gear shifting performed when the vehicle is traveling on a slippery (low-µ) road can be effectively prevented. When the traction control is not being performed and the main throttle valve opening ratio  MG is less than the upper guard value A%, there is little influence of wheel slippage due to gear shifting. In this case, the gear shifting is made on the basis of the actual main throttle valve opening ratio  MG . Hence, the engine 10 responds to manipulation of the accelerator pedal 12 until the degree of depression of the accelerator pedal 12 by the driver exceeds the upper guard value A%. Hence, the driver does not feel uncomfortable. In step 206 shown in Fig. 5, the main throttle valve opening ratio  MG-1 lower than the actual main throttle valve opening ratio  MG by one step is used instead of the valve opening ratio  MG when the actual valve opening ratio  MG exceeds the upper guard value A%. For example, when the actual main throttle valve opening ratio  MG is  8 ,  7 is used instead of  8 , and when  MG is  7 ,  6 is used instead of  7 . It is possible to employ step 206A shown in Fig. 9 instead of step 206 shown in Fig. 5. In step 206A, when the actual main throttle valve opening ratio  MG exceeds the upper guard value A%, the main throttle valve opening ratio to be used is set to a predetermined constant ratio  TH without exception. By using the predetermined constant ratio  TH , the occurrence of wheel slippage can be effectively prevented, particularly when the degree of depression of the accelerator pedal 12 is great. The up-shifting process from the first gear to the second gear in the state in which the main throttle valve opening ratio is  6 was explained with reference to Fig. 8. The up-shifting process with respect to other gear shifting and other main throttle valve opening ratios will be carried out in the same manner as has been explained previously. In the aforementioned embodiment, the constant upper guard value A% is used. Alternatively, it is possible to change the upper guard value in accordance with the slip ratio (V S - V R )/V R . In this case, it will be convenient to use a table mapping slip ratios and suitable upper guard values. In the aforementioned embodiment, the shift point is changed to a shift point lower than the normal shift point during execution of the traction control. Alternatively, it is possible to use a first shift point map to be used when the traction control is OFF and a second shift point map to be used when the traction control is ON and to select either the first shift point map or the second shift point map. In order to perform the traction control, the wheel speed sensors 22a and 22b are provided for the driving wheels 3a and 3b, respectively. Alternatively, it is possible to use, instead of the wheel speed sensors 22a and 22b, a single revolution speed sensor for detecting the revolution of the drive shaft 26. By using the above single revolution speed sensor, the number of sensors used can be reduced, and it is no longer necessary to take into account the difference between the right wheel speed and the left wheel speed. In the previously described embodiment, the engine 10 is equipped with the main throttle valve 14 and the sub-throttle valve 16. However, the present invention can be applied to an engine in which the traction control is performed using a single throttle valve provided for the engine. In this case, the quantity of depression of the accelerator pedal 12 is used as the main throttle opening ratio, and the main throttle valve opening ratio is used as the sub-throttle valve opening ratio. The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention.

Claims: An automatic transmission control system provided for an internal combustion engine (M4) having an automatic transmission system equipped with a traction control system in which a throttle valve (M2) is adjusted towards a closed state from a throttle position corresponding to the operation of an accelerator pedal (M1) when wheel slippage occurs, said automatic transmission control system comprising: detection means (M6) for detecting a degree of operation of the accelerator pedal and shift point changing means (M6) coupled to said detection means so that gear shifting occurs on the basis of the degree of operation of the accelerator pedal (12) in a normal state and gear shifting occurs at an engine speed lower than a predetermined engine speed at which gear shifting normally occurs when the degree of operation of the accelerator pedal is equal to or greater than a predetermined value wherein first means are provided for determining whether or not the traction control is ON and second means are provided for allowing the shift point changing means to change the shift point when the first means concludes that the traction control is ON. The automatic transmission control system as claimed in claim 1, characterized in that said shift point changing means (M6) comprises first means for changing the shift point on the basis of a degree of operation of the accelerator pedal (M1) less than the degree of operation thereof actually detected when the degree of operation of the accelerator pedal (M1) is equal to or greater than the predetermined value. The automatic transmission control system as claimed in claim 1, characterized by further comprising: a first throttle valve (14) cooperating with the accelerator pedal (M1); a second throttle valve (16); and driving means (18) for driving the second throttle valve (16) when the wheel slippage occurs, and in that said detection means comprises first means (34) for detecting a throttle valve opening ratio of the first throttle valve (14) as the degree of operation of the accelerator pedal (M1). The automatic transmission control system as claimed in claim 4, characterized in that said shift point changing means (M6) comprises: second means for converting the throttle valve opening ratio detected by said first means (34) into one of predetermined stepwise throttle valve opening ratios; and third means for selecting one of the predetermined stepwise throttle valve opening ratios which is one step lower than one of the predetermined stepwise throttle valve opening ratios that corresponds to the throttle valve opening ratio detected by said first means (34).

Inventors: UCHIDA KIYOYUKI, YAGI YOSHIFUMI, UCHIDA, KIYOYUKI, YAGI, YOSHIFUMI
Applicants: TOYOTA MOTOR CO LTD, TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1993
Main classification: F16H61
IPC codes: F02D29, B60W10, F16H61, F16H59, B60K28, B60W30