Control system for vehicle with automatic transmission

Abstract: A control system for a vehicle including an automatic transmission provided with multiple transmission gear mechanism in which a specific gear stage of a speed ratio is automatically established among a plurality of gear stages in accordance with an vehicle operating condition, shift control signal producing device for producing a shift control signal in order to make a shift operation between different gear stages in accordance with the vehicle operation condition, engine output control device for reducing an engine output in synchronism with the shift operation so as to suppress a torque shock due to the shift operation, detecting device for detecting a specific vehicle operation condition in which a change in a time lag between a generation of the shift control signal and an actual initiation of the shift operation in the transmission is greater than a predetermined level and for producing a signal denoting the specific vehicle operating condition, and restricting device for restricting the engine output control device from reducing the engine output when said specific vehicle operating condition is detected. The torque shock due to the shift operation can be effectively suppressed.

Description: BACKGROUND OF THE INVENTION Field of the invention The present invention relates to a control system for an internal combustion engine of a vehicle according to the preamble of claim 1 (EP-A-0 228 899). Description of the prior art In a vehicle provided with an automatic transmission, there have been various proposals for reducing a torque shock or jolt through a shift operation from one gear stage to another in the automatic transmission. In a control system disclosed in U.S. Patent No. 4,266,447, an ignition timing of the engine is controlled in accordance with a vehicle speed as a shift operation occurs so that an engine output power or torque is changed to reduce the torque shock due to the shift operation. U.S.Patent Nos. 4,355,550, 4,370,903 and 4,403,527 disclose similar control systems. In controlling the engine output during the shift operation, it should be noted that there is produced a time lag from a generation of a control signal for the shift operation to an actual initiation of the shift operation. In order to reduce the torque shock due to the shift operation effectively, it is desirable that the engine output control is made corresponding to the actual shift operation. In view of this, the conventional ignition timing output control is adapted to initiate the control of the engine output torque after a predetermined time period from the generation of the control signal for the shift operation so that the engine output control occurs in synchronism with an actual shift operation. It should however be noted that the time lag from the generation of the control signal for the shift operation to the actual initiation of the shift operation varies depending on a vehicle operating condition such as engine speed, engine load defined such as a throttle opening, intake gas amount and the like, line hydraulic pressure in the transmission, gear stages involved in the shift operation and the like. Specifically, a viscosity of a hydraulic fluid or oil in the transmission affects greatly the time lag since the shift operation is made in a manner that a specific gear stage is established by switching a power transmitting path in the transmission by virtue of the hydraulic fluid. Thus, where the viscosity of the hydraulic fluid is high, the shift operation may take long and become unstable. As a result, the engine output control may not correspond to the actual shift operation. This means that the torque shock due to the shift operation cannot be suppressed effectively because of the untimely engine output control. Moreover, the engine output control may deteriorate controllability (for example an acceleration property ) of the vehicle under the vehicle operating condition where the temperature of the hydraulic fluid is low. From the EP-A-0 228 899 a system is known for integrally controlling an automatic transmission and an engine, wherein gear stages are automatically switched in accordance with a preset shift map, and an engine torque is changed by a predetermined change value during shifting to thereby maintain satisfactorily shift characteristics, said system comprising means for detecting operating temperatures of said engine and wherein upon detection of a low operating temperature of said engine, conditions are determined to exist in said determining means such that said engine torque cannot be changed. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a control system which can accomplish an improved controllability of a vehicle with an automatic transmission even where the vehicle is in an operating condition where a time lag between a shift control signal for the transmission and an actual shift operation varies greatly. It is another object of the present invention to provide a control system which can suppress a torque shock due to a shift operation of an automatic transmission effectively. The above and other objects of the present invention can be accomplished by a control system for a vehicle with the features of claim 1. Preferably, the engine output control means is constituted by ignition timing control means for controlling an ignition timing of the engine. More specifically, the ignition timing control means retards the ignition timing in response to the shift operation. According to the present invention, a retard control signal for retarding the ignition timing is produced after a predetermined time period from a generation of a shift control signal for effecting the shift operation. Typically, a final ignition timing is calculated in accordance with a basic ignition timing which is determined based on an engine operating condition defined by such as engine speed, engine load, engine temperature and the like, a shift compensating value which is determined to reduce a torque shock due to the shift operation, and a knock compensating value which is determined to eliminate an engine knocking. The final ignition timing is compensated by a greater one of the shift compensating value and the knock compensating value. According to the present invention, the engine output control is restricted or not carried out under a vehicle operation condition where the viscosity of the hydraulic fluid in the transmission is relatively high. The viscosity will be known by detecting a running distance after starting the engine in the current driving operation. The above and other features of the present invention will be apparent from the following description taking reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of a power plant of a vehicle with an automatic transmission to which an engine control system in accordance with the present invention can be applied; Figure 2 is a flow chart of a shift control in a transmission control unit; Figure 3 is a flow chart of an ignition timing control in an engine control unit; Figure 4 is a flow chart of a procedure for obtaining a knocking retard angle in the engine control unit; Figure 5 is a graphical representation showing a time chart in the ignition timing control; Figure 6 is a graphical representation showing a conceptual view of a shift operation; Figure 7 is a flow chart of a shift control in the transmission control unit similar to Figure 2 but not part of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Hereinafter there will be described preferred embodiments of the present invention taking reference with drawings. Referring specifically to Figure 1, there is shown a schematic view of a power plant of a vehicle to which the present invention can be applied. The power plant is provided with an engine 1 and an automatic transmission 2. The transmission 2 is connected with at one end with the engine 1 through a torque converter 2a. The transmission 2 is connected at the other end with a wheel 8 through a propeller shaft 9 so that an engine output power or torque is transmitted to the wheel 8 with a predetermined speed ratio. An igniter 3 is connected with respective four cylinders of the engine 1 for providing ignition plugs 12 with firing signals. The transmission 2 is provided with a multiple transmission gear mechanism therein for establishing a plurality of shift gear stages automatically in accordance with a vehicle operating condition defined by an engine speed, an engine load obtained through such as throttle opening, a gear stage, an acceleration of the vehicle and the like. For this purpose, the transmission 2 is provided with shift solenoid valves 4, 5 and 6 which are adapted to control a hydraulic pressure for operating frictional elements therein so as to switch a power transmitting path of the gear mechanism. The transmission 2 is also provided with a lock-up control solenoid valve 7 for controlling an engagement and disengagement of a lock-up clutch provided in the torque converter 2a. Internal structure of the transmission 2 and a hydraulic circuit for controlling the transmission 2 including the solenoid valves 4, 5 and 6 are well known as shown in U.S.Patent No. 4,779,491. In order to control operation of the engine 1, there is provided an engine control unit 10 constituted by a microcomputer. The engine control unit 10 receives as control factors a crank angle, throttle valve opening, engine temperature, braking signal denoting braking operation of the vehicle, knocking signal denoting an engine knock and produces engine control signal such as an ignition signal. Likewise, in order to control operation of the transmission 2, there is provided with a transmission control unit 11. The transmission control unit 11 receives as control factors the throttle valve opening, vehicle speed, engine temperature, position of a shift lever showing a shift range currently selected, and the like. The transmission 2 controls the shift solenoid valves 4, 5 and 6 for carrying out a shift operation in which the gear stage of the multiple transmission gear mechanism is changed from one to another in accordance with a predetermined shift control map. General functions of the engine control unit 10 and the transmission control unit 11 are conventionally well known and they are not relevant to the features of the present invention so that the detailed explanation thereto are omitted. A shift control signal from the transmission control unit 11 for controlling the shift solenoid valves 4, 5 and 6 is also supplied to the engine control unit 10. The engine control unit 10 receives the shift control signal and produces an ignition control signal for retarding an ignition timing in response to the shift operation so that the engine output torque is reduced during the shift operation of the transmission. Hereinafter, there is described a retard control of an ignition timing in which the ignition timing is retarded in response to the shift operation. Referring to Figure 2, a retard control of the ignition timing of the engine is shown. Steps S1-6 relate to a control for judging as to whether or not the engine output should be controlled in accordance with a running distance of the vehicle after starting driving operation in the current running operation. Steps S7-20 relate to a procedure for confirming whether or not the engine output control is preferably to be actually initiated in light of a time lag between the generation of the shift operation signal and an actual start of the shift operation. Steps S21-29 relate to a control for producing a retard control signal to the igniter 3 so as to retard the ignition timing for thereby reducing the engine output. The retard control signal is not produced to retard the ignition timing to reduce the engine output until a change in the time lag between the generation of the shift operation signal and the actual start of the shift operation in the transmission 2 becomes small in view of the running distance, or a transmission oil temperature as a result that the transmisison oil is warmed up enough to provide a consistent time lag for the shift operation. In control, the transmission control unit 11 resets a flag XOIL for denoting allowance of the retard control (S1). Then the transmission control unit 11 reads a throttle valve opening TVO and the vehicle speed (S2). The transmission control unit 11 detects the running distance of the vehicle so as to detects the oil temperature in the transmission 2 indirectly and to judge whether or not the judges whether or not the shift operation is ready to be made (S4). If the judgment is No or the running distance is less than a predetermined value (for example 3 Km), the transmission control unit 11 keeps the flag XOIL=0 and reads the shift control map (S5). In this case, the retard control is not carried out. On the other hand, when a cumulative number of the pulse denoting the vehicle speed is more than a predetermined value and it is found that the running distance exceeds the predetermined value, the oil temperature is deemed to be warmed up enough to provide a stable shift operation. In this case, the transmission control unit 11 judges that the retard control is ready to be initiated and sets the flag XOIL at a value of 2 (S6). The flag XOIL is increased when the shift operation from 1-2 or 2-3 stages occurs, when the time lag TOIL is less than a predetermined value and when the shift operation is made smoothly within a predetermined time period. In step S7, the transmission control unit 11 judges whether or not the shift operation is to be made in light of the shift control map stored in a memory thereof (S7). If the judgment is No or, the shift operation is not to be made or the shift operation is being made, the control is returned to the starting step without any control. If the judgment is Yes or the shift operation is to be made, the transmission control unit 11 produces the shift control signals to the shift control solenoid valves 4, 5 and 6 to carry out the shift operation (S8). In this case, if the shift operation occurs between 1-2 stages or 2-3 stages, a shift flag XTIM is set at a value 1 (S11). If the shift operation occurs between two gear stages other than the 1-2 or 2-3, the shift flag is set at a value of 0 (S10). In this case, the control is returned to the starting step because the flag XOIL takes the value of 0 (S20) and goes to step S7. In step S7, it is judged that the shift operation is being made. This means that the judgment in step S7 is No. Therefore, the proceeding goes to the starting step again through the steps S12 due to the flag XOIL =0, S13 due to the flag XTIM=0 and S25. On the other hand, if the shift operation occurs between the 1-2 or 2-3 stages, the flag XTIM takes the value of 1 and the flag XOIL takes the value of 0 so that the proceeding reaches step S7 again. In this case, the proceeding is advanced to step S14 because of the flag XOIL=0 (S12) and the flag XTIM=1 (S13). In step S14, the transmisison control unit 11 judges whether or not the shift operation is actually initiated. In detail, when the shift operation is made between the 1-2 or 2-3 stages, the shift control signal is produced so that the solenoid valves 4, 5 and 6 are actuated. In this case, it takes a certain time lag before the oil or hydraulic fluid in the transmission moves frictional element such as clutches to actually initiate the shift operation. In the course of the shift operation, the engine speed (turbine speed) changes as shown in Figure 6. When the accelerating operation is made by kicking an acceleration pedal down to increase the stroke thereof so as to increase the engine speed, the transmission control unit 11 produces the shift control signal to the solenoid valves 4, 5 and 6 in light of the shift control map. In this case, the engine speed continues to be increased for a certain time period after the shift control signal is produced. When the shift operation is actually initiated, the engine speed begins to be reduced. The engine speed is finally controlled to a value in accordance with a gear ratio of the gear stage selected as shown in Figure 6. Where the shift operation is not initiated or an engine speed change dTREV is not a negative value, the time lag TOIL between the generation of the shift operation signal and the actual initiation of the shift operation is increased (S19). This proceeding continues until the engine speed change dTREV takes a negative value. In step S15, the value of the time lag TOIL is compared with a predetermined time period. If the time lag TOIL is greater than the predetermined value, that is when it takes long before the actual initiation of the shift operation, the flag XOIL is reset (S18). Then, the proceeding is returned to the starting step through the step S20. On the other hand, where the time lag TOIL is smaller than the predetermined value or where the shift operation is deemed to be smoothly and stably made, the flag XOIL is increased and the proceeding is returned to the starting step through step S17. This proceeding is carried out repeatedly until the flag XOIL takes the value of 2 ( until the shift operation between the 1-2 or 2-3 is completed smoothly and stably at least twice in series). Once the retard control is deemed from the above procedure to be conditioned for being started, the retard control is carried out unless a prohibiting condition is established as enumerated in step S22, S23 and S24. In proceeding the procedure for carrying out the retard control, the transmission control unit 11 sets a retard control counter T at a value zero (S21). The retard control counter T is provided for deferring a start of the retard control of the ignition timing by a predetermined time period after the shift control signal is generated. When the shift operation is to be a down shift from a fourth stage to a third stage, the retard control is not carried out because this down shift operation does not cause a serious torque shock inherently (S22). When the throttle opening is less than one-eighth, the retard control is not carried out because it may cause an ignition fail (S23). Further, when the braking operation is made (a brake switch is On), the retard control of the ignition timing is not carried out (S24). In the case where the retard control is carried out, the transmission control unit 11 increases the value of the timer T (S26) until the value attains a predetermined value (S27). When the value of the timer T reaches the predetermined value, the transmission control unit 11 produces the retard control signal (S28). In step S29, the value of the timer T is reset. Meanwhile, once the flag XOIL reaches the value of 2, the steps S14-S19 are skipped. Thus, the proceeding goes from the step S12 or S13 to the step S25. Hereinafter, there is described the retard control by the engine control unit 10. Referring to Figure 3, the engine control unit 10 receives as control factors the engine speed, the engine load (throttle opening) and the engine temperature (engine coolant temperature)(Q1) and determines a basic ignition timing ϑB (Q2). According to the illustrated embodiment, a retard angle ϑATR in the ignition timing is determined (Q8) in light of a map (not shown) stored therein when the engine temperature is higher than a predetermined value (72°C in this embodiment) (Q3), the throttle valve opening TVO is greater than one-eighth (Q4), the braking operation is not detected (Q5) and the retard control signal is introduced from the transmission control unit 11 (Q6). In this case, a retard control flag FR is set at a value of 1 (Q9) and a retard period counter Tr is reset (Q10). In step Q6, where the retard control flag FR is set at 1 even when the retard control signal is not introduced into the engine control unit 10 in the current processing cycle, it means that the retard control is now continued. Therefore, the retard period counter TR is increased (Q17) until it reaches a predetermined value (Q18). On the other hand, where the retard control is not carried out, the retard angle ϑATR is set at zero (Q14) and the retard control flag FR is reset (Q15). In step Q18, after the retard period counter TR reaches the predetermined value, the retard angle ϑATR is reduced by a value dϑ in each processing cycle (Q19) unless the retard angle ϑ is reduced below zero (Q20). Finally, the retard angle ϑATR is set at zero. The retard control flag FR is reset (Q22). After obtaining the retard angle ϑATR through the above procedure from step Q6 to Q22, the transmission control unit 11 determines a final ignition timing ϑ through steps Q11 to Q13. In step Q11, the transmission control unit 11 compares the retard angle ϑATR with a knocking retard angle ϑNR and uses a greater one as a final compensating angle ϑR for the ignition timing ϑ (Q12, Q16). The final ignition timing ϑ is obtained by adding the final compensating angle ϑR to the basic ignition timing ϑB (Q13). Referring to Figure 4, there is shown a flow chart of a procedure for obtaining the knocking retard angle ϑNR which is determined to suppress a knocking by controlling the ignition timing. The engine control unit 10 receives a signal from a knocking sensor (not shown) mounted on the engine 1 (R1). The knocking sensor is well known in the field of the present invention so that a detailed explanation thereto is omitted. For the purpose of the present invention, any kind of conventional knocking sensor can be employed. When the knocking is detected by the knocking sensor, the engine control unit 10 determines the knocking retard angle ϑNR in accordance with an intensity of the knocking (R3). On the other hand, when the knocking is not detected, the engine control unit 10 reduces the knocking retard angle ϑNR by the value dϑ toward zero in each processing cycle (R2-R6). Accordingly, when the shift operation is made from one gear stage G2 (for example 2nd stage) to another G1 (for example 1st stage), the retard control signal is introduced from the transmission control unit 11 to the engine control unit 10 after the predetermined period T from the generation of the shift control signal to the solenoid valves 4, 5 and 6 as shown in Figure 5. The retard control of the ignition timing continues for the predetermined time period TR with the constant value of the retard angle ϑR and thereafter the retard angle ϑR is gradually reduced toward zero. In this case, when the braking operation is made at a timing t1 at which the retard control signal is not introduced into the engine control unit 10, the retard control is cancelled. If the braking operation is made at a timing t2 at which the retard control is already initiated, the retard control is suspended immediately as shown in line 11 in Figure 5. Referring to Figure 7, there is shown a flow chart of a shift control in accordance with an embodiment which is not part of the present invention. In this embodiment, the oil temperature for the transmission is directly detected and used for the control. The oil temperature can be detected any conventional ways. In the control, the transmission control unit 11 sets the flag XOIL at the value of 0 (S1) and reads the throttle opening TVO, the vehicle speed and the like (S2). Then, the transmission control unit 11 judges whether or not the oil temperature is higher than a predetermined value (100°C in this embodiment) (S3). If the judgment is Yes or the oil temperature is higher than the predetermined value, the flag XOIL is set at the value of 2 so that the retard control is conditioned to be made (S4). If the judgment is No, the transmission control unit 11 keeps the flag XOIL=0. In this case, the retard control is not carried out. In step S5, the transmission control unit 11 reads the shift control map and judges as to whether or not the shift operation is to be made in light of the shift map (S6). If the judgment in step S6 is Yes, the transmission control unit 11 produces the control signals to the solenoid valves 4, 5 and 6 for carrying out the shift operation (S7). If the judgment in step S6 is No, the proceeding is returned to the starting step. In step S8, the transmission control unit 11 judges whether or not the flag XOIL is the value of 2 and therefore the retard control is ready to be made. If Yes, the transmission control unit 11 carries out the same steps as the former embodiment shown in Figure 2. Namely, the transmission control unit 11 produces the retard control signal when the counter T reaches the predetermined value (S9-S15 in Figure 7). If No, the proceeding is returned to the starting step. Receiving the retard control signal, the engine control unit 10 carries out the retard control in accordance with the procedures shown in Figures 3 and 4 as aforementioned. According to the above ignition timing control, the retard control is not carried out in the case where a specific vehicle operating condition in which a change in a time lag between a generation of the shift control signal and an actual initiation of the shift operation in the transmission is greater than a predetermined level is detected. However, this invention is not limited to this control but the retard angle ϑR can be reduced in response to the specific vehicle operating condition.

Claims: A control system for a vehicle having an automatic transmission (2) provided with a multiple transmission gear mechanism in which a specific gear stage of a speed ratio is automatically established among a plurality of gear stages in accordance with an vehicle operating condition, comprising shift control signal producing means (11) for producing a shift control signal in order to carry out a shift operation by virtue of a hydraulic fluid between different gear stages in accordance with the vehicle operating condition, engine torque control means (10) for reducing an engine torque in synchronism with the shift operation so as to suppress a torque shock due to the shift operation, detecting means (11) for detecting a specific vehicle operating condition in which a change in a time lag between a generation of the shift control signal and an actual initiation of the shift operation in the transmission is greater than a predetermined level and for producing a signal denoting the specific vehicle operating condition, and restricting means (10) for restricting the engine torque control means from reducing the engine torque when said specific vehicle operating condition is detected, characterized in that the specific vehicle operating condition is a running distance after starting driving operation of said vehicle so as to infer the temperature of the hydraulic fluid, A control system as recited in claim 1 wherein the engine torque is not controlled in connection with the shift operation when the running distance does not exceed a predetermined value. A control system as recited in claim 1 or 2, wherein the detecting means (11) detects the time lag (TOIL) between the generation of the shift control signal and the actual initiation of the shift operation between specific gear stages so as to infer the temperature of the hydraulic fluid. A control system as recited in claim 3 wherein the engine torque is not controlled in connection with the shift operation when the time lag (TOIL) is greater than a predetermined time period. A control system as recited in claim 1 wherein the engine torque control means (10) is constituted by ignition timing control means for controlling an ignition timing of the engine (1). An engine control system as recited in claim 5 wherein the ignition timing control means carries out a retard control in which the ignition timing (ϑ) is retarded in response to the shift operation. A control system as recited in claim 6 wherein a retard control signal for retarding the ignition timing (ϑ) is produced after a predetermined time period from a generation of a shift control signal for effecting the shift operation. A control system as recited in claim 5 wherein a final ignition timing (ϑ) of the engine (1) is calculated in accordance with a basic ignition timing (ϑB) which is determined based on an engine operating condition, a shift compensating value (ϑATR) which is determined to reduce a torque shock due to the shift operation, and a knock compensating value (ϑNR) which is determined to eliminate an engine knocking. A control system as recited in claim 8 wherein the final ignition timing (ϑ) is compensated by a greater one of the shift compensating value (ϑATR) and the knock compensating value (ϑNR). A control system as recited in claim 1 further comprising switching means (4,5,6) for switching a power transmitting path to change the gear stage from one to another in the automatic transmission (2), transmission control means (11) for introducing a shift control signal to the switching means (4,5,6) engine torque changing means (3,12) for being actuated to change the engine torque, engine control signal producing means (10) for producing an engine control signal to the engine torque changing means (3,12) so as to change the engine torque, said engine control signal producing means (10) receiving the shift control signal from the transmission control means (11) to change the engine torque. A control system as recited in claim 10 wherein said switching means comprises shift solenoid valves (4,5,6) for switching a hydraulic path to establish a selected gear stage of the transmission (2), said engine torque changing means (3,12) comprising an igniter (3).

Inventors: ABE MITSUTOSHI, FUJII MASAKI, KIKUCHI TOSHIYUKI, MATSUNO YUJI, ABE, MITSUTOSHI, FUJII, MASAKI, KIKUCHI, TOSHIYUKI, MATSUNO, YUJI
Applicants: MAZDA MOTOR, MAZDA MOTOR CORPORATION
Application year: 1990
Main classification: B60K41
IPC codes: F16H59, B60W10, F02D29, F02D41, F16H61, F16H63, F02P5, B60W30