ELECTRONIC CONTROL SYSTEM FOR AUTOMATIC VEHICLE TRANSMISSION

Abstract: An electronic control system for controlling an automatic transmission mounted on a vehicle determines whether a vehicle speed sensor is abnormal or not when the transmission gears are in a neutral gear position. If the vehicle speed sensor is abnormal, then vehicle speed data immediately before the vehicle speed sensor becomes abnormal is stored, and a gear position is determined based on the stored vehicle speed data for a predetermined period of time after the transmission gears are shifted from the neutral gear position to another gear position.

Description: The present invention relates to an electronic control system for an automatic vehicle transmission, and more particularly to an electronic control system for controlling a vehicle transmission based on a vehicle speed, an amount of depression of an accelerator pedal, or the like. Fig. 4 of the accompanying drawings schematically shows an automobile incorporating a conventional electronic control system 1 for automatically controlling a vehicle transmission. Denoted in Fig. 4 at 2 is an engine, 3 a clutch, 4 a transmission, 5 a final drive unit, 6 a wheel, 7 a selector lever, and 8 an accelerator pedal. Designated at 9 is an input shaft sensor for detecting the rotational speed of an input shaft of the transmission 4, 10 a vehicle speed sensor for detecting the speed of travel of the vehicle, 11 a gear position sensor for detecting a gear position of the transmission 4, and 12 an accelerator sensor for detecting the amount or depth to which the accelerator pedal 8 is depressed. Output signals from these sensors are supplied to the electronic control system 1. The clutch 3 and the transmission 4 are associated with a clutch actuator 13 and a transmission actuator 14, respectively, for mechanically operating the clutch 3 and the transmission 4. The clutch and transmission actuators 13, 14 are controlled by the electronic control system 1 based on the output signals from the sensors 9 through 12 and an output signal from the selector lever 7. Fig. 5 shows in block form the electronic control system for explaining main operation thereof. The electronic control system 1 includes a pulse input unit 101 for counting output pulses from the vehicle speed sensor 10 and an analog input unit 102 for converting an analog output from the accelerator sensor 12 to a digital signal through A/D conversion. In a processor 103, a count from the pulse input unit 101 is put in a variable "SPEED", and a digital signal from the analog input unit 102 is put in a variable "ACCEL". The processor 103 searches a predetermined speed change map (MAP) for an optimum gear position based on "SPEED" and "ACCEL". The processor 103 then issues the optimum gear position to an input unit 104 which operates the clutch actuator 13 and the transmission actuator 14 for speed changing operation. A processing sequence of the processor 103 will be described with reference to Figs. 6(a) and 6(b). Variables used in this processing sequence are shown in Fig. 7. A step a₁ in Fig. 6(a) determines whether the present gear position is a neutral gear position or not. If the present gear position is other than the neutral gear position, then control goes to a process for detecting an abnormality of the vehicle speed sensor in steps a₂ through a₄. In this detecting process, a step a₂ first determines a variable "SPD:REAL" is smaller than a preset value (1.5 km/h in this example). If smaller than 1.5 km/h, then the vehicle speed sensor is determined as being abnormal in a step a₃. If equal to or greater than 1.5 km/h, then the vehicle speed sensor is determined as being normal in a step a₄. Then, control goes to a step a₅ to confirm the result of the above process for detecting an abnormality of the vehicle speed sensor. If the vehicle speed sensor is normal, then a variable "SPEED:REAL" is subjected to a filtering process and then put in a variable "SPD" in a step a₆. If the vehicle speed sensor is abnormal, then a step a₇ determines whether the gear position is the neutral position or not. If not the neutral position, control goes to a step a₈. In the step a₈, the variable "SPD:REAL" is not used, but the vehicle speed is calculated from the rotational speed of the input shaft of the transmission and the gear ratio thereof, and put in "SPD". In a next step a₉, "SPD" obtained in the step a₆ or a₈ is put in the variable "SPEED". If the gear position is the neutral position in the step a₇, control does not go through the step a₉, and hence "SPEED" is retained as it is without being updated. In a step a₁₀, an optimum gear position is determined from the speed change map based on "SPEED" and "ACCEL", and put in a variable "GEAR". In a next step a₁₁, the value of "GEAR" is applied to the output unit 104 (Fig. 5) to operate the clutch actuator 13 and the transmission actuator 14. In the above conventional electronic control system, when the vehicle speed sensor fails, if the gears are in any of gear positions other than the neutral gear position, it is possible to calculate the vehicle speed from the gear ratio and the input shaft rotational speed (step a₈ in Fig. 6). Moreover, the proportion of the time in which the gears are in the neutral position to the entire running time of the automobile is very small. In view of these considerations, any abnormality of the vehicle sensor while the gears are in the neutral position has not been detected in the conventional electronic control system (steps a₁ to a₄). It has been found, however, that when the vehicle speed sensor fails while the gears are in the neutral gear position, the vehicle as it runs may become dangerous with the aforesaid processing sequence. This dangerous situation will be described with reference to Fig. 8, which shows the relationship between the vehicle speed and time when the vehicle is running. It is assumed here that the vehicle sensor fails at a time t₁₀ after the selector lever is operated by the driver into a neutral gear position at a time t₀. The processing of the electronic control system 1 now goes from the step a₁ to the step a₅ and to the step a₆ in Fig. 6. However, when the vehicle sensor fails, it does not issue vehicle speed pulses, and hence the variable "SPD:REAL" is "0". Therefore, "SPD" obtained in the step a₆ approaches "SPD:REAL" (= 0) at a certain gradient based on the filtering process as indicated by the dot-and-dash line, and then becomes "0" at a time t₁₁. Thus, the electronic control system 1 determines that the vehicle is already at rest at the time t₁₁ regardless of the fact that the actual vehicle speed (represented by the solid line) is still high. Thereafter, at a time t₂, when the driver shifts the selector lever into a drive position, the gears tend to be shifted into a second gear position irrespective of the fact that the actual vehicle speed a [km/h] is far in excess of a speed range (below b [km/h]) suitable for the second gear position. If the vehicle speed sensor were normal at this time, "SPD" would represent a [km/h], and the gears would not be shifted into the second gear position. However, since the vehicle speed sensor is abnormal, and hence "SPD" = 0 [km/h] as described above, the gears are shifted into the second gear position inasmuch as this value of "SPD" is in the speed range suitable for the second gear position. As a consequence, the transmission 4 is caused to rotate excessively, and the engine is liable to overrun. If the engine overruns, no safety running of the vehicle is ensured, and the life of the driver may be endangered. It is an object of the present invention to provide an electronic control system for controlling an automatic vehicle transmission to allow the vehicle to run safely after a vehicle speed sensor fails when the gears of the transmission are in a neutral gear position. According to the present invention, there is provided an electronic control system for controlling an automatic transmission mounted on a vehicle and having gear position detecting means, based on at least vehicle speed data from a vehicle speed sensor, the system comprising: detecting means for detecting an abnormality of the vehicle speed sensor; memory means for storing, when the abnormality of the vehicle speed sensor is detected, vehicle speed data obtained from the vehicle speed sensor immediately before the abnormality of the vehicle speed sensor is detected; and, gear position determining means for determining, when the abnormality of the vehicle speed sensor is detected, a gear position for the automatic transmission based on the vehicle speed data stored in the memory means; characterised in that: the detecting means detects a possible abnormality when the gear position of the transmission as detected by the gear position detecting means is a neutral gear position; and, the determining means determines a gear position based on the vehicle speed data stored in the memory means for a predetermined period of time after the gear position of the selector lever is changed from the neutral gear position to another gear position. With the above arrangement, if the vehicle speed sensor fails when the gears of the transmission are in the neutral gear position while the vehicle is running, the abnormality of the vehicle speed sensor is detected, and vehicle speed data obtained immediately before the vehicle speed sensor becomes abnormal are stored. For a predetermined period of time after the gears are shifted from the neutral gear position to another gear position, a gear position is determined based on the vehicle speed data stored in the memory means. Therefore, subsequent erroneous gear shifting operation is prevented to allow the vehicle to run safely. The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of an electronic control system according to an embodiment of the present invention; sequence of the electronic control system; Figs. 2(a) and 2(b) are a flowchart of a processing sequence of the electronic control system; Fig. 3 is a diagram showing by way of example a speed change map used in a step b₁₉ shown in Fig. 2(b); Fig. 4 is a schematic view of an automobile incorporating a conventional electronic control system; Fig. 5 is a functional block diagram explaining primary operation of the conventional electronic control system; Figs. 6(a) and 6(b) are a flowchart of a processing sequence of a processor shown in Fig. 5; Fig. 7 is a diagram illustrating variables and their contents which are employed in the processing sequences; and Fig. 8 is a diagram showing the relationship between vehicle speed and time when a vehicle speed sensor fails in a neutral gear position on the vehicle incorporating the conventional electronic control system. Fig. 1 shows an electronic control system 20 that can be incorporated in a vehicle such as an automobile for controlling an automatic vehicle transmission. The electronic control system 20 includes a pulse input unit 201 for counting output pulses from a vehicle speed sensor 10 and an analog input unit 202 for converting an analog output from an accelerator sensor 12 to a digital signal through A/D conversion. In a processor 203, a count "SPD:REAL" from the pulse input unit 201 is put in a variable "SPEED", and a digital signal from the analog input unit 202 is put in a variable "ACCEL". The processor 203 searches a predetermined speed change map (MAP) for an optimum gear position based on "SPEED" and "ACCEL". In a neutral gear position, any abnormality of the vehicle speed sensor is detected by vehicle speed sensor abnormality detector 203a according to the present invention. In the illustrated embodiment, the vehicle speed sensor is judged as being abnormal when an abrupt change in the number of output pulses from the vehicle speed sensor is detected based on the difference between the output "SPD:REAL" from the pulse input unit 201 and "SPEED" obtained immediately prior to "SPD:REAL". When the vehicle speed sensor is determined as being abnormal, the value of "SPEED" is retained, but not updated while the transmission gears are in the neutral gear position and for a fixed period of time after the neutral gear position is selected. The processor 203 issues an optimum gear position thus determined to an output unit 204 which operates the clutch actuator 13 and the transmission actuator 14 for speed changing operation. A processing sequence of the processor 203 will be described with reference to Figs. 2(a) and 2(b). This processing sequence is effected at the period of 64 msec. In Fig. 2(a), a process from a step b₁ through to step b₈ serves to detect any abnormality of the vehicle speed sensor 10. First, a step b₁ determines whether the present gear position is neutral or not. If in the neutral position, then control goes to a step b₂. In the step b₂, "SPD:REAL" (the vehicle speed prior to being subjected to the filtering process) is subtracted from "SPEED" (the vehicle speed after being subjected to the filtering process), and the difference is put in A. A next step b₃ determines if A exceeds a preset value (16 [km/h] in this embodiment) or not (i.e., whether a time-dependent change in the vehicle speed detected by the vehicle speed sensor is so rapid that it exceeds 16 [km/h]/64 msec. or not). If A > 16 [km/h], then the vehicle speed sensor is determined as being abnormal, and then "ERR" is set to "1" in a step b₄. The processing from the step b₁ through to step b₄ can determine any abnormality of the vehicle speed sensor when the gears are in the neutral position. If not in the neutral position in the step b₁, then the same processing as the conventional processing (indicated in Fig. 6(a) as the steps a₂ through a₄) is carried out in steps b₅ to b₇ to detect an abnormality of the vehicle speed sensor. When the vehicle speed sensor is normal (step b₇), "0" is put in "ERR" in a step b₈. The processing from a step b₉ through to step b₁₇ serves to determine the value of "SPEED" used for determining an optimum gear position in a step b₁₉, described later on. A step b₉ confirms whether the vehicle speed sensor is detected as being abnormal or not in the steps b₅ to b₇. If the vehicle speed sensor is normal, control goes to a step b₁₀ in which the variable "SPD:REAL" is subjected to a filtering process and then put in "SPD". If the vehicle speed sensor is abnormal, then a step b₁₁ determines if the gear position is neutral or not. If not neutral, a step b₁₂ checks a timer, and if the timer exceeds a preset value α, control proceeds to a step b₁₃. This timer is incremented at the period of 64 msec and started when the gears are shifted from the neutral position. In the step b₁₃, the vehicle speed is calculated from the rotational speed of the input shaft and the gear ratio of the transmission, and put in "SPD". Therefore, according to the processing from the step b₉ through to step b₁₃, the speed determined dependent on whether the vehicle speed sensor is normal or abnormal as detected other than when the gear position is in the neutral position is put in "SPD" except in a period of time in which the gear position is neutral after the vehicle speed sensor is detected as abnormal and in a fixed period of time α after the gears are shifted from the neutral position. Then, control goes to a step b₁₄ in Fig. 2(b) which confirms the value of "ERR" which has been set in the steps b₄, b₈. If "ERR" = 0 (when the vehicle speed sensor is normal or when the vehicle speed sensor is abnormal with the gears shifted and timer > α, then control goes to a step b₁₇ in which "SPD" obtained in the step b₁₀ or b₁₃ is put in "SPEED". If "ERR" ≠ 0 (when the vehicle speed sensor is abnormal in the neutral position), then control goes to a step b₁₇ only when the gear position is not neutral and the timer exceeds α in steps b₁₅, b₁₆. If the gear position is neutral in the step b₁₅, or if the timer is equal to or smaller than α in the step b₁₆, then the step b₁₇ is not executed. Therefore, according to the processing from the steps b₁₄ to b₁₇, if the vehicle speed sensor is detected as being abnormal in the neutral position, the value of "SPEED" is retained but not updated in a subsequent period of time in which the gear position is neutral and in a fixed period of time α after the gears are shifted from the neutral position. In other periods of time, the value of "SPEED" is updated from time to time by "SPD" obtained in the steps b₁₀, b₁₃. When "SPEED" is determined, a step b₁₈ determines whether the gear position is neutral or not. If not neutral, then control goes to a step b₁₉ in which an optimum gear position is determined from the speed change map (gear position determining map) shown in Fig. 3 by using as parameters "ACCEL" (the amount of depression of the accelerator pedal) and "SPEED" (vehicle speed), and the optimum gear position is put in "GEAR". Thereafter, control goes to a step b₂₀ in which the value of "GEAR" is given to the output unit 204 (Fig. 1) to operate the transmission actuator 14. If the gear position is neutral in the step b₁₈, the gear position is not changed and no gear shifting is effected. An example of running pattern of the vehicle or automobile which incorporates the electronic control system 20 will be described with reference to Fig. 8. It is assumed in Fig. 8 that the driver shifts the gears into the neutral position at a time t₀ and the vehicle speed sensor fails at a time t₁₀. If the vehicle speed sensor fails at the time t₁₀, its failure or abnormality is detected when the amount of change ("SPEED" - "SPD:REAL") in the vehicle speed per 64 msec exceeds 16 [km/h] (steps b₁, b₂, b₃, b₄), and "SPEED" retains a vehicle speed d [km/h] immediately prior to the vehicle speed sensor abnormality (steps b₉, b₁₀, b₁₄, b₁₅, b₁₈). At this time, since "SPD:REAL" is 0, "SPD" is also 0, and the vehicle is recognized as being at rest by confirming "SPD" only. It is assumed that the actual vehicle speed is lowered to a [km/h] at a time t₂ and the driver operates the selector lever at this time into a drive position (e.g., D range). Then, the gear position is determined from "SPEED" and "ACCEL" in the step b₁₉. If the values a ∼ d of "SPEED" with "ACCEL" set to A in the speed change map (Fig. 3) used at this time correspond respectively to the vehicle speeds a ∼ d in Fig. 8, then since "SPEED" retains d [km/h] at the time t₂, the optimum gear position is determined as a sixth gear position (6TH). Inasmuch as the sixth gear position is suitable enough for the actual vehicle speed a [km/h], the transmission is protected from seizure and the engine is prevented from overruning. After the gears have been shifted in this manner, the vehicle speed is backed up by the gear ratio and the input shaft rotational speed upon elapse of a fixed period of time α from the gear shifting, and is put in "SPEED" (steps b₁, b₅, b₆, b₉, b₁₁, b₁₂, b₁₃, b₁₄, b₁₅, b₁₆, b₁₇). If "SPEED" thus obtained is a [km/h] and "ACCEL" is A, because it can be seen from the speed change map (Fig. 3) that the vehicle can run in the third gear position (3RD), the optimum gear position is determined as the third gear position (step b₁₉), and a speed change is effected (step b₂₀). Thereafter, a speed change command is given based on backed-up "SPEED". With the present embodiment, as described above, abnormality of the vehicle speed sensor can be detected by detecting an abrupt change in the output from the vehicle speed sensor when the gears are in the neutral position while the vehicle is running. Therefore, abnormality of the vehicle speed sensor can be detected when the vehicle speed sensor fails in any of the gear positions if the vehicle is running. Moreover, "SPEED" is not updated during a period of time in which the gear position is neutral (and a fixed period of time after the gears are shifted from the neutral position) while a vehicle speed sensor failure is being detected. Consequently, any subsequent dangerous erroneous gear shifting operation is prevented to avoid troubles which would fatally affect the vehicle running capability, such as gear seizure of the transmission, destruction of the clutch disc, and engine overrunning. The processing sequence of the invention can be realized by a simple algorithm without affecting a conventional backup process. The process of detecting an abnormality of the vehicle speed sensor while the gears are in the neutral position is not limited to the sequence from the step b₁ through b₄. Although a certain preferred embodiment has been shown and described, it should be understood that many changes and modifications may be made therein without departing from the scope of the appended claims.

Claims: An electronic control system (1) for controlling an automatic transmission (4) mounted on a vehicle and having gear position detecting means (11), based on at least vehicle speed data from a vehicle speed sensor (10), the system comprising: detecting means (203a) for detecting an abnormality of the vehicle speed sensor (10); memory means for storing, when the abnormality of the vehicle speed sensor (10) is detected, vehicle speed data obtained from the vehicle speed sensor (10) immediately before the abnormality of the vehicle speed sensor (10) is detected; and, gear position determining means (103) for determining, when the abnormality of the vehicle speed sensor (10) is detected, a gear position for the automatic transmission (4) based on the vehicle speed data stored in the memory means; characterised in that: the detecting means (203a) detects a possible abnormality when the gear position of the transmission as detected by the gear position detecting means (11) is a neutral gear position; and, the determining means (103) determines a gear position based on the vehicle speed data stored in the memory means for a predetermined period of time after the gear position of the selector lever is changed from the neutral gear position to another gear position. An electronic control system (1) according to claim 1, wherein said detecting means (203a) includes means for detecting the abnormality of the vehicle speed sensor (10) when an amount of change of the vehicle speed data from the vehicle speed sensor (10) within a given period of time exceeds a predetermined value.

Inventors: SUGIMURA, TOSHIYA, YOISHIMURA, HIROSHI
Applicants: ISUZU MOTORS LIMITED
Application year: 1988
Main classification: B60K41
IPC codes: B60W10, F16H59, F16H61