Automatic transmission

Abstract: An automatic transmission which includes a clutch (6); a clutch actuator (7) for detecting and controlling a position of the clutch; a transmission (1); a transmission actuator (2) for driving the transmission; a vehicle speed detector (22) for detecting a vehicle speed; a throttle opening detector (11) for detecting a throttle opening; an automatic shift unit (30) including a gear shift map (30a, 30b) having a gear shift characteristic which is determined based on the vehicle speed and the throttle opening; a computer unit (30c) for computing an instant gear position of the transmission based on the vehicle speed and the throttle opening according to the gear shift map; a gear position selector (30d) for controlling the transmission actuator based on the instant gear position to upshift or downshift the transmission; a shift prohibit unit (40) for determining whether the instant gear position matches the previous gear position from a memory (40a) for a predetermined times in a predetermined period and, if they do not match for the predetermined times, invalidating the instant gear position and prohibiting any shift operation according to the gear shift map; and a shift determination unit (41) for establishing an upshift prohibit condition when the throttle opening is equal to or less than a predetermined value while releasing the upshift prohibit condition when the vehicle speed is low or the clutch is in a position toward disengagement from a half clutch position, or with a low-speed gears even if the throttle opening is equal to or less than the predetermined value.

Description: The present invention relates to a automatic transmission with the features of the preamble of claim 1 as known from JP-A-59 001 855. Fig. 4 shows such a conventional automatic transmission. A well known parallel axis gear type transmission 1 is controlled by a transmission actuator 2 which consists of a select actuator 2a and a shift actuator 2b. Both of the actuators 2a and 2b are driven by a hydraulic drive system 3 which consists of a tank 3a, a pump 3b, an accumulator 3c, and a hydraulic pressure switching electromagnetic valve (not shown) to control the drive gear of the transmission 1 via a pair of piston rods 2c and 2d. The actuator 2 is controlled by a drive unit (D/U) 2e, which in turn is controlled by a main control unit 4. Feedback control is made such that the actual position signals of a pair of potentiometers 2f and 2g agree with the target position signals M fed from the main control unit 4. Consequently, as shown in Fig. 5, the gear position is shifted from the neutral position 5g to the first gear 5a, second gear 5b, third gear 5c, fourth gear 5d, fifth gear 5e, or reverse driving 5f. A clutch 6 is linked to the piston rod 7a of a clutch actuator 7 for engagement and disengagement. The hydraulic drive system 3 drives the clutch actuator 7. The actual position of the piston rod 7a is detected by the potentiometer 7c, and the actual position signal is fed back to a drive unit 7b. The drive unit 7b is controlled by the main control unit 4 such that the actual position signal agrees with the target position signal F fed by the main control unit 4. An engine 8 has a control unit 9 which is controlled by the main control unit 4. The rotation of the engine 8 is transmitted to an axle 10 via the clutch 6 and the transmission 1. Respective signals of an accelerator opening detector 11, a brake pedal detector 12, a key switch 13, an exhaust brake switch 14, and a selector 15 and the rpm output signal W of a vehicle speed detector 22 are fed to the main control unit 4 to control the drive units 2e and 7b and the engine control unit 9, a display panel 16, and a control unit 17a for controlling a gear position display panel 17. The rpm output signal W from the vehicle speed detector 22 is multiplied in the main control unit 4 by a constant which consists of the radius r of car wheels 23 and the gear ratio of a differential gear 24 to provide a vehicle speed V, which is displayed on an instrument panel (not shown) along with the engine rpm and the fuel reserve. Thus, the main control unit 4 controls the clutch 6 and the transmission 1 based on the throttle opening S or accelerator pedal depression, the vehicle speed V, and the position of the selector 15. The gear position is' shifted from the neutral 5g to one of the shift positions 5a-5f as shown in Fig. 5. The main control unit 4 includes an automatic shift unit 30 for effecting automatic shifting according to input signals such as the vehicle speed and the throttle opening. The automatic shift unit 30 includes the first and second gear shift maps 30a and 30b having a gear shift characteristic N which is determined by the vehicle speed V (rpm W x constant ) and the throttle opening S (accelerator pedal depression) as shown in Fig. 6, a computer unit 30c for computing the gear position of the transmission 1 based on the gear shift characteristic N of the first or second gear shift maps 30a or 30b, and a gear selector 30d for controlling the actuator 2 based on the gear position from the computer unit 30c to make upshift or downshift. When the selector 15 is set in the automatic shift position "4", the automatic shift unit 30 controls the transmission 1 between the first and fourth gears based on the -first gear shift map 30a while when the selector 15 is set in the automatic shift position "5", it controls the transmission 1 between the second and fifth gears based on the second gear shift map 30b. For example, when the accelerator pedal is released to reduce the vehicle speed, with the transmission 1 in the second gear (point A of the gear shift map 30a), the automatic shift unit 30 upshifts the transmission 1 to the third gear despite the fact that the vehicle speed is reduced, thus failing to provide satisfactory engine braking. Japanese Patent Application Kokai No. (JP-A-58 211 061) discloses an automatic transmission which is able to detect the rate of accelerator pedal depression and, if the rate is above a certain value, prohibit any shift. Thus, if the rate of accelerator pedal change is above the certain value, no upshift from A to B is made so that the transmission 1 remains in the second gear, thereby providing satisfactory engine braking. In the conventional automatic transmission, when the driver tries to apply engine braking by releasing the accelerator pedal at the certain rate, the transmission can be upshifted because the perception of the certain rate varies with the individual driver. In addition, to detect the certain rate, it is necessary to provide a differential circuit for differentiating changes of the accelerator pedal. This differential circuit is so sensitive to noise that it suffers from frequent malfunctions. When the accelerator pedal is released abruptly after the vehicle starts to move with low speed gear and half clutch, the clutch is kept disengaged to prevent engine stop when the vehicle stops while the automatic transmission is put into the upshift prohibit condition. As a result, when the vehicle starts to descend downhill, for example, no upshift is made while the clutch is kept disengaged even when the vehicle speed is increased, thus presenting very dangerous running conditions. When the accelerator pedal is depressed under the upshift prohibit condition, the upshift prohibit condition is released instantly, failing to provide satisfactory acceleration despite the fact that the accelerator pedal is depressed for acceleration. Accordingly, it is an object of the invention to provide an automatic transmission which is able to provide satisfactory acceleration or deceleration while preventing the vehicle from running under dangerous conditions. According to the invention this object is solved by the features of claim 1. Subject matter of subclaims 2-4 are preferred embodiments of the invention. The above and other object, features, and advantages of the invention will be more apparent from the following description when taken in conjunction with the accompanying drawings. Fig. 1 is a schematic diagram of an automatic transmission according to an embodiment of the invention; Figs. 2 and 3 are flowcharts showing the operation of the automatic transmission; Fig. 4 is a schematic diagram of a conventional automatic transmission; Fig. 5 is a top plan view of a gear shift pattern for the conventional automatic transmission; and Fig. 6 is a graph showing a gear shift map. In Fig. 1, like reference characters denote like or corresponding parts in Figs. 4 and 6, and their description will be omitted. A shift prohibit unit 40 includes a memory 40a for storing computation results of the computer unit 30c according to the gear shift maps 30a and 30b and a counter 40b for counting the gear determination results. The shift prohibit unit 40 compares the instant gear position fed from the computer unit 30c with the previous gear position stored in the memory 40a. If they agree, the counter 40b count it and determines whether the count is equal to a predetermined value or 4, for example, in a predetermined period. If the count is less than 4, the present gear position is invalidated, and any shift according to the gear shift maps 30a and 30b is prohibited. A shift determination unit 41, which establishes an upshift prohibit condition when the throttle opening S is below a predetermined value or during idling, releases the upshift prohibit condition when the vehicle speed is low, the clutch 6 is in a position toward disengagement more than the half clutch, or at the low speed gear. However, it keeps the upshift prohibit condition for a predetermined period after the accelerator pedal is depressed (throttle opening S becomes above the predetermined value). In operation, the computer unit 30c computes gear positions by reading changes in the throttle opening S at a predetermined frequency and computes gear positions based on the throttle openings S and the vehicle speed V as shown in Fig. 6. This gear positions are determined according to the gear shift characteristic N; the second gear from A to A₂ and the third gear from B₁ to B. The shift prohibit unit 40 is controlled according to the flowchart of Fig. 2. In step S1, the instant gear position computed by the computer unit 30c is fed to the shift prohibit unit 40. In step S2, the previous gear position is read out of the memory 40a. In step S3, the instant gear position is compared with the previous gear position to determine whether they are the same. In step S4, the counter 40b is incremented by one because the gear position of A₁ is the same as that of A. In step S5, whether the count is equal or greater than 4 is determined. In step S6, if the count is 4, the present gear position is made valid. In step S7, however, since the instant gear position of B₁ is different from the previous gear position of A₂, the counter 40b is cleared. In step S8, the new gear position or third gear is stored in the memory 40a. The subsequent instant gear positions are compared in the same way. Even if the throttle opening S changes to B as shown in Fig. 6, the count of the counter 40b is 3 from B₁ to B so that the instant gear position is not made valid for shifting. In other words, even if the accelerator pedal is released for deceleration, no upshift,is made, thereby providing satisfactory engine braking. In Fig. 3, if the gear position is made valid by the shift prohibit unit 40, whether the throttle opening S is no more than a predetermined value (idling position) is determined in step L1. If it is below the predetermined value, whether the vehicle speed V is low (5 km/h) is determined based on the vehicle speed V, the position of the clutch 6, and the gear position in step L2. If it is higher than 5 km/h, whether the clutch 6 is in a position toward disengagement more than the half clutch is determined in step L3. If it is not, whether the gear is at a low-speed position such as the first or second gear is determined in step L4. If the throttle opening S is below a predetermined value even when the gear is determined at a high-speed position, acceleration is not desired so that upshift is prohibited in step L5. In step L6, the timer is set for keeping the upshift prohibit condition. On downhill grades, it is dangerous to drive with low speed gears, with the clutch 6 disengaged so that the upshift prohibit condition is released in step L8. For example, when the vehicle is decelerated with the accelerator pedal released as shown in Fig. 6, the gear position moves from B to C. At this point, the count of the counter 40b is 4, thus making the gear position at C valid. Thus, it is possible to shift the transmission from the third gear to the second gear. When the vehicle speed is increased on a downhill grade, bringing the gear position to D which is in the idling range of the throttle opening S, it is possible to upshift from the second gear to the third gear because of low speed positions. When the throttle opening S is not in the idling range, or under ordinary running conditions, whether a predetermined time has passed since the upshift prohibit condition is established in step L7. If the predetermined time has passed, the upshift prohibit condition is released in step L8. Even if non-deceleration conditions are determined in steps L2-L4, the upshift prohibit condition is released. Unless the predetermined time has passed in the timer, the upshift prohibit condition is held so that the timer is subtracted in step L9. In other words, even if the accelerator pedal is depressed at B, no instant upshift is made. That is to say, as shown in Fig. 6, when the gear position changes from A to B and to C, the shift prohibit unit 40 and the shift determination unit 41 determine whether the instant gear position computed by the computer unit 30c matches the previous gear position for a predetermined times within a predetermined period. Unless it does not match the previous gear position for the predetermined times, the instant gear position is invalidated to prohibit any shift according to the gear shift maps 30a and 30b while when the throttle opening S is below a predetermined value, the upshift prohibit condition is established, thereby providing satisfactory acceleration or deceleration. In addition, the gear shift is made regardless of the rate of changes in the accelerator pedal thus accommodating different drivers reactions. Moreover, no differential circuit is required so that the automatic transmission is resistant to noise, thus suffering from few malfunctions. When the vehicle speed is low or the clutch is in a position toward disengagement from the half clutch position, or with low-speed gears, the shift determination unit 41 releases the upshift prohibit condition so that it is possible to prevent the vehicle from running under dangerous conditions. In addition, even if the accelerator pedal is depressed, the upshift prohibit condition is held for the predetermined time, thereby providing satisfactory acceleration. As has been described above, with the shift prohibit unit according to the invention, when to shift is determined regardless of the rate of changes in the accelerator pedal so that the drivers can drive the vehicles depending on their own feelings. In addition, no differential circuit is required so that the automatic transmission is resistant to noise, suffering few malfunctions. The shift determination unit establishes a upshift prohibit condition when the throttle opening S is below the predetermined value. However, if the vehicle speed is low or the clutch is in a position toward disengagement from the half clutch position, or with low-speed gears when the throttle opening S is below the predetermined value, it releases the upshift prohibit condition, thereby preventing the vehicle from running under dangerous conditions. In addition, even if the accelerator pedal is depressed, it keeps the upshift prohibit condition for a predetermined time, thereby -assuring satisfactory acceleration.

Claims: An automatic transmission comprising: a clutch (6); a clutch actuator (7) for controlling a position of said clutch (6); a transmission (1); a transmission actuator (2) for driving said transmission (1); a vehicle speed detector (22) for detecting a vehicle speed; a throttle opening detector (11) for detecting a throttle opening; an automatic shift unit (30) including a gear shift map (30a, 30b) having a gear shift characteristic which is determined based on said vehicle speed and said throttle opening; a computer unit (30c) for computing at a predetermined clock cycle an instant gear position of said transmission (1) based on said vehicle speed and said throttle opening according to said gear shift map (30a, 30b); a gear position selector (30d) for controlling said transmission actuator (2) based on said instant gear position to upshift or downshift said transmission (1); characterized by a shift prohibit unit (40) for determining whether said instant gear position matches a previous gear position for a predetermined number of times repeatedly in a predetermined period and, if they do not match for said predetermined number of times repeatedly, invalidating said instant gear position and prohibiting any shift operation according to said gear shift map (30a, 30b); and a shift determination unit (41) for establishing an upshift prohibit condition when said throttle opening is equal to or less than a predetermined value while releasing said upshift prohibit condition when said vehicle speed is low or said clutch (6) is in a position toward disengagement from a half clutch position, or with a low-speed gear even if said throttle opening is equal to or less than said predetermined value. An automatic transmission according to claim 1, characterized in that said shift determination unit keeps the upshift prohibit condition for a predetermined time even if the accelerator pedal is depressed under the upshift prohibit condition. The automatic transmission of claim 1 or 2, wherein said shift prohibit unit (40) comprises: a memory (40a) for storing said gear position computed by said computer unit (30); and a counter (40b) for counting a number of matches between said instant gear position and said previous gear position from said memory (40a). The automatic transmission of one of the preceding claims, wherein said automatic shift unit (30) includes a plurality of gear shift maps (30a, 30b) for storing different gear shift characteristics based on set gear positions.

Inventors: KONO HIROMI C O ZEXEL CORPORAT, OTSUKA MASUHIRO C O ZEXEL CORP, SATOH YUJI ZEXEL CORPORATION, SODA HIROYUKI C O ZEXEL CORPOR, KONO, HIROMI, OTSUKA, MASUHIRO, SATOH, YUJI, ZEXEL CORPORATION, SODA, HIROYUKI, KONO, HIROMI, C/O ZEXEL CORPORATION, OTSUKA, MASUHIRO, C/O ZEXEL CORPORATION, SODA, HIROYUKI, C/O ZEXEL CORPORATION
Applicants: ZEXEL CORP, ZEXEL CORPORATION
Application year: 1991
Main classification: B60K41
IPC codes: F16H61, B60W30, B60W10