Transmission control system with gear shift failure detection

Abstract: A transmission control system with gear shift failure detection includes a transmission (1), each gear of which is equipped with a synchromesh mechanism (1e); an actuator unit (2) consisting of a shift actuator (2a) for making a gear shift in a shift direction and a select actuator (2b) for making a gear shift in a select direction; a control unit (4) for calculating a target position signal (M) from an amount of pressdown of an accelerator pedal, a vehicle speed, and a set position of a gear selector to control not only said actuator unit so that a gear is set within a target range but also a clutch so that connection or disconnection is made according to an operation of said transmission; a position detector (2f, 2g) provided in each of said shift and select actuators for detecting a position of a piston rod (2c, 2d); a servo cylinder (2a, 2b) in response to a signal from said position detector to position said piston rod at a given position of each gear; a speed detector (4a) in response to a signal from said position detector of said shift actuator to detect an operational speed of said piston rod of said shift actuator; and a decision maker (4b) in response to a signal from said speed detector to decide that a gear shift is faulted if said operation speed is lower than a reference speed for a predetermined time outside a synchromesh mechanism operational range of said transmission.

Description: The present invention relates to a transmission control system having a shift actuator and a select actuator to control the transmission and the clutch according to the amount of pressdown of the accelerator pedal and the vehicle speed with the features of the preamble of claim 1 as known from EP-A-0 161 521. Fig. 3 shows a conventional transmission control system which includes a parallel axis gear type transmission 1; an actuator 2 consisting of a select actuator 2a and a shift actuator 2b to control the transmission 1 for making a gear shift. Both of the actuators 2a and 2b are driven by a hydraulic drive system 3 which consists of a tank 3a, a pump 3b, and an accumulator 3c. The driving gear of the transmission 1 is controlled by a pair of piston rods 2c and 2d. This control is made by the drive unit 2e, which in turn is controlled by the main control unit 4. A pair of potentiometers 2f and 2g are provided to detect the positions of the piston rods 2c and 2d. The drive unit 2e performs a feedback control so that the actual position signals from the potentiometers 2f and 2g match the target position signal M from the main control unit 4. Consequently, the shift lever 50 drives shift blocks 51-53 to make a gear shift from the neutral "N" to the first gear "1", second gear "2", third gear "3", fourth gear "4", fifth gear "5", or reverse "R" as shown in Fig. 5(a). A clutch 6 is linked to the piston rod 7a of a clutch actuator 7 for making connection or disconnection. The hydraulic pressure is supplied to the clutch actuator 7 from the hydraulic drive system 3 to make a feedback control by the drive unit 7b so that the actual position signal of the piston rod 7a matches the target position signal C from the main control unit 4. The drive unit 7b is controlled 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. The main control unit 4 receives signals from an accelerator pedal sensor 11, a brake pedal sensor 12, a key switch 13, an exhaust brake switch 14, and a selector 15 and controls the drive units 2e and 7b, the control unit 9, a display panel 16, and a control unit 17a which controls a gear position display panel 17. Thus, the main control unit 4 controls the clutch 6 and the transmission 1 in response to the amount of pressdown of the accelerator pedal, the vehicle speed, and the shift position of the selector 15. The fourth and fifth gears "4" and "5" of the selector 15 are automatic transmission modes between first and fourth gears, and second and fifth gears, respectively. As Fig. 4 shows, the transmission 1 has a synchromesh mechanism 1e consisting of a synchronizer hub 1f and a cone clutch 1c for preventing gear noise upon gear shift. The synchronizer hub 1f of a sleeve 1d rotatably and slidably mounted on the shaft 1a is pressed to the cone clutch 1c of a gear 1b so that the shaft 1a and the gear 1b are synchronized and connected. As Fig. 5(a) shows, a gear shift is made by moving the shift lever 50 to the select position with the select actuator 2a and then shifting one of the shift blocks 51-53 in the shift direction with the shift actuator 2b. At this point, the dog clutch 1d is slidably moved on the shaft 1a by the actuators 2a and 2b for engagement with the gear 1b. When the gear 1b and the shaft 1a are connected, the driving power is transmitted via another gear 1m and shaft 1n. As Fig. 5(b) shows, however, the shift lever 50 can be stuck between the shift blocks 52 and 53, for instance, or the actuator 2a and/or 2b can simply malfunction, failing to make a gear shift. In order to detect this gear shift failure, a variety of measures have been proposed in JP-A-60 11759, JP-A-60 222328, JP-A-62 278342, JP-A-62 278343, and JP-A-62-288755. All of these measures detect the gear shift failure based on the time elapsed since the gear shift operation is started so that it has been impossible to detect the failing conditions such as the position of the failed actuator 2a or 2b. Thus, it has been difficult to provide an appropriate countermeasure. Then, JP-A-62-288756 has proposed to detect the operational speed of the actuator to determine that the actuator is faulted when the operational speed is low for a predetermined time and stop the shift operation to the target gear so that the gear shift can be repeated later. In the above conventional transmission control system, however, the transmission 1 is equipped with the synchromesh mechanism 1e so that the operational speed of the actuator 2b is reduced in the operational range of the synchromesh mechanism 1e with the friction produced by the engagement between the synchronizer hub and the gear. This reduction in the operational speed have often been mistaken as a gear shift failure. Accordingly, it is an object of the invention to provide a reliable transmission control system in which the actuator speed outside the synchromesh mechanism operational range is detected to decide whether the actuator is faulted, thereby preventing the low actuator speed within the synchromesh mechanism operational range from being mistaken as a gear shift failure. According to the invention this object is solved by the features of claim 1. The above and other objects, features, and advantages of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings. Fig. 1 is a schematic diagram of a transmission control system according to an embodiment of the invention; Fig. 2 is a flow chart useful for explaining how the transmission control system works; Fig. 3 is a schematic diagram of a conventional transmission control system; Fig. 4 is a side, partially sectional, view of a synchromesh mechanism of the conventional transmission control system; and Figs. 5(a) and 5(b) are sectional views of a shift lever of the conventional transmission control system. In Fig. 1, like numeral characters denote like or corresponding parts or components of Figs. 3-5. The shift actuator 2a and the select actuator 2b of an actuator 2 each have a servo cylinder which is able to stop the piston rod 2c or 2d at a given position. These piston rods are mechanically connected to the shift lever 50 of a transmission 1. These actuators 2a and 2b also have hydraulic pressure switching electromagnetic valves 31a-31c and 32a-32c, respectively, for controlling the hydraulic pressure from the hydraulic drive system 3 to stop the piston rods 2c and 2d at a given position. The first hydraulic pressure switching electromagnetic valves 31a and 32a are normally closed two-way valves for conducting the hydraulic pressure from the hydraulic drive system 3, and the second and third hydraulic pressure switching electromagnetic valves 31b and 32b, and 31c and 32c are normally opened two-way valves for moving the piston rods 2c and 2d. The main control unit 4 has a speed detector 4a for detecting the operational speed with the potentiometers 2f and 2g of the respective actuators 2a and 2b and a decision maker 4b for deciding that the gear shift failure has occurred when the operational speed from the speed detector 4a is less than the reference speed for a predetermined time, with the position signal from the potentiometer 2g indicating that the piston rod 2d is outside the synchromesh mechanism operational range. In operation, as Figs. 2(a) and (b) show, in response to the output signals from the respective detectors, the main control unit 4 calculates the target gear. If the target gear is different from the present gear, it sets a gear shift requesting flag while outputting a target gear signal M. Then, the drive unit 2e drives the respective actuators 2a and 2b for gear shift so that the actual gear signal matches the target gear signal M. The gear shift is made by shifting the shift lever 50 out of the present gear (shift-out) with the shift actuator 2b, positioning the shift lever 50 at the select position with the shift actuator 2a, and moving one of the shift blocks 51-53 into the gear (shift-in) with the shift actuator 2b. Then, as Figs. 2(c) and (d) show, the speed detector 4a detects the operational speed of the shift actuator 2b during the gear shift based on changes in the shift stroke. If the operational speed of the actuator 2b is less than the reference speed for a predetermined time, the decision maker 4b decides that the gear shift is a failure and sets a shift-in speed low flag. Then, it decides whether the present position of the piston rod 2d is within the synchromesh mechanism operational range 1. If it is, the operation is continued to make a gear shift as usual. If it is outside of the synchromesh mechanism operational range, based on the comparison between the present position signal and the target position signal M, the decision maker decides whether the present position is at a deep position in the shift-in operation. If it is, the shift actuator 2b is shifted out and into the neutral for performing another shift-in operation. Whether the shift-in position is "deep" or "shallow" is decided based on the fact that the difference between the present position and the target position M is greater or smaller than a predetermined level. In the case of a shallow position, all of the switching electromagnetic valves 32a-32c are turned off so that the hydraulic pressure on the piston rod 2d becomes zero, making the operational power of the shift actuator 2b zero. Then, whether the select position signal is off the target position signal M is decided. If the select position signal is off, the select actuator 2a is positioned so that the select position signal matches the target position signal M for making a shift-in. If the select position signal is on the target position signal M, a predetermined correction is added for making a shift-in. As Fig. 5(b) shows, the shift lever 50 can be stuck between the gear boxes 52 and 53, for instance, to cause a shift failure in the shallow shift-in position. In order to correct this failure, the hydraulic drive system 3 is started again to return the select actuator 2a to the target position F as shown in Fig. 1, and the target position signal M is gradually increased by a predetermined correction increment ±α so that the target position F is shifted in the direction Fa or Fb into the select position for making correction and shift-in. More specifically, the select position Fa is corrected in the direction Fa by α (+α) for positioning and then shift-in. If the shift-in failed, correction is made in the direction Fb by α (-α) for positioning and shift-in again. If it is still failed, further correction by ±α from the above corrected position is made for positioning and shift-in. This operation is repeated until the shift-in operation is successful or deep in the position. The operation of each of the above flow charts is repeated at predetermined intervals. Whether the shift lever 50 is stuck in the gear box is determined by detecting the time when the movement of the shift lever 50 is zero because the shift lever 50 cannot move in the select direction under the stuck conditions. As has been described above, according to the invention, the transmission control system detects the gear position of the shift actuator 2b, and the decision maker 4b decides that the gear shift is faulted by a malfunction of the actuator 2b when the operational speed of the actuator 2b is lower than the reference speed for a predetermined time outside the synchromesh mechanism operational range so that the gear select position is corrected based on the decision, whereby the low speed of the actuator 2b in the synchromesh mechanism is not mistaken as a malfunction, thereby increasing the system reliability.

Claims: A transmission control system with gear shift failure detection, comprising: a transmission (1), each gear of which is equipped with a synchromesh mechanism (1e); an actuator unit (2) consisting of a shift actuator (2b) for making a gear shift in a shift direction and a select actuator (2a) for making a gear shift in a select direction; a control unit (4) for calculating a target position (M) signal from an amount of pressdown of an accelerator pedal, a vehicle speed, and a set position of a gear selector to control not only said actuator unit (2) so that a gear is set within a target range but also a clutch so that connection and disconnection is made according to an operation of said transmission; a position detector (2f, 2g) provided in each of said shift and select actuators (2b, 2a) for detecting a position of a piston rod (2c, 2d) of said actuator, and a servo cylinder in response to a signal from said position detector to position said piston rod (2c, 2d) at a given position of each gear, characterized by a speed detector (4a) in response to a signal from said position detector (2f, 2g) of said shift actuator to detect an operational speed of said piston rod (2c, 2d) of said shift actuator (2b); and a decision maker (4b) in response to a signal from said speed detector to decide that a gear shift is faulted if said operation speed is lower than a reference speed for a predetermined time outside a synchromesh mechanism operational range of said transmission. The transmission control system of claim 1, wherein said speed detector (4a) and said decision maker (4b) are incorporated in said control unit (4). A method of controlling a transmission control system with gear shift failure detection with the features of claim 1, characterized by the following steps: turning off said shift actuator (2b) so that a hydraulic pressure on said piston rod (2c, 2d) becomes zero if said decision maker (4b) decides that said shift actuator (2b) failed to make a gear shift and if said piston rod (2c, 2d) is at a relatively shallow shift-in position; or driving said shift actuator (2b) into a neutral position if said piston rod (2c, 2d) is at a relatively deep shift-in position and then making a shift-in operation again. The method of claim 3, which further comprises the steps of: moving a gear select position of said select actuator (2a) from a set position by an increment if said piston rod (2c, 2d) is at a relatively shallow shift-in position; and driving said shift actuator (2b) for making a gear shift. The method of claim 4, which further comprises the step of turning on said shift actuator (2b) whenever correction is made from said set gear position for making a shift-in. The method of claim 5, which further comprises the step of deciding that said shift actuator (2b) is at a shallow or deep position if a difference between a shift position signal and a target signal is small or large.

Inventors: KONO HIROMI C O KABUSHIKI KAIS, OTSUKA MASUHIRO C O KABUSHIKI, SATOH YUJI C O KABUSHIKI KAISH, SODA HIROYUKI C O KABUSHIKI KA, KONO, HIROMI, C/O KABUSHIKI KAISHA ZEXEL, OTSUKA, MASUHIRO, C/O KABUSHIKI KAISHA ZEXEL, SATOH, YUJI, C/O KABUSHIKI KAISHA ZEXEL, SODA, HIROYUKI, C/O KABUSHIKI KAISHA ZEXEL
Applicants: ZEXEL CORP, KABUSHIKI KAISHA ZEXEL
Application year: 1990
Main classification: F16H61
IPC codes: F16H61, F16H59