System and method for controlling vehicle speed to prevent gear shift shock applicable to automatic transmission equipped vehicles

Abstract: To prevent gear shift shock in a vehicle power train associated with a turbocharged engine (10) and an automatic transmission (12), an air charging efficiency for engine cylinders is reduced during the gear shifting transient period, e.g., when shifting from first gear range to a higher second gear range. Therefore, when engine output is reduced by means of retardation of ignition timing at the time of gear shifting, no misfire occurs due to prevention of internal pressure increase in any engine cylinder. Thus, shift shock can be prevented with the smooth reduction of engine output and air charging efficiency is smoothly recovered after completion of the gear shift transient period.

Description: BACKGROUND OF THE INVENTION : (1) Field of the invention The present invention relates to a system and method for controlling vehicle speed applicable to automatic transmission equipped vehicles in which output of an engine having a turbo charger is transmitted to a driven wheel via an automatic transmission. The present invention particularly relates to a system and method for controlling vehicle speed in which gear shifting control is carried out using switching pressure generated by means of on-and-off action of a plurality of solenoid valves. (2) Background of the art In general, automatic transmissions mounted in vehicles include a combination of coupled toothed gear components including a plurality of pairs of planetary gears so that several stages of gear range changes may be carried out by hydraulically operated frictional elements. A Japanese Patent Application First publication No. Tokkai Showa 62-62047 published on March 18, 1987 exemplifies a shock reduced automatic transmission in which a working fluid pressure for engaging and releasing each frictional element is controlled by means of two shift valves. The change in the shift valves is carried out by means of a change pressure generated by on-and-off action of a solenoid valve, a so called shift solenoid installed corresponding to the shift valves. An system for carrying out shift valve switching using solenoid valves has been applied to an RE4R01A type automatic transmission, described in "NISSAN FULL RANGE ELECTRONIC CONTROL AUTOMATIC TRANSMISSION", a service manual published in 1987. On and off control of the shift solenoids can finely control the change shift valve pressure. For example, at a transient time of gear shift change in which the gear position is shifted from the first range to the second range, timing control is carried out such that one of the shift valves is changed from on to off within a short period of time, a rise in the engaged pressure of the frictional elements is gradually carried out. Thus, a reduction of the gear range shock can be achieved. In addition, to reduce shock generated during a transient period of gear change, the engine output is reduced so that speed control of the vehicle is desirably carried out. This is exemplified by a Japanese Patent Application First publication showa 63-71530 published on March 31, 1983. To reduce engine output, the ignition timing can normally be retarded as described in the Japanese Patent Application First Publication No. Showa 63-71530. However, in previously proposed running speed controlling systems and methods, when internal cylinder pressure is increased with the ignition timing being retarded at the transient time of gear change, mis-firing occurs and engine operation becomes erratic. Conversely, if cylinder pressure is reduced, vibration at the time of gear change becomes great. Even though required secondary voltage may be reduced, an ignition device for igniting a mixture fuel supplied to the engine is large and costly. GB-A-2 151 727 according to the precharacterising parts of claims 1 and 9, discloses an automatic transmission in which shift shocks are alleviated. An engagement and release of frictional elements provides gear shifting, wherein solenoid valves control said shifting valves. Shift detecting means are provided for detecting a gear shift from a low gear speed range to a next higher gear speed range. The engine includes a relief valve for relieving an intake air pressure supplied to the engine. In order to reduce engine output torque, the intake air flow rate of the turbocharger supercharged pressure respectively is gradually decreased. SUMMARY OF THE INVENTION : It is an object of the present invention to provide a system and method for controlling a vehicle speed in which the change in the frictional elements at the time of the gear range change is carried out, the engine output control at the transient time of the gear range change is smoothly carried out, together with a timing control through an on-and-off of the solenoid valves. The above-described object can be achieved by an apparatus according to claim 1 and a method according to claim 9. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a simplified block circuit diagram of a vehicle speed controlling system in a preferred embodiment according to the present invention. Fig. 2 is a timing chart showing each element of the vehicle speed controlling system shown in Fig. 1. Fig. 3 is an operational flowchart executed by a control unit of the vehicle speed controlling system shown in Fig. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS: Reference will hereinafter be made to the drawings in order to facilitate a better understanding of the present invention. Fig. 1 shows a preferred embodiment of a vehicle speed controlling system according to the present invention. In Fig. 1, an engine 10 provides an output revolutional speed for an automatic transmission via a torque converter (not shown ). The automatic transmission 12 properly changes gear range according to engine revolutions and transmits driving force to driven wheels (not shown). The automatic transmission 12 includes a main transmission 12a which carries out gear range shifting of 4 forward speeds and a subtransmission 12b which switches between a speed increase position and a constant speed position, both main transmission 12a and subtransmission 12b being arranged in series with each other. Then, the combination of the four stages of the main transmission 12a and the additional speed increase stage of the subtransmission 12b results in a five stage shift range in the forward direction as shown in the following table I. Whole shift R Main Tr 12a Sub Tr 12b 1 st R 1st R Constant 2nd R 2nd R Constant 3rd R 3rd R Constant 4th R 3rd R Increase 5th R 4th R Increase The main transmission 12a and sub transmission 12b have power trains, respectively including a plurality of frictional elements such as clutches and brakes which engage or disengage (release) so that a changing of each gear speed range may be carried out. The engagement and disengagement of respective frictional elements is then carried out by means of a controlled fluid pressure supplied from a control valve (C.V.) 14 installed in the automatic transmission 12. That is to say, the above-described control valve 14 includes first and second shift valves for changing the main transmission 12a, and a third shift valve for changing the subtransmission 12b (all of the first, second, and third shift valves are omitted in Fig. 1). The changeover of the first, second, and third shift valves due to a change pressure allows the controlled fluid pressure to be supplied to or removed from respective frictional elements. It is noted that the structure of the main transmission 12a is exemplified as disclosed in Japanese Patent Application First Publication (Unexamined) No. showa 62-62047 published on March 18, 1987, the disclosure of which is hereby incorporated by reference. It is also noted that the automatic transmission disclosed in the Japanese Patent Application First publication No. Showa 62-62047 is coupled with the sub transmission 12b having a two-stage change capability so as to constitute the automatic transmission 12 of the preferred embodiment. The first, second, and third shift valves include a first, second, and third solenoids 16, 18, and 20, respectively (each solenoid 16, 18, and 20 being an offdrain type). When a drive signal transmitted from an A/T (automatic transmission) control unit 22 is caused to energize (turn on) any one of the first, second, and third solenoids 16, 18, and 20, a change pressure in the corresponding shift valve is generated. It is noted that the drive signal for each shift solenoid 16, 18, and 20 is derived from the A/T control unit 22 and is determined on the basis of such vehicle running conditions as opening angle of the throttle valve, vehicle speed, and so forth. The first, second, and third shift solenoids 16, 18, and 20 are controlled in an on-and-off mode so as to achieve each gear speed range shown in Table I, as appreciated from the following Table II. A charger such as a turbo charger 32 or super charger is installed in an intake air passage 30 of the engine 10. A charge pressure generated in the super charger 32 is supplied to each of the engine cylinders. A relief valve 34 is installed as an intake air quantity varying means in the intake air passage 30 downstream of the super charger 32. When the relief valve 34 is controlled in the open-and-close mode, a charge pressure supplied to each cylinder , i.e., a charging efficiency of air into the cylinder, is controlled. An engine control unit 36 for governing the engine is attached to the engine 10, the engine control unit 36 providing an ignition timing control signal for the engine 10 and providing an open-and-close control signal for the relief valve 34. The engine control unit 36 functionally includes gear changing point detecting means 38 for detecting a gear range changing point from a signal introduced as an ON or OFF signal to the first, second, and third shift solenoids 16, 18, and 20 from the A/T control unit 22. The gear changing point detecting means 38, at first, detects OFF signals of the first, second, and third shift solenoids 16, 18, and 20, when, as shown in Fig. 2, the gear range changing means detects the change from N (Neutral) range to D (Drive) range from a range signal, and then detects the first speed range (as appreciated from Table II) when each shift solenoid 16, 18, and 20 receives the ON signal. From thereon each gear range change is detected according to the Table II. The second shift solenoid 18 and third shift solenoid 20 are on-and-off controlled within a short period of time at a gear change transient time in which the first, low speed gear range is transferred to the second, higher speed gear range and thus smoothly changes the change pressure generated by the second and third shift solenoids 18, 20, thus providing a slight slip on the corresponding frictional element to prevent a gear change shock. In the preferred embodiment, the charge pressure caused by the turbo charger 32 is set to a lower value at the gear change transient time in which the gear range is transferred from the first speed range to the second speed range, as shown in Fig. 2. It is noted that the turbo charge pressure can be set to a lower value even in the N range as denoted by a broken line in Fig. 2. A timer 40 is provided in the engine control unit 36 for controlling the gear changing point detecting means 38 to detect the changeover signal, indicating the change from the first speed to the second speed, so that the gear change transient is detected with a time delay. Fig. 3 shows an operational flowchart for explaining the operation of the vehicle speed controlling system in the preferred embodiment described above. The operational flowchart shown in Fig. 3 is repeatedly executed by the engine control unit 36 at each predetermined period of time. In a step I, the engine control unit 36 reads the drive signal contents from the driven states of the first, second, and third shift solenoids 16, 18, and 20. In a step II, the control unit 36 determines the gear shift range position from the ON and OFF drive signals of the first, second, and third shift solenoids 16, 18, and 20. In a step III, the control unit 36 determines whether the gear shift range position is in the first speed range. If YES (first gear range), the routine goes to a step IV in which the timer 40 (which counts a predetermined time) is set. Thereafter, in a step V, the turbo charged pressure is reduced. Since the set time of the timer 40 corresponds to a transient time required for a gear change in the vehicle speed controlling system of the preferred embodiment, recovery of the charged pressure by means of the turbo charger 32 can be assured after the second speed range is set and resumption of the higher turbo charged pressure midway through the gear change transient time can be prevented. On the other hand, in a subsequent cycle of program execution, after the vehicle is in motion, if NO is determined, at the step III, the routine goes to a step VI in which the timer 40, set in the step IV is decremented for each execution of the flowchart shown in Fig. 3 and the routine goes to a step VII in which the control unit determines whether the timer indicates zero. If the timer indicates zero (YES) in the step VII, the routine goes to a step VIII in which the turbo charged pressure reduced in the step V is recovered and increased to a steady state. If the timer does not indicate zero (NO) in the step VII, the routine goes to the step V to continue reduction of the turbo charged pressure. It will be noted that, since operation of the automatic transmission does not allow gear shifting from N directly to the D2 range, when a vehicle initially begins to move the control program will proceed from steps I to V, steps VI to VIII being engaged only after the vehicle is in motion on subsequent cycles of program execution. In the previously proposed vehicle speed controlling system, misfiring occurs due to increase of internal pressure in each or any cylinder due to resumption of a higher turbo charged pressure midway through the gear change transient period, e.g., in a case such as when engine output is reduced during retardation of the ignition timing in the gear change transient time. On the other hand, in the preferred embodiment of the invention, resumption of turbo charged pressure is carried out after completion of the gear transient period at which time the ignition timing is recovered. Therefore, the engine 10 does not run erratically due to misfire and smooth gear changing becomes possible. Although, in the preferred embodiment, the turbo charger 32 is equiped with the engine 10, the present invention is applicable to an engine in which no turbo charger is mounted. In this case, the intake air quantity varying means must be mounted in place of the relief valve 34. In a case where the air charging efficiency is reduced in the gear change transient period by means of the intake air quantity varying means, the present invention is applicable so that no shock occurs due to change of the gear shift position and smooth gear changing can be achieved. Although, in the preferred embodiment, the present invention is applied to an automatic transmission having a main transmission and a sub transmission so that five forward gear speeds can be achieved, the present invention is applicable to automatic transmissions having four forward speeds as disclosed in the Japanese Patent Application First Publication No Showa 62-62047. As described hereinabove, in the vehicle speed controlling system and method according to the present invention, the engine air charging efficiency is set to a relatively lower value at the time of a gear change transient period from a low speed gear range to a higher speed gear range in response to a gear change signal detected with a predetermined time delay via a delay means (timer), the predetermined delay of time corresponding to the time required for the gear change transient period, resumption of the air charging efficiency can be smoothly carried out after the gear range is set to the higher gear range position. Hence, in a case where control to reduce the engine output in the gear change transient period is carried out, prevention from resumption increasing the air charging efficiency in the gear change transient period can be assured. Thus, it is possible to prevent increase in the internal pressure due to the retardation of the ignition timing and the engine operates smoothly at the time of the gear change. This, together with the reduction of shock generated when the frictional elements are engaged due to the ON and OFF control of the solenoid valves in a short period of time, insures that engine output is smoothly controlled. Consequently, shock generated when gear change occurs in an automatic transmission can remarkably reduced and riding comfort of the vehicle can remarkably improved. It will fully be appreciated by those skilled in the art that the foregoing description has been made in terms of the preferred embodiment and various changes and modifications may be made without departing from the scope of the present invention which is to be defined by the appended claims.

Claims: An apparatus for controlling gear shifting characteristics to prevent a gear shift shock in a vehicle equipped with an engine (10) and an engine driven automatic power transmission (12), a) said automatic power transmission (12) including: a plurality of frictional elements, combination of engagement and release thereof shifting gears of said automatic power transmission; a plurality of shifting valves which respectively engage and release said frictional elements to cause shifting of the gears; a plurality of solenoid valves installed individually on the respective shifting valves for controlling a pressure change of the shifting valves associated therewith, at least one of the solenoid valves being switched on during the gear shifting transient period in response to a drive signal; means for detecting vehicle running conditions and providing said drive signal according to the detected running conditions; b) said engine (10) having relief valve means (34) for operatively relieving an intake air pressure supplied to the engine; c) said apparatus (10) being provided with shift detecting means (36,38) for detecting a gear shift in said automatic power transmission from a low gear to a next higher gear, and control means for controlling said relief valve means (34) so that an air charging efficiency is at a low level after the detection of the gear shift, and said means (36) having a timer (40) which is set upon detection of said gear shift and which outputs a delay completion signal upon the elapse of a predetermined time, said predetermined time corresponding to the transient time required for the gear change, characterized in that said apparatus is provided with means (38, step V) for controlling the relief valve means (34) so that the air charging efficiency is at the low level from the time at which the gear shift is detected until the time at which the delay completion signal is received and with means (38, step VIII) for controlling the relief valve means (34) so that the air charging efficiency is increased to a steady state level upon receipt of the delay completion signal. An apparatus as set forth in claim 1, wherein the automatic transmission (12) includes a main transmission (12a) in which four forward speed range shifts may be carried out and a sub transmission (12b) in which an additional speed range shift is carried out, both main transmission (12a) and sub transmission (12b) being arranged in a series with each other so that a total of five forward speed range shifts may be carried out in the automatic transmission (12). An apparatus as set forth in claim 2, wherein the automatic transmission includes first and second shift valves for switching the gear speed ranges of the main transmission and a third shift valve for switching the gear speed ranges of the sub transmission, first, second and third shift solenoids (16,18,20) being installed on the first, second and third shift valves, respectively, the first, second and third shift valves being switched in combination to change any one of the gear speed ranges of the automatic transmission (12) under change pressure, generated when the corresponding shift solenoids (16,18,20) are driven in response to an ON signal, the combination of ON and OFF signals supplied to the first, second and third shift solenoids (16,18,20) causing the following forward gear speed ranges: An apparatus as set forth in claim 3, wherein the vehicular engine includes extra air charging means (32) installed in an intake air passage (30) thereof so that extra air charging pressure is supplied to the engine (10) and wherein the relief means comprises a relief valve (34) installed downstream of the extra air charging means (32) so that the air charging efficiency of engine cylinders is controlled via the relief valve (34). An apparatus as set forth in claim 4, wherein the shift control means (36) detects the point of time at which the automatic transmission (12) shifts the gear speed range from the combination of the ON and OFF signals supplied to the first, second and third shift solenoids (16,18, 20). An apparatus as set forth in claim 5, wherein the second shift solenoid valve and the third shift solenoid valve are repeatedly driven and not driven in response to the ON and OFF signals within the transient time for shifting from the first gear speed range to the second gear speed range so that the change pressure generated by the second and third shift solenoid valves is changed gradually to provide a slight slip for the corresponding frictional elements, thus preventing a shift shock from being generated when the gear range is shifted from a first range to a second range. An apparatus as set forth in one of claims 1 to 6, wherein the time delay means (40) comprises a preset timer associated with the gear shift detecting means (38) which provides the signal when the gear shifting transient time has elapsed. An apparatus as set forth in one of claims 1 to 7, which further includes means for retarding engine ignition timing during the gear shifting transient time. A method for controlling a vehicle speed so as to prevent shift shock from occurring in a power train associated with a vehicular engine and an automatic transmission, comprising the steps of: detecting vehicle running conditions and providing a drive signal according to the detected vehicle running conditions, detecting a gear shift in said automatic transmission (12) from a gear to a higher gear, controlling a change pressure of a shift valve in response to said drive signal, controlling a relief valve (34) so that an air charging efficiency is at a low level upon the detection of the gear shift, and providing a predetermined time delay upon the detection of said gear shift, characterized by the steps of: producing a delay completion signal upon a lapse of said predetermined time delay and of controlling the relief means so that the air charging efficiency is increased to a steady state level upon receipt of the delay completion signal.

Inventors: KATO YUJI, KATO, YUJI
Applicants: NISSAN MOTOR, NISSAN MOTOR CO., LTD.
Application year: 1990
Main classification: B60K41
IPC codes: F16H59, B60W10, F16H61, F02D41, F02D23, F16H63, F02B33, F02D29, F02B37, B60W30