METHOD OF CONTROLLING SPEED CHANGE IN HYDRAULICALLY WORKING MULTISTAGE TRANSMISSION

Abstract: The present invention relates to a method of controlling a speed change in a hydraulically working multistage transmission, for the purpose of preventing the engagement shock of a direct-coupled clutch provided on a torque converter from occurring. This method of controlling the speed change includes the steps of: temporarily performing shift-down from a high speed stage to a low speed stage with the direct-coupled clutch (8) engaged when a vehicle is normally stopped; and, thereafter, further performing shift-down with an accelerator not stepped on and the clutch (8) kept disengaged.

Description: The present invention relates to a method and a system of controlling the shifting of a hydraulic-actuated type multi-step transmission for use on a large-sized construction vehicle and so forth. In EP-A-0394498, published after the priority date of the present invention, a method of and a system for controlling the shifting a multi-step power transmission are disclosed. The multi-step transmission is equiped with a plurality of hydraulic clutches and gear trains, whereby a shift can be made into a desired speed gear by engaging a specific hydraulic clutch. This type of hydraulic-actuated multi-step transmission is used in combination with a torque converter. This torque converter has a direct-coupled clutch in which pump and turbine blades of the torque converter are connected. During travelling the direct-coupled clutch is engaged for efficient transmission of a great torque. In case a vehicle should be decelerated from any high speed stage between the 7th speed and the 4th speed, i.e. a high transmission speed range, to coasting speed or the vehicle should be decelerated from any low speed stage, as for example the 3rd or 2nd speed, i.e. a low transmission speed range, to a coasting speed, the coasting speed is only obtainable by releasing an accelerator and brake pedal of the vehicle. During down-shift from the high transmission speed range to coasting speed the direct-coupled clutch is in engaged condition and during down-shift from the low transmission speed range to a coasting speed the direct-coupled clutch is disengaged. Before it is decided according to EP-A-0394498 if a deceleration from a high or a low speed stage will take place it is detected if the accelerator is inoperative and the brake is inoperative, that means that accelerator and brake pedal are released. Only in case both detections are positive the deceleration by down-shifting will take place. The present invention has as its object the provision of a method of and a system for controlling the shifting of a hydraulic-actuated type multi-step transmission in which no engagement shock will occur at the time of engagement of a direct-coupled clutch of a torque convertor. To attain the above-described object, the present invention provides a method of controlling the shifting of a multi-step power transmission and a system for controlling of a transmission speed ratio of an automatic power transmission with the features of claim 1 and 2, respectively. According to the invention a down-shift first takes place with the lock-up clutch in an engaged state and thereafter a further down-shift takes place with said lock-up clutch in a disengaged state. The down-shift will take place if the shift command for down-shift is given and the accelerator is only partially depressed. In this case the down-shift from high speed stages may be performed when additionally the accelerator and brake pedal are released. That means, that such a deceleration by down-shifting will only take place if coasting is detected. Subsequently, even if the accelerator is still partially depressed, the down-shift can take place from low speed stages, that means from 3rd and 2nd speed stages. In this case coasting is no requirement for down-shifting. Moreover, according to the afore-mentioned shifting method system, it is possible to decrease a shock accommpanying a shifting operation by preventing the occurance of an engagement shock at the time of direct-coupled clutching engagement (ON), thereby giving no unpleasant feeling to the driver and improving the durability of the power transmission system. In the following a preferred embodiment of the present invention will be described in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS : Fig. 1 is a diagrammatic view for explaining the constitution of a power transmission system of a motor vehicle in which a method of controlling the shifting of the present invention is adopted; Fig. 2 is a hydraulic circuit diagram of the power transmission system illustrated in Fig. 1; Fig. 3 is a control circuit diagram; Fig. 4 is an operation flowchart; and Fig. 5 is a graph showing a relationship between hydraulic pressure changes and the lapse of time in a direct-coupled clutch and other hydraulic clutches. DESCRIPTION OF THE PREFERRED EMBODIMENT : As shown in Fig. 1, an output shaft 2 of an engine 1 is connected to the input side of a torque converter 3, and its output side is connected to the input side of the hydraulic-actuated type transmission 4. Also the output side is connected to the right and left driving wheels 7 through a drive shaft 5 and a differential 6. The above-mentioned torque converter 3 has a direct-coupled clutch 8 which connects a pump (impeller) on the input side to a turbine wheel on the output side. The hydraulic-actuated type transmission 4 is equipped with a high-speed hydraulic clutch H, a low-speed hydraulic clutch L, a fourth hydraulic clutch IV, a third hydraulic clutch III, a reverse hydraulic clutch R, a second hydraulic clutch II, and a first hydraulic clutch I, and changes gear ratios as tabled below by engaging and disengaging these hydraulic clutches. Hydraulic clutch Speeds Forward Reverse 1st 2nd 3rd 4th 5th 6th 7th 1st H ON ON L ON ON ON ON ON IV ON ON III ON ON R ON II ON ON I ON The direct-coupled clutch 8 stated above, as shown in Fig. 2, has a direct-coupled clutch valve 10 for controlling the supply of a hydraulic oil from the pump P; and each hydraulic clutch has a high-speed valve 11, a low-speed valve 12, a fourth valve 13, a third valve 14, a reverse valve 15, a second valve 16, and a first valve 17 to control the supply of the hydraulic oil delivered from the pump P. The direct-coupled clutch valve 10 is switched by a first solenoid valve 20, and each valve is switched by means of a second, third, fourth, fifth, sixth, seventh and eighth solenoid valves 21, 22, 23, 24, 25, 26 and 27. These solenoid valves are designed to be operated by solenoids 20a to 27a. These solenoids, when energized, switch these valves for engagement of the direct-coupled clutch valve 10 and hydraulic clutches. The above-described constitution, known as a prior art, will not be described in detail. The solenoids 20a to 27a previously stated are controlled by means of a controller 30. To this controller 30 are inputted a speed signal γ from a shift lever 31, a vehicle speed V from a vehicle speed sensor 32, an accelerator off signal S from an acceleration sensor 33, and a brake off signal S from a brake pedal 34. Also, as shown in Fig. 4, the controller 30 controls the solenoids 20a to 27a, thereby controlling shifting operation. In the flowchart shown in Fig. 4, with the on-off operation of the solenoid 20a, the delay timer is operated upon receiving a shift command, so that the hydraulic pressure at the hydraulic clutch and the hydraulic pressure at the direct-coupled clutch 8 will increase or decrease as shown in Fig. 5. That is, when coasting and shifting down from for example one of the seventh to fourth speeds with the accelerator and brake pedals released, a downshift is automatically performed with the direct-coupled clutch 8 kept engaged, thus decelerating smoothly within a short time by effectively utilizing the engine brake. Also, when just stopping the vehicle, a downshift is automatically made once to low, for example from the third to the second speed with the direct-coupled clutch 8 held engaged. Then, with the accelerator released, and besides with the direct-coupled clutch held in the disengaged state, when disengaged at the time of shifting, until its engagement is required, a downshift is automatically made, thereby preventing the occurrence of an engagement shock when the direct-coupled clutch 8 is engaged. After a downshift was made into low as previously stated, the vehicle speed is substantially low, and therefore it is unnecessary to use the engine brake. No problem will occur if a downshift is effected with the direct-coupled clutch 8 disengaged. In case the vehicle speed decreases notwithstanding that the accelerator is fully depressed at the entry of an upgrade, the direct-coupled clutch 8 is disengaged only at the time of shifting and engaged after the completion of the shifting.

Claims: A method of controlling the shifting of a multi-step power transmission which is shiftable between a plurality of transmission speed ratios including a first group of transmission speed ratios falling within a high transmission speed range and a second group of transmission speed ratios falling within a low transmission speed range, in which down-shifting of said transmission from a higher ratio within said high transmission speed range is performed with a direct-coupled clutch of a torque converter maintained in an engaged state and shifting-down of the transmission within said low transmission speed range is performed with said direct-coupled clutch maintained in a disengaged state, wherein automatic down-shifting is performed in a sequence of operations comprising the steps of: automatically effecting a down-shifting of said transmission from a higher transmission speed ratio within said high transmission speed range to a lower transmission speed ratio for deceleration with said direct-coupled clutch of said torque converter maintained in an engaged state, when coasting is detected; and subsequently and automatically effecting a further shifting-down of the transmission from a higher transmission speed ratio within said low transmission speed range to a lower transmission speed ratio independently of coasting with said direct-coupled clutch maintained in a disengaged state while the accelerator is only partially depressed. A system for controlling of a transmission speed ratio of an automatic power transmission (4) which is cooperated with a torque converter (3) incorporating a lock-up clutch for direct coupling of an output of a prime mover (1) of the vehicle to an input of said power transmission including a first group of transmission speed ratios falling within a high transmission speed range and a second group of transmission speed ratios falling within a low transmission speed range, in which down-shifting of said transmission is performed from a higher ratio within said high transmission speed range with a direct-coupled clutch (8) of said torque converter maintained in an engaged state and a shifting-down of the transmission is performed within said low transmission speed range with said direct-coupled clutch (8) maintained in a disengaged state, comprising: means for detecting a current transmission speed ratio; means (33) for detecting a depression magnitude of a vehicular accelerator; means for detecting a predetermined lock-up condition for establishing a lock-up condition of said lock-up clutch in said torque converter (3); means for detecting a down-shifting demand; means for effecting down-shifting from the current transmission speed ratio to a lower transmission speed ratio in response to said down-shifting demand, wherein means for controlling the condition of said lock-up clutch (8) between the lock-up condition and a released condition based on said current transmission speed ratio and said depression magnitude of said accelerator during down-shifting operation of the transmission speed ratio are provided, which means maintain said lock-up clutch (8) at the lock-up condition during down-shift through several ratios starting from a high transmission speed ratio and said high range after coasting is detected and, subsequently, maintaining the lock-up clutch at the released condition during further down-shift within said low range independantly of coasting and the detected condition of the accelerator pedal during the down-shifting within low range.

Inventors: KUSAKA KOHEI, OHKURA YASUNORI, KUSAKA, KOHEI, OHKURA, YASUNORI, KUSAKA, KOHEI KAWASAKI FACTORY OF K.K. KOMATSU, OHKURA, YASUNORI TECHNICAL INST. OF K.K. KOMATSU
Applicants: KOMATSU MFG CO LTD, KABUSHIKI KAISHA KOMATSU SEISAKUSHO
Application year: 1990
Main classification: F16H61
IPC codes: F16H61, F16H59