Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Transmission control
Reexamination Certificate
2000-04-14
2001-08-07
Nguyen, Tan (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Transmission control
C477S125000
Reexamination Certificate
active
06272415
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a shift control apparatus of a working vehicle, and particularly to a shift control apparatus of a dump truck or the like which carries a heavy load and repeats starting, stopping, ascending and descending.
DESCRIPTION OF THE PRIOR ART
A working vehicle, for example, a dump truck, carries a heavy load, in which a transmission having multiple speed stages is used for repeating starting, stopping, ascending and descending and an automatic transmission apparatus is provided with taking an operability of an operator into consideration because of multiple speed stages. A plurality of hydraulic clutches are provided in an inner portion of the transmission, and a speed stage is set by turning on and off a hydraulic pressure to the clutch and combining the clutch to which the hydraulic pressure is applied and the clutch to which no hydraulic pressure is applied. The automatic transmission apparatus determines an up shift for increasing a speed when a transmission output shaft rotational speed becomes greater than a predetermined rotational speed and a down shift for reducing a speed when the transmission output shaft rotational speed becomes smaller than a predetermined rotational speed, in accordance with a speed change graph which is set on the basis of an operation amount of an accelerator pedal and the transmission output shaft rotational speed, and outputs a command to an electromagnetic proportional control valve which controls a hydraulic pressure of the clutch in a corresponding speed stage, thereby performing a shift operation.
When the shift operation is determined, the clutch after the shift operation corresponding to a determined new speed stage has a relative speed which is determined by the transmission output shaft rotational speed, a speed reduction ratio of the speed stage before the shift operation and a speed reduction ration of the speed stage after the shift operation. In this state, since a rotational inertia in a side of a transmission input shaft including a rotational inertia of the engine has a rotational acceleration when gradually increasing the clutch hydraulic pressure in point of time and engaging the clutch while slipping, an inertia torque calculated by multiplying the rotational inertia by the rotational acceleration is generated. The inertia torque is one of reasons by which a shift shock is generated. The inertia torque can be reduced by reducing an incline at which the clutch hydraulic pressure is gradually increased in point of time, however, a time for which the clutch slips becomes long, so that a quantity of heat generated in the clutch is increased and a durability of the clutch is deteriorated. Further, when reducing the incline of the clutch hydraulic pressure, a slow feeling is applied to an operator and a shift operability is not well.
For the purpose of reducing a shift shock of the working vehicle mentioned above so as to improve a shift operability, thereby maintaining a service life of the clutch, there is suggested a method of reducing a relative rotational speed of the clutch engaged at a shifting time and applying the hydraulic pressure. For example, there is a method described in Unexamined Japanese PCT Publication No. 9-509237. In accordance with the publication, it is structured such as to calculate a desired engine rotational speed corresponding to a desired transmission input shaft rotational speed so that the relative rotational speed becomes smaller than a predetermined set value and control the engine rotational speed so that a difference between the desired engine rotational speed and an actual engine rotational speed becomes 0. Further, a control of the engine rotational speed is started at a time when the hydraulic pressure of the clutch starts up after the shift operation which is started at a fixed time after the shift operation is determined, and is maintained for a control maintaining time which is adjusted by learning a data obtained by measuring the transmission input and output shaft rotational speed at every shift operation. Further, in the publication, it is supposed that a finish time of the maintaining time coincides with a finish time of the clutch engagement after the shift operation by learning the control maintaining time.
However, there are the following problems in the technique mentioned above.
The time of controlling the engine is an average time which is learned under respective travel conditions, and is a fixed time. Accordingly, in an actual work field in which an incline of a travel path, a loading amount and a road condition always change, the result of the learning can not sufficiently achieve an intended control function. Further, in the case that the work field is changed, a shift control performance is not sufficient and a shift operability is not good until learning the respective work field and being applied thereto.
Here,
FIG. 9
shows an example of a typical change in point of time of a clutch hydraulic pressure Pc in an automatic shift control apparatus of a work vehicle. A description will be given of a clutch engagement time in the case of a maximum loading time and an empty loading time. When setting a time t when starting the shift operation to 0, a hydraulic pressure (not shown) of the clutch before the shift operation corresponding to the speed stage before the shift operation is set to 0 when the shift operation is determined at a time when the time t is 0. Further, the oil starts being supplied to the clutch after the shift operation corresponding to the speed stage after the shift operation from the 0 time of the time t, and a filling time Tf is required before the clutch chamber is filled with the oil. After being filled with the oil, the clutch hydraulic pressure stands up at a predetermined incline and is increased to a predetermined maximum hydraulic pressure Pm. The predetermined incline is within a range of a time before the clutch is engaged after the shift operation, that is, a time range that a time Tt for which the clutch slips after the shift operation can secure a durability of the clutch, and is determined so that a small shift shock can be obtained, with taking into consideration a heavy load condition at a time of a maximum loading, traveling on a steep slope, traveling on a muddy road or the like.
However, in the predetermined incline of the clutch hydraulic pressure determined in this manner, there is the following problem. In general, when a vehicle body load which expresses a load to the clutch is small, for example, at an empty load time, the clutch is engaged in accordance with a small hydraulic pressure. Accordingly, since a start incline of the clutch hydraulic pressure is too large when the vehicle body load is small, a time Tk for which the clutch slips after the shift operation is smaller than the time Tt for which the clutch slips after the shift operation at the maximum loading time and the clutch is engaged for a short time. Accordingly, a rotational change of the output shaft of the transmission per a time is increased, and a shift shock is large. Further, since a time for which the shift operation is completed is not fixed due to a load change such as a weight of a load, an incline of a travel road and the like, a shift operability is not good.
Further, in accordance with the automatic shift control apparatus of the working vehicle, even in a state of pedaling the accelerator pedal (hereinafter, a shift operation in a state of pedaling the accelerator pedal is called as a power-on shift), in the case of shifting when the vehicle moves from a flat road to an ascending road having a large incline, a vehicle speed is suddenly reduced due to an insufficient traction force, so that there is a case that the shift operation is too late for the reduction of the vehicle speed when the shift operation is performed one step by one step until the speed stage capable of traveling is obtained. That is, since the time required for the shift operation, for example, 0.5 to 1 second is required for one shift op
Tanaka Satoshi
Uematsu Kouji
Armstrong Westerman Hattori McLeland & Naughton LLP
Komatsu Ltd.
Nguyen Tan
Tran Dalena
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