Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Reexamination Certificate
2002-11-27
2003-10-21
Pang, Roger (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
Reexamination Certificate
active
06634990
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of controlling hydraulic pressures in a speed changing mechanism having a plurality of hydraulic clutches, that is, a hydraulic power shift speed change mechanism. Particularly, the invention relates to a method of controlling hydraulic pressures in a multistep-speed-type speed change mechanism constituted such that a plurality of hydraulic type speed change units are connected in tandem, wherein each of the hydraulic type speed change units is constituted of a plurality of transmission trains, and a hydraulic clutch is provided in each of the transmission trains.
BACKGROUND ART
Conventionally, there is publicly known a so-called hydraulic power shift speed change mechanism configured of a plurality of hydraulic clutches (fluid-operated multidisc clutches). Particularly, there is publicly known a multistep-speed-change-type speed change mechanism constituted such that a plurality of hydraulic type speed change units are connected in tandem, wherein each of the hydraulic type speed change units is constituted of a plurality of transmission trains, and a hydraulic clutch is provided in each of the transmission trains. In vehicles including the speed change mechanism, such as an agricultural and other work tractors, speed-changing for the number of steps obtained by multiplying the numbers of transmission trains provided in individual speed change units. Suppose a speed change mechanism configured of two hydraulic type speed change units, in which two transmission trains are provided in one of the hydraulic type speed change units, and three transmission trains are provided in the other hydraulic type speed change unit. In this case, 2×3 steps are obtained; that is, totally, six-step speed changes can be performed.
Conventionally, to perform input/output control for engagement/disengagement operating fluid for individual hydraulic clutches in the above-described speed change mechanism, electromagnetic-type selector valves are used.
In connection with the conventional hydraulic-pressure control for the hydraulic clutches at the time of speed-changing, first of all, the relationship in time between engagement-objective clutches and disengagement-objective clutches will be described below. Essential things regarding speed-changing include the prevention from a case where double transmission trains are operated to be in transmission states. Specifically, in the above-described multistep-speed-change-type speed change mechanism configured by combining the plurality of hydraulic type speed change units, it is essential to avoid a case where two clutches are operated in an engaged state in each of the speed change units. Therefore, conventionally, a disengagement-objective clutch is first disengaged substantially completely; and after a nontransmission state is once made in the speed change mechanism, the engagement of the engagement-objective clutch is then started. However, a high load is imposed during a nontransmission state, the vehicle is likely stopped. In addition, since a hydraulic pressure begins to rise from the nontransmission state when the engagement-objective clutch starts engagement, there remain problems which cannot be solved in that great shocks occur, thereby causing an operator to feel uncomfortable.
In view of the above, as described below in the “Disclosure of Invention” and in other portions, even when the transmission efficiency is reduced to the lowest level during speed-changing, at least either the disengagement-objective clutches or the engagement-objective clutches are controlled to be in slip states. Specifically, operating timing and a time-transitional hydraulic pressure property for the individual disengagement-objective clutch and the individual engagement-objective clutch are set so that a region representing a slip state (the region will hereinbelow be referred to as a “common slip region”) for the two clutches can be secured.
Hereinbelow, a brief description will be made regarding clutch hydraulic pressures in the slip state. The pressure for a disengaged clutch in a fluid chamber is substantially 0, and a piston for operating a clutch disc is in a free state. To engage the disengaged clutch, first, fluid is fed to a fluid chamber therefor to be filled out, and the filled out fluid must be used to increase the pressure to hold the piston. When a hydraulic pressure having a value that is sufficiently high to hold at least the piston is set to a piston-holding pressure, the hydraulic piston is brought to a slip state at an operating hydraulic pressure that is higher than the piston-holding pressure.
However, different from the above-described conventional hydraulic-pressure control for which the relationship between the individual hydraulic pressure states for the disengagement-objective clutch and the engagement-objective clutch need not be taken into account, in the hydraulic-pressure control of the present invention, when the individual time-transitional hydraulic pressure properties for the engagement-objective clutch and the disengagement-objective clutch are fixed as have been set under specific conditions where, for example, the engine is operated at a rated revolution frequency, there occurs cases wherein no common slip region can be secured because of the conditional variations.
For example, in a speed change mechanism configured of two hydraulic type speed change units, there are two speed-changes. One of the speed changes is performed such that in one of the hydraulic type speed change units, clutches remain held in engaged states; and in the other hydraulic type speed change unit, one engaged clutch is disengaged, and a different clutch is newly engaged (one-objective-based hydraulic clutches are disengaged/engaged). The other speed change is performed such that, in each of the hydraulic type speed change units, one engaged clutch is disengaged, and a different clutch is newly engaged; that is, in the overall speed change mechanism, totally, two clutches are disengaged, and two clutches are engaged (two-objective-based hydraulic clutches are disengaged/engaged). As described above, before an engagement-objective clutch is controlled to be in a slip state, wait time is required until the pressure increases up to the level of the piston-holding pressure after the fluid is injected into the fluid chamber of the clutch. For two-objective-based hydraulic clutches to be disengaged/engaged, aforementioned time is required substantially twice as much as that in the case where one-objective-based hydraulic clutches are disengaged/engaged. Therefore, when clutch-timing and a time-transitional hydraulic pressure property are set to secure a common slip region according to the case where the one-objective-based hydraulic clutches are disengaged/engaged, they are not suitable to the case where the two-objective-based hydraulic clutches are disengaged/engaged.
When the engine revolution frequency is reduced, time required for filling out the fluid in the clutch fluid chamber is increased. Therefore, for example, hydraulic-pressure control is set to obtain a common slip region during a rated revolution. However, problems similar to the above can arise during idle revolution.
In comparison between a speed-changing operation at a shifting-up time and a speed-changing operation at a shifting-down time, in the former case, since the relative revolution speed of a secondary-side rotation shaft with respect to that on a primary side of an engaged/disengaged is increased, a common-slip-region period needs to be set to be relatively long. On the other hand, in the latter case, the speed-changing is performed to reduce the relative revolution speed of the same secondary-side rotation shaft, and rotational inertia at a time of preshift operation is imposed on the secondary-side rotation shaft. Therefore, the common-slip-region period may be short; and when it is long, smooth speed-changing is impaired.
As in the conventional case, in speed-changing in which an engagement-objective clutch is engaged a
Katou Katsunori
Matsufuji Mizuya
Pang Roger
Sterne Kessler Goldstein & Fox P.L.L.C.
Yammar Co., Ltd.
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