Interrelated power delivery controls – including engine control – Transmission control – With clutch control
Reexamination Certificate
2002-12-04
2004-06-29
Pang, Roger (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
With clutch control
C477S175000, C192S003580
Reexamination Certificate
active
06755766
ABSTRACT:
CROSS REFERENCES TO RELATED APPLICATIONS
This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in Japanese Patent Application No.2001-380272 filed Dec. 13, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vehicle power transmission device, and more particularly to a vehicle power transmission device in which a fluid coupling and a wet friction clutch capable of engagement/disengagement control are provided in series.
2. Description of the Related Art
As is illustrated in
FIG. 1
, the present inventors have developed a new vehicle power transmission device in which a fluid coupling
2
and a wet friction clutch
3
are provided in series at points along a power transmission path which extends from an engine E to a transmission T/M, and in which the wet friction clutch
3
automatically engages and disengages during transmission. In this case, following an operation to put a vehicle in gear when the vehicle is stationary, the clutch is automatically engaged, thereby generating creep. A typical AT automobile is similar in this respect.
If the clutch engages too quickly, clutch engagement shock (so-called garage shock or the like) is produced, and if the clutch engages too slowly, creep generation takes time following the operation to put the vehicle into gear such that the driver does not know when best to step on the accelerator (large time lag). Thus, in order to strike a balance between reducing the engagement time and the occurrence of clutch engagement shock, control is performed such that the clutch is rapidly engaged in the clutch bite region prior to the beginning of clutch connection, and once the clutch begins to connect the engagement speed is switched to low speed and the clutch is slowly connected (slowly engaged).
More specifically, the operating fluid pressure for driving the engagement/disengagement of the clutch is varied in accordance with duty pulses outputted from an electronic control unit (to be referred to as ECU hereinafter), and the clutch is engagement/disengagement controlled thereby. Further, since this control is open control, the ECU outputs duty pulses in accordance with a predetermined program.
As is illustrated by the broken line in
FIG. 5
, conventional clutch engagement control is performed by first outputting a predetermined starting duty Dst′ from the ECU such that the clutch is engaged to a large extent up to a position near the beginning of clutch connection (this being known as “one-shot engagement control”), then by outputting predetermined slow engagement duties Dk′ from the ECU at predetermined time intervals such that the clutch becomes slowly engaged, and finally, when a predetermined final slow engagement duty Ded′ has been reached, by outputting a full engagement duty Dc′ (=0%) from the ECU such that the clutch becomes fully engaged.
The position at which clutch connection begins, or in other words the torque transmission starting point at which predetermined torque can first be transmitted, will be referred to as the torque point. This torque point is learned by the ECU and used as a reference value for engagement speed switching. The torque point is set as a learning value because of irregularities and individual differences among clutches caused by construction errors, and because the torque point differs from clutch to clutch or from vehicle to vehicle.
In
FIG. 5
, the torque point is Dlt, and the starting duty Dst′ is typically a value which is slightly further toward the disengagement side than the torque point Dlt. As a general principle, provision is made such that excessive engagement shock is not generated by the one-shot engagement control.
Attention will now be focussed upon a garage shift performed during vehicle start-up. Clutch engagement control similar to that described above is also performed here.
FIG. 6
shows the state of creep variation during an operation to put the vehicle in gear directly preceding start-up (when a so-called garage shift is being performed), and also illustrates the state of rotation speed variation of the input side (pump) and output side (turbine) of the fluid coupling. The rotation speed of the input side of the fluid coupling is switched to the engine rotation speed Ne (unbroken line). The rotation speed of the output side of the fluid coupling is switched to the turbine rotation speed Nt (dot/dash line) and may be switched as is to the rotation speed of the clutch input side.
Any time earlier than time t0 indicates a braking operation, neutral gear, and clutch disengagement. At time t0, the gear is fully engaged from the aforementioned state to the start-up level, and clutch engagement control begins. Since the output side of the clutch is damped by a brake from the drive wheel side, slippage of the fluid coupling increases as clutch engagement proceeds, and the pump, which is the input side of the fluid coupling, rotates at a constant idling rotation speed which is equal to the engine rotation speed Ne, whereas the turbine rotation speed Nt gradually drops. By this process, creep gradually increases.
Now focussing on control at the point of half clutch completion, this is conventionally performed using a method in which the full engagement duty Dc′ (=0%) is outputted during the output of the slow engagement duties Dk′ when the predetermined final slow engagement duty Ded′ has been reached, whereupon slow engagement control is switched to full engagement control. In other words, if the outputted duties reach the final slow engagement duty Ded′ at the point of half clutch completion, then the clutch is fully engaged.
When this method is used in reality, however, the clutch transmission torque at the point of half clutch completion may be unstable due to fluid pressure fluctuation or micro fluctuations in the wet friction clutch during control, and consequently the clutch cannot be engaged smoothly. The cause of this may be the moment at the point of half clutch completion when the clutch plates move from kinetic friction to static friction and the relative rotation difference therebetween is small. As a result of this moment, stability cannot be achieved on a micro level, and there is little redundancy with respect to fluctuation.
Problems arise in particular when the half clutch state (or the amount of time of slow engagement control) is protracted: hunting is produced in the turbine rotation due to temperature rises or the like in the clutch; irregular vehicle behavior (such as shock) is produced; and rattling sounds are produced due to collisions among the gears in the transmission.
SUMMARY OF THE INVENTION
The present invention has been devised in consideration of these problems, and it is an object thereof to create stability in the clutch transmission torque at the point of half clutch completion during a garage shift upon vehicle start-up, and thereby to engage the clutch smoothly.
The present invention is a vehicle power transmission device in which a fluid coupling and a wet friction clutch are provided in series at points on a power transmission path which extends from an engine to a transmission, and which performs engagement/disengagement control of the clutch by varying the operating fluid pressure used for engagement/disengagement driving the clutch in accordance with duty pulse signals outputted from an electronic control unit, wherein, when a vehicle starts up from a standstill, clutch engagement control is begun at the same time as the transmission is put into gear during a braking operation and a state of clutch disengagement, and a duty pulse signal corresponding to full clutch engagement is outputted from the electronic control unit when the rotation difference on the input and output sides of the fluid coupling reaches or exceeds a predetermined value during engagement control.
In this case it is preferable that this clutch engagement control be such that initially, one-shot engagement control,
Inoue Eiji
Kishi Satoshi
Shinojima Takumi
Isuzu Motors Limited
McCormick Paulding & Huber LLP
Pang Roger
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