Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Clutch control
Reexamination Certificate
2002-03-21
2003-12-02
Marc-Coleman, Marthe Y. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Clutch control
C701S059000, C477S120000, C192S085060
Reexamination Certificate
active
06658341
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a torque point learning method and control method of a clutch, and particularly to a torque point learning method and control method of a wet friction clutch provided to the power transmission of vehicles.
This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in Japanese Patent Application No. 2001-085303 filed Mar. 23, 2001 and Japanese Patent Application No. 2001-085304 filed Mar. 23, 2001 and Japanese Patent Application No. 2001-093252 filed Mar. 28, 2001.
2. Description of the Related Art
In a power transmission device of vehicles, there are those which serially provide a fluid coupling (including a torque converter) and a wet friction clutch in the middle of a power transmission path from the engine to the transmission, and automatically disconnect/connect the wet friction clutch during a gear shift. Here, if a gear-in operation is made when the vehicle is not in motion, the clutch is thereafter automatically connected, and a creep is generated thereby. This point is similar to an ordinary AT vehicle.
Connection of the clutch will generate a clutch connection shock (so-called garage shock, etc.) when too fast, and much time will be required from the gear-in operation to the creep generation when too slow, and the driver will not know when to step on the acceleration (large time lag). Thus, in order to seek the successful combination of such clutch connection shock and shortened connection time, a control is performed so as to rapidly connect the clutch in the allowance region up to when the clutch begins to connect, and to slowly connect the clutch by switching the connection speed once the clutch begins to connect.
More specifically, the working fluid pressure for driving the disconnection/connection of the clutch is altered in accordance with the duty pulse output from the electronic control unit (ECU), and, when connecting the clutch from a disconnected state, a prescribed start duty is foremost output from the electronic control unit such that the clutch will be broadly connected up to a position near where the clutch begins to connect (this is referred to as a single connection), and a gradual connection duty is thereafter output from the electronic control unit in prescribed time intervals for gradually connecting the clutch.
The aforementioned control is an open control, and the ECU outputs a duty pulse pursuant to a predetermined prescribed program.
As shown with the broken lines in
FIG. 11
, the clutch connection control of the prior inventions foremost outputs from the ECU a prescribed start duty Dst' so as to broadly connect the clutch up to a position near where the clutch begins to connect (this is referred to as a single connection control), thereafter outputs from the ECU in prescribed time intervals a prescribed gradual connection duty Dk' so as to gradually connect the clutch, and, when reaching a prescribed gradual connection end duty Ded', outputs a complete connection duty Dc' (=0%) such that the clutch is completely connected.
The position where the clutch begins to connect; that is, the torque transmission starting point capable of initially transmitting a prescribed torque, is referred to as a torque point, and this torque point is used, for example, as a connection speed switching point by making the control unit learn such point, and a torque point plays an important role in the clutch control. The torque point is made a learning value because clutches have variations or individual differences caused by manufacturing errors or the like, and the torque point differs for each clutch.
Meanwhile, with respect to torque point learning, conventionally, in a dry friction clutch, a clutch stroke value for transmitting a prescribed torque was initially detected, and such value was learned as the torque point.
Nevertheless, in the case of a dry friction clutch, since the clutch plate is constantly sliding in the oil and the torque transmission is achieved with the clutch piston pressing the plates together, the concept of stroke does not exit in the first place. Moreover, although the clutch piston will make a stroke, the stroke length is small (approximately 2 mm for example). Therefore, it is not possible to adopt the method of detecting the clutch piston stroke and making this the learning value as with a dry [friction clutch.
Further, with a wet friction clutch, also considered may be a method of detecting the hydraulic pressure applied to the clutch piston. Nonetheless, a hydraulic sensor is expensive, and the detection of hydraulic pressure is difficult from a structural perspective. In addition, not only is there a problem with respect to the reliability of the detected value itself due to the large hydraulic pulse, there is also the problem in that individual variations exist since the same torque is not necessarily transmitted to the same hydraulic pressure value. Thus, this method may not be adopted either.
On the other hand, with respect to the clutch control and torque point learning, the following problems arise if the gradual connection duty output is commenced immediately after the start duty output. In other words, although the fluid pressure of the clutch piston chamber will rapidly rise pursuant to the output of the start duty, the clutch piston commences the pressing of the clutch plates after a small stroke (approximately 2 mm) of the initial allowance is made. The response will therefore be delayed for the stroke portion, and, when commencing the output of the gradual connection duty immediately after the output of the start duty, the response delay of such deviance will be carried over into the gradual connection. Since similar control is performed during the torque point learning, there is a problem in that the value of the connection side is learned rather than the true torque point of the clutch upon such learning. Moreover, there is an additional problem of the clutch connection shock becoming large upon employing the learning value deviating toward the connection side and due to the aforementioned response delay during the clutch connection control.
Meanwhile, as shown in
FIG. 11
, with respect to the clutch control, in reality, the torque point may vary due to disturbances such as individual differences, operational conditions, change in properties with time or the like of the clutch, and the optimum start duty value may vary or deviate as illustrated with Dst
1
′ and Dst
2
′. Moreover, it is not possible to detect such variance or deviation prior to renewing the torque point learning. Therefore, in this case also, if control is performed with the start duty value remaining at Dst′, the connection time lag will become large when deviating to Dst
1
′, and the connection shock will become large when deviating to Dst
2
′.
The following explanation is made with particular reference to the state upon starting the vehicle.
FIG. 13
represents the state of the creep change when the gear-in operated is made (when the so-called garage shift is made) immediately before the vehicle is put into motion, and also illustrates changes in the revolution of the input side (pump) and output side (turbine) of the fluid coupling. Revolution of the input side of the fluid coupling may be replaced with engine revolution Ne (solid line), and the revolution of the input side of the fluid coupling, or the turbine revolution Nt (chain line), may be replaced with the clutch input side revolution as is.
At time t
0
, let it be assumed that the gear-in operation has been completed and that the clutch connection control has been commenced. Since the output side of the clutch is being stopped with a brake from the drive wheel side, the fluid coupling slides more in accordance with the connection of the clutch, and while the pump, which is the input side of the fluid coupling, revolves at a prescribed idle revolution equivalent to the engine rev
Inoue Eiji
Shinojima Takumi
Isuzu Motors Limited
Marc-Coleman Marthe Y.
McCormick Paulding & Huber LLP
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