Machine element or mechanism – Gearing – Interchangeably locked
Reexamination Certificate
2000-07-18
2002-02-12
Estremsky, Sherry (Department: 3681)
Machine element or mechanism
Gearing
Interchangeably locked
C477S906000
Reexamination Certificate
active
06345548
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an automatic transmission which comprises a power transmission mechanism incorporating a plurality of power transmission paths and a plurality of hydraulically operated frictionally engaging means. These hydraulically operated frictionally engaging means are controlled to select these power transmission paths individually, by means of hydraulic oil which is supplied through a plurality of shift control valves.
BACKGROUND OF THE INVENTION
Such automatic transmissions have been known and are utilized, for example, as automatic transmissions for vehicles. Typically, an automatic transmission designed for use in a vehicle operates such that the transmission automatically controls the actuation of hydraulic clutches to change the speed change ratio in correspondence to the driving condition of the vehicle. Generally, the automatic transmission includes a speed change hydraulic unit which comprises a plurality of shift control valves, a solenoid valve to control the actuation of these shift control valves, and a manual valve operated in correspondence to the movement of the shift lever manipulated by a driver. In this arrangement, the automatic transmission automatically performs speed change control for a plurality of ranges, i.e., a reverse drive range, a neutral range and a forward drive range (D range, Second, First, etc.) which are individually selected by the operation of the manual valve operated in correspondence to the manipulation of the shift lever (generally, this automatic control is effective only in the forward drive range).
Recently, another type of automatic transmission has been introduced. This automatic transmission does not use a manual valve for the selection of a range and controls the shift of speed change ratios in each range solely by electrical signals. Such transmissions are disclosed in Japanese Laid-Open Patent Publication Nos. H5 (1993)-209683 (A) and H5 (1993)-215228 (A). Each automatic transmission disclosed there comprises a plurality of solenoid valves to control the actuation of shift control valves. The selection of the ranges, i.e., the forward drive range, the neutral range, and the reverse drive range, as well as the selection of the speed change ratios in the forward drive range are performed in correspondence to the command signals (electrical signals) which actuate these solenoid valves.
In such a speed change control system, as the selecting or switching of drive ranges and the setting of speed change ratios are controlled solely by the control pressures which are supplied from solenoid valves, if a solenoid valve malfunctions, then there can be a problem of inaccuracy in the selection of the drive ranges. As a preparation for such a problem, Japanese Laid-Open Patent Publication No. H5 (1993)-223156 (A) discloses a method for determining the drive ranges. In this method, hydraulic sensors are provided for detecting the control pressures that are generated for the respective drive ranges, and through the detection of the control pressures, the drive range selected actually at the moment is determined. In addition, drive range determination means determines the momentary drive range from the signals used for actuating the solenoid valves, and the drive range determined as presently selected from the actuation signals of the solenoid valves is compared with the drive range determined as actually selected from the detection of the control pressures, to confirm the selection of a right drive range and to determine whether there is an occurrence of abnormality.
Because a plurality of hydraulic sensors are provided to detect the command pressures that are generated for establishing the respective drive ranges, this method is likely to be affected from another problem. If any one of the hydraulic sensors malfunctions, then the determination of the drive ranges and of abnormality will become unreliable. To solve this problem, spare hydraulic sensors can be provided for each drive range. However, such solution is very costly because the sensors provided in a large number are used only for the detection of abnormality in the selection of the drive ranges.
SUMMARY OF THE INVENTION
To solve the above mentioned problem, the present invention provides a control system for an automatic transmission, which system performs a reliable determination of abnormality by determining whether a drive range is selected correctly. This system according to the present invention is capable of utilizing hydraulic pressure detecting means used for the above mentioned abnormality detection, for other purposes.
In order to achieve these objectives, the present invention provides a control system for an automatic transmission. This system comprises a power transmission mechanism (for example, the parallel shaft speed change mechanism TM of the embodiment described in the following section), a plurality of hydraulically operated frictionally engaging means (for example, the LOW clutch
11
, the SECOND speed clutch
12
, the THIRD speed clutch
13
, the FOURTH speed clutch
14
and the FIFTH speed clutch
15
of the following embodiment), a plurality of shift control valves (for example, the first shift valve
60
, the second shift valve
62
, the third shift valve
64
, the fourth shift valve
66
, the fifth shift valve
68
, the CPB valve
56
and the D inhibitor valve
58
of the following embodiment) and a forward/reverse hydraulic servomechanism (for example, the forward/reverse selection hydraulic servomechanism
70
of the following embodiment). Here, the power transmission mechanism incorporates a plurality of power transmission paths, and the hydraulically operated frictionally engaging means are activated by the supply of hydraulic pressure regulated by the shift control valves for the selection of the power transmission paths individually in the power transmission mechanism. The forward/reverse hydraulic servomechanism selects either the power transmission paths which belong to the forward drive range or the power transmission paths which belong to the reverse drive range. The control system further comprises a plurality of solenoid valves (for example, the first~fifth on/off solenoid valves
81
~
85
of the following embodiment) for supplying and draining a line pressure. In this arrangement, the line pressure supplied and drained through the solenoid valves is used to actuate the shift control valves and the forward/reverse hydraulic servomechanism for selecting the power transmission paths in speed change control. The system also comprises first pressure detecting means (for example, the hydraulic switch
93
of the following embodiment) and second pressure detecting means (for example, the hydraulic switch
92
of the following embodiment). The first pressure detecting means detects the hydraulic pressure which is supplied to a forward drive servo-oil chamber (for example, the right side oil chamber
73
of the forward/reverse selection hydraulic servomechanism
70
of the following embodiment) for selecting the power transmission paths of the forward drive range. The second pressure detecting means detects the hydraulic pressure which is supplied to one of the hydraulically operated frictionally engaging means (for example, the SECOND speed clutch
12
of the following embodiment), utilizing the hydraulic pressure supplied to the forward drive servo-oil chamber, for establishing a specific speed ratio for the forward drive range. With this construction, the control system can determine whether the forward drive range is set correctly or not, based on a result of pressure detection by the first and second pressure detecting means.
In this arrangement, the first pressure detecting means detects the hydraulic pressure supplied to the forward drive servo-oil chamber of the forward/reverse hydraulic servomechanism while the second pressure detecting means detects the hydraulic pressure supplied from the forward drive servo-oil chamber to a specific hydraulically operated frictionally engaging means. Therefor
Asatsuke Shouji
Ohashi Tatsuyuki
Shimada Takamichi
Wakamatsu Hideki
Yamaguchi Takayuki
Arent Fox Kinter Plotkin & Kahn PLLC
Estremsky Sherry
Honda Giken Kogyo Kabushiki Kaisha
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