Machine element or mechanism – Gearing – Interchangeably locked
Reexamination Certificate
1999-10-05
2001-07-24
Marmor, Charles A (Department: 3681)
Machine element or mechanism
Gearing
Interchangeably locked
C477S906000, C192S083000
Reexamination Certificate
active
06263751
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
The invention relates to a hydraulic circuit for controlling an automatic transmission in an automotive vehicle, and particularly a hydraulic circuit for controlling operation of forward and reverse clutches within an automatic transmission whereby the hydraulic circuit controls selection of torque transmission state, such as a forward drive state, a reverse drive state and a neutral state of the automatic transmission.
B. Description of the Background Art
An automatic transmission of a vehicle such as a construction machine or an industrial machine has forward and reverse hydraulic clutches which are hydraulically operated for forward drive and reverse drive, respectively. These clutches are controlled by a hydraulic circuit to set a vehicle in motion a forward drive state, a reverse drive state or a neutral state, where the drive state is selected by a vehicle driver or operator.
FIG. 7
shows a known structure of such a control hydraulic circuit (i.e., hydraulic circuit for control). A control hydraulic circuit
601
has a main pressure transmission line
602
which provides fluid pressure to a forward hydraulic clutch
611
and a reverse hydraulic clutch
612
via an accumulator
691
, an inching valve
692
and a forward/reverse selector valve
641
, and a pilot pressure transmission line
603
which is branched from the main pressure transmission line
602
and is connected to the forward/reverse selector valve
641
via a solenoid valve
671
. Each of the transmission lines
602
and
603
carries working fluid that provides hydraulic pressure to the above valves for operation thereof.
The main pressure transmission line
602
extends through the accumulator
691
and the inching valve
692
and is thereafter divided into two main pressure transmission lines
621
and
622
, which are connected to different portions of the forward/reverse selector valve
641
, respectively. The forward/reverse selector valve
641
is internally provided with a forward selector spool
642
and a reverse select spool
652
, which are opposed to each other with a spring
643
therebetween. The main pressure transmission lines
621
and
622
are connected via the forward/reverse selector valve
641
to main pressure transmission lines
623
and
624
, which are connected to the forward and reverse hydraulic clutches
611
and
612
, respectively.
A pilot pressure transmission line
603
is connected to the solenoid valve
671
, and then is divided into two pilot pressure transmission lines
631
and
632
, which are connected to different portions of the forward/reverse selector valve
641
, respectively, as shown in FIG.
6
. The solenoid valve
671
is internally provided with a direction select spool
672
, which can move leftward or rightward depending on a signal sent to the solenoid valve
671
. The pilot pressure transmission line
631
is connected to the side in the forward/reverse selector valve
641
near the forward selector spool
642
, and the pilot pressure transmission line
632
is connected to the side near the reverse select spool
652
.
In this control hydraulic circuit
601
, a vehicle driver specifies or selects the forward, reverse or neutral setting via a control panel or control switch (not shown), whereby an electric signal is sent to the solenoid valve
671
. Thereafter, the direction select spool
672
moves to a predetermined position corresponding to the forward drive state, the reverse drive state or the neutral state so that a flow path of the working fluid applying a pilot pressure is changed.
When the forward drive state is selected, the direction select spool
672
is pulled leftward by the solenoid. Thereby, the pilot pressure transmission line
631
opens so that the pilot pressure is transmitted via the pilot pressure transmission line
631
to the forward/reverse selector valve
641
. The working fluid in the pilot pressure transmission line
631
flows into the side in forward/reverse selector valve
641
near the forward selector spool
642
. Thereafter, the fluid pressure of the working fluid causes the forward selector spool
642
to move rightward against resistance of the spring
643
. Since a right enlarged portion of the forward selector spool
642
, which has closed the main pressure transmission line
623
, moves rightward, the main pressure transmission line
623
opens. Thereby, the main pressure which has been cut off at an outlet of the main pressure transmission line
621
is transmitted to the main pressure transmission line
623
, and further is supplied to the forward hydraulic clutch
611
to activate the forward hydraulic clutch
611
. In this manner, the forward drive selected by the vehicle driver is executed.
When the reverse drive is selected, the direction select spool
672
is pushed rightward by the solenoid
671
. Thereby, the pilot pressure transmission line
632
opens so that the pilot pressure transmitted through the pilot pressure transmission line
603
is transmitted to the forward/reverse selector valve
641
via the pilot pressure transmission line
632
. The working fluid in the pilot pressure transmission line
632
flows toward the reverse select spool
652
of the forward/reverse selector valve
641
. Thereafter, the fluid pressure of the working fluid pushes the reverse select spool
652
leftward against the biasing force of the spring
643
. Since the left enlarged portion of the reverse select spool
652
which has closed the main pressure transmission line
624
moves leftward, the main pressure transmission line
624
opens. Thereby, the main pressure in the main pressure transmission line
622
which had been obstructed by the reverse select spool
652
, is now transmitted into the main pressure transmission line
624
, and then is supplied to the reverse hydraulic clutch
612
so that the reverse hydraulic clutch
612
is operated. In this manner, the reverse drive selected by the vehicle driver is executed.
When the neutral position is selected, the direction select spool
672
moves to a position where the left enlarged portion closes the pilot pressure transmission line
631
, and the right enlarged portion closes the pilot pressure transmission line
632
. Thereby, the pilot pressure is cut off by the solenoid valve
671
, and is not transmitted to the forward/reverse selector valve
641
. Accordingly, the forward/reverse selector valve
641
maintains the main pressure transmission lines
621
and
622
in the interrupted state, and the main pressure is transmitted to neither the forward hydraulic clutch
611
nor the reverse hydraulic clutch
612
. In this manner, the neutral position selected by the vehicle driver is achieved.
However, a so-called “stick” may occur. More specifically, the select spools
642
and
652
sometimes are not able to return to the initial neutral position due to clogging of dust particles or the like which may enter the forward/reverse selector valve. In this case, the hydraulic circuit having the above structure may drive the vehicle in a direction opposite to that selected by the vehicle driver. For example, let us assume that a “stick” occurs where the forward drive has been selected in
FIG. 7
, and thus the forward selector spool
642
moved to the right position cannot return to the initial neutral position shown in FIG.
7
. In this case, if the vehicle driver who is not aware of the stick releases the forward drive state and selects the reverse drive state, the reverse select spool
652
cannot move leftward because the forward selector spool
642
cannot return from the right position. Therefore, it is impossible to open the main pressure transmission line
624
for operating the reverse hydraulic clutch
612
, and the main pressure transmission line
623
remains open so that the main pressure is supplied to the forward hydraulic clutch
611
. As a result, the vehicle is driven forward although the driver has selected the reverse drive state. Conversely, the stick may occur in the reverse drive state, in w
Exedy Corporation
Marmor Charles A
Parekh Ankur
Shinjyu Global IP Counselors, LLP
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