Planetary gear transmission systems or components – Fluid drive or control of planetary gearing – Fluid pump and motor in one of plural paths to or from...
Reexamination Certificate
2000-09-14
2002-05-14
Bonck, Rodney H. (Department: 3681)
Planetary gear transmission systems or components
Fluid drive or control of planetary gearing
Fluid pump and motor in one of plural paths to or from...
Reexamination Certificate
active
06387005
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a hydraulic drive apparatus for a working machine which transmits an output torque of a plurality of hydraulic motors to an output shaft.
BACKGROUND OF THE INVENTION
In conventional, in a working machine such as a wheel loader or the like, there has been known a hydraulic drive apparatus which transmits an output torque of a plurality of hydraulic motors to an output shaft.
FIG. 9
is a skeleton view of a hydraulic drive apparatus disclosed in Unexamined Japanese Patent Publication No. 2000-193065. In
FIG. 9
, a hydraulic drive apparatus
1
is provided with an output shaft
2
connected to a load
20
, an output gear
3
adhered to the output shaft
2
, a first input gear
4
engaged with the output gear
3
, a first input shaft
5
to which the first input gear
4
is adhered, a second input gear
6
engaging with the first input gear
4
, and a second input shaft
7
to which the second input gear
6
is adhered. The output gear
3
, the first input gear
4
and the second input gear
6
are respectively spur gears.
A first hydraulic motor
8
having a high vehicle speed and a low torque and a control pump
9
are respectively connected to one end side portion of the first input shaft
5
and another end side portion thereof. Further, a second hydraulic motor
11
having a low vehicle speed and a high torque is connected to an axial end portion of the second input shaft
7
via a clutch
10
.
The first hydraulic motor
8
and the second hydraulic motor
11
are connected to a hydraulic pump (not shown) via a hydraulic parallel circuit and are driven by a discharged pressurized oil thereof.
The clutch
10
is normally in an engaging state due to an urging force of a spring
12
and is broken down in accordance that a clutch oil pressure P
3
supplied from an oil pressure source via an oil passage
13
becomes greater than the urging force. The clutch oil pressure P
3
is controlled to be supplied or broken down by a two position switching valve
14
interposed in the oil passage
13
.
An orifice
16
, a check valve
17
and a relief valve
18
are arranged in parallel in a discharged oil passage
15
of the control valve
9
. When an oil pressure P
1
of the discharged oil passage
15
detected by the orifice
16
is over a set oil pressure, a pilot pressure is supplied to the two position switching valve
14
and the two position switching valve
14
is opened, whereby the clutch oil pressure is applied and the clutch
10
is broken down.
At a time of low speed traveling, the clutch
10
is in an engaging state, both of the first hydraulic motor
8
and the second hydraulic motor
11
are connected to the output shaft
2
, thereby driving the load
20
at a high torque. Further, at a time of high speed traveling, a discharge amount of the control pump
9
is increased in accordance with an increase of a rotational number of the first hydraulic motor
8
. Further, when the oil pressure of the discharged oil passage
15
detected by the orifice
16
becomes over the set oil pressure, a pilot pressure P
2
is supplied to the two position switching valve
14
. Accordingly, the two position switching valve
14
is opened, the clutch
10
is broken down in accordance with the clutch oil pressure P
3
, and the torque is transmitted to the output shaft
2
from only the first hydraulic motor
8
, thereby driving the load at a high speed.
Further, at a time of changing to the low speed traveling from the high speed traveling, the discharge amount of the control pump
9
is reduced in correspondence to a reduction of the rotational speed of the first hydraulic motor
8
. Accordingly, the pilot pressure P
2
supplied to the two position switching valve
14
is reduced and the two position switching valve
14
is closed. As a result, the clutch oil applied to the clutch
10
at the clutch pressure P
3
passes to a drain
34
through a drain line
23
from the two position switching valve
14
, and the clutch pressure P
3
is reduced to be lower than the urging force of the spring
12
, whereby the clutch
10
in a broken state is engaged due to the urging force.
However, in accordance with the prior art mentioned above, there are the following problems.
That is, in accordance with an arrangement of the prior art, the spur gear is used for the output shaft
2
, and the first input shaft
5
and the second input shaft
7
are connected thereto. In the spur gear, it is necessary to largely change a size between axes and an outer diameter in order to change a speed reduction ratio, so that a freedom of setting a speed reduction gear of the first and second hydraulic motors
8
and
11
with respect to the output shaft
2
is low. Accordingly, there is a problem that it is hard to set an optimum speed reduction ratio with respect to each of the hydraulic motors
8
and
11
.
Further, since the second input shaft
1
is connected to the output shaft
2
via the first input shaft
5
, it is necessary to arrange a center axis of the first input shaft
5
in a left portion (or a right portion) of a center axis of the output shaft
2
and arrange a center axis of the second input shaft
7
in a further left portion (or a further right portion) thereof, so that the hydraulic drive apparatus is shifted in a lateral direction. Accordingly, in a working vehicle in which it is necessary to arrange the output shaft
2
at a substantially center in a lateral direction of the vehicle, for example, an articulate type working vehicle, there is a problem that a size of the hydraulic drive apparatus
1
in a lateral direction of the vehicle is increased and it is hard to mount in the working vehicle.
Further, since the second hydraulic motor
11
is connected onto the second input shaft
7
via the clutch
10
, the second input gear
6
and the clutch
10
are coaxially arranged, and an axial length of the second input shaft
7
is increased. Accordingly, there is a problem that the size of the hydraulic drive apparatus
1
is caused to be increased.
Further, since the clutch
10
is provided in the second input shaft
7
having a high peripheral speed, a difference of the rotational numbers between both side of the clutch
10
is large at a time of engaging the clutch
10
. Accordingly, there is a problem that an abrasion is easily generated in the clutch
10
and a shock is great at a time of engaging.
Here,
FIG. 10
shows a change with the passage of time of the clutch pressure P
3
at a time of changing from the high speed traveling to the low speed traveling. The clutch oil applied to the clutch
10
from a time t
1
when the two position switching valve
14
is opened passes to the drain
34
at a substantially fixed flow rate through the two position switching valve
14
and the drain line
23
. In accordance therewith, the clutch pressure P
3
is reduced in accordance a with a substantially fixed incline, and the clutch
10
is engaged at a time t
2
when the clutch pressure P
3
reaches a predetermined pressure PC.
At this time, when reducing a flow rate at which the clutch oil passes to the drain
34
, a long time is required for engaging the clutch
10
, so that the working vehicle can not obtain a torque required at a desired timing and a travel and an operation become unstable. Accordingly, it is necessary to set the flow rate at which the clutch oil passes to a level equal to or more than a predetermined flow rate.
However, when setting the flow rate at which the clutch oil passes to the level equal to or more than the predetermined flow rate, the clutch pressure P
3
is suddenly reduced and a magnitude thereof becomes smaller than the urging force of the spring
12
, so that the clutch
10
is suddenly engaged. Accordingly, a great engagement shock is generated at a time of engaging the clutch
10
, whereby an uncomfortable ride of the working vehicle is generated, and a load is applied to the clutch
10
due to the sudden engagement, whereby a service life of the clutch
10
is reduced.
That is, in accordance with the prior art, ther
Ikari Masanori
Matsuyama Nobuo
Uchimura Toshio
Armstrong Westerman & Hattori, LLP
Bonck Rodney H.
Komatsu Ltd.
Williams Eric M.
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