Machine element or mechanism – Gearing – With fluid drive
Reexamination Certificate
2001-03-22
2003-09-23
Graham, Matthew C. (Department: 3683)
Machine element or mechanism
Gearing
With fluid drive
C074S731100
Reexamination Certificate
active
06622594
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus for controlling a plurality of hydraulic motors and a clutch and, more particularly to, an apparatus for controlling a plurality of hydraulic motors and a clutch that is adapted to output the output torque of the plurality of hydraulic motors by connecting the output torque via the clutch in a hydraulic drive unit for a working machine, such as a wheel loader, a hydraulic excavator, or the like.
BACKGROUND OF THE INVENTION
Hitherto, in a hydraulic travel drive unit for a vehicle driven by connecting the output torque of a plurality of hydraulic motors through the intermediary of a clutch, the output torque, vehicle speed, and the like are controlled by connecting and disconnecting the clutch when a vehicle speed reaches a predetermined value.
FIG. 6
is a control circuit diagram of a control apparatus for a plurality of hydraulic motors and a clutch of a conventional hydraulic travel drive unit. The control circuit is constituted primarily by a hydraulic pump
50
, a first hydraulic motor
51
, a second hydraulic motor
52
, a clutch
53
, and a vehicle speed detection pump
54
. The first hydraulic motor
51
and the second hydraulic motor
52
are connected in parallel to the hydraulic pump
50
driven by an engine
15
, and are driven by the discharge pressure oil of the hydraulic pump
50
. A motor gear
51
b
is fixedly provided on a first output shaft
51
a
of the first hydraulic
51
, and the motor gear
51
b
is in mesh with a driving shaft gear
55
a
of a driving shaft
55
for driving a vehicle. The output torque of the first hydraulic motor
51
is always transmitted to the driving shaft
55
via the motor gear
51
b
and the driving shaft gear
55
a.
A wheel
70
is installed on a shaft end of the driving shaft
55
.
A clutch
53
is provided on a second output shaft
52
a
of the second hydraulic motor
52
. A second motor gear
53
b
is fixedly provided on a third output shaft
53
a
of the clutch
53
, and the second motor gear
53
b
is in mesh with the driving shaft gear
55
a
of the driving shaft
55
for driving a vehicle. The clutch
53
has a spring
72
therein. The second output shaft
52
a
and the third output shaft
53
a
are engaged at a surface S by the spring
72
when no oil pressure is being supplied to an oil chamber
73
. When oil pressure is supplied to the oil chamber
73
, an oil pressure force overcomes the urging force of the spring
72
, causing the surface S to separate thereby to disengage the second output shaft
52
a
and the third output shaft
53
a.
The output torque of the second hydraulic motor
52
is transmitted to the driving shaft
55
for driving the vehicle through the intermediary of the clutch
53
, the second motor gear
53
b,
and the driving shaft gear
55
a
when the clutch
53
is in mesh. A rod distal end of a first cylinder
62
controlled by a first servo valve
61
is attached to one end of a first swash plate
65
of the first hydraulic motor
51
. Furthermore, a rod distal end of a second cylinder
64
controlled by a second servo valve
63
is attached to one end of a second swash plate
66
of the second hydraulic motor
52
.
The vehicle speed detection pump
54
is connected to the driving shaft
55
. The discharge oil of the vehicle speed detection pump
54
is drained into a tank
71
through a throttle
32
c.
The discharge port of the vehicle speed detection pump
54
is connected to a pressure receiving portion of a tilt rotation fixing control valve
58
and a pressure receiving portion of a clutch switching valve
59
. The oil introduced from the tank
71
and discharged from a control pump
56
is set at a constant oil pressure by a relief valve
57
, and supplied to port P
1
of the tilt rotation fixing control vale
58
. Port P
2
of a tilt rotation fixing valve
58
is connected to a port P
3
of the clutch switching valve
59
. A port P
4
of the clutch switching valve
59
is connected to the oil chamber
73
of the clutch
53
, and a port P
5
is connected to the tank
71
. The port P
2
of the tilt rotation fixing control valve
58
is connected to the pressure receiving portion of a zero tilt rotation fixing valve
60
. The drive pressure for driving the second hydraulic motor
52
is supplied to a port P
6
of the zero tilt rotation fixing valve
60
, and a port P
7
thereof is connected to the second servo valve
63
.
FIG. 6
illustrates a state of the control circuit when an accelerator pedal is depressed to start acceleration. More specifically, since the vehicle speed is zero, so that the oil pressure output from the vehicle speed detection pump
54
is zero, and both the tilt rotation fixing control valve
58
and the clutch switching valve
59
are set at position “a” by the urging forces of springs
67
and
68
. The zero tilt rotation fixing valve
60
is also set at position “a”, the oil pressure in the oil chamber
73
is zero, so that the clutch
53
is engaged at surface S by the urging force of the spring
72
.
When the acceleration is begun, the first cylinder
62
and the second cylinder
64
are extended and retracted in response to the commands from the first servo valve
61
and the second servo valve
63
, causing the first swash plate
65
and the second swash plate
66
of the first hydraulic motor
51
and the second hydraulic motor
52
, respectively, to be at their maximum tilts.
FIG. 7
shows a relationship between discharge capacity D (cc/rev) indicating a tilt rotation amount and vehicle speed V. The drive pressure of the second hydraulic motor
52
that decreases as vehicle speed V increases acts on the second servo valve
63
to conduct control so as to reduce the tilt rotation amount of the second swash plate
66
along curve A shown in FIG.
7
. As the vehicle speed increases, the discharge volume of the vehicle speed detection pump
54
increases, and the oil pressure on the upstream side from the throttle
32
c
also increases. When the second swash plate
66
of the second hydraulic motor
52
reaches an approximately zero tilt rotation amount as the vehicle speed increases, that is, when vehicle speed V
1
is reached in
FIG. 7
, the tilt rotation fixing control valve
58
is switched to position “b”. This causes the constant oil pressure output by the control pump
56
through the port P
2
of the tilt rotation fixing control valve
58
to be supplied to the pressure receiving portion of the zero tilt rotation fixing valve
60
, so that the zero tilt rotation fixing valve
60
overcomes the urging force of the spring
69
and acts at position “b”. Thus, the drive pressure of the second hydraulic motor
52
is supplied to the second servo valve
63
through the port P
7
of the zero tilt rotation fixing valve
60
. Based on the supplied drive pressure, the second servo valve
63
outputs a command for fixing the position of the second cylinder
64
to the second cylinder
64
thereby to fix the tilt rotation amount of the second swash plate
66
. This means that the second swash plate
66
is fixed to the zero tilt rotation amount.
The vehicle speed continues to increase after the second swash plate
66
of the second hydraulic motor
52
is fixed to the zero tilt rotation amount; hence, the oil pressure output by the vehicle speed detection pump
54
continues to increase, and the clutch switching valve
59
acts at position “b” when vehicle speed V
2
is reached. Thus, the constant oil pressure output by the control pump
56
is supplied to the oil chamber
73
of the clutch
53
through the ports P
1
and P
2
of the tilt rotation fixing control valve
58
and the ports P
3
and P
4
of the clutch switching valve
59
. The surface S of the clutch
53
is separated to clear the engagement; therefore, the vehicle is driven only by the first hydraulic motor
51
thereafter.
Meanwhile, in the first hydraulic motor
51
, the first swash plate
65
that has been fixed at the maximum tilt rotation amount is released from the maximum tilt rotation amount by an oil pressure signal (not show
Ikari Masanori
Matsuyama Nobuo
Armstrong Westerman & Hattori, LLP.
Graham Matthew C.
Komatsu Ltd.
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