Power plants – Pressure fluid source and motor – Having a mechanical clutch or brake device in the power train
Reexamination Certificate
2001-06-04
2003-05-20
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Having a mechanical clutch or brake device in the power train
C060S445000
Reexamination Certificate
active
06564549
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device which controls the displacement of a hydraulic pump and a brake control device which controls to brake a hydraulic motor by controlling the displacement of the hydraulic pump, and more particularly to a device which is applied to the hydraulic pump which is not provided with a feedback servo valve.
2. Description of the Related Art
The displacement of the hydraulic pump can be controlled by two methods. One of them is a method to control the displacement by feeding back the present displacement of the hydraulic pump by the feedback control valve. It is called a servo method.
The other is a direct control method which is not provided with a feedback control valve. Operation of a hydraulic pump of the direct control method will be described with reference to the hydraulic circuit of FIG.
17
.
FIG. 17
shows a closed circuit which is comprised of hydraulic pump
11
and hydraulic motor
12
. For example, it is assumed that a vehicle is driven by rotating crawler belts (or wheels)
13
by the hydraulic motor
12
.
When operation lever
14
a
is operated, a pilot pressure oil with a pilot pressure corresponding to the operated amount is supplied to piston
15
for controlling the displacement. The pilot pressure oil is supplied by pilot pump
16
used as oil pressure source. The displacement control piston
15
is connected to a swash plate, namely locker cam
11
a,
of the hydraulic pump
11
. The displacement control piston
15
moves to a position according to the pilot pressure. When the displacement control piston
15
moves, the swash plate
11
a
of the hydraulic pump
11
is tilted. The hydraulic pump
11
is changed to have a displacement corresponding to the operated amount of the operation lever
14
a.
The pressure oil delivered from the hydraulic pump
11
is delivered to the hydraulic motor
12
, and the hydraulic motor
12
is driven to rotate. When the hydraulic motor
12
is driven to rotate, the crawler belts
13
connected to shaft
12
a
of the hydraulic motor
12
are rotated.
The hydraulic pump
11
is easily influenced by a tilting moment because it does not have a feedback servo valve. This function that the hydraulic pump
11
is influenced easily by the tilting moment is used to control pump absorption torque and to control for preventing a shock involved in starting or stopping motion of a vehicle.
In the hydraulic pump
11
of the direct control method, the tilting moment corresponding to the pump pressure acts on the locker cam to change the pump displacement. This is achieved by a shape of a delivery port of the valve plate of the hydraulic pump
11
.
The hydraulic pump
11
for a closed circuit has a port shape allowing to deliver from both delivery ports
11
b,
11
c.
This port shape is suitable for delivering a high pressure oil but not suitable for sucking a low pressure oil. To raise the pressure of the suction side of the hydraulic pump
11
, it is necessary to make supplemental supply of the pressure oil to the suction side port of the hydraulic pump
11
. It is not illustrated but for example a charge circuit for discharging the pressure oil of about 3 MPa from the charge pump is generally disposed. The pressure supplied to the hydraulic pump
11
is sufficient in about 1 to 1.5 MPa. But, a charge pump for discharging a pressure of about 3 MPa is used because the charge pump is often used also as an oil pressure source of the pilot circuit.
The charge circuit is comprised of the charge pump, a charge relief valve for setting a charge pressure, and two sets of suction valves (check valves) for supplying the charge pressure to a low-pressure side port of the hydraulic pump
11
, namely to a low-pressure side oil passage.
The closed circuit shown in
FIG. 17
is provided with two sets of safety valves in order to prevent equipment from being broken resulting from an excessive increase in pressure within the oil passage. A suction safety valve which has the safety valve and the suction valve (check valve) combined into one body is often used.
It is assumed that a vehicle is started forward. When the vehicle starts to move, the pressure oil is sucked from oil passage
10
R into the port
11
b
of the hydraulic pump
11
and then delivered from the port
11
c
to oil passage
10
F. The delivery side oil passage
10
F has a pressure higher than the intake side oil passage
10
R. It is when the hydraulic pump
11
is pumping. The hydraulic pump
11
is designed to have a characteristic that the swash plate
11
a
is returned toward a neutral position as the delivery side oil passage
10
F has a higher pump pressure. In other words, the tilting moment corresponding to the pump pressure on the delivery side acts on the locker cam to return the swash plate
11
a
to the neutral position, so that the displacement of the hydraulic pump
11
becomes small as the pump pressure on the delivery side becomes high.
Thus, when the vehicle starts to move and the delivery pressure increases, the pump displacement can be reduced. Specifically, the pump displacement to an instruction value is delayed from changing to the maximum side to prevent the pump pressure from increasing sharply, thereby limiting the torque output by the hydraulic motor
12
. Accordingly, the shock caused when the vehicle starts to move can be lowered.
The same is also applied to a case of stopping the vehicle.
When the vehicle is to be stopped, the oil passage
10
R on the intake side has a pressure higher than that of the delivery side oil passage
10
F. It is when the hydraulic motor
12
is pumping. The hydraulic pump
11
is provided with a characteristic that the swash plate
11
a
is raised to the maximum displacement side as the suction side oil passage
10
R has a higher pump pressure. Specifically, the tilting moment according to the intake side pump pressure acts on the locker cam to raise the swash plate
11
a
to the maximum displacement side, so that the hydraulic pump
11
has a larger displacement as the intake side pump pressure becomes higher.
The operation when the vehicle is braking will be described specifically.
To apply the hydraulic brake to the hydraulic motor
12
, a flow rate which the hydraulic pump
11
sucks in through the port
11
b
can be reduced with respect to the flow rate that the hydraulic motor
12
discharges.
When the operation lever
14
a
is returned to the neutral or the brake pedal is depressed while the vehicle is moving forward, the piston
15
is about to return to the neutral by the spring force.
Thus, the pressure oil flowing through the oil passage
10
R is stopped by the hydraulic pump
11
and its pressure is increased to brake the hydraulic motor
12
. When the pressure of the oil passage
10
R is increased, the displacement of the hydraulic pump
11
is increased by the tilting moment, and the flow rate taken in by the hydraulic pump
11
through the port
11
b
is increased. Therefore, the pressure oil which was stopped by the hydraulic pump
11
flows out, and the pressure becomes. A braking torque is prevented from becoming excessive by the above operation.
If braking is effective, the speed of the vehicle lowers, and the rotating speed of the hydraulic motor
12
lowers, too. When the rotating speed of the hydraulic motor
12
lowers, the flow rate discharged from the hydraulic motor
12
is decreased, and a brake pressure decreases. When the brake pressure lowers, the tilting moment becomes small, and the piston
15
can be moved in the neutral direction by the spring force. Here, the flow rate to be taken in becomes smaller than that discharged from the hydraulic motor
12
, and the brakes are applied continuously.
The piston
15
gradually returns to the neutral while keeping such a balance.
When the piston
15
has returned to the neutral while keeping the balance, it means that the flow rate discharged by the hydraulic motor
12
has become zero and the vehicle has stopped.
Thus, when the suction side pressure (brake pressure) rises a
Hayashi Seita
Nagura Shinobu
Komatsu Ltd.
Lazo Thomas E.
Look Edward K.
Varndell & Varndell PLLC
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