Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Reexamination Certificate
1999-04-20
2001-09-04
Nguyen, Hoang (Department: 3748)
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
C060S452000
Reexamination Certificate
active
06282892
ABSTRACT:
BACKGROUND OF THE INVENTION
1 Field of the Invention
The present invention relates to a pump controller for a construction machine equipped with a hydraulic circuit to execute a negative control.
2 Description of the Related Art
FIG. 10
illustrates a general negative control circuit in a hydraulic excavator. In the negative control circuit shown in the drawing, the discharge port of a variable displacement hydraulic pump
30
is connected to a tank
34
by a center bypass
31
through a plurality of control valves, for example, a swing motor control valve
32
and an arm control valve
33
. Each of the control valves
32
,
33
is supplied in parallel with a pressure oil discharged from the variable displacement hydraulic pump
30
in the operation mode.
A negative control restrictor
35
is installed on the downstream of the arm control valve
33
in the center bypass
31
. An upstream point a to the negative control restrictor
35
is connected by a hydraulic signal line b to a regulator
36
that varies a discharge from the hydraulic pump
30
. Thereby, the negative control is designed such that when the pressure of the hydraulic signal line b becomes low, the discharge from the hydraulic pump
30
is increased, and when the pressure of the hydraulic signal line b becomes high, the discharge is decreased. Here in the drawing, the symbol
37
and
38
signify a swing motor and an arm cylinder, as actuators, each supplied with a pressure oil in which the flow rate and direction are controlled.
In the circuit, the discharge from the variable displacement hydraulic pump
30
is determined by the magnitudes of the loads to the actuators and the sizes of the bleeding-off control restrictors of the control valves
32
,
33
. However, since the magnitudes of the loads vary from moment to moment, the discharge in the hydraulic circuit is set appropriately although the minimum and maximum discharges are grasped.
However, in a work with a hydraulic excavator, there is such a situation that the maximum speed in the swing mode is desirably suppressed, and the speed of the arm is desirably not to be lowered.
As the measures for this case, as shown in the opening area characteristic (in
FIG. 11
) of the control valves
32
,
33
, the maximum speed of a specific actuator can be lowered by making the opening area characteristic of the bleeding-off control restrictor without a closure. However, when the pressure on the load is high, since the flow rate passing through the bleeding-off control restrictor of the control valve increases, the flow rate passing through the negative control restrictor
35
increases, as shown in FIG.
12
. As a result, the effect by the negative control extremely lowers the pump discharge, creates a state in which the operation lever has to be manipulated deeper than needed for activating the actuator, or makes the pump discharge insufficient so that the maximum pressure cannot be generated, which is a shortcoming.
And, as shown in
FIG. 13
, the negative control characteristic is forcibly made into a head suppression, and conceivably the maximum pump discharge is varied for each actuator. However in this case, when an operator manipulates the operation lever of the swing motor
37
in full to switch the swing motor control valve
32
from a position c to a position d (see FIG.
10
), since the center bypass
31
is blocked by the swing motor control valve
32
, the pressure oil passing through the negative control restrictor
35
runs short, and the pressure of the signal line b becomes low, whereby the discharge from the variable displacement hydraulic pump
30
is increased. Therefore, when the operator manipulates the arm operation lever still further, the pump discharge flow rate increases at a stroke. On the contrary, when returning to a single operation, the pump flow rate rapidly decreases. Thus, since the discharge fluctuates greatly at each time when the actuator is switched from the single operation into the compound operation, or on the contrary, when switched from the compound operation into the single operation, the operator gets into a state of difficulty with operation.
Further, in case a plurality of pumps are controlled independently, the pump maximum discharge is needed to be varied as to a confluent flow. Furthermore, in case a heavyweight optional equipment is mounted on in replacement of a normal front attachment, the pump maximum discharge is needed to be varied in correspondence with the optional equipment.
SUMMARY OF THE INVENTION
The invention has been made in view of the foregoing problems in the conventional hydraulic circuit, and an object of the invention is to provide a pump controller for a construction machine that allows an operator to set the maximum speed of a specific actuator arbitrarily without altering the negative control and acquire a smooth operation.
In order to accomplish the object, the first invention of a pump controller for a construction machine is disclosed. The construction machine has a variable displacement hydraulic pump, a plurality of control valves connected in series to a center bypass attached to the variable displacement hydraulic pump and a plurality of actuators to receive and drive a pressure oil whose flow rate and direction are controlled by the control valves. The controller comprises means for generating a control pressure for negatively controlling a discharge from the variable displacement hydraulic pump, which is installed at a terminal part of a center bypass line extending from a discharge port of the variable displacement hydraulic pump, passing through the center bypass, recognition means for recognizing an operation of each actuator, a sensor that converts the control pressure into an electric signal and outputs the converted signal, pump characteristic setting means for storing a pump discharge characteristic for each actuator, selecting the pump discharge characteristic corresponding to the actuator whose operation is recognized by the recognition means and setting the selected pump discharge characteristic, pump discharge operation means for calculating a pump discharge in accordance with a pressure control signal outputted from the sensor, using the set pump discharge characteristic, and variable discharge means for converting the calculated pump discharge into a pump control signal and outputting the converted pump control signal to the variable displacement hydraulic pump.
The recognition means in this invention can be made up with a pressure sensor that detects a remote control pressure introduced at a pilot port of the control valve. Preferably, the recognition means detects the manipulated variable and direction of each actuator for each of them.
The pump characteristic setting means in this invention preferably sets a basic pump discharge characteristic, with regard to an actuator whose maximum speed is desirably suppressed, and preferably sets an extra increment pump discharge characteristic made by continuously increasing the maximum discharge point from a specific point on the basic pump discharge characteristic, with regard to an actuator whose maximum speed is desirably secured.
The second invention of a pump controller for a construction machine is disclosed. The construction machine has a plurality of variable displacement hydraulic pumps, a plurality of control valves connected in series to a center bypass attached to each of the variable displacement hydraulic pumps and a plurality of actuators to receive and drive a pressure oil whose flow rate and direction are controlled by the control valves. The controller comprises means for generating a control pressure for negatively controlling a discharge from each of the variable displacement hydraulic pumps, which is installed at a terminal part of a center bypass line extending from a discharge port of each of the variable displacement hydraulic pumps, passing through the center bypass, in which, as to a specific actuator, pressure oils discharged from a plurality of the variable displacement hydraulic pumps are combined
Kobelco Construction Machinery Co., Ltd.
Nguyen Hoang
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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