Pump controller for construction machine

The invention provides 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. The pump controller comprises a plurality of control valves to supply actuators with a controlled pressure oil, a variable displacement hydraulic pump to supply the plural control valves with the pressure oil in parallel, a center bypass connected in parallel to the control valves, and a restrictor to generate a control pressure for negatively controlling the variable displacement hydraulic pump installed at a terminal end of the center bypass. The pump controller further comprises pressure sensors to recognize the operation of the actuator, a controller that sets a pump discharge characteristic individually to the control valve for the actuator in accordance with the operation state of the actuator, calculates a pump discharge corresponding to the control pressure using the set pump discharge characteristic, and controls the angle of inclination of a regulator.

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 through a confluent
 valve, a sensor that converts the control pressure into an electric signal
 and outputs the converted electric signal, pump characteristic setting
 means for setting a basic pump discharge characteristic, when the specific
 actuator does not receive a confluent flow, and setting an extra increment
 pump discharge characteristic made by continuously increasing a maximum
 discharge point from a specific point on the basic pump discharge
 characteristic, when the specific actuator receives the confluent flow,
 pump discharge calculation 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
 outputs the converted pump control signal to the variable displacement
 hydraulic pump.
 The third 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 an actuator 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, a
 sensor that converts the control pressure into an electric signal and
 outputs the converted electric signal, second recognition means for
 recognizing that a load mounted on the actuator is replaced by a different
 load, pump characteristic setting means for setting a pump discharge
 characteristic made by continuously increasing or decreasing a maximum
 discharge from a specific point on a normal pump discharge characteristic
 to the actuator with the different load mounted thereon, when the load is
 replaced by the different load, pump discharge calculation 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.

DETAILED DESCRIPTION OF THE EMBODIMENTS
 The invention will now be described in detail according to the embodiment
 illustrated in the drawing.
 FIG. 1 illustrates a construction of a pump controller relating to the
 first invention. In the drawing, the discharge port of a variable
 displacement hydraulic pump (hereunder, abbreviated as a hydraulic pump) 2
 whose flow rate is designed to be varied by a regulator 1 is connected by
 a center bypass 3 to a tank 8 through a control valve 5 that drives a
 swing motor (actuator) 4 and a control valve 7 that drives an arm cylinder
 (actuator) 6. A pressure oil is supplied to each of the control valves 5,
 7 in parallel from the hydraulic pump 2, whereby a confluent control can
 be achieved.
 A negative control restrictor (means to generate a control pressure for
 executing the negative control) 9 is installed on the downstream of the
 control valve 7 in the center bypass 3. A pressure sensor 10 is installed
 at a point e on the upstream of the negative control restrictor 9 in the
 center bypass 3. A pressure detected by this pressure sensor 10 is
 converted into an electric signal Pneg, which is supplied through a signal
 line 10a to a controller (variable discharge means) 11 made up with a CPU.
 Pressure sensors 5a and 5b (recognition means) are installed on pilot lines
 connected to each of pilot ports of the control valve 5, which can detect
 remote control pressures generated from a remote control valve (not
 illustrated) directly connected to an operation lever. The remote control
 pressures detected by the pressure sensors 5a and 5b are converted into
 electric signals P5a and P5b, which are supplied to the controller 11.
 And, pressure sensors 7a and 7b are installed on pilot lines connected to
 each of pilot ports of the control valve 7, which can detect remote
 control pressures. The remote control pressures detected by the pressure
 sensors 7a and 7b are converted into electric signals P7a and P7b, which
 are supplied to the controller 11. The pressure sensors 5a, 5b and 7a, 7b
 each are to detect the manipulated variables and directions, respectively,
 of the control valves 5 and 7.
 The controller 11 regularly monitors the electric signals outputted from
 the foregoing sensors, and carries out the processes in correspondence
 with each of the electric signals. Concretely, the controller 11 stores
 the pump discharge characteristic of each actuator in the ROM. A pump
 characteristic setting means 11a selects a pump discharge characteristic
 in correspondence with the actuator whose operation is recognized by the
 pressure sensor, and sets the selected pump discharge characteristic. A
 pump discharge calculation means 11b calculates a pump discharge in
 accordance with a pressure control signal outputted from the pressure
 sensor, using the pump discharge characteristic thus set. A variable
 discharge means 11c converts the calculated pump discharge into a pump
 control signal qctl, which is supplied to an electromagnetic proportional
 pressure-reducing valve 1a through a signal line 10b. Thereby, a hydraulic
 control signal is generated, and the angle of inclination of the regulator
 1 is controlled by the hydraulic control signal.
 In the conventional system, the hydraulic signal line connects the upstream
 point of the negative control restrictor 35 on the center bypass to the
 regulator 36 that varies the discharge of the variable displacement
 hydraulic pump, which introduces the upstream pressure of the negative
 control restrictor directly into the valve inlet port of the valve-type
 regulator as a hydraulic signal. However, in this invention, the hydraulic
 signal line is disconnected, and the upstream pressure of the negative
 control restrictor is converted into an electric signal, which is taken in
 by the controller 11, whereby the hydraulic pump 2 is able to set a
 discharge arbitrarily from a minimum to a maximum in accordance with a
 pump discharge command value electrically set by the controller 11.
 The method to vary a discharge in the hydraulic circuit with the above
 construction will now be described.
 FIG. 2 illustrates a relation of the discharge of the hydraulic pump 2 with
 a differential pressure of the negative control. That is, when a pressure
 oil discharged from the hydraulic pump 2 flows through the center bypass 3
 into the tank 8 in a state that the spools of the control valves 5, 7 are
 in neutral positions, namely, when the differential pressure of the
 negative control between the inlet of the negative control restrictor 9
 and the outlet thereof is more than p min, the pump discharge at this
 moment is set to be minimum. Here, the pump discharge is expressed by the
 displacement (cc/rev).
 On the other hand, when the spool of the control valve is moved to decrease
 the flow into the tank 8 through the center bypass 3, when the
 differential pressure of the negative control is brought to pmax, the
 maximum flow point of the pump is set to "c " point corresponding to the
 basic setting qBASE, or "c'" point corresponding the maximum setting q max
 where the discharge is set higher than the basic setting. In this manner,
 the feature of this invention lies in that the maximum flow point can be
 altered in correspondence with each actuator.
 Concretely, the pump control characteristic corresponding to the actuator
 whose maximum speed is most desirably suppressed of the actuators attached
 to one and the same hydraulic pump 2 is set to the basic characteristic Li
 illustrated by the solid line in FIG. 2. Here, the "b" point (specific
 point on the basic discharge characteristic) next to the maximum flow
 point is set to an appropriate point on the solid line L1 based on the
 performance adjustment of an actual machine.
 When the basic characteristic L1 illustrated in FIG. 2 is assigned to, for
 example, the pump control characteristic corresponding to the requirements
 for both operational directions in the swing motor 4, the discharge can be
 removed from the control object to be varied with regard to the swing
 motor 4. Therefore in this case, the controlled object whose discharge is
 varied is the other actuator, namely, the arm cylinder 6. Accordingly, the
 pump control characteristic is set so that the arm cylinder 6 can be
 operated with a maximum discharge qM in the arm push direction as shown in
 FIG. 3, and with a maximum discharge qN in the arm pull direction as shown
 in FIG. 4.
 The characteristic curves shown in FIG. 3 and FIG. 4 can be set to as many
 patterns as desired for each of the actuators, or for each of the
 operational directions. And, "M-qBASE" indicates that the difference
 between the maximum discharge qmax and the qBASE on the basic
 characteristic L1 is a variable range. Therefore, the discharge increment
 can be set arbitrarily within this range. For example, the discharge
 increment qM in regard to the arm push can be set low, and the discharge
 increment qN in regard to the arm pull can be set high. In FIG. 3 and FIG.
 4, the discharge increment qM or qN is increased from virtually the center
 of the manipulated variable (symbol d.fwdarw.e, symbol f.fwdarw.g in the
 drawings), which intends to prevent the pump control operation from
 becoming unstable when the pump control is executed immediately in a state
 that the manipulated variable is small.
 And, even when many actuators are accompanied with the hydraulic pump 2 to
 be controlled other than the swig motor 4 and the arm cylinder 6, if only
 the foregoing curve of the control characteristic is set, it becomes
 possible to vary the maximum discharge for each actuator.
 Next, the control operation of the controller 11 will be described
 according to the flow chart as shown in FIG. 5.
 First, the controller 11 detects the manipulated variable of each lever and
 the operational direction thereof on the basis of the pressure signal
 outputted from each of the pressure sensors 5a, 5b and 7a, 7b. And at the
 same time, the controller 11 detects the differential pressure of the
 negative control on the basis of the pressure signal outputted from the
 pressure sensor 10 (step S1).
 Next, according to the control characteristic curves corresponding to the
 operations (FIG. 3 in case of the arm push operation, and FIG. 4 in case
 of the arm pull operation), the increment qM (cc/rev) in case of the arm
 push operation and the increment qN (cc/rev) in case of the arm pull
 operation are obtained (step S2) in correspondence with each operation
 state.
 Next, the flow rate qmax at the point c' (see FIG. 2) is calculated by the
 following equation (step S3).
EQU qmax=qBASE+qM+qN (step S4).
 Using the flow rate qmax at the point c' calculated, the characteristic
 curve of the pump discharge control is compensated. In this compensation,
 a curve continuously connecting the point c' and the point b, for example,
 a straight line connecting the point c' and the point b is set as a curve
 corresponding to the negative control pressure between pmax and pmid (step
 S5).
 Using the compensated characteristic curve of the pump discharge control,
 the final pump discharge instruction qct1 is introduced on the basis of
 the differential pressure of the negative control, and after the
 saturation processing is applied thereto with the critical discharge qmax
 of the pump hardware, the pump discharge instruction qct1 is outputted to
 the electromagnetic proportional pressure-reducing valve 1a (step SG).
 Thereby, the maximum speed of a specific actuator can be set arbitrarily.
 Here, the control characteristic curve corresponding to each operation and
 the control characteristic curve of the pump discharge may be stored in
 terms of functional forms, or in terms of data maps.
 Next, the 2-pump system will be described, in which the pressure oil is
 supplied to the actuators through a first and second variable displacement
 hydraulic pumps.
 In FIG. 6, the pressure oil supply lines of the control valves 20, 21 are
 connected in parallel to the first variable displacement hydraulic pump
 (hereunder, abbreviated as the first hydraulic pump) 22. On the other
 hand, the pressure oil supply lines of the control valves 23, 24 are
 connected in parallel to the second variable displacement hydraulic pump
 (hereunder, abbreviated as the second hydraulic pump) 25.
 A discharge port of the first hydraulic pump 22 is connected to a tank 26
 by a center bypass f through the control valves 20, 21; and a discharge
 port of the second hydraulic pump 25 is connected to a tank 27 by a center
 bypass g through the control valves 23, 24.
 A negative control restrictor 28 is installed on the downstream of the
 control valve 21 in the center bypass f. A pressure sensor 29 is installed
 at a point between the control valve 21 and the negative control
 restrictor 28. In the same manner, the center bypass g is provided with a
 negative control restrictor 30 and a pressure sensor 31.
 A point h on the upstream of the control valve 23 in the center bypass g is
 connected to a point i on a flow passage that supplies a pressure oil to
 the head side of the actuator 21a through a flow passage j, and a
 confluent valve 32 is installed on this flow passage j.
 A bypass cut-off valve 33 to perform a confluent control is installed
 between the control valve 24 and the negative control restrictor 30 in the
 center bypass g.
 Here, 20a, 21a, 23a, 24a denote actuators driven by the control valves 20,
 21, 23, 24, respectively.
 In the hydraulic circuit with the above construction, the actuator 21a
 employs the first hydraulic pump 22 as a main hydraulic power source, and
 receives the supply of a pressure oil from the second hydraulic pump 25
 through the flow passage j and the confluent valve 32. Thereby, a
 confluent circuit is formed.
 The pump control in this case is how to calculate a discharge of the second
 hydraulic pump 25 including a pressure oil confluence to this actuator
 21a.
 A pressure signal Pnegl detected by the pressure sensor 29 and a pressure
 signal Pneg2 detected by the pressure sensor 31 each are supplied to a
 controller (variable discharge means) 34. The manipulated valuables of the
 actuators each are detected by pressure sensors (operational state
 detection means) that each detect pilot pressures of the control valves,
 which are supplied to controller 34 in the same manner.
 Thus, in the foregoing construction, the controller 34 sets a discharge
 increment qG (described later) of the requirements for the confluence to
 the actuator 21a, in the same method as the setting of the required
 discharge increments qM, qN, as explained in FIG. 3 and FIG. 4.
 In the hydraulic circuit illustrated in FIG. 6, since the pilot pressure
 signal P21a by the directional operation of the actuator 21a is branched
 and introduced into the confluent valve 32 and the bypass cut-off valve
 33, the opening area characteristics of the confluent valve 32 and the
 bypass cut-off valve 33 also vary in accordance with the pilot pressure
 signal P21a. FIG. 7 illustrates the opening area characteristics of the
 confluent valve 32 and the bypass cut-off valve 33.
 In FIG. 6, since the confluent circuit to the actuator 21a requires a
 confluence from near the opening start point of the confluent valve, the
 discharge increment of a confluence covering from the increment "zero" to
 a value (G-qBASE) , as shown in FIG. 8, in which the basic maximum
 discharge qBASE is subtracted from the maximum required pump discharge G,
 is set as a control range to the control valve 21 for the actuator 21a. In
 detail, when the actuator does not receive a confluent flow, the basic
 discharge characteristic is set; and when the actuator receives a
 confluent flow, the extra increment discharge characteristic is set which
 is made by continuously increasing the maximum discharge point from a
 specific point (corresponding to the point b in FIG. 2) on the basic
 discharge characteristic, and the pump discharge corresponding to the
 control pressure (by the negative control restrictor 28) is acquired using
 the pump discharge characteristic thus set.
 Next, a pump control will be described, in case an optional equipment such
 as a shredder is mounted as a front attachment. In this type of optional
 equipment, the load imposed onto the control valve is increased in
 comparison to the normal mode, namely, the case where the normal
 attachment is mounted. Therefore, as shown in FIG. 9, a lower value i'
 compared to the discharge increment i in the normal mode is set, with
 regard to the discharge increment qAR (AR-qBASE).
 That is, an operator switches the operation mode into the use of the
 shredder using an option mode switch (second recognition means), and by
 this selection the controller (pump characteristic setting means, pump
 discharge operation means, variable discharge means) recognizes that the
 optional equipment is installed, and decreases, for example, the maximum
 pump discharge flow rate in the arm pull operation.
 Thereby, in the arm pull operation corresponding to the free fall drop by
 the self-weight, the arm pull speed can be suppressed. As a result, it
 becomes possible to prevent an impact by the piston of the hydraulic
 cylinder colliding against the stroke end from destroying the hydraulic
 cylinder or the peripheral equipment, or from shortening its life.
 Therefore, in a work with heavyweight options such as a shredder or
 breaker mounted on the front end of the front attachment, a stable
 operation becomes possible, which lightens the burden on the operator.
 Further in this invention, the means to generate a control pressure for the
 negative control is not limited to the fixed restrictor in the foregoing
 embodiment; and the means can adopt an arbitrary one as, for example, an
 unload valve, as long as it generates a control pressure.
 In the foregoing embodiment, the remote control pressure on the pilot line
 is detected as a means to recognize the operation; however, it is not
 limited to this. For example, it may be designed to mount a potentiometer
 on the operation lever and recognize the operation by detecting a signal
 from this potentiometer.
 As clearly understood from the above description, according to the first
 invention, the maximum pump discharge to a specific actuator can be varied
 without altering the negative control.
 Further, according to the first invention, it has an advantage that the
 maximum speed of a specific actuator can be set arbitrarily to achieve a
 smooth operation. And, in correspondence with the manipulated variable and
 operational direction of an actuator, the maximum speed of the specific
 actuator can be controlled.
 According to the second invention, when a plurality of pumps are controlled
 individually, the pump discharge can be controlled in accordance with the
 manipulated variable, with regard to the confluence to the actuator.
 According to the third invention, when a heavyweight optional equipment is
 mounted in replacement of a normal front attachment, the maximum speed of
 the control drive for driving the optional equipment can be controled, and
 the impact at the stroke end can be prevented.