# Patent

## Title
Power source apparatus and hybrid construction machine equipped with same

## Abstract

A controller carries out horsepower control to determine a flow rate of a hydraulic pump based on first characteristics and second characteristics, which each define a maximum input setting of the hydraulic pump by a discharge pressure of the hydraulic pump and a flow rate of the hydraulic pump, and based on the discharge pressure. When the discharge pressure is less than a set pressure and when a state where the discharge pressure is equal to or greater than the set pressure has not continued for a set time period, then the controller determines the flow rate based on the first characteristics, and when the state where the discharge pressure is equal to or greater than the set pressure has continued for the set time period, then the controller determines the flow rate based on the second characteristics.

## Background
TECHNICAL FIELD
The present invention relates to a power source apparatus for a hybrid construction machine which combines use of motive power of an engine and electrical power of an electric storage device.
BACKGROUND ART
The background art is described by taking a shovel machine as an example.
In a normal shovel which has only an engine as a power source, horsepower control is carried out to control a flow rate of a hydraulic pump in accordance with a load pressure of a hydraulic pump (discharge pressure of a hydraulic pump). The horsepower control is carried out in accordance with the characteristics shown in FIG. 4. More specifically, the characteristics shown in FIG. 4 are set in such a manner that the flow rate is a maximum at control starting pressure (the pressure division A in FIG. 4) and the flow rate is a minimum at maximum pressure (relief pressure).
In the characteristics shown in FIG. 4, the maximum input setting of the hydraulic pump is set to be no greater than the maximum output of the engine, in such a manner that the engine does not become overloaded. More specifically, the maximum input setting of the hydraulic pump is set so as to be smaller than the maximum output of the engine by a substantially constant value.
More specifically, with the characteristics shown in FIG. 4, the following relationship is established.

Maximum output of engine>Maximum input of hydraulic pump=Discharge pressure of hydraulic pump×flow rate

(Note that the efficiency and the coefficient are omitted here)
Generally, a combination of flow rate control and the horsepower control described above is used to control the flow rate of the hydraulic pump. More specifically, the lower flow rate is selected, of the flow rates calculated respectively by flow rate control and horsepower control, and the selected flow rate is instructed to the regulator of the hydraulic pump. The flow rate control described above is a control system for controlling the flow rate of the hydraulic pump in accordance with the amount of operation of operating means which operates a hydraulic actuator (called “lever operation amount” below).
In the flow rate control described above, the flow rate is set to a standby flow rate (the standby flow rate is determined by taking account of the system responsiveness at the start of operation) when the operating means is in a neutral state, whereas the flow rate is set to a maximum flow rate when the operating means is fully operated.
On the other hand, in the horsepower control described above, the flow rate is set to a maximum flow rate when at the control starting pressure, whereas the flow rate is set to a minimum flow rate when at the relief pressure.
Consequently, in the pressure division A described above, a flow rate for the hydraulic pump is instructed on the basis of flow rate control in accordance with the amount of operation of the operating means, and in the pressure range of the hydraulic pump exceeding this division A, a flow rate for the hydraulic pump is instructed on the basis of horsepower control.
On the other hand, the hybrid shovel includes a hydraulic pump which drives a hydraulic actuator, a generator-motor which can operate as an electric generator and as an electric motor, and an engine to which the hydraulic pump and the generator-motor are connected. In this hybrid shovel, an electric storage device is charged by operation of the generator-motor as an electric generator, and driving of the hydraulic pump is assisted by operation of the generator-motor as an electric motor, using electric power discharged from the electric storage device.
The flow rate characteristics of the hydraulic pump in the hybrid shovel are basically set to be the same as a normal shovel, in order to maintain the mechanical characteristics of the normal shovel.
However, the assistance provided by the generator-motor (electric storage device) as described above is added to the power of the engine in the hybrid shovel. Consequently, as shown in FIG. 5, the maximum output of the engine in the hybrid shovel is set to a value that is lower than the maximum output of the engine in a normal shovel, taking account of the assistance described above (normally, an average power; this applies to the following description as well).
More specifically, with the characteristics shown in FIG. 5, the following relationship is established.

Maximum output of engine<Maximum input of hydraulic pump

Moreover, with the characteristics shown in FIG. 5, the following relationship is also established.

(Maximum output of engine+Maximum assistance power)>Maximum input of hydraulic pump

This hybrid shovel has the following two intrinsic problems. Firstly, when the amount of charge of the electric storage device has declined, the assistance capability described above declines, and when the remaining amount of charge of the electric storage device falls below a limit, the assistance capability is lost. Therefore, the engine becomes overloaded and there is a risk of stalling.
Secondly, with frequent high-level charging and discharging, severe deterioration of the electric storage device occurs.
As a countermeasure for problems of this kind, technology has been proposed for limiting the maximum input of the hydraulic pump in accordance with the amount of charge in the electric storage device (see, for example, Patent Document 1).
The control described in Patent Document 1 is control based on a supportive approach in that the progress of discharging and the occurrence of sudden charging and discharging is suppressed by limiting the maximum input of the hydraulic pump in accordance with decline in the amount of charge in the electric storage device. Consequently, during normal work where the wear (discharging) of the electric storage device is gradual, the control described in Patent Document 1 is effective.
However, under high-load pressure conditions (and in particular, relief pressure conditions) such as a warm-up operation immediately after starting up the engine in cold conditions, or rock excavation work, if the hydraulic pump is operated continuously, in other words, if the hydraulic pump is continuously operated at full power, then the electric storage device wears (discharges) rapidly at a high level. In circumstances such as these, even if the control described in Patent Document 1 is implemented, wear of the electric storage device cannot be suppressed and the assistance capability of the electric storage device declines suddenly. Consequently, during subsequent normal work, the assistance capability becomes insufficient or it becomes impossible to provide assistance, thus creating a hindrance to work tasks.
Patent Document 1: Japanese Unexamined Patent Publication No. 2005-83242
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a power source apparatus for a hybrid construction machine whereby an optimal maximum input setting can be determined for a hydraulic pump, respectively for normal working and for continuous operation of the hydraulic pump under the high-load pressure conditions.
In order to resolve the problems described above, the present invention provides a power source apparatus for a hydraulic actuator, including: a hydraulic pump which drives the hydraulic actuator; a generator-motor capable of operating as an electric generator and an electric motor; an engine to which the hydraulic pump and the generator-motor are connected; an electric storage device which is charged by operation of the generator-motor as an electric generator, and which is capable of supplying charged electric power to the generator-motor in order to cause the generator-motor to operate as an electric motor so as to assist driving of the hydraulic pump; a pump pressure detector which detects a discharge pressure of the hydraulic pump as a load pressure of the hydraulic pump; and a controller which implements horsepower control for determining a flow rate for the hydraulic pump on the basis of first characteristics and second characteristics that each define a maximum input setting for the hydraulic pump by the discharge pressure of the hydraulic pump and the flow rate of the hydraulic pump, and the discharge pressure detected by the pump pressure detector, wherein the first characteristics are set in such a manner that maximum input of the pump is greater than maximum output of the engine throughout a whole pressure range of the discharge pressure of the hydraulic pump, and the second characteristics are set in such a manner that the maximum input setting for the hydraulic pump is greater than the maximum output of the engine when the discharge pressure is at a predetermined reference pressure, gradually becomes smaller as the discharge pressure changes from the reference pressure towards higher pressure, and becomes smaller than the maximum output of the engine when the discharge pressure is at maximum pressure, and the controller: (i) determines the flow rate on the basis of the first characteristics when the discharge pressure detected by the pump pressure detector is less than a set pressure and when a state where the discharge pressure is equal to or greater than the set pressure has not continued for a set time period; and (ii) determines the flow rate on the basis of the second characteristics when the state where the discharge pressure is equal to or greater than the set pressure has continued for the set time period.
Furthermore, the present invention provides a hybrid construction machine which includes a hydraulic actuator, and the power source apparatus which supplies power to the hydraulic actuator.
According to the present invention, it is possible to set an optical maximum input setting for the hydraulic pump, respectively for normal working and for continuous operation of the hydraulic pump under high-load pressure conditions.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a general composition of a power source apparatus relating to an embodiment of the present invention.
FIG. 2 is a graph showing a relationship between a discharge pressure of a hydraulic pump and a flow rate of the hydraulic pump.
FIG. 3 is a flowchart for describing processing executed by the controller in FIG. 1.
FIG. 4 is a graph showing a relationship between a discharge pressure of a hydraulic pump and a flow rate of the hydraulic pump, in a normal shovel.
FIG. 5 is a graph showing a relationship between a discharge pressure of a hydraulic pump and a flow rate of the hydraulic pump, in a conventional hybrid shovel.



BEST MODE FOR CARRYING OUT THE INVENTION
Below, an embodiment of the present invention is described with reference to the accompanying drawings. The embodiment described below is one example of a concrete embodiment of the present invention, and is not intended to limit the technical scope of the present invention.
An embodiment relating to the present invention is described here with reference to FIG. 1 to FIG. 3. In this embodiment, the invention is applied to a hybrid shovel.
FIG. 1 is a block diagram showing a general system composition. The hybrid shovel relating to the present embodiment includes: a hydraulic actuator, a hydraulic pump 3 which drives the hydraulic actuator, a generator-motor 2 capable of operating as an electric generator and an electric motor, an engine 1 to which the hydraulic pump 3 and the generator-motor 2 are connected, an electric storage device 9 which is charged with electric power in order to assist driving of the hydraulic pump 3, an inverter 8 which controls the electric storage device 9 and the generator-motor 2, a pump pressure sensor (pump pressure detector) 11 which detects a discharge pressure of the hydraulic pump 3, a regulator 5 capable of adjusting a discharge amount of the hydraulic pump 3, a control valve 6 which controls supply of hydraulic oil to the hydraulic actuator and discharging of hydraulic oil from the hydraulic actuator, a remote control valve 7 which generates pilot pressure for operating the control valve 6, a pilot pressure sensor 10 which detects a pilot pressure generated by the remote control valve 7, and a controller 4 which controls the inverter 8 and the regulator 5.
The hybrid shovel may employ a so-called parallel system or a series system as a system for supplying power to the hydraulic pump 3. The present invention can be applied to either of these systems.
The hydraulic pump 3 is a pump of a variable-capacity type. More specifically, the tilting of the hydraulic pump 3 is changed by controlling the regulator 5 by the controller 4. Consequently, the discharge amount (flow rate) of the hydraulic pump 3 changes. Hydraulic oil from the hydraulic pump 3 is supplied to a plurality of hydraulic actuators via the control valve 6. The hydraulic actuators include, for instance, a boom cylinder, an arm cylinder, a bucket cylinder and a hydraulic motor for travel, which are provided in the shovel.
The regulator 5 may be one which is operated directly by an electrical signal from the controller 4. Furthermore, the regulator 5 may be one which is operated on the basis of hydraulic pressure from an electromagnetic valve operated by a signal from the controller 4.
The remote control valve 7 generates a pilot pressure in accordance with the amount of operation of the remote control valve 7 (lever operation amount). The control valve 6 operates in accordance with the pilot pressure from the remote control valve 7. The control valve 6 controls supply of hydraulic oil to the hydraulic actuator and discharging of hydraulic oil from the hydraulic actuator (the direction of operation and speed of the hydraulic actuator), in accordance with this operational state of the control valve 6.
The generator-motor 2 is connected to the electric storage device 9 via the inverter 8.
The inverter 8 controls switching of the generator-motor 2 between operation as an electric generator and operation as an electric motor. Furthermore, the inverter 8 controls the current applied to the generator-motor 2 or the torque of the generator-motor 2. Moreover, the inverter 8 controls charging and discharging of the electric storage device 9 in accordance with the operational state of the generator-motor 2.
The electric storage device 9 can be charged by the generator-motor 2 operating as an electric generator. Furthermore, the electric storage device 9 can supply the charged power to the generator-motor 2. Consequently, the generator-motor 2 operates as an electric motor and the driving of the hydraulic pump 3 is assisted.
The pilot pressure sensor 10 detects the pilot pressure (lever operation amount) of the remote control valve 7 in order to control the flow rate in accordance with the lever operation amount described above. The flow rate control described above is a control system for controlling the flow rate of the hydraulic pump 3 in accordance with the lever operation amount (the magnitude of the pilot pressure produced by the remote control valve 7) for operating the hydraulic actuator.
The pump pressure sensor 11 detects the discharge pressure of the hydraulic pump 3 as a load pressure of the hydraulic pump 3.
The controller 4 calculates a flow rate of the hydraulic pump 3 based on flow rate control and horsepower control, on the basis of the lever operation amount and the discharge pressure of the hydraulic pump 3, as detected by the sensors 10, 11. More specifically, the controller 4 selects the lower flow rate, of the flow rate of the hydraulic pump 3 as determined by flow rate control and the flow rate of the hydraulic pump 3 as determined by horsepower control. The controller 4 controls the regulator 5 so as to obtain the determined flow rate of the hydraulic pump 3.
Furthermore, in the horsepower control described above, the controller 4 determines the flow rate of the hydraulic pump 3 on the basis of the first characteristics shown in FIG. 5 and the second characteristics shown in FIG. 2, and the discharge pressure detected by the pump pressure sensor 11. More specifically, the controller 4 switches the characteristics used, between the first characteristics and the second characteristics, in accordance with the magnitude of the discharge pressure detected by the pump pressure sensor 11.
The first characteristics and the second characteristics are each set and stored in advance in the controller 4. The first characteristics and the second characteristics each define the maximum input setting of the hydraulic pump 3 by the discharge pressure and the flow rate. The “maximum input of the hydraulic pump” is obtained by multiplying the discharge pressure of the hydraulic pump 3 by the flow rate (note that the efficiency and the coefficient are omitted here). Furthermore, the first characteristics are similar to a conventional hybrid system. On the other hand, the second characteristics are intrinsic to the power source apparatus relating to the present embodiment.
More specifically, as shown in FIG. 5, in the first characteristics, the maximum input setting of the hydraulic pump 3 is set so as to establish the following relationship, throughout the whole pressure range of the discharge pressure of the hydraulic pump 3, from a low-pressure state to a maximum pressure state.

Maximum output of engine<Maximum input of hydraulic pump

On the other hand, in the second characteristics, the maximum input setting of the hydraulic pump 3 is set as shown in FIG. 2. More specifically, the maximum input setting of the hydraulic pump 3 according to the second characteristics is determined so as to become greater than the maximum output of the engine when the discharge pressure of the hydraulic pump 3 is the discharge pressure Pp1 (reference pressure), to gradually become smaller as the discharge pressure changes from the discharge pressure Pp1 towards the high-pressure side, and to become smaller than the maximum output of the engine when the discharge pressure is a maximum pressure.
In other words, the following relationship is established at the discharge pressure Pp1 which is the maximum flow rate point in the second characteristics.

Maximum output of engine<Maximum input of hydraulic pump

The discharge pressure Pp1 is the pressure which has been set previously as the maximum discharge pressure that makes it possible to set a maximum flow rate.
On the other hand, at the maximum discharge pressure Pp3 (relief pressure) which is the minimum flow rate point in the second characteristics, then the relationship described above is reversed as shown in the following expression.

Maximum output of engine>Maximum input of hydraulic pump

In the second characteristics, the maximum input setting of the hydraulic pump 3 changes smoothly in the intermediate region between the discharge pressure Pp1 and the discharge pressure Pp3.
The discharge pressure (reversal pressure) Pp2 in FIG. 2 is the pump pressure that represents the reversal boundary point. In other words, the following relationship is established at the discharge pressure Pp2.

Maximum output of engine=Maximum input of hydraulic pump

In this way, the maximum input setting for the hydraulic pump 3 shown in FIG. 2 is greater than the maximum output of the engine 1 throughout the whole pressure range from the discharge pressure Pp1 to the discharge pressure Pp2, and is smaller than the maximum output of the engine 1 throughout the whole pressure range from the discharge pressure Pp2 to the maximum pressure.
The controller 4 executes the processing in (i) or (ii) below on the basis of the discharge pressure which has been detected by the pump pressure sensor 11.
(i) If the discharge pressure detected by the pump pressure sensor 11 is less than a predetermined set pressure, and if a state where the discharge pressure is equal to or greater than the set pressure has not continued for a predetermined set time, then the maximum input setting (flow rate) of the hydraulic pump 3 is determined on the basis of the first characteristics and the discharge pressure. A timer for measuring the time is incorporated into the controller 4.
(ii) If a state where the discharge pressure detected by the pump pressure sensor 11 is equal to or greater than the set pressure has continued for the set time, then the maximum input setting (flow rate) of the hydraulic pump 3 is determined on the basis of the second characteristics and the discharge pressure.
Here, the “set pressure” of the discharge pressure which forms the switching point of the characteristics may be the discharge pressure Pp2 which is a boundary point of the reversal, or may be a pressure slightly lower than this discharge pressure Pp2.
Furthermore, the “time” during which the state where the discharge pressure is equal to or greater than the set pressure continues is set to between several minutes to several tens of minutes in accordance with the capacitance of the electric storage device 9, and the like.
Below, the processing which is implemented by the controller 4 is described with reference to the flowchart shown in FIG. 3.
After the start of control, the discharge pressure of the hydraulic pump 3 is determined in step S1. Next, in step S2, it is judged whether or not the discharge pressure detected in step S1 is equal to or greater than the set pressure.
If the result in step S2 is NO, in other words, if the discharge pressure is less than the set pressure, then the first characteristics in FIG. 5 are selected. In this case, in the subsequent step, step S3, the hydraulic pump 3 is controlled in accordance with the discharge pressure, on the basis of the maximum input setting of the hydraulic pump 3 based on the first characteristics, and the discharge pressure detected by the pump pressure sensor 11.
On the other hand, if the result in step S2 is YES, in other words, if the discharge pressure of the hydraulic pump 3 is equal to or greater than the set pressure, then in step S4, it is judged whether or not the following relationship has been established continuously for the set time period.

Discharge pressure of hydraulic pump≧Set pressure

If the result in step S4 is YES, then in step S5, the second characteristics in FIG. 2 are selected.
In other words, the hydraulic pump 3 is controlled in accordance with the discharge pressure, on the basis of the maximum input setting of the hydraulic pump 3 based on the second characteristics, and the discharge pressure detected by the pump pressure sensor 11. Thereafter, the processing described above is repeated.
By this control, during normal working where the pump pressure continues in state of being less than the set pressure or only becomes equal to or greater than the set pressure in an extremely temporary fashion, then the essential operation of the hybrid system using the assistance action of the electric storage device 9 is carried out. On the other hand, during continuous operation of the hydraulic pump 3 under high-load pressure conditions, it is possible to bear most of the maximum input of the hydraulic pump 3 by the output of the engine 1 by selecting the second characteristics, and therefore it is possible to suppress wear (discharging) of the electric storage device 9. Accordingly, the assistance capability is preserved during continuous operation under high-load pressure conditions and a sufficient assistance capability can be displayed during subsequent normal work. Continuous operation under high-load conditions means operation of the hydraulic pump 3 continuously at full power, as in a warm-up operation immediately after starting the engine in cold conditions, or when performing rock excavation work.
More specifically, since the hybrid system operates efficiently at all times during normal working at medium load or low load, it is possible to enhance energy saving effects. On the other hand, since frequent high-level charging and discharging of the electric storage device 9 can be avoided during continuous operation under high-load pressure conditions, then deterioration of the electric storage device 9 can be suppressed.
Moreover, during operation under high-load pressure conditions, there is an inherent requirement for force (pressure), but little requirement for speed (flow rate). Consequently, there is little disadvantage caused by setting the maximum input setting of the hydraulic pump 3 to be smaller than the maximum output of the engine 1, when the discharge pressure is a maximum pressure. Furthermore, since the flow rate is decreased gradually, no sense of incongruity is produced during operation.
In the embodiment described above, the flow rate is determined by using the first characteristics and the second characteristics which are stored previously. Consequently, it is possible to simplify the processing performed by the controller 4, compared to a case where the flow rate is calculated by using a pressure detected by the pump pressure sensor 11.
In the embodiment described above, the maximum input setting for the hydraulic pump 3 according to the second characteristics is greater than the maximum output of the engine 1 throughout the whole pressure range from the discharge pressure Pp1 to the discharge pressure Pp2, and is smaller than the maximum output of the engine 1 throughout the whole pressure range from the discharge pressure Pp2 to the discharge pressure Pp3. Accordingly, during high-pressure work in which the discharge pressure is higher than the discharge pressure Pp2, it is possible to reliably suppress wear of the electric storage device 9.
In the embodiment described above, the set pressure is a pressure that is equal to or lower than the discharge pressure Pp2. Consequently, wear of the electric storage device 9 can be suppressed reliably under load conditions where the discharge pressure is at least equal to or greater than the discharge pressure Pp2.
Incidentally, the present invention is not limited to a shovel; for example, it can be applied broadly to other hybrid construction machines, such as a dismantling machine or a breaker which incorporates a shovel as a parent body.
The concrete embodiment described above principally includes an invention having the following composition.
The present invention provides a power source apparatus for a hydraulic actuator, including: a hydraulic pump which drives the hydraulic actuator; a generator-motor capable of operating as an electric generator and an electric motor; an engine to which the hydraulic pump and the generator-motor are connected; an electric storage device which is charged by operation of the generator-motor as an electric generator, and which is capable of supplying charged electric power to the generator-motor in order to cause the generator-motor to operate as an electric motor so as to assist driving of the hydraulic pump; a pump pressure detector which detects a discharge pressure of the hydraulic pump as a load pressure of the hydraulic pump; and a controller which implements horsepower control for determining a flow rate for the hydraulic pump on the basis of first characteristics and second characteristics that each define a maximum input setting for the hydraulic pump by the discharge pressure of the hydraulic pump and the flow rate of the hydraulic pump, and the discharge pressure detected by the pump pressure detector; wherein the first characteristics are set in such a manner that maximum input of the pump is greater than maximum output of the engine throughout a whole pressure range of the discharge pressure of the hydraulic pump, and the second characteristics are set in such a manner that the maximum input setting for the hydraulic pump is greater than the maximum output of the engine when the discharge pressure is at a predetermined reference pressure, gradually becomes smaller as the discharge pressure changes from the reference pressure towards higher pressure, and becomes smaller than the maximum output of the engine when the discharge pressure is at maximum pressure, and the controller: (i) determines the flow rate on the basis of the first characteristics when the discharge pressure detected by the pump pressure detector is less than a set pressure and when a state where the discharge pressure is equal to or greater than the set pressure has not continued for a set time period; and (ii) determines the flow rate on the basis of the second characteristics when the state where the discharge pressure is equal to or greater than the set pressure has continued for the set time period.
According to the present invention, it is possible to switch the characteristics relating to the maximum input setting of the hydraulic pump, between normal working where the hydraulic pump is operating under load pressure conditions from a low-pressure to a medium-pressure region, and continuous operation where the hydraulic pump is operating continuously under high-load pressure conditions in a high-pressure region.
More specifically, in the present invention, when the discharge pressure is less than the set pressure, and when a state where the discharge pressure is equal to or greater than the set pressure has not continued for a set period of time, the flow rate is determined on the basis of the first characteristics, whereas when the state where the discharge pressure is equal to or greater than the set pressure has continued for the set period of time, the flow rate is determined on the basis of the second characteristics.
Therefore, during normal working, it is possible to operate the power source apparatus in a state where the following relationship is established.

Maximum input of hydraulic pump>Maximum output of engine

On the other hand, during continuous working at high-load pressure, it is possible to operate the power source apparatus in a state where the following relationship is established.

Maximum input of hydraulic pump<Maximum output of engine

In other words, during normal working, the essential energy saving operation of the hybrid system using the assistance capability of the electric storage device is carried out. On the other hand, during continuous operation under high-load pressure conditions, it is possible to bear most of the maximum input of the hydraulic pump by the output of the engine, and therefore wear (discharging) of the electric storage device can be suppressed. Accordingly, the assistance capability is preserved during continuous operation under high-load pressure conditions and a sufficient assistance capability can be displayed during subsequent normal work. Continuous operation under high-load pressure conditions means operation of the hydraulic pump continuously at full power, as in a warm-up operation immediately after starting an engine in cold conditions, or when performing excavation work.
More specifically, since the hybrid system operates efficiently at all times during normal working at medium load or low load, it is possible to enhance energy saving effects. On the other hand, during continuous operation under high-load pressure conditions, it is possible to avoid high-level charging and discharging, such as sudden discharge and subsequent charging of the electric storage device, and therefore deterioration of the electric storage device can be suppressed.
Moreover, during operation under high-load pressure conditions, there is an inherent requirement for force (pressure), but little requirement for speed (flow rate). Consequently, there is little disadvantage caused by setting the maximum input setting of the hydraulic pump to be smaller than the maximum output of the engine, when the discharge pressure is a maximum pressure. Furthermore, since the flow rate is decreased gradually, no sense of incongruity is produced during operation.
In the power source apparatus described above, desirably, the controller previously stores the first characteristics, and the second characteristics in which the flow rate decreases continuously as the discharge pressure changes from the reference pressure towards the maximum pressure.
In the aspect, the flow rate is determined by using the first characteristics and the second characteristics which are stored previously. Consequently, it is possible to simplify the processing performed by the controller, compared to a case where the flow rate is calculated by using a pressure detected by the pump pressure detector.
In the power source apparatus described above, desirably, the maximum input setting of the hydraulic pump in the second characteristics is greater than the maximum output of the engine in a whole pressure range from the reference pressure to a predetermined reversal pressure, and is smaller than the maximum output of the engine in a whole pressure range from the reversal pressure to the maximum pressure.
According to the aspect, it is possible to reliably suppress wear of the electric storage device in the case of high-pressure work where the discharge pressure is higher than the reversal pressure, while making efficient use of assistance by the electric storage device when the discharge pressure is lower than the reversal pressure.
In the power source apparatus described above, desirably, the set pressure is a pressure that is equal to or lower than the reversal pressure.
According to the aspect, it is possible reliably to suppress wear of the electric storage device, under load pressure conditions where the discharge pressure is at least equal to or greater than the reversal pressure.
More specifically, the reference pressure can be set previously as the maximum discharge pressure at which the flow rate can be set to a maximum flow rate.
Furthermore, the present invention provides a hybrid construction machine which includes a hydraulic actuator, and the power source apparatus which supplies power to the hydraulic actuator.
INDUSTRIAL APPLICABILITY
According to the present invention, it is possible to set an optical maximum input setting for the hydraulic pump, respectively for normal working and for continuous operation of the hydraulic pump under high-load pressure conditions.
EXPLANATION OF REFERENCE NUMERALS
Pp1 discharge pressure (reference pressure)
Pp2 discharge pressure (reversal pressure)
Pp3 discharge pressure (maximum pressure)
1 engine
2 generator-motor
3 hydraulic pump
4 controller
9 electric storage device
11 pump pressure sensor (pump pressure detector)

## Claims

1. A power source apparatus for a hydraulic actuator, comprising:
a hydraulic pump which drives the hydraulic actuator;
a generator-motor capable of operating as an electric generator and an electric motor;
an engine to which the hydraulic pump and the generator-motor are connected;
an electric storage device which is charged by operation of the generator-motor as an electric generator, and which is capable of supplying charged electric power to the generator-motor in order to cause the generator-motor to operate as an electric motor so as to assist driving of the hydraulic pump;
a pump pressure detector which detects a discharge pressure of the hydraulic pump as a load pressure of the hydraulic pump; and
a controller which implements horsepower control for determining a flow rate for the hydraulic pump on the basis of first characteristics and second characteristics that each define a maximum input setting for the hydraulic pump by the discharge pressure of the hydraulic pump and the flow rate of the hydraulic pump, and the discharge pressure detected by the pump pressure detector,
wherein the first characteristics are set in such a manner that maximum input of the pump is greater than maximum output of the engine throughout a whole pressure range of the discharge pressure of the hydraulic pump, and
the second characteristics are set in such a manner that the maximum input setting for the hydraulic pump is greater than the maximum output of the engine when the discharge pressure is at a predetermined reference pressure, gradually becomes smaller as the discharge pressure changes from the reference pressure towards higher pressure, and becomes smaller than the maximum output of the engine when the discharge pressure is at maximum pressure, and
the controller:
(i) determines the flow rate on the basis of the first characteristics when the discharge pressure detected by the pump pressure detector is less than a set pressure and when a state where the discharge pressure is equal to or greater than the set pressure has not continued for a set time period; and
(ii) determines the flow rate on the basis of the second characteristics when the state where the discharge pressure is equal to or greater than the set pressure has continued for the set time period.

2. The power source apparatus according to claim 1, wherein the controller previously stores the first characteristics, and the second characteristics in which the flow rate decreases continuously as the discharge pressure changes from the reference pressure towards the maximum pressure.

3. The power source apparatus according to claim 1, wherein the maximum input setting of the hydraulic pump in the second characteristics is greater than the maximum output of the engine in a whole pressure range from the reference pressure to a predetermined reversal pressure, and is smaller than the maximum output of the engine in a whole pressure range from the reversal pressure to the maximum pressure.

4. The power source apparatus according to claim 3, wherein the set pressure is a pressure that is equal to or lower than the reversal pressure.

5. The power source apparatus according to claim 1, wherein the reference pressure is a pressure which is predetermined as a maximum discharge pressure at which the flow rate can be set to a maximum flow rate.

6. A hybrid construction machine, comprising:
a hydraulic actuator; and
the power source apparatus according to claim 1, which supplies power to the hydraulic actuator.