# Patent

## Title
Work machine driving device

## Abstract

Provided is a work machine driving device which can reduce unnecessary switching control of switching valves. The present invention is configured so that at least two closed-circuit hydraulic pumps 2a to 2f can be connected in a closed loop to any one of hydraulic actuators 7a to 7c, 10c through electromagnetic switching valves 12, in which a controller 16 includes a priority order calculating circuit 31 which calculates the allocation of the closed-circuit hydraulic pumps 2a to 2f to the hydraulic actuators 7a to 7c, 10c according to operation of operation levers 17a, 17b and a priority order map 32 determining priority connection relationships between the closed-circuit hydraulic pumps 2a to 2f and the hydraulic actuators 7a to 7c, 10c, and the priority order calculating circuit 31 selects and allocates an unallocated closed-circuit hydraulic pump 2a to 2f when the number of closed-circuit hydraulic pumps 2a to 2f to be allocated increases.

## Background
TECHNICAL FIELD
The present invention relates to a driving device used in a work machine such as a hydraulic excavator and more particularly to a driving device which drives a hydraulic actuator through a hydraulic pump.
BACKGROUND ART
In the recent years, energy saving has been demanded from the viewpoint of environmental problems, etc., and in order to achieve energy saving in a work machine such as a hydraulic excavator or wheel loader, it is important to save energy in the entire hydraulic system for driving the work machine. From the viewpoint of energy saving, a hydraulic closed-circuit system has been developed in which a hydraulic pump is connected in a closed loop to a hydraulic actuator to control the hydraulic actuator directly by the hydraulic pump.
Since the hydraulic closed-circuit system does not need a control valve which controls the supply direction and flow rate of hydraulic oil discharged from the hydraulic pump, no pressure loss attributable to the control valve occurs and it is only necessary to discharge hydraulic oil at a required flow rate from the hydraulic pump and there is little flow rate loss. In addition, the potential energy of the hydraulic actuator to be driven and the kinetic energy during deceleration can be regenerated so that energy saving can be achieved.
On the other hand, in the hydraulic closed-circuit system, in order for the amount of hydraulic oil discharged from a single hydraulic pump to cover the required amount of hydraulic oil to drive each hydraulic actuator, a large hydraulic pump with a high discharge rate is needed for each hydraulic actuator. Therefore, Patent Literature 1 discloses a conventional technique which converges flows of hydraulic oil discharged from a plurality of hydraulic pumps and achieves the drive speed of a hydraulic actuator without increasing the size of the hydraulic pumps. In Patent Literature 1, a hydraulic pump is allocated to each hydraulic actuator according to a priority order map which determines priority connection relationships between hydraulic pumps and hydraulic actuators and switching valves are controlled depending on this allocation.
CITATION LIST
Patent Literature
PTL 1: Japanese Examined Patent Publication No. 1987-25882
SUMMARY OF INVENTION
Technical Problem
In the conventional technique disclosed in Patent Literature 1, a hydraulic pump is always allocated to each hydraulic actuator according to the priority order map and switching of the switching valves is controlled depending on the allocation, so the following problems may arise.
For example, if during operation of one hydraulic actuator another hydraulic actuator is to be driven, namely if the number of hydraulic pumps to be allocated increases, it may happen that according to the priority order map the hydraulic pump connected to one hydraulic actuator is connected to the hydraulic actuator to be started according to its priority order and another hydraulic pump is reconnected to the one hydraulic actuator. Also, if during operation of a plurality of hydraulic actuators the flow rate to one hydraulic actuator is decreased for deceleration, namely if the number of hydraulic pumps to be allocated is decreased, the state in which a plurality of hydraulic pumps are allocated to the hydraulic actuator to which the flow rate is decreased is changed to the state in which a certain hydraulic pump among the allocated hydraulic pumps is not connected. Therefore, this certain hydraulic pump becomes unused. However, if the unused hydraulic pump has a higher priority for another hydraulic actuator than the hydraulic pump connected to it, it may happen that according to the priority order map, the hydraulic pump connected to the other hydraulic actuator is unallocated and the unused hydraulic pump is reconnected to it. As a consequence, when changing the connection of a hydraulic pump, it may happen that switching of switching valves is made more times than necessary (hereinafter sometimes called the number of switching times) to perform control. This may result in increased vehicle body vibration due to a shock caused by pressure variation during switching, worsened operability, and shortened life due to deterioration of components including the switching valves.
The present invention has been made in view of the above circumstances of the conventional technique and an object thereof is to provide a work machine driving device which can reduce unnecessary switching control of switching valves.
Solution to Problem
In order to achieve the above object, the present invention is characterized in that a driving device for a work machine includes a plurality of hydraulic actuators, a plurality of variable displacement hydraulic pumps to drive the hydraulic actuators, a plurality of switching valves connected between the hydraulic actuators and the hydraulic pumps, an operation part to operate the hydraulic actuators, and a controller to control the hydraulic pumps and the switching valves, in which at least two of the hydraulic pumps can be connected in a closed loop to any one of the hydraulic actuators through the switching valves, the controller includes a priority order calculating circuit which calculates allocation of the hydraulic pumps to the hydraulic actuators according to operation of the operation part and a priority order map determining priority connection relationships between the hydraulic pumps and the hydraulic actuators, and the priority order calculating circuit selects and allocates an unallocated one of the hydraulic pumps when the number of hydraulic pumps to be allocated increases.
In the present invention thus configured, when the priority order calculating circuit of the controller calculates the allocation of the hydraulic pumps to the hydraulic actuators according to operation of the operation part and the priority order map determining the priority connection relationships between the hydraulic pumps and the hydraulic actuators, if the number of hydraulic pumps to be allocated increases, it allocates an unallocated hydraulic pump just before the increase. As a consequence, if during operation of one hydraulic actuator, another hydraulic actuator is to be driven, namely even if the number of hydraulic pumps to be allocated increases, an unused hydraulic pump can be connected to the hydraulic actuator to be started without changing the connection of the hydraulic pump connected to the one hydraulic actuator, so unnecessary switching control of electromagnetic switching valves can be reduced. As a consequence, the frequency of shock caused by pressure variation during switching can be reduced, leading to reduction of vehicle body vibration, improved operability and improvement in the life of the components including the switching valves.
In addition, the present invention is characterized in that a driving device for a work machine includes a plurality of hydraulic actuators, a plurality of variable displacement hydraulic pumps to drive the hydraulic actuators, a plurality of switching valves connected between the hydraulic actuators and the hydraulic pumps, an operation part to operate the hydraulic actuators, and a controller to control the hydraulic pumps and the switching valves, in which at least two of the hydraulic pumps can be connected in a closed loop to any one of the hydraulic actuators through the switching valves, the controller includes a priority order calculating circuit which calculates allocation of the hydraulic pumps to the hydraulic actuators according to operation of the operation part and a priority order map determining priority connection relationships between the hydraulic pumps and the hydraulic actuators, and when the number of hydraulic pumps to be allocated to a given hydraulic actuator decreases, the priority order calculating circuit maintains allocation of the hydraulic pumps allocated to the other hydraulic actuators than the given hydraulic actuator.
In the present invention thus configured, when the priority order calculating circuit of the controller calculates the number of hydraulic pumps to be allocated to the hydraulic actuators according to operation of the operation part and the priority order map determining the priority connection relationships between the hydraulic pumps and the hydraulic actuators, if the number of hydraulic pumps to be allocated to a given hydraulic actuator decreases, the allocation of the hydraulic pumps allocated to the hydraulic actuators other than the given hydraulic actuator is maintained. Consequently, if during operation of a plurality of hydraulic actuators the flow rate to one hydraulic actuator is decreased for deceleration, namely even if the number of hydraulic pumps to be allocated decreases, a hydraulic pump is unallocated from the hydraulic actuator to which the flow rate is decreased and the allocation of the hydraulic pumps to the other hydraulic actuators is maintained, so unnecessary switching control of the switching valves is reduced. As a consequence, the frequency of shock caused by pressure variation during switching can be reduced, leading to reduction of vehicle body vibration, improved operability and improvement in the life of the components including the switching valves.
Advantageous Effects of Invention
The present invention is configured so that when the priority order calculating circuit calculates the allocation of the hydraulic pumps to the hydraulic actuators according to operation of the operation part and the priority order map determining the priority connection relationships between the hydraulic pumps and the hydraulic actuators, if the number of hydraulic pumps to be allocated increases, it allocates an unallocated hydraulic pump just before the increase. Also the present invention is configured so that if the number of hydraulic pumps to be allocated to a given hydraulic actuator decreases, the allocation of the hydraulic pumps allocated to the other hydraulic actuators than the given hydraulic actuator is maintained. The present invention thus configured can reduce unnecessary switching control of the switching valves. The other issues, configuration and effects will become apparent from the following description of embodiments.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a side view which shows a hydraulic excavator including an embodiment of the work machine driving device according to the present invention.
FIG. 2 is a circuit configuration diagram which shows the essential part of the driving device provided in the hydraulic excavator shown in FIG. 1.
FIG. 3 is a block diagram which shows a controller in the driving device shown in FIG. 2.
FIG. 4 shows graphs which indicate calculations in the required pump number calculating circuit of the controller shown in FIG. 3, in which (a), (b), (c), and (d) are for the boom cylinder, arm cylinder, bucket cylinder, and swing motor, respectively.
FIG. 5 is a table which shows the priority order map of the controller shown in FIG. 3.
FIG. 6 is a time chart which shows the operation of the controller shown in FIG. 3 when the number of pumps required increases, in which (a) indicates the lever manipulated variable, (b) indicates the number of pumps required, (c) indicates the number of pumps used, (d) indicates the state of the switching valves before time t1, and (e) shows the state of the switching valves at time t1 and after time t1.
FIG. 7 is a time chart which shows the operation of the controller shown in FIG. 3 when the number of pumps required decreases, in which (a) indicates the lever manipulated variable, (b) indicates the number of pumps required, (c) indicates the number of pumps used, (d) indicates the state of the switching valves from time t1 before time t2, and (e) indicates the state of the switching valves at time t2 and after time t2.
FIG. 8 is a flowchart showing allocation control of the hydraulic pumps by the controller shown in FIG. 3.
FIG. 9 is a time chart which shows the operation of a conventional hydraulic excavator when the number of pumps required increases, in which (a) indicates the lever manipulated variable, (b) indicates the number of pumps required, (c) indicates the number of pumps used, (d) indicates the state of the switching valves before time t1, and (e) indicates the state of the switching valves at time t1 and after time t1.
FIG. 10 is a time chart which shows the operation of the conventional hydraulic excavator when the number of pumps required decreases, in which (a) indicates the lever manipulated variable, (b) shows the number of pumps required, (c) indicates the number of pumps used, (d) indicates the state of the switching valves from time t1 before time t2, and (e) indicates the state of the switching valves at time t2 and after time t2.



DESCRIPTION OF EMBODIMENTS
Next, an embodiment of a work machine driving device according to the present invention will be described referring to drawings. FIG. 1 is a side view which shows a hydraulic excavator 1 including an embodiment of the work machine driving device according to the present invention.
The hydraulic excavator 1 as an example of the work machine according to the embodiment of the present invention includes a travel base 101 and a revolving upperstructure 102 over the travel base 101. The main body is comprised of the travel base 101 and the revolving upperstructure 102. The travel base 101 has crawler belts on the left and right sides of the main body and traveling motors 10a, 10b which are hydraulic actuators to give traveling power to the left and right crawler belts. The revolving upperstructure 102 is rotatable with respect to the travel base 101 by means of a bearing mechanism (not shown) interposed between it and the travel base 101 and a swing motor 10c as a hydraulic actuator. In the revolving upperstructure 102, a working device 103 is mounted in front of a main frame 105 and a counterweight 108 is mounted on the back and a cab 104 is mounted on the left front. An engine 106 as a motor and a drive system 107 to be driven by driving power from the engine 106 are housed in the front part of the counterweight 108.
The working device 103 is a front work machine which has a structure comprised of a boom 111, arm 112 and bucket 113 connected by a link mechanism and makes rotary movement around each link axis to perform excavation work or the like. The working device 103 has a boom cylinder 7a, an arm cylinder 7b, and a bucket cylinder 7c which rotate the boom 111, arm 112, and bucket 113.
FIG. 2 is a circuit configuration diagram which shows the essential part of the driving device provided on the hydraulic excavator 1 shown in FIG. 1. In the description of the driving device, response time from an instruction to operation is not taken into consideration.
As shown in FIG. 2, the drive system 107 as a driving device includes variable displacement closed-circuit hydraulic pumps 2a to 2f (hereinafter sometimes simply called hydraulic pumps), a hydraulic closed-circuit system in which the boom cylinder 7a, arm cylinder 7b, bucket cylinder 7c and swing motor 10c are connected by piping without control valves, and a hydraulic open-circuit system in which variable displacement open-circuit hydraulic pumps 1a, 1b and the traveling motors 10a, 10b are connected by piping through a control valve 11 as a hydraulic controller for controlling the supply flow rate and the supply direction.
Although the hydraulic closed-circuit system and hydraulic open-circuit system are mixed in this embodiment, the invention is not limited thereto but depending on the application purpose of the work machine, it may be embodied in another form: for example, a hydraulic closed-circuit system is used for all hydraulic actuators.
Next, the above hydraulic closed-circuit system will be described.
The hydraulic closed-circuit system includes an engine 106, a power transmission device 15 comprised of a gear mechanism, etc., for example, a total of six closed-circuit hydraulic pumps 2a to 2f to which driving power as torque and revolving speed is supplied by the engine 106 through the power transmission device 15, and hydraulic regulators 3a to 3f as discharge rate varying devices which can vary the discharge rates of the closed-circuit hydraulic pumps 2a to 2f. The hydraulic closed-circuit system includes: the boom cylinder 7a, arm cylinder 7b, bucket cylinder 7c and swing motor 10c; electromagnetic valves 12 as connecting devices for enabling hydraulic closed-loop connection of at least one of the closed-circuit hydraulic pumps 2a to 2f to the boom cylinder 7a, arm cylinder 7b, bucket cylinder 7c and swing motor 10c; an operation device 17 which generates a lever manipulated variable as an operation signal to the boom cylinder 7a, arm cylinder 7b, bucket cylinder 7c and swing motor 10c; and a controller 16 as a control device which controls the hydraulic regulators 3a to 3f and the electromagnetic valves 12 depending on the lever manipulated variable of the operation device 17.
The closed-circuit hydraulic pumps 2a to 2f are two-way discharge mechanisms which can discharge hydraulic oil (pressure oil) from two connection ports of the closed-circuit hydraulic pumps 2a to 2f in order to give the drive direction and the discharge rate of the boom cylinder 7a, arm cylinder 7b, bucket cylinder 7c and swing motor 10c. The two-way discharge mechanisms are controlled by the hydraulic regulators 3a to 3f. 
When hydraulic oil is discharged from one of the two connection ports of the closed-circuit hydraulic pump 2a to 2f by the two-way discharge mechanisms, connection is made to one of the two connection ports of any hydraulic actuator among the boom cylinder 7a, arm cylinder 7b, bucket cylinder 7c and swing motor 10c through the electromagnetic switching valve 12 and the hydraulic oil returned from the other connection port of the two connection ports of the hydraulic actuator is returned to the other connection port of the two connection ports of the closed-circuit hydraulic pump 2a to 2f through the electromagnetic valves 12. In short, the hydraulic oil circulates between the closed-circuit hydraulic pump 2a to 2f and the hydraulic actuator without returning to a hydraulic oil tank 9, thereby making up a hydraulic closed circuit.
In the hydraulic closed-circuit system, the potential energy of the boom 111 and arm 112 which is generated when the boom 111 and arm 112 move down in the direction of gravitational force or when the rotary motion of the revolving upperstructure 102 is stopped and the kinetic energy of the revolving upperstructure 102 are turned into regenerative energy which is transmitted to the return hydraulic oil and conveyed to one of the closed-circuit hydraulic pumps 2a to 2f. At this time, the closed-circuit hydraulic pumps 2a to 2f perform regenerative operation by the regenerative energy. The regenerative energy is conveyed as driving power to another one of the closed-circuit hydraulic pumps 2a to 2f which drives another hydraulic actuator through the power transmission device 15. As a consequence, for the engine 106, energy is saved by the amount equivalent to the regenerative energy.
Although omitted in FIG. 2, the hydraulic closed-circuit system includes: a charge pump which increases the circuit pressure to prevent cavitation; a make-up check valve; a flushing valve which absorbs the flow rate difference between the head side and rod side of the hydraulic actuator as a single-rod hydraulic cylinder and changes the hydraulic oil in the closed circuit; and a relief valve which relieves the hydraulic oil when the hydraulic oil pressure reaches a prescribed value or more.
The electromagnetic valves 12 include a total of eighteen valves including “BM” switching valves, “AM” switching valves, “BK” switching valves and “SW” switching valves for connecting two or more ones of the closed-circuit hydraulic pumps 2a to 2f to one of the boom cylinder 7a, arm cylinder 7b, bucket cylinder 7c and swing motor 10c. 
Among the electromagnetic switching valves 12, the “BM” switching valve is a switching valve for connection to the boom cylinder 7a which enables connection of at most all the closed-circuit hydraulic pumps 2a to 2f located upstream of the electromagnetic switching valves 12. The “AM” switching valve is a switching valve for connection to the arm cylinder 7b which enables connection of at most the closed-circuit hydraulic pumps 2a to 2d among the closed-circuit hydraulic pumps 2a to 2f located upstream of the electromagnetic switching valves 12. The “BK” switching valve is a switching valve for connection to the bucket cylinder 7c which enables connection of at most all the closed-circuit hydraulic pumps 2a to 2f located upstream of the electromagnetic switching valves 12. The “SW” switching valve is a switching valve for connection to the swing motor 10c which enables connection of at most the two closed-circuit hydraulic pumps 2e and 2f among the closed-circuit hydraulic pumps 2a to 2f located upstream of the electromagnetic switching valves 12.
The form of connection of the electromagnetic switching valves 12 is not limited to the above but another form of connection may be adopted depending on the application purpose of the work machine.
The cab 104 where an operator boards is equipped with the operation device 17 to give an operation instruction to each hydraulic actuator. The operation device 17 has operation levers 17a, 17b which can tilt back and forth and left and right and a detector (not shown) which electrically detects the amount of tilt of the operation lever 17a, 17b as an operation signal, namely a lever manipulated variable, and outputs the lever manipulated variable detected by the detector as a lever manipulated variable signal to the controller 16 through an electric wire.
The operation device 17 has a mechanism which electrically detects the lever manipulated variable but instead it may have another type of mechanism such as a hydraulic mechanism. In the case of a hydraulic mechanism, typically it is a mechanism which has a pilot hydraulic pump separately and reduces the discharge pressure of the hydraulic pump depending on the lever manipulated variable.
The controller 16 performs prescribed control calculations and outputs an opening instruction signal to the hydraulic regulators 3a to 3f, outputs a switching valve connection instruction signal to the electromagnetic switching valves 12 to control them. In other words, the controller 16 controls the hydraulic regulators 3a to 3f, the electromagnetic switching valves 12, and the control valve 11 according to such information as the lever manipulated variable signal outputted from the operation device 17 and hydraulic oil pressure signals outputted from pressure sensors 18a to 18h connected to the connection ports of the hydraulic actuators.
In the hydraulic open-circuit system, as mentioned above, the control valve 11 to give the drive direction and discharge rate of the traveling motors 10a, 10b is located downstream. The open-circuit hydraulic pumps 1a and 1b are one-way discharge mechanisms with two connection ports in which one of the two connection ports is connected to the hydraulic oil tank 9 by piping as a suction port for suction from the hydraulic oil tank 9 for storing pressure oil temporarily. The other connection port of the open-circuit hydraulic pumps 1a, 1b is connected as a discharge port to the connection port of the control valve 11. The discharge rate from the discharge port is controlled by the one-way discharge mechanism. The one-way discharge mechanism is controlled by the hydraulic regulators 3g, 3h. 
The return hydraulic oil from the traveling motors 10a, 10b goes back to the hydraulic oil tank 9 through the control valve 11. The control valve 11 and the hydraulic regulators 3g, 3h are controlled depending on the lever manipulated variable generated by the operation device (not shown) provided in the cab 104. The lever manipulated variable is outputted to the controller 16. The controller 16 performs control calculations which are different from those for the hydraulic closed-circuit system, makes conversion into an output signal and outputs it to the control valve 11 and the hydraulic regulators 3g, 3h through an electric wire.
Next, the configuration of the controller 16 will be described referring to FIG. 3. FIG. 3 is a block diagram which shows the controller in the driving device shown in FIG. 2. FIG. 4 shows graphs which indicate calculations in the required pump number calculating circuit 30 of the controller 16 shown in FIG. 3, in which (a), (b), (c), and (d) are for the boom cylinder 7a, arm cylinder 7b, bucket cylinder 7c, and swing motor 10c, respectively. FIG. 5 is a table which shows the priority order map of the controller 16 shown in FIG. 3.
The controller 16 includes a required pump number calculating circuit 30, a priority order calculating circuit 31, and a priority order map 32. The required pump number calculating circuit 30 calculates the number of pumps required to be connected to a hydraulic actuator according to the manipulated variable of the operation levers 17a, 17b of the operation device 17, namely the lever manipulated variable. As indicated in FIG. 4(a) to FIG. 4(d), the required pump number calculating circuit 30 calculates the number of hydraulic pumps required from the hydraulic oil amount required to drive the boom cylinder 7a, arm cylinder 7b, bucket cylinder 7c, and swing motor 10c, according to the lever manipulated variable signal outputted from the operation device 17 upon operation of the operation levers 17a, 17b. FIG. 4(a) to FIG. 4(d) show an example that the amount of hydraulic oil increases in proportion to the lever manipulated variable but instead a different specification may be adopted depending on the work machine.
The priority order map 32 determines the priority connection relationships between the closed-circuit hydraulic pumps 2a to 2f and the hydraulic actuators as the boom cylinder 7a, arm cylinder 7b, bucket cylinder 7c, and swing motor 10c and as shown in FIG. 5, the vertical axis represents the hydraulic actuators and the horizontal axis represents the closed-circuit hydraulic pumps 2a to 2f, and for example, “1”, “2” . . . “7” are indicated as priorities in the boxes corresponding to the axes. “-” in a box expresses that the closed-circuit hydraulic pumps 2a to 2f and hydraulic actuators are not connected through the electromagnetic switching valves 12.
For example, if the actuator to be operated is the boom cylinder 7a which requires a high flow rate, when the closed-circuit hydraulic pumps 2a to 2f are expressed by P1 to P6 respectively, the connectable hydraulic pumps are all P1 to P6 and the order of connection is P1, P4, P2, P5, P6, and P3 in the order of mention. If the actuator to be operated is the arm cylinder 7b, the connectable hydraulic pumps are P1 to P4 and the order of connection is P2, P1, P3, and P4 in the order of mention. If the actuator to be operated is the bucket cylinder 7c which requires a high flow rate, the connectable hydraulic pumps are all P1 to P6 and the order of connection is P3, P6, P5, P5, P2, and P1 in the order of mention. If the actuator to be operated is the swing motor 10c which only requires a low flow rate, the connectable hydraulic pumps are P5 and P6 and the order of connection is P5 and P6 in the order of mention. The numbers “1” to “7” in the priority order map 32 indicate the priority order in which higher priority is given to connect a given closed-circuit hydraulic pump 2a to 2f to a hydraulic actuator corresponding to a smaller number.
The priority order calculating circuit 31 calculates the allocation of the closed-circuit hydraulic pumps 2a to 2f to the hydraulic actuators according to the number of pumps required calculated from the manipulated variable of the operation levers 17a, 17b by the required pump number calculating circuit 30 and the priority order map 32. A switching valve connection instruction signal for controlling switching of a given electromagnetic switching valve 12 and a hydraulic pump connection instruction for connecting a given closed-circuit hydraulic pump 2a to 2f are outputted according to the result of calculation by the priority order calculating circuit 31 and switching of the given electromagnetic switching valve 12 is controlled according to the outputted switching valve connection instruction signal and hydraulic pump connection instruction and the closed-circuit hydraulic pumps 2a to 2f are thus connected to the hydraulic actuators.
Furthermore, the priority order calculating circuit 31 is configured so that when the number of pumps allocated to the closed-circuit hydraulic pumps 2a to 2f increases (in the case of increase in the number of pumps), the closed-circuit hydraulic pumps 2a to 2f which are not allocated just before the increase or unused are allocated, and also configured so that when the number of plural closed-circuit hydraulic pumps 2a to 2f allocated to a given hydraulic actuator decreases (in the case of decrease in the number of pumps), the allocation of the closed-circuit hydraulic pumps 2a to 2f to the other hydraulic actuators than the given hydraulic actuator is maintained.
Next, the operation of the controller 16 will be described in further detail referring to FIGS. 6 to 8.
FIG. 6 is a time chart which shows the operation of the controller 16 shown in FIG. 3 when the number of pumps required increases, in which (a) indicates the lever manipulated variable, (b) indicates the number of pumps required, (c) indicates the number of pumps used, (d) indicates the state of the electromagnetic switching valves 12 before time t1, and (e) indicates the state of the electromagnetic switching valves 12 at time t1 and after time t1. FIG. 7 is a time chart which shows the operation of the controller 16 shown in FIG. 3 when the number of pumps required decreases, in which (a) indicates the lever manipulated variable, (b) indicates the number of pumps required, (c) indicates the number of pumps used, (d) indicates the state of the electromagnetic switching valves 12 from time t1 before time t2, and (e) indicates the state of the electromagnetic switching valves 12 at time t2 and after time t2. FIG. 8 is a flowchart which shows allocation control of the closed-circuit hydraulic pumps 2a to 2f by the controller 16 shown in FIG. 3. In FIG. 6(a) to FIG. 6(c) and FIG. 7(a) to FIG. 7(c), the horizontal axis represents time, and the vertical axis represents the lever manipulated variable in FIG. 6(a) and FIG. 7(a) and the number of pumps required in FIG. 6(b) and FIG. 7(b), and the number of pumps used in FIG. 6(c) and FIG. 7(c).
For the lever manipulated variable at each time, the required pump number calculating circuit 30 calculates the number of pumps required for the hydraulic actuators as the boom cylinder 7a, arm cylinder 7b, bucket cylinder 7c, and swing motor 10c. The priority order calculating circuit 31 calculates the pump allocation of the closed-circuit hydraulic pumps 2a to 2f according to the number of pumps required at each time as calculated by the required pump number calculating circuit 30 and referring to the priority order map 32.
(In the Case of Increase)
Let's assume, for example, that as shown in FIG. 6(b), when before time t1, the number of pumps required for the boom cylinder 7a is “0”, the number of pumps required for the arm cylinder 7b is “2”, the number of pumps required for the bucket cylinder 7c is “0”, and the number of pumps required for the swing motor 10c is “0” (hereinafter expressed as “0, 2, 0, 0”), the operation levers 17a, 17b are operated at time t1 and consequently the number of pumps required becomes “1, 2, 0, 0” or the number of pumps required increases by “1, 0, 0, 0”.
In this case, as shown in FIG. 8, the number of pumps required at time t1 and after time t1, “1, 2, 0, 0” and the number of pumps used before time t1 “0, 2, 0, 0” are entered in the priority order calculating circuit 31 (step S1) and whether or not the number of pumps required NPr is the number of pumps used NPu or more, namely NPr≧NPu is decided (step S2). In the flowchart shown in FIG. 8, control begins at START and upon arrival at RETURN, the sequence returns to START. This control is performed in a predetermined cycle by an internal timer (not shown) provided in the controller 16.
If it is decided at step S2 that the number of pumps required NPr is the number of pumps used NPu or more (Yes), whether or not the number of pumps required NPr is equal to the number of pumps used NPu, namely NPr=NPu, is decided (step S3).
If it is decided at step S3 that the number of pumps required NPr is equal to the number of pumps used NPu (Yes), calculation for allocation of the closed-circuit hydraulic pumps 2a to 2f is not newly performed. On the other hand, if it is decided at the step S3 that the number of pumps required NPr is not equal to the number of pumps used NPu (No), whether or not there is an unused pump among the closed-circuit hydraulic pumps 2a to 2f is decided (step S4).
If it is decided at the step S4 that there is an unused pump among the closed-circuit hydraulic pumps 2a to 2f (Yes), the difference between the number of pumps required NPr and the number of pumps used NPu, namely NPr−NPu, is calculated and the unused hydraulic pump is allocated according to the difference (step S5). On the other hand, if it is decided at the step S4 that there is no unused hydraulic pump (No), a given closed-circuit hydraulic pump 2a to 2f is allocated to a given hydraulic actuator according to the priority order map 32 (step S6).
Specifically, as shown in FIG. 6(a), the lever manipulated variable for the boom cylinder 7a is entered at time t1 in a manner to be combined with the lever manipulated variable entered before time t1 for the arm cylinder 7b. As a consequence, as shown in FIG. 6(b), the number of pumps required NPr changes from “0, 2, 0, 0” before time t1 to “1, 2, 0, 0”. Also, as shown in FIG. 6(c), before time t1 the pumps used are P1 and P2 and the number of pumps used NPu is “0, 2, 0, 0”. Next, the number of pumps required NPr “1, 2, 0, 0” and the number of pumps used NPu “0, 2, 0, 0” are entered in the priority order calculating circuit 31 (step S1) and the number of pumps required NPr and the number of pumps used NPu are compared and it is decided that there is an increase of “0, 1, 0, 0”, namely the number of pumps required NPr is the number of pumps used NPu or more (step S2). Furthermore, it is decided that the number of pumps required NPr is not equal to the number of pumps used NPu (step S3) and the sequence goes to decision about whether or not there is an unused hydraulic pump. In this case, since there are unused hydraulic pumps P3, P4, P5, and P6, it is decided that there are unused hydraulic pumps, namely YES (step S4), the hydraulic pump with the highest priority for the boom cylinder 7a among the unused hydraulic pumps in the priority order map 32 is allocated (step S5). The priorities of the closed-circuit hydraulic pumps 2a to 2f for the boom cylinder 7a are “6” for P3, “2” for P4, “4” for P5, and “5” for P6 as shown in FIG. 5, so P4, which has the highest priority “2”, is allocated.
On the other hand, regarding the electromagnetic switching valves 12, as shown in FIG. 6(d), before time t1, as P1 and P2 are connected to the arm cylinder 7b, the “AM” switching valves located downstream of P1 and P2 are on. Furthermore, as shown in FIG. 6(e), at time t1, as the allocated P4 is connected to the boom cylinder 7a, the “BM” switching valve located downstream of P4 is on.
As a consequence, as shown in FIG. 6(b) and FIG. 6(c), the number of pumps used NPu after time t1 meets the number of pumps required NPr and the number of pumps used NPu is the same as the number of pumps required NPr, so the hydraulic actuator operation speed as required is achieved and also the number of switching times of the electromagnetic switching valves 12 is only one for the “BM” switching valve.
(In the Case of Decrease)
Furthermore, when at the step S2 the number of pumps required NPr is not the number of pumps used NPu or more (No), namely the number of pumps required NPr has decreased, if the allocation of the closed-circuit hydraulic pumps 2a to 2f is returned to the original allocation according to the priority order map 32 shown in FIG. 5, unnecessary switching of the electromagnetic switching valves 12 would be required as described later; for this reason, the number of pumps as closed-circuit hydraulic pumps 2a to 2f used to drive the hydraulic actuator for which the number of pumps required decreases is decreased and the connection of the closed-circuit hydraulic pumps 2a to 2f to another hydraulic actuator than the hydraulic actuator concerned, namely the arm cylinder 7b, that is the boom cylinder 7a, is not changed (step S7).
Specifically, as shown in FIG. 7(a), at time t2, the lever manipulated variable of the arm cylinder 7b, which is one of the lever manipulated variables of the boom cylinder 7a and arm cylinder 7b as entered before time t2, decreases. As a consequence, as shown in FIG. 7(b), the number of pumps required NPr changes from “1, 2, 0, 0” to “1, 1, 0, 0”. Also, as shown in FIG. 7(c), the pumps used before time t2 are P1, P2, and P4 and the number of pumps used NPu is “1, 2, 0, 0”. Next, as in the case of increase, the number of pumps required NPr “1, 1, 0, 0” and the number of pumps used NPu “1, 2, 0, 0” are entered in the priority order calculating circuit 31 (step S1) and the number of pumps required NPr and the number of pumps used NPu are compared and it is decided that there is a decrease of “0, 1, 0, 0”, namely the number of pumps required NPr is smaller than the number of pumps used NPu (step S2). Then, the number of pumps used as the hydraulic pumps connected to the arm cylinder 7b as the hydraulic actuator for which the number of required pump decreases is decreased (step S7). As shown in FIG. 5 and FIG. 7(c), before time t2, the hydraulic pumps connected to the arm cylinder 7b are P1 having priority “2” and P2 having priority “1” and at time t2 the decrease in the number of pumps required is “0, 1, 0, 0”, so, as shown in FIG. 5, P1, which has the lower priority “2”, is unused.
On the other hand, regarding the electromagnetic switching valves 12, as shown in FIG. 7(d), before time t2, as P1 and P2 are connected to the arm cylinder 7b, the “AM” switching valves located downstream of P1 and P2 are on. Also, as shown in FIG. 7(e), at time t2, as the number of pumps required NPr decreases, the “AM” switching valve located downstream of P1 is off.
As a consequence, P1, having priority “1” for the boom cylinder 7a, becomes unused or free but the connection of the closed-circuit hydraulic pumps 2a to 2f to the other hydraulic actuators than the arm cylinder 7b for which the number of pumps required NPr decreases is not changed and as shown in FIG. 7(c), the boom cylinder 7a remains connected to P4 and is not reconnected to P1. Also, as shown in FIG. 7(e), regarding the electromagnetic switching valves 12, after time t2, only the “AM” switching valve changes from the on state to the off state and the number of switching times is only one.
(Conventional Drive System)
Here, operation of the conventional drive system is described referring to FIGS. 9 and 10. FIG. 9 is a time chart which shows the operation of a conventional hydraulic excavator 1 when the number of pumps required increases, in which (a) indicates the lever manipulated variable, (b) indicates the number of pumps required, (c) indicates the number of pumps used, (d) indicates the state of the electromagnetic switching valves 12 before time t1, and (e) indicates the state of the electromagnetic switching valves 12 at time t1 and after time t1. FIG. 10 is a time chart which shows the operation of the conventional hydraulic excavator 1 when the number of pumps required decreases, in which (a) indicates the lever manipulated variable, (b) indicates the number of pumps required, (c) indicates the number of pumps used, (d) indicates the state of the electromagnetic switching valves 12 from time t1 before time t2, and (e) indicates the state of the electromagnetic switching valves 12 at time t2 and after time t2. The horizontal and vertical axes of FIG. 9(a) to FIG. 9(c) and FIG. 10(a) to FIG. 10(c) are the same as those of FIG. 6(a) to FIG. 6(c) and FIG. 7(a) to FIG. 7(c).
(In the Case of Increase)
As shown in FIG. 9(b), before time t1, the number of pumps required for the boom cylinder 7a is “0”, the number of pumps required for the arm cylinder 7b is “2”, the number of pumps required for the bucket cylinder 7c is “0”, and the number of pumps required for the swing motor 10c is “0” and this is expressed as “0, 2, 0, 0”. In this case, since the number of pumps required for the arm cylinder 7b is “2” and the other hydraulic actuators require no pumps, referring to the priority order map 32 shown in FIG. 5, pumps with higher priorities, namely P2 and P1 in the order of mention, are allocated to the arm cylinder 7b. 
At time t1, as shown in FIG. 9(a), the lever manipulated variable for the boom cylinder 7a is entered at time t1 in a manner to be combined with the lever manipulated variable entered before time t1 for the arm cylinder 7b. As a consequence, as shown in FIG. 9(b), the number of pumps required changes from “0, 2, 0, 0” to “1, 2, 0, 0”, which means an increase of “1, 0, 0, 0” or change in the number of pumps required for the boom cylinder 7a from “0” to “1”. In this case, referring to the priority order map 32 shown in FIG. 5, in the closed-circuit hydraulic pumps 2a to 2f to be allocated to the boom cylinder 7a, the priority of P1 is “1”, the priority of P4 is “2”, and the priority of P2 is “3” and in the closed-circuit hydraulic pumps 2a to 2f to be allocated to the arm cylinder 7b, the priority of P2 is “1”, the priority of P1 is “2”, and the priority of P3 is “3” and thus P1 has priority “1” for the boom cylinder 7a and priority “2” for the arm cylinder 7b. Therefore, as shown in FIG. 9(c), P1 is reallocated from the arm cylinder 7b to the boom cylinder 7a for which it has higher priority, and P3, which has priority “3” or next to P1 in priority, is allocated to the arm cylinder 7b. 
In this case, as shown in FIG. 9(c), the number of pumps used meets the number of pumps required and thus the operation speed to be achieved by the number of pumps required is achieved, but as shown in FIG. 9(d) and FIG. 9(e), regarding the electromagnetic switching valves 12, the “AM” switching valve located downstream of P1 for connection to the arm cylinder 7b is changed from the on state to the off state, the “BM” switching valve located downstream of P1 for connection to the boom cylinder 7a is changed from the off state to the on state and the “AM” switching valve located downstream of P3 for connection to the arm cylinder 7b is changed from the off state to the on state, so three switching times of the electromagnetic switching valves 12 are required.
On the other hand, as shown in FIG. 10(a) and FIG. 10(b), in the period from time t1 to before time t2, P4 is connected to the boom cylinder 7a and P1 and P2 are connected to the arm cylinder 7b and at time t2, the number of pumps required changes from “1, 2, 0, 0” to “1, 1, 0, 0”, which means a decrease of “0, 1, 0, 0” or change in the number of pumps required for the arm cylinder 7b from “2” to “1”. In this case, referring to the priority order map 32 shown in FIG. 5, P1 has priority “1” for the boom cylinder 7a and priority “2” for the arm cylinder 7b and P4 has priority “2” for the boom cylinder 7a. Therefore, as shown in FIG. 10(c), P1 is reallocated from the arm cylinder 7b to the boom cylinder 7a for which it has higher priority, and P4 becomes unused.
Regarding the electromagnetic switching valves 12, as shown in FIG. 10(d) and FIG. 10(e), the “AM” switching valve for connection of P1 to the arm cylinder 7b is changed from the on state to the off state, the “BM” switching valve for connection of P1 to the boom cylinder 7a is changed from the off state to the on state and the “BM” switching valve for connection of P4 to the boom cylinder 7a is changed from the on state to the off state, so three switching times of the electromagnetic switching valves 12 are required.
On the other hand, in the drive system 107 according to the above embodiment of the present invention, for example, as shown in FIG. 6(b), if at time t1 the number of pumps required NPr is changed from “0, 2, 0, 0” to “1, 2, 0, 0”, or in the case of an increase of “1, 0, 0, 0”, and if there is an unused hydraulic pump, the unused hydraulic pump is first allocated as the hydraulic pump to be added when allocating given closed-circuit hydraulic pumps 2a to 2f to a given hydraulic actuator according to the priority order map 32. In other words, as shown in FIG. 5, since the priorities of the closed-circuit hydraulic pumps 2a to 2f for the boom cylinder 7a are “6” for P3, “2” for P4, “4” for P5, and “5” for P6 as shown in FIG. 5, P4, having the highest priority, is allocated.
As a consequence, the number of pumps used NPu meets the number of pumps required NPr and the number of pumps used NPu is the same as the number of pumps required NPr and thus the hydraulic actuator operation speed as required is achieved and also as shown in FIG. 6(e), regarding the electromagnetic switching valves 12, at time t1 only the “BM” switching valve for connection of P4 to the boom cylinder 7a is changed from the off state to the on state, so the number of switching times of the electromagnetic switching valves 12 is only one. Therefore, when during operation of one hydraulic actuator another hydraulic actuator is started, namely even when the number of hydraulic pumps to be allocated increases, an unused hydraulic pump is connected to the hydraulic actuator to be started without changing the connection of the hydraulic pump connected to the one hydraulic actuator, so that whereas the number of electromagnetic valve switching times is 3 in the case of increase in the number of pumps required in the conventional drive system, the number of switching times of the electromagnetic switching valves 12 is 1 in the drive system 107 according to the embodiment of the present system, so unnecessary switching control of the electromagnetic switching valves 12 is reduced.
Furthermore, for example, as shown in FIG. 7(b), when at time t2 the number of pumps required NPr is changed from “1, 2, 0, 0” to “1, 1, 0, 0” or in the case of decrease of “0, 1, 0, 0”, if as shown in FIG. 5 and FIG. 7(c), P1 having priority “2” and P2 having priority “1” are used before time t2, P1, having the lower priority “2” for the arm cylinder 7b for which the number of pumps required NPr decreases, is unused.
As a consequence, P1, having priority “1” for the boom cylinder 7a, becomes unused but the connection of the closed-circuit hydraulic pumps 2a to 2f to the other hydraulic actuators than the arm cylinder 7b for which the number of pumps required NPr decreases is not changed and the boom cylinder 7a remains connected (allocated) to P4 and is not reconnected to P1. Also, as shown in FIG. 7(e), regarding the electromagnetic switching valves 12, at time t2 only the “AM” switching valve for connection of P1 to the arm cylinder 7b is changed from the on state to the off state and the number of switching times of the electromagnetic switching valves 12 is only one.
As a consequence, the number of pumps used NPu meets the number of pumps required NPr, so the hydraulic actuator operation speed as required is achieved and as shown in FIG. 7(e), at time t2 the number of switching times of the electromagnetic switching valves 12 is 1. Therefore, if during operation of a plurality of hydraulic actuators the flow rate to one hydraulic actuator is decreased for deceleration, namely even if the number of hydraulic pumps to be allocated decreases, a hydraulic pump is unallocated from the hydraulic actuator to which the flow rate is decreased and the allocation of the hydraulic pumps to the other hydraulic actuators is maintained, so whereas the number of electromagnetic valve switching times is 3 in the case of decrease in the number of pumps required in the conventional drive system, the number of switching times of the electromagnetic switching valves 12 is 1, so unnecessary switching control of the electromagnetic switching valves 12 is reduced.
As mentioned so far, in both the cases of increase and decrease in the number of pumps required, the number of switching times of the electromagnetic switching valves 12 can be decreased, so the frequency of shock caused by hydraulic oil pressure variation during switching of the electromagnetic switching valves 12 can be reduced, which leads to reduction of vehicle body vibration, improved operability and improvement in the life of the components including the electromagnetic switching valves 12. In addition, thanks to the decrease in the number of switching times of the electromagnetic switching valves 12, the power consumption for switching of the electromagnetic switching valves 12 can be reduced.
Other Embodiments
The present invention is not limited to the above embodiment but the invention includes various modified embodiments. For example, the above embodiment has been described for easy understanding of the invention and the invention is not limited to an embodiment which includes the whole configuration described above.
Also, in the above embodiment, an explanation has been made by taking a case that the drive system 107 is mounted on the hydraulic excavator 1 as an example; however the present invention is not limited thereto but the invention can be applied to work machines other than the hydraulic excavator 1, such as hydraulic cranes and wheel loaders, if they have hydraulically drivable hydraulic actuators.
Furthermore, the closed-circuit hydraulic pumps 2a to 2f of the drive system 107 according to the above embodiment may have the same discharge capacity or may have different discharge capacities.
The above embodiment is configured so that the number of switching times of the electromagnetic switching valves 12 is decreased in both the cases of increase and decrease in the number of pumps required; however, instead a process according to the present invention may be performed so that the number of switching times of the electromagnetic switching valves 12 is decreased only in the case of increase in the number of pumps required or only in the case of decrease in the number of pumps required.
REFERENCE SIGNS LIST


    
    
        1 . . . hydraulic excavator (work machine),
        1a, 1b . . . open-circuit hydraulic pump,
        2a to 2f . . . closed-circuit hydraulic pump (hydraulic pump),
        3a to 3g . . . hydraulic regulator,
        7a . . . boom cylinder (hydraulic actuator),
        7b . . . arm cylinder (hydraulic actuator),
        7c . . . bucket cylinder (hydraulic actuator),
        9 . . . hydraulic oil tank,
        10a, 10b . . . traveling motor,
        10c . . . swing motor (hydraulic actuator),
        11 . . . control valve,
        12 . . . electromagnetic switching valve (switching valve),
        15 . . . power transmission device,
        16 . . . controller,
        17 . . . operation device (operation part),
        17a, 17b . . . operation lever,
        18a to 18h . . . pressure sensor,
        30 . . . required pump number calculating circuit,
        31 . . . priority order calculating circuit,
        32 . . . priority order map,
        101 . . . travel base,
        102 . . . revolving upperstructure,
        103 . . . working device,
        104 . . . cab,
        105 . . . main frame,
        106 . . . engine,
        107 . . . drive system (driving device),
        108 . . . counterweight,
        111 . . . boom,
        112 . . . arm,
        113 . . . bucket

## Claims

1. A driving device (107) for a work machine (1) comprising:
a plurality of hydraulic actuators (7a to 7c, 10c);
a plurality of variable displacement hydraulic pumps (2a to 2f) to drive the hydraulic actuators (7a to 7c, 10c);
a plurality of switching valves (12) connected between the hydraulic actuators (7a to 7c, 10c) and the hydraulic pumps (2a to 2f);
an operation part (17) to operate the hydraulic actuators (7a to 7c, 10c); and
a controller (16) to control the hydraulic pumps (2a to 2f) and the switching valves (12),
at least two of the hydraulic pumps (2a to 2f) connected in a closed loop to any one of the hydraulic actuators (7a to 7c, 10c) through the switching valves (12),
wherein: the controller (16) includes a priority order calculating circuit (31) which calculates allocation of the hydraulic pumps (2a to 2f) to the hydraulic actuators (7a to 7c, 10c) according to operation of the operation part (17) and a priority order map (32) determining priority connection relationships between the hydraulic pumps (2a to 2f) and the hydraulic actuators (7a to 7c, 10c); and
the priority order calculating circuit (31) selects and allocates an unallocated one of the hydraulic pumps (2a to 2f) when the number of the hydraulic pumps (2a to 2f) to be allocated increases.

2. A driving device (107) for a work machine (1) comprising:
a plurality of hydraulic actuators (7a to 7c, 10c);
a plurality of variable displacement hydraulic pumps (2a to 2f) to drive the hydraulic actuators (7a to 7c, 10c);
a plurality of switching valves (12) connected between the hydraulic actuators (7a to 7c, 10c) and the hydraulic pumps (2a to 2f);
an operation part (17) to operate the hydraulic actuators (7a to 7c, 10c); and
a controller (16) to control the hydraulic pumps (2a to 2f) and the switching valves (12),
at least two of the hydraulic pumps (2a to 2f) connected in a closed loop to any one of the hydraulic actuators (7a to 7c, 10c) through the switching valves (12),
wherein: the controller (16) includes a priority order calculating circuit (31) which calculates allocation of the hydraulic pumps (2a to 2f) to the hydraulic actuators (7a to 7c, 10c) according to operation of the operation part (17) and a priority order map (32) determining priority connection relationships between the hydraulic pumps (2a to 2f) and the hydraulic actuators (7a to 7c, 10c); and
when the number of the hydraulic pumps (2a to 2f) to be allocated to a given hydraulic actuator (7a to 7c, 10c) decreases, the priority order calculating circuit (31) maintains allocation of the hydraulic pumps (2a to 2f) allocated to the other hydraulic actuators (7a to 7c, 10c) than the given hydraulic actuator (7a to 7c, 10c).