Drive system for industrial machinery

Abstract

To improve work efficiency and power efficiency in industrial machinery. [Solution] The drive system 100 of the work machine includes a rotating member C that can rotate relative to a connection point, and an electric motor 86 that is a power source for the rotating member. The electric motor 86 has a plurality of windings to which an AC power source is connected, and includes a switching circuit 104 that can switch the connection state of the windings between a first connection state and a second connection state that allows rotation at a lower torque and higher rotation speed than the first connection state.

Description

Technical Field

[0001] The present disclosure relates to a drive system for a work machine.

Background Art

[0002] Patent Document 1 discloses a work machine provided with an electric motor that causes a revolving structure to revolve. The electric motor of such a work machine is required to be capable of outputting high torque. On the other hand, in order to perform work promptly using the work machine, the electric motor is required to be capable of outputting a high rotational speed. However, it is difficult for a single electric motor to exhibit high power efficiency in both the high torque range and the high rotational speed range. That is, when enabling output of high torque and enabling output of high rotational speed, a plurality of electric motors having different characteristics must be employed to improve power efficiency.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] Improvements in work efficiency and power efficiency are required for work machines.

Means for Solving the Problem

[0005] A drive system for a work machine according to one aspect of the present disclosure includes a rotating member that is rotatable relative to a connection point, and an electric motor that is a power source of the rotating member. The electric motor includes a plurality of windings to which an AC power source is connected, and is provided with a switching circuit capable of switching a connection state of the windings to either one of a first connection state and a second connection state in which rotation is possible at lower torque and higher rotational speed than in the first connection state.

[0006] According to the above configuration, the electric motor can be switched by a switching circuit between a first connection state that operates in the high torque range and a second connection state that operates in the high rotation range. Therefore, the rotational speed-torque characteristics over which the electric motor can be used with high power efficiency are expanded. Thus, power efficiency can be improved while simultaneously improving the working efficiency of the work machine.

[0007] In a drive system for a work machine, each winding has a first end to which an AC power source is connected, a second end opposite to the first end, and a midpoint between the first end and the second end, and the switching circuit may be switchable between a first connection state in which the midpoints of the multiple windings are disconnected and the second ends are connected, and a second connection state in which the midpoints of the multiple windings are connected.

[0008] In the drive system of a work machine, the rotatable range of the rotating member around the connection point may be 180 degrees or more. In a drive system for a work machine, the system comprises a main body, a boom rotatably connected to the main body, an arm rotatably connected to the boom, and an attachment rotatably connected to the arm, wherein the rotating member may be one selected from the boom, the arm, and the attachment.

[0009] In a drive system for a work machine, the system comprises a lower body having a traveling device and an upper body rotatably connected to the lower body, wherein the rotating member may be the upper body. A drive system for a work machine may include a changeover switch that can be operated by the operator of the work machine, and a control device that switches the changeover circuit to either the first connection state or the second connection state based on the operation of the changeover switch.

[0010] A drive system for a work machine may include a control device that switches the switching circuit to the first connection state when the torque of the electric motor is equal to or greater than a predetermined specified value, and switches the switching circuit to the second connection state when the torque of the electric motor is less than the specified value.

[0011] A drive system for a work machine may include a control device that switches the switching circuit to the second connection state when the rotational speed of the electric motor is equal to or greater than a predetermined specified rotational speed, and switches the switching circuit to the first connection state when the torque of the electric motor is less than the specified rotational speed.

[0012] In a drive system for a work machine, the rotating member is the boom, and the system may include a control device that switches the switching circuit to the first connection state when the angle of the boom with respect to the ground is less than a specified angle, and switches the switching circuit to the second connection state when the angle of the boom with respect to the ground is equal to or greater than the specified angle.

[0013] In a drive system for a work machine, a control device may be provided that switches the switching circuit to the first connection state until the rotating member rotates from a stopped state to a predetermined angle.

[0014] The drive system for the work machine may include a conversion circuit that outputs AC power to the electric motor, and a cooling device for cooling the conversion circuit. [Effects of the Invention]

[0015] According to the above configuration, it is possible to improve power efficiency while also improving the working efficiency of the machinery. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a side view of a work machine according to one embodiment. [Figure 2] Figure 2 is a top view of the work machine. [Figure 3] FIG. 3 is a side view showing the configuration of a traveling device of a work machine and the movable range of a working member. [Figure 4] FIG. 4 is a diagram showing the electrical configuration and power transmission path of the drive system of the work machine. [Figure 5] FIG. 5 is a circuit diagram showing the circuit configuration of an electric motor. [Figure 6] FIG. 6 is a graph showing the rotational speed-torque characteristics of the electric motor. [Figure 7] FIG. 7 is a circuit diagram showing a circuit configuration of an electric motor according to a modified example. [Figure 8] FIG. 8 is a circuit diagram showing a circuit configuration of an electric motor according to another modified example. [Mode for Carrying Out the Invention]

[0017] Hereinafter, embodiments of the drive system for a work machine according to the present disclosure will be described with reference to the accompanying drawings. Note that for the sake of simplicity and clarity, the constituent elements shown in the drawings are not necessarily drawn to a constant scale. The accompanying drawings are merely illustrative of the embodiments of the present disclosure and should not be construed as limiting the present disclosure.

[0018] The following detailed description includes apparatuses, systems, and methods that embody exemplary embodiments of the present disclosure. This detailed description is merely illustrative in nature and is not intended to limit the embodiments of the present disclosure or the application and use of such embodiments.

[0019] <Embodiment> [Drive System for Work Machine] The drive system 100 for a work machine will be described with reference to FIG. 1 to FIG. 6. First, an excavator 10 as a work machine to which the drive system 100 is applied will be described.

[0020] As shown in Figure 1, the excavator 10 comprises a main body 12 and a working member 50. The main body 12 constitutes the body of the excavator 10. The main body 12 comprises a lower body 14 and an upper body 16. The upper body 16 is located on the opposite side of the ground G from the lower body 14. In this embodiment, the direction in which the upper body 16 is located when viewed from the lower body 14 is the upward direction, and the opposite direction is the downward direction. Furthermore, a specific direction perpendicular to the upward direction is the forward direction, and the opposite direction is the backward direction. In addition, one of the directions perpendicular to both the upward and forward directions is the left direction, and the other is the right direction. The forward and backward directions are sometimes collectively referred to as the X direction. The left and right directions are sometimes collectively referred to as the Y direction. The upward and downward directions are sometimes collectively referred to as the Z direction.

[0021] The lower body 14 is, for example, rectangular parallelepiped. The upper body 16 comprises a main housing section 18 and a front housing section 20. The main housing section 18 is, for example, rectangular parallelepiped. The interior of the main housing section 18 is a hollow storage space. The storage space houses various equipment for operating the excavator 10.

[0022] The front section 20 of the housing is located on the front side relative to the main section 18 of the housing. As shown in Figure 2, the front section 20 of the housing is located approximately in the center of the main section 18 in the Y direction. The front section 20 of the housing is fixed to the front of the main section 18 of the housing. The front section 20 of the housing is, for example, a rectangular parallelepiped that is smaller than the main section 18 of the housing. The inside of the front section 20 of the housing is hollow. Although not shown in the figure, the upper section 16 is equipped with a cabin in which an operator sits. The cabin is fixed integrally with the main section 18 of the housing. The upper section 16 is sometimes referred to as the upper slewing section.

[0023] As shown in Figure 1, the excavator 10 is equipped with a slewing bearing 22. The slewing bearing 22 is located between the lower body 14 and the upper body 16 in the Z direction. In Figure 1, the vertical width of the slewing bearing 22 in the Z direction is exaggerated and shown as larger.

[0024] As shown in Figure 2, the slewing bearing 22 comprises an annular inner ring 24, an annular outer ring 26, and a plurality of rolling elements. Note that the rolling elements are not shown in Figure 2. The outer diameter of the inner ring 24 is smaller than the inner diameter of the outer ring 26. The fifth axis J5, which is the central axis of the inner ring 24, coincides with the central axis of the outer ring 26. The fifth axis J5 extends vertically through the vehicle body, i.e., in the Z direction. As shown in Figure 1, the fifth axis J5 passes vertically through both the upper body 16 and the lower body 14.

[0025] As shown in Figure 2, the multiple rolling elements are located between the inner ring 24 and the outer ring 26. The multiple rolling elements support the inner ring 24 and the outer ring 26 so that they can rotate relative to each other. That is, the outer ring 26 is rotatable relative to the inner ring 24 about the fifth axis J5. The inner ring 24 is fixed to the lower body 14. The outer ring 26 is fixed to the main housing portion 18 of the upper body 16. That is, the upper body 16 is rotatable relative to the lower body 14 about the fifth axis J5. It can also be said that the upper body 16 is rotatable relative to the lower body 14.

[0026] As shown in Figures 2 and 3, the drive system 100 includes a pair of traveling devices 30. As shown in Figure 2, the pair of traveling devices 30 are located on both the left and right sides of the lower body 14. The pair of traveling devices 30 are configured symmetrically. In the following description, the traveling device 30 located to the left of the lower body 14 will be described.

[0027] As shown in Figure 3, the travel device 30 includes a travel crawler 32 and a travel mechanism 34. The travel mechanism 34 includes an idler 36, a drive sprocket 38, multiple rollers 40, a crawler frame 42, and a travel actuator 44.

[0028] The crawler track 32 is an endless belt-like structure. The crawler track 32 is made of, for example, metal or rubber. The crawler track 32 surrounds the running mechanism 34. The crawler track 32 extends in the X direction as a whole and opens to both sides in the Y direction. The crawler track 32 has a constant width in the Y direction. Although not shown in the illustration, multiple grooves are provided on the inner circumferential surface of the crawler track 32.

[0029] The idler 36 is located at the front end of the travel mechanism 34. More specifically, the idler 36 is located at the front end of the inside of the travel crawler 32. The idler 36 is annular in shape. Although not shown in the illustration, the idler 36 is movable in the forward and rearward directions by a linear actuator. The tension of the travel crawler 32 can be adjusted by moving the idler 36 in the forward and rearward directions.

[0030] The drive sprocket 38 is located at the rear end of the running mechanism 34. More specifically, the drive sprocket 38 is located at the rear end on the inside of the running crawler 32. The drive sprocket 38 is annular in shape. Although not shown in the illustration, multiple teeth are formed on the outer surface of the drive sprocket 38. These multiple teeth are arranged at equal intervals in the circumferential direction around the sixth axis J6, which is the central axis of the drive sprocket 38. The multiple teeth of the drive sprocket 38 mesh with multiple grooves of the running crawler 32. The sixth axis J6 extends in the Y direction.

[0031] Multiple rollers 40 are positioned between the idler 36 and the drive sprocket 38 in the X direction. The multiple rollers 40 are aligned in the X direction. Each roller 40 is annular. The diameter of each roller 40 is smaller than the diameters of the idler 36 and the drive sprocket 38. The multiple rollers 40 are in contact with the portion of the running crawler 32 that is located closer to the ground G.

[0032] The crawler frame 42 extends in the X direction inside the running crawler 32. The crawler frame 42 rotatably supports the idler 36, the drive sprocket 38, and the multiple rollers 40. The crawler frame 42 is fixed to the lower body 14 of the main body 12.

[0033] The travel actuator 44 is connected to the drive sprocket 38. More specifically, the travel actuator 44 is fixed to the center of the drive sprocket 38. The drive sprocket 38 rotates in accordance with the torque output by the travel actuator 44. As the drive sprocket 38 rotates, the travel crawler 32 rotates, causing the excavator 10 to move. In the following description, the travel actuator 44 may be referred to as the sixth actuator 84F.

[0034] In a pair of traveling devices 30, the operation of each traveling actuator 44 is not necessarily synchronized. That is, the traveling actuator 44 of the traveling device 30 on the left side and the traveling actuator 44 on the right side, as viewed from the lower body 14, may have different rotation directions, rotation speeds, torques, etc. By having the left and right traveling actuators 44 operate differently, the excavator 10 can change direction and perform turning movements. Details of the traveling actuators 44 will be described later.

[0035] [Working materials] As shown in Figures 1 and 2, the working member 50 comprises a swing bracket 52, a boom 58, an arm 60, and an attachment 62. The swing bracket 52 is located on the front part 20 of the housing. The swing bracket 52 comprises a first swing wall 54 and a second swing wall 56. The first swing wall 54 is located on the upper surface of the front part 20 of the housing on the upper body 16. As shown in Figure 2, the first swing wall 54 is, for example, disc-shaped. The first swing wall 54 is connected to the front part 20 of the housing.

[0036] The swing bracket 52 is rotatable relative to the main body 12. More specifically, the first swing wall 54 is rotatable relative to the front of the housing 20 about a first axis J1. The first axis J1 is approximately parallel to the Z direction. The second swing wall 56 protrudes upward from the upper surface of the first swing wall 54. The second swing wall 56 is, for example, a rectangular plate.

[0037] The boom 58 is a long, plate-like or columnar shape. The boom 58 is bent midway along its longitudinal direction. The boom 58 is located on the front side of the main housing portion 18 of the upper body 16. As shown in Figure 2, the first longitudinal end 581 of the boom 58 is aligned with the second swing wall 56 of the swing bracket 52 in the direction along the second axis J2. The second axis J2 is a virtual axis that is approximately perpendicular to the fifth axis J5.

[0038] The boom 58 is rotatable relative to the main body 12. More specifically, the boom 58 is rotatable relative to the main body 12 about a first axis J1 and a second axis J2. The boom 58 rotates in conjunction with the rotation of the swing bracket 52 about the first axis J1. The boom 58 is rotatable relative to the front of the housing 20 about the first axis J1 as the swing bracket 52 rotates relative to the front of the housing 20.

[0039] The first end 581 of the boom 58 is rotatably connected to the second swing wall 56 about the second axis J2. By rotating the boom 58 relative to the second swing wall 56, the boom 58 can rotate relative to the main body 12 about the second axis J2. The boom 58 is an example of a rotating member C. The main body 12 is an example of a connection point for the boom 58. The swing bracket 52 can also be said to be an example of a rotating member C.

[0040] As shown in Figure 1, the arm 60 is a long, plate-like or columnar shape. The arm 60 is connected to the second end 582 of the boom 58, which is opposite to the first end 581. More specifically, the longitudinal first end 601 of the arm 60 is connected to the second end 582 of the boom 58. As shown in Figure 2, the longitudinal first end 601 of the arm 60 is aligned with the second end 582 of the boom 58 in the direction along the third axis J3. The third axis J3 is a virtual axis that is approximately parallel to the second axis J2. The arm 60 is rotatable relative to the boom 58. Specifically, the first end 601 of the arm 60 is connected to the second end 582 of the boom 58 so as to be rotatable about the third axis J3. The arm 60 is an example of a rotating member C. The boom 58 is an example of a connection point for the arm 60. In other words, the boom 58 is a rotating member C that can rotate relative to the upper body 16, and is also the connection point for the arm 60.

[0041] As shown in Figure 1, the attachment 62 is located near the second end 602 of the arm 60, opposite to the first end 601. In this embodiment, the attachment 62 is a bucket. The attachment 62 comprises a bucket body 66, a plurality of claws 68, and a bucket connecting wall 70. The bucket body 66 is box-shaped. That is, as shown in Figure 2, the bucket body 66 has an opening 641. The claws 68 protrude from one side of the edge of the rectangular opening 641 in the bucket body 66. The bucket connecting wall 70 protrudes from the outer wall of the bucket body 66, on the opposite side of the opening 641 from the claws 68.

[0042] As shown in Figure 2, the bucket connecting wall 70 is aligned with the second end 602 of the arm 60 in the direction along the fourth axis J4. The fourth axis J4 is a virtual axis that is substantially parallel to both the second axis J2 and the third axis J3.

[0043] The attachment 62 is rotatable relative to the arm 60. Specifically, the bucket connecting wall 70 of the attachment 62 is rotatably connected to the second end 602 of the arm 60 around the fourth axis J4. The attachment 62 is an example of a rotating member C. The arm 60 is an example of a connection point for the attachment 62. That is, the arm 60 is a rotating member C that is rotatable relative to the boom 58, and is also a connection point for the attachment 62.

[0044] As shown in Figure 3, the swing bracket 52 is rotatable by more than 180 degrees relative to the main body 12. In other words, the boom 58 is rotatable by more than 180 degrees relative to the main body 12 about the first axis J1. The swing bracket 52 may be rotatable by more than 360 degrees relative to the main body 12. Furthermore, the attachment 62 is rotatable by more than 180 degrees relative to the arm 60. More specifically, the attachment 62 is rotatable by more than 180 degrees relative to the arm 60 about the fourth axis J4.

[0045] Although not shown in the diagram, the boom 58 may be rotatable by 180 degrees or more around the second axis J2 relative to the main body 12. Also, the arm 60 may be rotatable by 180 degrees or more relative to the boom 58. More specifically, the arm 60 may be rotatable by 180 degrees or more around the third axis J3 relative to the boom 58.

[0046] [actuator] As shown in Figure 4, the drive system 100 comprises a battery 80, a plurality of conversion circuits 82, and a plurality of actuators 84. The plurality of conversion circuits 82 are connected to the battery 80. Each actuator 84 is connected to a corresponding conversion circuit 82. That is, each conversion circuit 82 connects the corresponding actuator 84 to the battery 80.

[0047] The battery 80 can supply DC power to a plurality of conversion circuits 82. The battery 80 may be, for example, a lithium-ion battery. Each conversion circuit 82 can convert the DC power supplied from the battery 80 into three-phase AC power. Each conversion circuit 82 can supply the converted three-phase AC power to the corresponding actuator 84. In other words, each conversion circuit 82 is the AC power source for the corresponding actuator 84. Furthermore, each conversion circuit 82 can control the voltage, frequency, and current vector of the AC power supplied to the actuator 84. Each conversion circuit 82 may be an inverter circuit including a plurality of transistors. Also, each conversion circuit 82 may include a converter that converts the voltage of the DC power supplied from the battery 80 to a predetermined voltage.

[0048] The drive system 100 includes a plurality of conversion circuits 82, namely a first conversion circuit 82A, a second conversion circuit 82B, a third conversion circuit 82C, a fourth conversion circuit 82D, a fifth conversion circuit 82E, and a sixth conversion circuit 82F. The drive system 100 also includes a plurality of actuators 84, namely a first actuator 84A, a second actuator 84B, a third actuator 84C, a fourth actuator 84D, a fifth actuator 84E, and a sixth actuator 84F.

[0049] The first actuator 84A is connected to the first conversion circuit 82A. The second actuator 84B is connected to the second conversion circuit 82B. The third actuator 84C is connected to the third conversion circuit 82C. The fourth actuator 84D is connected to the fourth conversion circuit 82D. The fifth actuator 84E is connected to the fifth conversion circuit 82E. The sixth actuator 84F is connected to the sixth conversion circuit 82F.

[0050] As shown in Figure 1, the first actuator 84A is housed in the front part 20 of the housing of the upper body 16. As shown in Figure 4, the first actuator 84A comprises a first electric motor 86A and a first reduction gear 88A. The first electric motor 86A is a three-phase AC motor. The first electric motor 86A is electrically connected to the battery 80 via a first conversion circuit 82A.

[0051] The first electric motor 86A comprises a housing 90A and an output shaft 92A rotatable relative to the housing 90A. The housing 90A is attached to the front part 20 of the upper body 16. The output shaft 92A protrudes from the inside to the outside of the housing 90A. The output shaft 92A is cylindrical. The output shaft 92A is rotatable relative to the housing 90A about its own central axis, the first axis J1. That is, the output shaft 92A outputs torque about the first axis J1. The output shaft 92A is configured to rotate in both forward and reverse directions about the first axis J1.

[0052] As shown in Figure 4, the first reduction gear 88A comprises a housing 94A, a reduction mechanism 96A, and an output member 98A. The housing 94A is fixed to the housing 90A of the first electric motor 86A. The reduction mechanism 96A is located inside the housing 94A.

[0053] The reduction gear 96A receives torque input from the output shaft 92A of the first electric motor 86A. The reduction gear 96A amplifies the torque from the first electric motor 86A at a predetermined ratio and outputs it to the output member 98A. The reduction gear 96A may be, for example, an eccentric oscillating gear type or a planetary gear type. The output member 98A is cylindrical. The central axis of the output member 98A substantially coincides with the first axis J1. The output member 98A is rotatable relative to the housing 94A. The output member 98A rotates about the first axis J1 in accordance with the rotation of the output shaft 92A of the first electric motor 86A.

[0054] The output member 98A of the first reduction gear 88A is attached to the first swing wall 54 of the swing bracket 52. As shown in Figure 4, the output member 98A outputs torque around the first axis J1. The swing bracket 52 rotates around the first axis J1 by receiving torque from the output member 98A. In other words, the first actuator 84A is an electrically powered device that drives the swing bracket 52 using the first electric motor 86A as its drive source. It can also be said that the first actuator 84A is an electrically powered device that drives the boom 58 using the first electric motor 86A as its drive source.

[0055] As shown in Figure 2, the second actuator 84B is located between the second swing wall 56 of the swing bracket 52 and the first end 581 of the boom 58. The configuration of the second actuator 84B is basically the same as that of the first actuator 84A, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the second actuator 84B will be briefly described below.

[0056] As shown in Figure 4, the second actuator 84B comprises a second electric motor 86B and a second reduction gear 88B. The second electric motor 86B is electrically connected to the battery 80 via a second conversion circuit 82B. The housing 90B of the second electric motor 86B is mounted on the second swing wall 56 of the swing bracket 52. The output shaft 92B of the second electric motor 86B outputs torque around its own central axis, the second axis J2. As shown in Figure 2, the second axis J2 passes through both the second swing wall 56 of the swing bracket 52 and the first end 581 of the boom 58.

[0057] The output member 98B of the second reduction gear 88B is attached to the first end 581 of the boom 58. As shown in Figure 4, the output member 98B outputs torque around the second axis J2. The boom 58 rotates around the second axis J2 by ​​receiving torque from the output member 98B. The functions of the housing 94B and reduction mechanism 96B of the second reduction gear 88B are the same as those of the housing 94A and reduction mechanism 96A of the first reduction gear 88A. That is, the second actuator 84B is an electrically powered device that drives the boom 58 using the second electric motor 86B as the drive source.

[0058] As shown in Figure 2, the third actuator 84C is located between the second end 582 of the boom 58 and the first end 601 of the arm 60. The configuration of the third actuator 84C is basically the same as that of the first actuator 84A, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the third actuator 84C will be briefly described below.

[0059] As shown in Figure 4, the third actuator 84C comprises a third electric motor 86C and a third reduction gear 88C. The third electric motor 86C is electrically connected to the battery 80 via a third conversion circuit 82C. The housing 90C of the third electric motor 86C is mounted on the second end 582 of the boom 58. The output shaft 92B of the third electric motor 86C outputs torque around its own central axis, the third axis J3. As shown in Figure 2, the third axis J3 passes through both the second end 582 of the boom 58 and the first end 601 of the arm 60.

[0060] The output member 98C of the third reduction gear 88C is attached to the first end 601 of the arm 60. As shown in Figure 4, the output member 98C outputs torque around the third axis J3. The arm 60 rotates around the third axis J3 by receiving torque from the output member 98C. The functions of the housing 94C and reduction mechanism 96C of the third reduction gear 88C are the same as those of the housing 94A and reduction mechanism 96A of the first reduction gear 88A. That is, the third actuator 84C is an electrically powered device that drives the arm 60 using the third electric motor 86C as the drive source.

[0061] As shown in Figure 2, the fourth actuator 84D is located between the second end 602 of the arm 60 and the bucket connecting wall 70 of the attachment 62. The configuration of the fourth actuator 84D is basically the same as that of the first actuator 84A, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the fourth actuator 84D will be briefly described below.

[0062] As shown in Figure 4, the fourth actuator 84D comprises a fourth electric motor 86D and a fourth reduction gear 88D. The fourth electric motor 86D is electrically connected to the battery 80 via a fourth conversion circuit 82D. The housing 90D of the fourth electric motor 86D is attached to the second end 602 of the arm 60. The output shaft 92D of the fourth electric motor 86D outputs torque around its own central axis, the fourth axis J4. As shown in Figure 2, the fourth axis J4 passes through both the second end 602 of the arm 60 and the bucket connecting wall 70.

[0063] The output member 98D of the fourth reduction gear 88D is attached to the bucket connecting wall 70. As shown in Figure 4, the output member 98D outputs torque around the fourth axis J4. The attachment 62 rotates around the fourth axis J4 by receiving torque from the output member 98D. The functions of the housing 94D and reduction mechanism 96D of the fourth reduction gear 88D are the same as those of the housing 94A and reduction mechanism 96A of the first reduction gear 88A. That is, the fourth actuator 84D is an electrically powered device that uses the fourth electric motor 86D as a drive source to drive the attachment 62.

[0064] The fifth actuator 84E is housed in the main housing portion 18 of the upper body 16. The configuration of the fifth actuator 84E is basically the same as that of the first actuator 84A, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the fifth actuator 84E will be briefly described below.

[0065] As shown in Figure 4, the fifth actuator 84E comprises a fifth electric motor 86E and a fifth reduction gear 88E. The fifth electric motor 86E is electrically connected to the battery 80 via a fifth conversion circuit 82E. The housing 90E of the fifth electric motor 86E is attached to the main housing 18 of the upper body 16. The output shaft 92E of the fifth electric motor 86E outputs torque around its own central axis, the fifth axis J5.

[0066] Multiple teeth are formed on the output member 98E of the fifth reduction gear 88E. These teeth mesh with the teeth formed on the inner ring 24 of the slewing bearing 22. The output member 98E outputs torque coaxial with the fifth electric motor 86E. By receiving this torque, the upper body 16 rotates with the housing 90E of the fifth electric motor 86E relative to the inner ring 24 and, consequently, the lower body 14. In other words, the fifth actuator 84E causes the upper body 16 to rotate relative to the lower body 14. The functions of the housing 94E and reduction mechanism 96E of the fifth reduction gear 88E are the same as those of the housing 94A and reduction mechanism 96A of the first reduction gear 88A. That is, the fifth actuator 84E is an electrically powered device that uses the fifth electric motor 86E as a driving source to drive the upper body 16.

[0067] As shown in Figure 3, the sixth actuator 84F is located on the crawler frame 42 of the travel mechanism 34. The configuration of the sixth actuator 84F is basically the same as that of the first actuator 84A, except for details such as dimensions, reduction ratio, and output. Therefore, the configuration of the sixth actuator 84F will be briefly described below.

[0068] As shown in Figure 4, the sixth actuator 84F comprises a sixth electric motor 86F and a sixth reduction gear 88F. The sixth electric motor 86F is electrically connected to the battery 80 via a sixth conversion circuit 82F. The housing 90F of the sixth electric motor 86F is mounted on the crawler frame 42 of the travel mechanism 34. The output shaft 92F of the sixth electric motor 86F outputs torque around its own central axis, the sixth axis J6.

[0069] The output member 98F of the sixth reduction gear 88F is attached to the drive sprocket 38. As shown in Figure 4, the output member 98F outputs torque around the sixth axis J6. The drive sprocket 38 rotates around the sixth axis J6 by receiving torque from the output member 98F. The functions of the housing 94F and reduction mechanism 96F of the sixth reduction gear 88F are the same as those of the housing 94A and reduction mechanism 96A of the first reduction gear 88A. That is, the sixth actuator 84F is an electrically powered device that uses the sixth electric motor 86F as a power source to drive the drive sprocket 38.

[0070] As mentioned above, the drive system 100 is equipped with a pair of travel devices 30, and the operation of each travel actuator 44 is not synchronized. Therefore, the drive system 100 is equipped with two sixth conversion circuits 82F and two sixth electric motors 86F. In other words, the drive system 100 is equipped with a sixth conversion circuit 82F for the left travel device 30 as viewed from the lower body 14, and a sixth conversion circuit 82F for the right travel device 30. The drive system 100 is also equipped with a sixth actuator 84F for the left travel device 30 as viewed from the lower body 14, and a sixth actuator 84F for the right travel device 30. Since the configuration of the two sixth actuators 84F is the same, their description and illustration are omitted.

[0071] [Cooling device] As shown in Figure 4, the drive system 100 is equipped with a plurality of cooling devices. Specifically, the drive system 100 is equipped with a plurality of cooling devices: a first cooling device 102A, a second cooling device 102B, a third cooling device 102C, a fourth cooling device 102D, a fifth cooling device 102E, and a sixth cooling device 102F. Each cooling device 102A to 102F is adjacent to a corresponding conversion circuit 82. Each cooling device 102A to 102F is capable of cooling the corresponding conversion circuit 82. That is, the first cooling device 102A is capable of cooling the first conversion circuit 82A. The second cooling device 102B is capable of cooling the second conversion circuit 82B. The third cooling device 102C is capable of cooling the third conversion circuit 82C. The fourth cooling device 102D is capable of cooling the fourth conversion circuit 82D. The fifth cooling device 102E is capable of cooling the fifth conversion circuit 82E. The sixth cooling device 102F is capable of cooling the sixth conversion circuit 82F. Each cooling device 102A to 102F is air-cooled. Specifically, each cooling device 102A to 102F includes a fan that blows outside air toward the corresponding conversion circuit 82, and an air passage through which the air blown by the fan circulates. The conversion circuit 82 is cooled when the air from the fan comes into contact with the conversion circuit 82, which is located in the middle of the air passage.

[0072] [Sensor] The drive system 100 is equipped with multiple torque sensors. Specifically, the drive system 100 is equipped with multiple torque sensors: a first torque sensor TA, a second torque sensor TB, a third torque sensor TC, a fourth torque sensor TD, a fifth torque sensor TE, and a sixth torque sensor TF. The first torque sensor TA can detect the torque of the first electric motor 86A. The second torque sensor TB can detect the torque of the second electric motor 86B. The third torque sensor TC can detect the torque of the third electric motor 86C. The fourth torque sensor TD can detect the torque of the fourth electric motor 86D. The fifth torque sensor TE can detect the torque of the fifth electric motor 86E. The sixth torque sensor TF can detect the torque of the sixth electric motor 86F.

[0073] In one example, each torque sensor TA to TF may be able to detect the torque of the corresponding electric motor 86A to 86F from the amount of current flowing through the electric motor 86A to 86F. In another example, each torque sensor TA to TF may be able to detect the torque of the corresponding electric motor 86A to 86F from the strain on the output shaft of the electric motor 86A to 86F. Each torque sensor TA to TF may be able to detect the torque of the corresponding electric motor 86A to 86F by a method other than those described above.

[0074] The drive system 100 is equipped with multiple rotational speed sensors. Specifically, the drive system 100 is equipped with multiple rotational speed sensors: a first rotational speed sensor NA, a second rotational speed sensor NB, a third rotational speed sensor NC, a fourth rotational speed sensor ND, a fifth rotational speed sensor NE, and a sixth rotational speed sensor NF. The first rotational speed sensor NA can detect the rotational speed of the first electric motor 86A. The second rotational speed sensor NB can detect the rotational speed of the second electric motor 86B. The third rotational speed sensor NC can detect the rotational speed of the third electric motor 86C. The fourth rotational speed sensor ND can detect the rotational speed of the fourth electric motor 86D. The fifth rotational speed sensor NE can detect the rotational speed of the fifth electric motor 86E. The sixth rotational speed sensor NF can detect the rotational speed of the sixth electric motor 86F. Note that rotational speed here refers to the number of rotations per unit time.

[0075] In one example, each rotational speed sensor NA to NF may be a sensor capable of detecting the rotational speed of the corresponding electric motor 86A to 86F from the amount of current flowing through the electric motor 86A to 86F. In another example, each rotational speed sensor NA to NF may be an optical sensor or magnetic sensor capable of detecting the rotational speed by being attached to the corresponding electric motor 86A to 86F. Each rotational speed sensor NA to NF may be capable of detecting the rotational speed of the corresponding electric motor 86A to 86F by methods other than those described above.

[0076] The drive system 100 is equipped with multiple angle sensors. Specifically, the drive system 100 is equipped with a first angle sensor DA, a second angle sensor DB, a third angle sensor DC, a fourth angle sensor DD, a fifth angle sensor DE, and a sixth angle sensor DF. The first angle sensor DA can detect the angular position of the first electric motor 86A. The second angle sensor DB can detect the angular position of the second electric motor 86B. The third angle sensor DC can detect the angular position of the third electric motor 86C. The fourth angle sensor DD can detect the angular position of the fourth electric motor 86D. The fifth angle sensor DE can detect the angular position of the fifth electric motor 86E. The sixth angle sensor DF can detect the angular position of the sixth electric motor 86F.

[0077] In one example, each angle sensor DA to DF may be an electromagnetic induction type sensor that detects the angular position of the corresponding electric motors 86A to 86F from electromagnetic induction caused by the rotation of the rotor of the electric motors 86A to 86F. In another example, each angle sensor DA to DF may be an optical sensor capable of detecting the angular position by being attached to the corresponding electric motors 86A to 86F. Each angle sensor DA to DF may be capable of detecting the angular position of the corresponding electric motors 86A to 86F by methods other than those described above. Each angle sensor may be the same as the rotation speed sensor described above. In this case, the sensor may detect the angular position of the corresponding electric motor 86 and detect the rotation speed of the electric motor 86 based on the amount of change of the angular position per unit time.

[0078] Although not shown in the diagram, the excavator 10 is equipped with various sensors necessary for its operation, in addition to the sensors mentioned above. For example, the excavator 10 is equipped with sensors that detect the temperature of the battery 80 and the conversion circuit 82.

[0079] [Details of the electric motor] Referring to Figure 6, the circuit configuration of the electric motor 86 will be explained. Note that the following explanation will focus on the circuit configuration of the first electric motor 86A. The second electric motor 86B, third electric motor 86C, fourth electric motor 86D, fifth electric motor 86E, and sixth electric motor 86F have the same circuit configuration as the first electric motor 86A, therefore, their explanations will be omitted.

[0080] As shown in Figure 5, the electric motor 86A has three wirings corresponding to each phase of the three-phase AC. Specifically, the electric motor 86A has U-phase wiring U, V-phase wiring V, and W-phase wiring W. The U-phase wiring U, V-phase wiring V, and W-phase wiring W are connected to the first conversion circuit 82A, which is a conversion circuit corresponding to the first electric motor 86A.

[0081] The first electric motor 86A has multiple windings. Specifically, the electric motor 86A has a U-phase winding LU, a V-phase winding LV, and a W-phase winding LW. Each winding has a first end and a second end opposite to the first end. In detail, the U-phase winding LU has a U-phase first end EU1 and a U-phase second end EU2. The V-phase winding LV has a V-phase first end EV1 and a V-phase second end EV2. The W-phase winding LW has a W-phase first end EW1 and a W-phase second end EW2.

[0082] The first end of each winding is connected to the corresponding wiring. Specifically, the first end EU1 of the U phase is connected to the U phase wiring U. The first end EV1 of the V phase is connected to the V phase wiring V. The first end EW1 of the W phase is connected to the W phase wiring W.

[0083] Each winding has a midpoint between its first and second ends. Specifically, the U-phase winding LU has a U-phase midpoint MU between the first U-phase end EU1 and the second U-phase end EU2. The V-phase winding LV has a V-phase midpoint MV between the first V-phase end EV1 and the second V-phase end EV2. The W-phase winding LW has a W-phase midpoint MW between the first W-phase end EW1 and the second W-phase end EW2.

[0084] The U-phase winding LU comprises a first U-phase winding LU1 and a second U-phase winding LU2. The first U-phase winding LU1 is the portion of the U-phase winding LU between the first U-phase end EU1 and the U-phase midpoint MU. The second U-phase winding LU2 is the portion of the U-phase winding LU between the U-phase midpoint MU and the U-phase second end EU2. The number of turns of the first U-phase winding LU1 and the number of turns of the second U-phase winding LU2 may be different from each other. Alternatively, the number of turns of the first U-phase winding LU1 and the number of turns of the second U-phase winding LU2 may be equal to each other. In other words, the term "midpoint" in this embodiment does not mean the midpoint of the winding length.

[0085] The V-phase winding LV comprises a V-phase first winding LV1 and a V-phase second winding LV2. The V-phase first winding LV1 is the portion of the V-phase winding LV between the V-phase first end EV1 and the V-phase midpoint MV. The V-phase second winding LV2 is the portion of the V-phase winding LV between the V-phase midpoint MV and the V-phase second end EV2. The number of turns of the V-phase first winding LV1 and the number of turns of the V-phase second winding LV2 may be different from each other. The number of turns of the V-phase first winding LV1 and the number of turns of the V-phase second winding LV2 may be equal to each other.

[0086] The W-phase winding LW comprises a first W-phase winding LW1 and a second W-phase winding LW2. The first W-phase winding LW1 is the portion of the W-phase winding LW between the first W-phase end EW1 and the W-phase midpoint MW. The second W-phase winding LW2 is the portion of the W-phase winding LW between the W-phase midpoint MW and the W-phase second end EW2. The number of turns of the first W-phase winding LW1 and the number of turns of the second W-phase winding LW2 may be different from each other. The number of turns of the first W-phase winding LW1 and the number of turns of the second W-phase winding LW2 may be equal to each other.

[0087] [Switching circuit] As shown in Figure 4, the drive system 100 is equipped with multiple switching circuits 104. One of the multiple switching circuits 104 is applied to each of the electric motors 86A to 86F. Specifically, the first switching circuit 104A is applied to the first electric motor 86A. The second switching circuit 104B is applied to the second electric motor 86B. The third switching circuit 104C is applied to the third electric motor 86C. The fourth switching circuit 104D is applied to the fourth electric motor 86D. The fifth switching circuit 104E is located for the fifth electric motor 86E. The sixth switching circuit 104F is applied to the sixth electric motor 86F.

[0088] In the following explanation, we will describe the first switching circuit 104A. The second switching circuit 104B, third switching circuit 104C, fourth switching circuit 104D, fifth switching circuit 104E, and sixth switching circuit 104F have the same circuit configuration as the first switching circuit 104A, so we will omit the explanation of these switching circuits.

[0089] As shown in Figure 5, the first switching circuit 104A includes a first switch SW1, a second switch SW2, a third switch SW3, a fourth switch SW4, a fifth switch SW5, and a sixth switch SW6. Each switch SW1 to SW6 can be switched between a conductive state, in which electrical conduction occurs between the first end of the switch and the second end opposite the first end, and a disconnected state, in which electrical conduction is interrupted between the first end and the second end. Each switch SW1 to SW6 may be a semiconductor switch or a physical switch.

[0090] The first terminal of the first switch SW1 is connected to the U-phase midpoint MU. The second terminal of the first switch SW1 is connected to the V-phase midpoint MV. The first terminal of the second switch SW2 is connected to the V-phase midpoint MV. The second terminal of the second switch SW2 is connected to the W-phase midpoint MW. The first terminal of the third switch SW3 is connected to the W-phase midpoint MW. The second terminal of the third switch SW3 is connected to the U-phase midpoint MU. In other words, the first switch SW1, the second switch SW2, and the third switch SW3 connect the U-phase midpoint MU, the V-phase midpoint MV, and the W-phase midpoint MW in a ring shape.

[0091] The first end of the fourth switch SW4 is connected to the second end EU2 of the U-phase winding LU. The second end of the fourth switch SW4 is connected to the second end EV2 of the V-phase winding LV. The first end of the fifth switch SW5 is connected to the second end EV2 of the V-phase winding LV. The second end of the fifth switch SW5 is connected to the second end EW2 of the W-phase winding LW. The first end of the sixth switch SW6 is connected to the second end EW2 of the W-phase winding LW. The second end of the sixth switch SW6 is connected to the second end EU2 of the U-phase winding LU. In other words, the fourth switch SW4, the fifth switch SW5, and the sixth switch SW6 connect the second end EU2 of the U-phase winding LU, the second end EW2 of the V-phase winding LV, and the second end EW2 of the W-phase winding LW in a ring shape.

[0092] The first switch SW1, the second switch SW2, and the third switch SW3 operate in conjunction. That is, when any one of the first switch SW1, the second switch SW2, and the third switch SW3 is in a conductive state, the other two are also in a conductive state. Also, when any one of the first switch SW1, the second switch SW2, and the third switch SW3 is in an interrupted state, the other two are also in an interrupted state.

[0093] Switches SW4, SW5, and SW6 operate in conjunction. That is, when any one of the switches SW4, SW5, or SW6 is in a conductive state, the other two are also in a conductive state. Conversely, when any one of the switches SW4, SW5, or SW6 is in an interrupted state, the other two are also in an interrupted state.

[0094] The set of switches SW1, SW2, and SW3, and the set of switches SW4, SW5, and SW6, are in complementary states. That is, when switches SW1, SW2, and SW3 are in the closed state, switches SW4, SW5, and SW6 are in the open state. When switches SW1, SW2, and SW3 are in the open state, switches SW4, SW5, and SW6 are in the closed state.

[0095] In other words, the switching circuit 104 can be switched to either the first connection state or the second connection state. When the switching circuit 104 is in the first connection state, the first switch SW1, the second switch SW2, and the third switch SW3 are in the off state, and the fourth switch SW4, the fifth switch SW5, and the sixth switch SW6 are in the conduction state. In other words, when the switching circuit 104 is in the first connection state, the midpoints MU, MV, and MW of the multiple windings LU, LV, and LW are disconnected from each other, and the second ends EU2, EV2, and EW2 are connected to each other.

[0096] When the switching circuit 104 is in the second connection state, the first switch SW1, the second switch SW2, and the third switch SW3 are in a conductive state, and the fourth switch SW4, the fifth switch SW5, and the sixth switch SW6 are in an interrupted state. In other words, when the switching circuit 104 is in the second connection state, the midpoints MU, MV, and MW of the multiple windings LU, LV, and LW are connected to each other.

[0097] When the switching circuit 104 is in the first connection state, the windings of each phase, from the first end to the second end, are responsible for driving the first electric motor 86A. Specifically, of the U-phase windings LU, the first U-phase winding LU1 and the second U-phase winding LU2 are responsible for driving the first electric motor 86A. Of the V-phase windings LV, the first V-phase winding LV1 and the second V-phase winding LV2 are responsible for driving the first electric motor 86A. Of the W-phase windings LW, the first W-phase winding LW1 and the second W-phase winding LW2 are responsible for driving the first electric motor 86A.

[0098] When the switching circuit 104 is in the second connection state, the windings of each phase from the first end to the midpoint are responsible for driving the first electric motor 86A. Specifically, of the U-phase windings LU, the U-phase first winding LU1 is responsible for driving the first electric motor 86A. Of the V-phase windings LV, the V-phase first winding LV1 is responsible for driving the first electric motor 86A. Of the W-phase windings LW, the W-phase first winding LW1 is responsible for driving the first electric motor 86A.

[0099] In other words, when the first switching circuit 104A is in the first connection state, the number of turns in the winding that drives the first electric motor 86A is longer compared to when it is in the second connection state. Therefore, when the first switching circuit 104A is in the first connection state, the first electric motor 86A operates in the high torque range. Also, when the first switching circuit 104A is in the second connection state, the first electric motor 86A operates in the high rotation range.

[0100] [Control device] As shown in Figure 4, the control system of the work machine includes a control device 106. The control device 106 is a computer equipped with a processing circuit. The processing circuit includes a CPU 108 and a memory 110. The memory 110 includes three types: RAM, ROM, and electrically rewritable nonvolatile memory. In this embodiment, these three types are collectively referred to as memory 110. The memory 110 pre-stores various control programs 112 that describe the processing to be executed by the CPU 108. The memory 110 pre-stores various data 114 necessary for the CPU 108 to execute the control programs 112. The processing circuit includes a communication circuit for wireless communication with the outside.

[0101] The control device 106 can control each conversion circuit 82. More specifically, the control device 106 can control the AC power supplied to the corresponding actuator 84 through the control of each conversion circuit 82.

[0102] The control device 106 can control the switching circuit 104. More specifically, the control device 106 can switch the switching circuit 104 between a first connected state and a second connected state. Specifically, the control device 106 is configured to switch the switching circuit 104 between a first connected state and a second connected state by switching the conduction state and the disconnection state of each switch in the switching circuit 104.

[0103] The control device 106 can acquire information from various sensors placed on the excavator 10. Specifically, the control device 106 can acquire torque information from the first to sixth electric motors 86A to 86F from the first to sixth torque sensors TA to TF, respectively. In addition, the control device 106 can acquire rotational speed information from the first to sixth electric motors 86A to 86F from the first to sixth rotational speed sensors NA to NF, respectively. Furthermore, the control device 106 can acquire angular position information from the first to sixth electric motors 86A to 86F from the first to sixth angle sensors DA to DF, respectively.

[0104] In the following description, an example of control that the control device 106 can perform on the first switching circuit 104A will be explained. The control device 106 can perform similar control on the second switching circuits 104B to the sixth switching circuits 104F. A detailed explanation of the control of these second switching circuits 104B to the sixth switching circuits 104F by the control device 106 will be omitted.

[0105] In one example, the control device 106 can perform control to switch the first switching circuit 104A to either a first connection state or a second connection state based on the torque information of the first electric motor 86A. In one example, the control device 106 can perform control to switch the first switching circuit 104A to the first connection state when the torque of the first electric motor 86A is equal to or greater than a predetermined value. In addition, the control device 106 can perform control to switch the first switching circuit 104A to the second connection state when the torque of the first electric motor 86A is less than the predetermined value.

[0106] In another example, the control device 106 can perform control to switch the first switching circuit 104A to either a first connection state or a second connection state based on the rotational speed information of the first electric motor 86A. In one example, the control device 106 can perform control to switch the first switching circuit 104A to the first connection state when the rotational speed of the first electric motor 86A is equal to or greater than a predetermined value. The control device 106 can also perform control to switch the first switching circuit 104A to the second connection state when the rotational speed of the first electric motor 86A is less than the predetermined value.

[0107] In yet another example, the control device 106 can perform control to switch the first switching circuit 104A to either a first connection state or a second connection state based on the angular position information of the first electric motor 86A. In one example, the control device 106 determines the attitude of the boom 58 relative to the main body 12 based on the angular position of the first electric motor 86A. The control device 106 then determines the angle of the boom 58 with respect to the ground G. This angle is the acute angle of the angle formed by the virtual line passing through the second axis J2 and the center of gravity of the boom 58 and the horizontal plane, when viewed from a direction parallel to the second axis J2. Therefore, this angle is 90 degrees or less. When this angle is less than a predetermined specified angle, the control device 106 can perform control to switch the first switching circuit 104A to the first connection state. Also, when the above angle is greater than or equal to the specified angle, the control device 106 can perform control to switch the first switching circuit 104A to the second connection state.

[0108] As a control based on the angular position information of the first electric motor 86A, the control device 106 can execute control to switch the switching circuit 104 to the first connection state until the first electric motor 86A rotates by a predetermined specified angle from its stopped position. In other words, the control device 106 can execute control to switch the switching circuit 104 to the first connection state until the rotating member C rotates by a predetermined specified angle from its stopped position.

[0109] As shown in Figure 4, the control device 106 is equipped with a changeover switch 116 that can be operated by the operator of the work machine. Based on the operation of the changeover switch 116, the control device 106 can perform control to switch the first switching circuit 104A to either the first connection state or the second connection state.

[0110] <Operation of this embodiment> Next, the operation of this embodiment will be described with reference to Figure 6. Note that in the following description, the first to sixth electric motors 86A to 86F may be referred to simply as electric motor 86.

[0111] Figure 6 shows the rotational speed-torque characteristics of the electric motor 86. In Figure 6, the rotational speed-torque characteristics of the electric motor 86 in the first connection state and the second connection state are shown by solid lines. As a comparative example, the rotational speed-torque characteristics of an electric motor without the switching circuit 104 are shown by a dashed line. The electric motor of the comparative example has the same number of turns as the electric motor 86 in the first connection state.

[0112] As shown in Figure 6, when the electric motor 86 is in the first connection state, the electric motor 86 operates in the high torque range. Similarly, the electric motor of the comparative example also operates in the high torque range. Specifically, the electric motor 86 in the first connection state and the electric motor of the comparative example can exert a first torque T1 in the region where the rotational speed is ω1 or less. When the rotational speed of the electric motor reaches the first rotational speed ω1, the back electromotive force generated by the electric motor becomes equal to the input voltage. As a result, no current flows to the electric motor 86. Therefore, in the region where the rotational speed of the electric motor exceeds the first rotational speed ω1, the torque decreases rapidly as the rotational speed increases.

[0113] One possible method for achieving operation in both high-torque and high-speed ranges is to equip the system with two electric motors, one for high torque and one for high speed. However, equipping the system with two electric motors increases the volume and weight occupied by the motors. In particular, there are limitations on the volume and weight of the electric motor that drives the working member 50 of the work machine.

[0114] Field weakening control is one method for operating a single electric motor in a region where the rotational speed is greater than the first rotational speed ω1. As shown in Figure 6, the electric motor in the comparative example can output a certain amount of torque even in a region where the rotational speed is greater than the first rotational speed ω1 by performing field weakening.

[0115] However, field weakening control reduces the power efficiency of the electric motor. Specifically, in the comparative example, the power efficiency of the electric motor decreases when the rotational speed exceeds the first rotational speed ω1. This decrease in the power efficiency of the electric motor leads to a reduction in the operating time of the work machine and an increase in energy costs.

[0116] In this embodiment, the electric motor 86 can be switched from a first connection state to a second connection state by the switching circuit 104. The electric motor 86 in the second connection state can rotate at a lower torque and higher speed than the electric motor 86 in the first connection state. Specifically, the electric motor 86 in the second connection state can exert a second torque T2 in the region where the rotational speed is ω2 or less than the second rotational speed ω1. The second rotational speed ω2 is greater than the first rotational speed ω1. The second torque T2 is less than the first torque T1.

[0117] In the region where the rotational speed is greater than the first rotational speed ω1, the power efficiency of the electric motor 86 in the second connection state is higher than that of the comparative example electric motor in which field weakening was performed. In other words, by switching between the first connection state and the second connection state, the electric motor 86 can achieve operation in both the high torque range and the high rotational speed range with high power efficiency.

[0118] Incidentally, in Figure 1, the electric motor 86 in the first connection state operates in a range greater than the first rotational speed ω1. Similarly, the electric motor 86 in the second connection state operates in a range greater than the second rotational speed ω2. As described above, in the electric motor 86 in the first and second connection states, when the rotational speed reaches the first rotational speed ω1 and the second rotational speed ω2, respectively, the motor's back electromotive force becomes equal to the input voltage. In this state, theoretically, the current becomes zero and no torque is generated. However, in actual motors, the inductance component of the windings delays the change in current, so current is supplied for a short time even when the base speed is exceeded. This current continues to generate torque, and the rotational speed increases further. Furthermore, because the rotor has inertia, it continues to rotate until the torque becomes completely zero. Therefore, in Figure 6, the rotational speed-torque characteristics for the first and second connection states show that the torque is zero at rotational speeds greater than ω1 and ω2, respectively.

[0119] <Effects of this embodiment> This embodiment has the following advantages. (1) The drive system 100 of the work machine includes an electric motor 86 which is the power source for the rotating member C. The switching circuit 104 can switch the connection state of the windings of the electric motor 86 between a first connection state and a second connection state which allows rotation at a lower torque and higher speed than the first connection state. Therefore, by switching the switching circuit 104 between the first connection state and the second connection state, the electric motor 86 can operate in both the high torque range and the high rotation range with high power efficiency. Thus, the work efficiency of the work machine can be improved while also improving power efficiency.

[0120] (2) The switching circuit 104 can be switched between a first connection state in which the midpoints of the multiple windings are disconnected and the second ends are connected, and a second connection state in which the midpoints of the multiple windings are connected. In the first connection state, of the windings of each phase, the winding from the first end to the second end drives the electric motor 86. In the second connection state, of the windings of each phase, the winding from the first end to the midpoint drives the electric motor 86. That is, in the second connection state, the number of turns of the winding that drives the electric motor 86 is less than in the first connection state. Therefore, in the second connection state, the electric motor 86 can rotate at a lower torque and higher speed than in the first connection state.

[0121] (3) The range of rotation of the rotating member C around the connection point is 180 degrees or more. With this configuration, the larger the rotatable range of the rotating member C, the larger the range of the required rotational speed-torque characteristics tends to be, in terms of both work efficiency and power efficiency. Specifically, the larger the rotatable range, the greater the effect of reducing working time by increasing the rotational speed. Also, the larger the rotatable range, the greater the effect of improving power efficiency by using the low-torque, high-speed range. Therefore, both work efficiency and power efficiency can be improved.

[0122] (4) The rotating member C driven by the electric motor 86 is selected from the boom 58, arm 60, and attachment 62. The load on the boom 58, arm 60, and attachment 62 differs depending on the work performed by the machine. Therefore, the required range of rotational speed-torque characteristics tends to be large. Also, depending on the work performed by the machine, the power consumption of members such as the boom 58, arm 60, and attachment 62 may account for a large proportion of the total power consumption of the machine. Therefore, by using an electric motor 86 equipped with a switching circuit 104 in the drive unit of the boom 58, arm 60, and attachment 62, work efficiency and power efficiency can be improved.

[0123] (5) The drive system 100 comprises a lower body 14 and an upper body 16. The lower body 14 has a traveling device 30. The upper body 16 is rotatably connected to the lower body 14. The rotating member C is the upper body 16. The rotational movement of the upper body 16 relative to the lower body 14 tends to have a large range of rotation. Therefore, by using an electric motor 86 equipped with a switching circuit 104, work efficiency and power efficiency can be improved.

[0124] (6) The drive system 100 includes a changeover switch 116 and a control device 106. The changeover switch 116 is operable by the operator of the work machine. Based on the operation of the changeover switch 116, the control device 106 switches the switching circuit 104 to either the connected state or the second connected state. With this configuration, the operator can switch the electric motor 86 to either the first connected state or the second connected state by operating the changeover switch 116. Therefore, it is easier to achieve the operation desired by the operator. Therefore, work efficiency is easily improved when using the electric motor 86.

[0125] (7) The drive system 100 includes a control device 106 that switches the switching circuit 104 to a first connection state when the torque of the electric motor 86 is equal to or greater than a predetermined value, and switches the switching circuit 104 to a second connection state when the torque of the electric motor 86 is less than the predetermined value.

[0126] In industrial machinery, the required torque may change during operation. For example, when performing excavation work, if the attachment 62 is in contact with hard bedrock, a higher torque is required compared to when excavating soft soil. By using an electric motor 86 to which the switching circuit 104 is applied, as in the embodiment described above, when the torque of the electric motor 86 increases, it is possible to maintain high power efficiency while exhibiting high torque. Therefore, both work efficiency and power efficiency are improved.

[0127] (8) The drive system 100 includes a control device 106 that switches the switching circuit 104 to the second connection state when the rotational speed of the electric motor 86 is equal to or greater than a predetermined specified rotational speed, and switches the switching circuit 104 to the first connection state when the torque of the electric motor 86 is less than the specified rotational speed. In working machinery, the required rotational speed may change during operation. One example is when an object is held and moved. When holding and releasing an object, the electric motor 86 needs to accurately determine its position at a low rotational speed. On the other hand, during movement, it may be required to move quickly at a high rotational speed. Therefore, by using an electric motor 86 to which the switching circuit 104 is applied as in the above embodiment, when the rotational speed of the electric motor 86 increases, it is possible to maintain high power efficiency while exhibiting high rotational speed. Thus, work efficiency and power efficiency are improved.

[0128] (9) The rotating member C is the boom 58. When the angle of the boom 58 with respect to the ground G is less than a specified angle, the rotating member C switches the switching circuit 104 to the first connection state. When the angle of the boom 58 with respect to the ground G is greater than or equal to a specified angle, the rotating member C is equipped with a control device 106 that switches the switching circuit 104 to the second connection state. The smaller the angle of the boom 58 with respect to the ground G, that is, the closer the boom 58 is to being parallel to the ground G, the greater the torque required to drive the boom 58. Also, the larger the angle of the boom 58 with respect to the ground G, that is, the closer the boom 58 is to being perpendicular to the ground G, the smaller the torque required to drive the boom 58. The boom 58 has a large longitudinal dimension and is subjected to force at its tip due to the weight of the arm 60 and attachment 62. Therefore, the torque required to drive the boom 58 changes easily depending on the angle. Therefore, by controlling according to the angle of the boom 58, the work efficiency and power efficiency of the work machine can be improved.

[0129] (10) The device includes a control device 106 that switches the switching circuit 104 to a first connection state until the rotating member C rotates from a stationary state to a predetermined angle. In a working machine, the required torque is high when the rotating member C starts rotating from a stationary state and in the initial stages of rotation. Therefore, by switching the switching circuit 104 to the first connection state from a stationary state until it rotates to a predetermined specified angle, the working efficiency and power efficiency of the working machine can be improved.

[0130] (11) The drive system 100 includes a conversion circuit 82 and an air-cooled cooling device. The conversion circuit 82 outputs AC power to the electric motor 86. The cooling device cools the conversion circuit 82.

[0131] When using the switching circuit 104 of the above embodiment, the load on the conversion circuit 82 can be reduced compared to when the torque and speed of the motor are changed by controlling the current supplied to the motor. Therefore, overheating of the conversion circuit 82 can be suppressed. Consequently, the conversion circuit 82 can be cooled even with an air-cooled cooling system, which has lower cooling efficiency than a water-cooled cooling system.

[0132] [Example of changes] This embodiment can be implemented with the following modifications. This embodiment and the following modifications can be implemented one or more of them in combination with each other to the extent that they do not contradict each other technically.

[0133] The drive system 100 only needs to include at least one of the first to sixth electric motors 86A to 86F. In other words, at least one of the first to sixth actuators 84A to 84F needs to be configured to operate using the electric motor 86 as a drive source.

[0134] The configuration of the switching circuit 104 can be changed as appropriate. For example, the first switching circuit 204A shown in Figure 7 differs from the first switching circuit 104A in Figure 5 in the arrangement of the first to sixth switches SW1 to SW6. The first terminal of the first switch SW1 is connected to the U-phase wiring U. The second terminal of the first switch SW1 is connected to the first U-phase terminal EU1 of the U-phase winding LU. The first terminal of the second switch SW2 is connected to the V-phase wiring V. The second terminal of the second switch SW2 is connected to the first V-phase terminal EV1 of the V-phase winding LV. The first terminal of the third switch SW3 is connected to the W-phase wiring W. The second terminal of the third switch SW3 is connected to the first W-phase terminal EW1 of the W-phase winding LW.

[0135] The first terminal of the fourth switch SW4 is connected to the U-phase wiring U. In other words, the U-phase wiring U branches to the first switch SW1 and the fourth switch SW4, and the branching points are the first terminal of the first switch SW1 and the first terminal of the fourth switch SW4. The second terminal of the fourth switch SW4 is connected to the U-phase midpoint MU. The first terminal of the fifth switch SW5 is connected to the V-phase wiring V. In other words, the V-phase wiring V branches to the second switch SW2 and the fifth switch SW5, and the branching points are the first terminal of the second switch SW2 and the first terminal of the third switch SW3. The second terminal of the third switch SW3 is connected to the V-phase midpoint MV. The first terminal of the sixth switch SW6 is connected to the W-phase wiring W. In other words, the W-phase wiring W branches to the third switch SW3 and the sixth switch SW6, and the branching points are the first terminal of the third switch SW3 and the first terminal of the sixth switch SW6. The second terminal of switch SW6 is connected to the W-phase midpoint MW.

[0136] Similar to the first switching circuit 104A, the first switching circuit 204A can be switched to either the first connection state or the second connection state. When the first switching circuit 204A is in the first connection state, the first switch SW1, the second switch SW2, and the third switch SW3 are in the off state, and the fourth switch SW4, the fifth switch SW5, and the sixth switch SW6 are in the conduction state. When the first switching circuit 204A is in the second connection state, the first switch SW1, the second switch SW2, and the third switch SW3 are in the off state, and the fourth switch SW4, the fifth switch SW5, and the sixth switch SW6 are in the conduction state.

[0137] When the first switching circuit 204A is in the first connection state, the windings of each phase, from the first end to the second end, are responsible for driving the first electric motor 86A. Specifically, of the U-phase windings LU, the first U-phase winding LU1 and the second U-phase winding LU2 are responsible for driving the first electric motor 86A. Of the V-phase windings LV, the first V-phase winding LV1 and the second V-phase winding LV2 are responsible for driving the first electric motor 86A. Of the W-phase windings LW, the first W-phase winding LW1 and the second W-phase winding LW2 are responsible for driving the first electric motor 86A.

[0138] When the first switching circuit 204A is in the second connection state, the windings of each phase from the midpoint to the second end are responsible for driving the first electric motor 86A. Specifically, of the U-phase windings LU, the second U-phase winding LU2 is responsible for driving the first electric motor 86A. Of the V-phase windings LV, the second V-phase winding LV2 is responsible for driving the first electric motor 86A. Of the W-phase windings LW, the second W-phase winding LW2 is responsible for driving the first electric motor 86A.

[0139] In other words, when the first switching circuit 204A is in the first connection state, the number of turns in the winding that drives the first electric motor 86A is greater than in the first connection state. Therefore, when the first switching circuit 204A is in the first connection state, it operates in the high torque range. Also, when the first switching circuit 204A is in the second connection state, the number of turns in the winding that drives the first electric motor 86A is less than in the first connection state. Therefore, when the first switching circuit 204A is in the second connection state, the first electric motor 86A operates in the high rotation range.

[0140] The method for switching the electric motor 86 between the high-torque range and the high-speed range is not limited to changing the number of turns in the windings. For example, the drive system 100 can employ a method of switching the connection of multiple turns in each phase between series and parallel. That is, the switching circuit can achieve switching between the high-torque range and the high-speed range by switching the connection of multiple turns in each phase of the electric motor 86 between series and parallel.

[0141] Figure 8 shows the first switching circuit 304A and the first electric motor 86A, which enable switching between high torque and high rotational speed ranges by switching between series and parallel connections. As shown in Figure 8, the first electric motor 86A is equipped with U-phase first winding LU1 and U-phase second winding LU2, V-phase first winding LV1 and V-phase second winding LV2, W-phase first winding LW1 and W-phase second winding LW2. The first switching circuit 304A is equipped with first switch SW1, second switch SW2, third switch SW3, fourth switch SW4, fifth switch SW5, sixth switch SW6, seventh switch SW7, eighth switch SW8, and ninth switch SW9.

[0142] The first switch SW1 is connected in series with the first U-phase winding LU1. The first U-phase winding LU1 is positioned closer to the U-phase wiring U than the first switch SW1. The second switch SW2 is connected in series with the second U-phase winding LU2. The second switch SW2 is positioned closer to the U-phase wiring U than the second U-phase winding LU2.

[0143] The first switch SW1 and the first U-phase winding LU1 are connected in parallel to the second switch SW2 and the second U-phase winding LU2. The third switch SW3 connects the first switch SW1 and the first U-phase winding LU1, and the second switch SW2 and the second U-phase winding LU2.

[0144] The fourth switch SW4 is connected in series with the V-phase first winding LV1. The V-phase first winding LV1 is positioned closer to the V-phase wiring V than the fourth switch SW4. The fifth switch SW5 is connected in series with the V-phase second winding LV2. The fifth switch SW5 is positioned closer to the V-phase wiring V than the V-phase second winding LV2.

[0145] The fourth switch SW4 and the first V-phase winding LV1 are connected in parallel to the fifth switch SW5 and the second V-phase winding LV2. The sixth switch SW6 connects the fourth switch SW4 and the first V-phase winding LV1, and the fifth switch SW5 and the second V-phase winding LV2.

[0146] Switch SW7 is connected in series with the W-phase first winding LW1. The W-phase first winding LW1 is positioned closer to the W-phase wiring W than switch SW7. Switch SW8 is connected in series with the W-phase second winding LW2. Switch SW8 is positioned closer to the W-phase wiring W than the W-phase second winding LW2.

[0147] Switch SW7 and the W-phase first winding LW1 are connected in parallel to switch SW8 and the W-phase second winding LW2. Switch SW9 connects the space between switch SW7 and the W-phase first winding LW1, and the space between switch SW8 and the W-phase second winding LW2.

[0148] The first switching circuit 304A can be switched between a first connection state and a second connection state. In the first connection state, the first switch SW1, second switch SW2, fourth switch SW4, fifth switch SW5, seventh switch SW7, and eighth switch SW8 are in the off state, and the third switch SW3, sixth switch SW6, and ninth switch SW9 are in the conduction state. In the first connection state, the U-phase first winding LU1 and the U-phase second winding LU2 are connected in series, the V-phase first winding LV1 and the V-phase second winding LV2 are connected in series, and the W-phase first winding LW1 and the W-phase second winding LW2 are connected in series.

[0149] In the second connection state, the first switch SW1, second switch SW2, fourth switch SW4, fifth switch SW5, seventh switch SW7, and eighth switch SW8 are in a conductive state, while the third switch SW3, sixth switch SW6, and ninth switch SW9 are in an interrupted state. In the second connection state, the first U-phase winding LU1 and the second U-phase winding LU2 are connected in parallel, the first V-phase winding LV1 and the second V-phase winding LV2 are connected in parallel, and the first W-phase winding LW1 and the second W-phase winding LW2 are connected in parallel.

[0150] When the first switching circuit 304A is in the first connection state, that is, when the windings of each phase are connected in series, the first electric motor 86A operates in the high torque range. Also, when the first switching circuit 304A is in the second connection state, that is, when the turns of each phase are connected in parallel, the first electric motor 86A operates in the high rotation range.

[0151] The arrangement of the switching circuits 104 can be changed as appropriate. Each switching circuit 104 may be placed in each conversion circuit 82. That is, each switch in the switching circuit 104 may be placed in each conversion circuit 82. Alternatively, the switching circuit 104 may be placed between each conversion circuit 82 and the motor 86 to which each conversion circuit 82 corresponds.

[0152] The rotatable range of the rotating member C around the connection point does not have to be 180 degrees or more. Specifically, the rotatable range of the swing bracket 52 relative to the main body 12 may be less than 180 degrees. The rotatable range of the boom 58 relative to the main body 12 may be less than 180 degrees. The rotatable range of the arm 60 relative to the boom 58 may be less than 180 degrees. The rotatable range of the attachment 62 relative to the arm 60 may be less than 180 degrees.

[0153] The work machine is not limited to the excavator 10. The work machine may be, for example, a crane. Also, the configuration of the work member 50 may be changed in accordance with the change in the work machine. In one example, the work member 50 may be configured without the swing bracket 52. In this case, the boom 58 may be connected to the main body 12. Alternatively, the work member 50 may be configured without the boom 58. In this case, the arm 60 may be connected to the swing bracket 52. Alternatively, the work member 50 may be configured without the arm 60. In this case, the attachment 62 may be connected to the boom 58.

[0154] The configuration of the main body 12 can be changed as appropriate. The main body 12 may consist of a lower body 14 and an upper body 16 as a single unit. The upper body 16 does not need to be rotatably connected to the lower body 14. In this case, the fifth actuator 84E and the slewing bearing 22 may be omitted. Also, the lower body 14 does not need to have a traveling device 30. In this case, the sixth actuator 84F may be omitted.

[0155] The shape of the upper body 16 can be changed as appropriate. For example, the upper body 16 does not have to have a cabin for an operator to ride in. That is, the excavator 10 may perform operations based on operation signals received from outside the vehicle body. Also, the front part 20 of the housing may be positioned off-center to one side in the Y direction of the main housing part 18. Furthermore, the excavator 10 can adopt a configuration in which the front part 20 of the housing is omitted. In this case, the swing bracket 52 may be attached to the main housing part 18. Also, the boom 58 may be attached to the main housing part 18.

[0156] The running gear 30 can employ configurations other than the running crawler 32 and the running mechanism 34. In one example, the running gear 30 may have multiple wheels. In this case, the sixth actuator 84F may be connected to the wheel that will be the drive wheel among the multiple wheels.

[0157] The control device 106 can adopt a configuration that omits the changeover switch 116. In this case, the drive system 100 may change the connection state of the switching circuit 104 based on the information received from each sensor.

[0158] The configuration of each cooling unit 102A to 102F can be changed as appropriate. Cooling units 102A to 102F may be water-cooled, or they may be a hybrid of water-cooled and air-cooled. The drive system 100 does not need to be equipped with cooling units 102A to 102F.

[0159] In the above embodiment, a structure composed of multiple objects may be integrated, or conversely, a structure composed of a single object may be divided into multiple objects. Whether or not the objects are integrated, the structure should be configured in a way that achieves the objective of the invention.

[0160] In the above embodiment, if multiple functions are provided in a distributed manner, some or all of those multiple functions may be consolidated and provided together. Conversely, if multiple functions are consolidated and provided together, some or all of those multiple functions may be distributed and provided together. Regardless of whether the functions are consolidated or distributed, it is sufficient that the device is configured to achieve the objective of the invention.

[0161] The above description is illustrative only. Those skilled in the art will recognize that many more possible combinations and substitutions are possible beyond the components and methods (manufacturing processes) enumerated for the purpose of illustrating the technology of this disclosure. This disclosure is intended to encompass all alternatives, variations, and modifications that fall within the scope of this disclosure, including the claims. [Explanation of symbols]

[0162] 100…Drive system, 10…Excavator, 12…Main body, 14…Lower body, 16…Upper body, 18…Main housing, 20…Front housing, 22…Swivel bearing, 30…Traveling device, 32…Traveling crawler, 34…Travel mechanism, 36…Idler, 38…Drive sprocket, 44…Travel actuator, 50…Working parts, 52…Swing bracket, 58…Boom, 60…Arm, 62…Attachment, 80…Battery, 82…Conversion circuit, 84…Actuator, 86…Electric motor, 102A~102F…Cooling device, 104…Switching circuit, SW1…First switch, SW2…Second switch, SW3 ...3rd switch, SW4...4th switch, SW5...5th switch, SW6...6th switch, 106...control device, TA~TF...torque sensor, NA~NF...rotation speed sensor, DA~DF...angle sensor, LU...U-phase winding, LU1...U-phase 1st winding, LU2...U-phase 2nd winding, LV...V-phase winding, LV1...V-phase 1st winding, LV2...V-phase 2nd winding, LW...W-phase winding, LW1...W-phase 1st winding, LW2...W-phase 2nd winding, MU...U-phase midpoint, MV...V-phase midpoint, MW...W-phase midpoint, EU1...U-phase 1st end, EU2...U-phase 2nd end, EV1...V-phase 1st end, EV2...V-phase 2nd end, EW1...W-phase 1st end, EW2...W-phase 2nd end

Claims

1. A rotating member that can rotate relative to the connection point, The electric motor is the power source for the rotating member, Equipped with, The electric motor comprises a plurality of windings to which an AC power source is connected. The winding connection state is provided with a switching circuit that can switch between a first connection state and a second connection state that allows rotation at a lower torque and higher rotation speed than the first connection state. A drive system for industrial machinery.

2. Each winding has a first end to which an AC power source is connected, a second end opposite to the first end, and a midpoint between the first and second ends. The switching circuit is switchable between a first connection state in which the midpoints of the multiple windings are disconnected and the second ends are connected, and a second connection state in which the midpoints of the multiple windings are connected. A drive system for a work machine according to claim 1.

3. The rotatable range of the rotating member around the connection point is 180 degrees or more. A drive system for a work machine according to claim 1.

4. The main body and A boom rotatably connected to the main body, An arm rotatably connected to the boom, An attachment rotatably connected to the aforementioned arm, Equipped with, The rotating member is one selected from the boom, the arm, and the attachment. A drive system for a work machine according to claim 1.

5. A lower body having a running gear, An upper body rotatably connected to the lower body, Equipped with, The rotating member is the upper body. A drive system for a work machine according to claim 1.

6. A changeover switch that can be operated by the operator of the work machine, A control device that switches the switching circuit to either a first connection state or a second connection state based on the operation of the changeover switch, Equipped with, A drive system for a work machine according to claim 1.

7. The control device includes a mechanism that switches the switching circuit to the first connection state when the torque of the electric motor is equal to or greater than a predetermined value, and switches the switching circuit to the second connection state when the torque of the electric motor is less than the predetermined value. A drive system for a work machine according to claim 1.

8. The control device includes a mechanism that switches the switching circuit to the second connection state when the rotational speed of the electric motor is equal to or greater than a predetermined specified rotational speed, and switches the switching circuit to the first connection state when the torque of the electric motor is less than the specified rotational speed. A drive system for a work machine according to claim 1.

9. The rotating member is the boom, The control device includes a mechanism that switches the switching circuit to the first connection state when the angle of the boom with respect to the ground is less than a specified angle, and switches the switching circuit to the second connection state when the angle of the boom with respect to the ground is equal to or greater than the specified angle. The drive system for the work machine according to claim 4.

10. The control device switches the switching circuit to the first connection state until the rotating member rotates from a stationary state to a predetermined angle. A drive system for a work machine according to claim 1.

11. A conversion circuit that outputs AC power to the aforementioned electric motor, A cooling device for cooling the aforementioned conversion circuit, Equipped with, A drive system for a work machine according to claim 1.

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