Control device, agricultural machine, construction machine, control method, and control program

Abstract

This control device controls a rotary electric machine that drives a work machine provided to a vehicle. The control device comprises: an inverter control unit that controls an inverter for supplying power to the rotary electric machine which is a drive source of an electric cylinder that drives the work machine; and a control unit that, if an overload state of the electric cylinder is detected, reduces the absolute value of torque generated by the rotary electric machine to less than the absolute value of torque prior to the detection of the overload state.

Description

Control device, agricultural machine, construction machine, control method, and control program CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on and claims the benefit of priority from Patent Application No. 2024-146935, filed August 28, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a control device, an agricultural machine, a construction machine, a control method, and a control program.

[0003] Patent Document 1 discloses a technology for driving a work implement, such as a boom, arm, or bucket of an excavator, using an electric cylinder incorporating a ball screw type reduction gear. By replacing the drive force transmission means of the work implement from a conventional hydraulic cylinder with an electric cylinder, the work implement can be rotationally driven by a link connection similar to that of a hydraulic cylinder. Furthermore, compared to when a hydraulic cylinder is used, the system for driving the rotating electric machine is simplified, allowing the overall system to be made smaller and lighter, and the weight of the vehicle equipped with the work implement can be reduced.

[0004] Japanese Patent Application Laid-Open No. 2003-082707

[0005] However, after detailed investigation by the inventors, the inventors discovered a problem with the prior art of Patent Document 1: the electric cylinder lacks a hardware load relief mechanism, such as a relief valve used in hydraulic cylinders. This means that if the electric cylinder becomes overloaded, the work machine may be unable to continue operating. For example, if the bucket of a work machine excavating earth collides (comes into contact with) a large rock buried in the soil, the load on the electric cylinder may increase sharply. In other words, the impact force caused by the bucket colliding with the rock, which is an external load of the work machine, and a certain torque generated by the rotating electric machine are applied to the electric cylinder as loads. This increases the torsion applied to the mechanical elements of the electric cylinder, increasing the burden on the mechanical elements and potentially impeding the operation of the electric cylinder. Thus, the prior art leaves room for improvement in terms of continuing the operation of the work machine even in situations where an overload condition may occur.

[0006] The present disclosure aims to provide a control device, agricultural machinery, construction machinery, control method, and control program that can continue operation of a work machine even in situations where an overload condition may occur.

[0007] A control device according to a first aspect of the present disclosure is a control device that controls a rotating electric machine that drives a work machine provided on a vehicle, and includes an inverter control unit that controls an inverter that supplies power to the rotating electric machine, which is the driving source of an electric cylinder that drives the work machine, and a control unit that, when an overload state of the electric cylinder is detected, reduces the absolute value of the torque generated by the rotating electric machine below the absolute value of the torque before the overload state was detected.

[0008] A control program according to a second aspect of the present disclosure causes at least one processor to execute processing including controlling an inverter that supplies power to a rotating electric machine that is a drive source for an electric cylinder that drives a work machine provided on a vehicle, and, when an overload state of the electric cylinder is detected, reducing the absolute value of the torque generated by the rotating electric machine below the absolute value of the torque before the overload state was detected.

[0009] A control method according to a third aspect of the present disclosure executes processing including: at least one processor controls an inverter that supplies power to a rotating electric machine that is a driving source of an electric cylinder that drives a work machine provided on a vehicle; and, when an overload state of the electric cylinder is detected, reduces the absolute value of the torque generated by the rotating electric machine below the absolute value of the torque before the overload state is detected.

[0010] According to the present disclosure, there are provided a control device, an agricultural machine, a construction machine, a control method, and a control program that are capable of continuing operation of a work machine even in a situation where an overload state may occur.

[0011] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. The drawings include: FIG. 1 is a diagram illustrating a vehicle 100 equipped with a control device 7 according to an embodiment of the present disclosure; FIG. 2 is a cross-sectional view of an electric cylinder 54; FIG. 3 is a diagram illustrating a hardware configuration of the control device 7 according to an embodiment of the present disclosure; FIG. 4 is a diagram illustrating an example configuration of a drive unit 60 including a rotating electric machine 54a and an inverter 10; FIG. 5 is a block diagram illustrating an example functional configuration of a CPU 21A of the control device 7; FIG. 6 is a timing chart illustrating the rotation speed and torque of the rotating electric machine 54a; FIG. 7A is a diagram illustrating the relationship between upper limit torque and stroke position; FIG. 7B is a diagram illustrating the relationship between upper limit torque and stroke position; FIG. 7C is a diagram illustrating the relationship between upper limit torque and stroke position; FIG. 8 is a flowchart illustrating a control process for torque output from the rotating electric machine 54a; and FIG. 9 is a timing chart illustrating an example control performed by a control device according to a comparative example.

[0012] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. To facilitate understanding of the description, the same components in the drawings will be denoted by the same reference numerals as much as possible, and duplicated descriptions will be omitted.

[0013] FIG. 1 is a diagram showing a vehicle 100 equipped with a control device 7 according to an embodiment of the present disclosure. The vehicle 100 may be interpreted as an agricultural construction machine (hereinafter, agricultural construction machine). The agricultural construction machine may include agricultural machinery and construction machinery. The agricultural construction machine may include an electric tractor, an electric wheel loader, an electric bulldozer, an electric backhoe, an electric crane, and the like. FIG. 1 shows an electric backhoe as an example of agricultural machinery. The agricultural construction machine may include a vehicle 100 that moves using crawlers as well as a vehicle 100 that moves using tires. Note that the control device 7 according to the present disclosure may be provided in a vehicle 100 other than an agricultural construction machine. The control device 7 may be interpreted as a device that controls a rotating electric machine 54a that drives a work implement 5 provided on the vehicle 100.

[0014] The vehicle 100 may include a traveling device 2 and a main body 3. The traveling device 2 may be provided below the main body 3 and may support the main body 3 so that it can rotate freely in the horizontal direction. The traveling device 2 may include a pair of left and right crawlers. The main body 3 may include a cab 4 in which an operator rides, a work implement 5 provided in front of the cab 4, a battery 6, and a control device 7.

[0015] (Control Device 7) The control device 7 may be interpreted as a device that controls one or more electric cylinders 54. Specifically, the control device 7 may independently control the rotation speed, rotation direction, rotation torque (hereinafter, torque), etc. of the rotating electric machine 54a included in each of, for example, three electric cylinders 54. For example, the control device 7 may rotate the rotating electric machine 54a included in the electric cylinder 54 that drives the boom 51 in a first rotation direction, while rotating the rotating electric machine 54a included in the electric cylinder 54 that drives the arm 52 in a second rotation direction opposite to the first rotation direction. At this time, the control device 7 may stop the rotation of the rotating electric machine 54a included in the electric cylinder 54 that drives the bucket 53.

[0016] (Battery 6) The battery 6 is a storage battery for supplying power to the rotating electric machine 54a. The battery 6 is, for example, a lithium ion battery.

[0017] (Working Machine 5) The working machine 5 may have a multi-joint structure including a boom 51, an arm 52, and a bucket 53. The boom 51 may be supported so as to be swingable in the vertical direction relative to the cab 4. The arm 52 may be supported so as to be swingable at the tip of the boom 51. The bucket 53 may be supported so as to be swingable at the tip of the arm 52. Each of the boom 51, the arm 52, and the bucket 53 may be driven by an electric cylinder 54.

[0018] (Electric Cylinder 54) The electric cylinder 54 may be interpreted as a mechanism in which the rod 54b is reciprocated by being driven by the rotating electric machine 54a. The work machine 5 of the present disclosure uses a ball screw type electric cylinder 54, but the electric cylinder 54 is not limited to the ball screw type and may be of another type, for example, a linear motor type.

[0019] As shown in FIG. 2, the electric cylinder 54 may include a rotating electric machine 54a, a speed reducing mechanism 54c, a case 54d, a nut 54e, a ball screw 54f, and a rod 54b.

[0020] The reduction mechanism 54c reduces the rotation speed of the rotating electric machine 54a and transmits the torque of the rotating electric machine 54a to the ball screw 54f in the case 54d. The reduction mechanism 54c may reduce the rotation speed by, for example, using a small-diameter first pulley 54c1 connected to the rotating shaft 54a1 of the rotating electric machine 54a, a large-diameter second pulley 54c2 connected to the ball screw 54f, and a belt 54c3 connecting the first pulley 54c1 and the second pulley 54c2. The configuration of the reduction mechanism 54c is not limited thereto, and the reduction mechanism 54c may reduce the rotation speed by, for example, using a small-diameter gear connected to the rotating shaft 54a1 of the rotating electric machine 54a and a large-diameter gear connected to the ball screw 54f.

[0021] The ball screw 54f may convert the rotational motion of the rotating electric machine 54a into the linear motion of linearly moving members such as the nut 54e and the rod 54b. The ball screw 54f may include a screw shaft 54f1 and balls 54f2. The balls 54f2 may be interpreted as rolling elements provided between the nut 54e and the screw shaft 54f1.

[0022] When the rotating electric machine 54a rotates, i.e., when the rotary shaft 54a1 rotates, the torque of the rotating electric machine 54a is transmitted to the ball screw 54f. As the ball screw 54f rotates, the rotational motion of the ball screw 54f is converted into linear motion of the nut 54e provided in the case 54d. As a result, the rod 54b connected to the nut 54e reciprocates, i.e., moves forward and backward, relative to the case 54d.

[0023] The rotating shaft 54a1, the reduction gear mechanism 54c, the ball screw 54f, the nut 54e, etc. may be considered as a mechanical element 540 that moves the rod 54b, which drives the work machine 5, forward and backward. More strictly, the rotating shaft 54a1, the first pulley 54c1, the belt 54c3, the second pulley 54c2, the ball screw 54f, and the nut 54e may be considered as the mechanical element 540 that moves the rod 54b forward and backward. Note that the electric cylinder 54 of the present disclosure may include the rotating electric machine 54a, the case 54d, the nut 54e, the ball screw 54f, and the rod 54b without including the reduction gear mechanism 54c. In this case, the rotating electric machine 54a may be directly or indirectly connected to the ball screw 54f.

[0024] Next, the hardware configuration of the control device 7 will be described with reference to Fig. 3. Fig. 3 is a diagram showing the hardware configuration of the control device 7 according to an embodiment of the present disclosure. The control device 7 includes a control unit 21, a communication unit 22, and a storage unit 23.

[0025] The control unit 21 is configured as a device including a general computer. The control unit 21 includes a CPU (Central Processing Unit) 21A, a ROM (Read Only Memory) 21B, a RAM (Random Access Memory) 21C, and an input / output interface (I / O) 21D. The CPU 21A, ROM 21B, RAM 21C, and I / O 21D are connected to each other via a bus 21E. The bus 21E includes a control bus, an address bus, a data bus, etc.

[0026] The I / O 21D is connected to a communication unit 22, a storage unit 23, and a sensor group 200. The communication unit 22 is an interface for communicating with external devices such as the inverter 10.

[0027] The storage unit 23 is configured as a non-volatile external storage device such as a hard disk, etc. The storage unit 23 stores a control program 23A.

[0028] The CPU 21A is an example of a computer. The term "computer" as used herein refers to a processor in a broad sense, and includes a general-purpose processor (e.g., the CPU 21A) or a dedicated processor (e.g., a graphics processing unit (GPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a programmable logic device, etc.).

[0029] The control program 23A may be stored in a non-volatile, non-transitory recording medium or distributed via a network and appropriately installed in the control device 7, thereby being stored in the storage unit 23. The control program 23A may also be appropriately updated via so-called OTA (Over The Air).

[0030] Examples of non-volatile non-transient recording media include CD-ROMs (Compact Disc Read Only Memory), magneto-optical disks, HDDs (Hard Disk Drives), DVD-ROMs (Digital Versatile Disc Read Only Memory), flash memories, memory cards, etc.

[0031] The sensor group 200 may include a wheel speed sensor, an acceleration sensor, a current sensor, an accelerator sensor, a temperature sensor, a gradient sensor, a brake sensor, a yaw rate sensor, a rotation speed sensor, and the like.

[0032] The rotation speed sensor may be understood as a sensor for detecting the rotation angle and rotation speed of the rotating electric machine 54 a. The rotation speed sensor is, for example, a resolver or a rotary encoder, and detects the rotation angle and rotation speed of the rotor of the rotating electric machine 54 a. A signal indicating the rotation speed detected by the rotation speed sensor is input to the control device 7.

[0033] The current sensor may be understood as a sensor for detecting the value of the current flowing through the rotating electric machine 54a. As an example, the current sensor detects the current flowing through any two windings (e.g., the V phase and the W phase) among the windings of the U phase, V phase, and W phase. A signal indicating the value of the drive current detected by the current sensor is input to the control device 7.

[0034] The temperature sensor may be interpreted as a sensor for detecting the temperatures of a plurality of switch elements included in the inverter 10. A signal indicating the temperature detected by the temperature sensor is input to the control device 7.

[0035] The inverter 10 may convert the DC power supplied from the battery 6 into AC power in accordance with instructions from the control device 7, and supply the AC power to the rotating electric motors 54a in the electric cylinders 54 provided in each of the boom 51, arm 52, and bucket 53, thereby controlling the rotation of the rotating electric motors 54a.

[0036] A boom 51, an arm 52, a bucket 53, etc. are connected to each of the multiple electric cylinders 54, and these may be considered as part of the load of the electric cylinder 54 or the rotating electric machine 54a.

[0037] 4 is a diagram showing an example configuration of a drive unit 60 including a rotating electric machine 54a and an inverter 10. The rotating electric machine 54a includes a stator 153, a rotor 154, a current sensor 203, and a rotation speed sensor 211. The rotating electric machine 54a is a three-phase motor generator, and the stator 153 has windings 155U, 155V, and 155W of multiple phases. The winding 155U is a U-phase winding, the winding 155V is a V-phase winding, and the winding 155W is a W-phase winding. The current sensor 203, for example, detects the current flowing through the winding 155V and the current flowing through the winding 155W. The rotation speed sensor 211 is, for example, a resolver, and detects the rotation angle and rotation speed of the rotor 154.

[0038] The inverter 10 has six power elements 156Uu, 156Ud, 156Vu, 156Vd, 156Wu, and 156Wd. Hereinafter, when there is no need to distinguish between the six power elements 156Uu, 156Ud, 156Vu, 156Vd, 156Wu, and 156Wd, the six power elements 156Uu, 156Ud, 156Vu, 156Vd, 156Wu, and 156Wd will be referred to as "power elements 156." These power elements 156 may be interpreted as inverter elements or switch elements. Each power element 156 is, for example, a power transistor. The power elements 156Uu and 156Ud are U-phase power elements, the power elements 156Vu and 156Vd are V-phase power elements, and the power elements 156Wu and 156Wd are W-phase power elements. The power elements 156Uu and 156Ud are bridge-connected to the winding 155U, the power elements 156Vu and 156Vd are bridge-connected to the winding 155V, and the power elements 156Wu and 156Wd are bridge-connected to the winding 155W.

[0039] The inverter 10 has a plurality of temperature sensors 157. The temperature sensor 157 may be provided for each of the plurality of power elements 156.

[0040] Next, an example of the functional configuration of the CPU 21A of the control device 7 will be described with reference to FIGS. 5, 6, 7A, 7B, and 7C.

[0041] FIG. 5 is a block diagram showing an example of the functional configuration of the CPU 21A of the control device 7.

[0042] 6 is a timing chart showing the rotation speed and torque of the rotating electric machine 54a. FIG. 6 shows the change in rotation speed and torque of the rotating electric machine 54a over time. The solid line represents the rotation speed. The thick solid line represents the load applied to the electric cylinder 54, the dashed line represents the torque generated by the rotating electric machine 54a, and the dashed line represents the impact force applied to the electric cylinder 54.

[0043] 7A, 7B, and 7C are diagrams showing the relationship between the upper limit torque and stroke position. The horizontal axis in each of FIGS. 7A, 7B, and 7C represents the stroke position. The stroke position may also be interpreted as the stroke amount of the rod 54b. The vertical axis in each of FIGS. 7A, 7B, and 7C represents the upper limit torque set by the CPU 21A. The normal solid line represents the upper limit torque when the rotation speed of the rotating electric machine 54a is relatively low, and the thick solid line represents the upper limit torque when the rotation speed of the rotating electric machine 54a is relatively high.

[0044] FIG. 7A shows the change in the upper and lower limit torque calculated by the upper and lower limit torque calculation unit 31c (described later) with respect to the stroke position of the rod 54b of the electric cylinder 54 when an overload state is not detected, for example, when the rotating electric machine 54a rotates in the first rotation direction to extend the rod 54b of the electric cylinder 54.

[0045] 7B and 7C show how the upper and lower limit torques calculated by the upper and lower limit torque calculation unit 31c (described later) change with respect to the stroke position of the rod 54b of the electric cylinder 54 when an overload state is detected, for example, when the rotating electric machine 54a rotates in the first rotation direction to extend the rod 54b of the electric cylinder 54.

[0046] Although the lower limit torque is not shown in Figures 7A, 7B, and 7C, the lower limit torque may be interpreted as, for example, a torque that defines the lower limit of the torque generated by the rotating electric machine 54a when the rod 54b is retracted, and may be interpreted as the change in torque relative to the stroke position of the rod 54b of the electric cylinder 54 when an overload state is not detected or when an overload state is detected.

[0047] (CPU 21A) As shown in Fig. 5, the CPU 21A reads and executes a control program 23A stored in the storage unit 23 (see Fig. 3), thereby functioning as each functional unit shown in Fig. 5. The CPU 21A may include a control unit 31 and an inverter control unit 32.

[0048] When the control unit 31 detects an overload state of the electric cylinder 54, the control unit 31 may reduce the torque generated by the rotating electric machine 54a to a value lower than the torque before the overload state was detected. The control unit 31 may include a rotation speed calculation unit 31a, a correction torque calculation unit 31b, an upper and lower limit torque calculation unit 31c, a torque calculation unit 31d, a torque limiting unit 31e, and a final command torque output unit 31f.

[0049] (Rotational speed calculation unit 31a) The rotational speed calculation unit 31a may calculate the rotational speed of the rotating electric machine 54a based on the rotational angle detected by the rotational speed sensor 211, i.e., a signal indicating the electrical angle, and input the calculated rotational speed to the correction torque calculation unit 31b and the upper / lower limit torque calculation unit 31c.

[0050] The torque calculation unit 31 d may calculate a command torque that serves as a target for causing the rotation speed of the rotating electric machine 54 a to follow a required target speed. The target speed is calculated based on, for example, the amount of operation of a lever provided on the vehicle 100 by the driver.

[0051] (Example of Calculation of Load Increase Position Information by Correction Torque Calculation Unit 31b) The correction torque calculation unit 31b may calculate the correction torque based on the estimated load.

[0052] The load (load amount) applied to the rotating electric machine 54a may be calculated by any method as long as it can be calculated quantitatively. For example, the load amount may be estimated from at least one of the rotation speed of the rotating electric machine 54a, the torque of the rotating electric machine 54a, the current value of the rotating electric machine 54a, the angular velocity of the rotating electric machine 54a, and the angular acceleration of the rotating electric machine 54a. In this case, the correction torque calculation unit 31b may determine the load amount as at least one of the rotation speed of the rotating electric machine 54a, the torque of the rotating electric machine 54a, the current value of the rotating electric machine 54a, the angular velocity of the rotating electric machine 54a, and the angular acceleration of the rotating electric machine 54a. Alternatively, the correction torque calculation unit 31b may determine the load amount by applying a value calculated using at least one of the values ​​to an arbitrary function, such as a linear function.

[0053] When the rotation speed of the rotating electric machine 54a is used to estimate the load amount, the rotation speed can be obtained by using the rotation speed sensor 211. Depending on the type of rotating electric machine 54a, the rotation speed of the rotating electric machine 54a decreases as the load applied to the rotating electric machine 54a increases, and therefore the load amount can be estimated as a value proportional to the rotation speed.

[0054] When the torque of the rotating electric machine 54 a is used to estimate the load amount, the torque is obtained as, for example, a final command torque of the rotating electric machine 54 a for controlling the rotating electric machine 54 a. The final command torque may be interpreted as a drive torque of the rotating electric machine 54 a, an instruction torque of the rotating electric machine 54 a, or the like.

[0055] When the current value of the rotating electric machine 54a is used to estimate the load amount, the current value is obtained from the current sensor 203. In the case of a circuit that controls an induction motor, a synchronous motor, or the like using the inverter 10, an ammeter is usually provided, so that the load amount can be estimated from the current without any additional cost. Note that, since the actual torque value is reflected in the current value of the rotating electric machine 54a, the load amount may be estimated after converting the current value into torque.

[0056] When the angular acceleration of the rotating electrical machine 54a is used to estimate the load amount, the angular acceleration can be calculated from the change in angular velocity per unit time detected by a rotational speed detector, for example, a resolver or rotary encoder. When a brushless AC motor is controlled by the inverter 10, the brushless AC motor is usually equipped with a resolver or the like, so the load amount can be estimated from the detected value of the resolver or the like without incurring any additional costs. Since the rotational torque is calculated by multiplying the moment of inertia by the angular acceleration, if the moment of inertia does not change significantly, the angular acceleration may be converted into torque and then the load amount may be estimated.

[0057] The correction torque calculation unit 31b may input the estimated load as load increase position information to the upper / lower limit torque calculation unit 31c. The load increase position information may be interpreted as information associating a specific stroke position of the rod 54b with the load. For example, if the position at which the rod 54b is fully retracted is defined as Psta, the positions at which the rod 54b extends from position X at regular intervals are defined as Psta+1, Psta+2, ..., Psta+n (n is a natural number greater than or equal to 1), and the position at which the rod 54b is fully extended is defined as Pend, the load increase position information may include the loads calculated at each of the positions Psta, Psta+n, and Pend. The correction torque calculation unit 31b may estimate the amount of change in the load based on the rotation speed and the final command torque.

[0058] (Example of Torque Limit Control by Correction Torque Calculation Unit 31b) When the rotating electric machine 54a is in an overload state, the correction torque calculation unit 31b may execute torque limit control. The torque limit control may be interpreted as control that limits (reduces) the final command torque in stages or at a constant rate of change when a sudden change occurs in the external load of the work machine 5.

[0059] Specifically, as torque limit control, the correction torque calculation unit 31b determines whether the estimated load or the change in the estimated load exceeds a predetermined threshold, and if the load or the change in the load exceeds the predetermined threshold, detects that the rotating electric machine 54a is in an overload state due to, for example, a collision of the work machine 5 with a work target. The overload state may be detected based on, for example, at least one of the torque and rotation speed of the rotating electric machine 54a. By using at least one of the torque (final command torque) and rotation speed, torque limit control can be performed in real time while the rotating electric machine 54a and the inverter 10 are operating.

[0060] The correction torque calculation unit 31b, which has detected an overload state in this manner, may reduce (reduce) the absolute value of the torque generated by the rotating electric machine 54a below the absolute value of the torque before the overload state was detected. Specifically, the correction torque calculation unit 31b may reduce the absolute value of the torque generated by the rotating electric machine 54a below the absolute value of the torque generated at the time the overload state was detected until a certain period of time has elapsed since the overload state was detected or until the absolute value of the torque falls below a predetermined threshold. The correction torque calculation unit 31b may input the reduced torque to the final command torque output unit 31f as the correction torque.

[0061] The external load of the work machine 5 may be interpreted as an object of work performed by the work machine 5, with which the work machine 5 may come into contact (collide) while being driven and thereby interfere with the operation of the work machine 5. Specifically, the external load may be interpreted as rocks, concrete, very viscous soil, etc. contained in the soil being excavated by the bucket 53. Note that the external load of the work machine 5 is not limited to these, and may include elements with which the work machine 5 may collide and interfere with the operation of the work machine 5, such as structures at a demolition site or bridges.

[0062] A fluctuation in the external load may be interpreted as, for example, an increase in the burden (load) on the work machine 5 and the electric cylinder 54 while excavating soil, as a result of the work machine 5 coming into contact (colliding) with rocks, concrete, etc. contained in the soil being excavated, compared to before the contact (collision).A sudden fluctuation in the external load may be interpreted as, for example, an increase in the burden (load) on the work machine 5 and the electric cylinder 54 while excavating soil, as a result of the soil's viscosity suddenly changing from a low state to a high state, compared to before the viscosity increased.

[0063] For example, when the work machine 5 repeatedly excavates relatively soft soil, as shown in the period from time t1 to time t2 in Figure 6, there is no sudden change in the external load, so torque limit control is not executed and the torque of the rotating electric machine 54a that drives the work machine 5 remains constant. In this example, the viscosity of the soil does not fluctuate much, so the load (bold solid line) applied to the electric cylinder 54 shows a constant value. This load (bold solid line) is approximately equal to the torque (dashed dotted line) of the rotating electric machine 54a.

[0064] 6 , if the bucket 53 of the work implement 5 comes into contact with (collides with) a large rock buried in the soil, an impact force (dashed line) is added to the torque (dashed line) of the rotating electric machine 54a from time t2 onwards, causing the load on the electric cylinder 54 to tend to increase. In this way, when a fluctuation in the external load on the work implement 5 occurs due to the work implement 5 colliding with the work target, the correction torque calculation unit 31b may execute torque limit control to reduce the absolute value of the torque generated by the rotating electric machine 54a below the absolute value of the torque before the overload state was detected.

[0065] When an overload state is detected and the load applied to the electric cylinder 54 falls below a predetermined threshold, the correction torque calculation unit 31b may change the torque generated by the rotating electric machine 54a from decreasing to increasing. For example, when torque limitation is initiated at time t2 in FIG. 6 , the torque is limited at a constant rate or in stages. This gradually releases the torsion acting on the mechanical element 540 of the electric cylinder 54, which is caused by the collision of the work implement 5 with the work object. When the load falls below a predetermined threshold at time t3 in FIG. 6 , the torque is changed from decreasing to increasing, thereby bringing the torque closer to the command torque. This allows the user operating the work implement 5 to continue working without feeling any discomfort.

[0066] The correction torque calculation unit 31b may increase the torque in stages when it changes from decreasing to increasing, or may increase the torque at a constant rate as shown in FIG. 6. The correction torque calculation unit 31b may also set the rate of change of the torque when it changes from decreasing to increasing to be smaller than the rate of change of the torque when it is decreasing. This reduces the impact even if the work implement 5 collides with the work object again, thereby further reducing the load on the mechanical element 540.

[0067] (Upper and lower limit torque calculation unit 31c) The upper and lower limit torque calculation unit 31c may calculate upper and lower limit torques based on the rotation speed and load increase position information, and input the calculated upper and lower limit torques to the torque limit unit 31e.

[0068] Specifically, the upper and lower limit torque calculation unit 31c may calculate the stroke position of the rod 54b based on the rotation speed, and may calculate upper and lower limit torques corresponding to the rotation speed based on the calculated stroke position and the load increase position information. The upper and lower limit torques may be interpreted as torque thresholds that change the limit on the torque generated by the rotating electric machine 54a depending on the stroke position of the rod 54b included in the work machine 5.

[0069] (First Example of Torque Calculation by Upper / Lower Torque Limit Calculation Unit 31c) If no overload is detected when the rod 54b extends from the fully retracted position to the fully extended position (second stroke position), the upper / lower torque limit calculation unit 31c may calculate the upper limit torque as shown in FIG. 7A . That is, the upper limit torque may be reduced near the fully retracted position of the rod 54b and near the fully extended position of the rod 54b, and the upper limit torque may remain at a large value at other positions. The upper / lower torque limit calculation unit 31c may similarly calculate the lower limit torque. By calculating the upper and lower limit torque in this manner, impact can be reduced even in situations where the work implement 5 is likely to collide with the work object near the fully retracted position of the rod 54b and near the fully extended position of the rod 54b, thereby further reducing the load on the mechanical element 540.

[0070] (Second example of torque calculation by upper / lower limit torque calculation unit 31c) As shown in Figure 7B, the upper / lower limit torque calculation unit 31c may change the limit of the torque generated by the rotating electric machine 54a depending on the stroke position when an overload state of the electric cylinder 54 caused by a previous collision of the work machine 5 with the work target is detected.

[0071] For example, if the bucket 53 collides with a rock at a specific timing while the work machine 5 is repeating the same excavation operation, load increase position information including the load of the overload state estimated at the stroke position of the rod 54b at that time is input to the upper / lower limit torque calculation unit 31c. Based on this load increase position information and the calculated stroke position, the upper / lower limit torque calculation unit 31c may calculate the upper limit torque until the rod 54b extends from the fully retracted position to the stroke position (e.g., the first stroke position) when the overload state was previously detected, as shown in FIG. 7B . In the example shown in FIG. 7B , the position at which the upper limit torque is reduced changes from near the second stroke position to near the first stroke position.

[0072] 7B, the upper / lower limit torque calculation unit 31c may reduce the upper limit torque near the fully retracted position of the rod 54b and near the first stroke position, and may increase the upper limit torque at other positions. The upper / lower limit torque calculation unit 31c may similarly calculate the lower limit torque.

[0073] By setting the upper limit torque in this manner, the torque generated by the rotating electric machine 54a can be limited at a constant rate of change or in stages before the stroke position reaches near the first stroke position where an overload state of the electric cylinder 54 due to the previous collision was detected. This prevents excessive load from occurring again near the first stroke position and prevents repeated execution of torque limit control due to repeated detection of overload. This allows the user of the work machine 5 to continue working without feeling any discomfort when operating the work machine 5. Furthermore, by making it less likely that a strong impact similar to the previous impact will be applied to the electric cylinder 54, the life of the electric cylinder 54 can be extended.

[0074] (Third Example of Torque Calculation by Upper / Lower Limit Torque Calculation Unit 31c) Even when the rotating electric machine 54a generates the same torque at high and low rotation speeds, the acceleration of the work machine 5 increases at high rotation speeds, which tends to increase the impact on the electric cylinder 54. In order to mitigate the impact caused by such a difference in rotation speed, the upper / lower limit torque calculation unit 31c may change the upper / lower limit torque limits in accordance with the rotation speed of the rotating electric machine 54a when changing the upper / lower limit torque limits in accordance with the stroke position.

[0075] 7A and 7B , the upper limit torque when the rotating electric machine 54a is at a low rotation speed may be higher than the upper limit torque when the rotating electric machine 54a is at a high rotation speed. Specifically, the upper / lower limit torque calculation unit 31c may reduce the amount of upper limit torque reduction at low rotation speed compared to the amount of upper limit torque reduction at high rotation speed when the rod 54b is near the fully retracted position. Similarly, the upper / lower limit torque calculation unit 31c may reduce the amount of upper limit torque reduction at low rotation speed compared to the amount of upper limit torque reduction at high rotation speed when the rod 54b is near the first stroke position or the second stroke position.

[0076] In other words, the amount of upper limit torque reduction at high revolutions may be increased more than the amount of upper limit torque reduction at low revolutions. At positions other than these, the upper / lower limit torque calculation unit 31c may not reduce either the upper limit torque at low revolutions or high revolutions, but may leave them at large values, or may set the upper limit torque at high revolutions to a value slightly smaller than the upper limit torque at low revolutions. The upper / lower limit torque calculation unit 31c may similarly control the lower limit torque.

[0077] In this way, even if the acceleration of the work machine 5 is high, the occurrence of excessive load can be effectively suppressed by increasing the narrowing of the upper and lower limit torques at high rotation speeds. Also, by decreasing the narrowing of the upper and lower limit torques at low rotation speeds, the occurrence of excessive load can be suppressed while making it less likely that the user operating the work machine 5 will feel uncomfortable.

[0078] (Fourth example of torque calculation by upper / lower limit torque calculation unit 31c) If the upper / lower limit torque calculation unit 31c does not detect an overload state again at the first stroke position of the rod 54b at which an overload state was previously detected, when the work machine 5 is driven next time onwards, as shown in Figure 7C, the upper / lower limit torque calculation unit 31c may not change the limit on the torque generated by the rotating motor 54a at the first stroke position, but may change the limit on the torque according to a second stroke position different from the first stroke position.

[0079] For example, after calculating the upper / lower limit torque as shown in FIG. 7B , if the excavation position of the work implement 5 changes or the rock that collided with the bucket 53 is removed, and collisions no longer occur near the first stroke position shown in FIG. 7B , the upper / lower limit torque calculation unit 31c may again calculate the upper limit torque as shown in FIG. 7A based on the updated load increase position information at that time. In other words, if a similar overload state is no longer detected near the first stroke position where the overload state was detected, the upper / lower limit torque calculation unit 31c may increase the amount of upper limit torque reduction, i.e., change the torque limit, near a second stroke position different from the first stroke position. Note that FIG. 7C shows a position where the rod 54b is fully extended as an example of the second stroke position, but the second stroke position is not limited to this.

[0080] In this way, when a similar overload state is no longer detected near the first stroke position where an overload state was detected, the stroke position at which torque is limited can be changed to avoid unnecessary torque limiting at the first stroke position, allowing the user of the work machine 5 to continue working without feeling any discomfort in operation.

[0081] (Torque limiting unit 31e) The torque limiting unit 31e may calculate a limited torque, which is the torque obtained by limiting the command torque by the upper and lower limit torques, based on the upper and lower limit torques and the command torque, and input the calculated limited torque to the final command torque output unit 31f.

[0082] (Final command torque output unit 31f) The final command torque output unit 31f may select either the limited torque or the correction torque as the protection torque, feed the selected protection torque back to the correction torque calculation unit 31b as the final command torque, and further input it to the vector control unit 32a.

[0083] For example, the final command torque output unit 31f may limit either the limited torque or the correction torque based on at least one of the temperature of the rotating electric machine 54a and the temperature of the inverter 10. Specifically, the final command torque output unit 31f may calculate the upper and lower limit torques based on at least one of the temperature of the coils in the rotating electric machine 54a and the temperature of the switch elements in the inverter 10. The upper and lower limit torques calculated by the final command torque output unit 31f are different from the upper and lower limit torques calculated by the upper and lower limit torque calculation unit 31c. The upper limit torque calculated by the final command torque output unit 31f can prevent the rotational torque from exceeding the upper limit torque, thereby preventing an excessive load (i.e., a specific load) from occurring that makes it impossible to maintain rotation of the rotating electric machine 54a. The lower limit torque calculated by the final command torque output unit 31f can prevent the rotational torque from falling below the lower limit torque, thereby preventing the thrust from decreasing too much, i.e., preventing the work machine 5 from continuing to work.

[0084] When an overload state is not detected, the final command torque output unit 31f may select the limited torque calculated by the torque limiting unit 31e as the protection torque, and output the selected protection torque limited by the upper and lower limit torques calculated by the final command torque output unit 31f as the final command torque.

[0085] When an overload condition is detected, the final command torque output unit 31f may select the correction torque calculated by the correction torque calculation unit 31b as the protection torque, and output the selected protection torque limited by the upper and lower limit torques calculated by the final command torque output unit 31f as the final command torque.

[0086] (Inverter control unit 32) The inverter control unit 32 controls the inverter 10 that supplies power to the rotating electric machine 54a that is the drive source of the electric cylinder 54 that drives the work machine 5. The inverter control unit 32 may include a vector control unit 32a. The vector control unit 32a executes torque control that corresponds to the final command torque.

[0087] FIG. 8 is a flowchart for explaining the control process of the torque output from the rotary electric machine 54a.

[0088] In step S1, the CPU 21A may calculate a command torque that serves as a target for making the rotation speed of the rotary electric machine 54a follow the required target speed.

[0089] In step S2, the CPU 21A may calculate the stroke position of the rod 54b based on the rotation speed. In step S3, the CPU 21A may calculate upper and lower limit torques according to the rotation speed based on the calculated stroke position and the load increase position information.

[0090] In step S4, the CPU 21A may calculate a limited torque, which is a torque obtained by limiting the command torque with the upper and lower limit torques, based on the upper and lower limit torques and the command torque.

[0091] In step S5, the CPU 21A may estimate the load generated at a specific stroke position of the rod 54b, which is calculated based on the rotation speed, based on the rotation speed and the final command torque, which is the protection torque.

[0092] In step S6, the CPU 21A may determine whether the estimated load exceeds a predetermined threshold. If the load exceeds the predetermined threshold (step S6, YES), the CPU 21A may execute the process of step S8, and if the load does not exceed the predetermined threshold (step S6, NO), the CPU 21A may execute the process of step S7.

[0093] In step S7, the CPU 21A may determine whether the estimated change in load has exceeded a predetermined threshold. If the change in load has exceeded the predetermined threshold (YES in step S7), the CPU 21A may execute the process of step S8, and if the change in load has not exceeded the predetermined threshold (NO in step S7), the CPU 21A may execute the process of step S9.

[0094] In step S8, the CPU 21A may perform torque limit control by decreasing (reducing) the absolute value of the torque generated by the rotating electrical machine 54a below the absolute value of the torque before the overload state was detected. The CPU 21A may input the reduced torque to the final command torque output unit 31f as a correction torque.

[0095] In step S10, the CPU 21A selects, as a protection torque, either the limited torque calculated in step S4 or the correction torque, which is the torque reduced by the torque limit control in step S8, and limits the selected protection torque by the upper and lower limit torques calculated by the final command torque output unit 31f. In step S10, the CPU 21A may feed back the selected protection torque as the final command torque to the correction torque calculation unit 31b and further input it to the vector control unit 32a.

[0096] In step S11, a plurality of switch elements in the inverter 10 are turned on and off in accordance with the final command torque, and in step S12, the value of the torque output from the rotary electric machine 54a is controlled.

[0097] Fig. 9 is a timing chart for explaining an example of control by a control device according to a comparative example. Similar to Fig. 6, Fig. 9 shows the changes in the rotation speed and torque of the rotating electric machine 54a over time. The normal solid line represents the rotation speed, the thick solid line represents the load applied to the electric cylinder 54, the dashed-dotted line represents the torque generated by the rotating electric machine 54a, and the dashed line represents the impact force applied to the electric cylinder 54.

[0098] For example, if the bucket 53 of the work implement 5 collides (comes into contact with) a large rock buried in the soil at time t2 in Figure 9, the load applied to the electric cylinder 54 may increase sharply. In other words, the impact force caused by the bucket 53 colliding with the rock, which is an external load on the work implement 5, and the constant torque generated by the rotating electric machine 54a are applied to the electric cylinder 54 as a load on the electric cylinder 54. This increases the torsion applied to the mechanical element 540 of the electric cylinder 54, increasing the burden on the mechanical element 540 and potentially interfering with the operation of the electric cylinder 54.

[0099] As described above, the control device 7 according to an embodiment of the present disclosure may include a control unit 31 that, when an overload state of the electric cylinder 54 is detected, reduces the absolute value of the torque generated by the rotating electric machine 54a below the absolute value of the torque before the overload state was detected.

[0100] With this configuration, even if the external load suddenly increases, the torque applied to the electric cylinder 54 from the rotating electric machine 54a is reduced, thereby preventing the load from being concentrated on a part of the mechanical element 540 included in the electric cylinder 54.

[0101] Although the present embodiment has been described above, the present disclosure is not limited to the above-described embodiments, and various modifications and applications are possible within the scope of the gist of the present disclosure.

[0102] Furthermore, the configuration of the control device 7 described in the above embodiment is one example, and it goes without saying that unnecessary parts may be deleted or new parts may be added within the scope of the present disclosure.

[0103] Furthermore, the processing flow of the control program 23A described in the above embodiment is also an example, and it goes without saying that unnecessary steps may be deleted, new steps may be added, or the processing order may be rearranged within the scope of the present disclosure.

[0104] The present invention is also applicable to program products.

[0105] The controller and method described herein may be implemented by a special-purpose computer having a processor programmed to perform one or more functions embodied in a computer program. Alternatively, the apparatus and method described herein may be implemented by a special-purpose computer having a processor configured with dedicated hardware logic circuits. Alternatively, the apparatus and method described herein may be implemented by one or more special-purpose computers configured by a combination of a processor executing a computer program and one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by a computer on a computer-readable non-transitory storage medium.

[0106] The following notes are provided regarding the technology of the present disclosure.

[0107] (Supplementary Note 1) A control device (7) for controlling a rotating electric machine (54a) that drives a work machine (5) provided on a vehicle (100), comprising: an inverter control unit (32) that controls an inverter (10) that supplies power to the rotating electric machine, which is a drive source of an electric cylinder (54) that drives the work machine; and a control unit (31) that, when an overload state of the electric cylinder is detected, reduces the absolute value of the torque generated by the rotating electric machine below the absolute value of the torque before the overload state is detected.

[0108] (Supplementary Note 2) The control device according to Supplementary Note 1, wherein the control unit reduces the torque generated by the rotating electric machine so that the load on the electric cylinder becomes equal to or less than a predetermined threshold when an overload state of the electric cylinder caused by a collision of the work machine with a work target is detected.

[0109] (Supplementary Note 3) The control device according to Supplementary Note 1 or 2, wherein the control unit changes a limit on the torque generated by the rotating electric machine depending on a stroke position of a rod (54b) included in the work machine.

[0110] (Supplementary Note 4) The control device according to Supplementary Note 3, wherein the control unit changes a limit on the torque generated by the rotating electric machine in accordance with a rotation speed of the rotating electric machine.

[0111] (Supplementary Note 5) The control device according to Supplementary Note 3, wherein the control unit changes the limit of the torque generated by the rotating electric machine depending on the stroke position when an overload state of the electric cylinder caused by a previous collision of the work machine with a work target is detected.

[0112] (Appendix 6) The control device described in Appendix 5, wherein if the control unit does not detect the overload state again at the first stroke position of the rod at which the overload state was last detected, the control unit does not change the limit on the torque generated by the rotating electric machine at the first stroke position when the work machine is driven next time onwards, but changes the limit on the torque according to a second stroke position of the rod that is different from the first stroke position.

[0113] (Supplementary Note 7) The control device according to any one of Supplementary Notes 1 to 6, wherein the control unit detects the overload state of the electric cylinder caused by a collision of the work machine with a work target based on at least one of a torque and a rotation speed of the rotating electric machine.

[0114] (Supplementary Note 8) The control device according to Supplementary Note 2, wherein the control unit changes the torque generated by the rotating electric machine from a decrease to an increase when the load applied to the electric cylinder becomes equal to or less than a predetermined threshold when the overload state is detected.

[0115] (Appendix 9) The control device according to any one of Appendices 1 to 8, wherein the electric cylinder includes a ball screw (54f) that converts the rotational motion of the rotating electric machine into linear motion of a linearly moving member, and the ball screw includes a nut (54e), a screw shaft (54f1), and balls (54f2) that are rolling elements provided between the nut and the screw shaft.

[0116] (Supplementary Note 10) An agricultural machine including the control device according to any one of Supplementary Notes 1 to 9.

[0117] (Supplementary Note 11) A construction machine equipped with the control device according to any one of Supplementary Notes 1 to 9.

[0118] (Supplementary Note 12) A control program (23A) that causes at least one processor (21A) to execute processing including: controlling an inverter that supplies power to a rotating electric machine that is a drive source of an electric cylinder that drives a work machine provided on a vehicle; and, when an overload state of the electric cylinder is detected, reducing the absolute value of the torque generated by the rotating electric machine below the absolute value of the torque before the overload state is detected.

[0119] (Supplementary Note 13) A control method that executes processing including: at least one processor controls an inverter that supplies power to a rotating electric machine that is a drive source of an electric cylinder that drives a work machine provided on a vehicle; and when an overload state of the electric cylinder is detected, reduces the absolute value of the torque generated by the rotating electric machine below the absolute value of the torque before the overload state is detected.

Claims

1. A control device (7) for controlling a rotating electric machine (54a) that drives a work machine (5) provided on a vehicle (100), comprising: an inverter control unit (32) that controls an inverter (10) that supplies power to the rotating electric machine, which is the driving source of an electric cylinder (54) that drives the work machine; and a control unit (31) that, when an overload state of the electric cylinder is detected, reduces the absolute value of the torque generated by the rotating electric machine below the absolute value of the torque before the overload state is detected.

2. The control device described in claim 1, wherein the control unit reduces the torque generated by the rotating electric machine so that the load applied to the electric cylinder is below a predetermined threshold when an overload state of the electric cylinder caused by a collision of the work machine with a work object is detected.

3. The control device according to claim 1, wherein the control unit changes the limit on the torque generated by the rotating electric machine in accordance with the stroke position of a rod (54b) included in the work machine.

4. The control device according to claim 3, wherein the control unit changes the limit on the torque generated by the rotating electric machine in accordance with the rotation speed of the rotating electric machine.

5. A control device as described in claim 3, wherein the control unit changes the limit on the torque generated by the rotating electric machine depending on the stroke position when an overload state of the electric cylinder caused by a previous collision of the work machine with a work object is detected.

6. A control device as described in claim 5, wherein, if the control unit does not detect the overload state again at the first stroke position of the rod at which the overload state was previously detected, the control unit does not change the limit on the torque generated by the rotating electric machine at the first stroke position when the work machine is driven next time onwards, but changes the limit on the torque according to a second stroke position of the rod that is different from the first stroke position.

7. The control device according to claim 1, wherein the control unit detects the overload state of the electric cylinder caused by a collision of the work machine with a work target based on at least one of the torque and rotation speed of the rotating electric machine.

8. The control device according to claim 2, wherein the control unit changes the torque generated by the rotating electric machine from a decrease to an increase when the load applied to the electric cylinder falls below a predetermined threshold when the overload state is detected.

9. The control device described in claim 1, wherein the electric cylinder is provided with a ball screw (54f) that converts the rotational motion of the rotating electric machine into linear motion of a linearly moving member, and the ball screw includes a nut (54e), a screw shaft (54f1), and a ball (54f2) that is a rolling element provided between the nut and the screw shaft.

10. An agricultural machine equipped with a control device according to any one of claims 1 to 9.

11. A construction machine equipped with a control device according to any one of claims 1 to 9.

12. A control program (23A) that causes at least one processor (21A) to execute processing including controlling an inverter that supplies power to a rotating electric machine that is the drive source of an electric cylinder that drives a work machine provided on a vehicle, and when an overload state of the electric cylinder is detected, reducing the absolute value of the torque generated by the rotating electric machine below the absolute value of the torque before the overload state was detected.

13. A control method that executes processing including the steps of: at least one processor controlling an inverter that supplies power to a rotating electric machine that is the drive source of an electric cylinder that drives a work machine provided on a vehicle; and, when an overload state of the electric cylinder is detected, reducing the absolute value of the torque generated by the rotating electric machine below the absolute value of the torque before the overload state was detected.

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