Control system for industrial machinery

Abstract

In a work machine equipped with an electric motor as the power source for a hydraulic pump, the flow rate of the hydraulic pump is controlled by controlling the rotational speed of the electric motor and the capacity of the hydraulic pump, so as to ensure that the electric motor and hydraulic pump are driven efficiently even when the temperature of the electric motor changes. [Solution] A temperature detection means 17 is provided to detect the temperature of the electric motor, and a control device 14 is provided to control the electric motor 12 and the hydraulic pump 11 by determining the rotational speed of the electric motor 12 and the capacity of the hydraulic pump 11 that result in high overall efficiency of the power transmission system from the electric motor input to the hydraulic pump output, according to the temperature of the electric motor 12.

Description

Technical Field

[0001] The present invention relates to the technical field of a control system for a working machine provided with a variable displacement hydraulic pump and an electric motor for driving the hydraulic pump.

Background Art

[0002] Among working machines such as hydraulic excavators, a variable displacement hydraulic pump is used as a hydraulic supply source for various hydraulic actuators such as hydraulic motors and hydraulic cylinders provided in the working machine, and an electric motor is used as a power source for driving the hydraulic pump. When an electric motor is used as a power source for a variable displacement hydraulic pump in this way, the flow rate control of the hydraulic pump can be performed by controlling the rotational speed of the electric motor and the capacity of the hydraulic pump. In this case, considering the efficiency characteristics of the electric motor and the efficiency characteristics of the hydraulic pump, it is required to perform the rotational speed control of the electric motor and the capacity control of the hydraulic pump so that the overall efficiency of the power transmission system from the electric motor input to the hydraulic pump output becomes high. Therefore, conventionally, when controlling the flow rate of the hydraulic pump by controlling the rotational speed of the electric motor and the capacity of the hydraulic pump, an arithmetic means for calculating a combination of the rotational speed of the electric motor and the capacity of the hydraulic pump at which the efficiency of the power transmission system from the electric motor input to the hydraulic pump output becomes maximum is provided, and the rotational speed of the electric motor and the capacity of the hydraulic pump are controlled based on the calculation result of the arithmetic means (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, the overall efficiency of a power transmission system from electric motor input to hydraulic pump output is determined by the product of the efficiency of the electric motor (motor efficiency) and the efficiency of the hydraulic pump (pump efficiency). However, in determining the motor efficiency, the aforementioned Patent Document 1 does not take into account the effect of temperature changes in the electric motor. However, electric motors experience energy losses such as copper loss, iron loss, and mechanical loss, and motor efficiency is affected by these losses. Of these losses, copper loss (loss caused by the resistance component of the coil windings) is known to increase with rising temperature, reducing motor efficiency. Therefore, when the control described in Patent Document 1 is performed, there is a risk that the overall efficiency of the power transmission system will fall out of the optimal range when the temperature of the electric motor rises, and this is the problem that the present invention aims to solve. [Means for solving the problem]

[0005] The present invention was created in view of the above circumstances and with the aim of solving these problems, and the invention of claim 1 is a control system for a work machine that is equipped with a variable displacement hydraulic pump and an electric motor that drives the hydraulic pump, wherein a control system is provided to control the flow rate of the hydraulic pump by controlling the rotational speed of the electric motor and the capacity of the hydraulic pump, and the control system is provided with a temperature detection means for detecting the temperature of the electric motor, and a control device that controls the electric motor and hydraulic pump by determining the rotational speed of the electric motor and the capacity of the hydraulic pump according to the temperature of the electric motor detected by the temperature detection means, so that the flow rate of the hydraulic pump becomes the pump-required flow rate required for the hydraulic pump and the overall efficiency of the power transmission system from the electric motor input to the hydraulic pump output is a preset high efficiency. The invention of claim 2 is a control system for a work machine, characterized in that, in claim 1, the control device includes a control map showing the relationship between the required pump flow rate, the rotational speed of the electric motor, and the capacity of the hydraulic pump, which results in a high overall efficiency depending on the temperature of the electric motor. The invention of claim 3 is a control system for a work machine, characterized in that, in claim 2, the control maps are set in multiple locations according to the temperature of the electric motor. The invention of claim 4 is a control system for a work machine, characterized in that, in claim 3, a reference control map is set when the temperature of the electric motor is at a preset reference temperature, and a control map is set when the temperature of the electric motor is at a temperature other than the reference temperature by correcting the reference control map based on the change in motor efficiency due to the temperature change of the electric motor. [Effects of the Invention]

[0006] By adopting the invention of claim 1, when controlling the flow rate of a hydraulic pump by controlling the rotational speed of an electric motor and the capacity of a hydraulic pump, even if the temperature of the electric motor changes, the electric motor and hydraulic pump can be driven in such a way that the overall efficiency of the power transmission system from the electric motor input to the hydraulic pump output is high, thereby reducing power loss in the power transmission system from the electric motor input to the hydraulic pump output as much as possible. By adopting the invention of claim 2, it is possible to easily and accurately determine, using a control map, the rotational speed of the electric motor and the capacity of the hydraulic pump that result in the flow rate of the hydraulic pump becoming the required flow rate of the pump and the overall efficiency increasing according to the temperature of the electric motor. By adopting the invention of claim 3, control can be simplified. By adopting the invention of claim 4, the creation of control maps can be facilitated. [Brief explanation of the drawing]

[0007] [Figure 1] This is a side view of a hydraulic excavator. [Figure 2] Block diagram showing the input and output of a control device. [Figure 3] (A) shows the relationship between rotational speed / torque and efficiency at room temperature, and (B) shows the relationship at high temperature. [Figure 4] This figure shows the first control maps for room temperature and high temperature. [Figure 5](A) is the second control map for room temperature, and (B) is the second control map for high temperature. [Modes for carrying out the invention]

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In Figure 1, 1 is an electric hydraulic excavator, which is an example of a work machine of the present invention. The hydraulic excavator 1 consists of a crawler-type lower traveling body 2, an upper rotating body 3 that is rotatably supported on the lower traveling body 2, and a front working section 4 mounted on the upper rotating body 3. It is equipped with various hydraulic actuators A, such as a boom cylinder 8, an arm cylinder 9, and a bucket cylinder 10 that swing the boom 5, arm 6, and bucket 7 that form the front working section 4, as well as left and right traveling motors (not shown) for traveling the lower traveling body 2 and a rotating motor (not shown) for rotating the upper rotating body 3. Furthermore, the upper rotating body 3 is equipped with a variable displacement hydraulic pump 11 that supplies hydraulic fluid to these hydraulic actuators A, and an electric motor 12 that is linked to the drive shaft of the hydraulic pump 11 in order to drive the hydraulic pump 11. In this embodiment, the electric motor 12 is configured to be powered by an external power source (not shown) located outside the hydraulic excavator 1 via a power cable 13. In this embodiment, as described above, the electric motor 12 is configured to be powered by an external power source. However, the present invention is not limited to this, and of course, it can also be implemented in a configuration in which, for example, the work machine is equipped with an engine as a power source, and the engine drives a generator, and the electricity generated by the generator is supplied to the electric motor.

[0009] Furthermore, the hydraulic excavator 1 is equipped with a control device 14 that controls the electric motor 12 and the hydraulic pump 11. Various controls are performed by the control device 14. As shown in the block diagram of Figure 2, the control device 14 is configured such that, on the input side, there are multiple operation detection means 15 that detect the operation of each hydraulic actuator A (not shown, but such as an operation lever or pedal), a pressure detection means (pressure sensor) 16 that detects the discharge pressure (pump pressure) of the hydraulic pump 11 and the pressure of the hydraulic actuator A, a temperature detection means (temperature sensor) 17 that detects the temperature of the electric motor 12, a motor output detection means 18 that detects the output of the electric motor 12, and an information input means 19 for inputting and changing various data and information such as maps. On the output side, there are motor control means 21 that controls the output, torque, rotational speed, etc. of the electric motor 12, a pump control means 22 that controls the pump volume, etc. of the hydraulic pump 11, and an information storage unit 24 that stores various data and information such as a control map 23, which will be described later, and a motor / pump control unit 25, which will be described later. In this invention, the rotational speed of the electric motor (motor rotational speed) is the number of rotations per unit time and is synonymous with rotational speed.

[0010] Next, the control map 23 stored in the information storage unit 24 will be described. In this embodiment, the control map 23 includes a room temperature control map (first and second room temperature control maps 23ATn and 23BTn, described later) used when the temperature of the electric motor 12 is at room temperature, and a high temperature control map (first and second high temperature control maps 23ATh and 23BTh, described later) used when the temperature of the electric motor 12 is at a high temperature. Here, when the hydraulic pump 11 is driven using the electric motor 12 as a power source, the efficiency (overall efficiency) η of the power transmission system from the input of the electric motor 12 to the output of the hydraulic pump 11 is calculated by the product of the efficiency (motor efficiency) ηm of the electric motor 12 and the efficiency (pump efficiency) ηp of the hydraulic pump 11 (η = ηm × ηp). However, as shown in Figures 3(A) and (B), the rotational speed / torque range in which the motor efficiency ηm is high differs from the rotational speed / torque range in which the pump efficiency ηp is high. Furthermore, the rotational speed / torque range in which the motor efficiency ηm is high changes with the temperature of the electric motor 12, and consequently, the rotational speed / torque range in which the overall efficiency η is high also changes with the temperature of the electric motor 12. Figure 3 is an example of this, where (A) shows the case when the temperature of the electric motor 12 is a predetermined ambient temperature Tn (e.g., 40°C), and (B) shows the case when the temperature is a predetermined high temperature Th (e.g., 60°C). In Figure 3, in the region where motor efficiency ηm is high, the effect of copper loss due to high temperature (loss caused by the resistance component of the coil windings) is greater in the high rotational speed region than in the low rotational speed region. Therefore, it is thought that the difference between the region at room temperature Tn (Figure 3(A)) and the region at high temperature Th (Figure 3(B)) will be larger in the high rotational speed region. Also, at high temperature Th, copper loss in the electric motor 12 increases compared to room temperature Tn. Therefore, it is thought that the region where overall efficiency η is high at high temperature Th will shift towards the region where pump efficiency ηp is high. However, this is not limited to the example in Figure 3, and various cases are possible depending on the efficiency characteristics of the individual electric motor and the hydraulic pump, such as when overall efficiency shifts to the low torque, high rotation side, or when overall efficiency shifts to the high torque, low rotation side when temperature rises. Furthermore, the resistance of copper wiring is expressed by the following formula (1). RT = Rt × {1 + αt(Tt)} ... (1) In equation (1) above, RT is the resistance value at T°C, Rt is the resistance value at t°C, and αt is the temperature coefficient of resistance at t°C (for copper, it is 0.0038 at 20°C). From equation (1), the wiring resistance at 40°C is 1.076 times that at 20°C, and the wiring resistance at 65°C is 1.171 times that at 65°C.

[0011] Furthermore, Figure 4 shows a high-efficiency rotational speed / torque curve created based on the rotational speed / torque distribution that maximizes the overall efficiency η when the output is increased or decreased (the region of high overall efficiency η in Figures 3(A) and (B) above). In Figure 4, X (solid line) and Y (dashed line) represent the high-efficiency rotational speed / torque curves when the temperature of the electric motor 12 is at room temperature Tn and high temperature Th, respectively. In this case, the high-efficiency rotational speed / torque curve is created to be a smooth curve within the range where the overall efficiency η is a predetermined high efficiency (maximum efficiency or a high efficiency at the same level as the maximum efficiency (for example, 90% or more of the maximum efficiency)). The high-efficiency rotational speed / torque curves X and Y for room temperature Tn and high temperature Th are then set as the first control map 23ATn for room temperature and the first control map 23ATh for high temperature. Furthermore, the aforementioned high-efficiency rotational speed / torque curve will differ depending on the efficiency characteristics of each electric motor and hydraulic pump, and will be created based on efficiency calculated from actual measurements or analysis from specifications, etc.

[0012] Furthermore, based on the high-efficiency rotational speed / torque curves X and Y in Figure 4 (first control map 23ATn for ambient temperature, first control map 23ATh for high temperature), a combination of motor rotational speed N and pump volume q that yields high overall efficiency η according to the required pump flow rate for the hydraulic pump 11 is determined for ambient temperature Tn and high temperature Th, and these are set as the second control map 23BTn for ambient temperature and the second control map 23BTh for high temperature (see Figures 5(A) and (B)). Furthermore, the first and second control maps 23ATn and 23BTn for ambient temperature, and the first and second control maps 23ATh and 23BTh for high temperature, constitute control maps that show the relationship between the pump required flow rate, the rotational speed of the electric motor, and the capacity of the hydraulic pump, which result in high overall efficiency depending on the temperature of the electric motor of the present invention.

[0013] Next, the control performed by the motor / pump control unit 25 will be described. When the operation detection means 15 inputs an operation signal of the operating tool for the hydraulic actuator A, the motor pump control unit 25 sets the pump required flow rate Q and the pump required pressure P required for the hydraulic pump 11 according to the operation amount of the operating tool for the hydraulic actuator A based on the operation signal. Incidentally, the pressure of the hydraulic pump 11 is controlled so as to become the pump required pressure P required according to the operation amount of the operating tool by controlling the opening area of a bypass valve (not shown) disposed in a bypass oil passage from the discharge oil passage of the hydraulic pump 11 to the oil tank, but detailed description of the control is omitted.

[0014] Furthermore, the motor pump control unit 25 reads the second control map 23BTn for normal temperature and the second control map 23BTh for high temperature, and reads the temperature of the electric motor 12 detected by the temperature detection means 17. Then, according to the detected temperature of the electric motor 12, either the second control map 23BTn for normal temperature or the second control map 23BTh for high temperature is selected. Here, when selecting either the second control map 23BTn for normal temperature or the second control map 23BTh for high temperature according to the detected temperature of the electric motor 12, for example, when a predetermined high temperature Th is 60°C, either the second control map 23BTn for normal temperature or the second control map 23BTh for high temperature is selected using this 60°C as a threshold value. In this case, for example, when the temperature of the electric motor 12 rises, the second control map 23BTn for normal temperature is selected when the temperature of the electric motor 12 is lower than 60°C, and the second control map 23BTh for high temperature is selected after reaching 60°C. On the other hand, when the temperature drops, the second control map 23BTh for high temperature is selected when the temperature of the electric motor 12 is higher than 60°C, and the second control map 23BTn for normal temperature is selected after reaching 60°C.

[0015] Furthermore, the motor pump control unit 25 uses the second control map 23BTn or 23BTh for normal temperature or high temperature selected according to the temperature of the electric motor 12 to obtain a combination of the rotational speed N of the electric motor 12 and the pump volume q at which the overall efficiency η becomes highly efficient according to the pump required flow rate Q.

[0016] The motor / pump control unit 25 then sets an instruction current value I for the hydraulic pump 11, which corresponds to the pump volume q determined using the second control maps 23BTn and 23BTh for ambient temperature or high temperature selected according to the temperature of the electric motor 12, and outputs the instruction current value I to the pump control means 22. Furthermore, the motor / pump control unit 25 sets the rotational speed N of the electric motor 12, which is determined using the second control map 23BTn for ambient temperature or the second control map 23BTh for high temperature selected according to the temperature of the electric motor 12, and the output torque T of the electric motor 12, which is determined using the following equation (2), as instruction signals to the electric motor 12, and outputs these instruction signals to the motor control means 21. T=P×q / 2π...Equation (2) In equation (2) above, T is the motor torque [N·m], P is the pump required pressure [MPa], and q is the pump volume (cm³). 3 ( / rev)

[0017] However, the motor / pump control unit 25 controls the flow rate of the hydraulic pump 11 to the required pump flow rate Q according to the amount of operation of the hydraulic actuator A, and determines, according to the temperature of the electric motor 12, the combination of the rotational speed of the electric motor 12 and the capacity of the hydraulic pump 11 that maximizes the overall efficiency η of the power transmission system from the electric motor input to the hydraulic pump output. Based on the determined result, the rotational speed of the electric motor 12 and the capacity of the hydraulic pump 11 are controlled.

[0018] In this configuration as described, the hydraulic excavator 1 is equipped with a variable displacement hydraulic pump 11 that serves as a hydraulic power source for various hydraulic actuators A, and an electric motor 12 that drives the hydraulic pump 11. In this configuration, in controlling the flow rate of the hydraulic pump 11 by controlling the rotational speed of the electric motor 12 and the capacity of the hydraulic pump 11, a temperature detection means 17 for detecting the temperature of the electric motor 12 and a control device 14 for outputting control signals to the motor control means 21 and the pump control means 22 are provided. The control device 14 determines the rotational speed of the electric motor 12 and the capacity of the hydraulic pump 11 according to the temperature of the electric motor 12 detected by the temperature detection means 17, so that the flow rate of the hydraulic pump 11 becomes the required pump flow rate Q and the overall efficiency η of the power transmission system from the electric motor input to the hydraulic pump output becomes a preset high efficiency, and controls the electric motor 12 and the hydraulic pump 11.

[0019] As described above, in this embodiment, when controlling the flow rate of the hydraulic pump 11 by controlling the rotational speed of the electric motor 12 and the capacity of the hydraulic pump 11, even if the temperature of the electric motor 12 changes, the rotational speed of the electric motor 12 and the capacity of the hydraulic pump 11 are controlled so that the overall efficiency η of the power transmission system from the electric motor input to the hydraulic pump output is high according to the temperature of the electric motor 12. As a result, even if the motor efficiency ηm changes with the temperature change of the electric motor 12, the electric motor 12 and the hydraulic pump 11 can be driven in a region with high overall efficiency η, thereby reducing power loss in the power transmission system from the input of the electric motor 12 to the output of the hydraulic pump 11 as much as possible, and greatly contributing to improved fuel efficiency. In particular, in working machines such as hydraulic excavators 1, various hydraulic actuators A are driven by the hydraulic power output from the hydraulic pump 11, so reducing power loss in the power transmission system from the input of the electric motor 12 to the output of the hydraulic pump 11 greatly contributes to improving the fuel efficiency of the entire working machine.

[0020] In this system, the control device 14 includes a control map 23 (in this embodiment, first and second control maps 23ATn and 23BTn for normal temperature, and first and second control maps 23ATh and 23BTh for high temperature) that shows the relationship between the required pump flow rate Q, which results in a high overall efficiency η depending on the temperature of the electric motor 12, and the rotational speed of the electric motor 12 and the capacity of the hydraulic pump 11. By including such a control map, the control device 14 can easily and accurately determine the rotational speed of the electric motor and the capacity of the hydraulic pump that result in a flow rate of the hydraulic pump 11 that matches the required pump flow rate Q and also results in a high overall efficiency η depending on the temperature of the electric motor 12.

[0021] Furthermore, the control map 23 is configured in multiple ways, depending on the temperature of the electric motor 12. By configuring the control map 23 according to temperature in this way, the control process can be simplified.

[0022] It should be noted that the present invention is not limited to the above embodiments. For example, in the above embodiments, two types of control maps (a control map for normal temperature and a control map for high temperature) are provided for different temperatures of the electric motor, but it is also possible to provide three or more types of control maps for different temperatures. Furthermore, among the multiple (two or more) temperature-dependent control maps, the control map used for controlling the electric motor and hydraulic pump will be switched according to the rise or fall in temperature of the electric motor. To prevent frequent switching of control maps and ensure smooth switching, hysteresis can be introduced into the temperature at which the switch occurs, a rate limit can be set, or the values ​​between control maps can be linearly interpolated. In addition, a rate limit or low-pass filter may be set as a countermeasure against rapid temperature changes (false detection) in a very short time.

[0023] Furthermore, when setting up the multiple temperature-specific control maps, the control map may be set based on efficiency analyzed from actual measurements or specifications for each temperature. However, it is not limited to this, and a standard control map for when the electric motor temperature is a predetermined reference temperature can be set based on efficiency analyzed from actual measurements or specifications, and the standard control map can be corrected based on the change in motor efficiency due to the change in electric motor temperature to set a control map for when the electric motor temperature is other than the reference temperature. This makes it easier to create a control map for when the electric motor temperature is other than the reference temperature. [Industrial applicability]

[0024] This invention can be used in control systems for various types of work machines equipped with an electric motor as a power source for a variable displacement hydraulic pump. [Explanation of symbols]

[0025] 11. Hydraulic pump 12 Electric motors 14 Control device 17 Temperature detection means 23 Control Map

Claims

1. In a work machine equipped with a variable displacement hydraulic pump and an electric motor for driving the hydraulic pump, In installing a control system that controls the flow rate of a hydraulic pump by controlling the rotational speed of an electric motor and the capacity of a hydraulic pump, A control system for a work machine, characterized in that the control system is provided with a temperature detection means for detecting the temperature of an electric motor, and a control device that controls the electric motor and hydraulic pump by determining, according to the temperature of the electric motor detected by the temperature detection means, the rotational speed of the electric motor and the capacity of the hydraulic pump so that the flow rate of the hydraulic pump becomes the required pump flow rate for the hydraulic pump and the overall efficiency of the power transmission system from the electric motor input to the hydraulic pump output becomes a preset high efficiency.

2. A control system for a work machine according to claim 1, characterized in that the control device includes a control map showing the relationship between the required pump flow rate, the rotational speed of the electric motor, and the capacity of the hydraulic pump, which results in a high overall efficiency depending on the temperature of the electric motor.

3. The control system for a work machine according to claim 2, characterized in that a plurality of control maps are set according to the temperature of the electric motor.

4. A control system for a work machine according to claim 3, characterized in that a reference control map is set when the temperature of the electric motor is at a preset reference temperature, and a control map is set when the temperature of the electric motor is at a temperature other than the reference temperature by correcting the reference control map based on the change in motor efficiency due to the temperature change of the electric motor.

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