JP3877909B2 - Swivel drive device for construction machinery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a turning drive device for a construction machine using an electric motor as an actuator.
[0002]
[Prior art]
Conventionally, in the field of construction machinery, hydraulic actuators have been widely used due to the small size and light weight of the equipment for output. However, hydraulic actuators are less energy efficient than electric actuators. For example, when the operation direction, output and speed of the hydraulic actuator are controlled, the direction, pressure and flow rate of the oil discharged from the hydraulic pump are controlled by a control valve. Therefore, there are many portions where hydraulic energy is squeezed out by the control valve, and energy loss is large.
[0003]
In particular, in the case of a turning operation of a construction machine, for example, it is often performed simultaneously with, for example, an excavator boom raising operation, and it is preferable to control with an actuator independent from the viewpoint of energy efficiency. In view of this, a so-called hybrid construction machine has been proposed in which a hydraulic actuator and an electric actuator are used in combination according to the operation and purpose of the construction machine.
[0004]
In general, the operating characteristics of an electric actuator such as an electric motor do not necessarily match the operating characteristics of a hydraulic actuator.
[0005]
When the motor is an actuator, the rotation direction of the motor is switched according to the direction of the operation lever with respect to the neutral position, and the rotation speed (or torque) is controlled according to the operation amount of the operation lever. In rotational speed control, the maximum torque of the system is always commanded. In the torque control, the motor torque is 0 at the neutral position, and no driving force or braking force is generated. When braking the upper revolving structure, the operating lever is operated in the direction opposite to the turning direction to generate a torque in the reverse direction in the electric motor.
[0006]
On the other hand, when the hydraulic motor is used as an actuator, the rotation direction of the hydraulic motor is switched according to the direction of the operation lever with respect to the neutral position, and the flow rate of the discharged oil is controlled according to the operation amount of the operation lever. The number is controlled. When the operation lever is returned, a braking force is applied, and the hydraulic motor does not rotate at the neutral position, and the brake is locked with the maximum torque of the hydraulic motor.
[0007]
[Problems to be solved by the invention]
However, even for a hybrid construction machine using both a hydraulic actuator and an electric actuator, it is desirable for the user who is used to the operation of the construction machine using a conventional hydraulic actuator to have the same or similar operating characteristics. For example, when braking is applied to the upper turning body turning at high speed, the braking distance becomes longer if the braking torque of the electric motor is small. Therefore, compared to the conventional hydraulic actuator, braking must be applied considerably before the stop position, making it difficult to stop at an accurate position and increasing the operation cycle time. Had.
[0008]
In addition, electric actuators such as electric motors are inherently inferior in terms of small size and light weight with respect to output compared to hydraulic actuators. However, using electric motors with large braking torque further increases the size of the electric motor itself, resulting in construction. There was a problem that it was not suitable for mounting on machines, particularly self-propelled ones.
[0009]
The present invention has been made to solve the above-described problems of the conventional example, and an object of the present invention is to provide a turning drive device for a construction machine that can obtain desired operation characteristics while using a small electric motor as an actuator. It is said.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a turning drive device for a construction machine according to the present invention drives an upper turning body with respect to a lower traveling body using an electric motor as an actuator, and uses the electric motor with electric motor characteristics during turning acceleration. When turning and decelerating, use the motor with the generator characteristics, and when using the torque characteristics that are different between turning acceleration and turning, and when using the motor with the generator characteristics, the maximum absorption torque of the motor Is controlled to a constant value regardless of the rotational speed .
[0011]
Further, where that put during turning acceleration at a constant rotational speed or more areas, it is preferable that the field-weakening control of the electric motor.
[0012]
Furthermore, it is preferable that the motor is regeneratively braked at the time of turning deceleration.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The turning drive device for a construction machine according to the present invention will be described by taking an excavator as an example thereof as an example. The configuration of the excavator of this embodiment is shown in FIG.
[0014]
In FIG. 1, a lower traveling body 10 includes a pair of crawlers 11 and a crawler frame 12 (only one side is shown in the figure), a pair of hydraulic motors 13 and 14 (see FIG. 2) that independently drive and control each crawler 11, and The speed reduction mechanism is used.
[0015]
The upper swing body 20 includes a swing frame 21, an engine 22 as a drive source provided on the swing frame 21, a generator 23 driven by the engine 22, and a battery for storing electric power generated by the generator. 24, an electric motor 25 as a drive source driven by electric power from the generator 23 or the battery 24, and a reduction mechanism that decelerates the rotation of the electric motor 25. It comprises a turning mechanism 26 and the like for driving the body 20 (the turning frame 21) to turn.
[0016]
Further, the upper swing body 20 drives a boom 31 that can be raised and lowered, a boom cylinder 32 for driving the boom 31, an arm 33 that is rotatably supported near the tip of the boom 31, and the arm 33. An excavator mechanism 30 including an arm cylinder 34 for rotating, a bucket 35 rotatably supported at the tip of the arm 33, a bucket cylinder 36 for driving the bucket 35, and the like is mounted. Further, on the swing frame 21 of the upper swing body 20, a hydraulic pump 41 for driving and controlling the boom cylinder 32, the arc cylinder 34, and the bucket cylinder 36, and a hydraulic control valve 42 provided for each cylinder (see FIG. 2). ) Etc. are mounted.
[0017]
Next, a block configuration of the control system of the present embodiment is shown in FIG. In FIG. 2, a thick line indicates a mechanical drive system, a middle line indicates a hydraulic drive system, and a thin line indicates an electrical drive system. As shown in FIG. 2, the driving force of the engine 22 is transmitted to the hydraulic pump 41. The hydraulic control valve 41 discharges the operating oil to the right traveling hydraulic motor 13, the left traveling hydraulic motor 14, the boom cylinder 32, the arm cylinder 34, and the bucket cylinder 36 in accordance with an operation command from an operating unit (not shown). And the discharge direction is controlled.
[0018]
On the other hand, the driving force of the engine 22 is transmitted to the generator 23 via the speed increasing mechanism 29. The generator 23 generates predetermined AC power, and the generated AC power is converted into DC by the controller 27 and the like and stored in the battery 24. On the other hand, DC power from the controller 27 or the battery 24 is converted into a pulse signal having a predetermined voltage and frequency by the inverter 28 and input to the electric motor 25. As will be described later, when the electric motor 25 is used with generator characteristics when the upper-part turning body 20 is decelerated, the electric power regenerated by the electric motor 25 is converted into direct current and stored in the battery 24.
[0019]
As the electric motor 25, a DC brushless motor (also referred to as an IPM: Internal Permanent Magnet motor) using a rare earth permanent magnet as a rotor is used. When the electric motor 25 is used with electric motor characteristics when the upper swing body 20 is accelerated to rotate, the controller 27 and the inverter 28 are arranged so that the armature and the field position of the DC brushless motor are always advantageous for torque generation. Is detected and armature DC feedback control is performed. Furthermore, the field weakening control is performed by changing the timing of the current flowing through the armature and slightly shifting the rotational position of the strongest field and the peak position of the current, and in a region where the torque decreases as the rotational speed increases. The torque is increased.
[0020]
The rotation speed-torque characteristic of the electric motor 25 is shown in FIG. In the figure, the broken line shows the rotational speed-torque characteristic when there is no magnetic saturation, and the solid line shows the actual rotational speed-torque characteristic subjected to field-weakening control. Since the motor output is represented by the product of torque and rotation speed, high output can be obtained with a small motor by increasing the rotation speed (or increasing the torque at the same rotation speed) by performing field-weakening control. Can do. In the present embodiment, when the upper swing body 20 is turned and decelerated, the electric motor 25 is used with the generator characteristics as described later.
[0021]
Next, FIG. 4 shows the relationship between the rotational speed N of the electric motor 25 and the torque T in the turning drive device of this embodiment. In FIG. 4, a region where the rotational speed N is positive is left-turning, and a region where N is negative is turning right. The first quadrant shows a case where the electric motor 25 is used with motor characteristics during left turn acceleration, and the fourth quadrant shows a case where the electric motor 25 is used with generator characteristics during left turn deceleration. The third quadrant shows the case where the electric motor 25 is used with motor characteristics during right turn acceleration, and the second quadrant shows the case where the electric motor 25 is used with generator characteristics during right turn deceleration.
[0022]
As can be seen from FIG. 4, at the time of turning acceleration shown in the first quadrant and the third quadrant, the output torque of the electric motor 25 is constant in the region below the predetermined rotational speed, and according to the increase in the rotational speed in the region above the predetermined rotational speed. Control is performed so that the output torque decreases. Further, at the time of turning deceleration shown in the second quadrant and the fourth quadrant, the electric motor is used with the generator characteristics, and the absorption torque of the electric motor is controlled to a constant value regardless of the rotational speed.
[0023]
The characteristic drawn with a thick solid line in FIG. 4 represents a case where the control is performed with the maximum torque T ₀ of the turning system in the present embodiment. If the system can control the turning torque, it is indicated by an arrow in the figure. as, for example, to start the turning torque T _1, to start decelerating torque T _2, any characteristics can be obtained.
[0024]
For comparison, a case will be described in which the electric motor 25 is used with the characteristic that the torque decreases as the number of rotations increases during turning deceleration as in the conventional example. When the electric motor 25 is decelerated with electric motor characteristics, that is, when reverse torque is generated in the electric motor, braking is performed in the reverse direction along the rotational speed-torque characteristic of the electric motor shown in FIG. For example, when the rotational speed at the start of deceleration is between Na and Nb, the higher the rotational speed N at the start of deceleration, the smaller the braking torque and the smaller the braking force. Therefore, the time until stopping and the braking distance become longer. In addition, if a large output motor with a wide torque constant region is used, the characteristics at the time of turning deceleration as shown in the second quadrant and the fourth quadrant of FIG. 4 can be obtained, but the motor itself becomes large, This is contrary to the miniaturization of the electric motor which is the object of the present invention, and is not appropriate.
[0025]
FIG. 5 shows the relationship between the rotational speed N and torque T when the electric motor 25 in the turning drive device of the present embodiment is decelerated with electric motor characteristics as in the conventional example. In FIG. 5, a region where the rotational speed N is positive is left-turning, and a region where N is negative is turning right. The first quadrant shows a case where the electric motor 25 is used with electric motor characteristics during left turn acceleration, and the fourth quadrant shows a case where the electric motor 25 is used with electric motor characteristics during left turn deceleration. The third quadrant shows a case where the electric motor 25 is used with electric motor characteristics during right turn acceleration, and the second quadrant shows a case where the electric motor 25 is used with electric motor characteristics during right turn deceleration.
[0026]
FIG. 6 shows the relationship between the braking force, the braking time, and the braking distance. In FIG. 6, the horizontal axis represents time, and the vertical axis represents the rotation speed (angular velocity ω (rad / s)) and braking distance (rotation angle θ (rad) from the start to stop of braking) of the motor 25. A curve denoted by ω represents braking force, and a curve denoted by θ represents braking distance. Each solid line indicates a case where the braking force is large, and a broken line indicates a case where the braking force is small.
[0027]
Next, the difference between the motor characteristics and the generator characteristics of the motor 25 will be described using a DC motor as an example. The power supply voltage is E ₀ , the internal resistance of the motor is R, the current flowing through the motor is i, the counter electromotive force constant of the motor is K, and the angular velocity of the rotor of the motor is ω.
[0028]
When used with motor characteristics, in steady state,
E ₀ = Ri + Kω, therefore i = (E ₀ −Kω) / R (1)
Holds. The current i is expressed by the above formula (1). As the angular velocity ω increases, the back electromotive force increases and the current decreases. Since the torque of the motor is proportional to the current, the braking torque is also reduced by the amount that the current does not flow easily.
[0029]
On the other hand, when used with generator characteristics, in steady state,
E ₀ = Ri−Kω, therefore i = (E ₀ + Kω) / R (2)
Holds. The current i is expressed by the above equation (2). As the angular velocity ω increases, the back electromotive force increases, the current increases, and the braking torque also increases. In the case of motor characteristics, Fleming's left-hand rule is followed. In the case of generator characteristics, Fleming's right-hand rule is followed. Therefore, in the generator characteristics, the direction of the force is reversed as compared with the case of the motor characteristics, and a braking force is generated. In the case of a DC brushless motor, regenerative braking is performed only by inputting a chopper at the timing of rotating in the direction opposite to the current rotation direction.
[0030]
As described above, when the electric motor is used with the generator characteristics, the braking force can be increased by increasing the current value. However, when the current value increases, the efficiency of the electric motor decreases and internal heat generation increases, which may cause insulation breakdown of the coil. On the other hand, the turning drive device of the construction machine is not always driven, and the amount of one turn is about 180 degrees at the maximum. Also, the braking time by the electric motor is at most about several seconds. Therefore, the heat capacity of the electric motor can be calculated with a short-time rating, and no particular problem occurs even if a small electric motor 25 is used.
[0031]
Although the above embodiment has been described by taking an excavator as an example, the present invention is not limited to this, and any swing drive device using an electric motor as an actuator such as a mobile crane or a stationary crane can be used. Needless to say, it can be applied to construction machinery.
[0032]
【The invention's effect】
As described above, according to the turning drive device for a construction machine of the present invention, the electric motor is used as an actuator to drive the upper turning body with respect to the lower traveling body. It is characterized in that the motor is used as a generator characteristic during turning deceleration, and different torque characteristics are used during turning acceleration and turning deceleration.
[0033]
That is, at the start of turning deceleration, the motor is used with the generator characteristics instead of the normal motor characteristics, so that the braking force is large, and the time and braking distance from the start of braking to the stop can be shortened.
[0034]
In addition, when using the motor with generator characteristics, the maximum value of the absorption torque of the motor is controlled to a constant value regardless of the rotational speed, so that a constant and maximum braking force can be obtained from the start of braking. it can.
[0035]
Furthermore, in the region of the predetermined number of revolutions or more during turning acceleration, it is possible to obtain a large output while being a small motor by performing field-weakening control of the motor.
[0036]
Furthermore, by regenerative braking of the electric motor during turning deceleration, the electric power generated during braking can be stored in the battery, and energy saving can be achieved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an excavator as an embodiment of a turning drive device for a construction machine according to the present invention.
FIG. 2 is a diagram illustrating a block configuration of a control system according to the embodiment.
FIG. 3 is a diagram showing a rotational speed-torque characteristic of a general electric motor.
FIG. 4 is a diagram showing the relationship between the rotational speed N and torque T of the electric motor in the turning drive device of the one embodiment.
FIG. 5 is a diagram showing the relationship between the rotational speed N and torque T of an electric motor when the turning drive device of the one embodiment is controlled by a method similar to that of a conventional example as a comparative example.
FIG. 6 is a diagram illustrating a difference in braking time and braking distance between the control method of the embodiment and the conventional control method.
[Explanation of symbols]
10: Lower traveling body 11: Crawler 12: Crawler frame 13: Hydraulic motor for right traveling 14: Hydraulic motor for left traveling 20: Upper rotating body 21: Turning frame 22: Engine 23: Generator 24: Battery 25: Electric motor 26: Turning mechanism 27: Controller 28: Inverter 29: Speed increasing mechanism 30: Excavator mechanism 31: Boom 32: Boom cylinder 33: Arm 34: Arm cylinder 35: Bucket 36: Bucket cylinder 40: Hydraulic control mechanism 41: Hydraulic pump 42: Hydraulic control valve

Claims (3)

A swing drive device for a construction machine that uses an electric motor as an actuator to drive the upper swivel with respect to the lower traveling body, and uses the motor with the motor characteristics when accelerating the turn and uses the motor with the generator characteristics when decelerating the turn. When using torque characteristics that differ between turning acceleration and turning deceleration, and when using the motor with generator characteristics, the maximum absorption torque of the motor must be controlled to a constant value regardless of the rotational speed. A swing drive device for a construction machine. Turning the place that put when accelerating at a constant rotational speed or more regions, swing drive system for a construction machine according to claim 1 Symbol mounting, characterized in that the field-weakening control of the electric motor. 3. The turning drive device for a construction machine according to claim 1, wherein the electric motor is regeneratively braked during turning deceleration.

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