JP3758568B2 - ELECTRIC HYDRAULIC CIRCUIT AND CONSTRUCTION MACHINE WITH THE SAME - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrohydraulic circuit configured to drive a hydraulic pump for a hydraulic actuator with an electric motor, and a construction machine including the same.
[0002]
[Prior art]
Conventionally, in a construction machine such as a hydraulic excavator or a crane, a hydraulic pump is driven by an electric motor, and hydraulic actuators such as a hydraulic cylinder and a hydraulic motor are driven by pressure oil discharged from the hydraulic pump (hereinafter referred to as an electric drive type hydraulic circuit). This is known as an electric hydraulic circuit).
[0003]
In this type of electrohydraulic circuit, when an operating lever (or operating means such as an operating pedal) is operated, the operating angle is converted into an electrical signal, and the controller controls the rotation speed of the motor according to the magnitude of the electrical signal. The hydraulic oil is discharged from the hydraulic pump in proportion to the controlled rotational speed.
[0004]
By the way, a hydraulic excavator as a construction machine may perform leveling of the ground or spreading of earth and sand in addition to excavation work by operating a drilling attachment provided in the upper swing body.
[0005]
This earth and sand spreading work is carried out, for example, when covering the pipe installed in the groove with earth and sand, storing the earth and sand in the bucket, extending the arm and quickly moving the bucket back and forth in a short cycle. The operation of shaking is performed.
[0006]
[Problems to be solved by the invention]
When the above-mentioned electrohydraulic circuit is mounted on a construction machine in which such an operation is performed, the control valve spool can be switched following the quick reciprocating operation of the operation lever, but the motor is in the neutral position of the operation lever. Since the rotation stops once, if the operating lever is further operated from the neutral position to the opposite side, the motor with slow response cannot follow the rotation speed and remains at a halfway rotation speed that does not reach the desired rotation speed. End up. As a result, the bucket cannot be swung quickly in the front-rear direction, and the inconvenience that the work of spreading the earth and sand cannot be performed occurs.
[0007]
The present invention has been made in consideration of the problems in the conventional hydraulic excavator equipped with the above-described electrohydraulic circuit, and is a range in which the operating amount of the operating lever is small, particularly when the operating lever is operated for reciprocal switching. It is an object of the present invention to provide an electrohydraulic circuit capable of eliminating a response delay of an electric motor that occurs in the vicinity of a neutral position, and a construction machine including the same.
[0008]
[Means for Solving the Problems]
The electrohydraulic circuit of the present invention includes a hydraulic pump driven by an electric motor, a switching valve for switching the direction and flow rate of pressure oil discharged from the hydraulic pump, and a hydraulic actuator to which pressure oil controlled by the switching valve is supplied And an operating means for giving a switching command to the switching valve and commanding the rotational speed to the electric motor, a control means for controlling the rotational speed of the electric motor based on the command from the operating means, and an operation for detecting the operating speed of the operating means A speed detecting means, wherein the control means controls the rotation speed of the electric motor to a set rotation speed when the operation amount of the operation means is returned to zero according to the operation speed detected by the operation speed detection means. And the second control for controlling the motor speed based on the operation amount when the operation amount is returned to zero. To.
[0009]
According to the present invention, when the operation speed when returning the operation means to zero is switched to the first control when the operation speed is high, and when the operation speed is low, the control is switched to the second control, for example, an operation lever as the operation means Since the rotation of the electric motor does not stop at the neutral position even if it is operated further to the opposite side beyond the neutral position, the response delay of the electric motor can be eliminated. In addition, when the operating lever is returned to the neutral position at a slow operating speed, the motor speed is controlled following the operating amount of the operating lever, so the motor can be stopped as in the conventional operation. it can.
[0010]
In the electrohydraulic circuit, the control means is preferably configured to switch to the first control when the operation speed detected by the operation speed detection means exceeds the response speed of the electric motor.
[0011]
In addition, the control means can be configured to determine a control period based on the set rotational speed in accordance with the operation speed detected by the operation speed detection means. If the period for controlling the motor at the set speed is determined according to the operation speed, the motor can be operated at the set speed only when the motor is operated faster than the response speed of the motor, for example. become.
[0012]
In the present invention, the set rotational speed is at least the rotational speed at which the discharge flow rate of the hydraulic pump with respect to the operation amount of the operating means is stably obtained regardless of the load, and specifically, approximately 30% of the maximum rotational speed. The corresponding number of revolutions.
[0013]
The construction machine of the present invention has a lower traveling body, an upper swing body mounted on the lower traveling body, and a front attachment equipped on the upper swing body, and a bucket as the hydraulic actuator is provided on the front attachment. A gist is that a bucket cylinder to be driven is provided, and an electrohydraulic circuit having the above-described configuration for driving the bucket cylinder is provided in the upper swing body.
[0014]
In accordance with the present invention, when the bucket is shaken back and forth in a short cycle to perform the sand and sand dispersion operation, the motor is operated at the neutral position even if the operation lever as the operation means is reciprocated via the neutral position. Since the motor does not stop, the response delay of the electric motor is eliminated, and the bucket can be operated according to the operation lever.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on the embodiments shown in the drawings.
[0016]
FIG. 1 shows an embodiment of an electrohydraulic circuit according to the present invention.
[0017]
In the figure, reference numeral 1 denotes a hydraulic cylinder as a hydraulic actuator, which has a head side oil chamber 1a and a rod side oil chamber 1b, and expands and contracts by supplying and discharging pressure oil to and from both oil chambers 1a and 1b. Operation is to be performed.
[0018]
A constant displacement hydraulic pump 2 is provided as a hydraulic pump for supplying pressure oil to the hydraulic cylinder 1, and a control valve 3 as a switching valve is connected between the hydraulic pump 2 and the hydraulic cylinder 1.
[0019]
The control valve 3 is switched from the neutral position a to the cylinder extension position b or from the neutral position a to the cylinder reduction position c by the movement of the valve spool. The extension side solenoid 3a and the reduction side solenoid 3b are respectively controlled by the control means. Are connected to the controller 4. A bleed-off circuit 3c for returning excess pressure oil to the tank T is connected to the neutral position a.
[0020]
The hydraulic pump 2 is driven by an electric motor 5, the speed of the electric motor 5 is controlled by an inverter 6, and the inverter 6 is controlled by the controller 4.
[0021]
The controller 4 is connected to an operation lever 7 as an operation means. The operation lever 7 includes a lever 7a itself and a converter 7b that converts an operation angle of the lever 7a into an electric signal.
[0022]
Killing the lever 7a from the neutral position in the direction d, the operation angle signal S ₁ is supplied to the control valve switching section 4a of the controller 4. The control valve switching unit 4a gives a switching signal S ₃ corresponding to the operation angle with respect to the expansion side solenoid 3a of the control valve 3 to switch the valve spool of the control valve 3 from the neutral position a to the position b, whereby the hydraulic pump 2 Is supplied to the head side oil chamber 1a of the hydraulic cylinder 1, and the rod 1c extends.
[0023]
Conversely, when defeat lever 7a from the neutral position in the direction e, the operation angle signal S ₂ is applied to the control valve switching unit 4a, applied switching signal S ₄ on the reduced side solenoid 3b of the control valve 3 Then, the valve spool is switched from the neutral position a to the c position, the pressure oil from the hydraulic pump 2 is supplied to the rod-side oil chamber 1b of the hydraulic cylinder 1, and the rod 1c is contracted.
[0024]
Then, when the lever 7a is reciprocated between the d-direction side and the e-direction side with the neutral position as a boundary, the rod 1c of the hydraulic cylinder 1 moves forward and backward.
[0025]
The function of the controller 4 will be described later. In brief, the operation angle signal S ₁ or S ₂ output by lever operation is given to the control valve switching unit 4a, and further, an operation speed calculation as an operation speed detecting means is performed. Given to part 4b.
[0026]
When the lever 7a is operated, the operation speed calculation unit 4b calculates the operation speed, gives the calculated operation speed to the comparison unit 4c and compares it with the motor response speed, and the result is a rotational speed control as a control means. To part 4d.
[0027]
The rotation speed control unit 4d selects the motor rotation speed characteristic stored in the rotational speed characteristic storage unit 4e according to the comparison result, given the speed signal S ₅ to the inverter 6 in accordance with the rotational speed characteristics, whereby, The rotation speed of the electric motor 5 whose rotation is controlled by the inverter 6 is controlled from a low speed rotation range (for example, 100 rpm) to a high speed rotation range (for example, 3000 rpm). In the figure, 8 indicates a check valve.
[0028]
FIG. 2 shows a hydraulic excavator to which the electrohydraulic circuit is applied.
[0029]
In the figure, 10 is a lower traveling body, 11 is an upper revolving body that is rotatably mounted on the lower traveling body 10, and 12 is an excavation attachment (front attachment) that is mounted on the front of the upper revolving body 11. is there.
[0030]
The excavation attachment 12 includes a boom 12a, a boom cylinder 12b for raising and lowering the boom 12a, an arm 12c connected to the tip of the boom 12a, an arm cylinder 12d for swinging the arm 12c, and a tip of the arm 12c. And a bucket cylinder 12f that pushes and pulls the bucket 12e.
[0031]
The lower traveling body 10 has crawlers 10b mounted on left and right crawler frames 10a (only the front side is shown), and the crawler 10b is driven by a traveling motor 10c.
[0032]
The hydraulic circuit shown in FIG. 1 can be applied to a specific or all hydraulic actuators in this hydraulic excavator, but is particularly preferably applied to a bucket drive circuit in which a sudden switching operation is performed.
[0033]
Hereinafter, the case where the electrohydraulic circuit shown in FIG. 1 is applied to the bucket drive circuit will be described. In the following description, the hydraulic cylinder 1 is referred to as a bucket cylinder 12, and the cylinder extension side is described as the bucket pulling side, and the cylinder reduction side is described as the bucket pushing side.
[0034]
By operating the lever 7a as described above, the displacement of the valve spool and the motor rotation speed are commanded from the controller 4, but if the lever 7a is suddenly operated, the valve spool with good responsiveness will follow, but the motor with poor responsiveness will follow. As for No. 5, the rotation speed cannot follow the lever operation, and as a result, the displacement of the valve spool is also affected and shifts.
[0035]
Specifically, when the bucket 12e is shaken to perform the earth and sand dispersion operation, the bucket 12e is quickly and repeatedly switched between pushing (e direction) and pulling (d direction) of the lever 7a via the neutral position. If the motor speed is reduced in proportion to the decrease in the lever operating angle as in the conventional motor rotation speed characteristic (see characteristic N in FIG. 3), the lever 7a is moved. When switching from the + side (bucket pulling side) to the-side (bucket pushing side), the motor 5 temporarily stops. Therefore, when the motor 5 shifts to the-side, the rotation of the motor 5 does not quickly start up and the bucket operates slowly. . If it does so, it will become impossible to vibrate the bucket 12e little by little, and the operation | work which spreads earth and sand over a wide range cannot be performed.
[0036]
Accordingly, in the present embodiment, the rotational speed characteristic M and the bleed-off characteristic B shown in FIG.
[0037]
In the figure, the horizontal axis indicates the lever operation angle (lever operation amount), the upper limit of the operation range on the bucket pulling side is + 100% from the neutral position “0”, and the upper limit of the operation range on the bucket pushing side is −100%. Show. The vertical axis indicates the motor rotation speed and the bleed-off opening area in percent, and 100% as the upper limit of the rotation speed corresponds to approximately 3000 rpm in this embodiment.
[0038]
In the operating range on the + side, the rotational speed characteristic M1 rises up to the rotational speed N1 at the lever operating angle L1, reaches a constant speed until the lever operating angle L2, and rotates from the lever operating angle L2 in proportion to the lever operating angle. Is set to increase. The rotational speed characteristic M1 is also set symmetrically with respect to the minus side operation range (see the rotational speed characteristic M2 in the figure).
[0039]
The rotational speed N1 is set to a speed slightly lower than the medium speed range, specifically 1000 rpm. In this embodiment, N1 is set to be flat, but may have a gradient so as to increase gradually.
[0040]
On the other hand, the bleed-off characteristic B1 is opened to an opening area of 100% in a range where the lever operating angle is less than + L1, is decreased as the lever operating angle increases, and is closed to 0% near + L2. Accordingly, when the bleed-off characteristic B2 in the -side lever operation range is also included, the range L between -L2 and + L2 in the figure becomes the bleed-off region.
[0041]
Conventionally, when the lever 7a is switched back and forth via the neutral position, the rotation of the electric motor 5 is once stopped at the neutral position. Therefore, even if the operation angle of the lever 7a is increased by shifting to the negative side, The rotational speed could not follow and the pump flow rate was insufficient.
[0042]
On the other hand, the controller 4 of the present invention controls the rotation of the electric motor 5 according to the rotational speed characteristic M1 in the + side operation range, for example, but in the range of + L1 to + L2, the rotational speed is set to N1 close to the medium speed range. In addition, when the lever 7a is suddenly operated from the + side to the-side with the neutral position as a boundary, the rotation speed is maintained at N1 even if the lever 7a is returned to the neutral position (in the figure, as the set rotation speed). Therefore, when the lever 7a is operated deeply by shifting to the negative side, the rotational speed of the electric motor 5 is preliminarily accelerated halfway. Response delay can be reduced.
[0043]
Similarly, when operating from the-side to the + side, the rotational speed is kept at N1 (see the set rotational speed P2 as the set rotational speed in the figure).
[0044]
When the electric motor 5 is operated at the set rotational speeds P1 and P2, the response delay of the electric motor can be eliminated even if the lever 7a is operated across the neutral position.
[0045]
When the lever 7a is operated across the neutral position, the valve spool of the control valve 3 follows the operation of the lever 7a and returns to the neutral position a. Therefore, excess pressure oil is removed from the bleed-off circuit 3c. It is returned to the tank T through.
[0046]
It should be noted that the relationship between the motor rotation speed and the bleed-off opening area is not necessarily proportional when the lever operation amount is in the range of + L1 to + L2 (or -L1 to -L2), but the gradient of pressure rise or pressure drop is slightly steep. There is no problem in practical use.
[0047]
Further, the controller 4 of the present embodiment is configured to control the period of operation at the set rotational speed P1 or P2 based on the return speed of the lever 7a.
[0048]
First, the response speed of the electric motor 5 can be measured in advance. That is, when the amount of change in the rotation speed of the motor is ΔNd and the time required for the rotation speed to reach the commanded rotation speed when a command is given from the operation lever 7 is Δsd, the response speed S of the motor is ΔNd / It is obtained by Δsd.
[0049]
On the other hand, the operation speed calculation unit 4b calculates the operation speed when the lever 7a is operated. When the change amount of the command rotational speed when the lever 7a is returned is ΔNd ′ and the time required for the return operation is Δsd ′, the lever return speed S ′ is obtained from ΔNd ′ / Δsd ′.
[0050]
The comparison unit 4c compares the response speed S of the motor with the operation speed S ′ and gives the result to the rotation speed control unit 4d. When the lever return speed S ′ is slower than the motor response speed S, the rotation speed control unit 4d rotates the motor 5 according to the motor rotation speed characteristic M stored in the rotation speed characteristic storage unit 4e as the second control. To control. In this case, when the lever 7a is returned to the neutral position, the lever operation amount is maintained at the rotational speed N1 in the range of + L2 → + L1, and the lever operation amount is decreased from the point m1 to zero in the range of + L1 → zero.
[0051]
On the other hand, when the lever return speed S ′ is faster than the motor response speed S, the set speed P1 (or P2) is set in the motor speed characteristic M stored in the speed characteristic storage unit 4e as the first control. The rotational speed of the electric motor 5 is controlled according to the added characteristics. Specifically, in the range where the lever operation amount exceeds + L1, the electric motor 5 is controlled according to the motor rotation speed characteristic M as in the second control, but when the lever operation amount falls below + L1, the motor rotation speed N1 is held for a certain period. The electric motor 5 is controlled according to the set rotational speed P1. The holding period of the set rotational speed P1 is made proportional to the lever return speed.
[0052]
Specifically, it is assumed that the lever operation is returned from + L3 to + L1, thereby changing the motor rotation speed by N2. If the lever operation time required from + L3 to + L1 is Δsd ′, when N2 / Δsd ′> ΔNd / Δsd, the set rotational speed P1 is maintained. The holding period of the set rotational speed P1 is determined by the following equation.
[0053]
When the lever operation is continuously operated from + L3 → + L1 → −L1, specifically, when the bucket 12e is operated from the pull side to the push side beyond the neutral position, the time that the lever 7a is returned from + L3 to + L1 is Δsd When it is ′, the lever operation time required for + L1 → zero and zero → −L1, that is, 2L1, is obtained by the ratio, and is obtained by Δsd ′ × 2L1 / (L3−L1).
[0054]
If the electric motor 5 is controlled at the set rotational speed P1 for at least this period, theoretically, the response delay of the electric motor 5 can be eliminated. However, in actual control, a margin α is added to this,
(1 + α) × Δsh × 2L1 / (L3-L1)
The motor 5 is controlled at the set rotational speed P1 for the period obtained in step (1).
[0055]
As described above, when the operating lever 7 is operated to return beyond the response speed of the electric motor 5, the controller 4 maintains the electric motor rotation speed at N1 without dropping to zero at the lever neutral position and sets the holding period of the lever 7a. It is configured to be determined according to the operation speed.
[0056]
In the above embodiment, the measurement point of + L3 is set on the horizontal axis for the purpose of detecting the operation speed of the lever 7a, but this measurement point can be substituted by + L2. In this case, control of the controller 4 becomes easier.
[0057]
In the above embodiment, the lever 7a is operated from the + side to the − side, specifically, the case where the bucket cylinder 12f that has been extended is reduced is described as an example. However, the lever 7a is operated from the − side to the + side. Specifically, even when the bucket cylinder 12f that has been reduced is extended, the same control as described above, that is, when the lever 7a is suddenly operated and the operation of crossing the neutral position is performed, from the point m2. Control for holding the motor rotation speed N1 for a certain period is performed.
[0058]
The present invention is not limited to the construction machine shown in the above embodiment, but can be applied to a construction machine having an arbitrary configuration in which a hydraulic pump for driving a hydraulic actuator is driven by an electric motor.
[0059]
【The invention's effect】
As is apparent from the above description, according to the present invention of claim 1, the hydraulic pump is driven by an electric motor, and the rotation speed of the electric motor is controlled by the control means based on a command from the operating means. In the electrohydraulic circuit, the control means controls the rotation speed of the motor to the set rotation speed when the operation amount of the operation means is returned to zero according to the operation speed detected by the operation speed detection means. And, when the operation amount is returned to zero, since it is configured to switch to one of the second control for controlling the motor rotation speed based on the operation amount, the operation speed when returning the operation means to zero is high If the control is switched to the first control and the control is switched to the second control when the operation speed is slow, for example, the operation lever as the operation means is returned, and the operation is performed further to the opposite side beyond the neutral position. Since the rotation of the motor at the neutral position even if not stop, it is possible to eliminate the response delay of the motor. In addition, when the operating lever is returned to the neutral position at a slow operating speed, the motor speed is controlled following the operating amount of the operating lever, so the motor can be stopped as in the conventional operation. it can.
[0060]
According to the present invention of claim 2, since the control means is configured to switch to the first control when the operation speed detected by the operation speed detection means exceeds the response speed of the motor, the response delay of the motor is reduced. It can be surely solved.
[0061]
According to the present invention of claim 3, since the control means is configured to determine a control period based on the set rotational speed in accordance with the operation speed detected by the operation speed detection means, the response speed of the motor The motor can be operated at the set rotational speed only when the operating means is operated faster than this.
[0062]
According to this invention of Claim 4, in the construction machine which has a lower traveling body, the upper turning body mounted in the lower traveling body, and the front attachment with which the upper turning body is equipped, this front attachment has the above-mentioned A bucket cylinder that drives the bucket is provided as a hydraulic actuator, and an electro-hydraulic circuit having the above-described configuration for driving the bucket cylinder is provided. Therefore, when the bucket is shaken back and forth in a short cycle, the operation is performed when the earth and sand are dispersed. For example, even if the operation lever as a means is reciprocated via the neutral position, the electric motor does not stop at the neutral position, the response delay of the electric motor is eliminated, and the bucket can be operated as the operation lever. .
[Brief description of the drawings]
FIG. 1 is an electrohydraulic circuit diagram according to the present invention.
FIG. 2 is an external view of a construction machine to which the electrohydraulic circuit of the present invention is applied.
FIG. 3 is a rotation speed characteristic diagram of an electric motor controlled by the controller shown in FIG. 1;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Hydraulic cylinder 2 Hydraulic pump 3 Control valve 4 Controller 4a Control valve switching part 4b Operation speed calculating part 4c Comparison part 4d Rotational speed control part 4e Rotational speed characteristic memory | storage part 5 Electric motor 6 Inverter 7 Operation lever 7a Lever 10 Lower traveling body 11 Upper part Revolving body 12 Excavation attachment

Claims (4)

A hydraulic pump driven by an electric motor, a switching valve for switching the direction and flow rate of pressure oil discharged from the hydraulic pump, a hydraulic actuator to which pressure oil controlled by the switching valve is supplied, and a switching command to the switching valve Operating means for giving a rotational speed to the motor, control means for controlling the rotational speed of the motor based on a command from the operating means, and an operating speed detecting means for detecting the operating speed of the operating means, With
The control means is a first control for controlling the rotational speed of the motor to a set rotational speed when the operation amount of the operating means is returned to zero according to the operating speed detected by the operating speed detecting means; An electrohydraulic circuit configured to switch to one of the second controls for controlling the motor rotation speed based on an operation amount when the operation amount is returned to zero. The electrohydraulic circuit according to claim 1, wherein the control means switches to the first control when the operation speed detected by the operation speed detection means exceeds a response speed of the electric motor. The electrohydraulic circuit according to claim 1 or 2, wherein the control means is configured to determine a control period based on the set rotational speed in accordance with the operation speed detected by the operation speed detection means. A lower traveling body, an upper swing body mounted on the lower traveling body, and a front attachment mounted on the upper swing body, a bucket cylinder for driving a bucket as the hydraulic actuator is provided on the front attachment. A construction machine equipped with an electrohydraulic circuit, wherein the upper rotating body is provided with the electrohydraulic circuit according to any one of claims 1 to 3 for driving the bucket cylinder.

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