JP3256425B2 - Hydraulic control circuit for hydraulic motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of hydraulic motors used for various machines such as construction machines and industrial machines.

[0002]

2. Description of the Related Art Generally, in order to stop a driven hydraulic motor, supply of hydraulic oil from a hydraulic supply source is cut off. In this case, however, there is no relief at the outlet side oil passage of the hydraulic motor. An abnormally high pressure state occurs, and a surge pressure is generated by the inertia of the hydraulic motor itself and the load, and an impact is generated. For this reason, for example, when the supply of pressure oil is cut off, a part of the oil flowing through the outlet-side oil passage is applied to the inlet-side oil passage while applying back pressure to the outlet-side oil passage of the hydraulic motor when the supply of pressurized oil is cut off. A braking circuit is provided for supplying and braking the hydraulic motor. However, since the braking circuit is configured to be closed when the pressure of the outlet side oil passage becomes equal to or less than the back pressure, the surge pressure is not sufficiently absorbed, and the hydraulic motor swings back. Not only is smooth stop impaired, but there is also a risk that the stop position of a rotating body (for example, an upper swing body of a hydraulic shovel) that is rotated by a hydraulic motor may be shifted.

[0003]

Conventionally, as shown in FIG. 5, in addition to the braking circuit A, a throttle valve passage for connecting an outlet oil passage and an inlet oil passage to a hydraulic circuit of a hydraulic motor 1 as shown in FIG. There is one in which an anti-reversing valve 21 provided with 21a is provided. However, since the reversing prevention valve 21 has a complicated structure, the cost is not only high, but also the throttle valve path 21a is opened not only by the pressure of the outlet side oil path but also by the pressure of the inlet side oil path. When starting or driving the motor 1,
There is a problem that the pressure oil in the inlet-side oil passage flows to the outlet-side oil passage through the throttle valve passage 21a, and the rotational force of the hydraulic motor is reduced. Further, a stop device (parking brake device) is provided to prevent the hydraulic motor or the rotating body rotated by the hydraulic motor from being inadvertently rotated when an external load acts while the hydraulic motor is stopped. Sometimes. In this case, when the pressure oil supply from the pressure oil supply source to the hydraulic motor is changed from the supply stopped state to the supply state, the stopping device is automatically released, and the supply state is changed from the supply state to the supply stopped state. There is a device that automatically activates the stop device upon detection of this.However, in this device, if the stop device works while the hydraulic motor is still rotating, the wear of the stop device will increase, so the hydraulic motor It is preferable that the stopping device is operated after the stop is securely performed. Conventionally, when it is detected that the supply state has been changed from the supply state to the supply stop state, the stop device is operated in a state where there is a time delay (margin) until the hydraulic motor completely stops after the brake state. A delay circuit for causing the delay is provided. However, in this case, a slight time delay occurs between the stop of the rotating body and the operation of the stopping device, so that the rotating body may move due to its own weight during the slope on a slope or the like. There are also problems.

Accordingly, the applicant of the present invention has proposed that
As disclosed in Japanese Patent No. 8701, an open / close switching valve for opening and closing a communication oil passage that communicates an outlet oil passage and an inlet oil passage is provided,
It is proposed that the switching operation of the open / close switching valve is performed based on a command from the control unit or the operation of the operation lever, whereby the hydraulic motor can swing back without using the anti-reverse valve. You can now avoid it.
However, there is still room for study on the timing of operating the stopping device, and there is a problem to be solved by the present invention.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems in view of the above-mentioned circumstances, and has been developed based on the supply of pressurized oil from a pressurized oil supply source. Hydraulic motor, hydraulic oil supply detecting means for detecting whether or not hydraulic oil is supplied from the hydraulic supply source, speed detecting means for detecting the rotational speed of the hydraulic motor, and stopping the hydraulic motor Control means for opening and closing a communication oil passage provided to communicate a pressure oil inlet side oil passage and an outlet side oil passage of a hydraulic motor, and a control unit to which these units are connected, Evacuate oil in the oil passage on the outlet side of the hydraulic motor.
And a control command output for outputting a control command to the stopping means and the opening / closing means based on detection signals from the pressure oil supply detecting means and the speed detecting means. Upon Ru provided with means,
The control command output means is configured such that the pressure oil supply detection means
When the stop state is detected, the opening / closing means is
Includes the rotational speed status of the hydraulic motor when the leaf valve closes.
The hydraulic motor to the preset low speed setting range.
Speed detection means that there is a rotation speed of
An open command is output, and the rotation speed of the hydraulic motor is
The speed detector detects that the speed is lower than
Output a close command, and the rotation speed of the hydraulic motor stops.
Is set in advance when the speed detection means detects that
The release command shall be output during the set time,
For the step, the speed detection means that the hydraulic motor has stopped
To output a closing command based on the detection of the step
It is a hydraulic control circuit device of the set hydraulic motor ,
This allows the hydraulic motor to stop almost in time
The stop device works automatically to ensure that the stop position is maintained.
The communication oil passage is open and the outlet oil passage and the inlet oil passage
And eliminates the swing-back force.
Oil passage when the hydraulic motor is started, etc.
Will remain open and the oil pressure will decrease
In this way, the low speed setting range can be avoided.
And smooth hydraulic deceleration
Can be reliably stopped. In this one,
When the pressure oil supply detection means detects the pressure oil supply state within the set time when the output of the open command to the opening / closing means is performed, the closing command is replaced with the opening command output to the opening / closing means. In this case, even when the hydraulic motor is restarted within the set time, the communication oil passage is opened and the oil pressure is prevented from being reduced. it can. Further, by providing the communication oil passage or the opening / closing means with a throttle function, a part of the outlet oil passage is supplied to the inlet oil passage in a state where the communication oil passage is open. Further, the amount of oil flowing through the communication oil passage can be adjusted by making the opening / closing means or the throttle function adjustable. In these things,
The opening / closing means or the throttle function can adjust the opening amount. In yet these things, the relief valve, when the pressure oil supplied from the pressurized oil source is interrupted, part of the oil flowing through the outlet side oil passage while applying back pressure on the outlet side hydraulic passage of the hydraulic motor Is supplied to the inlet-side oil passage to apply braking to the hydraulic motor, and the supply of oil to the inlet-side oil passage of the relief valve is performed by setting the oil pressure of the outlet-side oil passage to a preset pressure. It is set until the damping, and the start of the opening command output to the opening / closing means of the control command output means assuming that the low speed setting range is reached, the oil supply amount to the inlet side oil passage of the relief valve is set in advance. Start of the closing command output to the opening / closing means of the control command output means assuming that the speed has fallen below the low speed setting range,
By performing the setting after the supply of oil to the oil passage on the inlet side of the relief valve is stopped, a smooth deceleration operation after the operation of the braking unit is stopped can be performed. In this case, it is preferable that the preset amount is set to about several times the amount of oil supplied to the inlet side oil passage via the communication oil passage when the opening / closing means is fully opened. By doing so, the communication oil passage is opened immediately before the operation of the braking means is stopped, and a smoother operation can be performed without feeling a shock caused by a temporary reduction of the braking force caused by the opening of the communication oil passage. A deceleration operation can be performed. Still further, the pressure oil supply detection means detects an operation state of an operation means operated to supply pressure oil to the hydraulic motor, or a direction switching valve provided in a pressure oil supply circuit to the hydraulic motor. It can be configured to detect the switching state. As a hydraulic motor provided with such a hydraulic control circuit device, there is a turning motor or the like for turning an upper turning body of a construction machine.

[0006]

Next, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 1 denotes a hydraulic motor for turning an upper revolving structure provided on a hydraulic excavator, and pressure oil from a hydraulic pump 2 is supplied to the hydraulic motor 1 via a direction switching valve 3. On the other hand, the oil discharged from the hydraulic motor 1 is configured to return to the oil tank 4 again via the direction switching valve 3, but the oil is discharged to the oil passage between the direction switching valve 3 and the hydraulic motor 1. Is provided with a braking circuit A and a communication oil passage B as described later.

The direction switching valve 3 is a three-position switching valve. The first port 3a is for the hydraulic pump 2, the second port 3b is for the oil tank 4, and the third port 3c is the left turning of the hydraulic motor 1. The side port 1a and the fourth port 3d are connected to the right turning port 1b of the hydraulic motor 1, respectively.
Further, the direction switching valve 3 is formed with a left-turning pilot port 3e and a right-turning pilot port 3f.
The pilot pressure oil from the pilot pump 16 is supplied via a pilot valve 6 that is switched based on the operation of the operation lever 5.

When the pilot pressure oil is not supplied to both pilot ports 3e and 3f, the direction switching valve 3 closes the third and fourth ports 3c and 3d, and connects the first port 3a to the second port 3a. Although the port 3b is located at a neutral position communicating with the port 3b, the first port 3
a to the third port 3c and the fourth port 3d
The valve path from the hydraulic pump 2 to the second port 3b is opened, and the hydraulic oil from the hydraulic pump 2 is switched to the left turning position where it is supplied to the left turning port 1a of the hydraulic motor 1, and the right turning pilot port is switched. When the pilot pressure oil is supplied to 3f, a valve path from the first port 3a to the fourth port 3d and a valve path from the third port 3c to the second port 3b are opened, respectively. The configuration is such that the pressure oil is switched to the right turning position where the pressure oil is supplied to the right turning port 1b.

On the other hand, the braking circuit A includes a relief valve 7,
8, the check valves 9 and 10 are used. These valves 7, 8, 9 and 10 are arranged as follows.
That is, the relief valve 7 branches from the connection point D in the left turning oil passage C connecting the third port 3c of the direction switching valve 3 and the left turning port 1a of the hydraulic motor 1 to the oil tank 4. It is located in the oilway. The relief valve 8 branches from a connection point F in a right-turning oil passage E that connects the fourth port 3d and the right-turning port 1b, and extends from the relief valve 7 to the oil tank 4 in the oil passage. Are arranged in an oil passage merging with the connection point G. On the other hand, the check valve 9 is disposed in an oil passage that branches off from a connection point H in the left turn-side oil passage C and joins a connection point J in the oil passage from the connection point G to the oil tank 4. Have been. The check valve 10 is disposed in an oil passage that branches off from a connection point K in the right turn side oil passage E and joins the connection point J.

For example, when the direction switching valve 3 is switched from the left turning position to the neutral position, the right turning side oil passage E
When the oil pressure in the (outlet side oil passage) becomes higher than the relief cracking pressure of the relief valve 8, the relief valve 8 is opened, whereby the oil in the right turn side oil passage E is discharged to the oil tank 4 via the relief valve 8. On the other hand, the oil from the right turning oil passage E via the oil tank 4 or the relief valve 8 is supplied to the left turning oil passage C (the inlet oil passage) via the check valve 9. It has become. At this time, check valve 10
Prevents the oil in the right-turning oil passage E from flowing into the oil tank 4 or the left-turning oil passage C without passing through the relief valve 8.

The communication oil path B is an oil path that connects the left-turning oil path C and the right-turning oil path E. A throttle valve 12 is provided. The opening / closing switching valve 11 is an electromagnetic two-position switching valve, and is configured to switch between a closed position and a opened position where the communication oil passage B is closed based on a control command from a control unit 13 described later. Have been.

On the other hand, reference numeral 14 denotes a braking device (parking brake device) for the hydraulic motor 1, and a brake lining plate 14 a constituting the braking device 14 is pressed against a brake disk 20 fixed integrally to the hydraulic motor 1. The hydraulic motor 1 is movably provided between a stop position where the hydraulic motor 1 is stopped by contacting the brake disk 1 and a release position where the brake motor 20 is separated from the brake disk 20. And this brake lining plate 14a
Although the pressurizing oil is supplied to the release-side oil chamber 14c of the restraint device 14, the urging device 14b always moves toward the release position against the biasing force of the elastic device 14b. Is configured.

Reference numeral 15 denotes a blocking oil passage switching valve,
This is an electromagnetic three-port two-position switching valve,
The first port 15a is connected to the release-side oil chamber 14c of the braking device 14, and the second port 15b is connected to the pilot pump 16c.
The third port 15c is connected to the oil tank 4.

The valve path from the first port 15a to the third port 15c is opened, the second port 15b is closed, and the blocking oil passage switching valve 15 is released based on a control command from the control unit 13. The stop position where the oil in the side oil chamber 14c is discharged to the oil tank 4, the valve path from the second port 15b to the first port 15a is opened, and the third port 15c is closed. Is the release side oil chamber 1
4c.

On the other hand, reference numeral 18 denotes a speed detection sensor for detecting the rotation speed of the hydraulic motor 1, and 19 denotes the operation lever 5
An operation detection sensor for detecting the operation state of
The detection signals of these sensors 18 and 19 are transmitted to the controller 1
3 is input.

The control unit 13 is constituted by a microcomputer or the like. The control unit 13 is configured to open and close the switching unit based on detection signals input from the speed detection sensor 18, the operation detection sensor 19 and the like. A control command is output to the switching valve 11 and the blocking oil passage switching valve 15.

Next, the output of the control command from the control unit 13 will be described with reference to a timing chart shown in FIG. If the operating lever 5 is operated to the left or right turning side, the direction switching valve 3 is located at the left or right turning position, and the hydraulic motor 1 rotates at a constant high speed. are doing. In this rotation state, a control command is output from the control unit 13 to the open / close switching valve 11 so as to close the communication oil passage B, and a control instruction is issued to the stop oil passage switching valve 15 so as to be in the release position. Output, whereby the braking device 14 is in the release position spaced from the brake disc 20.

In this state, when the operating lever 5 is operated from the turning position to the neutral position, the direction switching valve 3 is accordingly switched from the corresponding turning position to the neutral position,
The supply of hydraulic oil to the hydraulic motor 1 via the direction switching valve 3 and the discharge of oil to the hydraulic motor 1 are cut off, and the oil pressure on the inlet side of the hydraulic motor 1 becomes negative while the oil pressure on the outlet side becomes high. When the pressure becomes high, the relief valve 7 of the braking circuit A
Or 8 is opened, whereby the oil in the outlet-side oil passage flows to the inlet-side oil passage and the oil tank 4 via the corresponding relief valve 7 or 8. Thus, a part of the oil flowing through the outlet-side oil passage is supplied to the inlet-side oil passage while applying a back pressure to the outlet-side oil passage, so that the hydraulic motor 1 having no impact is provided.
Is performed, and the rotation speed of the hydraulic motor 1 gradually decreases. When the rotation speed of the hydraulic motor 1 decreases to a preset low speed setting range, the control unit 1
An opening command is output from 3 to the open / close switching valve 11 so as to open the communication oil passage B.

Here, the predetermined low speed setting range, that is, the range of the rotation speed of the hydraulic motor 1 in which the communication oil passage B is opened, is determined by the pressure of the oil passage on the outlet side of the hydraulic motor 1 and the relief valves 7 and 8. When the opening / closing switching valve 11 is opened, the oil supply amount which decreases to be close to the cracking pressure and is supplied from the outlet side oil passage to the inlet side oil passage of the hydraulic motor 1 through the relief valves 7 and 8 is opened. The rotation speed of the hydraulic motor 1 when the oil supply amount is reduced to about several times the oil supply amount supplied through the communication oil passage B is substantially the upper limit, the relief valves 7 and 8 are closed, and the communication is performed. The rotation speed of the hydraulic motor 1 at which the brake pressure does not rise even when the oil passage B is closed and the outlet oil passage is closed is set to be substantially the lower limit. Thus, when the relief valves 7 and 8 of the braking circuit A are about to be changed from the open state to the closed state, the communication oil passage B is opened substantially at the same time, whereby the throttle valve provided in the communication oil passage B is opened. 12, a part of the oil in the outlet side oil passage flows to the inlet side oil passage, so that the hydraulic motor 1 can smoothly decelerate without a brake pressure even after the braking circuit A is closed. It can operate.

Further, when the rotation speed of the hydraulic motor 1 falls below the low speed setting range, the control unit 13 outputs a closing command to the open / close switching valve 11 to close the communication oil passage, Stop the motor 1 without fail. Then, when the rotation speed of the hydraulic motor 1 becomes substantially zero, the control unit 13 outputs a control command to the stop oil passage switching valve 15 to switch to the stop position, and also sends a control instruction to the open / close switch valve 11 in advance. An open command is output for a set predetermined time. Thus, the hydraulic motor 1 is stopped in the stopped state by the stopping device 14, and the communication oil passage B is opened for a predetermined time, so that the oil pressure difference between the inlet oil passage and the outlet oil passage is reduced. As a result, it is possible to reliably avoid swinging back at the time of stopping. Further, after the lapse of the predetermined time, a closing command is output from the control unit 13 to the open switching valve 11 so as to close the communication oil passage B, so that when the hydraulic motor 1 is started or the like. This avoids a situation where the communication oil passage B remains open and the hydraulic pressure to the hydraulic motor 1 drops. Further, even within the predetermined time, the operation detection sensor 19
When the control unit 13 detects that the operation lever 5 has been operated to the turning position, the control unit 13 is set to immediately output a close command to the open / close switching valve 11, whereby the control unit 13 outputs the close command within the predetermined time. However, even when the hydraulic motor 1 is restarted, the hydraulic motor 1 is started while the communication oil passage B is open, and the hydraulic pressure to the hydraulic motor 1 is reduced. It can be avoided. In this embodiment, the hydraulic motor 1
When the rotation speed of the motor is lowered to a preset low speed setting range, an opening command is output to the open / close switching valve 11 during the low speed setting range. However, as shown in FIG.
During the low speed setting range, a control command may be output to the opening / closing switching valve 11 such that the opening / closing switching operation is repeated several times or frequently. Further, as shown in FIG. The opening amount can be adjusted, and the opening of the open / close switching valve 11 is gradually reduced as the speed of the hydraulic motor 1 decreases within the low speed setting range, and is completely closed when the speed falls below the low speed setting range. You can also. Furthermore, in the present embodiment, the opening command is output to the opening / closing switching valve 11 for a predetermined time after the hydraulic motor 1 stops, but the opening / closing switching operation is repeated several times without being limited to this. Such a control command may be output. The point is that the communication oil passage B until the pressure difference between the outlet oil passage and the inlet oil passage disappears.
Just open it.

In the embodiment of the present invention constructed as described above, when the operating lever 5 is operated from the swing side to the neutral position to stop the upper swing body, as described above, first, the brake circuit A operates to operate the hydraulic motor. The braking operation of 1 is performed,
When the pressure in the outlet-side oil passage decreases and the relief valves 7 and 8 of the braking circuit A try to close, that is, when the rotation speed of the hydraulic motor 1 decreases to a preset low-speed setting range, the control unit 13 The open / close switching valve 11 is switched to the open position on the basis of the control command, the oil passage B communicating the outlet oil passage and the inlet oil passage is opened, and the smooth deceleration operation of the hydraulic motor 1 is performed. Will be When the rotational speed of the hydraulic motor 1 falls below the low speed setting range, the open / close switching valve 11 is switched to the closed position based on a command from the control unit 13 when the rotational speed of the hydraulic motor 1 falls below the low speed setting range. By closing, the hydraulic motor 1 can be reliably stopped.

Further, when the hydraulic motor 1 is stopped, that is, when the rotational speed becomes substantially zero, a control command is outputted from the control unit 13 to the blocking oil passage switching valve 15 to switch to the blocking position, and the opening / closing switching valve is opened. 11, a control command is output to switch to the open position.
Is stopped by the stopping device 14 and the communication oil passage B is opened, so that the pressure difference between the inlet oil passage and the outlet oil passage is eliminated, and the swing back at the time of the stop is reliably performed. Can be avoided.

As a result, the stopping device 14 automatically operates almost simultaneously with the stop of the hydraulic motor 1 to reliably hold the hydraulic motor 1 at the stop position. When the rotation of the upper revolving unit is stopped on a slope or the like, as in the conventional case where there is a time delay between the stopping operation and the stopping operation, the upper turning unit is operated between the time when the hydraulic motor 1 is stopped and the time when the stopping device 14 is operated. It is possible to avoid a problem that the body is rotated by its own weight or the like. Further, since the communication oil passage B is also opened substantially at the same timing as the operation of the braking device 14, the hydraulic motor 1 is stopped by the braking device 14 in a stopped state and there is no danger of movement. The swing-back force can be reliably eliminated by eliminating the pressure difference from the inlet-side oil passage, so that the stop position of the upper revolving unit can be easily positioned and the operability is improved.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram of a hydraulic motor.

FIG. 2 is a block diagram showing an input / output state of a control unit.

FIG. 3 is a timing chart of a control command output.

FIG. 4 (X) is a timing chart showing the relationship between the rotational speed of the hydraulic motor and the open / close switching valve in the second embodiment and in the third embodiment.

FIG. 5 is a conventional hydraulic circuit diagram provided with a check valve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hydraulic motor 2 Hydraulic pump 3 Direction switching valve 5 Operating lever 11 Opening / closing switching valve 12 Throttle valve 13 Control part 14 Suppression device 15 Suppression oil path switching valve 18 Speed detection sensor 19 Operation detection sensor A Brake circuit B Communication oil path

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F15B 11/00-11/22

Claims (7)

(57) [Claims] 1. A hydraulic motor that rotates based on a supply of pressurized oil from a pressurized oil supply source, a pressurized oil supply detection unit that detects whether or not a pressurized oil supply is made from the hydraulic oil supply source,
A speed detecting means for detecting a rotation speed of the hydraulic motor, a stopping means for stopping the hydraulic motor, and a communication oil passage provided to communicate the hydraulic oil inlet side oil passage and the outlet side oil passage of the hydraulic motor. Opening / closing means for opening / closing, a control unit to which these means are connected, and a device for releasing oil in an oil passage on the outlet side of the hydraulic motor
And a control command output means for outputting a control command to the stopping means and the opening / closing means based on detection signals from the pressure oil supply detecting means and the speed detecting means. Upon Ru is provided, the control finger
Command output means that the pressure oil supply detection means
When it is detected, the relief valve is
To include the rotational speed state of the hydraulic motor when it closes
Rotation speed of the hydraulic motor to a preset low speed setting range
Release command when the speed detection means detects that there is a degree
And the rotation speed of the hydraulic motor is lower than the low speed setting range.
Closed when the speed detection means detects that the speed has decreased
Command to output that the rotation speed of the hydraulic motor has stopped.
Set time preset by speed detection means
During this time, the release command shall be output, and
Speed detection means detects that the hydraulic motor has stopped
Is set to output a closing command based on
And that the hydraulic control circuit system for a hydraulic motor. 2. The apparatus according to claim 1, wherein when the pressure oil supply detection means detects a pressure oil supply state within a set time during which an open command is output to the open / close means, the output is output to the open / close means. A hydraulic control circuit device for a hydraulic motor that is set to output a close command instead of an open command. 3. An apparatus according to claim 1 or 2, the hydraulic control circuit system for a hydraulic motor which is provided with an aperture function communicating oil passage or opening and closing means. 4. The hydraulic control circuit device for a hydraulic motor according to claim 1, 2 or 3, wherein the opening / closing means or the throttle function is capable of adjusting an opening amount. 5. A method according to claim 1, 2, 3 or 4, Li
When pressure oil supply from the pressure oil supply source is cut off , the leaf valve applies a part of oil flowing through the outlet side oil passage to the inlet side oil passage while applying back pressure to the outlet oil passage of the hydraulic motor. supplied by the one configured to provide a braking hydraulic motor, the Lily
The supply of oil to the inlet-side oil passage of the valve is set until the oil pressure of the outlet-side oil passage attenuates to a preset pressure. start of opening command output for opening and closing means, the Lily
The timing is adjusted when the oil supply amount to the oil passage on the inlet side of the valve has decreased to the preset amount, and it is determined that the oil supply amount has fallen below the low speed setting range. The hydraulic control circuit device of the hydraulic motor is set to start after the oil supply to the oil passage on the inlet side of the relief valve is stopped. 6. The method according to claim 1 to 5, the pressure oil supply detection means that detects an operation state of the operation is the operation means to supply pressure oil to the hydraulic motor, or the pressure oil supply circuit to the hydraulic motor A hydraulic control circuit device for a hydraulic motor for detecting a switching state of a direction switching valve disposed in a hydraulic motor. 7. The method of claim 1 to 6, the hydraulic motor, the hydraulic control circuit system for a hydraulic motor is turning motor allowed to pivot the upper rotating body of the construction machine.