JPH11324949A - Scroll compressor and turning scroll to be used for scroll compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively cool a double scroll type turning scroll formed with a scroll lap in both surfaces of a panel board. SOLUTION: An oil free scroll compressor having a high capacity is formed with spiral scroll laps 3c, 3d in both sides of a panel board 3a of a turning scroll 3. These laps and spiral laps 1b, 2b of fixed scrolls 1, 2 are engaged with each other so as to form compression operating chambers 4, 5 in both sides of the panel board of the turning scroll 3. When the turning scroll 3 is turned, the working gas sucked from the periphery of the scroll is moved to the center with the movement of the compression operating chambers, and high temperature heat is generated. The panel board 3a of the turning scroll 3 is formed with plural cooling holes 7 passed from one peripheral part to the other peripheral part, and the heat generated in the center of the scroll is radiated by the gas flowing through this hole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air compressor,
The present invention relates to a scroll compressor used as an air-conditioning compressor and an orbiting scroll used therefor. In particular, it has a structure having wraps on both sides suitable for realizing a large-sized scroll compressor. The present invention relates to a scroll compressor which is suitable for general industry, that is, in the fields of food industry, pharmaceutical manufacturing, clean room of semiconductor manufacturing equipment, air conveying apparatus and the like, and a revolving scroll used therefor.

[0002]

2. Description of the Related Art As a conventional scroll compressor cooling method, such as an oilless scroll compressor disclosed in Japanese Patent Application Laid-Open No. 63-125188, a fixed scroll is provided with cooling fins and a scroll fin is provided. A method of cooling from the outside was adopted.

[0003]

The discharge pressure is 0.7 to
A large oil-free scroll compressor for air compression having a pressure of 0.85 MPa, and a conventional oil-free scroll compressor having no cooling medium in the compression process,
The discharge air temperature is as high as about 200 ° C. only by external cooling from the fixed scroll. As a result, unless the radial gap and the thrust gap of the orbiting scroll and the fixed scroll are made large by estimating the thermal expansion during the operation between the orbiting scroll and the fixed scroll, the scroll is not compressed during the compression operation. The wraps come into contact. As described above, the gap at the time of assembling is increased, so that the performance of the compressor is reduced. The oil-free scroll compressor is provided with a tip seal at the tip of the normal scroll to prevent the compressed gas from leaking. Usually, a tetrafluoroethylene resin resin is used as the material for the chip seal, but the life of the chip seal is shortened because the chip seal is exposed to a high temperature condition of about 200 ° C. during operation of the compressor.

[0004] It is an object of the present invention to provide an effective cooling method for orbiting scrolls in a double scroll compressor. Another object of the present invention is to improve the performance of a double scroll compressor by reducing the radial gap and the thrust gap between the orbiting scroll and the fixed scroll. Still another object of the present invention is to provide
An object of the present invention is to improve the life of a double scroll compressor against wear of a tip seal provided at the tip of a scroll wrap. Another object of the present invention is to balance the thrust force acting on the revolving scroll of the oil free double scroll compressor, thereby reducing the load acting on the tip seal and extending its life. .

[0005]

SUMMARY OF THE INVENTION The present invention has been made based on the above object, and a cooling hole through which a gas flows is provided in a head plate (body plate) of an orbiting scroll.
In particular, the high temperature portion (near the discharge port) of the nozzle is directly cooled.

That is, a first feature of the present invention is that the orbiting scroll has a spiral wrap on both sides of the end plate, and a wrap that meshes with the wrap of the orbiting scroll, and is disposed on both sides of the orbiting scroll. In a scroll compressor including two fixed scrolls and a main crankshaft and an auxiliary crankshaft rotatably supported by both of the fixed scrolls and held by the orbiting scroll,
This is because a plurality of through holes penetrating from one outer periphery of the end plate to the other outer periphery are formed.

[0007] In this scroll compressor,
The orbiting scroll and the two fixed scrolls formed a communication hole for communicating the compression working chambers formed on both sides of the end plate; the orbiting scroll and the two fixed scrolls were
The fixed scroll is an aluminum alloy containing silicon and has an anodized film treatment applied to the surface of the wrap; a groove is formed on the end of the orbiting scroll opposite to the end plate of the wrap; It is preferable to provide a chip seal made of tetrafluoroethylene resin or polyimide resin in this groove.

[0008] A second feature of the present invention is that a turning scroll having spiral wraps provided on both sides of a head plate, and the turning scroll wraps are respectively disposed on both left and right sides of the turning scroll. Left and right fixed scrolls having spiral wraps meshing with the respective spiral wraps, and the left and right fixed scrolls are rotatably supported via bearings, respectively, and are disposed on the outer peripheral side of the spiral wraps to form the revolving scroll. A scroll shaft provided with a drive shaft and an auxiliary crankshaft for rotating the shaft, and a timing belt for synchronously rotating the drive shaft and the auxiliary crankshaft.
A cooling hole for allowing the cooling gas of the scroll compressor to pass therethrough is formed in the end plate of the orbiting scroll from the outer peripheral side of one end plate to the outer peripheral side of the other end plate, and the left and right fixed scrolls are further formed. Cooling fins are formed on the outer surface, and the drive shaft and the auxiliary crank shaft are arranged on substantially opposite sides of a scroll wrap.

A third feature of the present invention is that in a revolving scroll having spiral scroll wraps on both sides of a head plate, cooling is performed by penetrating a central portion from one outer peripheral side to the other outer peripheral side of the head plate. That the holes were formed. The orbiting scroll preferably has a mounting portion for bearing means for supporting a drive shaft for orbiting the orbiting scroll and an auxiliary crankshaft substantially opposite to the scroll wrap of the end plate.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A scroll compressor performs compression by an eccentric motion of an orbiting scroll with respect to a fixed scroll. A crankshaft is used to give this eccentric movement to the orbiting scroll. The orbiting motion of the orbiting scroll gradually reduces the compression space between the orbiting scroll and the fixed scroll, and the compression proceeds. During the compression process, the temperature of the compressed air gradually increases, and accordingly, the fixed and orbiting scrolls themselves also increase in temperature from the outer periphery toward the center. The heat of compression can be indirectly cooled by being attached to the outside of the fixed scroll, and can be radiated to the outside of the scroll compressor through cooling fins. Thus, the fixed scroll portion is cooled, but the cooling fins cannot sufficiently cool the orbiting scroll. For this reason, in the present invention, a plurality of cooling holes are formed in the end plate (body plate) of the orbiting scroll. That is, the cooling hole is preferably provided so as to penetrate the central portion from the outer peripheral surface of the orbiting scroll. Is formed close to the suction side of the compression working chamber, a part of the suction air to the compressor passes through the cooling hole due to the pressure difference between both ends of the cooling hole. That is, the suction air of the compressor flows through the cooling hole from the position closer to the suction port toward the suction negative pressure, and the orbiting scroll is directly cooled by the suction air. This cools the high-temperature portion of the orbiting scroll, especially near the discharge port, reduces thermal expansion at the center of the orbiting scroll, and cools the discharge air temperature to prevent contact between the orbiting scroll and the fixed scroll and improve performance. And reliability can be improved.

A specific embodiment of the present invention will be described below with reference to the drawings. First, an overall configuration of a scroll compressor in a case where the present invention is used as an air compressor will be described with reference to FIG. In the figure, reference numeral 101 denotes a housing. Inside the housing, a main body block (compressor) 10 of a double scroll compressor is provided.
2, a motor 103 for driving the scroll compressor via a V-belt 112, a starter panel 104 for controlling the driving of the motor, a cooling fan 105 for cooling the equipment in the housing, and the like. I have. The discharge gas from the compressor 102 is guided to the outside through a discharge pipe 106. In the middle of the discharge gas, a check valve 107, a pre-cooler 108, an after-
A cooler 109 is provided. In the figure, 1
10 is an unloader for controlling the suction gas to the compressor, 11
Reference numeral 113 denotes a suction filter provided on the suction pipe, 113 denotes a motor base, 114 denotes a mount supporting a motor, a compressor, and the like, and 115 denotes a fan casing.

Next, a first embodiment of the present invention will be described with reference to FIGS. Figure 1 shows a double scroll type (double tooth type)
FIG. 2 is a cross-sectional plan view showing the structure of the main body block portion of the oil-free scroll compressor, FIG. 2 is a view taken along the line II-II of FIG. 1, and FIG. FIG. 4 is a right side view of the orbiting scroll shown in FIG. 1, and FIG. 5 is a view taken along line VV of FIG.

In FIG. 1, reference numerals 1 and 2 denote fixed scrolls made of an aluminum alloy, respectively, which are arranged in parallel with each other, and between which a orbiting scroll 3 also made of an aluminum alloy is interposed. , 2 and the spiral wraps 3c and 3d of the orbiting scroll 3 mesh with each other,
Thereby, compression working chambers 4 and 5 are formed on both sides of the end plate (body plate) 3a of the orbiting scroll 3. Tip seals 1a, 2a, 3b are provided at the tips of the wraps of the fixed scroll and the orbiting scroll, respectively. These tip seals are formed of an inorganic material such as carbon or a composite material of tetrafluoroethylene resin or polyimide resin. A communication hole 6 for communicating the compression working chambers 4 and 5 is provided at the center of the end plate 3a of the orbiting scroll.
As shown in FIGS. 3 to 5, cooling holes 7 communicating from one outer peripheral end to the other outer peripheral end of the end plate are provided on both sides of the end plate.
Is formed so that a part of the intake air is sucked into one suction side of the scroll compressor through the cooling holes 7.

A drive shaft (crankshaft) 8 having a crank portion 8a and an auxiliary crankshaft 9 having a crank portion 9a having the same eccentric amount are arranged on the outer peripheral portion of the end plate of the orbiting scroll 3. Are pivotally engaged via rolling bearings 11a and 11b having elastic support portions. On the other hand, fixed scroll 2
Has a discharge port 12 at a substantially central portion thereof, and further has radiation fins 1c and 2 on the entire outer surfaces of the fixed scrolls 1 and 2.
c are provided, and flange portions 1d and 2d are provided on their outer peripheral portions, respectively, and they are connected by bolts 13 as shown in FIGS. At the time of this connection, the relative positions of the fixed scrolls 1 and 2 are adjusted by positioning means 14 such as a knock pin. Further, the positional relationship between the fixed scrolls 1 and 2 and the orbiting scroll 3 is also properly determined, and then, with the phases of the drive shaft 8 and the auxiliary crankshaft 9 properly adjusted, the two shafts 8 and 9 are Combined, the shafts 8 and 9 are configured to rotate synchronously. The timing belt 15 includes a drive shaft 8 and a pulley 2 attached to an auxiliary crank shaft 9.
Multiplied by 1,22. V from a power source such as a motor
Rotational power is supplied to the drive shaft 8 via the belt 112 and the pulley 23.

The drive shaft 8 is axially supported by a rolling bearing (load-side bearing) 16 fixed to the fixed scroll 1 in a state where it is fixed in the axial direction. Is supported by a bearing (anti-load side bearing) 17 fixed to the shaft. A balance weight 18 is mounted on the drive shaft 8 so as to be disposed in the suction atmosphere of the scroll compressor. The auxiliary crankshaft 9 is also axially supported by a rolling bearing (load-side bearing) 19 fixed to the fixed scroll 1 in a state of being positioned in the axial direction. The tip of the auxiliary crankshaft 9 is fixed to the other fixed scroll 2. Bearing (anti-load side bearing) 20.

FIG. 3 shows a suction port 24 for handling gas such as air.
As shown in the figure, the shafts 8 and 9 are provided across both fixed scrolls in a direction perpendicular to the shafts. As shown in FIG. 2, a leg 25 for installing the compressor is mounted on the lower side of the opposite side. As described above, each of the fixed scrolls 1 and 2 and the orbiting scroll 3 is preferably made of a light material having good heat conductivity as represented by an aluminum alloy or the like. In the case of a non-lubricating scroll compressor, it is desirable to use an aluminum alloy containing silicon. Further, in order to improve the lubricity at the time of contact with the lap surface, a surface treatment such as an anodic oxide film may be performed.

As shown in FIG. 3, a cooling hole 7 formed in the end plate 3a of the orbiting scroll 3 has one outer peripheral end side (a suction side of the outermost peripheral portion of the wrap 2b of the fixed scroll 2).
A to the other outer peripheral end (the wrap 3c of the turning scroll 3)
The suction space of the fixed scroll is formed so that most of the air sucked from one suction side B passes through the cooling hole 7. Partitions 27 and 28 are provided to separate A and B. With this configuration, a part of the intake air is sucked into the suction side of one scroll compressor through the cooling hole 7 as shown by the arrow in FIG. The scroll compressor can be cooled using air.

Since the oil-free scroll compressor is designed to obtain a clean compressed gas without putting a cooling medium such as oil into the compression chamber, the discharge pressure is 0.7 to 0.1.
Even at about 8 MPa, the temperature rises to about 200 ° C. due to the heat of compression generated in the compression chamber. Cooling fins 1c, 2c are provided on the outer surfaces of the left fixed scroll 1 and the right fixed scroll 2 for cooling the compression heat, and the cooling air is forced to flow by a cooling fan (see FIG. 12) to release the compression heat. And let it cool. On the other hand, in the present embodiment, the communication hole 6 is interposed in the end plate 3a of the orbiting scroll 3, and
(In the same direction as above), and at least two cooling holes 7 are provided, so that the compressor can be cooled from the inside. The cooling hole 7 passes through the center of the orbiting scroll 3 where the temperature is the highest.

As shown in FIG. 3, the outer periphery of the orbiting scroll 3 forms suction spaces A and B of the compressor.
The air sucked from 4 is flowing. The cooling outlet 7b has a slightly lower pressure than the cooling inlet 7a of the cooling hole 7 (differential pressure of about 100 mmAq). This differential pressure is 100mmA
Using q, the suction air passes through the cooling hole 7 and is sucked into the compression chamber. Since the air passing through the cooling hole 7 is outside air, it has a temperature of about 0 to 40 ° C., which is much lower than the discharge gas temperature of the compressor. Heat exchange with part and cooling.

The gas sucked from the suction port 24 is supplied to the orbiting scroll 3, the left fixed scroll 1 and the right fixed scroll 2
The pressure is raised to a predetermined pressure as the rotation proceeds, and is discharged from the discharge port 12. In the drive system for orbiting the orbiting scroll 3, first, power is transmitted from a power source 103 such as a motor to the V-pulley 23 to rotate the drive shaft 8. The drive shaft 8 is supported by a load-side rolling bearing 16 and a non-load-side rolling bearing 17.
Scroll 3 via crank bearing 11a provided in
Is swiveled. The crank bearing 11a supports a gas load generated by compression and the like. The auxiliary crankshaft 9 is rotated by the timing belt 15 in synchronization with the drive shaft 8. The auxiliary crankshaft 9 is supported by a rolling bearing 19 on the load side and a rolling bearing 20 on the non-load side.
Of the drive shaft 8 via a rolling bearing 11b provided in
Cooperates to drive the turning scroll 3.

When rotational power is transmitted to the pulley 23, the drive shaft 8 and the auxiliary crankshaft 9 rotate synchronously by the timing belt 15, whereby the orbiting scroll 3 reduces the eccentricity of the drive shaft 8 and the auxiliary crankshaft 9. Perform a turning motion with a radius. The external air is sucked from the suction port 24 with this swirling motion and enters the suction chamber (suction space) A. Thereafter, the sucked air further flows into the compression working chambers 4 and 5 formed by the orbiting scroll 3 and the fixed scrolls 1 and 2, and is compressed to a predetermined pressure. The air compressed in the compression working chambers 4 and 5 is finally discharged from the discharge port 12, but the gas compressed in the compression working chamber 4 on the side opposite to the discharge port 12 with the end plate 3a interposed therebetween. Through the communication hole 6 provided in the central portion of 3a, it flows into the compression operation chamber 5 in the opposite central portion and merges, and discharges from the discharge space to the outside from the discharge port 12 provided in the fixed scroll 2 from the discharge space. Is done.

Since the compression working chamber has almost no lubricating oil, the temperature of the compressed gas is higher than that of an oil-cooled compressor. However, forced air cooling is performed around the radiation fins 1c and 2c provided on the outer surface of the fixed scroll as a duct structure. Thereby, the cooling effect can be further improved. 3 and 4, reference numeral 30 denotes a pressure equalizing hole for maintaining the pressure balance of the compression working chambers 4 and 5 formed on both sides of the revolving scroll 3, and a double (double tooth) scroll compression according to the present invention. In the machine, the sum of the thrust forces caused by the gas in the compression working chambers on both sides of the head plate 3a is made substantially equal by the pressure equalizing holes 30, so that the wraps 1b, 2b, 3c, 3d
A large thrust load does not act on the tip seals 1a, 2a, 3b on the front end face of the first. Therefore, the sliding loss at the tip of the wrap can be kept to a minimum. Furthermore, since the thrust forces acting on the orbiting scroll 3 are substantially balanced, the means for positioning the bearings 11a and 11b that support the orbiting scroll 3 can be simplified, and the assemblability can be improved.

According to the embodiment described above, the following effects can be obtained. (1) Not only can the fixed scrolls 1 and 2 be cooled from the outside by the radiation fins 1c and 2c, but also the orbiting scroll 3 disposed inside can be directly cooled by the cooling holes 7, so that the center of the orbiting scroll is also conventional. The temperature can be lowered by about 30 ° C. Thereby, the gap formed by the fixed scroll and the orbiting scroll can be made smaller, and as a result, the compressor performance can be improved by 3 to 5%. (2) The temperature of the discharge air of the compressor can be reduced, the cooling of the discharge air can be facilitated, and the reliability of the compressor can be improved. (3) The temperature of the tip seal provided at the tip of each wrap of the oil-free double scroll compressor is about 30 times lower than the conventional temperature.
Since the temperature can be lowered by ° C., the material of the tip seal can be easily selected, and the life of the tip seal can be improved. In particular, in the present embodiment, since the turning scroll head plate is provided with the pressure equalizing holes 30 which communicate the compression working chambers on both sides of the head plate to balance the pressure, the thrust force acting on the turning scroll can be more balanced. The load acting on each chip seal can be reduced, and its life can be increased.

FIGS. 6 and 7 show another modification of the present invention. FIG. 6 shows a cooling hole 7 formed in the end plate of the revolving scroll.
Is a chrysanthemum shape in place of the round hole shown in FIG. 5, so that the heat transfer area of the cooling hole can be increased and the cooling effect can be improved.

FIG. 7 shows that the number of cooling holes 7 formed in the end plate of the revolving scroll is four instead of the two shown in FIG. 4, and the passage area of the intake air passing through the cooling holes 7 is increased. Increase
By reducing the passage resistance, the amount of air passing therethrough is increased, the cooling effect is improved, and cooling can be performed over the entire swirling scroll. By making the passage area of the cooling hole near the center larger than the passage area of the cooling hole formed on the outside, a cooling capacity corresponding to the amount of heat generated in the swirl scroll can be generated.

In each of the embodiments described above, (1) Even if the orbiting scroll cannot be cooled from outside by the cooling fins or the like due to the cooling holes formed in the end plate of the orbiting scroll, the orbiting is made from the inside. The scroll can be cooled directly, and the temperature of the orbiting scroll can be reduced. Thereby, the gap formed by the fixed scroll and the orbiting scroll can be made smaller, and the performance of the compressor can be improved. (2) In the case where the radiation fin is provided on the fixed scroll,
The fixed scroll can be efficiently cooled from the outside. (3) Since the temperature of the tip seal provided at the tip of each wrap of the oil-free double scroll compressor can also be reduced, the material of the tip seal can be easily selected,
In addition, the life can be improved with respect to wear.

(4) If the revolving scroll head plate is provided with a pressure equalizing hole which communicates the compression working chambers on both sides of the revolving scroll plate and balances the pressure, the thrust force acting on the revolving scroll can be more balanced. The load acting on each tip seal can be further reduced, and the life of the tip seal can be increased. (5) Although the swirl scroll is cooled by its own intake air, another cooling fluid (for example, external air or cooled low-temperature air) is guided from the outside to form the cooling formed in the swirl scroll. If the cooling fluid is forced to flow directly through the holes, the cooling effect can be further improved.

[0028]

As described above, according to the present invention, the orbiting scroll can be effectively cooled because the through-hole is provided from the intended outer end of the end plate of the orbiting scroll to the other outer peripheral end.

[Brief description of the drawings]

FIG. 1 is a plan sectional view of a partial structure of a main body block of a double scroll oil-free scroll compressor according to an embodiment of the present invention.

FIG. 2 is a view taken along line II-II of FIG.

FIG. 3 is a view showing a state in which the fixed scroll on the right side of FIG.
It is the right view seen from the line direction.

FIG. 4 is a right side view of the orbiting scroll shown in FIG. 1;

FIG. 5 is a view taken along line VV of FIG. 4;

FIG. 6 is a view corresponding to FIG. 5 showing a modification of the shape of the cooling hole 7 formed in the end plate of the revolving scroll.

FIG. 7 is a view corresponding to FIG. 4, showing a modification of the cooling hole formed in the end plate of the revolving scroll.

FIG. 8 is a diagram illustrating an overall configuration of a scroll compressor.

[Explanation of symbols]

1: fixed left scroll, 2: fixed right scroll, 1c,
2c: heat dissipating (cooling) fin, 3: orbiting scroll, 3a
... orbiting scroll head plate, 1a, 2a, 3b ... tip seal
1b, 2b, 3c, 3d wrap, 4, 5 compression working chamber, 7 cooling hole, 7a cooling hole inlet, 7b cooling hole outlet, 8 drive shaft, 9 auxiliary crank shaft , 8a, 9
a: Crank portion, 11a, 11b: Rolling bearing (crank bearing), 12: Discharge port, 15: Timing belt, 16, 19: Rolling bearing (load-side bearing), 17, 2
0: Rolling bearing (anti-load side bearing), 21, 22, ...
R, 23 V pulley, 24 Suction port, 25 Leg, 2
7, 28 ... partition, A, B ... suction side (suction space).

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeru Machida 502, Kandachicho, Tsuchiura-shi, Ibaraki Pref.

Claims (8)

[Claims] An orbiting scroll having spiral wraps on both sides of an end plate, wraps which mesh with the wraps of the orbiting scroll, and two fixed scrolls arranged on both sides of the orbiting scroll; In a scroll compressor rotatably supported by both scrolls and provided with a main crankshaft and an auxiliary crankshaft held by the orbiting scroll, a plurality of through holes penetrating from one outer periphery of the end plate to the other outer periphery A scroll compressor characterized by forming. 2. A scroll compressor according to claim 1, wherein a communication hole is formed by said orbiting scroll and said two fixed scrolls to communicate a compression working chamber formed on both sides of a head plate. 3. The scroll compressor according to claim 1, wherein the orbiting scroll and the two fixed scrolls are made of an aluminum alloy. 4. The scroll compressor according to claim 3, wherein the fixed scroll is made of an aluminum alloy containing silicon, and has a wrap surface subjected to an anodic oxide film treatment. 5. A wrap provided in the orbiting scroll has a groove formed at an end opposite to the end plate, and a chip seal made of a tetrafluoroethylene resin or a polyimide resin is provided in the groove. The scroll compressor according to any one of claims 1 to 4. 6. A turning scroll having spiral wraps provided on both sides of a head plate, and spiral wraps disposed on both left and right sides of the turning scroll and meshing with the respective turning scroll wraps. Left and right fixed scrolls having: a driving shaft that is rotatably supported by the left and right fixed scrolls via bearings, is disposed on the outer peripheral side of the spiral wrap, and turns the turning scroll; A scroll compressor having an auxiliary crankshaft and a timing belt for synchronously rotating the drive shaft and the auxiliary crankshaft, wherein a cooling gas for passing a cooling gas of the scroll compressor passes through the end plate of the orbiting scroll. A hole is formed through the center from the outer peripheral side of one end plate to the outer peripheral side of the other end plate, and cooling fins are formed on the outer surfaces of the left and right fixed scrolls. A scroll compressor, wherein the drive shaft and the auxiliary crankshaft are disposed on substantially opposite sides of a scroll wrap. 7. A revolving scroll having spiral scroll wraps on both sides of a head plate, wherein a cooling hole is formed through a center portion from one outer peripheral side to the other outer peripheral side of the head plate. Features an orbiting scroll. 8. A mounting portion for bearing means for supporting a drive shaft for orbiting the orbiting scroll and an auxiliary crankshaft is formed substantially on the opposite side of the end plate with respect to the scroll wrap. 7. The orbiting scroll according to 7.