CN215762553U

CN215762553U - Adjustable bidirectional buffer oil cylinder

Info

Publication number: CN215762553U
Application number: CN202122457518.6U
Authority: CN
Inventors: 张丽; 宋大维; 汪健; 吴少杰; 张亚军
Original assignee: Jinan Huachen Industrial Co ltd
Current assignee: Shenyang Gongliang Hydraulic Equipment Co.,Ltd.
Priority date: 2021-10-13
Filing date: 2021-10-13
Publication date: 2022-02-08
Anticipated expiration: 2031-10-13

Abstract

The utility model discloses an adjustable bidirectional buffer oil cylinder. A rod cavity oil port and a rodless cavity oil port are formed in the cylinder barrel, and a front buffer sleeve and a rear buffer sleeve are respectively arranged on the front portion and the rear portion of the piston on the piston rod; the front part of the oil port of the rod cavity is provided with a front buffer hole, and when the piston rod and the piston extend forwards to the tail end of the stroke, the distance between the front buffer hole and the cylinder head is smaller than the distance between the front buffer sleeve and the cylinder head; the rear part of the rodless cavity oil port is provided with a rear buffer hole, and when the piston rod and the piston retract backwards to the tail end of the stroke, the distance between the rear buffer hole and the cylinder bottom is smaller than the distance between the rear buffer sleeve and the cylinder bottom; one-way throttle valves are arranged between the rod cavity oil port and the front buffer hole and between the rodless cavity oil port and the rear buffer hole. The piston rod is stably decelerated by controlling the buffer oil quantity through the one-way throttle valve, the structure is simple, the processing, the installation and the maintenance are convenient, and the manufacturing cost is low; the opening degree of the one-way throttle valve is adjusted, the buffering speed can be changed, the operation is convenient, and the application range is wide.

Description

Adjustable bidirectional buffer oil cylinder

Technical Field

The utility model relates to the technical field of hydraulic oil cylinders, in particular to a hydraulic oil cylinder with a buffering function.

Background

The oil cylinder is an actuating element of a hydraulic system and comprises a cylinder barrel, a piston and a piston rod, wherein the piston moves at a high speed in the oil cylinder under the driving of hydraulic pressure. The front end of the cylinder barrel is provided with an end cover, when a piston rod reaches the front end of the oil cylinder in the process of rapid movement of the hydraulic oil cylinder, strong impact, noise and even mechanical collision can be generated at a stroke terminal, and particularly under the condition of high pressure, the influence is more obvious, and the service life of the oil cylinder is seriously influenced.

In order to reduce the impact of the piston on the cylinder cover (also called the cylinder head), especially when the working pressure of the cylinder is greater than 25MPa and the moving parts have large mass, in order to prevent the piston from mechanically colliding with the cylinder cover at the stroke end to cause noise and impact, even damage to the parts of the cylinder, a buffer structure needs to be arranged on the cylinder, and proper braking and buffering are performed before the movement is finished to relieve the impact of the piston on the cylinder cover and ensure the service life of the system and the cylinder.

At present commonly used buffer oil cylinder generally has an oil inlet and an oil return opening, sets up damping hole and buffering plunger at the both ends of hydro-cylinder, and its buffering effect is general. In order to prevent pistons of a plurality of oil cylinders from colliding when the pistons move at high speed at two ends of the oil cylinders, buffer devices are designed in rod cavities and rodless cavities of the oil cylinders, and the buffer principle is that two conical buffer rods are respectively arranged at two ends of the pistons, and when the pistons move to the two ends, the conical buffer rods gradually block off normal oil paths to achieve the throttling buffer effect. Due to accumulated errors of machining and assembling, the conical buffer rod structure is difficult to be concentric with the buffer hole and immediately and effectively cut off an oil way, so the designed single-end buffer distance is generally 20-30 mm, the problem of poor buffer effect often occurs, the requirement on machining precision is high, the cost is greatly increased, the machining precision is reduced, the good buffer effect is difficult to ensure, the buffer is too weak or too hard, and the design requirement cannot be met; especially, the buffer distance is 20-30 mm at a single end, 40-60 mm at double ends, and the short-stroke oil cylinder cannot adopt the buffer structure. The buffering hole matched with the conical buffering rod is generally designed on the end cover, and the buffering gap between the buffering hole and the conical buffering rod is formed by accumulating a plurality of parts such as a cylinder barrel, a piston rod, the conical buffering rod and the like, so the size of the buffering hole cannot be reduced, the buffering distance is long, the buffering effect is not easy to control, and the parts are positioned in the cylinder body, so that the processing precision requirement is high, and the assembly is complex.

Disclosure of Invention

The utility model aims to solve the technical problem of overcoming the defects in the prior art and provides the adjustable bidirectional buffer oil cylinder which is simple in structure, good in buffer effect, short in buffer distance, convenient to install and maintain and low in manufacturing cost.

The technical scheme adopted by the utility model for realizing the purpose is as follows:

an adjustable bidirectional buffer oil cylinder comprises a cylinder bottom, a cylinder barrel and a cylinder head which are connected in sequence, wherein a piston which is matched with the cylinder barrel to slide is fixedly arranged at the rear end of a piston rod, and the front end of the piston rod can extend out of the cylinder head when the piston rod moves; the piston divides the cylinder barrel into a rod cavity and a rodless cavity; one side that is located there is the pole chamber on the cylinder is provided with pole chamber hydraulic fluid port, and one side that is located no pole chamber on the cylinder sets up no pole chamber hydraulic fluid port, its characterized in that: the piston rod is provided with a front buffer sleeve and a rear buffer sleeve which are positioned at the front part and the rear part of the piston and are matched with each other to slide in the cylinder barrel respectively; the front part of the oil port of the rod cavity is provided with a front buffer hole, and when the piston rod and the piston extend forwards to the tail end of the stroke, the distance between the front buffer hole and the cylinder head is smaller than the distance between the front buffer sleeve and the cylinder head; the rear part of the oil port of the rodless cavity is provided with a rear buffer hole, and when the piston rod and the piston retract backwards to the tail end of the stroke, the distance between the rear buffer hole and the cylinder bottom is smaller than the distance between the rear buffer sleeve and the cylinder bottom; a first one-way throttle valve is arranged between the oil port of the rod cavity and the front buffer hole, and a second one-way throttle valve is arranged between the oil port of the rodless cavity and the rear buffer hole.

By adopting the technical scheme, the piston rod is stably decelerated by utilizing the control of the one-way throttle valve on the buffer oil quantity, the structure is simple, and the one-way throttle valve is arranged outside the oil cylinder, so that the processing, the installation and the maintenance are convenient, the processing quality is easy to ensure, and the manufacturing cost is low;

in the adjustable bidirectional buffer oil cylinder, the outer side surface of the cylinder barrel is provided with a front oil port joint and a rear oil port joint, and the front oil port joint is respectively provided with a front oil hole communicated with the oil port of the rod cavity and a front orifice communicated with the front buffer hole; the rear oil port joint is respectively provided with a rear oil hole communicated with the rodless cavity oil port and a rear orifice communicated with the rear buffer hole; the first one-way throttle valve is connected between the front oil hole and the front throttle hole, and the second one-way throttle valve is connected between the rear oil hole and the rear throttle hole.

Further, the distance between the axis of the front oil inlet hole on the front oil port joint and the axis of the front orifice is smaller than the distance between the axis of the oil port of the rod cavity and the axis of the front buffer hole; the distance between the axis of the rear oil inlet hole on the rear oil port connector and the axis of the rear orifice is smaller than the distance between the axis of the rodless cavity oil port and the axis of the rear buffer hole.

Through adopting above-mentioned technical scheme, have the pole chamber hydraulic fluid port to be linked together but stagger each other with advancing the oilhole, stagger each other that preceding cushion hole and preceding orifice are linked together can reduce pressure shock.

Furthermore, when the piston rod and the piston extend forwards to the tail end of the stroke, the piston shields the oil port of the rod cavity; when the piston rod and the piston retract backwards to the tail end of the stroke, the piston shields the oil port of the rodless cavity.

By adopting the technical scheme, the piston is used for replacing the traditional conical buffer rod to shield the oil port, and the cylinder barrel and the piston are originally a pair of very precise matched parts, so that the clearance between the cylinder barrel and the piston is very small, the oil way can be immediately closed, the buffer stroke can be very small, and a good buffer effect is achieved; and does not increase the processing cost.

Has the advantages that:

1. the piston rod is stably decelerated by controlling the buffer oil quantity through the one-way throttle valve, the structure is simple, the one-way throttle valve is arranged outside the oil cylinder, the processing, the installation and the maintenance are convenient, the processing quality is easy to ensure, and the manufacturing cost is low;

2. two ends of the oil cylinder are respectively provided with two oil ports, one is a normal oil port (a rod cavity oil port and a rodless cavity oil port), and the other is an oil port (a front buffer hole and a rear buffer hole) with a one-way throttle valve; when the piston moves to two ends, the piston can shield normal oil ports (a rod cavity oil port and a rodless cavity oil port), and oil can only flow out through the oil ports (a front buffer hole and a rear buffer hole) with the throttle valves, so that the throttling buffer effect can be achieved;

3. the opening of the one-way throttle valve is adjusted, the size of a throttle opening of the throttle valve is adjusted to control the return oil flow, the buffering speed can be changed, and therefore the throttling buffering effect of the hydraulic cylinder is controlled, and the hydraulic cylinder is convenient to operate, large in adjusting range, high in adaptability, reliable in performance and wide in application range;

4. the two ends of the oil cylinder are provided with the one-way throttle valves to realize two-way buffering, so that the piston rod slowly decelerates when the piston rod extends out of or retracts into the tail end of the stroke, the piston rod can only slowly move forwards or backwards, soft landing is realized, the damage of the oil cylinder caused by collision is avoided, and the service life of the oil cylinder is prolonged; the one-way throttle valve can also adjust the buffering effect; the buffering effect can be realized by adjusting the valve opening of the corresponding one-way throttle valve, and when the opening is adjusted to the maximum, no buffering is realized;

5. the piston is adopted to replace a traditional conical buffer rod to shield the oil port, and since the cylinder barrel and the piston are originally a pair of very precise parts which are matched with each other, the clearance between the cylinder barrel and the piston is very small, and the oil way can be closed immediately, so that the buffer stroke can be very small and a good buffer effect is achieved; and does not increase the processing cost.

Drawings

Fig. 1 is a schematic overall cross-sectional view of the present invention (piston rod and piston retracted back to the end of stroke).

Figure 2 is a schematic view, partially in section, of one end of the cylinder bottom of the present invention (with the piston rod and piston retracted back to the end of the stroke).

FIG. 3 is a schematic diagram of the piston rod extending forward to move to the piston, the rear cushion sleeve leaving the rear cushion hole, the rodless cavity port or the piston rod retracting backward to move to the piston, the rear cushion sleeve approaching the rodless cavity port in the present invention.

Fig. 4 is a schematic diagram of the piston rod of the utility model when the piston rod extends forwards and moves to the front buffer sleeve to shield the oil port of the rod cavity, or the piston rod retracts backwards and moves to the front buffer sleeve to leave the oil port of the rod cavity without continuously shielding the oil port.

FIG. 5 is a schematic diagram of the piston rod and piston, front cushion collar and rear cushion collar of the present invention extending forward to the end of the stroke.

In the figure: 1 cylinder head, 2 first one-way throttle valve,

3 front oil port joint, 3-1 front throttling hole, 3-2 front oil port,

4 cylinder barrels, 4-1 front buffer holes, 4-2 rod cavity oil ports, 4-3 rodless cavity oil ports, 4-4 rear buffer holes,

5 piston rod, 6 front buffer sleeve, 6-1 first conical inclined plane, 7 piston, 8 rear buffer sleeve, 8-1 second conical inclined plane,

a 9 rear oil port joint, a 9-1 rear oil inlet hole, a 9-2 rear orifice,

10 second one-way throttle valve, 11 cylinder bottom, 12 rodless cavity and 13 rod cavity.

Detailed Description

In order to clearly illustrate the technical features of the present invention, the present invention is further illustrated by the following non-limiting examples in combination with the accompanying drawings.

The front, rear, left and right directions of the present invention are described with reference to the front, rear, left and right directions shown in the drawings. For ease of illustration, only the portions relevant to the embodiments of the present invention are shown.

Referring to fig. 1 to 5, the extending direction of the piston rod 5 is set to be the front, and the opposite direction is set to be the rear, the adjustable bidirectional buffer oil cylinder of the embodiment includes a cylinder head 1, a cylinder barrel 4 and a cylinder bottom 11 which are sequentially connected from front to back (from left to right in the figure), the cylinder barrel 4 is a tubular cylinder whose inner hole is precisely processed, the rear end of the cylinder barrel 4 is welded on the cylinder bottom 11, the inner hole at the front end of the cylinder barrel 4 is processed with a threaded hole, the diameter of the threaded hole is greater than that of the inner hole of the cylinder barrel 4, and the cylinder head 1 is in threaded connection with the threaded hole; the outer cylindrical surface at the rear end of the cylinder head 1 is matched with the inner hole of the cylinder barrel 4 and is provided with a seal; the front part and the rear part of the piston 7 on the piston rod 5 are respectively provided with a front buffer sleeve 6 and a rear buffer sleeve 8; specifically, the rear end of the piston rod 5 is provided with a piston mounting section and a threaded section, the outer diameters of the piston mounting section and the threaded section are sequentially reduced, the piston mounting section is sequentially sleeved with a front buffer sleeve 6, a piston 7 and a rear buffer sleeve 8 which are matched and slide in the cylinder barrel 4, and a lock nut on the threaded section presses the buffer sleeve 6, the piston 7 and the rear buffer sleeve 8 against a shaft shoulder of the piston rod 5; a sealing ring is arranged between the piston rod 5 and the piston 7; a sealing component is arranged between the cylinder barrel 4 and the piston 7, the front end of the piston rod 5 can extend out of a cylinder head hole of the cylinder head 1 when moving, and the sealing component is arranged between the piston rod 5 and the cylinder head 1; the piston 7 divides the cylinder 4 into a rod chamber 13 and a rodless chamber 12; a rod cavity oil port 4-2 is arranged on one side of the cylinder barrel 4, which is positioned with the rod cavity 13, and a rodless cavity oil port 4-3 is arranged on one side of the cylinder barrel 4, which is positioned with the rodless cavity 12.

For convenient assembly, a first conical inclined surface 6-1 is arranged at one end, close to the cylinder head 1, of the front buffer sleeve 6, the diameter of the first conical inclined surface 6-1 is gradually reduced towards the direction of the cylinder head 1, a second conical inclined surface 8-1 is arranged at one end, close to the cylinder bottom 11, of the rear buffer sleeve 8, and the diameter of the second conical inclined surface 8-1 is gradually reduced towards the direction of the cylinder bottom 11; the front part of the rod cavity oil port 4-2 is provided with a front buffer hole 4-1, and when the piston rod 5 extends forwards to the tail end of the stroke, the distance between the front buffer hole 4-1 and the cylinder head 1 is smaller than the distance between the first conical inclined surface 6-1 and the cylinder head 1; the rear part of the rodless cavity oil port 4-3 is provided with a rear buffer hole 4-4, and when the piston rod 5 retracts backwards to the tail end of the stroke, the distance between the rear buffer hole 4-4 and the cylinder bottom 11 is smaller than the distance between the second conical inclined surface 8-1 and the cylinder bottom 11.

A front oil port connector 3 and a rear oil port connector 9 are arranged on the outer side surface of the cylinder barrel 4, a front oil hole 3-2 communicated with the rod cavity oil port 4-2 and a front orifice 3-1 communicated with the front buffer hole 4-1 are respectively arranged on the front oil port connector 3, the distance between the axis of the front oil hole 3-2 and the axis of the front orifice 3-1 is smaller than the distance between the axis of the rod cavity oil port 4-2 and the axis of the front buffer hole 4-1, and a first one-way throttle valve 2 is connected between the front oil hole 3-2 and the front orifice 3-1; specifically, a conducting port of the first one-way throttle valve 2 is communicated with an oil advancing hole 3-2, and a throttling port of the first one-way throttle valve 2 is communicated with a front throttling hole 3-1;

the rear oil port joint 9 is respectively provided with a rear oil inlet hole 9-1 communicated with the rodless cavity oil port 4-3 and a rear orifice 9-2 communicated with the rear buffer hole 4-4; the distance between the axis of the rear oil inlet 9-1 and the axis of the rear orifice 9-2 is smaller than the distance between the axis of the rodless cavity oil port 4-3 and the axis of the rear buffer hole 4-4, and a second one-way throttle valve 10 is connected between the rear oil inlet 9-1 and the rear orifice 9-2; specifically, a conduction port of the second one-way throttle valve 10 is communicated with the rear oil inlet hole 9-1, and a throttling port of the second one-way throttle valve 10 is communicated with the rear throttling hole 9-2;

when the piston rod 5 and the piston 7 extend forwards to the tail end of the stroke, the piston 7 shields the oil port 4-2 of the rod cavity; when the piston rod 5 and the piston 7 retract backwards to the stroke end, the piston 7 shields the rodless cavity oil port 4-3.

In this embodiment, the first one-way throttle valve 2 and the second one-way throttle valve 10 are adjustable one-way throttle valves, and the flow rate can be changed by adjusting the size of the throttling oil port of the adjustable one-way throttle valve, so as to adjust the buffering effect.

The working process is as follows:

referring to fig. 1 and 2, when the rear oil inlet hole 9-1 is filled with oil, the rodless cavity oil port 4-3 communicated with the rear oil inlet hole 9-1 is shielded by the piston 7, the oil enters the rear orifice 9-2 through the second one-way throttle valve 10, the second one-way throttle valve 10 plays a role of a one-way valve, the oil directly and rapidly enters the rear orifice 9-2 and the rear buffer hole 4-4 and then enters the rodless cavity 12, and the oil in the rodless cavity 12 pushes the front buffer sleeve 6, the piston 7, the rear buffer sleeve 8 and the piston rod 5 to move forward together; when the piston rod 5 extends forwards and moves to the piston 7, and the rear cushion collar 8 does not shield the rodless cavity oil port 4-3 (see fig. 3), oil in the rear oil inlet hole 9-1 directly enters the rodless cavity 12 from the rodless cavity oil port 4-3; when the piston rod 5 continues to extend forwards and move to approach the stroke end (see figure 4), the front buffer sleeve 6 and the piston 7 gradually shield the rod cavity oil port 4-2, the oil in the rod cavity 13 can not flow out from the rod cavity oil port 4-2 and the forward oil hole 3-2 any more, the oil in the rod cavity 13 is forced to flow into the forward oil hole 3-2 through the front buffer hole 4-1 and the front throttling hole 3-1 and then flow out through the throttling valve of the first one-way throttling valve 2, the first one-way throttling valve 2 plays a role of a throttling valve, as the oil flowing outwards in the rod cavity 13 is suddenly throttled, a large back pressure is generated in the rod cavity 13, so that the piston rod 5 slowly decelerates, the piston rod 5 can only move forwards slowly until the end surface of the front buffer sleeve 6 is attached to the cylinder head 1 (see figure 5), and the speed when approaching the cylinder head 1 is low, no obvious noise and impact load exist, and the soft landing of the extending end part of the piston rod 5 is realized.

Similarly, when the piston rod 5 starts to retract, please refer to fig. 5, when the front oil inlet hole 3-2 feeds oil, the rod cavity oil port 4-2 communicated with the front oil inlet hole 3-2 is shielded by the piston 7, the oil enters the front orifice 3-1 through the first one-way throttle valve 2, the first one-way throttle valve 2 functions as a one-way valve, the oil directly and rapidly enters the front orifice 3-1, the front buffer hole 4-1 and then enters the rod cavity 13, and the oil in the rod cavity 13 pushes the front buffer sleeve 6, the piston 7, the rear buffer sleeve 8 and the piston rod 5 to move backwards together; when the piston rod 5 retracts backwards and moves to the piston 7, and the front buffer sleeve 6 does not shield the rod cavity oil port 4-2 any more, oil in the front oil hole 3-2 directly enters the rod cavity 13 from the rod cavity oil port 4-2; when the piston rod 5 continues to retract backwards and move to approach the stroke end (see fig. 3), the rear buffer sleeve 8 and the piston 7 gradually shield the rodless cavity oil port 4-3, the oil in the rodless cavity 12 can not flow out from the rodless cavity oil port 4-3 and the rear oil inlet hole 9-1 any more, the oil in the rodless cavity 12 is forced to flow into the rear oil inlet hole 9-1 through the throttle valve of the second one-way throttle valve 10 by the rear buffer hole 4-4 and the rear throttle hole 9-2 and then flow out, the second one-way throttle valve 10 acts as a throttle valve, as the oil flowing outwards in the rodless cavity 12 is suddenly throttled, great back pressure is generated in the rodless cavity 12, so that the piston rod 5 slowly decelerates, the piston rod 5 only slowly moves backwards until the rear end of the piston rod 5 is attached to the cylinder bottom 11 (see fig. 2), and the speed approaching the cylinder bottom 11 is very low, no obvious noise and impact load exist, and the soft landing of the retraction end part of the piston rod 5 is realized.

In the description of the present invention, it should be noted that the terms "left", "right", "front", "back", "upper", "lower", "inner", "outer", etc., indicate orientations or positional relationships based on those shown in the drawings, and the above terms are only for convenience in describing the present invention and simplifying the description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.

Unless expressly stated or limited otherwise, the terms "mounted," "connected," and "connected" are intended to be inclusive and mean, for example, that they may be fixedly connected, detachably connected, or integrally connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

In addition to the technical features described in the specification, the technology is known to those skilled in the art.

The above-mentioned embodiments are only for understanding the present invention, and are not intended to limit the technical solutions of the present invention, and those skilled in the art can make various changes or modifications based on the technical solutions described in the claims, and all equivalent changes or modifications should be covered by the scope of the claims of the present invention.

Claims

1. An adjustable bidirectional buffer oil cylinder comprises a cylinder bottom, a cylinder barrel and a cylinder head which are connected in sequence, wherein a piston which is matched with the cylinder barrel to slide is fixedly arranged at the rear end of a piston rod, and the front end of the piston rod can extend out of the cylinder head when the piston rod moves; the piston divides the cylinder barrel into a rod cavity and a rodless cavity; one side that is located there is the pole chamber on the cylinder is provided with pole chamber hydraulic fluid port, and one side that is located no pole chamber on the cylinder sets up no pole chamber hydraulic fluid port, its characterized in that: the piston rod is provided with a front buffer sleeve and a rear buffer sleeve which are positioned at the front part and the rear part of the piston and are matched with each other to slide in the cylinder barrel respectively; the front part of the oil port of the rod cavity is provided with a front buffer hole, and when the piston rod and the piston extend forwards to the tail end of the stroke, the distance between the front buffer hole and the cylinder head is smaller than the distance between the front buffer sleeve and the cylinder head; the rear part of the oil port of the rodless cavity is provided with a rear buffer hole, and when the piston rod and the piston retract backwards to the tail end of the stroke, the distance between the rear buffer hole and the cylinder bottom is smaller than the distance between the rear buffer sleeve and the cylinder bottom; a first one-way throttle valve is arranged between the oil port of the rod cavity and the front buffer hole, and a second one-way throttle valve is arranged between the oil port of the rodless cavity and the rear buffer hole.

2. The adjustable bidirectional cushion cylinder of claim 1, wherein: a front oil port joint and a rear oil port joint are arranged on the outer side surface of the cylinder barrel, and a front oil hole communicated with the oil port of the rod cavity and a front orifice communicated with the front buffer hole are respectively arranged on the front oil port joint; the rear oil port joint is respectively provided with a rear oil hole communicated with the rodless cavity oil port and a rear orifice communicated with the rear buffer hole; the first one-way throttle valve is connected between the front oil hole and the front throttle hole, and the second one-way throttle valve is connected between the rear oil hole and the rear throttle hole.

3. The adjustable bidirectional cushion cylinder of claim 2, wherein: the distance between the axis of the front oil inlet hole on the front oil port joint and the axis of the front orifice is smaller than the distance between the axis of the oil port of the rod cavity and the axis of the front buffer hole; the distance between the axis of the rear oil inlet hole on the rear oil port connector and the axis of the rear orifice is smaller than the distance between the axis of the rodless cavity oil port and the axis of the rear buffer hole.

4. An adjustable bi-directional cushion cylinder as claimed in claim 1, 2 or 3, wherein: when the piston rod and the piston extend forwards and move to the tail end of the stroke, the piston shields the oil port of the rod cavity; when the piston rod and the piston retract backwards to the tail end of the stroke, the piston shields the oil port of the rodless cavity.