CN107237852B

CN107237852B - Shock absorber

Info

Publication number: CN107237852B
Application number: CN201710672048.0A
Authority: CN
Inventors: 项文峰; 李超; 邹湾华
Original assignee: Taizhou Jiuju Technology Co ltd
Current assignee: Taizhou Jiuju Technology Co ltd
Priority date: 2017-08-08
Filing date: 2017-08-08
Publication date: 2022-07-12
Anticipated expiration: 2037-08-08
Also published as: CN107237852A

Abstract

The invention provides a shock absorber, and belongs to the technical field of automobile parts. It has solved the problem that the valve system of current bumper shock absorber received the damage easily. This bumper shock absorber, including cylinder body and connecting rod, cylinder body inner chamber is separated into air cavity and oil storage chamber through unsteady outer piston, be equipped with piston assembly in the oil storage intracavity, form the cushion chamber between this piston assembly and the unsteady outer piston, the connecting rod lower extreme stretches into the oil storage chamber and links firmly with piston assembly through logical fuel rod, it is equipped with unsteady inner piston in the fuel rod to lead to, this unsteady inner piston will lead to the inner chamber of fuel rod and separate into oil inlet chamber and play oil chamber, it is equipped with the support disk seat to go out the oil intracavity, the last damping channel that has seted up of this support disk seat, it is equipped with the constant current core still to slide in the fuel rod, constant current core outer wall and lead to have the damping clearance between the fuel rod inner wall. This bumper shock absorber improves the shock attenuation effect when guaranteeing life.

Description

Shock absorber

Technical Field

The invention belongs to the technical field of automobile parts and relates to a shock absorber.

Background

The shock absorber is mainly used on an automobile and used for absorbing shock and impact from a road surface, when the automobile passes through an uneven road surface, although the shock absorbing spring can filter the shock of the road surface, the spring can still do reciprocating motion, the shock absorber is used for inhibiting the spring from jumping, the shock absorber is too soft, the automobile body can jump up and down, and the shock absorber is too hard, so that too large resistance is brought, and the normal work of the spring is prevented.

The ring type floating piston single-cylinder shock absorber disclosed in the Chinese patent application (application number: 201510411381.7) comprises a cylinder body and an aluminum floating piston arranged in the cylinder body, wherein the aluminum floating piston moves up and down along the inner wall of the cylinder body, a sealing ring and a guide piston ring are arranged between the cylinder body and the aluminum floating piston in a circumferential direction, the floating piston divides the inner cavity of the cylinder body into an air cavity and an oil storage cavity, a connecting rod is connected to the cylinder body, one end of the connecting rod extends into the oil storage cavity, a piston assembly is fixedly connected to the inner end of the connecting rod, a buffer cavity is formed between the piston assembly and the floating piston, a valve system is arranged on the piston assembly, oil in the oil storage cavity enters the buffer cavity through the valve system when the connecting rod moves upwards, the oil in the buffer cavity returns to the oil storage cavity through a valve core when the connecting rod moves downwards in a resetting manner, so that shock absorption is realized, but in the actual use process, vehicles often pass through notches at high speed, because the speed of a vehicle is fast, the moving stroke of the connecting rod is short, but oil still needs to flow through the valve system, so that the opening times of the valve system are excessive, and the service life is shortened.

In view of the above problems, as disclosed in the chinese patent application (application No. 200810184865.2), a shock absorber includes a cylinder and a piston valve disposed in the cylinder and connected to a piston rod to divide the cylinder into a first chamber and a second chamber, the piston rod including: a hollow cavity formed in the piston rod; first and second holes formed in upper and lower ends of the hollow chamber and connected to the first and second chambers, respectively; a floating piston disposed in the hollow chamber to move up and down and dividing the hollow chamber into an upper chamber and a lower chamber; and a moving mechanism formed in the hollow cavity to move the working fluid to the upper part and the lower part of the floating piston, when the vehicle passes through the notch at high speed, when the moving stroke of the connecting rod is short, the oil in the oil storage cavity enters the upper part cavity and moves downwards through the floating piston, so that the oil in the lower part cavity enters the compression cavity through the shaft hole, namely the oil does not need to pass through the valve system, further the opening times of the valve system is reduced, the valve system is protected, but if the shaft hole of the structure is too large, the resistance of the oil passing through is too small, the buffering effect cannot be achieved, when the shaft hole is too small, the oil passes through difficultly, the pressure in the compression cavity is rapidly increased when the connecting rod moves downwards in a resetting way, the pressure can impact the valve system, and the valve system is damaged.

Disclosure of Invention

The invention aims to solve the problems in the prior art and provides a shock absorber which has the advantage that the shock absorption effect is improved while the service life of the shock absorber is ensured.

The purpose of the invention can be realized by the following technical scheme: a shock absorber comprises a cylinder body and a connecting rod connected to the upper end of the cylinder body in a sliding manner, the inner cavity of the cylinder body is divided into an air cavity and an oil storage cavity by a floating outer piston, a piston assembly is arranged in the oil storage cavity, a buffer cavity is formed between the piston assembly and the floating outer piston, the lower end of the connecting rod extends into the oil storage cavity and is fixedly connected with the piston assembly through an oil through rod, the floating inner piston is arranged in the oil through rod, the floating inner piston divides the inner cavity of the oil through rod into an oil inlet cavity communicated with the oil storage cavity and an oil outlet cavity communicated with the buffer cavity, it is characterized in that a supporting valve seat is arranged in the oil outlet cavity, a plurality of damping channels for oil to pass through are arranged on the supporting valve seat, a constant flow core is arranged in the oil through rod in a sliding manner, the constant flow core is positioned between the supporting valve seat and the buffer cavity, and a damping gap for oil to pass through is formed between the outer wall of the constant flow core and the inner wall of the oil through rod.

The connecting rod is abutted against the floating outer piston through the piston assembly, the floating outer piston is supported by high-pressure gas in the gas cavity, when the connecting rod has a long stroke, the connecting rod drives the piston assembly to move upwards, the oil storage cavity becomes small, so that oil in the oil storage cavity enters the buffer cavity through the valve system on the piston assembly, when the connecting rod moves downwards in a resetting way, the buffer cavity becomes small, the oil in the buffer cavity returns to the oil storage cavity through the valve system, and the damping effect on the oil is generated through the valve system, when the connecting rod has a short stroke, if a vehicle passes through a pit at high speed, the connecting rod also drives the piston assembly to move upwards for a small distance, the oil in the oil storage cavity enters the oil inlet cavity of the oil through rod, so that the floating inner piston in the oil through rod is pushed downwards, the oil in the oil outlet cavity enters the buffer cavity under the action of the floating inner piston, and the oil in the buffer cavity returns to the oil outlet cavity when the connecting rod moves downwards in the resetting way, the floating inner piston moves upwards and enables oil in the oil inlet cavity to return to the oil storage cavity, namely the oil does not need to pass through a valve system on a piston assembly when the connecting rod has short stroke, so that the opening times of the valve system are reduced, the valve core is protected, the service life is prolonged, wherein a damping channel is formed by the supporting valve seat, a damping gap is formed by the constant flow core, and the oil in the buffering cavity needs to pass through the damping gap and the damping channel in sequence, so that the damping of the oil returning to the oil outlet cavity is increased, so that the damping effect is improved, further, the oil in the buffering cavity is subjected to larger pressure due to larger pressure of a vehicle body when the connecting rod moves downwards in a resetting way, and if the damping received at the moment when the oil passes through is too large, the oil in the buffering cavity can impact the valve system to influence the service life of the valve system, and therefore, the constant flow core is arranged in a sliding way, the resistance when the constant flow core slides is smaller, when the pressure in the buffer cavity becomes larger, the oil can push the constant flow core first, the damping received by the oil is mainly generated by the damping channel of the supporting valve seat at the moment, so that a certain damping effect is ensured, meanwhile, the partial pressure in the buffer cavity is released quickly, the impact on the valve system is reduced, when the constant flow core leans against the supporting valve seat and cannot slide, the oil needs to pass through the damping gap, namely, the damping received by the oil is generated by the damping channel and the damping gap together, so that the damping is increased, the time of upward resetting and moving of the connecting rod is prolonged after the partial pressure of the buffer cavity is released quickly, a better damping effect is obtained, and the impact of the oil on the valve system is reduced.

In the above shock absorber, the lower end of the oil rod has a tubular part, the upper end of the tubular part is communicated with the oil outlet cavity, the lower end of the tubular part is communicated with the buffer cavity, the constant flow core is located in the tubular part, and the length of the constant flow core is smaller than that of the tubular part. Tubular part has less area of passing through to increase the damping, and the length of tubular part is greater than the length of deciding the class core, makes to decide the class core and can slide and stretch out and draw back in tubular part, reduces the connecting rod and resets down in the twinkling of an eye the impact of fluid to the valve system, optimizes damped size simultaneously, makes the damping grow gradually, has better shock attenuation effect.

In the shock absorber, the piston assembly is fixedly connected to the tubular part, the buffer cavity is located on the upper end face of the floating outer piston, when the piston assembly abuts against the floating outer piston, the lower end of the tubular part extends into the buffer cavity, a gap is formed between the lower end of the tubular part and the bottom face of the buffer cavity, and the gap is smaller than the length of the constant flow core. Have the clearance between the lower extreme terminal surface of tubulose portion and the bottom surface of cushion chamber, be favorable to fluid to get into the cushion chamber, and this clearance is less than the length of deciding the class core, avoids deciding the class core and roll off tubulose portion completely, provides great slip stroke for deciding the class core again to the hydraulic pressure force of quick release cushion intracavity reduces the impact to the valve system, and improves the shock attenuation effect.

In the above damper, the bottom surface of the cushion chamber is a tapered surface, and the lower end of the tubular portion is opposite to the center position of the bottom surface of the cushion chamber. The conical surface plays a role in guiding and gathering oil, when the oil in the buffer cavity returns to enter the oil outlet cavity, the conical surface enables the oil to gather flow towards the central position and pushes the constant flow core positioned at the central position, and therefore impact of the oil on a valve system is reduced.

In the above damper, the inner hole of the tubular portion is a circular hole, the cross section of the constant flow core is circular, and the outer diameter of the constant flow core is smaller than the inner diameter of the tubular portion. The constant flow core is positioned in the round hole, so that the constant flow core slides more smoothly, the clamping stagnation is avoided, and the damping effect is improved.

In the shock absorber, the oil through rod is provided with a limiting step, the tubular part penetrates through the piston assembly, the penetrating end part is screwed with the fixing nut, and the upper end surface of the piston assembly abuts against the limiting step under the action of the fixing nut. The piston assembly is locked between the fixing nut and the limiting step, and the structure enables the gasket to be additionally arranged between the piston assembly and the limiting step in the actual machining process, so that the length of the tubular part extending into the buffer cavity is adjusted, and the sliding distance of the constant flow core is adjusted to optimize the protection and damping effects on the valve system.

In the above shock absorber, the support valve seat is disc-shaped, the plurality of damping channels are circumferentially and uniformly distributed, each damping channel comprises an axial section and a radial section, the axial section is located on the outer peripheral surface of the support valve seat and penetrates through the support valve seat, and the radial section is located on the lower end surface of the support valve seat. Fluid gets into the axial section through radial section, reentries the oil feed intracavity to produce great damping, and damping passageway circumference equipartition can avoid supporting disk seat local throughput and too big and lead to the atress uneven, can protect promptly to support the disk seat, also can optimize the shock attenuation effect.

In the shock absorber, the central position of the lower end face of the support valve seat is provided with a circular groove, the radial sections of the damping channels are communicated with the groove, the groove is opposite to the upper end of the tubular part, and the inner diameter of the groove is larger than the aperture of the tubular part. Even support the disk seat and when leading to oil pole inner chamber terminal surface and leaning on, still have the grooved space between the two, this recess all the time with tubulose portion intercommunication, be favorable to the oil to reset get into out the oil pocket through tubulose portion in the twinkling of an eye to quick release cushion intracavity's oil hydraulic pressure power reduces the impact to the valve system.

In the shock absorber, the outer peripheral surface of the support valve seat is in transition fit with the inner peripheral surface of the oil through rod, the upper end surface of the support valve seat is a plane, and the outer edge of the lower end surface of the support valve seat is provided with a conical surface adapted to the inner end surface of the oil through rod. The conical surface on the supporting valve seat is matched with the conical surface of the oil rod, so that the supporting valve seat and the oil rod are kept coaxially, and the phenomenon that the supporting valve seat is inclined or blocked when oil impacts is avoided.

In foretell bumper shock absorber, the floating inner piston includes the skeleton of tube-shape and links firmly the block rubber in the skeleton, the both ends terminal surface of block rubber all has spacing convex part, and spacing convex part is located the central point of block rubber terminal surface and puts. The connecting rod moves up and down, the rubber block moves down, the limiting convex part is located at the center, the oil can be guided, the oil is pushed to the peripheral position, so that the damping channel is arranged in the circumferential direction, when the limiting convex part at the lower end of the rubber block is abutted to the upper end face of the supporting valve seat, the space communicated with the damping channel is formed around the limiting convex part, the connecting rod is favorable for moving downwards in a resetting mode, the oil in the damping channel can rapidly pass through due to the sliding of the constant flow core in the moment, the pressure of the oil in the buffer cavity is released, and the impact on a valve system is reduced.

Compared with the prior art, the shock absorber has the following advantages:

1. because when the connecting rod short stroke appears, the fluid in oil storage chamber and the buffer chamber flows through the oil rod, namely the fluid need not to pass through the valve system on the piston assembly when the connecting rod short stroke appears to reduce the number of times of opening of valve system, play the protection to the case, improve life.

2. Because the damping channel is formed by the supporting valve seat, the damping gap is formed by the constant flow core, and the oil in the buffer cavity needs to sequentially pass through the damping gap and the damping channel, the damping of the oil returning to the oil outlet cavity is increased, the resetting time of the connecting rod is prolonged, and the damping effect is improved.

3. Because the constant flow core is arranged in a sliding mode, the resistance of the constant flow core during sliding is small, the oil can push the constant flow core first when the pressure in the buffer cavity becomes large, the damping channel provides damping to guarantee a certain damping effect, partial pressure in the buffer cavity is released quickly, and impact of the oil on a valve system is reduced.

Drawings

Fig. 1 is a partial structural sectional view of a shock absorber.

Fig. 2 is an enlarged view of a structure at a in fig. 1.

Fig. 3 is a perspective view of a support valve seat.

Fig. 4 is an enlarged view of a structure at B in fig. 1.

Fig. 5 is a state diagram when the link of the shock absorber moves upward.

In the figure, 1, a cylinder body; 11. a floating outer piston; 12. a piston assembly; 121. a valve system; 13. an air cavity; 14. an oil storage chamber; 15. a buffer chamber; 2. a connecting rod; 3. an oil rod is communicated; 31. a floating inner piston; 311. a framework; 312. a rubber block; 313. a limiting convex part; 32. an oil inlet cavity; 33. an oil outlet cavity; 34. a tubular portion; 341. a damping gap; 35. a limiting step; 36. fixing a nut; 37. an oil through hole; 4. a support valve seat; 41. a damping channel; 411. an axial section; 412. a radial segment; 42. a groove; 5. and (4) a constant flow core.

Detailed Description

The following are specific embodiments of the present invention and are further described with reference to the accompanying drawings, but the present invention is not limited to these embodiments.

As shown in fig. 1, a shock absorber includes a cylindrical cylinder body 1, a connecting rod 2 is slidably connected to an upper end of the cylinder body 1, a floating outer piston 11 is slidably disposed in the cylinder body 1, the floating outer piston 11 divides an inner cavity of the cylinder body 1 into an oil storage cavity 14 at the upper end and an air cavity 13 at a lower end, high-pressure gas is provided in the air cavity 13, a piston assembly 12 is disposed in the oil storage cavity 14, a buffer cavity 15 is formed between the piston assembly 12 and the floating outer piston 11, a lower end of the connecting rod 2 extends into the oil storage cavity 14, an oil feed rod 3 is fixedly connected to a lower end of the connecting rod 2, the oil feed rod 3 has an inner cavity, a floating inner piston 31 is slidably disposed in the inner cavity, the floating inner piston 31 divides the inner cavity of the oil feed rod 3 into an oil feed cavity 32 and an oil discharge cavity 33, wherein the oil feed cavity 32 is communicated with the oil storage cavity 14 through an oil feed hole 37 opened in a side wall of the oil feed rod 3, and a lower end of the oil feed rod 3 has a tubular portion 34, the upper end of the tubular part 34 is communicated with the oil outlet cavity 33, the lower end is communicated with the buffer cavity 15, the oil through rod 3 is provided with a limit step 35, the tubular part 34 penetrates through the piston assembly 12, the penetrating end part is screwed with a fixing nut 36, the upper end face of the piston assembly 12 is abutted against the limit step 35 under the action of the fixing nut 36, the piston assembly 12 is provided with a valve system 121, and the lower end of the tubular part 34 extends into the buffer cavity 15 when the piston assembly 12 is abutted against the floating outer piston 11.

Specifically, as shown in fig. 2, the inner hole of the tubular portion 34 is a circular hole, a rod-shaped constant flow core 5 is slidably disposed in the tubular portion 34, the cross section of the constant flow core 5 is circular, and the outer diameter of the constant flow core 5 is smaller than the inner diameter of the tubular portion 34, so that a damping gap 341 is formed between the outer wall of the constant flow core 5 and the inner wall of the oil feed rod 3, the length of the constant flow core 5 is smaller than the length of the tubular portion 34, and when the piston assembly 12 abuts against the floating outer piston 11, a gap is formed between the lower end of the tubular portion 34 and the bottom surface of the buffer cavity 15, and the gap is smaller than the length of the constant flow core 5. The bottom surface of the buffer chamber 15 is a tapered surface, and the lower end of the tubular portion 34 is opposite to the center of the bottom surface of the buffer chamber 15.

Referring to fig. 3, a supporting valve seat 4 is disposed in the oil outlet chamber 33, the supporting valve seat 4 is disc-shaped, a plurality of damping passages 41 are disposed on the supporting valve seat 4, the damping passages 41 are circumferentially and uniformly distributed, each damping passage 41 includes an axial section 411 and a radial section 412, the axial section 411 is disposed on the outer peripheral surface of the supporting valve seat 4 and penetrates through the supporting valve seat 4, the radial section 412 is disposed on the lower end surface of the supporting valve seat 4, a circular groove 42 is disposed at the center of the lower end surface of the supporting valve seat 4, the radial sections 412 of the damping passages 41 are communicated with the groove 42, the groove 42 is opposite to the upper end of the tubular part 34, and the inner diameter of the groove 42 is greater than the aperture of the tubular part 34. The outer peripheral face of the support valve seat 4 is in transition fit with the inner peripheral face of the oil through rod 3, the outer edge of the lower end face is provided with a conical face matched with the inner end face of the oil through rod 3, the upper end face of the support valve seat 4 is a plane, as shown in a combined view of fig. 4, the floating inner piston 31 comprises a cylindrical framework 311 and a rubber block 312 fixedly connected in the framework 311, the end faces of two ends of the rubber block 312 are respectively provided with a limiting convex part 313, and the limiting convex parts 313 are located at the central position of the end face of the rubber block 312.

When the connecting rod 2 is used, the connecting rod 2 is abutted against the floating outer piston 11 through the piston assembly 12, the floating outer piston 11 is supported by high-pressure gas in the air cavity 13, when the connecting rod 2 has a short stroke, if a vehicle passes through a pit at high speed, as shown in a combined figure 5, the connecting rod 2 drives the piston assembly 12 to move upwards for a small distance, oil in the oil storage cavity 14 enters the oil inlet cavity 32 of the oil through rod 3, so that the floating inner piston 31 in the oil through rod 3 is pushed downwards, the oil in the oil outlet cavity 33 passes through the tubular part 34 under the action of the floating inner piston 31 and pushes the constant flow core 5 downwards, then enters the buffer cavity 15, the oil in the buffer cavity 15 returns to the oil outlet cavity 33 when the connecting rod 2 moves downwards in a resetting way, the floating inner piston 31 moves upwards and enables the oil in the oil inlet cavity 32 to return to the oil storage cavity 14, namely, the oil does not need to pass through a valve system 121 on the piston assembly 12 when the connecting rod 2 has a short stroke, thereby reducing the opening times of the valve system 121, protecting the valve core and prolonging the service life.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.

Although the terms cylinder 1, floating outer piston 11, piston assembly 12, etc. are used more herein, the possibility of using other terms is not excluded. These terms are used merely to more conveniently describe and explain the nature of the present invention; they are to be construed as being without limitation to any additional limitations that may be imposed by the spirit of the present invention.

Claims

1. A shock absorber comprises a cylinder body (1) and a connecting rod (2) which is connected to the upper end of the cylinder body (1) in a sliding manner, wherein the inner cavity of the cylinder body (1) is divided into an air cavity (13) and an oil storage cavity (14) by a floating outer piston (11), a piston assembly (12) is arranged in the oil storage cavity (14), a buffer cavity (15) is formed between the piston assembly (12) and the floating outer piston (11), the lower end of the connecting rod (2) extends into the oil storage cavity (14) and is fixedly connected with the piston assembly (12) by an oil through rod (3), a floating inner piston (31) is arranged in the oil through rod (3), the floating inner piston (31) divides the inner cavity of the oil through rod (3) into an oil inlet cavity (32) communicated with the oil storage cavity (14) and an oil outlet cavity (33) communicated with the buffer cavity (15), and is characterized in that a supporting valve seat (4) is arranged in the oil outlet cavity (33), and a plurality of damping channels (41) for oil to pass through are arranged on the supporting valve seat (4), a constant flow core (5) is further arranged in the oil through rod (3) in a sliding mode, the constant flow core (5) is located between the supporting valve seat (4) and the buffer cavity (15), and a damping gap (341) for oil to pass through is formed between the outer wall of the constant flow core (5) and the inner wall of the oil through rod (3).

2. The shock absorber according to claim 1, wherein the lower end of the oil rod (3) has a tubular portion (34), the upper end of the tubular portion (34) communicates with the oil outlet chamber (33), the lower end communicates with the buffer chamber (15), the constant flow core (5) is located in the tubular portion (34), and the length of the constant flow core (5) is smaller than the length of the tubular portion (34).

3. The shock absorber according to claim 2, wherein the piston assembly (12) is attached to the tubular portion (34), the buffer chamber (15) is located on the upper end face of the floating outer piston (11), the lower end of the tubular portion (34) extends into the buffer chamber (15) when the piston assembly (12) abuts against the floating outer piston (11), and a gap is provided between the lower end of the tubular portion (34) and the bottom face of the buffer chamber (15), the gap being smaller than the length of the constant flow core (5).

4. A shock absorber according to claim 3, wherein the bottom surface of the buffer chamber (15) is tapered and the lower end of the tubular portion (34) is located opposite the central position of the bottom surface of the buffer chamber (15).

5. The damper according to claim 2, 3 or 4, characterized in that the inner bore of the tubular part (34) is a circular bore, the cross section of the constant flow core (5) is circular, and the outer diameter of the constant flow core (5) is smaller than the inner diameter of the tubular part (34).

6. The shock absorber according to claim 3 or 4, wherein the oil rod (3) is provided with a limit step (35), the tubular part (34) penetrates through the piston assembly (12), a fixing nut (36) is screwed at the penetrating end, and the upper end face of the piston assembly (12) is abutted against the limit step (35) under the action of the fixing nut (36).

7. Shock absorber according to claim 2 or 3 or 4, wherein said support seat (4) is disc-shaped, a plurality of said damping channels (41) being circumferentially distributed, said damping channels (41) comprising an axial section (411) and a radial section (412), said axial section (411) being located on the outer peripheral surface of the support seat (4) and extending through the support seat (4), said radial section (412) being located on the lower end surface of the support seat (4).

8. Shock absorber according to claim 7, wherein the lower end face of the support valve seat (4) has a central position provided with a circular recess (42), the radial sections (412) of the damping channels (41) are all in communication with the recess (42), the recess (42) is opposite the upper end of the tubular portion (34), and the internal diameter of the recess (42) is greater than the aperture of the tubular portion (34).

9. The shock absorber according to claim 8, wherein the outer peripheral surface of the support valve seat (4) is in transition fit with the inner peripheral surface of the oil through rod (3), the upper end surface of the support valve seat (4) is a plane, and the outer edge of the lower end surface is provided with a conical surface adapted to the inner end surface of the oil through rod (3).

10. The shock absorber according to claim 7, wherein the floating inner piston (31) comprises a cylindrical framework (311) and a rubber block (312) fixedly connected in the framework (311), the end faces of the two ends of the rubber block (312) are provided with limit convex parts (313), and the limit convex parts (313) are positioned in the center of the end faces of the rubber block (312).