CN213799676U

CN213799676U - Elastic daub core

Info

Publication number: CN213799676U
Application number: CN202023000527.4U
Authority: CN
Inventors: 周元辉; 陈文韬; 喻建文; 院磊; 赵春先
Original assignee: Zhuzhou Lince Group Shock Absorber Co ltd; Hunan Lince Rolling Stock Equipment Co Ltd
Current assignee: Zhuzhou Lince Group Shock Absorber Co ltd; Hunan Lince Rolling Stock Equipment Co Ltd
Priority date: 2020-12-14
Filing date: 2020-12-14
Publication date: 2021-07-27
Anticipated expiration: 2030-12-14

Abstract

The utility model provides an elasticity daub core, including barrel, direction spiral shell lid, outer spiral shell lid subassembly and piston assembly, the both ends of barrel are equipped with the internal thread with the external screw thread adaptation of direction spiral shell lid and outer spiral shell lid subassembly respectively, direction spiral shell lid plug-in connection is in the one end of barrel, the other end at the barrel is connected to the outer spiral shell lid subassembly, the cavity that barrel, direction spiral shell lid and outer spiral shell lid subassembly enclose is used for holding elasticity daub, is equipped with the through-hole that is used for piston assembly to pass at the central point of outer spiral shell lid subassembly, piston assembly's central cross-section is T shape structure, and its T shape head is located the barrel, and the T shape afterbody is located outside the barrel piston assembly's central point puts and is equipped with and is used for direction spiral shell lid male first counter bore, but the relative piston assembly reciprocating motion of barrel. The elastic daub core has good guidance, strong impact resistance and good sealing property.

Description

Elastic daub core

Technical Field

The utility model relates to a machine car coupler delays technical field, concretely relates to elasticity daub core.

Background

The train is used for a coupler buffer for connecting adjacent carriages, not only can transfer train traction, but also has the functions of buffering and absorbing longitudinal impact energy between the adjacent carriages in the running process of the train, thereby reducing the damage effect on a train body structure and loaded goods. The working principle of the coupler draft gear is to alleviate the impact force by compressing the elastic element, and simultaneously absorb the impact energy by friction and damping in the deformation process of the elastic element. The elastic daub core is used as one of core elastic parts of the coupler buffer, and has the advantages of large capacity, small volume, small impedance, light weight, long overhaul period and the like. However, the existing elastic daub core has the problems of poor guidance quality, poor impact resistance and poor sealing performance, and cannot meet the use requirements.

SUMMERY OF THE UTILITY MODEL

An object of the utility model is to provide an elasticity daub core, concrete technical scheme is as follows:

the utility model provides an elasticity daub core, includes barrel, direction spiral shell lid, outer spiral shell subassembly and piston assembly, the both ends of barrel are equipped with the internal thread with the external screw thread adaptation of direction spiral shell lid and outer spiral shell subassembly respectively, the one end at the barrel is connected in the insertion of direction spiral shell lid, the other end at the barrel is connected to the outer spiral shell subassembly, the cavity that barrel, direction spiral shell lid and outer spiral shell subassembly enclose is used for holding elasticity daub, and central point at outer spiral shell lid subassembly puts and is equipped with the through-hole that is used for piston assembly to pass, piston assembly's central cross-section is T shape structure, and its T shape head position is located the barrel, and the T shape afterbody is located outside the barrel the central point of piston assembly puts and is equipped with the first counter bore that is used for direction spiral shell lid male, but the relative piston assembly reciprocating motion of barrel.

Preferably, the outer screw cap subassembly includes outer screw cap body, first guide ring, first sealing member and first check valve, the through-hole sets up on outer screw cap body, and the hoop is equipped with first recess on the inner wall of through-hole, the quantity of first guide ring is two and the interval sets up in first recess to hug closely with piston assembly, first sealing member sets up in first recess and is located between two first guide rings to hug closely with piston assembly, provide the guide effect for the relative piston assembly motion of outer screw cap body, first check valve sets up and is used for realizing separation and the intercommunication of cavity and outside on outer screw cap body.

Preferably, the outer screw cap assembly further comprises a shaft sleeve and a first clamping ring, the shaft sleeve is arranged between the outer screw cap body and the first guide ring close to the T-shaped head of the piston assembly, one end, close to the T-shaped head of the piston assembly, of the shaft sleeve is abutted to the first clamping ring, and the first clamping ring is arranged in the first groove. The first snap ring is preferably an elastic snap ring, and a certain deformation amount is ensured so that the first snap ring is arranged in the first groove and the first snap ring is tightly abutted to the shaft sleeve.

Preferably, the first check valve comprises a reducing channel, a steel ball, a baffle and a second snap ring, the reducing channel is arranged on the outer screw cap body, the central axis of the reducing channel is parallel to the central axis of the piston assembly, the reducing channel comprises a first channel, a second channel and a third channel which are sequentially communicated, the first channel is communicated with the outside, the third channel is communicated with the cavity, the inner diameter of the second channel is larger than the inner diameter of the first channel and smaller than the inner diameter of the third channel, the steel ball is arranged in the second channel, the diameter of the steel ball is larger than the inner diameter of the first channel and smaller than the inner diameter of the second channel, the baffle is arranged on a step surface formed by the third channel and the second channel, a hole structure is arranged on the baffle, part of elastic daub in the cavity enters the reducing channel through the second snap ring and the hole structure on the baffle, and the steel ball is pushed to the step surface formed by the second channel and the first channel, make first check valve is in the closed condition all the time, when needing to open, can open first check valve from the outside and realize the elasticity daub pressure release to the cavity inside be equipped with the second recess on the inner wall of third passageway, the second snap ring sets up in the second recess and with baffle next-door neighbour's setting, the preferred elasticity snap ring of second snap ring ensures certain deflection so that the second snap ring sets up in the second recess.

Preferably, the outer screw cap body is further provided with a first hand taking position, the first hand taking position is formed by two symmetrically arranged counter bores, one counter bore is communicated with the first channel, and the outer screw cap body is convenient to mount and dismount.

Preferably, the piston assembly comprises a piston rod body, a second one-way valve and a second guide ring, the central cross section of the piston rod body is of a T-shaped structure, the number of the second one-way valves is at least two, the second one-way valves are arranged on the T-shaped head of the piston rod body in an annular symmetry manner, the structure of the second one-way valve is the same as that of the first one-way valve, the opening end of the first channel of the second one-way valve is further provided with a horn-shaped opening structure, when the elastic daub core is impacted, the second one-way valve is closed, when the impact of the elastic daub core is eliminated, the elastic daub elastic force in the accommodating space is greater than that in the cavity, the elastic force difference exists, so that the steel ball of the second one-way valve is jacked open under the elastic daub elastic force in the accommodating space, and the elastic daub in the accommodating space quickly returns to the cavity through the hole structure on the baffle plate, the second snap ring can be spacing to the baffle in order to avoid first check valve and second check valve to lose efficacy because of the baffle drops, first counter bore setting is equipped with the third recess on the piston rod body and on the inner wall of first counter bore open end hoop, the second guide ring sets up in the third recess and hugs closely with the section of inserting of direction spiral shell lid, provides the guide effect for the insertion of direction spiral shell lid.

Preferably, the section of inserting of direction spiral shell lid is equipped with the second counter bore that communicates with first counter bore, packs elastic daub in the counter bore region that first counter bore and second counter bore enclose, provides supplementary damping force when being convenient for elastic daub core receives the impact, further absorbs the impact energy be equipped with the first micropore that is used for first counter bore and cavity intercommunication on the piston rod body the section of inserting of direction spiral shell lid is equipped with the second micropore that is used for second counter bore and cavity intercommunication, and the elastic daub pressure release in the counter bore region is convenient for in first micropore and the setting of second micropore the section of inserting of direction spiral shell lid still is equipped with the second and gets the hand position, the second is got the counter bore that the hand position was two symmetrical arrangement, the installation and the dismantlement of the spiral shell lid of being convenient for to lead.

Preferably, the elastic daub core further comprises two second sealing elements, and the two second sealing elements are respectively arranged at the joint between the guide screw cap and the cylinder body and the joint between the outer screw cap body and the cylinder body.

Preferably, the first sealing element is a combined sealing element formed by stacking a plurality of v-shaped rubber rings, the second sealing element is a rubber ring, and the sealing performance of the elastic cement core is effectively guaranteed by the arrangement of the first sealing element and the second sealing element.

Preferably, the elasticity daub core, still include connecting plate, guide cylinder and two third guide rings, piston assembly's the terminal laminating of T shape afterbody is on the connecting plate, the one end and the connecting plate fixed connection of guide cylinder, and the outer wall sliding connection of the other end and barrel the interval is equipped with two fourth recesses on the inner wall of the one end that guide cylinder and barrel are connected, the setting of third guide ring one-to-one is hugged closely in the fourth recess and with the barrel, provides the guide effect for the relative guide cylinder motion of barrel.

Use the technical scheme of the utility model, following beneficial effect has:

elastic daub core is when receiving the impact, the section of inserting of direction spiral shell lid progressively sinks in first counter bore, for the motion of the relative piston assembly of barrel provides the direction, barrel motion makes and forms accommodation space between the T shape head of outer piston assembly and piston assembly, make the cavity volume diminish, elastic daub volume in the cavity produces elastic force absorption impact energy by compression, and will absorb impact energy and convert thermal energy consumption into and scatter or convert into elastic energy and store, and the part elastic daub that receives compression can be extruded into accommodation space through the gap between piston assembly and barrel. When the impact is eliminated, the elastic daub core forces the guide screw cap to be away from the piston assembly quickly under the action of elastic force, and the elastic daub located in the accommodating space can also return to the cavity under the action of the elastic force until the elastic daub core recovers to the initial position. Elasticity daub core guidance quality is good and shock resistance is strong.

In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be described in further detail with reference to the drawings.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. In the drawings:

fig. 1 is a schematic structural view of a central section of an elastic daub core according to embodiment 1 of the present invention (fig. 1 does not show elastic daub filled in a counter bore region and a first micropore and a second micropore);

FIG. 2 is an enlarged view of area A of FIG. 1;

FIG. 3 is an enlarged view of area B of FIG. 1;

the hydraulic cylinder comprises a cylinder body 1, a cylinder body 2, a guide screw cap 2.1, a second counter bore 2.2, a second hand taking position 3, an outer screw cap component 3.1, an outer screw cap body 3.1.1, a first hand taking position 3.2, a first guide ring 3.3, a first sealing element 3.4, a first one-way valve 3.4.1, a reducing channel 3.4.2, a steel ball 3.4.3, a baffle 3.4.4, a second snap ring 3.5, a shaft sleeve 3.6, a first snap ring 4, a piston component 4.1, a first counter bore 4.2, a piston rod body 4.3, a second one-way valve 4.4, a second guide ring 5, a second sealing element 6, a connecting plate 7, a guide cylinder 8, a third guide ring 9 and elastic cement.

Detailed Description

The embodiments of the invention will be described in detail hereinafter with reference to the accompanying drawings, but the invention can be implemented in many different ways, which are defined and covered by the claims.

Example 1:

referring to fig. 1 to 3, an elastic daub core includes a cylinder 1, a guide screw cap 2, an outer screw cap assembly 3 and a piston assembly 4, two ends of the cylinder body 1 are respectively provided with an internal thread matched with the external threads of the guide screw cap 2 and the external screw cap component 3, the guide screw cap 2 is inserted into one end of the cylinder body 1, the outer screw cap component 3 is connected with the other end of the cylinder body 1, a cavity surrounded by the cylinder body 1, the guide screw cap 2 and the outer screw cap component 3 is used for containing elastic daub 9, a through hole for the piston component 4 to pass through is arranged at the central position of the external screw cap component 3, the central section of the piston component 4 is of a T-shaped structure, the T-shaped head part is positioned in the cylinder body 1, the T-shaped tail part is positioned outside the cylinder body 1, a first counter bore 4.1 for inserting the guide screw cap 2 is arranged at the center of the piston assembly 4, and the cylinder body 1 can reciprocate relative to the piston assembly 4.

Referring to fig. 1-2, the outer screw cap assembly 3 includes an outer screw cap body 3.1, first guide rings 3.2, first sealing members 3.3 and first check valves 3.4, the through hole is disposed on the outer screw cap body 3.1, and a first groove is circumferentially disposed on an inner wall of the through hole, the number of the first guide rings 3.2 is two, and the first guide rings are disposed in the first groove at intervals and tightly attached to the piston assembly 4, the first sealing members 3.3 are disposed in the first groove and located between the two first guide rings 3.2 and tightly attached to the piston assembly 4, so as to provide a guiding function for movement of the outer screw cap body 3.1 relative to the piston assembly 4, and the first check valves 3.4 are disposed on the outer screw cap body 3.1 for blocking and communicating the cavity with the outside.

Referring to fig. 1-2, the outer cap assembly 3 further includes a sleeve 3.5 disposed between the outer cap body 3.1 and the first guide ring 3.2 adjacent to the T-shaped head of the piston assembly 4, and an end of the sleeve adjacent to the T-shaped head of the piston assembly 4 abuts against the first snap ring 3.6, and the first snap ring 3.6 is disposed in the first groove. First snap ring 3.6 is preferably the elastic snap ring, ensures certain deflection in order to make things convenient for first snap ring 3.6 to set up in first recess and first snap ring 3.6 and axle sleeve closely to butt.

Referring to fig. 1-2, the first check valve 3.4 includes a reducing channel 3.4.1, a steel ball 3.4.2, a baffle 3.4.3 and a second snap ring 3.4.4, the reducing channel 3.4.1 is disposed on the outer screw cap body 3.1, and the central axis thereof is parallel to the central axis of the piston assembly 4, the reducing channel 3.4.1 includes a first channel, a second channel and a third channel which are sequentially communicated, the first channel is communicated with the outside, the third channel is communicated with the cavity, the inner diameter of the second channel is larger than that of the first channel and smaller than that of the third channel, the steel ball 3.4.2 is disposed in the second channel, and the diameter of the steel ball 3.4.2 is larger than that of the first channel and smaller than that of the second channel, the baffle 3.4.3 is disposed on the step surface formed by the third channel and the second channel, and the baffle 3.4.3 is provided with a hole structure, part of the elastic daub in the cavity enters the reducing channel 3.4.1 through the second snap ring 3.4.4.4, the hole structure on the baffle 3.4.3, and push away steel ball 3.4.2 to the second passageway with on the step face that the first passageway formed, make first check valve 3.4 is in the closed condition all the time, when needing to open, can open first check valve 3.4 from the outside and realize the pressure release to the inside elasticity daub 9 of cavity be equipped with the second recess on the inner wall of third passageway, second snap ring 3.4.4 sets up in the second recess and with baffle 3.4.3 close neighbour's setting, the preferred elasticity snap ring of second snap ring 3.4.4 ensures certain deflection so that second snap ring 3.4.4 sets up in the second recess.

Referring to fig. 1-2, a first hand taking position 3.1.1 is further arranged on the outer screw cap body 3.1, the first hand taking position 3.1.1 is formed by two counter bores which are symmetrically arranged, and one of the counter bores is communicated with the first channel, so that the outer screw cap body 3.1 can be conveniently mounted and dismounted.

Referring to fig. 1 and 3, the piston assembly 4 includes a piston rod body 4.2, a second check valve 4.3 and a second guide ring 4.4, the central cross section of the piston rod body 4.2 is a T-shaped structure, at least two sets of second check valves 4.3 are arranged at the T-shaped head of the piston rod body 4.2 in circumferential symmetry, the structure of the second check valve 4.3 is the same as that of the first check valve 3.4, the open end of the first channel of the second check valve 4.3 is further provided with a trumpet-shaped opening structure, when the elastic daub core is impacted, the second check valve 4.3 is closed, when the impact of the elastic daub core is eliminated, the elastic force of the elastic daub 9 in the accommodating space is greater than the elastic daub elastic force in the cavity, there is an elastic force difference, so that the steel ball of the second check valve 4.3 is pushed open under the elastic force of the elastic daub 9 in the accommodating space, and the elastic daub 9 in the accommodating space quickly returns to the cavity through the hole structure on the baffle plate, second snap ring 3.4.4 can be spacing in order to avoid first check valve 3.4 and second check valve 4.3 to lose efficacy because of the baffle drops, first counter bore 4.1 sets up on piston rod body 4.2 and the hoop is equipped with the third recess on the inner wall of first counter bore 4.1 open end, second guide ring 4.4 sets up and hugs closely in the third recess and with the section of inserting of direction spiral shell lid 2, provides the guide effect for the insertion of direction spiral shell lid 2.

Referring to fig. 1, the insertion section of the guide screw cap 2 is provided with a second counter bore 2.1 communicated with the first counter bore 4.1, a counter bore region surrounded by the first counter bore 4.1 and the second counter bore 2.1 is filled with elastic cement 9, so that an auxiliary damping force is provided when the elastic cement core is impacted, and impact energy is further absorbed, the piston rod body 4.2 is provided with a first micropore used for communicating the first counter bore 4.1 with the cavity, the insertion section of the guide screw cap 2 is provided with a second micropore used for communicating the second counter bore 2.1 with the cavity, the arrangement of the first micropore and the second micropore is convenient for pressure relief of the elastic cement 9 in the counter bore region, the non-insertion section of the guide screw cap 2 is further provided with a second hand taking position 2.2, and the second hand taking positions 2.2 are two counter bores symmetrically arranged, so that the guide screw cap 2 is convenient to install and detach.

Referring to fig. 1, the elastic daub core further includes two second sealing members 5, and the two second sealing members 5 are respectively disposed at a joint between the guide screw cap 2 and the cylinder 1 and a joint between the outer screw cap body 3.1 and the cylinder 1.

Referring to fig. 1, the first sealing element 3.3 is a combined sealing element formed by stacking a plurality of v-shaped rubber rings, the second sealing element 5 is a rubber ring, and the arrangement of the first sealing element 3.3 and the second sealing element 5 effectively ensures the sealing performance of the elastic daub core.

Referring to fig. 1, the elastic daub core further comprises a connecting plate 6, a guide cylinder 7 and two third guide rings 8, the tail end of the T-shaped tail of the piston assembly 4 is attached to the connecting plate 6, one end of the guide cylinder 7 is fixedly connected with the connecting plate 6, the other end of the guide cylinder is connected with the outer wall of the cylinder 1 in a sliding mode, two fourth grooves are formed in the inner wall of one end, connected with the cylinder 1, of the guide cylinder 7 at intervals, the third guide rings 8 are arranged in the fourth grooves in a one-to-one mode and are tightly attached to the cylinder 1, and a guiding effect is provided for the cylinder 1 to move relative to the guide cylinder 7.

This embodiment the elasticity daub core is when receiving the impact, the section of inserting of direction spiral shell lid 2 progressively sinks in first counter bore 4.1, for the motion of barrel 1 relative piston assembly 4 provides the direction, barrel 1 motion makes and forms accommodation space between the T shape head of outer piston assembly 3 and piston assembly 4, make the cavity volume diminish, elasticity daub 9 volume in the cavity receives compression and produces elastic force and absorb impact energy, and will absorb impact energy and convert thermal energy consumption and scatter or convert the elastic energy storage into, and partial elasticity daub 9 that receives compression can be crowded into accommodation space through the gap between piston assembly 4 and barrel 1. When the impact is eliminated, the elastic daub core forces the guide screw cap 2 to be away from the piston assembly 4 quickly under the action of elastic force, and the elastic daub 9 located in the accommodating space can also return to the cavity under the action of the elastic force until the elastic daub core recovers to the initial position. The elastic daub core has good guidance, strong impact resistance and good sealing property.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The utility model provides an elasticity daub core, its characterized in that, includes barrel, direction spiral shell lid, outer spiral shell subassembly and piston assembly, the both ends of barrel are equipped with the internal thread with the external screw thread adaptation of direction spiral shell lid and outer spiral shell subassembly respectively, the one end at the barrel is connected in the direction spiral shell lid insertion, the other end at the barrel is connected to the outer spiral shell subassembly, the cavity that barrel, direction spiral shell lid and outer spiral shell subassembly enclose is used for holding elasticity daub, and the central point of spiral shell lid subassembly puts and is equipped with the through-hole that is used for piston assembly to pass outside, piston assembly's central cross-section is T shape structure, and its T shape head is located the barrel, and the T shape afterbody is located outside the barrel the central point of piston assembly puts and is equipped with the first counter bore that is used for direction spiral shell lid male, but the relative piston assembly reciprocating motion of barrel.

2. The elastic daub core as claimed in claim 1, wherein the outer screw cap assembly comprises an outer screw cap body, first guide rings, first sealing members and first check valves, the through hole is formed in the outer screw cap body, a first groove is circumferentially formed in the inner wall of the through hole, the number of the first guide rings is two, the first guide rings are arranged in the first groove at intervals and tightly attached to the piston assembly, the first sealing members are arranged in the first groove and located between the two first guide rings and tightly attached to the piston assembly, and the first check valves are arranged on the outer screw cap body and used for achieving blocking and communication between the cavity and the outside.

3. The elastomeric mastic core of claim 2, wherein the outer cap assembly further comprises a bushing disposed between the outer cap body and the first guide ring proximate the T-shaped head of the piston assembly, and a first snap ring disposed in the first groove, wherein an end of the bushing proximate the T-shaped head of the piston assembly abuts the first snap ring.

4. The elastic daub core as claimed in claim 3, wherein the first check valve comprises a diameter-variable channel, a steel ball, a baffle plate and a second snap ring, the diameter-variable channel is arranged on the outer screw cap body, and the central axis of the variable diameter channel is parallel to the central axis of the piston assembly, the variable diameter channel comprises a first channel, a second channel and a third channel which are sequentially communicated, the first channel is communicated with the outside, the third channel is communicated with the cavity, the inner diameter of the second channel is larger than that of the first channel, and is smaller than the inner diameter of the third channel, the steel ball is arranged in the second channel, the diameter of the steel ball is larger than the inner diameter of the first channel and smaller than the inner diameter of the second channel, the baffle is arranged on the step surface formed by the third channel and the second channel, and a hole structure is arranged on the baffle, and a second groove is formed in the inner wall of the third channel, and the second clamping ring is arranged in the second groove and is closely adjacent to the baffle.

5. The elastic daub core as claimed in claim 4, wherein a first hand-fetching position is further provided on the outer nut cap body, the first hand-fetching position is formed by two symmetrically arranged counter bores, and one counter bore is communicated with the first channel.

6. The elastic daub core according to claim 5, wherein the piston assembly comprises a piston rod body, a second one-way valve and a second guide ring, the central section of the piston rod body is of a T-shaped structure, the number of the second one-way valves is at least two, the second one-way valves are annularly and symmetrically arranged on the T-shaped head of the piston rod body, the structure of the second one-way valve is the same as that of the first one-way valve, the open end of the first channel of the second one-way valve is further provided with a horn-shaped opening structure, the first counter bore is arranged on the piston rod body, a third groove is annularly arranged on the inner wall of the open end of the first counter bore, and the second guide ring is arranged in the third groove and is tightly attached to the insertion section of the guide screw cap.

7. The elastic daub core according to claim 6, wherein the insertion section of the guide screw cap is provided with a second counter bore communicated with the first counter bore, the counter bore region surrounded by the first counter bore and the second counter bore is filled with the elastic daub, the piston rod body is provided with a first micro-hole for communicating the first counter bore with the cavity, the insertion section of the guide screw cap is provided with a second micro-hole for communicating the second counter bore with the cavity, the non-insertion section of the guide screw cap is further provided with a second hand-taking position, and the second hand-taking position is formed by two symmetrically arranged counter bores.

8. The elastic daub core as claimed in claim 7, further comprising two second sealing members respectively provided at a junction between the guide screw cap and the barrel and at a junction between the outer screw cap body and the barrel.

9. The elastomeric mastic core of claim 8, wherein the first seal is a composite seal having a plurality of v-shaped rubber rings stacked together, the second seal is a rubber ring, and the first snap ring and the second snap ring are both snap rings.

10. The elastic daub core according to any one of claims 1 to 9, further comprising a coupling plate, a guide cylinder and a third guide ring, wherein the end of the T-shaped tail of the piston assembly is attached to the coupling plate, one end of the guide cylinder is fixedly connected with the coupling plate, the other end of the guide cylinder is slidably connected with the outer wall of the cylinder, a fourth groove is formed in the inner wall of the end of the guide cylinder connected with the cylinder, and the third guide ring is arranged in the fourth groove and is tightly attached to the cylinder.