EP3140461A1

EP3140461A1 - Crumber for trencher

Info

Publication number: EP3140461A1
Application number: EP15789841.2A
Authority: EP
Inventors: Stewart James Wright
Original assignee: Digga Australia Pty Ltd
Current assignee: Digga Australia Pty Ltd
Priority date: 2014-05-07
Filing date: 2015-05-06
Publication date: 2017-03-15
Also published as: WO2015168737A1; AU2015255633A1; US20170067225A1; EP3140461A4

Abstract

A crumber for a trencher machine, the crumber comprising a crumber mount (12) for mounting to a crumber boom (11), and a crumber arm (14), the crumber arm (14) being mounted to the crumber mount (12) by a linkage, the linkage comprising a first linkage arm (20) and a second linkage arm (22), the linkage being arranged to allow rotation of at least one of the linkage arms of at least 75°. The crumber mount (12) has at least one edge or surface that is of complementary shape to an edge or surface of the crumber arm (14), wherein the least one edge or surface of the crumber mount and the complementary edge or surface of the crumber arm abut on each other when the crumber arm is in a lowermost position. In this manner, the crumber arm is supported along an extended length when in the lowermost position.

Description

TITLE

Crumber for trencher. TECHNICAL FIELD

[00011 The present invention relates to a crumber for trencher. BACKGROUND ART

[0002] A conventional trencher machine includes an elongated boom which is connected to a frame of the trencher machine for vertical pivotal movement. A digging chain and tooth assembly is supported by the boom for orbital movement thereabout. The trencher boom can be lowered to commence digging a trench.

[0003] A crumber is typically arranged in combination with the chain and tooth assembly of the trencher machine. The crumber assists in cleaning out the trench. In use, the di stal end of the crumber extends past the distal end of the trencher boom. The crumber will typically have a crumber foot or a crumber shoe (which may also called a scraper plate) at the distal end thereof and the crumber foot or crumber shoe acts to keep rocks and other debris loosened by digging of the trench in close proximity to the digging chain and tooth, thereby assisting in the dirt, rocks or other debris being removed from the trench by the digging chain and tooth assembly.

[0004] A typical crumber comprises a crumber boom that is mounted to the trencher machine. A crumber ann is mounted to the crumber boom in a manner such that the crumber arm can move upwardly and downwardly in a vertical plane relative to the crumber boom. For example, the crumber arm may be linked to the crumber boom by a linkage arrangement in which a first linkage arm is pivotally mounted at one end to the crumber boom (or to a crumber mount that is mounted to the crumber boom) and pivotally mounted at a second end to the crumber ann and a second linkage arm is pivotally mounted at one end to the crumber boom (or to a crumber mount that is mounted to the crumber boom) and pivotally mounted at a second end to the crumber arm.

[0005] The crumber arm is typically spring-loaded such that it is biased to a lowermost position. When a new trench is to be dug, the trencher boom is lowered until the distal end comes to contact with the ground stop the chain and tooth arrangement is operated to commence digging a trench. Continue lowering of the boom causes the trench to become deeper. Once the trencher boom has been lowered to be desired depth of the trench, the trencher machine is then moved along the line along which the trench is to be dug.

[0006] It will be appreciated that the distal end of the crumber extends past the distal end of the trencher boom. As a result, at the commencement of excavation of a new trench, the distal end of the crumber arm will contact the earth beyond the distal end of the trencher boom. As the trencher boom is continued to be lowering during the initial stages of excavation of the trench, the distal end of the crumber arm will remain in contact with the essentially undisturbed soil that is beyond the extent of the trench being dug. This causes the crumber arm to pivot upwardly relative to the trencher boom (it being appreciated that the crumber arm remains essentially at ground level whilst the trencher boom is progressively lowered into the ground). Unfortunately, it is a common occurrence that the crumber arm is pivoted upwardly relative to the trencher boom to an extent such that the maximum travel of the crumber arm is reached. In these circumstances, further lowering of the trencher boom will cause damage to the crumber arm.

[0007| To avoid this problem, in practice the operator of the trencher machine will remove the crumber arm from the crumber boom prior to commencing excavation of a new trench. Once the full depth of the trench has been dumped, the operator must then reattach the crumber arm to the crumber boom. Although this protects the crumber arm from damage, these steps lengthen the time required to excavate a trench. They also have the potential to cause is some occupational health and safety issues during removal and reattachment of the crumber arm to the crumber boom.

[0008] It has also been found that the linkage arms used to connect the crumber arm to the crumber boom (or to the crumber mount that is attached to the crumber boom) may be damaged during use of the crumber. Further, wear can occur in regions where the crumber arm comes into contact with the crumber mount. This wear can be accentuated during transport of the trenching machine because the crumber arm will be typically in its down position due to the action of the biasing spring during transport of the trenching machine.

[0009] It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.

SUMMARY OF INVENTION

[0010] The present invention is directed to crumber, which may at least partially overcome at least one of the abovementioned disadvantages or provide the consumer with a useful or commercial choice.

[00111 With the foregoing in view, the present invention in one form, resides broadly in a crumber for a trencher machine, the crumber comprising a crumber mount for mounting to a crumber boom, and a crumber arm, the crumber arm being mounted to the crumber mount by a linkage, the linkage comprising a first linkage arm and a second linkage arm, the linkage being arranged to allow rotation of at least one of the linkage arms of at least 75°.

[0012] In one embodiment, at least one of the linkage arms can rotate by between 75 to 120°, more preferably from 80 to 1 10°, even more preferably from 85 to 100°, even more preferably about 90°.

[0013] In one embodiment, the linkage comprises a first linkage arm pivotally connected to the crumber mount and pivotally connected to the crumber arm, and a second linkage arm pivotally connected to the crumber mount and pivotally connected to the crumber arm.

[0014] In another embodiment, the linkage comprises a pair of first linkage arms each pivotally connected to the crumber mount and pivotally connected to the crumber arm, and a pair of second linkage arms each pivotally connected to the crumber mount and pivotally connected to the crumber arm.

[0015] In one embodiment, the crumber arm comprises a first crumber arm side plate and a second crumber arm side plate, the first and second crumber arm side plates being connected to each other. The two side plates maybe connected to each other by one or more intermediate connectors. The intermediate connectors may be welded to the first and second crumber arm side plates.

[0016] In some embodiments, the linkage comprises a first proximal linkage arm and a second distal linkage arm, with the second distal linkage arm having a distal end pivotally connected to a crumber side plate, the distal end of the second linkage arm being located between the first crumber arm side plate and the second crumber arm side plate. In this manner, the distal end of the second linkage arm is located inside a volume defined by the first crumber arm side plate and the second crumber arm side plate. Thus, the crumber arm side plates act to protect the distal end of the second linkage arm from damage that may otherwise be caused by contact with dirt or debris.

[0017] In one embodiment, the crumber arm is movable from a first lowermost position to a second uppermost position, the second proximal linkage arm lying approximately parallel to the crumber boom when the crumber arm is in the first lowermost most position.

[0018] In one embodiment, the first proximal, arm can rotate by at least 75° when the crumber arm is moving from the first downward most position to the second uppemiost position. Preferably, the first proximal, arm can rotate can rotate by between 75 to 120°, more preferably from 80 to 1 10°, even more preferably from 85 to 100°, even more preferably about 90°, ° when the crumber arm is moving from the first lowermost position to the second uppermost position.

[0019] In some embodiments, the first proximal linkage arm is shorter than the second distal linkage arm.

[0020] In some embodiments, the crumber mount has at least one edge or surface that is of complementary shape to an edge or surface of the crumber arm, wherein the least one edge or surface of the crumber mount and the complementary edge or surface of the crumber arm abut on each other when the crumber arm is in a lower most position.

[0021] In a second aspect, the present invention provides a crumber for a trencher machine, the crumber comprising a crumber mount for mounting to a crumber boom, and a crumber arm, the crumber arm being mounted to the crumber mount by a linkage, the crumber mount having at least one edge or surface that is of complementary shape to an edge or surface of the crumber arm, wherein the least one edge or surface of the crumber mount and the complementary edge or surface of the crumber arm abut on each other when the crumber arm is in a lowermost position.

[0022] In this embodiment, the at least one edge or surface of crumber arm comes into contact with and is supported by the complementary edge or surface of the crumber mount when the crumber arm is in the lowermost position. Thus, the crumber arm is supported by the crumber mount along an extended length (being the length of the complementary edge or surface of the crumber mount) when in the lowermost position. This is in contrast to prior art crumbers where the crumber arm would often just come into contact with a point of the crumber mount when the crumber arm was in the lowermost position, thereby increasing wear.

[0023] The crumber mount may be provided with two or more apertures to enable the crumber mount to be fixed to the crumber boom. The crumber mount may be fixed to the crumber boom by use of appropriate fastening pins, bolts, screws or any other suitable fasteners.

[0024] The crumber mount may comprise two spaced mount side plates. The two side plates may be mounted to the crumber boom. The two spaced side plates may be connected together. [0025] The crumber may further comprise a biasing means to bias the crumber arm to a lowermost position. The biasing means may comprise a spring. The spring may be mounted within the crumber mount. The spring may have an end that bears against the crumber arm in order to bias in the crumber arm to a lower most position.

[0026] In some embodiments, the second distal linkage arm has a proximal end located between the two spaced crumber mount side plates and a distal end located between the two spaced crumber arm side plates.

[0027] In some embodiments, the first proximal crumber arm extends at an angle of about 20 to 30°, preferably about 25°, to the crumber boom when the crumber arm is in a lower most position, and extends at an angle of about 95° to 145°, more preferably from 105° to 135°, even more preferably from 1 10° to 125°, even more preferably about 1 15° to the crumber boom, when the crumber arm is an uppermost position.

[0028] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention.

[0029] The reference to any prior art in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.

BRIEF DESCRIPTION OF DRAWINGS

[0030] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows:

[0031] Figure 1 shows a side view of a crumber for a trencher in accordance with an embodiment of the present invention. In figure 1, the crumber arm is in a lowermost position;

[0032] Figure 2 shows a side view of the crumber shown in figure 1 , with the crumber arm shown in an uppermost position;

[0033] Figure 3 shows a perspective view of the crumber shown in figure 1, with the crumber being shown apart and in line for assembly; [0034] Figure 4 shows a side cross-secti onal view of the crumber mount of the crumber shown in figures 1 to 3;

[0035] Figure 5 shows an end view of the crumber mount shown in figure 4;

[0036] Figure 6 shows a side view of the crumber arm of the crumber shown in figure 1 ;

[0037] Figure 7 shows a perspective view of the crumber arm shown in figure 6;

[0038] Figures 8 and 9 show side views of the crumber shown in figures 1 and 2, respectively, with angles of rotation added thereto; and

[0039] Figures 10 and 11 show side views of a prior art crumber, with the crumber ami shown in a lowermost position in figure 10 and the crumber arm shown in an uppermost position in figure 1 1.

DESCRIPTION OF EMBODIMENTS

[0040] The crumber 10 shown in figures 1 to 3 comprises a crumber mount 12 and a crumber arm 14. The crumber mount 12 has apertures 16, 18 formed therein. The apertures 16, 18 can be placed in line with similar apertures formed in a crumber boom and fasteners, such as fastening pins or bolts, can be passed through the aligned apertures to fix or mount the crumber mount to the crumber boom. The crumber boom 1 1 is shown in dashed outline in figure 1.

[0041 ] The crumber arm 14 is connected to the crumber mount 12 by means of a linkage. The linkage comprises a first linkage arm 20 and a second linkage arm 22. The first linkage arm 20 comprises a proximal linkage ann and the second linkage and 22 comprises a distal linkage arm. In this regard, the trencher machine is located proximal to end 24 of the crumber mount 12.

[0042] Turning now to figure 3, the crumber mount 12 comprises a first crumber mount side plate 26 and a second crumber mount side plate28. Side plate 26 is spaced from side plate 28. An intermediate support plate 30 is positioned between the side plates 26 and 28. The side plates are provided with openings 32, 34 (see figure 1 ) that receive tabs on the intermediate support plate 32 thereby holding the intermediate support plate 30 in position. Intermediate support plate 30 may be welded to the side plates 26, 28.

[0043] The crumber arm 14 includes first crumber arm side plate 36 and second crumber arm side plate 38. Crumber ann side plates 36 and 38 are spaced from each other. A stiffener 40 is located between the crumber arm side plates 36 and 38 and welded thereto. A scraper plate 42 is welded to the lower end of the crumber arm 14 and acts to rigidly fix the lower end of the crumber arm side plates 36 and 38 together. In use, the lower end of the scraper plate 42 contacts the bottom of the trench and acts to move dirt and debris into close proximity with the trencher boom, thereby facilitating removal of dirt and debris from the trench by the chain and teeth rotating around the trencher boom. In practice, the scraper plate 42 may be fitted with removable feet. The removable feet may be replaced when they are worn. Alternatively, the scraper plate 42 may be hard-faced in order to increase its useful working life. The scraper plate may have one or more points or intensifiers formed at its lower end. The improves operation of the crumber.

[0044] The side plates of the crumber arm 14 are provided with apertures 44 and 46.

Similarly, the crumber mount side plates 26, 28 are provided with apertures 48. A linkage arm assembly 50 is connected at its proximal end by a pin that passes through apertures 48 and aligned apertures 52 formed in the linkage arm assembly 50. This connects the proximal end of the linkage arm assembly 50 to the crumber mount side plates 26, 28. Similarly, the linkage arm assembly 50 is connected at its distal end by a pin that passes through apertures 44 in the crumber arm side plates 36, 38 and through an aligned aperture 54 in the distal end of the linkage am assembly 50. This pivotally connects the distal end of the linkage am assembly 50 to the crumber arm 14. It will be appreciated that the linkage arm assembly 50 comprises two spaced second linkage arms 22. In some embodiments, screw button head sockets 64 may be used to fasten the pivotal connections.

[0045] As best shown in figures 1 and 2, the two spaced distal linkage arms 22 are located between the two spaced crumber mount side plates and the two spaced crumber arm side plates. As a result, the two distal linkage arms 22 are located to the inside of the si de plates of the crumber mount and the crumber arm. Consequently, the side plates provide a degree of protection to the linkage arms as the linkage arms are not fully exposed to the working environment.

[0046] The crumber mount side plates 26, 28 are each provided with an aperture 56. A screw button head socket 58 passes through an aperture in the proximal end of the first linkage arm 20 and is used to pivotally connect the proximal end of the first linkage arm 14 to the crumber mount side plate 26. A similar arrangement utilising screw button head socket 62 is used to connect another proximal linkage arm to the other crumber mount side plate 28. The distal end of the proximal linkage arms 14 are connected in a similar fashion to the proximal end of the crumber arm side plates 36, 38, with the socket 62 passing through openings in the distal end of the proximal linkage arms 20 and two proximal apertures 46 in the side plates of the crumber arm. In this manner, the proximal linkage arms 14 are pivotally connected to both the crumber mount 12 and the crumber ami 14.

[0047] The crumber arm 14 is biased to the lowermost position shown in figure 1. In order to enable this to occur, a biasing spring 64 is fitted over a spring support 66. Spring support 66 is held in place by the pin 68 that forms part of the pivotal connection for the proximal end of the proximal linkage arms 20 to the crumber mount 12. A distal end of a biasing spring 64 extends over the end 70 of the crumber arm 14. A proximal end of the biasing spring 64 rests in recess 72 formed in intermediate support plate 30 that is fitted between the side plates 26, 28 of the crumber mount 14. In this manner, the spring acts to push downwardly on the crumber arm 14, thereby biasing the crumber arm 14 to the lowermost position shown in figure 1 in the absence of any external applied force.

[0048] Returning now to figures 1 and 2, the crumber arm 14 can move between the lowermost position shown in figure 1 and an uppermost position shown in figure 2. During movement of the crumber arm, the linkage arms 20, 22 rotate about the pivotal connections to both the crumber mount 12 and the crumber arm 14. As shown in figure 2, the second linkage arm 22 is significantly longer than the first linkage arm 20. Indeed, the second linkage and 22 may be from 1.5 to 2 times longer than the first linkage arm 20, more preferably from 1.75 to 2 times longer than the first linkage arm.

[0049] Turning now to figures 8 and 9, the arrangement and geometry of the crumber 10 results in the first linkage arm 20 extending at an angle of approximately 25° to the longitudinal axis of the crumber boom 1 1 when the crumber arm 14 is in the lowermost position. This is shown in figure 8. The crumber arm 14 may move upwardly to its uppermost position by rotation of both the first linkage arms 20 and the second linkage arms 22 about their respective pivotally connected ends. The arrangement and geometry of the crumber 10 results in the first linkage arms 20 extending an angle of approximately 1 15° to the longitudinal axis of the crumber when in its uppermost position, as shown in figure 9. Therefore, the first linkage arm has rotated by approximately 90°.

[0050] Figures 10 and 1 1 show a prior art crumber having a first linkage arm 20A that extends any angle of approximately 33° when the crumber arm 14A is in the lowermost position (see figure 10). When the crumber arm 14A is in the uppermost position as shown in figure 1 1 , the first linkage arms 20 A extend an angle of approximately 100° to the longitudinal axis of the crumber boom. Thus, the first linkage arms have only rotated by approximately 67°, significantly less than the rotation of the first linkage anns of the crumber 10 shown in figures 8 and 9. Furthermore, when the crumber arms are in the uppermost position, the lower end of the scraper plate 42A of the prior art crumber shown in figure 1 1 is significantly lower than the lower end of the scraper plate 42 of the crumber 10 shown in figure 9.

[0051] By virtue of the crumber arm being able to move to a higher position, excavation of a new trench may commence without the requirement to undo or release the crumber 10 from the crumber boom, as is required with present crumbers. Rather, as the crumber 10 of the present invention can move to a higher uppermost position, the crumber arm 14 can move sufficiently high relative to the trencher blade such that the crumber arm 14 can rest on undisturbed ground whilst the trencher blade moves to the required depth for the trench and the crumber arm can then move down into the trench once the trencher starts to move along the length of the new trench. Thus, it is not necessary to remove the crumber 10 from the crumber boom when commencing a new trench with the crumber of the present invention.

[0052] Returning to figures 1 and 2, it can be seen that the crumber mount side plate 26 is provided with an extended upper edge 74. Indeed, upper edge 74 includes an extended straight edge portion 74. Crumber mount side plate 28 is similarly shaped. The crumber arm side plate 36 is provided with a proximal lower edge 76 that also includes an extended straight portion. When the crumber arm 14 is in its lowermost position, as shown in figure 1 , the complimentary edges 74, 70 abut on each other such that the edge 76 of the crumber arm 14 lies on the edge 74 of the crumber mount 12. In this manner, the force required to support the crumber arm 14 is distributed along the length of the complimentary edges 74, 76. This acts to minimise the load concentrations between the crumber mount 12 and the crumber arm 14.

[0053] The crumber in accordance with embodiments of the present invention provides a robust crumber having lower wear at contact positions between the crumber mount and the crumber arm. The crumber ami can move upwardly to a significantly larger degree than in prior art crumbers, thereby avoiding the necessity of having to undo at least one of the pins holding the crumber to the crumber boom when excavation of a new trench commences. This, of course, also obviates the requirement to reattach the crumber to the crumber boom once a length of the new trench has been excavated. Th us, the crumber of the present inventi on provides for significant ease-of-use and increased efficiency.

[0054| In this specification, the term "proximal" is used to refer to positions located relatively closer to the trencher machine and the word "distant" is used to refer to positions located relatively farther away from the trencher machine. The terms "lowermost" and

"uppermost" are used in the context of a position of the crumber arm relative to the crumber [0055] In the present specification and claims (if any), the word 'comprising' and its derivatives including 'comprises' and 'comprise' include each of the stated integers but does not exclude the inclusion of one or more further integers.

[0056] Reference throughout this specification to 'one embodiment' or 'an embodiment' means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases 'in one embodiment' or 'in an embodiment' in various places throughout this specification are not necessarily all referring to the same embodiment.

Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

[0057] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.

Claims

1. A crumber for a trencher machine, the crumber comprising a crumber mount for mounting to a crumber boom, and a crumber arm, the crumber arm being mounted to the crumber mount by a linkage, the linkage comprising a first linkage arm and a second linkage arm, the linkage being arranged to allow rotation of at least one of the linkage arms of at least 75°.

2. A crumber for a trencher as claimed in claim 1 wherein at least one of the linkage arms is rotatable by between 75 to 120°, more preferably from 80 to 1 10°, even more preferably from 85 to 100°, even more preferably about 90°.

3. A crumber for a trencher as claimed in claim 1 or claim 2 wherein the linkage comprises a first linkage arm pivotally connected to the crumber mount and pivotally connected to the crumber arm, and a second linkage arm pivotally connected to the crumber mount and pivotally connected to the crumber arm.

4. A crumber for a trencher as claimed in any one of the preceding claims wherein the linkage comprises a pair of first linkage arms each pivotally connected to the crumber mount and pivotally connected to the crumber arm, and a pair of second linkage arms each pivotally connected to the crumber mount and pivotally connected to the crumber arm.

5. A crumber for a trencher as claimed in any one of the preceding claims wherein the crumber arm comprises a first crumber arm side plate and a second crumber arm side plate, the first and second crumber arm side plates being connected to each other.

6. A crumber for a trencher as claimed in claim 5 wherein the two side plates are connected to each other by one or more intermediate connectors.

7. A crumber for a trencher as claimed in claim 5 or claim 6 wherein the linkage comprises a first proximal linkage arm and a second distal linkage arm, with the second distal linkage arm having a distal end pivotally connected to one of the crumber side plates, the distal end of the second linkage arm being located between the first crumber arm side plate and the second crumber arm side plate.

8. A crumber for a trencher as claimed in any one of claims 5 to 7 wherein the crumber arm is movable from a first lowermost position to a second uppermost position, the second distal linkage arm lying approximately parallel to the crumber boom when the crumber arm is in a first lowermost most position.

9. A crumber for a trencher as claimed in any one of claims 5 to 8 wherein the first proximal arm is rotatable by at least 75° when the crumber arm is moving from a first lowermost position to a second uppermost position.

10. A crumber for a trencher as claimed in claim 9 wherein the first proximal arm is rotatable by between 75 to 120°, or from 80 to 1 10°, or from 85 to 100°, or about 90°, ° when the crumber arm is moving from the first lowermost position to the second uppermost position.

1 1. A crumber for a trencher as claimed in any one of claims 5 to 10 wherein the first proximal linkage ann is shorter than the second distal linkage arm.

12. A crumber for a trencher as claimed in any one of the preceding claims wherein the crumber mount has at least one edge or surface that is of complementary shape to an edge or surface of the crumber arm, wherein the least one edge or surface of the crumber mount and the complementary edge or surface of the crumber ann abut on each other when the crumber ann is in a lowermost position.

13. A crumber for a trencher, the crumber comprising a crumber mount for mounting to a crumber boom and a crumber arm, the crumber arm being mounted to the crumber mount by a linkage, the crumber mount having at least one edge or surface that is of complementary shape to an edge or surface of the crumber arm, wherein the least one edge or surface of the crumber mount and the complementary edge or surface of the crumber arm abut on each other when the crumber arm is in a lowermost position.

14. A crumber for a trencher as claimed in claim 13 wherein the at least one edge or surface of the crumber arm comes into contact with and is supported by the complementary edge or surface of the crumber mount when the crumber arm is in the lowermost position and the crumber arm is supported by the crumber mount along the length of the complementary edge or surface of the crumber mount when the crumber arm is in the lowermost position.

15. A crumber for a trencher as claimed in any one of the preceding claims wherein the crumber mount comprises two spaced mount side plates for mounting to the crumber boom, the two spaced side plates being connected together.

16. A crumber for a trencher as claimed in any one of the preceding claims wherein the crumber further comprises a biasing means to bias the crumber arm to a lowermost position.

17. A crumber for a trencher as claimed in claim 7 wherein, the second distal linkage arm has a proximal end located between the two spaced crumber mount side plates and a distal end located between the two spaced crumber arm side plates.

18. A crumber for a trencher as claimed in any one of claims 5 to 11 or 17 wherein the first proximal crumber ami extends at an angle of about 20 to 30°, preferably about 25°, to the crumber boom when the crumber arm is in a lower most position, and extends at an angle of about 95° to 145°, more preferably from 105° to 135°, even more preferably from 110° to 125°, even more preferably about 1 15° to the crumber boom, when the crumber arm is an uppermost position.