GB1601378A

GB1601378A - Draft sensing apparatus

Info

Publication number: GB1601378A
Application number: GB3306380A
Authority: GB
Original assignee: Massey Ferguson Services NV
Current assignee: Massey Ferguson Services NV
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1981-10-28

Description

(54) DRAFT SENSING APPARATUS (71) We, MASSEY-FERGUSON SERVICES N.V. of Abraham de Veerstraat 7A, Curacao, Netherlands Antilles, a company organised under the laws of the Netherlands Antilles, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to draft sensing apparatus for tractors.

Tractor draft sensing apparatus are already known which include an elongated shaft having support portions for mounting in spaced fulcrum supports and end portions positioned axially outward of said support portions for mounting a pair of draft members, the arrangement being such that draft forces imposed on the shaft by the draft members cause the shaft to bend, and sensing means are arranged to produce a draft signal proportional to the amount of bending of the shaft. One example of such a system is described in U.K. Patent Number 1 493 379.

One problem experienced with draft sensing apparatus of the above type is the amount of internal friction which may occur and with results in the apparatus exhibiting considerable hysteresis which tends to make the apparatus imprecise in its response to changes in draft loads.

It is an object of the present invention to provide a tractor draft sensing apparatus which at least reduces the above problem.

According to the present invention there is provided a tractor draft sensing apparatus including an elongated shaft having support portions for mounting in spaced fulcrum supports and end portions positioned axially outward of said support portions to receive a pair of draft members for imposing draft forces on the shaft as a result of which the shaft bends, an elongate member attached at one end to the shaft and arranged to extend generally parallel thereto, a pivotally mounted cam member, a cam follower carried by the other end of the elongate member, a guidance member provided with a guide surface, and a separate follower carried by the other end of the elongate member for engagement in the guide surface the arrangement being such that bending of the shaft results in said other end of the elongate member moving relative to the shaft generally in a single plane under the control of the guide surface and the guide surface follower causing the cam follower to pivot the cam by an amount proportional to the draft forces imposed on the shaft.

The use of a separate cam follower and guide surface follower reduced the internal friction of the apparatus since if a single follower were used for contact with both the cam and guide surface such a single follower would inevitably at certain times have to slide relative to one or other of the contacted components. The use of separate followers makes it possible to eliminate this sliding friction.

As will be appreciated the forces applied to the shaft by the draft members have both vertical and horizontal components. The vertical component is primarily due to the resultant implement weight and soil suction forces while the horizontal component is primarily due to the horizontal draft forces.

Since it is changes in the draft forces that are useful indicators to control the vertical position of the draft members in order to maintain a substantially constant draft load, it is desirable to eliminate the effect of the vertical components on any draft sensing apparatus. This can be conveniently achieved by orientating the guidance member so that the relative movement between the elongate member and shaft is confined to a substantially horizontal plane. This has the effect of removing the influence of the vertical components of any forces applied to the shaft by the draft members so that the signal given by apparatus is primarily derived from the draft forces.

Preferably rotation of the shaft about its longitudinal axis is controlled by co-operating pin and slot means associated one with an adjacent portion of the tractor and the other with the shaft.

The guidance member is preferably carried on the shaft and the cam member is pivotally mounted on the guidance member.

Preferably the pivotal mounting of the cam member is provided by pin means of an appreciably smaller diameter than the transverse dimensions of the shaft.

Conveniently the cam follower and guide surface follower comprise separate rollers rotatably mounted on the elongated member.

Each end portion of the shaft may extend through a ball member which is received in a complementarily shaped socket member carried by the associated draft member, the axially outward movement of each ball member relative to its respective end portion being limited to prevent fouling of the ball member, socket or draft member on any adjacent structure of the tractor.

One embodiment of the present invention will now be described, by eay of example only, with reference to the accompanying drawings in which: Figure 1 is a plan view, partly in section of a draft sensing apparatus embodying the present invention; Figure 2 is a diagrammatic perspective view of an increased scale of part of the apparatus of Figure 1; Figure 3 is a part sectional view on an increased scale of one end portion of the sensing shaft of the apparatus of Figure 1; Figure 4 is a section of the line IV-IV of Figure 1; Figure 5 is a diagrammatic view of the sensing shaft in a zero load condition; Figure 6 is a diagrammatic view of the sensing shaft when subjected to vertical forces; Figure 7 is a diagrammatic view of the sensing shaft when subjected to horizontal forces, and Figure 8 shows a partially sectioned portion of Figure 1 with an alternative arrangement for preventing rotation of the sensing shaft.

Referring to Figures 1 and 2 the draft sensing apparatus comprises an elongate shaft 10 having support portions 11 which are mounted in fulcrum supports 12 which are carried by parts 9 of the rear axle housing of the tractor. The shaft 10 also has end portions 13 which receive ball members 14 on which draft members in the form of lower links 15 are supported. The lower links are arranged to apply draft forces to the shaft 10 as indicated by the arrows X in Figure 1.

The shaft 10 is made from a steel with a high ultimate tensile strength (e.g. an AISI 4150-4155 steel with an ultimate tensile strength of 180,000 p.s.i. minimum) and the shaft is heat treated to further improve its mechanical properties. In particular, the- support and end portions of the shaft are hardened.

In a typical example the total length of of the shaft 10 is 21-5 inches and the distance of Figure 1 between the support portions is approximately 12 inches.

The shaft 10 is provided with flats 16 intermediate the support and end portions.

These flats are engaged by plates 17 which are held against rotation relative to the rear axle housing parts 9 by bushes 18 carried on bolts 19. The bushes extend through slots 20 in the plates thus holding the plates 17 and also the shaft 10 against rotation relative to the rear axle housing parts 13.

The ball members 14 are located against axially outward movement relative to the shaft 10 by the fastening arrangement 21 shown in greater detail in Figure 3. This arrangement comprises a sleeve 22 which is arranged to hold a two piece abutment ring in an annular groove 24 in the respective end portion 13 of the shaft. The ring 23 is split diametrically being retained in the groove 24 by an inclined surface 25 on the sleeve 22 which contacts a corresponding inclined surface 26 on the ring 23. The ring also provides an inclined abutment surface 27 which contacts a corresponding abutment surface 28 on the ball member to prevent axially outward movement of the ball member.

The sleeve 22 is held in position against the ring 23 by a washer 29 carried on a bolt 30 which is screwed into the end face 31 of the shaft 10.

As can be seen from Figures 1 and 3 the sleeve 22 extends within a bore 32 provided in a movement limiting member 33. As can be seen from Figure 3 the bore 32 is of larger diameter than the outside diameter of the sleeve 22 and has the effect of limiting the bending which the shaft 10 can be subjected to by the draft links 15.

The movement limiting member 33 comprises a bush member 34 having the bore 32, the bush member being secured to a shaft 35 which is retained in two horizontally extending fork arms 36 provided on the rear axle housing by a washer 37 and bolt 38.

The support portions 11 and end portions 13 of the shaft 10 are of circular cross-section but, as can be seen from Figures 1 and 4, the major portion of the length of the shaft between the support portions 11 has the crosssectional shape of the major segment of a circle of a diameter of 162 inches in a typical example. The use of this cross-sectional shape has the important effect of displacing the neutral axis of the shaft between the support portions 11 to the location shown by the dotted line Z in Figure 1. With a 1-62 diameter section the dimensions p and q of Figure 4 are typically 0-164 inches and 0-275 inches respectively.

Since the support portions 11 are circular in cross-section their neutral axis lie on the overall longitudinal axis Y of the shaft 10.

The neutral axis portion Z is thus displaced transversely relative to the general direction of elongation of the shaft 10 from the neutral axes of the support portions 11. This displacement is generally in the direction in which the draft links 15 load the shaft 10, that is the direction X.

An elongate member in the form of a draft force indicator 40 is secured at one end to the shaft 10 adjacent the left hand support portion 11 as shown in Figure 1.

The draft force indicator is clamped to the shaft 10 by a clamp assembly 41 which is tightened by a bolt 42. The other end of the draft force indicator carries a shaft 43 on which separate rollers 44 and 45 are mounted.

These rollers are supported from the shaft 43 by roller bearings. The width w of the indicator 40 is appreciably greater than the width of the indicator used in, for example, the apparatus described in the previously referred to U.K. Patent Number 1 493 379.

A guidance member for the draft force indicator 40 is provided in the form of a plate 46 shown in Figures 1 and 2. This plate is mounted on the shaft 10 and held against rotation by a pin 47 carried by the adjacent axle housing part 13. This pin 47 extends into a slot 48 in the plate 46 thus preventing rotation of the plate.

As can be seen from Figure 2 the plate 46 includes a larger slot 49 which receives the roller 45. The plate 46 is arranged to be held relative to the housing portion 13 so that the direction of extension of the slot 49 is substantially horizontal so that the roller 45, which is maintained in contact with the upper side of the slot, can only move substantially horizontally relative to the shaft 10.

As can be seen from Figures 1 and 2 the plate 46 carries a smaller diameter pin 50 which forms the pivotal mounting for a cam 51. The cam 51 has a bush 52 which encircles the pin 50 and is connected at its other end with a rod 53 which is connected with the draft control system of the tractor.

As can be seen from Figure 2 the cam 51 has a cam surface 54 which is arranged to be engaged by the roller 44. The cam is biassed against the roller 44 by spring means not shown.

Figure 8 shows an alternative arrangement for preventing rotation of shaft 10. In this arrangement the plates 17 and flats 16 are eliminated and the clamp assembly 41 is provided with a horizontally disposed slot 41a which is engaged by a pin 41b screwthreadedly received in the housing 9. The close fit of the pin 41b in the slot 41a prevents rotation of the shaft 10 and the indicator 40. This arrangement has been found more effective at controlling rotation of the shaft 10 and the indicator 40 than the plates 17 and this ensures greater draft signal accuracy.

Figure 5 shows the geometry of the shaft 10 and draft force indicator 40 when the shaft 10 is in an unstressed condition. If the shaft 10 is subjected to vertical forces, as shown diagrammatically in Figure 6, the shaft 10 assumes a curved configuration together with the draft force indicator 40. The draft force indicator 40 is caused to assume a curved configuration together with the shaft 10 by the action of the slot 49 in the plate 46 on the roller 45. Thus the roller 44 does not apply any pivotting force to the cam 51.

However, if the shaft 10 is subjected to draft forces, which will be applied in a substantially horizontal plane, the shaft 10 and indicator 40 assume the position shown in Figure 7. As can be seen from Figure 7 the indicator 40 remains substantially straight and the free end of the indicator which carries the cam engaging roller 44 moves away from the adjacent portion of the shaft so that the guidance roller 48 moves along the slot 49.

Co-operation between the cam surface 54 and the roller 44 thus causes the cam 51 to pivot on the pin 50 thus resulting in vertical movement of the rod 53 which acts as a draft force signal to the draft control system.

The use of a shaft 10 with a displaced neutral axis as described above enables the effects of the moments of the functional forces which arise in the fulcrum supports during bending of the shaft to be reduced and enables a cross-sectional shape to be adopted for the portion of the shaft with the displaced neutral axis which results in a reduced level of tensile stress in the outer surface layers of the shaft during bending.

A full explanation as to how these benefits are achieved is provided in the Applicant's co-pending Application No: 24606/78 from which the present Application is divided.

Serial No. 1601377.

It will be appreciated that in addition to reducing the effects of the internal friction in the shaft supports by using the shaft shape described above the internal friction of the apparatus is reduced by the use of the two rollers 44 and 45 as compared, for example, with arrangements in which a single roller acts on both the guidance plate and cam. This reduction in friction occurs since any single roller trying to engage both the guidance plate slot and the cam profile would at certain times have to slide relative to one or other of these components. By using two rollers it is possible for this sliding friction to be eliminated.

The internal friction within the apparatus is further reduced by the manner in which the cam 51 is mounted on the small diameter pin 50. By mounting the cam in this way the area of contact between the cam and its mounting pin is appreciably reduced compared with arrangements in which, for example, the cam is pivotally mounted on the shaft 10 itself.

We have found that using the various measures described above to reduce the effects of the internal friction of of the draft sensing apparatus it has been possible to reduce the hysteresis of the apparatus by up to 80% if all the measures described above are employed.

When ploughing with a nominal draft load of 3000 kg the variation in draft load with a correctly operating draft control apparatus is typically within i 10% of the nominal load. Using a draft load sensing apparatus employing all the measures described above in such circumstances it has been found possible to achieve a hysteresis value of approximately i 75% so that the apparatus will produce a change in draft signal when the draft load changes by more than say 22-5 kg.

This is an appreciable improvement over the previous draft sensing apparatus in which the levels of hysteresis have often been so high as to prevent efficient operation of the apparatus.

WHAT WE CLAIM IS:- 1. A tractor draft sensing apparatus including an elongated shaft having support portions for mounting in spaced fulcrum supports and end portions positioned axially outward of said support portions to receive a pair of draft members for imposing draft forces on the shaft as a result of which the shaft bends, an elongate member attached at one end to the shaft and arranged to extend generally parallel thereto, a pivotally mounted cam member, a cam follower carried by the other end of the elongate member, a guidance member provided with a guide surface, and a separate follower carried by the other end of the elongate member for engagement in the guide surface, the arrangement being such that bending of the shaft results in said other end of the elongate member moving relative to the shaft generally in a single plane under the control of the guide surface and the guide surface follower causing the cam follower to pivot the cam by an amount proportional to the draft forces imposed on the shaft.

2. An apparatus according to claim 1 in which the guidance member is carried on the shaft and the cam member is pivotally mounted on the guidance member.

3. An apparatus according to claim 1 or 2 in which the pivotal mounting of the cam member is provided by pin means of an appreciably smaller diameter than the transverse dimensions of the shaft.

4. An apparatus according to any one of claims 1 to 3 in which the cam follower and guide surface follower comprise separate rollers which are rotatably mounted on the elongate member.

5. An apparatus according to any one of claims 1 to 4 in which the rotation of the shaft about its longitudinal axis is controlled by co-operating pin and slot means associated one with an adjacent portion of the tractor and the other with the shaft.

6. An apparatus according to any one of claims 1 to 5 in which each end portion of the shaft extends through a ball member which is received in a complementarily shaped socket member carried by the associated draft member, the axially outward movement of each ball member relative to its respective end portion being limited to prevent fouling of the ball member, socket or draft member on any adjacent structure of the tractor.

7. An apparatus according to claim 6 in which the axially outward movement of each respective ball member is limited by an annular sleeve which is arranged to hold an abutment ring in an annular groove in the respective end portion, the abutment ring being split chordally and providing an abutment surface for contact by the respective ball member to limit said axially outward movement.

8. An apparatus according to claim 7 in which each sleeve is held in place on its respective end portion by a washer carried by a bolt screwed into the end face of the shaft.

9. An apparatus according to claim 7 or 8 in which the sleeve extends axially within a bore in an adjacent movement limiting member, said bore having a diameter larger than the external diameter of the sleeve, the amount of clearance between the sleeve and bore serving to limit the degree of bending to which the shaft can be subjected.

10. A tractor draft sensing apparatus according to claim 1, said system being constructed and arranged substantially as herein before described with reference to and as shown in Figures 1 to 3 and 5 to 8 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. reduce the hysteresis of the apparatus by up to 80% if all the measures described above are employed. When ploughing with a nominal draft load of 3000 kg the variation in draft load with a correctly operating draft control apparatus is typically within i 10% of the nominal load. Using a draft load sensing apparatus employing all the measures described above in such circumstances it has been found possible to achieve a hysteresis value of approximately i 75% so that the apparatus will produce a change in draft signal when the draft load changes by more than say 22-5 kg. This is an appreciable improvement over the previous draft sensing apparatus in which the levels of hysteresis have often been so high as to prevent efficient operation of the apparatus. WHAT WE CLAIM IS:-

1. A tractor draft sensing apparatus including an elongated shaft having support portions for mounting in spaced fulcrum supports and end portions positioned axially outward of said support portions to receive a pair of draft members for imposing draft forces on the shaft as a result of which the shaft bends, an elongate member attached at one end to the shaft and arranged to extend generally parallel thereto, a pivotally mounted cam member, a cam follower carried by the other end of the elongate member, a guidance member provided with a guide surface, and a separate follower carried by the other end of the elongate member for engagement in the guide surface, the arrangement being such that bending of the shaft results in said other end of the elongate member moving relative to the shaft generally in a single plane under the control of the guide surface and the guide surface follower causing the cam follower to pivot the cam by an amount proportional to the draft forces imposed on the shaft.