GB2099092A

GB2099092A - Adjusting and centring mechanism for an internal-shoe servo-brake

Info

Publication number: GB2099092A
Application number: GB8209209A
Authority: GB
Original assignee: Deutsche Perrot Bremse GmbH
Current assignee: Deutsche Perrot Bremse GmbH
Priority date: 1981-03-30
Filing date: 1982-03-29
Publication date: 1982-12-01
Also published as: IT8212486A0; ATA93282A; FR2502717A1; IT1157668B; GB2099092B; DE3112550C2; FR2502717B1; DE3112550A1; AT386263B

Abstract

The adjusting and centring mechanism of an internal-shoe servo- brake comprises a bolt (2) acting on each brake shoe and held against rotation. Each bolt (2) is screw- threaded within an adjusting nut (3) and each nut (3) may be rotated by a toothed wheel (9) in order to alter the separation between the bolts (2). A pawl (19, 20) is pivoted on the brake body to cause rotation of its toothed wheel (9) when a lever (21, 22) on the pawl contacts the opposite wheel (9) due to movement of the mechanism relative to the body. The pawls (19, 20) are arranged to pivot with one pawl moving in a plane at 90 degrees to the plane of the other pawl. <IMAGE>

Description

SPECIFICATION Adjusting and centring mechanism for sliding lock of an internal-shoe servo-brake The invention relates to an adjusting and centring mechanism on the sliding lock of an internal-shoe servo-brake, having a respective adjusting nut for each direction of sliding through, into each of which nuts is screwed a respective threaded bolt held against rotation and acting on a respective brake shoe end and each of which nuts carries a respective adjusting gearwheel, coaxial therewith with a unidirectional ratchet mechanism, in which a respective adjusting pawl engages which executes a circumferential movement on the gearwheel on sliding-through movement of the sliding lock and which, in the event of sliding through too far in the direction of its associated brake shoe, jumps over a tooth and during the subsequent centring of the sliding lock, caused by spring force, and return circumferential movement engages the tooth over which it has previously jumped and turns the associated adjusting nut in the sense of unscrewing the associated threaded bolt and which pawl is mounted on a respective plate-shaped adjusting lever held by a respective pin on stationary parts of the brake, each of which adjusting levers has a central position of rest, from which it can be pivoted about its pin while tensioning an adjusting spring interposed between the two adjusting levers while sweeping over the respective adjusting gearwheel with its associated pawl, and on which adjusting levers parts of the brake connected to the sliding lock act on an axial line which is offset in relation to the respective pin for pivoting each lever during sliding through.

Such a mechanism is already known through the DE-AS 1 2 02 593. For reasons of space, the adjustment of an internal-shoe servo-brake is preferably effected at the side of the brake shoe situated opposite to the brake expander, at which side an assembly called a sliding lock transmits the movement and the braking force from the primary shoe to the secondary shoe.

In the adjusting and centring mechanism mentioned at the beginning (DE-AS 12 02 593), two cams are provided on each plate-shaped adjusting lever equipped with an adjusting pawl, one of which cams cooperates with a flange of a separate sleeve of the sliding lock and the other is held by spring force against a fixed stop. The manufacture, storage and mounting of these two adjusting levers, which are not interchangeable, increases the expense of the known adjusting mechanism considerably. What is particularly serious, however, is the fact that its operational reliability leaves much to be desired. Such levers, simply mounted on a pin, are not only rotatable about the axis of the pin but can also incline and tilt when acted upon by lateral forces.If, as with the construction in question according to the prior art, it is a question of a sliding lock which is mounted floating and practically hung on gimbals, with which there can be no guiding with entrainment of the brake-shoe webs, but rather there is the risk of tilting, and wherein, moreover, with increasing lining wear, the gearwheels travel radially outwards, that is to say out from the region of engagement of the adjusting pawl, so that a change in the transmission ratio results, there is the risk of an unsatisfactory adjusting operation.

Here it must be mentioned that an adjusting and centring mechanism of a different type is further known (DE-PS-23 1 1 166) in which the two adjusting pawls are components of a single, common plate-shaped member and in which the two pins each pass through one of two slots formed arcuately in the plate-shaped component and lie at the end of their particular slot, in the centre of the arc of the other slot, in the centred position of rest. It is true that this mechanism is simpler in comparison with that of the kind referred to at the beginning and accordingly normally reliable in operation. The use of such a plate-shaped member with two adjusting pawls is, however, less suitable for vehicles with comparatively high braking torques and used for reversing, as is the case, in particular, with fork-lift trucks.Under these extreme operating conditions, a turnover of the brake may occur while retaining a plate position in which the pins do not lie in the centred position of rest at the end of their particular slot, and then decay is possible at the pins and at the plate.

It is the object of the invention to make the mechanism of the kind referred to at the beginning more operationally reliable and more efficient, particularly under extreme conditions of use, as for example, in vehicles with a reversing mode of operation, without increasing the cost of production.

According to the invention, this problem is essentially solved in that the sliding lock is disposed for axial displacement in bores in a stationarily mounted guide frame, and secured against tilting about an axis extending transversely to the lock axis, that the parts of the brake connected to the sliding lock and acting on the adjusting levers are formed by the adjusting gearwheels and that the two plate-shaped adjusting levers are mounted for pivoting on the guide frame in planes offset by about 900.

In such a construction with a stationarily mounted guide frame having a U-shaped crosssection, on one arm of which the pin serving as a pivot point for the adjusting lever is provided, projecting at the end, the feature according to which the pin associated with the other adjusting lever is disposed projecting at the side of the other arm of the guide frame has proved particularly advantageous from the structural point of view.

Particularly satisfactory operating conditions result if, in a further development, each adjusting lever acts with its adjusting pawl on that adjusting gearwheel which is remote from that arm of the guide frame on which there is the pin as a pivot point for the associated adjusting lever.

Further details, advantages and features of the invention are apparent from the following description and the drawings to which express reference is made with regard to the disclosure of all details not described in the text.

Figure 1 shows a view of the adjusting and centring mechanism in the brake release position, partially in section; Figure 2 shows a plan view of the mechanism according to the invention as shown in Figure 1; and Figure 3 shows an end view of the mechanism shown in Figure 1.

Disposed between the ends of the brake shoes situated opposite to the expanding device of an internal-shoe servo-brake, in a guide frame 1 which is rigidly connected to the brake cover plate and which has a substantially U-shaped crosssection, is a sliding lock which is displaceable in its axial direction and in the course of this transmits the brake actuating force from the particular primary shoe to the secondary shoe. The sliding lock is constructed in the form of an adjusting and centring mechanism which, on wear of the brake lining at one of the brake shoes, increases its axial length in relation to its centred position at the worn side and so keeps the brake release clearance constant for each of the two brake shoes.

Mounted held against rotation on each end of the brake shoes is a threaded bolt 2 which is screwed into an adjusting nut 3 associated with the particular brake shoe. The two adjusting nuts 3 are mounted for rotation in a sliding sleeve 4 and each comprise a flange 5 on which the sliding sleeve is supported through one or more spacers 6. The sliding sleeve 4 is provided, at its outside, in its central region, with a recess which is necessary to receive a centring spring 7 via two divided angle rings 8. The angle rings 8 are supported both against the sliding sleeve 4 and against the guide frame 1 and so cause a centring of the sliding lock which consists essentially of the parts 2, 3, 4 and 5.The braking force is transmitted from the threaded bolt closer to the primary shoe via the particular adjusting nut 3, the flange 5, the sliding sleeve 4 and the same parts disposed symmetrically thereto at the other side, that is to say again the flange 5, the adjusting nut 3 and the threaded bolt 2.

Each adjusting nut 3 carries an adjusting gearwheel 9 which is coaxial therewith and the teeth of which consist of locking teeth acting at one side. The direction of the locking teeth depends on the thread direction between the adjusting nut 3 and the threaded bolt 2 and is selected so that the direction of rotation in which a pawl action on the teeth of the gearwheel 9 entrains this, leads to the unscrewing of the threaded bolt 2.

Mounted on the guide frame 1, for pivoting independently of one another, are adjusting levers 10 and 11 by pins 12 and 13 which are firmly anchored in the guide frame 1. The pin 1 2 projects at the end on the one arm of the guide frame 1 and the other pin 1 3 is disposed projecting at the one side of the other arm of the guide frame. Thus the axes of the two pins 12 and 13 substantially form a right angle with one another. Accordingly, the two adjusting levers 10 and 11 are mounted on the guide frame 1 in planes offset by about 900 for pivoting about the pins 12 and 13.The two adjusting levers 10 and 11 are each provided with an arm 14 or 1 5 projecting transversely, at a distance from the pivot point formed by the associated pin 1 2 or 13, which corresponds to the spacing of the two arms of the guide frame 1. An adjusting spring 16, which is common to the two adjusting levers 10 and 11, acts on these two arms 14 and 15. Each adjusting lever 10 and 11 is provided with a stop finger 1 7 and 18, which is bent out of its plane at an angle and through which it is supported on the associated arm of the guide frame 1 under the action of the adjusting spring 16, in its position of rest.The end of each adjusting lever 10 and 11 projecting beyond the arm 14 or 15 is constructed in the form of an adjusting pawl 1 9 or 20 which is in engagement with the teeth of the associated adjusting gearwheel 9. Since the plane of the one plateshaped adjusting lever 10 or 11 is higher than the end of the arm 15 or 14 on which the common adjusting spring 1 6 acts, in each case, this spring exerts a component of force directed towards the adjusting gearwheel 9 on the adjusting levers.

Each adjusting lever 10 or 11 comprises a sliding projection 21 or22 which, in the centred initial position of the sliding lock, approaches the adjacent lateral face of the adjusting gearwheel 9 to within a short clearance 23. The size of this clearance 23 can be selected by suitable selection of the spacers 6.

The mechanism described works as follows: If, during the braking, the sliding lock is displaced for example from left to right in the illustration shown in Figure 1 or 2, then the lefthand adjusting gearwheel 9 presses on the sliding projection 22 and entrains it, in which case the adjusting lever 11 is turned in clockwise direction about the pin 13. After lining wear has occurred, the adjusting pawl 20 locks over a tooth of the right-hand adjusting gearwheel 9. During the subsequent return of the brake and the centring of the sliding lock by the centring spring 7, the adjusting lever 11 is also pivoted back into its position of rest as shown in Figure 1, as a result of the adjusting gearwheels 9 moving back and reinforced by the adjusting spring 1 6. In the course of this, the adjusting pawl 20 acts on the tooth of the saw-tooth-like locking teeth of the right-hand adjusting gearwheel, over which it has locked, and turns this gearwheel with its adjusting nut 3 so that the right-hand threaded bolt 2 in the drawing is unscrewed.

On displacement of the sliding lock from right to left, the adjusting lever 11 remains in the position of rest illustrated in Figure 1. On the other hand, the adjusting lever 10 is acted upon by the right-hand adjusting gearwheel 9 through its sliding projection 21. Pivoting of the adjusting lever 10 occurs and possibily, in the event of lining wear, locking over of a tooth of the saw-tooth-like locking teeth of the left-hand adjusting gearwheel 9 by the adjusting pawl 19.

Since the adjusting spring 1 6 exerts a certain radial force, in relation to the sliding lock, on the adjusting lever 10 or 11, apart from the pivoting force, it thus also produces a moment which guarantees a reliable engagement of the adjusting pawl in the next tooth of the adjusting gearwheel 9. The angle of the adjusting spring 16 determining the radial component of force is selected so small that an accompanying turning of the adjusting gearwheel 9 by friction in the direction freed by the free-wheeling action is reliably avoided. As can be seen from the drawing, the outer end of each arm 14 and 1 5 is bent somewhat out of the plane of the plate-shaped adjusting lever 10 or 1 The said radial component of force can be altered by altering this angle.

If a manual adjustment is to be carried out, it is only necessary to turn the adjusting gearwheel 9 in question by means of a suitable tool, for example a screwdriver. Turning back of the gearwheels is an advantage, for example when the brake has been worn in, in order to be able to remove the drum.

Claims

1. An adjusting and centring mechanism on the sliding lock of an internal-shoe servo-brake, having a respective adjusting nut for each direction of sliding through, into each of which nuts is screwed a respective threaded bolt held against rotation and acting on the respective brake shoe end and each of which nuts carries a respective adjusting gearwheel coaxial therewith with a unidirectional ratchet mechanism in which a respective adjusting pawl engages which executes a circumferential movement on the gearwheel on sliding-through movement of the sliding lock and which, in the event of sliding through too far in the direction of its associated brake shoe, jumps over a tooth and during the subsequent centring of the sliding lock, caused by spring force, and return circumferential movement engages the tooth over which it has previously jumped and turns the associated adjusting nut in the sense of unscrewing the associated threaded bolt and which pawl is mounted on a respective plate-shaped adjusting lever held by a respective pin on stationary parts of the brake, each of which adjusting levers has a central position of rest, from which it can be pivoted about its pin while tensioning an adjusting spring interposed between the two adjusting levers and while sweeping over the respective adjusting gearwheel with its associated pawl and on which adjusting levers parts of the brake connected to the sliding lock act on an axial line which is offset in relation to the respective pin for pivoting each lever during sliding through, characterised in that the sliding lock is disposed for axial displacement in bores in a stationarily mounted guide frame and secured against tilting about an axis extending transversely to the lock axis, that the parts of the brake connected to the sliding lock and acting on the adjusting levers are formed by the adjusting gearwheels and that the two plate-shaped adjusting levers are mounted for pivoting on the guide frame in planes offset by about 900.

2. A mechanism as claimed in Claim 1, having a stationarily mounted guide frame which has a Ushaped cross-section and on one arm of which the pin serving as a pivot point for the adjusting lever is provided projecting at the end, characterised in that the pin associated with the other adjusting lever is disposed projecting at the side of the other arm of the guide frame.

3. A mechanism as claimed in Claim 2, characterised in that each adjusting lever acts with its adjusting pawl on that adjusting gearwheel which is remote from that arm of the guide frame on which there is the pin as a pivot for its associated adjusting lever.

4. A mechanism as claimed in one of the preceding Claims 1 to 3, characterised in that the two adjusting levers are each provided with an arm projecting transversely at a distance from their respective pivot point which distance corresponds to the spacing of the two arms of the guide frame and that an adjusting spring which is common to the two adjusting levers, acts on the two arms.

5. A mechanism as claimed in Claim 4, characterised in that each adjusting lever is provided with a stop finger which is bent out of its plane at an angle and through which it is supported on the associated arm of the guide frame under the action of the adjusting spring, in its position of rest.

6. A mechanism for an internal-shoe servobrake substantially as described hereinbefore with reference to the accompanying drawings.