EP1165982A1

EP1165982A1 - Automatic drum brake adjusting device and drum brake comprising same

Info

Publication number: EP1165982A1
Application number: EP00920593A
Authority: EP
Inventors: Peter Johannes LÜDTKE; Frank Biebricher; Franz Blaeser
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1999-04-01
Filing date: 2000-03-27
Publication date: 2002-01-02
Also published as: US20020014959A1; WO2000060250A1; DE19915007C1

Abstract

The invention relates to a drum brake (10) which comprises an automatic adjusting device (40) to compensate for the wear on brake linings (60, 62) and a drum (34). To detect drum brake wear the adjusting device (40) has a signaling device (79) which transmits a signal which depends on an adjustment path travelled by the adjusting device (40). The adjustment path (x) is generated by a length-adjustable adjusting brace (41) comprising a pressure sleeve (42) in which a threaded rod (44, 78) is housed which can be screwed out of the pressure sleeve by means of a star wheel (46).

Description

Automatic drum brake adjustment device and drum brake with such an adjustment device

The invention relates to an automatic drum brake adjustment device for compensating for friction lining and drum wear with a signal device which delivers a signal dependent on an adjustment path. The invention further relates to a drum brake with such an adjusting device.

EP 0 460 378 A2 describes a brake actuation device with a device for adjusting a brake, which is used to maintain an approximately constant brake clearance between brake shoes and a brake drum and to monitor brake lining wear. Here, a first signal generator is provided, which generates a signal corresponding to the path when overcoming the brake clearance, and a second signal generator, which generates a signal corresponding to the path when adjusting. The signals can be evaluated electrically. Attaching two signal transmitters to the adjusting device is cost-intensive and complex.

A drum brake with an automatic adjustment device is known from DE 25 08 614 C2. The adjusting device comprises a variable-length strut, which is arranged between a brake shoe and an actuating lever and is held in contact with the brake shoe by spring force. A ratchet lever is pivotally mounted on the brake shoe and engages in a ratchet gear rotatably mounted on the strut. If the friction lining on the brake shoe wears, the ratchet lever rotates the ratchet wheel and thus adjusts the length of the adjustable strut.

EP 0 140 241 proposes to equip such a drum brake with a wear warning conductor, which is attached to a stopper made of elastic, electrically insulating plastic one end of a brake shoe is attached. The wear warning conductor is looped around the stopper in such a way that it comes into contact with the brake drum during braking if the friction lining has been largely but not yet completely worn out. Similar systems of wear warning are known from US 1,902,759, US 2,146,357, US 2,217,176 and DE 709 251. The aim of these known devices is to determine when friction linings of the drum brakes of the vehicle have to be replaced or when brake shoes have to be adjusted.

DE 709 251 and US Pat. No. 2,182,554 disclose devices with which it can be recognized whether all brakes are set identically and can therefore also be applied uniformly and simultaneously. DE 709 251 provides, on the basis of the above-described principle of sliding contact between a wear warning conductor and the brake drum, that each drum brake is equipped with such a wear warning conductor. By means of an associated light, the driver is informed by its simultaneous

Illuminate additionally indicated when all wear warning conductors come into contact with the drum brake at the same time, i.e. when all brakes are applied at the same time. US 2,182,554 proposes to determine by means of a temperature-dependent resistance on each drum brake whether the drum brakes heat up evenly. In the event of uneven heating, it is concluded that the brakes are applied unevenly.

Braking systems generally have the task of decelerating a vehicle, keeping its speed constant when driving downhill and determining it when parking. In such brake applications, the brakes are usually loaded evenly at least axially.

However, additional tasks are set for new brake systems. For example, to prevent locking wheels (anti-lock control) and spinning wheels one with Differential gear axle (anti-slip control) individual wheels of the vehicle are braked. To stabilize the driving state (control of driving dynamics), individual wheels of the vehicle must also be braked. With these brake applications individual brakes of the

Brake system stressed very differently and used differently accordingly. The different wear of the brakes is exacerbated by the fact that, in modern brake systems, such as an electro-hydraulic brake, particularly high and strongly fluctuating braking forces can be applied. The wear of the friction linings can therefore vary widely.

In addition, new, particularly light materials are used in today's brake systems, but they are sensitive to wear and are relatively expensive. For example, light metal alloys and / or light metal composite materials are used for brake drums. The surface of such materials can easily be damaged in the case of metallic frictional engagement (metal on metal), so that it is particularly necessary to identify worn friction linings at an early stage.

The invention has for its object to provide an automatic drum brake adjuster, which makes it easy to precisely recognize wear of the friction linings.

To achieve this object, the invention provides an automatic drum brake adjustment device of the type mentioned, in which a variable-length adjustment strut is used, which comprises a sleeve and a threaded rod received in the latter, which can be unscrewed from the sleeve by means of a pinion. Such an adjusting device, known per se (see DE 25 08 641 C2), has the advantage with regard to the signal determination according to the invention that the required readjustment by a mechanism with a threaded rod and sleeve travel can be adjusted particularly sensitively, so that an accurate signal is generated.

The signal generated by the signal device is advantageously brought to a vehicle driver for visual and / or acoustic perception by means of a warning lamp or a warning tone. This is possible in a particularly simple manner and can, for example, point out to the vehicle driver that maintenance of the drum brakes is required. However, it is also possible to process the signal in a control unit of the brake system (ABS, ASR, brake-by-wire) and to take into account a change in the signal during predetermined periods. A strong change in the signal during such a period indicates particularly strong, brief brake wear and shows a high load on the brake. Appropriate countermeasures can prevent individual brakes from being overstressed.

According to a particularly simple embodiment of the adjustment device according to the invention, a switch is actuated by the threaded rod after a predetermined adjustment path, which immediately triggers a warning signal (optically and / or acoustically).

In order to achieve a space-saving arrangement of the switch which is protected from environmental influences, it is preferably arranged in the sleeve.

Since a drum brake - due to its attachment directly to the wheels - is exposed to high loads from impacts, water and dust, the signaling device should be designed to be particularly robust. This can be achieved, for example, by a switch with a purely mechanical switch contact.

According to another embodiment, the switch is designed as a magnetic switch, inductive or capacitive switch. In this way, on the one hand, an influencing of the readjustment direction excluded by the switch and on the other hand the time course of the adjusted path can be determined particularly advantageously. A friction lining that wears particularly quickly for a short time indicates, for example, overheating of the drum brake.

A drum brake, in which the adjusting device according to the invention is used, is developed according to one embodiment in such a way that at least one running brake shoe is provided with an additional signal device for indicating wear of the friction lining. This allows two redundant signals to be obtained, which indicate wear of the drum brake with extremely high security. The signal of the signaling device on the adjusting device is dependent on the friction lining and drum wear, while the signal of the additional signaling device is exclusively dependent on the friction lining wear. By forming the difference from these two signals, wear on the drum alone can be deduced.

In one embodiment, the drum brake is developed in such a way that a conductor leading to the signal device is guided within the return springs, which reset the brake shoes. Furthermore, such a conductor can extend through an opening in an anchor plate of the drum brake, which is arranged axially symmetrically with respect to another opening which is provided for the passage of a hand brake cable, a component of a plug-in coupling preferably being fastened in the other opening. In addition, the drum brake can be further developed in that the conductor extends through an opening in a dome of the anchor plate, a plug-in coupling preferably being fastened in the opening by means of a hollow rivet. In this way, the attachment of the conductors is particularly secure and durable. The functionality of the signaling devices is checked particularly advantageously in that a conductor leading to the signaling device is monitored for quiescent current.

The additional signal device is preferably attached to a brake shoe by means of a locking washer, spreading arms or a locking nut. In this way, it is particularly easy to assemble and disassemble.

Preferred exemplary embodiments of a drum brake adjusting device according to the invention are explained in more detail below with reference to the attached schematic figures. It shows:

1 shows an embodiment of a drum brake according to the invention in front view,

2 shows the section II-II in Fig. 1,

3 shows the section III-III in Fig. 1,

Fig. 4 shows a first embodiment of an inventive

Adjusting device in a partially sectioned view in a position as it is assumed for new friction linings,

5 shows the adjusting device in FIG. 4 in a position as it is assumed when the friction linings are worn,

6 shows a second embodiment of an adjusting device according to the invention in a partially sectioned view with a contactless switch,

7 shows a first embodiment of the contactless switch from FIG. 6 on an enlarged scale, 8 shows a second embodiment of the contactless switch from FIG. 6 on an enlarged scale,

9 shows a third embodiment of the contactless switch from FIG. 6 on an enlarged scale,

10 is a circuit diagram of an adjusting device according to the invention,

Fig. 11 shows a first embodiment of an additional

Signal device in a section through a brake shoe,

12 shows a second embodiment of an additional signal device in a section through a brake shoe, and

13 shows a third embodiment of an additional signal device in a section through a brake shoe.

1 shows a drum brake 10 with two brake shoes, a left, running brake shoe 12 and a right, running brake shoe 14, which are fastened to an anchor plate 16 by means of holding-down devices 18 and 20, respectively. The brake shoes 12 and 14 are supported with their lower ends 22 and 24 in the figure on a dome 26 which protrudes from the anchor plate 16 from the plane of the figure. A hydraulic wheel brake cylinder 32 is arranged between the upper ends 28 and 30 of the two brake shoes 12 and 14 in a known manner. The two brake shoes 12 and 14 are radially surrounded by a brake drum 34 which is circular in section. There are two pistons (not shown) in the wheel brake cylinder 32, which spread the brake shoes 12 and 14 apart when hydraulic fluid is supplied and press them against the inside of the brake drum 34. In addition to this hydraulic actuation, which is provided for service braking, the drum brake 10 can also be used as a parking brake. For this purpose, there is a hand brake lever 36 (shown partly in dashed lines) which is rotatably mounted in a bearing 38 in the upper end region of the right brake shoe 14.

To adjust the brake shoes 12, 14 in the event of wear of the friction lining, an adjustment device 40 is provided, to which an adjustment strut 41 belongs, which extends in the upper region of the drum brake 10 between the two brake shoes 12 and 14. The adjusting strut 41 comprises a pressure sleeve 42, a push rod 44 received therein and an adjusting pinion 46 screwed onto the latter. Below the bearing 38, the hand brake lever 36 is coupled to the left brake shoe 12 via the adjusting strut 41. The free end of the hand brake lever 36 is connected to a hand brake cable 48. If this is pulled to the left, the hand brake lever 36 pivots about the bearing 38 and presses the brake shoes 12, 14 against the drum 34 via the adjusting strut 41. The braking torque is transmitted via the dome 26 into the

Anchor plate 16 and initiated by this in the vehicle axis.

In the upper and lower end region of the brake shoes 12 and 14, brake shoe retraction springs 50 and 52 are arranged, which bias the brake shoes away from the brake drum, so that the

Brake shoes 12, 14 return to their rest position after releasing the brake. In the rest position, the spring forces of the return springs 50 and 52 are absorbed by the adjusting strut 41 and the dome 26.

A return spring 54 wound spirally around the hand brake cable 48 supports the pivoting back of the hand brake lever 36 into the rest position until it strikes a stop 56 on a web plate 58 of the right brake shoe 14 which extends radially inwards. On the outside of the brake shoes 12 and 14, a friction lining 60 or 62 is attached, which moves to the drum 34 when the brake is actuated and is pressed against its inside. The brake shoes 12 and 14 pivot about the support surfaces of the dome 26. Here, the adjustment strut 41 is relieved of the retraction force of the upper shoe return spring 52 and the distance between the support surfaces of the adjustment strut 41 on the web plate 58 of the right brake shoe 14 (or the stop surface on the Hand brake lever 36) and a web plate 64 of the left brake shoe 12 increases.

On the web plate 64, a two-armed adjusting lever 66, which also belongs to the adjusting device 40, is pivotably supported by a clamping sleeve 68 serving as a bearing and pressed into the web plate. The adjusting lever 66 is supported on the push rod 44 with a shorter left lever arm 70, while a right, longer lever arm 72 engages in a saw toothing 74 of the adjusting pinion 46. An adjusting spring 75 is arranged between the adjusting lever 66 and the lower region of the web plate 64 and pulls the adjusting lever 66 downward. The readjusting spring 75 thus constantly exerts a torque acting clockwise around the clamping sleeve 68 on the adjusting lever 66.

If the distance between the support surfaces of the adjustment strut 41 on the web plates 58 and 64 increases, the adjustment lever 66 can pivot about the clamping sleeve 68. The right lever arm 72 rotates the adjustment pinion 46, which unscrews the push rod 44 from the push sleeve 42. The push rod 44 is thereby fixed relative to the push sleeve 42 in a more extended position. After releasing the brake and resetting the brake shoes 12 and 14, the adjusting lever 66 is also pivoted back into the starting position. The adjusting lever 66 slides back over the saw toothing 74 of the adjusting pinion 46 in accordance with the extent of the previously performed pivoting movement and engages behind a tooth of the saw toothing 74. So that is an overall Cycle of an adjustment movement carried out on the adjustment strut 41.

4 and 5 show the adjustment strut 41 in an enlarged view. The adjustment strut 41 comprises the pressure sleeve 42 with a tubular section 76, into which the pressure rod 44 projects with part of a threaded rod 78. The adjusting pinion 46 is screwed onto the threaded rod 78 until it abuts the pressure sleeve 42. Clamping forces which act on the ends of the adjustment strut 41 are thus transmitted via the tubular section 76 of the pressure sleeve 42 to the adjustment pinion 46 and from there to the threaded rod 78 of the pressure rod 44.

In the tubular section 76 of the pressure sleeve 42, a switch 79 with an insulating sleeve 80, an electrically conductive contact pin 82 guided therein and a compression spring 84 biasing it is arranged at the bottom. An electrical line 86 connects the contact pin 82 to a display device (not shown), which can emit a warning tone or a warning light, or to a circuit arrangement 88, which is described below and is shown in FIG. 10.

The compression spring 84 can consist of an electrically insulating material, but can also be designed as a metal wire spring if additional insulation is present between the contact pin 82 and the base of the tubular section 76. An insulating disk can also be inserted between the compression spring 84 and the contact pin 82, or a head 92 of the contact pin 82 consists of insulating material.

4 shows the state of new friction linings 60 and 62. The contact pin 82 lies under the force of the compression spring 84 against the end face 90 of the threaded rod 78 arranged in the tubular section 76. An electrical monitoring current flows through line 86, contact pin 82, the end face 90, the push rod 44, the brake shoes 12 and 14 and the anchor plate 16.

By rotating the adjustment pinion 46 described above, the pressure rod 44 is moved out of the pressure sleeve 42 to produce an adjustment path. With increasing wear of the friction linings 60, 62, the end face 90 of the pressure rod 44 is moved further and further out of the pressure sleeve 42 until the contact pin 82 has covered a distance x and the head 92 lies against the bottom of the insulating sleeve 80.

If the friction linings 60 and 62 wear even further, the end face 90 of the push rod 44 moves away from the contact pin 82 (FIG. 5) and the monitoring current is interrupted.

10 shows the circuit arrangement 88 which actuates an active warning lamp when the monitoring current is interrupted. The monitoring current flows from a voltage source with an output voltage of 12 volts, such as a vehicle battery, via a series resistor R1, which is, for example, 330 Ω. The switch 79 shown closed in FIG. 10 closes the circuit with low resistance to a connection connected to ground. An interruption of the switch 79 (shown in dashed lines) causes the current to be conducted to ground via a resistor R2, for example 510 Ω, and an active warning lamp L. The signal triggered by the wear of the friction linings 60 and 62 thus causes the warning lamp L to light up.

The circuit arrangement can also be designed in such a way that a single interruption of the monitoring current leads to the warning lamp lighting up continuously.

The switching path x of the switch 79 and thus the permissible wear of the friction linings 60 and 62 and the drum 34 can be defined over the length of the contact pin 82. The sleeve 80 can for this purpose, are pressed into the pressure sleeve 42 to a predetermined depth.

In the exemplary embodiment explained above, a brush, which is well known from electric motor construction and also from generator construction, a spring-guided sliding contact made of graphite, for example natural, metal or electrographite, can be provided as contact pin 82 and compression spring 84, which leads to the current transfer conveyed to a collector or to a slip ring.

In further embodiments, the switch 79 is designed as a contactless switch. Figures 6 to 9 show three examples. FIG. 7 shows an inductive, FIG. 8 a capacitive and FIG. 9 a magnetic force-operated scanning of the adjustment path.

In such embodiments, provision is also made for an additional signal device 94 to be arranged on one of the friction linings of the drum brake. As shown in FIG. 1, the additional signaling device 94 is let into the friction lining 60 in the lower region of the running brake shoe 12.

11 to 13 show details of embodiments of this additional signaling device 94. The signaling device 94 is inserted into a cavity of a rivet shank 96, as is provided for a lining rivet, and comprises a wire loop 98 embedded in plastic Wire loop 98 into a recess 100 of the friction lining 60, so that when the friction lining 60 wears, the wire loop 98 is severed and a signal can thus be supplied to a circuit arrangement 88.

The additional signal device 94 can be attached to the brake shoe 12 in various ways. The additional signal device 94 shown in FIG. 11 is pressed into the cavity of the rivet shaft 96, flanged and additionally attached by a lock washer 102. The additional signal device 94 shown in FIG. 12 is inserted directly into the rivet shaft 96 and has a plurality of spreading arms 104 which spread apart after the rivet shaft 96 has penetrated and secure the signal device 94 against wandering out. The additional signaling device 94 shown in FIG. 13 carries a nut 108 on a threaded shaft 106. After passing through the rivet shaft 96, the warning device 94 is secured by means of the nut 108.

The electrical conductors or lines leading to the wire loop 98 and correspondingly also the electrical line 86 of the switch 79 lead to plug-in couplings 110 and 112 which, as shown in FIGS. 1 to 3, in a hollow rivet 114 of the dome 26 and an opening 116 in the anchor plate 16 are attached, which is symmetrical to an opening for attaching the hand brake cable 48 to the anchor plate 16. The lines are also passed through the lower and upper jaw return springs 50 and 52 and through an opening 118 of the web plate 58.

The illustrated embodiments of the signaling device 79 can be used in existing series brakes practically without changes, which is why the adjusting device 40 is also suitable for retrofitting drum brakes that have already been supplied.

Claims

claims

1. Automatic drum brake adjustment device (40) for compensating for friction lining and drum wear, with a signal device (79) which delivers a signal dependent on an adjustment path (x), characterized in that the adjustment path (x) is of a variable length adjustment strut ( 41) is produced, which comprises a pressure sleeve (42) and a threaded rod (44, 78) accommodated in the latter, which can be screwed out of the pressure sleeve by means of a pinion (46).

2. Adjusting device according to claim 1, characterized in that the signal is brought to a vehicle driver for visual and / or acoustic perception.

3. Adjusting device according to claim 1 or 2, characterized in that a change in the signal is evaluated in predetermined periods.

4. Adjusting device according to claim 3, characterized in that the threaded rod (44, 78) actuates a switch (79) after a predetermined adjustment path (x).

5. Adjusting device according to claim 4, characterized in that the switch (79) is arranged in the pressure sleeve (42).

6. Adjusting device according to one of claims 4 or 5, characterized in that the switch (79) has a switch contact (82, 90).

7. Adjusting device according to one of claims 4 or 5, characterized in that the switch (79) is a magnetic switch, an inductive or a capacitive switch.

8. drum brake (10), characterized by an automatic adjusting device (40) according to one of the preceding claims.

9. drum brake according to claim 8, characterized in that at least one running brake shoe (12) is provided with an additional signal device (94) for indicating a worn friction lining (60).

10. Drum brake according to one of claims 8 or 9, characterized in that a conductor leading to the signaling device (94) is guided within helical brake shoe return springs (50).

11. Drum brake according to one of claims 8 to 10, characterized in that a conductor leading to the signaling device (94) extends through a first opening (116) in an anchor plate (16) of the drum brake, which is axially symmetrical to a second opening ( 117) is arranged, which is provided for the passage of a hand brake cable (48), a component of a plug-in coupling (112) preferably being fastened in the first opening (116).

12. Drum brake according to claim 11, characterized in that a conductor leading to the signaling device (94) extends through an opening (114) in a dome (26) of the anchor plate, in the opening (114) preferably a component of a plug-in coupling (110 ) is attached by means of a hollow rivet (114).

13. Drum brake according to one of claims 8 to 12, characterized in that a conductor (86, 98) leading to the signaling device (79, 94) is monitored for quiescent current.

14. Drum brake according to one of claims 8 to 13, characterized in that the additional signal device (94) on the brake shoe (12) by means of a lock washer (102), spreading arms (104) or a lock nut (108) is attached.