EP0768147A1 - Grinding machine for brake discs - Google Patents

Abstract

The machine is mounted on a moveable frame (32), and includes a motor and two cylindrical abrasive tools (2,3) with means for displacing the tools longitudinally parallel to a reference plane, and transversally with respect to the reference plane. The disc brakes are centred and rotated (13). The tools are mounted on rotating shafts (4) arranged parallel to each other and parallel to the reference plane and on either side of it. The shafts are mounted so as to slide in mandrels to ensure the longitudinal displacement of the tools.

Description

The invention relates to grinding machines for brake discs.

The appearance of the disc brake was a revolution in the automobile industry in its time. The disc rotating in a plane parallel to the wheel is clamped between two plates mounted on a stirrup; the large surface of the disc allows excellent heat dissipation of the energy absorbed during braking and the application of significant braking torques without braking losses due to expansion.

Disc brakes are not without their drawbacks. As they are mounted in the open air, they are at the mercy of dust capable of scratching them and the very power of braking can cause the localized appearance of melting points ("fire points"); thermal stresses and the quality of the machining can, finally, cause a more or less marked veiling which causes vibrations and can, at the limit, make them unfit for use.

As a result, periodic checks and replacement of brake discs have become routine operations for many garage owners. In addition, an increasingly frequent problem encountered by these garage owners is the placing on the market of new cars on which discs with imperfect flatness are mounted from the start.

If the disassembled disc appears healthy, it can, for a lower cost than an outright replacement, have it rectified on a workshop tour.

As this workshop tour is generally used for multiple functions, it is rare that rectified discs are available immediately, much to the users' displeasure. It is also always necessary to disassemble the vehicle discs to perform the operation.

We therefore sought to make rectification of the discs easier, without having to resort to dismantling them.

US-A-3,592,088 describes a brake disc grinder with an invertible tool holder arm; the tool holder is inverted to successively correct each of the faces of the disc to be reworked.

Patent DE-A-2540187 proposes to rectify a disc in a single pass using a U-shaped tool, the spacing of the branches of which therefore has a fixed value.

International patent application WO-A-82/01678 describes a grinding machine for a brake disc in place on a vehicle hub. This grinding machine comprises a hub drive device as well as two tool-carrying carriages that can be arranged on either side of a disc, the entire vehicle train being raised relative to the ground. The grinder according to WO 82/01678, is relatively bulky and therefore relates rather to large workshops.

In the various grinding devices mentioned above, as in particular in document EP-A-0 283 391 (which relates to the grinding of abrasive wheels), sharp tools are used to grind the surface of the discs, which involves the removal, on each side of the disc, of a significant thickness of material. A disc can hardly undergo rectification once under these conditions. In addition, when the disc has irregularities or a haze, the cutting tool undergoes repeated shocks each time it enters the material, which requires the use of tools with pointed tips, which are more expensive.

US-A-4,262,452 discloses a rapid grinding device for a brake disc affecting the shape of a pistol. This device comprises two rotors of frustoconical shape. At least one of these rotors is an abrasive wheel. A suitable mechanism makes it possible to converge the axes of the two rotors and to pinch a disc with rectify between these two rotors.

Such a grinder does not allow high precision work; in particular, it is not possible to compensate for a veiling of the disc to be rectified or to guarantee perfect flatness of the faces (depending on the condition of the grinding wheels) or perfect parallelism of the rectified faces (due to the convergence of the axes and the wear of tapered grinding wheels).

Attempts have been made to produce a grinding machine for a brake disc, generally not requiring the disassembly of the disc, which, despite its small dimensions, is capable of rectifying a disc simultaneously on its two faces with very high precision and which makes it possible to remove the "fire points" with an extremely reduced material removal.

Another object of the invention is to put on the market a grinding machine which can straighten the hazy discs, also with a very reduced material removal.

Another object is to produce such a grinder thanks to which the thickness of material removed is small enough to avoid having to systematically change the brake pads.

Another object is the development of a device which makes it possible to obtain, after rectification, a braking power comparable to that of a new disc.

The subject of the invention is a device for grinding a brake disc, in particular for a brake disc mounted on a vehicle, this device comprising a frame, a motor, two grinding tools, longitudinal displacement means capable of displacing these tools parallel to a reference plane and transverse displacement means able to move these tools transversely relative to this plane, means for centering and driving in rotation of this disc; grinding tools are grinding wheels with a cylindrical abrasive surface mounted on rotating shafts arranged parallel to each other and parallel to the reference plane, on either side thereof, these rotary shafts being slidably mounted in mandrels so as to ensure the longitudinal movement of the grinding wheels.

Preferably, the rotary shafts are supported at their end opposite to the abrasive wheels by thrust bearings mounted in a fork capable of moving along a worm screw driven by a drive means (either manual or automatic ).

The abrasive wheels preferably rotate in opposite directions from each other so that the surfaces coming into contact with the disc move in the same direction as said disc but not at the same linear speed, so as to obtain a polishing with a minimum of material removal.

The means for centering and driving the disc in rotation advantageously comprise a rotary plate capable of holding the disc along the reference plane of the device.

This provides an apparatus capable of also rectifying disassembled discs.

Preferably, each mandrel is able to be moved in the frame transversely to the reference plane by an independent transverse displacement control.

The device advantageously comprises a relative transverse displacement control common to the two mandrels capable of spreading and bringing together simultaneously these two mandrels relative to each other; this relative transverse displacement control preferably consists of a device with differential screw pitch.

According to an advantageous embodiment, pulleys are fixed on the rotary shafts; these pulleys being driven by a belt, said belt passing over a drive pulley actuated by the motor and comprising a tensioning device capable of compensating for variations in tension due to a change in the relative position of the shafts of these two abrasive wheels.

Preferably, the device comprises an articulated arm provided with a fixing lug capable of being secured to a brake caliper support so as to correspond the reference plane of the device with the plane of a disc mounted on a vehicle.

The very simple to use grinding machine thus considerably shortens the downtime of vehicles.

• des moyens de centrage et d'entraînement ajustables de façon à pouvoir entraîner, en lieu et place d'un disque, un tambour de frein à tambour et
• une meule à surface abrasive cylindrique apte à rectifier la face intérieure du dit tambour de frein, l'axe de cette meule abrasive cylindrique étant parallèle à l'axe de rotation du dit tambour de frein.

Optionally, the device comprises

• centering and driving means adjustable so as to be able to drive, in place of a disc, a drum brake drum and
• a grinding wheel with a cylindrical abrasive surface capable of grinding the inner face of said brake drum, the axis of this cylindrical abrasive wheel being parallel to the axis of rotation of said brake drum.

• la Fig. 1 est une vue en perspective de la face avant de la rectifieuse;
• la Fig. 2 est une vue schématique du système d'entraînement de la rectifieuse;
• la Fig. 3 est une vue schématique du dispositif de tension et d'amortissement des vibrations du moteur;
• les Fig. 4 et 5 sont des vues respectivement de profil (avec arrachement) et de face de la rectifieuse suivant l'invention;
• la Fig. 6 est une vue schématique des deux meules lorsqu'elles ont été amenées en contact avec le disque à rectifier et
• la Fig. 7 est une vue en coupe suivant le plan VII - VII de la fig. 6.

Other particularities or advantages of the invention will emerge from the description below of particular embodiments, reference being made to the drawings, in which

• Fig. 1 is a perspective view of the front face of the grinder;
• Fig. 2 is a schematic view of the grinder drive system;
• Fig. 3 is a schematic view of the tensioning and vibration damping device of the engine;
• Figs. 4 and 5 are respectively side views (with cutaway) and front view of the grinding machine according to the invention;
• Fig. 6 is a schematic view of the two grinding wheels when they have been brought into contact with the disc to be ground and
• Fig. 7 is a sectional view along the plane VII - VII of FIG. 6.

The grinding machine 1 is essentially provided on its face turned towards the disc to be rectified, which we will call the front face, with two rotary grinding wheels 2,3 rotating in opposite directions to each other at a speed of about 7000 rpm.

Each of these grinding wheels 2,3 is mounted on a shaft 4 which can move parallel to the reference plane emerging from the front face 5, the two shafts 4 moving together so that the two grinding wheels 2,3 remain in screw -to each other.

The two shafts 4 are rigidly supported and driven by mandrels 6 which can be moved as will be seen below by an endless screw perpendicular to the reference plane to the left or to the right of the front face or to be brought together one of the other.

Each mandrel is supported by a shock absorber 7 (visible in Fig. 4) which ensures its stability and absorbs vibrations.

The grinding machine is driven by an electric motor 8. This motor is provided with an angular gear 9 driving pulleys 10,11. These pulleys 10, 11 actuate, by means of a belt 12, a drive device 13 intended to drive the hub in rotation (not shown) on which the disc to be ground is fixed (shown in broken lines). Depending on the position (right or left) of this hub, the drive device 13 can be mounted on either side of the grinder 1 by moving the support arm 14 from a sleeve 15, 16 to the other.

The hub is driven by a plate 17 provided with fixing means 18, 19 in variable number, so that it can be adapted to hubs of different configurations, for example with an even number of studs or odd. This plate 17 has in its middle a centering tip 20 which allows it to be quickly aligned on the hub of a vehicle.

The grinding machine 1 is generally held in place relative to the braking disc thanks to an adjustable arm 21 which carries a suitable attachment 22 and perfectly aligned with respect to the plane of the disc. This fixing 22 can be fixed for example to the support of the stirrup of a disc still mounted on its hub.

The arm 21 can be mounted both on the left side and on the right side of the grinding machine 1 which is thus, with minor adjustments, rigorously aligned on the brake disc to be machined.

A tensioner 23 makes it possible to maintain the tension of the belt 12 when the relative position of the plate 17 is adjusted relative to the grinding machine 1.

Note that the position of the plate 17 can also easily be reversed depending on whether one operates on the left or right side of the vehicle.

A protective cover 24 prevents accidental contact with the moving parts of the drive device 13. The transmission by pulleys and belt could perfectly be replaced by a cardan shaft.

The internal structure of the grinding machine will be described with particular reference to Figures 2, 3, 4, 5.

Fig. 2 shows the movement transmission device in the grinding machine 1. This device uses a single belt 25. The belt 25, which drives both the two shafts 4 of the grinding wheels 2,3 and the disc to be ground, is trapezoidal shape. It passes successively on a drive pulley 26 fixed to the motor shaft 8, then on a return pulley 27, then on one of the pulleys 28 secured to the shaft 4 of one of the two grinding wheels 2, then on the pulley 29 causing the bevel gear 9.

All these pulleys 26, 27, 28, 29 have a trapezoidal groove. The belt finally passes, inverted, in the rectangular groove of the second pulley 30, integral from the shaft 4 of the grinding wheel 3, and returns to the drive pulley.

This arrangement makes it possible to rotate the two shafts 4 in opposite directions, which is advantageous, as will be seen below. Other similar configurations can be used to achieve this result. A major advantage of such training lies in the lightness it gives to the construction of the grinder, without compromising on its degree of precision.

The distance between the two shafts 4 varying during grinding, it is necessary to adjust the tension of the belt 25 at any time.

Fig. 3 shows how the belt tension is ensured. The motor 8 as a whole is fixed to an oscillating cradle 31. This oscillating cradle 31 is secured to the frame 32 on one side by a hinge 33, the axis of this hinge 33 being parallel to that of the shafts 4 on the other side of the cradle is suspended from the frame 32 by means of a damping device 34 under tension.

The thrust of this shock absorber directed downwards is adjustable and keeps the belt 25 tensioned and, at the same time, attenuates the vibrations generated by the assembly.

Figs. 4 and 5 show in more detail the whole of the device for longitudinal displacement and transverse displacement of the shafts.

Each of the pulleys 28.30 is provided with a wedging means 35, here a flat, (but we could also use a wedge and a groove) which leaves it free to move longitudinally on its shaft 4. We can thus advancing the shaft 4 without varying the relative position of the drive pulleys 28.30. The rear end of each shaft 4 is supported by a thrust bearing 36 mounted in a fork 37 surmounted by a threaded portion 38 guided by an endless screw 39 mounted on the frame 32 parallel to the axis of the shafts 4. This worm screw supports a handle 40. The rotation of the handle 40 causes the longitudinal displacement of the fork 37 and therefore the advancement or retreat of the grinding wheels 2,3.

The upper part of the fork 37 supports an index 41a which moves in front of a graduated batten 42a.

The pulley 29 is supported by bearings integral with the frame 32. It drives via the bevel gear 9 an axis 41 disposed transversely to the plane of the disc, which axis 41 ends with the drive pulleys 10,11.

Fig. 4 shows more precisely the way in which the grinding wheel positioning device 2, 3 is arranged.

Each mandrel 6 is attached to the frame 32 by means of a damper 7 pivotally mounted around an axis parallel to the axis of the grinding wheels. These shock absorbers contribute both to the maintenance of the mandrels and to the damping of vibrations generated during grinding.

The position of the mandrels is determined transversely by knobs 42 acting on endless screws 43. A sleeve 44 acting on rods with differential screw threads 45, 46 allows micrometric adjustment of the respective position of the mandrels.

The grinding machine according to the invention is in an extremely compact form. We can therefore correct a brake disc without even removing it from its hub. In the case of the front wheels, the disc is accessed by turning the direction sharply to the right or to the left, as the case may be.

The operation of the grinding machine according to the invention will be described with particular reference to Figs. 2 and 3.

The grinding machine being suitably centered and aligned as explained above, we act on the longitudinal displacement lever so as to assess (without contact between the disc and the grinding wheels) the maximum extension to be given to the grindstone trees 2.3.

The motor 8 having been started, thanks to its individual control, one of the grinding wheels is brought into contact with the face of the corresponding disc and a round trip is carried out over the entire width of the disc, which already makes it possible to give a assessment of the condition of the brake disc.

After setting the transverse movement control of the first grinding wheel 2 in this position, the same is done for the second grinding wheel 3.

The grinders 2,3 are then started and brought together simultaneously using the relative precision displacement adjustment (44,45,46). A series of successive passes is made by tightening, after each pass, the interval between the grinding wheels, until the desired degree of finish is obtained.

These operations can be performed manually or using an automatic feed device.

As shown schematically in FIG. 7, the disc is actuated by the plate 17 in the same direction as the grinding wheels 2,3. This reduces the tearing of material, which limits heating and allows a more rigorous rectification of the surfaces; for example, the disc can be rotated at around 580 rpm and the grinding wheels 2.3 at 800 rpm.

While removing material only to a minimal depth, we eliminate "fire points" and we obtain a polished surface conducive to effective braking.

The two faces of the disc being rectified simultaneously under conditions of perfect parallelism, even an initial warping of the disc can be completely eliminated.

The small width of the cylindrical grinding wheels (with regard to the diameter of the disc) and their longitudinal displacement ensures very high precision in rectification (which would not be permitted, in particular, conical grinding wheels or very large grinding wheels as described in US-A-4,262,452 whose rigorous surface condition is more difficult to verify).

In addition, the disc being treated "in situ", its rectification eliminates the influence of random factors (timing accuracy etc.) which cannot be taken into account in any other method.

The speed of the operation with the grinding machine according to the invention is, literally, a factor of safety for the motorist. It is indeed common practice, when braking problems appear, to simply change the pads of the brake caliper, when the surface of the discs is already badly damaged or distorted and the performance or braking is already falling. sensitive.

The use of the grinding machine according to the invention, simple, quick and inexpensive gives a vehicle all its braking power without having to change the discs, hence saving money and delivery time.

The grinding wheels moving parallel to the disc only via the rotary axes 4, it is possible to use the grinding machine according to the invention in places inaccessible to devices known from the prior art.

When it is not possible, for reasons of space, to insert the grinder in place opposite the hub and to secure it to the vehicle, the grinding of the discs remains, despite this, extremely easy: it suffices, in Indeed, to disassemble the discs and fix them via an intermediate piece on the drive plate 18 using the adjustable fingers 19.

The disc, driven in rotation by the plate between the grinding wheels 2,3, is rectified according to the same procedure, while keeping practically all the advantages mentioned above: rigorous parallelism of the faces, extremely passes reduced, negligible material removal.

It will be noted that it is possible, by modifying the shape of the drive device 13, to also rectify brake drums (in this case using only one of the two abrasive wheels 2,3).

It is also possible to drive, using the drive device 13, via different adapters, a brake drum with its axis arranged in the same way as that of a disc to be rectified, in this case using an abrasive wheel. auxiliary, the axis of rotation of which is arranged parallel to that of the brake drum to be ground, auxiliary positioning means making it possible to bring said auxiliary abrasive wheel tangentially to the internal surface of the drum to be ground.

This auxiliary wheel generally having a diameter smaller than that of the abrasive wheels 2, 3, one can advantageously use as auxiliary wheel one of the used wheels 2, 3, the diameter of which is therefore reduced.

The principle developed above for the grinding of used discs also applies to the grinding of drums (respective rotational speeds of the drum to be ground and the abrasive wheel, polishing, low material removal).

The auxiliary wheel operating in the same speed range as the wheels 2, 3 can be driven by the same motor via a return belt.

A transparent protective cover can be mounted around the moving parts during grinding on the bench, giving the use of the grinding machine according to the invention optimum working safety.

In addition, this protective cover can be designed to be dustproof and be fitted with a dust extraction system.

The rotation of the grinder motor putting in operation a blower, according to a mechanism known per se, the engine block is put in slight overpressure. The overpressure air is evacuated by one or more holes drilled in the front face of the grinder (for example between the mandrels 6), contributing both to the cooling of the parts and to the evacuation of residues.

Claims (10)

Device for grinding a brake disc, in particular for a brake disc mounted on a vehicle, this device comprising a frame (32), a motor (8), two grinding tools, longitudinal displacement means able to move these tools parallel to a reference plane and transverse displacement means able to move these tools transversely relative to this plane, means for centering and driving in rotation (13) of this disc characterized in that the rectification tools are grinding wheels with a cylindrical abrasive surface (2,3) mounted on rotary shafts (4) arranged parallel to each other and parallel to the reference plane, on either side thereof, these rotary shafts (4 ) being slidably mounted in mandrels so as to ensure the longitudinal movement of the grinding wheels (2,3). Device according to Claim 1, characterized in that the rotary shafts (4) are supported at their opposite end to the grinding wheels with a cylindrical abrasive surface (2,3) by thrust bearings (36) mounted in a fork (37) capable of being move along an endless screw (39) driven by a drive means (40). Device according to either of Claims 1 and 2, characterized in that the abrasive wheels (2,3) rotate in opposite directions to each other and in that the surfaces coming into contact with the disc move in the same direction as said disc, but not at the same linear speed, so as to obtain a polishing with a minimum of material removal. Device according to any one of claims 1, 2 and 3 characterized in that the means for centering and driving in rotation of the disc comprise a rotary plate (17) capable of maintaining the disc according to the reference plane of the device (1). Device according to any one of the preceding claims, characterized in that each mandrel (6) is capable of being moved in the frame (32) transversely to the reference plane by an independent transverse displacement control (42, 43). Device according to claim 5 characterized in that it comprises a relative transverse displacement control (44,45,46) common to the two mandrels (6) capable of simultaneously separating and bringing these two mandrels relative to each other (6). Device according to Claim 6, characterized in that the relative transverse displacement control consists of a device with differential screw pitch (44,45,46). Device according to any one of the preceding claims, characterized in that pulleys (28,30) are fixed on the rotary shafts (4); these pulleys (28,30) being driven by a belt (25), said belt (25) passing over a drive pulley (26) actuated by the motor (8) and comprising a tensioning device (31,33,34) suitable compensating for variations in tension due to a change in the relative position of the shafts (4) of these two abrasive wheels (2,3). Device according to any one of the preceding claims, characterized in that it comprises an articulated arm (21) provided with a fixing lug (22) capable of being secured to a brake caliper support so as to align the plane of reference of the device on the plane of a disc mounted on a vehicle. Device according to any one of the preceding claims, characterized in that it comprises centering and driving means (13) adjustable so as to be able to drive, in place of a disc, a drum brake drum and - a grinding wheel with a cylindrical abrasive surface suitable for rectify the inner face of said brake drum, the axis of this cylindrical abrasive wheel being parallel to the axis of rotation of said brake drum.

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