DE4116502A1 - Disc brake with stepped cylinder and piston - has rapid initial travel with high final braking force - Google Patents

Abstract

The disc brake has a caliper (1) which supports brake blocks (2) and (3) on opposite sides of the disc (5). The brake block (3) is actuated directly by the piston (6) which operates in the brake cylinder (7). The piston (6) has an extension (12), of reduced dia. which operates in a cylinder (10) of corresponding dia. When the brake pedal is applied, brake fluid flows into the cylinder (10) and acts on the piston extension (12) so the brake block (3) is rapidly brought into contact with the brake disc (5). As the pressure increases the lip (16) of the valve (13) is pressed clear of the opening so that high pressure brake fluid acts on the main piston (6) to provide a high braking force. USE/ADVANTAGE - Disc brake with rapid initial operation and high final braking force.

Description

The invention relates to a with a pressure medium cylinder provided saddle for a disc brake. Such cylinders are required to have a piston guided in the cylinder at least one brake pad (fixed caliper brake) at the Apply the brake to the brake disc.

With disc brakes it is an advantage to comparatively great clearance for the brake blocks compared to the Brake disc to have so that outside the brake application no residual torque exerted by the disc on the brake pads can be. This is due to the distance of the brake pads from the Brake disc defined outside the brake application Air play ensures that when it is big enough that due to the missing residual moments, the lining wear is reduced and thus the fuel consumption is reduced. Besides, will the cooling behavior due to the sufficient pane spacing the disc improved.

On the other hand, introduces the known disc brakes large air gap that a comparatively large Pedal travel is required, the brake pads are first Apply comparatively late to the brake disc.  

The pedal travel can be reduced by reducing the Reduce the piston diameter, but by reducing it the transmission ratio of the braking force is thereby a greater foot strength is required for the operator, if you do not take appropriate countermeasures on the master cylinder that increases its dimensions.

The object of the invention is therefore a new brake caliper indicate which one allows a large clearance, without an increased foot strength through the Operator or a large pedal travel would be necessary taking these measures without changing the master cylinder (Magnification) should be achieved.

The invention is therefore based on a brake caliper genus resulting from the preamble of claim 1 and solves the task by the from the characteristic part combination of features resulting from the main claim.

In principle, the invention consists of several Cylinders in which an associated piston is guided is to couple with each other. It is special advantageous if a first small cylinder is provided, the one with a small pedal travel at a comparatively lower one Power transmission conveys the brake pad up to the disc and then the one in the no longer changing first Cylinder chamber built up pressure in the second cylinder chamber is directed towards a greater power transmission brings the first cylinder space and that to brake  builds up the necessary braking force. By the invention it is so possible, the individual cylinder levels different Assign tasks on brake application to which they are assigned are appropriately designed for their size.

The invention is in particular according to claim 2 therefor suitable to use a liquid as a pressure medium, the can preferably be brake fluid.

A particularly simple design that the Operation of a disc brake is well adapted, results resulting from the combination of features described in claim 3. In principle, this advantageous development consists in the stepped cylinder from two series connected Build cylinders with the appropriate pistons. Here the pistons should preferably be connected to each other and the pressure exerted on the pistons in the same Promote direction of movement so that they are in their Support the effect of strength. So the two pistons work, once they're both pressurized in the same Direction on the assigned brake pad or both Brake pads if the disc brake acts as a floating caliper brake is designed. Regarding the activation of the two pistons it should be noted that the pressure in the second cylinder should only be initiated if above the first Cylinder of the brake pad has moved to the disc and through the resulting resistance at first Piston pressure increases in the first cylinder. This increasing pressure opens the valve and thus gives the second Cylinder free to build up an actuation pressure. Since the  both pistons act in the same direction is through this In any case, measure the force acting on the brake pad elevated. However, the second piston is preferably in its effective area considerably larger, especially one Several times larger than the effective area on the first piston do. This is the possible advantage of the invention fully realized by only taking a comparatively long way with low volume consumption to put on the brake pads the brake pads is used and then a small way with great force from the second piston in the second Cylinder for applying the required braking torque.

A particularly simple structure for this is obtained from the Application of the features according to claim 4, because of the movement a corresponding movement of the first piston second piston is forced so that this in a suitable starting point for applying the large required Braking forces is driven.

A simple construction for a connecting valve is obtained in an advantageous development of the invention by the Measure according to claim 5. Here is the lip seal preferably constructed such that a significant Pressure increase in the first cylinder the elastic seal pressed together and thus an opening to the second cylinder is created depending on a minimum pressure. Around opening the connection valve only from the pressure, not but depending on the position of the piston (which is with the wear of the brake pads), that is  Connection valve preferably stationary over at least arranged the first piston, approximately in one to the Piston connecting cavity, the elastic Can support valve member on the first piston. To a getting a suitable gear ratio, you will preferably that resulting from claim 6 Apply combination of features.

Due to the appropriate coupling of the described above Movement of the two pistons is recommended in advanced training the invention a combination of features according to claim 7. This ensures that the second cylinder during the movement of the. following the movement of the first piston second piston does not receive a vacuum that at Open the connection valve only with pressure medium should be replenished. Rather, the movement of the first piston at the same time via the compensating valve Enlargement of the second cylinder space with pressure medium filled, which, however, only under the pressure of Reservoir stands. This measure is made sure that when moving the brake pad to the Brake disc of the second cylinder always with pressure medium remains filled.

In order to enable a return movement of the first piston after the end of the brake actuation despite the closing compensating valve, the development of the invention recommends the use of the measures resulting from claim 8. The connecting valve thus not only creates a pressure-dependent passage from the first to the second cylinder, but also ensures a pressure medium return from the first to the second cylinder as soon as the pressure in the second cylinder is greater than in the first cylinder. This is expediently done by lifting the sealing lip of a lip seal, as is known for example from the brake manual of the Bartsch publishing house, 9th edition, page 249, from FIGS. 56 to 58.

For the construction of the cylinders and pistons are under the Invention different possibilities provided. So can for example the combination of features according to claim 9 be applied, which is a particularly simple and represents reliable working structure. At this Design results in a particularly simple structure taking into account the features of claim 10 by the connection valve together with the first piston movably arranged and thus in its pressure-dependent Effect is independent of the position of the first piston.

A particularly space-saving construction is obtained through the Features according to claim 11, which has a particularly short overall length allowed if you insert the measures according to claim 12. There the hollow cylinder, however, both compared to the second Cylinder as well as opposite that along its inner The outer surface of the running guide disc must be sealed and the entire cavity of the hollow cylinder is kept tight must be, here is a reliable seal special to watch out for.

The principle of the configuration according to claim 12 consists in  to guide the second piston in the second cylinder, wherein in the interior of the second piston, the first cylinder is arranged, the effective cross-sectional area with the Internal cross section of the hollow cylinder matches.

The invention is according to claim 13 for both Fixed caliper brakes, but especially for floating caliper brakes suitable.

The invention is explained below with reference to the drawing.

It shows

Fig. 1 in a sectional representation the caliper of a floating-caliper brake using a first embodiment of the invention,

Fig. 2 in a symbolic representation of the caliper of a floating caliper brake in cross section using a second embodiment of the invention.

FIGS. 3 to 6 in a greatly enlarged and simplified representation of sketched possible embodiments of the valve connection for the embodiment of FIG. 2.

Fig. 1 shows the caliper 1 of a floating caliper brake, which comprises two brake pads 2 and 3 from the outside. The brake pads are sold in conjunction with the saddle as a tradable unit, being held apart by a spacer 4 in the absence of the brake disc. Instead of the spacer 4 , a brake disc 5 indicated by broken lines projects between the brake pads 2 and 3 in the case of an operational brake.

A second piston 6 acts on the brake pad 3 in a manner which has hitherto been conventional, which is driven by pressure medium which is pressurized in a cylinder 7 . The second piston 6 moves in a manner known per se on the inner lateral surface 8 of the second cylinder 7 . The second piston 6 moves to the left in FIG. 1 and moves the brake pad 3 against the brake disc 5 , the clearance L being overcome. By means of a plurality of elastic fingers holding springs 9 , the back plate of the brake pad is held in contact with the end face of the second piston 6 , so that when the piston 6 is returned by the roll-back effect of the piston seal, the brake pad 3 is safely brought back and thus Air play L is available. Such a construction of a floating caliper brake is described, for example, in connection with the European patent application EP-OS 3 73 333 or the German patent application DE-PS 40 07 721.

The novelty of the present invention is as follows. In addition to the second cylinder 7 , the present disc brake also has a first cylinder 10 , into which the pressure required to actuate the brake is introduced via a pressure line 11 . Within the first cylinder 10 , a first piston 12 is sealingly guided by means of the seal 13 , the effective area of the first piston 12 being given by the cross-sectional area of the first cylinder 10 . The first piston 12 is connected in one piece to the second piston 6 , the two pots of the pistons facing each other with their bottoms and being combined in one piece, which can be done, for example, by a casting process or by welding.

If an actuating pressure is now exerted on the pressure line 11 via the brake pedal at the beginning of the braking process, the stepped piston 6 , 12 is conveyed to the left in FIG. 1 due to the relatively small diameter of the first cylinder 10 . As soon as the air gap L is overcome in this direction, the brake pad 3 bears against the brake disc 5 . The outer brake pad 2 is then pulled against the brake disc in the case of a floating caliper brake. During this movement, the opening 14 , which connects the first cylinder 10 to the second cylinder 7 , is closed by a lip seal 13 .

However, after the brake pads 2 , 3 rest firmly on the brake disc, a further movement of the pistons 12 , 6 to the left in FIG. 1 is only possible with very great effort. A growing pressure thus builds up in the first cylinder 10 .

Due to the previous movement of the first piston 6 , the space of the second cylinder 7 increases . Since the connecting valve formed by a lip seal 13 keeps the connecting opening 14 closed, an underpressure would have to arise as a result of the enlargement of the second cylinder space 7 . In order to prevent this and to keep the second cylinder chamber filled with pressure medium, a symbolically represented compensating valve 15 is provided, which connects the compensating tank, not shown, to the second cylinder 7 , as long as there is a negative pressure with respect to the compensating tank.

As soon as the connection valve is compressed due to the increasing pressure in the first cylinder 10 and thus the lip 16 of the valve opens the opening 14 , the pressure of the pressure medium in the first cylinder propagates onto the second cylinder 7 . However, due to the considerably enlarged effective area of the second piston 6, there is now a much greater force transmission of the pedal force compared to the force exerted on the brake pad 3 , the path required by the pedal for filling the second cylinder 7 being comparatively small. After initially applying the brake pads 2 , 3 to the brake disc 5 with little effort and a small pedal travel, the necessary braking force is subsequently applied to the brake pads 2 , 3 with great force and a small pedal travel.

If the brake actuation is ended and the pressure in the first cylinder 10 is greatly reduced, the brake fluid cannot reach the expansion tank via the compensating valve 15 because of the excess pressure, but can flow back from the second to the first cylinder via the sealing lip 16 . In this way, the required clearance L can be regained via the roll-back effect of the seals of the stepped piston 12 , 6 .

Fig. 2 shows a slightly modified configuration of the stepped cylinder and the stepped piston. As in the exemplary embodiment according to FIG. 1, a first cylinder 20 and a second cylinder 21 are again provided, wherein these two cylinders can be connected to one another in a pressure-dependent manner via a connection valve 13 . A compensating valve 15 is also arranged in FIG. 2, which connects the second cylinder 21 to the compensating container, insofar as there is a negative pressure in the second cylinder 21 with respect to the compensating container. With regard to the first cylinder 20 , the piston 23 is effective with a diameter d 1 , while with respect to the second cylinder 21, the piston 24 is effective with a diameter d 2 . Here d 2 is greater than d 1 .

The second embodiment according to FIG. 2 now works as follows. If the brake pedal is actuated, a corresponding pressure occurs in the pressure line 11 . The pressure in the pressure line 11 is fed into the first cylinder 20 via a supply line which is fixedly connected to the housing and which is delimited via a guide disk 26 fixed to the housing and the first piston 23 opposite it. Due to the increasing pressure in the first cylinder 20 , the stepped piston 27 is moved to the left together with the piston 23 until, as has already been described above, the air gap of the brake pad is overcome. If the brake pads lie firmly on the brake disk (not shown), the pressure in the first cylinder 20 rises sharply, as has already been described above, the pressure increase also appearing in the feed line 25 . Because of the pressure increase there, the connecting valve 13 (not shown in detail) opens, so that this pressure can be transferred to the second cylinder 21 which, as already described above, is filled with pressure medium via the compensating valve 15 . This now increasing pressure in the second cylinder 21 acts on the second piston 24 , which is formed by the outer dimensions of the bottom of the stepped piston 27 . In addition to the surface of the first piston 23 , the surface of the second piston, which has an increased force transmission, also acts, so that there is a considerable increase in force on the back surfaces of the brake pads, which generates the necessary braking torque.

If the pressure in the pressure line 11 is reduced again after the brake has been actuated, the excess pressure in the second cylinder 21 , as already described above, can escape via the connecting valve 13 into the supply line 25 and thus the first cylinder 20 .

The apparent from Fig. 2 embodiment is opposite the embodiment according to Fig. 1 space-saving.

FIGS. 3 and 4 show, in a greatly enlarged and simplified representation of the arrangement of the connecting valve 13, which establishes the connection between the lead 25 and the second cylinder 21 in the form of a lip seal. If the pressure in the first cylinder space 20 and thus in the supply line 25 increases , the seal 13 is pressed together towards the wall 28 of the housing 1 , as a result of which the connection opening 14 to the second cylinder 21 is released. The second cylinder filled with pressure medium via the compensating valve shown in FIG. 2 is pressurized via the feed line 25 , as a result of which the brake pads apply the braking torque required for braking.

Fig. 4 also shows that the connection opening 14 consists of individual slots. It is not necessary for the tappet to be integrally connected to the saddle 1 , since it is pressed against the wall 28 of the saddle 1 by the pressure force in the first cylinder 20 in FIG. 2 and is held there permanently.

If the pressure within the supply line 25 decreases after the braking process, the overpressure within the second cylinder 21 can pass through the connection opening 14 and the sealing lip 16 bent radially inward by the excess pressure into the interior of the supply line 25 and thus to the pressure line (pressure line 11 in Fig. 1) escape.

FIGS. 5 and 6 show a sketch of other possibilities for design of the connecting valve 13. In particular, the connection opening 14 is designed as an inclined feed line, which connects the second cylinder 21 to the inside of the feed line. The main advantage of the embodiments according to FIGS. 5 and 6 is the enlarged contact surface of the feed line 25 with respect to the wall 28 of the housing 1 . The connection seal 13 is also of a simpler design than according to FIGS. 3 and 4, since an inner lip has been dispensed with. The difference between Fig. 5 and 6 is that in Fig. 5, the seal with its end facing away from the lip 16 sits on an annular projection 29 which extends radially inward from the feed line 25 and rests against the saddle wall 28 and for an enlarged contact surface ensures.

In Fig. 6 has been omitted on the protrusion 29, so that the connecting valve 13 directly rests on the seat wall 28, which leads to a simplified embodiment of the valve. The mode of operation of the connection valve corresponds to the mode of operation described in connection with the figures already explained.

A vacuum should preferably prevail in the space 30 (see FIG. 2) between the two cylinders 20 and 21 . The following applies to correct functioning:
The piston motion force must be greater than the counterforce of the space 30 (due to vacuum), in other words, the piston motion pressure must be greater than 1 bar.

Claims (13)

1. With a pressure medium cylinder ( 7 ) provided caliper ( 1 ) for a disc brake, characterized in that the cylinder is a step cylinder ( 7 , 10 ), with a piston ( 6 or 12 ) in each cylinder step ( 7 or 10 ) is led. 2. Saddle according to claim 1, characterized characterized in that the pressure medium Fluid, especially brake fluid. 3. Saddle according to claim 1 or 2, characterized in that the cylinder ( 7 , 6 ) is two-stage, wherein when the pressure in the first cylinder ( 10 ) increases due to the brake actuation via a connecting valve ( 13 ) the way ( 14 ) in the second cylinder ( 7 ) is released and that the pressure acting on the two pistons ( 6 , 12 ) of the two cylinders ( 7 , 10 ) by the pressure medium is effective in the same direction. 4. Saddle according to claim 3, characterized in that the first piston ( 12 ) in the first cylinder ( 10 ) and the second piston ( 12 ) in the second cylinder are designed as a one-piece stepped piston ( 6 , 12 ). 5. Saddle according to one of claims 3 to 5, characterized in that the connecting valve is formed by a pressure-dependent valve ( 13 ), preferably an elastic lip seal. 6. Saddle according to one of claims 3 to 5, characterized in that the effective against the pressure medium second surface of the second piston ( 6 ) is a multiple of the effective first surface of the first piston ( 6 ). 7. Saddle according to one of claims 3 to 6, characterized in that the second cylinder chamber ( 7 ) via a compensating valve ( 15 ) is connected to the brake fluid container, which opens at negative pressure in the second cylinder ( 7 ). 8. Saddle according to one of claims 3 to 7, characterized in that the connecting valve ( 13 ) is designed such that it is at an excess pressure in the second cylinder ( 7 ) compared to the first cylinder ( 10 ) a pressure reduction in the second cylinder ( 7 ) enables. 9. A saddle according to any one of claims 3 to 8, characterized in that the stepped piston (6, 12) united by two with their bottoms cylinder pots (6, 12) is formed. 10. Saddle according to claim 9, characterized in that the bottom surface of the second piston ( 6 ) is larger than that of the first piston ( 12 ) and that the lip seal ( 13 ) with an opening near the bottom of the first piston ( 12 ) ( 14 ) cooperates, which opens into the second cylinder ( 7 ). 11. Saddle according to one of claims 1 to 10, characterized in that the pistons effective in the cylinder are double-acting stepped pistons ( 27 ). 12. Saddle according to claim 11, characterized in that the two pistons ( 23 , 24 ) are formed by a hollow cylinder body ( 27 ) which is closed on both sides and which is sealingly guided on the outside in a second cylinder ( 21 ) and on the inside on a saddle-fixed guide disk ( 26 ) is that the inner space in the stepped piston ( 27 ) adjacent to the guide disk ( 26 ) and the brake block-side base ( 23 ) forms the first cylinder ( 20 ), into which the brake pressure is fed via a supply line ( 25 ) and the brake block-side first base of the first cylinder forms the first piston ( 23 ) and the opposite bottom of the stepped piston ( 27 ) forms the second piston ( 24 ). 13. Saddle according to one of claims 1 to 12, characterized characterized in that the disc brake a Floating caliper brake is.