Disc brake of hydraulic self-energizing design with force transmission unit

A self-energizing disc brake includes a brake-internal hydraulic arrangement with a supply circuit and an expansion vessel; a brake application device having a cylinder for applying a brake pad toward a brake disc; a force transmission unit supporting the brake pad at a wedge angle on the brake application device; a tangential-force absorbing cylinder for switching over the wedge angle, which is operatively connected to the force transmission unit; an electric-motor actuator for acting on the brake application device via the hydraulic arrangement; and a control unit. The force transmission unit has a deflection lever and a shoulder element attached thereto. Rolling surfaces thereof are in contact with respective corresponding rolling surfaces of a brake application element of the cylinder and a brake pad support device. The deflection lever has a pressure section with a rolling surface in operative connection with the tangential-force absorbing cylinder.

This application contains subject matter related to U.S. application Ser. No. 13/713,273, entitled “Disc Brake of Hydraulic Self-Energizing Design With Parking Brake Device,” and U.S. application Ser. No. 13/713,791, entitled “Disc Brake of Hydraulic Self-Energizing Design With Adjusting Device,” both filed on even date herewith.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a disc brake of hydraulic self-energizing design with a force transmission unit.

A disc brake with an electromotive actuator of self-energizing design and with a brake-internal hydraulic arrangement is described in the Applicant's application WO 2007/045430 A1.

Such a disc brake consists of a considerable number of parts and is associated with corresponding costs.

It is the object of the present invention to improve a generic disc brake.

It is thereby possible to realize a disc brake which permits the construction of a compact disc brake with a smaller number of parts than in the prior art.

According to the invention, the disc brake is equipped with at least one force transmission unit which has a diverting lever and a shoulder element attached thereto. The diverting lever and the shoulder element have rolling surfaces which are in contact with respective corresponding rolling surfaces of a brake-application element of the at least one brake-application cylinder and of a support device of the brake pad. The diverting lever has a thrust portion with a rolling surface which is operatively connected to the at least one tangential force absorption cylinder.

Therefore, in a simple manner, a disc brake having a force transmission unit is provided which has an element for transmitting brake-application forces and an element for transmitting tangential forces, wherein as a result of the design of rolling surfaces which are in contact, friction losses are reduced and robustness is increased.

A self-energizing disc brake includes the following: a brake-internal hydraulic arrangement with a reservoir circuit and an expansion vessel; a brake-application device having at least one brake-application cylinder for the brake-application movement of at least one brake pad in the direction of a brake disc; at least one force transmission unit which supports the at least one brake pad on the brake-application device at a wedge angle; at least one tangential force absorption cylinder for wedge angle switching, which tangential force absorption cylinder is operatively connected to the at least one force transmission unit; an electromotive actuator which acts on the brake-application device via the hydraulic arrangement; and a control unit which is provided for controlling the wedge angle switching between the tangential force absorption cylinder and the electromotive actuator. At least one force transmission unit has a diverting lever and a shoulder element attached thereto, wherein the diverting lever and the shoulder element have rolling surfaces which are in contact with respective corresponding rolling surfaces of a brake-application element of the at least one brake-application cylinder and of a support device of the brake pad, and further wherein the diverting lever has a pressure portion with a rolling surface which is operatively connected to the at least one tangential force absorption cylinder.

In the case of two or more brake-application cylinders, a distributor cylinder for pressure boosting may be arranged in series between the electromotive actuator and the brake-application device. This also offers the advantage that it compensates oblique wear of the brake pads and reduces a pressure level between the tangential absorption cylinder and the distributor cylinder.

A particularly large reduction of friction in the interacting functional units is attained in that the diverting lever has a tooth portion which is provided for interacting with a tooth counterpart of the brake-application element. The tooth contour is selected such that the toothing behaves, on both sides, in the manner of two gearwheels running into one another. This means that the same low-friction processes as those encountered during the rolling of tooth flanks on one another arise.

The tooth counterpart may be a separate component for attaching to the at least one brake-application element. In this way, a machining process for creating the toothing can be performed separately on a corresponding machine.

The support device may also be formed with a portion produced for example as a tooth. Between the support device and a force transfer portion of the lever and a shoulder connected thereto there may be arranged a roller element which rolls on the surface.

It is preferable for the shoulder of the diverting lever to have a planar surface and for the support portion of the support device, in particular in the form of a tooth, to have a curved surface. Combinations are however also possible: the shoulder of the diverting lever may have a planar or curved surface, wherein the support portion of the support device likewise has a curved or planar surface.

The curvatures of the surfaces may be calculated so as to correspond exactly harmonically to rolling movements on the support device.

A pitch point, at which sliding-free rolling takes place, between the at least one force transmission unit, the at least one brake-application cylinder and the support device of the brake pad may be selected so as to be situated at one third of a maximum tangential deflection of the brake pad. There is therefore no relative displacement, for example between tooth and counterpart contour, at one third of the maximum deflection. This is advantageous because, in the frequency distribution of brake-application movements, the greatest number of brake actuations takes place with one third of the maximum deflection, that is to say with one third of a maximum brake-application force, whereas a maximum brake-application force is encountered relatively rarely.

Such a pitch point may self-evidently also be provided in the embodiment in which the diverting lever has the tooth portion which is provided for interacting with the tooth counterpart of the brake-application element.

The shoulder element may be connected to the diverting lever by way of a resilient plate-spring screw connection. It is ensured in this way that, even in the case of broadened production tolerances, no slippage with increased friction arises during a rolling process.

The shoulder element may have portions for brake-application force transmission for interacting with the at least one brake-application cylinder and the support device of the brake pad. The portions may be provided with rolling surfaces, whereby friction is reduced. Furthermore, a splitting-up of forces is made possible, wherein the shoulder element preferably transmits brake-application forces and the diverting lever transmits tangential forces.

In one embodiment, the shoulder element may have a narrowed portion for generating a small degree of elasticity. Rolling without slipping is permitted in this way.

The shoulder element has freedom of movement relative to the diverting lever, which advantageously simultaneously permits a slippage-free rolling movement of the vertical brake-application force by way of the shoulder element and of the horizontal braking force by way of the roller element.

The disc brake may furthermore include a readjustment device for readjustment of brake pad wear, wherein the readjustment device has an adjustable screw spindle, which is operatively connected to the brake-application device for the purpose of generating a follow-up movement of the at least one brake pad and can be coupled to the electromotive actuator in order to be driven, and a readjustment piston, which can be hydraulically adjusted in the tangential force absorption cylinder during a follow-up movement of the at least one brake pad.

In a further embodiment, it is provided that the control unit is connected to the reservoir circuit and to an intermediate circuit, wherein the electromotive actuator is connected to the reservoir circuit by way of a suction valve and can be connected to the intermediate circuit by way of a switching valve when the latter is in a first position.

It may be the case here that, in the first position of the switching valve, a change in a brake application movement can be performed only through adjustment of the electromotive actuator. The control unit may be designed, in interaction with a stepped absorption piston of the tangential force absorption cylinder, to select an effective wedge angle closest to a present friction coefficient of the brake pad.

It is particularly advantageous here that the brake force can be increased or reduced only through an adjustment of a control disc, which may for example be in the form of a perforated disc. Here, the control disc can selectively connect pressure chambers, which are connected to the stepped absorption piston of the tangential force absorption cylinder, to the reservoir circuit and/or to the intermediate circuit.

A particular graduation of wedge angles is made possible in that the selective connection of the pressure chambers to the reservoir circuit and/or to the intermediate circuit can be switched, based on the operating principle of binary coding, in seven stages with increasing effective piston surface area of the stepped absorption piston.

The electromotive actuator can be connected to the hydraulic control drive of the control unit, in order to switch the selective connections for the purpose of selecting a shallower or steeper wedge angle, by use of the switching valve when the latter is in a second position. Here, the electromotive actuator performs an additional function and saves space. During switching, it is, for example, possible for a pump suction line of the actuator to be blocked with a pump pressure line. A change in a brake-application position is then not possible during the short switching process.

It may advantageously also be provided that, to save power during relatively long, uniform braking operations, despite a pressure difference existing across the electromotive actuator, the electric motor thereof can be switched into a deenergized state by virtue of the switching valve being switched from the first position into the second position.

In order that a presently selected brake-application position remains unchanged, the control unit may have further switching positions, such that between each of the selective connections or each of the possible switchable wedge angles, there exists a blocking position in which the pressure chambers and connections to the reservoir circuit and/or to the intermediate circuit are shut off.

The electromotive drive is operatively connected only to the control drive of the control unit for the entire duration of a braking operation.

In a further embodiment, it may be provided that, during a period in which a brake-application position is constant, the perforated or control disc is in a blocking position situated between a wedge angle more supercritical in relation to the present wedge angle and a wedge angle more subcritical, and that in this position, the electromotive actuator is deenergized.

In the event of a demand for a slightly more intense brake application by way of the electromotive actuator and the control drive, the perforated or control disc may be adjustable such that the perforated or control disc is adjusted, in the manner of operation of a proportional valve, from the blocking position slowly in the direction of the position of a supercritical wedge angle. In the event of a contrary demand, the perforated or control disc is, in a similar manner, adjusted from the blocking position slowly in the direction of the position of a subcritical wedge angle.

Furthermore, for the purpose of a fast release of the brake, for example in the event of a fault or in the event of a failure of the supply voltage of the brake, the brake-internal hydraulic arrangement may have a release valve, which generates a through-connection in the deenergized state, for an immediate and reliable release of the brake.

DETAILED DESCRIPTION OF THE DRAWINGS

Components of identical or similar function are denoted by the same reference numerals unless stated otherwise.

Here, the expression “oil” refers to hydraulic fluid.

FIG. 1is a schematic illustration of a first exemplary embodiment of a disc brake1according to the invention.FIG. 1will be described in conjunction withFIG. 2andFIG. 3.FIG. 2is a schematic, partially sectional illustration of a second exemplary embodiment of the disc brake according to the invention in a normal position, andFIG. 3is a schematic, partially sectional illustration of the second exemplary embodiment as perFIG. 2in a position of maximum brake application.

The disc brake1has a brake caliper40which engages over a brake disc2. At both sides of the brake disc2there is arranged in each case one brake pad3,3′ with brake pad carrier4, wherein the brake pad3′ shown at the bottom inFIG. 2(and not illustrated inFIG. 1) bears against the brake caliper40, and the other brake pad3is operatively connected to a brake-application device. The axis of the brake disc2is not shown and runs, as is readily understood, vertically upward below the plane of the drawing. A forward movement of a vehicle to which the disc brake1is assigned is intended to run from right to left inFIGS. 1 to 3, wherein the brake disc2then rotates counterclockwise.

Here, the pad carrier4is formed with two wedge-shaped support devices5, wherein the support devices are supported at a wedge angle on the brake-application device, with which the support devices are operatively connected in each case by way of a force transmission unit7to, in each case, one brake-application element9. The brake-application elements9are connected at their top end in each case to a brake-application piston10of a brake-application cylinder11. The brake-application cylinders11are arranged adjacent to one another such that the brake pads3,3′ can be pressed uniformly against the brake disc2during a brake application.

A screw spindle12with a thread is screwed into the brake-application piston10in each case in the longitudinal direction. The screw spindles12are each provided, on the top ends thereof, with a screw spindle wheel13, wherein each screw spindle wheel13engages with a readjustment pinion14. The readjustment pinions14are in each case rotationally conjointly connected by way of readjustment shafts15to readjustment shaft wheels16which jointly engage with a readjustment drive wheel17. The readjustment shaft wheel16and the readjustment drive wheel17are formed, for example, as a hydraulically operated gear motor19, and in this case are equipped with an emergency release device18which can be adjusted for example by use of a tool in order to actuate the readjustment drive wheel17. The readjustment wheels13,14,16and17have toothings, for example, and are used for wear-compensating readjustment of the brake pads3,3′, as will be explained in more detail further below. The readjustment wheels13,14,16and17, the emergency release device18, the readjustment shafts15and the gear motor19form, together with the screw spindles12, a readjustment device20of the disc brake1. Alternatively, the readjustment shaft15may be identical to the respective screw spindle12, such that the gearwheel's screw spindle wheel13and readjustment pinion14are dispensed with, wherein the two readjustment shaft wheels16have a slightly larger outer diameter, while at the same time the readjustment drive wheel17has a smaller outer diameter.

Return springs12aare arranged in each case between the brake caliper40and screw spindles12in the longitudinal direction of the screw spindles12and, in the normal position shown inFIG. 2, pull the brake pad3,3′ back from the brake disc2to generate a certain so-called air play. Further springs (not illustrated) are provided for holding the brake-application piston10and brake pad3together.

The force transmission units7have, in each case, a diverting lever6, wherein the diverting levers6are situated opposite one another and thrust portions8are operatively connected to a plunger23of a tangential force absorption cylinder21. Here, the plunger23is part of a stepped absorption piston22which, together with the tangential force absorption cylinder21, defines first to third pressure chambers24,25and26. In a preferred embodiment (FIGS. 2 to 4), the force transmission units7include in each case, a shoulder element60and a roller element66. These will be described and explained in detail further below.

The pressure chambers24,25and26are connected in each case via intermediate lines55to a control unit27which is a constituent part of a hydraulic system of the disc brake1. The hydraulic system will now be explained in more detail on the basis ofFIG. 1.

An electromotive actuator30, for example an electric motor with a gearwheel pump, is connected to a reservoir circuit46via a pump suction line50with a suction valve39, for example a directional valve. The reservoir circuit46is hydraulically connected at one side to an expansion vessel36and to a first pressure sensor41. At the other side, the reservoir circuit46can be connected by way of a release valve37to a pump pressure line51of the electromotive actuator30. Furthermore, the reservoir circuit46is connected to the control unit27and to an admission pressure chamber33of a distributor cylinder31.

The reservoir circuit46is, for example, charged with a reservoir pressure of approximately 1 to 4 bar.

The electromotive actuator30is furthermore connected via the pump pressure line51to an inlet pressure chamber35of the distributor cylinder31and to a hydraulic switch44. Also connected to the pump pressure line51is a control drive pressure line49which leads to a control drive28of the control unit27. A control drive return line48is connected between the control drive28and a second position b of a switching valve38. Here, a closed, that is to say first position a of the switching valve38connects the pump suction line50to an intermediate circuit47which is connected to the control unit27via connecting lines56. Furthermore, the intermediate circuit47is connected to the gear motor19of the readjustment device20, wherein a gear motor pressure line52connects the gear motor19at the pressure side to the hydraulic switch44. The hydraulic switch44is furthermore connected via a hydraulic switch control line53to the control unit27.

The control unit27is, for example, a plate-like, rotatable control disc with control bores which perform different functions of the disc brake1in different operating states and perform control tasks. The control disc is for example coupled to a hydraulic gear motor as control drive28. The control disc is furthermore operatively connected to a control transmitter29which detects, and transmits to a control unit, the rotational angle position of the control disc. A superordinate, for example electronic brake control unit (not shown) controls and regulates the braking processes and states of the disc brake1. For this purpose, the brake control unit controls the valves37and38, which are for example electromagnetic valves, and the electromotive actuator30. The control unit also communicates with the first pressure sensor41and with further pressure sensors, of which a second pressure sensor42determines a pressure in the intermediate circuit46. A third pressure sensor43serves for determining a pressure in the pump pressure line51, wherein the pressure in the sensors42,43may be up to 130 bar.

The control disc may, in one embodiment, have eight switching positions in order to permit a selection of seven different wedge angles.

In a second embodiment, there is situated between each of the eight switching positions a position in which all of the connecting lines55of the stepped absorption piston22are shut off. An activation of the braking force is thus possible merely by use of a switch between supercritical and subcritical wedge angles. As a result of the possibility of a proportional adjustment of the switching cross sections and a blocking position between each of the eight switching positions, it is possible to increase or reduce the brake force merely by rotating the control disc.

The distributor cylinder31has a stepped piston32for pressure boosting, synchronization and uniform loading of the brake-application cylinder11with a brake-application pressure of up to approximately 350 bar. For this purpose, the stepped piston32forms, together with the brake-application cylinder11, high-pressure chambers34,34′ which are connected in each case via a high-pressure line54to the brake-application cylinders11.

In the initial position of the piston (left-hand stop), both pressure chambers34,34′ are connected to the admission pressure chamber by virtue of the stepped piston32being designed to be slightly shorter than the cylinder chamber31. In this way, the two brake-application pistons10can be hydraulically newly balanced in their rest position (pulled back against the stop). At the same time, this serves to return excess oil from the brake-application cylinders11into the expansion vessel36in the event of a pad change, when the brake-application pistons10are fully retracted again.

The expansion vessel36may be designed as a form of exchangeable cartridge, similarly to presently commercially available oil filters in motor vehicle engines. A fast exchange of the hydraulic oil is thus possible.

Since the filtering-out of dirt particles is of high importance for the durability of the oil in any hydraulic system, the cartridge-like compensation vessel may be equipped with an oil filter. It is expedient for this purpose for the connecting line to the expansion vessel to be composed of two individual lines which are each equipped with a directional throughflow valve. By arranging the two backflow preventers so as to have antiparallel flow directions, it is possible to force a situation in which, during every change in volume of the expansion vessel, any oil flowing in and/or out is conducted through the oil filter. The oil filter may also be jointly exchanged during an exchange of the cartridge-like expansion vessel.

The disc brake1is a hydraulic, self-energizing disc brake, the function of which will now be explained.

Upon the start of a braking operation, hydraulic fluid is sucked out of the reservoir circuit46and out of the expansion vessel36via the suction valve39by way of the electromotive actuator30. Here, the electromotive actuator30increases the pressure in the pump pressure line51, as a result of which the stepped piston32of the distributor cylinder31is adjusted and the brake-application cylinder11is charged with pressure. The brake pads3,3′ are thus pressed by the brake-application elements9, via the force-transmission units7, against the brake disc2until a self-energizing process is initiated.

Here, the brake pad3is displaced to the left inFIG. 3, against a stop of the brake caliper40, owing to friction. As a result of the horizontal or tangential deflection of the brake pad3, owing to a supercritical mechanical wedge angle of the support device5, one of the two diverting levers6moves upward. The left-hand force transmission unit7, as diverting lever6, is pivoted downward, and the right-hand force transmission unit7, as the other diverting lever6, is pivoted upward. The diverting levers6are pivoted by the tangential force thus generated. The right-hand diverting lever6diverts the tangential force into a vertical force which is transmitted, via the thrust portion8of the diverting lever, to the plunger23of the tangential force absorption cylinder21. Here, a thrust plate23aserves for a friction-free transmission of force by virtue of the top edge of the diverting lever6rolling, with linear contact, on the underside of the thrust plate23a. At the same time, the thrust plate23arolls, on the top side thereof and likewise with linear contact offset horizontally through approximately 90°, with respect to the plunger. The brake pad which moves spatially horizontally during a braking operation can thus transmit its vertical force without friction to the stepped absorption piston.

The braking forces are transmitted via the two force transmission units7. On the right-hand side, the braking forces are introduced into the brake caliper40by way of the brake-application cylinder11. On the left-hand side, the diverting lever6, with its portion arranged between the brake-application element9and the support device5, transmits the brake-application force of the left-hand brake-application cylinder11and also, as a result of its rolling surfaces which run parallel but obliquely, a part of the braking forces. On the right-hand side, the transmission of the brake-application force of the right-hand brake-application cylinder11is performed by a shoulder element60of the right-hand force transmission unit7. If the vehicle (not shown) travels backward, the above-described process is reversed, as is easily comprehensible, and the left-hand diverting lever6transmits the tangential force to the tangential force absorption cylinder21. A detailed description of the transmission of brake-application forces and tangential forces by the force transmission units will be given further below in conjunction withFIGS. 7 to 10.

Here, the control disc of the control unit27is set by way of the control drive28such that the pressure chambers24,25and26of the tangential force absorption cylinder21can be connected in seven different combinations either to the reservoir circuit46and/or to the intermediate circuit47, which is connected by way of the switching valve38to the pump suction line50. It is thus possible for the disc brake1to be adapted to a present friction coefficient. Different so-called wedge angles can be set by virtue of the effective surface areas of the three pressure chambers24,25,26being formed preferably in the ratio 2:1 (and thus 1/7, 2/7, 4, 7). By binary combination of the active surface areas, it is possible to produce seven different sizes of effective surface areas of the stepped piston22. Measurement values for the determination of the present friction coefficient are provided by the pressure sensors42,43taking into consideration the respectively active pressure chambers24,25,26and further parameters, for example from a vehicle controller. The tangential force absorption cylinder21thus delivers a pressure which, to boost the pressure in the pump pressure line51, acts on the brake-application cylinder11via the distributor cylinder31and thus minimizes the pumping power of the electromotive actuator30. The distributor cylinder31may, together with the two brake-application cylinders11, synchronize the brake-application movement thereof, compensate oblique wear of the brake pads3,3′, and lower a pressure level between the tangential absorption cylinder21and the distributor cylinder31in the intermediate circuit47. Here, the distributor cylinder31serves as a pressure booster for the brake-application cylinder11.

At the end of the braking process, the electromotive actuator30is deactivated, and the release valve37is activated. As a result, the pressure in the pump pressure line51is dissipated, wherein with falling brake-application pressure in the brake-application cylinders11, the return springs12areturn the brake pad3again into its normal position with air play.

The release valve37may also be used, in the event of a fault, as an emergency release valve for releasing the disc brake1. The release valve is, for example, a solenoid valve which is open in the deenergized state.

The expansion vessel36furthermore serves for receiving the volumes of the pressure chambers24,25,26, which are connected to the reservoir circuit46by way of the control unit27, of the tangential force absorption cylinder21. The expansion vessel36also has sensors for determining the respectively present oil quantity. The expansion vessel thus has sensors for detecting pad wear of the brake pads3,3′, the present horizontal displacement of the brake pad3as a result of braking, and hydraulic fluid losses.

In the event of wear being detected in this way, at a certain wear value, the switching valve38is switched by the brake control unit into position b, and the electromotive actuator30is activated. Here, the control drive return line48is connected to the pump suction line50, and the hydraulic gear motor28of the control unit27adjusts the control disc such that, via the hydraulic switch control line53, a slide45of the hydraulic switch44is displaced into an open position, for example, by the pressure acting on the hydraulic switch of the pump pressure line51connected to the hydraulic switch. The open position of the slide45then connects the pump pressure line51to the gear motor pressure line52and exerts the pressure on the gear motor19of the readjustment device20. The readjustment wheels16,17thus rotate the screw spindles12via the gearwheels16,14,13in a synchronous adjustment movement, whereby the brake-application elements9of the brake-application cylinders11are adjusted in the direction of the brake disc2and readjust the determined wear travel of the brake pad3or3′ until the air play of the normal state is re-established. Various sensors, for example angle sensors on the gear motor19, may serve for the precise measurement of the readjustment travel. The sensor may, for example, be a multi-turn potentiometer, the electrical resistance of which varies proportionally with respect to the readjustment travel over a rotational angle which is proportional to the readjustment travel, and thus provides a measure for the readjustment travel.

The electric drive30may also be used as a measurement variable of the adjustment, because the electric drive often already has a rotational angle sensor for the control thereof, wherein the rotational angle can thus be used as an adjustment measurement variable if the slippage of the two gearwheel drives19,30is negligible.

The readjustment process is ended, when the normal air play is reached, in that, by way of the switching valve38, the control drive28is actuated for the deactivation of the hydraulic switch44by way of the hydraulic switch control line53, as a result of which the gear motor19is deactivated, and then the electromotive actuator30is deactivated.

FIG. 4is a schematic, partially sectional illustration of the second exemplary embodiment as perFIG. 2in a normal position with maximum brake wear of the brake pads3,3′. It can be clearly seen that the brake-application pistons10have been adjusted in the brake-application cylinders11downward in the direction of the brake disc2by the screwed-out screw spindles12. Here, brake-application pressure chambers57of the brake-application cylinders11are subsequently filled with hydraulic fluid in order to compensate the readjustment travel. This may take place by way of the reservoir circuit46and furthermore via the admission pressure chamber33, which in turn are connected to the high-pressure chambers34,34′. The stepped piston32is for this purpose in a rest position (left-hand stop). The process also ensures a continuous, slow follow-up flow of new oil over the time period of pad wear. Here, relatively old oil may accumulate in the brake-application chambers57. Furthermore, the wear-compensating readjustment of the brake pad3has the result that the diverting levers6are likewise adjusted, with their thrust portions8, by the readjustment travel. Without compensation of the readjustment travel, a function of the tangential force absorption cylinder21would not be possible over the entire readjustment travel. For this purpose, the stepped absorption piston22of the tangential force absorption cylinder21is provided with a readjustment piston23b, which is arranged, between the plunger23and the stepped absorption piston22, in the stepped absorption piston so as to be displaceable coaxially with respect thereto. The readjustment piston23bis situated in the stepped absorption piston22and forms with the latter a readjustment chamber58which communicates via a directional valve59with the third pressure chamber26of the tangential force absorption cylinder21.

The readjustment of the readjustment piston23blikewise takes place by way of the reservoir circuit46, in that the pressure chambers24to26are filled from the reservoir circuit46by use of the control unit27. After the stepped absorption piston22has reached its outer stop, the readjustment chamber58is also filled via the directional valve59until the readjustment piston23bis stopped by the two diverting levers6via the plunger23. The pressure in the reservoir circuit46must be adequate for this purpose. The pressure may, however, also be increased by way of additional pressure-increasing measures by way of the electromotive actuator30using additional valves and regulating means, wherein the readjustment travel of the readjustment piston23bmay be detected by the measurement of the residual volume in the expansion vessel36or by other suitable sensors. If force is now introduced into the readjustment piston23bvia the plunger23during a braking process, the hydraulic fluid in the readjustment chamber58cannot escape owing to the directional valve59. In the event of a pad change and resetting of the readjustment device20, the readjustment chamber58is likewise evacuated, which may be realized, for example, by opening the directional valve59by use of a suitable tool or by way of a pin positioned centrally in the base of the pressure chamber26. This will be explained below.

A readjustment of the pad wear takes place in each case after the release of the immobilizing brake or parking brake. The working chamber of the cylinder of the stepped absorption piston22, that is to say the pressure chambers24,25and26, permits a slightly greater movement travel than the diverting levers6require at their maximum deflection. The readjustment pistons23bcan thus adjust themselves automatically. To deploy the piston23b, additional oil is admitted through the directional valve59as backflow preventer into the cylinder chamber (readjustment chamber58) above the readjustment piston23b. This occurs when, by way of spindles12, the brake-application pistons10have been adjusted further in the direction of the brake disc2(owing to pad wear) after the end of the parking brake or handbrake actuation. The stepped absorption piston22thereby abuts against its outer movement stop. The hydraulic pressure in the readjustment piston23b, that is to say in the readjustment chamber58, falls, such that the directional valve59opens and oil flows into the readjustment chamber58.

The reversed retraction of the readjustment piston23btakes place during an exchange of the brake pads3,3′ and/or of the brake disc2. For this purpose, the spindles12are hydraulically actuated by the gear motor19such that the brake-application pistons10are retracted. The stepped absorption piston22is thereby also retracted. The hydraulic oil above the brake-application pistons10and above the stepped absorption piston22is forced into the expansion vessel36. Here, the stepped absorption piston22is retracted until the piston base surface thereof makes contact with the cylinder chamber base of the third pressure chamber26. Shortly before the contact point, a pin (not illustrated but easily conceivable) which is positioned centrally in the base of the third pressure chamber26presses against the directional valve59, such that the latter opens and the oil situated in the readjustment chamber58is forced via the third pressure chamber26and onward via the high-pressure chambers34,34′ and the admission pressure chamber33into the expansion vessel36. Position regulation for the stepped absorption piston22is thus realized in a simple manner, such that the stepped absorption piston, despite occasional pad wear-compensating readjustment, can follow the movement profile of the diverting lever without being hindered by its mechanical stops.

FIG. 5shows a schematic perspective view of the second exemplary embodiment as perFIG. 2, andFIG. 6shows a schematic perspective view of a detail fromFIG. 5.

FIG. 5shows a portion of a brake caliper40in which, in this case, all of the hydraulic components are arranged. Between the brake-application cylinders11, of which in this case the upper ends of the screw spindles12with the return springs12aare visible, the tangential force absorption cylinder21and the distributor cylinder31are arranged one behind the other, wherein the cylinders11,21and13are substantially all situated parallel to one another. In the lower region, illustrated from another perspective inFIG. 6, a stop element40ais arranged, between the brake caliper40and pad carrier4, below the tangential force absorption cylinder21. Whereas the stop element40ais situated on the outer side below the stepped piston22, a spring for holding together the brake-application piston10and brake pad3may also be positioned on the inner side below the distributor cylinder31. The brake pad3is of circular-arc-shaped form corresponding to the brake disc2, wherein the diverting levers6with the shoulder elements60are arranged between piston elements9and the support device5, and the thrust portions8point radially outward and bear against the thrust plate23a.

FIG. 7shows a schematic side view of an exemplary embodiment of a diverting lever6according to the invention. The second diverting lever6situated on the right-hand side is not shown but is easily conceivable on the basis of the preceding figures.

As already described above, the force-transmission unit7has a diverting lever6and a shoulder element60. The shoulder element60is connected to the diverting lever6on that side thereof which is situated opposite the thrust portion8, in this example resiliently by way of a loosely screwed plate spring connection in the longitudinal direction of the diverting lever6, that is to say from left to right as can be seen inFIG. 8. The shoulder element60is arranged between the brake-application element9and the pad carrier4of the brake pad3(see alsoFIGS. 2 to 6). The shoulder element has, on its top side, a shoulder portion for brake-application force introduction61. The shoulder portion is provided with a rolling surface for brake-application force introduction. The curved rolling surface makes linear contact with a corresponding planar rolling surface64on the underside of the brake-application element9. The brake-application force thus introduced by the brake-application element9into the shoulder element60(in the vertical direction inFIG. 7) is transmitted by a shoulder portion for brake-application force transmission62of the shoulder element60into the lower portion of the shoulder element. On the underside of the shoulder element60, a likewise curved rolling surface is formed in a planar shoulder portion for brake-application force transfer63. The lower rolling surface of the shoulder portion for brake-application force transfer63is in contact with a first support portion5aof the support device5and transmits the brake-application force into the support device5and thus into the brake pad3. The first support portion5aforms a rolling surface which corresponds to the rolling surface of the shoulder portion for brake-application force transfer63. The shoulder portions62,63,64extend substantially perpendicular to the plane of the drawing ofFIG. 7, as can be clearly seen fromFIGS. 9 and 10. In this way, the shoulder element60serves for transmitting brake-application forces even when the brake pad3has been deflected in the tangential direction during the braking process. Here, the rolling surfaces of the shoulder portions61and63roll on the rolling surfaces64and5awhich correspond therewith in each case, in the manner of a cylindrical body between two parallel surfaces. As a result of the loosely screwed plate spring connection, it can be ensured that, even in the case of broadened production tolerances, no slippage occurs during the rolling.

The shoulder element60has freedom of movement relative to the diverting lever6. A slippage-free rolling movement of the vertical brake-application force by way of the shoulder element60and of the horizontal braking force by way of a roller element66are thus simultaneously made possible (seeFIG. 8).

The support device5has a second support portion5bwhich is in contact with a force transfer portion6aof the diverting lever6. In this regard,FIG. 8shows a schematic, longitudinal sectional view of the force transmission unit7according to the invention as perFIG. 7.

FIG. 8shows a central region of the force transmission unit7in longitudinal section. In this regard,FIG. 10with the associated description serves for further orientation.

The diverting lever6is in contact, at the underside thereof, with the second support portion5bvia the force transfer portion6a. Between the first support portion5aand the second support portion5b, the support device5is formed with a support portion for tangential force5c. The support portion for tangential force5cis of tooth-like form and, like the support portions5aand5b, extends perpendicular to the plane of the drawing. Between the tooth-like support portion for tangential force5cand a rear shoulder6bof the force transfer portion6aof the diverting lever6is arranged the roller element66, preferably a cylindrical roller, the longitudinal axis of which also extends perpendicular to the plane of the drawing. On the rear upper side thereof, the diverting lever6is formed, above a fastening portion for the shoulder element60, with a tooth portion67which is in contact with a corresponding tooth counterpart68in the brake-application element9. The shoulder element60is attached with a shoulder central portion65to the rear side of the diverting lever by way of the plate spring connection specified above.

The diverting lever6transmits tangential forces in the region of engagement with the second support portion5a, in the region of engagement with the support portion for tangential force5cvia the roller element66, and in the region of engagement with the tooth counterpart68. The tangential forces are also referred to as horizontal braking forces. The forces cause the diverting lever6, as described above, to pivot and transmit the tangential forces via its thrust portion8to the tangential force absorption cylinder21via the thrust plate23a. The roller element66transmits tangential forces from the tooth-like support portion for tangential force5cto the rear shoulder6bof the force transfer portion6aof the diverting lever6, wherein the rear shoulder6bmay have a specially curved surface for the rolling of the roller element. The curvature on the support portion for tangential force5c(and on the rear shoulder6bof the diverting lever6, if present) is calculated so as to correspond exactly harmoniously with the rolling movement on the support device5(5c,5b). In this way, a transmission of braking and brake-application forces is possible with low friction.

The braking forces are transmitted via the tooth portion67of the diverting lever6from the diverting lever6to the brake-application cylinder11, from which the braking forces are in turn dissipated into the brake caliper40. Here, only braking forces which exceed the braking forces of the mechanical basic wedge angle must be dissipated to the housing via the tooth portion67and the roller element66. The braking forces which correspond to the mechanical wedge angle are transmitted via the oblique rolling surfaces of the support device5directly from the pad carrier4into the two brake-application elements9via the force transmission unit7.

The tooth contour of the tooth portion67and of the tooth counterpart68is selected such that these roll on one another in the manner of gearwheels. Here, the pitch point at which sliding-free rolling takes place is selected so as to be situated at one third of a maximum deflection. This means that, at one third of the maximum deflection, no frictional relative displacement between the tooth portion67and the tooth counterpart68takes place. This selection is made because, in the frequency distribution of brake-application movements, the greatest number of brake actuations takes place with one third of the maximum brake-application force, whereas a maximum brake-application force is encountered relatively rarely.

The shoulder element60for transmitting the brake-application forces has an intensely narrowed portion in order thereby to generate a certain small degree of elasticity, such that the rolling process takes place without slippage.

The transmission of the braking forces from the diverting lever6via the thrust portion8into the thrust plate23aand into the plunger23of the tangential force absorption cylinder21takes place exclusively by way of rolling movements.

FIG. 9shows a schematic perspective view of a brake pad3with the force transmission unit7according to the invention, the force transmission unit being shown in this case only on the right-hand side between the brake-application element9and the support device5(that on the left-hand side is easily conceivable). The support device5of the pad carrier4is shown on the left-hand side with the portions5a,5band5c, which extend rectilinearly radially with respect to a brake disc (not shown). Extending in the same radial direction is the shoulder element60, in the central region of which is shown an opening which serves for receiving the above-mentioned plate spring connection for fastening the shoulder element60to the diverting lever6. Shown on the underside of the shoulder element60, the shoulder portion for brake-application force transfer63is in contact with the first support portion for brake-application force5a. The contact of the support portion for tangential force5cis hidden on the right-hand side by the shoulder element60.

Since the lines of contact of the two rolling planes of the support device5are arranged in each case perpendicular to the circular movement of the brake disc2, the brake pad3, during its horizontal displacement, follows approximately the circular movement of the brake disc2. As a result, the transverse forces on the two force transmission units7are minimized, while at the same time optimum utilization of the area of the brake pad3on the brake disc2is made possible.

A further advantage of the arrangement consists in that the movement profile of the brake pad3is virtually identical to the circular movement of the brake disc2.

Furthermore, it can be seen inFIG. 9that the thrust portion8of the diverting lever6is provided with a rolling surface.

Finally,FIG. 10illustrates a further perspective view of a brake pad3with brake carrier4having two force transmission units7according to the invention and having a readjustment piston23bwhich, with its underside (thrust plate23anot visible), makes contact with the thrust portions8of the diverting levers6. The diverting levers6pivot in each case about radially arranged pivot axes, wherein the radial arrangement relates to a brake disc (not shown). The diverting levers6are arranged substantially at right angles to the radial pivot axis, wherein the width and height of the diverting levers become smaller toward the thrust portion8.

The shoulder elements60have, at both sides of a central portion, in each case one of two shoulder portions for brake-application force introduction61. The tooth portion67of the respective diverting lever6is situated in each case centrally between the shoulder portions. On the left-hand side, the tooth counterpart68, in this case in the form of a cuboidal piece, is shown in contact with the left-hand tooth portion67. The tooth counterpart68may, as shown here, be produced as a separate part and subsequently inserted into the underside of the brake-application element9.

The disc brake1according to the invention thus has the following characteristics and advantages:

Low electrical actuation power (for example approximately 60 W to a maximum of 150 W);

High energy density and force density (180 kN brake-application force can be realized in the structural space);

Automatic self-energization in both directions of travel;

Simple and reliable emergency release function as a result of normally-open magnetic valve (release valve37);

Hydraulic force transmission by means of brake fluid;

Hydraulic components are a reliable and known standard technology;

Good sliding and lubricating properties of the components as a result of the use of oil;

Inexpensive gearwheel pump instead of expensive mechanical heavy-duty gearing;

Shorter braking travel as a result of improved ABS regulation (small masses to be accelerated);

Short response and adjustment time (small masses to be accelerated together with simultaneously high self-energization action);

Intelligent wear-compensating readjustment for rear-side pads without additional motor;

One electric motor drives, via the gearwheel pump, the brake application, the drive of the control unit (valve disc), the readjustment device, and the parking brake (self-energizing, purely mechanical and active in both directions of travel, reliable release of the locked brake);

Simple and precise force measurement by means of pressure sensors;

Insensitive to vibrations;

Robust regulation as a result of being free from play, no mechanical gearwheel pairings for braking force transmission;

Direct measurement of the brake-application force and of the braking force possible;

Precise measurement or detection of the contact point/biting point of the brake pads by differential pressure measurement; and

Measurement of the pad wear without additional wear travel sensors, wherein a travel sensor of a liquid level in the expansion vessel can advantageously be used for measurement of the horizontal adjustment of the brake pads, detection of hydraulic fluid losses, and determination of the brake pad wear status.

Even though the present invention has been described above on the basis of preferred exemplary embodiments, it is not restricted thereto, but rather may be modified in a variety of ways.

The design of the diverting lever6may differ from the form shown.

The control unit27may also have magnetic valves instead of or in addition to a control disc.

The readjustment device20may also be used as a parking brake by virtue of the screw spindles12being adjusted so as to clamp the brake pads3,3′ against the brake disc2by way of the readjustment device20driven by the electromotive actuator30. For this purpose, the electromotive actuator30is activated in a suitable manner by a brake control unit via the control unit27. After the clamping of the brake pads3,3′ in this way, the brake pads remain in their parking brake position by way of the wedge action of the support device5, without hydraulic action. A reliable release is again realized by the correspondingly controlled electromotive actuator30, wherein the simultaneous build-up of a hydraulic brake-application pressure in the brake-application pistons10by the pressure-boosting piston, that is to say stepped piston32, causes the screw spindles12to be mechanically relieved of load, and thus permits an easy release of the spindles12.

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