Pneumatic wheel brake for a vehicle

A pneumatic wheel brake for a vehicle includes a brake lever operable by a compressed air cylinder, and a brake application device operable by the lever. Employing the brake application device, a first brake element can be pressed against a second when the lever is operated. The wheel brake also includes an actuating device, which can be motor driven, which force can be applied to parts of the brake application device, at least when the lever is not operated, to press the first brake element against the second. The wheel brake also has a spring accumulator element arranged outside the compressed air cylinder. Force can be applied to the spring accumulator element by the actuating device; and force can be applied to parts of the brake application device by the spring accumulator element, at least when the lever is not operated. Thereby, the first brake element can be pressed against the second.

FIELD OF THE INVENTION

The present invention generally relates to a pneumatic wheel brake for a vehicle.

BACKGROUND OF THE INVENTION

A generic pneumatic wheel brake is disclosed in EP 1 384 913 B1, which proposes a second expansion device in addition to a first expansion device. The second expansion device is part of an electrically actuated brake application device. Thus, a parking brake function may be implemented with a reduced space requirement, in particular because a long combination cylinder does not have to be used as a pneumatic actuating cylinder, but a simple, short brake cylinder may be used.

In the electrically actuatable parking brake function described in EP 1 384 913 B1, after engaging the parking brake, i.e., after parking the vehicle, in particular when the brakes are heated, it is necessary to compensate for a reduction in the braking force of the parking brake function, as a result of the brakes being cooled, by a resetting procedure by means of the electrical brake application device, in order to ensure secure braking of the vehicle. Such resetting by means of the electrical brake application device, however, may be undesirable, for example when electrical energy is to be saved.

SUMMARY OF THE INVENTION

Generally speaking, it is an object of the present invention to provide a pneumatic wheel brake with an electrically actuatable parking brake function that, after parking the vehicle, ensures secure braking of the vehicle without further consumption of electrical energy.

It will be appreciated that an advantage of the invention is that, by providing a spring accumulator element, resetting and/or retensioning via the actuating device, which may be driven by electric motor, is not required when the vehicle is parked. Thus, the consumption of electrical energy when the vehicle is parked, within the context of the parking brake function, may be entirely avoided. By means of the spring accumulator element, contraction in the braking mechanism as a result of cooling is automatically compensated for.

A further advantage is that service brake cylinders of simple construction without a spring accumulator element may be used as compressed air cylinders, i.e., a long, combination cylinder is not necessary.

An electrically actuatable parking brake function may be implemented via the actuating device. Advantageously, the spring accumulator element is subjected to force by the actuating device. As a result, the spring accumulator element is located in the power flow with the actuating device, such that the spring accumulator element itself is able to exert a brake application force onto a first braking element, and additionally the spring accumulator element may be pretensioned by the actuating device to a specific pretensioning force. This permits a cost-effective and compact implementation of a parking brake function, which may be actuated electrically for a pneumatic wheel brake, for example in the form an electromechanical hand brake (EMH).

Thus, the first braking element may be subjected to a brake application force both from the actuating device and from the spring accumulator element.

According to an embodiment of the invention, the actuating device is used for compensating air play.

According to another embodiment, the actuating device, which may be driven by electric motor when actuating the brake lever, i.e., when the compressed air cylinder is subjected to pressure, is not, or not fully, subjected to the forces thus produced. The actuating device is arranged outside the main power flow produced when the wheel brake is applied via the compressed air cylinder, and thus not subjected to the load of the relatively high brake application forces that occur during the braking process. As the actuating device serves for the parking brake function and optionally serves for the compensation of air play, the actuating device may be constructed to have a reduced load-bearing capacity than if it were located in the main power flow, as proposed in EP 1 384 913 B1. Thus, depending on the design of the brake system for the parking brake function, in a heavy utility vehicle of conventional design, a brake application force of 120 kN may be required, for example, while the maximum braking force present during actuation of the service brake may be approximately 230 kN. According to the reduced load bearing capacity, the actuating device may thus be constructed using more simple components that do not have a high load-bearing capacity, and, as a result, it can be configured to be more compact and more lightweight overall.

According to a further embodiment of the invention, the spring accumulator element, as set forth above for the actuating device, is not located in the main power flow of the service brake function of the wheel brake. So, when the brake lever is actuated, the spring accumulator element is not, or not fully, subjected to the forces produced thereby. Accordingly, the spring accumulator element may also be designed for the lower loads that are present for the parking brake function, i.e., configured to be correspondingly smaller and more lightweight than if it were arranged in the main power flow.

According to another embodiment, the spring accumulator element may be pretensioned to a pretensioning force by the actuating device. This has the advantage that the actuating device, which may be driven by electric motor when receiving a parking brake actuating signal, is accordingly able to subject the spring accumulator element to a pretensioning force, “in reserve” so to speak, so that after parking the vehicle as a result of sufficient pretensioning force, the spring accumulator element automatically effects secure braking of the vehicle in the context of the parking brake function.

According to yet another embodiment of the invention, the spring accumulator element is configured as a disk spring. This has the advantage that a small component of compact construction may be used as a spring accumulator element, so that the components required for implementing the parking brake function may be integrated in a very compact manner overall in the wheel brake. Additionally, by the use of a disk spring, a favorable path/force characteristic curve of the spring is produced for resetting the parking brake function when the vehicle is parked. In particular, when setting a corresponding pretensioning force, the substantially horizontally extending part of the characteristic curve of a disk spring may be utilized, in which the force output by the spring does not change or changes only insignificantly over the path.

According to a further embodiment, the actuating device is coupled via a variable gear mechanism to the brake application device. The variable gear mechanism may comprise, in particular, a ball-ramp arrangement. The use of a variable gear mechanism has the advantage that a variable gear ratio of the gear mechanism may be implemented over the actuating path of the actuating device. Thus, in particular at the start of the actuating movement of the actuating device, a higher gear ratio may be provided and subsequently a reducing gear ratio. As a result, the available actuating force of the actuating device may be used particularly expediently and efficiently to apply the brake in the context of the parking brake function by the gear ratio being reduced, in particular with increased brake application force via the variable gear mechanism, so that even with an actuating device provided with a relatively low-powered electric motor, a high brake application force of the parking brake function may be implemented.

According to another embodiment, when the brake lever is actuated, the variable gear mechanism is not, or not fully, subjected to forces produced thereby. As a result, the variable gear mechanism is not arranged in the main power flow of the service brake function and not subjected, or only slightly subjected, to this power flow. Accordingly, the variable gear mechanism may also be produced with components that have a reduced load-bearing capacity and that are configured to be more simple, more cost-effective and more lightweight. In particular, in the case of a ball-ramp arrangement, use is made of smaller balls, so that the constructional space required for the variable gear mechanism may be minimized further.

According to a still further embodiment, the variable gear mechanism has a degressive path characteristic curve in the direction of the brake application. This has the advantage that, in the direction of the brake application, the actuating device may initially deliver an actuating path with a higher gear ratio, and in the course of the actuating movement may deliver an actuating path with a diminishing gear ratio. As a result, overall, greater maximum brake application forces of the parking brake function may be implemented than with a linear or progressive path characteristic curve.

According to another embodiment, the actuating device may be connected to a switchable coupling device, via which the actuating device may be selectively coupled to the brake application device or disconnected therefrom. The switchable coupling device has the advantage that the actuating device may be optionally used for various functions, in particular for a direct application of the wheel brake in the context of the parking brake function, for compensating for air play and specific pretensioning of the spring accumulator element to a desired pretensioning force. In an advantageous embodiment, the switchable coupling device is arranged between the actuating device and the parts of the brake application device used for the parking brake function, i.e., the actuating device is permanently connected to the spring accumulator element.

According to a further embodiment, the variable gear mechanism may be locked by the switchable coupling device. This makes it possible to lock the variable gear mechanism by means of the coupling device and thus neutralize the variable gear mechanism relative to its transmission function. In this state, the actuating movement provided by the actuating device may be transmitted directly and without gearing to the parts of the brake application device that may be actuated by the actuating device. By unlocking the variable gear mechanism by means of the switchable coupling device, however, the actuating device is decoupled from the parts of the brake application device. In this state, the variable gear mechanism becomes effective, i.e., via the variable gear mechanism a variable transmission of the actuating path provided by the actuating device takes place, depending on the actuating position.

According to yet another embodiment of the invention, the wheel brake additionally comprises the compressed air cylinder.

According to an embodiment of a method for securing a vehicle comprising a pneumatic wheel brake of the type described above:

a) when receiving a parking brake actuating signal, the actuating device is actuated in the direction of the application of the wheel brake, whereby the actuating device is coupled by the coupling device to the brake application device,

b) when reaching a first predetermined actuating position and/or brake application force, the actuating device is disconnected from the brake application device by the coupling device, whereby the actuating device is actuated further in the direction of the application of the wheel brake, and

c) when reaching a second predetermined actuating position and/or brake application force, the actuating device is switched off.

For activating the parking brake function, the previously described sequence is carried out in reverse. Initially, the actuating device is actuated by the open coupling device counter to the direction of the brake application. When reaching a predetermined actuating position and/or brake application force, the coupling device is closed and the actuating device is actuated counter to the direction of the brake application until the parking brake function is lifted.

The present invention accordingly comprises the features of construction, combination of elements, arrangement of parts, and the various steps and the relation of one or more of such steps with respect to each of the others, all as exemplified in the constructions herein set forth, and the scope of the invention will be indicated in the claims.

The same reference numerals are used for corresponding elements in the figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a pneumatic wheel brake for a vehicle including a compressed air cylinder10and a brake application device20connected to the compressed air cylinder10and able to be actuated by the compressed air cylinder10. The brake application device20comprises a brake lever11, which comprises at its end remote from the point of application of the compressed air cylinder10an actuating element12provided with an actuating contour, which may be configured, for example, in the form of an eccentric or a camshaft. The actuating element12acts on a first pressure part13configured with a correspondingly opposing contour, which ultimately acts on a first braking element in the form of a brake lining1. The actuating element12is supported to the rear via a bearing element14on a component of the wheel brake fixed to the housing, for example a brake cover15.

By actuating the compressed air cylinder10, which is effected by filling a compressed air chamber with compressed air via a compressed air line17, the compressed air cylinder10exerts via a piston rod an actuating force on the brake lever11. As a result, the brake lever11is actuated in the direction of the brake application. Via the actuating element12and the pressure part13, a brake application force is exerted on the brake lining1. As a result, the brake lining1is pressed against a second brake element in the form of a brake disk2. Alternatively, the wheel brake may also be configured as a drum brake. In this case, the second brake element is configured as a brake drum.

The brake application device further comprises a spindle nut7, a threaded spindle8, which may be rotated in the spindle nut, and a second pressure part9connected to the threaded spindle8. The second pressure part9, as in the case of the first pressure part13, is in contact with the brake lining1and may, with appropriate rotation of the spindle nut7, exert relative to the threaded spindle8a brake application force on the brake lining1.

The parts7,8,9of the brake application device20are conventionally configured to be integrated in modern wheel brakes with the first pressure part13. In this case, the spindle nut7and the threaded spindle8serve to compensate for the length as a result of wear of the brake lining, via an integrated mechanical resetting device. In this case, the first pressure part13is advantageously configured to be integrated as a single component with the second pressure part9. Additionally, the threaded spindle8and/or the spindle nut7are passed through an opening of the actuating element12. For a clearer view, the elements of this arrangement inFIG. 1, however, are shown adjacent to one another.

The spindle nut7is coupled fixedly in terms of rotation to an output element50of a variable gear mechanism5configured in the form of a ball-ramp arrangement. The variable gear mechanism5comprises, in addition to the output element50, a drive element52as well as balls51arranged between the drive element and the output element. Advantageously, three balls51are provided, arranged uniformly over the periphery of the drive element and/or output element50,52. As a result, in a simple manner, a statically determined transmission of force may be carried out from the drive element52to the output element50.

A switchable coupling device6is fastened to the variable gear mechanism5. The switchable coupling device6comprises an output coupling part63connected to the output element50and a drive coupling part62connected to the drive element52. For producing an electrically actuatable switching function, the coupling device6comprises an electromagnet60fastened, for example, to the drive coupling part62, via which a coupling pin64may be retracted and extended. When the coupling pin64is extended, the drive coupling part62is connected fixedly in terms of rotation to the output coupling part63. As a result, the variable gear mechanism5is locked, i.e., the drive element52is connected fixedly in terms of rotation to the output element50. The electromagnet60is able to be actuated via an electrical cable61.

A transmission shaft34of an actuating device3, which may be driven by electric motor, is connected fixedly in terms of rotation to the drive element52of the variable gear mechanism5. The transmission shaft34is connected fixedly in terms of rotation at its end remote from the drive element52to a gearwheel33. The gearwheel33is in contact with a pinion32. The pinion32is connected to an electric motor30. The electric motor30is able to be actuated via an electric cable31. The pinion32and the gearwheel33form a gear mechanism. In this case, the pinion32is of relatively long configuration, in order to be able to accommodate positional alterations of the gearwheel33in the longitudinal direction of the transmission shaft34during operation of the actuating device3.

On the side of the gearwheel33remote from the transmission shaft34, a spring accumulator element4is arranged which, optionally decoupled via a bearing, is clamped between the gearwheel33and a stop16of the wheel brake fixed to the housing.

As shown inFIG. 1, the coupling device6, the variable gear mechanism5, the actuating device3, as well as the spring accumulator element4are arranged outside the power flow of the parts of the brake application device, which may be acted upon by the compressed air cylinder10, so that the forces produced thereby do not act on the coupling device6, the variable gear mechanism5, the actuating device3and the spring accumulator element4.

For activating the parking brake function, the wheel brake is actuated as follows according toFIG. 1.

Initially, when the coupling device6is closed, i.e., when the coupling pin64is extended, the electric motor30is actuated in the direction of the brake application. The rotational movement transmitted via the transmission shaft34is transmitted directly to the spindle nut7by the locked variable gear mechanism5. As a result, the threaded spindle8and, thus, the second pressure part9move against the brake lining1. The electric motor30in this operating state is operated for a sufficient length of time until the brake application force able to be produced thereby is at least approximately reached. Then, the coupling device6is opened, i.e., the coupling pin64is retracted. To this end, optionally the electric motor30is briefly stopped or actuated slightly counter to the direction of the brake application in order to relieve the load from the coupling device6. As a result, the drive element52is decoupled from the output element50, so that both parts are able to move toward one another. Then, the electric motor30is again actuated in the direction of the brake application. As a result, the transmission shaft34and the gearwheel33are moved to the right, due to an alteration in the length of the ball-ramp arrangement5. As a result, the spring accumulator element4is tensioned further. At the same time, the brake application force exerted on the brake lining1is increased further via the further pressure part9. When a sufficient pretensioning of the spring accumulator element4and/or a sufficient brake application force is reached, the electric motor30is switched off.

FIG. 2shows a further embodiment of a pneumatic wheel brake for a vehicle, in which the elements described with reference toFIG. 1, in particular the brake application device, are designed to be structurally integrated with one another. The brake lever11, the first pressure part13, the spindle nut7and the threaded nut8are shown. The spindle nut7and the threaded spindle8are arranged in a through-opening of the first pressure part13. The first pressure part13is mounted via a bearing131opposite the spindle nut7.

The threaded spindle8is coupled to a pressure plate91, via which the brake application force is ultimately transmitted via a backplate101of the brake lining1to the brake disk2. For absorbing the reaction force, a further brake lining100with a backplate102is arranged on the opposing side of the brake disk2.

The threaded spindle8is connected fixedly in terms of rotation via a connecting element90to the pressure plate91. Via the connecting element90undesired rotation of the threaded spindle8relative to the pressure plate91is prevented to ensure the desired relative rotation between the threaded spindle8and the spindle nut7.

Also shown are the output element50of the variable gear mechanism5designed as a component comprising the output coupling part63, a ball51of the ball-ramp arrangement of the variable gear mechanism5, the extendable pin64and the drive element52of the variable gear mechanism5designed as a component comprising the drive coupling part62. Additionally, the gearwheel33is also configured to be integrated with the drive element52, namely, in the form of an external toothing provided on the outside of the drive element52. As a result of the integration of the gearwheel33with the drive element52, the transmission shaft34as a separate component is dispensed with. The drive element52is mounted via a bearing cover49with a bearing40relative to the spring accumulator element4in the axial direction. Additionally, the drive element52is mounted via the bearing cover49with a bearing41relative to the housing of the electromagnet60in the radial direction. Relative to the electromagnet60, an armature65is shown, which, when actuating the electromagnet, penetrates therein and drives the pin64. The electric motor30is also shown.

FIG. 3shows, in an enlarged view, the right-hand part of the wheel brake shown inFIG. 2with the elements previously described.

FIG. 4shows the wheel brake according toFIGS. 2 and 3from above. Also shown are the elements described with reference toFIGS. 2 and 3, which are provided with the same reference numerals inFIG. 4. Additionally inFIG. 4, a gear arrangement35is shown, which is connected to the electric motor30and the gearwheel33. The gear arrangement35may be configured as a multi-stage gear mechanism and, in particular, may comprise the pinion32. Also shown inFIG. 4is the actuating element12, the bearing element14as well as a bearing120arranged for minimizing friction between the actuating element12and the first pressure part13.

FIG. 6shows an advantageous path of the path characteristic curve of the variable gear mechanism5. The path x produced by the gear mechanism5in the longitudinal direction of the transmission shaft34is shown over the rotational angle φ of the transmission shaft34. As is shown, the characteristic curve has a degressive characteristic, i.e., it drops away in the direction of greater values of φ. The characteristic curve shown inFIG. 6at the same time corresponds to a profiled contour600of the ball-ramp arrangement, for example a degressive contour provided on the drive element52instead of the linear contour shown inFIG. 1. In this case, at the start and at the end of the contour600, latching recesses601,602are provided, in which the balls51may be engaged. As a result, the actuating device, which may be driven by electric motor3, is relieved of load in the end positions of the contour600.

FIG. 7ashows a path of the brake application force F over the rotational angle φ of the transmission shaft34. InFIG. 7b, the path of the actuating path x provided is shown in the direction of the brake application. The diagram, in principle, has the same characteristic for the actuating period t of the electric motor. Thus, the variables are indicated as alternatives inFIG. 7.

Based on an initial value 0, the electric motor30is actuated. In a first angular portion or time period700, initially no brake application force is produced but possible air play is overcome. After overcoming the air play, in a time period701, a rising linear brake application force, for example, is produced. At a time t1and/or at an actuating angle φ1, the coupling device6is opened. As a result, the transmission function of the variable gear mechanism5is activated. A rotation of the threaded spindle8relative to the spindle nut7substantially no longer takes place. The opening of the coupling device6takes place at a time before the maximum actuating force Fmaxthat is able to be delivered by the electric motor30is reached, i.e., before the electric motor30locks. The electric motor30is actuated further after opening the coupling device6. As a result of the transmission of the variable gear mechanism5, the force rises in a time period702with a reduced gradient, so that a further increase in the brake application force F is possible. The value Fmaxindicates up to which value of the brake application force the electric motor could apply the brake when the coupling device6is closed. The line703indicates the theoretical further path of the line701when the coupling device6remains closed.