COMPRESSED-AIR BRAKING SYSTEM FOR A MOTOR VEHICLE

Abstract

A compressed-air braking system (DBA*) for a motor vehicle, includes a compressed-air supply device (1) with a compressor (2) and several brake circuits which are connected to the compressed-air supply device (1) via a multi-circuit protection valve (7) and include at least one parking brake circuit with parking brake cylinders (25.1, 25.2). In order to reduce the operating noise of the compressed-air braking system (DBA*) occurring in particular on venting of the parking brake cylinders (25.1, 25.2), it is provided that the parking brake cylinders (25.1, 25.2) can be vented, per wheel or per vehicle axle, alternately either to the surrounding atmosphere or into an additional reservoir (31) via a respective quick-venting valve (29) connected to a connecting line (28) and a changeover valve (30) arranged downstream thereof.

Claims

1. A compressed-air braking system (DBA*) for a motor vehicle, the compressed-air braking system comprising: a compressed-air supply device (1) with a compressor (2) and several brake circuits which are connected to the compressed-air supply device (1) via a multi-circuit protection valve (7), and include at least one parking brake circuit with parking brake cylinders (25.1, 25.2), wherein the parking brake cylinders (25.1, 25.2) are configured to be vented, per wheel or per vehicle axle, alternately either to the surrounding atmosphere or into a reservoir (31) via a respective quick-venting valve (29) connected to a connecting line (28) and a changeover valve (30) arranged downstream thereof in the at least one parking brake circuit.

2. The compressed-air braking system as claimed in claim 1, wherein the quick-venting valve (29) comprises an input port (35), a working port (36) and an output port (37), wherein the input port (35) is connected via a pressure line (27) to the output port of a relay valve (24) controlled by a handbrake valve (23), wherein the working port (36) is connected via the connecting line (28) to the parking brake cylinders (25.1, 25.2), and wherein the output port (37) is connected via an output line (38) to an input port (40) of the changeover valve (30).

3. The compressed-air braking system as claimed in claim 1, wherein the changeover valve (30) is configured as a pressure-controlled 3/2-way directional valve with a control pressure input (39), an input port (40) and two output ports (41, 42), the 3/2-way directional valve having an unactuated rest state, in which the input port (40) is connected to the first output port (41), and a switched state, in which the input port (40) is connected to the second output port (42), wherein the control pressure input (39) is connected to the input port (40), the first output port (41) leads to the surrounding atmosphere, and the second output port (42) is connected to the reservoir (31).

4. The compressed-air braking system as claimed in claim 3, wherein the changeover valve (30) has a valve spring (44) with at least a spring stiffness or a set preload, dimensioned such that the input port (40) is connected to the first output port (41) below a predefined changeover pressure (p.sub.S) present at the control pressure input (39), and to the second output port (42) on reaching or exceeding of the changeover pressure (p.sub.S).

5. The compressed-air braking system as claimed in claim 4, wherein the changeover pressure (p.sub.S) of the changeover valve (30) is set to a value above which outflowing compressed air in the narrowest cross-section of an air outlet of the parking brake cylinders (25.1, 25.2) reaches the speed of sound.

6. The compressed-air braking system as claimed in claim 5, wherein the changeover pressure (p.sub.S) of the changeover valve (30) is set to a value in the range of 1.9×10.sup.5 Pa through 2.5×10.sup.5 Pa.

7. The compressed-air braking system as claimed in claim 4, wherein the narrowest cross-section of the air outlet at the first output port (41) of the changeover valve (30) is larger by a factor of 1.1 to 2.5 than the narrowest cross-section of an air outlet of an associated parking brake cylinder (25.1, 25.2).

8. The compressed-air braking system as claimed in claim 1, wherein the reservoir (31) is connected via a connecting line (32) to an intake tank (33) of the compressor (2), and wherein a check valve (34), which blocks an air flow into the surrounding atmosphere, is arranged in a suction line (43) connecting the intake tank (33) to the environment.

9. The compressed-air braking system as claimed in claim 1, wherein the parking brake cylinders (25.1, 25.2) connected to the quick-venting valve (29) and the changeover valve (30) are configured to be arranged on a trailerless motor vehicle, or on a trailer vehicle, or on a rear part of an articulated bus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the drawings,

[0022] FIG. 1 shows a compressed-air braking system according to the invention in a schematic general depiction;

[0023] FIG. 1a shows a first enlarged extract A from FIG. 1 in a schematic depiction;

[0024] FIG. 1b shows a second enlarged extract B from FIG. 1 in a schematic depiction;

[0025] FIG. 2 shows a time diagram of pressure curves of parking brake cylinders and pressure vessels of the compressed-air braking system from FIG. 1, and the operating state of a compressor;

[0026] FIG. 3 shows a time diagram of a pressure curve of parking brake cylinders and a flow speed curve at the air outlet of the parking brake cylinders of the compressed-air braking system from FIG. 1;

[0027] FIG. 4 shows a time diagram of pressure curves of parking brake cylinders and a pressure vessel, and flow speed curves at the air outlet of the parking brake cylinders and a changeover valve of the compressed-air braking system from FIG. 1; and

[0028] FIG. 5 shows a known compressed-air braking system in a schematic general depiction, with reference to which the invention is explained as an example.

DETAILED DESCRIPTION OF THE DRAWINGS

[0029] The invention is described as an example below with reference to a compressed-air braking system DBA of a tractor vehicle, known from DE 10 2013 000 275 A1, which is illustrated in FIG. 5 in a schematic general depiction.

[0030] The compressed-air braking system DBA has a compressed-air supply device 1 and several brake circuits connected to the compressed-air supply device 1 via a multi-circuit protection valve 7. The compressed-air supply device 1 comprises a compressor 2, a pressure regulator 3, a dryer 4 and a storage tank 5. The compressor 2 can be driven by a drive motor (not shown) of the tractor vehicle, and in the engaged or coupled state conveys compressed air from the environment via the pressure regulator 3 and the dryer 4 to a pressure line 6. The storage tank 5 is also connected to the dryer 4 and may store compressed air for any required regeneration of the dryer 4. Four brake circuits are each connected by a respective storage line 8.1, 8.2, 8.3, 8.4 to the pressure line 6 of the compressed-air supply device 1 via a multi-circuit protection valve 7, which in this case is configured as a four-circuit protection valve. These circuits are two non-pressure-limited service brake circuits, a pressure-limited trailer control and parking brake circuit, and a pressure-limited service brake and auxiliary consumer circuit.

[0031] The storage line 8.1 of the first service brake circuit leads via a storage tank 9.1 to an ALB regulator 10 (ALB—automatic load-dependent brake) and to a tractor vehicle brake valve 11, from which a control pressure is conducted to the ALB regulator 10 and to a trailer control valve 12. From the ALB regulator 10, the compressed air is conducted via two 2-way valves 13.1, 13.2, and via two ABS solenoid valves 14.1, 14.2 (ABS=anti-lock braking system) to the service brake cylinders 15.1, 15.2 of the wheel brakes on the rear axle of the tractor vehicle. A control pressure picked up between the ALB regulator 10 and the two 2-way valves 13.1, 13.2 is conducted via a control line to a control pressure input of the tractor vehicle brake valve 11.

[0032] The storage line 8.2 of the second service brake circuit leads via a storage tank 9.2 to the tractor vehicle brake valve 11 and from there, via a quick-venting valve 16 and two ABS solenoid valves 17.1, 17.2, to the service brake cylinders 18.1, 18.2 of the wheel brakes on the front axle of the tractor vehicle. A control pressure picked up between the quick-venting valve 16 and the two ABS solenoid valves 17.1, 17.2 is conducted via a control line to a control pressure input of the trailer control valve 12.

[0033] The storage line 8.3 of the trailer control and parking brake circuit leads, via a storage tank 9.3 and the trailer control valve 12, to a “storage” coupling head 19, which serves to connect the storage line of the compressed-air braking system of a trailer. From the trailer control valve 12, a control line also leads to a “braking” coupling head 20 which serves to connect the brake control line of the trailer's compressed-air braking system. The storage line 8.3 has a branch 21 between the storage tank 9.3 and the trailer control valve 12, which branch leads via a check valve 22 to a handbrake valve 23 and a relay valve 24. From the handbrake valve 23, which serves for manual actuation of the parking brake, one control line leads to the trailer control valve 12 and one control line leads to the relay valve 24. When the handbrake valve 23 is actuated, compressed air is conducted from the storage line 8.3 through the relay valve 24, via a pressure line 27 and a connecting line 28, to the parking brake cylinders 25.1, 25.2 of the wheel brakes on the rear axle of the tractor vehicle, whereby the parking brake engaged by spring accumulators is released.

[0034] The storage line 8.4 of the service brake and auxiliary consumer circuit leads firstly via a storage tank 9.4 and two ASR brake valves 26.1, 26.2 (ASR=traction control), the two 2-way valves 13.1, 13.2 and the two ABS solenoid valves 14.1, 14.2, to the service brake cylinders 15.1, 15.2 of the wheel brakes on the rear axle of the tractor vehicle. Secondly, the storage line 8.4 of the service brake and auxiliary consumer circuit leads to auxiliary consumers which are not shown in detail.

[0035] The schematic general depiction of FIG. 1 shows a compressed-air braking system DBA* according to the invention, which is formed by an extension of the known compressed-air braking system DBA from FIG. 5 with some components. As shown in FIG. 1 in the region of the rear axle, and in the extract A from FIG. 1 shown enlarged in FIG. 1a, now additionally a quick-venting valve 29, a changeover valve 30 and an additional reservoir 31 are assigned to the parking brake circuit.

[0036] As FIG. 1a illustrates, the quick-venting valve 29 has an input port 35, a working port 36 and an output port 37. The input port 35 is connected via the pressure line 27 to the output port of the relay valve 24 which can be actuated by the handbrake valve 23. The working port 36 is connected to the parking brake cylinders 25.1, 25.2 via said connecting line 28. The output port 37 is connected to an input port 40 of the changeover valve 30 via an output line 38. In the quick-venting valve 29, in the case of high pressure in the input-side pressure line 27, the working port 36 is connected to the input port 36, and in the case of low pressure in the input-side pressure line 27 or a pressureless pressure line 27, it is connected to the output port 37.

[0037] The changeover valve 30 is a pressure-controlled 3/2-way directional switching valve with a control pressure input 39, an input port 40 and two output ports 41, 42. In its unactuated rest state shown, the input port 40 of the changeover valve 30 is connected to the first output port 41; in the switched state, it is connected to the second output port 42. The control pressure input 39 is connected to the input port 40. The first output port 41 leads to the surrounding atmosphere, and the second output port 42 is connected to the reservoir 31. A spring stiffness and/or a set preload of a valve spring 44 of the changeover valve 30 is such that the input port 40 is connected to the first output port 41 below a predefined changeover pressure p.sub.S present at the control pressure input 39, and to the second output port 42 on reaching or exceeding of the changeover pressure p.sub.S. The changeover pressure p.sub.S of the changeover valve 30 is set to a value in the range between 1.9×10.sup.5 Pa and 2.5×10.sup.5 Pa inclusive of range limits, above which the outflowing compressed air in the narrowest cross-section of the air outlet of the parking brake cylinders 25.1, 25.2 reaches the speed of sound.

[0038] The described arrangement of the quick-venting valve 29, changeover valve 30 and reservoir 31 ensures that, in the case of a reduced pressure or pressureless pressure line 27, the parking brake cylinders 25.1, 25.2 of the parking brake on the rear axle of the tractor vehicle are vented via the quick-venting valve 29 and changeover valve 30 to the surrounding atmosphere below the changeover pressure p.sub.S in the parking brake cylinders 25.1, 25.2, and internally into the reservoir 31 on reaching or exceeding of the changeover pressure p.sub.S in the parking brake cylinders 25.1, 25.2. In this way, the noise level on discharge of compressed air from the parking brake cylinders 25.1, 25.2 is significantly reduced, so that the whooshing noise concerned is lost in the ambient noise and is no longer perceived as disruptive.

[0039] As can be seen in FIG. 1 in the region of the compressed-air supply device 1 and in the enlarged extract B from FIG. 1 shown in FIG. 1b, an intake tank 33 is assigned to the compressor 2 via a connecting line, and is connected on one side via a connecting line 32 to the rear axle reservoir 31 and on the other side via a suction line 43 to environment. For security against outflow of compressed air to the environment, a check valve 34 which blocks in the direction of the surrounding atmosphere is arranged in the suction line 43. This arrangement ensures that when the rear axle reservoir 31 is empty, the compressor 2 draws in air from the environment via the suction line 43, and when the rear axle reservoir 31 is filled, it draws in compressed air under residual pressure from this reservoir 31 via the connecting line 32. The intake of compressed air from the rear axle reservoir 31 allows a reduction of up to 13% in the energy consumption of the compressor 2.

[0040] A compressed-air braking system DBA* having the features of the invention would have a slightly more complex structure if, in contrast to FIG. 1, it had a quick-venting valve 29 and a changeover valve 30 for each parking brake cylinder 25.1, 25.2. It would however function similarly.

[0041] The function method of the compressed-air braking system DBA* from FIG. 1 on discharge of compressed air from the parking brake cylinders 25.1, 25.2 is now explained below with reference to three time diagrams shown in FIGS. 2 to 4, the curves of which were determined by a numerical simulation.

[0042] The diagram in FIG. 2 shows the time curves of the pressure p.sub.FBZ in the parking brake cylinders 25.1, 25.2, the pressure p.sub.VB in the assigned storage tank 9.3, the pressure p.sub.SB in the additional rear axle reservoir 31, and the switching state K of the compressor 2 (0=compressor switched off, 1=compressor switched on) over a time period from t=0 s to t=8 s.

[0043] In a first sequence in time portion t=0 s to around t=2 s, the rear axle reservoir 31 is empty, i.e. the pressure p.sub.SB in the rear axle reservoir 31 is 0 Pa. Actuation of the handbrake valve 23 to release the parking brake at time t=0 fills the parking brake cylinders 25.1, 25.2, so that the pressure p.sub.FBZ rises to around 8.5×10.sup.5 Pa. At the same time, the pressure p.sub.VB in the storage tank 9.3 falls below a switch-on pressure, so that the compressor 2 is switched on and draws in air from the environment via the suction line 43 (switching state of compressor=1). As a result, the pressure p.sub.VB in the storage tank 9.3 rises as the time goes on.

[0044] At a time of around t=1.6 s, the handbrake valve 23 is again actuated to engage the parking brake, whereby compressed air is discharged from the parking brake cylinders 25.1, 25.2. Since the pressure p.sub.FBZ in the parking brake cylinders 25.1, 25.2 at 8.5×10.sup.5 Pa lies significantly above the changeover pressure p.sub.S of the changeover valve 30, the changeover valve 30 is switched and compressed air flows from the parking brake cylinders 25.1, 25.2 via the quick-venting valve 29 and changeover valve 30 into the rear axle reservoir 31, whereby the pressure p.sub.SB in the reservoir 31 rises to around 0.45×10.sup.5 Pa. On reaching the switch-off pressure, because of the pressure p.sub.VB in the storage tank 9.3 at the time around t=1.85 s, the compressor 2 is switched off again (compressor switching state=0).

[0045] In a second sequence in time portion t=5 s to t=7 s, firstly at time t=5 s the handbrake valve 23 is actuated to release the parking brake, whereby the parking brake cylinders 25.1, 25.2 are filled and the pressure p.sub.FBZ rises to around 8.5×10.sup.5 Pa. This reduces the pressure p.sub.VB in the storage tank 9.3 below the switch-on pressure, so that the compressor 2 is switched on at the time around t=5.2 s (compressor switching state=1). The compressor 2 initially draws in air under a residual pressure of 0.45×10.sup.5 Pa from the rear axle reservoir 31 until this is empty at the time around t=6.5 s. From this time, the compressor 2 draws in air from the environment via the suction line 43. Because of operation of the compressor 2, the pressure p.sub.VB in the storage container 9.3 rises further.

[0046] At the time around t=6.7 s, the handbrake valve 23 is again actuated to engage the parking brake, whereby the compressed air is discharged from the parking brake cylinders 25.1, 25.2. Since the pressure p.sub.FBZ in the parking brake cylinders 25.1, 25.2 at 8.5×10.sup.5 Pa lies significantly above the changeover pressure p.sub.S of the changeover valve 30, the changeover valve 30 is switched and compressed air flows from the parking brake cylinders 25.1, 25.2 via the quick-venting valve 29 and changeover valve 30 into the rear axle reservoir 31, whereby the pressure p.sub.SB in the reservoir 31 rises to around 0.45×10.sup.5 Pa. When the pressure p.sub.VB in the storage tank 9.3 reaches the switch-off pressure at the time around t=6.95 s, the compressor 2 is switched off again (compressor switching state=1).

[0047] The diagram in FIG. 3 shows the time curves of the pressure p.sub.FBZ in the parking brake cylinders 25.1, 25.2 and the flow speed v.sub.FBZ at the air outlet of the parking brake cylinders 25.1, 25.2 over a time period from t=1.4 s to t=2.0 s.

[0048] Initially, the parking brake is released by activation of the spring accumulator brake cylinders 25.1, 25.2, and the spring accumulator brake cylinders 25.1, 25.2 are under a pressure of p.sub.FBZ=8.5×10.sup.5 Pa. At time t=1.5 s, the handbrake valve 23 is actuated to engage the parking brake, whereby the spring accumulator brake cylinders 25.1, 25.2 are vented and the pressure p.sub.FBZ in the spring accumulator brake cylinders 25.1, 25.2 falls. Because of the initially high pressure p.sub.FBZ, in the narrowest cross-section at the air outlet of the parking brake cylinders 25.1, 25.2, the outflowing compressed air initially reaches the speed of sound at approximately v.sub.FBZ=300 m/s, which leads to loud and unpleasant noises on a direct discharge of air to the environment. Only when the pressure p.sub.FBZ in the spring accumulator brake cylinders 25.1, 25.2 falls from the time around t=1.86 s, does the flow speed v.sub.FBZ of the outflowing compressed air also fall.

[0049] In addition to the time curves of the pressure p.sub.FBZ in the parking brake cylinders 25.1, 25.2 and the flow speed v.sub.FBZ at the air outlet of the parking brake cylinders 25.1, 25.2, the diagram of FIG. 4, in contrast to the diagram of FIG. 3, also shows the time curves of the pressure p.sub.SB in the additional rear axle reservoir 31 and the flow speed v.sub.UV at the first output port 41 of the changeover valve 30 over a time period from t=1.5 to t=2.0 s.

[0050] As long as the pressure p.sub.FBZ in the parking brake cylinders 25.1, 25.2 lies above the changeover pressure p.sub.S of the changeover valve 30 on discharge of compressed air, the changeover valve 30 is switched and the compressed air from the parking brake cylinders 25.1, 25.2 flows via the quick-venting valve 29 and changeover valve 30 into the reservoir 31, so that the pressure p.sub.SB in the reservoir 31 rises to approximately 0.45×10.sup.5 Pa. At the time around t=1.78 s, the pressure p.sub.FBZ in the parking brake cylinders 25.1, 25.2 has fallen below the changeover pressure p.sub.S of the changeover valve 30, so that the changeover valve 30 is switched to its rest position and the compressed air then escapes from the parking brake cylinders 25.1, 25.2 directly to the environment via the quick-venting valve 29 and the changeover valve 30. As the diagram in FIG. 4 shows, during the switching process of the changeover valve 30, at the first output port 41 which is larger than the narrowest cross-section of the air outlet of the parking brake cylinders 25.1, 25.2, the flow speed v.sub.UV briefly reaches the speed of sound. Because the compressed air which is initially under a higher pressure p.sub.FBZ flows into the rear axle reservoir 31, the noise level on venting of the parking brake cylinders 25.1, 25.2 is substantially reduced.

LIST OF REFERENCE SIGNS

[0051] 1 Compressed-air supply device [0052] 2 Compressor [0053] 3 Pressure regulator [0054] 4 Dryer [0055] 5 Storage tank [0056] 6 Pressure line [0057] 7 Multi-circuit protection valve, four-circuit protection valve [0058] 8.1, 8.2 Storage line [0059] 8.3, 8.4 Storage line [0060] 9.1, 9.2 Storage container [0061] 9.3, 9.4 Storage container [0062] 10 ALB regulator (ALB=automatic load-dependent brake) [0063] 11 Tractor vehicle brake valve [0064] 12 Trailer control valve [0065] 13.1, 13.2 Two-way valve [0066] 14.1, 14.2 ABS solenoid valve [0067] 15.1, 15.2 Service brake cylinder [0068] 16 Quick-venting valve [0069] 17.1, 17.2 ABS solenoid valve [0070] 18.1, 18.2 Service brake cylinder [0071] 19 “Storage” coupling head [0072] 20 “Braking” coupling head [0073] 21 Branch [0074] 22 Check valve [0075] 23 Handbrake valve [0076] 24 Relay valve [0077] 25.1, 25.2 Parking brake cylinder [0078] 26.1, 26.2 ASR brake valve [0079] 27 Pressure line [0080] 28 Connecting line [0081] 29 Quick-venting valve [0082] 30 Changeover valve [0083] 31 Rear axle reservoir [0084] 32 Connecting line [0085] 33 Intake tank [0086] 34 Check valve [0087] 35 Input port [0088] 36 Working port [0089] 37 Output port [0090] 38 Output line [0091] 39 Control pressure input [0092] 40 Input port [0093] 41 First output port [0094] 42 Second output port [0095] 43 Suction line [0096] 44 Valve spring of changeover valve 30 [0097] A Extract from FIG. 1 [0098] B Extract from FIG. 1 [0099] p Pressure [0100] p.sub.FBZ Pressure in parking brake cylinders (25.1, 25.2) [0101] p.sub.SB Pressure in reservoir (31) [0102] p.sub.S Changeover pressure of changeover valve (30) [0103] p.sub.VB Pressure in storage tank (9.3) [0104] t Time [0105] v Flow speed [0106] v.sub.FBZ Flow speed at air outlet of parking brake cylinder [0107] v.sub.UV Flow speed at first output port of changeover valve