Abstract:
A brake system for a vehicle includes a parking brake with an air-quantity-boosting-valve device for aerating and deaerating at least one spring brake cylinder of the parking brake, at least one electrically actuatable control valve for controlling the air-quantity-boosting-valve device, an electrical control device electrically coupled to the electrically actuatable control valve for controlling the electrically actuatable control valve, and an electrical actuating device coupled to the control device for actuating the parking brake. In order to be able to resort to available series-produced components, the air-quantity-boosting-valve device, the control valve, the electrical control device and the actuating device are, in each case, embodied as autonomous components arranged spatially separate from one another.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to a brake system for a vehicle having a parking brake. 
     BACKGROUND OF THE INVENTION 
     A brake system of the general type under consideration is described in DE 10336611 A1. This known brake system is equipped not only with a service brake but also with a parking brake, in order that the vehicle can be parked with the brake engaged. Such a parking brake is also known as a handbrake. 
     Parking brakes are usually provided with spring-actuated brake cylinders, in which an actuator spring engages the brake, so that the vehicle is braked or held immobile. This parking brake is released by pressurizing the spring-actuated brake cylinders with compressed air, so that the actuator spring is compressed and, thus, the parking brake is released. 
     Such spring-actuated brake cylinders are usually designed as combination service-brake and spring-actuated brake cylinders. They therefore have a spring-actuator part and a service-brake part. Service braking is conventionally actuated via a brake pedal. 
     The compressed-air supply of the spring-actuator part for releasing the parking brake is achieved by means of an air-flow-boosting valve device, especially a relay valve. At its output the air-flow-boosting valve device delivers the same pressure that is present at its control input, but with a boosted air flow, which is drawn from a compressed-air reservoir tank. 
     The control input of the air-flow-boosting valve device is supplied with the control pressure via at least one control valve. This control valve is designed as an electrically actuatable control valve, wherein the switched condition of this valve is determined by an electrical control device. The control device, in turn, is electrically connected to an actuating device for actuation of the parking brake. This actuating device may be actuated by the driver of the vehicle. The driver is able to release or engage the parking brake by means of this actuating device. 
     In the brake system described in DE 10336611 A1, the control device is integrated in a parking-brake module, as is a valve module, in which the valves of the parking brake are structurally integrated. As a result, a compact parking-brake module is realized that can be integrated easily into existing air-brake systems. However, this integration requires special housing parts and modules that have to be specially developed. 
     SUMMARY OF THE INVENTION 
     Generally speaking, it is an object of the present invention to provide an improved brake system with reduced development time and effort. 
     In accordance with embodiments of the present invention, the air-flow-boosting-valve device, the control valve or valves, the electrical control device and the actuating device of the brake system are, in each case, embodied as autonomous, separate components arranged spatially separate from one another. Because of the stand-alone, separate design of the components, and because of the spatially separated arrangement of these components, it is possible to use conventional series parts without the need for special additional modules or components. By eliminating integration of the components in a module, an inexpensive, dispersed structure of the parking-brake device is achieved. Not only are the manufacturing costs reduced by the use of already available components, but the approval process for new brake systems is shortened. 
     Advantageously, a pressure sensor is additionally provided that is also designed as a stand-alone separate component and that is electrically connected to the electrical control device and disposed in a manner spatially separated from the other components. Preferably, the pressure sensor measures the pressure in a compressed-air reservoir tank for supplying the spring-actuated brake cylinder with compressed air, and, for this purpose, the control device is designed such that it compares the measured pressure value with an upper and/or lower pressure limit value. If the measured pressure is below the lower pressure limit value, the control valve is activated to control the air-flow-boosting valve device, such that the spring-actuated brake cylinder can be vented by the air-flow-boosting valve device. However, when the measured pressure does not exceed an upper pressure limit value, the control valve cannot be activated, and air cannot be admitted to the spring-actuated brake cylinder by means of the air-flow-boosting valve device. 
     If the pressure in the compressed-air reservoir tank (or tanks) falls below a minimum value, automatic venting of the spring-actuated brake cylinder is advantageously effected, and the parking brake is applied. In contrast, when the upper limit value of the pressure is not yet reached in the compressed-air reservoir tank, it is possible to prevent the spring actuators from being released. In this way, it is ensured that a minimum pressure is always provided in the compressed-air reservoir tank before the parking brake can be released. 
     In another embodiment of the present invention, the electrical actuating device is provided with one or two electrical switches for selective setting of a released condition or engaged condition, respectively, of the parking brake. One switch is sufficient in vehicles operated without a trailer. In such cases, the parking brake can be engaged or released by means of the one switch. If the vehicle is a tractor of a vehicle train containing one or more trailers, however, it is advantageous to provide a second switch, by means of which the parking brake(s) of the trailer(s) can be controlled. 
     In a further embodiment, the electrical actuating device is also provided with a further operator-control element for activating an anti jackknifing brake function. When the anti jackknifing brake is activated, it brakes the rear wheels—that is, for example, the wheels of a trailer, especially a semi-trailer. This is advantageous when the vehicle or the vehicle train is traveling on a smooth roadway, since the anti-jackknifing brake keeps the vehicle train stretched out. By means of this additional operator-control element, the driver of the vehicle is also able to test whether a stationary trailer is actually being braked, by actuating this operator-control element and exerting a tractive force on the trailer by means of the tractor vehicle. Furthermore, by means of the anti jackknifing brake, the driver is able to check secure closing of the connection between tractor and trailer, especially semitrailer, or, in other words, the articulated coupling. 
     In a still further embodiment of the present invention, the control device is connected to one or more sensors for detecting operating conditions of vehicle components. For this purpose, the control device is designed such that it can engage or release the parking brake depending on the detected operating conditions. In this way, the spring-actuated brake cylinders can be selectively engaged or released by means of the electrical actuating device and, therefore, manually, or by means of an automatic external controller. Advantageously, at least one sensor for detection of the condition of the service brake is provided and connected to the control device. The control device prevents release of the parking brake if the service brake is not actuated. This makes it compulsory for the service brake to be actuated before the parking brake can be released. This is advantageous in preventing the vehicle from rolling away due to release of the parking brake. 
     Furthermore, a sensor for detecting the position of a vehicle door can be provided and connected to the electrical control device. The control device engages the parking brake or prevents release of the parking brake when the vehicle door is open. Such a function is particularly advantageous in a bus, for example. This function ensures that the bus cannot be moved if one of the doors is open. 
     In another embodiment of the present invention, the control device is integrated into the control device of an anti-lock braking system. In this way an additional control device can be dispensed with, leading to savings and to simplified assembly of the components of the parking brake. Alternatively, the control device can also be designed as a separate control device for the parking brake. 
     In yet another embodiment, an overload-protection valve is connected upstream from the control input of the air-flow-boosting valve device. The overload-protection valve has a first input in communication with the control valve for control of the air-flow-boosting valve device. Also, the overload-protection valve has a second input in communication with the brake pedal of the service brake, and an output in communication with the control input of the air-flow-boosting valve device. By this overload-protection valve, it is possible to prevent mechanical overloading due to addition of the brake forces of the service brake and parking brake, since, if the service brake and the parking brake are actuated simultaneously, the pressure of the service brake raises the pressure of the parking brake and, in this way, also reduces the braking effect. Advantageously, the overload-protection valve is integrated together with the air-flow-boosting valve device in a common unit. 
     Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification. 
     The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings in which: 
         FIG. 1  is a simplified schematic view of an air-brake system having a parking brake and a service brake together with some essential components in accordance with an embodiment of the present invention, and 
         FIG. 2  shows an air-brake system in accordance with an embodiment of the present invention having the components shown in  FIG. 1  as well as further brake system components. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawing figures,  FIG. 1  schematically depicts a part of an air-brake system  10  for a vehicle and, in particular, an electropneumatic brake-control device for control of a parking brake of the vehicle. Such air-brake systems are used, for example, in commercial vehicles, heavy motor trucks or buses, and, in particular, in vehicle trains comprising a tractor and a trailer. 
       FIG. 1  shows selected components of brake system  10 . Brake system  10  is provided with an electrical control device  12  for control of certain of the components, especially of the parking brake. The brake cylinders are designed partly or completely as combination service and spring-actuated brake cylinders  14 , although, for clarity, only one such brake cylinder is illustrated in  FIG. 1 . The term “spring-actuated brake cylinders” used herein in connection with the present invention should be understood to also encompass such combination service and spring-actuated brake cylinders. 
     Brake system  10  is provided with a brake-actuating device  16 , which senses braking intent of the driver. Brake-actuating device  16  includes a pneumatic part and, possibly, an electrical part, only the pneumatic part being illustrated in  FIG. 1 . Via compressed-air lines (not illustrated), the pneumatic part is supplied with compressed air from a compressed-air reservoir tank  18  (circuit I) and another compressed-air reservoir tank  20  (circuit II). The compressed-air reservoir tanks  18 ,  20  are used to supply compressed air to the brake cylinders of the service brake, as will be described in greater detail hereinafter with reference to  FIG. 2 . As illustrated in  FIG. 1 , however, they may also be used to supply compressed air to the parking brake. Alternatively, the compressed air for the parking brake is supplied by a separate compressed-air reservoir tank, although this is not illustrated in the drawing figures. 
     By actuation of a brake pedal  22 , brake-actuating device  16  generates—e.g., by electrical activation of electropneumatic devices or directly—a pneumatic manipulated variable that is relayed via a compressed-air line  24 ,  26  to combination service and spring-actuated brake cylinder  14 . 
     Combination service and spring-actuated brake cylinder  14  is designed as a combination spring-actuator/diaphragm cylinder. Apart from the function of a diaphragm cylinder, it additionally has a spring-actuator function. Brake cylinder  14  therefore comprises a diaphragm part  28 , which is in communication pneumatically with the service-brake system and can be pressurized with the actual brake pressure, and a spring-actuator part  30 , which is pneumatically separated from diaphragm part  28  and can be pressurized with compressed air via a separate compressed-air line  32 . Spring-actuator part  30  forms part of the parking brake. It includes the spring-actuator function, which preloads an actuator spring upon pressurization of spring-actuator part  30  and, thus, prevents or diminishes braking action of the spring-actuator function, whereas the actuator spring relaxes upon venting of spring-actuator part  30  and, thus, in connection with the spring-actuator function, exerts a braking action on the brake in communication with the respective brake cylinder. In the present context, brake cylinders of this type will be referred to as “spring-actuated brake cylinders”. 
     By means of spring-actuated brake cylinder  14 , a parking-brake function that also permits the vehicle to be braked or immobilized even in the absence of compressed air is achieved. The parking-brake function is active when the respective spring-actuator part  30  of spring-actuated brake cylinder  14  is vented below a minimum pressure value or is vented completely. Via compressed-air line  32 , spring-actuator part  30  of brake cylinder  14  is pneumatically in communication with an air-flow-boosting valve device  34 , which permits pressure control by way of electrical control means, especially, electrical control device  12 . 
     A manually actuatable parking-brake signal transducer (not illustrated in  FIG. 1 ) is electrically connected via electrical lines (not illustrated) to electrical control device  12 . By means of this parking-brake signal transducer, the driver is able to activate the parking brake by admitting air to or venting spring-actuator part  30  by means of air-flow-boosting valve device  34 . For venting, air-flow-boosting valve device  34  is provided with a vent output  35 . The parking brake is released by admission of air to spring-actuator part  30 . In contrast, the parking brake is engaged by venting of spring-actuator part  30 . 
     Air-flow-boosting valve device  34  is preferably designed as a relay valve, and includes an inlet  42 , which, via compressed-air lines  36 ,  38 ,  40 , is in direct or indirect communication with compressed-air reservoir tanks  18 ,  20 . Furthermore, air-flow-boosting valve device  34  has an outlet  44 , which, via compressed-air line  32 , is in communication with spring-actuator part  30  of brake cylinder  14 . Air-flow-boosting valve device  34  also has a control input  46 , which, via compressed-air lines  48 ,  50 , is in communication with a control valve  52  for control of the parking brake of the tractor. 
     Control valve  52  is designed as a 3/2-way solenoid valve. This means that it has three ports and can assume two conditions. In the de-energized condition illustrated in  FIG. 1 , an outlet  54  of control valve  52  is in communication with compressed-air line  50 , which, via an overload-protection valve  56  described in greater detail hereinafter and compressed-air line  48 , is in communication with control input  46  of air-flow-boosting valve device  34 . In the de-energized condition of control valve  52 , outlet  54  is in communication with a vent  58 . In the de-energized condition, therefore, control valve  52  ensures venting of control input  46  of air-flow-boosting valve device  34  and, thus, also venting of spring-actuator part  30  of brake cylinder  14 . The parking brake is engaged as a result of this venting. 
     Control valve  52  further has an inlet  60 , which, via compressed-air lines  62 ,  64  as well as compressed-air lines  36 ,  38  and  40 , is in communication with compressed-air reservoir tanks  18  and  20 . In the energized condition of control valve  52 , inlet  60  is in communication with outlet  54 , whereby the reservoir pressure, and, by virtue of a double check valve or what is known as a select-high valve  66  between compressed-air reservoir tanks  18 ,  20  and inlet  60  of control valve  52 , the higher of the two reservoir pressures of compressed-air reservoir tanks  18 ,  20  is transmitted via compressed-air lines  50 ,  48  to control input  46  of air-flow-boosting valve device  34 . Thereupon, air-flow-boosting valve device  34  modulates, at its output  44 , the same pressure as is present at its control input  46 , such that air-flow-boosting valve device  34  delivers, at its outlet  44 , an air flow boosted by a multiple compared with that needed at control input  46 . For this purpose, inlet  42  of air-flow-boosting valve device  34  is placed in communication with compressed-air reservoir tanks  18 ,  20 . This modulated pressure at outlet  44  of air-flow-boosting valve device  34  is supplied via compressed-air line  32  to spring-actuator part  30  of brake cylinder  14 , causing air to be admitted to spring-actuator part  30  and the parking brake to be released. 
     A pressure sensor  68  is connected between double check valve  66  and inlet  42  of air-flow-boosting valve device  34  or inlet  60  of control valve  52  to ensure that the order of magnitude of the reservoir pressure momentarily available can be sensed. This pressure sensor transmits a correspondingly measured pressure value via an electrical line (not illustrated) to electrical control device  12 . 
     Via further electrical lines (not illustrated), electrical control device  12  is further connected to control valve  52 , so that control valve  52  can change its condition depending on corresponding electrical signals of electrical control device  12 . 
     Overload-protection valve  56  has two inputs  70 ,  72  and one output  74 . A first input  70  is in communication with outlet  54  of control valve  52 . A second input  72  is in communication via compressed-air line  24  with brake pedal  22  or the pneumatic part thereof. Output  74  of overload-protection valve  56  is in communication via compressed-air line  48  with control input  46  of air-flow-boosting valve device  34 . 
     Overload-protection valve  56  selects the higher of the two pressures present at its inputs  70 ,  72  and supplies this to control input  46  of air-flow-boosting valve device  34 . It is therefore also referred to as a “select-high valve”. 
     Overload-protection valve  56  prevents addition of the brake force supplied to brake cylinder  14  by the service brake, or, in other words, via the pneumatic part of brake pedal  16 , and the brake force supplied to spring-actuator part  30  by the parking brake via compressed-air lines  32 ,  36 ,  38 ,  40 , thus, preventing mechanical overloading of the brake mechanism in the wheel brake associated with brake cylinder  14 . By virtue of the illustrated structure, the brake force supplied via compressed-air lines  24 ,  26  to diaphragm part  28  of brake cylinder  34  is not increased by the brake force exerted by the actuator spring, since, in the case of actuation of the service brake, the brake force exerted by the actuator spring is reduced by a force corresponding to actuation of the service brake. In this way, critical overloading of the wheel brakes can be avoided. 
     The components discussed above relate to the brake device of the tractor. If a trailer can be coupled to the tractor, compressed-air brake system  10  is additionally provided with a second control valve  76 , which, via a compressed air line  78 , is also in communication with compressed-air reservoir tanks  18 ,  20 . Control valve  76  is disposed in parallel with control valve  52 . Otherwise, it is designed to be functionally identical to control valve  52 , and, so, in this regard, the foregoing discussion of control valve  52  and of its ports and switched conditions can be consulted. Only the output of control valve  76  is in communication with one other component, namely a tractor-truck protection valve  80 . 
     In the exemplary embodiment depicted in  FIG. 1 , overload-protection valve  56  is integrated in a common valve unit  82  together with air-flow-boosting valve device  34 . 
     By means of pressure sensor  68 , the controller provided in the electrical control device senses the higher of the two reservoir pressures of compressed-air reservoir tanks  18 ,  20 . The pressure sensed in this way as well as the switch condition or conditions of the actuating device (not illustrated) for the parking brake of the tractor and, possibly, of the trailer, are read in and evaluated by electrical control device  12 . Depending on the result of the logical combinations or of the programmed control, control valves  52 ,  76  for the parking brake of the tractor or of the trailer are then switched. If the control valves are switched, or, in other words, are energized, air can be admitted to air-flow-boosting valve device  34  or a corresponding valve device  34  in the trailer and, thus, to spring-actuator part  30  or a corresponding spring-actuator part of a spring-actuated brake cylinder of the trailer, with the result that the parking brake of the tractor or of the trailer is released. In contrast, if control valves  52 ,  76  are switched to de-energized condition, air-flow-boosting valve device  34  or the corresponding valve device of the trailer switches to venting. The spring-actuator parts of the spring-actuated brake cylinders are then vented and, thus, the parking brake is engaged. 
       FIG. 2  depicts the subsystem of brake system  10  illustrated in  FIG. 1  in a broader context, specifically, for vehicles having four wheels that can be individually braked by means of compressed-air brake cylinders  14 ,  84 . Brake cylinders  14  are provided for the rear axle and brake cylinders  84  for the front axle. As discussed in connection with  FIG. 1 , brake cylinders  14  are designed as combination service brake/spring-actuated brake cylinders, in order to permit braking by means of the service brake and also braking by means of the parking brake. Electrically actuatable valves  86  are connected upstream from brake cylinders  14 ,  84 , respectively. Valves  86  are connected via electrical lines  88  to electrical control device  12 . Furthermore, valves  86  of the rear axle are in communication via compressed-air lines  90 ,  92 ,  94 ,  96 ,  98  with compressed-air reservoir tank  20 , and they form circuit II. Analogously, valves  86  of the front axle are in communication via compressed-air lines  100 ,  102 ,  104 ,  106 ,  108  with compressed-air reservoir tank  18 , and, in this way, they form circuit I. The two compressed-air reservoir tanks  18 ,  20  are supplied with compressed air via a compressed-air supply  110  and especially via a compressor. 
     In the illustrated exemplary embodiment, brake-actuating device  16  is in communication by means of pneumatic lines, namely, compressed-air lines  112 ,  114 , and then further via compressed-air lines  100 ,  102 , with valves  86  for compressed-air brake cylinders  84  of the front axle, in order to provide a pneumatically operated service brake. Analogously, brake-actuating device  16  is in communication, via compressed-air lines  116 ,  118 ,  120 , and as compressed-air lines  90 ,  92 , with valves  86  of combination service and spring-actuated brake cylinders  14 , in order that the rear axle can also be braked pneumatically. 
     The further components shown in  FIG. 1 , especially, valve unit  82  comprising air-flow-boosting valve device  34  as well as overload-protection valve  56 , and control valves  52 ,  76  as well as pressure sensor  68 , are also illustrated in  FIG. 2 . Regarding these components, the discussion above in connection with  FIG. 1  can be consulted. 
       FIG. 2  further shows electrical actuating device  122  for actuating the parking brake. Actuating device  122  is provided with a first switch  124  for actuation of the parking brake of the tractor as well as with a second switch  126  for actuating the parking brake of the trailer. Each of the two switches has a released position and an engaged position and, possibly, a neutral position, for releasing or engaging the parking brake. Furthermore, in a special embodiment for vehicles with trailers, an additional electrical operator-control element  128  is provided, so that the anti jackknifing function discussed above can be effected. 
     Electrical actuating device  122  is disposed in the driver&#39;s cab of the vehicle. Thus, there is no need to provide pneumatic switches for actuating the parking brake in the driver&#39;s cab, and tubing comprising compressed-air lines for the parking brake can be avoided in the driver&#39;s cab, but the parking brake can nonetheless be actuated. 
     The essential components of the parking brake, especially, air-flow-boosting valve device  34 , control valves  52 ,  76 , pressure sensor  68 , electrical control device  12  and actuating device  122 , are each designed as stand-alone, separate components that can be disposed in a manner spatially separated from one another. By virtue of this dispersed structure without integration of these components in one module, it is possible, according to the present invention, to use already available series parts. This simplifies not only the engineering design but also the approval procedures for such brake systems. 
     It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween. 
     LIST OF REFERENCE NUMERALS 
     
         
           10  Air-brake system 
           12  Electrical control device 
           14  Brake cylinder 
           16  Brake-actuating device 
           18  Compressed-air reservoir tank 
           20  Compressed-air reservoir tank 
           22  Brake pedal 
           24  Compressed-air line 
           26  Compressed-air line 
           28  Diaphragm part 
           30  Spring-actuator part 
           32  Compressed-air line 
           34  Air-flow-boosting valve device 
           35  Vent output 
           36  Compressed-air line 
           38  Compressed-air line 
           40  Compressed-air line 
           42  Inlet 
           44  Outlet 
           46  Control input 
           48  Compressed-air line 
           50  Compressed-air line 
           52  Control valve 
           54  Outlet 
           56  Overload-protection valve 
           58  Vent 
           60  Inlet 
           62  Compressed-air line 
           64  Compressed-air line 
           66  Double check valve 
           68  Pressure sensor 
           70  Input 
           72  Input 
           74  Output 
           76  Control valve 
           78  Compressed-air line 
           80  Tractor-truck protection valve 
           82  Valve unit 
           84  Brake cylinder 
           86  Valves 
           88  Electrical line 
           90  Compressed-air line 
           92  Compressed-air line 
           94  Compressed-air line 
           96  Compressed-air line 
           98  Compressed-air line 
           100  Compressed-air line 
           102  Compressed-air line 
           104  Compressed-air line 
           106  Compressed-air line 
           108  Compressed-air line 
           110  Compressed-air supply 
           112  Compressed-air line 
           114  Compressed-air line 
           116  Compressed-air line 
           118  Compressed-air line 
           120  Compressed-air line 
           122  Electrical actuating device 
           124  Switch 
           126  Switch 
           128  Operator-control element