Abstract:
An electrical, decentralized braking system includes at least four sensors for sensing the actuation of a brake actuating device; one braking module for each vehicle wheel, for acquiring sensor data and for controlling braking of the wheel; at least one first communication device with which all braking modules are connected to one another for the exchange of data; an electrical connecting device by which each sensor is connected to at least one braking module; and at least one further communication device for receiving and/or exchanging data between at least two braking modules of different sides of the vehicle.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an electrical, decentralized braking system in a vehicle, and in particular to an electrical, decentralized brake-by-wire system for a four-wheeled motor vehicle. 
     BACKGROUND INFORMATION 
     In brake-by-wire braking systems, which as a rule are not provided with a mechanical, hydraulic, or pneumatic backup system, particular emphasis must be placed on availability, i.e. a braking function, even in case of error. Brake-by-wire systems having a centralized brake pedal module are described, for example, in the published German patent document DE 198 26 131 A1, the VDI report no. 1641 (2001), “Error-tolerant Components for Drive-by-wire Systems,” by R. Isermann, and the publication “Error-tolerant Pedal Unit for An Electromechanical Braking System,” by Stefan Stölzl, published in the year 2000 by VDI-Verlag, ISBN 3-18-342612-9. 
     A main priority in systems having such a central module is the reliable acquisition of the actuation of the brake pedal (the parking brake will not be considered in the present context), as well as the distribution of the information concerning the brake actuation to decentralized intelligent wheel brake modules. The reliability of such a system is ensured on the one hand by a diversified and multiply redundant sensor design (see, e.g., brake pedals S 1  to S 3  according to  FIG. 3 ) and on the other hand by a redundant processor and communication design (see first and second communication bus  14 ,  14 ′ between central brake pedal module  15  and the four brake modules  10 , each controlling a wheel  13 ), with the boundary condition of a multi-circuit on-board network. 
     In addition, the communication device or communication system is required to have a deterministic characteristic, from which the use of time-controlled communication systems, such as, for example, FlexRay, TTCAN, or TTP, results immediately. In this context, the brake pedal module and the communication system must have a fail-safe operational characteristic. In order to meet the requirement of a fail-safe operational characteristic in the case of simple errors, the brake pedal module must have at least three redundant processors as well as three redundant, diversified if necessary, sensors for the service brake. At least two redundant communication channels are required for the communication system. 
     Published German patent document DE 199 37 156 discloses an electromechanical braking system having a decentralized acquisition of the brake pedal actuation. This can be referred to as a distributed, decentralized pedal module functionality. 
     Within this electromechanical braking system design, shown with reference to  FIG. 4 , four diversified sensors S 1  to S 4  are provided for the acquisition of the actuation of a brake actuation device (not shown), respectively determining for example the pedal path and the pedal angle. Each of the sensors S 1  to S 4  is connected to exactly one wheel module  10  having a device  11  for determining a braking demand. Wheel modules communicate with one another via a system bus  14  and exchange the required sensor information or data, and, parallel thereto, calculate functional algorithms, agreeing on a protocol in such a way that in each wheel module  10  the same data, i.e. sensor actual values and sensor/function status, are present, and identical decisions can be made. 
     Consequently, in this way a symmetrical, decentralized system architecture is provided in which the required fail-safe operational approach of the central pedal module according to  FIG. 3  is here (i.e. according to  FIG. 4 ) reproduced via the redundancy of intelligent wheel modules  10 ,  11 . However, if a common mode error now occurs in communication system  14 , for example due to a mechanical wiring harness breakage in the area of the wheel housing caused by a foreign influence, e.g. during off-road operation, this will lead unavoidably to a total loss of communication, in particular given a bus topology of communication system  14 . In such a case, each wheel module  10  will then have access only to one sensor value, which however will no longer be able to be sufficiently tested for plausibility. This can result in differing braking forces being applied to the different wheels  13  of the vehicle, resulting in a yawing moment, and thus in pulling to one side of the vehicle. Already in the case of a single error, this represents a significant loss of safety, independent of the backup management strategy. 
     SUMMARY 
     In comparison with the known approach, the electrical, decentralized braking system according to the present invention has the advantage that, even after a common mode error or after the occurrence of two simple errors, at least a part of the wheel modules can test for plausibility of sensor values through comparison with at least one additional sensor value, thus ensuring safety against a second error. 
     In this way, increased reliability and availability of the service brake is ensured in case of error, which is required in pure brake-by-wire systems without mechanical/hydraulic backup systems for a safe trip to a workshop. 
     The underlying idea of the present invention is essentially that at least a part of the wheel modules can test for plausibility of sensor values through comparison with at least one additional sensor value even after a common mode error or after the occurrence of two simple errors. 
     In other words, an electrical, decentralized braking system is provided with: at least four sensors for acquiring the actuation of a brake actuating device; one brake module per brakable wheel of the vehicle for acquiring sensor data and controlling a braking device of a corresponding wheel; at least one first communication device with which all braking modules are connected to one another for the exchange of data; and an electrical connection device by which each sensor is connected at least to one brake module, the braking system having at least one additional communication device for receiving and/or exchanging data between at least two wheel modules of opposite sides of the vehicle. 
     According to an example embodiment of the present invention, the second communication device is constructed identically to the first communication device, and each sensor is connected to a second wheel module of the opposite side of the vehicle. In this way, the necessary and reliable test for plausibility of the sensor values can take place via the additional duplex system of the two local sensors, even when a common mode error has occurred in the communication system, i.e., both communication devices or communication lines fail. 
     According to an example embodiment of the present invention, a front wheel module of one side of the vehicle is connected to a rear wheel module of the other side of the vehicle via a second communication device, and a front wheel module of the other side of the vehicle is connected to a rear wheel module of the one side of the vehicle via a third communication device for exchanging data. This has the advantage that after the occurrence of two independent simple errors affecting the communication devices, or one common mode error (e.g. due to mechanical foreign influence in the area of the wheel housing), a communication, and thus a test for plausibility, of the sensor values is still possible between at least two wheel braking modules on opposite sides of the vehicle. 
     According to a further example embodiment, more than four sensors, allocated to the wheel modules in pairs, are provided for acquiring the actuation of the brake actuating device. This is advantageous because it provides an additional increase in redundancy at a low expense. 
     According to a further example embodiment, the communication devices are formed by serial bus systems. This advantageously permits the use of known communication platforms. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic block diagram of a braking system according to a first example embodiment of the present invention. 
         FIG. 2  shows a schematic block diagram of a braking system according to a second example embodiment of the present invention. 
         FIG. 3  shows a schematic block diagram of a conventional braking system. 
         FIG. 4  shows a schematic block diagram of an additional conventional braking system. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIGS. 1-4 , identical reference characters designate identical or functionally identical components. 
       FIG. 1  schematically shows a block diagram of an electrical braking system that has four sensors S 1 , S 2 , S 3 , and S 4 . The four sensors S 1  to S 4  determine an actuation of a brake actuating device (not shown), such as, for example, a brake pedal, that is actuated by a user of the vehicle. The four sensors S 1  to S 4  all detect the same parameters, such as, for example, a pedal path and a pedal angle: Intelligent wheel braking modules  10 , which are provided with a device  11  for determining the brake demand or a desired braking (brake demand distribution), are each connected with one of the four sensors S 1  to S 4  via an electrical line  12 . Four wheels  13  are connected to wheel braking modules  10  or wheel braking devices (not shown) connected therewith. 
     Moreover, wheel braking modules  10  are all connected to one another via a communication device  14  that permits an exchange of data between wheel braking modules  10 . According to the example embodiment in  FIG. 1 , a second and a third communication device  14 ′ and  14 ″ are additionally provided, such that each of these communication devices  14 ′,  14 ″ connects a wheel module  10  of one side of the vehicle, e.g., right or left, with a wheel braking module  10  of the other side of the vehicle, in order to exchange data. For example, the front right wheel RV is connected to the rear left wheel LH and conversely, so that a diagonally opposite connecting is ensured. First, second, and third communication devices  14 ,  14 ′, and  14 ″ are a serial bus system, for example. 
     Communication device  14  enables communication among all four wheel braking modules  10 , and also with additional control devices, such as, for example, ABS or VDM control modules. Via this communication device  14 , the pedal sensor values of sensors S 1  to S 4  of the four wheel braking modules  10  are exchanged. In addition, via the second and third communication devices, i.e., two braking circuit data buses  14 ′ and  14 ″, the pedal sensor values of the two associated wheel braking modules  10 VL (front left), HR (rear right); VR (front right), HL (rear left) are mutually exchanged. This creates the possibility of monitoring, via the two braking circuit data buses  14 ′,  14 ″, of the data sent via the first communication device  14 . 
     After the occurrence of two independent simple errors affecting communication devices  14 ,  14 ′,  14 ″, or the occurrence of a common mode error, e.g. due to mechanical foreign influence in the area of the wheel housing resulting in breakage of the communication bus connections to the corresponding wheel, one communication device  14 ′ or  14 ″ is thus still intact, so that a test of plausibility of the pedal sensor values of sensors S 1  to S 4  is still possible between at least two wheel braking modules  10  VR, HL or VL, HR. A system of this sort therefore has the possibility of switching off wheel braking modules  10  that can no longer communicate via a communication device  14 ,  14 ′,  14 ″, in order to avoid undesirable or unmatched braking forces, and thus a possible pulling of the brakes of the vehicle. This results in increased safety, both in the case of a simple error and also in the case of a double simple error, or of a common mode error. 
       FIG. 2  shows a schematic block diagram of an electrical braking system according to a second example embodiment of the present invention. The embodiment according to  FIG. 2  is distinguished from the embodiment explained with reference to  FIG. 1  by the modified communication or connection structure between individual wheel braking modules  10 . As in the first embodiment, the braking system according to the second embodiment also has a communication device  14 , e.g., a serial data bus, that connects all wheel braking modules  10  of wheels  13  to one another. In addition, a second communication device  14 ′, redundant to the first communication device  14 , is provided that likewise connects all wheel braking modules  10  to one another. Besides electrical connections  12  between sensors S 1  to S 4  for acquiring the actuation of a brake actuating device (not shown) and wheel braking modules  10  according to  FIG. 1 , in  FIG. 2  additional electrical connections  12 ′ are provided. Electrical connections  12 ′ extend from a respective sensor, e.g. S 2 , to a wheel braking module  10  that is situated axially next to the wheel braking module  10  that is connected to the electrical connection  12  of the sensor S 2 . That is, each of sensors S 1  to S 4  is electrically connected, via connection  12  and connection  12 ′, to two wheel braking modules  10  situated on one axle. 
     The decentralized system for acquiring a user brake request according to the second example embodiment thus has exactly two of the four sensors S 1  to S 4  connected to each of the four wheel modules. Alternatively, embodiments are also conceivable in which more than four physical sensors S 1 , S 2 , . . . , are allocated in pairs to the four wheel braking modules  10 . The advantage of the proposed second example embodiment is that even after the occurrence of two independent simple errors or the occurrence of a common mode error in communication system  14 ,  14 ″, wheel braking modules  10  are indeed no longer able to communicate with one another, but a necessary and reliable test for plausibility of the sensor values of sensors S 1  to S 4  can nonetheless take place via the additional redundant system of the two local sensors S 1  to S 4 . In this way, it is possible to safely brake wheel braking modules  10  that can no longer communicate with one another via a communication system  14 ,  14 ′. This results in increased safety in the case of failure of the communication system, both in the case in which two simple errors occur and in the case of a common mode error. 
     Although the present invention has been explained above on the basis of exemplary embodiments, it is not limited to these, but rather can be modified in a multiplicity of ways. 
     Although it has been described for vehicles having two axles, the present invention can also be correspondingly applied to multi-axle vehicles, such as, for example, three-axle trucks. In addition, it is likewise conceivable to realize connections  12 ,  12 ′ between sensors S 1  to S 4  so as to be not only unidirectional (as is indicated by the arrows in the drawings) but rather, e.g., for the second embodiment, so as to enable bidirectional communication, via a corresponding sensor, between the two wheel braking modules  10  connected to the sensor. Under this precondition, it would also be possible to realize a diagonal cross-connection of wheel braking modules  10  via connecting devices  12 ,  12 ′ between wheel braking modules  10 , in contrast to the described connection of wheel braking modules  10  of one axle.