Patent Publication Number: US-2006006738-A1

Title: Device and method for the redundant voltage supply of safety-relevant systems

Description:
The invention relates to a device and a method for the redundant voltage supply of safety-relevant systems, in particular in motor vehicles.  
      To date, various systems with a redundant voltage supply have been proposed for ensuring the supply to safety-relevant systems, in particular in motor vehicles.  
      WO 99/42331 discloses a voltage-supply circuit for safety-relevant systems, for example electric brakes, in motor vehicles, in which circuit the systems have their own associated additional batteries which can be connected to a battery of a vehicle electrical system and/or to the generator using a charging circuit and switchover unit and via means for monitoring and distributing the electric power. In normal operation, the safety-relevant systems are supplied from their associated additional battery, a switchover is made if there is fault with the additional battery or if the additional battery is excessively discharged, and the safety-relevant systems are supplied directly from the battery of the vehicle electrical system. On account of this switchover to the battery of the vehicle electrical system if there is no longer sufficient power in the additional battery, there is no need for a monitoring circuit for the additional battery.  
      Furthermore, DE 100 53 584 A1 discloses a redundant voltage supply for safety-relevant loads. This device has a first voltage supply, which is arranged in the vehicle electrical system, and a second voltage supply, the first and second voltage supplies being connected by a decoupling element. The decoupling element, for example a diode, a switch with current-direction detection or field-effect transistors with internal short circuit-current detection, ensures a directed flow of current from the first to the second voltage supply. In addition, the first voltage supply, a second decoupling element and the second voltage supply are connected to the safety-relevant load by means of a third decoupling element and ensure a directed flow of current. If the voltage of the first voltage supply falls below that of the second voltage supply, voltage is transmitted through the decoupling element, with the result that the second voltage supply takes over the function of supplying voltage to the safety-relevant load.  
      Finally, DE 198 55 245 A1 specifies a redundant voltage supply for electrical loads in a vehicle electrical system which is used, in particular, in electrically operated brakes. In order to ensure the voltage supply, the electrical load is simultaneously connected to two separate voltage paths via disconnecting modules, said voltage paths each being connected to a dedicated voltage store via charge-disconnecting modules. If a fault, which endangers the voltage supply for the load, occurs in one supply path, this supply path is opened by means of suitable switching means and the function of supplying voltage is taken over solely by the voltage path which is operational. Disconnecting modules and charge-disconnecting modules can be integrated in a battery connector.  
      The prior art described above thus provides various solutions for improving the fail-safety of safety-relevant systems, to be precise in the event of a failure of the voltage supply, as a result of which, for example, a braking or steering action would no longer be available without a fallback level in the case of an electrohydraulic brake (EHB), an electrohydraulic steering system (EHL) etc., by switching over to a back-up power supply.  
      However, these conventional embodiments do not contain a safety function which could also compensate for a failure of the drive logic which likewise may also lead to a complete failure of safety-relevant systems, for example of the electrohydraulic brake (EHB), the electrohydraulic steering system (EHL) etc., since a switchover in the event of a voltage failure is then no longer possible. To be precise, specific voltages in the vehicle are usually made available to the vehicle electrical system by means of driven relays and are driven exclusively.  
      It is therefore the object of the present invention to design a device for the redundant voltage supply of safety-relevant systems with which both a failure of the voltage supply and a failure of the drive logic for switching over in the event of a failure of the voltage supply can be compensated for in a simple and cost-effective manner.  
      This object is achieved by a device for the redundant voltage supply of safety-relevant systems which has the features of claim  1  and by a method for the redundant voltage supply of safety-relevant systems which has the features of claim  3 .  
      In the device according to the invention and in the method according to the invention, both monitoring of whether different voltages are present across safety-relevant systems and monitoring of whether a first drive device and/or a second drive device has/have switched on a voltage are thus carried out as the first fallback level, and if the first and second drive devices fail, a third drive device switches on the voltage.  
      In this way, the availability of the voltage supply increases on ignition “on” and a considerable increase in the fail-safety as a result of the formation of two fallback levels which can likewise perform the switchover.  
      Furthermore, the device according to the invention for the redundant voltage supply of safety-relevant systems represents an extremely cost-effective solution since the individual drive devices for driving exclusive relays for one voltage supply in each case are already present in conventional devices and all that is additionally required is to provide the connection and the exchange of information via communication channels, for example the CAN bus, and to make it possible for each of the drive devices to drive all of the relays. 
    
    
      These and further objects, features and advantages of the invention are explained in more detail below with reference to the drawing, in which:  
       FIG. 1  is a simplified block diagram of the device according to the invention for the redundant voltage supply of safety-relevant systems, and  
       FIG. 2 , which consists of  FIGS. 2   a  and  2   b,  is a flowchart which illustrates the functional sequence of the method according to the invention for the redundant voltage supply of safety-relevant systems. 
    
    
      The following text firstly describes in more detail the simplified structure of the device according to the invention for the redundant voltage supply with reference to  FIG. 1 .  
      In  FIG. 1, 11  denotes a CAN bus as an example of communication channels via which communication signals are transmitted. The device according to the invention for the redundant voltage supply has a first drive device  1  which monitors for the presence of a voltage across one or more safety-relevant system or systems  5  via a line Sp 1  and, if no voltage is present there, can drive one or more relays contained in a relay unit  4  by means of a control signal St 1 , so that a voltage is then applied to the safety-relevant system or systems  5  again. In addition, the first drive device  1  outputs a request message Anf 1  to the CAN bus  11  if one or more relays in the relay unit  4  is to be driven in order to re-establish a voltage supply to the safety-relevant system or systems  5 . These relays of the relay unit  4  switch on and off a voltage supply for safety-relevant electrical systems  5 , for example an electrohydraulic brake (EHB), an electrohydraulic steering system (EHL) etc.  
      Furthermore, the device according to the invention comprises a second drive device  2  which monitors for the presence of a voltage across one or more safety-relevant system or systems  5  via a line Sp 2  and, if no voltage is present there, can likewise drive the relays in the relay unit  4 . If the second drive device  2  receives the request message Anf 1  from the first drive device  1  via the CAN bus  11 , it checks whether the first drive device  1  has initiated switching of the relay unit  4 , that is to say whether the voltage supply of the one or more safety-relevant systems  5  has been re-established. If the relay unit  4  has not switched and in addition it is determined via line Sp 2  that no voltage is applied to the safety-relevant system or systems  5 , the second drive device drives the relay or relays in the relay unit  4  in order to re-establish a voltage supply. The second drive device  2  is also designed in such a way that it sends a request message Anf 2  to the CAN bus  11  if it cannot switch the relay or relays in the relay unit  4  despite the absence of voltage across the safety-relevant system or systems  5 .  
      In addition to these two first and second drive devices  1  and  2 , there is also a third drive device  3  which monitors for the presence of a voltage across one or more safety-relevant system or systems  5  via a line Sp 3  and, if no voltage is present there, can likewise drive the relays in the relay unit  4 . If the drive device  3  receives both a request message Anf 1  from the first drive device  1  and a request message Anf 2  from the second drive device  2  via the CAN bus and detects the absence of a voltage across the safety-relevant system or systems  5 , the drive device  3  drives the relay unit  4  in such a manner that the relay or relays are/is switched over, so that a voltage supply to the safety-relevant system or systems  5  is re-established.  
      The method according to the invention for the redundant voltage supply of safety-critical systems is explained in greater detail in the text which follows with reference to  FIG. 2 , which consists of  FIGS. 2   a  and  2   b.    
      Initially, in step  1 , the drive device  1  monitors via a line Sp 1  whether a voltage can be detected across one or more safety-relevant systems  5 . If this is the case, the sequence is terminated and returns to the start (monitoring) again.  
      If it is determined in step S 1  that no voltage is applied to one or more safety-relevant systems  5 , in step S 2  the first drive device  1  drives the relay unit  4  by means of a control signal St 1  so that a voltage is again applied to the safety-relevant system or systems. Otherwise, the sequence ends after step S 1 .  
      Subsequently, in step S 3 , a request message Anf 1 , which states that it is necessary to switch over the relay in order to supply voltage, is output to the CAN bus  11 . This request message Anf 1  is received by the second drive device  2  in step S 4 . Following this, the second drive device  2  checks in step S 5  whether the first drive device  1  has successfully driven/switched over the relay unit  4 . If this is the case, the sequence ends. Otherwise, the sequence proceeds to step S 6 , in which it is determined via a line Sp 2  whether a voltage is applied to one or more safety-relevant systems  5 . In the affirmative, the sequence ends, and in the negative case, the sequence proceeds to step S 7 , in which a check is made as to whether it is possible for the second drive unit  2  to drive/switch the relay unit  4 . If driving/switching is judged to be possible in step S 7 , then in step S 8  the second drive device  2  drives/switches the relay unit  4  by means of the control signal St 2  and then the sequence ends.  
      If it is not possible for the second drive device  2  to drive/switch the relay unit  4  for whatever reasons, for example due to an interruption in the line for the control signal St 2 , the second drive device  2  outputs, in a step S 9 , a request message Anf 2  to the CAN bus  11 . In step S 10 , the third drive device  3  receives this request message Anf 2  from the second drive device  2  together with the request message Anf 1  from the first drive device  1 . This is followed in step S 11  by the third drive device  3  driving/switching the relay unit  4  by means of a control signal St 3 . The sequence then ends.  
      The above-described device according to the invention and the method for the redundant voltage supply of safety-relevant systems is cost-effective to implement since the individual drive devices for driving exclusive relays for one voltage supply in each case are already present in conventional devices and all that is additionally required is to provide the connection and the exchange of information via the CAN bus, as one example of communication channels, for example also control lines, LIN etc., and to make it possible for each of the drive devices to drive all of the relays.  
      In this way, a reliable device and a method for the redundant voltage supply of safety-relevant systems can be realized in a straightforward and cost-effective manner, without a large amount of additional outlay on circuitry and components.  
      Here, the advantage of the device according to the invention and of the method for the redundant voltage supply of safety-relevant systems is the double redundancy for switching the relays. Ensuring the provision of special-purpose voltage supplies leads to a higher availability level of safety-critical systems.  
      It goes without saying that a person skilled in the art may, in place of the three drive devices used in the preferred exemplary embodiment, also use more drive devices or in each case 3 drive devices from amongst the multiplicity of drive devices in the vehicle for relays.