Abstract:
A method for furnishing a sensor signal in a braking system, in which in the event of a failure of the brake control unit signal transfer is switched over and the signal is transmitted to a further control unit.

Description:
RELATED APPLICATION INFORMATION 
       [0001]    The present application claims priority to and the benefit of German patent application no. 10 2014 221 901.9, which was filed in Germany on Oct. 28, 2014, the disclosure of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method for furnishing a sensor signal in the braking system in a vehicle. 
       BACKGROUND INFORMATION 
       [0003]    Patent document DE 10 2009 046 339 A1 discusses a hydraulic braking system in a vehicle, which has two brake circuits for supplying hydraulic brake fluid to wheel brake devices, the brake circuits being connected to one shared brake master cylinder that is actuated by the driver, via a hydraulic brake booster, by way of the brake pedal. Located in each brake circuit is a delivery pump that is a constituent of an antilock braking system or electronic stability program by way of which an automatic intervention in the braking system can be carried out. 
         [0004]    The antilock braking system or electronic stability program requires wheel rotation speed information that is ascertained by wheel rotation speed sensors, so that the brake pressure in the braking system can be manipulated as desired. In the event of a failure of the control unit of the antilock braking system or electronic stability program, the braking function by way of driver actuation is retained, but the automatic braking intervention that is required for autonomous driving is not guaranteed. 
       SUMMARY OF THE INVENTION 
       [0005]    The object on which the invention is based is that of enhancing the fail-safe performance of braking systems in vehicles. 
         [0006]    This object is achieved according to the present invention with the features described herein. The further descriptions herein describe useful refinements. 
         [0007]    The method according to the present invention refers to a braking system in a vehicle, for example to a hydraulic braking system that is actuatable by the driver via the brake pedal and advantageously can also be actuated independently of driver actuation in the context of an automatic braking operation. For that purpose, the braking system advantageously has a controllable braking unit or booster unit to which control can be applied via positioning signals of a control unit, so that a braking operation can be carried out independently of a driver actuation. The braking unit or booster unit encompasses, for example, an electric positioning motor that influences, directly or via a linkage, the hydraulic brake pressure in the braking system. 
         [0008]    According to an advantageous embodiment, the braking system has at least two mutually independently actuatable booster units by way of which the braking force generated in the braking system can respectively be influenced. Each booster unit advantageously has associated with it a control unit in which positioning signals for adjusting the booster unit can be generated on the basis of delivered input signals. 
         [0009]    The method according to the present invention is based on the furnishing of a sensor signal in the braking system that has a brake control unit by way of which a booster unit in the vehicle is adjustable. In the event of a failure of the brake control unit, signal transfer is switched over to a further control unit to which the sensor signal is transmitted. The same procedure is carried out in the event of a faulty transmission of the sensor signal to the brake control unit. 
         [0010]    This procedure has the advantage that a braking-relevant sensor signal is further processed even in the event that said signal does not arrive at, or cannot be processed in, the brake control unit. Because operation switches over to a second control unit, the braking-relevant information of the sensor signal is available in the braking system or optionally also outside the braking system. This makes it possible in particular to carry out an automatic braking operation even in the event of a failure of the brake control unit or in the event of a failure in transmission of the sensor signal to the brake control unit. The braking operation to be triggered and carried out manually remains unaffected thereby in all cases. 
         [0011]    According to an exemplary embodiment, the sensor signal is a wheel rotation speed signal. Such signals are ascertained via wheel rotation speed sensors or probes, and in normal circumstances (when the braking system is functional) are transmitted as an input signal to the brake control unit, in which, in particular when a driver assistance system is activated, influence is exerted on, for example, the antilock braking system or electronic stability program. Such wheel rotation signals can, however, also be processed outside the brake system, for example for engine control or in order to apply control to a steering system having electrical servo assistance. 
         [0012]    Alternatively to wheel rotation signals, other sensor signals that are relevant to a braking operation in the vehicle are also appropriate. These are, for example, vehicle status variables regarding longitudinal or transverse dynamics. 
         [0013]    According to a further useful embodiment, the further control unit to which signal transfer is switched over in the event of a fault applies control to an electric motor used as a brake booster. Actuation thereof may be controlled via an electronic brake pedal, the motion of the electronic brake pedal being ascertained sensorially and the sensor signals being delivered as input signals to the control unit. The electric motor is then actuated and a brake cylinder is acted upon, optionally via a linkage, in order to establish the desired brake pressure in the braking system. 
         [0014]    In conjunction with the brake control unit in the embodiment as a control unit of an electronic stability program (ESP) or antilock braking system (ABS), this creates the possibility of carrying out, in the event of a failure of the ESP control unit or ABS control unit, an autonomous or automatic braking operation at least in part, and optionally entirely, by way of the further control unit and the associated brake booster. The functional failure of the ESP control unit or ABS control unit can thus be partly, optionally entirely, compensated for by transferring functions to the further control unit and to the associated brake booster. 
         [0015]    According to a further useful embodiment, control signals are generated in a microcontroller and/or an ASIC of the brake control unit and are evaluated in a switchover unit or in a switchover logic system associated with the switchover unit. The control signals generated in the microcontroller are, for example, signals that indicate the autonomous/non-autonomous driving mode, signals of a test mode for testing the switchover unit, or a trigger signal that is generated in the event of a fault in the ESP control unit or ABS control unit or a fault in a system component associated with that control unit, for example an electric pump motor or a pump unit. 
         [0016]    According to a further useful embodiment, in the event of a fault the supply of voltage to the sensor, which in normal circumstances is handled by the voltage supply of the brake control unit, is switched over to an alternative power source. This is, in particular, the vehicle battery. Voltage supply to the sensor in the event of a fault is thereby ensured. 
         [0017]    The braking system for carrying out the method encompasses at least one sensor for ascertaining a braking-relevant sensor signal that is present, for example, as a wheel rotation speed signal, as well as furthermore a brake control unit for applying control to a booster unit with which the braking force generated by the braking system can be influenced. The braking system is furthermore equipped with a switchover unit that enables a switchover and forwarding of the sensor signal to a further control unit in the event of a fault in the brake control unit or in the event of a faulty transmission of the sensor signal to the brake control unit. The braking system furthermore encompasses wheel brake units with which the wheels of the vehicle are decelerated. 
         [0018]    In an advantageous embodiment, the switchover unit is coupled directly to the brake control unit and communicates therewith. 
         [0019]    Further advantages and useful embodiments are evident from the further claims, from the description of the Figures, and from the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a hydraulic circuit diagram of a vehicle brake having two brake circuits associated with the front axle and the rear axle, and having an electronic stability program (ESP) and having an electrically actuatable brake booster. 
           [0021]      FIG. 2  is a block diagram having an ESP control unit to which a switchover unit is coupled, and having a further control unit that is associated with an electrical brake booster. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Hydraulic braking system  1  depicted in the hydraulic circuit diagram according to  FIG. 1  has a front-axle brake circuit  2  and a rear-axle brake circuit  3  for supplying hydraulic brake fluid respectively to wheel brake apparatuses  8  and  9  on the front wheels and  10  and  11  on the rear wheels. Also appropriate in principle are braking systems in which the brake circuit distribution is diagonal, so that a wheel brake apparatus is provided for each brake circuit on a front wheel and on a rear wheel. 
         [0023]    The two brake circuits  2 ,  3  are connected to one shared brake master cylinder  4  that is supplied with brake fluid via a brake fluid reservoir  5 . Brake master cylinder  4  is actuated by the driver via brake pedal  6 , and the pedal travel exerted by the driver is measured via a pedal travel sensor  7 . Located between brake pedal  6  and brake master cylinder  4  is a brake booster  16  that encompasses, for example, an electric motor may actuate brake master cylinder  4  via a linkage. The positioning motion of brake pedal  6  measured by pedal travel sensor  7  is transmitted as a sensor signal to a control unit  17  of brake booster  16 , in which positioning signals for applying control to brake booster  16  are generated. 
         [0024]    Disposed in each brake circuit  2 ,  3  is a switchover valve  12  that is located in the flow path between the brake master cylinder and the respective wheel apparatuses  8 ,  9  and  10 ,  11 . Switchover valves  12  are open in their zero-current idle state. Each switchover valve  12  has associated with it a check valve, connected in parallel, through which flow can occur toward the respective wheel brake apparatuses. 
         [0025]    Located between switchover valves  12  and the respective wheel brake apparatuses  8 ,  9  and  10 ,  11  are inlet valves  13  that are likewise open at zero current and have check valves associated with them through which flow can occur in the opposite direction, i.e. from the wheel brake apparatuses to the brake master cylinder. 
         [0026]    Each wheel brake apparatus  8 ,  9  and  10 ,  11  has associated with it an outlet valve  14  that is closed at zero current. Outlet valves  14  are each connected to the suction side of a pump unit  15  that has a respective delivery pump  18 ,  19  in each brake circuit  2 ,  3 . The pump unit has associated with it an electric drive motor or pump motor  22  that actuates both delivery pumps  18  and  19  via a shaft  23 . The discharge side of the respective delivery pump  18 ,  19  is connected to a conduit segment between switchover valve  12  and the two inlet valves  13  for each brake circuit. 
         [0027]    The suction sides of delivery pumps  18  and  19  are each connected to a high-pressure switching valve  24  that is hydraulically connected to brake master cylinder  4 . In the context of a vehicle-dynamics control intervention, for rapid brake pressure buildup the high-pressure switching valves  24  that are closed in the zero-current state can be opened so that delivery pumps  18  and  19  draw hydraulic fluid directly out of brake master cylinder  4 . This brake pressure buildup can be carried out independently of an actuation of the braking system by the driver. Pump unit  15 , having the two delivery pumps  18  and  19 , electric pump motor  22 , and shaft  23 , is part of a driver assistance system and is a component of an electronic stability program (ESP) or of an antilock braking system (ABS). Electric pump motor  22  is adjusted via positioning signals of a brake control unit or ESP control unit  27 . 
         [0028]    Located between outlet valves  14  and the suction side of delivery pumps  18  and  19 , for each brake circuit  2 ,  3 , is a reservoir chamber  25  that serves for temporary storage of brake fluid that is released through outlet valves  14  from wheel brake apparatuses  8 ,  9  and  10 ,  11  during a vehicle dynamics intervention. Associated with each reservoir chamber  25  is a check valve that opens in the direction of the suction sides of delivery pumps  18 ,  19 . Reservoir chambers  25  are also part of the electronic stability program (ESP). 
         [0029]    A pressure sensor  26  is disposed in brake circuit  3 , adjacently to brake master cylinder  4 , for pressure measurement. 
         [0030]    Braking system  1  is furthermore equipped at each vehicle wheel  20  with a wheel rotation speed sensor  21  with which the respective wheel rotation speed can be ascertained. The sensor signal of wheel rotation sensor  21  is delivered as an input signal to ESP control unit  27 , in which positioning signals for adjusting electric pump motor  22  are generated. Each vehicle wheel has associated with it a wheel rotation speed sensor whose sensor signals are conveyed to ESP control unit  27 . 
         [0031]      FIG. 2  is a block diagram depicting the interaction of control unit  17 , which is associated with brake booster  16 , and ESP control unit  27 . Each control unit  17 ,  27  respectively encompasses a microcontroller  17   a,    27   a  and an ASIC  17   b,    27   b.  The block diagram describes the interaction of control units  17  and  27  in the event of a fault in ESP control unit  27 , the consequence of which is that autonomous, automatic braking interventions can no longer be carried out via the ESP system. In order to allow autonomous braking interventions to continue to be carried out despite a failure of ESP control unit  27 , in the event of a fault a functional displacement to control unit  17  of brake booster  16  occurs, whereupon the hydraulic brake pressure in the braking system is modulated via the electrically actuatable brake booster  16  so that single-channel ABS braking can be effected with a stabilized vehicle. 
         [0032]    A switchover unit  29 , preceded by a switchover logic system  28 , is coupled to ESP control unit  27 . Switchover logic system  28  controls switchover unit  29  with a control signal as a function of input variables that switchover logic system  28  receives from microcontroller  27   a  and from ASIC  27   b  of ESP control unit  27 . The control signal generated by switchover logic system  28  in order to apply control to switchover logic system  29  contains, for example, the autonomous/non-autonomous driving mode, a test mode for testing switchover unit  29 , or a trigger signal in the event of an electrical fault in the ESP system, in particular in ESP control unit  27 . 
         [0033]    Switchover unit  29  switches the switches  29   a  and  29   b  between two different switching states as a function of the control signal that is delivered. First switch  29   a  switches the rotation speed sensor signal from the rotation speed sensor either to ASIC  27   b  of the ESP control unit or alternatively to ASIC  17   b  of brake control unit  17  of brake booster  16 . In the normal case (when all components are fully functional) switch  29   a  is set to convey the rotation speed sensor signal to ASIC  27   b  of ESP control unit  27  in order to allow an autonomous braking intervention to be carried out, as applicable, by the ESP system as a function of the delivered rotation speed sensor signals. In the presence of a fault that is detected in switchover logic system  28 , however, switch  29   a  is reset so that the wheel rotation speed sensor signals are delivered to ASIC  17   b  of brake control unit  17 . This makes it possible for the ESP functions performed in the context of an autonomous braking intervention to be carried out by brake control unit  17  and by the associated brake booster  16 . 
         [0034]    Second switch  29   b  in switchover unit  29  relates to the supply of electricity to wheel rotation speed sensors  21 . In the normal case, electricity is supplied to wheel rotation speed sensors  21  via the electricity supplied to ASIC  27   b  of ESP control unit  27 . In the event of a fault, switch  29   b  is reset and electricity is supplied, as indicated by dashed line  30 , from a supply voltage obtained from the battery voltage of the vehicle battery. 
         [0035]    As indicated by the dashed box, switchover logic system  28  and switchover unit  29  are coupled onto ESP control unit  27 .