Abstract:
A method for operating a brake system of a motor vehicle, which has at least one operating mode (normal, sporty, etc.), includes prefilling, to at least partially overcome a clearance of one or a plurality of wheel brake(s) prior to an expected actuation of a brake pedal, an actuation of the brake pedal being expected at specific positions and/or gradients of the actuation of operating devices of the motor vehicle, in particular an accelerator pedal. The method includes an operating mode in which the gradient is specified as a function of the dynamics and/or limit values of the actuation of the operating devices.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to Application No. 10 2006 029 979.5, filed in the Federal Republic of Germany on Jun. 29, 2006, which is expressly incorporated herein in its entirety by reference thereto. 
     FIELD OF THE INVENTION 
     The present invention relates to a method for operating a brake system of a motor vehicle, e.g., which has at least one operating mode including prefilling, to at least partially overcome a clearance of one or a plurality of wheel brake(s) prior to an expected actuation of a brake pedal, an actuation of the brake pedal being expected at specific positions and/or gradients of the actuation of operating devices of the motor vehicle, e.g., an accelerator pedal. Furthermore, the present invention relates to a device, e.g., a control device, as well as a computer program for implementing the program. 
     BACKGROUND INFORMATION 
     German Published Patent Application No. 10 2004 030 464 describes a method for electronic brake control, in which the clearance is overcome by prefilling the servo-hydraulic brake systems if the accelerator is released at a gradient that exceeds a minimum gradient. In this context it is assumed that, in an emergency situation, for example, the driver will release the accelerator pedal abruptly, and the prefilling will be activated in such a situation. 
     The method allows the clearance to be overcome by prefilling the brake system only in those instances where the driver releases the accelerator abruptly. This is typically provided only in an emergency situation. With a so-called sporty or dynamic driving style, in which there is a frequent change between acceleration by operating the accelerator pedal, and deceleration by operating the brake pedal, and in which the accelerator pedal is normally not released abruptly, the clearance of the service brake is therefore not overcome. The driver of the motor vehicle perceives this as a delayed response of the service brake. 
     SUMMARY 
     Example embodiments of the present invention provide a method, a device, as well as a computer program that allow the clearance of the wheel brake to be overcome even outside of danger situations. 
     According to an example embodiment of the present invention, a method is for operating a brake system of a motor vehicle, which has at least one operating mode including prefilling, to at least partially overcome a clearance of one or a plurality of wheel brake(s) prior to an expected actuation of the brake pedal, an actuation of the brake pedal being expected at specific positions and/or gradients of the actuation of operating devices of the motor vehicle, e.g., an accelerator pedal, the method including an operating mode in which the gradient is specified as a function of the dynamics and/or limit values of the actuation of the operating devices. The gradient of the actuation of the operating device, e.g., the accelerator pedal, may become randomly low, that is to say, it may basically even become zero. This has the result that the prefilling of the brake, and therefore the overcoming of the clearance of the wheel brake, i.e., the application of the brake linings, is already activated upon any randomly slow release of the accelerator pedal. To this end, an operating state in which the randomly slow release of the accelerator pedal already causes prefilling of the brake is defined and detected during operation and possibly activated, if appropriate. Here, this operating state is referred to as “sporty driving style” or “dynamic driving style.” In addition, any number of other operating states may exist, e.g., a “normal driving style” operating state, in which a minimum gradient of the release of the accelerator thus is required to overcome the clearance of the wheel brake, i.e., prefilling of the brake takes place only in an emergency situation, as in certain conventional systems. The dependence of the gradient on the dynamics and/or limit values of the actuation of the operating devices means that the type of actuation, in the form of actuation speed, maximum displacements or maximum pressures, is monitored over a specific period of time and analyzed. Unlike in certain conventional systems, the prefilling of the brake is thus no longer solely a function of the one-time release of the accelerator at a minimum gradient, but of the actuations of a plurality of operating devices monitored over a specified time interval, e.g., the actuation of the accelerator and the brake pedal. However, additional operating parameters of the motor vehicle, such as speed, dynamic response of the requested torque (both brake and engine torque), maximum accelerations both in the longitudinal vehicle direction and in the transverse vehicle direction, etc., may be taken into account in this context. 
     It may be provided to activate the prefilling in the operating mode as soon as the position of the accelerator pedal is modified to a lower torque request, i.e., as soon as the accelerator pedal is released. In addition, the operating mode is determined as a function of the dynamics and/or limit values of a driver-side torque request, e.g., the position of the accelerator pedal, and/or a requested deceleration, i.e., the position of the brake pedal. Both the maximum value of the driver-side torque request and the gradient of the modification of the driver-side torque request, e.g., the rate at which the accelerator-pedal position is modified, are able to be taken into account in the driver-side torque request. In the deceleration request, it is possible to consider the maximum actuation travel or the maximum actuation force, and also the gradient of the brake pedal actuation. 
     The operating mode may be activated when an index, which is formed from the dynamics and/or limit values of the actuation of the operating device, exceeds a specified value. The index may be evaluated in the form of a loop, i.e., it is permanently evaluated at specific time intervals or in the presence of specific other triggering events, such as after traveling a specific distance, etc. In this context, it may be provided that, if the maximum braking wish is above an upper threshold, the index is increased by a specific value in the loop-type evaluation of the operating parameters of the motor vehicle. It may be provided that, if the maximum braking wish is below the upper threshold and above a lower threshold, the index remains unchanged in the loop-type evaluation of the operating parameters of the motor vehicle. In addition, it may be provided that, if the maximum braking wish is below the lower threshold, the index is decreased by a specific value in the loop-type evaluation of the operating parameters of the motor vehicle. 
     A computer program includes program codes for implementing the steps of the method when the program is executed on a computer. 
     A device, e.g., a control device, includes a device for operating a brake system of a motor vehicle, e.g., a power-assisted or power-actuated brake system, having at least one operating mode which includes prefilling, to at least partially overcome a clearance of one or a plurality of wheel brake(s) prior to an expected operation of a brake pedal, an operation of the brake pedal being expected at specific positions and/or gradients of the actuation of operating devices of the motor vehicle, e.g., an accelerator pedal, the device including an operating mode in which the gradient is specified as a function of the dynamics and/or limit values of the actuation of the operating devices. 
     Exemplary embodiments of the present invention are described in greater detail below with reference to the appended Figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a power-assisted, hydraulic brake system. 
         FIG. 2  is a flow chart illustrating a method according to an example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     A power-assisted, hydraulic brake system (wheel brake system)  10  for passenger cars illustrated in  FIG. 1  has a brake circuit I assigned to wheel brakes  11 ,  12  of front axis VA of the vehicle, and a brake circuit II assigned to wheel brakes  13 ,  14  of rear axis HA. A servo-pressure source  15 , which supplies the energy required to generate braking force, is connected to both brake circuits I and II. Brake system  10  also has a service brake, which is activated by external forces. Brake system  10  also includes a secondary brake, which is actuated by muscular energy. It has a main brake cylinder  17 , which is actuable by a brake pedal  16  and includes a pressure-medium reservoir  18 . Main brake cylinder  17  has a one-circuit design, i.e., it is connected to brake circuit I by a line  19  and a first valve  20  disposed therein. In the illustrated position of valve  20 , the secondary brake thus acts only on wheel brakes  11  and  12  of front axis VA. With an active service brake, valve  20  blocks the connection between the main brake cylinder and wheel brakes  11  and  12 . First valve  20  assigned to main brake cylinder  17  is therefore denoted as shutoff valve in the following text. 
     Servo-pressure source  15  aspirates pressure medium from reservoir  18  of main brake cylinder  17  and pressurizes it to high pressure for the functionality of the service brake. Pressure medium withdrawn from wheel brakes  11  to  14  while the service brake is in action is returned to reservoir  18 . To block brake circuit I with respect to pressure medium reservoir  18  when the secondary brake is active, a shutoff valve  24  is disposed in a line  23  leading to the pressure medium reservoir. In addition, two valves  25  and  26  for the brake-pressure modulation in an active service brake are assigned to each wheel brake  11  to  14 . 
     Brake system  10  is equipped with an electronic control device  29  to which a displacement sensor  30 , which detects the displacement of brake pedal  16 , is connected in addition to valves  20 ,  24 ,  25  and  26 , as well as six pressure sensors  31  to  36  by which the pressure generated by main brake cylinder  17 , the pressure supplied by servo-pressure source  15 , and also the pressures applied into wheel brakes  11  to  14  are able to be detected. While the secondary brake operates hydraulically in a conventional manner, without involvement of control device  29 , the service brake operates electro-hydraulically, i.e., when the driver of the passenger car actuates brake pedal  16 , the electrical displacement signal detected by displacement sensor  30 , and possibly additional electrical signals are analyzed by control device  29  for the control of valves  29 ,  24 ,  25  and  26  in order to generate brake pressure inside wheel brakes  11  to  14  according to the requested brake torque, the brake pressure being monitored by the control device with the aid of the electrical signals from pressure sensors  31 ,  33  to  36 . 
     The following exemplary embodiment of the method assumes an electromechanical brake system as described, for instance, as piezo-hydraulic wheel brake device in German Published Patent Application No. 198 18 156, or as electro-hydraulic brake system in German Published Patent Application No. 195 46 647, or as electromechanical brake in German Published Patent Application No. 103 21 159 and German Published Patent Application No. 199 43 601. 
     In the following text, an exemplary embodiment of the method is described with reference to  FIG. 2 . The function of the electronic prefilling of the service brake (electronic brake prefill, EBP) overcomes the clearance of the wheel brake by already applying the brake pads when releasing the accelerator pedal. By overcoming the clearance, the response time of the wheel-brake system (service brake) in a subsequent actuation of the brake pedal is shortened. This leads to a shorter pressure-generation time, which reduces the stopping distance. The clearance is overcome by the hydraulic control unit, a slight wheel pressure being set for applying the brake pads. According to example embodiments of the present invention, the prefilling activation takes place independently of the accelerator-pedal gradient, and thus independently of a potential emergency situation. To this end, a “sporty” operating mode is provided. In the sporty operating mode the prefilling is no longer activated as a function of the accelerator-pedal gradient, but already implemented when the torque request is reduced by the accelerator-pedal position, i.e., when the accelerator pedal is released by the driver, independently of the gradient at which the accelerator pedal is released. To this end, it is provided to detect the sporty operating mode on the basis of the driver&#39;s driving style. The driving style of the driver is detected via the dynamics of the actuation of the service brake as one of a plurality of operating devices of the driver, and/or on the basis of limit values of this actuation. That is to say, the brake-pedal actuations of the driver are recorded over a defined period of time and evaluated. To this end, the braking wish of the driver is detected, for instance, by detecting the brake pressure and/or brake force and/or pedal displacement. If the amount of the braking wish exceeds a threshold value, then the sporty driving style is detected, and a transition takes place into the sporty operating mode. This method is illustrated in the following text on the basis of the flow chart from  FIG. 2 . The method begins in step  101 . In step  102 , it is checked whether admission pressure P adm  exceeds a first threshold Sw 1 , P adm &gt;threshold Sw 1 . If this is the case, marked by the Y branching, then branching to step  103  takes place; if this is not the case, marked by the N branching, then branching to step  104  occurs. In step  103 , it is checked whether admission pressure P adm  is greater than a stored admission pressure P adm,merk . In step  104  it is checked whether stored admission pressure P adm,merk  is greater than zero. If stored admission pressure P adm,merk  is greater than zero in step  104 , then branching to step  105  takes place, which is indicated by the Y branching. In step  105 , it is checked whether stored admission pressure P pre,merk  is greater than an upper threshold Sw u . If this is the case, marked by the Y branching, then branching to step  106  takes place. In step  106 , a value Delta-Index is formed from the difference of the stored admission pressure minus upper threshold value Sw u , Delta-Index=P adm,merk −Sw u . In step  107 , index I is then increased by the Delta-Index value. In doing so, index I is limited to a maximum value of index I max . If the check in step  105  indicates that stored admission pressure P adm,merk  is smaller than upper threshold Sw u , indicated by the N branching, then branching to step  108  takes place. In step  108 , it is checked whether stored admission pressure P adm,merk  is smaller than a lower threshold Sw l . If this is the case, marked by the Y branching, then it is branched to step  109 . In step  109 , the overall index is reduced by a constant value, the overall index being limited to the value of zero in the downward direction. If stored admission pressure P adm,merk  is greater than lower threshold Sw l , indicated by the N branching, in the check in step  108 , then branching to step  110  takes place. In step  110  stored admission pressure P pre,merk  is set back to zero. 
     If it is determined in step  103  that admission pressure P adm  is greater than stored admission pressure P adm,merk , indicated by the Y branching, then branching to step  111  takes place. In step  111 , stored admission pressure P adm,merk  is assigned the value of admission pressure P adm , the value of stored admission pressure P adm,merk  being limited to an upper limit P adm,merk,max . Branching to step  112  takes place next. Branching to step  112  also takes place from step  110 , and from step  103  and  104 , if the checks here branch to the N option, in which case it is then branched to step  112 . In step  112 , it is checked whether overall index I n  is greater than a threshold Sw n  for the overall index. If this is the case, marked by the Y branching, then the sporty operating mode will be activated in step  113 . If the check in step  112  indicates that the overall index is not greater than the threshold for overall index Sw n , marked by the N option, then the sporty operating mode will be deactivated in step  114 . The method ends in step  115 . From step  115  it is branched back again to step  101 , in a loop, possibly with a time delay.