Abstract:
A method and a device for the open- and/or closed-loop control of a generator or a dynamo in a vehicle. The generator supplies, at least part of the time, an electric motor located in a braking system, e.g., a pump motor, with electrical power. A main feature is that the generator is activated as a function of the pressure in the brake master cylinder, it being activated as soon as the pressure in the brake master cylinder exceeds an initial threshold value.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a method and a device for open- and/or closed-loop control of a generator to supply electrical power to an electric motor located in the braking system of a vehicle. 
     BACKGROUND INFORMATION 
     A method and a device for open- and/or closed-loop control of an electric motor are described in German Patent Application No. DE 10 2005 060859 (not a prior publication), in which the electric motor is powered by a generator. Here, the high-frequency pulse-width modulation used to provide open- and/or closed-loop control is utilized for continuously increasing the current required to operate the electric motor. 
     SUMMARY OF THE INVENTION 
     The present invention describes a method and a device for open- and/or closed-loop control of a generator or a dynamo in a vehicle. It is provided that the generator supplies electrical power, at least part of the time, to an electric motor in a braking system, such as a pump motor. A main feature of the present invention is that the generator is activated as a function of the pressure in the brake master cylinder, it being provided that the generator is activated as soon as the pressure in the brake master cylinder exceeds an initial threshold value. This makes it advantageously possible to ensure an adequate supply of electrical power to the electric motor. 
     In one embodiment of the present invention it is furthermore provided that the generator is activated in an initial step, so that a sufficient supply of electrical power to operate the electric motor is available. It is advantageously provided that the electric motor is operated under load only in a second step. Between the first and the second steps a delay may be provided for, which may be stipulated as a function of the current gradient which may be produced by the generator. Since operating the electric motor under load requires a higher level of electrical current than idling it, the delay makes it possible to ensure an adequate supply of electrical power to the electric motor. 
     The electric motor may be set in operation when the generator is activated, and it is idled until a second threshold value for the pressure in the brake master cylinder is reached. As an alternative, it may also be provided that the electric motor is activated only after the second threshold value has been exceeded and is then to be operated immediately under load. 
     In order to enable early activation of the generator and therefore an adequate run-up for current generation, it is provided that the initial threshold value, at which the generator is activated, is set lower than the second threshold value, at which the electric motor is operated under (full) load. It is advantageous if the second threshold value is stipulated as a function of the pressure level at which one wheel brake in the braking system locks up. This lock-up pressure level may be sensed within an ABS/ESP controller and signals the point in time at which the pump in the braking system must be activated in order to reduce the pressure in at least one wheel brake. 
     In a further embodiment of the present invention, it is provided that the generator is activated in response to the change in the pressure in the brake master cylinder. Here it is possible to detect whether there is an imminent intent to rapidly change the pressure in at least one wheel brake in the braking system, in order to ensure the prompt supply of electrical power to the electric pump in the braking system whose function is to reduce the pressure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows schematically in a block diagram a device according to the present invention for open- and/or closed-loop control of a generator or of an electric motor. 
         FIG. 2  shows in a graph the relationships of the activation moments relative to the sensed admission pressure levels. 
         FIG. 3  shows a possible open-/closed-loop control algorithm with the aid of a flow chart. 
     
    
    
     DETAILED DESCRIPTION 
     When an electrically driven pump motor is operated as part of an ABS/ESP braking system, then, in the event of a high wheel pressure and consequently a high load torque during the run-up of the motor, there may be a high demand for current, possibly resulting in a collapse of the voltage in the vehicle&#39;s electrical system. As a result of such a collapse the motor may be unable to start up quickly enough and unable to reduce quickly enough the braking pressure at the wheel that has locked up. One possible way of preventing such a collapse of the voltage in the vehicle&#39;s electrical system is to activate a generator or the vehicle&#39;s dynamo, in order to compensate for the increased demand for electrical power. Since typical generators, however, are designed with current gradients of approximately 300 A/s to 1000 A/s, the current required for the operation of the pump motor cannot be supplied immediately after the generator starts. 
     In order to provide the current required for the operation of the pump motor in a timely manner, it is provided that the generator is started before the pump motor starts or before full load is reached, taking the current gradient of the generator into account. 
     To this end a processing unit  110  is provided within a control unit  100 , which detects an admission pressure p admission . This admission pressure signal p admission  may, for example, represent the pressure in brake master cylinder  130  and thus the intent of the driver to brake. As an alternative the admission pressure signal may, however, also represent the pressure in the brake on at least one of the wheels. Furthermore, processing unit  110  determines the lock-up pressure level in at least one of the vehicle&#39;s wheel brakes with the aid of a suitable device  135 . ABS or ESP systems may be utilized here as typical devices to sense such lock-up and thereby to detect the lock-up pressure level. 
     If the detected admission pressure signal p admission  and under certain circumstances also the lock-up pressure level result in the decision that a response of the pump in the braking system with a high load torque is imminent, for example in order to reduce the pressure at one wheel brake owing to a sensed or imminent lock-up, then generator  140  is activated by processing unit  110 , before pump motor  150  is operated to reduce the pressure. The dependence of the activation of the generator on the admission pressure signal or the response to the lock-up pressure level and the time delay between the activation of the generator and the electric motor are stipulated in the form of one or more characteristic curves, which processing unit  110  can access. 
     In order to make it possible to adjust the dependencies between the admission pressure signal and the activation of the generator, a memory  120  is provided, from which processing unit  110  can read differing characteristic curves as required. These characteristic curves may be modified if necessary, for example using an external input unit  160  via an interface if individual components of the braking system such as pump motor  150  or generator  140  are replaced. 
     A typical characteristic curve, showing a relationship between admission pressure p admission  and the activation times for generator  140  or electric motor  150 , is shown in  FIG. 2 . Here, value p 2  corresponds to a lock-up pressure at one of the vehicle&#39;s wheel brakes. At the latest when this lock-up pressure is reached at point in time T 2 , the pump is activated in order to reduce the excessively high braking pressure in the wheel brake. Thus, starting from point in time T 2  pump motor  150  will require a sufficiently high power supply for its operation, and this, owing to the limited capacity of the on-board battery, has to be supplied by generator  140 , in order to prevent a collapse of the voltage in the vehicle&#39;s electrical system. According to the present invention this supply of electrical current is made possible by the timely activation of generator  140 . Taking into account the current gradient of generator  140 , in other words the maximum current that can be produced by the generator during running up to speed, makes it possible to calculate in advance at what point in time T 1  before lock-up pressure p 2  is reached, and thus before full-load operation of pump motor  150 , generator  140  must be activated. As a function of the time difference thus obtained (T 2 −T 1 ), and assuming that the rise in admission pressure p admission  is linear, it is possible to determine an initial threshold value p 1 . When this threshold value p 1  is reached, generator  140  is activated. 
     In another exemplary embodiment, in addition to the linear pressure rise shown in  FIG. 2 , differently shaped characteristic curves may also be used. Furthermore, consideration may also be given to detecting admission pressure p admission  as a function not of the brake master cylinder pressure but of one or more wheel brake pressures. 
     A possible open- or closed-loop control strategy for the present invention is shown by the flow chart in  FIG. 3 . Once the appropriate algorithm has started, in a first step  300  admission pressure p admission  (T 1 ) at point in time T 1  is detected. As already stated, this may be either the pressure in the brake master cylinder or one of the wheel brake pressures. Since this admission pressure signal is normally accompanied by signal noise, the signal is filtered in order to remove the high frequency components. In addition, lock-up pressure p 2  is determined, with the relevant value being ascertainable in different ways. One possibility, for example, is reading the value in directly from the ABS controller in the vehicle&#39;s ABS system. 
     Next the detected admission pressure signal p 1  is differentiated in step  320 , in order to be able to predict the rise in the admission pressure. In step  340  the decision is made whether according to
 
 P   1   +d/dt ( p   1 *( T   2   −T   1 ))≧ p   2  
 
the rise in admission pressure p admission  at point in time T 1  will cause admission pressure p admission  after the passage of time (T 2 −T 1 ) to exceed the second threshold value p 2 , which represents the lock-up pressure. If this is the case, it is thereby understood that an increased demand for electrical power to operate pump motor  150  will occur at point in time T 2 . Thereupon in step  360  generator  140  is activated, in order to be able to produce at point in time T 2  the level of current called for at that time.
 
     As an option, a step  380  may also be provided in which not only generator  140  is activated but also pump motor  150 . In this case, however, it is provided that up to point in time T 2  pump motor  150  is operated essentially only at idle. This has the advantage that in the event the brakes lock up, pump motor  150  will reach operation under full load more quickly, in order to be able to reduce the high wheel brake pressure. 
     Since the lock-up pressure level may vary with driving conditions, in a further exemplary embodiment it may be provided, for example, that brake fade may be taken into account in the calculation of value p 2  and in creating the characteristic curve and thus in calculating value p 1 . In addition, however, it is also conceivable to take other influencing variables that result in a change in the lock-up pressure into consideration in creating or modifying the characteristic curve. This consideration may naturally also be undertaken during operation of the braking system, for example during step  300  of the algorithm in  FIG. 3 .