Control device and method for operating an electromechanical brake booster of a brake system of a vehicle

Abstract

The disclosure relates to a control device and a corresponding method for operating an electromechanical brake booster of a brake system of a vehicle, comprising an electronics unit that defines a target variable with respect to a target rotational speed of a motor of the electromechanical brake booster, taking into account a brake input signal with respect to a braking request, and that sends at least one control signal to the motor. The electronics unit defines a maximum target variable with respect to a maximum target rotational speed of the motor, taking into account a current intensity of a motor current of the motor and a current angle of rotation of a rotor of the motor, and defines the target variable with respect to the target rotational speed of the motor of the electromechanical brake booster to be at the most equal to the defined maximum target variable.

Claims

1. A control device for at least one electromechanical brake booster of a brake system of a vehicle, the control device comprising: an electronic device configured to: specify a target rotational speed of a motor of the at least one electromechanical brake booster based on at least one brake-specifying signal that is output to the electronic device in relation to at least one of (i) a braking request of a driver of the vehicle and (ii) an automatic speed-controlling system of the vehicle; output at least one control signal to the motor of the at least one electromechanical brake booster based on the target rotational speed; and specify a maximum target rotational speed of the motor of the at least one electromechanical brake booster based on at least one prevailing current strength of a motor current of the motor of the at least one electromechanical brake booster and a prevailing rotation angle of a rotor of the motor of the at least one electromechanical brake booster, wherein the target rotational speed of the motor of the at least one electromechanical brake booster is specified less than or equal to the maximum target rotational speed.

2. The control device as claimed in claim 1, the electronic device being further configured to: estimate a value for a braking force of the at least one electromechanical brake booster that is upstream of a master brake cylinder of the brake system based on the at least one prevailing current strength of the motor current of the motor and the prevailing rotation angle of the rotor of the motor, wherein the maximum target rotational speed is specified based on the estimated value for the braking force.

3. The control device as claimed in claim 2, the electronic device being further configured to: estimate a load torque, which the brake system sets against the motor of the at least one electromechanical brake booster, based on the at least one prevailing current strength of the motor current of the motor and the prevailing rotation angle of the rotor of the motor, wherein at least one of (i) the maximum target rotational speed and (ii) the estimated value for the braking force is specified based on the estimated load torque.

4. The control device as claimed in claim 3, the electronic device being further configured to: specify a motor torque of the motor of the at least one electromechanical brake booster based on the at least one prevailing current strength of the motor current of the motor; specify an angular acceleration of the rotor of the motor of the at least one electromechanical brake booster based on the prevailing rotation angle of the rotor of the motor; specify a product of the angular acceleration of the rotor of the motor of the at least one electromechanical brake booster and an inertia of the motor; and specify the load torque based on a difference between the motor torque of the motor and the product of the angular acceleration and the inertia.

5. The control device as claimed in claim 3, the electronic device being further configured to: estimate a load change of a load, which the brake system sets against the motor of the at least one electromechanical brake booster, based on the at least one prevailing current strength of the motor current of the motor and the prevailing rotation angle of the rotor of the motor, wherein at least one of (i) the maximum target rotational speed and (ii) the estimated value for the braking force is specified based on the estimated load change.

6. The control device as claimed in claim 5, the electronic device being further configured to: specify an adjustment travel of a piston of the at least one electromechanical brake booster based on the prevailing rotation angle of the rotor of the motor; specify a motor force that is exerted by the motor of the at least one electromechanical brake booster based on the load torque; specify one of (i) a time derivative and (ii) a gradient of the motor force that is exerted by the motor of the at least one electromechanical brake booster; and specify the load change as a quotient of the one of (ii) the time derivative and (ii) the gradient of the motor force divided by the adjustment travel of the piston of the at least one electromechanical brake booster.

7. The control device as claimed in claim 1, wherein the control device is a component of the at least one electromechanical brake booster.

8. A brake system for a vehicle comprising: an electromechanical brake booster; and a control device configured to operate the at least one electromechanical brake booster the control device having an electronic device configured to: specify a target rotational speed of a motor of the at least one electromechanical brake booster based on at least one brake-specifying signal that is output to the electronic device in relation to at least one of (i) a braking request of a driver of the vehicle and (ii) an automatic speed-controlling system of the vehicle; output at least one control signal to the motor of the at least one electromechanical brake booster based on the target rotational speed at; and specify a maximum target rotational speed of the motor of the at least one electromechanical brake booster based on at least one prevailing current strength of a motor current of the motor of the at least one electromechanical brake booster and a prevailing rotation angle of a rotor of the motor of the at least one electromechanical brake booster, wherein the target rotational speed of the motor of the at least one electromechanical brake booster is specified less than or equal to the maximum target rotational speed.

9. The brake system as claimed in claim 8 further comprising: a master brake cylinder, the electromechanical brake booster being upstream of the master brake cylinder.

10. A method for operating an electromechanical brake booster of a brake system of a vehicle, the method comprising: specifying a target rotational speed of a motor of the at least one electromechanical brake booster based on at least one brake-specifying signal in relation to at least one of (i) a braking request of a driver of the vehicle and (ii) an automatic speed-controlling system of the vehicle; actuating the motor of the electromechanical brake booster based on the target rotational speed; and specifying a maximum target rotational speed of the motor of the electromechanical brake booster based on at least one prevailing current strength of a motor current of the motor of the at least one electromechanical brake booster and a prevailing rotation angle of a rotor of the motor of the electromechanical brake booster, wherein the target rotational speed of the motor of the electromechanical brake booster is specified less than or equal to the maximum target rotational speed.

11. The method as claimed in claim 10 further comprising: estimating a value for a braking force of the at least one electromechanical brake booster that is upstream of a master brake cylinder of the brake system based on the at least one prevailing current strength of the motor current of the motor and the prevailing rotation angle of the rotor of the motor, wherein the maximum target rotational speed is specified based on the estimated value for the braking force.

12. The method as claimed in claim 11 further comprising: estimating at least one load torque, which the brake system sets against the motor of the at least one electromechanical brake booster, based on the at least one prevailing current strength of the motor current of the motor and the prevailing rotation angle of the rotor of the motor, wherein at least one of (i) the maximum target rotational speed and (ii) the estimated value for the braking force is specified based on the load torque.

13. The method as claimed in claim 12, the estimating the at least one load torque further comprising: specifying a motor torque of the motor of the electromechanical brake booster based on the at least one prevailing current strength of the motor current of the motor; specifying an angular acceleration of the rotor of the motor of the electromechanical brake booster based on the prevailing rotation angle of the rotor of the motor; specifying a product of the angular acceleration of the rotor of the motor of the electromechanical brake booster and an inertia of the motor; and specifying the load torque based on a difference between the motor torque of the motor and the product of the angular acceleration and the inertia.

14. The method as claimed in claim 12 further comprising: estimating at least one load change of a load, which the brake system sets against the motor of the electromechanical brake booster, based on the at least one prevailing current strength of the motor current of the motor and the prevailing rotation angle of the rotor of the motor, wherein at least one of (i) the maximum target rotational speed and (ii) the estimated value for the braking force is specified based on the at least one load change.

15. The method as claimed in claim 14, the estimating the at least one load change further comprising: specifying an adjustment travel of a piston of the electromechanical brake booster based on the prevailing rotation angle of the rotor of the motor; specifying a motor force that is exerted by the motor of the at least one electromechanical brake booster based on the at least one load torque; specifying one of (i) a time derivative and (ii) a gradient of the motor force that is exerted by the motor of the at least one electromechanical brake booster; and specifying the at least one load change as a quotient of the one of (i) the time derivative and (ii) the gradient of the motor force divided by the adjustment travel of the piston of the at least one electromechanical brake booster.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the present disclosure are explained below with the aid of the figures. In the drawings:

(2) FIGS. 1a and 1b illustrate flow diagrams for explaining an embodiment of the method for operating an electromechanical brake booster of a brake system of a vehicle; and

(3) FIG. 2 illustrates schematically an embodiment of the control device for at least one electromechanical brake booster of a brake system of a vehicle.

DETAILED DESCRIPTION

(4) FIGS. 1a and 1b illustrate flow diagrams for explaining an embodiment of the method for operating an electromechanical brake booster of a brake system of a vehicle.

(5) A capability of implementing the method described below is neither limited to a specific brake system type of the brake system that is fitted with the electromechanical brake booster nor to a specific vehicle type/motor vehicle type of the vehicle/motor vehicle that is fitted with the brake system. The term “electromechanical brake booster” is understood to mean a brake booster that is fitted with an (electric) motor. Moreover, the electromechanical brake booster is upstream of a master brake cylinder of the brake system in such a manner that at least one adjustable piston of the master brake cylinder may be adjusted/is adjusted into the master brake cylinder by means of operating the motor of the electromechanical brake booster.

(6) In the case of the method described below, in order to operate the electromechanical brake booster, a desired value ω in relation to a desired rotational speed ω of the motor of the electromechanical brake booster is specified taking into account at least one (not illustrated) brake-specifying signal in relation to a braking request of a driver of the vehicle and/or an automatic speed-controlling system of the vehicle. The method is characterized by virtue of the fact that a highest desired value ω.sub.max is specified in relation to a maximum desired rotational speed ω.sub.max of the motor of the electromechanical brake booster, wherein the desired value ω in relation to the desired rotational speed ω of the motor of the electromechanical brake booster is specified at most equal to the highest desired value ω.sub.max that is specified. (The highest desired value ω.sub.max is therefore used as the “upper limit” or as the “highest threshold” when the desired value ω is specified in relation to the desired rotational speed ω of the motor of the electromechanical brake booster.) In the case of the method described here, the desired rotational speed ω of the motor of the electromechanical brake booster is specified in an exemplary manner as the desired value ω and the maximum desired rotational speed ω.sub.max is specified as the highest desired value ω.sub.max. However, reference is made to the fact that other values that correspond to the desired rotational speed ω of the motor of the electromechanical brake booster and the maximum desired rotational speed ω.sub.max may also be specified as the desired value w and the highest desired value ω.sub.max.

(7) The highest desired value ω.sub.max is specified taking into account at least one prevailing current strength I of a motor current of the motor of the electromechanical brake booster and a prevailing rotation angle φ of a rotor of the motor of the electromechanical brake booster. Values that may be easily estimated or measured may consequently be used in order to specify the highest desired value ω.sub.max in relation to the maximum desired rotational speed ω.sub.max of the motor of the electromechanical brake booster. (The prevailing rotation angle φ of the rotor of the motor may be determined/estimated by way of example by means of a rotor position signal.) The prevailing current strength I of the motor current and the prevailing rotation angle φ of the rotor of the motor of the electromechanical brake booster are moreover values/signals having particularly high dynamics. The method described here is therefore advantageously suitable for promptly reacting to a change in a hydraulic rigidity of the brake system that interacts with the electromechanical brake booster.

(8) In the case of the embodiment of the method described here, in a partial step that is reproduced schematically by means of FIG. 1a an estimated value F.sub.estimated for a braking force of the electromechanical brake booster (upstream of the master brake cylinder of the brake system) into the master brake cylinder is estimated so as to specify the highest desired value ω.sub.max in relation to the maximum desired rotational speed ω.sub.max of the motor of the electromechanical brake booster. It is apparent that the estimated value F.sub.estimated for the braking force of the electromechanical brake booster into the master brake cylinder is estimated taking into account at least the prevailing current strength I of the motor current of the motor and the prevailing rotation angle φ of the rotor of the motor.

(9) In particular, at least one load torque/counter torque L, which the brake system sets against the motor of the electromechanical brake booster, is estimated in order to estimate the estimated value F.sub.estimated for the braking force taking into account at least the prevailing current strength I of the motor current of the motor and the prevailing rotation angle φ of the rotor of the motor.

(10) For this purpose, a motor torque M.sub.motor of the motor of the electromechanical brake booster is specified taking into account at least the prevailing current strength I of the motor current of the motor. Motor-specific data that are stored in a block 10 are taken into account in order to derive the motor torque M.sub.motor of the motor of the electromechanical brake booster from the prevailing current strength I of the motor current of the motor. The motor torque M.sub.motor of the motor of the electromechanical brake booster initiates a “dynamic of the motor” in response to a dynamic portion M.sub.dyn and initiates a “step of overcoming” the load torque/counter torque L that counteracts the motor of the electromechanical brake booster in response to a static portion M.sub.stat. The dynamic portion M.sub.dyn may be calculated as a product of an angular acceleration ω⋅ of the rotor of the motor of the electromechanical brake booster and an inertia θ of the motor of the electromechanical brake booster. The angular acceleration ω⋅ of the rotor of the motor of the electromechanical brake booster may be easily specified taking into account at least the prevailing rotation angle φ of the rotor of the motor. By way of example, the angular acceleration ω⋅ of the rotor of the motor is derived from a value that is twice the time derivative of the prevailing rotation angle φ of the rotor of the motor, said derivative being performed in a block 12. The static portion M.sub.stat of the motor torque M.sub.motor of the motor of the electromechanical brake booster therefore results from a difference between the motor torque M.sub.motor and the dynamic portion M.sub.dyn of the motor torque M.sub.motor. The load torque L that counteracts the motor of the electromechanical brake booster may subsequently be estimated taking into account the static portion M.sub.stat of the motor torque M.sub.motor of the motor of the electromechanical brake booster. By way of example, the static portion M.sub.stat may be converted using an (accordingly stored) characteristic curve and/or a filter, which is/are stored in a block 14, into the load torque L that counteracts the motor of the electromechanical brake booster. (Afterward, the estimated value F.sub.estimated may be specified for the braking force and/or the highest desired value ω.sub.max in relation to the maximum desired rotational speed ω.sub.max of the motor of the electromechanical brake booster taking into account the estimated load torque L).

(11) In the case of the embodiment described here, at least one load change C.sub.total of a load, which the brake system sets against the motor of the electromechanical brake booster, is estimated so as to specify the highest desired value ω.sub.max in relation to the maximum desired rotational speed ω.sub.max of the motor of the electromechanical brake booster or so as to estimate the estimated value F.sub.estimated for the braking force. The load change C.sub.total is likewise estimated taking into account at least the prevailing current strength I of the motor current of the motor of the electromechanical brake booster and the prevailing rotation angle φ of the rotor of the motor of the electromechanical brake booster. Afterward, the estimated value F.sub.estimated may be specified for the braking force or the highest desired value ω.sub.max in relation to the maximum desired rotational speed ω.sub.max taking into account the estimated load change C.sub.total.

(12) An adjustment travel/a translation .sub.T of a piston of the electromechanical brake booster may be specified taking into account at least the prevailing rotation angle φ of the rotor of the motor. For example, an angular velocity ω of the rotor of the motor is derived by means of a time derivative of the prevailing rotation angle φ of the rotor of the motor of the electromechanical brake booster, said derivative being performed in a block 16. A transmission value r of a transmission of the electromechanical brake booster is stored in a block 18 and the angular velocity ω of the rotor of the motor is converted by means of said transmission value into the adjustment travel/the translation .sub.T of the piston of the electromechanical brake booster, said piston being arranged downstream of the transmission. The piston that is arranged downstream of the transmission may be for example a valve body or a boost body of the electromechanical brake booster.

(13) A motor force/supporting force F.sub.sup that is exerted by means of the motor of the electromechanical brake booster is specified taking into account the load torque L. By way of example, the transmission value r of the transmission of the electromechanical brake booster and an efficiency η of the electromechanical brake booster are stored in a block 20. A motor force/supporting force F.sub.sup that is exerted by means of the motor of the electromechanical brake booster may be derived from the load torque L by means of these values. Moreover, a time derivative/a gradient Fsup⋅ of the motor force/supporting force Fsup that is exerted by means of the motor of the electromechanical brake booster is determined in a block 22.

(14) In a further block 24, a quotient C.sub.total is calculated from the time derivative/the gradient Fsup. divided by the adjustment travel/the translation .sub.T of the piston of the electromechanical brake booster, said quotient indicating the load change C.sub.total The load change C.sub.total may also be described as a rigidity (stiffness).

(15) The load change C.sub.total is output to a block 26 in which the inertia θ of the motor of the electromechanical brake booster and the transmission value r of the transmission of the electromechanical brake booster are stored. A dynamic force F.sub.dyn that is exerted by means of the electromechanical brake booster may therefore be calculated from the load change C.sub.total. The dynamic force F.sub.dyn that is to be exerted by means of the electromechanical brake booster may also be described as a “force from a kinetic energy” of the rotor of the motor of the electromechanical brake booster.

(16) The estimated value F.sub.estimated for a braking force (or “pressure increasing force”) of the electromechanical brake booster, with which the electromechanical brake booster brakes into the master brake cylinder and initiates/increases the master brake cylinder pressure that is present therein, may be calculated from a sum of the motor force/supporting force F.sub.sup that is exerted by means of the electromechanical brake booster and the dynamic force F.sub.dyn that is exerted by means of the electromechanical brake booster. A (not illustrated) frictional correction may also be optionally performed for the estimated value F.sub.estimated for the braking force.

(17) The partial steps that are described in the above paragraphs offer a particularly advantageous possibility that may be rapidly performed for reliably estimating the estimated value F.sub.estimated for the braking force. However, a capability of implementing the method is not limited to these partial steps. The highest desired value ω.sub.max is subsequently specified taking into account the estimated value F.sub.estimated for the braking force. This is illustrated by means of the method step that is represented schematically in FIG. 1b:

(18) Initially, a difference ΔF is determined between the estimated value F.sub.estimated for the braking force of the electromechanical brake booster into the master brake cylinder, said estimated value being specified by means of the above-described method step, and a predetermined comparison force F.sub.0. (It is possible by means of the comparison force F.sub.0 to investigate whether the prevailing pending braking force is too high by precisely the estimated value F.sub.estimated) The difference ΔF is subsequently output in a block 28 in which the inertia θ of the motor of the electromechanical brake booster, the transmission value r of the transmission of the electromechanical brake booster and the load change C.sub.total are present, is converted into a speed value v.sub.Δ.

(19) A starting value ω.sub.0 in relation to a starting rotational speed ω.sub.0 of the motor of the electromechanical brake booster is specified taking into account at least the (not illustrated) brake-specifying signal (in relation to the braking request of the driver of the vehicle and/or the automatic speed-controlling system of the vehicle). The starting value ω.sub.0 in relation to the starting rotational speed ω.sub.0 of the motor is converted into a starting speed v.sub.0 in a block 30 in which the transmission value r of the transmission of the electromechanical brake booster is stored. Afterward, a minimum v.sub.min is determined from the starting speed v.sub.0 and a prevailing speed v. A limit speed v.sub.limit is determined as the difference between the minimum v.sub.min and the speed value v.sub.Δ. The limit speed v.sub.limit is converted into a limit value ω.sub.limit by means of the transmission value r of the transmission of the electromechanical brake booster, said transmission value being stored in a block 32. The limit value ω.sub.limit indicates a rotational speed with which the motor of the electromechanical brake booster may also be operated without any problems with regard to the prevailing hydraulic rigidity of the brake system.

(20) If the difference ΔF between the estimated value F.sub.estimated for the braking force and the comparison force F.sub.0 is greater than 0, it is dictated to a block 36 by means of a signal 34 to assume the limit value ω.sub.limit that is output to said block as the highest desired value ω.sub.max. Moreover, the block 36 is activated by means of the signal 34 so as to limit the desired value ω by means of the highest desired value ω.sub.max. In this case, the block 36 outputs a minimum from the starting value ω.sub.0 and the highest desired value ω.sub.max as the desired value ω. If the difference ΔF between the estimated value F.sub.estimated for the braking force and the comparison force F.sub.0 is less than 0, the signal 34 is thus not output to the block 36. The desired value w is therefore specified as identical to the starting value ω.sub.0. (The highest desired value ω.sub.max therefore corresponds to a rotational speed that may be executed maximally by means of the motor of the electromechanical brake booster.) In both cases, the desired value ω in relation to the desired rotational speed ω of the motor of the electromechanical brake booster (for actuating the motor of the electromechanical brake booster) is consequently specified at most equal to the highest desired value ω.sub.max that is specified.

(21) After the desired value ω is specified in relation to the desired rotational speed ω of the motor of the electromechanical brake booster, the motor of the electromechanical brake booster is actuated taking into account the desired value ω that is specified. It is preferred that this is performed in such a manner that during the resulting operation of the electromechanical brake booster an actual rotational speed of the motor of the electromechanical brake booster does not exceed the desired value ω that is previously specified (or the corresponding desired rotational speed ω).

(22) The method described here initiates a limitation of the operation of the electromechanical brake booster in such a manner that even in the event of load changes owing to an altered hydraulic rigidity of the brake system, fears of an excess pressure or of pressure spikes therein are unfounded. In addition to preventing a brake system overload however it is possible by means of the method described here to also rule out braking procedures that are insufficiently intense. Furthermore, in the case of the method described here it is possible to react promptly to wheel inlet valves of the brake system being (actually) closed, wherein however it is simultaneously ensured that the corresponding reduction of the operation of the motor of the electromechanical brake booster only occurs after the wheel inlet valves have actually closed. The method described here consequently not only initiates a limitation of the operation of the motor of the electromechanical brake booster so as to preserve the brake system that cooperates with said brake booster but said method also ensures by means of the electromechanical brake booster furthermore that a significant brake boosting procedure may be initiated in such situations in which this is not crucial.

(23) In conclusion, further reference is made to the fact that the partial steps that are illustrated in FIGS. 1a and 1b may be performed more rapidly than a data transfer/signal transfer via a data bus of a measured value that is measured by means of at least one pressure sensor. An implementation of the method described here consequently renders it possible to “predict” a change in the hydraulic rigidity of the brake system (with respect to measuring the change in the hydraulic rigidity of the brake system).

(24) FIG. 2 illustrates schematically an embodiment of the control device for at least one electromechanical brake booster of a brake system of a vehicle.

(25) A capability of using the control device 50 that is described below is neither limited to a specific brake system type of the brake system nor to a specific vehicle type/motor vehicle type of the vehicle/motor vehicle that is fitted with the brake system. Reference is made to the above description in relation to the electromechanical brake booster 52 that cooperates with the control device 50. The electromechanical brake booster 52 is upstream of the master brake cylinder 60 of the brake system.

(26) The control device 50 comprises an electronic device 54 that is designed for the purpose of specifying at least one desired value ω in relation to a desired rotational speed ω of a motor of the electromechanical brake booster taking into account at least one brake-specifying signal 56 that is output to the electronic device 54 in relation to a braking request of a driver of the vehicle and/or a (not illustrated) automatic speed-controlling system of the vehicle. Moreover, the electronic device 54 is designed for the purpose of outputting at least one control signal 58 to the motor of the electromechanical brake booster 52 taking into account the desired value ω that is specified, or for the purpose of operating the electromechanical brake booster 52. It is preferred that the at least one control signal 58 is output to the motor of the electromechanical brake booster 52 in such a manner that during the resulting operation of the electromechanical brake booster 52 an actual rotational speed of the motor of the electromechanical brake booster 52 does not exceed the desired value ω that is previously specified (or the corresponding desired rotational speed ω).

(27) Moreover, the electronic device 54 is designed for the purpose of specifying a highest desired value ω.sub.max in relation to a maximum desired rotational speed ω.sub.max of the motor of the electromechanical brake booster 52 taking into account at least one prevailing current strength I of a motor current of the motor of the electromechanical brake booster 52 and a prevailing rotation angle φ of a rotor of the motor of the electromechanical brake booster 52 and for the purpose of specifying the desired value ω in relation to the desired rotational speed ω of the motor of the electromechanical brake booster 52 at most equal to the highest desired value ω.sub.max that is specified.

(28) The use of the control device 50 consequently also brings about the advantages already described above. The electronic device 54 may in addition be embodied so as to implement at least one of the method steps that are described above.