Method for controlling a brake booster of a hydraulic auxiliary vehicle braking system

Abstract

Method for controlling a brake booster (1) of a hydraulic auxiliary vehicle braking system, which has a muscle-operated master brake cylinder and a controllable brake booster (1) which exerts an auxiliary force on the master brake cylinder in addition to the muscle force when the brake is applied, characterized in that the auxiliary force of the brake booster (1) is controlled as a function of a relative movement between a brake pedal (5) and / or a piston rod (3) and a movement of a booster body (9) of the brake booster (1).

Description

State of the art

[0001] The invention relates to a method for controlling a brake booster of a hydraulic auxiliary vehicle braking system with the features of the preamble of claim 1. The terms control, control, etc. are also used here in the sense of regulation, control, etc.

[0002] Modern motor vehicles are typically equipped with hydraulic braking systems featuring a manually operated master cylinder and a vacuum brake booster. Manual operation is achieved either by foot using a brake pedal or by hand using a brake lever. The brake booster provides an additional force to the master cylinder, supplementing the driver's effort. This force is actually applied to a piston, specifically a primary piston, rather than the master cylinder itself. The driver's effort and the booster's force combine to create an actuating force that acts upon the master cylinder and its piston. For simplicity, we will refer to this as the actuation or application of force to the master cylinder.Because part of the actuating force exerted on the master brake cylinder is applied by the driver as muscle force, and the remaining part is the auxiliary force generated by the brake booster, such vehicle braking systems are referred to as power-assisted braking systems. The auxiliary force of a vacuum brake booster, or the force amplification—that is, the ratio of actuating force to muscle force—is controlled by a servo valve that vents the so-called working chamber of the brake booster. The servo valve is controlled by a relative movement between a piston rod, which is articulated to the brake pedal, and a working piston of the brake booster, ultimately by pedal travel and / or pedal force. Pedal travel is the distance traveled by the brake pedal or piston rod and will subsequently also be referred to as actuating travel. Pedal force is the force applied to the brake pedal.The piston rod is controlled by the muscle force exerted. The control of the brake booster's auxiliary force, or the force amplification, therefore depends on the actuation distance and / or the muscle force exerted by the driver.

[0003] Electromechanical brake boosters are also known. These can also be considered electromechanical actuators, which generate the auxiliary force for actuating the master brake cylinder electromechanically, in addition to the muscle force exerted by the driver. For example, reference is made to German patent application DE 100 57 557 A1, which discloses an electromechanical brake booster with a linear motor or an electromagnet. It is also possible to generate the auxiliary force with an electric motor via a gearbox. The control of the auxiliary force of the known electromechanical brake booster depends on a pedal travel, referred to here as the actuation travel, and / or on a pedal force, referred to here as the muscle force. To measure the pedal travel or actuation travel and / or the muscle force, the known electromechanical brake booster has a displacement sensor and a force sensor.A distinction must be made here between the actuation travel, namely the pedal travel or the travel of the piston rod, on the one hand, and the actuation force on the other, which is the sum of the muscle force exerted by the driver to actuate the brakes and the auxiliary force generated by the brake booster, both acting together on the master cylinder or its piston. The actuation travel, i.e., the travel of the brake pedal or the piston rod connected to it by a joint, does not necessarily equal the piston travel, i.e., the displacement of the piston in the master cylinder, because the piston rod can move relative to the piston.

[0004] Patent application FR 2 860 474 A1 also discloses an electromechanical brake booster, but with a hollow shaft motor instead of a linear motor, which couples an auxiliary force to a piston rod via a ball screw drive. Muscle force is transmitted from a pedal rod via a sliding disc and a helical compression spring to an auxiliary piston, the helical compression spring being supported against an annular force sensor. Disclosure of the invention

[0005] The inventive method with the features of claim 1 provides for controlling the auxiliary force of the brake booster or its amplification factor as a function of a quantity that is neither the actuation distance of, for example, the brake pedal or piston rod nor the muscle force, but rather a relative movement between a brake pedal or piston rod and a movement of an amplifier element of the brake booster. The invention enables hysteresis-free brake actuation or the selection of hysteresis, which can be variable. Hysteresis means that the auxiliary force of the brake booster differs at a specific brake pedal position, depending on whether the brake is applied or released.

[0006] The hysteresis of the vehicle's braking system can be controlled by software, allowing for easy modification and adaptation to different vehicles. Hysteresis can also be easily controlled based on the type of brake application, such as the speed of application and / or the vehicle's driving conditions.

[0007] Other factors on which the control of the brake booster's auxiliary force may depend include, for example, the direction of actuation (i.e., actuation or release of the vehicle's braking system), the time since a reversal of the direction of actuation, and / or, as already mentioned, the actuation speed.

[0008] The auxiliary force of the brake booster can also be controlled in such a way as to compensate for hysteresis of the vehicle braking system (e.g. due to friction of mechanical components).

[0009] Instead of or in addition to the aforementioned parameters that act on the vehicle braking system during brake application, the control of the brake booster can also be controlled depending on a driving condition of a vehicle equipped with the vehicle braking system (claim 5). Such driving conditions can include vehicle speed, cornering, and / or forward and reverse travel. The auxiliary force of the brake booster, and thus its amplification factor and / or hysteresis, can be made dependent on high and low speed, walking speed (maneuvering / parking), and cornering speed using the method according to the invention. The cornering speed can be determined, for example, by a rotational accelerometer used for vehicle dynamics control (FDR, ESP; stability control).

[0010] Instead of or in addition to the aforementioned parameters of brake actuation or a vehicle's driving condition, the control of the brake booster can also be based on driver settings, e.g., setting a transmission and / or chassis characteristic (e.g., comfort- or sport-oriented) or based on adaptation algorithms of the braking system or other vehicle systems that evaluate the driver's driving style (e.g., gradient of accelerator pedal actuation).

[0011] Preferably, but not necessarily, the auxiliary force of the brake booster is also controlled depending on the actuation distance and / or the muscle force exerted by a driver to actuate the brakes, as is known per se. This is the subject of claim 5.

[0012] The controllability of the brake booster according to the invention is not possible with a conventional vacuum brake booster that has a servo valve controlled by the pedal rod. Instead of the servo valve, or preferably in addition to it, a controllable valve, for example a solenoid valve, and for better controllability, in particular a proportional valve, is necessary. Claim 7 provides an electromechanical brake booster that inherently possesses the required controllability by design. Brief description of the drawing

[0013] The invention is explained in more detail below with reference to an embodiment illustrated in the drawing. The drawing shows: Fig. 1 an axial section of an electromechanical brake booster for carrying out the method according to the invention; Fig. 2 a flowchart of an embodiment of the method according to the invention; and Fig. 3 a pedal characteristic curve according to the method according to the invention.

[0014] The drawing is to be understood as a schematic and simplified representation for the purpose of understanding and explaining the invention. embodiment of the invention

[0015] The in Fig. The brake booster 1 shown is an electromechanical brake booster 1 with an electromechanical actuator 2 (to be explained later) and a piston rod 3, which is articulated to a brake pedal 5. Furthermore, the brake booster 1 has a push rod 7 with a piston-shaped foot 6, with which a primary or rod piston (not shown) of a hydraulic master brake cylinder (also not shown) of a hydraulic vehicle brake system can be actuated with a force in a manner known per se.

[0016] The actuator 2 has an amplifier body 9, which in the illustrated embodiment is cylindrical and has an axial through-hole 10 in which the piston rod 3 is axially displaceable. The through-hole 10 of the amplifier body 9 opens into a cylindrical recess 11, which has a larger diameter than the through-hole 10 and in which the foot 6 of the push rod 7 is axially displaceable. The amplifier body 9, like the piston rod 3 and the push rod 7, is axially displaceable, which is symbolically represented in the drawing by a rolling bearing on the underside of the amplifier body 9.

[0017] An elastic reaction disk 8 is arranged between the foot 6 of the pushrod 7 and a base 12 of the recess 11. The reaction disk 8 is subjected in its center by the piston rod 3 to a muscle force exerted on the brake pedal 5 by a driver, and in a ring-shaped manner around the piston rod 3 by the base 12 of the recess 11 of the amplifier body 9 to an auxiliary force generated electromechanically by the actuator 2. The reaction disk 8 sums the muscle force and the auxiliary force into an actuating force and transmits it to the foot 6 of the pushrod 7, which in turn, as already mentioned, acts on the primary or rod piston of the master brake cylinder (not shown). Due to its elasticity, the reaction disk 8 compensates to a limited extent for relative displacements between the piston rod 3 and the amplifier body 9. When the reaction disk 8 is acted upon by the amplifier body 9, it bulges in its center as shown in the diagram. Fig. The reaction disc 8, indicated by dashed lines, extends into the through-hole 10 of the amplifier body 9 until it abuts the end of the piston rod 3 facing it. In doing so, the reaction disc 8 closes a gap, here designated as the guide path d, between itself and the piston rod 3, so that the muscle force is transferred from the piston rod 3 to the foot 6 of the push rod 7. The recess 11 of the amplifier body 9 encompasses the reaction disc 8 like a socket, thereby preventing or at least limiting its radial expansion.

[0018] For drive, the actuator 2 has an electric motor 14, which drives the amplifier body 9 axially via a gear 15. The gear 15 meshes with a rack 16 of the amplifier body 9. A reduction gear (not shown) can be interposed between the gear 15 and the electric motor 14. Instead of an electric motor drive, the electromechanical actuator 2 can also have, for example, an electromagnetic drive or a linear motor (not shown).

[0019] The electromechanical brake booster 1 has a displacement sensor 17, which measures the displacement, and thus also the velocity and acceleration, of the booster body 9, and a position sensor 18, which measures the relative movement, i.e., the displacement of the piston rod 3 relative to the booster body 9. Furthermore, a displacement sensor 19 may be present for measuring the displacement of the piston rod 3, i.e., for measuring the pedal travel of the brake pedal 5, and a force sensor 20 for measuring the muscle force exerted on the brake pedal 5. The displacement of the piston rod 3 and the pedal travel of the brake pedal 5 are also referred to here as the actuation travel.An electronic control unit 21 receives the signals from sensors 17, 18, 19, and 20 and controls the electric motor 14, thereby controlling the displacement of the amplifier body 9 and the auxiliary force generated by the actuator 2 of the brake booster 1 and transmitted via the reaction disk 8 to the foot 6 of the pushrod 7. Instead of the position sensor 19 for pedal travel, a rotary angle sensor can also be provided on the electric motor 14 (not shown). Certain motor types, for example, electronically communicated electric motors, provide a rotary angle signal, so that no special sensor is necessary.

[0020] To apply the brakes, the brake pedal 5 is pressed as usual. The position sensor 18 measures the displacement of the piston rod 3 relative to the booster body 9 and energizes the electric motor 14 so that the booster body 9 moves in the same direction as the piston rod 3, i.e., in the direction of the pushrod 7, as in the case of brake application. The displacement between the piston rod 3 and the booster body 9 is regulated to zero during brake application, meaning the booster body 9 moves synchronously with the piston rod 3. Due to the gap d between the piston rod 3 and the reaction disk 8, the brake pedal 5 initially moves almost without force along with the piston rod 3; the actuating force exerted on the pushrod 7 is solely the auxiliary force of the actuator 2 or the brake booster 1.Under load, the reaction disc 8 deforms elastically in its center, as previously described, into the through-hole 10 of the amplifier body 9 until it abuts the end of the piston rod 3 facing it. From the moment the reaction disc 8 contacts the piston rod 3, or vice versa, the reaction disc 8 transmits the muscle force from the piston rod 3 to the push rod 7, in addition to the auxiliary force of the amplifier body 9 of the actuator 2. The muscle force is felt at the brake pedal 5 and must be applied to the brake pedal 5. In the described case, the control variable is the displacement of the piston rod 3 relative to the amplifier body 9. However, it is also possible, either additionally or instead, to control the actuator 2 and thus the brake booster 1, depending on other variables such as the muscle force applied to the brake pedal 5 or the pedal travel (actuation distance).

[0021] According to one embodiment of the method according to the invention, in a first step the direction of movement of the piston rod 3 or the brake pedal 5 is determined. In other words, it is determined whether the brake is being applied or released. In the flowchart of the Fig. 2. The direction of movement is determined by querying V. Ped ≥0 is queried, where V Ped The pedal speed is V. Ped If the value is >0, i.e., the brake is applied, the displacement of the piston rod 3 relative to the amplifier body 9 is checked in the next process step. If the displacement x > 0, i.e., the piston rod 3 is displaced further than the amplifier body 9, the auxiliary force F BoostThe force of actuator 2, and thus of the brake booster 1, is increased to reduce the displacement of the piston rod 3 relative to the booster body 9. The query, i.e., the inventive method, then begins anew; the method is continuously repeated. The subscript "Boost" for the auxiliary force stands for "booster," i.e., amplifier. If, in the second process step, the displacement of the piston rod 3 is not greater than that of the booster body 9, the auxiliary force F is increased. Boost not increased. If the first query determines that the pedal speed V PedIf the brake is released, i.e., the pressure is negative, a second check is performed to determine whether the displacement x of the piston rod 3 relative to the amplifier body 9 is less than a hysteresis value c, where the hysteresis value c is selectable and, in embodiments of the method according to the invention, modifiable. The hysteresis value c is initially assumed to be negative, thus defining a hysteresis. Hysteresis means that the displacement of the piston rod 3 relative to the amplifier body 9 differs when the brake is applied compared to when the brake is released. Up to this point, the displacement of the piston rod 3 relative to the amplifier body 9 when the brake is applied has been assumed to be zero. When the brake is released, the piston rod 3 moves relative to the amplifier body 9, leading by the hysteresis value c.The hysteresis value c is negative because the piston rod 3 leads the amplifier 9 in the direction of brake release, i.e., opposite to the direction of actuation, which, at least here, has a positive sign. Therefore, if, in the second process step, the displacement x of the piston rod 3 relative to the amplifier body 9 is greater than the hysteresis value c when the brake is released, the auxiliary force F... Boost The force of actuator 2, and thus of brake booster 1, is reduced so that the overrun of the booster body 9 relative to the piston rod 3 when the brake is released does not exceed the hysteresis value c. Otherwise, the auxiliary force F remains constant. Boost unchanged.

[0022] The hysteresis value c can also be chosen to be positive, which results in a lead of the piston rod 3 relative to the amplifier body 9, i.e. a displacement of the piston rod 3 in the direction of actuation onto the reaction disk 8 and the foot 6 of the push rod 7 relative to the amplifier body 9 when the brake is actuated.

[0023] Apart from the direction of movement of the piston rod 3 and the brake pedal 5, the hysteresis value c can depend on other parameters of the brake actuation, such as the actuation speed and the muscle force exerted on the brake pedal 5, and / or the displacement of the piston rod 3, i.e., the pedal travel 5. The hysteresis value c can depend on one, several, or all of the aforementioned parameters and possibly other parameters as well. Furthermore, the hysteresis value c can depend on parameters not directly related to the brake actuation, in particular on the driving conditions of a vehicle equipped with the vehicle braking system. Such parameters include, for example, the vehicle speed, cornering, and / or forward or reverse travel. The auxiliary force F can be determined using the method according to the invention. BoostThe brake booster 1 controls and regulates the force amplification and pedal response curve as a function of various parameters related to brake application and / or reflecting driving conditions. The magnitude of the displacement, i.e., the hysteresis, can change with the pedal travel. A change in the hysteresis value c is also possible when the brake is applied and released; for example, a positive hysteresis value c when the brake is applied and a negative hysteresis value c when the brake is released.

[0024] Fig. Figure 3 shows a pedal characteristic curve when the brake booster 1 is controlled according to the method according to the invention. The pedal characteristic curve is the relationship between the muscle force exerted on the brake pedal 5, which is also generally referred to as pedal force, and the pedal travel or the displacement of the piston rod 3. The muscle force is in Fig. 3 on the ordinate and marked with F PedThe pedal travel is plotted on the abscissa and labeled s. It can be seen that the pedal characteristic curve has a different shape when the brake is applied than when it is released; when the brake is applied, the muscle force F to be exerted on the brake pedal 5 is shown. Ped The hysteresis is greater at a specific pedal position than when the brake is released. If the brake is only partially released and then reapplied, the pedal characteristic curve reverts from its behavior when the brake is released to its behavior when the brake is applied. As explained, the shape of the pedal characteristic curve and the hysteresis can change depending on various factors, and changes can even occur during braking.

Claims

[1] Method for controlling a brake booster (1) of a hydraulic auxiliary vehicle braking system comprising a muscle-operated master brake cylinder and a controllable brake booster (1) which, when the brakes are applied, exerts an auxiliary force in addition to the muscle force on the master brake cylinder, characterized by , that the auxiliary force of the brake booster (1) is controlled as a function of a relative movement between a brake pedal (5) and / or a piston rod (3) and a movement of a booster body (9) of the brake booster (1). [2] Method according to claim 1, characterized by , that the brake booster (1) is controlled such that a pedal characteristic curve exhibits hysteresis. [3] Method according to claim 1, characterized by , that the brake booster (1) is controlled in such a way as to compensate for hysteresis of the vehicle braking system [4] Method according to claim 1, characterized by, that the parameter for controlling the brake booster (1) is a driving condition of a vehicle equipped with the vehicle braking system. [5] Method according to claim 1, characterized by , that the auxiliary force of the brake booster (1) is controlled depending on the size and depending on the actuation distance and / or the muscle force. [6] Method according to claim 1, characterized by , that the vehicle braking system has an electromechanical brake booster (1).

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