DE102022200191B4 - Brake pedal system, brake-by-wire braking system and motor vehicle - Google Patents

Abstract

Brake pedal system (2) for a motor vehicle, with a brake pedal (4) that can be pivoted about a pedal axis (14), and with a brake force simulator (6) that has an elastic element (32) that imparts a counterforce to the brake pedal (4) when the brake pedal (4) is actuated, wherein the brake force simulator (6) has a transmission lever (26) that interacts with the brake pedal (4) and is mounted so that it can be pivoted about a lever axis (30) such that actuation of the brake pedal (4) leads to a deflection of the elastic element (32), wherein when the brake pedal (4) is actuated, a contact element (18) arranged on the brake pedal (4) moves along a contact surface (38) of the transmission lever (26) that runs parallel to the lever axis (30), and wherein the contact surface (38) is designed such that the contact surface (38) has at least one axis that can be pivoted about a direction that runs parallel to the lever axis (30). curved section (40, 42, 44), characterized in that the contact surface (38) is arranged on a side of the transmission lever (26) opposite the pedal axis (14).

Description

The invention relates to a brake pedal system for a motor vehicle, with a brake pedal that can be pivoted about a pedal axis, and with a brake force simulator that has an elastic element that imparts a counterforce to the brake pedal when the brake pedal is actuated, wherein the brake force simulator has a transmission lever that interacts with the brake pedal and is mounted so that it can pivot about a lever axis such that actuation of the brake pedal leads to a deflection of the elastic element, wherein when the brake pedal is actuated, a contact element arranged on the brake pedal moves along a contact surface of the transmission lever that runs parallel to the lever axis, and wherein the contact surface is designed such that the contact surface has at least one section that is curved in a direction parallel to the lever axis. The invention further relates to brake-by-wire brake systems and to a motor vehicle with such a brake pedal system.

Such brake pedal systems are becoming increasingly important, particularly in connection with vehicles designed for autonomous driving and in the context of electromobility. Particularly in motor vehicles in which there is no longer a mechanical connection to the brake pedal in the braking system - so-called brake-by-wire systems - it is desirable to adapt the counterforce acting on the brake pedal during braking to the behavior of a conventional motor vehicle with a direct connection between the brake pedal and the wheel brakes. The brake-by-wire systems can also have a hydraulic component up to the wheel brakes or can be completely dry, i.e. without any hydraulic components at all.

In motor vehicles, and in particular in automobiles, the driver's braking request is usually implemented using a brake pedal. The historical standard is to provide a mechanical link between the brake pedal and the actual braking device that brakes the wheels. Various brake boosters are known to assist the driver. For safety reasons, however, there is usually still a mechanical connection between the brake pedal and the brake, so that the brake can still be operated even if the brake booster is defective.

In the future, particularly in connection with autonomous vehicles, systems will increasingly be used in which the previously described mechanical coupling between the brake pedal and the brake is eliminated. With such a system, the driver does not receive any haptic feedback from the brake pedal, since only the position of the brake pedal is used to identify the braking request and the further process of braking is electrified and takes place independently of the brake pedal. The braking process desired by the user is therefore determined by sensors that directly or indirectly detect the current position of the brake pedal and is used via suitable electronics to control servo motors, which then in turn carry out the actual braking process and brake the wheels to be braked.

It has been shown that haptic feedback from the vehicle regarding various parameters such as surface conditions, vehicle speed, current steering angle and also a current braking process is important for the driver's assessment of the driving situation and is therefore also relevant to safety. It also has a positive influence on the purchase decision if the vehicle's handling differs as little as possible from the handling of familiar vehicles. It is therefore desirable to replicate the reaction of a conventional brake pedal as accurately as possible.

For example, from the DE 299 21 027 U1 A brake pedal system and brake-by-wire braking system of the type mentioned above is known. A brake pedal is connected to a control and power unit via a simulator. The control and power unit controls lines of the electric wheel brakes, for which purpose it receives position and force signals from a measuring device that is connected to the simulator. The simulator has a damper unit with a working piston that is connected to a piston rod, which in turn is connected to the brake pedal. Two working chambers are filled with hydraulic oil and separated from each other by the working piston. The simulator has an inner and an outer spring element.

From the CN 2 07 842 910 U A brake pedal is known in which a first spring, which is stretched when the brake pedal is operated, is attached to the brake pedal itself, and a second spring is compressed by a cam, which is arranged on a shaft that rotates when the brake pedal is operated, in such a way that the second spring also generates a counterforce on the brake pedal. The two independent springs can be used to create different characteristics for the counterforce.

The current connection of the brake booster on the engine-side bulkhead to the brake pedal in the passenger compartment according to the state of the art causes an unfavorable block dimension for displacement into the passenger compartment in the event of a crash and thus a high risk of injury. By loosening the mechanical connection between the brake pedal and the brake booster, new possibilities arise for cleaning up the engine system and reducing intrusions into the passenger compartment. An improved brake pedal system would therefore be an essential necessary step towards autonomous driving at levels 4 and 5.

From the US 2009 / 0 000 418 A1 A pedal device for a vehicle is known which makes it possible to reduce driver fatigue by reducing the pedal effort required when operating the pedal arm and which enables the driver to easily recognize the maximum operating position of the pedal arm.

The DE 198 36 691 A1 describes a pedal, in particular for electrically actuated motor vehicle brakes, with a pedal body that can be moved in the actuation direction and is subject to the force of a spring acting as a return means that counteracts the actuation direction. The pedal actuation characteristics are to be improved using simple means in that the spring preferably has a linear characteristic curve and the pedal body has contact means, the contact means converting at least one linearly increasing actuation travel increment into progressively increasing spring travel increments and impressing them on the adjacent spring.

The EN 10 2012 217 541 A1 discloses a clutch pedal device whose progression of the pedal force over the pedal travel has a section with a positive gradient and then a section with a negative gradient. This results in a pedal feel that is very similar to the pedal feel when operating a conventional clutch pedal that hydraulically operates the clutch. It is provided that the pedal arm acts on a pivotally mounted lever arm that is subjected to a counterforce and is moved on a contour of the lever arm when the clutch pedal is operated.

It is therefore an object of the present invention to improve a brake pedal system in such a way that the restoring force can be adapted with high precision to the behavior of a conventional brake pedal system. Furthermore, it is an object of the present invention to provide a device that is as compact as possible and requires little installation space.

The object is achieved according to the invention by a brake pedal system of the type mentioned at the outset, in which the contact surface is arranged on a side of the transmission lever opposite the pedal axis. The object is further achieved by a brake-by-wire braking system with a brake pedal system according to the invention and a brake, wherein the brake-by-wire braking system further comprises a control unit which is connected to a sensor of the brake pedal system, and wherein the control unit is designed to control the brake according to measured values of the sensor. The object is also achieved by a motor vehicle with a brake pedal system according to the invention.

The brake pedal system according to the invention has the advantage that a desired characteristic curve for the counterforce acting on the brake pedal can be set as a function of the deflection of the brake pedal by means of a targeted design of the contact surface. In contrast to systems that work with one or two spring elements, for example, but which are each deflected at a constant rate over the entire deflection of the brake pedal, the characteristic curve can be set almost as desired. The deflection rate of the elastic element then depends on the local curvature or the gradient of the contact surface.

A transmission lever is understood to mean, in particular, a lever-like element that transmits the movement of the brake pedal to the elastic element. The transmission lever can in particular be designed in such a way that the deflection rate of the elastic element changes over the range of movement of the brake pedal.

In the context of this description, the deflection rate is understood to mean in particular a ratio between a deflection difference of the elastic element and a deflection difference of the brake pedal. If a change in the angular coordinate of the brake pedal by a certain amount results in a large change in the deflection of the elastic element, the deflection rate in this area is also large. If a change in the angular coordinate of the brake pedal by a certain amount results in a small change in the deflection of the elastic element, the deflection rate in this area is also small. In colloquial terms, the deflection rate can be interpreted as the speed at which the elastic element is deflected, i.e. stretched or compressed.

In the context of the present description, the fact that a section of the contact surface is curved in a direction parallel to the lever axis is understood in particular to mean that the section at least approximately follows the shape of the Surface of a part of the lateral surface of a cylinder or a prism with an ellipsoidal base.

For this purpose, a deflection or an angular position of the brake pedal can be assigned to each point along a surface direction of the contact surface. The contact surface is usually aligned parallel to the lever axis. The lever axis is in turn usually aligned parallel to the pedal axis. In order to achieve the desired characteristic curve, the contact surface can be curved or flat in sections. Different gradients along the surface direction then result in different deflection speeds of the elastic element, which depend on the gradient at the current position of the contact element on the contact surface, and thus a dynamic change in the counterforce on the brake pedal felt by the user.

In the context of the present description, the surface direction is understood to mean in particular a reference direction that extends along a longitudinal axis of the transmission lever. For example, the surface direction can be defined as a connection between the lever bearing and the fastening point at which the elastic element is connected to the transmission lever. The gradient along the surface direction then corresponds to a gradient in an imaginary diagram whose x-axis is the surface direction. In other words, the gradient describes the angle between a section of the contact surface and the surface direction.

By using the transmission lever according to the invention, a characteristic curve or a path-force curve can be generated that can be very closely approximated to a conventional brake pedal with a mechanical connection to the brake system. The contact surface can be shaped in such a way that its cross section corresponds to a curved path. This curved path can be designed similarly to a cam on a camshaft. The path-force curve can then be designed over a large area. In the acceleration area, a small counterforce can be applied to the brake pedal, which increases progressively towards the end of the pedal travel. Here, the desired characteristic can be designed in all variations using the transmission lever in a comfortable and space-saving manner. Additional springs can be integrated, which can be designed as simple compression springs or as leaf springs. The integration of progressively wound springs is also possible. In summary, in this invention, the force-path characteristic is produced using a roller or a sliding piece in combination with a curved path on a transmission lever and in combination with any elastic elements, for example with springs. Furthermore, at least two sensors can be integrated into the brake pedal system to ensure redundant transmission of the movement.

According to a further development of the invention, the contact surface is arranged on a side of the transmission lever opposite the pedal axis. In other words, the transmission lever then partially covers the brake pedal, viewed in a direction parallel to the lever axis. The brake pedal can have a flat support portion that projects beyond a pedal body and carries the contact element. The entire brake pedal can be roughly T-shaped, with the foot of the T corresponding to the foot part of the brake pedal or the actuating element. The pivot bearing of the brake pedal and thus the pedal axis is then arranged in the area of one of the two outer ends of the crossbar of the T, and the contact element is arranged in the area of the other end of the crossbar of the T. The contact element extends in a direction parallel to the pedal axis and parallel to the lever axis.

According to an advantageous embodiment, the contact surface has a gradient that changes several times along the contact surface in a direction extending perpendicular to the lever axis. The change in the gradient can in particular be continuous. In other words, the contact surface can have a different curvature in different areas.

The contact element can advantageously be a roller mounted so that it can rotate about a roller axis. The roller axis is preferably aligned parallel to the lever axis. Alternatively, it is also possible for the contact element to be a sliding element that slides along the contact surface when the brake pedal is actuated.

A particularly practical design is when the elastic element is a spring that is compressed when the brake pedal is pressed. Such a design is easy to implement and can be made compact. Furthermore, another setting parameter for the desired characteristic curve is obtained by selecting the spring constant of the spring accordingly.

A particularly compact brake pedal system is achieved when the elastic element is arranged above the pedal axis in the vertical direction. It is also advantageous in terms of a compact design of the brake pedal system if a longitudinal axis of the elastic element is tical element extends essentially in one direction of travel. It is then possible to make the end of the transmission lever to which the elastic element is attached perform a movement in the opposite direction to the actuating element of the brake pedal. The overall space requirement of the brake pedal system is thereby reduced, so that a relatively compact housing is sufficient.

According to an advantageous embodiment, one end of the transmission lever, which exerts a force on the elastic element when the brake pedal is actuated, carries out a movement in the direction of the pedal axis when the brake pedal is actuated in the horizontal direction. In other words, the distance between the end of the transmission lever and the pedal axis is reduced during such a movement. This embodiment also contributes to the compactness of the brake pedal system.

According to a preferred embodiment, the lever axis is arranged below the pedal axis when viewed in the vertical direction. The elastic element can expediently be arranged on a side of the transmission lever opposite the lever axis and can be attached to the transmission lever.

It is also possible for a stop element to be arranged on a pedal body of the brake pedal, which, when a predetermined deflection of the brake pedal is reached, comes into contact with a stop element arranged on a simulator housing that corresponds to the stop element and thus prevents further deflection of the brake pedal. This offers the possibility of advantageously reducing the pedal travel, which leads to increased free space in the footwell. Furthermore, this results in a better allocation of the pedals to the driver, easier access to the end position of the brake pedal for smaller people and a defined end position of the brake pedal at which the entire braking force is called up.

In a special embodiment, the contact element is attached to the brake pedal on two opposite sides. If the contact element is considered to be part of the brake pedal, then the transmission lever penetrates a cavity within the brake pedal. In other words, the brake pedal body encloses the transmission lever on three sides, while the contact element is arranged on the fourth side of the transmission lever.

In order to achieve a particularly realistic driving experience, the contact surface can be designed in such a way that a characteristic curve of the counterforce has a progressive course depending on the deflection of the brake pedal. To this end, both the gradient and the radius of curvature of the contact surface can be changed in sections or continuously.

The brake-by-wire braking system according to the invention has a brake pedal system according to the invention and a brake, wherein the brake-by-wire braking system further has a control unit that is connected to a sensor of the brake pedal system, and wherein the control unit is designed to control the brake according to measured values of the sensor. The sensor typically measures a deflection of the brake pedal and/or a force. The sensor system is preferably designed redundantly. In order to keep the system functional even if the power supply is interrupted, it can be provided that the two redundant sensors or sensor systems are supplied with electrical energy via different circuits and from different voltage sources.

• 1: ein erstes Ausführungsbeispiel eines erfindungsgemäßen Bremspedalsystems in einer perspektivischen teilgeschnittenen Ansicht.

An embodiment of the invention is explained in more detail with reference to the drawing and the following description. It shows:

• 1 : a first embodiment of a brake pedal system according to the invention in a perspective partially sectioned view.

1 shows a first embodiment of a brake pedal system 2 according to the invention in a perspective, partially cutaway view. The brake pedal system 2 essentially consists of the brake pedal 4 and the simulator 6, which exerts a counterforce on the brake pedal 2 and thus simulates the behavior of a conventional brake. The brake pedal 4 and the simulator 6 are combined in the housing 24, with the pedal shaft 10 with the actuating element 8 protruding from the housing 24. The housing 24 is shown partially cutaway so that the simulator 6 is visible and the interaction between the brake pedal 4 and the simulator 6 becomes clear.

The brake pedal 4 is pivotably mounted about the pedal axis 14 by means of the pedal bearing 12. When a user applies pressure with his foot to the actuating element 8, which can also be referred to as the foot part, this causes a pivoting movement of the brake pedal 4 about the pedal axis 14. The brake pedal 4 has a roughly T-shaped form when viewed in a direction parallel to the pedal axis 14. The lower end of the T-shaped structure is formed by the actuating element 8. The pedal bearing 12 is attached to the upper left end in the figure and thus in the area of one end of the crossbar of the T-shaped structure. The contact element 18 is arranged at the upper right end in the figure and thus in the area of the other end of the crossbar of the T-shaped structure. This configuration has the effect that when a user actuates the brake pedal 4, the contact element 18 moves on a part-circular path around the pedal axis 14. The distance between the pedal axis 14 and the contact element 18 and thus the radius of the part-circular path described by the contact element 18 is more than 30% of the distance between the pedal bearing 12 and the actuating element 8. The crossbar of the T-shaped structure, which contains both the pedal bearing 12 and the contact element 18, can also be referred to as the pedal body. The pedal body then comprises the bearing area and the projection 16 on which the contact element 18 is arranged.

In addition to the brake pedal 4, the simulator 6 is the second essential element of the brake pedal system 2 according to the invention. The core of the simulator 6 is the transmission lever 26, which is pivotably mounted about the lever axis 30 by means of the lever bearing 28. The lever axis 30 runs parallel to the pedal axis 14. At one end of the transmission lever 26, it is in contact with the elastic element 32, which in the embodiment shown is designed as a spring. The elastic element 32 extends in the direction of travel F. In other words, the longitudinal axis of the elastic element 32 is aligned in the direction of travel F. The longitudinal axis corresponds to the deflection direction of the elastic element 32, in the case shown thus the compression direction of the spring. The elastic element 32 is attached to the attachment point 34 on the transmission lever 26. The attachment point 32 is located at an end 36 of the transmission lever 26 that is remote from the bearing.

As already described, actuation of the brake pedal 4 causes a pivoting movement of the contact element 18 about the pedal axis 14. The contact element 18 extends in a direction parallel to the lever axis 30 and thus also parallel to the pedal axis 14. It is in contact with the contact surface 38 of the transmission lever 26. The contact surface 38 corresponds to a side surface of the contact element 18. Due to the pivoting movement of the contact element 18, a force that has a force component perpendicular to the contact surface 38 acts on the contact surface 38 and thus on the transmission lever 26. This also carries out a pivoting movement, but about the lever axis 30. As a result of this pivoting movement, the elastic element 32 is deflected and then exerts a counterforce on the transmission lever 26. In the present embodiment, the spring visible in the upper area of the figure is compressed accordingly.

The contact surface 38 is curved so that the relative speed of the pivoting movement of the transmission lever 26 in relation to the speed of the pivoting movement of the brake pedal 4 varies depending on the deflection of the brake pedal 4. In other words, the deflection rate of the elastic element 32 is not only dependent on an angular speed of the brake pedal 4 but also on the current angular coordinate of the brake pedal 4. By using different sections with different curvatures, almost any force-displacement characteristic curve can be generated for the restoring force acting on the brake pedal 4 and exerted by the elastic element 32 depending on the pedal position.

In the exemplary embodiment shown, the contact surface 38 can be roughly divided into a first section 40, a second section 42 and a third section 44. The contact surface 38 is arranged on the side of the transmission lever 26 opposite the pedal bearing 12. In other words, the contact surface 38 corresponds to the back of the transmission lever 26 as viewed from the brake pedal 4. The contact element 18 arranged on the flat projection 16 of the brake pedal 4, which in the case shown consists of a roller that can rotate about a roller axis aligned parallel to the lever axis 30, thus exerts a force on the transmission lever 26 that is directed towards the brake pedal 4. The first section 40 of the contact surface 38 is inclined relatively strongly towards the inner region of the transmission lever 26 as viewed along the direction of movement of the contact element 18. It follows that at the beginning of a movement of the brake pedal 4 from a rest position only a small torque acts on the transmission lever, so that the elastic element 32 is only deflected at a low deflection rate. The second section 42 is flatter than the first section 40, so that when the contact element 18 moves in this area along the contact surface 38, the resulting torque on the transmission lever 30 increases. The third section 44 is in turn steeper than the second section 42, so that the torque exerted by the contact element 18 on the transmission lever 30 is even greater than before. The entire contact surface 38 thus has a substantially concave design with sections of different curvature.

The brake pedal 4 has a stop 22 on the back of the pedal shaft 10, which, at a maximum deflection of the brake pedal 4, is held against a correspondingly designed stop 22 Housing 24 is arranged against a counter stop 46 and thus limits the movement of the brake pedal. Both the stop 22 and the counter stop 46 can be made of a material with limited elasticity or can have a corresponding coating.

List of reference symbols

2

Brake pedal system

4

Brake pedal

6

simulator

8th

Actuator

10

Pedal shaft

12

Pedal bearing

14

Pedal axle

16

head Start

18

Contact element

20

Element axis

22

attack

24

Housing

26

Gear lever

28

Lever bearing

30

Lever axis

32

elastic element

34

Attachment point

36

end away from the camp

38

Contact surface

40

first section

42

second part

44

third section

46

Counter stop

F

Direction of travel

Claims (9)

Brake pedal system (2) for a motor vehicle, with a brake pedal (4) that can be pivoted about a pedal axis (14), and with a brake force simulator (6) that has an elastic element (32) that imparts a counterforce to the brake pedal (4) when the brake pedal (4) is actuated, wherein the brake force simulator (6) has a transmission lever (26) that interacts with the brake pedal (4) and is mounted so that it can be pivoted about a lever axis (30) such that actuation of the brake pedal (4) leads to a deflection of the elastic element (32), wherein when the brake pedal (4) is actuated, a contact element (18) arranged on the brake pedal (4) moves along a contact surface (38) of the transmission lever (26) that runs parallel to the lever axis (30), and wherein the contact surface (38) is designed such that the contact surface (38) has at least one axis that can be pivoted about a direction that runs parallel to the lever axis (30). curved section (40, 42, 44), characterized in that the contact surface (38) is arranged on a side of the transmission lever (26) opposite the pedal axis (14). Brake pedal system (2) after Claim 1 , characterized in that the elastic element (32) is arranged above the pedal axis (14) when viewed in the vertical direction. Brake pedal system (2) according to one of the preceding claims, characterized in that one end of the transmission lever (26), which exerts a force on the elastic element (32) when the brake pedal (4) is actuated, executes a movement in the direction of the pedal axis (14) when the brake pedal (4) is actuated in the horizontal direction. Brake pedal system (2) according to one of the preceding claims, characterized in that a longitudinal axis of the elastic element (32) extends substantially in a direction of travel (F). Brake pedal system (2) according to one of the preceding claims, characterized in that the lever axis (30) is arranged below the pedal axis (14) when viewed in the vertical direction. Brake pedal system (2) according to one of the preceding claims, characterized in that the contact element (18) is a roller mounted rotatably about a roller axis. Brake pedal system (2) after Claim 6 , characterized in that the contact element (18) is a sliding element which slides along the contact surface (38) when the brake pedal (4) is actuated. Brake-by-wire braking system with a brake pedal system (2) according to one of the preceding claims and a brake, wherein the brake-by-wire braking system further comprises a control unit which is connected to a sensor of the brake pedal system, and the control unit is adapted to control the brake according to measured values of the sensor. Motor vehicle with a brake pedal system (2) according to one of the Claims 1 until 7 or with a brake-by-wire braking system Claim 8 .

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