Device for generating a counterforce on a brake pedal and motor vehicle

Abstract

Device (10) for generating a counterforce on a brake pedal (2), comprising a force introduction element (9), a first elastic element (12) for generating a counterforce on the force introduction element (9), and a second elastic element (14) which is kinematically connected in series with the first elastic element (12), characterized by a hydraulic system (18, 70) which mediates a hydraulic force coupling between the first elastic element (12) and the second elastic element (14), wherein the hydraulic system (18, 70) has a compensation volume (24) which can accommodate a hydraulic fluid which is displaced due to a movement of the force introduction element (9), and wherein the device (10) is designed such that, upon reaching a predetermined position of the force introduction element (9), a fluid connection is established between a first volume in which the force introduction element (9) or a piston (18) moves,and the compensation volume (24) is closed, or that the size of the compensation volume (24) and the quantity of hydraulic fluid are adjusted such that the compensation volume (24) is completely filled when the predetermined position is reached and thus can no longer absorb any further hydraulic fluid.,

Description

The invention relates to a device for generating a counterforce to a brake pedal, having a force introduction element, a first elastic element for generating a counterforce to the force introduction element, and having a second elastic element which is kinematically connected in series with the first elastic element. The invention further relates to a motor vehicle having such a device.In motor vehicles and in particular in automobiles, a braking intention of the driver is usually implemented with the aid of a brake pedal. In this case, it is a historical standard to provide a mechanical penetration between the brake pedal and the actual brake device braking the wheels. Various brake boosters are known which assist the driver. For safety reasons, however, a mechanical connection is generally still present between the brake pedal and the brake, so that actuation of the brake remains possible even in the event of a defect in the brake booster.In the future, systems will increasingly be used, in particular in connection with autonomously driving motor vehicles or when automatic and autonomous driving functions are used, in which the above-described mechanical coupling between brake pedal and brake is omitted. The omission of the mechanical coupling likewise eliminates the haptic feedback when the pedal is actuated and the mechanism for returning to the rest position of the brake pedal. In such a system, the driver thus easily receives no haptic feedback of the brake pedal, since here only the position of the brake pedal or the actuating force is used to identify the braking request and the further process of the brake actuation is electrified and takes place independently of the brake pedal. The braking process desired by the user is thus determined by sensors which directly or indirectly record the current position of the brake pedal and are used via suitable electronics for the direct or indirect activation of the wheel brake, the recuperation unit or the parking brake which may be present in the case of electric drives, which then in turn carry out the actual braking process and generate a braking torque at the wheels.It has been found that haptic feedback of the vehicle with respect to various parameters such as the nature of the underlying surface, the speed of the vehicle, the current steering angle and indeed also a current braking process is important for the assessment of the driving situation by the driver and therefore also relevant for safety. Furthermore, it positively influences the purchase decision if the driving behavior of the vehicle differs as little as possible from the driving behavior of customary vehicles. It is therefore desirable to simulate or simulate as accurately as possible the reaction of a conventional brake pedal with regard to force, travel and hysteresis as a function of different actuation speedsVarious embodiments of so-called brake pedal force simulators are known in the prior art. For example, DE 10 2012 113 154 A1 describes a brake pedal simulator device for implementing a change in a pedal effort applied to a brake pedal for each pedal travel, which has trapezoidally arranged connecting members connected to the brake pedal. Upon actuation of the brake pedal, the trapezoid is stretched and thereby a spring is compressed, which then in turn exerts a restoring force on the brake pedal.From CN 207842910 U a brake pedal is known, in which a first spring, which is stretched upon actuation of the brake pedal, is attached to the brake pedal itself, and a second spring is compressed by a cam, which is arranged on a shaft rotating upon actuation of the brake pedal, such that the second spring also generates a counterforce on the brake pedal. By means of the two independent springs, different characteristic curves for the counterforce can be realized.DE 10 2019 216 477A1 describes a method for setting a brake pedal feedback in a brake-by-wire vehicle brake system. The brake system includes a brake pedal and a simulation device associated with the brake pedal such that the simulation device provides brake pedal feedback to the driver in a brake-by-wire brake mode. An input signal is provided to a processor circuit of a control unit of the brake system. The input signal relates to a desired brake pedal feedback associated with a driver of the vehicle. The processor circuit generates a brake pedal feel output signal based on data regarding vehicle deceleration versus a path of the brake pedal and data regarding vehicle deceleration versus a force on the brake pedal.Based on the brake pedal feel output signal, the controller controls an output of the simulation device to establish the desired brake pedal feedback. There is a hydraulic connection between the brake pedal and the simulation device.The known solutions each take up a lot of installation space and, owing to the simple construction, are not capable of completely simulating the feedback of a conventional brake pedal. Thus, the possibilities for influencing the characteristic curve are limited in the case of only up to two spring elements. It is likewise not possible to realize a hysteresis, i.e. a different force-travel characteristic curve between the application and the release of the brake.It is therefore the object of the present invention to specify a device for generating a counterforce on a brake pedal, in which the restoring force can be matched with high precision to a conventional brake pedal. It is also desirable to realize different, path-dependent force gradients. Furthermore, it is the object of the present invention to specify a device which is as compact as possible and requires little installation space.The object is achieved by a device of the type mentioned at the beginning, which is characterized by a hydraulic system which provides a hydraulic force coupling between the first elastic element and the second elastic element, wherein the hydraulic system has a compensation volume which can absorb a hydraulic fluid which is displaced on account of a movement of the force introduction element, and wherein the device is designed such that, when a predefined position of the force introduction element is reached, a fluid connection between a first volume in which the force introduction element or a piston moves and the compensation volume is closed, or that the size of the compensation volume and the quantity of the hydraulic fluid are adapted such that the compensation volume is completely filled when the predefined position is reached and therefore can no longer absorb any further hydraulic fluid. The object is furthermore achieved by a motor vehicle having such a device.The hydraulic force coupling between the first elastic element and the second elastic element enables a multiplicity of possibilities for setting both the profile of the counterforce as a function of the pedal position and as a function of the pedal movement speed. Furthermore, an extremely compact configuration is possible, since the two elastic elements do not have to be arranged collinearly. The pedal force simulator according to the invention can be designed so compactly that it can be arranged completely in the foot space of the motor vehicle. In other words, no portion of the pedal force simulator then protrudes into the front vehicle or the engine compartment of the motor vehicle. In particular, the pedal force simulator is then arranged on a side facing the passenger compartment of an end wall separating the passenger compartment from the front end of the vehicle.By the fact that the second elastic element is kinematically connected in series with the first elastic element is understood in particular that when a force is exerted by the force introduction element on the first elastic element, the first elastic element is caused to exert at least a part of the force on the second elastic element at least when a limit force is exceeded. In other words, the first elastic element absorbs the force from the force introduction element and forwards at least a part of the force to the second elastic element.In the context of the present description, a force introduction element is understood to mean, in particular, a component which can absorb a force, in particular absorb it from the brake pedal, and in particular transmit it to the first elastic element or to a component connected to the first elastic element. The force introduction element can be designed as a plunger or as a push rod. The length of the force introduction element is preferably less than 5 cm and particularly preferably less than 3 cm.The two elastic elements can have different spring constants or different force-displacement characteristic curves. By suitable combination, it is thus possible to influence the force-displacement characteristic curve of the entire device. The pedal is preferably mechanically connected to a plunger or piston which, upon actuation of the pedal, simultaneously deflects, in particular compresses, the first elastic element and displaces the hydraulic fluid and thus actuates the hydraulic system. The hydraulic system can be configured such that a frictional connection to the second elastic element is present over the entire range of movement of the pedal. It is likewise and preferably possible for the system to be configured such that only the first elastic element is deflected over a first travel range of the pedal. The second elastic element can thus be connected when a predetermined deflection point of the pedal is exceeded and, in addition to the first elastic element, can likewise exert a counterforce on the pedal. Thus, different force gradients are realized and, upon actuation of the brake pedal, so-called pressure points are to be sensed for the driver.The first elastic element and / or the second elastic element can be a spring, in particular a spiral spring, but also an elastomer or another elastic element.According to a further development of the invention, the hydraulic system has a compensating volume which can absorb hydraulic fluid which is displaced on account of a movement of the force introduction element, and which is separated from the second elastic element in terms of fluid technology up to a predefined position of the force introduction element. Such a configuration is an example of a pedal force simulator in which the second elastic element is only connected when a predefined position of the pedal is reached. The pedal force simulator can be designed in such a way that, although hydraulic fluid is already displaced during each movement of the pedal out of the rest position, it initially flows completely or at least predominantly into a compensation volume, for example a compensation chamber or a compensation container, and thus reduces or eliminates the hydraulic pressure on the second elastic element.When the predefined position is reached, a fluid connection between a first volume, in which the force introduction element or, for example, the plunger or piston moves, and the compensation volume is then closed, or the size of the compensation volume and the quantity of the hydraulic fluid are adapted in such a way that the compensation volume is completely filled when the predefined position is reached and can therefore no longer absorb any further hydraulic fluid.A specific design possibility has a piston element which is movable along a first displacement direction and is connected to the first elastic element and opens up a snifting bore in a first position region and closes off the snifting bore in a second position region. The second position range can be reached starting from an freely selectable piston travel. The snifting bore represents a connection between the volume in which the piston element moves and the compensation volume. When the piston element enters the second position region, the snifting bore is closed and no further hydraulic fluid is transported into the compensation volume. In other words, the snifting bore travels past the compensation container after a specific actuation or deflection of the piston element and then automatically displaces the volume into the second chamber. The full force exerted by the pedal or by the force introduction element then acts both on the first elastic element and on the second elastic element.According to an advantageous development of the invention, the device has a throttle device which, when the force introduction element is relieved of load, throttles a return flow of hydraulic fluid counter to an actuating direction of the force introduction element. In this way, the counterforce acting on the pedal can be designed as a function of the direction of movement. In other words, it is possible to achieve hysteresis in which the returning motion of the pedal is attenuated after operation of the pedal as compared with the forward motion.It is possible for the throttle device to comprise at least one valve seal. Such a valve seal can open a connection between two volumes for one flow direction and block it for the opposite flow direction. In a preferred embodiment, at least two valve seals can be present, which are each assigned to a connection between the two volumes. In particular, the valve seals can open or open the two connections for opposite flow directions. One connection is then opened for a flow direction from the first volume into the second volume, and the other connection is opened for a flow direction from the second volume into the first volume. The valve seal or the valve seals can be designed as a valve spring or as valve springs.According to a preferred embodiment, it is provided that the force introduction element is connected to a displacement element which can displace hydraulic fluid in such a way that a force is exerted on the second elastic element by the hydraulic fluid, wherein the hydraulic fluid in this case flows towards the second elastic element through a connection which has a larger cross section than a connection through which the hydraulic fluid flows away from the second elastic element when the force introduction element is relieved.A preferred embodiment has a first sensor for determining the position of a brake pedal connected to the force introduction element and at least one second sensor for determining the position of the brake pedal. A redundant execution of the position determination of the pedal or brake pedal is thus possible. This is a particularly safety-relevant feature, since otherwise, in the event of a failure of a sensor, the pedal can no longer perform its function and, for example, no braking request of the driver can be implemented any longer.A particularly comfortable configuration is achieved by an elastic stop for limiting the travel of the brake pedal. The driver thus receives an elastic stop in addition to the progressive increase of the counterforce at the end of the deflection range of the pedal, so that the driver notes when the maximum braking power is requested and thus full braking is carried out.A particularly compact configuration results if a distance between an end of the force introduction element on the brake pedal side and an opposite end of the device is less than 15 cm, preferably less than 12 cm. It then becomes possible to arrange the entire pedal force simulator in the vicinity of the pedal itself and in particular outside the front carriage or the engine compartment of the motor vehicle.In a preferred embodiment, an angle between a longitudinal axis of the first elastic element and a longitudinal axis of the second elastic element is at least 10°, preferably at least 30° and particularly preferably at least 60°. This configuration makes it possible to keep the expansion of the entire pedal force simulator particularly small in the load direction of the first elastic element, typically thus in the direction of travel. The second elastic element can then point, for example, obliquely or vertically upwards or downwards.According to a preferred embodiment, the device is arranged on the side facing a footwell of the vehicle of a boundary separating the footwell from a front carriage. As already described above, this is possible in particular by the compact dimensions of the pedal force simulator.Exemplary embodiments of the invention are explained in more detail on the basis of the drawings and the following description. The following are shown: FIG. 1 : a first exemplary embodiment of a pedal force simulator according to the invention in a first position in the context of a motor vehicle, FIG. 2 : shows the first exemplary embodiment in a second position in the context of a motor vehicle, FIG. 3 : shows a schematic section through the first exemplary embodiment and the enlarged representation of a detail, FIG. 4 : an enlarged representation of a second detail, FIG. 5 is an exploded view of the second detail, FIG. 6 : an enlarged representation of a third detail, FIG. 7 : shows a schematic illustration of the first exemplary embodiment in a first position, FIG. 8 : shows a schematic illustration of the first exemplary embodiment in a second position, FIG. 9 : shows a schematic illustration of the first exemplary embodiment in a third position, and FIG. 10 : shows a schematic illustration of the first exemplary embodiment in a fourth position.FIG. 1 shows a first exemplary embodiment of a pedal force simulator 10 according to the invention in a first position in the context of a motor vehicle. The pedal force simulator 10 is actuated by the brake pedal 2 via the push rod 9. The brake pedal 2 is mounted rotatably about an axis 3 in the bearing block 4. The pedal force simulator 10 includes a first spring 12 and a second spring 14. The front wall 6 separates the foot space in which the pedal force simulator 10 and the brake pedal 2 are arranged from the front carriage 8, in which, for example, drive components are arranged.In FIG. 1, the brake pedal 2 is in its rest position, in other words in a non-deflected position in which no braking request is applied by the driver. Accordingly, the springs 12 and 14 are also in their rest position. The position of the brake pedal 2 can be determined, for example, by a rotational angle sensor, not shown, which can be arranged in the region of the axle 3.FIG. 2 shows the first exemplary embodiment in a second position in the context of the same motor vehicle. In FIG. 2, the brake pedal 2 is shown in a maximum displacement.The brake pedal 2 abuts against the elastic stopper 16. Accordingly, the first spring 12 is in a compressed position.FIG. 3 shows a schematic section through the first exemplary embodiment and the enlarged representation of a detail in the lower left-hand region of the figure. The pedal force simulator 10 is shown, to which a force is applied by the push rod 9. The brake pedal itself is not shown. The push rod 9 engages the push rod receptacle 32, which is part of the first piston 18. This encloses a large part of the first spring 12, which is guided by the guide pin 34. In the lower right-hand region, the pressure sensor 36 can also be seen, which measures the hydraulic pressure present within the volume 30.In the upper region of the figure, the fluid container 24 with the fluid membrane 26 can be seen. The connection of the fluid container 24 to the cylindrical volume 30, in which the first piston 18 moves, is illustrated in detail in the lower right-hand region of the figure. The outer wall 40 of the first piston 18 has a so-called snifting bore 38 through which hydraulic fluid can exit from the volume 30. In the illustrated state, which corresponds to an non-deflected state of the brake pedal, a line 42 is situated behind the snifting bore 38 and in turn leads to the fluid container 24. In this position, a movement of the piston 18 to the right and an associated displacement of the hydraulic fluid can thus lead to a transfer of hydraulic fluid from the volume 30 into the fluid container 24.The piston 18 is sealed by two lip seals 28, one of which is located in front of the snifting bore 38 and one of which is located behind the snifting bore 38. The connection 44 extends the region in which the fluid transfer mentioned can take place in the direction of movement of the piston 18 as far as the lip seal 28. When the snifting bore 38 reaches the lip seal 28 on the right in the figure, the snifting bore 38 is closed and the volume 30 is separated from the fluid container 24 in terms of fluid technology. No further hydraulic fluid then flows into the fluid container 24 any longer; instead, only a single possible path remains for the hydraulic fluid, which is described further first with reference to section A in FIG. 4.FIG. 4 shows an enlarged illustration of the region A from FIG. 3. in the lower left-hand region of the figure, a section of the cylindrical volume 30 can be seen, in which the spring 12 is arranged. The volume 30 is connected to the feed line 48 and to the discharge line 50, which are each connected to the line 56 via an intermediate chamber 58, wherein the line 56 in turn leads to the second spring, not shown in the detail shown. The feed line 48 is closed off from the intermediate chamber 58 and thus in the direction of the second spring by a first valve seal 54. The first valve seal 54 is spring-elastic and releases the feed line 48 toward the intermediate chamber 58 when a hydraulic pressure is built up from the side of the volume 30.The discharge line 50 is of identical construction, wherein here the second valve seal 52 is arranged on the side of the discharge line 50 facing the volume 30, such that the connection between the intermediate chamber and the volume 30 is released when a hydraulic pressure is applied from the direction of the intermediate chamber 58 and thus from the direction of the second spring. Furthermore, the feed line 48 and the discharge line 50 have different cross sections or diameters, so that, with the same applied hydraulic pressure, different fluid flow rates are realized through the two connections. The cross section of the feed line 48 is smaller than the cross section of the discharge line 50, so that, with the pressure applied in each case being the same, the hydraulic fluid flows more quickly in the direction of the second spring than in the direction of the volume 30. The ratio of the two cross sections mentioned is not necessarily designed in such a way that the cross section of the discharge line 50 is larger than the cross section of the feed line 48. however, in each case the reflux speed from the intermediate chamber 58 or from the direction of the second spring towards the first spring 12 can be adjusted with the construction shown. In this way, it becomes possible to set hysteresis so that the movement of the brake pedal is attenuated at rapid operation speeds. Furthermore, it is achieved that the respective force-displacement characteristic curves for the forward and rearward movement differ from one another, whereby the driver can better dose the braking action.FIG. 5 shows an exploded view of the element from FIG. 4 forming the intermediate chamber 58, and a base element 62 can be seen in which the feed line 50 and the discharge line, which is covered by the first valve seal 54 in the illustrated state, are designed as bores. The bottom member 62 is sealed with a seal 60 inserted into a groove on the top. The two valve seals 52, 54 are fixed in bores provided therefor by an upper fastening 64 and a lower fastening 66.FIG. 6 shows an enlarged illustration of the region B from FIG. 3 The line 78, which is connected to the line 56 from the preceding figure, can be seen in the lower left-hand region. As hydraulic fluid flows into the conduit 78, a force is applied to the second piston 70 urging it to the upper right in the figure. The second spring 14 exerts an opposing force on the second piston 70. When the hydraulic pressure is high enough, the second spring 14 is compressed and the second piston rear portion 76 moves toward the second spring 14, and the second piston 70 is again sealed by an O-ring seal 72 and a lip seal 74. Within the spring volume 80 are the spring and air which is easily compressible as the second piston 14 moves into the volume 80. In the example shown, the second piston is comprised of the front portion 70 and the rear portion 76.FIG. 7 shows the first exemplary embodiment in a rest position of the brake pedal. Both the first spring 12 and the second spring 14 are in an non-deflected equilibrium position in which they do not exert any forces on the pistons 18, 70. The snifting bore 38 allows communication between the volume within the first piston 18 and the fluid reservoir 24.FIG. 8 shows the first exemplary embodiment in a position in which the brake pedal is deflected by a first angle of rotation. The first piston 18 has performed a transverse movement towards the interior of the pedal force simulator 10, so that the snifting bore 38 would also be displaced in this direction. In the position shown, the snifting bore 38 is almost completely covered by the lip seal 28, so that a fluid flow from the interior of the first piston 18 into the fluid container 24 is almost no longer possible. At the same time, the first valve seal 54 still closes the feed line 48, so that no hydraulic fluid yet flows into the intermediate chamber 58. The position shown can correspond to a piston travel of 7 mm in the exemplary embodiment shown. The counterforce felt by the driver results from the frictions of the seals and from the fluid flow through the sniffing bore 38 and from the spring constants of the first spring 12.FIG. 9 shows the first embodiment in a position in which the brake pedal is displaced by a second rotational angle which is greater than the first rotational angle. Meanwhile, the snifting bore 38 is completely closed, so that the complete hydraulic pressure is applied to the first valve seal 54 and opens the latter, so that a hydraulic flow can flow into the intermediate chamber 58. Accordingly, a hydraulic pressure builds up in the hydraulic line 78, which already minimally deflects the second piston 70 compared to the position shown in FIG. 8 and thus has also already slightly compressed the second spring 14. The friction caused by the seal 72 together with the housing of the second piston 70 in this case provides a further counterforce component felt by the driver.FIG. 10 shows the first exemplary embodiment in a fully deflected position of the brake pedal. The brake pedal, not shown, has received contact with the stop and both the first spring 12 and the second spring 14 have reached their fully deflected position. Accordingly, both the first piston 18 and the second piston 70 have been displaced by a significant proportion. The distance covered by the first piston can be between 20 and 25 mm, for example.List of reference characters2 Brake pedal 3 Axle 4 Bearing block 6 End wall 8 Front carriage 9 Push rod 10 Pedal force simulator 12 First spring 14 Second spring 16 Elastic stop 18 First piston 20 First cylinder 22 First piston wall 24 Fluid container 26 Fluid membrane 28 Lip seal 30 Cylinder volume 32 Tappet receptacle 34 Guide pin 36 Pressure sensor 38 Sniffer bore 40 Piston wall 42 Line 44 Opening 46 Lip seal 48 Feed line 50 Discharge line 52 Second valve seal 54 First valve seal 56 Line 58 Intermediate chamber 60 Seal 62 Base element 64 Upper fastening 66 Lower fastening 68 Second cylinder 70 Second piston 72 Seal 74 Lip seal 76 Spring piston 78 Hydraulic line / fluid space 80 Spring space A Cutout / detail B Cutout / detail

Claims

Device (10) for generating a counterforce to a brake pedal (2), having a force introduction element (9), a first elastic element (12) for generating a counterforce to the force introduction element (9), and having a second elastic element (14) which is kinematically connected in series with the first elastic element (12), characterized bya hydraulic system (18, 70) which provides a hydraulic force coupling between the first elastic element (12) and the second elastic element (14), wherein the hydraulic system (18, 70) has a compensation volume (24) which can absorb a hydraulic fluid which is displaced on account of a movement of the force introduction element (9), and wherein the device (10) is configured such that, when a predefined position of the force introduction element (9) is reached, a fluid connection between a first volume in which the force introduction element (9) or a piston (18) moves, and closing the compensating volume (24), or that the size of the compensating volume (24) and the quantity of hydraulic fluid are adapted such that the compensating volume (24) is completely filled when the predetermined position is reached and can thus no longer receive any further hydraulic fluid.Device (10) according to Claim 1, characterized bya piston element (18) which is movable along a first displacement direction and is connected to the first elastic element (12) and opens up a snifting bore (38) in a first position region and closes off the snifting bore (38) in a second position region.Device (10) according to one of the preceding claims, characterized bya throttle device (52, 54) which, when the force introduction element (9) is relieved, throttles a return flow of hydraulic fluid counter to an actuating direction of the force introduction element (9).Device (10) according to claim 3, characterised in that the throttle device comprises at least one valve seal (52, 54).Device (10) according to one of the preceding claims, characterized in that the force introduction element (9) is connected to a displacement element (18), which can displace hydraulic fluid in such a way that a force is exerted on the second elastic element (14) by the hydraulic fluid, wherein the hydraulic fluid flows towards the second elastic element (14) in this case through a connection (48), which has a cross section that is greater than a cross section of a connection (50), through which the hydraulic fluid flows away from the second elastic element (14) when the force introduction element (9) is relieved.Device (10) according to one of the preceding claims, characterized in that a distance between an end of the force introduction element (9) on the brake pedal side and an opposite end of the device (10) is less than 15 cm, preferably less than 12 cm.Device (10) according to one of the preceding claims, characterized byan angle between a longitudinal axis of the first elastic element (12) and a longitudinal axis of the second elastic element (14), which is at least 10°, preferably at least 30° and particularly preferably at least 60°.Motor vehicle having a device (10) according to one of the preceding claims.Motor vehicle according to Claim 8, characterized in that the device (10) is arranged on the side of a delimitation (6) which separates the footwell from a front vehicle (8) and faces a footwell of the vehicle.

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