Patent Application
20220297659
The invention relates to an electromechanical brake actuator fora brake, in particular a commercial vehicle disc brake, having: an electric motor for generating a driving torque, a cam disc which is mounted so that it can move in rotation and is actively connected to the electric motor, and a brake plunger, which can move along a plunger axis, for actuating a brake lever of the brake, wherein the cam disc and the brake plunger have contact surfaces which bear against each other and slide or roll on each other for the purpose of directly transmitting the driving torque between the cam disc and the brake plunger, wherein the contact surface of the cam disc extends about the pivot point D at a radial distance r defined as a function r(φ) with a rate of change r′(φ) which is dependent on the angular position φ of the cam disc, and the contact surface is configured to effect a non-linear transfer between the driving torque of the cam disc and the force transmitted to the brake plunger, wherein the radial distance r(φ) is at its minimum for an angular position φ=φmin and is at its maximum for an angular position φ=φmax.
This non-linear transfer is preferably configured such that, for example in order to overcome the play between the brake shoe or brake lining and the brake disc, large forward travel distances can be achieved with a relatively low braking force transmitted, whereas a higher braking force with a shorter forward travel of the brake plunger can be obtained in a situation which requires the application of high braking forces.
Electromechanical brake actuators are generally known in the automotive industry and in particular for commercial vehicles. For example, AT 516801 A2 proposes an electromechanical actuator with two transmission links in order to achieve sufficiently short brake actuation times and at the same time to obtain a desired braking performance by means of an electric motor which is as small and economical as possible. A coupling link, on which a tracing element is arranged, is provided on the first transmission link. The second transmission link has a lift curve. The tracing element traces the shape of the lift curve, wherein the second transmission link applies the input torque for the first transmission link and the input torques of the first transmission link result in a zero curve over the angle of rotation for different wear states of the brake lining.
Systems such as that mentioned above have the disadvantage that their structural configuration is very complex and are, on the one hand, costly in terms of manufacture and assembly and, on the other hand, difficult to maintain. The large number of components also requires a relatively large structural space for the arrangement.
DE 10 2017 004 436 A1 proposes an electromechanical brake actuator, in which a cam disc and a brake plunger have contact surfaces which bear against each other and slide or roll on each other for the purpose of directly transmitting the driving torque between the cam disc and the brake plunger. In this way, the cam disc can be used, in conjunction with the brake plunger which bears on the contact surface, to convert a rotational movement of the cam disc directly into a non-linear movement of the brake plunger.
The contact surface of the cam disc is here shaped in such a way that the brake plunger can be moved back and forth between a retracted position and a deflected position, and the cam disc can be moved back and forth between a starting position and a final position, wherein the starting position of the cam disc corresponds to the retracted position of the brake plunger and the final position of the cam disc corresponds to the deflected position of the brake plunger.
In the deflected position, the brake is fully applied. Because of the inevitable flexibility of the structure, the kinematic chain of the transmission of force is subject to mechanical elastic deformations. Mechanical energy is thus stored within the kinematic chain, for example in the brake caliper. If the final position of the cam disc is exceeded or the brake is opened in an uncontrolled fashion, for example by being wrongly activated or as a result of a failure of the electric motor, the brake plunger and its contact surface moves suddenly from the deflected position into the retracted position. At this point in time, the energy stored in the kinematic chain is fed into the brake actuator in an uncontrolled fashion. This causes the actuator to be mechanically stressed and can result in a reduction of the service life which would otherwise be possible and can adversely affect the functionality of the brake actuator.
Against this background, the object of the present invention is to provide an electromechanical brake actuator which as far as possible overcomes the above described disadvantages. The object is in particular to provide an actuator which allows fault-tolerant operation with a long service life.
The invention achieves the object on which it is based, with an actuator of the type described above, by the rate of change r′(φ) being positive at least in certain regions in a first angular range φmin≤φ≤φmax and the rate of change r′(φ) being negative at least in certain regions in a second angular range φmax≤φ≤360°. The invention makes use of the recognition that the energy which is released in the event of a fault, i.e. for example when the cam disc is over-rotated beyond the angular position φ=φmax, is gradually dissipated in the second angular range owing to friction losses. Damage to the actuator is thus prevented.
There is at least one angular range between φmax and φmin in which a defined negative slope ensures a controlled decrease in r such that a jump from rmax to rmin is prevented.
The invention primarily relates to disc brakes, wherein in a disc brake the counterpart corresponding to the brake lining is the brake disc. However, the invention can in principle also be used in conjunction with drum brakes.
According to a preferred embodiment, at an angular position φ=φmin the rate of change is r′(φmin)=0. The function r(φ) thus has a saddle point or minimum at an angular position φ=φmin.
More preferably, at an angular position φ=φmin the derivative of the rate of change after the angle is r″(φmin)>0. r(φ) thus has a positive curvature, i.e. a curve that curves to the left.
If, at an angular position φ=φmin, the derivative of the rate of change is r′(φmin)=0 and the function r(φ) has a positive curvature at this angular position, the function r(φ) at the angular position φ=φmin has a low point. Beginning from this starting angular position φmin, the radial distance thus increases at least in some sections. The minimum radial distance rmin which is achieved at the angular position φ=φmin thus defines the withdrawn position of the plunger.
More preferably, at an angular position φ=φmax the rate of change is r′(φmax)=0. The function r(φ) thus has a saddle point or maximum at an angular position φ=φmax.
At an angular position φ=φmax the rate of change is preferably r″(φmax)<0. r(φ) thus has a negative curvature, i.e. a curve that curves to the right.
If, at an angular position φ=φmax, the rate of change is r′(φmax)=0 and the function r(φ) has a negative curvature at this angular position, not only is a saddle point defined but also a maximum of the function. In this case, the angle φmax defines the angular position at which the radial distance r(φ) assumes a maximum value and hence the position at which the plunger is maximally deflected.
The range of movement of the plunger is thus defined by the function r(φ) which has a minimum at φ=φmin and a maximum at φ=φmax. This angular range φmin≤φ<(Pmax thus defines the range of movement within which the plunger can move from a withdrawn position into a deflected position in order to apply a braking force. This range corresponds to the intended operation of the cam disc within the brake actuator. By definition, the cam disc has a positive slope in this range.
According to a preferred embodiment, the radial distance r(φ), at at least one angular position φ=φp′ with φmax≤φp′≤360°, changes suddenly by a value Δr, wherein the jump is preferably Δr≤ 1/10r(φmax).
The value Δr by which the radial distance r(φ) changes is dependent on the diameter of the plunger in the region of the contact surface with the corresponding contact surface of the cam disc. Such a contact surface can moreover be formed on a roller unit, for example a pressure roller. The value Δr and hence the magnitude of the jump advantageously corresponds to at least the radius of the pressure roller.
By virtue of such a jump, firstly, in the case of a malfunction of the brake actuator which, for example, results in over-rotation of the cam disc, the braking force is dissipated suddenly in a predefined range the brake after a tolerance range, here φmax≤φ≤360°, is exceeded. Such a predefined jump makes it possible to rapidly reduce the stored energy and at the same time prevents excessive energy from being imparted to the brake actuator by the sudden springing back of the plunger as a consequence of the sudden reduction in the radial distance r(φ) between the contact surfaces.
Secondly, by virtue of such a jump, in the case of a malfunction which results in rotation of the cam disc counter to the direction of rotation, over-rotation of the disc from this direction, which occurs only in the event of a fault and hence in an uncontrolled state, is prevented.
Such a sudden change is understood to mean that the rate of change is
and the jump is preferably Δr≤ 1/10r(φmax).
The radial distance r(φ) preferably rises strictly monotonically in an angular range φmin≤φ≤φmax such that r′(φmin≤φ≤φmax)>0. The radial distance r(φ) thus increases permanently in the angular range φmin≤φ≤φmax, wherein the rate of change r′(φ) in the whole angular range is >0. It is thus ensured that the plunger, which is in contact with the contact surface of the cam disc and slides or rolls on the latter, undergoes continuous forward travel until, at an angular position φ=φmax, the radial distance r(φ) is at its maximum and the plunger is deflected to the maximum extent.
More preferably, the radial distance r(φ) falls strictly monotonically in an angular range φmax≤φ≤360° such that r′(φmax≤φ≤360°)<0. Thus, when the angular position φ=φmax is exceeded, the radial distance r(φ) is reduced continuously such that the braking force is continuously dissipated until the plunger has finally been brought into its retracted position in which φ=φmin.
It is understood that, if for example φmin=0, it is also true that φmin=360° because the rotation of the cam disc would start again once 360° has been exceeded.
According to a preferred embodiment, in the first angular range φmin≤φ≤φmax, the function r(φ) has a first function profile r1(φ), wherein, in the second angular range φm<<360°, it has a second function profile r2(φ) which differs from r1(φ). The profile of the radial distance r(φ) is described by a function profile r1(φ) depending on the angular position φ in a first range in which the radial distance r(φ) increases at least in some sections, and is described by a function profile r2(φ) in a second angular range in which the radial distance r(φ) decreases at least in some sections. Because these function profiles are different, the function profile can thus be described suitably within the angular range and thus enables a simplified representation of the radial distance of the contact surface from the pivot point.
r1(φ) and r2(φ) preferably meet at an angular position φ1,2 at which r′1(φ) and r′2(φ) are smooth and r1(φ) has a negative curvature, i.e. a curve which curves to the right. The function profiles r1(φ) and r2(φ) thus preferably merge into each other with no jump. By virtue of the smooth profile of the function profiles r1(φ) and r2(φ), it is moreover ensured that the function profiles meet at just one point of the angular position φ1,2.
More preferably, r1(φ) and r2(φ) meet at a second angular position φ2,1 at which r′2(φ2,1) and r′1(φ2,1) are likewise smooth and r1(φ) has a positive curvature, i.e. a curve which curves to the left. The function profile r2(φ) thus also merges into r1(φ) with no jump.
r1(φ) and r2(φ) preferably meet at at least one angular position φ1,2 at which r′1=r′2. The function profiles r1(φ) and r2(φ) thus meet at the angular position with no kinks. This favors smooth travel of the plunger on the contact surface of the cam disc and hence the low-wear transmission of force. Such an angular position can be situated, for example, at a distance from the angular position φmax or φmin such that the rate of change r2(φ) is negative in an angular range φ>φmax and the function profile r1(φ) falls in this range such that the slope of the function profile r1(φ) at the angular position φ1,2 is negative and corresponds to the slope r′2(φ) of the second function profile of r2(φ).
More preferably, the angular position φ1,2 is a first angular position at which r1(φ) preferably has a negative curvature, and r1(φ) and r2(φ) moreover meet at a second angular position φ2,1 at which r′2=r′1 and r1(φ) preferably has a positive curvature. The function profiles r2 (φ) and r1(φ) thus meet at the angular position with no kinks.
According to a preferred embodiment, the function r(φ) has a transition function r3 (φ) which meets the first function profile r1 (φ) at a first angular position φ1,3, wherein preferably r′1(φ1,3)=r′3(φ1,3), and which meets the second function profile r2(φ) at an angular position φ3,2, wherein preferably r′2(φ3,2)=r′3(φ3,2). A linear increase of the radial distance r1(φ) can thus, for example, be ensured in an angular range φmin≤φ≤φmax which is described by the function profile r1(φ). A linear function profile r2(φ), in which the radial distance decreases linearly, can moreover be provided in a second angular range with φmax≤φ≤360°. Such function profiles would then be connectable with each other, in particular smoothly and with no kinks, in a simple fashion by a higher-order transition function. In such a case, the plunger, which slides or rolls on the contact surface of the cam disc, does not undergo any jerking or vibrations.
Moreover, if r′1(φ1,3)={dot over (r)}3(φ1,3) applies, the function r(φ) is smooth and the function profile r1(φ) merges into the transition function r3(φ) with no kinks. If r′2(φ3,2)=r′3(φ3,2) applies, the second function profile r2(φ) merges into the transition function with no kinks. In such a case, the plunger slides or rolls smoothly over the contact surface of the cam disc.
According to a further preferred embodiment, the transition function r3(φ) is a first transition function, and the function r(φ) also has a second transition function r3(φ)′ which meets the first function profile r1(φ) at a third angular position φ3,1, wherein preferably r′1(φ3,1)=r′3(φ1,3)′, and which meets the second function profile r2(φ) at an angular position φ2,3, wherein preferably r′2(φ2,3)=r′3(φ2,3)
The rate of change is preferably r′(φmax≤φ<φp)=0 in an angular range φmax≤φ<φp, wherein preferably φmax−φp≤0.1·(φmax−φmin). A plateau or a range in which the radial distance r(φ) is constant is thus provided in an angular range φmax≤φ<φbp. By virtue of such a range following the maximum radial distance r(φmax), over-rotation of the cam discs beyond the angular position φmax, for example in the event of an incorrect amount of play or play which has been set within permissible tolerances, will prevent a sudden decrease in the braking force because the position of the plunger is held constant in a predefined range. The width of the plateau should accordingly be selected dependent on the specified tolerances of the play setting.
A further preferred embodiment is characterized in that the cam disc has an indentation on its periphery for defining a parking brake position, wherein the indentation is arranged between a contact point with the brake plunger in the starting position and contact point with the brake plunger in the final position. If the cam disc with its indentation is situated in such a contact position, the braking power supplied in this position and imparted by the brake plunger remains constant, even when the electrical energy is no longer being supplied to the driving electric motor. The parking brake force can be modulated by expedient positioning of the indentation. This functionality is associated with a low degree of structural complexity and is furthermore easy to maintain and mechanically reliable.
The indentation is preferably arranged in such a way that the brake plunger, when arranged in the indentation, transmits a braking force in a range of approximately 20% to approximately 50% of the maximum braking force. Parking brake functionality with a small number of components can be obtained by virtue of such a functional integration. This moreover has a positive effect on the structural space required by the device. In order to not modulate the braking force unnecessarily during normal operation and to prevent the braking force from being modulated unintentionally by a driver, this region can advantageously be placed in the region of the negative slope of the cam disc.
The object of the invention is achieved in a first aspect, as described above, by a brake actuator. The invention relates in a second aspect to a cam disc for such a brake actuator, which is configured to be connected to the driveshaft of an electric motor, wherein the cam disc has a contact surface which can be brought to bear against the contact surface of the brake plunger in order to directly transmit the driving torque between the cam disc and the brake plunger in such a way that the contact surfaces slide or roll on each other, wherein the contact surface of the cam disc runs with a radial distance r in the radial direction around the pivot point D, which is defined as a function r(φ) with a rate of change r′(φ) dependent on the angular position φ of the cam disc, and the contact surface is configured in such a way that there is a non-linear transfer between the driving torque of the cam disc and the force transmitted to the brake plunger, wherein the radial distance r(φ) is at its minimum at an angular position φ=φmin and is at its maximum at an angular position φ=φmax. The invention achieves the object on which it is based in a second aspect by the rate of change r′(φ) being positive at least in certain regions in a first angular range φmin≤φ≤φmax and the rate of change r′(φ) being negative at least in certain regions in a second angular range φmax≤φ≤360°. Preferred embodiments and advantages of the brake actuator according to the invention are at the same time preferred embodiments and advantages of the cam disc for such a brake actuator.
Exemplary embodiments of the invention are now described below with the aid of the drawings which are not necessarily intended to illustrate the exemplary embodiments to scale and instead, where useful for explanation, the drawings are made in a schematic and/or slightly distorted form. Reference is made to the relevant prior art with regard to supplementary information about the teachings which are immediately apparent from the drawings. It should be noted here that numerous modifications and changes relating to the form and detail of an embodiment can be made without departing from the general idea of the invention. The features of the invention disclosed in the description, in the drawings, and in the claims can be essential for the development of the invention both taken individually and in any combination. Additionally within the scope of the invention are all combinations of at least two of the features disclosed in the description, the drawings, and/or the claims. The general idea of the invention is not limited to the exact form or the detail of the preferred embodiments shown and described below and not limited to a subject which would be restricted in comparison with the subject of the claims. For the measurement ranges indicated, it is intended that the values which lie within the said limits are also disclosed as limit values and can be used and claimed as desired. For the sake of simplicity, the same reference numerals are used below for identical or similar parts or parts with an identical or similar function.
Further advantages, features, and details will become apparent from the subsequent description of the preferred embodiments and with the aid of the appended drawings.
In the drawings,
The brake plunger 114 can in particular be deflected linearly in the illustrated direction of the arrows. The brake plunger 114 has a plunger head 112 at its end facing the cam disc 108. This plunger head 112 surrounds a rolling element 110 which is mounted by means of the bearing 116. The rolling element 110 slides on the periphery of the cam disc 108. Transmission of the rotational movement of the cam disc 108 into a linear movement of the brake plunger 114 is obtained herewith. The electromechanical actuator 102 can be connected in particular to a brake (not illustrated) via a connecting section 118.
The already mentioned transmission 119 is shown in detail in
A configuration, by way of example, of the cam disc 108 can be seen in
This has the additional effect that a change in the angle of rotation of the cam disc 108, with such a shape of the cam disc, has the result that in a change in the angle of rotation of the cam disc 108 within a range of small deflections of the brake plunger 114 causes a larger distance to be covered on the sides of the brake plunger 114 with a smaller transmitted braking force, and wherein, in the region of the maximum deflection 114 of the brake plunger, an equivalent change in the angle of rotation of the cam disc 108 entails a smaller deflection of the brake plunger 114 with a higher transmitted braking force.
A second exemplary embodiment of the electromechanical actuator 202 is illustrated in
A plan view of the embodiment already known from
A view in section of the actuator 202 is illustrated in
The transmission 219 is exposed in
The force required for this is transmitted to the brake lining 356 via the brake lever 358. The brake lever 358 is in turn activated by the brake plunger 314. The latter is activated in a known manner by the cam disc 308.
With regard to the guidance of the brake plunger 314, two alternative brake plunger guides 315, 315′ are shown. The straight brake plunger guide 315 serves to guide the brake plunger 314 (in translation) purely linearly.
Alternatively, a curved brake plunger guide 315′ can be provided which enables non-linear guidance of the brake plunger 314.
The electromechanical actuator 302 illustrated in
A further alternative embodiment of this system for storing and delivering energy is illustrated in
When the cam disc 408 rotates, the roller bearing 474 follows the axial track 478 in the axial direction. If the roller bearing 474 thus moves in the direction of the bearing 470, the spring element 436 arranged between the bearing 470 and the spring head 472 is compressed and therefore energy is stored therein.
If, in contrast, the roller bearing 474 moves on such a section of the axial track 478 where the roller bearing 474 moves in the direction of the cam disc 408, the spring element 436 assists the rotational movement of the cam disc 408 and therefore delivers its stored energy to the latter. It should be understood that the axial track 478 can in principle be positioned on both sides of the cam disc 408.
A plan view of such a cam disc 408 provided with an axial track 478 is illustrated in
It is understood that if, for example, φmin=0, it is also true that φmin=360° because the rotation of the cam disc would start again once 360° has been exceeded. The angular positions and radii shown are given only by way of example and can be adapted or shifted as desired.
The function r(φ) rises strictly monotonically in a first angular range 0°≤φ≤270° and falls strictly monotonically in a second angular range 270°≤φ≤360°.
The function r(φ) has, as shown in particular in
The radial distance r(φ) decreases strictly monotonically in the angular range 270°≤φ≤360° such that the rate of change r′(φ) in this range is negative, as also shown in particular in
As the function profile of the rate of change r′(φ) according to
The function r(φ) according to the second exemplary embodiment differs from the function shown in
As shown in particular in
The function r(φ) according to the third exemplary embodiment differs from the function shown in
As shown in particular in
The function r(φ) according to the fourth exemplary embodiment differs from the function shown in
The first angular position φ=φp1,2 here describes an angular position which follows the angular position φ=φmax at which the radial distance r(φ) is at its maximum. The second angular position φp2,1 follows the angular position φ=φmin at which the radial distance is at its minimum. The region of the cam disc in which the radial distance r2(φ) of the contact surface from the pivot point of the plunger decreases thus merges smoothly and in particular with no kinks into the region of the cam disc in which the radial distance r1(φ) increases in particular linearly.
As shown in particular in
The function r(v) according to a fifth exemplary embodiment differs from the function shown in
Such a transition function enables a smooth function profile of the rate of change of r′(φ) according to
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2019 122 088.2 | Aug 2019 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/072117 | 8/6/2020 | WO |
