EP2734428A1

EP2734428A1 - Method for tightening an electromechanical brake, and electromechanical brake

Info

Publication number: EP2734428A1
Application number: EP12738088.9A
Authority: EP
Inventors: Wolfgang Richter; Christoph Buelte
Original assignee: Continental Teves AG and Co OHG
Current assignee: Continental Teves AG and Co OHG
Priority date: 2011-07-19
Filing date: 2012-07-16
Publication date: 2014-05-28
Also published as: US20140222307A1; DE102011079362B4; KR20140054083A; DE102011079362A1; CN103687767A; WO2013010969A1

Abstract

A method for tightening an electromechanical brake having an actuator which is driven by an electric motor and which presses a brake element against a brake body with a force stroke in order to implement a parking brake functionality, wherein for the purpose of tightening a number of chronologically successive force strokes are carried out, the intention being to configure the tightening process as effectively and reliably as possible. For this purpose, the force strokes are each applied as soon as the tensioning force of the brake drops below a predefined tensioning force minimum setpoint value, wherein the respective force stroke is applied in such a way that a predefined maximum tensioning force is not exceeded, wherein the expected total loss of tensioning force is determined on the basis of the initial temperature of the brake body and the expected final temperature of the brake body, and wherein the time of a last force stroke is selected in such a way that at this time the sum of the previous force strokes, the last force stroke and the still expected loss of tensioning force exceeds the expected total loss of tensioning force.

Description

Method for tensioning an electromechanical brake and electromechanical brake

The invention relates to a method for tensioning an electromechanical brake with a driven by an electric motor actuator, a brake element ge ^¬ gene suppressed to realize a parking brake functionality in a power stroke a brake body, which for tensioning a plurality of temporally successive power strokes is exerted. It further relates to a corresponding electro-mechanical brake.

In an electromechanical brake (EMB) or electromechanically actuated brake, the corresponding wheel is braked purely electrically by an electrically operated actuator. Usually, such brakes are designed as disc brakes ^¬, wherein a brake piston is pressed against a brake disc during a braking operation by an electric motor via a spindle drive driven by it. The ^¬ like brakes are usually controlled by a control unit and usually each include their own electronics on the brake caliper to set a wheel-individual braking force. EMBs can be used in brake-by-wire brake systems, where each of the four wheels is braked purely electrically. They can continue to be used in so-called combined braking systems in which, for example, the wheels on the front axle are hydraulically braked and the wheels are electrically braked on the rear axle. Another requirement for an EMB is the parking brake function, which effectively replicates the handbrake in conventional vehicles.

This parking brake function, as well as the normal or Be ^{¬ service} brake function, made available due to an electronic request by another electronics or software imple ^¬ mented routine available. Must be kept safe against rolling slope - the statutory requirement that a fully loaded out of the certification vehicle at a 20% it applies to the parking brake ^¬ function. In practice, this results in the challenge of keeping a parked with hot rotors vehicle accordingly safe. If one sets a specific clamping force between the brake pad and the brake disc with hot brake discs, this value decreases in the course of the cooling, where ^¬ out a rolling of the vehicle can result.

For this reason, must either by constructional measures, which usually have drawbacks, the mög ^¬ Liche power loss can be limited or the control electric ^¬ technology must ensure suitably that the necessary clamping force is guaranteed ^¬ efficiency even at cooling of the brake disk, for example by in certain time intervals, the clamping force on the brake disc is brought by a ^¬ tension again from a low to a higher level. Structurally, a reduction of the force drop during cooling can be achieved by lower stiffness of the caliper, but this can lead to noticeably worse behavior when operating the service brake.

The clamping forces should always lie in an area that ensures a secure hold of the vehicle. The on This Nachspannvorgang involved control devices must be energized during this time continue to prevent unwanted loss of power. This period, during which the corresponding control units are still active, was to conserve energy and to keep the risk of failure mög ^¬ lichst low turn out as short as possible. However, it must be long enough to be able to ensure by a sufficient distribution of Nachspannvorgängen that is switched off in the safe state at a deactivation of the control units and completely abge ^¬ cooled brake disc. In known systems in which the clamping force is increased by the brake at fixed time intervals, the period of re-tensioning must be chosen to be very long to ensure that after the last Nachspannvorgang the voltage applied to the cooled brake clamping force ^¬ sufficient to hold the vehicle.

The invention is therefore based on the object to make the Nachspannvorgang as effective and safe as possible.

In respect to the method this object is achieved Invention ^¬ according to the fact that the power strokes are respectively applied as soon as the clamping force of the brake drops below a predetermined clamping force minimum reference value, said jeweili ^¬ ge power stroke is applied such that a predetermined Ma ^¬ ximalspannkraft is not exceeded , And being determined on the basis of the initial temperature of the brake body and the expected end temperature of the brake body, an expected total loss of clamping force, the time ei ^¬ nes last power stroke is chosen such that at this time the sum of the previous power strokes, the last power stroke and the expected loss of clamping force exceeds the expected total loss of clamping force. Advantageous embodiments of the invention are the subject of the dependent claims.

The invention is based on the consideration that notwen for an effective and lasting as short as possible time lag strategy for EMB knowledge or estimates of the total expected loss of clamping force are ^¬ dig. Once this total expected loss of clamping force is known, the sum of the force strokes necessary during the overrun strategy or the post-tensioning process can be calculated from this.

As has now been detected, the loss of clamping force is possible on a brake disc and the temperature decrease of the Bremskör ^¬ pers or the brake disc in an approximately linear to ^¬ connexion. However, the temperature history as such during cooling can not be used as a decision value for retensioning because it depends on unpredictable environmental conditions such as wind and rain. That is, depending on environmental conditions, the brake disc may cool down faster or slower, making predictions about a cooling time difficult.

However, it is possible due to, e.g. from a

Window temperature model, available brake discs ^¬ bentemperatur an expected (total)

To calculate the loss of tension during the cooling process. That is, once the Bremsscheibenanfangs- temperature when stopping the e.g. Cars and the too

expected brake disk end temperature known, it can be calculated using a suitable parameterization of the total expected loss of clamping force. In these considerations, the final cooling time then no longer matters. The final temperature at the brake is ty- Typically, the ambient temperature that is available in the vehicle, for example, as "outside temperature." The calculation of the loss of clamping force occurs once at the beginning of the shutdown process.

This concept also works when no linear relationship is assumed between brake discs ^¬ bentemperatur or temperature difference and loss of clamping force, but the disc temperature model contains another functional relationship. It is essential here that the total loss of clamping force can be determined in this way. The sum of all Nachspannvorgänge or the corresponding force strokes must then compensate for the total loss of power, so that at the end of the cooling phase again the first set ^{¬ is} set, safe force level is reached. For the

Cooling over time, i. for the temperature development as a function of time, an exponential function is to be considered as a first approximation. Although this mathematically approaches its final value asymptotically, it never reaches it.

If you were to set this temperature history of a run-strategy basis, which would, however, signified ^¬ th that the follow-up phase of the participating HEADUNITS ^¬ te would take forever, which of course is practical in any way. Since, as noted above, for the si ^¬ chere parking the vehicle the timing of the ex ^¬ cooling of the brake disc son ^¬ countries is not even relevant, but the total loss of clamping force, only has to be ensured for a si ^¬ cheres off that Clamping ^¬ force of the higher force level is sufficiently greater than the clamping force, which is at least needed to prevent the vehicle from rolling away. This security buffer can be used to determine the last part of the time Compensate for loss of tension. As a result, towards the end of the cooling phase, the force level of the

Minimum clamping force and has completed the last Nachspannvorgang finite time.

If the course of the cooling of the brake disk was to be taken as the basis for a follow-up strategy, the times for the necessary post-tensioning operations could be determined only with difficulty because of the above-mentioned environmental influences. So it needs another criterion, which is decisive for the respective Nachspannvorgang. It is advantageous to know the instantaneous clamping force of the brake. In doing so, the clamping force of the brake disc is monitored and tightened whenever a defined minimum force value or minimum clamping force target value is undershot. Since ^¬ at lifts a Nachspannvorgang the clamping force to a higher level of force.

The maximum size of such power strokes and the clamping force while maxi ^¬ adjusted times depend on the design of the brake system and are constants that is limited by structural conditions. On the one hand, the highest possible power strokes are desirable in order to keep the maximum number of power strokes for retightening the brake of a parked vehicle as low as possible. On the other hand, too much set clamping forces can also lead to material damage ^¬.

Since the total clamping force loss was calculated and is now be ^¬ known, the time of the last power stroke is then chosen so that at this time the sum of the vorheri ^¬ gen power strokes the last to operate end power stroke and from that time still expected loss of clamping force the exceeds the expected total loss of tension. With their words, the sum of the payments already made power strokes corresponds to at this time the total expected force ^¬ loss minus the power of a power stroke. In this case, a safety buffer can still be planned, so that the last power stroke is selected so that the end of a ^¬ adjusting clamping force to the value of this safety buffer is greater than the minimum necessary clamping force for holding the motor vehicle.

In a preferred embodiment of the method, the time of the last power stroke is selected as early as possible. That is, as soon as a final power stroke is sufficient to compensate for the expected loss of clamping force such that the adjusting at the end of clamping force is large enough and at the same time adjusting itself at this power stroke

Clamping force is less than the maximum clamping force, this ^¬ last power stroke is executed. Due to the fact that the total loss of clamping force has been determined, the remaining loss of tension is known at any time during re-tensioning, as it simply results from the total loss of tension minus the size of the previous power strokes. In this way, therefore, the earliest possible time at which a last power stroke must be made, be determined. The choice of the earliest possible time allows the earliest possible shutdown of the control units, so that no more energy than necessary for the entire Nachspannvorgang must be applied.

Advantageously, the time of the last power stroke is selected such that the gradient of the clamping force ^¬ amount falls below a predetermined gradient setpoint. The gradient of the clamping force characterizes the rate at which the tension decreases. The smaller the Gra ^¬ serves, the smaller the loss of clamping force per unit time. Through the weave of the time of last power stroke to the condition that the amount-gradient of not below Spann ^¬ force a predetermined Gradientensollwert about ^¬ is ensured that the temporal variation of the clamping force loss remains below a certain value and thus, the clamping force only sufficiently slowly changes or degrades.

In a further preferred embodiment of the method, the time of the last tightening is selected at the latest when a maximum period of time between the first and the last power stroke is exceeded. The maximum time span ^¬ can also be defined between the locking of the parking brake or parking the vehicle and the last power stroke. The definition of a maximum time ensures that the control units do not need to be supplied with electrical power for too long and there is a risk of the power supply becoming too weak to carry out a final power stroke. The maximum time does not allow to ensure a sufficient clamping force. Therefore, the maximum time must have sufficient safety buffer beinhal ^¬ th and are checked through trials. The maximum time ensures, however, that the participating control units are switched off and the vehicle battery is not completely discharged. The maximum time can be carried out depending on the temperature.

The determination of the instantaneous clamping force of the brake can be done in various ways. For example, it can be determined by a force sensor which directly measures the force exerted by the brake piston or brake lining on the brake disk. An indirect but less robust and Weni ^¬ ger reliable way to determine the actual or instantaneous clamping force can by measuring the motor current the electric motor that drives the actuator to be performed.

The temperature determination of the brake body or the brake disc is advantageously carried out by means of a tempera ^¬ turmodells, in particular on the basis of the clamping force loss of the brake body. The temperature of the brake disc or the

Brake body correlates with the loss of power, which can be measured approximately in the first minute after locking the parking brake. In this way the disc temperature can be made plausible. Alternatively or in combination therewith, if redundancy is desired or required, the brake discs ^¬ bentemperatur can also be measured directly.

A typical window temperature model has during the ex ^¬ cooling to an exponential curve, wherein the high temperature difference between the brake and a correspondingly high ambient air temperature decrease is calculated. As Nä ^¬ herungs formula:

T (t) = T _end + [(T _start -T _end ) * (e ^" ^ ')]

When heating by braking the temperature increase is much more dependent on ^¬ of clamping force, friction coefficient of the brake pads, vehicle speed ^¬.

The above object is achieved with respect to the electro-mechanical brake with a control unit with means for performing the above method. These means preferably comprise hardware and / or soft ware ^¬ moderately implemented routines. These routines can be imple ^¬ mented, for example into an existing control unit. Alternatively, a separate control unit may be provided, into which the speaking routines or method steps hardware and / or software implemented.

The advantages of the invention are, in particular, that are not required by the determination of the expected total clamping force loss on the basis of the initial and final temperature of the brake ^¬ body Information about the actual cooling of the brake body, but the time ^¬ point of the last power stroke rather only by the Sum of the previous power strokes and the expected loss of tension depends. If this time of the last power stroke ^¬ elected as early as possible, the time period over which the control devices must be active as much as possible is held.

By determining the temperature of the brake body, using a temperature model, in particular by means of the clamping force ^¬ loss of the braking body can be ver ^¬ dispensed to temperature sensors or a redundancy to be created in their presence. For the method described, not necessarily the absolute temperatures, but only the temperature difference between the initial temperature and the end temperature must be measured or determined.

An electromechanical brake with a control ^¬ rule unit with means for carrying out the above method allows energy-saving, yet reli ^¬ siges parking a corresponding vehicle. For carrying out the method described electronic components that are used for other control processes can be shared, for example, by the procedural ^¬ ren is implemented as a software routine.

An embodiment of the invention will be described with reference to a Drawing explained in more detail. In it show in a highly schematic representation:

FIG. 1 is a flowchart of a method for retightening an electromechanical brake in a preferred embodiment, and

FIG. 2 the temporal course of the clamping force of a

Brake during an exemplary Nachspannvorganges using the in FIG. Shown Ver ^¬ proceedings. 1

A flowchart of the method according to the invention in a preferred embodiment is shown in FIG. 1 shown. To start 2, the vehicle is turned off and the Parkbremsfunk ^¬ tion activated. In block 8, after the start of 2 and the on ^¬ initial temperature T _A and the expected final temperature T _E, or the difference T _A -T _E of the brake disc of the total expected loss of clamping force S _T of the brake is based on the Spannkraftverlus ^¬ tes within the first minute certainly.

The calculation of the total loss of clamping force S _T can also be carried out, not only at the beginning of the method, as shown here, but also between the further method steps, so that the value determined initially can, so to speak, be corrected as required.

In decision 20, it is checked whether the currently applied force or clamping force F is smaller than a nominal low-end load value Fi (1 for limit). If so, the process branches to block 26 by performing a power stroke Ki by which the force or tension F is increased again. This ensures that the clamping force set by the power stroke does not cause a maximum paint value S _max exceeds. This will prevent damage to the brake. Was the tension or force F still above the clamping force minimum setpoint Fi, no power stroke is ^¬ leads. In the present embodiment, the maxi ^¬ male size of the power strokes K _± 4.000 N. is

In any case, the method now goes to the decision 32, in which the sum of the previous power strokes, the remaining clamping force loss S _r and a possible final power stroke K _{f is} formed, whereby only those power strokes K _{f be} taken into account ^¬ , the set clamping force can not rise above ei ^¬ nen maximum clamping force value S _max. If this sum is smaller than the ^¬ me still expected total loss of clamping force S _T, SO the method branches back to check whether the instantaneous clamping force is smaller than the predetermined clamping force setpoint. If the sum formed in the decision 32 is greater, then a final final power stroke is sufficient to ensure that after complete cooling of the brake disk, the then applied clamping force is large enough to hold the vehicle. In this case, a final power stroke K _{f is} performed in block 38, and the method ends at stop 44.

An exemplary force curve during the implementation of the in connection with FIG. 1 described method is shown in FIG. 2 shown. On the abscissa 60, the time in seconds ^¬ (s), plotted on the ordinate 66, the clamping force in Newton (N). The curve 72 represents the current applied clamping force value. A clamping force minimum setpoint ^¬ 78, either during the follow-up phase or the Nachspannvorganges un ^¬ to be undershot even after completion of this process lies in the present example 19.5 kN. From the time t = 0 s cools the brake disc until the time t = 150 s the clamping force minimum setpoint 78 ^¬ he can see. At this time, a first power stroke 84 of 4,000 N size is performed. As a result, the force F is again guided to an upper force level 88 of 23,500 N, which was also present at the time t = 0 s. The upper force level 88 corresponds to a predetermined maximum value of the clamping force S _max to be set, which should not be exceeded in order to avoid material damage.

The brake disc cools after the first power stroke from further so that the clamping force is smaller again and the time ^¬ point about 460 s t again the clamping force minimum setpoint 78 reached. For this reason, a second power stroke 90 is now performed, which again leads the clamping force to the upper power level ^¬ 88. The brake disc now cools down further. Was currency ^¬ rend the entire period of the expected total clamping force loss ^¬ S _T is known, so that be ^¬ revoked at any time how much is still expected loss of clamping force S _r. The last or final power stroke 96 is performed exactly then (in the present example at approximately t = 850 s), if the current clamping force minus the remaining clamping force loss S _r does not fall below a predetermined level. This level can at the minimum clamping force set point 78 lie ^¬ gene, but it is preferably somewhat higher, so that a ge ^¬ wisser buffer is granted, which compensates for uncertainties or irregularities of the individual variables. The final power stroke 96 is in contrast to the power strokes 84 and 90 only about 2,000 N. An additional condition in the choice of the last power stroke is given by the fact that the applied clamping force F does not exceed the upper force ^¬ level 88. LIST OF REFERENCE NUMBERS

2 start

8 block

20 decision

26 block

32 decision

38 block

44 stop

60 abscissa

66 ordinates

72 curve

78 Clamping force minimum setpoint

84 first power stroke

88 upper strength level

90 second power stroke

96 final power stroke

F force

K _f final power stroke

F _L Clamping force minimum setpoint

_For residual loss of clamping force

Ki power stroke

S _r loss of tension

S _T total loss of tension

T _A start temperature

T _E final temperature

Claims

claims

1. Method for tensioning an electromechanical

Brake with an actuator driven by an electric motor, which presses a braking element against a brake body for the realization of a parking brake functionality at a power stroke, for tensioning a number of successive force strokes is exercised, characterized in that the power strokes are exerted in each case as soon as the clamping force of Brake falls below a predetermined Mindestkraftmindestsollwert, the respective power stroke is exerted such that a predetermined maximum clamping force is not exceeded, based on the initial temperature of the brake body and the expected end temperature of the brake body an expected total loss of clamping force is determined, and wherein the time of a last power stroke so is chosen that at this time the sum of the previous power strokes, the last power stroke and the expected loss of clamping force exceeds the expected total loss of clamping force.

2. The method of claim 1, wherein the time of the last power stroke is selected as early as possible.

3. The method of claim 1 or 2, wherein the time of the last power stroke is selected such that the gradient of the clamping force falls below a predetermined gradient setpoint.

4. The method according to any one of claims 1 to 3, wherein the time of the last Nachspannens ge ^¬ selected at the latest when a maximum period of time between the first and the last power stroke is exceeded.

5. The method according to any one of claims 1 to 4, wherein the clamping force is determined by a force sensor.

6. The method according to any one of claims 1 to 4, wherein the clamping force is based on the motor current of the electric motor he ^¬ averages.

7. The method according to any one of claims 1 to 6, wherein the temperature of the brake body by means of a temperature ^¬ model, in particular based on the loss of clamping force of the brake body is determined.

8. Electromechanical brake with a control and regulating ^¬ unit with means for performing a method according to one of claims 1 to 7.