Patent Application
20240149851
This application claims the benefit of and right of priority under 35 U.S.C. § 119 to German Patent Application no. 10 2022 211 503.1, filed on 28 Oct. 2022, the contents of which are incorporated herein by reference in its entirety.
The invention relates to the checking of an actual-pressure sensor of a motor vehicle brake system.
The invention relates in particular to so-termed off-highway vehicles, such as agricultural tractors, which comprise a motor vehicle brake system with an electronic trailer control system. In order to provide a trailer control system of that type with as few sensors as possible, the correct functioning of the electronic trailer control system is typically verified by plausibility checks. Particularly in the case of sensors that measure a pressure of 0 bar for long periods, however, it is difficult for the electronic trailer control system to recognize and to maintain the correct functioning of the electronic trailer control system. Thus, when a desired brake operating pressure is smaller than 1 bar and an actual-pressure sensor measures an actual brake pressure value of 0 bar, the deviation between the desired service brake pressure and the actually measured value is less than 1 bar. The natural reaction of the regulating system is then problematic: since the measured actual braking pressure value is 0 bar, typically it is attempted to reach the desired value by opening the inlet valve of a trailer control valve system. But since the actual-pressure sensor continues to indicate 0 bar, the inlet valve is continuously opened. This results in a sudden increase of the brake pressure and undesired full braking, even though the desired pressure assumes a value of lower than 1 bar.
A purpose of the present invention can be regarded as to improve the regulation of a motor vehicle brake system with an electronic trailer control system in such a way that, in particular, in the event of an incorrectly measuring actual-pressure sensor, full braking is prevented. This objective is achieved by embodiments disclosed in the claims, the description, and the figures.
According to the present invention, a plausibility check to recognize an incorrectly functioning outlet pressure sensor (“actual-pressure sensor” in what follows) is proposed. The invention describes a special plausibility check for the prompt recognition of a defective function of the actual-pressure sensor. The plausibility check described relates to a sensor defect or a system defect that results in a pressure measurement value of 0 bar by the actual-pressure sensor. The idea is that at the beginning of every braking operation carried out by virtue of an electronic trailer braking mode, a specially developed plausibility check is initiated. In the electronic braking mode the braking of the motor vehicle, and in the present case also the braking of the trailer, takes place only indirectly, whereby a far-reaching electronic regulation of the braking power by driver assistance systems, such as an anti-blocking system or a starting regulator, is made possible. In particular, this electronic regulation enables precise adjustment of the braking performance so as to achieve effective braking of the motor vehicle that is appropriate for the situation. The actual braking pressure values measured by the actual-pressure sensor constitute an important input parameter for the further regulation of the brake system of the motor vehicle. The plausibility check is intended to confirm whether a minimum outlet pressure at the actual-pressure sensor, in particular as the result of multiple inlet valve actuations, is reached within a predetermined time. If the minimum outlet pressure is not reached within the predetermined time, then the system automatically switches off the electronic trailer braking control and can, in particular, change to a mechanical redundancy mode in order to avoid the over-braking of the trailer described above.
In this sense, according to a first aspect of the invention, a method for checking an actual-pressure sensor of a motor vehicle braking system is provided. The method comprises in particular the following process steps:
The distinguishing feature of the method according to the invention is that no additional actual-pressure sensor is needed for the plausibility check. Furthermore, the driver of the motor vehicle does not recognize or notice the plausibility check, since it takes place in the background. In addition, an early recognition of a fault enables the initiation of the system reaction, so that unintentional full braking is prevented, in particular including a warning to the driver.
The process steps (400) to (600) can be carried out with every braking process which is initiated when the motor vehicle brake system is operating in the electronic braking mode. In that way a particularly high safety standard can be achieved. On the other hand, computation time can be saved, since in particular the process steps (500) and (600) are only carried out when in process step (400) the value 0 bar is measured as the starting brake pressure. Alternatively, it can be provided that the process steps (500) and (600) are only carried out if in process step (400) a starting pressure between 0 bar and the established threshold value is measured.
For the in particular pneumatic or hydraulic brake pressure, according to an embodiment, a target value is established which is not in excess of 1 bar, such that the brake pressure is regulated on the basis of the established target value for the brake pressure and on the basis of the actual brake pressure value measured by the actual-pressure sensor. Thus, the method according to the invention can be used in particular for gentle braking demands, for which no test has hitherto been known from the prior art. The threshold value can in particular be established at a value between 0 bar and the target value of the brake pressure. The reaction interval can for example be set with a duration between 50 milliseconds and 300 milliseconds.
The motor vehicle brake system can comprise in particular an electro-pneumatic trailer control valve system with an inlet valve. By means of the inlet valve the output pressure of the motor vehicle brake system can be regulated, since the inlet valve is moved to an open position in order to increase the output pressure. In this connection one can speak of a pulse which increases the output pressure or the pneumatic braking pressure. The inlet valve can also be returned again to a closed position in order to prevent an increase of the output pressure, or at least to reduce it. By the extent to which the inlet valve is opened, the intensity of the pressure increase can further be varied. Thus, if the inlet valve is opened wider, then as a rule the pressure increase is more rapid than with a narrower opening. In particular, the inlet valve can be moved to the open and closed condition multiple times within the reaction interval. According to an embodiment, in this sense it is provided that the inlet valve is opened at least once within the reaction interval in order to increase the braking pressure of the motor vehicle brake system in such manner that the measured reaction braking pressure exceeds the threshold value. For this, the trailer control valve system can be directed by an electronic control unit. The inlet valve can also be opened in such manner that not only is the threshold value, but instead a service brake pressure required or desired for the braking process is exceeded.
The pressure regulation can in particular take place in such manner that the pneumatic braking pressure is increased “cautiously” to a desired service brake pressure below 1 bar, for example, to 0.5 bar, without exceeding that target pressure. For that purpose, the inlet valve can, for example, not be opened completely, but only partially. This cautious pressure regulation could have the result that the minimum pneumatic pressure is not exceeded within the reaction interval and the test fails because the regulation process is too slow. To guard against that, the pressure regulation process is adjusted in such manner that an initial opening pulse of the inlet valve of the trailer control valve system is artificially prolonged in order to compel the reaction pressures to reach a particular value, in particular the pneumatic threshold value, more rapidly. In that sense, according to an embodiment it is provided that the inlet valve is moved to an open condition several times within the reaction interval, so that when the inlet valve is moved to the open condition for the first time it remains open for longer than when it is moved to the open condition again after the first time. At the beginning of the reaction interval this results in a very small pressure peak during the time variation of the pneumatic brake pressure. That pressure peak is small enough not to overshoot the desired service brake pressure. Instead, the pressure peak signals to the control unit software within the reaction interval that the actual-pressure sensor will not remain at 0 bar, but it is capable of providing correct values.
Furthermore, it is possible to increase the scope of diagnosis. The plausibility check described above is carried out during a braking demand by the driver. This leads to a high degree of diagnosis cover, but a system-fault or sensor-fault function is only recognized at the beginning of the braking process. To alert the driver to reduced performance, it could be helpful to check the sensor performance before the braking operation. Since the pressure peaks can be very small (for example˜100 mbar), it is possible to trigger a single high inlet valve pulse even when there is no braking demand. In that sense, according to an embodiment it is provided that the inlet valve is moved once to an open condition while no braking operation is being carried out, so that a pressure peak occurs in the time variation of the brake pressure while no braking process is in progress.
The inlet valve pulse can in particular be followed by an outlet valve pulse, so that the said short pressure increase has no effect on the brake pressure of the trailer, but it is nevertheless possible to perceive a value at the actual pressure sensor. In that case, the sensor can be classified as “OK” and the system remains in normal operation. In that sense, according to an embodiment it is provided that, in particular, the electro-pneumatic trailer control valve system comprises an outlet valve, so that the inlet valve is moved to a closed condition after having previously been moved to the open condition while no braking operation is in progress, so that the pressure peak is counteracted. The advantage of this strategy consists in the continuous use of this “test pulse” (slight pressure increase by way of the inlet valve) while the vehicle is at rest or while it is driving. With this solution the degree of diagnosis cover is even greater and faults are recognized already before a braking process. With this type of checking it is also advantageous for the actual-pressure sensor to be located close to the source from which the pressure is produced. In that way the possibility that the sensor does not perceive the effect of the brief impulse can be avoided. With this in mind, according to an embodiment it is provided that the actual-pressure sensor is arranged close to the inlet valve.
According to a second aspect of the invention, a motor vehicle is provided. The motor vehicle comprises a motor vehicle brake system with an electronic control unit. The motor vehicle brake system is designed to be operated in an electronic braking mode, wherein the motor vehicle brake system delivers to a trailer connected to the motor vehicle an in particular pneumatic or hydraulic brake pressure so that a trailer brake system of the trailer can be actuated by means of the said brake pressure. The electronic control unit is designed in particular to implement the process steps (400) to (600) in accordance with a method according to the first aspect of the invention. The motor vehicle is in particular an off-highway vehicle. An off-highway vehicle is understood to be a vehicle which can be operated at least predominantly away from roads. Basically, the vehicle can be any vehicle that does not run on rails. It can be an articulated or semitrailer vehicle. The vehicle can have a trailer. For example, such a vehicle with a trailer can be in the form of a tractor-trailer combination, a truck train, or a semitrailer truck. The tractor-trailer combination can, for example, be an agricultural machine (tractor) with a trailer. The vehicle can also be a dumper, a towing vehicle, or a truck.
Below, example embodiments of the invention are explained in greater detail with reference to the schematic drawing, wherein the same or similar elements are denoted by the same indexes and which shows:
The motor vehicle 1 has a motor vehicle brake system 8. The motor vehicle brake system 8 is connected to the trailer brake system 7 by way of a compressed-air line 9 (the “trailer control line”). The term “connected” is in particular understood to mean that the elements respectively connected to one another are pneumatically linked with one another, i.e., that a pneumatic pressure medium, in particular compressed air, is supplied under pressure by one element and can act on or in the other element. In the example embodiment shown, the motor vehicle brake system 8 produces a pneumatic brake pressure paus which is delivered via the compressed-air line 9 to the brake system 7 of the trailer, which uses the pneumatic brake pressure paus to brake the wheels 6. Thus, the compressed-air line 9 serves for the pressure control of the trailer's brake system 7 and can therefore be regarded as the trailer control line.
A driver of the motor vehicle 1 (not shown) can actuate the foot pedal 14 with his foot, which pedal is connected to the foot-brake valve 15. Depending on the actuation intensity of the foot pedal 14, the foot-brake valve 15 produces a control pressure for the motor vehicle brake system 8. In the example embodiment shown, the motor vehicle brake system 8 comprises two independent control circuits 18 and 19. Alternatively, only one control circuit can be provided, which is then connected to the trailer control valve 10 and the required-pressure sensor 16.
The required-pressure sensor 16 conveys electronically the value of a desired service brake pressure psoll (the desired value of the pneumatic brake pressure paus) called for by the driver by way of the foot pedal 14, to the electronic control unit 17. On the basis of the service brake pressure psoll required and the actual brake pressure values (pist) measured by the actual-pressure sensor 13, the electronic control unit 17 regulates the output pressure paus of the electronically controlled trailer control valve system 10. For that purpose, the trailer control valve system 10 that acts in a closed control circuit with the actual-pressure sensor 13 can comprise an inlet valve 20a and an outlet valve 20b. The actual brake pressure value pist measured by the actual-pressure sensor 13 is conveyed electronically to the electronic control unit 17. Thus, the electronic control unit 17 can access the actual brake pressure value pist measured by the actual-pressure sensor 13 and the desired brake pressure value psoll determined by the required-pressure sensor 16. The actual pressure value pist measured by the actual-pressure sensor 13 can then be linked with the desired service brake pressure psoll by way of a braking characteristic diagram 21 stored in the electronic control unit 17.
The motor vehicle brake system 8 can be operated in an electronic braking mode, in accordance with which a service brake pressure psoll desired by the driver is automatically regulated, so that the output pressure paus is produced in the compressed-air line 9. In that case the driver does not have to intervene in the regulating process. The actual brake pressure value pist detected by the actual-pressure sensor 13 normally corresponds to the output pressure paus. Now and then, however, it can happen that the actual-pressure sensor 13 measures an actual pressure value of 0 bar and/or conveys it to the electronic control unit 17. This can be attributed to a defect of the actual-pressure sensor 13 itself, or to a defect in the connection, in particular the measurement line 12, between the actual-pressure sensor 13 and the output pressure paus.
In that event the cases described below can be distinguished. In a first case the desired service brake pressure psoll can be greater than 1 bar. If the actual-pressure sensor 13 measures an actual brake pressure value of 0 bar and conveys that to the electronic control unit 17, then the difference between the desired service brake pressure psoll and the value actually measured is larger than 1 bar. In such a case, known plausibility checks stored in the electronic control unit 17 can recognize a functional fault, the trailer control valve system 10 is brought to a mechanical redundancy mode, and the electronic braking mode is switched off.
In a second case, for the pneumatic brake pressure paus, a target value psoll can be established, which is not greater than 1 bar. If the actual-pressure sensor 13 measures an actual brake pressure value of 0 bar and conveys that to the electronic control unit 17, then the difference between the desired service brake pressure psoll and the value actually measured is less than 1 bar. In that case, in systems known from the prior art, no plausibility check is available. The natural reaction of the regulating system then poses a problem: since the measured actual brake pressure value pist is 0 bar, the electronic control unit 17 tries to reach the target value psoll, typically by opening the inlet valve 20a of the trailer control valve 10. But since the actual-pressure sensor 13 still indicates 0 bar, the inlet valve 20a also remains continually open. This results in a sudden increase of the pneumatic brake pressure paus in the trailer control line 9 and an undesired full braking, even though the target pressure psoll has a value below 1 bar.
In order to provide a solution for the second case group described, namely (psoll<=1 bar; pist=0 bar), a plausibility check is carried out which relates to a defect of the actual-pressure sensor 13 or a system defect that results in an actual brake pressure value of pist=0 bar at the actual-pressure sensor 13. In this case the plausibility check is in particular carried out at each beginning of a braking operation carried out in the electronic trailer braking mode. The plausibility check is intended to confirm whether a minimum output pressure pmin (threshold value) at the actual-pressure sensor 13 has been reached as a result of multiple actuations of the inlet valve 20a within a predetermined time tmax. If the minimum output pressure pmin has not been reached within the predetermined time tmax, then the motor vehicle brake system 8 automatically switches off the electronic trailer control system and changes to a mechanical redundancy mode in order to avoid the above-mentioned over-braking of the trailer 2.
In a second process step 200, a pneumatic threshold value pmin is established. For example, the pneumatic threshold value pmin can be stored in the memory of the electronic control unit 17, for example, by way of the above-mentioned man-machine interface. As shown in
In a third process step 300, as described earlier the motor vehicle brake system 8 is operated in the electronic braking mode, wherein the motor vehicle brake system 8 delivers the pneumatic braking pressure paus to the trailer 2 connected to the motor vehicle 1, so that the trailer brake system 7 can be actuated by means of the pneumatic braking pressure paus, or so that the trailer brake system 7 can use the pneumatic breaking pressure paus for its actuation.
When the driver of the motor vehicle initiates a braking operation by actuating the foot pedal 14, the required-pressure sensor 16 communicates the corresponding desired service brake pressure psoll to the electronic control unit 17, and this can be regarded as the starting time tstart. The desired service brake pressure psoll adopts a value which is lower than 1 bar, for example 0.7 bar. The threshold value pmin can be set, for example, at a value of 0.2 bar (second process step 200). The reaction interval Δt can be set, for example, at a duration of 150 milliseconds. In a fourth process step 400, at the starting time tstart a pneumatic starting brake pressure pstart of the motor vehicle brake system 8 is then measured by the actual-pressure sensor 13. Moreover, the value of the measured pneumatic starting brake pressure pstart can be conveyed electronically to the electronic control unit 17. In addition, in the fourth process step 400 the reaction interval Δt is started at the starting time tstart.
In a sixth process step 600 it is checked whether the reaction braking pressures pre1, pre2, pre3 exceed the minimum pneumatic pressure pmin. In the example shown in
In this case the first reaction braking pressure pre1 is above the pneumatic starting brake pressure pstart (0 bar). The electronic control unit 17 has previously compared the value of the pneumatic braking pressure paus (0 bar), measured by the actual-pressure sensor 13 and sent to the electronic control unit 17, with the desired service brake pressure psoll=0.7 bar. To increase the pneumatic braking pressure paus to the desired service brake pressure psoll, the electronic control unit 17 has directed the trailer control valve 10 system to move its inlet valve 20a to an open condition. As shown by the first graph 22, by this opening of the inlet valve 20a the pneumatic braking pressure paus has increased in such manner that the measured first reaction braking pressure pre1 is higher than the pneumatic starting brake pressure pstart (0 bar). However, the minimum pneumatic pressure pmin does not exceed the first reaction braking pressure pre1.
As shown by the first graph 22, the second reaction braking pressure pre2 is higher than the first reaction braking pressure pre1. The electronic control unit 17 has previously compared the value of the first reaction braking pressure pre1, measured by the actual-pressure sensor 13 and sent to the electronic control unit 17, with the desired service brake pressure psoll, which has not yet been reached. To increase the pneumatic braking pressure paus to the desired service brake pressure psoll, the electronic control unit 17 has directed the trailer control valve system 10 to move its inlet valve 20a to the open condition or to leave it in the open condition. As shown by the first graph 22, by this opening of the inlet valve 20a the pneumatic braking pressure paus has increased in such manner that the measured second reaction braking pressure pre2 is higher than the first reaction braking pressure pre1. However, the second reaction braking pressure pre2 still does not exceed the minimum pneumatic pressure pmin.
However, the third reaction braking pressure pre3 located within the reaction interval Δt adopts a value that does exceed the minimum pneumatic pressure pmin. The electronic control unit 17 has previously compared the value of the second reaction braking pressure pre2, measured by the actual-pressure sensor 13 and sent to the electronic control unit 17, with the desired service brake pressure psoll=0.7 bar, which has not yet been reached. To increase the pneumatic braking pressure paus to the desired service brake pressure psoll, the electronic control unit 17 has directed the trailer control valve system 10 to move its inlet valve 20a to the open condition or to leave it in the open condition. As shown by the first graph 22, by this opening of the inlet valve 20a, the pneumatic braking pressure paus has increased in such manner that the measured third reaction braking pressure pre3 is now higher than the minimum pneumatic pressure pmin. Thus, the check in process step 600 shows that at least one measured reaction braking pressure, namely, the third measured reaction braking pressure pre3, is higher than the minimum pneumatic pressure pmin. On that basis it can be concluded that the actual-pressure sensor 13 has measured the value 0 bar for the pneumatic starting pressure correctly and is not defective. Consequently, the operation of the motor vehicle brake system 8 in accordance with a process step 600a in the electronic braking mode is continued (Alternative 1).
In the sixth process step 600 it is checked whether the reaction braking pressures pre exceed the minimum pneumatic pressure pmin. Since none of the reaction braking pressures pre gets above the value 0 bar, the check shows that none of the measured reaction braking pressures pre exceed the minimum pneumatic pressure pmin. On this basis it can be concluded that the actual-pressure sensor 13 has measured the value 0 bar for the pneumatic starting brake pressure pstart incorrectly and is therefore defective. Consequently, in a process step 600b the operation of the motor vehicle brake system 8 in its electronic operating mode is discontinued (Alternative 2). Instead, from that time-point onward the motor vehicle brake system 8 can be operated in the mechanical redundancy mode already mentioned earlier.
For the above-described type of checking, special prerequisites and settings of the pressure regulation may be required. With a desired service brake pressure psoll of 0.5 bar, for example, the control system increases the pressure “cautiously” to the desired value psoll and the attempt is made not to exceed that desired value psoll. That would normally result in the minimum pneumatic pressure pmin not being exceeded within the reaction interval Δt and the test would then fail because the regulation process is too slow. Accordingly, the pressure regulation is adjusted in such manner that the initial opening pulse of the inlet valve 20a of the trailer control valve system 10 is artificially prolonged in order to compel the reaction pressures to reach a particular value, specifically the pneumatic threshold value pmin, more quickly.
Moreover, the scope of diagnosis can be increased still more. The above-described plausibility check is carried out during a braking demand by the driver. This leads to a high degree of diagnostic cover, but a system-fault or sensor-defect function is only recognized at the beginning of the braking process. To alert the driver to a reduced performance level, it can be helpful to check the correct functioning, in particular of the actual-pressure sensor 13, already before the braking. Since the aforesaid pressure peak can be very small (for example 100 mbar), it is possible to trigger a single high inlet valve pulse even when no braking demand has been made. For that purpose, the inlet valve 20a is moved to the open condition just once while no braking process is being carried out. In that way a further pressure peak (not shown) is produced in the time variation of the pneumatic braking pressure, while no braking process is being carried out. The inlet valve pulse can in particular be followed by an outlet valve pulse, so that the brief pressure rise has no effect upon the braking pressure paus of the trailer 2, although it is still possible to see a value at the actual-pressure sensor 13. In that case the actual-pressure sensor 13 can be classified as “OK” and the system 8 remains in normal operation. For this, the inlet valve 20a can be moved to a closed condition after it has previously been moved just once to the open condition. Thereafter, in particular a very short time later, the outlet valve 20b can be moved just once to an open condition while no braking process is being carried out. In that way, the pressure peak produced by opening the inlet valve 20a just once can be counteracted.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 211 503.1 | Oct 2022 | DE | national |
