DE19936435A1 - Detecting depletion of volume of pressure medium in brake lines of vehicles involves measuring pressure variation in main brake cylinder chamber(s), evaluating this to detect volume depletion - Google Patents

Abstract

Method involves measuring variation in pressure in one or more main cylinder (1) chambers and evaluating this to detect volume depletion. For main cylinder with several brake circuits the variations in braking pressure in individual circuits are measured, compared and evaluated.

Description

The present invention relates to a method for detection of pressure medium volume depletion in brake circuits or master cylinder chambers of single-circuit or multi-circuit Vehicle braking systems.

In the known hydraulic dual or multi-circuit brake plants can occur the case that under unfavorable loading driving conditions over the stroke of a master cylinder in the brake system does not have displaceable fluid volume is sufficient to the Er in the wheel brakes of the vehicle pressure required to obtain a maximum delay build up. This condition can be used for the purpose of the present Revelation can be called volume depletion. A Such volume depletion can occur in particular with one Brake fading, with an excessive axle load and thus excessive blocking pressures and / or with a poor ent ventilated brake system occur. For example a Volu Exhaustion in a tandem master cylinder leads to one not optimal braking performance with high Pe at the same time dalweg. Such a condition can initially also slowly develop unnoticed by the driver, e.g. B. at egg Gradual overheating of the brake during long periods tender downhill runs. The prior art therefore shows Disadvantages in that an undetected one Volume depletion of the imperfect braking behavior leads to a safety-critical state.

The invention is therefore based on the object to avoid parts of the prior art, and in particular to specify a procedure by which to increase the  Brake safety and braking comfort are exhausted is recognized quickly, easily and inexpensively.

This object of the invention is in a method of type mentioned solved in that the pressure curve measured and evaluated to detect volume depletion is tested. Through monitoring and further evaluation the pressure or pressure curve in the brake circuits and / or Master cylinder chambers of single or multi-circuit brakes was according to the invention directly or indirectly on the Closed in case of volume depletion. Under measurement the pressure curve is particularly in the sense of the invention a single or multiple, especially periodic, measurement solution of the pressure and / or the temporal dependence of the Pressure understood.

The pressure curve is preferably in one or more master cylinder chambers measured. This can in particular also serve pressure sensors that are used in a conventional ESP Hydraulic system serve other purposes.

Taking advantage of the effect of decoupling the individual Brake circuits in the event of volume depletion are preferred for a master cylinder with multiple brake circuits, the Ver Brake pressure curves measured in the individual brake circuits sen, compared and for the detection of volume depletion evaluated.

An application in which is particularly advantageous the master cylinder is a tandem master cylinder with one pressure rod brake circuit and a floating piston brake circuit.  

It is preferably the ge in the push rod brake circuit measured pressure with that measured in the floating piston brake circuit compared pressure. A pressure medium volume depletion in Push rod brake circuit is recognized if the pressure in the Floating piston brake circuit is greater than the pressure in the pressurizer brake circuit. A pressure medium volume depletion in Floating piston brake circuit is recognized if the pressure in the Floating piston brake circuit less than the pressure in the pressure rod brake circuit.

A variant of the invention preferred in terms of measurement technology before pressure changes in the master cylinder as a result of fluctuations in volume requirements to detect volu evaluate men’s creations.

Fluctuations in volume requirements can be caused by a drive-related actuation of brake pressure control valves one regulated brake system. The Operation of the brake pressure control valves for the purpose of the invention used.

Alternatively or additionally, fluctuations in the volume can occur by controlling brake pressure control valves regulated brake system for test purposes.

The brake pressure is advantageously controlled control valves pulsed. Based on the response behavior thus a volume exhaustion can be concluded.

The case of the volume is preferably recognized creation on the evaluation of the dynamic course of a or more pressure sensor signals in the event of fluctuations the volume requirement in the brake circuits.  

The fluctuations in the volume requirement in the Brake circuits through interventions by an ABS / ESP hydraulic system evoked.

A volume depletion in the swimming is advantageous piston brake circuit and / or in the push rod brake circuit imprinted control pulsations of the pressure medium volume requirement in the floating piston brake circuit and / or in the push rod Brake circuit based on one or more of the following criteria Rien recognized: increase, degradation and / or unchanging the induced pressure medium pulsations in the pool piston brake circuit and / or in the push rod brake circuit compared to the case of no volume depletion.

To compensate for what occurs when the volume is exhausted Braking loss can occur when volume is detected in at least one brake circuit the brake pressure in the at least one brake circuit by suitable control ei ner ABS / ESP hydraulics over that in the master cylinder of the little at least one brake circuit prevailing pressure can be increased.

To increase operational safety, the driver is on egg ne detected volume exhaustion pointed out. This can happen with for example by a warning lam installed in the passenger compartment pe done.

The invention, as well as further advantages and refinements the same will be described below with reference to the accompanying drawings explained in more detail. In doing so all described and / or illustrated features for itself or in any meaningful combination the Ge subject of the present invention, independently from their summary in the claims or theirs  Relationship. Throughout the drawings denote the the same reference numerals the same or corresponding elements.

The drawings show:

Figure 1 shows a tandem master cylinder of a two-circuit brake system in the unactuated state.

Figure 2a is a tandem master cylinder of a two-circuit brake system in the actuated state, wherein no volume depletion is present.

FIG. 2b shows a simplified, highly schematic hydrauli cal equivalent circuit of Fig. 2a;

3a shows a dual-circuit tandem master cylinder of a brake system, wherein the volume is exhausted from the pushrod circle.

FIG. 3b is a simplified, highly schematic hydrauli cal equivalent circuit of FIG. 3a;

4a is a tandem master cylinder of a two-circuit brake system, wherein the volume is depleted in Schwimmkolben- circuit.

FIG. 4b is a simplified, highly schematic hydrauli cal equivalent circuit shown in Fig. 4a;

Figure 5a shows a dual-circuit tandem master cylinder of a brake system, wherein the volume in the circuit and in the pushrod floating piston circle is exhausted.

Fig. 5b shows a simplified, highly schematic hydraulic equivalent circuit according to Fig. 5a; and

Fig. 6 is a table which shows schematically the effects of volume depletion in the push rod circuit and / or in the floating piston circuit on the signals of a pressure sensor in the push rod circuit and floating piston circuit when a control intervention takes place in each of the circuits.

The tandem master cylinder 1 of a two-circuit brake system shown in its rest position in Fig. 1 consists of two series-connected master cylinders. The push rod piston 3 and the floating intermediate piston or floating piston 4 are located in a common housing 2 . The illustration on Fig. 1 is highly schematic table and other elements necessary for operation, such as. B. sealing sleeves and springs are wegge to simplify. In Fig. 1, an unactuated position of the tandem master cylinder 1 is shown schematically. The pressure prevailing in the pressure rod circuit is denoted by P _DK and the pressure prevailing in the floating piston is denoted by P _SK . Connections 5 and 6 of the push rod brake circuit and the floating piston brake circuit are connected to an expansion tank 7 in the unactuated position shown in FIG. 1 in connection. By connecting the two pressure chambers to the expansion tank 7 , in particular the brake fluid can be compensated for when it heats up or cools down.

A brake actuation, as it is schematically shown in Fig. 2a, is initiated by the displacement of the push rod piston 3 (in Fig. 2a to the right). By a (not shown) biased piston spring and so on the floating piston 4 is moved. Both pistons 3 , 4 thereby run over their respective compensating holes 8 , 9 and complete the pressure chambers. The pressure build-up in both brake circuits follows at the same time.

The hydraulic equivalent circuit diagram of FIG. 2b shows that when the brake is actuated and the volume is not exhausted, the pressure P _driver controlled by the _{driver is} equal to the pressure P _DK in the pressure rod piston circuit and equal to the pressure P _SK in the floating piston circuit, since the corresponding brake circuits in Fluid connection.

The case of volume depletion in the push rod circle is shown schematically in FIG. 3a. Due to the pressure with in the pressure rods telvolumenerschöpfung circuit is of the push rod piston 3 on to the floating piston. 4 A movement of the push rod piston 3 to the right in accordance with the view of FIG. 3a does not produce a pressure increase in the pressure P _{DK of} the push rod circuit. This can also be seen from the schematic, hydraulic equivalent circuit diagram of FIG. 3b. The pressure P _{SK of} the floating piston circuit can still be influenced by controlling the brake pressure P _driver .

The case of volume depletion in the floating piston circle is shown schematically in Fig. 4a. The floating piston 4 lies against the wall of the housing 2 . Thus, a driver-controlled pressure P _{driver can} only act on the pressure P _{DK of} the push rod circuit and not on the floating piston circuit. As can be seen from FIG. 4b, the floating piston circuit is hydraulically decoupled from the introduction of force via the brake pedal.

The case of a volume depletion both in the push rod circle and in the floating piston circle is shown schematically in FIG. 5a. The decoupling of the pressures in the pressure rod circuit and floating piston circuit P _DK or P _SK from the control via the brake pedal results from the fact that the push rod piston 3 and the floating piston 4 lie next to each other and by the bearing of the floating piston 4 on the wall of the Housing 2 . For safety reasons, this is the particularly alarming complete decoupling of the brake pressures from the control of the brake pedal by the driver (cf. FIG. 5b).

A combination of FIGS. 2 to 5 is used for understandable nis the inventive principle of the detection of the Volu menerschöpfung. If volume exhaustion occurs in one of the two hydraulic circuits, namely the push rod circuit or the floating piston circuit, this brake circuit is decoupled from the respective other hydraulic circuit and also from the force introduction via the pedal. In a slip control brake system according to the Invention, which is in particular an ESP hydraulic system, two ge separate pressure sensors are preferably used for the push rod circuit and the floating piston circuit. According to the invention, the volume depletion is recognized by comparing the measured pressure P _DK in the push rod circuit and P _SK in the floating piston circuit. The tandem master cylinder 1 is in a safety-acceptable normal state, that is, an operating state without volume depletion (see FIG. 1 and FIG. 2a), so prevails in both circuits is substantially the same static pressure. Small deviations can result from a difference ε due to friction of the floating piston 4 . If the sensors (not shown) indicate that the pressure in the pressure rod circuit is greater than the pressure in the floating piston circuit, ie P _DK <P _SK , it follows that the volume is at least exhausted in the floating piston circuit is. Preferably, the difference ε of the pressures in the two circles based on the friction of the floating piston 4 is also taken into account, so that a volume depletion is recognized at least in the floating piston circle when P _DK <P _SK + ε applies. If a comparison of the measured values of the sensors shows that P _DK <P _SK applies, it can be concluded that pressure medium volume has been created in the pressure rod circuit. Taking into account friction losses ε, a volume depletion in the push rod circuit is recognized if P _DK <P _SK + ε applies.

Previously, a first embodiment of the present invention was described using two separate pressure sensors in the push rod circuit and in the floating piston circuit by measuring and comparing the static pressures. In the following a further embodiment of the present invention is presented, which is based on the evaluation of dynamic profiles of the pressure signals and in particular detects and localizes the case of volume depletion with only one pressure sensor. From the above description in conjunction with FIGS . 2b to 5b it can be seen that that circuit of the brake system is hydraulically decoupled from the rest of the brake system in which the volume is exhausted. Any further volume requirement in this circuit leads to a drop in pressure, since the volume of brake fluid contained in this circuit or the surrounding line elements relax elastically. This effect occurs statically, ie the pressure remains permanently low in this brake circuit because no brake fluid can flow in. The effect is correspondingly reversed if the volume requirement of a brake circuit decreases as long as the volume is still exhausted. Pressure fluctuations in this circuit will not affect the rest of the hydraulic system.

In contrast, if the volume in a brake circuit is not exhausted, a change in the volume requirement in this circuit leads to a comparatively small and only temporary pressure fluctuation, since brake fluid can flow into or out of the tandem master cylinder 1 and become static the pedal force corresponds to the pressure again. In such a hydraulic circuit, pressure fluctuations also have repercussions on the brake pedal and the other hydraulic circuit, provided that the volume is not exhausted.

This consideration is the starting point for the second version Example of the present invention, which Fluctuations in the volume requirements of the brake circuits. The Similar fluctuations can occur during operation through control interventions an ABS or ESP regulation. Through this Fluctuations in volume requirements also arise per se knew vibration of the brake pedal. In addition to that or also alternatively, special ones can hardly be true for the driver Acceptable test pulses in the form of short pressure reductions and pressure structures for the detection of a volume depletion via the Hydraulics can be controlled.

The table shown in FIG. 6 shows the effects of volume depletion in the push rod circuit and / or in the floating piston circuit, which result from the different response behavior, on the signals from a pressure sensor in the push rod circuit or floating piston circuit, if in one of the circuits a control intervention takes place. Here, (○) stands for pulsations unchanged compared to the normal case, ie the case without volume depletion, (+) for increased pulsations and (-) for reduced pulsations at the respective pressure sensor. From the table shown in Fig. 2 there are a variety of possibilities in the detection and localization of a volume depletion. In a variant of the invention, two pressure sensors are used, namely in the push rod circuit and in the floating piston circuit. If there is a control intervention both in the push rod circuit and in the floating piston circuit, the resulting four measured values for the pulsation amplitudes can be used to detect and localize a volume depletion. For explanation, the signals of the sensors are presented in the following form: (relative pulsation measured at the sensor in the push rod circuit during a control intervention in the push rod circuit; relative pulsation at the sensor of the floating piston circuit during a control intervention in the push rod circuit; relative pulsation at Pressure rod circuit sensor during control intervention in the floating piston circuit; relative pulsation at the sensor of the floating piston circuit during control intervention in the floating piston circle). A state recognized according to this notation (+; -; -; ○) indicates volume exhaustion in the push rod circuit. A status (○; -; -; +) indicates volume exhaustion in the floating piston circle. A state (+; -; -; +) indicates a volume exhaustion in both circles, ie in the push rod circle and in the floating piston circle. A state (○; ○; ○; ○) shows the normal state, ie there is no volume depletion in any brake circuit.

In a further variant of the invention, a pressure sensor in the push rod circuit or in the floating piston circuit can also be used in conjunction with control interventions in one or both circles. As an example, only a pressure sensor is provided in the push rod circuit. The following notation is used for illustration: (relative pulsation at the pressure sensor during a control intervention in the push rod circuit; relative pulsation at the pressure sensor during a control intervention in the floating piston circle). A status (+; -) indicates volume exhaustion in the push rod circle. One state (○; -) indicates a volume depletion in the floating piston circle. It is clear to a person skilled in the art that further evaluation options from the table shown in FIG. 2 with one or more pressure sensors and corresponding control interventions are possible.

Previously, using several exemplary embodiments, he explained how volume exhaustion can be detected and localized using one or more pressure sensors which measure static and / or dynamic signals, which may result from operation or may be impressed for test purposes. In the event of a detected volume depletion, the driver is warned according to the invention. This can be done, for example, by lighting up a warning lamp in the passenger compartment. Alternatively or additionally, if the volume is detected, the braking force can also be actively increased, so that in spite of the volume exhaustion, there is a safety-free state. By using a suitable hydraulic lik the brake pressure in the volume-exhausted brake circuit can be actively increased by the system via the pressure of the tandem master cylinder 1 of the volume-exhausted circuit. For this purpose, the hydraulic system uses a return pump in the braked-down state to actively build up pressure in the volume-exhausted circuit. For this purpose, for example, a hydraulic system with an electrically controllable switching valve and / or isolating valve can be provided.

The pressure increase in the exhausted brake circuit can be there at least so far until the pressure in the main cy of the affected circle has sunk so far that the return pump does not have enough pre-pressure Brake fluid can deliver more.

In this situation there may also be other brake flows flow from the reservoir, causing a Pressure build-up in the brakes of the affected circuit up to Control pressure level is safely enabled. To do this are the tan the master cylinder, the return pump and other elements te, such as B. a pre-charge pump, designed accordingly.  

Reference list

1

Tandem master cylinder

2nd

casing

3rd

Push rod piston

4th

Floating piston

5

Connection

6

Connection

7

surge tank

8th

Compensating hole

9

Compensating hole

Claims (16)

1. A method for detecting a pressure medium volume creation in brake circuits or master cylinder chambers of single-circuit or multi-circuit brake systems of vehicles, characterized in that the pressure curve is measured and evaluated for the detection of volume exhaustion. 2. The method according to claim 1, characterized in that the pressure curve in one or more main cylinders derkammern is measured. 3. The method according to claim 1 or 2, characterized net that with a master cylinder with multiple brakes circle the courses of the brake pressures in the individual Brake circuits measured, compared and for detection of volume depletion can be evaluated. 4. The method according to claim 3, characterized in that the master cylinder is a tandem master cylinder with one Push rod brake circuit and a floating piston Brake circuit is. 5. The method according to claim 4, characterized in that the pressure measured in the pushrod brake circuit with the Compare the pressure measured in the floating piston brake circuit will. 6. The method according to claim 5, characterized in that a pressure medium volume depletion in the push rod Brake circuit is recognized if the pressure in the float  piston brake circuit greater than the pressure in the pressure ram brake circuit. 7. The method according to claim 6, characterized in that a pressure medium volume depletion in the floating piston Brake circuit is recognized if the pressure in the float piston brake circuit less than the pressure in the pressure ram brake circuit. 8. The method according to any one of the preceding claims characterized in that pressure changes in the main cy linder due to imprinted fluctuations in the volume volume requirements for the detection of volume depletion get ranked. 9. The method according to claim 8, characterized in that Fluctuations in volume requirements due to operational Actuation of a brake pressure control valve brake system. 10. The method according to claim 8 or 9, characterized in net that fluctuations in volume requirements due to An control of brake pressure control valves of a regulated Brake system can be stamped for test purposes. 11. The method according to claim 10, characterized in that the control of the brake pressure control valves pulsed he follows. 12. The method according to any one of the preceding claims, since characterized in that the detection of the case of Volume depletion based on the evaluation of the dynamic Course of one or more pressure sensor signals in the  In case of fluctuations in volume requirements in the Brake circuits are done. 13. The method according to any one of the preceding claims, since characterized in that the fluctuations in the volu quantity requirements in the brake circuits through control interventions an ABS / ESP hydraulic system. 14. The method according to any one of claims 8 to 13, characterized characterized in that a volume depletion in Floating piston brake circuit and / or in the push rod Brake circuit with impressed control pulsations of the Pressure medium volume requirement in the floating piston brake circuit and / or in the push rod brake circuit using one or several of the following criteria are recognized: hung, humiliation and / or unchanged ind decorated pressure medium pulsations in the floating piston Brake circuit and / or in the push rod brake circuit against above the case of no volume depletion. 15. The method according to any one of the preceding claims, since characterized in that when volume is detected creation in at least one brake circuit of the Brake pressure in the at least one brake circuit suitable control of an ABS / ESP hydraulic system via the in the master cylinder of the at least one brake circuit prevailing pressure is increased. 16. The method according to any one of the preceding claims characterized by that the driver recognized on a Volume exhaustion is indicated.