DE10254818A1 - Electrohydraulic brake fluid monitoring procedure, measures load related temperatures and pressures and applies control measures to individual components - Google Patents

Abstract

An electrohydraulic brake fluid monitoring procedure measures (300) load related temperature and pressure and compares (310, 330, 350) them with thresholds to select corrective action for the valve (340), pump (320) or control system (360) An Independent claim is included for equipment using of the procedure to control hydraulic brake fluid thermal loadings.

Description

State of technology

The invention relates to a method and a monitoring device one with a hydraulic fluid equipped braking system of a vehicle, making a comparison a recorded company size, the represents an operating parameter of the hydraulic fluid, is carried out with a predetermined threshold value and dependent at least one measure is initiated by your comparison, the functionality the brake system ensures.

The safe operation of hydraulic units and the associated ones Add-on control devices in a conventional Vehicle is for a temperature range within certain maximum or minimum temperatures designed. These components are used, for example, at temperatures above the maximum temperature operated, it can lead to functional losses up to complete destruction the components come due to thermal stress. But also a lowering of the temperature below a critical low temperature can lead to a reduction in operational safety.

For recording various state variables such as the temperature and / or the pressure of a lubricant, the DE 199 59 145 C2 a method and a device with which the state variables can be detected by suitable sensors. The sizes can be determined and further processed by positioning the sensors on the cables in real time.

From the DE 36 39 664 C2 a method and a device for monitoring the state of a hydraulic fluid is known. The boiling point is determined using hooves of a sensor element and the instantaneous temperature of the liquid is derived.

In the DE 196 19 127 A1 proposes a cooling device in which the (brake) fluid-carrying line is guided through a housing which is filled with a medium and adapts to the shape of the line and the housing. This ensures the best possible heat transfer from the line to the housing. The heat transferred to the housing is transferred to a heat-absorbing component and dissipated.

In the DE 197 14 920 C1 an additional hydraulic pressure medium connection is provided, via which a forced flow from the reservoir to the pressure chamber of the wheel brake cylinder can be generated by an additional pump during driving between two braking processes. Through this connection, a heated brake fluid enriched with vapor bubbles is pressed into the reservoir connected to the atmosphere, from which the vapor bubbles can escape to the outside.

Act in the present invention it is a method and a device by means of which a company size one Brake system of a vehicle is monitored becomes. It is for monitoring provided that the farm size is an operational parameter the hydraulic fluid represents. An operating parameter is advantageously selected here: at the same time as the company size of the other components serves the braking system. It is also planned. that the captured Company size and / or the change over time the recorded company size with at least a predeterminable threshold value is compared, which is a limit value fair operation of the hydraulic fluid and / or represents one of the other components of the brake system. The core the invention consists in it. that depending on the monitoring of yours Comparison at least one predefinable measure is carried out, the functionality the brake system.

For example, the control can be used as a measure various components of the brake system to compensate for the load be provided.

The interpretation of the Company size as a measure of the load the braking system. The predefinable threshold value can continue to be used as one that represents the operational safety of the hydraulic fluid Operational safety variable shown become. In a special embodiment of the invention a limit load of the brake system is assigned to the threshold value, in which, for example, the brake system still has sufficient functionality.

A further development of the invention leads to backup of functionality suitable measures for the braking system that lead to a reduction in the load. Here is particular provided that by the measures a reduction in the thermal load is caused. All conducted activities control that the driving stability and / or driving safety of the Vehicle operation is secured.

In a special design the invention is as a measure a revolution the hydraulic fluid provided within the hydraulic system of the brake system. Thereby can, for example, by mixing the brake fluid local heating can be avoided.

In an advantageous embodiment of the invention, the circulation of the hydraulic fluid within the hydraulic system can be achieved by different measures. Activation of at least one pump in the brake circuit can result in a flushing of the hydraulic lines and that associated fluid reservoir to mix the hydraulic fluid. The targeted activation of at least one wheel brake is also conceivable by means of a corresponding pressure build-up. Mixing of the liquid can be achieved by simultaneously controlling an inlet and outlet valve on a wheel brake. A so-called hydraulic overlap is also conceivable, which is characterized by simultaneous pressure build-up and pressure reduction. - Furthermore, a circulation of the hydraulic fluid is possible through a targeted first braking of a rear wheel. the braking forces on the other wheels may have to be compensated for.

In one embodiment of the invention provided as hydraulic fluid a brake fluid to monitor the brake system. However, it is also conceivable that an additional cooling circuit in the brake system is present in which the cooling the components of the brake system by another hydraulic fluid can be achieved. Advantageously, another Training of the invention as a company size monitors at least one size, which is a temperature and / or a pressure of the hydraulic fluid represents. there is intended to help the company size of sensors at several points distributed independently of one another in the brake system take.

A special design of the Invention provides that depending from the performed Compare different measures to maintain functionality the braking system become. It is provided at least one valve and / or one To control the pump and / or a control and / or regulating system of the brake system or to modify. For example, with local heating individual hydraulic components outside of a braking operation a rinse pulse are generated by the pump, which cools the hydraulic components through cooler brake fluid causes.

A particularly advantageous embodiment of the Invention provides that the braking system is an electro-hydraulic Braking system.

Further configurations are the dependent claims refer to.

The invention is explained below with reference to the embodiments shown in the drawings. It poses 1 schematically represents an electro-hydraulic brake system in a block diagram. 2 also schematically illustrates the monitoring of the operating variable of a brake system in a block diagram. The flow diagram in 3 shows schematically the process of monitoring the thermal load on the brake system.

Ausfüfrungsbeispiel

In 1 the essential components of an electro-hydraulic brake system are shown as a possible embodiment. However, it should be noted that the invention can generally be used in hydraulic brake systems which have a suction system with a separate suction line and return line. In the 1 is with 100 a brake pedal shown. This brake pedal can apply pressure in a master brake cylinder 110 being constructed. This master brake cylinder stands with a reservoir 115 in contact. The master brake cylinder also stands 110 with a safety valve 120 connected, which works as a isolation valve. This safety valve 120 is to ensure that the electrohydraulic braking system can also perform a braking operation when the power is off. A suitable pressure sensor 130 measures the pressure generated by the pedal in the master brake cylinder 110 is built up. Just like the master brake cylinder 110 is the reservoir 115 with the isolation valves or the safety valve 120 connected. Furthermore shows the 1 Inlet valves ( 162 . 161 . 163 . 164 ) and exhaust valves ( 142 . 141 . 143 . 144 ), which are assigned to the individual wheels or the wheel brakes. Through pressure sensors on each wheel brake cylinder ( 152 . 151 . 153 . 154 ) the current brake pressure can be determined on each wheel. For example, the front left wheel brake cylinder (VL) is through the intake valve 162 and the exhaust valve 142 driven. The pressure prevailing directly at the wheel brake cylinder can be determined by the pressure sensor 152 be determined.

By energizing the pump motor 195 becomes the pump 190 driven and delivers hydraulic fluid from the reservoir 115 in the pressure accumulator 185 , This has the consequence that the pressure in the pressure accumulator 185 from the pressure sensor 180 is measured, increases. By opening the intake valves 161 to 164 and closing the exhaust valves 141 to 144 , the pressure in the wheel brake cylinders is increased depending on the driver's request. By opening the exhaust valves 141 to 144 and closing the intake valves 161 to 164 the pressure in the wheel brake cylinders can be reduced according to the pedal actuation.

The block diagram iu 2 shows schematically the monitoring of individual components of the brake system, the hydraulic fluid, the valves and the control and / or regulating devices in the brake system being monitored in the present exemplary embodiment. Without, however, restricting the invention to the components mentioned, monitoring of any further components of the brake system is also conceivable.

In the present exemplary embodiment, the temperature of the hydraulic fluid or brake fluid is monitored, whereby Exemplary embodiments are also conceivable which carry out the monitoring as a function of the detected pressure. For better characterization of the thermal properties of the components of the brake system, temperature measurement sensors ( 220 . 230 . 240 ) appropriate. With their help, the temperature of the individual components of the brake system can be recorded independently of one another over the entire brake system. Measuring points in the fluid circuit, on the control units in the brake system, the valves and the other hydraulic components are conceivable. As a result of this distributed recording of the temperature, local heating of the components of the brake system, in particular the hydraulic components, can be determined. The temperature sensors 220 thus detect the temperatures T _{Fl, i} at various points i within the liquid circuit. Furthermore, a number of n temperature sensors are recorded 230 the temperatures T _{V, n} at the valves and a number of m temperature sensors 240 the temperatures T _{S, m} on the control devices. For example, each valve or control and regulating device has at least one temperature sensor, which can promptly detect overheating of the corresponding components.

If the control and regulation devices for the valves and the pumps in the brake system are located close to the controlled components, a thermal interaction between the control device and the hydraulic fluid occurs. The operation of the control units, for example due to a high response frequency and a high power loss, results in the control units being heated above the ambient temperature. The internal control unit temperature exceeds a load limit. a loss of function up to a total failure of the control unit must be expected. Due to the possible thermal interaction between the control unit and the hydraulic fluid in the brake circuit, this heat, which is generated by the operation of the control unit as inherent heat, can be dissipated with a suitable control of the fluid flow. As with the control units, the heat that occurs during frequent valve operation can be dissipated through a suitable liquid flow. The discharge takes place through the transport of the heat with the help of the brake fluid. Through an exchange or circulation, brake fluid is transferred from a region of elevated temperature to a colder region, for example into the pressure accumulator 185 promoted. For this purpose, it is conceivable that the pressure accumulator 185 is attached to the bulkhead, for which a much lower ambient temperature is specified than for the rest of the brake system. Furthermore, by suitable positioning of the pressure accumulator 185 the release of the tub to the environment easier depending on the temperature gradient.

To simplify the representation of the monitoring is in 2 with the blocks 220 . 230 and 240 each shown a system of temperature sensors. The temperature sensors record in the block 220 the temperatures T _{Fl, i} ( 225 ) the brake fluid in the brake system at critical points i. For example, the temperatures immediately before or after the inlet valve 162 and / or the exhaust valve 142 be recorded. Temperature recording directly at the wheel brake cylinders (VL, VR, HL, HR) is also provided. Further points of the temperature uptake of the liquid are provided at predetermined intervals within the liquid lines. In addition, temperature monitoring in front of and behind the pump 190 and in the storage container enables 115 and the pressure accumulator 185 to determine an exact determination of the temperature conditions of the hydraulic fluid within the brake circuit. For further monitoring and determination of the temperature conditions within the brake system, in addition to the temperature of the hydraulic fluid (225), the valves ( 120 . 141 to 144 . 161 to 164 ) also monitored for their thermal behavior by means of temperature sensors 230. Each valve n can have at least one temperature T _{V, n} ( 235 ), where n is an index for numbering the monitored valves from 1 to the maximum number n. As already explained, the control units generate their own heating due to their operation due to heat loss. For this reason, with block 240 described a system of temperature sensors. that at least one temperature T _{S, m} ( 245 ) each control unit m recorded.

The recorded temperatures are in block 210 processed. It is checked whether there is a maximum permissible temperature that affects the functionality of the hydraulic fluid, the valves and / or the control units. If the temperature is exceeded above a predetermined limit or threshold. appropriate measures can be taken. It is also possible to compare the change in temperature over time with a corresponding threshold value. The limit values used in the monitoring are read from the memory 295 as individual threshold values for the hydraulic fluid, each individual valve and the control units. It is provided that these threshold values are external, for example during a service stay 299 can be updated in a workshop. This may be necessary, for example, if a new hydraulic component has been installed in the vehicle.

Is in the monitoring in the block 210 If at least one limit value of the thermal load has been exceeded, appropriate measures can be taken to reduce the to minimize or compensate for the resulting stress. For example, by circulating the hydraulic fluid within the brake system, a local temperature increase can be reduced. A suitable measure is the activation of one or more valves ( 270 ) and / or the actuation of at least one pump present in the brake system ( 280 ). Furthermore, the driver is provided with information via 260 via an optical and / or acoustic display, which represents an increase in the temperature of the monitored components and thus warns of possible functional restrictions.

zur Überprüfung verwendet werden. Wird einer der Schwellenwerte überschritten, so wird zumindest lokal eine zu hohe Temperatur der Hydraulikflüssigkeit am Ort i festgestellt und zu Schritt 320 verzweigt. Innerhalb dieses Schrittes 320 werden geeignete Maßnahmen ergriffen, um die Temperatur der Hydraulikflüssigkeit am Ort i zu senken, und so die Funktionalität der Bremsanlage zu sichern. Bei diesen Maßnahmen handelt es sich beispielsweise um ein Umwälzen der Hydraulikflüssigkeit im Bremskreislauf. Befindet sich der Druckspeicher 185 bzw. der Bremsflüssigkeitsbehälter 115 innerhalb des Fahrzeugs an einer Stelle, für die wesentlich geringere Umgebungstemperaturen spezifiziert sind (z.B. an der Spritzwand), so kann Hydraulikflüssigkeit aus dem Druckspeicher 185 bzw. dein Bremsflüssigkeitsbehälter 115 angesaugt werden und durch das hydraulische Leitungssystem geleitet werden. Dabei kann die kältere Bremsflüssigkeit aus dem Druckspeicher 185 bzw. dem Bremsflüssigkeitsbehälter 115 an den lokal erhitzten Stellen Wärme aufnehmen und abführen. Auch ein Umpumpen der Bremsflüssigkeit von einer lokalen wärmeerzeugenden Stelle hin zu dem mit einer geringeren Umgebungstemperatur versehenen Druckspeicher 185 ist möglich. Dies funktioniert jedoch nur außerhalb einer Bremsung, da ein Mindestdruck im Druckspeicher zu jedem Zeitpunkt hinsichtlich einer Bremsanforderung gewährleistet werden muss. Ebenso kann in einer gezielten Kühlroutine durch Ansteuerung der Einlassventile Bremsflüssigkeit aus dem Speicher langsam abgelassen und über das nicht angesteuerte Auslassventil durch das Hydraulikaggregat geschickt werden. So kann die Eigenwärme aufgenommen werden und über die Rücklaufleitung in das Reservoir abtransportiert werden. Bei der dort herrschenden kälteren Umgebung kann die Wärme aufgenommen und über die Wände abgegeben werden. Innerhalb einer Bremsung kann eine Spülung im Fahrzeugstillstand gezielt an einem Rad durchgeführt werden, indem eine sog. hydraulische Überdeckung (d.h. ein gleichzeitiger Druckauf- und Druckabbau) erzeugt wird. Vorraussetzung ist dabei jedoch ein Bremsdruck von p_Bremsdruck ≈ 0. Weiterhin ist eine Entbremsung eines Hinterrades mit eventueller zusätzlicher Kompensation der Bremskräfte an den anderen Rädern denkbar.The flow diagram in 3 shows schematically the monitoring of the temperature using a program algorithm. In the first step 300, the temperatures T _{FL, i} ( 225 ), T _{V, m} ( 235 ) and / or T _{S, m} ( 245 ), as well as the threshold values SW _FL , SW _{V, m} , SW _{S, n} belonging to the individual hydraulic components. In the following step 310, according to T FL, i > SW FL for all points i checked whether the temperature T _{FL, i} ( 225 ) of the hydraulic fluid at a location i above a predetermined threshold value SW _{F L.} Instead of the temperature, however, the change in temperature over time can also be adjusted according to

be used for verification. If one of the threshold values is exceeded, an excessively high temperature of the hydraulic fluid at location i is determined at least locally and at step 320 branches. In this step 320, suitable measures are taken to lower the temperature of the hydraulic fluid at location i and thus to ensure the functionality of the brake system. These measures involve, for example, circulating the hydraulic fluid in the brake circuit. The pressure accumulator is located 185 or the brake fluid reservoir 115 Hydraulic fluid can escape from the pressure accumulator inside the vehicle at a location for which much lower ambient temperatures are specified (e.g. on the bulkhead) 185 or your brake fluid reservoir 115 be sucked in and passed through the hydraulic pipe system. The colder brake fluid can come from the pressure accumulator 185 or the brake fluid reservoir 115 absorb and dissipate heat at the locally heated areas. Pumping around the brake fluid from a local heat-generating point to the pressure accumulator 185 provided with a lower ambient temperature is also possible. However, this only works outside braking, since a minimum pressure in the pressure accumulator must be guaranteed at all times with regard to a braking request. Likewise, brake fluid can be slowly drained from the reservoir in a targeted cooling routine by controlling the inlet valves and sent through the hydraulic unit via the non-actuated outlet valve. In this way, the natural heat can be absorbed and transported to the reservoir via the return line. In the colder environment there, the heat can be absorbed and released via the walls. During braking, a flush can be carried out specifically on a wheel when the vehicle is at a standstill by generating a so-called hydraulic overlap (ie a simultaneous pressure build-up and pressure reduction). However, a brake pressure of p _{brake pressure} ≈ 0 is a prerequisite. Furthermore, braking of a rear wheel with possible additional compensation of the braking forces on the other wheels is also conceivable.

By mixing and transporting the locally generated heat is the heat balance, however so that the hydraulics despite additional heat caused by the control of the individual valves and the pump control, cools down. In order to the limit temperature (saturation temperature the hydraulic system is lowered during long operation in the high temperature range).

After the appropriate measures for reducing the temperature of the hydraulic fluid have been carried out in step 320, reference is made to the beginning of the algorithm and the temperature parameters are read in again in step 300. If the threshold value SW _{FL is} not exceeded in step 310, then in step 330 according to T V, m > SW V, m for all valves 1, ..., m checks whether a temperature T _{V, m} ( 235 ) is measured, which is above the maximum operating temperature valid for the corresponding valve. Overall, the operating temperature of at least one valve of the brake system is checked during the check in step 330. If it is determined that at least one of the valves has a high temperature which is detrimental to operation, measures are initiated in step 340 which lead to a reduction in the temperature at the corresponding valve. This can be done, for example, by flushing the hydraulic fluid along the valve (when the vehicle is at a standstill). This liquid flow along the valve allows the liquid to absorb the heat of the valve and to transport it to colder areas of the liquid circuit. Thus, as described in step 320, the brake fluid can be pumped into the pump's memory. As a result, the gas volume heats up due to the thermodynamics in the store, but depending on the temperature gradient, this heat can be released to the outside via the wall of the store. It is also possible that the colder brake fluid in the pressure accumulator 185 the war entry reduced. After the measures in step 340 have been carried out, the algorithm is run through again from the beginning with the reading in of the parameters.

If it is determined in step 330 that no valve has a temperature above the threshold value SW _{V, n} , the monitoring is continued with step 350. In this step 350, the temperatures T _{S, n} ( 245 ) of the control units 1 ...., n with predetermined limit values SW _{S, n} according to T S, n > SW S, n checked. _R is found too high Betriebstemperatu at a controlled control device, so the program will be continued with step 360th In this step 360 suitable measures are carried out which lead to a reduction in the temperature at and / or in the monitored control devices. As was already illustrated in step 340 with the aid of the valves, there is the possibility of cooling a control device by dissipating the heat due to a liquid flow which can absorb the heat of a control device as a result of a thermal interaction. The cooling of the control units is particularly important because, due to the self-heating that a control unit produces in the form of heat loss, destruction of certain components due to thermal stress cannot be ruled out if the internal temperature rises above a certain limit. For example, the temperature of the control devices can be cooled by gradually reducing the functions of the control device, so that less heat is produced and the components are protected from thermal destruction. In addition to installing the control units in the vehicle at correspondingly cooler locations, there is also the option of cooling the control units using external fans. After the temperature-reducing measures have been carried out in step 360, reference is made to the beginning of the algorithm and a new cycle is started with reading in the temperatures and the limit values. However, if temperatures T _{S, n} ( 245 ) below the predetermined threshold values SW _{S, n} , the program is ended.

Through the presented embodiment the temperature load on the components can be reduced, resulting in a Ensuring functionality of the braking system. Any restrictions the functions due to thermal stress can thus be delayed or be avoided.

The query algorithm as in 3 shown and described above, can be started both in the presence of certain circumstances and at regular times.

VL, VR

description for the Front wheels left and front right

HL, MR

description for the Rear wheels left and back right

T _{Fl, i}

temperature the hydraulic fluid in place i

T _{V, n}

temperature of the valve n

T _{S, m}

temperature that of the control unit m

100

brake pedal

110

Master Cylinder

115

reservoir

120

isolation valves

130

pressure sensor

141 142, 143, 144

exhaust

151 152, 153, 154

pressure sensors on the wheel brake cylinders

161 162, 163, 164

intake valves

180

pressure sensor

185

accumulator

190

pump

195

pump motor

220

sensor for measuring a hydraulic fluid temperature

230

sensor for measuring a valve temperature

240

sensor for measuring a control unit temperature

260

acoustic and / or visual information display

270

Valve

280

pump

290

Tax- and / or control device

Claims (12)

Method for monitoring a brake system of a vehicle that has a hydraulic fluid, wherein at least one operating variable of the brake system that represents an operating parameter of the hydraulic fluid is recorded, characterized in that - a comparison - of the recorded operating variable, and / or - of the temporal change in the recorded operating variable with at least one predefinable threshold value, and - depending on your comparison ( 310 . 330 . 350 ) at least one definable measure ( 320 . 340 . 360 ) is carried out to ensure the functionality of the brake system. Method according to Claim 1, characterized in that the detected operating variable represents a load on the brake system and the threshold value represents an operational safety which represents the operational safety of the brake system represents size, in particular it is provided to assign a threshold load of the brake system to the threshold. A method according to claim 2, characterized in that to ensure the functionality of the braking system. in particular to ensure driving stability and / or driving safety during vehicle operation, at least one suitable measure ( 320 . 340 . 360 ) to reduce the load, especially the thermal load. the components of the brake system is carried out. A method according to claim 1, characterized in that as a measure ( 270 . 280 ) circulation of the hydraulic fluid is provided within the hydraulic system. A method according to claim 4, characterized in that upheaval the hydraulic fluid at least within the hydraulic system by a control - one Pump (190) present in the brake circuit, and / or - one Wheel brake, and / or - two Valves for generating a hydraulic overlap, being under hydraulic overlap the simultaneous pressure build-up and pressure reduction in the hydraulic system to be understood he follows. A method according to claim 1, characterized in that - as a hydraulic fluid, a brake fluid, and / or - as an operating variable at least one - a temperature ( 225 . 235 . 245 ), and / or - a pressure representing size is provided. A method according to claim 1, characterized in that depending on the comparison ( 310 . 330 . 340 ) at least - one valve ( 270 ), and / or - a pump ( 280 ), and / or - a control and / or regulation system ( 290 ) the firing system is controlled. A method according to claim 1, characterized in that the brake system is an electro-hydraulic brake system is. Device for monitoring a brake system of a vehicle having a hydraulic fluid, wherein at least one operating variable is recorded which represents an operating parameter of the hydraulic fluid. characterized in that means ( 200 ) are provided which - perform a comparison - of the recorded operating variable, and / or - of the temporal change in the recorded operating variable with at least one predeterminable threshold value, and - as a function of the comparison ( 310 . 330 . 350 ) at least one definable measure ( 320 . 340 . 360 ) to ensure the functionality of the brake system. Device according to claim 9, characterized in that the captured farm size is a burden represents the braking system and the threshold value is the operational safety of the hydraulic fluid representing Represents operational safety variable, in particular, your threshold is a limit load assign to the brake system. Apparatus according to claim 10, characterized in that means are provided to ensure the functionality of the brake system, in particular to ensure driving stability and / or driving safety of vehicle operation, the at least one suitable measure ( 320 . 340 . 360 ) to reduce the load, especially the thermal load, of the brake system. Apparatus according to claim 9, characterized in that as a measure ( 270 . 280 ) circulation of the hydraulic fluid is provided within the hydraulic system.