ZF FRIEDRICHSHAFEN AG Fi|e 000Q18
Fnednchshafen 2006-05-18
Method and Device for Adjustment and Control of a Hydrodynamic Retarder of a Motor Vehicle
This invention relates to a method and a device for adjustment and con^ trol of a hydrodynamic retarder of a motor vehicle according to the preamble of patent claim 1 or patent claim 17.
Hydrodynamic retarders are used in motor vehicles, especially in com¬mercial vehicles, as additional nonwearing continuous-service brake systems relieving the normally friction-type wheel brakes. Retarder systems reduce wear and prevent thermal overloading of the friction brakes, for example during high¬speed braking, for high TW vehicles, and during prolonged downhill driving. In addition, braking comfort is increased by adaptive braking and by a constant speed being maintained during downhill driving, for example.
The mechanical energy of a drive shaft is converted In hydrodynamic re¬tarders into the kinetic energy of a fluid, usually oil, with the physical mode of operation corresponding to that of a hydrodynamic clutch featuring a combus¬tion-engine-driven pump wheel as drive and a turbine wheel as output, but with the turbine being fixed. A hydrodynamic retarder thus features a rotor arranged in the power flow and a retarder-housing-fixed stator with blades. Retarder activation results in the retarder chamber being filled with the amount of oil corresponding to the braking power desired. The flow of oil in this process is mostly controlled by an electric proportioning valve with correspondingly electi-cally powered proportional magnet. The oil in the retarder chamber is entrained by the turning rotor and hits the stator blades, with kinetic flow energy being converted into heat, which results in a braking effect being exerted on the rotor and its driving shaft and thus in deceleration of the entire vehicle.

ZF-FRIEDRICHSHAFEN AG Fried rich shafen

File 000018 2006-05-18

Such a hydrodynamic retarder is known, for example, from DE 101 40 220 A1. For retarder control, a working circuit (retarder circuit) is provided com¬prising a hydraulilc pump driveable by a controllable electric motor, a heat ex¬changer for cooling, a valve system with inlet and outlet valve, as well as a control or changeover valve and a control unit for pump and valve control. This arrangement permits adjustment of control independent of the current vehicle speed, or propshaft speed, or retarder speed. A comparable arrangement is also known from DE 101 41 794 A 1.
Hydrodynamic retarder brake torque is usually set as a result of a pres¬sure in the retarder circuit, which is preset by a control unit. The connection between a specific control variable of the control unit, such as a current on the proportioning valve and the resulting brake torque, is established, for example, via a map. The resulting retarder brake torque corresponds to a point on a brake characteristic or brake torque characteristic in which the retarder brake torque is plotted against the retarder speed preset by the drive of the retarder rotor.
Accuracy of the set brake torque is a fundamental problem. This is mainly due to the quality of the retarder blades, the tolerances of the oil-carrying housings, and the tolerances of mechanical setting elements {actua¬tors, control pistons, spring elements, etc.).
Testing of the retarder brake torque on a production test bench is a known procedure used to minimize deviations of the actual brake torque of a unit from a desired brake torque. Depending on the deviation of a measured actual torque from the desired torque, corrections will be implemented for verifi¬cation of the brake characteristic of the retarder as precisely as possible. This can be realized through brake torque measurement on the test bench and cor¬rection of the brake torque by means of a setting element, such as a setting screw, or through brake torque measurement on the test bench and selection of

ZF-FRIEDRICHSHAFEN AG
Fried rich shaf en

File 000018 2006-05-18

one of several maps of resistors or coded controls stored in the electronic con¬trol.
These familiar means, which are adjusted during a test run to each sin¬gle unit, permit only very inadequate and general brake torque adjustment (one set point for the entire working range). With the increasing integration of retard-ers into other systems, such as electronic brake systems requesting supporting retarder brake torque, the demands regarding the precision of brake torque adjustment or the accuracy of the feedback of the current brake torque setting are increasing.
An improvement resulting in increased accuracy is described in the un¬published DE 10 2005 021 718 A1. This improvement involves electronic alignment on a test bench, with each single unit being measured with regard to a brake characteristic and the required correction values being stored in a non¬volatile memory of the electronic control. This is realized by individual offsets (increases/decreases) of the control variable at various checkpoints of the brake characteristic.
The drawback this entails is that correction is rather empirical, with the hydraulic pressure in the working circuit, which is especially relevant for the functioning of the retarder, not being explicitely considered.
WO 2003 020 562 A1 describes a method involving measurement of the oil pressure in the working circuit of the retarder, with a brake torque being derived and compared with a desired brake torque. The desired brake torque usually corresponds to the position of a control element (e.g. brake pedal) and is initiated by the driver. Any deviation of the generated brake torque from the desired brake torque can be adjusted. Control quality can be improved by means of adaptation involving storage of deviations determined during preced¬ing activations and their use for renewed activations. In addition to adjustment

ZFFRIEDRICHSHAFEN AG Friedrichshafen

File 000018 2006-05-18

of pressure deviations regarding the driver's desired brake torque, the driver can also be alerted if a defined threshold is exceeded. This may happen as a result of defects on components or if the oil level in the retarder is too low.
The drawback this entails is that alignment of the brake torque deter¬mined on the basis of the measured actual pressure relies exclusively on the driver's request, or a corresponding momentary setting of a control element. Such adjustment can diverge from a retarder-favorable brake characteristic, which may result in rather ineffective retarder utilization, especially in electronic brake systems. Moreover, control accuracy essentially depends on the setting accuracy of the respective control element, such as a brake pedal. If such an element is affected by a relatively sizeable production tolerance, or if control element setting parameters are changed over time, a constant high level of accuracy of adjustment according to the driver's request cannot be easily guar¬anteed.
Furthermore, there are hydrodynamic retarders with pneumatic control systems, with the hydraulic pressure in the working circuit being set by a pneu¬matic setting pressure acting on the oil level in the retarder chamber.
Such a pneumatic control system, in which a pneumatic setting pressure is determined, is known from DE 199 29 152 A1. With the aid of such a meas¬ured pneumatic pressure and a driver-set value, that is the current driver re¬quest for a specific brake torque, any nominal/actual deviation can be deter¬mined and adjusted. Furthermore, any excessive setting pressure resulting from a malfunctioning valve installation of the pneumatic system can be de¬tected and, if necessary, deactivated with the aid of a (further) control valve in the air supply line of the entire retarder system.
Another pneumatic retarder control system is known from DE 103 61 448 A1- The method described there involves a pressure sensor installed in a pneumatic setting-pressure control circuit, by means of which the pattern of the

ZF-FRIEDRICHSHAFEN AG Friedrichshafen

File 000018 2006-05-18

pneumatic setting pressure of the retarder is measured. The measured tempo¬ral pressure characteristic is compared with stored nominal characteristics {early warning and immobilization characteristic). If preset criteria are not ful¬filled, an alert message will be issued and/or further activation of the retarder by the operator, that is the driver, will be prevented. At the same time, the dynamic pressure patterns during activation or deactivation of the retarder, and option¬ally also the pattern of brake torque variation, are monitored and checked against a preselected target brake torque. The characteristics used can be calculated during the design of the retarder system, or they may be determined by testing, or they may be learned during initial vehicle operation. Apart from the comparison of temporal patterns, the measured intervals between two specified pressure points or setting-pressure curve gradients may be com¬pared.
Pneumatic retarder control systems entail the drawback represented by the relatively high additional cost and the design effort for the pneumatic sys¬tem. Moreover, the control response of the known systems of this type is rather restricted.
In view of this background, the task of the invention is to present a me¬thod for adjustment and control of a hydrodynamic retarder which improves the accuracy of brake torque setting, is inexpensive, and which avoids the men¬tioned drawbacks of the state of the art.
The solution of this task results from the features of the independent claims while favorable basic features and further development of the invention can be found in the respective subclaims.
The invention is based on the insight that the possibility of improving the accuracy of pressure setting in the retarder entails the possibility of improve¬ment of the accuracy of the resulting brake torque. Essentially, this is achieved

ZF FRIEDRICHSHAFEN AG File 000018
Friedrichshafen 2006-05-18
by means of preadustment on the retarder, with pressure being considered as a correction value for a control variable of the retarder.
The invention thus starts from a method for adjustment and control of a hydrodynamic retarder of a motor vehicle, with the retarder featuring a control¬lable hydraulic circuit and means for registration of the hydraulic pressure in the hydraulic circuit, and with this method involving at least one preadjustment for generation of a brake torque following a preset brake torque characteristic, with this preadjustment being permanently stored in a control unit and used for con¬trol of the retarder during driving. For the set task to be solved, the invention also provides for consideration of the hydraulic pressure in the hydraulic circuit of the retarder at least for preadjustment.
Use of the hydraulic pressure in the working circuit of the retarder pro¬vides the basis for a more precise adjustment or determination of the brake torque. Via a control variable, a pressure is set which, in combination with the speed of the retarder, results in a specific brake torque. For this purpose, a unit-specific hydraulic nominal pressure is determined and stored in the control unit. This entails the advantage that neither a pneumatic control system is re¬quired nor a comparison with the driver's request during driving operation needs to be evaluated.
In hydrodynamic retarders featuring a pressure sensor for pressure con¬trol in the working circuit, the sensor's information can be used for the inventive method of presetting, which is particularly cost-saving.
Moreover, alignment between the presetting value stored in the control unit and a hydraulic actual pressure measured in the hydraulic circuit of the retarder, preferably during driving, may be provided for. Presetting results in determination of a nominal pressure which already significantly improves the accuracy of the control variable.

ZF.FRIEDRICHSHAFEN AG Friedrichshafen

File 000018 2006-05-18

By means of alignment of this nominal pressure, determined through preadjustment, with the current measured actual pressure, and adjustment of any deviation, accuracy of adjustment of the control variable can be increased further, so that the actual retarder brake torque corresponds precisely to a requested nominal brake torque on the braking characteristic, or deviates only marginally. The fact that the electronic brake management system can be fed with exact data on the currently set brake torque is also of great benefit.
This entails the possibility, which may also be provided for, that during operation a current nominal brake torque, which is determined on the basis of operating parameters relevant for the brake operation of the vehicle, can be set very precisely via a corrected nominal current, which activates an electric valve installation belonging to the hydraulic circuit of the retarder, with the respective nominal current being determined via the preadjustment value and alignment of the preadjustment value with the actual pressure.
Morever, it may be provided that the preadjustment value contains at least a preset unit-independent basic setting and a unit-specific correction set¬ting determined for the respective retarder prior to or simultaneously with initial operation of the vehicle, with a unit-specific correction setting performed on a test bench being of particular benefit.
Starting from a basic setting, which is determined once for all units of a type and permanently stored in the control unit, unit-specific correction on the test bench permits neutralization of production tolerances, which ensures the same high level of setting accuracy for ail units. Preadjustment can be easily realized by means of maps stored in the control unit.
For this purpose, it may be prescribed that the basic setting contains a current reference map in which a connection is specified between an electric

ZF-FRIEDRICHSHAFEN AG
Friedrichshafen

File 000018 2006-05-18

reference current powering an electric valve installation of the retarder and the nominal brake torque of the retarder, and that the basic setting contains a pres¬sure reference map in which a connection is specified between a hydraulic reference pressure in the hydraulic circuit of the retarder and the nominal brake torque of the retarder.
Furthermore, it may be prescribed that the correction setting comprises a current correction map for unit-specific correction of the current reference map and a pressure correction map for unit-specific correction of the pressure refer¬ence map.
Explicit inclusion of a pressure map and a pressure correction map re¬sults in a more accurate setting of the control variable for retarder adjustment, as the unit-specific determined pressure or the current actual pressure are crucial for the accuracy of the setting of the control variable for generation of the nominal brake torque.
Setting accuracy can even be increased further if the correction setting includes a current correction map and/or a pressure correction map in which the temperature dependence of the viscosity of the hydraulic oil in the hydraulic circuit of the retarder is considered. Since oil viscosity changes with tempera¬ture changes, influences resulting from varying volume flows during charg¬ing/discharging of the retarder and temperature-dependent pressure changes in the retarder can automatically be considered during adjustment of the control variable for the valve installation.
Furthermore, a pressure-monitoring system may be provided for monitoring of the hydraulic pressure of at least the hydraulic circuit of the retarder, with this system generating an error response if an impermissible pressure deviation from a nominal pressure specification or a derived value is detected.

F'FRIEDRICHSHAFEN AG iedrichshafen

File 000018 2006-05-18

In addition to allowing a high level of precision in brake torque setting, pressure measurement in the working circuit of the retarder permits monitoring of the functional readiness and operating safety of a retarder. The desired no¬minal value may be defined by a temporal pressure pattern relevant for the operational safety of the retarder and/or by one or several threshold values.
Meaningful failure responses may include alerts and operational restric-tiions as well as retarder deactivation. Detected errors can be stored and /or displayed for the driver. Even operation with reduced braking power is possible.
Peripheral conditions can assist in the determination of the type of failure response. They can be represented by information on vehicle weight and/or current road grades and/or current road conditions. In a light vehicle, for exam¬ple, use of the retarder might be dispensed with completely, while the retarder might be only limited in its braking power in a heavy vehicle. Depending on the error, full retarder operation but with limited precision of brake torque and cor¬respondingly restricted braking comfort might make sense. Further peripheral conditions may also be represented by information on road grades provided by a navigation system or by sensor data on road conditions (grip, evenness).
tt is particularly advantageous in a retarder featuring a common oil circuit with a transmission if pressure monitoring includes monitoring of the oil level in the transmission. In retarders sharing a common oil circuit with the transmis¬sion, pressure measurement in the working circuit of the retarder provides the possibility of monitoring the oil level in the transmission. Dependent on current operating conditions (speeds, desired brake torque, oil temperature), this per¬mits use of the retarder oil pressure or of the deviation from a nominal pressure to determine whether there is a lack of oil in the transmission and whether ap¬propriate protective measures need to be initiated.

Finally, functional monitoring involving control of the functional capability of the retarder with the aid of a plausibility check may be provided, with at least the current hydraulic retarder pressure being included. Such a plausibility check may also have to include the oil temperature. Apart from pressure monitoring, this additional aspect serves the purpose of hydraulic retarder control. Monitor¬ing of the oil pressure, possibly also of the oil temperature or further variables, may serve the purpose of a plausibility check of the function of the hydraulic control.
Sensor signals may also be plausibility-checked. For example, if no oil pressure is measured although the retarder is activated by the control, this may also be due to a defective pressure sensor, If the measured oil temperature increases, it can be assumed that the pressure sensor is defective. If the oil temperature remains constant, this would suggest that the retarder was acti¬vated by the electronic control but that the hydraulic control is defective (e.g. jamming valve), or that there is not enough oil in the system.
Another task of the invention is to create a device for adjustment and control of a hydrodynamic retarder which will permit improvement of the accu¬racy of brake torque adjustment at low cost and design expenditure.
The solution of this task results from the features of the device of the in¬dependent claim.
In this regard, the invention starts from a device for adjustment and con¬trol of a hydrodynamic retarder of a motor vehicle. For the set task to be solved, the invention specifies that the retarder must feature a controllable hydraulic circuit with at least one pressure sensor, and that the hydraulic circuit has a control unit assigned to it which features a nonvolatile memory and a processor unit, with which current input data and stored data can be processed, with which the processed data can be used to generate an output signal for the

control of an electric valve system and/or an oil-filling system of the retarder, and with which a prescribed nominal brake torque can be set.
Use of a pressure sensor for measurement of the pressure in the work¬ing circuit permits relatively easy and low-cost realization of a high level of ac¬curacy of retarder brake torque adjustment. Such pressure measurement can be used on a test bench during preadjustment for determination of a control variable. Preadjustment can be stored in the control unit in the form of refer¬ence and correction maps taking into account the hydraulic pressure.
The design of the control unit is such that it processes a nominal brake torque as in input signal with the aid of the maps, and if necessary of a control correction, with the current actual pressure, and issues a corresponding output signal for a control variable of the retarder. During driving, the current pressure in the working circuit can be measured and adjusted to the unit-specific nominal pressure determined on the test bench. For generation of the nominal brake torque, this can be used to generate an adjusted nominal current, for example to actuate a proportioning valve through which a retarder pressure is set, which in combination with the retarder speed generates the prescribed nominal brake torque on the retarder with a high level of accuracy,
Adustment accuracy can be even further increased with the aid of an oil temperature sensor having a signalling link with the control unit and also permit¬ting viscosity correction of the control variable.
A drawing of a design example is added to this description to illustrate the invention. This includes:
Fig. 1 A diagram of a retarder circuit of a hydrodynamic retarder with
pressure and temperature sensors. Fig. 2 A diagram showing retarder brake torque adjustment.

Fig. 1 thus represents a retarder circuit 15 of a motor vehicle designed as the working circuit of a hydrodynamic retarder 1. Design and operating prin¬ciple of such a retarder are known. Therefore, only components relevant for the invention are dealt with in more detail.
For oil supply, the working circuit 15 features a pump 10 with a primary filter 12, with the pump 10 being driveable and controllable via an electric motor 2, and fed from an oil sump 11. For removal of the heat resulting from conver¬sion of the kinetic flow energy in the retarder 1, a heat exchanger 3 is provided. To charge and discharge the retarder 1, two check valves 4, 5 are arranged on the inlet side or outlet side, with the retarder outlet featuring also a discharge valve 14 for complete emptying of the retarder 1 when necessary.
The working circuit 15 can be contolled by a control unit 6. The control unit 6 is linked to a pressure sensor 9 for registration of the hydraulic pressure in the working circuit 15, and to two temperature sensors 7, 8 for registration of the oil temperature in the circuit, or direct to the heat exchanger 3. For retarder control, the control unit 6 is also linked via control lines to a control valve 13 and the electric motor 2, The control valve 13 has been practically designed as an electric proportioning valve, with the retarder 1 being controllable via the cur¬rent-supplied valve.
According to the invention, the control unit 6 features a nonvolatile data memory and a processor unit with which current input data and stored data can be processed, and with which the processed data can be used to generate an output signal for control of the control valve 13. The arrangement shown in Fig. 1 permits retarder control both via the control valve 13 and via the controllable electric motor 2.

A method according to the invention for adjustment and control of a hy-drodynamic retarder of a motor vehicle essentially relies on a preadjustment, with the hydraulic pressure measured in a hydraulic working circuit 15 of the retarder being taken into account.
Fig. 2 shows a diagram for adjustment and control of a retarder or of a retarder circuit according to the design shown in Fig. 1 on the basis of which the method according to the invention is described below:
As a set value in retarder control, a nominal brake torque Mnom is determined on the basis of relevant requirements, such as the brake torque requirements of the driver or other systems; and this set value may be reduced by vehicle-related or system-related limitations (ABS, temperature resetting, etc.). The object of the control unit 6 of the retarder 1 is to generate the resulting set value, i.e. the nominal brake torque Mnom, by setting a corre¬sponding current on the control valve 13 by means of the retarder 1.
For the required accuracy to be realized, the nominal brake torque M nom and the current retarder speed are used to determine a current lret based on the current reference map 16. In the current reference map 16, the reference current lr%i is defined for the nominal brake torque Mnom and the retarder speed. This refer¬ence map 16 was determined by advance testing for all units and is perma¬nently stored in the control unit 6.
The reference current lref of the reference map 16 is subsequently loaded with a current offset Icorrfrom a unit-specific current correction field 17 in which the offset Icorr is entered for the nominal brake torque Mnom and the retarder speed. This unit-specific correction map 17 is determined on the test bench for each single retarder and is permanently stored in the control unit 6.

Subsequently, a current correction is additionally performed for the tem¬perature-dependent viscosity of the oil in the working circuit 15 by means of a permanently stored current correction map 18 in which another current offset Icorr. n for the oil temperature is entered. A nominal current lnom is determined by addition of the individual current shares lret, lMrri and Icorr, n-
According to the invention, a nominal pressure Pnom
is determined simultane¬ously in the same manner as the nominal current lnom. This involves storage in the control unit 6 of a pressure reference map 19 for all units, in which a refer¬ence pressure pref is entered for the nominal brake torque Mmm and the retarder speed. This pressure pr6f of the reference pressure map 19 is now loaded with a pressure offset Peon from a unit-specific pressure correction map 20 in which the pressure offset Pcorr is entered for the nominal brake torque Mnom and the retarder speed. The unit-specific correction map 20 is also determined on the test bench for each single retarder, and permanently stored in the control unit 6.
Pressure correction of the viscosity of the oil is also considered and en¬tered in a pressure correction map 21, in which a further pressure offset Pc^, ^ is entered for the oil temperature. The nominal pressure pnom is determined through addition of the individual pressure shares ptaf. Pwr, and Pccn.vi-
The maps or characteristics 16 thru 21 represent a preadjustment of the retarder 1 for brake torque setting according to a prescribed nominal brake characteristic (brake torque vs retarder speed), with the pressure in the working circuit 15 being taken into account.
The nominal pressure pnom can generally be applied in a suitable manner as additional control variable to the nominal current lnom. According to the inven¬tion, alignment is performed during driving of the nominal pressure presetting, the measured current actual pressure pBCl, and adjustment of any deviation. This involves processing of the nominal pressure pnom and the actual pressure

pac, in a controller 22 (PID controller), which on the basis of the difference be¬tween the stated values determines a control variable, which is added to the nominal current \noin as a further correction value. The resulting corrected nomi¬nal current lnom, corr is finally set as the control variable on the proportional con¬trol valve 13 of the retarder 1.

Patent Claims
1. Method for adjustment and control of a hydrodynamic retarder (1) of a motor vehicle, with the retarder (1) featuring a controllable hydraulic circuit (15) and means for registration of the hydraulic pressure in the hydraulic circuit (15), and with at least one preadjustment being made for generation of a bralte torque following a prescribed brake torque characteristic, which is permanently stored in a control unit (6) and with the aid of which the retarder (1) is controlled in the driving mode, characterized in that at least during preadjustment the hydraulic pressure in the hydrauliccircuit (15) of the retarder (1) is taken into account.
2. Method according to claim 1, characterized in that during driving a-lignment takes place between the preadjustment value stored in the control unit (6) and a current hydraulic actual pressure (pact) measured in the hydraulic circuit (15) of the retarder (1).
3. Method according to claim 1 or 2. characterized in that during driv¬ing a nominal brake torque (Mnom) determined on the basis of operating para-menters re\e\/ant for a braking operation of the vehicle is set essentiaKy via a corrected nominal current (Inom.cor) vvhich actuates an electric valve installation (13) belonging to the hydrauliccircuit (15) of the retarder (1), with the respective nominal current (lrwn,corr) being determined via the preadjustment value and alignment of the preadjustment value with the actual pressure (pacO-
4. Method according to at least one of the claims 1 thru 3, character¬ized in that the preadjustment value contains at least one prescribed unit-Independent basic setting and a unit-specific correction setting determined for the respective retarder before or durina initial vehicle ooeration.

5. Method according to claim 4, characterized in that unit-spectfic cor¬rection setting is performed on a test bench.
6. Method according to at least one of the claims 1 thru 5, character¬ized in that the basic setting includes a current reference map (16) defining a connection between an electric reference current (Iref) for the electric supply of the electric valve installation (13) of the retarder (1) and the nominal brake torque (Mnom) of the retarder (1), and that the basic setting includes a pressure reference map (19) defining a connection between a hydraulic reference pres¬sure (pref) in the hydraulic circuit (15) of the retarder (1) and the nominal brake torque (Mnom) of the retarder (1).
7, Method according to at least one of the claims 1 thnj 6, characterized in
that the correction setting includes a current correction map (17) for unit-
specific correction of the cun-ent reference map (16) and a pressure correction
map (20) for unit-specific correction of the pressure reference map (19).
8. Method according to at least one of the claims 1 thru 7, characterized in
that the correction setting includes a current correction characteristic (18)
and/or a pressure correction characteristic (21) considering the temperature
dependence of the viscosity of the hydraulic oil in the hydraulic circuit of the
retarder (1).
9. Method according to at least one of the claims 1 thru 8, character^ ized in that a pressure-monitoring system is provided for monitoring of the hy¬draulic pressure at least in the hydraulic circuit (15) of the retarder (1), with an error response being initiated in case of impermissible pressure deviation from a nominal value or values derived from that value.

10. Method according to claim 9. characterized in that the nominal va¬lue is defined by a temporal pressure pattern relevant for the operational safety of the retarder (1) and/or by one or several threshold values.
11. Method according to claim 9 or 10, characterized in that pressure monitoring in a retarder sharing a common oil supply with a transmission in¬cludes monitoring of the oil level in the transmission.
12. Method according to at least one of the claims 9 thru 11, character¬ized in that the failure response consists of at least one measure concerning the retarder (1} from the group of alerts, operating restrictions, and shutdown.
13. Method according to at least one of the claims 9 thru 12, cliaracter-ized in that determination of the failure response involves consideration of at least one peripheral condition relevant for the braking behavior of the vehicle.
14. Method according to claim 13. characterized in that peripheral conditions are provided in the form of information about vehicle weight and/or current road grade and/or current road condition.
15. Method according to at least one of the claims 1 thru 14, character¬ized in that a functional monitoring system is provided for control of the func¬tional capability of the control of the retarder (1) with the aid of a plausibility check which includes at least the current hydraulic pressure (pact) of the re¬tarder.
16. Method according to claim 15, characterized in that the plausibility check also includes the oil temperature.

17. Method for adjustment and control of a hydrodynamic retarder (1) of
a motor vehicle, characterized in that the retarder (1} features a controllable
hydraulic circuit (15) with at least one pressure sensor (9), that the hydraulic
circuit (15) has a control unit (6) assigned to it which features a nonvolatile data
memory and a processor unit with which current input data and stored data can
be processed and with which the processed data can be used to generate an
output signal for control of an electric valve system (13) and/or an oil-filiing
system of a retarder (1) via a prescribed nominal brake torque (Mnom)-
18. Device according to claim 17, characterized in that the hydraulic
circuit (15) features at least one oiUemperature sensor (7, 8).