DE102010047076A1 - Method for limiting the maximum retrievable braking power of a hydrodynamic brake - Google Patents

Abstract

The invention relates to a method for limiting the maximum available braking power of a hydrodynamic brake in a motor vehicle, the heat generated by the hydrodynamic brake being diverted into an engine cooling circuit of the vehicle drive engine by means of a coolant, and the coolant being circulated in the engine cooling circuit by means of a coolant pump driven by the vehicle drive motor , with the following steps: - a control intervention temperature is specified; - The temperature of the coolant is recorded continuously or at time intervals; - If the temperature of the coolant rises to the control intervention temperature or beyond, the maximum braking power of the hydrodynamic brake is reduced. The invention is characterized by the following steps: the current deceleration of the motor vehicle when braking with the hydrodynamic brake is detected or calculated; wherein the control intervention temperature is changed as a function of the current deceleration of the motor vehicle.

Description

The invention relates to a method for limiting the maximum retrievable braking power of a hydrodynamic brake in a motor vehicle when the heat generated by the hydrodynamic brake is dissipated by means of the cooling medium in an engine cooling circuit of the motor vehicle, in detail according to the preamble of claim 1.

Such brakes, which have become known as hydrodynamic retarders, generate heat during operation due to fluid friction. So that the hydrodynamic brake is not damaged, the resulting heat must be dissipated. This is done in a arranged in a motor vehicle hydrodynamic brake usually on the engine cooling circuit, that is, the coolant in the engine cooling circuit is either used directly as a working fluid of the hydrodynamic brake or used to cool the working fluid of the hydrodynamic brake via a heat exchanger.

In order to avoid damaging operating states for the hydrodynamic brake, the maximum retrievable braking power of the hydrodynamic brake must be controlled sufficiently reliably.

For this purpose, a number of approaches to avoid these unfavorable operating conditions has become known in the past. Thus, for example, the coolant temperature is detected and monitored by means of temperature sensors, so that when reaching a lower limit temperature, which is referred to herein as the control intervention temperature, the maximum retrievable by the hydrodynamic brake braking power is reduced to reduce the heat input into the coolant through the hydrodynamic brake. In this way, very rapid temperature increases, which would lead to an overshoot in the temperature in the engine cooling circuit can be reduced. Such overshoots are disadvantageous because they can lead to destruction of the coolant expansion tank in the engine cooling circuit.

In the European patent specification EP 0 699 144 B1 Therefore, it is proposed to limit the maximum usable braking effect of a hydrodynamic brake as a function of the engine speed. For this purpose, the course of the maximum usable braking power of the hydrodynamic brake is set directly above the engine speed, wherein the engine speed is detected via an engine speed sensor. The course of the maximum usable braking effect on the engine speed is mapped in a control unit which controls the hydrodynamic brake accordingly depending on the engine speed.

Although the patent suggests, according to a modified embodiment, to additionally use the motor water temperature for controlling the maximum usable braking effect of the hydrodynamic brake by shifting the stored control curve downwards at a high cooling water temperature and shifting it upwards at a low cooling water temperature, then the basis is for the limitation of the maximum usable braking effect, the immediate course of the permissible braking effect over the engine speed. In practice it has been found that the course of the maximum usable braking effect on the engine speed must be given very conservative in order to avoid overheating of the coolant in any case. As a result, however, the availability of the hydrodynamic brake is undesirably limited.

The German patent DE 10 2006 036 185 B3 describes a method for limiting the maximum retrievable braking power of a hydrodynamic brake, wherein in addition to the control intervention temperature, a control target temperature is specified. Both temperatures are given dynamically as a function of the rotational speed of the vehicle drive motor, so determined during the driving operation in dependence on the present engine speed, the relevant temperature and used to set the maximum retrievable braking power.

The known from the prior art method for limiting the braking power of the hydrodynamic brake is common, however, that the available retrievable braking power is not optimally utilized in every driving situation. Such driving situations are, for example, sustained braking, which are necessary, for example, in mountain downhills and characterized by keeping the speed substantially constant, as well as adaptation braking, which are characterized by high delays, for example, to set the distance to a vehicle in front.

The invention has for its object to increase the availability of the hydrodynamic brake, without at the same time to increase the risk of temperature increase in the engine cooling circuit. Furthermore, the maximum possible retrievable braking power should be optimized depending on the driving situation of the vehicle.

The object of the invention is achieved by a method according to the independent claim. The dependent claims describe advantageous and particularly expedient embodiments of the method according to the invention.

By means of the method according to the invention, the maximum retrievable braking power of a hydrodynamic brake is limited. If this is the case that braking power is called up, this can for example be done automatically by a controller or manually by a driver. The braking power of the hydrodynamic brake can also be called up, for example, by a driver actuating a selector lever or setting a specific brake level. This actuation or setting is detected by the control unit, which controls the hydrodynamic brake, for example via a compressed air system, in such a way that a certain amount of working medium is set in the working space of the hydrodynamic brake. The desired braking power is generated via a circulation flow of the working medium which forms in the working space, which supplies a given braking torque.

It is also conceivable that an automatic control takes place, for example, due to certain detected driving situations. In this case, the controller can determine depending on certain driving situations, whether currently a hydrodynamic braking is advantageous. The hydrodynamic braking is then automatically initiated without the driver having to be active.

Due to the fluid friction resulting in the braking operation due to the circulation flow, heat is generated in the hydrodynamic brake, which must be dissipated via the engine cooling circuit, indirectly or directly, the latter for example by virtue of the fact that the working fluid of the hydrodynamic brake is also the coolant in the engine cooling circuit. In this case, operating conditions of the motor vehicle may occur in which, for example due to a low flow rate of the coolant pump, by means of which the coolant is circulated in the engine cooling circuit and which is driven by the vehicle drive motor or an additionally provided for this purpose engine, in particular electric motor, or by a current large temperature input of other units in the cooling circuit or a small dissipation of heat from the cooling circuit an impermissible temperature increase of the coolant occurs when the requested braking power is actually implemented. In this case, the braking request can not be fully implemented, but it is the maximum retrievable braking power of the hydrodynamic brake, which is an upper barrier set. As long as the specifically called braking power is below this limit, the braking request is fully implemented. Otherwise, only the maximum permitted braking power is set.

The inventive method provides that initially a control intervention temperature T _{1 is} specified. This temperature can be initially set dynamically, for example, depending on the speed of the vehicle drive motor. In particular, the temperature may be stored in a control unit in the form of a diagram or a table which directly assigns the control intervention temperature T ₁ to the speed of the vehicle drive engine over a predetermined speed range. The dynamic specification then consists in determining the relevant temperature at the actual engine speed during the driving operation either only when initiating the braking operation or during braking operation or in particular both in braking operation and in non-braking operation from the diagram or the table maximum retrievable braking power is used. The temperature of the coolant in the engine cooling circuit is detected continuously or at predetermined, in particular regular time intervals and compared with the control intervention temperature T ₁ at the current engine speed or a dependent thereon size. If the detected temperature of the cooling medium rises to the control intervention temperature T ₁ , the maximum retrievable braking power of the hydrodynamic brake is reduced so that the maximum permissible temperature of the coolant in the engine cooling circuit is not exceeded.

The thus set in particular as a function of the speed braking power can then either serve as the output value for the further reduction or increase of the maximum retrievable braking power or further as an input to adjust the maximum retrievable braking power, as described below.

According to the present invention, the actual deceleration of the motor vehicle when braking with the hydrodynamic brake is detected or calculated, wherein the control intervention temperature T _{1 is changed} as a function of the current deceleration of the motor vehicle. This means in the described case, in which the speed of the vehicle drive motor is used to set the maximum retrievable braking power that at least for the duration of braking (ie in braking mode) the setting of the braking power depending on the speed of the vehicle drive motor suspended - or at least less is prioritized - and instead the braking power is controlled in dependence of the current deceleration of the motor vehicle. Alternatively, the actual deceleration is used in addition to the speed of the vehicle drive motor for setting the maximum retrievable braking power.

The current deceleration can also be detected or calculated continuously or at predetermined time intervals, in particular exclusively during braking. For this purpose, suitable sensors are provided.

In this case, the resulting braking deceleration of the moving motor vehicle-that is, the speed decrease from the drive per time interval-is meant by the hydrodynamic brake as well as a combination of operating and hydrodynamic brake and indicates the negative acceleration of the vehicle. The latter can for example be detected by suitable acceleration sensors or calculated by the speed difference of a shaft (for example drive shaft) over a certain time interval.

However, the combination of speed and delay-dependent limitation of the retrievable braking power described here is not absolutely necessary. Thus, alternatively, the braking power limitation could also be effected only as a function of the deceleration of the motor vehicle. It is also possible to use other input variables for limiting the maximum retrievable braking power, for example the rotational speed of the vehicle drive motor, the rotational speed of the coolant pump, the delivery rate or absorption capacity of the coolant pump, the heat input of further units cooled by the engine cooling circuit, the ambient temperature.

Advantageously, in addition, a control target temperature T _{2 is} specified, wherein the control target temperature T _{2 is} also changed during braking with the hydrodynamic brake as a function of the current deceleration of the motor vehicle. The control target temperature T ₂ serves as the upper limit and not to exceed the maximum possible temperature occurring in the engine cooling circuit or only by a predetermined amount. Incidentally, the control target temperature T ₂ already applies to the control intervention temperature T ₁ .

In general, the control intervention temperature T ₁ and the control target temperature T ₂ are different in terms of their values.

A braking state of the motor vehicle is preferably closed in braking operation as a function of the current deceleration, with at least one adaptation braking and one continuous braking being distinguished in that the current deceleration is compared by means of a limit deceleration pointing to the braking state and if a current deceleration is present or at the limit deceleration Delay (retardation) only the control intervention temperature T ₁ changes and thus in particular the spreading of the Abregelbandes (difference between the course of the control target temperature T ₂ and the control intervention temperature T ₁ on the speed of the vehicle drive motor or the coolant pump speed and below the limit delay (adjustment braking) both the control intervention temperature T. ₁ and the control target temperature T _{2 are} changed.

By adaptive braking in the sense of the present invention is meant braking for a short-term reduction of the speed of the motor vehicle. Adjustment brakes may be made, for example, to adjust the distance to a preceding vehicle or to reduce speed on the deceleration strip prior to highway exits. The adaptation braking is characterized, in particular, by a deceleration of the motor vehicle which remains constant over the braking period.

The term retardation describes in particular a braking state of the motor vehicle, in which the speed of the same does not change or only slightly. As an example, here is a downhill to call, in which such a braking power is called that the vehicle does not accelerate and thus essentially downhill drives at a constant speed. The acceleration at least in the direction of movement of the motor vehicle is thus substantially zero.

If the limit delay is set to zero in terms of absolute value, then both braking conditions sustained braking and adaptation braking can be clearly distinguished. Of course, it is possible for the limit delay to set another, for example, non-zero value, which is in particular less than zero.

Advantageously, the control intervention temperature T ₁ is shifted toward low temperatures and moved below the limit deceleration, both the control intervention temperature T ₁ and the control target temperature T ₂ to higher temperatures in the presence of a lying at or above the limit deceleration current delay. In the first case occurs when the control target temperature is constant, at least at a certain speed of the vehicle drive motor of the coolant pump, held, a spread of the Abregelbandes.

This ensures that during a sustained braking, the maximum retrievable braking power is already "earlier" and thus limited at lower temperatures of the engine cooling circuit. Thus, the difference .DELTA.T between the control intervention temperature T ₁ and the control target temperature T _{2 is increased,} in particular over the entire default range. This will on the one hand achieved that in Engine cooling circuit is a greater heat capacity for dissipating heat for the upcoming downhill mountain pass (compared to the adaption braking relatively long-lasting braking) is available, on the other hand, a gentle course of the retarder braking torque is achieved, thereby increasing the comfort and the endurance braking behavior of the hydrodynamic brake.

On the other hand, if the current delay below the limit delay is present, the difference between the two temperatures is preferably kept constant, but both temperatures are shifted toward higher temperatures. As a result, the maximum retrievable braking power and thus the maximum retrievable braking torque of the retarder is briefly provided for a short time. However, this also means that the current temperature of the engine cooling circuit may also be briefly above the actual control target temperature T ₂ in terms of retardation. Due to the fact that such adaptation brakes occur very limited in time, an overshoot of the current temperature in the engine cooling circuit above the control target temperature T _{2 is} expressly accepted.

Advantageously, the current road gradient of the route on which the motor vehicle moves, recorded or calculated, the control intervention temperature T ₁ and / or the control target temperature T _{2 is} also changed depending on the road gradient / are. With the slope of the road is meant here the increase or the slope of a roadway in the direction of movement of the motor vehicle and is given in percent. Due to the current road gradient, which can be directly detected or indirectly calculated by means of corresponding sensors, it can be better understood whether it is in particular a slow-down, so for example, a mountain passage. Data of a GPS system or other navigation systems, in particular satellite-based, can also be evaluated for evaluating the topography of the route ahead of the vehicle and used as an input variable for changing the control intervention temperature and / or control target temperature.

The invention will now be explained by way of example with reference to the figures.

Show it:

1 an engine cooling circuit of a motor vehicle with a hydrodynamic brake introduced therein, the maximum retrievable braking power can be controlled according to the invention;

2a the specification of a course of the control intervention temperature T ₁ and the control target temperature T ₂ over the speed n of the vehicle drive motor in the case of a continuous braking;

2 B the current speed profile of the motor vehicle as a function of the time t during a sustained braking;

2c the speed history in 2 B associated acceleration curve of the motor vehicle during the continuous braking;

3a the specification of a course of the control intervention temperature T ₁ and the control target temperature T ₂ over the speed n of the vehicle drive motor in the event of an adaptation braking;

3b the current speed curve of the motor vehicle as a function of the time t during an adaptive braking;

3c the speed history in 3b associated acceleration curve of the motor vehicle during the adaptation braking.

In the 1 can be seen in a schematic representation of the engine cooling circuit 2 of a motor vehicle. In this engine cooling circuit 2 is a coolant by means of the coolant pump 4 circulated in a cycle, this cycle through a vehicle radiator 5 (Liquid-air heat exchanger) leads, in which the heat absorbed by the coolant is dissipated to the environment. The coolant also flows through the vehicle drive motor 3 to cool it, and is working fluid in the engine cooling circuit 2 arranged hydrodynamic brake 1 ,

The arrangement of the various elements in the engine cooling circuit 2 is in the 1 chosen arbitrarily and can be designed differently.

In the 2a If one recognizes a diagram of which the speed n of the vehicle drive motor 3 assigns exactly two temperature profiles directly. The two temperature profiles are in the speed range, which passes through the drive motor during operation, in the present case in the form of straight sections with a constant pitch. The corresponding speed range extends from the idle speed n _min up to the maximum allowable or possible speed n _max . The predetermined temperature profiles consist of the course of the control intervention temperature T ₁ and the course of the control target temperature T ₂ . Both courses are given here continuously and have no discontinuities. Alternatively or in addition to the specification by means of stored diagrams, the specification can be achieved by mathematical functions, for example, straight-line equations, or tables.

Particularly advantageous are the corresponding specifications or assignments in a control device or its memory or in an external memory, which is accessed by a control unit deposited.

According to the specification of the 2a is the difference .DELTA.T between the control intervention temperature T ₁ and the control target temperature T ₂ over the entire default range, in particular from the idle speed n _min to the maximum speed n _{max of} the vehicle drive motor constant, since both lines have the same slope.

This could be different. Thus, the two temperatures T ₁ and T ₂ could not run parallel to each other. In particular, the difference ΔT could change over the rotational speed n.

The control of the maximum available, on-demand, for example, by a driver, the braking torque or the maximum braking power of the hydrodynamic brake is for example, first depending on the speed of the vehicle drive motor as follows: As long as the measured coolant temperature at a predetermined instantaneous rotational speed n of the vehicle driving motor under the control intervention temperature T ₁ , which is assigned to this speed n, is immediately before or upon activation of the hydrodynamic brake by appropriate filling of the working space of the hydrodynamic brake by means of the hydrodynamic brake, the braking torque or braking power, as set forth in the introduction, set which / which of the Driver (or a control unit) is requested. If, however, the measured coolant temperature at a certain speed n of the vehicle drive motor reaches or exceeds the control intervention temperature T ₁ at this speed n, the maximum retrievable braking torque or the maximum retrievable braking power of the retarder is reduced. This means, for example, if the driver, the maximum braking torque, which can afford the retarder due to its design, is required, and results in setting this requested braking performance correspondingly high coolant temperature, which reaches or exceeds the control intervention temperature T ₁ , so despite the existing requirement of the driver reduces the braking torque generated by the hydrodynamic brake or the corresponding braking power, so that the heat input is reduced by the hydrodynamic brake in the coolant.

In addition, in the present case during braking, the current deceleration of the motor vehicle is detected in order to obtain the maximum retrievable braking power.

In this case, to limit the braking power in the presence of a continuous braking according to the invention, the temperature profile of the control intervention temperature T ₁ is shifted towards lower temperatures, see the dashed temperature curve of the new control intervention temperature T _1D in the 2a , In the present case, the original control intervention temperature T ₁ differs from the new control intervention temperature T _1D by the difference ΔT _D. Deviating from the illustration in 2a , the difference ΔT _D could vary over time, for example, become larger or smaller.

The new control intervention temperature T _1D is thus always set when a sustained braking is present. The latter is concluded by comparing the actual deceleration of the motor vehicle with a limit delay, which was here assumed to be 0 m / s ² . The current deceleration is detected as the quotient of the speed of the motor vehicle in a time interval t ₂ -t ₁ . Such a course is in 2 B shown. Such a course may be characteristic of the entire braking process, but need not be mandatory. As shown, the speed v _{D is} compared to the time. For slow braking, for example braking during downhill driving, the course of the speed is characteristic. In this case, a constant speed is reached over the time interval t ₂ -t ₁ , which in the present case is indicated as a horizontal to the time axis t.

Since such retardation essentially means a rectilinear movement of the motor vehicle, the acceleration a _D in the same time interval t ₂ -t ₁ , as from 2c refer to.

In the 3a to 3c Essentially, the same diagrams are shown as in FIGS 2a to 2c with the exception that there is an adjustment braking. That's how it shows 3a in the dashed lines, the two new curves of the control intervention temperature T _1A and T _2A , which are shifted from the original temperatures T ₁ and T ₂ towards higher temperatures. In the present case, the two new temperatures T _1A and T _2A differ by the difference ΔT _A. The differences ΔT and ΔT _A can have the same amount. However, this does not necessarily have to be the case. Again, the difference ΔT _{A could} vary over the entire time course. For the new temperature curves T _1A and T _2A , the statements made regarding the other temperature curves T ₁ and T ₂ apply.

Since an adaptive braking means a momentary speed change, the speed of the vehicle in time interval t ₂ -t _{1 will change} from the initial speed v _A1 at time t ₁ (for example before braking) to the final speed v _A2 at time t ₂ (for example after adjustment braking). This speed change is as in 3b shown as a straight line with a negative slope. In 3c is the associated acceleration (based on the delay a _A ) of the motor vehicle in the corresponding time interval t ₂ -t ₁ shown. As can be seen from this, the deceleration a _A during the adaptation braking in this time interval is constant, which is indicated here by the parallel to the time axis.

The elevation of the temperature curves T ₁ and T ₂ toward the higher temperature curves T _1A and T _2A is preferably always carried out when the actual delay is below the limit delay a _G , as shown in FIG 3c on the negative course of the delay a _A can be seen. In other words, this increase takes place whenever the currently detected deceleration of the vehicle deviates from the lag characterizing deceleration.

Due to the fact that the driving situation or the braking state of the motor vehicle can now be closed by means of the method according to the invention, the maximum braking power of the hydrodynamic brake can always be optimally retrieved. This is achieved by providing more heat capacity for dissipating the relatively long-lasting braking during sustained braking by shifting the control intervention temperature T ₁ according to the invention. On the other hand, that during adaptation braking the entire temperature band enclosed by the control intervention temperature T ₁ and control tap temperature T _{2 is} shifted towards upper temperatures.

LIST OF REFERENCE NUMBERS

1

hydrodynamic brake

2

Engine cooling circuit

3

Vehicle drive motor

4

Coolant pump

5

vehicle radiator

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0699144 B1 [0005]
• DE 102006036185 B3 [0007]

Claims (6)

Method for limiting the maximum retrievable braking power of a hydrodynamic brake ( 1 ) in a motor vehicle, wherein the hydrodynamic brake ( 1 ) generated by means of a coolant in an engine cooling circuit ( 2 ) of the vehicle drive motor ( 3 ) and the coolant by means of a vehicle drive motor ( 3 ) or another motor-driven coolant pump ( 4 ) in the engine cooling circuit ( 2 ) is circulated, comprising the following steps: 1.1 a control intervention temperature (T ₁ ) is specified; 1.2 the temperature of the coolant is measured continuously or at intervals; 1.3 when the temperature of the coolant rises to the control intervention temperature (T ₁ ) or beyond, the maximum retrievable braking power of the hydrodynamic brake ( 1 ) decreased; characterized by the following steps: 1.4 it is the current deceleration of the motor vehicle when braking with the hydrodynamic brake ( 1 ) recorded or calculated; wherein 1.5 the control intervention temperature (T ₁ ) is changed depending on the current deceleration of the motor vehicle. A method according to claim 1, characterized in that in addition a control target temperature (T ₂ ) is specified and the control target temperature (T ₂ ) is also changed depending on the current deceleration of the motor vehicle. A method according to claim 1 or 2, characterized in that depending on the current deceleration is concluded on a braking condition of the motor vehicle, wherein at least one adjustment braking and a sustained braking are distinguished by the current delay is compared by means of a braking state indicating limit delay; and 3.1, if there is a current deceleration at or above the limit delay, only the control intervention temperature (T ₁ ) is changed and below the limit deceleration both the control intervention temperature (T ₁ ) and the control target temperature (T ₂ ) are changed. A method according to claim 3, characterized in that in the presence of a present at or above the limit delay current delay, the control intervention temperature (T ₁ ) shifted to lower temperatures and below the limit delay both the control intervention temperature (T ₁ ) and the control target temperature (T ₂ ) is / are shifted to higher temperatures. Method according to one of claims 1 to 4, characterized in that the current road gradient of the route on which the motor vehicle moves, is detected or calculated, wherein the control intervention temperature (T ₁ ) and / or the control target temperature (T ₂ ) additionally in dependence the road gradient is / are changed. Method according to one of claims 1 to 5, characterized in that the control intervention temperature (T ₁ ) and / or control target temperature (T ₂ ) additionally in dependence of one or more of the following variables is changed: - speed of the vehicle drive motor ( 3 ) - Speed of the coolant pump ( 4 ) - delivery rate or capacity of the coolant pump ( 4 ) - heat input further through the engine cooling circuit ( 2 ) cooled units - ambient temperature

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