DE102022208079A1 - Method for determining the braking torque of an engine brake, method for determining a target value of an intake manifold pressure for obtaining a target braking torque by an engine brake, computing unit and computer program - Google Patents

Abstract

The invention relates in one aspect to a method for determining a braking torque of an engine brake in a vehicle with an internal combustion engine (1), comprising obtaining a value of an intake manifold pressure in an intake tract of the internal combustion engine (1); determining the braking torque based on at least the value of the intake manifold pressure. In a further aspect, the invention relates to a method for determining a setpoint (320) of an intake manifold pressure for obtaining a setpoint braking torque through an engine brake in a vehicle with an internal combustion engine (1), comprising determining a setpoint value of an intake manifold pressure from the setpoint braking torque; activating the internal combustion engine (1) so that the setpoint (320) of the intake manifold pressure is established.

Description

The present invention relates to a method for determining a braking torque of an engine brake in a vehicle, a method for determining a target value of an intake manifold pressure for obtaining a target braking torque through an engine brake, and a computing unit and a computer program for carrying out the method.

Background of the invention

Supporting continuous brakes can be used in particular in the commercial vehicle sector to provide wear-free support for the service brake actuated via the brake pedal. The way the engine brake works, which is an example of a continuous brake, is based on the fact that work done in the compression cycle is left unused for the following cycle, thereby increasing the braking torque for the internal combustion engine. This can be achieved in particular by opening the exhaust valves of one or more cylinders of the internal combustion engine at the end of the compression stroke, whereby the pressure in the cylinder is reduced (decompression). The opening of the exhaust valves occurs when the piston is near top dead center, so that the compressed gas charge is expelled. As soon as the piston has passed top dead center or later, but at the latest before the next compression stroke starts, the exhaust valves are closed again and the process is repeated in the next cycle.

Disclosure of the invention

According to the invention, a method for determining a braking torque of an engine brake, a method for determining a target value of an intake manifold pressure for obtaining a target braking torque by an engine brake, as well as a computing unit and a computer program for carrying it out with the features of the independent patent claims are proposed. Advantageous refinements are the subject of the subclaims and the following description.

The invention provides a simple way to determine and control the braking torque generated by an engine brake, so that in particular higher-level braking coordination of different braking systems can be carried out sensibly.

For this purpose, the invention uses in particular a model with a linear approach, in particular in the pressure variables involved, in order to determine the engine braking torque, for example in an engine control unit, based on existing signals from the sensors installed in the internal combustion engine and possibly models that run on a control unit. Furthermore, a desired braking torque, which is to be generated by the engine brake of the internal combustion engine, can be adjusted by adjusting the pressure variables involved, in particular the intake manifold pressure.

Advantageously, the applied engine braking torque can be determined as precisely as possible using a linear model based on control unit signals that are usually present anyway. An advantage of the invention is that a suitable physical relationship can be mapped by the control unit using less data that is already available and does not have to be determined using data from several characteristic maps, as was previously the case.

Another advantage is that a linear relationship can be easily inverted and so not only can the engine braking torque be calculated, but also the necessary target pressure at the cylinder inlet (so-called target value of an intake manifold pressure) can be determined for a given engine braking torque. This setpoint of the intake manifold pressure can then be adjusted via existing charge pressure regulators or intake manifold pressure regulators, so that the driver's braking torque request is implemented quickly and precisely.

In one aspect, the invention comprises a method for determining a braking torque of an engine brake in a vehicle with an internal combustion engine, wherein, in particular in a control device, a value of an intake manifold pressure in an intake tract, for example in an intake manifold of the internal combustion engine or at the cylinder inlet, is obtained and the braking torque is determined based on at least the value of the intake manifold pressure.

The intake manifold pressure in the intake tract of the internal combustion engine can be measured by a sensor. However, it is also possible for the intake manifold pressure to be determined by the control unit based on other parameters, for example by calculation or comparison with previously measured or predetermined values or based on a model.

In another aspect, the invention further comprises a method for determining a target value of an intake manifold pressure for obtaining a target braking torque by an engine brake in a vehicle. For this purpose, a setpoint of an intake manifold pressure is first determined from the setpoint braking torque and then the internal combustion engine is controlled in such a way that the setpoint of the intake manifold pressure is established. This control can be designed in such a way that the control device controls an existing charge pressure regulator or intake manifold pressure regulator in such a way that the specific setpoint of the intake manifold pressure is established in the intake tract. The target braking torque can, for example, be specified by a driver using a control element such as a pedal or lever (steering column switch) or an assistance system.

According to one embodiment, a value of an exhaust gas back pressure of an exhaust gas turbocharger of the internal combustion engine is further used to determine the braking torque or the setpoint of the intake manifold pressure. The exhaust back pressure can be measured by a sensor. Alternatively, the exhaust back pressure can be determined using other parameters by calculation or comparison with previously measured or predetermined values or using a model. By using the exhaust back pressure, the determination of the braking torque and/or the intake manifold pressure can be improved, especially during operation with a strong dependence on the exhaust back pressure. Such operation takes place, for example, in braking mode with an exhaust flap.

When determining the braking torque, in one embodiment the difference between the intake manifold pressure in the intake manifold and the exhaust back pressure of the exhaust gas turbocharger is used.

According to one embodiment, at least one further parameter is used to determine the braking torque or the setpoint of the intake manifold pressure, for example selected from: displacement of the internal combustion engine, combustion process, friction torque of the internal combustion engine and stage parameters of the engine brake. The displacement of the internal combustion engine and the selected combustion method (2-stroke or 4-stroke) are known in advance and can be stored in the control unit, for example.

The friction torque of the internal combustion engine can be determined, for example, based on a sum of a constant friction torque and a friction torque that is dependent on the current speed of the internal combustion engine. Usually, suitable maps are already available in a control unit in which the engine's friction torque can be entered depending on the oil temperature and the engine speed.

A corresponding stage parameter is determined for each stage of the engine brake. A stage of the engine brake corresponds to a certain fixed number of braking cylinders or the exhaust flap. In a 6-cylinder engine, for example, all six cylinders, but also fewer cylinders, can be used for the engine brake. Depending on this, the step parameter changes.

The use of one or more of the further parameters means that the braking torque or the setpoint of the intake manifold pressure required for a desired braking torque can be determined more precisely and therefore, for example, the coordination of various brakes (rim brake, retarder, engine brake, etc.) is improved or The driver's desired braking torque can be adjusted more precisely via the engine brake.

According to one embodiment, the braking torque or the setpoint of the intake pipe pressure is determined based on a linear relationship. This is a particularly simple but still sufficiently accurate way of determining.

The relationship for determining the braking torque using the aforementioned parameters has the following form in particular: $$\begin{array}{l}{\text{M}}_{\text{Brake}}=f\left(\text{Motor speed}\text{,Stages}\text{,Intake manifold pressure}\right)\\ ={\text{C}}_{\text{rub}}+f_{\text{conv}}\cdot f_{\text{Level}\text{,x}}\cdot p_{\text{Suction pipe}}\left[\text{Nm}\right]\end{array}$$

The factor C _friction describes the friction torque of the internal combustion engine, which can be represented as the sum of a constant friction torque and a friction torque that depends on the engine speed: $${\text{C}}_{\text{rub}}={\text{C}}_{\text{const}}+f_{\text{rub}}\cdot n_{\text{engine}}$$

f _Friction is a friction factor and n _Motor is the speed of the internal combustion engine. Furthermore, the factor f _konv is a conversion factor for converting pressure into torque and is determined as follows: $$f_{\text{conv}}=v_{\text{displacement}}\cdot \frac{1000}{2\cdot i\cdot \pi }\left[\frac{\text{Nm}}{\text{bar}}\right]$$

V _displacement is the displacement of the internal combustion engine, i is the number of revolutions of the internal combustion engine per working stroke (for a 4-stroke engine, i = 2, for a 2-stroke engine, i = 1) and π the circle number.

f _stage,x is the stage parameter which represents a calibration factor to relate the braking torque to the number of cylinders used for engine braking.

f_Abgas ist ein Kalibrierungsparameter und p_Abgas der Abgasgegendruck. Die restlichen Parameter sind dieselben wie zuvor.When the exhaust gas back pressure is taken into account, the linear relationship changes in particular to the following equation: $$\begin{array}{l}\text{M}{\text{'}}_{\text{Brake}}=f\left(\text{Motor speed}\text{,Level}\text{,Intake manifold pressure}\text{,Exhaust back pressure}\right)\\ ={\text{C}}_{\text{rub}}+f_{\text{conv}}\cdot \left[f_{\text{Level}\text{,x}}\cdot p_{\text{Suction pipe}}+f_{AbGas}\cdot \left(p_{\text{exhaust}}-p_{\text{Suction pipe}}\right)\right]\left[\text{Nm}\right]\end{array}$$

f _exhaust is a calibration parameter and p _exhaust is the exhaust back pressure. The rest of the parameters are the same as before.

Both relationships (without taking the exhaust gas back pressure into account and taking the exhaust gas back pressure into account) can be easily changed in such a way that, given the braking torque (setpoint braking torque, M _{brake, setpoint} ), the necessary intake manifold pressure (setpoint value of the intake manifold pressure) can be calculated. The following equation results for the target value of the intake manifold pressure (p _{intake manifold, target} ), taking the exhaust gas back pressure into account: $$p_{\text{Suction pipe}\text{,should}}=\frac{{\text{M}}_{\text{Brake}\text{,should}}-{\text{C}}_{\text{rub}}-f_{\text{exhaust}}\cdot p_{\text{exhaust}}\cdot f_{\text{conv}}}{f_{\text{conv}}\cdot \left(f_{\text{Level}\text{,x}}-f_{\text{exhaust}}\right)}\left[\text{bar}\right]$$

A computing unit according to the invention, for example a control unit of a motor vehicle, is set up, in particular in terms of programming, to carry out a method according to the invention.

The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous because this causes particularly low costs, especially if an executing control device is used for additional tasks and is therefore present anyway. Finally, a machine-readable storage medium is provided with a computer program stored thereon as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard drives, flash memories, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.). Such a download can be wired or wired or wireless (e.g. via a WLAN network, a 3G, 4G, 5G or 6G connection, etc.).

Further advantages and refinements of the invention result from the description and the accompanying drawing.

The invention is shown schematically in the drawing using exemplary embodiments and is described below with reference to the drawing.

Brief description of the drawings

• 1 shows an internal combustion engine as the basis for the invention.
• 2 shows a block diagram of an embodiment of a method for determining a braking torque of an engine brake.
• 3 shows a block diagram of an embodiment of a method for determining a target value of an intake manifold pressure for obtaining a target braking torque through an engine brake.

Embodiments of the invention

1 shows an internal combustion engine 1 of a vehicle with six cylinders, a control unit 2 and a sensor 3, which is arranged on the internal combustion engine 1 in such a way that it measures an intake manifold pressure at a cylinder inlet and transmits the measured value of the intake manifold pressure to the control unit 2. Furthermore, another sensor 4 is shown, which is arranged on the internal combustion engine 1 in such a way that it measures an exhaust gas back pressure of an exhaust gas turbocharger of the internal combustion engine 1 and transmits the measured value of the exhaust gas back pressure to the control unit 2. In addition, the internal combustion engine also has an exhaust gas recirculation cooler 6 and an associated exhaust gas recirculation valve 7, by means of which part of the exhaust gas can be returned to the engine. A braking torque of the Internal combustion engine 1 can be determined quickly and precisely. This improves the coordination of various braking processes (rim brake, retarder, engine brake, etc.), which optimizes the braking process and reduces wear (e.g. on the brake rim). Furthermore, based on a braking torque displayed by a driver via a brake pedal, the necessary setpoint of the intake manifold pressure p _{suction pipe, should} be determined by the control unit 2 and set via a charge pressure regulator or intake manifold pressure regulator 5. This allows the driver's desired braking torque to be set quickly and precisely.

2 shows a block diagram of an embodiment of a method for determining a braking torque of an engine brake. One or more of the input variables 201, 202, 203 enter a calculation block 210. The calculation block 210 processes these input variables and then outputs an output variable 220.

Such a computing block 210 is preferably implemented as a computer program in a computing unit or a control device 2.

In the method for determining a braking torque of an engine brake in a vehicle with an internal combustion engine 1, the computing block 210 receives as a first input variable 201 a value of an intake manifold pressure in an intake tract, for example the intake manifold of the internal combustion engine 1. This can be measured, for example, by the sensor 3 or based on others Parameters can be determined, for example by calculation or comparison with previously measured or predetermined values or based on a model. Furthermore, the computing block can receive the exhaust gas back pressure of the exhaust gas turbocharger as the second input variables 202. This is measured, for example, by the sensor 4 or can be calculated using a model. In addition, the computing block 201 receives the third input variables 203. The third input variables 203 are, for example, the displacement of the internal combustion engine 1, the combustion process, the friction torque of the internal combustion engine 1 or the stage parameter of the internal combustion engine 1. The third input variables 203 are in the control unit 2, in which the Calculation block 210 is implemented as a computer program, stored or can be determined from values stored in the control unit 2 and/or other measured values. As an output variable 220, the computing block 210 determines the braking torque of the engine brake, in particular using equation 1, if the computing block 210 does not obtain any values from the second input variable 202. If the calculation block 210 receives values from the second input variable 202, regardless of whether these were determined by the sensor 4 or were calculated by a model, equation 3 in particular is used to determine the output variable 220. The braking torque determined in this way (output variable 220) can then be used, for example, to coordinate a total braking torque generated by different braking systems. This can, for example, reduce the wear on another brake by having to generate a reduced braking torque.

3 shows a block diagram of an embodiment of a method for determining a setpoint 320 of an intake manifold pressure for obtaining a setpoint braking torque by an engine brake. One or more of the input variables 202, 203 and 301 are received in a calculation block 310. The calculation block 310 processes these unit sizes and then outputs an output size 320.

Such a computing block 310 is preferably implemented as a computer program in a computing unit or a control device 2.

In the method for determining the setpoint 320 of an intake manifold pressure for obtaining a setpoint braking torque through an engine brake in a vehicle with an internal combustion engine 1, the computing block 310 receives a fourth input variable 301, a desired setpoint braking torque. This target braking torque is, for example, a braking torque desired by a driver or driving assistance system, which is specified, for example, by actuating the brake pedal or a cruise control, etc. Furthermore, the computing block 310 can receive the second input variables 202, the exhaust gas back pressure of the exhaust gas turbocharger. This can be measured by the sensor 4 or determined using a model or from comparison with previously measured or predetermined values. In addition, the computing block 310 receives third input variables 203. The third input variables 203 are, for example, the displacement of the internal combustion engine 1, the combustion process, the friction torque of the internal combustion engine 1 or the stage parameter of the internal combustion engine 1. These third input variables 203 are in the control unit 2, in which the computing block 310 is implemented as a computer program, stored or can be determined from values stored in the control unit 2 and/or other measured values. As an output variable 320, the computing block 310 determines a setpoint of an intake manifold pressure, in particular based on equation 3, if the computing block 310 obtains values from the second input variable 202, regardless of whether these were determined by the sensor 4 or were calculated by a model. However, the computing block 310 can also determine the output variable without the second input variable 202, i.e. without the intake pressure of the exhaust gas turbocharger. The setpoint of the intake manifold pressure (initial variable 320) determined in this way can then be adjusted by a charge pressure regulator or intake manifold pressure regulator 5 at the cylinder inlets of the cylinders used for the engine brake. This makes it possible, for example, to reduce the wear on a friction brake by providing the desired braking torque through the engine brake and therefore the friction brake does not have to intervene.

Claims (13)

Method for determining a braking torque (220) of an engine brake in a vehicle with an internal combustion engine (1), comprising the following steps: Obtaining a value (201) of an intake manifold pressure in an intake tract of the internal combustion engine (1); Determining the braking torque (220) based on at least the value of the intake pipe pressure (201). Procedure according to Claim 1 , wherein the intake manifold pressure (201) in the intake tract is measured by a sensor (3). Method for determining a setpoint (320) of an intake manifold pressure for obtaining a setpoint braking torque (301) through an engine brake in a vehicle with an internal combustion engine (1), comprising the following steps: Determining a target value (320) of an intake pipe pressure from the target braking torque (301); Controlling the internal combustion engine (1) so that the setpoint (320) of the intake manifold pressure is established. Method according to one of the preceding claims, wherein a value of an exhaust gas counterpressure (202, 302) of an exhaust gas turbocharger of the internal combustion engine (1) is further used to determine the braking torque (230) or the setpoint (320) of the intake manifold pressure. Method according to the preceding claim, wherein the exhaust gas back pressure (202, 302) is measured by a sensor (4) or is determined using a model. Procedure according to one of the Claims 4 or 5 related back to one of the Claims 1 or 2 , wherein the difference between the value of the exhaust back pressure (202) of the exhaust gas turbocharger and the value of the intake manifold pressure (201) in the intake tract is used to determine the braking torque (220). Method according to one of the preceding claims, wherein at least one further parameter (203, 303) is used to determine the braking torque (220) or the setpoint (320) of the intake manifold pressure, which is selected from: displacement of the internal combustion engine (1), combustion method, friction torque of the combustion engine (1) and stage parameters of the engine brake. Method according to the preceding claim, wherein the friction torque of the internal combustion engine (1) is determined based on the sum of a constant friction torque and a friction torque dependent on the current speed of the internal combustion engine (1). Procedure according to Claim 8 or 9 , where the engine brake stage parameter is determined based on the number of cylinders used for engine brake. Method according to one of the preceding claims, wherein the braking torque (220) or the setpoint (320) of the intake manifold pressure are determined based on a linear relationship. Computing unit (5) which is set up to carry out all process steps of a method according to one of the preceding claims. Computer program that causes a computing unit (5) to carry out all process steps of a method according to one of the Claims 1 until 10 to be carried out when it is executed on the computing unit (5). Machine-readable storage medium with a computer program stored on it Claim 12 .

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