Method for controlling a motor brake of an internal combustion engine

Abstract

The invention relates to a method for controlling a motor brake of an internal combustion engine of a powertrain of a motor vehicle (10). In one step, the motor brake (40) is activated. In another step, a reversing process (42) is detected. A step is then carried out in which a deactivation time of the motor brake is determined on the basis of the detected reversing process (44), and in another step, the motor brake is deactivated at the deactivation time (46). The invention additionally relates to a controller (12).

Description

[0001] Method for controlling an engine brake of an internal combustion engine

[0002] Technical area

[0003] The present invention relates to a method for controlling an engine brake of an internal combustion engine. Furthermore, the invention relates to a control device for controlling an engine brake of an internal combustion engine.

[0004] State of the art

[0005] An engine can be used to decelerate a motor vehicle, for example in addition to or alternatively to a service brake. This puts the engine into overrun mode, which can cause the engine speed to rise. There is a limit to the overrun speed which must not be exceeded. Otherwise, damage to the drive train could occur. If this limit to the overrun speed is exceeded, the transmission automatically switches to neutral for protection. To ensure that the engine can still decelerate reliably, an engine brake can be provided. The engine brake can be a function in which the engine or the drive train causes additional deceleration which is not caused purely by friction. The engine brake can significantly increase the deceleration compared to a simply not driven engine, thus preventing the limit to the overrun speed from being exceeded.

[0006] For this purpose, the engine brake is controlled as a function of the engine speed, for example by taking predefined speed thresholds into account. For example, when decelerating in overrun mode, the engine brake is activated when a maximum speed is exceeded. For example, the engine brake is only deactivated again when the speed falls below the maximum speed or a different minimum speed, or when the engine returns to a drive state. When the engine brake is used, a delay may occur before drive power can be drawn from the engine again. This can lead to restrictions, particularly when changing direction by reversing, which is usually preceded by deceleration of the vehicle. This can cause the driving performance to fall below a desired and normally available level.In exceptional cases, it may even happen that the engine stops due to the reversing process and during deceleration with the engine brake activated.

[0007] Description of the invention

[0008] A first aspect of the invention relates to a method for controlling an engine brake of an internal combustion engine in a drive train of a motor vehicle. An engine brake can be a function of the internal combustion engine itself or a separate device by means of which additional deceleration is effected by the internal combustion engine. For example, the engine brake can influence a valve control or an exhaust tract in such a way that deceleration of the motor vehicle by the internal combustion engine is increased. An internal combustion engine can be part of a drive train. An internal combustion engine can be an internal combustion engine that converts chemical energy into mechanical work. For this purpose, fuel can be injected into a combustion chamber. A drive train of a motor vehicle can, for example, provide drive power and also braking power for the motor vehicle.The drivetrain can include the combustion engine, a transmission, and, for example, an output in the form of tires. Optionally, the drivetrain can also be configured to provide power take-off. The motor vehicle can be configured, for example, as a passenger car, a work machine, or an agricultural machine. For example, the motor vehicle can be configured as a wheel loader.

[0009] The method comprises a step of activating the engine brake. Activating the engine brake can cause additional deceleration. When the engine brake is activated, the internal combustion engine can, for example, be in a coasting state. In the coasting state, a shaft of the internal combustion engine can be driven by the rolling vehicle. In its coasting state, the internal combustion engine can cause a deceleration of the motor vehicle, which can be amplified by the activated engine brake. In the coasting state, the internal combustion engine does not, for example, provide any drive power. In a drive state, the internal combustion engine can drive the motor vehicle and, for example, accelerate it. In the drive state, an injection process can take place. In this process, fuel can be injected into a combustion chamber of the internal combustion engine.In the drive state, the shaft of the internal combustion engine can be driven by a combustion process. In the drive state, the engine brake is deactivated, for example. The engine brake can be activated as a function of a speed of the internal combustion engine and, alternatively or additionally, a control of the motor vehicle, for example, a predetermined speed. The engine brake can also be controlled as a function of the speed of the internal combustion engine and, alternatively or additionally, the control of the motor vehicle, for example, in order to change the level of deceleration caused by the engine brake. For example, the engine brake can have a first deceleration stage and a second deceleration stage, wherein the second stage decelerates more strongly than the first stage.

[0010] The method comprises a step of detecting a reversing operation. For example, the reversing operation can be detected based on control of the motor vehicle by the driver. For example, the driver can actuate a control element, such as a direction selector lever, to request the reversing operation. By detecting this actuation, the reversing operation can be detected, for example as imminent. However, the reversing operation can also be predicted and thus detected, for example, based on vehicle status information, such as a driving speed, a position in a working range, and a selected gear. A reversing operation can be a change in direction of travel, for example from reversing to forward travel. A reversing operation can comprise actuating a reversing device of the motor vehicle, for example a reversing device of its transmission.For the reversing process, for example, one clutch of the reversing device can be opened and then another clutch of the reversing device can be closed. The reversing process can cause a reversal of the direction of rotation on an output shaft of the drive train.

[0011] The method includes a step of determining a deactivation time of the engine brake depending on the detected reversing process. For example, the deactivation time can be determined relative to specific times of the reversing process, such as a clutch actuation, a pivoting of a hydrostatic transmission, or the start of an injection process. The deactivation time can relate to the timing at which the engine brake is deactivated. This allows the engine brake to be controlled in a time dependent on the reversing process, rather than depending on the engine speed. This can prevent an undesirable influence on the reversing process and, in particular, a power restriction of the drive train during reversing or shortly thereafter.

[0012] The method includes a step of deactivating the engine brake at the deactivation time. At the deactivation time, a rotational speed of the combustion engine may still require the engine brake to be activated with a conventional engine brake control. Therefore, the engine brake can now be deactivated early in order to provide full drive power for reversing in a timely manner. This allows for the fact that the engine brake itself may have a certain reaction time to be taken into account. For example, several hundred milliseconds may elapse between a deactivation signal and the actual complete deactivation of the engine brake.In addition, due to combustion processes and, alternatively or additionally, respective pressures in the internal combustion engine, an injection process to provide normal drive power cannot take place immediately even after the engine brake has already been completely deactivated, for example because a backflow in the exhaust tract impedes the combustion process. This can also be taken into account. In this way, it can be prevented that the engine brake is deactivated too late and, as a result, for example, that the engine is depressed too much. Accordingly, the method can prevent a reduction in acceleration during a reversing process due to a previously active engine brake. The method can also provide for the engine brake to be deactivated when an engine speed falls below an engine speed threshold.For example, the vehicle's driving behavior may indicate that the engine brake is deactivated even before the deactivation point. In this case, the engine brake can be deactivated using the usual control system, as this would no longer limit the drive power during the reversing process.

[0013] In a further embodiment of the method, the deactivation time of the engine brake is determined as a function of a delay time between the deactivation of the engine brake and the permissibility of starting an injection process in the internal combustion engine, as well as as a function of the start time of the injection process in the internal combustion engine during the reversing process. The delay time can be a time period that lies between the deactivation signal for the engine brake and an actual deactivation. Alternatively, the delay time can be a time period that lies between the deactivation signal for the engine brake and the permissibility of starting the injection process in the internal combustion engine. Alternatively, the delay time can be a time period that lies between the actual deactivation of the engine brake and the permissibility of starting the injection process in the internal combustion engine.The start of the permissible injection process can be a point in time at which fuel may again be fed into the combustion chamber of the internal combustion engine, either at all or in a manner not limited by the engine brake. Injection can involve supplying fuel into the combustion chamber, for example, with atomization and air supply. The start point in time of the injection process in the internal combustion engine during the reversing process can correspond to a point in time at which drive power is again required by the internal combustion engine during the reversing process. This can ensure that the engine brake is deactivated in time for unrestricted acceleration during the reversing process. For example, the deactivation point in time can be set so that it precedes the start point of the injection process by the delay time.In a further embodiment of the method, the deactivation time of the engine brake is determined depending on a deactivation delay time of the engine brake. For example, the adjustment time of an engine brake flap in the exhaust tract can be known. The deactivation time can thus take this adjustment time into account. The deactivation delay time can correspond to an inertia of the engine brake with respect to control signals.

[0014] In a further embodiment of the method, the deactivation time is determined such that the internal combustion engine is still in a coasting state when the engine brake is deactivated. This ensures that the engine brake does not inhibit a drive state or a transition to the drive state. For example, the internal combustion engine may still be in its coasting state when the reversing process is detected and may transition to the drive state during the reversing process. The engine brake is then deactivated, for example, before this transition.

[0015] In a further embodiment of the method, the engine brake is activated depending on the engine speed. This allows the engine brake to be activated as needed, for example, when a maximum speed is exceeded during overrun. Furthermore, the drivetrain can be protected in this way. For example, a hydrostatic transmission of a hydrostatic power-split transmission in the drivetrain can be reliably protected from damage by the engine brake. For example, the strength of the engine brake can also be adjusted depending on the engine speed. Alternatively or additionally, the engine brake can also be activated manually.

[0016] In a further embodiment of the method, the engine brake adjusts a flap in an exhaust tract. This makes it possible to increase the back pressure in the respective combustion chambers of the internal combustion engine. For example, the back pressure against which the pistons must expel gas can be increased, and thus also the deceleration caused by the internal combustion engine. Such an engine brake is simple, reliable, and efficient. However, if it is not deactivated in time by fully opening the flap, such an engine brake can significantly impede the combustion process when changing to the drive state. This impediment is reliably prevented by the engine brake control method.

[0017] In a further embodiment of the method, variable valve timing is controlled by the engine brake. The variable valve timing can be used to achieve a particularly strong and, alternatively or additionally, particularly variably adjustable deceleration using the engine brake. For example, the variable valve timing can shift the closing and opening times of respective valves. However, if the engine brake is not deactivated in a timely manner to restore the valve timing optimized for the combustion process, the combustion process can also be significantly impaired.

[0018] In a further embodiment of the method, the drive train is designed as a hydrostatic power-split drive train. A hydrostatic power-split drive train has a hydrostatic transmission. This allows a transmission ratio to be continuously adjusted. During the reversing process, the hydrostatic transmission is then typically pivoted, which can, however, result in particularly strong deceleration of the combustion engine. Overall, with a hydrostatic power-split drive train, a high drive power can quickly be demanded from the combustion engine during the reversing process, which is then possible without restrictions thanks to the method, despite previously used engine braking.

[0019] In a further embodiment of the method, the deactivation time is determined relative to a pivot angle of a hydrostat of the drive train. The hydrostat can have a variable displacement pump and a fixed displacement pump. The pivot angle can correspond to a setting of the variable displacement pump. This allows the deactivation time to be adapted to an actual power requirement and, alternatively or additionally, to a gear ratio. This allows the engine brake to be used for a particularly long time, enabling a particularly strong deceleration before the reversing process. For example, the engine brake can not be completely switched off at the start of the injection process and yet the power required during the reversing process can still be fully provided at all times.

[0020] In a further embodiment of the method, it is provided that the deactivation time is determined relative to a time at which a currently closed clutch is released during the reversing process. The timing for deactivating the engine brake can thus be particularly simple and precise. The clutch can be a clutch of the reversing device. The time at which the clutch is released can be known very precisely as soon as the reversing process has been detected. For example, the reversing process can also only be detected when this release takes place. Nevertheless, the engine brake can still be deactivated in good time, since drive power may not be required, for example, until another clutch is engaged, i.e., when this additional clutch of the reversing device is closed. The release can correspond to the beginning of the opening of this clutch.

[0021] Alternatively or additionally, the deactivation time is determined relative to a pre-filling time of a clutch for the reversing process. Pre-filling can be the initial pressurization of a clutch before it is engaged. For example, pre-filling closes a fan gap on the clutch and fills a piston with oil. The respective clutch plates can then almost touch each other. The pre-filled clutch can be the additional clutch of the reversing device, which is engaged during the reversing process after the other clutch is released. The timing for deactivating the engine brake can thus also be particularly simple and precise.

[0022] In a further embodiment of the method, the deactivation time is determined depending on the transmission dynamics during the reversing process. The transmission dynamics can be a required change in a gear ratio, for example, by a hydrostatic transmission. The transmission dynamics can also correspond to a required acceleration during the reversing process in the opposite direction. For example, this can take into account the fact that with high transmission dynamics, high drive power must be provided by the combustion engine early on, which can be ensured by deactivating the engine brake accordingly.

[0023] A second aspect relates to a control device for controlling an engine brake of an internal combustion engine of a drive train of a motor vehicle. The control device can be configured to carry out the method according to the first aspect. Respective advantages and further features can be derived from the description of the first aspect, wherein embodiments of the first aspect also form embodiments of the second aspect, and vice versa. The control device can be configured, for example, by a transmission control unit, such as a TCU, or a vehicle control unit, such as a VCU.

[0024] The control device has a detection device designed to detect a reversing operation. The detection device can, for example, be connected to respective sensors of the motor vehicle in order to detect the reversing operation as a function of respective sensor signals and, alternatively or additionally, respective vehicle status information. The control device has a determination device designed to determine a deactivation time of the engine brake as a function of the detected reversing operation. For example, the determination device can be designed as a microchip and calculate the deactivation time as a function of the time elapsed during the reversing operation. The control device has a deactivation device designed to deactivate the engine brake at the deactivation time, provided the engine brake is activated.The deactivation device can, for example, transmit a corresponding control signal to the engine brake at the time of deactivation. Additionally, the deactivation device can be designed to deactivate the engine brake when the engine speed falls below a minimum. The minimum speed can be fixed or gear-dependent.

[0025] In addition, the control device can have an activation device designed to activate the engine brake. The activation device can activate the engine brake, for example, depending on an engine speed, an acceleration, and alternatively or additionally a desired driving speed. Activating the engine brake can require that the combustion engine be in a coasting state.

[0026] Short description of the characters

[0027] Fig. 1 schematically illustrates a method for controlling an engine brake of an internal combustion engine of a drive train of a motor vehicle.

[0028] Fig. 2 schematically illustrates a control device for controlling the engine brake of the internal combustion engine of the drive train of the motor vehicle using the method according to Fig. 1 .

[0029] Detailed description of embodiments

[0030] Fig. 1 schematically illustrates a method for controlling an engine brake of an internal combustion engine in a drive train of a motor vehicle 10, which is shown together with a control device 12 in Fig. 2. The control device 12 is shown next to the motor vehicle 10 in Fig. 2, but in the example shown is actually integrated into the transmission control of the motor vehicle 10. In the example shown, the drive train is designed as a hydrostatic power-split drive train. Shown is a motor vehicle 10 designed as a passenger car, which in another embodiment is designed as a work machine.

[0031] In a first step 40, an activation device 14 of the control device 12 activates the engine brake in the motor vehicle 10 as a function of an engine speed when the internal combustion engine is overrunning, in order to increase the deceleration of the motor vehicle 10 caused by the internal combustion engine. This makes it possible to avoid exceeding a maximum speed, which could damage a hydrostatic transmission in the drive train. The engine brake is formed by a flap in an exhaust tract of the internal combustion engine. This flap is adjusted when the engine brake is activated in order to reduce or even completely close a passage opening in the exhaust tract. This increases a back pressure against which the respective pistons of the internal combustion engine must expel gases. Depending on the desired deceleration by the internal combustion engine, the flap is closed more or less.When the engine brake is deactivated, there is a time delay because the flap must be moved back to a position in which the exhaust tract is maximally exposed through the flap.

[0032] In a step 42, a reversing operation of the motor vehicle 10 is detected. For this purpose, the control device 12 has a detection device 16. The detection device 16 is designed to detect the reversing operation based on an actuation of a direction selector lever of the motor vehicle 10 by a driver of the motor vehicle 10.

[0033] In a step 44, a deactivation time of the engine brake is determined depending on the detected reversing process. For this purpose, the control device 12 has a determination device 18. The deactivation time is determined by first determining a time of pre-filling a clutch of a reversing device of the drive train during the reversing process. The pre-filling is a first pressurization of the clutch, which is adjusted from an open state to a closed state when the direction of travel changes. This time forms a reference time for the deactivation of the engine brake. During pre-filling, a fan clearance on the clutch is eliminated and a piston, which serves to adjust the clutch, is filled with oil. The deactivation time is determined relative to the reference time.Based on this reference time, a start time of an injection process in the internal combustion engine during the reversing process is determined. The deactivation time is determined as a time that precedes this start time of the injection process by a delay time between the deactivation of the engine brake and the permissibility of starting an injection process in the internal combustion engine. In addition, in one embodiment, a time tolerance can be provided as an additional time interval between the deactivation time and the start of the injection process in order to ensure complete, effective deactivation of the engine brake by completely and timely opening of the damper flap in the exhaust tract, even in the event of a slight temporal deviation in the control.

[0034] In step 46, the engine brake is deactivated at the deactivation time thus determined by means of a deactivation device 20 of the control device 12. For this purpose, the deactivation device 20 transmits a control signal to an adjustment motor for resetting the throttle valve and thus completely opening the exhaust tract via the throttle valve. This takes advantage of the fact that the sequence of the reversing process is known. It is known or determinable how long it will take in the current driving situation until the combustion engine is loaded by the reversing process and the change of the engaged clutch.With this information, and because a delay time until the engine brake is actually deactivated by fully resetting the throttle valve is known, the deactivation point of the engine brake can be calculated and thus set such that the engine brake is no longer effective at the time of clutch reversal and the combustion engine can inject fuel without restriction through the engine brake. This prevents excessive engine compression (in the example shown, a reduction in engine speed) due to the reversing process, and a dynamic demand on the drivetrain (in the example shown, an acceleration demand) does not have to be reduced in order to protect the combustion engine from excessive compression. This allows acceleration from the reversing process into a now changed, opposite direction of travel with a very continuous output speed curve.

[0035] Reference numeral Motor vehicle Control device Activation device Detection device Determination device Deactivation device Step: Activating the engine brake Step: Detecting a reversing process Step: Determining a deactivation time Step: Deactivating the engine brake at the deactivation time

Claims

Patent claims 1 . A method for controlling an engine brake of an internal combustion engine of a drive train of a motor vehicle (10), comprising at least the following steps: - Activation (40) of the engine brake; - detection (42) of a reversing operation; - determining (44) a deactivation time of the engine brake as a function of the detected reversing process; - Deactivation (46) of the engine brake at the deactivation time.

2. Method according to claim 1, characterized in that the determination (44) of the deactivation time of the engine brake takes place as a function of a delay time between the deactivation of the engine brake and a permissibility of a start of an injection process in the internal combustion engine and as a function of a start time of the injection process in the internal combustion engine during the reversing process.

3. Method according to claim 1 or 2, characterized in that the determination (44) of the deactivation time of the engine brake takes place as a function of a deactivation delay time of the engine brake.

4. Method according to one of the preceding claims, characterized in that the deactivation time is determined such that the internal combustion engine is still in a coasting state when the deactivation (46) of the engine brake takes place.

5. Method according to one of the preceding claims, characterized in that the activation (40) of the engine brake takes place as a function of an engine speed.

6. Method according to one of the preceding claims, characterized in that a damper flap in an exhaust tract is adjusted by the engine brake.

7. Method according to one of the preceding claims, characterized in that a variable valve control is controlled by the engine brake.

8. Method according to one of the preceding claims, characterized in that the drive train is designed as a hydrostatic power-split drive train.

9. The method according to claim 8, characterized in that the deactivation time is determined relative to a pivoting angle of a hydrostatic drive of the drive train.

10. Method according to one of the preceding claims, characterized in that the deactivation time is determined relative to at least one of the following times: - A time of release of a currently closed clutch during the reversing process; and - A time of pre-filling of a clutch for the reversing process.

11. Method according to one of the preceding claims, characterized in that the deactivation time is determined as a function of transmission dynamics during the reversing process.

12. Control device (12) for controlling an engine brake of an internal combustion engine of a drive train of a motor vehicle (10), wherein the control device (12) has a detection device (16) which is designed to detect a reversing process, a determination device (18) which is designed to determine a deactivation time of the engine brake as a function of the detected reversing process, and a deactivation device (20) which is designed to deactivate the engine brake at the deactivation time, provided the engine brake is activated.

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