Method for controlling engine brake of internal combustion engine

Abstract

The invention relates to a method for controlling an engine brake of an internal combustion engine of a drive train of a motor vehicle (10). In one step, an engine brake is activated (40). In a further step, a commutation process is detected (42). Furthermore, in one step, a point in time of deactivation of the engine brake is determined (44) as a function of the identified commutation process. In a further step, the engine brake is deactivated (46) at a deactivation time. The invention also relates to a control device (12).

Description

Field of the Invention

[0001] The present invention relates to a method for controlling an engine brake of an internal combustion engine. The present invention also relates to a control device for controlling an engine brake of an internal combustion engine. Background Art

[0002] In a motor vehicle, an engine can be used to cause deceleration, for example as an addition to or an alternative to a service brake. Here, the engine is brought into a coasting state so that the engine speed can be increased. At this time, there is a boundary coasting speed that is not allowed to be exceeded. Otherwise, damage to the drive train may occur. When the boundary coasting speed is exceeded, the transmission automatically switches to the neutral state for protection. In order to still be able to reliably cause deceleration by the engine, an engine brake can be provided. The engine brake can be a function that causes additional deceleration not purely generated by friction through the engine or the drive train. Compared with the deceleration caused only by the un-driven engine, the engine brake can significantly enhance the deceleration, thereby avoiding exceeding the boundary coasting speed.

[0003] For this purpose, the engine brake is controlled according to the engine speed, for example by considering a predetermined speed threshold. For example, during deceleration in the coasting state, when the maximum speed is exceeded, the engine brake is activated. For example, the engine brake is deactivated again only when it is below the maximum speed or a different minimum speed or the engine changes back to the driving state again.

[0004] When the engine brake is used, a delay may occur before the drive power can be called again from the engine. Thereby, especially during a direction change process (the vehicle usually decelerates during the direction change process), restrictions may occur. Thereby, the driving power may be lower than the desired and normally available level. In extreme cases, even engine stalling may occur due to the direction change process and during deceleration when the engine brake is activated. Summary of the Invention

[0005] A first aspect of the present invention relates to a method for controlling an engine brake of an internal combustion engine of a drive train of a motor vehicle. The engine brake can be a function of the internal combustion engine itself or a separate device by means of which the internal combustion engine causes additional deceleration. For example, the valve control mechanism or the exhaust passage can be influenced by the engine brake, thereby enhancing the deceleration of the motor vehicle by the internal combustion engine. The internal combustion engine can be part of the drive train. The internal combustion engine can be a combustion-powered machine that converts chemical energy into mechanical work. For this purpose, fuel can be injected into the combustion chamber. The drive train of the motor vehicle can, for example, provide drive power as well as braking power for the motor vehicle. The drive train can have an internal combustion engine, a transmission, and an output in the form of, for example, tires. Optionally, the drive train can also be configured to provide take-off power. The motor vehicle can, for example, be configured as a passenger car, a work machine, or an agricultural machine. For example, the motor vehicle can be configured as a wheel loader.

[0006] The method has a step of activating the engine brake. By activating the engine brake, additional deceleration can be provided. When the engine brake is activated, the internal combustion engine can, for example, be in a coasting state. In the coasting state, the shaft of the internal combustion engine can be driven by the vehicle rolling on its wheels. The internal combustion engine can cause the motor vehicle to decelerate in its coasting state, and this deceleration can be enhanced by the activated engine brake. For example, in the coasting state, the internal combustion engine does not provide any drive power. In the driving state, the internal combustion engine can drive the motor vehicle and, for example, accelerate the motor vehicle. In the driving state, an injection process can occur. Here, fuel can be injected into the combustion chamber of the internal combustion engine. In the driving state, the shaft of the internal combustion engine can be driven by the combustion process. For example, in the driving state, the engine brake is deactivated. The engine brake can be activated depending on the rotational speed of the internal combustion engine and alternatively or additionally depending on the control of the motor vehicle (such as a predefined speed). The engine brake can also be controlled depending on the rotational speed of the internal combustion engine and alternatively or additionally depending on the control unit of the motor vehicle in order to, for example, change the magnitude of the deceleration caused by the engine brake. For example, the engine brake can have a first deceleration stage and a second deceleration stage, where the second stage decelerates more strongly than the first stage.

[0007] The method has steps for recognizing a reversing process. For example, the driver can recognize the reversing process based on the control unit of the motor vehicle. For example, the driver can operate a control element (such as a travel direction selector lever) to request a reversing process. By detecting such an operation, the reversing process can be recognized, for example, as impending. However, the reversing process can also be predicted and thus recognized, for example, based on vehicle state information (such as travel speed, position within the working area, and selected gear). The reversing process can be a change in travel direction, for example, from reverse travel to forward travel. The reversing process can involve operating the reversing device of the motor vehicle, such as the reversing device of its transmission. For the reversing process, for example, the clutch of the reversing device can be disengaged and then another clutch of the reversing device can be engaged. By means of the reversing process, the rotational direction of the driven shaft of the drive train can be reversed.

[0008] The method has steps for determining the deactivation time point of the engine brake depending on the recognized reversing process. For example, the deactivation time point can be determined relative to the determined time point of the reversing process, such as clutch operation, hydrostatic device pivoting, or start of the injection process. The deactivation time point can relate to the timing at which the engine brake is cut off. Thereby, it is possible to perform real-time control of the engine brake depending on the reversing process rather than depending on the engine speed. Thereby, it is possible to avoid an undesired influence on the reversing process, in particular to avoid a power limitation of the drive train during or immediately after reversing.

[0009] The method has steps for deactivating the engine brake at the deactivation time point. In the case of the control of a conventional engine brake, at the deactivation time point, the rotational speed of the internal combustion engine would still cause the engine brake to be activated. In this regard, it is now possible to deactivate the engine brake earlier so that full drive power can be provided for reversing in a timely manner. Account is taken of the fact that the engine brake itself may have a certain response time. For example, several hundred milliseconds may pass between the signal for deactivation and the engine brake actually being fully switched off. In addition, due to the combustion process and alternatively or additionally the corresponding pressure in the internal combustion engine, even after the engine brake has been fully switched off, the injection process for providing conventional drive power cannot be carried out immediately because, for example, the back pressure in the exhaust duct hinders the combustion process. This can also be taken into account. Thereby, it is possible to avoid a too late deactivation of the engine brake, which would otherwise cause, for example, over-compression of the engine. Accordingly, the method can avoid a decrease in the acceleration ability during the reversing process due to a previously activated engine brake.

[0010] It can also be provided in the method that when the engine speed drops below the engine speed threshold, the engine brake is deactivated. For example, the driving behavior of a motor vehicle can indicate the deactivation of the engine brake even before the deactivation time point. In this case, the engine brake can be deactivated based on conventional control because no drive power limitation occurs during the commutation process.

[0011] In another embodiment of the method, it is provided that the deactivation time point of the engine brake is determined depending on the delay time between the deactivation of the engine brake and the time point at which injection process is allowed to start in the internal combustion engine, and depending on the start time point of the injection process in the internal combustion engine during the commutation process. The delay time can be the duration between the deactivation signal for the engine brake and the actual deactivation. Alternatively, the delay time can be the duration between the deactivation signal for the engine brake and the time point at which injection process is allowed to start in the internal combustion engine. Alternatively, the delay time can be the duration between the actual deactivation of the engine brake and the time point at which injection process is allowed to start in the internal combustion engine. The start of the allowed injection process can be the time point at which it is allowed to introduce fuel into the combustion chamber of the internal combustion engine again completely or in a manner not restricted by the engine brake. Injection can be the supply of fuel to the combustion chamber, for example also accompanied by atomization and air supply. The start time point of the injection process in the internal combustion engine during the commutation process can correspond to the time point at which the internal combustion engine requires drive power again during the commutation process. Thus, timely deactivation of the engine brake can be achieved, so that acceleration can be carried out without limitation during the commutation process. For example, the deactivation time point can be determined in such a way that the deactivation time point is delayed by the delay time before the start time point of the injection process.

[0012] In another embodiment of the method, it is provided that the deactivation time point of the engine brake is determined depending on the deactivation delay time of the engine brake. For example, the duration of the adjustment time of the valve of the engine brake in the exhaust passage can be known. The deactivation time point can thus take this adjustment time into account. The deactivation delay time can correspond to the inertia of the engine brake with respect to the control signal.

[0013] In another embodiment of the method, it is provided that the deactivation time point is determined in such a way that when the engine brake is deactivated, the internal combustion engine is still in the coasting state. This can ensure that the engine brake does not inhibit the drive state or a transition into the drive state. For example, when a commutation process is recognized, the internal combustion engine may still be in its coasting state and transitions into the drive state during the commutation process. For example, before such a transition, the engine brake can be deactivated.

[0014] In another embodiment of the method, it is provided that the engine brake is activated depending on the engine speed. Thereby, the engine brake can be activated as needed, for example when the maximum speed is exceeded in the coasting state. In addition, the drive train can be protected in this way. For example, the hydrostatic device of the hydrostatic power split transmission in the drive train 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.

[0015] In another embodiment of the method, it is provided that the choke valve in the exhaust passage is adjusted by the engine brake. This can increase the back pressure in the respective combustion chamber of the internal combustion engine. This can, for example, increase the back pressure that the piston has to overcome when expelling the gas, thereby enhancing the deceleration caused by the internal combustion engine. Such an engine brake is simple, reliable and efficient. However, if such an engine brake is not deactivated in time by fully opening the choke valve, the engine brake will seriously impede the combustion process when switching to the drive state. This kind of obstruction can be reliably avoided by the control method of the engine brake.

[0016] In another embodiment of the method, it is provided that the variable valve control mechanism is controlled by the engine brake. By means of the variable valve control mechanism, deceleration can be caused particularly strongly and, alternatively or additionally, particularly variably adjustable by means of the engine brake. For example, by means of the variable valve control mechanism, the closing time point and the opening time point of the respective valve can be changed. However, if the valve control timing optimized for the combustion process is not readjusted by turning off the engine brake in time, the combustion process may also be seriously impeded.

[0017] In another embodiment of the method provided, the drive train is configured as a hydrostatic power split drive train. The hydrostatic power split drive train has a hydrostatic device. Thereby, the transmission ratio of the transmission can be adjusted steplessly. During the reversing process, the hydrostatic device usually pivots, but this can lead to particularly strong compression of the internal combustion engine. Overall, in a hydrostatic power split drive train, a large drive power can be quickly demanded from the internal combustion engine during the reversing process, and based on this method, this can be carried out without limitation even if the engine brake has been used beforehand.

[0018] In another embodiment of the method, it is provided that the deactivation time point is determined relative to the pivot angle of the hydrostatic unit of the drive train. The hydrostatic unit can have a variable pump and a fixed-displacement pump. The pivot angle can correspond to the adjustment of the variable pump. Thereby, the deactivation time point can be adapted to the actual power demand and alternatively or additionally to the transmission ratio. In this way, the engine brake can be used for a particularly long time, so that a particularly strong deceleration can be achieved before the reversing process. For example, the engine brake may not be completely shut off at the start of the injection process, but can still fully provide the power required during the reversing process at any time.

[0019] In another embodiment of the method, it is provided that the deactivation time point is determined relative to the disengagement time point of the clutch that is closed at that time during the reversing process. The timing for deactivating the engine brake can be particularly simple and precise. The clutch can be the clutch of the reversing device. Once the reversing process is recognized, the disengagement time point of the clutch can be very precisely known. For example, the reversing process can only be recognized through this disengagement. Nevertheless, the engine brake can still be deactivated in a timely manner because drive power is only required when another clutch engages, i.e., when this other clutch of the reversing device is closed, for example. The disengagement can correspond to the start of the disconnection of the clutch.

[0020] Alternatively or additionally, the deactivation time point is determined relative to the pre-filling time point of the clutch during the reversing process. The pre-filling can be the first pressurization of the clutch before its closing. For example, the air gap at the closed clutch is filled by pre-filling and the piston is filled with oil. The corresponding clutch discs are then already almost in contact. The pre-filled clutch can be the other clutch of the reversing device, which is closed during the reversing process after the other clutch has disengaged. The timing for deactivating the engine brake can also be particularly simple and precise.

[0021] In another embodiment of the method, it is provided that the deactivation time point is determined depending on the transmission dynamics during the reversing process. The transmission dynamics can be the required change in the transmission ratio, for example transmitted by a hydrostatic unit. The transmission dynamics can also correspond to the acceleration required during the reversing process in the opposite direction. For example, it can be taken into account that at high transmission dynamics, the internal combustion engine must provide high drive power earlier, which can be ensured by deactivating the engine brake accordingly in a timely manner.

[0022] The second aspect relates to a control device for an engine brake of an internal combustion engine for controlling a drive train of a motor vehicle. The control device can be configured to perform the method according to the first aspect. Various advantages and other features are referred to the description of the first aspect, wherein the design of the first aspect also constitutes the design of the second aspect and vice versa. The control device can be constituted, for example, by a transmission controller (such as a TCU) or a vehicle controller (such as a VCU).

[0023] The control device has an identification device which is configured to identify a gearshift process. The identification device can be connected, for example, to a corresponding sensor of a motor vehicle in order to identify the gearshift process depending on the corresponding sensor signals and alternatively or additionally depending on the corresponding vehicle state information. The control device has a determination device which is configured to determine a deactivation time point of the engine brake depending on the identified gearshift process. For example, the determination device can be configured as a microchip and calculate the deactivation time point depending on the time sequence of the gearshift process. The control device has a deactivation device which is configured to deactivate the engine brake at the deactivation time point if the engine brake is activated. For example, the deactivation device can transmit a corresponding control signal to the engine brake at the deactivation time point. Additionally, the deactivation device can be configured to deactivate the engine brake when the minimum speed is below. The minimum speed can be set fixedly or can also depend on the gear.

[0024] Furthermore, the control device can have an activation device which is configured to activate the engine brake. The activation device can activate the engine brake, for example, depending on the engine speed, the acceleration and alternatively or additionally the desired driving speed. As a prerequisite for activating the engine brake, it may be required that the internal combustion engine is in a coasting state. Description of the Drawings

[0025] Figure 1 A method for controlling an engine brake of an internal combustion engine of a drive train of a motor vehicle is schematically illustrated.

[0026] Figure 2 A control device for controlling an engine brake of an internal combustion engine of a drive train of a motor vehicle by means of the method according to Figure 1 is schematically illustrated. Detailed Description

[0027] Figure 1 A method for controlling an engine brake of an internal combustion engine of a drive train of a motor vehicle 10 is schematically illustrated, the motor vehicle together with the control device 12 being shown in Figure 2 is shown. Figure 2 The control device 12 is shown next to the motor vehicle 10 in, but in the example shown, the control device 12 is actually integrated in the transmission control mechanism of the motor vehicle 10. In the example shown, the drive train is configured as a hydrostatic power split drive train. The motor vehicle 10 configured as a passenger car is shown, in another embodiment, the motor vehicle is configured as a work machine.

[0028] In a first step 40, an activation device 14 of a control device 12 activates an engine brake in a motor vehicle 10 depending on the engine speed in a coasting state of an internal combustion engine, in order to increase the deceleration of the motor vehicle 10 caused by the internal combustion engine. Thereby, it is possible to avoid exceeding a maximum speed that could damage a hydrostatic device of the drive train. The engine brake is formed by a choke valve in an exhaust passage of the internal combustion engine. When the engine brake is activated, the choke valve is adjusted so as to reduce or even completely close a through-opening in the exhaust passage. Thereby, the back pressure that needs to be overcome when the respective pistons of the internal combustion engine push out the gas is increased. Depending on the desired deceleration of the internal combustion engine, the choke valve can be closed more or less. When the engine brake is deactivated, there is a time delay because the choke valve has to be adjusted back again to a position where the choke valve releases the exhaust passage to the greatest extent.

[0029] In step 42, a reversing process of the motor vehicle 10 is recognized. For this purpose, the control device 12 has a recognition device 16. The recognition device 16 is configured to recognize the reversing process based on the driver of the motor vehicle 10 manipulating a travel direction selection lever of the motor vehicle 10.

[0030] In step 44, a deactivation time point of the engine brake is determined depending on the recognized reversing process. For this purpose, the control device 12 has a determination device 18. Determining the deactivation time point, that is, first determining a pre-filling time point of a clutch of a reversing device of the drive train during the reversing process. Pre-filling is the first pressurization of the clutch, and when the travel direction changes, the clutch is adjusted from a disengaged state to an engaged state. This time point forms a reference time point for deactivating the engine brake. During pre-filling, an air gap at the clutch is eliminated, and oil is supplied to a piston for adjusting the clutch. The deactivation time point is determined relative to the reference time point. Based on this reference time point, a start time point of an injection process in the internal combustion engine during the reversing process is determined. The deactivation time point is determined as a time point before which there is a delay time between deactivating the engine brake and allowing the start of the injection process in the internal combustion engine. Additionally, in one embodiment, a time tolerance can be set as an additional time interval between the deactivation time point and the start of the injection process, so as to ensure that the engine brake is actually completely deactivated by fully opening the choke valve in the exhaust passage in a timely manner even when there are slight temporal deviations in the control.

[0031] In step 46, the engine brake is deactivated at the thus determined deactivation time by means of the deactivation device 20 of the control device 12. For this purpose, the deactivation device 20 transmits a control signal to the engine brake to retract the choke valve, thereby completely opening the exhaust passage through the choke valve. Here, the known fact of undergoing a commutation process is utilized. Here, it is known or can be determined how long the internal combustion engine will still be loaded due to the commutation process and the alternately engaged clutch in the current driving situation. Using this information and since the delay time for actually shutting off the engine brake by fully retracting the choke valve is known, the deactivation time point of the engine brake can be calculated, and thus it is ensured that the engine brake no longer has an effect at the time of clutch commutation, and the internal combustion engine can inject fuel without being restricted by the engine brake. Thereby, engine over-compression (i.e., a drop in engine speed in the example) due to the commutation process is avoided, and it is not necessary to reduce the dynamic request for the drive train (i.e., the acceleration request in the example) to protect the internal combustion engine from over-compression. Thereby, it is possible to accelerate from the commutation process to the changed opposite driving direction with a very continuous output speed curve.

[0032] List of reference signs

[0033] 10 Motor vehicle

[0034] 12 Control device

[0035] 14 Activation device

[0036] 16 Recognition device

[0037] 18 Determination device

[0038] 20 Deactivation device

[0039] 40 Step: Activate the engine brake

[0040] 42 Step: Recognize the commutation process

[0041] 44 Step: Determine the deactivation time point

[0042] 46 Step: Deactivate the engine brake at the deactivation time point

Claims

1. A method for controlling an engine brake of an internal combustion engine of a drive train of a motor vehicle (10), the method having at least the following steps: - Activating (40) the engine brake; - Identifying (42) a gearshift process; - Determining (44) a deactivation time point of the engine brake depending on the identified gearshift process; - Deactivating (46) the engine brake at the deactivation time point.

2. The method according to claim 1, characterized in that, The deactivation time point of the engine brake is determined (44) depending on a delay time between deactivating the engine brake and an allowed start time of an injection process in the internal combustion engine and depending on a start time point of the injection process in the internal combustion engine during the gearshift process.

3. The method according to claim 1 or 2, characterized in that The deactivation time point of the engine brake is determined (44) depending on a deactivation delay time of the engine brake.

4. The method according to any one of the preceding claims, wherein The deactivation time point is determined in such a way that when deactivating (46) the engine brake, the internal combustion engine is still in a coasting state.

5. The method according to any one of the preceding claims, characterized in that, The engine brake is activated (40) depending on the engine speed.

6. The method according to any one of the preceding claims, characterized in that, A choke valve in an exhaust passage is adjusted by the engine brake.

7. The method according to any one of the above claims, characterized in that, A variable valve control mechanism is controlled by the engine brake.

8. The method according to any one of the above claims, characterized in that, The drive train is configured as a hydrostatic power split drive train.

9. The method according to claim 8, wherein The deactivation time point is determined relative to a pivot angle of a hydrostatic device of the drive train.

10. The method according to any one of the above claims, characterized in that, The deactivation time point is determined relative to at least one of the following time points: - A disengagement time point of a clutch that is closed at that time during the gearshift process; and - A pre-filling time point of the clutch for the gearshift process.

11. The method according to any one of the preceding claims, characterized in that, The deactivation time point is determined depending on the transmission dynamics during the gearshift process.

12. Control device (12) for an engine brake of an internal combustion engine of a drive train of a motor vehicle (10), wherein, The control device (12) has: an identification device (16) configured to identify a gearshift process; a determination device (18) configured to determine a deactivation time point of the engine brake depending on the identified gearshift process; and a deactivation device (20) configured to, if the engine brake is activated, deactivate the engine brake at the deactivation time point.

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