Control device and method for controlling a vehicle powertrain during engine braking

Abstract

Method (200) for controlling a vehicle powertrain (2) during engine braking, performed by a control device (100), wherein the vehicle powertrain (2) comprises: an internal combustion engine (3), a transmission (4) configured to selectively transmit drive torque from the internal combustion engine to drive wheels (7), and Service brakes (10) configured to brake the drive wheels (7); the procedure includes the following step: Activation (S107) of the service brakes (10) for the purpose of reducing the speed of the internal combustion engine (3) when the speed of the internal combustion engine (3) approaches a threshold value (v th ) to shift up the transmission (4), and wherein the step of activating (S107) the service brakes (10) is carried out based on a determination that the acceleration of a vehicle (1) comprising the vehicle powertrain (2) is below a preselected value.

Description

TECHNICAL AREA

[0001] The present disclosure relates generally to a method for controlling a vehicle powertrain during engine braking. The present disclosure further relates generally to a control device configured for controlling a vehicle powertrain during engine braking. The present disclosure also relates generally to a computer program and a computer-readable medium. The present disclosure further relates generally to a vehicle. BACKGROUND

[0002] A vehicle, such as a heavy vehicle, can be braked in various ways. In addition to service brakes, the vehicle may include a number of auxiliary braking systems that can be used in different situations. For example, engine braking is an efficient method for controlling the speed at which a vehicle travels downhill. During engine braking, the vehicle's internal combustion engine is controlled in such a way as to provide a braking effect, thereby slowing the vehicle down. The efficiency of engine braking therefore depends on the operation of the internal combustion engine, and the magnitude of any potential braking torque generally increases with the engine speed.

[0003] An internal combustion engine can be configured to operate up to a certain maximum speed. To avoid energy losses or damage to the engine, the transmission generally shifts up when the engine speed reaches a threshold. After the upshift, the engine speed will be lower than before. This, in turn, reduces the available engine braking torque compared to before the upshift.

[0004] German patent application DE 10 2004 003 901 A1 discloses a method for controlling engine braking in a motor vehicle, comprising a vehicle engine, an automatically shifted transmission, and service brakes. The method includes a step of activating the service brakes during engine braking when the engine speed exceeds a predetermined limit speed to maintain a constant vehicle speed. Simultaneously with activating the service brakes, the method performs a further step of upshifting the transmission to the next higher gear.

[0005] A method for controlling vehicle speed during downhill travel is known from US Patent 6,249,733 B1. The method includes determining whether an engine speed exceeds a predetermined engine speed limit and, based on this, activating the service brakes. Prior to this determination, an automatic transmission shift is performed during engine braking. Further powertrain control methods are known from US Patents GB 2,469,853 A and US Patents 2001 / 0016,795 A1. OVERVIEW

[0006] The object of the present invention is to enable more efficient use of engine braking for braking a vehicle.

[0007] The problem is solved by the subject matter of the attached patent claims 1 and 7.

[0008] According to the present disclosure, a method for controlling a vehicle powertrain during engine braking is provided, wherein the method is carried out by means of a control device. The vehicle powertrain comprises an internal combustion engine. The vehicle powertrain further comprises a transmission configured for selectively transmitting drive torque from the internal combustion engine to drive wheels. The vehicle powertrain further comprises service brakes configured for braking the drive wheels. The method comprises a step of activating the service brakes for the purpose of reducing the speed of the internal combustion engine when the speed of the internal combustion engine approaches a threshold for upshifting the transmission.

[0009] This prevents the transmission from upshifting, which would result in a loss of engine braking torque, in situations where engine braking is insufficient to maintain a constant vehicle speed. This, in turn, allows the desired braking torque to be maintained using engine braking, as the internal combustion engine speed can remain relatively high without the risk of upshifting. According to this method, the service brakes only need to be applied to the extent necessary to prevent the transmission from upshifting.

[0010] The activation of the service brakes is performed based on a determination that the acceleration of the vehicle, including the powertrain, is below a preselected value. This ensures that the procedure is only used when the engine speed is slowly approaching the upshift threshold, allowing the service brakes to be used efficiently for a relatively small reduction in engine speed without causing significant wear on the service brakes.

[0011] The step of activating the service brakes to reduce the internal combustion engine speed can include activating the service brakes to reduce the engine speed by a preselected value. This facilitates process control and ensures that the service brakes are not subjected to greater stress than necessary.

[0012] The preselected value can be between 100 rpm and 450 rpm. This reduces the engine speed sufficiently to avoid upshifting, but at the same time does not reduce it to a value where engine braking would be insufficient to provide the desired braking torque.

[0013] The procedure can further include a step of determining when the internal combustion engine speed is approaching a transmission upshift threshold, based on a detection that the engine speed is increasing and exceeding a predefined limit that depends on the transmission upshift threshold. This allows for a simple determination of when the service brakes should be applied to reduce the engine speed. This, in turn, improves the accuracy and reliability of the procedure.

[0014] The present disclosure further relates to a computer program comprising instructions which, when executed by a control device, cause the control device to execute the method according to any of the preceding claims.

[0015] The present disclosure further relates to a computer-readable medium comprising instructions which, when executed by a control device, cause the control device to execute the procedure as previously described.

[0016] Furthermore, according to the present disclosure, a control device is provided that is configured to control a vehicle powertrain during engine braking. The vehicle powertrain comprises an internal combustion engine, a transmission configured to selectively transmit drive torque from the internal combustion engine to drive wheels, and service brakes configured to brake the drive wheels. The control device is configured to activate the service brakes for the purpose of reducing the speed of the internal combustion engine when the engine speed approaches a threshold for upshifting the transmission.

[0017] The control device has the same advantages as the corresponding method described above for controlling a vehicle powertrain during engine braking, which is disclosed herein.

[0018] The control device can be configured to activate the service brakes for the purpose of reducing the speed of the internal combustion engine based on a determination that the acceleration of a vehicle, including the vehicle powertrain, is below a preselected value.

[0019] Furthermore, the control device for activating the service brakes can be configured to reduce the engine speed by a preselected value. The preselected value can, for example, be within a range of 100 rpm to 450 rpm.

[0020] The control device can be configured to determine that the internal combustion engine speed is approaching a threshold for upshifting the transmission, based on a detection that the internal combustion engine speed is increasing and is above a predefined limit, which depends on the threshold for upshifting the transmission.

[0021] The present disclosure further relates to a vehicle comprising a powertrain. The powertrain comprises an internal combustion engine, a transmission configured for selectively transmitting drive torque from the internal combustion engine to drive wheels, and service brakes configured for braking the drive wheels. The vehicle further comprises the control device configured for controlling a vehicle powertrain during engine braking, as previously described. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 schematically represents a side view of a vehicle, Fig. Figure 2 schematically represents an exemplary embodiment of a vehicle powertrain, Fig. Figure 3 shows a flowchart that schematically represents an exemplary embodiment of the method for controlling a vehicle powertrain during engine braking according to the present disclosure, Fig. Figure 4 shows a simplified drawing of a possible result of the method for controlling a vehicle powertrain during engine braking according to the present disclosure on the speed of the internal combustion engine, Fig. Figure 5 schematically represents a device that may form, comprise, or be part of a control device according to the present disclosure, wherein the control device is configured to control a vehicle powertrain during engine braking. DETAILED DESCRIPTION

[0022] The invention is described in more detail below with reference to exemplary embodiments and the accompanying drawings. However, the invention is not limited to the exemplary embodiments discussed and / or shown in the drawings, but can be varied within the scope of the accompanying claims. Furthermore, the drawings are not to be considered to scale, as some features may be exaggerated to better illustrate the invention or its features.

[0023] In the present disclosure, the term "engine braking" is understood to mean any form of braking action of a vehicle that uses the vehicle's internal combustion engine to provide a braking effect and thereby slow the vehicle down. Therefore, in the present disclosure, engine braking is considered to include, for example, compression release braking (CRB), variable plate braking (WB), exhaust braking, engine dragging, etc. Engine braking via engine dragging occurs when the accelerator pedal is released and the vehicle's wheels remain connected to the internal combustion engine via the transmission.

[0024] The method described herein for controlling a vehicle powertrain is intended for use in situations where engine braking is used to control the vehicle's speed, for example, when the vehicle is traveling downhill. If engine braking is insufficient to maintain a desired speed while descending, the vehicle's speed will increase. This, in turn, will lead to an increase in engine speed.

[0025] The braking torque achieved through engine braking depends on the engine speed, with optimal braking torque being reached near the engine's maximum permissible speed. However, once a certain engine speed is reached, the transmission initiates an upshift. This upshift results in an increase in engine speed during the shift and a lower engine speed when the gear change is complete. This, in turn, reduces the braking torque available through engine braking and may also increase the vehicle's speed.

[0026] According to the present disclosure, a method for controlling a vehicle powertrain during engine braking is provided. The method is carried out by means of a control device. The vehicle powertrain comprises an internal combustion engine and a transmission configured to selectively transmit drive torque from the internal combustion engine to the drive wheels. The vehicle powertrain further comprises service brakes configured to brake the drive wheels. The method includes a step of activating the service brakes for the purpose of reducing the speed of the internal combustion engine when the engine speed approaches a threshold for upshifting the transmission.

[0027] The engine speed can be understood as approaching a transmission upshift threshold when the speed increases and remains within a predefined range of that threshold. In other words, the engine speed exceeds a predefined limit, which is dependent on the transmission upshift threshold. This predefined limit may depend on the vehicle's current acceleration. More precisely, the predefined limit would be lower in the case of higher acceleration compared to a higher limit in the case of lower acceleration. Furthermore, the predefined limit may depend on the currently selected transmission gear or may be independent of the selected gear.The predefined limit can also be adjusted, if desired, depending on, for example, current road conditions. For instance, the predefined limit can be set 200 rpm below the threshold for upshifting the transmission.

[0028] The present method thus prevents the transmission from being upshifted during engine braking by briefly activating the service brakes. This ensures that there is no loss of braking torque during engine braking, as would occur with a transmission upshift. The service brakes only need to be activated briefly and only need to reduce the engine speed sufficiently to prevent an upshift. Therefore, the present method does not result in significant additional wear on the service brakes.

[0029] Given that the service brakes are automatically activated by the present procedure, the driver of the vehicle does not need to take any further separate measures to maintain an appropriate vehicle speed, but may nevertheless do so.

[0030] It should be noted that the rotational speed of the internal combustion engine corresponds to the rotational speed of the transmission's input shaft (in the case of multiple transmissions, the transmission located closest to the engine). Therefore, the engine's rotational speed can be determined either by measuring the rotational speed of the engine's output shaft or by measuring the rotational speed of the transmission's input shaft. In fact, knowing the vehicle's powertrain configuration and the currently selected gear, the engine's rotational speed can be determined from a measurement of any shaft in the powertrain, and the corresponding engine speed can be calculated from this measurement if desired.

[0031] The procedure described herein is primarily intended for use when the internal combustion engine speed is slowly approaching the transmission upshift threshold. Therefore, for example, the step of activating the service brakes can be performed based on a determination that the vehicle's acceleration is below a preselected value. If the vehicle's acceleration is above the preselected value, it may be preferable, for instance, to allow the transmission to upshift to avoid damaging the internal combustion engine, rather than temporarily activating the service brakes to only slightly reduce the engine speed.

[0032] The step of activating the service brakes to reduce the internal combustion engine speed can be performed to reduce the engine speed by a preselected value. The preselected amount of the engine speed reduction can be chosen from a range between 100 rpm and 450 rpm (including the end values), for example, from 100 rpm to 250 rpm.

[0033] If the engine speed has been reduced by activating the service brakes to such an extent that it does not reach the threshold for upshifting the transmission, the service brakes are deactivated. Should the engine speed again approach the upshift threshold, the process of activating the service brakes to reduce the engine speed can be repeated. It should be noted that during a long downhill stretch, the service brakes can be repeatedly activated (and deactivated) to temporarily reduce the engine speed and prevent upshifting. Therefore, this procedure allows for efficient use of the braking torque provided by engine braking.

[0034] The performance of the method described herein for controlling a vehicle powertrain during engine braking can be regulated by programmed instructions. These programmed instructions typically take the form of a computer program which, when executed in or by a control device, causes the control device to produce desired control actions. Such instructions can typically be stored on a computer-readable medium.

[0035] The present disclosure further relates to a control device configured for controlling a vehicle powertrain during engine braking according to the method described above. The control device can be configured to perform each of the steps of the method for controlling a vehicle powertrain during engine braking described herein.

[0036] More precisely, the control device is at least designed to activate the service brakes for the purpose of reducing the speed of the internal combustion engine when the speed of the internal combustion engine approaches a threshold for upshifting the transmission.

[0037] The present disclosure also relates to a vehicle comprising a vehicle powertrain. The vehicle powertrain comprises an internal combustion engine, a transmission, and drive wheels. The transmission is configured to selectively transmit the drive torque from the internal combustion engine to the drive wheels via different shafts of the vehicle powertrain. The drive wheels are also each equipped with a corresponding service brake configured to brake the associated drive wheel. The vehicle further comprises the control device described herein, which is configured to control the vehicle powertrain during engine braking.

[0038] Fig. Figure 1 schematically shows a side view of an example of a vehicle 1. The vehicle 1 comprises a powertrain 2, which includes an internal combustion engine 3 and a transmission 4. A clutch (not shown) may be arranged between the internal combustion engine 3 and the transmission 4. The transmission 4 is connected to the drive wheels 7 of the vehicle 1 via an output shaft 6 of the transmission 4. The vehicle includes service brakes 10, which are arranged on the respective drive wheels 7 and preferably also on the non-drive wheels 8. The vehicle 1 may further have one or more auxiliary braking systems. For example, the vehicle 1 may have a retarder 5. The retarder may be connected to the output shaft 6 of the transmission.

[0039] The in Fig. The vehicle shown may include additional auxiliary braking systems that utilize the internal combustion engine to provide braking for the vehicle. These systems are commonly referred to as engine braking systems in this disclosure and are capable of providing engine braking. Examples of engine braking systems include a compression release brake (CRB) system, a variable disc brake (WB) system, and an exhaust brake system. Engine drag can also provide engine braking.

[0040] Fig. Figure 2 schematically shows an exemplary embodiment of a vehicle powertrain 2. The vehicle powertrain 2 comprises an internal combustion engine 3, which is connected to a transmission 4 via a clutch 12. The transmission 4 can comprise one or more transmission units. The transmission 4 can, for example, comprise or form a conventional automated manual transmission (AMT), but is not limited to this. The vehicle powertrain 2 can optionally include a retarder. The retarder 5 can be configured to apply a braking torque to the output shaft 6 of the transmission when activated. The output shaft 6 of the transmission 4 can be connected to the drive wheels 7 via a conventional differential 11. Each of the drive wheels 7 has an associated service brake 10. The operation of one or more component parts of the vehicle powertrain 2 can be controlled by a control device 100.In particular, the control device 100 can be configured to control the service brakes 10 with respect to the rotational speed of the internal combustion engine 3. The control device 100 can also be configured to control the clutch 12 and / or the transmission 4, e.g., for the purpose of controlling a transmission shift. The control device 100 can be configured for braking purposes, specifically for controlling the retarder 5, if present.

[0041] Fig. Figure 3 shows a flowchart that schematically illustrates an exemplary embodiment of method 200 for controlling a vehicle powertrain during engine braking according to the present disclosure. In the flowchart, optional steps are represented by dashed lines. The method may include each of the optional steps independently of other optional steps. The method may include a first step of determining S101 that the speed of the internal combustion engine is approaching a threshold for upshifting the transmission. For example, step S101 may include determining that the speed of the internal combustion engine is increasing and is within a predetermined range of the transmission upshift threshold. The method may further include a step of determining S103 whether there is a possibility of activating an auxiliary brake, for example, a retarder.If it is possible to activate an additional auxiliary brake during engine braking, the procedure can proceed to step S104 of activating such an auxiliary brake in order to reduce the vehicle's speed and thus the internal combustion engine's speed. The procedure then returns to the start after step S104.

[0042] The procedure can proceed after step S101 and the optional step S103 (subject to a determination that no additional auxiliary brake is available to brake the vehicle) to a step S105 of determining whether the acceleration of the vehicle is below a preselected value or not.

[0043] If the vehicle's acceleration is not below the preselected value, the procedure can be terminated, for example. If the acceleration is below the preselected value, the procedure continues with step S107.

[0044] Procedure 200 includes a step (S107) of activating the service brakes based on the determination that the internal combustion engine speed is approaching the transmission upshift threshold, thereby reducing the engine speed. This prevents the transmission from upshifting. The engine speed can be reduced by a preselected value, for example, by activating the service brakes. Afterwards, the service brakes are deactivated. Following step S107, the procedure returns to the start.

[0045] Fig. Figure 4 shows a simplified drawing of a possible result of the method for controlling a vehicle powertrain during engine braking according to the present disclosure, based on the rotational speed v. e of the internal combustion engine over time t. In the figure, v represents threpresents the threshold for upshifting the transmission and represents v lThis represents a predefined limit value used to determine whether the engine speed is approaching the transmission upshift threshold. Time t1 represents the point at which it is determined that the engine speed is approaching the transmission upshift threshold. The service brakes are therefore activated and begin to exert a braking effect on the engine speed at t2. At t3, it is assumed that the engine speed has been reduced sufficiently to prevent the transmission from upshifting, and the service brakes are deactivated. If engine braking is insufficient to maintain the vehicle speed and thus the engine speed, the engine speed begins to increase again after t3.At t4, it is again determined that the speed of the combustion engine corresponds to the threshold value v. th As the transmission approaches upshifting, the service brakes are activated to begin reducing the engine speed at t5. At t6, the engine speed has been reduced sufficiently, and the service brakes are therefore deactivated.

[0046] Fig. Figure 5 schematically represents an exemplary embodiment of a device 500. The control device 100 described above can, for example, comprise the device 500, form the device 500, or be comprised by the device 500.

[0047] The device 500 comprises a non-volatile memory 520, a data processing unit 510, and a read / write memory 550. The non-volatile memory 520 includes a first memory element 530 in which a computer program, e.g., an operating system, is stored for controlling the function of the device 500. The device 500 further includes a bus controller, a serial communication interface, I / O means, an A / D converter, a time and date input and transmission unit, an event counter, and an interrupt controller (not shown). The non-volatile memory 520 also includes a second memory element 540.

[0048] A computer program P is provided that includes instructions for controlling a vehicle powertrain during engine braking. The vehicle powertrain comprises an internal combustion engine, a transmission configured to selectively transmit drive torque from the internal combustion engine to the drive wheels, and service brakes configured to brake the drive wheels. The computer program includes instructions to activate the service brakes for the purpose of reducing the internal combustion engine speed when the engine speed approaches a threshold for upshifting the transmission.

[0049] The program P can be stored in an executable form or in a compressed form in a memory 560 and / or in a read / write memory 550.

[0050] The data processing unit 510 can perform one or more functions, i.e., the data processing unit 510 can execute a specific part of the program P stored in memory 560 or a specific part of the program P stored in read / write memory 550.

[0051] The data processing unit 510 can communicate with a data interface 599 via a data bus 515. The non-volatile memory 520 is intended for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is intended for communication with the data processing unit 510 via a data bus 511. The read / write memory 550 is configured to communicate with the data processing unit 510 via a data bus 514. Communication between the individual components can be implemented via a communication link. A communication link can be a physical connection, such as an optoelectronic communication line, or a non-physical connection, such as a wireless connection, e.g., a radio link or a microwave link.

[0052] When data is received at data interface 599, it can be temporarily stored in the second memory element 540. Once the received input data has been temporarily stored, the data processing unit 510 is ready to execute the code as described previously.

[0053] Parts of the procedures described herein can be performed by the device 500 using the data processing unit 510, which executes the program stored in the memory 560 or in the read / write memory 550. When the device 500 executes the program, the procedures described herein are performed.

Claims

[1] Method (200) for controlling a vehicle powertrain (2) during engine braking, performed by a control device (100), wherein the vehicle powertrain (2) comprises: an internal combustion engine (3), a transmission (4) configured to selectively transmit drive torque from the internal combustion engine to drive wheels (7), and Service brakes (10) configured to brake the drive wheels (7); the procedure includes the following step: Activation (S107) of the service brakes (10) for the purpose of reducing the speed of the internal combustion engine (3) when the speed of the internal combustion engine (3) approaches a threshold value (v th ) to shift up the transmission (4), and wherein the step of activating (S107) the service brakes (10) is carried out based on a determination that the acceleration of a vehicle (1) comprising the vehicle powertrain (2) is below a preselected value. [2] Method (200) according to claim 1, wherein the step of activating (S107) the service brakes (10) for the purpose of reducing the speed of the internal combustion engine (3) comprises activating the service brakes to reduce the speed of the internal combustion engine by a preselected value. [3] Method (200) according to claim 2, wherein the preselected value is between 100 rpm and 450 rpm. [4] Method (200) according to one of the preceding claims, further comprising a step of determining (S101) that the rotational speed of the internal combustion engine (3) is below a threshold value (v th) approaches to upshift the transmission (4), based on a detection that the speed of the internal combustion engine (3) is increasing and exceeds a predefined limit (v l ) lies, which is below the threshold (v th ) depends on the upshifting of the transmission. [5] Computer program (P) comprising instructions which, when executed by a control device (100), cause the control device (100) to perform the method according to any of the preceding claims. [6] Computer-readable medium comprising instructions which, when executed by a control device (100), cause the control device (100) to carry out the method according to any one of claims 1 to 4. [7] Control device (100) configured to control a vehicle powertrain (2) during engine braking, the vehicle powertrain (2) comprises: an internal combustion engine (3), a transmission (4) configured to selectively transmit drive torque from the internal combustion engine (3) to drive wheels (7), and Service brakes (10) configured to brake the drive wheels (7); wherein the control device (100) is configured to activate the service brakes (10) for the purpose of reducing the speed of the internal combustion engine (3) when the speed of the internal combustion engine reaches a threshold value (v th ) to shift up the transmission (4), and wherein the control device for performing the activation of the service brakes (10) for the purpose of reducing the speed of the internal combustion engine (3) is configured based on a determination that the acceleration of a vehicle (1) comprising the vehicle powertrain is below a preselected value. [8] Control device (100) according to claim 7, wherein the control device is configured to activate the service brakes (10) for the purpose of reducing the speed of the internal combustion engine (3) by a preselected value. [9] Control device (100) according to claim 8, wherein the preselected value is between 100 rpm and 450 rpm. [10] Control device (100) according to one of claims 7 to 9, which is further configured to determine that the rotational speed of the internal combustion engine (3) falls below a threshold value (v th ) approaches upshifting the transmission, based on a detection that the internal combustion engine speed is increasing and exceeding a predefined limit (v l ) lies, which is below the threshold (v th ) depends on the upshifting of the transmission. [11] Vehicle (1) comprising a powertrain (2), the powertrain (2) comprises: an internal combustion engine (3), a transmission (4) configured to selectively transmit drive torque from the internal combustion engine (3) to drive wheels (7), and Service brakes (10) configured to brake the drive wheels (7); wherein the vehicle further comprises the control device (100) according to any one of claims 7 to 10.

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