ENGINE BRAKE METHOD FOR OPERATING A VEHICLE WITH A TURBOCHARGED INTERNAL COMBUSTION ENGINE AND ASSOCIATED VEHICLE

An engine brake method is for operating a vehicle with a turbocharged internal combustion engine. The engine comprises a boost pressure regulation device, which is configured to adjust the boost pressure in the intake manifold, and an exhaust gas restriction device, which is located downstream from a turbine of the turbocharger and which is configured to regulate an air exhaust pressure in an exhaust manifold. The engine brake method includes a dual phase during which, simultaneously, the boost pressure regulation device regulates the air exhaust pressure in the exhaust manifold in closed loop, and the exhaust gas restriction device controls the boost pressure in closed loop.

CROSS REFERENCE TO RELATED APPLICATION

This application claims foreign priority to European Application No. 23191108.2 filed on Aug. 11, 2023, the disclosure and content of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The disclosure relates generally to engine brake for turbocharged engine vehicles.

BACKGROUND

Engine brake is a critical feature for commercial vehicles as it makes it possible to maintain a constant speed downhill for long periods without using the foundation brakes, which is favorable to both safety and drivability. Engine brake is typically achieved by using both a compression release system, for example a so-called Jacobs bleeder brake, and an exhaust gas restriction device, for example a proportional flap, which is installed after the turbocharger's turbine and which controls a target air pressure in the exhaust manifold. Unfortunately, this control strategy achieves limited results in terms of braking power, since closing the flap also results in decreasing the airflow going through the engine. This has several secondary negative effects, such as overheating nozzle tips of the fuel injectors—by lack of air to cool them down—, increasing oil rejection at the outlet of the turbocharger's compressor—by lack of air pressure in the compressor housing to keep its seal tight—, etc.

Alternative approaches have tried to solve these issues. For example, on engines comprising a turbocharger with moveable elements to adjust an output of the turbocharger—also called VGT—, an alternative to using the exhaust flap is to control the exhaust back-pressure with the VGT instead: this is known as “VGT braking”. Increasing the exhaust back-pressure with the VGT also increases the air flow at the same time, which benefits the efficiency of the compression release system. However, since it also results in a reduced difference between intake pressure and exhaust pressure, braking power is actually not much improved with VGT braking. Another drawback of this strategy lies in its slow and sluggish response, up to several seconds, caused by the time it takes to pressurize the whole intake system.

SUMMARY

According to a first aspect of the disclosure, the invention concerns an engine brake method for operating a vehicle with a turbocharged internal combustion engine. The engine comprises:several cylinders, which are connected to an intake manifold, collecting fresh air, and to an exhaust manifold, collecting exhaust air from the cylinders,a turbocharger; with a compressor driven by a turbine, the compressor being configured to increase a boost pressure of the fresh air in the intake manifold, while the turbine is configured to be driven by the exhaust air flowing from the exhaust manifold;a boost pressure regulation device, which is configured to adjust the boost pressure in the intake manifold, andan exhaust gas restriction device, which is located downstream from the turbine and which is configured to adjust an exhaust air pressure in the exhaust manifold.

The engine brake method comprises a dual phase during which, simultaneously:the boost pressure regulation device regulates the air exhaust pressure in the exhaust manifold in closed loop, in order to regulate the exhaust pressure to a pre-determined first threshold, andthe exhaust gas restriction device controls the boost pressure in closed loop, in order to regulate the boost pressure to a pre-determined second threshold.

A technical benefit may include increasing both boost pressure and air exhaust pressure, thus resulting in a higher engine brake effect. Simultaneously, the air flow through the cylinders remains at a higher level, contributing to the cooling of the injector tips. Additionally, the pressure differential between boost pressure and air exhaust pressure remains positive, preventing oil leaks through the compressor seal. On steep downhill roads, it is therefore possible to increase the load of the vehicle, and/or to drive the vehicle on steeper roads, while regulating the speed of the vehicle solely based on engine brake, i.e. without using the foundation brake. The overall safety of the vehicle is therefore improved.

Optionally in some examples, including in at least one preferred example, the engine comprises an intake throttle valve, which is arranged between the turbocharger and the intake manifold and which is configured to control the boost pressure, whereas during the dual phase, the intake throttle valve forms the boost pressure regulation device and regulates the air exhaust pressure in the exhaust manifold in closed loop. A technical benefit may include implementing the dual phase by using commonly used equipment.

Optionally in some examples, including in at least one preferred example, the turbocharger is a variable geometry turbocharger, which comprises moveable elements to adjust an output of the turbocharger, whereas during the dual phase, the variable geometry turbocharger forms the boost pressure regulation device and regulates the air exhaust pressure in the exhaust manifold in closed loop. A technical benefit may include implementing the dual phase by using commonly used equipment.

Optionally in some examples, including in at least one preferred example, the engine brake method further comprising an initial phase, prior to the dual phase. The initial phase comprises a first phase, during which the exhaust air pressure is controlled by the restriction device while the turbocharger is in open loop, so as to let exhaust air pressure to increase up to the first threshold, and a second phase, which follows the first phase and during which, once the exhaust air pressure reaches the first threshold, the restriction device is locked in position, while the turbocharger controls the air exhaust pressure in the exhaust manifold in closed loop, so as to let boost pressure increase up to the second threshold. If, during the second phase, the boost-pressure reaches the second threshold before a pre-determined time period, then the initial phase ends and the dual phase starts. A technical benefit may include ensuring a smooth, stable and rapid transition from the motoring mode of the engine to the engine brake mode.

Optionally in some examples, including in at least one preferred example, the engine further comprises bleeder valves, each bleeder valve being associated with a respective cylinder and being configured to, when activated, let compressed air to leak from the cylinders through an opening of the bleeder valve, whereas the engine brake method comprises adjusting an opening of the bleeder valve, in order to maximize a braking effect of the engine during the dual phase. A technical benefit may include improving further the engine brake performance of the vehicle.

Optionally in some examples, including in at least one preferred example, the dual phase is engaged when the engine has a speed, given in revolutions per minute, above a pre-determined third threshold. A technical benefit may include ensuring a higher engine brake effect compared to prior art methods.

According to a second aspect of the disclosure, the invention concerns a vehicle, comprising a turbocharged internal combustion engine. The vehicle is configured to implement the engine brake method according to any one of preceding claims. The engine comprises:several cylinders, which are connected to an intake manifold, which is configured to collect fresh air, and to an exhaust manifold, which is configured to collect exhaust air from the cylinders,a turbocharger; with a compressor driven by a turbine, the compressor being configured to increase a boost pressure in the intake manifold, while the turbine is configured to be driven by the exhaust air flowing from the exhaust manifold;a boost pressure regulation device, which is configured to adjust the boost pressure in the intake manifold, andan exhaust gas restriction device, which is located downstream from the turbine and which is configured to increase an exhaust air pressure in the exhaust manifold.

The second aspect of the disclosure may seek to provide a vehicle, for example a truck, with an improved engine brake capacity. A technical benefit may include allowing a higher load on downhill roads and/or allowing speed regulation on steeper downhill roads.

DETAILED DESCRIPTION

Embodiments of the present disclosure are directed to solving the problems mentioned above, by providing an engine brake method achieving a high braking power output while keeping operating parameters-such as injector cooling-within their specified ranges. In particular aspects of the disclosure relates to an engine brake method for operating a vehicle with a turbocharged internal combustion engine and to a vehicle configured to implement such an engine brake method. The disclosure can be applied to heavy-duty vehicles, such as trucks, buses, and construction equipment, among other vehicle types. Although the disclosure may be described with respect to a particular vehicle, the disclosure is not restricted to any particular vehicle.

A vehicle10is represented onFIG.1a). The vehicle10is a road vehicle, in particular a truck, which comprises wheels11. The vehicle10comprises an engine12, which is schematically shown onFIG.1b). The engine12is an internal combustion engine, which is configured to use fuel in order to drive the wheels11in rotation, in order to move the vehicle10. When the engine12uses fuel to rotate the wheel10, the engine12is in a motoring mode. On the contrary, when the engine12is used to waste energy, the engine12is in an “engine brake” mode, that is to say the engine12applies a braking torque to the wheels11. OnFIG.1, the vehicle10is represented on a downhill slope S, where the vehicle10tends to naturally accelerate because of gravity. The engine12is used in the engine brake mode in order to regulate a speed of the vehicle10.

The engine12comprises a main block14with several cylinders16. In the illustrated example, the engine12is a four-stroke engine with six cylinders16. For each cylinder16, the four strokes include, successively, an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke.

When the engine12is running, during the intake stroke or each cylinder16, fresh air flowing through an intake manifold20is admitted into each cylinder16, through at least one intake valve. The at least one intake valve is not represented. During the exhaust stroke, air contained in the cylinder16is evacuated through at least one exhaust valve and collected in an exhaust manifold22. The at least one exhaust valve is not represented. In other words, the cylinders16are connected to the intake manifold20, which collects fresh air, and to the exhaust manifold22, which collects exhaust air from the cylinders16. When the engine12is in the motoring mode, fuel is injected in the cylinders and the air+fuel mix is ignited during the compression and expansion strokes. During the following exhaust stroke, the air evacuated from the cylinders16is hot and contains various substances and residues resulting from fuel combustion. Air containing these combustion residues is also called exhaust gas.

When the engine12is in the engine brake mode, no fuel is injected into the cylinders16and no combustion occurs. The air evacuated from the cylinders16during the exhaust stroke is mostly fresh air that has been admitted during the intake stroke, then compressed and expanded inside the cylinders16during the compression and expansion strokes.

Air flowing from the cylinders16into the exhaust manifold22is also called “exhaust air”. Fresh air flowing from the intake manifold20into the cylinders16is also called “charge air”. The intake manifold20is located upstream from the cylinders16relative to the normal flow of air in the engine12, while the exhaust manifold22is located downstream from the cylinders16relative to the normal flow of air in the engine12. In the following description, the notions of “upstream” and “downstream” are considered relatively to the flow of air during normal use of the engine12. “Normal use” means that the engine12is either in the motoring mode, or in the engine brake mode.

The engine12also comprises a turbocharger30. The turbocharger30comprises a compressor32and a turbine34, the compressor32being linked to the turbine34by an axle36. The turbine34is configured to be driven in rotation by the exhaust air flowing from the exhaust manifold22, while the compressor32is configured to increase a pressure of the charge air flowing in the intake manifold20then into the cylinders16.

When the engine12is in the engine brake mode, during the compression/expansion strokes in each cylinder16, air pressure reaches a peak, called “peak cylinder pressure” PCP. In the schematic example ofFIG.1b), one of the cylinder16comprises a first pressure sensor, here represented figuratively by a manometer, the first pressure sensor being configured to measure air pressure within the cylinder16. In particular, the first pressure sensor, also referenced PCP, is configured to measure the peak cylinder pressure. Of course, in reality there is no manometer inside any one of the cylinders16.

A second pressure sensor P2, represented figuratively by a manometer, is arranged on the intake manifold20, the second pressure sensor P2being configured to measure a boost pressure, that is to say an air pressure inside the intake manifold20. By extension, boost pressure is also referenced P2. A third pressure sensor P3, represented figuratively by a manometer, is arranged on the exhaust manifold22, the third pressure sensor P3being configured to measure an exhaust pressure, that is to say an air pressure inside the exhaust manifold22. By extension, exhaust pressure is also referenced P3.

The engine also comprises an exhaust gas restriction device40, which is located downstream from the turbine34and which is configured to regulate the exhaust pressure P3in the exhaust manifold22. In the illustrated example, the exhaust gas restriction device40is a flap, also called “exhaust flap”. The shape and type of the exhaust gas restriction device40are not limitative.

The engine10also comprises a fourth pressure sensor P4A, represented figuratively by a manometer, which is arranged downstream from the turbine34and which is configured to measure a turbine outlet pressure, that is to say a pressure of exhaust air at an outlet of the turbine34, between the turbine34and the exhaust gas restriction device40. By extension, the turbine outlet pressure is also referenced P4A.

The engine10also comprises a boost pressure regulation device42, which is configured to adjust the boost pressure P2in the intake manifold20. In the illustrated example, the boost pressure regulation device42is an intake throttle valve, which is represented by a flap and which is arranged between the turbocharger30and the intake manifold20, and which is configured to control the boost pressure P2. The shape and type of the boost pressure regulation device42are not limitative.

Schematically, braking torque from the engine12comes mainly from the combination of two phenomena. A first phenomenon is called pumping torque, which is caused by the exhaust pressure P3being higher than the boost pressure P2. The higher the difference between P3and P2, the higher the braking torque. A second phenomenon is called compression release torque, or compression brake. Each cylinder16is advantageously equipped with a bleeder valve17, which is configured to let the air compressed inside the cylinder16to leak from the cylinder16through an opening of the bleeder valve17when the engine12is in the engine brake mode, while each bleeder valve17remains closed when the engine12is in the motoring mode.

Without a bleeder valve, when air is compressed in the cylinders16during the compression stroke, the mechanical energy invested in compressing air is almost entirely recovered by the expansion within the cylinder16during the expansion stroke. Thanks to the bleeder valve17, the compressed air is released outside the cylinder16through the opening of the bleeder valve17, and the energy that went into making the compression is wasted by releasing the compressed air instead of letting it expand inside the cylinder16. The higher the peak cylinder pressure PCP, prior to releasing this compressed air, the higher the wasted energy, and the higher the braking torque generated by compression brake.

According to some examples, the bleeder valve17is a specific device, different from the intake and exhaust valves. Alternatively, the bleeder valve17comprises an actuator that is configured to slightly open one or more existing exhaust valve(s) when the engine12is in the engine brake mode. Such type of bleeder valve is also known as “Jacobs valve”, and compression brake using such a Jacobs valve is also called “Jacobs brake”.

In short, when the engine12is in the engine brake mode, maximizing braking torque involves maximizing both the peak cylinder pressure PCP and the pressure difference between exhaust pressure and intake pressure, P3-P2. To achieve this, the engine12is configured to implement an engine brake method, the engine brake method comprising a phase, called “dual phase”101, during which, simultaneously:the boost pressure regulation device42regulates the air exhaust pressure P3in the exhaust manifold22in closed loop, in order to regulate the exhaust pressure to a pre-determined first threshold, andthe exhaust gas restriction device40controls the boost pressure P2in closed loop, in order to regulate the boost pressure P2to a pre-determined second threshold.

Advantageously, the engine brake method comprises adjusting the opening of the bleeder valve17to a specific predetermined target value, in order to maximize a braking torque of the engine12during the dual phase. The target value of the opening of the bleeder valve depends on the type, size, power, etc., of the engine12.

Using the boost pressure regulation device42to control the exhaust pressure P3in closed loop makes the turbocharger30draw a lot of fresh air into the engine12, which increases peak cylinder pressure PCP and cools down the injector tips. Using the exhaust gas restriction device40to control P2in closed loop decreases an expansion ratio of the turbine34, thus limiting boost pressure P2to values significantly lower than P3and contributing to a higher pumping torque. The pressure differential P3-P2remains positive, which keeps the compressor32's seal tight.

Results and benefits of the dual phase are illustrated onFIGS.3to6.

A graph300is shown onFIG.3. The graph300shows the evolution, for an exemplary vehicle10, of the exhaust pressure P3—expressed in kilo Pascal, or kPa—vs. a speed of the engine12—expressed in revolutions per minute, or RPM—.

The graph300comprises a first curve301, which illustrates the exhaust pressure P3when the engine12is controlled according to a prior art method. Within the scope of the present description, engine brake according to the prior art method means that the exhaust air pressure P3is controlled by the restriction device40while the turbocharger30is in open loop. The graph300comprises a second curve302, which illustrated the exhaust pressure P3when the engine12is controlled with the dual phase101method according to the invention.

As seen on the graph300, the second curve302is significantly above the first curve301when the engine speed is higher than a pre-determined threshold T300, which is equal to 1800 RPM in the illustrated example. In other words, thanks to the invention, the exhaust pressure P3is higher when the engine speed is above the threshold T300.

A graph400is shown onFIG.4. The graph400shows the evolution, for an exemplary vehicle10, of the boost pressure P2—expressed in kPa—vs. the speed of the engine12—expressed in RPM—.

The graph400comprises a first curve401, which illustrates the boost pressure P2when the engine12is controlled according to the prior art method. The graph400comprises a second curve402, which illustrated the boost pressure P2when the engine12is controlled with the dual phase101method according to the invention.

As seen on the graph400, for all illustrated engine speed, the second curve402is significantly above the first curve401. In other words, thanks to the invention, the boost pressure P2is higher when the engine12is controlled with the method according to the invention compared to when the engine12is controlled with the prior art method. In particular, in the illustrated example, when the engine speed is above a threshold T400, which is here equal to 1400 RPM, the boost pressure P2when the engine12is controlled with the method according to the invention is at least ten times higher than the boost pressure P2when the engine12is controlled with the prior art method.

A graph500is shown onFIG.5. The graph500shows the evolution, for an exemplary vehicle10, of the engine brake power-expressed in kilo Watt, or kW-vs. the speed of the engine12—expressed in RPM—.

The graph500comprises a first curve501, which illustrates the engine brake power when the engine12is controlled according to the prior art method. The graph500comprises a second curve502, which illustrated the engine brake power when the engine12is controlled with the dual phase101method according to the invention.

As seen on the graph500, the second curve502is significantly above the first curve501when the engine speed is higher than a pre-determined threshold T500, which is equal to 1400 RPM in the illustrated example. In other words, thanks to the invention, the boost pressure P2is higher when the engine12is controlled with the method according to the invention compared to when the engine12is controlled with the prior art method.

In other words, in order to benefit from a higher braking power, the dual phase101is engaged when the engine speed is above a pre-determined threshold. In the illustrated example, this threshold is equal to 1400 RPM.

Thanks to control method according to the invention, it is possible to control simultaneously both boost pressure P2and exhaust pressure P3, which results in an engine brake power significantly higher than what was achievable with the prior art method.

A graph600is shown onFIG.6. The graph600shows the evolution, for an exemplary vehicle10, of a temperature of the tip of an injector's nozzle—nozzle tip temperature, or NTT, expressed in degrees Celsius, or ° C.—vs. the speed of the engine12—expressed in RPM—.

The graph600comprises a first curve601, which illustrates the nozzle tip temperature NTT when the engine12is controlled with the prior art method. The graph600comprises a second curve602, which illustrated the nozzle tip temperature NTT when the engine12is controlled with the dual phase101method according to the invention.

As seen on the graph600, for all illustrated engine speed, the second curve602is below the first curve601. In other words, thanks to the invention, the nozzle tip temperature NTT is lower when the engine12is controlled with the method according to the invention compared to when the engine12is controlled with prior art methods. This is caused by the higher air flow flowing through the cylinders16, since—among others—the boost pressure P2is higher in the dual mode compared to prior art methods, as illustrated on graph400.

When the vehicle10is running, moving between flat or uphill roads to downhill roads, the engine12may transition between motoring mode and engine brake mode. The dual phase101method correspond to an established state of the engine12in the engine brake method. Prior to the dual phase101, the engine brake method according to the invention also comprises an initial phase100, which is implemented to ensure the transition between the motoring mode and the dual phase101of the engine brake mode.

The initial phase100is divided in two sub-phase, which include and first phase100A and a second phase100B, which follows the first phase100A.

As the engine12is initially in the motoring mode, and the engine12is controlled to switch to the engine brake mode. The engine speed, which is linked to the rotation speed of the wheels11, is supposed to remain sensibly constant during the initial phase. During the first phase100A, the exhaust air pressure P3is controlled by the restriction device40while the turbocharger30is in open loop, so as to let exhaust air pressure P3to increase up to a pre-determined first threshold L1.

Once the exhaust air pressure P3reaches the first threshold L1, the second phase100B starts. During the second phase100B, the restriction device40is locked in position—in other words the restriction device40does not regulate exhaust air pressure P3—, while the turbocharger30controls the air exhaust pressure P3in the exhaust manifold22in closed loop, so as to let boost pressure P2increase up to a pre-determined second threshold L2.

During the second phase100B, if the boost-pressure P2reaches the second threshold before a pre-determined time period, then the initial phase ends and the dual phase101starts. If the boost-pressure P2does not reach the second threshold, then the dual phase101does not start, and the engine reverts to the first phase100A.

A graph700is shown onFIG.7. The graph700shows the evolution of several parameters of the engine12during the initial phase100and dual phase101. The horizontal axis is a time axis—expressed in seconds—. In the example ofFIG.7, engine speed is considered constant.

The graph700comprises a first curve701, which shows the evolution of a torque—expressed in Newton×meter, or N·m—of the engine12. On the left hand side vertical axis, the torque is negative, since the engine12is in the engine brake mode.

The graph700comprises a second curve702, which shows the evolution of the exhaust pressure P3, expressed in kPa relative to the right hand side vertical axis. The graph700comprises a second curve702, which shows the evolution of the boost pressure P2, expressed in kPa relative to the right hand side vertical axis. The graph700comprises a third curve703, which shows the evolution of the exhaust pressure P3, expressed in kPa relative to the right hand side vertical axis. The graph700comprises a fourth curve704, which shows the evolution of a set-point of the boost pressure P2, expressed in kPa relative to the right hand side vertical axis. The graph700comprises a fifth curve705, which shows the evolution of a set-point of the exhaust pressure P3, expressed in kPa relative to the right hand side vertical axis.

In the illustrated example, at an initial instant ti, the set-point of the exhaust pressure P3is gradually set to the first threshold L1. The initial instant ti marks the beginning of the first phase100A. In the illustrated example, starting at the initial instant ti, the set-point of the boost pressure P2is also gradually set to the second threshold L2. The torque701shows an initial plateau, around −330 N·m, prior to the initial instant ti. The exhaust pressure P3is controlled by the restriction device40.

At a first instant t1, which is posterior to the initial instant ti, the exhaust pressure P3starts to rise, in order to narrow the gap with the first threshold L1. Consequently, the torque701sharply decreases. In other words, the effect of the engine brake increase. In the illustrated example, the difference between the first instant t1and initial instant ti is about 0.1 s.

From the first instant t1, the boost pressure P2also starts to rise, narrowing the gap with the second threshold L2. At a second instant t2, which is posterior to the first instant t1, the boost pressure P2is sensibly equal to the second threshold L2, while the exhaust pressure P3continues to rise, and the torque701continues to decrease.

At a third instant t3, which is posterior to the second instant t2, the exhaust pressure P3reaches a maximal value, which is sensibly equal to the first threshold L1. Between the second instant t2and third instant t3, the torque701continues to decrease.

The third instant t3marks the end of the first phase100A and the beginning of the second phase100B. In the illustrated example, the boost pressure P2is already sensibly equal to the second threshold L2, so the second phase100B ends immediately and the dual phase101starts from the third instant t3on. In the illustrated example, a duration of the initial phase100is sensibly equal to the difference between the third instant t3and the first instant t1, which is here around 0.7 s.

More generally, if, during the second phase100B, the boost-pressure P2does not reach the second threshold L2before a pre-determined time period, then the initial phase restarts, back to the first phase100A. This situation might appear in abnormal situation, for example if one of the components of the engine12is dysfunctioning. In a normal situation, if during the second phase100B, the boost-pressure P2reaches the second threshold L2before the pre-determined time period, then the initial phase100ends and the dual phase101starts.

During the dual phase101, the boost pressure regulation device42regulates the air exhaust pressure P3in the exhaust manifold22in closed loop, in order to regulate the exhaust pressure P3to the pre-determined first threshold L1, while the exhaust gas restriction device40controls the boost pressure P2in closed loop, in order to regulate the boost pressure P2to the pre-determined second threshold L2. As shown onFIG.7, during the dual phase101, the exhaust pressure P3, the boost pressure P2and the torque701are relatively stable.

In the illustrated example, the boost pressure regulation device42is the intake throttle valve. During the dual phase101, the intake throttle valve forms the boost pressure regulation device42and regulates the air exhaust pressure in the exhaust manifold22in closed loop.

In a non-illustrated alternative embodiment, the turbocharger30is a variable geometry turbocharger VGT, which comprises moveable elements to adjust an output of the turbocharger30, thus forming the boost pressure regulation device42when the engine12is in the motoring mode. During the dual phase101of the engine brake method, the variable geometry turbocharger VGT forms the boost pressure regulation device42and regulates the air exhaust pressure P3in the exhaust manifold22in closed loop.