Method and system of controlling cylinder activation and deactivation in an internal combustion engine

Abstract

The present invention relates to a method (1) of controlling cylinder activation and deactivation in an internal combustion engine of a vehicle, said method comprising the steps of: - detecting an engine motoring condition (2); - deactivating all the engine cylinders (3) when said motoring condition is detected; - re-activating (4) at least one of the engine cylinders if: • a high load request to the internal combustion engine approaching is predicted (5), and / or • the speed of an internal combustion engine turbine drops below a predetermined turbine speed threshold (6). The present invention further relates to a system of controlling cylinder activation and deactivation in an internal combustion engine, comprising a control unit configured to perform the steps of said method.

Description

Technical field of the invention

[0001] The present invention relates to the field of thermal management of an internal combustion engine, in particular a diesel engine, during motoring of a vehicle, such as, for example, a heavy-duty truck. The present invention, for example, can be applied in internal combustion engines provided with a turbocharger, such as a turbo-diesel engine.Prior art

[0002] Cylinder Deactivation (in brief, CDA) in vehicles equipped with a multi-cylinder internal combustion engine, is a known technique where a combination of cylinders is disabled when the full power of the engine is not required. CDA can be used, for example, under motoring conditions, namely, when the engine is driven by the inertia of the vehicle. This generally improves engine efficiency and fuel economy. With specific reference to diesel engines, CDA results in airflow reductions, which, in turn, generally result in higher exhaust gas temperatures and lower exhaust flow rates. This reduction in air flow is achieved by controlling at least the intake valves of deactivated cylinders in order to remain closed during the deactivation. Preferably, the exhaust valves of the same group of cylinders are also controlled to remain closed during the deactivation. Considering the very stringent emission limits, this is beneficial for the after-treatment system, which must work in a predetermined temperature range and, accordingly, is prevented from being cooled.

[0003] In known CDA systems used during motoring in engines with a turbocharger, most but not all of the cylinders (e.g. 3 out of 6 cylinders) are deactivated, in the sense that fuel injection and the opening of at least the intake valves of the deactivated cylinders are inhibited. The deactivation of all the cylinders is avoided due to the impact on the subsequent load transient when more load is requested (for example in case of a necessary overtake or in case of an uphill road after a motoring condition). In fact, if all cylinders were deactivated, the turbine of the turbocharger would eventually spin down to rest and, at the next request of load, the load transient would be very slow and sluggish due to a large turbo-lag.

[0004] On the other hand, running in motoring conditions with all cylinders deactivated, in principle, would be beneficial due to the complete elimination of exhaust mass flow and, consequently, the maximum reduction in the cooling of the after-treatment system, with a consequent improvement in the fuel consumption. Additionally, the deactivation of all the cylinders would result in the elimination of increased engine noise and vibration which is typically associated with cylinder deactivation. Finally, the deactivation of all the cylinders would result in a minimal torque, resulting in reduction of fuel consumption due to improved vehicle rolling resistance.Summary of the invention

[0005] Therefore, it is an object of the present invention to provide a method and a system of controlling the activation and deactivation of cylinders in an internal combustion engine, in particular under motoring conditions, such that the benefits of the deactivation of all the cylinders are obtained with a substantial limitation of the above-mentioned drawbacks in the load transient after cylinder deactivation.

[0006] This and other objects are achieved by a method of controlling the activation and deactivation of cylinders in an internal combustion engine according to the claim 1 and a system of controlling the activation and deactivation of cylinders in an internal combustion engine according to the claim 11.

[0007] The Applicant has found that utilising an all-cylinder deactivation during motoring and then switching back some of the cylinders to active mode either based on a turbine speed threshold (in the case the engine is provided with a turbocharger) and / or based on the prediction of an upcoming load transient, optimizes the reduction of the after-treatment system temperatures, and maximises the benefits of motoring at minimal motoring torque with minimal engine vibrations. It should be clear that the two conditions are simultaneously monitored, but when at least one of the two conditions is verified the cylinder activation is executed.

[0008] The dependent claims define possible advantageous embodiments of the invention.Brief description of the figures

[0009] To better understand the invention and appreciate its advantages, some of its non-limiting exemplary embodiments will be described below, referring to the attached figures, in which: figure 1 shows a flowchart of exemplary steps of a method of controlling activation and deactivation of cylinders of an internal combustion engine according to an embodiment of the present invention. Detailed description of the invention

[0010] With reference to the figure 1, exemplary steps of a method 1 of controlling activation and deactivation of cylinders of an internal combustion engine, in particular a diesel engine, of a vehicle, such as, for example a heavy-duty truck, are depicted.

[0011] The method 1 comprises a step 2 of detecting a motoring condition. The term "motoring" refers to a condition of zero fuel and indicates a condition wherein the (running) engine remains coupled to the engine transmission (i.e., the clutch remains engaged), but no positive power is required from the engine. Under motoring conditions, the vehicle inertia motors the engine and the engine runs with zero fuel consumption. On the contrary, in the case of very small fuel injection amount, the engine will produce some small power, but still negative torque output (e.g., to overcome some internal engine friction). For example, a motoring condition can occur when a vehicle is cruising on a highway and the road gradient becomes slightly negative (downhill), such that the vehicle can retain its speed while just rolling without positive engine power. Another example of motoring condition is when the driver or the vehicle controller detects upcoming slow-moving traffic or an upcoming red traffic light and lets the vehicle roll ahead with gradual deceleration, while approaching the slow traffic or stop condition, without requesting engine power. During motoring, the engine is typically run in a manner to minimise the torque, resulting in a low load torque. It is important to observe that motoring conditions do not correspond, and the present invention does not apply to, conditions where the engine is requested to run with a large resisting torque, i.e. as an engine brake, which occurs for example when a downhill is very steep and the engine is requested to produce a very large negative torque to assist in vehicle braking.

[0012] The detection of the motoring condition can be carried out, for example, by the engine control unit on the basis of the signals coming from the sensor equipment of the vehicle, such as sensors of throttle and / or gas pedal opening, sensors for detecting service brake release, vehicle speed sensors, slope sensors, or the like. The engine control unit, when the engine is in motoring conditions, sets the fuel injection amount to zero, while the engine is running.

[0013] If a motoring condition is detected, the method further comprises a step 3 of deactivating all the engine cylinders. This step results in the above-mentioned advantages, i.e. maximum reduction in the cooling of the after-treatment system, elimination of engine noise and vibration, and reduction of fuel consumption (due to eventual further rolling of the vehicle with minimal engine torque). The deactivation of an engine cylinder implies not only the cut off of the fuel injection, but also the deactivation of, at least, the intake valves that remain closed during the deactivation period. Preferably, also the exhaust valves remain deactivated and closed during the same deactivation period.

[0014] After deactivation of all the cylinders, the method comprises a step 4 of re-activation of at least one cylinder (i.e. some or even all of the engine cylinders) if at least one of the following conditions is verified.

[0015] A first condition 5 which may result in the re-activation of at least one cylinder is the prediction, preferably on a short-term time horizon (e.g., less than 10 seconds, for example 5 seconds if the time horizon is fixed. Alternatively, the time horizon can be calibratable) of a request of high load to the engine approaching. This condition uses the prediction of an upcoming load transient to trigger the re-activation of some or all (depending on the actual load predicted) cylinders, such that, when the load transient actually occurs, at least some cylinder is already re-activated, thereby limiting the turbo-lag if a turbocharger is provided (since the turbine will be spinning at moderate speeds and can deliver boost when requested). For example, a high load request can be predicted: based on the actual position of the vehicle and the upcoming road conditions in a path to be followed. For example, a GPS navigation system can detect the vehicle actual position and the road attributes (for example a road uphill) on the path to be followed, which would result in a higher load request; on the other hand, for example on the basis of the traffic conditions, the high load prediction can be prevented, for example in the case of a queue on a path section where higher load would be requested in absence of traffic; based on images detected by a vision system, such as a camera, on the vehicle. For example, a camera could detect another vehicle running at a lower speed, which may result in the need of overtaking it. According to the present description, a "high" load means that the load is higher than a first predetermined load threshold or equivalently higher than a first predetermined percentage of a rated / maximum load. With high load also an increase of the current load can be meant. Indeed, when the some of the cylinders are re-activated when all the cylinder are deactivated, the current load is zero or negative due to the frictions, and high load is to be intended as positive load.

[0016] In general, the prediction may be based on the so-called "Advanced Driver-Assistance Systems" (ADAS), which are systems designed to help the driver in the driving process to increase car safety and more generally road safety. A drive assist system consists of hardware comprising radar and / or optical sensors and interfaces to several vehicle inputs, such as signals from driver's pedals / levers and on-board cameras. In some cases, the drive assist system has also an interface towards the cartographic navigation system of the vehicle. In the present case, the drive assist system is used for foreseeing a forthcoming high load request to the engine.

[0017] The drive assist system may foresee a forthcoming high load request on the basis of a radar sensor and / or a camera sensor. According to an embodiment, the drive assist system can recognize traffic lights, for example determining a forthcoming load request when the light is changing from red to green. According to an embodiment, the drive assist system is capable to detect the change of a speed limit along a road, for example determining a forthcoming load request when the speed limit increases. In an embodiment, ADAS relies on inputs from multiple data sources, including automotive imaging, LiDAR, radar, image processing, computer vision, and in-car networking. Additional inputs are possible from other sources separate from the primary vehicle platform, such as other vehicles, referred to as Vehicle-to-vehicle (V2V), or Vehicle-to-Infrastructure (such as mobile telephony or wi-fi data network) systems.

[0018] A second condition 6 which may result in the re-activation of at least one cylinder is the engine turbine speed dropping below a predetermined speed threshold. In this manner it is avoided that the turbine completely stops. The turbine is a part of a turbocharger of the engine, in particular a turbo-diesel engine. In case the engine is not provided with a turbine and a turbocharger, this second condition 6 does not apply.

[0019] In an embodiment, the predetermined turbine speed threshold is settable. For example, the driver can set different drive modes each corresponding to a different speed threshold. For example, the driver modes can comprise sport, normal and economy modes, wherein the predetermined speed threshold for sport mode is higher than the predetermined speed threshold for normal mode, which in turn is higher than the predetermined speed threshold for economy mode.

[0020] The two above-mentioned criteria can be combined for optimizing the cylinders re-activation following the full deactivation after a motoring condition has been detected. In the following some possible examples are given for the step of re-activating at least one of the engine cylinders starting from a full deactivation condition.Example 1

[0021] In case the high load request prediction is not available, the only criterion available for reactivating at least some of the cylinders is the internal combustion engine turbine speed dropping below a predetermined turbine speed threshold.Example 2

[0022] In case the high load request prediction is available and a vehicle stop is predicted, for example in case of oncoming traffic or red traffic light, the predetermined turbine speed threshold can be set to zero to maintain an all-cylinder deactivation. It is further observed that, as the vehicle comes to a stop, the clutch will need to be disengaged and the engine control unit can select whether to let the engine idle with the vehicle stopped (i.e., with some or all cylinders active) or let the engine come to rest (for engine stop). This depends on the calibration in the engine control unit strategy.Example 3

[0023] In case the high load request prediction is available and a slow engine acceleration is predicted, for example in case slow moving traffic ahead of in presence of gradual hill, the turbine predetermined speed threshold criterions can prevail. Accordingly, at least some cylinders can be reactivated when the turbine speed drops below the predetermined speed threshold.Example 4

[0024] In case the high load request prediction is available and an imminent, fast engine acceleration is predicted, for example in case of an upcoming hill or in case of traffic lights ahead ready to change from red to green, or in case of traffic ahead starting accelerating, the high load request prediction criterion can prevail. Accordingly, at least some cylinders can be reactivated even if the turbine speed does not drop below the predetermined speed threshold (or if the turbine speed is not even monitored). According to the present description, the acceleration indicates how fast the engine reached the desired torque. A fast acceleration indicates that the engine has to move to a desired torque according to an acceleration exceeding a first predetermined threshold. In the same way, slow acceleration means that the acceleration value is below a second threshold which is lower or equal to the first threshold.

[0025] The steps of the method according to the invention can be carried out by a proper system comprising a control unit capable of performing said method steps. For example, the control unit may be the vehicle control unit controlling the engine.

[0026] To the above-described embodiments of the method and system of controlling cylinder activation and deactivation in an internal combustion engine, the skilled person, in order to meet specific contingent needs, may make numerous additions, modifications, or substitutions of elements with functionally equivalent ones, without, however, departing from the scope of the attached claims.

Claims

1. A method (1) of controlling cylinder activation and deactivation in an internal combustion engine of a vehicle, said method comprising the steps of: - detecting an engine motoring condition (2); - deactivating all the engine cylinders (3) in response to a detection of the motoring condition; - re-activating (4) at least one of the engine cylin-derswhen at least one of the following conditions is verified: • Prediction of a high load request to the internal combustion engine approaching (5), wherein said high load exceeds a predetermined load threshold, • Detection that a current speed value of an internal combustion engine turbine drops below a predetermined turbine speed threshold (6).

2. Method (1) according to claim 1, wherein said motoring condition corresponds to a condition wherein the vehicle inertia motors the engine and the engine runs, connected to the vehicle transmission, with zero fuel consumption.

3. Method (1) according to claim 1 or 2, wherein the prediction of the high load request to the internal combustion engine approaching is based on at least one of: - signals coming from a radar and / or a vision system and / or other sensors of the vehicle; - information provided by a cartographic navigation system; - information from a Vehicle-to-Vehicle, and / or from a Vehicle-to-Infrastructure system.

4. Method (1) according to the preceding claim, wherein the information provided by the cartographic navigation system comprises at least one of: actual position of the vehicle, upcoming road conditions, real-time traffic information, topographical information, presence and status of traffic lights, speed limits in a path to be followed.

5. Method (1) according to claim 3 or 4, wherein the vision system of the vehicle is configured to detect traffic lights status.

6. Method (1) according to any of the preceding claims, wherein the high load request to the internal combustion engine approaching is predicted in a fixed or calibratable short-term time horizon.

7. Method (1) according to any of the preceding claims, wherein said predetermined turbine speed threshold is settable to at least two different values, each corresponding to a respective different drive mode.

8. Method (1) according to any of the preceding claims, wherein, following the step of deactivating all the engine cylinders (3), if a complete stop of the vehicle is predicted, the turbine predetermined speed threshold is set to zero to maintain all the cylinders deactivated.

9. Method (1) according to any of the preceding claims, wherein, following the step of deactivating all the engine cylinders (3), if an engine acceleration value is predicted which is below a first predetermined acceleration threshold, at least some cylinders are reactivated when the turbine speed drops below said turbine predetermined speed threshold value.

10. Method (1) according to any of the preceding claims, wherein, following the step of deactivating all the engine cylinders (3), if an engine acceleration is predicted which exceeded a second predetermined acceleration threshold, at least some cylinders are reactivated irrespective of the turbine speed dropping below the turbine predetermined speed threshold.

11. A system of controlling cylinder activation and deactivation in an internal combustion engine, comprising a control unit configured to perform the steps of the method according to any of the preceding claims.

12. System according to the preceding claim, wherein the control unit comprises an Advanced Driver-Assistance System (ADAS) configured to predict said high load request to the internal combustion engine approaching.

13. Diesel engine comprising a controlling system according to claim 11 or 12.

14. Vehicle comprising a diesel engine according to the preceding claim.

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