Method for reducing vibrations in an internal combustion engine

Abstract

The present disclosure relates to a method for vibration reduction in a compression-ignited four-stroke internal combustion engine. The internal combustion engine comprises exhaust valves and intake valves controlled by an exhaust camshaft and an intake camshaft (10, 12). When operating the internal combustion engine below a threshold rotational speed, the method comprises the steps of: - changing the timing of the exhaust camshaft (10) to advance the closing of the exhaust valves (20), and - changing the timing of the intake camshaft (12) to retard the opening of the intake valves (22).

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for vibration reduction in a compression-ignited four-stroke internal combustion engine, a control arrangement for controlling variable valve timing of a compression-ignited four-stroke internal combustion engine, a compression-ignited four-stroke internal combustion engine, and a vehicle. The present invention also relates to a computer program and a computer-readable storage medium. BACKGROUND

[0002] When operated at low rotational speeds, a compression-ignited four-stroke internal combustion engine, ICE, can vibrate excessively. Over time, such vibrations can damage the ICE. Such vibrations can cause discomfort to the driver and / or passengers of a vehicle propelled by the ICE. In stationary installations, such vibrations can cause structural resonance.

[0003] More specifically, in a diesel compression-ignited ICE, the compression ratio is in the range 14:1 to 26:1, which is higher compared to the compression ratio in a spark-ignited ICE. The high compression ratio, in combination with the resulting high-pressure combustion of the fuel in the cylinders of the ICE, and the ICE being operated at low rotational speeds, causes the ICE to vibrate excessively. That is, at low rotational speeds of the ICE, the combustion in the individual cylinders is separated in time to such a degree that it can be regarded as a single event, which in turn causes the ICE to vibrate excessively. The fewer the number of cylinders of the ICE, the greater the problem with vibrations. On the other hand, at high rotational speeds of the ICE, the combustion in the individual cylinders occurs more frequently, so that the vibrations from the individual cylinders cancel each other out to a greater extent, and the engine vibrations are reduced.

[0004] In the context of starting a spark-ignited internal combustion engine, US 2010 / 139591, US 2013 / 080026, and US 2014 / 060470 discuss the use of variable valve timing of one valve. SUMMARY

[0005] It would be advantageous to achieve a compression-ignited internal combustion engine that overcomes or at least alleviates at least some of the above disadvantages. In particular, it would be desirable to reduce vibrations in a compression-ignited internal combustion engine. To better address one or more of the concerns discussed above, one or more of a method, a control arrangement, a compression-ignited four-stroke internal combustion engine, and a vehicle having the features defined herein are provided.

[0006] According to an aspect of the present invention, there is provided a method for vibration reduction in a compression-ignition four-stroke internal combustion engine, ICE, comprising: an exhaust valve and an intake valve; an exhaust camshaft arranged to control opening and closing of the exhaust valve; and an intake camshaft arranged to control opening and closing of the intake valve. When operating the ICE below a threshold rotational speed, the method comprises the steps of:

[0007] - changing the timing of the exhaust camshaft to advance closing of the exhaust valve, and

[0008] - changing the timing of the intake camshaft to retard opening of the intake valve.

[0009] According to another aspect of the present invention, there is provided a control arrangement for controlling variable valve timing of a compression-ignition four-stroke internal combustion engine. The internal combustion engine comprises: an exhaust valve and an intake valve; an exhaust camshaft arranged to control opening and closing of the exhaust valve; and an intake camshaft arranged to control opening and closing of the intake valve. The control arrangement is configured to, when operating the ICE below a threshold rotational speed:

[0010] - changing the timing of the exhaust camshaft to advance closing of the exhaust valve, and

[0011] - changing the timing of the intake camshaft to retard opening of the intake valve.

[0012] As the timing of the exhaust camshaft is changed to advance closing of the exhaust valve and the timing of the intake camshaft is changed to retard opening of the intake valve when operating the internal combustion engine, ICE, below a threshold rotational speed, engine vibrations are reduced when the ICE is operated at a rotational speed below the threshold rotational speed.

[0013] More specifically, due to the above-mentioned changes in timing of the exhaust camshaft and the intake camshaft, the compression ratio in the cylinder of the ICE is reduced, providing lower combustion pressure, compared to when no changes in timing of the camshafts are performed. In addition, the pressure difference between top dead center of the piston, TDCp, and top dead center of gas exchange, TDCge, of the ICE is reduced. The low pressure combustion and the reduced pressure difference reduce the energy of the vibrations. The pressure increase at TDCge is achieved, which reduces the vibration energy at the fundamental frequency and increases the vibration energy at twice the fundamental frequency. The vibrations at twice the fundamental frequency are more easily isolated from the vibrations at the fundamental frequency.

[0014] Hence, the vibrations will be less harmful and / or cause less discomfort to the driver and / or passengers and / or reduce structural resonance, compared to when no changes in timing of the camshafts are performed.

[0015] According to another aspect of the application, there is provided a compression-ignition four-stroke internal combustion engine comprising a control arrangement according to any of the aspects and / or embodiments discussed herein.

[0016] The compression-ignition four-stroke internal combustion engine can be a diesel compression-ignition ICE. In this document, the compression-ignition four-stroke ICE can alternatively be referred to simply as an internal combustion engine, ICE, or engine.

[0017] The ICE comprises a crankshaft, an exhaust camshaft, an intake camshaft, and the control arrangement. The rotational speed of the crankshaft can in this document alternatively be referred to as the rotational speed of the ICE. Furthermore, the ICE can comprise at least one cylinder arrangement. The cylinder arrangement can comprise an exhaust valve and an intake valve controlled by the exhaust camshaft and the intake camshaft, respectively; a combustion chamber; a cylinder bore; and a piston configured to reciprocate in the cylinder bore and connected to the crankshaft. The cylinder arrangement can further comprise the exhaust valve and / or the intake valve.

[0018] As in any four-stroke ICE, during two rotations of the crankshaft, the piston performs an intake stroke, a compression stroke, an expansion stroke (also referred to as a power or combustion stroke), and an exhaust stroke in the cylinder bore of the cylinder arrangement. The ICE can comprise more than one cylinder arrangement, such as for example three, four, five, six, or eight cylinder arrangements.

[0019] In a diesel compression-ignition ICE, the combustion in each cylinder arrangement starts at a point during the power stroke of the associated piston and spreads as a flame front within the combustion chamber. This is referred to as diffusion combustion and involves simultaneous mixing of air and fuel in the combustion chamber as the combustion takes place. In other words, the compression-ignition ICE is configured for diffusion combustion during the power stroke of the piston of the cylinder arrangement. It can be noted that there are other forms of combustion, such as for example HCCI (homogeneous charge compression ignition combustion), where the mixing of air and fuel in the combustion chamber takes place before the combustion starts.

[0020] The compression ratio of the ICE can be in the range 14:1 to 26:1.

[0021] The exhaust camshaft is configured to control the opening and closing of the exhaust valve in a well-known manner, where a common cam lobe of the exhaust camshaft controls the exhaust valve. The intake camshaft is configured to control the opening and closing of the intake valve in a well-known manner, where a cam lobe of the intake camshaft controls the intake valve.

[0022] The rotation of the exhaust camshaft and the intake camshaft is synchronized with the crankshaft. However, the timing of the exhaust camshaft and the intake camshaft is changeable, i.e. the rotational position of the camshafts in relation to the crankshaft is controllable.

[0023] In practice, this means that the crank angle at which the valve opening and closing controlled by the relevant camshaft can be changed. The change in timing of the camshafts can be performed in any known manner. For example, WO 2017 / 217908 and US 8714123 disclose a timing control arrangement for changing the timing of the camshafts.

[0024] It is noted that when changing the timing of the valves, the angular length of the opening period of each of the exhaust valve and the intake valve can remain the same. This is in contrast to systems in which the closing and / or opening position of the valves is changed using e.g. a lost motion mechanism, which will thus also affect the angular length of the period during which the relevant valve remains open.

[0025] As mentioned above, the timing of the exhaust camshaft and the intake camshaft can be controlled by a control arrangement, i.e. a control arrangement configured to change the rotational position of the camshafts with respect to the crankshaft. In this context, reference is made to variable valve timing and timing change. This can alternatively be referred to as phase shifting or cam phasing.

[0026] The timing change angle of a respective camshaft is the angle by which the timing of the camshaft is changed with respect to its normal angular operating position with respect to the crankshaft.

[0027] If the cylinder arrangement comprises one or more additional intake valves and / or exhaust valves, these valves can also undergo variable valve timing in the manner discussed above. This will be the case if such additional valves are controlled by the first camshaft and / or the second camshaft. Thus, if the additional valves are controlled by an additional camshaft, the timing of any additional camshaft can also be changed as discussed herein.

[0028] It is noted that by permitting the exhaust gas to escape earlier during the power stroke and by reducing the amount of air compressed during the compression stroke, both as discussed above, the timing change of the exhaust camshaft and the intake camshaft will reduce the amount of air and pressure within the relevant cylinder around its top dead centre ignition TDCfire.

[0029] Furthermore, due to the timing change of the exhaust camshaft and the intake camshaft as discussed above, there will be no overlap between the exhaust valve and the intake valve at the top dead centre gas exchange TDCge, i.e. the exhaust valve will close before the piston reaches its TDCge, and the intake valve will open after the piston has reached its TDCge. Thus, in the transition between the exhaust stroke and the intake stroke, an amount of gas will remain trapped within the cylinder. The trapped amount of gas will be compressed in the cylinder, causing an increase in pressure within the cylinder during the exhaust stroke. Furthermore, in contrast to when there is no timing change of the camshafts and the pressure is only built up during the compression stroke, the pressure build-up in the combustion chamber is performed every time the piston travels up in the cylinder bore, i.e. during the compression stroke and the exhaust stroke. Thus, the frequency of the pressure build-up is increased, which in turn changes the characteristics of the vibrations and how they are perceived.

[0030] According to embodiments, the absolute value of the angle of change of the timing of the exhaust camshaft during the step of changing the timing of the exhaust camshaft can be the same as the absolute value of the angle of change of the timing of the intake camshaft during the step of changing the timing of the intake camshaft. In this way, a symmetrical timing change with respect to TDCge can be provided. Such a symmetrical timing change can also ensure that the exhaust gases are permitted to escape earlier during the power stroke, and that the amount of air compressed around the top dead center ignition TDCfire during the compression stroke is reduced. A more symmetrical pressure around both TDCge and TDCf within the combustion chamber is achieved compared to an asymmetrical timing change. In addition, a symmetrical timing change is beneficial from a fuel consumption point of view.

[0031] According to embodiments, prior to the steps of changing the timing of the exhaust camshaft and changing the timing of the intake camshaft, the method can comprise the steps of:

[0032] - sensing vibrations of the internal combustion engine, and wherein the steps of changing the timing of the exhaust camshaft and changing the timing of the intake camshaft are performed in response to the sensed vibrations exceeding a threshold level. In this way, the timing change of the exhaust camshaft and the intake camshaft can be performed when there is an actual requirement to reduce the vibrations of the ICE. More specifically, in addition to operating the ICE below a threshold rotational speed, sensing vibrations of the ICE above a threshold level can trigger the timing change of the exhaust camshaft and the intake camshaft, thereby reducing the vibrations of the ICE.

[0033] The term sensing should be interpreted broadly and encompasses both direct sensing and indirect sensing of vibrations. Vibrations can be directly sensed by means of, for example, one or more accelerometers. Vibrations can be indirectly sensed by means of, for example, a rotational speed sensor of the ICE and a mapping of rotational speed irregularities or vibration critical rotational speed irregularities. The term sensing vibrations can also encompass a measurement of vibrations.

[0034] According to embodiments, the method can be performed in a vehicle configured for land-based propulsion. In this way, the driver and / or passengers of the vehicle can travel comfortably in the vehicle due to the reduced level of vibrations provided by the method.

[0035] According to embodiments, prior to the steps of changing the timing of the exhaust camshaft and changing the timing of the intake camshaft, the method can comprise the steps of:

[0036] - determining whether the vehicle is propelled at a speed below a threshold speed, and wherein

[0037] The steps of changing the timing of the exhaust camshaft and changing the timing of the intake camshaft are performed in response to the vehicle being propelled at a speed below the threshold speed. In this way, timing changes to the exhaust camshaft and intake camshaft can be performed when there can be a likelihood of the ICE oscillating excessively. More specifically, in addition to operating the ICE at below a threshold rotational speed, determining whether the vehicle is propelled at a speed below a threshold speed can trigger timing changes to the exhaust camshaft and intake camshaft, thereby reducing oscillation of the ICE.

[0038] According to embodiments, the vehicle can comprise a positioning system, such as a GPS system, and wherein prior to the steps of changing the timing of the exhaust camshaft and changing the timing of the intake camshaft, the method can comprise the steps of:

[0039] determining a position of the vehicle, and wherein

[0040] The steps of changing the timing of the exhaust camshaft and changing the timing of the intake camshaft are performed in response to the position of the vehicle being determined to be within a particularly defined type of area. In this way, timing changes to the exhaust camshaft and intake camshaft can be performed when the vehicle is within an area where noise reduction can be preferred or required. More specifically, in addition to operating the ICE at below a threshold rotational speed, determining whether the vehicle is within a particularly defined type of area, such as near a hospital, near a retirement home or within a city limit, can trigger timing changes to the exhaust camshaft and intake camshaft, thereby reducing oscillation of the ICE, and thus reducing the noise level of the vehicle.

[0041] According to another aspect of the application, there is provided a vehicle comprising a spark-ignition four-stroke internal combustion engine according to any of the aspects and / or embodiments discussed herein.

[0042] The ICE can form part of a powertrain of the vehicle.

[0043] According to another aspect of the application, there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method according to any of the aspects and / or embodiments discussed herein.

[0044] According to another aspect of the application, there is provided a computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method according to any of the aspects and / or embodiments discussed herein.

[0045] Other features and advantages of the present application will become apparent from a study of the application content and the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0046] Various aspects and / or embodiments of the present application (including its particular features and advantages) will be understood by referring to the following example embodiments discussed in conjunction with the accompanying drawings, in which:

[0047] Figure 1 Embodiments of a vehicle are shown,

[0048] Figure 2 Embodiments of an internal combustion engine are shown schematically,

[0049] Figure 3 Control arrangements are shown,

[0050] Figure 4 Operation diagrams of an ICE are shown, and

[0051] Figure 5 Embodiments of a method for vibration reduction in a compression ignition four-stroke internal combustion engine are shown. DETAILED DESCRIPTION

[0052] Aspects and / or embodiments of the present application will now be described more fully. Like reference numerals are used to represent like elements throughout. Familiar functions or constructions are not described in detail for the sake of clarity and / or avoiding obscuring the present application.

[0053] Figure 1 Embodiments of a vehicle 2 configured for land-based propulsion are shown. The vehicle 2 comprises a compression ignition four-stroke internal combustion engine ICE 4 according to aspects and / or embodiments discussed herein, such as for example the ICE discussed below with reference to Figure 2 The ICE 4 comprises a control arrangement as discussed below with reference to Figure 2 and Figure 3

[0054] In these embodiments, the vehicle 2 is a heavy duty vehicle in the form of a truck. Although the present application is not limited to any particular type of vehicle, the present application is particularly directed to land-based propulsion vehicles comprising a larger compression ignition ICE, such as for example a bus or a construction vehicle.

[0055] Figure 2 Embodiments of the ICE 4 are shown schematically. The ICE 4 can be configured to form part of a powertrain of a vehicle, such as for example the vehicle 2 shown in Figure 1

[0056] The ICE 4 is a compression ignition four-stroke direct injection internal combustion engine, for example a diesel engine. The ICE 4 comprises at least one cylinder arrangement 6, a crankshaft 8, an exhaust camshaft 10, an intake camshaft 12.

[0057] ​​The cylinder arrangement 6 comprises a combustion chamber 14, a cylinder bore 16, a piston 18 configured to reciprocate in the cylinder bore 16, an exhaust valve 20, and an intake valve 22. The piston 18 is connected to the crankshaft 8 by a connecting rod 24.

[0058] The movement of the exhaust valve 20 is controlled by the exhaust camshaft 10, i.e. the exhaust camshaft 10 is configured to control the opening and closing of the exhaust valve 20. The movement of the intake valve 22 is controlled by the intake camshaft 12, i.e. the intake camshaft 12 is configured to control the opening and closing of the intake valve 22.

[0059] The intake valve 22 is configured for allowing charge air to enter the combustion chamber 14, and the exhaust valve 20 is configured for allowing exhaust gases to exit the combustion chamber 14. The timing of the exhaust camshaft 10 is configured to be controlled by a timing control arrangement 30, as indicated by the double arrow. Similarly, the timing of the intake camshaft 12 is configured to be controlled by a timing control arrangement 32, as indicated by the double arrow.

[0060] In a known manner, the intake valve 22 comprises an intake valve head configured to seal against an intake valve seat extending around the intake port 26. Similarly, the exhaust valve 20 comprises an exhaust valve head configured to seal against an exhaust valve seat extending around the exhaust port 28.

[0061] In a known manner, the camshafts 10, 12 can rotate at half the rotational speed of the crankshaft 8, and control the movement of the exhaust valve 20 and the intake valve 22 via cam lobes 40, 42 arranged on the camshafts 10, 12. The exhaust camshaft 10 is arranged for controlling the movement of the exhaust valve 20 and the opening and closing of the exhaust opening 28. The exhaust camshaft 10 comprises cam lobes 40. By abutment against the cam lobes 40, the exhaust valve 20 will follow the profile of the cam lobes 40, for example. The exhaust valve 20 can be biased towards its closed position by means of a spring, not shown. The movement of the intake valve 22 is controlled in a corresponding manner by the intake camshaft 12 and its cam lobes 42 for opening and closing the intake opening 26.

[0062] The piston 18 is arranged to reciprocate in the cylinder bore 16. The piston 18 performs four strokes in the cylinder bore 16, corresponding to an intake stroke, a compression stroke, an expansion stroke or a work stroke, and an exhaust stroke, see also Figure 4 In Figure 2 the piston 18 is shown with a continuous line at its bottom dead centre BDC, and with a dashed line at its top dead centre TDC. The combustion chamber 14 is formed above the piston 18 inside the cylinder bore 16.

[0063] The cylinder arrangement 6 has a total displacement V SAccording to some embodiments, the cylinder arrangement 6 can have a total displacement Vsin the range of 0.25 to 4 liters or in the range of 1 to 4 liters S .

[0064] The ICE 4 can comprise more than one cylinder arrangement 6, such as for example three, four, five, six or eight cylinder arrangements 6. It is merely mentioned as an example that the total displacement of the ICE 4, i.e. the sum of the displacements Vs of the cylinder arrangements of the ICE 4, can be in the range of 1 to 20 liters, or in the range of 5 to 20 liters.

[0065] The ICE 4 comprises a turbocharger 44. The turbocharger 44 comprises a compressor 50 and a turbine 52. The compressor 50 and the turbine 52 of the turbocharger 44 are connected via a common shaft 54. An inlet conduit 46 for charge air leads from the compressor 50 to the intake port 26. For the sake of clarity, the inlet conduit 46 is not shown in its entirety. An exhaust conduit 48 leads from the exhaust port 28 to the turbine 52. The turbocharger 44 generates a charge air pressure in the inlet conduit 46 and at the intake valve 22. More specifically, the gases expelled via the exhaust valve 20 drive the turbine 52, which in turn rotates the compressor 50. Thus, the compressor 50 provides charge air a to the intake valve 22.

[0066] The ICE 4 comprises a fuel injector 56 configured to inject fuel into the combustion chamber 14 when the ICE 4 generates positive torque during a power stroke of the piston 18, e.g. for propelling the vehicle 2.

[0067] The ICE 4 further comprises a control arrangement 38 according to aspects and / or embodiments discussed herein. The control arrangement 38 is configured to control the variable valve timing of the ICE 4. That is, the control arrangement 38 is configured to control at least the timing of the exhaust camshaft 10 and the timing of the intake camshaft 12. Thus, the timing control arrangements 30, 32 form part of the control arrangement 38.

[0068] To reduce vibrations of the ICE 4, said control arrangement 38 is configured to, when operating said ICE 4 below a threshold rotational speed:

[0069] - change the timing of said exhaust camshaft 10 to advance closing of said exhaust valve 20, and

[0070] - change the timing of said intake camshaft 12 to retard opening of said intake valve 22.

[0071] In addition to the threshold rotational speed, other conditions can apply to the timing change of the camshafts 10, 12 to be performed. As discussed herein, such other conditions can relate to the ICE vibration level, the vehicle speed and / or the vehicle position.

[0072] According to embodiments, the threshold rotational speed can be a rotational speed in the range of 1 to 1000 rpm. In this way, the threshold rotational speed of the engine 4 can define a rotational speed below which excessive engine vibrations occur.

[0073] The threshold rotational speed of the ICE 4 can be different for different conditions. For example, if the rotational speed of the ICE 4 is the only condition for performing the timing change of the crankshafts 10, 12, a first threshold rotational speed can be applied. If the condition comprises the rotational speed of the ICE 4 and another condition, such as for example the vehicle speed, a second threshold rotational speed different from the first threshold rotational speed can be applied.

[0074] The particular threshold speed can depend on the particular ICE, its size, the number of cylinders, etc., and the suspension of the ICE in the vehicle or other structure. The suspension of the vehicle cabin can affect which vibrations can be transmitted to the driver and / or passengers of the vehicle, and thus also the selection of the threshold speed.

[0075] The control arrangement 38 comprises a rotational speed sensor 75 for sensing the rotational speed of the crankshaft 8 of the ICE 4.

[0076] Reference is made below to Figures 3 to 6 The control arrangement 38 and the timing change of the camshafts 10, 12 are further discussed.

[0077] Figure 3 A control arrangement 38 for use in connection with various aspects and / or embodiments of the application is shown. In particular, the control arrangement 38 is configured for controlling the timing of the camshafts 10, 12 of an ICE 4 in connection with Figure 1 and Figure 2 discussed. The control arrangement 38 is also shown in Figure 2 The control arrangement 38 and the engine 4 can be provided in the vehicle 2. Thus, reference is made below to Figures 1 to 3 .

[0078] The control arrangement 38 comprises at least one computing unit 60, which can take the form of essentially any suitable type of processor circuitry or microcomputer, e.g. a circuit for digital signal processing (digital signal processor, DSP), a central processing unit (CPU), a processing unit, processing circuitry, a processor, an application-specific integrated circuit (ASIC), a microprocessor, or other processing logic which can interpret and execute instructions. The expression "computing unit" as used herein can denote processing circuitry comprising a plurality of processing circuits, such as e.g. any one, some or all of the processing circuits described above. The computing unit 60 can be configured to perform calculations, such as e.g. analyzing accelerometer data and / or rotational speed sensor measurements as discussed herein. The computing unit 60 can be configured to compare GPS data with map data. The computing unit 60 can be configured to compare measured or calculated data with threshold values.

[0079] The control arrangement 38 comprises a memory unit 62. The computing unit 60 is connected to the memory unit 62, which provides the computing unit 60 with e.g. program code, data tables, and / or other stored data which the computing unit 60 needs to enable it to perform calculations and control the ICE. The computing unit 60 is also adapted to store partial results and / or final results of calculations in the memory unit 62. The memory unit 62 can comprise a physical device to store data or a program, i.e. a sequence of instructions, on a temporary or permanent basis. According to some embodiments, the memory unit 62 can comprise an integrated circuit comprising silicon-based transistors. In different embodiments, the memory unit 62 can comprise e.g. a memory card, a flash memory, a USB memory, a hard disk, or another similar volatile or non-volatile storage unit for storing data, such as e.g. a ROM (Read-Only Memory), a PROM (Programmable-Read-Only Memory), an EPROM (Erasable PROM), an EEPROM (Electrically Erasable PROM), etc.

[0080] The control arrangement 38 is further provided with respective devices 70, 71, 72, 66, 68 for receiving and / or sending input and output signals. These input and output signals can comprise waveforms, pulses or other properties which can be detected as information by the signal receiving devices and can be converted into signals which can be processed by the computing unit 60. Input signals are supplied from the input receiving devices 70, 71, 72 to the computing unit 60. The output signal sending devices 66, 68 are arranged to convert the results of the computation from the computing unit 60 into output signals for transmission to signal receiving devices of other parts of the control arrangement 38. Each of the connections to the respective devices for receiving and sending input and output signals can take the form of one or more from among electrical cables, a data bus, such as a CAN (Controller Area Network) bus, a MOST (Media Oriented Systems Transport) bus or some other bus configuration, or a wireless connection. In the depicted embodiment, only one computing unit 60 and memory unit 62 are shown, but the control arrangement 38 can instead comprise more than one computing unit and / or memory unit.

[0081] By way of example, the output signal sending devices 66, 68 can send control signals to the timing control arrangements 30, 32 of the exhaust camshaft 10 and the intake camshaft 12. The input signal receiving devices 70, 71, 72 can receive signals from the ICE 4, such as, for example, from a rotational speed sensor 75, a vibration sensor 76 of the crankshaft 8 of the ICE 4, and a vehicle position sensor 78.

[0082] Examples of data tables can be, for example:

[0083] - a table containing accelerator measurements and engine vibration level coincidences,

[0084] - a table containing timing change angles for the exhaust camshaft 10 and the intake camshaft 12 at certain engine rotational speeds of the ICE 4,

[0085] - a table containing ICE rotational speed irregularities and their coincidences with vibrations,

[0086] - a table containing timing change angles for the exhaust camshaft 10 and the intake camshaft 12 at different vibration levels,

[0087] - a table containing map data relating to, for example, urban areas and / or noise restricted areas,

[0088] Examples of data can be measured, monitored, determined and / or calculated data, such as rotational speed data, engine vibration data, timing change angle data. The control arrangement 38 comprises or is connected to various sensors and actuators in order to receive inputs and provide outputs for performing various aspects and embodiments of the methods discussed herein. Some of the various sensors are exemplified above. Examples of actuators can be actuators configured for changing the timing of the camshafts 10, 12 and forming part of the timing control arrangements 30, 32.

[0089] The control arrangement 38 can be configured to perform the method 100 according to any of the aspects and / or embodiments discussed herein, see e.g. below with reference to Figure 5 .

[0090] As mentioned above, when operating the ICE 4 below a threshold rotational speed, the control arrangement 38 is configured to:

[0091] - change the timing of the exhaust camshaft 10 to advance closing of the exhaust valve 20, and

[0092] - change the timing of the intake camshaft 12 to retard opening of the intake valve 22.

[0093] In this text, reference is made to crank angle CA degrees, e.g. when discussing timing changes of camshafts. One complete rotation of a crankshaft is 360 CA degrees. The crank angle can e.g. be measured from top dead center ignition TDCfireor top dead center gas exchange TDCge. Negative timing change angles are related to advancing opening and closing of valves, and positive timing change angles are related to retarding opening and closing of valves.

[0094] Overlap between exhaust valve and intake valve means that the exhaust valve and the intake valve are opened synchronously at TDCge. Negative overlap between exhaust valve and intake valve means that the exhaust valve and the intake valve are not opened synchronously at TDCge.

[0095] According to embodiments, the control arrangement 38 can comprise sensors 75, 76 configured to sense vibrations of the ICE 4. When operating the internal combustion engine (4) below a threshold rotational speed, and in response to the sensed vibrations exceeding a threshold level, the control arrangement 38 can be configured to change the timing of the exhaust camshaft 10 to advance closing of the exhaust valve 20, and change the timing of the intake camshaft 12 to retard opening of the intake valve 22. In this way, in addition to the rotational speed of the ICE 4, information provided by the sensors 75, 76 configured to sense vibrations of the ICE 4 can be used to reduce vibrations of the engine 4 as the timing of the exhaust camshaft 10 and the intake camshaft 12 is changed.

[0096] The sensor configured to sense vibrations of the ICE 4 may be, for example, an accelerometer 76 mounted on or near the engine 4 in such a way that the accelerometer 76 is affected by engine vibrations. The computing unit 60 may be configured to evaluate the signal from the accelerometer 76 in order to establish a magnitude of the engine vibrations. According to an alternative embodiment, the sensor configured to sense vibrations of the engine 4 may include a speed sensor 75 of the engine 4. The speed sensor 75 forms part of the ordinary control system of the ICE 4. Such a speed sensor 75 may be, for example, a Hall effect sensor that is arranged to provide a large number of pulses during one rotation of the crankshaft 8. Based on the pulses, the computing unit 60 may determine speed irregularities / variations in the speed of the crankshaft 8. Specific speed irregularities / variations may be identified as engine vibrations or may cause engine vibrations above a threshold level.

[0097] According to an embodiment in which the control arrangement 38 is arranged in the vehicle 2, the control arrangement 38 may be configured to determine whether the vehicle 2 is being propelled at a speed below a threshold speed. When the internal combustion engine 4 is operating at a speed below the threshold speed, and in response to the vehicle 2 being propelled at a speed below the threshold speed, the control arrangement 38 may be configured to change the timing of the exhaust camshaft 10 to advance the closing of the exhaust valve 20, and change the timing of the intake camshaft 12 to retard the opening of the intake valve 22. In this way, not only the speed of the engine 4, but also the vehicle speed may determine whether to change the timing of the exhaust camshaft 10 and the intake camshaft 12. That is, certain combinations of engine speed and vehicle speed may cause excessive engine vibration.

[0098] According to an embodiment in which the control arrangement 38 is arranged in the vehicle 2, the vehicle 2 may include a positioning system 78, such as a GPS system. The control arrangement 38 may be configured to determine the location of the vehicle 2. When the internal combustion engine 4 is operating below a threshold speed, and in response to the location of the vehicle 2 being determined to be within a specially defined type of zone, the control arrangement 38 may be configured to change the timing of the exhaust camshaft 10 to advance the closing of the exhaust valve 20, and change the timing of the intake camshaft 12 to delay the opening of the intake valve 22. In this way, not only the speed of the engine 4 but also the location of the vehicle may determine whether to change the timing of the exhaust camshaft 10 and the intake camshaft 12. In other words, the specially defined type of zone may relate to a specific geographic area where excessive vehicle noise may be prohibited. In such areas, reducing engine vibration may be beneficial from the perspective of reducing vehicle noise.

[0099] Figure 4 Shown according to the above reference Figures 1 to 3 of the discussion Figure 2 Therefore, in the following, reference is also made to the diagram of the ICE 4 and its control. Figures 1 to 3 . Figure 4Four strokes of the piston 18 and the movement of the exhaust valve 20 (dashed line) and the intake valve 22 (dotted line) during operation of the ICE 4 are shown. When performing the four strokes of the piston 18, the crankshaft 8 of the ICE 4 rotates 720 degrees CA. For each stroke, the crankshaft 8 rotates 180 degrees CA, as indicated in Figure 4 the middle. The solid line represents the pressure within the combustion chamber 14 of the ICE 4.

[0100] Along line I. the opening and closing of the exhaust valve 20 and the intake valve 22 during normal combustion in the ICE 4 without applying variable valve timing is shown. During the respective exhaust and intake strokes, the exhaust valve 20 and the intake valve 22 open and close in a normal way, before and after TDCge.

[0101] Along line II. the opening and closing of the exhaust valve 20 and the intake valve 22 is shown, wherein variable valve timing is applied in order to reduce engine vibrations when the engine 4 is operated below a threshold rotational speed. The control arrangement 38 is configured to change the timing of the exhaust camshaft 10 to advance the closing of the exhaust valve 20 and to change the timing of the intake camshaft 12 to retard the opening of the intake valve 22.

[0102] Due to the later closing of the intake valve 12 and the earlier opening of the exhaust valve 10, the pressure within the combustion chamber 14 at TDCfire is lower than during normal combustion. In addition, due to the earlier closing of the exhaust valve 10 and the later opening of the intake valve 12, the pressure in the combustion chamber 14 accumulates at TDCge.

[0103] According to embodiments of the control arrangement 38 and the internal combustion engine 4, the absolute value of the angle a by which the timing of the exhaust camshaft 10 is changed during the change of the timing of the exhaust camshaft 10 can be the same as the absolute value of the angle β by which the timing of the intake camshaft 12 is changed during the change of the timing of the intake camshaft 12. In this way, a symmetrical change of the timing of the exhaust camshaft and the intake camshaft can be provided. The change of the timing can be symmetrical with respect to TDCge.

[0104] According to embodiments of the control arrangement 38 and the internal combustion engine 4, the angle a by which the timing of the exhaust camshaft 10 is changed to advance the closing of the exhaust valve 20 can be at least in the range of -5 to -80 degrees CA, or in the range of -10 to -80 degrees CA, and the angle β by which the timing of the intake camshaft 12 is changed to retard the opening of the intake valve 22 can be at least in the range of 5 to 80 degrees CA, or in the range of 10 to 80 degrees CA. In this way, angles a, β of the change of the timing can be provided, which enable a reduction of engine vibrations.

[0105] For example, during drive operation of the ICE 4, i.e. when fuel is injected into the combustion chambers 14 and combusted around TDCfire, a timing change angle of up to -60 degrees CA and 60 degrees CA, respectively, can be provided in order to reduce engine vibrations at low ICE rotational speeds. During motoring of the ICE, i.e. when no fuel is injected into the combustion chambers 14 and the crankshaft 8 of the ICE is driven by the rotation of the wheels of the vehicle, a timing change angle of up to -80 degrees CA and 80 degrees CA, respectively, can be provided in order to reduce vibrations at low ICE rotational speeds.

[0106] Figure 5 An embodiment of a method 100 for vibration reduction in a compression-ignited four-stroke internal combustion engine 4 is shown, the method 100 comprising the steps of:

[0107] - changing 102 the timing of the exhaust camshaft 10 to advance closing of the exhaust valves 20, and

[0108] - changing 104 the timing of the intake camshaft 12 to retard opening of the intake valves 22.

[0109] The above-discussed embodiments of the control arrangement 38 can be applied in the method 100 in a corresponding manner.

[0110] According to an embodiment, the threshold rotational speed can be a rotational speed in the range of 1 to 1000 rpm.

[0111] According to an embodiment, the method 100 can comprise the step of:

[0112] - sensing 106 vibrations of the internal combustion engine, and wherein the steps of changing 102 the timing of the exhaust camshaft 10 and changing 104 the timing of the intake camshaft 12 can be performed in response to the sensed vibrations exceeding a threshold level.

[0113] According to an embodiment, the method 100 can be performed in a vehicle 2 configured for land-based propulsion.

[0114] According to an embodiment, the method 100 can comprise the step of:

[0115] - determining 108 if the vehicle 2 is propelled at a speed below a threshold speed, and wherein in response to the vehicle 2 being propelled at a speed below the threshold speed, the steps of changing 102 the timing of the exhaust camshaft 10 and changing 104 the timing of the intake camshaft 12 are performed.

[0116] According to embodiments, the vehicle 2 can comprise a positioning system 78, such as a GPS system, and wherein prior to the steps of changing 102 the timing of the exhaust camshaft 10 and changing 104 the timing of the intake camshaft 12, the method 100 can comprise the steps of:

[0117] - determining 110 a position of the vehicle 2, and wherein in response to the position of the vehicle 2 being determined to be within a particularly defined type of area, the steps of changing 102 the timing of the exhaust camshaft 10 and changing 112 the timing of the intake camshaft 12 are performed.

[0118] According to another aspect, there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to implement the method 100 according to any one of the aspects and / or embodiments discussed herein.

[0119] The skilled person will appreciate that the method 100 of controlling the timing of the exhaust camshaft 10 and the intake camshaft 12 of a four-stroke ICE 4 can be implemented by programming instructions. These programming instructions are typically constituted by a computer program which, when executed in a computer or computing unit 60, ensures that the computer or computing unit 60 implements the required control, such as the method 100 and its related steps 102-110. The computer program is typically part of a computer-readable storage medium comprising a suitable digital storage medium on which the computer program is stored.

[0120] Figure 6 An embodiment of a computer-readable storage medium 99 comprising instructions which, when executed by a computer or computing unit 60, cause the computer or computing unit 60 to implement the steps of the method 100 according to any one of the aspects and / or embodiments discussed herein is shown.

[0121] The computer-readable storage medium 99 can for example be provided in the form of a data carrier carrying computer program code for performing at least some of the steps 102-110 according to some embodiments when loaded into the computing unit(s) 60. The data carrier can be for example a ROM (Read-Only Memory), a PROM (Programmable Read-Only memory), an EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), a hard disk, a CD-ROM optical disk, a memory stick, an optical storage device, a magnetic storage device, or any other appropriate medium such as a magnetic or optical disk that can hold machine readable data in a non transitory way, for example a disk or tape. The computer-readable storage medium can also be provided as computer program code on a server and can be downloaded to the computing unit 60 remotely, e.g. over the Internet or an intranet connection, or via other wired or wireless communication systems.

[0122] Figure 6 The computer-readable storage medium 99 illustrated in the middle is a non-limiting example in the form of a USB memory stick.

[0123] It is to be understood that the above description is example of various example embodiments. Those skilled in the art will recognize that modifications can be made to the example embodiments, and that different features of the example embodiments can be combined, without departing from the scope of the present disclosure.

Claims

1. A method (100) for vibration reduction in a compression-ignited four-stroke internal combustion engine (4), the internal combustion engine (4) comprising: - an exhaust valve (20) and an intake valve (22), an exhaust camshaft (10) arranged to control opening and closing of the exhaust valve (20), and an intake camshaft (12) arranged to control opening and closing of the intake valve (22), wherein when the internal combustion engine (4) is operated below a threshold rotational speed, the method (100) comprises the steps of changing the timing of the exhaust camshaft (10) to advance closing of the exhaust valve (20), and changing the timing of the intake camshaft (12) to retard opening of the intake valve (22), wherein the method (100) is performed in a vehicle (2) configured for land-based propulsion, wherein the vehicle (2) comprises a positioning system (78), and wherein prior to the steps of changing the timing of the exhaust camshaft (10) and changing the timing of the intake camshaft (12), the method (100) comprises the step of: - determining a position of the vehicle (2), and wherein in response to determining that the position of the vehicle (2) is determined to be located within a particularly defined type of area, the steps of changing the timing of the exhaust camshaft (10) and changing the timing of the intake camshaft (12) are performed, wherein the particularly defined type of area is an area where noise reduction is required.

2. The method (100) according to claim 1, wherein an absolute value of a timing change angle (a) of the exhaust camshaft (10) during the step of changing the timing of the exhaust camshaft (10) is the same as an absolute value of a timing change angle (b) of the intake camshaft (12) during the step of changing the timing of the intake camshaft (12).

3. The method (100) according to claim 2, wherein the timing change angle (a) of the exhaust camshaft (10) to advance closing of the exhaust valve (20) is at least in the range of -0.1 to -80 degrees CA, and the timing change angle (b) of the intake camshaft (12) to retard opening of the intake valve (22) is at least in the range of 0.1 to 80 degrees CA.

4. The method (100) according to any one of claims 1-3, wherein prior to the step of changing the timing of the exhaust camshaft (10) and changing the timing of the intake camshaft (12), the method (100) comprises the steps of: - sensing vibrations of the internal combustion engine (4), and wherein in response to the sensed vibrations exceeding a threshold level, the steps of changing the timing of the exhaust camshaft (10) and changing the timing of the intake camshaft (10) are performed.

5. The method (100) according to any one of claims 1-3, wherein the threshold rotational speed is a rotational speed in the range of 1 to 1000 rpm.

6. The method (100) according to claim 1, wherein prior to the step of changing the timing of the exhaust camshaft (10) and changing the timing of the intake camshaft (12), the method (100) comprises the steps of: - determining whether the vehicle (2) is propelled at a speed below a threshold speed, and wherein in response to the vehicle (2) being propelled at a speed below the threshold speed, the steps of changing the timing of the exhaust camshaft (10) and changing the timing of the intake camshaft (12) are performed.

7. The method (100) according to claim 1, wherein the positioning system (78) is a GPS system.

8. A control device (38) for controlling variable valve timing of a compression-ignition four-stroke internal combustion engine (4), the internal combustion engine (4) comprising: An exhaust valve (20) and an intake valve (22), an exhaust camshaft (10) arranged for controlling opening and closing of the exhaust valve (20), and an intake camshaft (12) arranged for controlling opening and closing of the intake valve (22), wherein the control device (38) is configured to, when operating the internal combustion engine (4) below a threshold rotational speed: change the timing of the exhaust camshaft (10) to advance closing of the exhaust valve (20), and change the timing of the intake camshaft (12) to retard opening of the intake valve (22), wherein the control device (38) is arranged in a vehicle (2), and wherein the vehicle comprises a positioning system (78), and the control device (38) is configured to: determine a position of the vehicle (2), and when operating the internal combustion engine (4) below a threshold rotational speed, and in response to determining that the position of the vehicle (2) is determined to be located within a particularly defined type of area, wherein the particularly defined type of area is an area where noise reduction is required, the control device (38) is configured to: change the timing of the exhaust camshaft (10) to advance closing of the exhaust valve (20), and change the timing of the intake camshaft (12) to retard opening of the intake valve (22).

9. The control device (38) according to claim 8, comprising sensors (75, 76) configured to sense vibrations of the internal combustion engine (4), wherein the control device (38) is configured to, when operating the internal combustion engine (4) below the threshold rotational speed, and in response to the sensed vibrations exceeding a threshold level: change the timing of the exhaust camshaft (10) to advance closing of the exhaust valve (20), and change the timing of the intake camshaft (12) to retard opening of the intake valve (22).

10. The control device (38) according to claim 8 or 9, wherein the threshold rotational speed is a rotational speed in the range of 1 to 1000 rpm.

11. A compression ignition four-stroke internal combustion engine (4) comprising a control device (38) according to any one of claims 8 to 10.

12. The internal combustion engine (4) according to claim 11, wherein an absolute value of a timing change angle (a) of the exhaust camshaft (10) during the change of the timing of the exhaust camshaft (10) is the same as an absolute value of a timing change angle (b) of the intake camshaft (12) during the change of the timing of the intake camshaft (12).

13. The internal combustion engine (4) according to claim 12, wherein the timing change angle (α) of the exhaust camshaft (10) for early closing of the exhaust valve (20) is at least in the range of -5 to -80 degrees CA, and the timing change angle (β) of the intake camshaft (12) for retarding opening of the intake valve (22) is at least in the range of 5 to 80 degrees CA.

14. A vehicle (2) comprising a compression-ignition four-stroke internal combustion engine (4) according to any one of claims 11 to 13.

15. A vehicle (2) according to claim 14, wherein the control device (38) is configured to: determine whether the vehicle (2) is being propelled at a speed below a threshold speed, and wherein when the internal combustion engine (4) is operated at a speed below the threshold speed, and in response to the vehicle (2) being propelled at a speed below the threshold speed, the control device (38) is configured to: - change the timing of the exhaust camshaft (10) to advance closing of the exhaust valve (20), and - change the timing of the intake camshaft (12) to retard opening of the intake valve (22).

16. The vehicle (2) of claim 14, wherein the positioning system (78) is a GPS system.

17. A computer program product comprising instructions which, when the program product is executed by a computer, cause the computer to carry out the steps of the method (100) according to any one of claims 1 to 7.

18. A computer-readable storage medium (99) comprising instructions which, when executed by a computer, cause the computer to perform the steps of the method (100) according to any one of claims 1 to 7.

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