METHOD FOR CONTROLLING ENGINE BRAKING OF AN INTERNAL COMBUSTION ENGINE

Abstract

The invention relates to controlling engine braking of an internal combustion engine wherein the method includes setting the engine in an engine braking mode comprising i) interrupting fuel supply to a first cylinder, ii) restricting the flow of gas through an exhaust duct using an adjustable flow restricting member, and iii) controlling inlet and exhaust valves of the first cylinder in a compression-release mode comprising controlling the valves to compress gas in a combustion chamber when the piston moves towards the top dead center position (TDC) and release compressed gas into the exhaust duct when the piston is near the TDC. The method includes, prior to ii and iii: reducing a total gas mass flow rate through the engine by controlling, for at least one of valve, reducing a valve lift and/or adjusting a timing of a valve opening or closing so as to reduce the gas mass flow rate through the cylinder.

Claims

1. A method for controlling engine braking of an internal combustion engine, wherein the internal combustion engine comprises: at least a first cylinder provided with an inlet valve and an exhaust valve for controlling communication between a combustion chamber in the first cylinder and an inlet duct and an exhaust duct, respectively; a piston configured to move in a reciprocating manner in said first cylinder between a top dead center position (TDC) close to the inlet valve and the exhaust valve and a bottom dead center position (BDC) away from said inlet valve and said exhaust valve; and a valve actuation arrangement configured to control opening and closing of the inlet valve and the exhaust valve, wherein the method comprises the steps of; setting the internal combustion engine in an engine braking mode comprising controlling the inlet valve and the exhaust valve in a compression-release mode comprising controlling the inlet valve and the exhaust valve so as to compress gas in the combustion chamber when the piston moves towards the TDC and release the compressed gas into the exhaust duct when the piston is near the TDC; and prior to the step of controlling the inlet valve and the exhaust valve in the compression-release mode, reducing a total mass flow rate of gas through the internal combustion engine by controlling the inlet valve and the exhaust valve in a mass flow reduction mode comprising, for at least one of the inlet valve and the exhaust valve of the first cylinder, reducing a valve lift and/or adjusting a timing of a valve opening or closing so as to reduce the mass flow rate of gas through the first cylinder compared to a nominal mass flow rate.

2. The method according to claim 1, wherein the internal combustion engine comprises a fuel supply system for supplying fuel to the first cylinder, and wherein the step of setting the internal combustion engine in the engine braking mode comprises a step of interrupting fuel supply to the first cylinder.

3. The method according to claim 1, wherein the internal combustion engine comprises an adjustable flow restricting member arranged in the exhaust duct, wherein the adjustable flow restricting member is configured to be controlled to restrict a flow of gas through the exhaust duct so as to allow building up of a backpressure during engine braking, and wherein the step of setting the internal combustion engine in the engine braking mode comprises restricting the flow of gas through the exhaust duct using the adjustable flow restricting member.

4. The method according to claim 1, wherein the step of reducing the total mass flow rate of gas through the internal combustion engine comprises: keeping at least one of the inlet valve and the exhaust valve closed during at least one revolution of a crankshaft connected to the piston.

5. The method according to claim 1, wherein the method further comprises the step of: determining whether the mass flow rate through the internal combustion engine has been reduced to a mass flow rate threshold indicative of a sufficient level for the particular application and situation.

6. The method according to claim 3, wherein the method further comprises the step of: gradually restricting the flow through the exhaust duct using the adjustable flow restricting member so as to gradually build up a backpressure in the exhaust duct.

7. The method according to claim 1, wherein the method further comprises the step of: controlling the inlet valve and the exhaust valve so as to change operation mode from the mass flow reduction mode to the compression-release mode.

8. The method according to claim 1, wherein the valve actuation arrangement is a fully variable valve actuation arrangement.

9. An internal combustion engine comprising at least a first cylinder provided with an inlet valve and an exhaust valve for controlling communication between a combustion chamber in the cylinder and an inlet duct and an exhaust duct, respectively; a piston configured to move in a reciprocating manner in said first cylinder between a top dead center position (TDC) close to the inlet valve and the exhaust valve and a bottom dead center position (BDC) away from said inlet valve and said exhaust valve; a valve actuation arrangement configured to control opening and closing of the inlet valve and the exhaust valve; an adjustable flow restricting member arranged in the exhaust duct and being configured to be controlled to restrict a flow of gas through the exhaust duct so as to allow building up of a backpressure during engine braking; a fuel supply system for supplying fuel to the first cylinder, and a control circuitry configured to control operation of the internal combustion engine, wherein the internal combustion engine is configured to be set in an engine braking mode comprising i) interrupting fuel supply to the first cylinder, ii) restricting the flow of gas through the exhaust duct using the adjustable flow restricting member, and iii) controlling the inlet valve and the exhaust valve in a compression-release mode comprising controlling the inlet valve and the exhaust valve so as to compress gas in the combustion chamber when the piston moves towards the TDC and release the compressed gas into the exhaust duct when the piston is near the TDC, wherein the control circuitry is configured to carry out the method steps of interrupting the fuel supply, restricting the flow of gas through the exhaust duct and controlling the inlet valve and the exhaust valve in the compression-release mode.

10. The internal combustion engine according to claim 9, wherein the valve actuation arrangement (is a fully variable valve actuation arrangement.

11. A computer program product comprising program code means for performing the steps of claim 1 when said program is run on a computer.

12. A computer readable medium carrying a computer program comprising program code means for performing the steps of claim 1 when said program product is run on a computer.

13. A control unit for controlling an internal combustion engine, the control unit being configured to perform the steps of the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

[0031] In the drawings:

[0032] FIG. 1 shows a vehicle provided with an internal combustion engine configured to be operated according to this disclosure.

[0033] FIG. 2 shows a schematic view of a cylinder, piston, etc. of the internal combustion engine according to FIG. 1.

[0034] FIG. 3 shows a schematic view of the internal combustion engine according to FIG. 1.

[0035] FIG. 4 shows an example flow chart of a method according to this disclosure.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0036] FIG. 1 shows a vehicle in the form of a truck 100 provided with an internal combustion engine 1 configured to be operated according to a method as described below.

[0037] FIG. 2 shows a schematic view of a first cylinder 2 forming part of the internal combustion engine according to FIG. 1. The first cylinder 2 is provided with an inlet valve 3 and an exhaust valve 4 for controlling communication between a combustion chamber 5 in the cylinder 2 and an inlet duct 6 and an exhaust duct 7, respectively. A piston 8 is connected via a connection rod 9 to a rotatable crankshaft 10 and is configured to move in a reciprocating manner in said first cylinder 2 between a top dead center position (TDC) close to the inlet and exhaust valves 3, 4 (i.e. an upper end position in FIG. 2) and a bottom dead center position (BDC) away from said valves 3, 4 (i.e. a lower end position in FIG. 2).

[0038] Further, the cylinder 2 is provided with a valve actuation arrangement 11a, 11b configured to control opening and closing of the inlet and exhaust valves 3, 4. In this example the valve actuation arrangement 11a, 11b is a fully variable valve actuation arrangement configured to be controllable by electronic means. That is, the engine 1 is in this case a so-called cam-less engine where timing and lifting of the valves is not activated by, nor dependent on, any camshaft but can instead be freely controlled by the fully variable valve actuation arrangement.

[0039] FIG. 2 also indicates that the cylinder 2 is provided with a fuel supply system 12 for supplying fuel, such as diesel, to the first cylinder 2.

[0040] FIG. 3 shows a schematic view of the internal combustion engine 1 according to FIG. 1. In this example the engine 1 is provided with six identical cylinders 2 all being arranged as shown in FIG. 2. In FIG. 3 it has been indicated in dashed lines that the engine 1 may be provided with a turbocharging arrangement 13 comprising a turbocharger compressor 14 and a turbine 15 connected via shaft 16. Also an optional charge air cooler 17 is indicated in FIG. 3.

[0041] A main intake duct 60 guides intake air via the turbocharger compressor 14 and the cooler 17 towards the inlet duct 6 of each of the cylinders 2. Exhaust gas leaving the cylinders 2 via each of the corresponding exhaust ducts 7 is channelled via main exhaust duct 70 to the turbine 15 which drives the compressor 14. Downstream the turbine 15 the main exhaust duct 70 is in this example provided with an adjustable flow restricting member 18 configured to be controlled to restrict a flow of gas through the main exhaust duct 70, and thereby also the flow through each of the individual exhaust ducts 7, so as to allow building up of a backpressure during engine braking. The adjustable flow restricting member 18 may be a butterfly valve.

[0042] FIG. 3 also indicates that the engine 1 comprises a control circuitry 19 configured to control operation of the internal combustion engine 1, including e.g. controlling the fuel supply system 12, the inlet and exhaust valves 3, 4 (by controlling the valve actuation arrangement 11a, 11b) and the adjustable flow restricting member 18, so as to set the engine 1 in an engine braking mode. In line with conventional engines, the control circuitry 19 is configured to control also various other components of the engine 1 and to receive various input signals from sensors of various kinds.

[0043] FIG. 4 shows an example flow chart of a method according to this disclosure:

[0044] Step S00 represents a normal engine operation mode, i.e. the engine 1 is not in a braking mode and the cylinders 2 are operated to combust fuel and generate a torque to the crankshaft 10 via piston 8 and connection rod 9.

[0045] Step S10 represents the entire step of setting the internal combustion engine 1 in the engine braking mode, which step in this example comprises the following sub-steps: [0046] S20—interrupting fuel supply 12 to the first cylinder 2; [0047] S25—reducing the total mass flow rate of gas through the internal combustion engine 1, i.e. through all the six cylinders 2, by controlling the inlet and exhaust valves 3, 4 in a mass flow reduction mode comprising, for at least one of the inlet valve 3 and the exhaust valve 4 of at least one of the cylinders 2, [0048] S25a—reducing a valve lift, and/or [0049] S25b—adjusting a timing of a valve opening or closing so as to reduce the mass flow rate of gas through that cylinder 2 compared to a nominal mass flow rate (which, as explained above, is the mass flow rate that would have been the result without step S25); [0050] S30—restricting the flow of gas through the exhaust duct 7, 70 using the adjustable flow restricting member 18; and [0051] S40—controlling the inlet and exhaust valves 3, 4 in a compression-release mode comprising controlling the valves 3, 4 so as to compress gas in the combustion chamber 5 when the piston 8 moves towards the TDC and release the compressed gas into the exhaust duct 7, 70 when the piston 8 is near the TDC.

[0052] Due to the reduction of mass flow rate achieved by step S25 the pressure pulses and accompanying noise generated in step S40 will be less powerful.

[0053] When engine braking is no longer desired the engine 1 can be re-set in its normal operation mode S00, for instance by pressing down an acceleration pedal of the vehicle.

[0054] As mentioned previously, there are many ways of controlling the valve lift and/or adjusting the timing of the valve opening or closing for the purpose of reducing the mass flow rate in step S25. Generally, a smaller amount of gas/air should be allowed to pass the cylinder than during normal valve lift and valve timing. In one example, only the inlet valve lift is reduced compared to normal operation of the engine. In another example the timing of only the opening of the inlet valve 3 is adjusted so that a smaller amount of gas/air enters the cylinder 2 compared to normal operation. In other examples only the lift or timing of the exhaust valve 4 is reduced or adjusted, respectively. Various combinations are also possible.

[0055] Since the engine 1 is provided with a plurality of cylinders 2, the step S25 may comprise the step of keeping at least one of the inlet and exhaust valves 3, 4 of at least one of the cylinders 2 closed during at least one revolution of the crankshaft. With at least one of the valves closed, no gas/air will pass through that/those particular cylinder(s), which reduces the total mass flow rate through the engine 1. The valve(s) may be kept closed during several revolutions of the crankshaft.

[0056] After some time, perhaps within some seconds, step S25 is interrupted and steps S30 and S40 are initiated (or continued if already started). It should be noted that the steps are not necessarily distinctly separated as indicated in FIG. 4. As an example, step S30 is preferably carried out gradually, i.e. by gradually/stepwise closing the adjustable flow restricting member 18 so as to gradually build up the backpressure in the exhaust duct 7, 70. Step 30 may start while step S25 is performed. Another example is that controlling the inlet and exhaust valves 3, 4 so as to change operation mode from the mass flow reduction mode (S25) to the compression-release mode (S40) also may be carried out in a gradual/stepwise manner which takes some time, and step S30 may be carried out while the change of valve control is carried out. In general it can be said that step S25 is carried out before step S40 and before the maximum backpressure has been built up in step S30.

[0057] The method may comprise the step of: determining, during step S25, whether the mass flow rate through the internal combustion engine 1 has been reduced to a mass flow rate threshold indicative of a sufficient level for the particular application and situation. When the threshold has been reached the change of valve operation mode may start. Alternatively, step S25 may be interrupted after a pre-set time period (i.e. the step of controlling the inlet and exhaust valves 3, 4 so as to change operation mode from the mass flow reduction mode (S25) to the compression-release mode (S40) may start after the pre-set time period).

[0058] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.