METHOD FOR CONTROLLING AIR FLOW TO AN ENGINE

Abstract: Methods for controlling intake air flow to an internal combustion engine comprising an output shaft driven by the internal combustion engine, an intake air pipe, an exhaust gas pipe, a compressor located in said intake air pipe, a turbine located in said exhaust gas pipe, a transmission system connecting turbine, compressore, and output shaft for energy transfer between turbine and compressor, between turbine and output shaft, and between output shaft and compressor, wherein said transmission system comprises a variable transmission between output shaft and compressor, and a control means for controlling the gear ratio in the variable transmission.

Description: Title Method for controlling air flow to an engine. Technical field The present invention relates to a method for controlling the intake air flow to an internal combustion engine in accordance with the preamble of claim 1, 7 and 8, and to a control circuit for implementing the control method according to claim 9. Particularly, the invention relates to a method for controlling the intake air flow to an internal combustion engine of so-called supercompound-type, where the internal combustion engine comprises an output shaft driven by the internal combustion engine, an intake air pipe, an exhaust gas pipe, a compressor located in said intake air pipe, a turbine located in said exhaust gas pipe, a transmission system connecting turbine, compressor and output shaft for energy transfer between turbine and compressor, between turbine and output shaft, and between output shaft and compressor, wherein said transmission system comprises a variable transmission between at least two of compressor, turbine and output shaft, and a control means for controlling the gear ratio in the variable transmission. Background of the invention When using internal combustion engines, it is of interest to ensure that as much as possible of the energy produced by the combustion can be utilised for the intended purpose. This has resulted in the manufacture of turbocharged engines in which energy from the exhaust gases is utilised for compressing the air on the inlet side of the engine, whereby the energy conversion of the engine can be increased. So-called turbocompound-engines are a further development in which the exhaust gas energy can be returned to the output shaft of the engine, whereby energy can be recovered from the exhaust gases. A further development of these two above-mentioned concepts is a so-called supercompound-engine in which energy from the exhaust gases can be returned to the output shaft, and can be utilised for operating a compressor located on the inlet side of the engine. By means of the connection between shaft, compressor and turbine, energy also can be transferred from output shaft to compressor in order to obtain a faster response of the turbochargmg pressure increase on the inlet side of the engine than when only a turbocharger is utilised. Internal combustion engines of supercompound-type are previously known. Such an internal combustion engine comprises an output shaft driven by the internal combustion engine, an intake air pipe, an exhaust gas pipe, a compressor located in said intake air pipe, a turbine located in said exhaust gas pipe, a transmission system connecting turbine, compressor, and output shaft for energy transfer between turbine and compressor, between turbine and output shaft, and between output shaft and compressor, wherein said transmission system comprises a variable transmission between output shaft and compressor, and a control means for controlling the gear ratio in the variable transmission. Furthermore, in connection with compressor-charged engines, it is known to regulate the charging pressure by means of comparing measured pressure on the inlet side of the intemal combustion engine with desired charging pressure calculated from given vehicle data, such as for example desired acceleration, engine speed, etc. In these cases, the control algorithms include known control algorithms such as P (proportional), PI (proportional and integrating), PID (proportional, integrating and derivative), and LQ. It has been found that the control algorithms which are utilised in supercharged systems are unreliable when they are utilised for controlling the flow of inlet air to internal combustion engines of supercompound-type. This results in the control system becoming slow and unstable, wherein undesired pressure fluctuations will occur on the inlet side of the internal combustion engine. As a result of these undesired pressure fluctuations, problems with controlling the air/fuel-mixture to achieve the correct proportions will also arise, something which is of importance, amongst other things, in order to reduce nitrogen oxide emissions from internal combustion engines of diesel-type. Summary of the invention A first object of the present invention is to provide a method for controlling the flow of intake air to an internal combustion engine of supercompound-type, wherein the control method enables a fast and stable control process in which the occurrence of undesired pressure fluctuations is reduced. This object is achieved by means of a method for controlling the intake air flow to an internal combustion engine of supercompound-type in accordance with the characterising portion of claim 1, 7 or 8. By means of creating a control signal in the control method for controlling a variable transmission between at least two of output shaft, turbine, and compressor, partly from a signal based on the difference between desired and actual value of a condition variable in the intake air pipe, and partly from a signal based on the rotational speed of compressor and/or turbine, a control system is obtained where changes in the considerable rotational energy stored in turbine and/or compressor is taken into consideration, which implies that the control method reduces the risk that undesired fluctuations of the intake air flow are generated. A second object of the invention is to provide a control circuit for implementing the control method. Brief description of the drawings In the following, the invention will be described in greater detail with reference to attached drawings, in which Fig. 1 shows an overview of an internal combustion engine of supercompound type, Fig. 2 is a schematic representation of a control system according to the invention, Fig. 3 shows an embodiment of torque compensation in accordance with the control system shown in Fig 2, and Fig.4 is a symbolic representation of energy transfer in a supercompound- system. Detailed description of preferred embodiments Figure 1 shows a six-cylinder diesel motor 1 having a turbocompressor, generally denoted with 2, which has a turbine element 3 and a compressor element 4. The turbocompressor 2 is rigidly supported by a bracket 6, secured by screws to the engine block, and has its exhaust gas inlet in the turbine element 3 connected to an exhaust manifold 8 included in the exhaust gas pipe 18 via a flexible connection 8, e.g. a bellows system, which allows a certain displacement of the outlet of the exhaust manifold 8 in relation to the inlet of the turbine element caused by thermal expansion. The compressor element 4 is connected to the inlet air pipe 17 of the engine in a conventional way, not illustrated in any greater detail, e.g. via an intermediate induction air cooler. The engine 1 can be equipped with a compression braking device 10, schematically indicated, which can be of the type disclosed and described in SE 466 320, and by means of which the cylinders of the engine can be connected to the exhaust gas manifold of the engine in the later portion of the compression stroke in order to increase the motor-brake power. Accordingly, for a closer description of the design and function, reference is made to SE 466 320. In one embodiment of the invention, a transmission system connecting turbine, compressor, and output shaft 7 for energy transfer between turbine and compressor, between turbine and output shaft, and between output shaft and compressor, which transmission system comprises a variable transmission between at least two of output shaft, turbine, and compressor, and a control means for controlling the variable transmission, is designed as follows. The rotor shaft 11 of the turbocompressor 2 is connected to the crankshaft 7 (not shown) of the engine via a high-speed driving gear 12, a transmission 13, preferably with a infinitely variable speed (so-called CNT), and a low-speed driving gear 14. A freewheel mechanism (not shown), by means of which the driving connection between the rotor shaft 11 and the crankshaft can be disconnected, may be included in the chain of components from the rotor shaft 11 to the crankshaft. In the highspeed driving gear 12, a first reduction of rotational speed is obtained from the working rotational speed of the turbocharger, about 100 000 rpm, down to the working rotational speed of the CNT-transmission 13, about 10 000 rpm. In the low- speed driving gear 14, the rotational speed is reduced further down to the working rotational speed of the crankshaft, which is about 2000 rpm. In alternative embodiments, a variable transmission can be connected between compressor and turbine, wherein the output shaft can be connected to compressor or turbine either via a variable transmission or a fixed transmission. In a preferred embodiment, the variable transmission is constituted of an indefinitely variable mechanical transmission. However, it is also conceivable that the transmission comprises power transmission via a controlled electric motor or hydrodynamic couplings. By means of fixing the turbocharger 2 to the engine block in the above-described way, the risk of a change in the alignment between the shafts of the turbocharger and the driving gear 12 is ehminated, something which otherwise could become the consequence of differences in the thermal expansion between the exhaust manifold and the engine block in case the turbocharger would be rigidly suspended from the exhaust manifold in a conventional way. A control unit 15, which preferably is a microprocessor, provides output signals for engagement or disengagement of the coupling (not shown), which engages the drive of the turbocharger 2 from the engine crankshaft, and which can be incorporated in the CNT-transmission 13. Furthermore, the control unit 15 provides a signal 19a for setting the gear ratio of the transmission 13, depending on a number of engine and vehicle data, via input channels 19b from a number of gauges which are known per se and not shown in any greater detail. Figure 2 shows a diagram for a control system 20 which is intended to generate desired charging pressure to the inlet side of the internal combustion engine 1. The desired charging pressure is determined in a conventional way from given engine data. In the present embodiment, the desired charging pressure is generated as follows. Three functional blocks are arranged in the control computer 15 of the engine: a first functional block 22 for controlling air and fuel-mixture; a second functional block 23 for controlling motor-brake function; and a third functional block 24 for limiting the rotational speed of the compressor. Input data to the first functional block 22 for controlling air and fuel-mixture includes a first signal 25 representing requested fuel quantity and a second signal 26 representing measured or calculated engine speed. The first signal 25 representing requested fuel quantity is created in a known way from, amongst other things, input data from a foot throttle (not shown). The second signal 26 representing measured or calculated engine speed is created in a known way, for example by means of a transmitter which emits a signal from a tooth wheel mounted in connection with the crankshaft or camshaft, wherein a pulsed signal having a frequency which constitutes a measure of the rotational speed of the engine is created. Input data to the second functional block 23 for controlling the engine- brake function includes the first signal 25 representing requested fuel quantity and the second signal 26 representing measured or calculated engine speed, but of course also input data from an engine-brake actuator (not shown), by means of which the requested engine-brake effect is controlled. Input data to the third functional block 24 for limiting the rotational speed of the compressor is constituted by the second signal 26 representing the engine speed and a third signal 27 representing the rotational speed of the turbine located in the exhaust gas pipe of the internal combustion engine. The third signal is created in a known way by means of measuring a reduced rotational speed of a shaft connected to the turbine shaft by means of a variable transmission Or, alternatively, by means of estimating the rotational speed from given or calculated data relating to pressure conditions upstream and downstream the turbine. Thereafter, the output signals from the above-mentioned functional blocks are filtered in a filter where the output signal from the first functional block 22 for controlling air and fuel mixture is restricted by the output signals from the second functional block 23 for controlling engine-brake function, and the third functional block 24 for limiting the rotational speed of the compressor. The reason for this is that the desired torque is restricted, taking overspeeding of the compressor into consideration and in case an input signal indicating presence of engine-braking has been emitted. When this first filtration has taken place, the signal is transformed via a- map-based filter 28 into a fourth signal for setting the desired charging pressure. The fourth signal relating to the desired charging pressure is fed into a Pl-regulator 30 together with a signal 37 representing measured charging pressure of the controlled system 38 for controlling the gear ratio between output shaft and compressor, wherein the compressor achieves intended rotational speed for generating a desired inlet air flow as a function of the first control signal 32 and the second control signal 36. The charging pressure is measured in a known way by means of a probe mounted downstream the compressor located in the inlet of the internal combustion engine. Thereafter, the Pi-regulator generates a first control signal 32 calculated from the difference between desired and actual charging pressure. This signal is compensated in a compensating circuit 33 which receives an output signal from a fourth functional block 34 for calculating torque compensation of the turbine and compressor system. The task of this functional block is to calculate or estimate the influence on the flow in the exhaust gas pipe and inlet pipe of the internal combustion engine which is created by the rotational energy and demands for torque supplied to the turbine and compressor system for changing said rotational energy. This means that the fourth functional block estimates the response required in order to achieve a requested change of rotational speed of the compressor and turbine system. Input data to the fourth functional block 34 for calculating torque compensation of the turbine and compressor system includes the first signal 25 representing requested fuel quantity, the second signal 26 representing the engine speed, and a tiiird signal 27 representing the rotational speed of the turbine located in the exhaust gas pipe of the internal combustion engine. From the fourth functional block, a second control signal is emitted which, accordingly, is based on actual rotational speed of turbine and/or compressor. In one embodiment of the invention, the first control signal corresponds to the torque which is to be applied onto the compressor starting from a feed-back signal based on a condition variable in the intake air pipe. This condition variable is preferably constituted by the pressure. In this embodiment, the second control signal corresponds to the disturbing torque which is caused by compressor, turbine, and variable transmission. In this case, these two signals are added in order to create a third control signal corresponding to torque applied onto the compressor. In a more advanced embodiment of the invention, the function when creating the third control signal further comprises parameter selection between charging pressure, energy recovery from exhaust gas flow, and emission values, and wherein different priorities between these parameters can be accomplished in different operation conditions. This means that the engine can be controlled towards more optimal values for torque generation, energy recovery, or emission values, depending on the requirements of a specific operation condition. In the compensating circuit 33, a third control signal 36 for controlhng the gear ratio between output shaft and compressor is created, wherein the compressor achieves the intended rotational speed for generating a desired intake air flow as a function of the first control signal 32 and the second control signal 36. Figure 3 shows a control system for feed forward control of the second control signal 35. The second control signal 35 is based on actual rotational speed of turbine and/or compressor. This control system corresponds to the fourth functional block 34 in Fig. 2. Input data to this control system include the first signal 25 representing requested fuel quantity, the second signal 26 representing the engine speed, and the third signal 27 representing the rotational speed of the turbine located in the exhaust gas pipe of the internal combustion engine. The fourth functional block 34 comprises two, preferably map-based, control circuits. A map-based control circuit is constituted by a control circuit which is known per se in which output data is created from a parameter volume of input data by means of a function defined by mappings between input and output data which are preferably based on experience. The two map-based control circuits are constituted by a first control circuit 40 for calculating driving torque of turbine and compressor system, and a second control circuit 41 for calculating how a variable transmission included in the turbine and compressor system influences the driving torque of turbine and compressor system. The control signal 35 calculated by the control circuit 34 compensates for the static torque on the turbine and compressor system which arises in a given operation point when engine speed, turbine speed, compressor speed, charging pressure, and fuel flow are concerned, in case the turbine torque does not correspond exactly to the compressor torque. By means of compensating for this lack of match between turbine and compressor, in an ideal condition it is achieved that the control signal 32 only has to supply the torque required in order to change the actual rotational condition to the desired one. Input data to the first control circuit 40 includes the first signal 25 representing requested fuel quantity, the second signal 26 representing the engine speed, and the third signal 27 representing the rotational speed of the turbine located in the exhaust gas pipe of the internal combustion engine. Input data to the second control circuit 41 includes the second signal 26 representing the engine speed, and the third signal 27 representing the rotational speed of the turbine located in the exhaust gas pipe of the internal combustion engine. From this input data, the condition of the variable transmission included in the turbine and compressor system is determined. Thereafter, a first output signal 42, representing the influence of the turbine and the compressor on torque transferred via the variable transmission, is created via the first map-based control circuit 40, and in the second map-based control circuit 41, a second output signal 43 representing the influence of the variable transmission on torque transferred via it is created. From these two output signals, the above-mentioned second control signal 35 is created in a third control circuit 44. Figure 4 is a schematic representation of an energy transfer system in a supercompound engine. The system comprises a turbine 50, a compressor 51, and an output shaft 52 from the engine. These components are connected via a transmission 53 which comprises a controlled variable unit 54. hr ■ this case, the variable transmission is arranged between output shaft 52 and turbine and compressor which are located on a common shaft 55. In order to maintain torque, it is required that p + M + MD = 0, where r constitutes torque transferred from the output shaft of the engine, ML constitutes torque delivered from turbine, and M D constitutes driving torque on the compressor. ML and M D are determined from input data relating to rotational speed of turbine and compressor, fuel supply, and engine speed. This is done in a way which is well known to the skilled person, for example by means of mapping speed to torque, wherein said mapping function has been obtained by means of calculations and testing in a known way. The invention is not limited to the above-described embodiments, but can be varied within the scope of the following claims.

Claims: Claims 1. A method for controlling intake air flow to an internal combustion engine comprising an output shaft (7) driven by the internal combustion engine, an intake air pipe (17), an exhaust gas pipe (18), a compressor (4) located in said intake air pipe, a turbine (3) located in said exhaust gas pipe, a transmission system (13, 53) connecting turbine, compressor, and output shaft for energy transfer between turbine and compressor, between turbine and output shaft, and between output shaft and compressor, where said transmission system comprises a variable transmission between at least two of said output shaft, turbine and compressor, and a control means for controlhng the variable transmission, and wherein said method comprises the following steps: - creating a first control signal as a function of the difference between actual and desired value of a condition variable in the intake air pipe; - creating a second control signal from actual rotational speed of compressor and/or turbine; and - creating a third control signal for controlling said variable transmission as a function of the first and the second control signal. 2. A control method according to claim 1, characterised in that said transmission system comprises a mechanical gearbox having a variable gear ratio. 3. A control method according to claim 2, characterised in that said transmission system comprises a mechanical gearbox having an infinitely variable gear ratio. 4. A control method according to any one of the preceding claims, characterised in that said transmission system comprises a variable transmission between the output shaft and the turbine. 5. A control method according to any one of the preceding claims, c h a r a c t e r i s e d i n that the first control signal corresponds to torque requested to be applied on said variable transmission, calculated from the difference between actual and desired value of the pressure condition in the intake air pipe, and that the second control signal corresponds to the disturbing torque from compressor and/or turbine calculated from actual rotational speed of compressor and/or turbine. 6. A control method according to any one of the preceding claims, c h a r a c t e r i s e d i n that the function when creating the third control signal further comprises parameter selection between charging pressure, energy recovery from exhaust gas flow, and emission values, and wherein different priorities between these parameters can be achieved in different operation conditions. 7. A method for controlling intake air flow to an internal combustion engine comprising an output shaft (7) driven by the internal combustion engine, an intake air pipe (17), an exhaust gas pipe (18), a compressor (4) located in said intake air pipe, a turbine (3) located in said exhaust gas pipe, a transmission system (13, 53) connecting turbine, compressor, and output shaft for energy transfer between turbine and compressor, between turbine and output shaft, and between output shaft and compressor, where said transmission system comprises a variable transmission between output shaft and compressor, and a control means for controlling the gear ratio in the variable transmission, wherein said method comprises the following steps: - determining desired charging pressure from given vehicle data; - measuring actual charging pressure; - calculating a first control signal from the difference between actual and desired charging pressure, c h ar a c t e r i s e d i n that a second control signal, which is based on actual rotational speed of compressor and/or turbine, is calculated, and that a third control signal, for controlling the gear ratio between output shaft and compressor whereby the compressor achieves intended rotational speed for generating a desired intake air flow, is created as a function of the first control signal and the second control signal. 8. A control method for a supercompound-engine, comprising generating a control signal to a variable transmission included in the supercompound-engine, wherein said control signal constitutes a function of a first control signal generated by means of feed-back coupling of a condition variable in an intake air pipe arranged at the supercompound-engine, and a second control signal generated by means of feed forward coupling of actual rotational speed of turbine and/or compressor arranged at the supercompound-engine. 9. A control circuit for implementing a control method according to any one of the preceding claims.

Inventors: ANDERSSON MATS, BERGLUND SIXTEN, ANDERSSON, MATS, BERGLUND, SIXTEN
Applicants: ANDERSSON MATS, BERGLUND SIXTEN, VOLVO LASTVAGNAR AB, ANDERSSON, MATS, BERGLUND, SIXTEN
Application year: 2001
Main classification: F02B37
IPC codes: F02B37, F02B39, F02D41