WO2002090745A1

WO2002090745A1 - Smoke reducer

Info

Publication number: WO2002090745A1
Application number: PCT/SE2002/000818
Authority: WO
Inventors: Peter Madsen
Original assignee: Scania Cv Ab (Publ)
Priority date: 2001-05-04
Filing date: 2002-04-26
Publication date: 2002-11-14
Also published as: DE10296753B4; SE0101563L; SE516907C2; SE0101563D0; DE10296753T5

Abstract

The invention relates to a waste gas limiter for a combustion engine. The combustion engine incorporates a charge pressure sensor whereby the waste gas limiter is arranged to limit the amount of power medium injected into the engine to a maximum amountof power medium per working cycle which depends on a charge pressure measured by the charge pressure sensor. The waste gas limiter itself incorporates an anticonstriction device designed to signal to the waste gas limiter that substitute charge pressure applies which is greater than the measured charge pressure when the difference between a required amount of power medium per working cycle and an injected amount of power medium per working cycle has during a certain time been greater than a certain amount while the charge pressure measured by the charge pressure sensor has at the same time been below a certain reference pressure. The invention further relates to a method for anticonstriction control, a computer program intended to execute steps to anticonstriction control, and a storage medium on which such a computer program is recorded.

Description

Smoke reducer

FIELD OF THE INVENTION, AND STATE OF THE ART

The present invention relates to a waste gas limiter according to the preamble to claim 1. The invention also relates to a method for anticonstriction control according to the preamble to claim 6. The invention further relates to a computer program according to the preamble to claim 11 and a medium for data storage according to the preamble to claim 12.

A known practice is to use waste gas limiters in connection with injection systems for combustion engines. Waste gas limiters set an upper limit to the amount of power medium injectable into the combustion engine per working cycle. This limit is set on the basis of a charge pressure which occurs in the engine and which is measured by a charge pressure sensor. The purpose is to ensure that there is sufficient oxygen for effective combustion of said power medium while at the same time limiting the occurrence of waste gases which have not undergone complete combustion. The result is not only a visual advantage in minimising the risk of smoke emission from the vehicle but also the environmental advantage of lower carbon monoxide content in the exhaust gases.

It sometimes happens that the charge pressure sensor is obstructed by dirt with the result that it indicates a lower charge pressure than the actual charge pressure. Holing of, for example, inlet pipes of the injection system may also lower the charge pressure. In such cases the waste gas limiter imposes an incorrect limit on the maximum permissible amount of power medium, resulting in the engine power becoming very low. This means that the engine cannot be used until the problem has been remedied. If the engine is in, for example, a vehicle, the vehicle therefore cannot be driven and it may be difficult to move the vehicle to a workshop. It may also be difficult to detect that the fault is due to, for example, obstruction of the charge pressure sensor. SUMMARY OF THE INVENTION

The object of the present invention is to provide an anticonstriction control of the waste gas limiter so that the aforesaid problems whereby charge pressure sensor obstruction or inlet pipe holing makes the engine stick in a neutral position with persistently low engine power due to an incorrect or correct measured low charge pressure.

This object is achieved with the waste gas limiter indicated in the introduction which is characterised by incorporating an anticonstriction device designed to signal to the waste gas limiter the occurrence of a substitute charge pressure which is higher than the measured charge pressure, when the difference between a required amount of power medium per working cycle and an injected amount of power medium per working cycle has during a certain time been greater than a certain amount while the charge pressure measured by the charge pressure sensor has at the same time been below a certain reference pressure. The waste gas arrangement assuming that a higher charge pressure applies results in the waste gas limiter allowing an increase in the amount of power medium per working cycle. This increases the power developed by the engine at which the engine will operate.

According to a preferred embodiment, the anticonstriction device is designed to signal to the waste gas limiter that a specified substitute charge pressure applies. If the problem is an obstructed charge pressure sensor, there is likely to be a sufficiently high charge pressure in the engine, whereas if the air intake is holed the charge pressure will be low. In the former case the substitute charge pressure may be set relatively high without causing problems, but in the latter case the substitute charge pressure needs to be kept moderate to avoid injecting too much power medium to be able to achieve full combustion, resulting in black smoke. Delivering a specified charge pressure makes it possible to deliver a substitute charge pressure appropriate to both of these situations.

According to a further preferred embodiment, the reference pressure is adjusted to the prevailing atmospheric pressure. This means that said device will operate in the same way irrespective of the vehicle's height above sea level and irrespective of prevailing weather conditions. According to another preferred embodiment of the invention, the waste gas limiter incorporates a means of tracing faults pertaining to the charge pressure sensor or to the air intake of the injection system, this means being designed to generate a fault signal when a charge pressure measured with respect to a working cycle is substantially lower than a verificatory charge pressure calculated for the working cycle by the fault tracing means on the basis of a calculation model which includes the engine speed and an amount of power medium injected into the engine. Defectiveness of the charge pressure sensor or of air inlet pipes is thus detected significantly more easily than without the aforesaid fault tracing means. Nerification of the condition of the charge pressure sensor and the air intake is possible in principle at each working cycle, which means that the method may be regarded as a continuous method.

According to a further embodiment of the invention, said calculation model for calculating a verificatory charge pressure includes a relationship with at least one of the following: engine temperature, crankshaft angular position relative to a reference angle at the beginning of power medium injection, and time filtration of the verificatory charge pressure. A calculation model including the above refinements provides a more reliable estimate of the charge pressure. The time filter incorporates a first-order time filter which is estimated from simulations of an engine or from experiments with a real engine with regard to step response to power mobilisation changes. There is thus no risk of the fault tracing means producing incorrect results due to time factors.

The object is also achieved with the method indicated in the introduction, which is characterised by: measurement of a difference between a desired amount of power medium and an injected amount of power medium, measurement of a charge pressure, and signalling to the waste gas limiter that the charge pressure has been replaced by a substitute charge pressure which is greater than said measured charge pressure, when the magnitude of said difference has during a certain time exceeded a certain level while the measured charge pressure has at the same time been below a certain reference charge pressure. Signalling to the waste gas arrangement to assume that a higher charge pressure applies results in the waste gas limiter allowing an increase in the amount of power medium per working cycle. This increases the power developed by the engine at which the engine will operate.

The object is further achieved by means of the computer program indicated in the introduction, which is characterised by incorporating software for implementing the method according to the immediately foregoing text.

The object is also achieved by means of the storage medium indicated in the introduction, which has recorded on it a computer program characterised by incorporating software for implementing the method according to the immediately foregoing text.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be explained in more detail on the basis of various embodiments taken as examples with reference to the attached drawings.

Fig. 1 depicts schematically a configuration of part of an engine incorporating a waste gas limiter with an anticonstriction device according to the invention,

Fig. 2 depicts schematically a flowchart of a dynamic calculation model of a verificatory charge pressure, and

Fig. 3 depicts schematically a flowchart of the method according to the invention.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

Fig. 1 depicts part of a combustion engine which comprises a cylinder 1 in which a piston 2 is designed to move in a vertical direction along the cylinder 1. The piston 2 is connected to a crankshaft 3 by a connecting rod 4. The engine further comprises a cylinder head 5. The cylinder head 5 has connected to it an injection system 6 which comprises not only an air intake 7 designed to convey air to the cylinder head 5 but also a power medium intake 8 designed to convey power medium to the cylinder head 5. The injection system 6 further comprises a charge pressure setting means 9 which is associated with the air intake 7 and which sets a charge pressure in the cylinder head 5. According to previously known and non-limitative standard versions, the charge pressure setting means 9 comprises either a compressor, which is normally connected to the crankshaft 3, or a fan which is driven by the engine's exhaust gases (so-called turbo). The injection system 6 also comprises a power medium dispensing means 10 which is associated with the power medium intake 8 and which is designed to deliver to the cylinder head 5 an amount of power medium which depends on a signal corresponding to the amount of power medium demanded via an accelerator pedal 11 operable by driver.

The cylinder head 5 incorporates a charge pressure sensor 12 arranged to measure the charge pressure prevailing in the cylinder head 5. The engine incorporates a waste gas limiter 13 which limits the amount of power medium delivered by the power medium dispensing means 10 to a maximum amount of power medium per working cycle on the basis of the measured charge pressure. This means that there will always be sufficient oxygen in the cylinder head 5 to effect good combustion of the power medium and thereby reduce the occurrence of exhaust smoke, carbon monoxide and other organic residual products.

To prevent a situation in which a faulty charge pressure sensor or a faulty air intake causes a neutral position such as described previously, the waste gas limiter incorporates an anticonstriction device 14 (here depicted outside the waste gas limiter 13 for the sake of clarity) which is connected to said accelerator pedal 11 and said charge pressure sensor 12. When the amount of power medium demanded by the driver via the accelerator pedal 11 has for a specified time exceeded by a specified amount the amount of power medium injected into the cylinder head 5 by the power medium dispensing means 10, the anticonstriction device 14 signals to the waste gas limiter 13 that a substitute charge pressure applies which is greater than the measured charge pressure, provided that the measured charge pressure is below a specified reference charge pressure P_ref. The waste gas limiter 13 then allows injection of a larger amount of power medium, with the result that the power developed by the engine increases and the engine is not at said neutral position. The aforesaid specified time, the aforesaid specified amount of power medium and the aforesaid reference pressure may be selected both in relation and not in relation to other external and internal parameters without thereby in any way limiting the invention.

In an advantageous version of the invention, the anticonstriction device 14 signals to the waste gas limiter 13 that a specified substitute charge pressure applies. The specified charge pressure may incorporate a relationship with external parameters such as atmospheric pressure P_atm, engine temperature Tw, engine speed n, etc. The specified charge pressure may also assume the same value each time the invention is employed, irrespective of external circumstances. The invention is not limited to either of the two above examples.

In a further advantageous version of the invention, said reference pressure is adjusted in keeping with the prevailing atmospheric pressure. Such adjustment may for example entail reducing the reference pressure in keeping with the prevailing atmospheric pressure. This enables the invention to function alike at different external atmospheric pressures, in different weather conditions or at different heights above sea level.

According to another advantageous version of the invention, the waste gas limiter 13 incorporates a fault tracing means 15 for tracing faults of the charge pressure sensor 9 and the air intake 7. The fault tracing means 15 is designed to generate a fault signal when a charge pressure measured by the charge pressure sensor 9 with respect to a working cycle is substantially lower than a verificatory charge pressure calculated by the fault tracing means 15 for the working cycle according to a calculation model which includes the engine speed and the amount of power medium injected into the engine for the working cycle by the power medium dispensing means 10.

Comparing a theoretically calculated verificatory charge pressure P_m with the charge pressure Pb measured by the charge pressure sensor makes it possible to assess the condition of the charge pressure sensor 9 and the air intake 7 on the basis of the degree of agreement between the two charge pressures. The fault tracing means may be designed to deliver fault signals either to the anticonstriction device 14 or to the waste gas limiter 13 or to some other means, e.g. a display in the driver's cab, without limiting the invention. The fault tracing device may of course be designed to deliver fault signals to more than one of said alternatives and even to alternatives not mentioned here.

Fig. 2 shows the calculation steps performed by one of the versions of the fault tracing means 15 in Fig. 1 when calculating a verificatory charge pressure. According to this embodiment, the calculation model also includes a relationship with engine temperature w, crankshaft angle α with respect to a reference angle at the beginning of the power medium injection, and a time filter τ. The fault tracing means 15 calculates the power E developed in the engine as a product of the engine speed n and the amount qb of power medium injected into the engine, less the amount q₀ of offset power medium at step 20 for power calculation. The power E thus arrived at is modified in a first modifying step 21 to a first modified power Ei on the basis of a vector [α] incorporating the crankshaft angle α with respect to a reference angle at the beginning of the power medium injection. In one embodiment, the power is further modified in a second modifying step 22 to a second modified power E₂ on the basis of a vector T incorporating the engine's working temperature. For example, the temperature of the engine may be estimated from the temperature of the cooling water. In a further embodiment, the power arrived at in the first-order time filter 23 is filtered to a third modified power E₃. The time filter 23 may be created, for example, by studying the change in operating point in either a simulated or a real engine. The time filter 23 takes into account the relationship between the charge pressure and time whereby, for example, the charge pressure increases at the earliest one working cycle after a working cycle in which there is a power medium increase. The final calculation step 24 then converts the power thus arrived at to a verificatory charge pressure P_m.

A fault signal may also result in a substitute charge pressure being delivered to the waste gas limiter 13 if there is risk of said neutral position because, for example, the charge pressure sensor

12 incorrectly provides too low a charge pressure measurement resulting in the waste gas limiter 13 limiting the amount of power medium. The fault tracing means 15 may then with advantage give a signal to the waste gas limiter 13 to assume that the specified substitute charge pressure applies and not the charge pressure measured by the charge pressure sensor 9. Said neutral position is thus avoided and the engine will continue to be usable, albeit with less power. The aforesaid fault tracing procedure may be repeated continuously at each working cycle of the engine. Faults can thus be detected significantly more quickly than without the fault tracing means 15. In one embodiment, the anticonstriction means 14 also generates a fault signal when a substitute charge pressure is signalled to the waste gas limiter 13.

With a view to summarising the proposed solution, the general method according to the invention will now be illustrated with respect to the flowchart in Fig. 3. A first step 31 measures the difference between an amount q_<j of drive medium demanded by driver and an amount q of medium injected into the engine. A second step 32 measures the charge pressure P in the cylinder head 5 by means of a charge pressure sensor 12. A third step 33 adjusts the measured charge pressure Pb with respect to the prevailing atmospheric pressure P_atm by subtraction to an adjusted charge pressure Pp. A fourth step 34 compares the adjusted charge pressure P_D with a reference charge pressure P_ref, and delivery of a substitute charge pressure to the waste gas limiter may be allowed in cases where the adjusted charge pressure is below the reference charge pressure. Step 33 and step 34 may also be executed by adjusting the reference pressure instead of the measured charge pressure, leading to the same result. A fifth step 35 calculates a verificatory charge pressure P_m, e.g. on the basis of the dynamic model described in connection with Fig. 2. A sixth step 36 compares the calculated verificatory charge pressure P_m with the charge pressure Pb measured at step 32, and step 36 gives a fault signal if the two said charge pressures differ by more than a certain value during more than a certain time. A seventh step 37 delivers a specified substitute charge pressure P_<j_ef to the waste gas limiter 13 if the difference at step 31 exceeds a certain value during a certain time while the measured charge pressure is at the same time below the reference charge pressure at step 34, or if a fault signal is received from step 36 and the measured charge pressure is below the reference pressure at step 34. If none of these conditions are fulfilled, step 37 does not deliver any substitute charge pressure Pd_f to the waste gas limiter 13.

All the process steps described with reference to Fig. 3 above may be controlled by a computer program which can be loaded directly into the internal memory of a computer and incorporates suitable software for controlling the necessary steps when the programme is run on the computer. The same applies to any desired subsequence of process steps. The computer program may of course be saved on any desired storage medium.

Claims

Patent claims

1. A waste gas limiter for a combustion engine, said combustion engine incorporating a charge pressure sensor, whereby the waste gas limiter is arranged to limit the amount of power medium injected into the engine to a maximum amount of power medium per working cycle on the basis of a charge pressure measured by the charge pressure sensor, characterised in that the waste gas limiter incorporates an anticonstriction device designed to signal to the waste gas limiter that a substitute charge pressure applies which is higher than the measured charge pressure when the difference between a required quantity of power medium per working cycle and an amount of power medium injected per working cycle has during a certain time been greater than a certain amount while the charge pressure measured by the charge pressure sensor has at the same time been below a certain reference pressure.

2. A waste gas limiter according to claim 1, characterised in that said anticonstriction device is designed to signal to the waste gas limiter that a specified substitute charge pressure applies.

3. A waste gas limiter according to claim 2, characterised in that said reference pressure is adjusted in keeping with the prevailing atmospheric pressure.

4. A waste gas limiter according to any one of claims 1 - 3, characterised in that the engine incorporates an injection system comprising an air intake and that the waste gas limiter incorporates a means for tracing faults of the charge pressure sensor and the air intake, which means is designed to generate a fault signal when the charge pressure measured with respect to a working cycle differs substantially from a verificatory charge pressure calculated by the fault tracing means for the working cycle according to a calculation model based on the engine's speed and an amount of power medium injected into the engine.

5. A waste gas limiter according to claim 4, characterised in that said calculation model depends on at least one of the following: a measured engine temperature, the crankshaft's angular position relative to a reference angle at the beginning of the power medium injection, and a time filtration of the verificatory charge pressure.

6. A method for anticonstriction control of a waste gas limiter for a combustion engine which incorporates a charge pressure sensor, characterised by measurement of the difference between a required amount of power medium and an injected amount of power medium, measurement of a charge pressure, and signalling to the waste gas limiter that a substitute charge pressure applies which is greater than said charge pressure, when the magnitude of said difference has during a certain time exceeded a certain level while the measured charge pressure has at the same time been below a certain reference charge pressure.

7. A method according to claim 6, characterised by signalling of a specified substitute charge pressure.

8. A method according to any one of claims 6 - 8 characterised in that said reference pressure is adjusted in keeping with the prevailing atmospheric pressure.

9. A method according to any one of claims 6 - 8, characterised by calculation of a verificatory charge pressure according to a calculation model based on the engine's speed and the amount of power medium injected per working cycle, comparison between verificatory charge pressure and measured charge pressure, and generating of a fault message when the measured charge pressure differs substantially from a verificatory charge pressure during a certain time.

10. A method according to claim 9, characterised in that the calculation model depends on at least one of the following: the engine's temperature, the crankshaft's angular position relative to a reference angle at the beginning of the power medium injection, and a filtration of the verificatory charge pressure in a time filter.

11. A computer program capable of being loaded directly into the internal memory of a computer, characterised in that the computer program incorporates software for executing steps in any one of claims 6 - 10.

12. A medium for data storage, which has a program recorded on it, characterised in that the program incorporates software for executing steps in any one of claims 6 - 10.