WO2007133157A1

WO2007133157A1 - Arrangement and method for a combustion engine and a turbo unit

Info

Publication number: WO2007133157A1
Application number: PCT/SE2007/050268
Authority: WO
Inventors: Ove Spónton
Original assignee: Scania Cv Ab
Priority date: 2006-05-12
Filing date: 2007-04-25
Publication date: 2007-11-22
Also published as: DE112007001160T5; BRPI0711434A2; BRPI0711434B1; SE0601069L; SE529874C2

Abstract

The present invention relates to an arrangement and a method for a combustion engine (2) and the turbo unit (5, 6) which is capable of being activated with a variety of load values (PT). The arrangement comprises a control unit (12) which is adapted to receiving information about the load (PT) on the turbo unit (5, 6), to determining various partial damage values (SL, SM, SH) which are deemed to occur on the turbo unit (5, 6) at different loads (PT) on the turbo unit (5, 6), and to adding the estimated partial damage values (SL, SM, SH) to a cumulative partial damage Sn which provides an estimate of the amount of the turbo unit's service life which has been used up.

Description

Arrangement and method for a combustion engine and a turbo unit

BACKGROUND TO THE INVENTION, AND STATE OF THE ART

The present invention relates to an arrangement and a method for a combustion engine and a turbo unit according to the preambles of claims 1 and 7.

Turbo units are increasingly being used in vehicles to provide increased performance of combustion engines. Almost all diesel engines for heavy vehicles are now equipped with a turbo unit. However, a turbo unit is a relatively expensive component to replace or repair. It is therefore advantageous that the service life of a turbo unit be as long as that of the whole vehicle. The service life of a turbo unit depends greatly on the load to which it is subject during operation. The service life of a turbo unit subject to heavy load during operation is usually considerably shorter than that of a corresponding turbo unit subject to a smaller load.

One way of lengthening the service life of a turbo unit is for the turbo unit as a whole or particular selected components of it to be given a more robust configuration or be made of stronger materials. A consequent disadvantage is that such turbo units are more expensive to manufacture. Another way of lengthening service life is to reduce the capacity of the turbo unit. The turbo unit's service life can thus be lengthened, particularly in cases where the turbo unit is subject to very heavy loading which substantially shortens its service life. In certain traffic situations, however, it is desirable to have available the engine power which the turbo unit produces at maximum load. There are also a relatively small number of drivers who load turbo units so much that their service life is shorter than expected. Against this background, providing all turbo units with reduced capacity is likewise not an optimum solution.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an arrangement and a method which make it possible for a turbo unit to achieve an expected service life substantially irrespective of who drives the vehicle.

The object indicated above is made possible with the arrangement of the kind mentioned in the introduction which is characterised by the features indicated in the characterising part of claim 1. It is possible, e.g. by sampling and statistical calculations, to determine with relatively good accuracy the extent to which various individual loads on a turbo unit reduce its service life. It is therefore possible to define a partial damage caused by each individual load on the turbo unit. The value of the partial damage indicates by how much the individual load shortens the turbo unit's expected service life. Partial damage may for example be expressed in millionths of the turbo unit's expected service life. The control unit calculates during operation a cumulative partial damage in the form of the aggregate of all the partial damages which occur. The cumulative partial damage provides a good theoretical estimate of how much of the turbo unit's service life has been used up. Knowledge of the cumulative partial damage is information which can be used in various ways for reducing turbo unit overload and thereby preventing turbo unit service life curtailment. The value of the cumulative partial damage may for example be displayed to a driver of a vehicle in which the turbo unit is applied. Information about the turbo unit's cumulative partial damage will make the driver aware of the turbo unit's having being loaded too heavily. A driver's having this information is likely to at least partly reduce the problem of heavily loaded turbo units so that more turbo units will achieve an expected service life.

According to an embodiment of the present invention, the control unit is adapted to comparing the cumulative partial damage with a normative cumulative partial damage. Such comparison makes it possible to tell immediately whether the turbo unit has been subject to greater load than is normally the case. It also makes it possible to estimate an expected service life for the turbo unit relative to that of a turbo unit subject to normal load. With advantage, the combustion engine and a turbo unit are arranged in a vehicle. In such cases, the control unit may be adapted to comparing the cumulative partial damage with a normative cumulative partial damage for a vehicle with a turbo unit whose mileage is similar to that of said vehicle. A vehicle's expected service life is usually expressed in terms of mileage. It is therefore also appropriate to express the turbo unit's service life in terms of the vehicle's mileage, since the turbo unit's needs to be similar to that of the vehicle.

According to another embodiment of the present invention, the control unit is adapted to limiting the turbo unit's load to a highest permissible load value if the cumulative partial damage exceeds the normative cumulative partial damage by a predetermined value. The predetermined value thus provides a measure of the extent to which the turbo unit can be overloaded before the control unit will reduce its load. The predetermined value need not be constant but may be a value which varies depending on, for example, the vehicle's mileage and the value of the cumulative partial damage. When the turbo unit's load is limited, a driver who loads a turbo unit too heavily is compelled, for at least a period thereafter, to drive the vehicle at reduced turbo unit load and hence at reduced engine power. Since in this situation maximum turbo unit load is impossible, the result is lower partial damage values and the difference between the cumulative partial damage and the normative cumulative partial damage therefore gradually decreases. When this difference has been eliminated completely or reduced to an acceptable level, the turbo unit load reduction ceases and the vehicle can again be driven with the turbo unit at maximum load. Such turbo unit load reduction thus only affects drivers who overload the turbo unit relative to a normative turbo unit load. Those who drive their vehicle in a normative manner will therefore not be affected by such turbo unit load reduction.

According to another embodiment of the present invention, the arrangement comprises an indicating means adapted to informing a driver of the vehicle of situations where the turbo unit can only be activated up to the highest permissible load value. With such information, the driver will be well aware that the engine power is reduced. The driver can therefore adapt his/her driving to the available reduced engine power. The control unit may also provide the indicating means with information so that it gives warning in good time that engine power reduction may occur if the driver does not reduce the load on the turbo unit. It is thus possible for a driver to prevent engine power reduction by voluntarily reducing the load on the turbo unit.

According to another embodiment of the present invention, the control unit comprises stored information which makes it possible to estimate how much partial damage is caused by different turbo unit load values. Such stored information may be based on statistics and experience of the specific turbo unit. The turbo unit's load values may be divisible into at least two different load ranges, each of which may have a corresponding partial damage value. The load on the turbo unit may, for example, be divided into a low- load range, a medium- load range and a high- load range. A period of turbo unit load within one of the aforesaid load ranges will result in a corresponding partial damage value. Any desired number of load ranges may of course be applied. It is also possible to use a mathematical formula expressing a relationship between load and partial damage so that a corresponding partial damage value can be calculated for each individual load.

According to another embodiment of the present invention, the control unit is adapted to receiving information from a speed sensor which detects the turbo unit's speed in order to determine the load on the turbo unit. The turbo unit's speed is a parameter related to the load on the turbo unit. On the basis of information about the turbo unit's speed, the control unit can therefore calculate the load on the turbo unit and estimate relevant partial damage values. The control unit can also use this information to control the combustion engine so as to achieve a desired load on the turbo unit, which may be important where the load on the turbo unit has to be reduced to a maximum permissible value.

The object indicated above is also made possible by the method of the kind indicated in the introduction which is characterised by the steps indicated in the characterising part of claim 10.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention is described below by way of example with reference to the attached drawings, in which:

Fig. 1 depicts schematically a vehicle powered by a combustion engine and a turbo unit where an arrangement according to the present invention is used,

Fig. 2 depicts an example of how the value of partial damage may vary at different loads of a turbo unit, Fig. 3 depicts in graph form how a cumulative partial damage of a turbo unit may vary with mileage, and Fig. 4 depicts a flowchart illustrating a method according to the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Fig. 1 depicts schematically a portion of a vehicle 1 powered by a supercharged combustion engine 2. The vehicle 1 may be a heavy vehicle powered by a supercharged diesel engine. The exhaust gases from the cylinders of the combustion engine 2 are led via an exhaust manifold 3 to an exhaust line 4. The exhaust gases in the exhaust line 4, which are at above atmospheric pressure, are led to a turbine 5 of a turbo unit. The turbine 5 is thereby provided with driving power which is transmitted, via a connection, to a compressor 6 of the turbo unit. The compressor 6 thereupon compresses air which is led into an inlet line 8 via an air filter 7. A charge air cooler 9 is arranged in the inlet line 8. The purpose of the charge air cooler 9 is to cool the compressed air before it is led to the respective cylinders of the combustion engine 2 via a manifold 10. A schematically depicted control unit 12 is adapted to controlling the operation of the combustion engine on the basis of information about a requested engine power P_B. A driver of the vehicle 1 requests a desired engine power P_B of the combustion engine 2 by means of an accelerator pedal 11. The control unit 12 takes the form of a computer unit comprising software 12a adapted to controlling the combustion engine 2. A speed sensor 13 is applied in the vehicle to detect the speed of the turbo unit 5, 6. The speed sensor 13 is adapted to substantially continuously transmitting signals conveying information about the speed of the turbo unit 5, 6 to the control unit 12. On the basis of information about the speed of the turbo unit, the control unit 12 can estimate the load P_T on the turbo unit 5, 6. An indicating means 14 is arranged in the vehicle at a location where it is easy for the driver to see.

A turbo unit 5, 6 is a relatively expensive component of a vehicle. It is therefore desirable that the turbo unit 5, 6 achieve the same service life as the vehicle, thereby making it possible in most vehicles to avoid the relatively large cost involved in replacing or repairing a turbo unit 5, 6. The service life of a turbo unit is closely related to the load P_T to which it is subject during operation. On the basis inter alia of experience and statistics it is possible to determine with good accuracy the extent to which individual loads P_T on a turbo unit 5, 6 reduce its service life. A reduction of a theoretical service life of the turbo unit 5, 6 is here referred to as the partial damage S. Partial damage S may be expressed in proportions of an estimated theoretical service life of the turbo unit 5, 6. It may for example be expressed in millionths of the turbo unit's service life. When a cumulative partial damage Σ S_n caused by individual loads n on a turbo unit reaches the value 1.0, theoretical service life of the turbo unit 5, 6 has been reached.

Fig. 2 depicts an example of a relationship between partial damage S_n and individual loads Pτ_n on a turbo unit 5, 6. This relationship is with advantage stored in the control unit 12. In this particular case the individual loads Pτ_n on the turbo unit 5, 6 are divided into three classes PL, PM, PH, where PL denotes a low-load range, PM a medium- load range and P_H a high- load range. In a region of lower load than range P_L, the load Pτ_n on the turbo unit 5, 6 will be so low that no partial damage S_n is deemed to occur. When the load on the turbo unit is in the low-load range P_L, partial damage with the value S_L occurs. When the load on the turbo unit is in the medium-load range P_M, partial damage with the value S_M occurs. When the load on the turbo unit is in the high-load range P_H, partial damage with the value S_H below occurs. The diagram shows the partial damage value S_n substantially rising with the turbo unit's load Pτ_n. The individual load value Pτ_n used for estimating the partial damage S_n may be the highest load value Pτ_n within a period of activation of the turbo unit 5, 6. During such a period, the control unit 12 is adapted to determining in which of the load ranges P_L, PM, PH the load value Pj_n is classifiable, after which a partial damage value SL, SM or S_H can be determined. The control unit 12 is thereafter adapted to adding this partial damage S_L, S_M or S_H to the aggregate of previous accumulated partial damage values Σ S_n.

Fig. 3 depicts a curve A in the form of a straight line representing how the cumulative partial damage Σ S_n is thought to increase with the mileage D during normative driving of the vehicle and with normative distribution of the load on the turbo unit 5, 6 within the various load ranges P_L, P_M, P_H- The turbo unit 5, 6 thus reaches a theoretical service life when the cumulative partial damage Σ S_n = 1.0, i.e. in this case at a mileage D of 10*10⁵ km. This mileage D will with advantage also correspond to the vehicle's total mileage during its service life. For good probability of the turbo unit 5, 6 achieving its theoretical service life D, it should therefore not be loaded more heavily than what may be regarded as normal. To prevent the turbo unit 5, 6 being loaded so heavily that the cumulative partial damage Σ S_n increases too quickly relative to the curve A, a limiting curve A' is used in this case. The limiting curve A' represents a maximum acceptable value of cumulative partial damage Σ S_n as a function of the mileage D. This curve A' is intended to constitute an upper limit which individual operating points B of the turbo unit 5, 6 should not exceed. The difference between the curve A' and the curve A represents a value which determines to what extent the normative curve A can be overloaded before the control unit initiates limitation of the load on the turbo unit 5, 6. The limiting curve A' nevertheless comes gradually closer to the normal curve A with increasing mileage D so that the curves A, A' coincide when theoretical service life of the turbo unit 5, 6 is reached.

During operation of the vehicle 1, the control unit 12 is adapted to estimating current operating points B for the vehicle on the basis of cumulative partial damage Σ S_n and information about the vehicle's mileage D. Fig. 3 shows how the operating points B for a turbo unit may vary with mileage. If a particular operating point B touches or exceeds the limiting curve A', the control unit 12 is adapted to limiting the load on the turbo unit 5, 6. In that situation, the control unit 12 may for example be adapted to preventing the load on the turbo unit 5, 6 from entering the high- load range P_H even if the driver uses the accelerator pedal 11 with a view to requesting an engine power P_B which would impose on the turbo unit 5, 6 a load P_T within the high- load range P_H. In such circumstances, the control unit 12 initiates a turbo unit load P_T within the medium-load range P_M, resulting in a lower engine power than the requested P_B. The high partial damage values S_H caused by turbo unit loads P_T within the high-load range P_H are thus avoided. When such turbo unit load limitation is applied, subsequent operating points B will, at least after a time, be below the limiting curve A'. In situations where the load on the turbo unit is limited, this is advantageously indicated by the indicating means 14 so that the driver becomes aware that the load on the turbo unit is limited. The indicating means 14 may also comprise the function of warning a driver if the current operating points B are beginning to come close to the limiting curve A'. The indicating means 14 may also continuously show current load points B and their position relative to the curves A, A'. When the operating points fall below the limiting curve A' by a certain value or reach the normative curve, the limitation on the load of the turbo unit 5, 6 ceases, making it possible to resume using the turbo unit 5, 6 within the high-load range P_H. In this case the operating points B form a curve B' which coincides with the curves A, A' when theoretical service life of the turbo unit 5, 6 is reached.

Fig. 4 depicts a flowchart illustrating a method according to the invention. The process starts at step 15. At step 16, the control unit 12 receives a request from the driver via the accelerator pedal 11 for a desired engine power P_B. On the basis of knowing the current cumulative partial damage Σ S_n and the mileage D, the control unit 12 determines, at step 17, the current operating point B for the turbo unit 5, 6. At step 18, the control unit 12 does a comparison to see whether the operating point B is touching or above the limiting curve A'. If such is not the case, the control unit 12 does not initiate limitation of the load P_T on the turbo unit 5, 6 and the combustion engine is provided, at step 19, with the requested engine power P_B. Thereafter the control unit 12 determines, at step 20, whether the load P_T on the turbo unit is an individual load value Pτ_n usable for estimating a partial damage S. Such an individual load value Pτ_n for determination of partial damage may thus take the form of a highest load value P_T within an activation period of the turbo unit 5, 6. If the load P_T is not deemed such an individual load value Pj_n, the process starts again from the beginning without any partial damage S being recorded. If however the load value P_T constitutes a load value Pj_n which determines partial damage, there is assessment, at step 21, as to which load range P_L, P_M or P_H the load value Pj_n is in, see Fig. 2. This is followed by determination , at step 21, of the partial damage S_L, S_M or S_H corresponding to the load value Pin- This S_L, S_M or S_H value will therefore constitute the partial damage S_n for the load value Pj_n. At step 22, the partial damage S_n is added to the previous cumulative partial damage Σ S_n to arrive at a new cumulative partial damage value Σ S_n. Thereafter the process starts again from the beginning.

If instead it finds, at step 18, that the operating point B is touching or higher than the limiting curve A', the control unit 12 is adapted to limiting the load P_T on the turbo unit 5, 6. To this end, the control unit 12 determines, at step 23, a maximum value Pτma_X with which the turbo unit may at most be loaded. The control unit 12 may for example limit the load on the turbo unit Pτ_maχ to the value P_M , thereby preventing a load on the turbo unit 5, 6 within the high- load range P_H. The control unit 12 may also, at step 23, determine the engine power Pjmax obtained with the maximum permissible load on the turbo unit Pjmax- At step 24, the control unit 12 decides whether the engine power P_B requested by the driver is equal to or lower than the maximum permissible engine power Pjmax- If such is the case, it means that the requested engine power P_B can be allowed and the load on the turbo unit at step 19 can be the load P_T, which is thus lower than the maximum permissible load on the turbo unit Pjmax. Thereafter the process continues with step 20 and, where applicable, steps 21 and 22 in a manner corresponding to that already described above.

If instead it finds at step 24 that the driver is requesting an engine power P_B greater than the maximum permissible engine power P_max , the control unit 12 is adapted to limiting the engine power to the maximum permissible engine power P_max. The control unit 12 therefore limits the load P_T on the turbo unit 5, 6, at step 25, to the maximum permissible load value Pτ_max- Thereafter the process continues with step 20 and, where applicable, steps 21 and 22 in a manner corresponding to that described above. As indicated by the description, the turbo unit's service life depends on the load to which it is subject, which depends indirectly on the engine's load. However, engine load will vary not only with the engine power requested by the driver but also with the environment which the engine operates in. For example, the temperature, air humidity and/or air pressure of the surroundings may cause a given engine power to result in different engine loads. A consequence of this may for example be that a vehicle travelling continuously in a low air pressure environment such as occurs at high altitudes will continuously produce a lower maximum engine power than a vehicle travelling at lower altitudes, but the service life of the turbo unit will in both cases be the same, hopefully equal to the service life of the whole engine.

The invention is in no way limited to the embodiment described with reference to the drawings but may be varied freely within the scopes of the claims. The above example is described with reference to a combustion engine for a vehicle, but the invention is not tied thereto but may be used in all contexts where a turbocharged combustion engine is used and where problems and requirements similar to those described above occur. Nor is it necessary to use an upper limiting curve A' for limiting the load P_T on the turbo unit 5, 6, since this can be effected in many different ways. The extent to which the load on the turbo unit is limited may of course vary, but should nevertheless be such that subsequent load points B come closer to a normative curve A.

Claims

1. An arrangement for a combustion engine (2) and a turbo unit (5, 6) which is capable of being activated with varying load values (Pj), whereby the combustion engine (2) and the turbo unit (5, 6) are arranged in a vehicle (1) and whereby the arrangement comprises a control unit (12) which is adapted to receiving information about the load (P_T) on the turbo unit (5, 6), to determining various partial damage values (S_L, S_M, S_H) which are deemed to occur on the turbo unit (5, 6) at different loads (P_T) on the turbo unit (5, 6), and to adding the estimated partial damage values (S_L, S_M, S_H) to a cumulative partial damage Σ S_n which provides an estimate of the amount of the turbo unit's service life which has been used up, characterised in that the control unit is adapted to comparing the cumulative partial damage Σ S_n with a normative cumulative partial damage (A) for a vehicle with a turbo unit (5, 6) which has recorded a similar mileage (D) to said vehicle (1).

2. An arrangement according to claim 1, characterised in that the control unit (12) is adapted to limiting the load (Pj) on the turbo unit (5, 6) to a highest permissible limit value (Pτma_X) if the cumulative partial damage Σ S_n exceeds the normative cumulative partial damage (A) by a predetermined value (A').

3. An arrangement according to claim 2, characterised in that arrangement comprises an indicating means (14) adapted to informing a driver of the vehicle (1) in situations where the turbo unit (5, 6) can only be activated up to the highest permissible load

Value (P_Tmax).

4. An arrangement according to any one of the foregoing claims, characterised in that the control unit (12) comprises stored information which makes it possible to estimate the extent of the partial damage (SL, SM, SH) caused by different load values (Pm) on the turbo unit (5, 6).

5. An arrangement according to claim 4, characterised in that the load values (Pm) on the turbo unit (5, 6) are divisible into at least two different load ranges (P_L, P_M, P_H) and that each of the load ranges (P_L, P_M, P_H) has a corresponding partial damage value (S_L,

6. An arrangement according to any one of the foregoing claims, characterised in that the control unit (12) is adapted to receiving information from a speed sensor (13) which detects the speed of the turbo unit (5, 6) in order to determine the load (Pj) on the turbo unit (5, 6).

7. A method for a combustion engine (2) with the turbo unit (5, 6) which is capable of being activated with varying load values (Pj), whereby the combustion engine (2) and the turbo unit (5, 6) are arranged in a vehicle (1) and whereby the method comprises steps of receiving information about the load (Pj) on the turbo unit (5, 6), of determining various partial damage values (S_L, S_M, S_H) which are deemed to occur on the turbo unit (5, 6) at different loads (Pj) on the turbo unit (5, 6), and of adding the estimated partial damage values (S_L, S_M, S_H) to a cumulative partial damage Σ S_n which provides an estimate of the amount of the turbo unit's service life which has been used up, characterised in that the control unit is adapted to comparing the cumulative partial damage Σ S_n with a normative cumulative partial damage (A) for a vehicle with a turbo unit (5, 6) which has recorded a similar mileage (D) to said vehicle (1).

8. A method according to claim 7, characterised by the step of limiting the load (Pj) of the turbo unit (5, 6) to a highest permissible limit value (Pτ_max) if the cumulative partial damage Σ S_n exceeds the expected partial damage (A) by a predetermined value (A').

9. A method according to claim 8, characterised by the step of informing a driver of the vehicle (1) in situations where the turbo unit (5, 6) can only be activated up to the highest permissible load value (Pτ_max).

10. A method according to any one of claims 7 to 9 above, characterised by the step of estimating the extent of the partial damage (S_L, S_M, S_H) caused by different load values (Pj_n) on the turbo unit (5, 6) on the basis of stored information.

11. A method according to claim 10, characterised by the step of dividing the load values (Pm) on the turbo unit (5, 6) into at least two different load regions (PL, PM, PH), each of which has a corresponding partial damage value (S_L, S_M, S_H).

12. A method according to any one of claims 7 to 11 above, characterised by the step of receiving information from a speed sensor (13) which detects the speed of the turbo unit (5, 6) in order to determine the load (PT) on the turbo unit (5, 6).