WO2008094115A1

WO2008094115A1 - Method and system for estimating the load of an aggregate being power supplied by a motor

Info

Publication number: WO2008094115A1
Application number: PCT/SE2008/050072
Authority: WO
Inventors: Henrik Pettersson; Kristian Lundh
Original assignee: Scania Cv Ab (Publ)
Priority date: 2007-01-31
Filing date: 2008-01-24
Publication date: 2008-08-07
Also published as: SE530828C2; SE0700234L; DE112008000312T5

Abstract

The present invention relates to a method for estimating the load of an aggregate being power supplied by a motor such as an internal combustion engine or electric motor in a vehicle, said vehicle including a gearbox for connecting an output shaft of said motor to half shafts for providing geared transmission of power from said engine to at least one driving wheel of said vehicle, said vehicle further including at least one power take-off (PTO) for providing power from said motor to one or more aggregates, said PTO being arranged on the engine side of said gearbox. The method includes the step of estimating the load said aggregate is exerting on the motor during a period of time when said half shafts are disconnected from said motor output shaft.

Description

Method and system for estimating the load of an aggregate being power supplied by a motor

Field of the invention

The present invention relates to vehicle transmission systems, and in particular to a method for estimating power take-off from a unit connected to a vehicle motor according to the preamble of claim 1.

Background of the invention

I general, motor vehicles contain a number of applications for which accurate control of the crank shaft torque generated by the vehicle internal combustion engine is of great importance. Such applications may, for example, include power train protection, clutch protection, manual and automatic gearbox systems .

In particular, a correct estimation of the crank shaft torque is important when it comes to shifting gears to avoid torque related snatches and shocks within the power train. Vehicles often comprise a gear changing mechanism, automatic or manual, wherein mechanical stepped gearboxes are used to automatically provide a suitable gear based on current driving conditions, and wherein a clutch is used to selectively engage gearbox and engine output shaft .

The clutch, however, in such vehicles, is often only sparsely used. As a matter of fact, it is often enough that the vehicle driver merely depresses the clutch pedal when standing still to select automatic drive, whereafter there is no need to use the clutch again until the vehicle stops. Of course, there are also gearbox systems having a fully automatically operated clutch .

In order to obtain a smooth gear change, i.e., avoiding torque related snatches and shocks within the power train, which apart from being discomforting to the driver, also imposes unnecessary wear on the drive train components, the gear change requires that the torque delivered from the engine is adjusted to a suitable level in order to reduce the torque transmitted at the point of contact of the relevant gears. At the time of both disengagement of the current gear and engagement of the new gear it is desirable to have a torque- free contact between the gears in the gearbox. If the excess torque is high when the vehicle gearbox is reconnected to the engine crank shaft, by, e.g., a gear change, there is a substantial risk that the excess torque will give rise to the above snatches and shocks, which at best are only discomforting to the vehicle driver, and at worst gives rise to wear and/or damages in the power train.

The torque-free contact is usually accomplished by adjusting the engine torque towards a so called zero-torque level. This zero-torque level, however, is not that easy to determine, since the torque should as close as possible equal the torque requirements of the engine itself, such as its moment of inertia, its internal torque and internal losses, in addition to the torque consumption from external aggregates, such as AC compressor, air compressors, fans etc. Further, the torque may also depend on whether any external aggregates connected to power take-offs (PTOs), such as refrigerators of refrigerated trucks, are operating or not. The characteristics of such aggregates, however, may not be known to the vehicle manufacturer, and, therefore, a correct torque level determination can be difficult to obtain.

Due to this difficulty, the zero-torque level is often set based on a qualified guess, with the inherent drawback that a guess is always a guess. Consequently, it would be highly desirable to correctly estimate the torque consumed by aggregates connected to the vehicle engine, so as to be able to ensure that the remaining crank shaft torque, at gear change and/or the engaging of the gear box, is as close to zero as possible to ensure a smooth gear change.

Accordingly, what is needed is an improved method for estimating engine torque load also in situations wherein unknown loads are connected to the shaft.

Summary of the invention

It is an object of the present invention to provide a method that solves the above mentioned problem. This object is achieved by a method according to the characterising portion of claim 1.

According to the present invention, a method for estimating load of an aggregate being power supplied by a motor in a vehicle is provided. The vehicle includes a gearbox for connecting an output shaft of said motor to half shafts for providing geared transmission of power from said motor to at least one driving wheel of said vehicle, said vehicle further including at least one power take-off (PTO) for providing power from said motor to one or more aggregates, said PTO being arranged on the motor side of said gearbox. The method is characterised in that it includes the step of estimating the load said aggregate is exerting on the motor during a period of time when said half shafts are disconnected from said motor output shaft. The inventive idea of performing the estimation of the load exerted on the vehicle motor by an aggregate when the half shafts are disconnected from the motor output shaft has the advantage that accurate estimations can be performed with a minimum of measurements using already existing sensors, and using relatively straightforward equations. Further, the ability of accurately estimating the load on the output shaft of the motor has the advantage that the torque generated by the motor in gear changing moments can be very accurately controlled so that smooth gear changes, with a minimum of snatches and shocks can be accomplished. Such smooth gear change is particularly important for many types of applications, such as in urban delivery trucks, where starts and stops are frequent, and therefore frequent gear changing is inevitable, and, as a consequence, the better timed and executed the gear changes are, the less the power train will suffer from sudden torque shocks and reactions.

Further characteristics of the present invention, and advantages thereof, will be evident from the following detailed description of preferred embodiments and appended drawings, which are given by way of example only, and are not to be construed as limiting in any way.

Brief description of the drawings

Fig. Ia discloses an example of a vehicle 100 with which the present invention advantageously may be utilised. Fig. Ib discloses part of the vehicle of fig. Ia more in detail .

Fig. 2 shows an example of the variation of engine speed and torque delivered by the engine output shaft during a vehicle acceleration and gear change process. Fig. 3 shows a flow diagram according to an exemplary process of the present invention.

Detailed description of preferred embodiments

Fig. Ia discloses an example of a vehicle 100 with which the present invention advantageously may be utilised. The vehicle 100 comprises a steering axle 114 and half shafts 115a, 115b. The vehicle 100 can, for example, constitute a refrigerator vehicle .

Fig. 1 also discloses part of a vehicle control system. Vehicle control systems in modern vehicles usually consist of a communication bus system consisting of one or more communications buses 101 to interconnect electronic control units (ECUs) and various components located on the vehicle. Examples of such control units include Gearbox Management System (GMS) 102, which controls the gearbox functions of the vehicle, Suspension Management System (SMS) 103, controlling the suspension functions of the vehicle, Engine Management System (EMS) 105, connected to such a communication bus (not shown) , which controls the engine functions of the vehicle and Brake Management System (BMS) 104, controlling the brake functions of the vehicle. If more than one communication bus is used, the various control units can be grouped onto different communication buses based on, e.g., criticality of functions said control units are controlling. The control units are generally widely distributed over a vehicle, and, accordingly, the communication bus system extends through large parts of the vehicle. Such communication bus systems are usually of CAN (Controller Area Network) type, although other kinds of suitable communication technologies can be used as well . The vehicle also includes a drive train, which is disclosed more in detail in fig. Ib, and as can be seen in the figure, the vehicle 100 is powered by a motor, which in this exemplary embodiment consists of an internal combustion engine 118, which, with regard to trucks or buses, usually consists of a diesel engine. The engine has an outgoing shaft 121, which is connected to the vehicle's driving wheels 127, 128 via a frictional engaging element, i.e., a clutch 119, a mechanical stepped gearbox 122, a propeller shaft 123, a differential 124 and the half shafts 115a, 115b. The clutch 119 is used to selectively provide a mechanical coupling between the engine output (crank) shaft 121 and a gearbox input shaft 126. In fig. Ib the gearbox management system GMS 102 is shown more in detail. GMS 102 comprises means 141 for receiving various signals from, e.g., various sensors in or near the gearbox 122. Such sensors can include position sensors 134, 135 providing signals representing the current position of gearbox internal shafts (gears). Other examples of such sensors include one or more of rotational sensors 131, 132, 133, 136 for measuring the rotational speed of the drive wheel (s), propeller shaft 123, engine output shaft 121, and gearbox input shaft 126, respectively. A further example is a position sensor 137 for sensing the position of, e.g., a clutch pedal. These signals can be received, e.g., via messages transmitted on the CAN bus 101 or by direct links from sensors to GMS 102. The received signals, together with other information, such as data transmitted from other control units, can then be used in a data processing unit 142. The data processing unit 142 can, using the received sensor signals and data, and by means of a computer program, which, e.g., can be stored in a computer program product in form of storage means 143 in, or connected to the processing unit 142, perform gearbox control calculations for controlling gearbox operation and generate control signals for transmission, by means of output means 144, to, e.g., gearbox function actuators and other control units. The GMS can also be used to perform calculations according to the present invention, which will be described below. The storage means can, for example, consist of one or more from the group: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory) , EPROM (Erasable PROM) , Flash memory, EEPROM (Electrically Erasable PROM), hard disk drive. As an alternative to implementing the present invention in the GMS, the present invention can be implemented in any suitable electrical control unit connected to said vehicle control system.

As was mentioned above, it is important in gearboxes that the torque transmitted from the engine output shaft 121 to the gearbox input shaft 126 is as close to zero as possible when disengaging the current gear.

Gear change in such gearboxes is usually fully automatic, i.e., gear change is initiated and executed automatically using the vehicle control system based on various parameters. Alternatively, the gearbox can be equipped with manual control options in which case gear changing can be initiated manually by the driver selecting a suitable gear, but irrespective of whether gear changing is initiated automatically by the control system or manually by the driver, however, it is the control system that controls the actual execution of the gear change, both in terms of appropriate engine control and the timing of the actual disengaging of the old gear and engaging of the new.

For a gear change to take place smoothly it is generally desirable first to reduce the engine torque to a level corresponding to zero torque in the gearbox, so that neutral position can be reached. To change to a new gear, the engine speed is thereafter adjusted so that it matches the propeller shaft speed, i.e. the speed of the gearbox output shaft.

Thereafter the engine torque is increased to a level as requested by the driver.

A gear change initiated in a wrong torque situation, e.g., because the predetermined zero-torque level is not correct, results in the vehicle being jerked, which is disturbing for the driver, and may cause unnecessary wear on mechanical components, e.g., the gearbox.

Therefore, it is of the utmost importance that a correct estimation of the zero torque level is accomplished. The vehicle power train can, with engaged clutch, be modelled according to the following:

combustion engine engineloss aggregate Drive ^ '

, wherein T_combustιon is the torque that theoretically is delivered by the combustion, T_engιneloss is the sum of internal losses in the engine, ή is rotational acceleration, J_engιne is the moment of inertia of the engine, T_aggregate is the torque take-off from the engine from various engine external aggregates, T_Drιve is the torque delivered from the propeller shaft and further onto the wheels of the half shafts. If all quantities of eq. 1 are known, it can at all times be ensured that the vehicle engine delivers a suitable torque for each situation. For example, when changing gears, the torque delivered by the engine can be set to an appropriate level to ensure that, e.g., torque related snatches and shocks within the power train during gear changing are minimised.

Unfortunately, however, eq. 1 usually contains more than one unknown, and can therefore not be used to perform the desired torque calculations.

The terms T_combmtwn - J _engιneή -T_engιneloss in eq . 1 equals the torque that the vehicle combustion engine can deliver on the engine crank shaft, i.e., crank combustion engine engineloss \ *-^* I

Consequently, T_crank constitutes the possible torque from the combustion itself reduced by engine losses such as internal friction, pump losses and losses from various other aggregates that are necessary in order to ensure that the engine operates properly. T_cmnk is further reduced by the moment of inertia of engine components.

T_crank is measured for the working range of the engine during engine calibration in the manufacturing process, and can be stored in a memory of the vehicle communication system for use in various vehicle control systems, such as engine control units and gearbox control units. T_crank will therefore always be known. Accordingly, the terms T_aggregate and T_Dnve remain to be determined. T_Dnve is constantly varying due to current driving conditions, and is therefore unknown.

^_aggregate i-^{s a sum} °f those aggregates that are directly connected to the engine crank shaft, e.g., by means of a fan belt. Such aggregates may, as can be seen in fig. Ib, e.g., include alternator, air conditioning (AC) compressor, air compressor ( s ) for the vehicle pneumatic system and fans, such as cooling fans.

Some of these aggregates, e.g., all of the ones mentioned above, are assembled during vehicle manufacturing, and therefore usually have known characteristics, e.g., they can either have their characteristics modelled or measured, so that appropriate models and/or characteristics of such aggregates can be stored in the vehicle control system to be used in calculations according to eq. 1 when required. The contribution to T_aggregate of such aggregates will therefore also always be known to the vehicle control system.

As an alternative to modelling and/or performing appropriate measurements on a particular aggregate, the aggregate can be considered to have such small torque consumption that it can be disregarded in comparison to larger consumers without any noteworthy effect on the result of torque calculations. Therefore, should the aggregates all be of any of the described kinds, T_nσσrt,_mtt, will always be known as well.

However, the vehicle manufacturer usually provides the vehicle with further power take-off (PTO) possibilities than the ones mentioned above, i.e., possibilities to draw energy from the vehicle's engine.

For example, it is common that commercial vehicle manufacturers, instead of only providing fully equipped vehicles also provide "chassis only" versions or "cab and chassis" versions, which a customer and/or vehicle body builder finish according to their own special requirements. For example, chassis provided by a vehicle manufacturer may, e.g., be used for building motor homes, fire engines, ambulances, mixer trucks, refrigerator trucks etc. These kinds of vehicles often have additional requests regarding vehicle engine power supply.

Depending on the kind of vehicle a vehicle body builder is building, the requirements on power take-off may vary. For example, some applications require that power is provided constantly while the vehicle engine is running, irrespective of whether the vehicle is moving or not. Examples of such applications are mixer trucks, refrigerators of refrigerator trucks and plough systems. Such PTOs can be engine driven, e.g., PTO 129 in fig. Ib, or flywheel driven, and have the advantage that they are clutch independent, and therefore can be driven for as long as the vehicle engine is running.

In general, PTO equipment covers a wide range of applications, and the power take-off can be performed from various positions in the vehicle structure. The power can, for example, be taken off from the engine directly as described, or the PTO can be gearbox driven, i.e., clutch dependent. Such PTOs have the advantage that rather high powers can be taken off. However, such PTOs also have the disadvantage that the power take-off can only be performed when the clutch is engaged. Such PTOs are therefore suitable for driving aggregates not having the requirement to be engaged irrespective of whether the truck is moving or standing still.

During manufacturing it is often not possible to know the specific use of a particular chassis, and even if so, not possible to know the characteristics of, e.g., a particular refrigerator or plough system to be used. Further, the particular aggregate (s) connected to a PTO may change during a vehicle lifecycle, e.g., the chassis may be provided with a new or rebuilt body. Therefore, it is often not possible to predefine an accurate behaviour and/or model of T_aggregate of eq. 1 even if the behaviours of manufacturer assembled aggregates are known, since T_aggregate , apart from the manufacturer assembled aggregates, also include later assembled PTO aggregates. Consequently, in order to ensure a torque relieved gear change, there exists a need for a suitable method for accomplishing an accurate estimation of T_aggregate irrespective of which kinds of aggregates that currently are active. Such an estimation is provided by the present invention.

When estimating T_aggregate , it can be modelled as a dynamic portion, J_Agg , and a static portion, T_Agg(ri) , according to the following :

-* aggregate ^~ ^ Agg ^{U ~} * Agg ( ^ )

As was stated above, T_aggregate is the sum of all engine mounted aggregates, such as alternators, (cooling) fans, PTOs etc. Consequently, in this exemplary solution, the total power consumption of all aggregates are estimated, whereafter "known" contributions, such as AC compressor (s) , air compressor (s) etc., are subtracted from the resulting estimation so that an estimation of the power taken off from a particular PTO, or aggregate, is obtained.

Naturally, there may be more than one aggregate, the characteristics of which being unknown. In such situations the estimation can, e.g., be performed when only one of the aggregates are active. Aggregates usually signal to the vehicle communication system when they are active and when they are not. This signalling can, for example, be accomplished by the aggregate sending messages on a vehicle communication bus, such as a CAN bus, on the vehicle communication system, said messages including information regarding whether a particular aggregate is connected to the system, and whether it is active or not. Alternatively, the aggregate can communicate that it is active by applying a voltage on an input of the vehicle communication system. Consequently, the vehicle communication system will always know which aggregate (s) that is running, and thereby which aggregate that currently is estimated.

There are, however, situations wherein at least one aggregate is always active, while others are active intermittently. In such situations the power consumption of an intermittently working aggregate can not be estimated on its own. Such aggregates can, instead, be estimated by estimating the power consumed by the aggregates together and then subtract the contribution from the always active aggregate, since this aggregate can be estimated alone while intermittently working aggregates are inactive. Still, during normal driving, eq. 1 have two unknowns, i.e., T_Dme and T_aggregate, and is therefore unsolvable.

According to the present invention, however, it has been realised that if the power transmission from engine to half shafts is broken, i.e., the clutch is disengaged or at least the gearbox is in a neutral position, the torque acting on the vehicle driving wheels will be zero, i.e., T_Dnve=0, and eq. 1 will reduce to T_aggregate -T_Crank . Therefore, the power consumption of a particular aggregate can be estimated by determining the current T_Crank and then subtract contributions from known aggregates, such as AC compressor (s) , air compressor (s) , fans etc .

In fig. 3 is shown a flow diagram 300 according to an exemplary process of the present invention. The process starts in step 301, wherein it is determined whether the propeller shaft is disconnected from the engine output shaft. If it is determined that the shaft is not disconnected, i.e., a gear and the clutch is engaged, the process remains in step 301. If, on the other hand, it is determined that the propeller shaft is disconnected from the engine output shaft the process continues to step 302. This determination can be performed in various ways. For example, a sensor can be arranged such that it senses when the clutch pedal reaches a certain position, where the clutch is known to be disengaged. Alternatively, the vehicle control unit controlling the clutch can signal, e.g., on the vehicle communication bus, that the clutch is disengaged. As yet another alternative, a gearbox control unit can signal that the gearbox is in a neutral position.

In step 302, it is determined whether the absolute rate of dn(t) change of the engine speed, exceeds a first threshold, dt thresl, e.g., 50*60 rps² (revolutions per s²) and if so, the process continues to step 303. The reason for setting this threshold will be explained with reference to fig. 2.

In fig. 2 is shown an example of the variation of engine speed and torque delivered by the engine output shaft during a vehicle acceleration and gear change process.

When engine speed reaches n=nl, in t=tl it is determined that a gear change is desirable, and a torque reduction is initiated, e.g., by reducing fuel supply to the engine cylinders. As can be seen in the figure, the torque reduction is shown as substantially linear, but can, in principle take on any suitable form. When the torque has been reduced to a desired level, i.e., a level that results in a torque relieved gear connection, at t=t2, the current gear is disengaged, and an engine speed drop is started to adjust engine speed so as to synchronise it with the speed of the new gear. As can be seen in the figure, there is a slight torque drop when disengaging the gear (correspondingly, there is a torque rise when engaging the new gear at t=t5) . It is in this (gear disengaging) instance that the present invention is applicable since in the time interval between t2 and t5 no gear is engaged and, accordingly, T_Dme=0. As can be seen in the dn⁽t) figure, at first has a large, relatively constant dt dn(t)

(negative) value, whereafter decreases to be dt substantially zero at t=t5. In the time interval between t2 and t3 the condition in step 302 in fig. 3 will be fulfilled, and the process will continue to step 303, wherein an estimation of the dynamic part of T_aggregate is started. As was stated above, T_aggregate can be modelled as T_aggregate = J_Aggή-T_Agg . According to an exemplary embodiment of the present invention, which now will be described, it is assumed that J_Agg and T_Agg(n) are constant for a certain number of samples, i.e., at least three. This assumption will be most accurate at the time

interval from t2 to t3 when has a large, relatively dt dn(t) constant value, and when has levelled out, i.e., the time dt dn(t) period from t=t4 to t=t5 wherein is substantially zero. dt dn(t)

In the time interval between t=t3 and t=t4, however, dt varies to such extent that neither the dynamic contribution or the static can be considered constant. Therefore, no measurements should be performed in this time interval, hence the thresholds in fig. 3. However, the time intervals t2-t3 and t4-t5 are usually of such length that at least three or possibly 4, 5 or more samples can be made in each interval. As can be understood, the actual number of samples is dependent on the particular hardware and software used, and the rate of change of the engine speed.

With the above prerequisites, estimation can be performed, in step 303, according to the following. Eq. 1 can, when put into eq. 2, be written as:

T_crank(t-Δt) - (J_Agg) ^dn(t~At) ₊τ_Agg(_n) ₍5)

, wherein J_Agg represents an estimation of J_Agg and TA_gg (n)

represents an estimation of T_Agg(n) , i.e., J_Agg ^anc^ TA_gg(ή) are to

be estimated. With the above assumption that J_Agg ^an(^ TA_gg(n) are constant for three samples, eq. 4 and eq. 5 can be rewritten as

- _ T_crank(t) -T_crank(t-At)

^Agg~ dn(t) _dn(t-At) dt dt dn(t) dn(t-At) provided that the difference is large enough. dt dt This function, however, can be difficult to use due to the difficulty in achieving a stable value on the acceleration dn(t) dn(t-At) difference, i.e., , which can be very near zero if dt dt the acceleration is rather constant as disclosed in fig. 2.

Therefore, an alternative method of solving the above equations is to solve JA_ee from eq. 4. However, in this method,

TAg_g (n) is unknown. With the assumption that TA_gg (n) is equal to the previous time step, i.e., (t-Δt) , eq. 4 can be solved for

J_Age i i-e., resulting in:

J _T_crank(t)-r_agg dn(t) ^{{ ]} dt , wherein T is the most recent existing estimation of the static contribution. For example, if each estimation is weighted with previous estimations, as will be described below, T_agg is the most recent weighted estimation of T_agg . If the change in engine speed is small between two consecutive dn(t) samples, the value of will be small, with the consequence dt that the estimation of J_Agg ^maY reach unreasonably high values. This is be accounted for by setting the above first threshold dn⁽t) dn(t) of according to the above, and if <first threshold, dt dt

J,„„ is set to zero..

The moment of inertia, J_Aggr ^can then simply be estimated as

J_Agg , but preferably J_Agg is weighted with previously determined estimations of the moment of inertia using a weighting factor R, i.e., J_Agg - RJΑ_gg +(1-R)J_AggO_{ld >} wherein the weighting factor R_f e.g., is set to 0.01 or any other suitable value, and wherein J_AggO_ld i-^s ^-he weighted estimation of a number of, or all of the previous estimations. The influence of the latest estimation J_A is kept rather small in order to provide estimation robustness against temporary disturbances.

When the dynamic torque has been estimated according to the above, in step 303, the process continues to step 304, wherein θn(t) it is determined whether < second threshold, thres2, e.g. dt 5*60 rps² (revolutions per s²) . If not, the process returns to step 301, and, as is realised, it is possible to perform more than one estimation of J_Agg before T_agg is estimated. For example, three estimations can be performed, as can be seen in fig. 2. These estimations can either be weighted to form a single estimation, or alternatively, each estimation can be weighted according to the above with previously performed estimations .

dn(t)

If, in step 304, < thres2, the process continues to step dt

305, wherein the static torque is estimated. The static torque can be estimated, in a similar manner, using eq. 4, as T_Agg(n) =T_crank(t)-V_Agg)^~ , ( 8 )

wherein T_agg is the most recent existing estimation of the static contribution. With regard to the estimation of the static contribution, it is, in contrast to the above, advantageous if the change in engine speed is small between two consecutive samples. This can be accounted for, as shown in step 304, by setting the above mentioned second threshold dn⁽t) of , and only perform the estimation of the static dt dn(t) contribution if < second threshold. For example, as was dt mentioned above, the second threshold can be set to 5. It is to be understood however, that these thresholds are only exemplary, and that they may vary substantially from these values. In fact, it can be possible to have overlapping dn⁽t) thresholds, i.e., for a certain range of both the static dt and dynamic contribution can be estimated at the same time.

Further, as was mentioned above, also the estimation of the static contribution can be weighted with previously determined estimations, using e.g., a similar weighting factor R, i.e.,

Λ Λ

T_Agg =RT_Agg+(l-R)T_AggOld .

When the estimation of T_agg , has been performed, the process continues to step 306, wherein it is verified that valid estimations of J_Agg , T_agg have been obtained, and if so, the process continues to step 307, wherein the estimation of the load of the particular aggregate is determined. Otherwise, the process returns to step 301. The resulting estimations of J and T are estimations of the total load on the engine output shaft. In order to obtain an estimation of a particular PTO, and/or aggregate, known contributions from other active aggregates must be subtracted from the estimated values, e.g., known contributions from AC compressor (s) , fan(s), alternator (s) and air compressor (s) are to be subtracted. Accordingly the resulting estimations of TPTO and JPTO can be expressed as:

T Pm (n) = T_Agg (n) - T_ALT - T_AC - T_FAN - T_AIR , and

J PTO ^{~ •}* Agg ^' J ALT ^~ J AC ^~ J FAN ^{~ •}* AIR *

Finally, the estimation of the load of the particular aggregate being measured can be expressed as

-* aggregate ^{~ •}* PTOⁿ + ^■* PTO \ⁿ>

J_PTO is considered to be independent of the engine speed, while T_pτo(n) varies with engine speed. The estimations of T_pτo(n) should therefore be divided into speed interval, e.g., stored in an array, wherein T_pτo(n) can be considered constant for each interval .

According to the present invention, a single estimation can be used. However, as was mentioned above, since the robustness in the estimations increases if values from a number of consecutive estimations are weighted together it is recommended that weighting according to the above is performed. Therefore, it may take a few gear changes until reliable values are achieved. Further, if there are more than one aggregate that needs to be estimated, further gear changes may be needed bef ore T_aggregate can be rel iably est imated in al l situations. However, when the estimation has been performed according to the above, the vehicle engine can be very accurately controlled to deliver precisely the desired torque that will result in smooth gear changes. Even further, the performed estimations can be stored in the vehicle control system, which means that once accurate estimations have been obtained, accurate torque control can be accomplished from the very first gear change the next time the vehicle is taken into use, e.g., the next time the engine is started, where each gear change can be used to further improve the estimations.

An important advantage of the method according to the invention is that it makes it possible to obtain a very accurate determination of torque consumption of PTO aggregates. Further, if the final estimation is a weighted sum of a plurality of consecutive estimations the present invention will also account for changes in engine and aggregates in time, e.g., due to wear or change of components. That is, if the engine characteristics changes in time, this changes will be accounted for in the aggregate estimations.

In the above description, a specific method of estimating torque consumed from PTOs has been disclosed. It is to be understood, however, that other methods of performing said estimations equally well can be utilised. For example, Kalman filtering and/or recursive least square methods can be used to perform said estimations, as long as the essential feature of the present invention, i.e., performing said estimations after disconnecting the propeller shaft from the engine output shaft, is complied with. Further, hitherto the present invention has been described for a vehicle having an internal combustion engine. It is, of course, envisaged that the present invention is applicable in a vehicle having another kind of motor, such as an electric motor. Even further, in the above description the present invention has primarily been described in connection to a vehicle having a clutch. It is to be understood that the present invention is equally applicable in a vehicle having a clutch-free gearbox.

Claims

Cl aims

1. Method for estimating the load of an aggregate being power supplied by a motor such as an internal combustion engine or electric motor in a vehicle, said vehicle including a gearbox for connecting an output shaft of said motor to half shafts for providing geared transmission of power from said engine to at least one driving wheel of said vehicle, said vehicle further including at least one power take-off (PTO) for providing power from said motor to one or more aggregates, said PTO being arranged on the engine side of said gearbox, characterised in that the method includes the step of estimating the load said aggregate is exerting on the motor during a period of time when said half shafts are disconnected from said motor output shaft.

2. Method according to claim 1, characterised in that said load is a torque exerted on an output shaft of said motor .

3. Method according to claim 1 or 2, characterised in that it further includes the step of detecting that said half shafts are disconnected from said motor output shaft.

4. Method according to claim 3, characterised in that said detection is performed by any from the group: detecting a pedal position, said pedal controlling a frictional engaging element provided for engaging/disengaging power transmitted from the motor to said the wheels, receiving a signal representing disengaged frictional engaging element, receiving a signal representing disengaged gearbox .

5. Method according to claim 4, characterised in that said signals are data messages transmitted on a vehicle communication bus.

6. Method according to any of the claims 1-5, characterised in that it further includes the step of estimating said aggregate load as a dynamic load portion and a static load portion, e.g., T_aggregate = J_Aggή-T_Agg .

7. Method according to claim 6, characterised in that it further comprises the step of estimating said dynamic load portion when the absolute rate of change of the dn(t) motor speed exceeds a first threshold. dt

8. Method according to claim 6 or 7, characterised in that it further comprises the step of estimating said static load portion when the absolute rate of change of the dn(t) motor speed is below a second threshold. dt

9. Method according to claim 7 or 8, characterised in that said first threshold is in the range 1500-6000 rps , and said second threshold is in the range e.g., 0-600 rps².

10. Method according to any of the preceding claims, wherein a plurality of aggregates exert load on said motor output shaft, characterised in that said estimation comprises the steps of: - estimating the total load from said motor output shaft, and

- subtracting load from aggregates for which load characteristics are known.

11. Method according to any of the preceding claims, characterised in that it further comprises the step of providing a final estimation, wherein the final estimation is said estimation weighted with previous estimations of the load of said aggregate.

12. Method according to any of the preceding claims, characterised in that said half shafts is a propeller shaft .

13. Method according to any of the preceding claims, characterised in that said motor output shaft is a crank shaft .

14. System for estimating the load of an aggregate being power supplied by a motor, such as an internal combustion engine or an electric motor in a vehicle, said vehicle including a gearbox for connecting an output shaft of said motor to half shafts for providing geared transmission of power from said motor to at least one driving wheel of said vehicle, said vehicle further including at least one power take-off (PTO) for providing power from said motor to one or more aggregates, said PTO being arranged on the motor side of said gearbox, characterised in that the system includes means for estimating the load said aggregate is exerting on the motor during a period of time when said half shafts are disconnected from said motor output shaft.

15. System according to claim 14, characterised in that said load is a torque exerted on an output shaft of said motor .

16. System according to claim 14 or 15, characterised in that it further includes means for detecting that said half shafts are disconnected from said motor output shaft.

17. System according to claim 16, characterised in that said detection is arranged to be performed by any from the group: detecting a pedal position, said pedal controlling a frictional engaging element provided for engaging/disengaging power transmitted from the motor to said the wheels, receiving a signal representing disengaged frictional engaging element, receiving a signal representing disengaged gearbox.

18. System according to claim 17, characterised in that said signals are arranged to be data messages transmitted on a vehicle communication bus.

19. System according to any of the claims 14-18, characterised in that it further includes means for estimating said aggregate load as a dynamic load portion and a static load portion, e.g., T_aggregate = J_Aggή -T_Agg .

20. System according to claim 19, characterised in that it further comprises means for estimating said dynamic load portion when the absolute rate of change of the motor dn(t) speed exceeds a first threshold. dt

21. System according to claim 19 or 20, characterised in that it further comprises means for estimating said static load portion when the absolute rate of change of the dn(t) motor speed is below a second threshold. dt

22. System according to claim 20 or 21, characterised in that said first threshold is arranged to be in the range 1500- 6000 rps², and said second threshold is arranged to be in the range e.g., 0-600 rps².

23. System according to any of the claims 14-22, wherein a plurality of aggregates are arranged to exert load on said motor output shaft, characterised in that said system comprises means for:

- estimating the total load from said motor output shaft, and

- subtracting load from aggregates for which load characteristics are known.

24. System according to any of the claims 14-23, characterised in that it further comprises means for providing a final estimation, wherein the final estimation is said estimation weighted with previous estimations of the load of said aggregate.

25. System according to any of the claims 14-24, characterised in that said half shaft is a propeller shaft .

26. System according to any of the claims 14-25, characterised in that said motor output shaft is a crank shaft .

27. Computer program product, characterised in code means, which when run on a control unit in a vehicle and connected to an internal communication system in said vehicle causes the control unit to execute the method according to any of the claims 1-13.

28. Computer program product including a computer readable medium according to claim 27, wherein the code means are included in the computer readable medium.

29. Vehicle, characterised in that it includes a system according to any of the claims 14-26.