Method for Onboard Diagnosis of a Wheel Alignment of a Vehicle and Vehicle

TECHNICAL FIELD

The invention relates to a method for onboard diagnosis of a wheel alignment of a vehicle and a vehicle comprising a unit for performing on-board diagnosis.

BACKGROUND OF THE INVENTION

When the wheels on a heavy truck, either on the tractor or trailer or both, are misaligned, the fuel consumption as well as the tire wear may increase significantly. By checking the tyres and finding that they are unevenly worn, it is possible to detect an error in wheel alignment.

It is also known in the art to use detection systems for detecting such misalignment of wheels. US 6,408,687 B1 discloses a method wherein a current steering wheel angle is compared to a historic steering wheel angle for determining a misalignment. An indicator informs the vehicle driver about the presence of a misalignment of the steering system.

However, in case of a truck comprised by a tractor and a trailer, it is not possible to determine which part of the vehicle needs to be adjusted.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved method for onboard diagnosis of a wheel alignment of a vehicle which particularly allows for determining if a misalignment is caused by a tractor or a trailer.

Another object is to provide a vehicle comprising a unit for performing such onboard diagnosis. The objects are achieved by the features of the independent claims. The other claims and the description disclose advantageous embodiments of the invention.

A method for onboard diagnosis of a wheel alignment of a vehicle is proposed, particularly for a tractor and/or a tractor-trailer combination. At least one parameter is monitored during driving which, in case a misalignment of one or more wheels is present, is indicative for the misalignment. An information is issued when an assumed misalignment of one or more wheels is detected by the at least one parameter and/or by a change of the at least one parameter, wherein the information is associated with a time stamp indicative of the time of occurrence of the assumed misalignment. The time stamp is associated with a configuration of the vehicle at the time of occurrence of the assumed misalignment.

Advantageously, by detecting a wheel misalignment high fuel efficiency and minimal tyre wear can be ensured. The information can be an error code and/or information comprising the value of the parameter and/or the value of change of the parameter. The information can be issued to a remote location where it is processed, particularly stored, and/or the information can be stored onboard the vehicle. The assumed wheel misalignment can be verified e.g. by a plausibility check. This plausibility check can be a misalignment identification where the change of the at least one parameter is compared to an absolute value of the at least one parameter and to recent indications such as a change in the vehicle state, an occurrence of a bump or no indication.

Particularly, changes in wheel alignment can be detected. The driver can then be notified that alignment service is required. Favourably, a deterioration in wheel alignment can be determined so that service can be carried out soon after occurrence. If calibrated by testing, the method can give an estimate on how large an eventual increase in fuel consumption can be with the estimated misalignment. Favourably, by carrying out the diagnosis continually and taking into account if and when a trailer is coupled or decoupled, it is possible to identify which part of the vehicle, i.e. tractor or trailer that is deviating in wheel alignment, thus reducing warranty costs if the source of misalignment is associated with the trailer. Optionally, by use of information and/or communication technique, an error message can be sent to the owner of the trailer if this turns out to be the part that is misaligned. Expediently, the wheel alignment can be determined when the vehicle is driving straight ahead. Additionally or alternatively, the wheel alignment can be determined when the vehicle is cornering. This can be done if sensors with sufficient signal quality are used. The steering device can be a steering wheel, a joystick, a slide actuator or the like.

According to a favourably method step, the at least one parameter indicative for the misalignment can be selected at least from the group of steering angle, yaw rate, lateral acceleration, tyre friction, side force, functional dependence of steering angle from yaw rate. These parameters are sensitive to a misalignment of the wheels and can easily be derived from already existing equipment in the vehicle.

According to a favourable method step, a source of misalignment can be derived by comparing the time stamp to one or more configurations and/or one or more states of the vehicle. Favourably, the time stamp can be associated with a configuration of the vehicle when no trailer was attached to the tractor or when a trailer was attached to the tractor and/ or a state of the vehicle has been changed e.g. by receiving an impact such as a bump.

According to a favourable method step, an information can be issued when the misalignment is reduced and/or is zero, i.e. the wheels are aligned. The source causing the misalignment can be identified with higher reliability.

According to a favourable method step, an operational mode when the vehicle is at least assumed to be driving straight ahead can be determined, wherein as parameter indicative for the misalignment a steering parameter of a steering device can be determined indicative for a steering position of the steering device during driving straight ahead. An information can be issued when a misalignment between the actual steering position of the steering device and a predetermined neutral position of the steering device is detected, wherein the information is associated with a time stamp indicative of the time of occurrence of the misalignment; and associating the time stamp with a configuration of the vehicle at the time of occurrence of the misalignment.

Favourably, driving straight ahead can be easily detected by various means. A misalignment of wheels can be easily detected by the steering wheel angle. A steering angle sensor working on a continuous basis can be used when it is determined the position that corresponds to the vehicle traveling straight forwardly. This is in principle already done by an ESP (electronic stability program) application so that basically such a parameter is already available in the vehicle when equipped with ESP. Favourably, use can be made of this parameter which can be transmitted e.g. by CAN bus to a controller for determining a misalignment. Determination of which position is the "straight-forward" position can be done e.g. by use of GPS data and/or satellite navigation data or simply by assuming that a position of the steering wheel that is used by the driver during a specified minimum amount of time must correspond to straight-forward driving. When this steering wheel position is determined, it is compared with the previous value. If a change has occurred, the wheel alignment is assumed to have changed. By measuring the steering wheel position corresponding to straight-forward driving both when a trailer is mounted and when the tractor is driving without trailer, it is possible to conclude which part of the vehicle has experienced deterioration in wheel alignment. Information regarding whether a trailer is mounted or not is available from various sensors. For instance, coupling can be used as well as attachment of electric connections to lamps and/or brakes of trailer can be used.

According to a favourable method step, the parameter indicative of the misalignment can be monitored permanently, thus providing a fast recognition if a wheel misalignment occurs. Expediently, an information is stored only if a misalignment is detected, which saves place in the memory.

According to a favourable method step, the parameter indicative of the misalignment can be monitored periodically, thus reducing calculator time and use of computer resources. According to a favourable method step, a time stamp can be issued when the configuration of the vehicle is changed, particularly if a trailer is coupled or uncoupled to a tractor. An information can be correctly associated with a configuration which was present when the information and its associated time stamp were stored.

According to a favourable method step, a time stamp can be issued when a state of the vehicle is changed. Particularly, the time stamp can be issued when an impact to the vehicle is detected, particularly by a sensor of an airbag system and/or of the gearbox. Already existing devices can be used and an eventual change in wheel alignment when the vehicle configuration is unchanged can be detected quickly after occurrence of the wheel misalignment. Favourably, when a bump can be identified as source for the wheel misalignment, it can be decided that the wheel misalignment is not caused by a built-in defect of the tractor or the trailer.

According to a favourable method step, a plausibility check can be performed for verifying or invalidating the recorded assumed misalignment, thus avoiding unnecessary service stops and increasing the reliability of the method.

According to a favourable method step, the information and the time stamp can be stored in a vehicle based and/or remote memory. Storing in the vehicle is advantageous as the history of the vehicle configuration and state is available on board the vehicle. Storing in a remote memory is advantageous as the on-board- diagnosis method can be integrated in a fleet management system. For instance, if it is decided that the source of misalignment is the trailer, a trailer identification can be stored within the fleet management system so that service for the trailer can be planned at a convenient time and/or location.

According to a favourably method step, an alarm can be issued to the driver if a misalignment is detected. The driver can decide whether a service is necessary or not. The method can be implemented as hardware, software or a combination of hardware and software. A computer program is proposed comprising a computer program code adapted to perform a method as described above or for use in a method as described above when said program is run on a programmable microcomputer. Preferably, the program can be adapted to be downloadable to a control unit or one of its components when run on a computer which is connected to the internet. Favourably, the computer program can be implemented in a processor device of an existing vehicle control unit.

A computer program product stored on a computer readable medium is proposed, comprising a program code for use in a method as described above on a computer. Favourably, the computer program product can be integrated in an existing vehicle control unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above-mentioned and other objects and advantages may best be understood from the following detailed description of the embodiments, but not restricted to the embodiments, wherein is shown schematically:

Fig. 1 a sketch of a tractor-trailer combination with a wheel misalignment on the trailer; Fig. 2 a flow chart of an example embodiment of a method according to the invention; Fig. 3 a flow chart of an example embodiment of an expanded method according to the invention;

Fig. 4 a logic scheme of a misalignment identification indicated in Fig. 2 and Fig. 3;

Fig. 5 a functional dependency of a rolling resistance increase as function of wheel misalignment; and Fig. 6 a functional dependency of a yaw rate as function of a road wheel angle. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In the drawings, equal or similar elements are referred to by equal reference numerals. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. Moreover, the drawings are intended to depict only typical embodiments of the invention and therefore should not be considered as limiting the scope of the invention.

Fig. 1 depicts schematically a vehicle 100, particularly a combination of a tractor 20 and a trailer 30. The tractor 20 comprises a steering device 10 embodied as a steering wheel. The tractor 10 comprises an airbag system with a crash sensor 12 and a navigation system 16 mounted e.g. on a dashboard 14. The tractor 20 comprises wheels 22a, 22b, 24a, 24b, 26a, 26b and is equipped with an electronic control unit (ECU) 40. A memory 42 is coupled to the ECU 40.

The trailer 30 comprises wheels 32a, 32b, 34a, 34b, 36a, 36b, wherein for instance one wheel pair with wheels 32a, 32b are misaligned.

The misaligned wheels generate a side force F_mis which in turn is transmitted to the steering device 10 causing a counterforce F_steer which has to be compensated by the driver holding the steering device 10. When driving straight ahead, the steering wheel (steering device 10) has to be turned to compensate the counterforce F steer instead of being held in a neutral position of the steering wheel. The driver has to exert a force to the steering device 10 when driving straight ahead. Besides the inconvenient and additional effort for the driver, the wheel misalignment increases the rolling resistance, as can be seen in Fig. 5. A wheel misalignment of 1 degree causes a rolling resistance increase of about

15%, a wheel misalignment of 2,5 degrees causes a rolling resistance increase of about 80%, thus increasing the fuel consumption as well as the tyre wear. Referring back to Fig. 1 , an information such as an error code associated with a time stamp indicating the time when the misalignment was first detected is stored in the memory 42 if a misalignment is detected. Additionally or alternatively, the information associated with the time stamp can be stored in a remote memory 42a which is arranged e.g. in a location of a freight company or the like with a vehicle fleet utilizing a management system.

Fig. 2 indicates by way of example a flow chart of a first procedure for on-board diagnosis of the wheel misalignment. In this first example, the on-board diagnosis can be done during driving straight ahead as a particularly convenient way of detecting wheel misalignment or in another driving state which allows for misalignment recognition. For instance, the operational mode of driving straight ahead can be determined e.g. when the steering device 10 is positioned in a fixed position for more than a predetermined time span and/or by a vehicle position detection system 16 (Fig. 1) particularly by GPS and/or satellite navigation. Of course, the wheel misalignment can also be detected in other driving operations. The procedure shown can be adjusted accordingly.

In step 300 one or more initial parameter Px are stored which are indicative of a wheel misalignment, including optionally a first time stamp ts init which identifies the initial state of the vehicle, and including an indication of an actual vehicle configuration trailer on/off which indicates whether the vehicle is a tractor trailer combination or not, i.e. whether a trailer is attached to the tractor or not. The parameter Px is a current misalignment value calibrated to be zero with zero misalignment. This is typically done in the factory where the vehicle, particularly the tractor, is built.

In step 302 it is checked whether the vehicle configuration trailer on/off has changed. If the vehicle configuration trailer on/off has changed ("y" in the flow chart), a time stamp ts_tr which identifies the time of occurrence of the change of the vehicle configuration is stored indicating the vehicle configuration trailer on/off in step 304 and the procedure continues again with step 302. If the vehicle configuration trailer on/off has not changed ("n" in the flow chart) the procedure continues within step 310 where measurement conditions are checked, i.e. if one or more parameters Px have been read. If no measurement conditions are detected ("n" in the flow chart), the routine continues with step 302.

If a measurement condition is detected ("y" in the flow chart) it is checked in step 312 if the change ΔPx of a parameter Px is above a predetermined limit Nm. ΔPx is the difference between the last saved misalignment value and the current parameter Px ("misalignment value").

The predetermined limit lim may include measurement tolerances and may indicate that a critical change of the parameter Px has been detected. One or more parameters Px can give an input to the ECU 40 (Fig. 1), such as steering angle and/or yaw rate and/or lateral acceleration and/or estimated tyre friction and/or side force and/or functional dependence of steering angle from yaw rate.

If the change ΔPx is below the predetermined limit Hm ("n" in the flow chart) the routine continues with step 302. If the change ΔPx is equal or above the predetermined limit Nm ("y" in the flow chart) the present value of the parameter Px and a time stamp ts px which identifies the time of occurrence of the parameter Px is stored in step 316. Optionally, an alarm can be issued in step 316 so that the driver is informed that a wheel misalignment was detected.

The routine then continues with step 302. Optionally, a misalignment identification can be performed in step 320. Step 320 is explained in more detail in Fig. 4.

Fig. 3 displays an extended method based on the embodiment of Fig. 2. In step 300 one or more initial parameters Px are stored which are indicative of a wheel misalignment, including optionally a first time stamp ts_init which identifies the time of the initial state of the vehicle, and including an indication of an actual vehicle configuration trailer on/off which indicates whether the vehicle is a tractor trailer combination or not, i.e. whether a trailer is attached to the tractor or not. The parameter Px is a current misalignment value calibrated to be zero with zero misalignment. This is typically done in the factory where the vehicle, particularly the tractor, is built.

In step 302 it is checked if the vehicle configuration trailer on/off has changed. If the vehicle configuration trailer on/off has changed ("y" in the flow chart), a time stamp ts tr which identifies the time of occurrence of the change of the vehicle configuration is stored indicating the vehicle configuration trailer on/off in step 304 and the procedure continues again with step 302.

If the vehicle configuration trailer on/off has not changed ("n" in the flow chart) the procedure continues within step 308 where it is checked whether a bump to the vehicle has been detected. A bump can be detected e.g. by a signal of a crash sensor of an airbag system. A bump is an impact to the vehicle which can be sensed by the crash sensor and may be above a certain limit. The bump may or may not cause ignition of the airbag. The bump may occur to any part of the vehicle and may or may not cause a wheel misalignment. If a bump has been detected ("y" in the flow chart) a time stamp ts_b which indicated the time of occurrence of the bump is stored as well as a bump information in step 308. The procedure continues with step 302.

If no bump is detected ("n" in the flow chart) the procedure continues within step 310 where measurement conditions are checked, i.e. if one or more parameters Px have been read. If no measurement conditions are detected ("n" in the flow chart), the routine continues with step 302.

If a measurement condition is detected ("y" in the flow chart) it is checked in step 312 whether the change ΔPx of a parameter Px is above a predetermined limit Hm. ΔPx is the difference between the last saved misalignment value and the current parameter Px ("misalignment value").

The predetermined limit lim may include measurement tolerances and may indicate that a critical change of the parameter Px has been detected. One or more parameters Px can give an input to the ECU 40 (Fig. 1), such as steering angle and/or yaw rate and/or lateral acceleration and/or and estimated tyre friction and/or side force and/or functional dependence of steering angle from yaw rate.

If the change ΔPx is below the predetermined limit Hm ("n" in the flow chart) the routine then continues with step 302.

If the change ΔPx is equal to or above the predetermined limit Nm ("y" in the flow chart) the present value of the parameter Px and a time stamp ts px which identifies the time of occurrence of the parameter Px is stored in step 316. Optionally, an alarm can be issued in step 316 so that the driver is informed that a wheel misalignment was detected.

The routine then continues with step 302. Optionally, a misalignment identification can be performed in step 320. Step 320 is explained in more detail in Fig. 4

Fig. 4 illustrates an example embodiment of a logic scheme of a misalignment identification 320 where by way of example the change from misaligned to aligned when uncoupling a trailer is explained. Other logic combinations for identifying one or more sources of wheel misalignment can be applied of course.

If a change ΔPx of a misalignment indicative parameter Px is equal or above the predetermined limit Hm (step 312) two states can be distinguished. In the first state the absolute value of the parameter Px can be equal or above the limit Hm (step 340). In the second state the absolute value of the parameter Px can be below the limit Hm (step 350). The states can be compared to a recent indication. The recent indication can comprise a change of the vehicle configuration, e.g. from trailer off to trailer on, from trailer on to trailer off, bump and no indication. It is also possible to include a change from trailer on to trailer off to trailer on, i.e. a change between two different trailers (not shown).

In the first state, with a recent indication of a change in the vehicle configuration from trailer off to trailer on (step 342), a wheel misalignment may be caused by the trailer. If the change in the vehicle configuration was from trailer on to trailer off (step 344), the wheel misalignment may be caused by the combination of trailer and tractor. If a bump was detected (step 346) as recent indication, at least one of trailer and tractor may be the source of the detected wheel misalignment. If no indication is reported (step 348), monitoring is continued and it is indicated that the parameter Px are above the predetermined limit Nm.

In the second state, with a recent indication of a change in the vehicle configuration from trailer off to trailer on (step 352), a wheel misalignment may be caused by the combination of trailer and tractor. If the change in the vehicle configuration was from trailer on to trailer off (step 354), the wheel misalignment may be caused by the trailer. If a bump was detected (step 356) as recent indication, monitoring is continued. If no indication is reported (step 358), monitoring is continued as well.

Favourably, the time stamp can be used to associate the wheel misalignment with a configuration of the vehicle at the time of occurrence of the misalignment, i.e. if a trailer was attached to the tractor or not. The source of misalignment can be derived by comparing the time stamp to one or more configurations of the vehicle. Further, it is also possible to associate the occurrence of the wheel misalignment with a state of the vehicle.

Particularly, a time stamp is issued and stored when the configuration of the vehicle is changed, particularly if a trailer is coupled or uncoupled to a tractor. A time stamp is also issued and stored when a state of the vehicle is changed. For instance, when the sensor 16 (Fig. 1) of the airbag system detects an impact experienced by the vehicle which is above a certain limit, it can be concluded that the wheels hit a bump or an obstacle and may have experienced a wheel misalignment.

In order to avoid unnecessary alarms or maintenance stops, a plausibility check can be done for verifying or invalidating the recorded misalignment. For instance, the determination of the wheel misalignment can be repeated.

Fig. 5 shows a rolling resistance curve of a wheel as a function of a wheel misalignment. The higher the wheel misalignment is, the higher is the observed rolling resistance, which results in increased wear and expensive maintenance for premature change of tyres.

Fig. 6 illustrates a functional dependency of a yaw rate on the road wheel angle based on a simplified theoretical model in which the yaw rate is the product of a vehicle speed and a sinus of the ratio of road wheel angle divided by axle distance (Yaw rate = speed ^• sin(road wheel angle)/(axle distance)).

It is assumed that the steering wheel angle when cornering is proportional to the road wheel angle. In case of another kind of steering device, e.g. a joystick, the position of the steering device will expediently be proportional to the road wheel angle.

The curves Y5, Y10, Y20 in Fig. 6 display the behaviour of the yaw rate as a function of the road wheel angle with a vehicle speed of e.g. 5 m/s (Y5), 10 m/s (Y10) or 20 m/s (Y20). The curves are almost linear around zero speed and are antisymmetric, i.e. a road wheel angle of 10° when the vehicle is cornering to the right hand side with a positive yaw rate of about 1 rad/s corresponds to a road wheel angle of -10° and a negative yaw rate of about -1 rad/s when the vehicle is cornering to the left hand side, according to the simplified model.

In case of a wheel misalignment, omitting an influence of wheel slip and the like, the absolute value of the yaw rate will be different for the same deflection of the steering device for cornering to the left hand side and the right hand side when the vehicle is driving with constant speed.

By taking into account wheel slip the determination of a misalignment of the wheels becomes more accurate. Assuming that the tyres are symmetric and the road conditions homogeneous when cornering right or left, the influence of the wheel slip can be eliminated in a first approximation. The theoretical model can be refined taking into account more parameters and measurements to distinguish the alignment or misalignment of the wheels from other sources which may influence the relationship of yaw rate versus road wheel angle. This modelling provides the possibility to determine the wheel misalignment during cornering instead of driving straight ahead.