WO2012025128A1

WO2012025128A1 - Method for calibrating an inclination sensor and inclination sensor system

Info

Publication number: WO2012025128A1
Application number: PCT/EP2010/005154
Authority: WO
Inventors: Johan SÖDERSTRÖM; Edvard Lundgren
Original assignee: Volvo Lastvagnar Ab
Priority date: 2010-08-23
Filing date: 2010-08-23
Publication date: 2012-03-01

Abstract

The present invention relates to a method for calibrating an inclination sensor of a vehicle, wherein vehicle altitude information is retrieved and use for determining a calibration value for the inclination sensor. The present invention further relates to an inclination sensor system comprising a calibration unit configured to calibrate an inclination sensor based on retrieved vehicle altitude information.

Description

METHOD FOR CALIBRATING AN INCLINATION SENSOR AND

INCLINATION SENSOR SYSTEM

Field of the Invention

The present invention relates to a method for calibrating an inclination sensor of a vehicle and to an inclination sensor system for a vehicle. For example, the method for calibration and the inclination sensor system can be used with vehicles, such as heavy vehicles, e.g. trucks, busses, used for e.g. transportation purposes, or personal vehicles. The present invention further relates to a computer program and a computer program product comprising program code, for performing the method for calibrating an inclination sensor, are disclosed.

Background Art

With the increasing development of control systems, such as micro processors in combination with control devices and sensors, it has become more common to provide vehicles with control systems arranged to support and regulate the operation of vehicles based on measured and/or calculated vehicle parameters. The control systems may assist a driver and provide efficient operation of and cooperation between e.g. the engine and

transmission.

It is known to provide vehicles with inclination sensors for measuring the inclination of the surface the vehicle is travelling on, such as the inclination, or grade, of a road. Vehicle inclination sensors may also be used for measuring the inclination, or tilt, of the vehicle which may differ for different loads, tire pressure, and suspension settings. Vehicle information sensors typically provide an inclination signal via a data bus system in the vehicle, wherein the inclination signal contain inclination information which may be used for determining and calculating vehicle operating parameters and vehicle mass parameters.

WO 2007/078225 describes a vehicle configuration comprising an engine, transmission and a transmission control unit arranged to control different pneumatically operated piston cylinder devices for engaging different gear ratios between an input shaft and an output shaft of the transmission. Gear selections and shift selections are made automatically based on measured parameters including road inclination which is sensed by a piezoelectric inclination sensor arranged in the transmission control unit.

Due to the development of more precise and more efficient control system, it has become increasingly important to control and operate vehicles control systems based on more reliable and accurate parameters. In particular, small variations, or errors, in the accuracy of the inclination sensor may lead to improper calculations of vehicle operating parameters. For example, the precision of engine and transmission controlling, gear and shift selection, vehicle mass calculation, vehicle position determination, etc. will be limited and/or of poor accuracy. Therefore, there is a need to provide improvements to the technology.

Summary of the Invention

The object of the present invention is to provide an improved vehicle inclination sensor and more accurate vehicle inclination information by increasing the accuracy of the inclination sensor.

These and other objects are met by the subject matter provided in the independent claims. Preferred embodiments of the invention are presented in the dependent claims.

According to a first aspect thereof, the present invention relates to a method for calibrating an inclination sensor of a vehicle, which method comprises retrieving vehicle altitude information, estimating a calibration value for the vehicle inclination sensor using the vehicle altitude information, and calibrating the inclination sensor by using the calibration value.

The present invention is based on the insight that it is possible to achieve highly accurate vehicle inclination information and vehicle inclination sensors, by retrieving or measuring vehicle altitude information and using the vehicle altitude information for calibrating the vehicle inclination sensor.

An advantage associated with the method according to the present invention is that the accuracy of the inclination sensor is improved by calibration based on vehicle altitude information. The proposed method also increases the reliability of vehicle inclination sensors.

The altitude of a vehicle is essentially not influenced by the inclination of the surface on which the vehicle is traveling. Therefore, vehicle altitude information between two different reference points forms an external source of information which may be used for calibrating the inclination sensor. This allows for improvements related to the accuracy and precision of the inclination sensor and the inclination information provided by the inclination sensor.

The present method is further advantageous in that vehicle control systems may be provided with more reliable and accurate vehicle inclination information which, in turn, may be used for calculating and determining improved vehicle controlling and operating parameters.

For example, vehicle inclination sensor may be used for gear and shift selections in a transmission control unit of a vehicle, wherein different factors, such as tire pressure, vehicle load, and suspension settings, may influence a vehicle inclination offset value. Advantageously, the method may be used for calibrating the offset value of an inclination sensor.

Furthermore, for some vehicles and vehicle controlling systems, the instantaneous inclination of a vehicle is derived by utilizing the vehicle mass and e.g. vehicle propulsion forces, wherein the vehicle mass is calculated using vehicle inclination information provided by an inclination sensor. Thus, an improved inclination sensor and improved vehicle inclination information also provide improved calculation and determination of vehicle mass.

Also, improved vehicle inclination sensors and information provided by the method according to the present invention further allow for more accurate and sophisticated gear and shift selections. For example, the timing and gear selection by automated control systems may be improved and configured for better fuel efficiency. In addition, improved pre-view or for-see functionality, and eco-roll functionality, is provided, wherein unnecessary and inefficient shifting prior to road sections having uphill or downhill road inclination profiles may be avoided. In particular, accurate road, or vehicle, inclination

information is highly important for these types of functions which require precise road/vehicle inclination information in order to be able to determine in which part of an uphill/downhill section of the road a vehicle is located.

Altitude information may be retrieved, or measured, by means of a vehicle altitude information device, such as an altitude or pressure indicator, arranged in the vehicle. For example, vehicle altitude information may be retrieved by using ambient air/atmospheric pressure sensors or pressure gauges. Also, vehicle altitude information may be determined based on the vehicle position and a known altitude value for that given position, wherein altitude values may be pre-stored in a memory, located as information in topographic charts or maps, retrieved via GPS-system, or sent to the vehicle wirelessly via external equipment.

In the method, the retrieved vehicle altitude information is used for estimating a calibration value for the vehicle inclination sensor. This may be achieved by comparing the vehicle altitude information with information received from the inclination sensor. For example, the accuracy of the vehicle inclination signal provided by the inclination sensor may be converted to altitude information and compared with the retrieved vehicle altitude information in order to estimate the calibration value which is used for calibrating the inclination sensor or for minimizing any errors of the inclination sensor's offset value.

For example, the retrieved altitude information is used to determine the altitude difference between two reference points, or locations, along the traveling path of the vehicle, wherein the retrieved altitude information is compared and evaluated with inclination information retrieved by the inclination sensor of a vehicle between the same reference points, or locations.

According to an exemplifying embodiment, the vehicle altitude information is based on a measuring distance travelled by the vehicle, which advantageously defines a two reference locations. In more detail, the measuring distance is a distance traveled, or covered, by the vehicle, wherein vehicle altitude information may be defined between a starting point and an end point of the measuring distance. In other words, the altitude difference between the starting and end point of the measuring distance may be used for defining the retrieved vehicle altitude information used for calibrating the inclination sensor. The measuring distance traveled by the vehicle may be between 5 meters and 100 kilometers, between 50 and 10000 meters, or between 200 and 2000 meters.

According to an exemplifying embodiment, the method further comprises determining a first altitude difference value for the measuring distance, which first altitude difference value is based on vehicle altitude information, wherein the step of estimating the calibration value comprises using the first altitude difference value. Determining a first altitude difference value allows for specification of a value which may be processed and compared with the output signal of the inclination sensor in order to estimate a suitable calibration value. The first altitude difference value typically is a parameter which specifies the altitude difference of the vehicle while driving between different points on a e.g. road having a specific inclination profile which may comprise essentially horizontal, uphill and/or downhill sections.

According to an exemplifying embodiment, the step of determining the first altitude difference value comprises retrieving vehicle altitude information at a starting point and at an end point of the measuring distance. For example, while the vehicle is in running, or traveling, mode, the method may comprise retrieving altitude information when the vehicle is located at a point A which forms the starting point of the measuring distance. Next, when the vehicle has moved to a difference location, point B, which forms the end point of the measuring distance, altitude information is retrieved again. The altitude difference between the starting point A and the end point B of the measuring distance forms the first altitude difference value and is the altitude difference experienced by the vehicle when driving from point A to B. The first altitude difference value associated with the measuring distance is

advantageous in that it is not dependent of the instantaneous inclination of the vehicle, rather it relates to the relative altitude difference between two locations, and may be used for calibrating the instantaneous output signal from the inclination sensor of the vehicle. The altitude difference value may also be logged and stored for road inclination analyzing and recognition purposes. According to an exemplifying embodiment, the method further comprises determining a second altitude difference value for the measuring distance, which second altitude difference is based on vehicle inclination information retrieved during the measuring distance by the inclination sensor, wherein the step of estimating the calibration value further comprises using the second altitude difference value. The second altitude difference value advantageously forms a second value of the altitude difference associated with the measuring distance. This allows for estimation of the calibration value by comparing and processing the results from the retrieved altitude

information associated with the measuring distance and the retrieved inclination information associated with the measuring distance.

According to an exemplifying embodiment, the second altitude difference value is determined by integrating instantaneous vehicle inclination information retrieved between the starting point and the end point of the measuring distance. This allows for that the second altitude difference may be determined by collecting and integrating the instantaneous vehicle inclination signal outputted by the inclination sensor while the vehicle is travelling between the starting point A and the end point B of the measuring distance. In other words, the integration combines, or summarizes the instantaneous inclination and processes it, or compares it, with covered distance, travel speed and/or travel duration in order to determine the relative altitude difference between starting and end points A and B. For example, the second altitude difference value may be determined by continuously retrieving and processing the output from the inclination sensor, or determined by reading the output from the inclination sensor in a repetitive manner while the vehicle is moving. Furthermore, the second altitude difference value may be determined based on any other possible process or technique utilizing the vehicle inclination information provided by the inclination sensor, wherein the output from the inclination sensor may be retrieved by using analog, discrete, and/or digital signal processing with suitable sampling frequency.

By integrating the inclination signal provided from an inclination sensor in order to determine an altitude difference between two reference points, any error or small deviation in the inclination sensor will be integrated and introduced in the resulting second altitude difference value. Hence, small errors or deviations in the retrieved vehicle inclination information originating from the inclination sensor signal may be identified since they are integrated into greater and more easily detectable error values.

According to a further exemplifying embodiment, the step of estimating the calibration value comprises using the difference between the first and second altitude difference values for the measuring distance. This allows for accurate calibration and estimation of the calibration value in a simple and efficient manner. Hence, the embodiment allows for calibration of the inclination sensor by collecting and comparing retrieve vehicle altitude and vehicle inclination information from two difference sources for the specific measuring distance, wherein a calibration value for the inclination sensor is determined.

For example, the first and second altitude difference values associated with the measuring distance may be compared and the difference, or error, between the two altitude difference values may be used for estimating a suitable calibration value for the inclination sensor, wherein the calibration value, in turn, may be used to calibrate the inclination sensor by use of signal processing and/or feedback controlling techniques.

The estimation and calibration is typically performed based on that the first altitude difference value is considered correct and that the second altitude difference value comprises errors originating from the retrieved vehicle inclination information.

According to a further embodiment of the method, it comprises evaluation and determination of suitable conditions for retrieving vehicle inclination information and e.g. interrupting the method if it is determined that the retrieved vehicle inclination information should be disqualified. This allows for controlling of the calibration of the inclination sensor and improves the method for calibration by ensuring that correct and reliable information and data is used. For example, collected vehicle inclination information which is retrieved during the measuring distance may by disqualified if the vehicle is subjected to intense breaking or turning which affect the inclination of the vehicle in a non-normal manner, compared to normal movement in an essentially straight direction without substantial acceleration or retardation. If disqualified inclination information is detected, the method for calibrating the inclination sensor may be interrupted or restarted, or the qualified inclination information may be excluded and not used for estimating the second altitude difference value or the calibration value for the inclination sensor.

According to a second aspect thereof, the present invention relates to a computer program comprising program code, or code means, for performing the method for calibrating an inclination sensor of a vehicle according to any one of the described embodiments, when the computer program is run on a computer. The present invention also relates to a computer program product comprising program code, or code means, stored on a computer readable medium for performing the method for calibrating an inclination sensor of a vehicle according to any one of the described embodiments, when the program is run on a computer.

According to a third aspect thereof, the present invention relates to an inclination sensor system for a vehicle, which comprises an inclination sensor for measuring the inclination of the vehicle, and an altitude information device for measuring vehicle altitude. The inclination sensor system further comprises a calibration unit arranged to calibrate the inclination sensor using information from the altitude information device.

An advantage of the inclination sensor system according to the invention is that the accuracy of the inclination sensor is improved by calibration based on vehicle altitude information, as described with reference to the disclosed advantages of the method for calibrating an inclination sensor. Also, the reliability of vehicle inclination sensors are improved since it may be controlled and compared against an external and independent source. Furthermore, an improved inclination sensor and more accurate inclination information allow for more accurate and precise calculations of vehicle operating parameters. For example, increased precision of engine and transmission controlling, better and more efficient gear and shift selection, improved vehicle mass calculation and vehicle position

determination may be realized. According to an exemplifying embodiment of the inclination sensor system, the calibration unit is configured to estimate a first altitude difference value for a measuring distance travelled by the vehicle, which first altitude difference value is based on vehicle altitude information provided by the altitude information device. According to an exemplifying embodiment of the inclination sensor system, the first altitude difference value is based on the relative altitude difference between a starting point A and an end point B of the measuring distance. In other words, the calibration unit is configured to derive the altitude difference between two points, or location, by retrieving altitude information for each location. This is advantageous in that the altitude variations of different points located between the starting point and end point of the measuring distance do not affect the derived first altitude difference value. In other words, an accurate measurement of the first altitude difference value is provided.

According to an exemplifying embodiment of the inclination sensor system, the calibration unit is further configured to estimate a second altitude difference value for the measuring distance travelled by the vehicle, which second altitude difference value is based on vehicle inclination information provided by the inclination sensor. This allows for a second altitude difference value associated with the measuring distance, wherein the second altitude difference value is derived from the inclination information outputted from the inclination sensor.

According to an exemplifying embodiment of the inclination sensor system, the second altitude difference value is based on vehicle inclination information measured during the measuring distance. For example, the inclination information may be continuously, or repeatedly, retrieved by the calibration unit from the inclination sensor while the vehicle is traveling between the starting point A and end point B of the measuring distance. The calibration unit may also be configured for sampling of inclination information outputted from the inclination sensor.

According to an exemplifying embodiment of the inclination sensor system, the calibration unit is further arranged to calibrate the inclination sensor by estimating a calibration value for the inclination sensor, which calibration value is based on the difference between the first and second altitude difference values. Advantageously, the difference, or error, between the first and second altitude difference values is used for determining a suitable calibration value to be assigned to the inclination sensor in order to calibrate it.

According to a further exemplifying embodiment, the present invention related to a road vehicle drive line system comprising a propulsion unit connected to a transmission, which transmission is further connected to output shafts connected to drive wheels, and at least one electronic control unit, wherein the drive line system further comprises an inclination sensor system according to any one of the described embodiments of the inclination sensor system. For example, the road vehicle drive line system is arranged for a heavy vehicle, such as a truck, provided with an internal combustion engine and a transmission, or gearbox, which may be an automatic

transmission or an automatically controlled manual transmission.

Other objectives, features, and advantages of the present invention will appear from the following detailed disclosure, from the attached dependent claims as well as from the drawings. Brief Description of Drawings

In the following, the present will be described in more detail with reference to the accompanying drawings which show exemplifying

embodiments of the present invention, where: Figure 1 is a flowchart describing an embodiment of the method for calibrating an inclination sensor of a vehicle according to the present invention.

Figure 2 is a flowchart describing a further embodiment of the method for calibrating an inclination sensor of a vehicle according to the present invention.

Figure 3 is a flowchart describing a further embodiment of the method for calibrating an inclination sensor of a vehicle according to the present invention. Figure 4 illustrates a schematic representation of the inclination profile between a starting point A and an end point B of a measuring distance travelled by a vehicle.

Figure 5 schematically shows an embodiment of an inclination sensor system for a vehicle according to the present invention.

Figure 6 schematically shows an embodiment of a road vehicle drive line system comprising an inclination sensor system according to the present invention. It is noted that the drawings are schematic non-limiting exemplifying representations of embodiments of the invention and the dimension of details may be exaggerated and not true to scale.

Detailed Description of Embodiments of the Invention The method for calibrating an inclination sensor of a vehicle may be performed as schematically indicated in the flowchart 1 in Fig. 1. The method is typically executed by a vehicle control system, arranged in a vehicle, while the vehicle is in motion and travels on a surface, such as a road, comprising uphill and downhill sections. In this embodiment, the method is initiated by retrieving vehicle altitude information 10. This information is typically based on the altitude difference between two different points along the road which defines a measuring distance. The vehicle altitude information may e.g. be retrieved from or measured by a vehicle altitude information device arranged to the vehicle. The vehicle altitude information device may be a separate unit dedicated to measure the instantaneous altitude of the vehicle, or be an integral part of a vehicle control system/subsystem.

As shown in Fig. 1 , the method further comprises estimating and/or calculating a calibration value, 40, for the vehicle inclination. The calibration value, CV, is estimated and/or calculated by e.g. a calibration unit arranged in the vehicle. The estimation of the calibration value is based on the retrieved altitude information associated with the measuring distance and which was retrieved in the previous step. The estimation may further be based on vehicle inclination information retrieved during the measuring distance while the vehicle is traveling between the starting point and end point, wherein retrieved vehicle inclination information is processed, for example, by integration.

Next, the method comprises calibrating the inclination sensor using the calibration value CV, 50. For example, a calibrated vehicle inclination signal Vl_cal may be defined as the sum the vehicle inclination signal VI_out outputted from the inclination sensor and the calibration value CV:

Vl_cal = VI_out + CV (1) The estimation of a calibration value and the assigning of the

calibration value to the inclination sensor may be done each time the method, and a measuring sequence, is executed and finalized.

Calibration of the inclination sensor according to the present method is performed while the vehicle is moving, and may be repeated for a plurality of different measuring distances. For example, different measuring distances may be defined, wherein measuring distances having high variation in inclination level may be used for calibrating the steep inclination accuracy of the inclination sensor, and measuring distances having essentially horizontal, or non-varying, inclination profile may be used for calibrating the long-term accuracy of the inclination sensor. In addition, multiple measuring distances may be defined separately or simultaneously, wherein two or more measuring distances may overlap.

The method for calibrating an inclination sensor of a vehicle may further be performed as schematically illustrated in flowchart 2 in Fig. 2. In this embodiment, the method comprises retrieving vehicle altitude information 1 and determining a first altitude difference value 12, as well as retrieving vehicle inclination information 21 and determining a second altitude difference value 22.

In more detail, retrieving vehicle altitude information 11 comprises retrieving vehicle altitude information at a starting point and an end point of a measuring distance which is used for determining the first altitude difference value AD1 in step 12. Hence, the first altitude difference value AD1 is indicative of the relative altitude difference experienced by the vehicle when traveling between the starting point and the end point of the measuring distance. In 21 , vehicle inclination information is retrieved while the vehicle is moving between the starting point and the end point of the measuring distance, wherein the retrieved vehicle inclination information is used for determining a second altitude difference value AD2. For example,

instantaneous vehicle inclination may comprise both positive and negative inclination information corresponding to uphill and downhill sections of e.g. a road. This information is retrieved or sampled while the vehicle is traveling the measuring distance and integrated, or summed, in order to determine the second altitude difference value AD2. Consequently, a first and second altitude difference value AD1 and AD2 for the specified measuring distanced travelled by the vehicle is provided during a measuring sequence, wherein the first and second altitude difference values AD1 and AD2 are derived from two separate and independent sources, or signals.

Thereafter, the first and second altitude difference values AD1 and

AD2 are used for estimating a calibration value CV, as illustrated by block 41 in Fig. 2. For example, the estimated calibration value is based on the difference between first and second altitude difference values, wherein the difference contain information indicative of the accuracy of the inclination sensor. In particular, if the inclination sensor is correctly adjusted and no calibration is required, the difference between the first and second altitude difference values is close or equal to zero. This means that the same altitude difference value has been determined for both the first and second altitude different values AD1 and AD2. However, if a difference is present, it is indicative of that the inclination sensor has not provided correct inclination information during the measuring distance, and calibration of the inclination sensor is required.

The estimation of a calibration value may be based on a weighted value of the difference of the first and second altitude difference values, or determined by suitable parameters and/or calculation, depending of the type of inclination sensor and/or the accuracy of the retrieved vehicle altitude information. Furthermore, the calibration value may also be used for calibrating the inclination sensor by regulating techniques comprising feedback and/or negative feedback.

According to a further embodiment, as illustrated in the flowchart in Fig. 3, the method steps related to retrieving vehicle altitude and vehicle inclination information comprise:

- determining that vehicle is in motion and move along a road or surface, 301 ,

- initiating a measuring sequence event by determining a starting point for a measuring distance for which altitude difference should be retrieved, 302,

- retrieving vehicle altitude information for the vehicle at the starting point, 303,

- starting retrieving vehicle inclination information, 304,

- interrupting the measuring sequence event by determining an end point for measuring distance, 305,

- ending retrieving vehicle inclination information, 306,

- retrieving vehicle altitude information for the vehicle at the end point, 307,

- determining a first altitude difference value for the measuring

distance based on the retrieved altitude information associated with the starting point and the end point, respectively, 308, and

- determining a second altitude difference value for the measuring distance based on the retrieved inclination information associated with the measuring distance, 309.

The above steps 301 to 309, however, are not limited to be performed in the described order, and certain steps may also be performed essentially simultaneously. As further illustrated, the method may comprise interrupting the measuring sequence, 310, if the information being retrieved is determined non-normal or should be disqualified and not used for calibration of the inclination sensor.

Fig. 4 illustrates a schematic representation of the inclination profile between a starting point A and an end point B of a measuring distance 60. The intermediate road inclination profile between the starting point A and end point B is illustrated by the dashed line and exemplifying intermediate positions are indicated with a, b, and c, wherein the inclination at each intermediate point a, b, and c is represented by respective tangent lines. The inclination may also be referred to as the gradient, slope or the ratio: rise over run.

As indicated by the inclination profile, the measuring distance typically comprise downhill sections having a negative inclination, uphill sections having a positive inclination, and sections which are essentially horizontal or flat. With reference to the above method, for a vehicle traveling along the measuring distance 60, instantaneous altitude information is collected at point A and B in order to determine the first altitude difference AD1 for the measuring distance. Furthermore, vehicle inclination information is collected and integrated while the vehicle is moving between point A and B wherein the inclination of the vehicle changes in correspondence with the inclination profile of the measuring distance 60. Inclination information is retrieved continuously during the whole measuring distance, or sampled with a suitable sampling frequency at discrete intervals in order to establish the second altitude difference AD2 for the measuring distance. For example, inclination information is retrieved at a plurality of locations along the measuring distance including points a, b and c.

The second altitude difference value may be determined by integrating the vehicle inclination information retrieved while the vehicle is moving between the starting and end points A and B, wherein the second altitude difference value AD2 may defined as follows:

AD2 = / a (s)ds = J- (s) + 5)ds = g fi ds + (B - A)o (2) wherein a{s) is an ideal function which represents ideal inclination output from the vehicle inclination sensor, and

Q3(V) 4- δ represent the corresponding non-ideal, or real, function and an unknown offset value <5.

The offset value o typically originates from an error or deviation of the inclination sensor and may be determined and used as calibration value for calibration of the inclination sensor, for example by using CV = o, with reference to equation (1).

The offset value δ may, for example, be derived from the relationship that the first and second altitude difference values AD1 and AD2 should be equal, according to the following:

ADl = AD2

ADl = f fi(s)ds

(8 -A^'

However, the offset value may also be non-linear and dependent on the instantaneous vehicle inclination value at each point along the measuring distance. Furthermore, the determining of the second altitude difference value and the calibration value may be approximated and derived using numerical values and methods. Hence, a non linear calibration value for non-linear calibration of the inclination sensor is provided.

Figure 5 schematically shows an embodiment of an inclination sensor system 00 for a vehicle according to the present invention. The inclination sensor system 100 comprises an inclination sensor 01 for measuring the inclination of a vehicle, an altitude information device 102 for measuring vehicle altitude, and a calibration unit 103 arranged to calibrate said inclination sensor using information from the altitude information device 102.

The inclination sensor 101 comprises, for example, a tilt sensor or an accelerometer separately arranged in the vehicle, or arranged integrally with circuits and/or control systems in the vehicle, and is adapted to provide a signal indicative of the inclination of the vehicle. The inclination sensor 101 is further connected to and capable to communicate with the calibration unit 103, for example, via direct communication or via an internal vehicle communication network or data bus.

The vehicle altitude information device 102 comprises, for example, a pressure sensor which provides altitude information by measuring the atmospheric pressure. Hence, the vehicle altitude information may be derived from pressure variations between different reference locations. The vehicle altitude information device 02 may alternatively comprise a Global

Positioning System device (GPS device) which is configured to receive information containing vehicle position and vehicle altitude information. The altitude information device 102 may alternatively comprise a vehicle positioning device and a memory storing altitude information via learned road profiles or pre-stored topographic charts or maps, wherein the vehicle altitude information may be retrieved from the memory by knowing the vehicle's instantaneous position.

The accuracy of the altitude information device 102 may be between 2 and 0,001 percent, between 5 and 0.01 percent, between 0.5 and 0.1 percent, or about 0.2 or 0.1 percent. For instance, for an accuracy of 0.1 percent and a measuring distance of 1000 m, the altitude information device 102 has an altitude accuracy of 1 m.

The calibration unit 103 comprises, for example, a processor 110, a non-volatile memory 11 , a read-write memory 2, and in-out data port 114, and is configured to communicate with and retrieve information from the altitude information device 102 and the inclination sensor 101. The non- volatile memory 11 may store a computer program and/or an operating system for controlling and performing calibration of the inclination sensor 101.

The calibration unit 03 may, for example, comprise a sub-unit enclosed in a vehicle control unit, such as a transmission control unit performing automated gear and shift selections for the vehicle based on calibrated vehicle inclination information received by the calibration unit 103.

In Fig. 6, a road vehicle drive line system 600 is schematically shown. The, drive line system comprises a propuslion unit 604, in the form of an internal combustion engine, a clutch 610, and a transmission 611. The transmission 611 is connected output shaft 605 which transfer power to drive wheels 606. The drive line system further comprises an internal

communication network, or data bus, 612, arranged to provide

communication between a inclination sensor calibration unit 603 arranged in a transmission control unit 607, an inclination sensor 601 , an altitude information device 602, and an engine control unit 608.

The transmission control unit 607 controls clutch, shift and gear selections during operation of the vehicle by using a plurality of different external and internal vehicle parameters including calibrated vehicle inclination information provided by the calibration unit 603. Furthermore, in order to provide efficient gear and shift operation, the transmission unit 607 may further be able to request, or determine, certain engine parameters via the engine control unit 608, such as rpm and engine output torque.

As illustrated, the calibration unit 603 is housed in the transmission control unit 607, and is further configured to calibrate the inclination sensor 601 by using vehicle altitude information from the altitude information device 602.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

1. Method (1) for calibrating an inclination sensor (101) of a vehicle, characterized by

retrieving (10) vehicle altitude information,

estimating (40) a calibration value for said inclination sensor using said vehicle altitude information, and

calibrating (50) said inclination sensor by using said calibration value.

2. Method according to claim ,

wherein said vehicle altitude information is based on a measuring distance (60) travelled by said vehicle.

3. Method according to claim 2, further comprising

determining (12) a first altitude difference value for said measuring distance, which first altitude difference value is based on vehicle altitude information,

wherein said step of estimating said calibration value comprises using said first altitude difference value.

4. Method according to claim 3,

wherein said step of determining said first altitude difference value comprises retrieving (11) vehicle altitude information at a starting point (A) and at an end point (B) of said measuring distance.

5. Method according to any one of claims 3 or 4, further comprising determining (22) a second altitude difference value for said measuring distance, which second altitude difference is based on vehicle inclination information retrieved during said measuring distance by said inclination sensor,

wherein said step of estimating said calibration value further comprises using said second altitude difference value.

6. Method according to claim 5, wherein said second altitude difference value is determined by integrating vehicle inclination information retrieved between said starting point (A) and said end point (B) of said measuring distance.

7. Method according to any one of claims 5 or 6,

wherein said step of estimating said calibration value comprises using the difference between said first and second altitude difference values for said measuring distance.

8. A computer program comprising program code means for

performing the method according to any one of claims 1-7, when said program is run on a computer.

9. A computer program product comprising program code means stored on a computer readable medium for performing the method according to any one of the claims 1-7, when said program is run on a computer. 10. An inclination sensor system (100) for a vehicle, comprising an inclination sensor (101) for measuring the inclination of the vehicle, and

an altitude information device (102) for measuring vehicle altitude, characterized in that said inclination sensor system ( 00) further comprises a calibration unit (103) arranged to calibrate said inclination sensor (101) using information from said altitude information device (102).

11. An inclination sensor system (100) according to claim 10, wherein said calibration unit (103) is configured to estimate a first altitude difference value for a measuring distance (60) travelled by said vehicle, which first altitude difference value is based on vehicle altitude information provided by said altitude information device ( 02).

12. An altitude sensor system (100) according to claim 1 ,

wherein said first altitude difference value is based on altitude information at a starting point (A) and an end point (B) of said measuring distance (60). 3. An inclination sensor system ( 00) according to any one of claims 11 or 12,

wherein said calibration unit is further configured to estimate a second altitude difference value for said measuring distance travelled by said vehicle, which second altitude difference value is based on vehicle inclination information provided by said inclination sensor (101).

14. An inclination sensor system (100) according to claim 13, wherein said second altitude difference value is based on vehicle inclination information measured during said measuring distance (60).

15. An inclination sensor system (100) according to any one of claims 13 or 14,

wherein said calibration unit (103) is arranged to calibrate said inclination sensor ( 01) by estimating a calibration value for said inclination sensor, which calibration value is based on the difference between said first and second altitude difference values.

16. A road vehicle drive line system (600) comprising a propulsion unit 604 connected to a transmission 611 , which transmission is further connected to output shafts 605 connected to drive wheels 606, and at least one electronic control unit, characterized in that said drive line system further comprises an inclination sensor system ( 00) according to any one of claims 10 to 15.