WO2020104567A1

WO2020104567A1 - System and method for updating a clock

Info

Publication number: WO2020104567A1
Application number: PCT/EP2019/082017
Authority: WO
Inventors: Denis COAT; Yasushia HAYAKAWA
Original assignee: Renault S.A.S; Nissan Motor Co., Ltd.
Priority date: 2018-11-22
Filing date: 2019-11-21
Publication date: 2020-05-28
Also published as: FR3089026B1; FR3089026A1

Abstract

This system (2) comprises a plurality of components (10, 12) and an electronic control unit (6) that is configured to communicate with each of the components (10, 12) via a communication network (4), each component (10, 12) being provided with a relative clock (14, 16), the control unit (6) comprising an absolute clock (8), the system (2) comprising an update unit (22) capable of transmitting an update term (∆T) for updating one of the relative clocks (14, 16). The update unit (22) comprises a filtering module (26) capable of applying a low-pass filter to the update term (∆T) calculated by the update unit (22).

Description

DESCRIPTION

TITLE: System and method for updating a clock The present application relates to the field of systems and methods for updating a relative clock fitted to a component, in particular for a component incorporated in a motor vehicle.

Nowadays, the number of components incorporated on board motor vehicles, such as, among others, sensors and estimators, is constantly increasing. In addition, more and more driving assistance devices are being offered. As a result, more and more importance is given to data fusion.

One of the main challenges of data fusion is to recover the data provided by components in order to extract coherent information. To do this, it is necessary to have an accurate dating of any event. Even a small dating error can lead to indecision and adversely affect the performance of the driver assistance system.

The Autosar standard aims to improve the accuracy of the dating of information supplied by non-synchronous components. The Autosar standard makes it possible to update the relative clocks fitted to the components from an absolute clock. More precisely, the Autosar standard consists in calculating an update term for a relative clock. The update term is added to the time measured by the relative clock. In this way, the relative clock is reset to the absolute clock.

To determine the update term, the Autosar standard processes and transmits information transmitted or received between an absolute clock and a relative clock. Processing and transmission operations can cause inaccuracies in the update term. In particular, there are inaccuracies linked to a network access time, to a flag coding time at the start and at the end of a transmission of the synchronization frame, to a processing time by computers, to truncation or rounding, to inaccuracies in calculation or to inaccuracies in clocks. Therefore, the registration of the relative clock on the absolute clock is imprecise. In view of the above, the invention aims to remedy the aforementioned drawbacks.

More specifically, the invention aims to allow the updating of a relative clock while respecting the Autosar standard and improving accuracy.

To this end, a system is proposed in particular for a motor vehicle, comprising a plurality of components and an electronic control unit configured to communicate with each of the components via a communication network, each component being equipped with a relative clock, l control unit comprising an absolute clock, the system comprising an update unit capable of transmitting an update term from one of the relative clocks.

According to one of its general characteristics, the update unit comprises a filtering module capable of applying a low-pass filter to the update term calculated by the update unit.

The application of a low-pass filter makes it possible to implement a correction of the update term to take account of an update noise when applying the Autosar standard. The system thus improves accuracy while remaining compatible with the Autosar standard.

According to one embodiment, the update unit is configured to determine the update term by applying the relation:

[Math 1] DG = s (t ₀ ) + t - t ₂

where AT is the update term, s (t ₀ ) is a variable depending on an absolute time to be transmitted, t ₂ is a relative time of reception of a synchronization frame containing s (t ₀ ) and t ₄ is a time sent by a tracking frame.

In an advantageous embodiment, s (t ₀ ) is the image of the absolute time to be transmitted by a function retaining only the most significant bits.

It can also be provided that the updating unit comprises a module for determining a coefficient, the filtering module being able to apply a filter with weighting by the coefficient determined by the determination module.

The determination module makes it possible, by modifying the coefficient, to implement a correction of the update term adapted to the update noise. Weighting filtering therefore makes it possible, in a simple manner, to reduce the influence of certain erroneous excursions.

In an advantageous embodiment, the determination module is configured to deliver a coefficient in the form:

[Math 2] c = ^

where c is the coefficient and n is a predetermined exponent.

The use of a coefficient in the form of a negative power of 2 facilitates the calculation operations.

Several variants are possible to determine the coefficient. According to a first variant, the determination module is configured to determine the coefficient by preliminary calculation. According to a second variant, the determination module is configured to determine the coefficient by tests in a final environment.

In one embodiment, the updating unit comprises a module for generating a bias term and a summator configured to calculate a corrected signal as the sum of a filtered signal delivered by the filtering module and a bias term generated by the generation module.

The corrected signal is a corrected update term, the bias term allowing to take into account a systematic bias in the update carried out by the Autosar standard.

Advantageously, the generation module is configured to determine the term of bias by testing in the final environment with final elements.

According to another aspect, a method is proposed for updating a relative clock equipping a component notably incorporated on a motor vehicle, comprising:

- the issuance of a relative clock update term,

- the application of a low-pass filter at the end of the update issued, and - updating the relative clock according to the filtered update term.

According to yet another aspect, a computer program is proposed comprising a code configured to, when executed by a processor or an electronic control unit, implement the method defined above.

Other objects, characteristics and advantages of the invention will appear on reading the following description, given solely by way of nonlimiting example, and made with reference to the appended drawings in which:

FIG. 1 schematically represents a system according to an embodiment of the invention,

FIG. 2 schematically represents time axes of an absolute clock and of a relative clock of the system of FIG. 1.

Referring to Figure 1, a system 2 is intended to be incorporated in a motor vehicle (not shown). The system 2 is in information link with a communication network 4. The network 4 can be, for example, a network well known to those skilled in the art under the Anglo-Saxon name "Controller Analogy Network" or under the 'corresponding acronym' CAN '.

The system 2 includes an electronic control unit 6. The electronic control unit 6 can be, for example, a driving aid calculator, known to the skilled person under the Anglo-Saxon name "Advanced Driver" -Assistance System ”or under the corresponding acronym“ ADAS ”.

The electronic control unit 6 comprises an absolute internal clock 8. In the present application, the expression “absolute time” will denote an instant read on the clock 8. The absolute clock 8 is also known to man of the profession by the expression "master of time".

The system 2 comprises several components such as for example a sensor 10 and an estimator 12. Although, in the example illustrated, the components of the system 2 are limited to a sensor and an estimator, it is of course possible to envisage other components of types different. The sensor 10 comprises a relative internal clock 14. The estimator 12 comprises a relative internal clock 16. Whatever a relative clock, in the present application, the expression “relative time” will be understood to mean an instant read on the clock relative considered. The relative clocks 14 and 16 are also known to those skilled in the art by the expression "time slave".

The electronic control unit 6, the sensor 10 and the estimator 12 are in information link via the network 4. In the example illustrated, the network 4 is not part of the system 2. However, it is of course possible consider incorporating network 4 into system 2.

The system 2 includes an update unit 22. The unit 22 includes hardware and software means 24 for calculating an uncorrected update term AT associated with one of the clocks 14 and 16. Although the unit update is schematically represented by a block independent of the other blocks and in particular independent of the blocks representing the components 10 and 12, the unit 22 is part, in the example illustrated, of the components 10 and 12. In particular, the unit 22 is a software resource usable by any time slave. Physically, there are as many implementations of this software resource as there are time slaves to synchronize.

The unit 22 includes a filter module 26 in connection with information with the means 24. A determination module 28 is in information link with the filter module 26.

The unit 22 comprises a generation module 30. The unit 22 comprises a summator 32 in connection with information with the module 26 and the module 30.

In this way, the unit 22 is able to deliver a corrected update term AT _corr from one of the clocks 14 and 16. The calculation of the term AT _corr for the clock 14 will now be explained. Of course, this calculation can be implemented in a similar manner for the clock 16.

Firstly, times are determined enabling the term AT associated with the clock 14 to be calculated. The determination of these times will be detailed with reference to FIG. 2. Figure 2 shows schematically a time axis 1 8 corresponding to the clock 8. In other words, the time read on the axis 18 is the absolute time. A time axis 19 corresponds to the relative clock 14. The time read on the axis 19 is therefore a relative time associated with the clock 14.

First of all, an absolute time to is chosen as the absolute time to be transmitted to the clock 14. The time to is processed then integrated into a synchronization frame 20 to be sent to the clock 14. In the example illustrated , the time to is subjected to a function s retaining only the most significant bits. Such a function is well known to those skilled in the art under the Anglo-Saxon name "most significant bit" or under the corresponding acronym "MSB". In this case, the function performs a truncation at the second of the time to. Subsequently, the image s (t ₀ ) is integrated into the frame 20. The frame 20 remains awaiting the availability of a transmission bus of the network 4.

At absolute time 11, a network bus 4 is available and the frame 20 is sent from clock 8 to clock 14. Frame 20 is received at relative time t2.

Later, a tracking frame 21, also known under the Anglo-Saxon name "Lollow Up" or under the corresponding acronym "LUP", transmits a time from clock 8 to clock 14. Time t ₄ is calculated by implementing the equation:

[Math 3] t ₄ = t ₁ - s (t ₀ )

From the times to, t2 and t4, the means 24 calculate an uncorrected update term AT associated with the clock 14 by applying the equation:

[Math 1] DG = s (t ₀ ) + t ₄ - t ₂

The module 28 delivers an exponent n. In the example illustrated, the exponent n is predetermined thanks to a preliminary calculation combined with tests in a final environment. The preliminary calculation is a theoretical calculation taking into account the digital elements available concerning the network 4, the electronic control unit 6, the components 10 and 12 and the clocks 8, 14 and 16. Thus, taking into account the synchronization periods, synchronization performance (convergence) and the sensitivity to hazards can be adjusted. For example, tests have shown that for n = 2, a time setting period is around 500 ms, the convergence of the time setting is 8 s for 1% error (i.e. 10 ps for a correction of 1 ms desired). The sensitivity to hazards is reduced with a low cutoff frequency of less than 1 Hz in this case.

Thus, the choice of exhibitor depends on the application and the desired sensitivity and / or stability.

Tests in a final environment may include, for example, tests on a platform representative of the vehicle for the electronic part.

The module 26 receives the term AT for the clock 14 and the exponent n. Module 26 processes this information to calculate a filtered update term by applying the equation:

[Math

In this way, the module 26 implements a low-pass filter of the term AT associated with the clock 14. More precisely, the filter applied is a digital low-pass filter with weighting by a coefficient in the form of a power negative of 2. Thus, the coefficient is indirectly estimated by module 28 by preliminary calculation and by tests in the final environment. However, it is of course without departing from the scope of the invention to envisage a different method of determination, for example by a preliminary calculation only, by tests in the final environment only, or even by any other means.

Preferably, the low-pass filter applied is a software filter. Therefore, no electrical signal as such is processed.

The module 30 determines a bias term tb iais by tests in a final environment with final elements. The final environment tests may include instrumentation of the parts on the network in its final configuration. The bias, potentially different for each relative clock 14 or 16, can thus be adjusted if necessary. To determine this bias, we will use for example a short CAN frame, preferably configured present in test phase. This frame can be sent by all the components of the system 2. For example, it can be sent by the absolute clock 8 every second. This makes it possible to measure the possible clock difference despite the synchronization mechanism.

The adder 32 receives the term ATf _ütré associated with the clock 14 and the term tbiais. The summator 32 calculates the term AT _corr associated with the clock 14 by applying the equation:

[Math 5] AT _Corr = T _filtered + t _bias

At a time t3 subsequent to the time of reception of the frame 21, the relative time associated with the clock 14 is offset by the term AT _corr . In other words, the clock 14 is readjusted so that the relative time t _3, the time T _set _ ^ _day delivered by the clock 14 satisfies the equation:

[Math

The same actions are implemented with respect to the clock 16. Likewise, these actions are repeated periodically. In this way, the clocks 14 and 16 are increasingly synchronized with the clock 8 and the update terms AT _corr associated with the clocks 14 and 16 converge to 0.

The invention therefore makes it possible to deliver a corrected update term taking account of an update noise and a systematic bias. The invention therefore makes it possible to improve the time synchronization of a slave clock in a motor vehicle while remaining compatible with the Autosar information dating standard.

In view of the above, the invention makes it possible to update a relative clock, in a manner compatible with the Autosar standard for dating information, with improved precision. Advantageously, the system and method according to the invention apply the Autosar standard for information dating. Specifically, the Autosar standard for dating information considered throughout this document includes the references "Specification of Time Synchronization over CAN, AUTOSAR, 674, Standard, release 4.2.2" and "Specification of Global Time Synchronization over Ethernet, AUTOSAR , 676, Standard, release 4.2.2 ”.

Claims

1. System (2) in particular for a motor vehicle, comprising a plurality of components (10, 12) and an electronic control unit (6) configured to communicate with each of the components (10, 12) via a communication network (4), each component (10, 12) being equipped with a relative clock (14, 16), the control unit (6) comprising an absolute clock (8), the system (2) comprising an updating unit (22 ) capable of transmitting an update term (DG) from one of the relative clocks (14, 16), characterized in that the update unit (22) comprises a filter module (26) capable of applying a low-pass filter to the update term (DG) calculated by the update unit (22).

2. System (2) according to claim 1, in which the update unit (22) is configured to determine the update term (DG) by applying the relation:

AT = s (t ₀ ) + t - t ₂

where AT is the update term, s (t ₀ ) is a variable depending on an absolute time to be transmitted (to), t ₂ is a relative time of reception of a synchronization frame (20) containing s ( t ₀ ) and t ₄ is a time sent by a tracking frame (21), s (t ₀ ) preferably being the image of the absolute time to be transmitted (to) by a function (s) retaining only the weight bits strong.

3. System (2) according to claim 1 or 2, wherein the updating unit (22) comprises a module for determining (28) a coefficient, the filtering module (26) being able to apply a filter with weighting by the coefficient determined by the determination module (28).

4. System (2) according to claim 3, in which the determination module (28) is configured to deliver a coefficient c in the form:

1

^{C ~} 2 ⁿ

where n is a predetermined exponent.

5. System (2) according to claim 3 or 4, wherein the determination module (28) is configured to determine the coefficient by preliminary calculation.

6. System (2) according to any one of claims 3 to 5, in which the determination module (28) is configured to determine the coefficient by tests in a final environment.

7. System (2) according to any one of claims 1 to 6, in which the updating unit (22) comprises a module (30) for generating a bias term (tb iai s) and a adder (32) configured to calculate a corrected signal (T _corr ) as the sum of a filtered signal (filtered _Tf ) delivered by the filtering module (26) and a bias term (tb iai s) generated by the generation module (30).

8. System (2) according to claim 7, in which the generation module (30) is configured to determine the term of bias (tb iais) by tests in the final environment with final elements.

9. Method for updating a relative clock (14, 16) fitted to a component (10, 12) in particular incorporated on a motor vehicle, comprising:

- the issue of an update term (DG) of the relative clock (14, 16),

- the application of a low-pass filter at the end of the update (DG) issued, and

- updating the relative clock (14, 16) as a function of the filtered update term (àTf _iltré ).

10. Computer program comprising a code configured to, when executed by a processor or an electronic control unit (6), implementing the method according to claim 9.