FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
PROVISIONAL SPECIFICATION
(See Section 10; rule 13)
TITLE OF INVENTION
Alternative Methodology For Integration Of Odometer Signal For Vehicle Positioning
APPLICANTS
TATA MOTORS LIMITED, an Indian company
having its registered office at Bombay House,
24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
INVENTORS
Dibyendu Palai and Jagarlamudi Phani Kumar
Both are Indian Nationals
of TATA MOTORS LIMITED,
an Indian company having its registered office
at Bombay House, 24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
PREAMBLE TO THE DESCRIPTION The following specification describes the invention


FIELD OF INVENTION
The present invention relates to vehicle integrated navigation systems in automotive vehicles to achieve vehicle positioning functionality.
BACKGROUND OF INVENTION
With the advent of GPS systems the need has arisen for reliable integration of GPS based navigation systems in automotive vehicles.
Existing car navigation systems are either pure GPS navigation systems or car integrated navigation systems. In pure GPS navigation systems, the GPS signal is the only reference signal used to achieve vehicle positioning. Whereas car integrated navigation systems use other signals suitably derived from vehicle in addition to GPS signals for improving vehicle positioning accuracy mainly at the time of short time loss of the GPS signals (e.g. when vehicle cruising in high rise buildings etc.,). Typically vehicle speed is derived from vehicle and fed to navigation systems. To feed these signals to navigation system, either the navigation ECU needs to be developed as a CAN node (node in Controller Area Network) the in-vehicle network systems or separate vehicle or wheel speed sensors to be integrated with navigation systems. Both of the methodologies will result in increase of cost both in terms of development cost and piece cost. The proposed methodology talks about an alternate approach for integration of odometer signal for navigation systems with a much lesser integration cost.
OBJECTS OF INVENTION
The main object of invention is to improve the accuracy of vehicle positioning by integrating odometer signal with the car navigation systems with a lesser cost of integration. The advantage for this new approach is that it does not require a

dedicated vehicle speed or wheel speed sensor (WSS) to be integrated with navigation ECU. Neither does it require CAN connectivity for the navigation ECU.
BRIEF DESCRIPTION OF INVENTION
To improve the accuracy of vehicle positioning, the navigation system requires vehicle speed or distance traveled data as an input from vehicle. The maximum allowed age of this speed or distance information is 50ms to achieve best performance of the navigation system. This information could be provided to navigation system in either of the following ways:-
a. Integrate a separate dedicated wheel speed or vehicle speed sensor to
provide necessary vehicle speed or distance signal to navigation ECU.
b. Integrate navigation ECU in vehicle CAN network and get the
necessary information (vehicle speed or distance) from vehicle CAN
network.
c. In vehicle variants with ABS, ABS ECU generates vehicle speed or
distance signal in the vehicle. By executing necessary hardware and
software changes ABS ECU can be forced to provide necessary vehicle
speed or distance signal to navigation ECU.
But all the above mentioned methodologies will result in increase of development cost and per piece cost of the vehicle. Hence an alternate methodology is proposed which significantly reduces the total development cost of integration and cost of vehicle without degrading the performance of vehicle positioning of the navigation system.
In the vehicle network, both ABS ECU and Instrument Cluster (IC) are connected with each other over CAN (Controller Area Network). Four wheel speed sensors are connected to ABS ECU. ABS ECU computes the odometer signal from four wheel speed sensor signals based on fixed wheel size (or fixed wheel radius). ABS ECU publishes odometer signal over CAN network. IC receives this odometer signal from
3 0 MAR 2009

CAN network. IC converts this odometer signal to an equivalent pulse train and provides this pulse train to navigation ECU over hardware line. By this approach distance traveled signal can be provided to navigation ECU within a maximum age of 41ms. So, by this approach the requirement of navigation system is met without increasing integration cost.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 shows the existing electrical architecture of the vehicle before integration of navigation system.
Figure 2 shows an alternate approach to provide wheel speed information via hardwired connection between ABS ECU and Navigation system
Figure 3 shows the electrical architecture for the proposed methodology. This shows how WSS signals are converted to un-calibrated odometer signal and provided to navigation ECU.
Figure 4 shows the Time delay analysis of un-calibrated odometer signal. This figure shows the total age of the signal fetched to navigation ECU.
Figure 5 shows the sequence and the time delay in which the odometer signal is generated by wheel speed sensor (WSS) and before fetching to navigation ECU.
Figure 6 shows the timing analysis of calibrated odometer signal. This figure shows the total age of the signal before fetching to navigation ECU.
DETAILED DESCRIPTION OF INVENTION
The focus of proposed methodology is to integrate car-integrated navigation system


with odometer signal to improve accuracy of vehicle positioning with minimum integration cost.
Following is the electrical architecture existing in the vehicle before integration of navigation system. Engine Management System (EMS), Anti-lock Braking System(ABS)/ electronic stability controller (ESC), Instrument Cluster (IC) are connected to each other over in vehicle CAN. As explained in figure 1, the four wheel speed sensors (WSS) are part of ABS/ESC system. ABS/ESC being safety critical system it is not allowed for any other system (like navigation system) to have direct access to WSS signals, as this may affect the safety of the vehicle. ABS receives signals from WSS and computes vehicle speed and odometer signals assuming a fixed wheel size. Actual wheel size information is not available with ABS/ESC. Vehicle speed and odometer signals are transmitted by ABS/ESC over CAN with a periodicity of 20ms. These signals need to be re-scaled by EMS to match the actual wheel size fitted to the vehicle.
EOL calibration for actual wheel size is done only for EMS for the following advantages:-
d. Only one ECU shall be calibrated with actual wheel size to avoid
redundancy of configuring the same information
e. For non-ABS/ESC variants, EMS should know the actual wheel size.
f. EMS is fitted in all vehicle variants.
So, in vehicles with ABS/ESC, EMS reads the vehicle speed and odometer signals sent by ABS/ESC, re-scale the signals to consider actual wheel size. Then EMS transmits re-scaled vehicle speed and odometer signals over CAN to IC. IC receives these signals over CAN and uses them for display.
The navigation system needs distance traveled data from vehicle to improve the accuracy of vehicle positioning when no/ weak GPS signal is available. Typically while driving through long tunnels or driving near high buildings or driving through

narrow streets between buildings GPS signal may be lost momentarily to navigation system. Also sometimes the resolution of GPS signal is poor and not sufficient for complex road grids. Navigation system needs to estimate the current position of the vehicle based on previous determined known positions using dead reckoning algorithm. So the signals which need to be provided to navigation system from vehicle side shall meet the following requirements of dead reckoning algorithm for correct execution of the algorithm:-
a. The accuracy of input distance traveled signal shall be very high. The error
in the input signal shall not be more than 0.5% and error shall be consistent.
b. The maximum allowed latency of the input signal is 50ms.
c. There shall not be any shift between input signals.
d. Input signals shall not be disrupted as the estimated vehicle position is the
integral over all input signals.
If the above requirements are not met then navigation system may go to a state of permanent re-calibration.
To meet the above requirements following could be possible approaches.
Approach 1: An extra WSS could be fitted to the vehicle. This extra WSS will be dedicated for navigation system and this WSS will not be related with ABS/ESC. Though this approach will meet all of the above requirements of navigation system, but the extra WSS will increase the cost of the vehicle. Also this will call for EOL calibration for actual wheel size at EOL.
Approach 2: As the odometer signal is available in vehicle network (high speed CAN), the navigation system could be integrated in the vehicle CAN network. Then navigation ECU could receive the required signal from network. But this will call for development of HS CAN interface for navigation system and in turn increase the integration cost and effort.

Approach 3: By executing both hardware and software modifications ABS/ESC ECU could isolate WSS signals and repeat them for navigation ECU. This is explained in figure 2. This approach also meets all requirements of navigation ECU, This will require considerable amount of hard ware and software efforts required for implementation in ABS/ESC system. Also navigation ECU needs to be calibrated at EOL for actual wheel size of the vehicle.
As all the three approaches have some or the other drawbacks, an alternate methodology is proposed which meets all the requirements of navigation system without increasing cost and time of integration.
The electrical architecture for the proposed methodology is explained in figure 3. Four WSS are connected to ABS/ESC and it is getting raw WSS signals from four wheels. Now based on the fixed wheel size ABS/ESC is computing odometer and vehicle speed signals and publishing them over CAN network. EMS receives these un-scaled (or un-calibfated) odometer and vehicle speed signals over CAN from ABS/ESC, and scales them for actual wheel size. EMS then publishes these calibrated odometer and vehicle speed signals over CAN. IC receives these calibrated signals from EMS and also receives un-calibrated odometer signal directly from ABS/ESC. Even though IC has information about both vehicle speed and odometer signals, the un-calibrated odometer signal is chosen to be fed to navigation system, because of the following advantages:-
a. Navigation system needs distance traveled input from vehicle to calibrate
against the distance measured from GPS signals. If odometer signal is chosen then
speed to distance conversions can be avoided and in turn conversion errors due to
value rounding can also be avoided.
b. It is sufficient to provide un-calibrated odometer signal to navigation ECU, as
navigation ECU will use odometer signal directly to calibrate the distance measured
from GPS signals. So, IC does not need to re-scale the received odometer signal

again. As IC is not processing the odometer signal value with any scaling factor, no quantization error is introduced by IC in the odometer value.
c. If IC receives the un-calibrated odometer signal directly from ABS/ESC, then
the maximum age of the odometer signal will be 41ms. This concept is explained in
figure 4. As per this figure 4, the HW pulses are generated by WSS and consumed
by ABS/ESC. The delay introduced in this HW conversion line is negligible. Now
ABS/ESC is processing this WSS data and computing odometer value in 20ms time
raster. So, the maximum delay introduced by ABS/ESC is 20ms. Assuming
maximum delay introduced in CAN network for transmission of the CAN frame
being 1ms, the age of the odometer signal when it is received by IC is 21ms. IC
processes this odometer signal and converts it to an equivalent pulse train in 20ms
time raster. So, the age of the signal after it is process in IC becomes.41ms.
Navigation receives this HW pulse train from IC. Assuming negligible delay in this
HW line, the age of the signal after it reaches navigation system becomes 41ms.
Figure 5 shows the generation and consumption sequence of this odometer signal. As
per figure 5, the signal which was generated at 0th ms by WSS is consumed by
navigation ECU at 41st ms. The signal which was generated at 20th ms by WSS is
consumed by navigation ECU at 61st ms. So, this meets the requirement of 50ms
allowed max age for the input signal.
d. If IC receives calibrated odometer signal coming from EMS, then the age of
the signal at navigation ECU becomes 62ms. This concept is explained in figure 6.
As per figure 6, the age of the signal when ABS/ESC transmits on CAN is 20ms.
Age of the signal when EMS transmits on CAN is 41ms. IC takes 20ms to process
this signal. Finally, age of the signal at navigation ECU is 62ms.
So, by choosing un-calibrated odometer signal as the input signal for navigation system we can avoid value rounding, quantization errors and we can maintain lesser than 0.5% error in value of the input signal and also we can meet maximum age requirement for the input signal.

Hence, IC receives the un-calibrated odometer signal and IC generates an equivalent HW pulse train and provides the same to navigation system. IC also receives calibrated odometer and vehicle speed signals and uses them only for display purpose for the driver.
So, in this proposed approach all the interface requirements of navigation system are met without increasing integration time and cost.
The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.
Dated this 30th day of March 2009
TATA Motors Limited By their Agent & Attorney

(Karuna Goleria) of De PENNING & De PENNING