1. What are the possible ways for calculating vehicle speed depends on the main operating data (Without sensor)?
2. How to calculate engine rpm without having the vehicle speed (km/hr)?
We may use the data from the major sensors in the vehicle.
the very basic one is to calculate the speed depending on engine rpm, gear ratio, and tire radius.
What else?
Dear Mohamed,
There is no other way to calculate vehicle speed than using tire radius and wheel rotational speed from ABS sensor or from engine rpm and gear ratio, as Zlatan Ajanović said. From wheel rotational speed you may calculate the engine rpm using gear ratio. Actually, every modern combustion engine has a crank shaft angle sensor and every modern car has ABS.
I do not see the aim of your question. What do need the vehicle speed or engine rpm for?
Best regards,
Martin
Dr. Martin,
The vehicle speed calculated by the stated method is not much accurate. Therefore, I am asking about vehicle speed estimation methods and the most accurate one.
Dear Mohamed
Yes, there is ways to achieve this. Within the ECU of electronic controlled engine.
You can get the signa which decides the fuel injection time interval from the bus of the ECU . With this you can have the rotating speed of the crank shaft.
Then if the transmission is electronic controlled, you can use the transmission rate information from it.
Then you have the spinning speed of the main shaft. You can use the radius of wheels to get the speed finally.
A precise answer to your question would depend on the context. Do you want to measure the speed continuously, when a private owner is driving his/her car? Is it a car test?
Other methods include GPS measurement, many radar technologies..
And the 'main operating data' depends on the type of car you have
Dear Mohamed,
using the engine rpm from the engine ECU (e.g. via OBD) is the easiest way. With the wheel speeds from ABS ECU you may also easily calculate the velocity of the center of mass. The errors you gain from this measurement come from a changing rolling radius of the wheel and the measurement method of the sensors. Both crank shaft angle and wheel speed sensor count increments/rev over time or frequency. This may lead to higher relative errors with higher speeds and to a measurable minimum speed. In addition you neglect the wheel slip, so you can't simply calculate v=omega*r.
You gain better results by incorperating several sensor systems for speed measurement, like wheel speed sensor + acceleration + GPS velocity in a multi-sensor data fusion or model-based observer, e.g. Kalman-Filter. You may find lots of publication on this topic "Navigation with Inertial Measurement Unit (IMU) and GPS". A modern car mostly has ABS wheel speed sensor, longitudinal acceleration sensor and GPS.
Best regards,
Martin
Good afternoon, Mohamed!
I suppose, that the most accurate approach to calculating the vehicle speed is the 'hybrid' approach when You will use different types of data so that to minimize the errors. In this case Kalman filters or Fuzzy logic can be used. I can suggest the next source for more information: U. Kiencke, L. Nielsen, “Automotive Control Systems for Engine, Driveline, and Vehicle” (2nd ed.), Berlin: Springer Verlag, 512 p., 2005.
From other side, if we're not talking about the inner vehicle sensors, one can use external devices: 1) optical sensors (e.g., CORREVIT S-CE w/Gyro); 2) 5th wheel; 3) GPS/Glonass+Inertial units... even smartphones... 4) cellular networks triangulation; 5) road infrastructure sensors + V2X and so on.
Best regards.
The most basic method is - as already stated - wheel rpms * tire circumference. In current cars, this is usually preferred to update the speedometer display.
In the not so distant "all mechanical" time the rpms of the drive shaft (gearbox output) were used for this purpose - which is equivalent to the above. Wheel slip is ignored (as it is not constant), and the influences of tire pressure and wear are ignored as well.
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