TLE4963-2M datasheet(17/91 Pages) INFINEON

17 / 91 page

XENSIV™ sensors in

hybrid powertrains

To maximize acceptance of new electric drive systems,

manufacturers must win over former combustion enthu-

siasts with ease of operation and a predictable, smooth

driving experience free of “nasty surprises”.

It’s important that a combustion engine can spring smooth-

ly and almost imperceptibly into action – as already expe-

rienced at traffic lights or in traffic jams in start-stop mode.

Here, it is essential that the car knows the angle of the

crankshaft at all times. If the car stops for three minutes in

a traffic jam, the crankshaft sensor is able to ignore a slight

temperature drift or, ideally, compensate for it. During a

30-minute drive on rough roads with a crankshaft that is

free to move when decoupled from traction wheels, how-

ever, the sensor could incorrectly count a slight shake or

vibration of a tooth or, in the worst case, interpret these

movements as a new, valid signal.

Drive interplay as experienced by the driver

To ensure a combustion engine can glide into action, it is

important that the sensor does not incorrectly count any of

the teeth moving past it. It is imperative that the sensor:

› Does not miss any teeth

› Does not count any additional teeth

› Does not mistake the rotational direction

These criteria are broken down inside the crankshaft sensor

as there is basically a magnet inside the sensor housing and

the field lines of this magnet are modulated by the teeth as

they spin past.

As such, the sensor’s performance is ultimately determined

by fluctuations in magnetic field strengths. And these are

dependent on a number of factors including the air gap

between the sensor and the trigger wheel and the tempera-

ture. To ensure we do not get sidetracked by the various

mechanical and electrical details, this paper focuses pri-

marily on the mechanical components that are relevant to

the sensor’s performance.

The following is a list of functions that help sensors to accu-

rately count teeth.

The conventional stop-start algorithm

The “smallest” solution for reducing fuel consumption

involves switching off the engine. It is already widely

deployed and available as a conventional stop-start algo-

rithm. This function is able to correctly interpret short stops

in congested traffic or at red lights and can compensate for

small temperature drifts.

Magnets are subject to very strong temperature drifts,

which can change the magnetic field by up to 40 percent

over the given temperature range. In the case of crank-

shafts with well-fitting bearings, the next most significant

factor to impact sensor behavior is electrical in source.

Number three in the lineup are changes in the air gap

between the trigger wheel on the crankshaft and the sensor

module on the engine block.

Ideally, the sensor remains fully calibrated and when the

combustion engine starts again, it is able to correctly out-

put the position and rotational direction of the crankshaft

as soon as the first tooth of the trigger wheel spins past.

This functionality can be implemented without any modi-

Diagram of a sensor module

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