RESULTADOS Y DISCUSIÓN
8 Las decisiones por parte de los directivos son comunicadas oportunamente Nota. Cuestionario aplicado
Application
The Hall-effect sensor is also used as the igni- tion-triggering sensor for the TI-H transistor- ized ignition system. The information contain- ed in the signal from the Hall generator located in the ignition distributor corresponds to that in the signal generated by the breaker points in a conventional breaker-triggered coil-ignition system. Whereas with the conventional ignition system the distributor cam defines the dwell angle via the contact-breaker points, on the transistorized system the Hall-effect sensor in the ignition distributor defines the on/off ratio by means of the rotor (trigger-wheel) vane.
Design and construction
The Hall-effect sensor (Fig. 1) is installed in the ignition distributor, and its vane switch is attached to the movable mounting plate. The Hall IC is mounted on a ceramic substrate and in order to protect it against moisture, dirt, and mechanical damage is encapsulated in plastic at one of the conductive elements. The conductive elements and the rotor are made of a soft-magnetic material. The number of vanes on the rotor corresponds to the number of cylinders in the engine. Depending on the type of ignition trigger box, the width b of the ro- tor’s individual conductive elements can define the ignition system’s maximum dwell angle. The dwell angle therefore remains practically constant throughout the Hall sensor’s service life and dwell-angle adjustment is unnecessary.
Operating concept
When the ignition-distributor shaft rotates, the rotor vane’s pass through the Hall IC air gap without making contact. If the air gap is not occupied by a vane, the magnetic field is free to permeate the Hall IC and the Hall-ef- fect sensor element (Fig. 1). The magnetic flux density is high, the Hall voltage is at its maxi- mum, and the Hall-IC is switched on. As soon as a rotor vane enters the air gap, the majority of the magnetic flux is diverted through the vane and is isolated from the Hall-IC. The
magnetic flux density at the Hall sensor ele- ment reduces to a negligible level which re- sults from the leakage field, and the Hall volt- age drops to a minimum. The dwell angle is defined by the rotor vane’s shape as follows: A ramp voltage is generated from the signal volt- age US(converted Hall voltage, Fig. 2). The
switch-on point for the dwell angle is shifted as required along this ramp. The Hall-effect sensor’s priniple of operation and its con- struction permit the ignition to be adjusted with the engine at standstill provided no pro- vision is made for peak-coil-current cut-off.
Speed and rpm sensors Hall-effect sensors for transistorized ignition 61
Fig. 2
US Signal voltage (con-
verted Hall voltage)
tz Ignition point
Fig. 1
1 Vane with width b 2a Permanent magnet 2b Soft-magnetic con-
ductive element 3 Hall-IC 4 Air gap
US Signal voltage (con-
verted Hall voltage)
0
tZ tZ
Time t
Signal voltage
US
Hall-effect sensor in the ignition distributor (characteristic curve) 2
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UM Z009 7 -2E + – US b 1 2a 3 2b 4Hall-effect sensor in the ignition distributor (principle of operation) 1
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UM Z009 7 -1YPiezoelectric "tuning-fork"
yaw-rate sensor
Application
In order that it can use the digital road map stored on the CD-ROM to calculate the dis- tance driven, the computer in the vehicle’s navigation system needs information on the vehicle’s movements (composite navi- gation).
When cornering (for instance at road junc- tions), the navigation system’s yaw-rate sen- sor registers the vehicles rotation about its vertical axis. With the voltage signal it gener- ates in the process, and taking into account the signals from the tachometer or the radar sensor, the navigation computer calculates the curve radius and from this derives the change in vehicle direction.
Design and construction
The angle-of-rotation sensor is comprised of a steel element shaped like a tuning fork. This incorporates four piezo elements (two above, two below) and the sensor elec- tronics.
This sensor measures very accurately and is insensitive to magnetic interference.
Operating concept
When voltage is applied, the bottom piezo elements start to oscillate and excite the up- per section of the "tuning fork", together with its upper piezo elements, which then starts counter-phase oscillation.
Straight-ahead driving
With the vehicle being driven in a straight line there are no Coriolis forces applied at the tuning fork, and since the upper piezo elements always oscillate in counter-phase and are only sensitive vertical to the direc- tion of oscillation (Fig. 1a) they do not generate a voltage.
Cornering
When cornering on the other hand, the Coriolis acceleration which occurs in con- nection with the oscillation (but vertical to it) is applied for measurement purposes. The rotational movement now causes the upper portion of the tuning fork to leave the oscillatory plane (Fig. 1b) so that an AC voltage is generated in the upper piezo ele- ments which is transferred to the navigation computer by an electronic circuit in the sen- sor housing. The voltage-signal amplitude is a function of both the yaw rate and the os- cillatory speed. Its sign depends on the di- rection (left or right) taken by the curve. 62 Speed and rpm sensors Piezoelectric tuning-fork yaw-rate sensor
Fig. 1 a Excursion during straight-ahead driving b Excursion when cornering 1 Tuning-fork direction of oscillation resulting from cornering 2 Direction of rotation of the vehicle 3 Directiion of oscilla-
tion resulting from straight-ahead driving 4 Coriolis force 5 Upper piezo elements
(sensing) 6 Bottom piezo elements (drive) 7 Excitation oscillation direction Ω Yaw
"Tuning-fork" piezo yaw-rate sensor
1
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U AE08 7 7Y a 3 3 7 6 5 7 5 b Ω 5 7 6 5 4 4 1 2 4 4 7Piezoelectric "oscillating
drum" yaw-rate sensors
ApplicationsIn vehicle’s with vehicle-dynamics control (ESP), the piezoelectric yaw-rate sensors (otherwise known as gyrometers) register the vehicle’s rotation about its vertical axis, for instance when cornering, but also when the vehicle swerves or goes into a skid.
Design and construction
The piezoelectric yaw-rate sensors are high- precision mechanical sensors. Two diametri- cally opposed piezoceramic elements (Fig. 1, 1 + 1) are used to cause sympathetic oscil- lations in a hollow metal cylinder. Another pair of piezoceramic elements (2 + 2) are used to control and maintain this oscillation at a constant amplitude which has four axi- ally aligned oscillation nodes (offset by 45° to the direction of excitation). Refer to Figs. 1...3.
When rotation takes place at a yaw rate Ω about the cylinder’s axis, the nodes are shifted slightly at the circumference due to the effects of Coriolis acceleration. The result is that in the nodes, which otherwise feature zero force, forces are now generated which are proportional to rotational speed and
which are detected by a third pair of piezo el- ements (3 + 3). Using a fourth pair of piezo excitation elements (4 + 4) in a closed con- trol loop, these forces are then controlled back to a reference value Uref= 0. The ma-
nipulated variable needed here is then care- fully filtered and subjected to phase-synchro- nous rectification before being used as a highly accurate output signal. The selective, temporary change of the desired value to
Uref= 0 permits an easy check of the overall sensor system ("built-in test"). This sensor’s temperature sensitivity necessitates a com- plex compensation circuit, and the material- based aging of the piezoceramic elements necessitates painstaking preliminary aging.
Speed and rpm sensors Piezoelectric yaw-rate sensors 63
Fig. 1 1....4 Piezo elements 5 Circuit 6 Bandpass filter (phase-locked) 7 Phase reference 8 Rectifier (phase- selective) UAOutput voltage Ω Yaw rate
Uref= 0 (normal opera-
tion)
Uref 0 ("built-in" test)
Fig. 3
1....4 Piezo element pairs 5 Oscillatory cylinder 6 Baseplate 7 Connection pins Ω Yaw rate 1’ 3’ 2’ 4’ 1 3 2 4 6 6 8 7 UA Uref Ω 5
Piezoelectric yaw-rate sensor (measuring principle)
1
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U AE0662-1Y 1 … 4 5 7 6 Ω ΩPiezoelectric yaw-rate sensor (design principle)
3
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U
AE0644-1Y
UAE0789Y
Piezoelectric yaw-rate sensor