JPS6040901A - Signal processinc circuit for engine-rotary-angle sensor - Google Patents

Abstract

PURPOSE:To change a threshold value in synchronization with the change in a crank sensor signal by a simple constitution, by digitally measuring the rotary period of an engine and directly determining the threshold value corresponding to the number of rotation. CONSTITUTION:A crank angle sensor signal corresponding to the rotary angle of an engine is compared with a threshold voltage by a comparator 10 and outputted as an engine-rotary-angle signal. The signal is processed by a differential circuit 11. Clearing and counting of the differential signal and the next differential signal are performed by a clock counter 12. Latching of the counted value to a latch circuit 13 is controlled. Then the rotary period of an engine is determined. The crank angle sensor signal is non-linearly changed with the change in the number of rotation of an engine through a decoder 14 and a D/A converter 15. The threshold value corresponding to the rotation of the engine for the crank-angle-sensor signal is directly determined. The threshold value signal is changed in synchronization with the change in the crank-angle-sensor signal by the change in the number of rotation of the engine by a simple constitution. Thus the engine-rotary-sensor signal is accurately processed without error.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an engine rotation angle sensor signal processing circuit using digital processing.

In engine control systems using a microprocessor (MPU), a magnetic detection type crank angle (0 person) sensor is often used as an engine rotation angle sensor. This CA sensor utilizes the fact that the voltage V across the detection coil changes due to the change in magnetic flux φ caused by the rotation of the crankshaft.

V By the way, as is clear from equation +11, the output of the CA sensor is a function of the engine speed, so it is necessary to shape the waveform using a comparator in order to input it to the MPU. In this case, when the engine speed is low, the output of the CA sensor is also small, so it is necessary to lower the threshold value of the comparator, and when the engine speed is high, it is necessary to increase the threshold value to avoid the effects of ignition noise, etc.

For this purpose, it is necessary to detect the engine speed and generate a threshold value accordingly. FIG. 1(a) shows a conventional example in which the frequency (F) indicating the engine speed is converted to the voltage (V) by rectifying and smoothing the CA sensor signal with the F/V converter 1
) and use it as the comparison voltage (threshold) of the comparator 2. tb) is a circuit example of the F/V converter 1. However, this method has the following drawbacks.

(i) Since the rotation speed and the sensor output are not linear, the circuit becomes complicated in order to obtain the optimal threshold value (comparison voltage).

(ii) The output of the rectifying/smoothing F/V converter includes ripple pull, but if you try to reduce the ripple, the response will deteriorate, and the signal will drop out when the rotation speed suddenly changes (the CA sensor signal voltage will be lower than the threshold voltage). (becomes smaller), etc., resulting in malfunction.

(iii) Since the L threshold value change is asynchronous with the GA sensor signal, there is a possibility that the threshold value changes at the time when the CA sensor signal crosses the threshold value, which also causes malfunction.

(iv) When the rotational speed (=sensor output voltage change) changes significantly, such as during cranking, it becomes difficult to obtain an optimal threshold value.

The present invention focuses on the fact that the relationship between engine speed and CA sensor output voltage is determined by the physical shape of the sensor, and attempts to eliminate the above drawbacks by digitally measuring the rotation period and directly obtaining a threshold value. That is.

The present invention includes a comparator that compares an engine rotation angle sensor signal with a threshold value and shapes the waveform, a differentiation circuit that differentiates the comparator output, and a differentiation circuit that is cleared by the output pulse of the differentiation circuit and is cleared by the next output pulse. A counter that counts pulses of a constant period until cleared, a launch that captures the counted value immediately before the counter is cleared, and a threshold value for the comparator that is generated by D/A converting the counted value held in the launched. The present invention is characterized in that it includes a D/A converter that corrects the threshold value according to the characteristics of the engine rotation angle sensor, and a correction circuit that corrects the threshold value according to the characteristics of the engine rotation angle sensor.This will be explained in detail below with reference to the illustrated embodiment. .

FIG. 2 is a block diagram showing an embodiment of the present invention, and 10 is a block diagram showing an embodiment of the present invention.
A comparator that shapes the waveform of the A sensor signal, 11 a differentiation circuit that differentiates the comparator output (CA sensor signal processing output) and detects a change point, 12 counts pulses of a constant period (for example, 0.1 m s ). counter, 1
3 is a lunch that holds the count value, 14 is a decoder (correction circuit) that decodes the digital value according to a predetermined conversion table (described later), and 15 is a circuit that converts the decoded output into an analog voltage and sets the threshold of the comparator 10. Value (comparison voltage)
This is a D/A converter that generates.

FIG. 3 is a waveform diagram of each part. The counter 12 is cleared at the rising edge of the output pulse of the differentiating circuit 11, and the latch 13
takes in the count value of the counter 12 at the rising edge immediately before that. This count value corresponds to a constant engine rotation angle (for example, 30° crank angle), but as the rotation speed increases, the count value decreases.

Therefore, if the decoder 14 is provided with a ROM (read-only memory) having conversion contents as shown in the table below, the output (counter value) of the latch 13 can be converted into an appropriate digital value as an address.

The table shows the final table after D/A conversion of the digital values. 1 Figure 5 shows the change in the threshold value (L-H) when the rotation speed decreases, and the solid line shows the change in the threshold value (L-H) when the rotation speed decreases, and the hysteresis generation in Figure 2 resistance 1
The threshold value (HL) according to 6 is shown by a broken line. In this case, care must be taken that the change point of the threshold value (L-+H), which is the D/A output, does not coincide with the intersection of the CA sensor signal and the threshold value (L-H). Furthermore, the decoder 14
It is also possible to use one with a built-in microprocessor.

FIG. 6 (A> is an example in which an R-2R type resistor ladder circuit network is used for the D/A converter 15, and its D/A output Vou
t becomes. In this case, the decoder 14 is used to convert the entire device into an IC.
It is possible to make the ROM part of
As in the other embodiment of the present invention shown in FIG. It becomes a correction circuit. In this case, the resistor network becomes a mask option. RP is a feedback resistor of 4°.As described above, the contents of the mask option are selected depending on the characteristics of the sensor used.

The engine rotation angle sensor signal processing circuit of the present invention described above has the following advantages.

la) Since the threshold value for the rotation period (=rotation speed) can be arbitrarily selected, the optimal threshold value can be determined in the entire rotation speed range.

(b) Since the time of change of the threshold value is synchronized with the CA sensor output waveform, the above problem (iii) can also be solved by appropriately selecting the point of change of the threshold value.

(C1 Unlike the conventional method, no capacitor is required, so IC
It is easy to convert.

(d1 Has a processing speed that can sufficiently cope with sudden changes in rotational speed.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of a conventional engine rotation angle sensor signal processing circuit, Fig. 2 is a block diagram showing an embodiment of the present invention, Fig. 3 is a signal waveform diagram of each part, and Fig. 4 is a CA sensor sensor. FIG. 5 is a waveform diagram showing a threshold change depending on the rotation speed, and FIG. 6 is a circuit diagram showing different examples of the D/A converter. In the figure, 10 is a comparator, 11 is a differential circuit, 12 is a counter, 13 is a latch, 14 is a decoder (correction circuit),
15 is a D/A converter, and 15' is a D/A converter using a resistor network as a threshold correction circuit. Applicant: Minoru Aoyagi, Patent Attorney, Fujitsu Ten Limited

Claims (1)

[Claims] A comparator that compares the engine rotation angle sensor signal with a threshold value to shape the waveform, a differentiation circuit that differentiates the output of the comparator, and a constant cycle that is cleared by the output pulse of the differentiation circuit until cleared by the next output pulse. A counter that counts the number of stitches of the pulse, a launch that captures the stitch value just before the counter is cleared, and a D/D that captures the count value held in the latch.
D/ which converts A and generates the threshold value of the comparator.
An engine rotation angle sensor signal processing circuit comprising: an A converter; and a correction circuit that corrects the threshold value according to characteristics of the engine rotation angle sensor.