JPS6339174B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an in-vehicle electronic control system that suppresses noise generated by a plurality of control devices (for example, control computers) mounted on the same vehicle and that interferes with reception of communication devices such as in-vehicle radios. Regarding the system.

In recent years, with the spread of super LSIs and microcomputers, technology is being adopted in automobiles that uses one or more microcomputers to control engines and various electrical components.

Figure 1 shows an example of the schematic configuration of a microcomputer used in an in-vehicle electronic control system.
1 is a microprocessor, 2 is a clock oscillator using a crystal resonator;
uses an internal circuit to shape the waveform of the oscillation output of the crystal resonator, and the rise and fall times are each several nanoseconds.
A rectangular clock pulse of ~ several tens of ns is obtained. 3 is a memory, 4 _A to 4 _D are control circuits, 5 _A to 5 _D are A/D converters and D/A for transmitting and receiving signals with external circuits.
This is an input/output interface group containing various circuits such as a converter and a sensor amplifier, and these memory, control circuits, and interface group are connected to the clock pulse or memory control signal and the clock pulse in order to synchronize with the microprocessor 1. A logical product signal is supplied. The digital block 6 consisting of the above parts is housed in a metal case 8 together with a power supply section 7.
It is stored in 9 _A to 9 _D are input/output signal lines, 1
0 is the power line.

As shown in Fig. 2, the case 8 is installed in a place where the environmental conditions such as temperature and humidity are relatively favorable inside the vehicle, such as under the instrument panel or the seat, and is connected to the input/output signal line _9A. ~9 _D uses input/output signals of the digital block 6, that is, input signals from various sensors for calculating control parameters, and digitally processes these signals to control operations of the engine, various electrical components, actuators, etc. Transmitting control output signals.

The frequencies of the signals originally transmitted by these input/output signal lines are from 0 to several tens of kHz, and these signal lines and power lines are made of ordinary vinyl-coated wires, bundled together with the harnesses of other electrical equipment, and It is normal for the wiring to be concentrated. Due to this wiring condition, the input/output signal lines of the microcomputer and the harnesses of other electrical components, such as the in-vehicle radio 11 and the antennas (glass antennas embedded in the windshield and rear glass) 12, 13,
It can be said that the harnesses 14 and 15 connecting between the two are extremely tightly coupled in terms of high frequency through induction, electromagnetic radiation, and the like. Further, since the microcomputer and the in-vehicle radio are powered by the same in-vehicle battery 16 and also use the vehicle body 17 as a common ground, they are also directly conductively coupled through these power lines and ground lines.

By the way, square wave clock pulses of several hundred kHz to several MHz, which are used as synchronization control signals for microcomputers, consist of a high-level (several volts) fundamental wave and its harmonic components, and its frequency covers a wide radio frequency band. Range i.e. AM band to FM,
Since it is distributed over the TV band, it can be regarded as a type of noise source, and if the noise component leaks to the input/output signal lines 9 _A to 9 _D and the power line 10, it will cause damage to these input/output signal lines and the power line. Direct or indirect coupling with the radio harness or antenna may cause interference with vehicle radio reception.

In particular, if multiple microcomputers are installed in the same vehicle and the frequencies of the fundamental wave components or harmonic components in the AM broadcasting frequency band of the clock pulses used for each are close to each other, the multiple microcomputers When these clock pulses are operated at the same time, mutual interference between the fundamental wave components and harmonic components of the clock pulses generated by them can generate extremely loud noise (interference noise) in the car radio compared to when they are operated individually. , was clarified from the experimental results of the present inventors.

In order to prevent noise components that cause such reception interference from leaking into the input/output signal lines and power supply lines, it is necessary to check the parts of the microcomputer that operate on clock pulses and the parts that do not (input/output interface, power supply section, etc.). It is necessary to completely separate the two at high frequency, which is technically and economically unfeasible.

In addition, to prevent the coupling of signal lines with leaked noise components due to clock pulses to radio harnesses and antennas, (a) Use shielded wires such as coaxial cables as signal lines, or shield the entire signal line.

(b) Route the signal line as far away from the radio harness and antenna as possible.

There are methods such as, but when there are many signal lines,
All of these methods are impracticable in cases where the wiring of the signal lines is complex and the terminals are located at various locations within the vehicle.

The present invention has been made in view of the above-mentioned problems, and when an in-vehicle electronic control system is configured using a plurality of control devices such as microcomputers that are synchronously controlled by clock pulses, each of the control devices is used. The frequency of the clock pulses to be transmitted is determined by the fundamental wave component or harmonic component of these clock pulses within the AM broadcast frequency band.
By setting the frequencies to have a difference of 8 kHz or more, the present invention provides an in-vehicle electronic control system that can easily and reliably prevent interference with in-vehicle radio reception due to mutual interference of these fundamental wave components or harmonic components.

Hereinafter, the present invention will be explained in detail with reference to FIG. 3 and subsequent figures of the drawings.

Figure 3a shows multiple microcomputers A,
This shows the spectrum of harmonic components within the AM broadcast frequency band of the clock pulses φ _A , φ _B , and φ _C used for B and C, respectively. When the clock frequency is set to the 100 kHz band, Harmonics are generated at 100kHz intervals as shown in the diagram above.

As shown in an enlarged view in FIG. 5B, in this case, the frequencies of the spectra of microcomputers A and B are extremely close to each other. Therefore, when these microcomputers A and B are operated simultaneously in a vehicle, extremely loud noise (interference noise) is generated in the vehicle radio compared to when they are operated individually.

On the other hand, if the clock frequencies of microcomputers A and C are shifted and the fundamental wave or harmonic spectrum is separated by 8 kHz or more in frequency as in the present invention, these microcomputers A and C
It has been found that even when the two systems are operated simultaneously in a vehicle, noise can be suppressed to the same extent as when they are operated individually.

This can be explained as follows based on experimental data.

FIG. 4 is a block diagram of a simulation circuit used for measuring two-signal interference noise, in which the signals S ₁ (frequency ₁ , level V ₁ ), S ₂ (frequency ₂ , Level V ₂ ) is synthesized by the signal mixer 23 and output to the test radio (vehicle FM/
AM radio, e.g. Clarion RN391i) 24
It was added to the antenna end via a matching circuit.

Using this simulation circuit, two signals
_The antenna end input level V ₁ , V 2 of S ₁ , S ₂ is 5~
Set approximately equal in the range of 20dBμV, and the frequency difference Δ
Radio speaker terminal voltage v ₀ (V _rns ) when ₂ is changed so that = | ₁ − ₂ | is 0 to 15kHz
The change in was measured using a voltmeter 25.

Furthermore, if the frequency difference Δ between the two signals S ₁ and S ₂ is constant (approximately 1 kHz), the level difference Δv=|v ₁ −v ₂ |=0~
Radio speaker terminal voltage v ₀ when v ₂ is varied in the range of 20 dBμV (1μV = 0dBμV)
(V _rns ) was measured with a voltmeter 25.

In FIG. 4, 26 is a spectrum analyzer used for spectrum analysis of the antenna input signal, and 27 is an oscilloscope 28 used for observing the waveform of the speaker output, which is located after 21 in order to prevent the signal generators 21 and 22 from interacting with each other. 29 is a speaker.

Other measurement conditions are that both signals S ₁ and S ₂ are unmodulated waves, the radio tuning frequency is ₁ , the radio volume is 400 Hz, and the signal is 30% modulated.
When input to the antenna end at a level of 80 dBμV (1μV = 0dBμV), the speaker terminal voltage v ₀ is
It was set to 0.775V (0dBm or 1mW at 600Ω load).

The speaker terminal voltage v ₀ measured in this way
is due to mutual interference noise, so-called beat noise, which corresponds to the frequency difference Δ between the two signals S ₁ and S ₂ .

The level of the speaker terminal voltage with respect to this frequency difference Δ was corrected using a hearing sensitivity correction film, and the change in the audible beat noise volume with respect to the input signal frequency difference was determined. The results are shown in FIG.
Figure 5 shows the case where v ₁ ≒ v ₂ = 5 dBμV, and two signals
The frequencies of S ₁ and S ₂ are ₁ ≒ 1000kHz, ₂ = 1000kHz +
It is Δ.

Further, FIG. 6 shows changes in the relative level of the speaker terminal voltage with respect to the two input signal level difference Δv when the frequency difference Δ=1 kHz is constant. In Figure 6, 2
If the frequency of the signal is ₁ = 1000kHz, ₂ = 1001kHz, the signal
The level of S ₁ was set to v ₁ =5 dBμV, and the standard of the speaker terminal voltage level was set to −13 dBm (600Ω load).

Here, the absolute level of the beat noise volume is shown in the S/N characteristic diagram of the car radio as shown in FIG. In Figure 7, S+N is the speaker terminal voltage level for the input voltage of 400Hz, 30% modulation wave, N
is the speaker terminal voltage level with respect to the unmodulated wave input voltage, a is the beat noise level when two signals S ₁ and S ₂ are input at v ₁ ≒ v ₂ = 25 dBμV, and b is the same as v ₁ ≒ v ₂ = Beat when inputting at 30dBμV
The noise levels a′ and b′ are each 25 dBμV,
It shows the noise level when only one signal of 30dBμV is input.

Considering the above measurement results, as shown in Figure 7, when two signals with close frequencies are received at the same time, even with an extremely weak unmodulated signal, a beat noise sound of approximately the same level as the modulated wave is output from the speaker. The beat noise volume level is approximately 10 dB higher than the noise volume level when only one unmodulated wave signal is received. Therefore, in order to suppress the noise volume level due to simultaneous reception of two signals to the same level as when receiving only one unmodulated wave signal, it can be said from FIG. 5 that the frequency difference should be set to Δ≧8kHz.

Regarding the relationship between Δ and noise volume level, other in-vehicle radios are considered to have almost the same characteristics as the test radio, so the appropriate conditions for the frequency difference Δ between the two signals described above also apply to other in-vehicle radios. It is safe to say that it is completely true.

When the frequency difference Δ is small, the beat noise generation mechanism due to two-signal interference is as follows: (1) The AM modulation component generated by the synthesis of two signals.
AM demodulation output (2) FM modulation component generated by combining two signals
There are two possibilities: FM demodulation output, but as a result of actually observing the noise waveform at the speaker terminal, if the antenna end level of the two signals S ₁ and S ₂ is approximately 30 dBμV or less, T
= 2π/(ω ₂ − ω ₁ ) period and approximately 2v ₁ (when v ₁ ≒ v ₂ )
It was found that the AM demodulated output of the AM modulation component with an amplitude of . (ω ₁ and ω ₂ are angular frequencies) Among in-vehicle digital electronic devices, especially microcomputers where noise level is a problem, the antenna end level of the AM band harmonic component of the clock is about 5 to 30 dBμV when installed in the car. ,
The interference noise generated when multiple microcomputers are operated simultaneously can be said to be the result of demodulating the AM modulated wave by combining their clock harmonic components and appearing in the output.

As shown in Figure 6, the level difference Δv between the two signals
When is large, the beat noise sound due to interference decreases rapidly. Therefore, even if the antenna end of the car radio receives the fundamental wave components or harmonic components of a plurality of clocks, beat noise will not be a problem as long as the level difference between them is large.
However, in reality, if multiple microcomputers of approximately the same size are installed in the same vehicle and operated simultaneously, the antenna end input level of the fundamental wave component or harmonic component of the clock generated by them can be approximately the same. The beat noise caused by their mutual negotiation may significantly impair the marketability of the car radio.

FIG. 8 is a diagram showing an embodiment of the present invention to prevent this, and shows an example in which three microcomputers A, B, and C are used as control computers in the electronic control system 30 of the same vehicle. . Digital blocks of these microcomputers (internal configuration not shown) 31 _A , 31 _B , 31 _C
are the frequencies from clock oscillators 32 _A , 32 _B , and 32 _C such as ceramic resonators and crystal resonators, respectively.
It operates by receiving clock pulses of _C1 , _C2 , and _C3 . According to the invention, these clock frequencies
_C1 , _C2 , and _C3 are set so that the fundamental wave components or harmonic components of each clock pulse within the AM broadcast frequency band have a frequency difference of 8 kHz or more.

This 8 kHz frequency difference is equivalent to separating the frequency by a maximum of 8 kHz x 100 kHz/530 kHz ≒ 1.5 kHz (530 kHz is the lower limit frequency of the AM broadcast band) in the 100 kHz band, assuming that the fundamental frequency band of the clock pulse is 100 kHz. do.

In reality, the oscillation frequency of the clock oscillator is
Even if you specify 100kHz, it is inevitable that some variation will occur depending on the oscillation frequency deviation and temperature characteristics of the resonator, and for example, for a ceramic resonator used as a clock oscillator in a microcomputer, the oscillation frequency Deviation: ±0.3% Fluctuation due to temperature: ±0.2% (-20° to +80°C), with a total uncertainty of up to 0.5% (500Hz for 100kHz oscillation frequency).

Considering this point and considering the safety factor, the frequency difference _req (kHz) in the 100kHz band required to prevent mutual interference is: _req (kHz) = 1.5 + 100 x 0.5 / 100 + (safety factor) ≒2.5kHz. (A safety factor of 0.5 kHz was used.) Using this value, an example of the clock frequency allocation band when three microcomputers are used is as follows.

1ch: 97.2~97.4 2ch: 99.9~100.1 3ch: 102.6~102.8 The oscillation frequency of the ceramic resonator can be specified within a frequency band that is n times the above value (n = 1, 2, 3,...) .

As explained above, according to the present invention, a plurality of control devices that are synchronously controlled by clock pulses are installed in the same vehicle (for example, a clock using a crystal oscillator and a microcomputer are used to control engine fuel amount, ignition timing, EGR, etc.). Even if they are operated simultaneously (devices that control idle speed, etc.), mutual interference between the fundamental wave components or harmonic components of these clock pulses can be prevented, and the fundamental wave components or harmonic components of individual clock pulses can be prevented from interfering with each other. Therefore, it is possible to prevent the generation of large interference noise that would interfere with the reception of the in-vehicle radio.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a configuration example of an on-vehicle microcomputer, Figure 2 is a wiring system diagram of a vehicle equipped with a microcomputer, Figure 3a is a spectrum of clock harmonic components within the AM broadcasting frequency band,
Fig. 4 is a block diagram of the simulation circuit used to measure the two-signal interference noise, and Fig. 5 is the relative level of the auditory volume of the beat noise sound with respect to the frequency difference between the two input signals. Figure 6 is an actual measurement diagram showing the relative level of speaker terminal voltage with respect to the level difference between two input signals. Figure 7 is an actual measurement diagram showing the absolute level of beat noise along with the S/N characteristics of the car radio. , FIG. 8 is a conceptual diagram showing an embodiment of the present invention. 30...In-vehicle electronic control system, 31 _A , 31
_B , 31 _C ...Digital block, 32 _A , 32
_B , 32 _C ... Clock oscillator, A, B, C... Control microcomputer.

Claims (1)

[Claims] 1. In an on-vehicle electronic control system configured using a plurality of control devices that are synchronously controlled by clock pulses, the frequency of the clock pulses used by each of the control devices is determined by the fundamental wave component of these clock pulses within the AM broadcast frequency band or An in-vehicle electronic control system that suppresses noise, characterized in that harmonic components are set to have a frequency difference of 8kHz or more.