Along with automobile industry’s unceasing development, the energy crisis as well as the automobile exhaust the pollution which creates to the atmospheric environment is day by day serious. But the engine ignition time’s accuracy control while enhances the automobile overall performance, alleviated this condition effectively. Compares with the traditional machinery adjustment type ignition time control system, has timeliness based on the micro controller’s electronic formula control system to be good, the precision is high, control nimble and so on merits. Therefore, embarked from the engine ignition control system’s control policy, designs one kind to be able to increase the engine ignition control precision the new electron ignition control device.
1 system principle of work
The engine ignition time is through the control ignition angle of advance (i.e. when ignition has transferred piston position to top dead center crank angle) realizes. The influence spark plug ignition time’s factor mainly has the engine speed, the load size, the engine cooling water temperature as well as the engine cylinder body engine knock and so on.
The entire ignition system hardware circuit mainly by parts and so on sensor and signal recuperation electric circuit, A/D switch, electrically controlled unit, electric firing circuit, power source and spark plug is composed. System principle diagram as shown in Figure 1.
Various sensors’ output signal after the corresponding recuperation electric circuit recuperation, a/D switch transforms, sends in the monolithic integrated circuit. The monolithic integrated circuit basis certain control policy, the algorithm to input signal operation processing, the basis operation result, give the control signal in the appropriate time. Control signal after driving circuit, the control ignition control electric circuit work, realizes the engine ignition finally through the spark plug.
2 system hardware designs
2.1 sensors
And recuperation electric circuit
Mainly includes the tachometer generator, the water temperature sensor, the knock meter and the damper opening sensor and recuperates the electric circuit correspondingly.
2.1.1 tachometer generators and recuperation electric circuit
Uses the electro-optical type tachometer generator, its function is surveys the engine speed and the crank corner position. Sensor output signal after recuperation electric circuit reshaping, enlargement the number sends on the monolithic integrated circuit exterior counter T0(P3.4) pin, withing certain amount of time counts by the monolithic integrated circuit to it then measurable quantity its rotational speed and the crank position.
2.1.2 water temperature sensors and recuperation electric circuit
Uses the integration temperature sensor MAX6611 survey engine cooling water temperature. The monolithic integrated circuit makes the corresponding adjustment based on the water temperature signal to the ignition angle of advance: When the water temperature is low increases the ignition angle of advance, but the water temperature is high time reduces the ignition angle of advance. Sensor output signal after diode double limiting and RC filter circuit recuperation receives ADC0809 the channel on 0.
2.1.3 knock meters and recuperation electric circuit
Uses installs on the engine cylinder body’s piezoelectricity acceleration instrument surveys the engine knock signal, and based on whether to have the engine knock, but makes the corresponding adjustment to the ignition angle of advance. Sensor output signal after two level of filter circuit recuperation receives ADC0809 the channel on 1.
2.1.4 damper opening sensor recuperation electric circuit
Engine’s load’s survey is realizes through linear output simulation type damper sensor (TPS). Sensor output signal after double limiting filter recuperation electric circuit receives ADC0809 the channel on 2.
2.2 electrically controlled units and A/D transformation circuit design
This system takes the controller by at89C2051 monolithic integrated circuit. A/D converter uses ADC0809 to carry on the mold/number transformation to the front end input signal. In the system needs to carry on the signal which A/D transforms to have the water temperature signal, the damper opening signal and the engine knock signal. The monolithic integrated circuit and A/D switch’s interface circuit as shown in Figure 2.
From ADDA, ADDB and the ADDC choice transformation channel, the channel 0 input temperature signal, the channel 1 input engine knock signal, the channel 2 input damper opening signal, after the transformed signal inputs through the P1 mouth to the monolithic integrated circuit. And AT89C2051 P3.4(T0) pair of crank rotational speed signal counting, definite rotational speed and crank position. Through P3.5 output ignition control signal.
2.3 ignition control circuit design
Electric firing circuit’s function produces the high pressure which the spark plug ignition needs. Its input is comes from the monolithic integrated circuit P3.5 pin the ignition control signal, the output termination to the spark plug on. Electric circuit as shown in Figure 3.
When monolithic integrated circuit’s P3.5 outputs the high level, T1 and T2 cut off, 12 V voltages through R4 and L1 to the C7 charge. When monolithic integrated circuit P3.5 outputs the low level (sends out ignition control signal), T1, T2 breakover, then the C7 both sides’ voltage dislodges the low level immediately (i.e. the C7 rapid electric discharge), thus causes to wind through L1 the electric current sudden change, the L2 both sides produce the ignition high pressure. And D1 plays protects T2 the role.
2.4 power circuit design
Only provides 12 V DC voltages generally in the automobile system, but the chip needs 5 V voltages mostly. This system used integrated chip W78L05 to design 12 V to 5 V DC-DC switching circuit.
3 system software designs
The system software mainly by the master routine and the time delay subroutine, the computation basic ignition angle of advance subroutine, counts the T0 interrupt servicing subroutine, a/D transformation subroutine, the ignition angle of advance revision subroutine and the ignition subroutine is composed. This system used the assembly language to compile the source program.
3.1 master routines
On after system electricity, first carries on the system initialization (including monolithic integrated circuit’s initialization, the ADC0809 initialization, the counter T0 initialization), then gains the rotational speed signal determination basic ignition angle of advance, carries on a/D transformation gathering water temperature, the engine knock and the damper opening signal again, carries on operation processing to the gathering signal, finally waited for that the ignition time the arrival and sends out the ignition control signal to realize the system ignition.
3.2 computation basic ignition angle of advance subroutine
This system’s basic ignition angle of advance determined by the rotational speed signal that uses the table look-up law determination basic ignition angle of advance. First establishes two data sheets, one for ratemeter v(v[0], v[1], v[2],…, v[i], v[i 1],…) and basic ignition angle of lead table. In two table’s element integers are equal, and rises foreword sorting. Vi correspondence basic spark lead for the basic ignition angle of lead table in ith element. In order to reduce the search the number of times, when design used the dichotomy to carry on the retrieval to the ratemeter.
3.3 water temperatures to ignition angle of advance revision subroutine
The water temperature carries on the dual revisions to the ignition angle of advance, namely warm machine repair just and overheated revision. When the water tank temperature is excessively low, should enlarge the ignition angle of advance, namely carries on the warm machine repair to be positive. When the engine water tank hyperpyrexia, should reduce the ignition angle of advance, namely carries on the overheated revision.
In this design the water temperature revises to the ignition angle of advance also uses the table look-up law, establishes 2 calibration corrections: The overheated calibration corrections (rise foreword table) the mild machine calibration corrections (descending sequence table). According to the experience water temperature to the ignition angle of advance most overhaul 5°, uses the direct search law. First determined revises water temperature T to ignition angle of advance zero, obtains water temperature t is bigger than T to search the overheated calibration corrections to carry on the overheated revision, otherwise searches the warm machine calibration corrections to carry on the warm machine repair to be positive.
3.4 engine knock signals to ignition angle of advance revision subroutine
The system is to enable the engine to the ignition angle of advance revision to approach the engine knock critical state throughout, namely is in one kind “the critical control” the way, causes the engine both the close engine knock area and not to enter the engine knock area, the cylinder internal combustion’s thermal efficiency is this time highest. Measured has the engine knock signal ignition angle of advance to increase 2°, obtains when the non-engine knock signal ignites the angle of advance to reduce 2°. Supposes the critical state correspondence the engine knock signal is F, when obtains engine knock signal f is bigger than when F ignites the angle of advance to reduce 2°, otherwise the ignition angle of advance adds 2°.
Moreover, the damper opening uses the direct table look-up law to the ignition angle of advance revision subroutine.
4 conclusions
This firing device has timeliness to be high, the control precision higher merit, has realized to the ignition angle of advance optimized control. This system has debugged successfully.
