GB1586013A

GB1586013A - Electronic fuel injection system for internal combustion engines

Info

Publication number: GB1586013A
Application number: GB1556378A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1977-10-04
Filing date: 1978-04-20
Publication date: 1981-03-11
Also published as: JPH0112933B2; JPS551458A; DE2744543C2; DE2744543A1

Description

(54) ELECTRONIC FUEL INJECTION SYSTEM FOR -INTERNAL COMBUSTION ENGINES (71) We, ROBERT BOSCH GMBH, a German company, of Postfach 50, 7 Stuttgart 1, Federal Republic of Germany do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by- which it is to be performed, to be particularly described in and by the following statement: The present invention relates to electronic fuel injection systems for internal combustion engines.

It is known to feed ignition pulses to a pulse shaper of an electronic fuel injection system and to connect a frequency divider to the output of the pulse shaper and in turn to use the output signals of the frequency divider as input signals for a control multivibrator acting aS a timer for the injection pulses. The injection pulses are determined in this control multivibrator in dependence upon the throughput of air in the intake pipe and, optionally, are corrected in a multiplier stage connected on the output side of the multivibrator. The frequency divider connected to the input of the control multivibrator serves to trigger only one injection operation during one revolution of the crankshaft.This is particularly desirable with respect to accurately determining the injection time, since, as a result of the frequency division, a longer period of time is available for determining the injection time.

In practice, it has transpired that specific changes in the engine speed can lead to unstable states (jolting) in vehicles which are equipped with an electronic injection system. In order to avoid this, dynamic rotational speed damping means (anti-jolting circuit) are provided.

When the ignition signal is used as a rotational speed signal, differing intervals of time can ensue from ignition operation to ignition operation particularly when oscillations occur in the ignition distributor system. This circumstance signals changes in the rotational speed and can thus lead to uncorrected injected times.

The present invention provides an electronic fuel injection system for an internal combustion engine, having a transducer for monitoring an operating parameter of the engine, the transducer output frequency varying in accordance with said parameter, a timer for producing a trigger signal for at least one fuel injection valve, and a frequency and/or phase lock loop arranged between the timer and the transducer.

The fuel injection system in accordance with the invention has the advantage that smooth adaptation of the injection time results despite an abrupt change in the rotational speed signal. This adaptation also prevents a jump in the quantity of fuel to be injected, thus avoiding jolting.

In future collective or central injection systems having only one injection valve it will be necessary to double the injection frequency (that is twice per revolution of the crankshaft) relative to the prior art in order to ensure. an acceptable dynamic behaviour, and this doubling of the injection frequency can be obtained by simple means when using a frequency and/or phase control circuit. The formation of the injection frequency by means of a frequency and/or phase lock loop is also unproblematic in the case of internal combustion engines having a greater number of cylinders, particularly in five-cylinder engines.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a highly simplified circuit diagram of an electronic fuel injection system; Figure 2 is a block circuit diagram of a phase control circuit; and Figure 3 is a circuit diagram shown in greater detail than the block circuit diagram of Figure 1.

The drawings illustrate an electronic fuel injection system for an internal combustion engine in which an injection time for at least one injection valve is ascertained on the basis of operating parameters. A pulse generator is designated 10 and responds to ignition signals. The pulse generator is followed by a pulse shaper 11 whose output 12 is connected to a frequency divider 13. The frequency divider is followed by a frequency and/or phase lock loop 14. The type of loop depends particularly upon economic considerations and upon the required accuracy or design of the circuit. The output of the frequency and/or phase lock loop (hereinafter referred to as "lock loop") is connected to a first input 16 of a timer 17 which has a further input 18 and an output 19. A signal dependent upon the throughput of air in the intake pipe Is applied to the second input 18 of the timer 17.The output 19 is optionally followed by a correction stage (not illustrated) for varying the injection time in dependence upon other operating parameters, and finally by at least one solenoid injection valve 20 whose winding receives the pulses produced in the timer 17.

The pulse generator 10 generates, in conformity with the ignition frequency, pulses which are prepared in the following pulse shaper stage 11 for further processing. The lock-loop 14 connected to the output of the frequency divider adjusts large fluctuations in the output signal of the pulse generator, whereby a signal whose frequency does not change abruptly is applied to the first input 16 of the timer 17. The timer 17 itself determines an injection time from this indirect speed signal and from a signal dependent upon the throughput of air in the intake pipe, the injection time being corrected, if required, in one or more stages.

The frequency divider 13, having the divider ratio n:1 and shown connected to the input of the lock-loop 14, may be omitted according to the design of the lock-loop, A lock-loop, such as may be used in the circuit of Figure 1, is shown in Figure 2 for the case in which the lock-loop.14 is in the form of a phase lock loop. These phase lock loops are prior art and essentially comprise a phase detector 30, a low-pass filter 31, a voltage-controlled oscillator 32, and a feedback loop 33. In the simplest case, the frequencies of the voltage-controlled oscillator and those of the input signal of the phase lock loop are identical. The phase detector 30 detects a difference between the phases of the inPut signal and the output signal and feeds the signal, characterising a phase difference, to a ow-pass filter.The output signal of the low-pass filter in turn influences the frequency of the voltage-controlled oscillator 32, whereby it is possible to change the frequency of the output signal of the phase lock loop. An EXCLUSIVE OR gate, also forming part of the prior art, may be used as the phase detector 30.

Frequency lock loops are also adequately known in the prior art in addition to phase lock loops, so that there is no need to describe them.

The ratios of the frequency of the ignition signal to the frequency of the injection signal vary according to the type of internal combustion engine. This is particularly evident in the case of a five-cylinder internal combustion engine in which five ignition operations are effected for two revolutions of the crankshaft, although only one injection operation per revolution of the crankshaft is desired. The frequency divider 13 of Figure 1 and the lock-loop 14 have to be designed in conformity with this frequency ratio. An optional frequency ratio can be realised by means of the intentionally generalized circuit arrangement of Figure 3.

The block circuit diagram of Figure 3 includes a total of three frequency dividers. The first frequency divider 13 has the ratio n:1, a frequency divider 40 connected to the output of the lock-loop has a divider ratio of p:l, and a frequency divider 41 arranged in the feedback loop has the frequency ratio m:1. If the output frequency of the pulse shaper 11 is designatedfo, the output frequency of the frequency divider 13 is designated fl, the output frequency of the controlled oscillator 32 is designated f2, the frequency of the signal fed back to the phase detector is designated f3, and the frequency of the output signal of the frequency divider 40 is designated f4, a frequency f4 of the value of f4 = f0 is obtained when fl and f3 have the same value.The relationship, with respect to th8Pformula, between the frequencies of the tachogenerator signal and the input signal of the timer 17 shows the interchangeability of the frequency dividers 13 and 40 having the ratios n:1 and p:1. One of the frequency dividers 13 or 40 can be omitted according to the nature of the individual division ratios, the choice being dependent on various criteria such as the type of lock-loop and the frequency range of the tachogenerator signal.

The divider ratio m:1 of the frequency divider 41 renders it possible for the voltage-controlled oscillator to oscillate to a higher frequency. The choice of m and n renders it possible to realise any standard ratio of injection frequency to ignition frequency (for any number of cylinders and any type of injection, normal or double injection frequency). An increase in the m divider value leads to an increase in thep divider value for a constant output frequency, whereby, in the individual case, an increase in the oscillator frequency, which is desirable owing to the asymmetric on/off times of the voltage-controlled oscillator, and symmetry of the on/off times of the output of the frequency divider 40 are obtained.The arrangement described not only renders it possible to perceive the anti-jolt function and to compensate for ignition intervals subjected to faults, but also renders it possible to realise a frequency divider system standardized for all numbers of cylinders and types of injection.

The following Table shows frequency divider ratios which are necessary and possible in the case of the frequency dividers of Figure 3. CS denotes crankshaft revolution. CII signifies "central injection intermittent", that is, only one injection point is provided in an intermittently operating injection system. In the present case, twice the number of injection operations is effected per revolution of the crankshaft than has hitherto been normal. The frequency dividers 13, 41 and 40 are designated FD1 to 3.

Number of Type of Frequency Total required FD1 FD2 FD3 cylinders injection Ignition Injection divider ratio n m p f4/fo = m/m.p 4- normal 4x per 2x per 2/4 = 1/2 2 1 1 cylinders 2 CS 2 CS 1 1 2 1 2 4 5- normal 5x per 2x per 2/5 = 1/2.5 5 2 1 cylinders 2 CS 2 CS 1 2 5 1 4 10 6- normal 6x per 2x per 2/6 = 1/3 3 1 1 cylinders 2 CS 2 CS 1 1 3 1 2 6 8- normal 8x per 2x per 2/8 = 1/4 4 1 1 cylinders 2 CS 2 CS 1 1 4 1 2 8 2 1 2 4-cylinders CII 4x per 4x per 4/4 = 1/1 1 1 1 2 CS 2 CS 1 2 2 5-cylinders CII 5x per 4x per 4/5 5 4 1 2 CS 2 CS 1 4 5 1 8 10 6-cylinders CII 6x per 4x per 4/6 = 2/3 3 2 1 2 CS 2 CS 1 2 3 1 4 6 8-cylinders CII 8x per 4x per 4/8 = 1/2 2 1 1 2 CS 2 CS 1 1 2 1 2 4 In the system described above, the lock-loop 14 is located between the pulse generator 10 for the engine speed and the timer 17 for the injection pulses.A corresponding lock-loop is also recommended in input circuits of other operating parameters when the latter exist, or are processed in a frequency-dependent form.

In connection with comprehensive processing of, for example, the rotational speed signals, it' is advisable for the operating parameter signal, free from interference owing to the presence of the lock-loop, also to be made available for further signal processing, such as processing for calculating the instant of ignition.

WHAT WE CLAIM IS: 1. An electronic fuel injection system for an internal combustion engine, having a transducer for monitoring an operating parameter of the engine, the transducer output frequency varying in accordance'with said parameter, a timer for producing a trigger signal for at least one fuel injection valve, and a frequency and/or phase lock loop arranged between the timer and the transducer.

2. An electronic fuel injection system as claimed in claim 1, wherein the transducer is a tachogenerator.

3. An electronic fuel injection system as claimed in claim 1 or 2, wherein a frequency divider is connected to the input and/or the output of the frequency aXnd/osr phase lock loop.

4. An electronic fuel inje'ction system as claimed in claim 1, 2 or 3, wherein a frequency divider is arranged in the feedback loop of the frequency' and/or phase lock loop.

5. An electronic fuel injection system as claimed in any of claims 1 to 4, wherein the frequency and/or phase lock loop includes a voltage-controlled oscillator whose frequency is a preselected multiple of the input frequency.

6. An electronic fuel injection system as claimed in any of claims 1 to 5, wherein the input or output signal 6f the voltage-controlled oscillator acts as a trigger signal for further circuit arrangements.

7. An electronic fuel injectiqn system constructed and adapted to operate substantially as hereinbefore described with reference ta and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. In the system described above, the lock-loop 14 is located between the pulse generator 10 for the engine speed and the timer 17 for the injection pulses. A corresponding lock-loop is also recommended in input circuits of other operating parameters when the latter exist, or are processed in a frequency-dependent form. In connection with comprehensive processing of, for example, the rotational speed signals, it' is advisable for the operating parameter signal, free from interference owing to the presence of the lock-loop, also to be made available for further signal processing, such as processing for calculating the instant of ignition. WHAT WE CLAIM IS:

1. An electronic fuel injection system for an internal combustion engine, having a transducer for monitoring an operating parameter of the engine, the transducer output frequency varying in accordance'with said parameter, a timer for producing a trigger signal for at least one fuel injection valve, and a frequency and/or phase lock loop arranged between the timer and the transducer.