APPARATUS FOR GENERATING SYNCHRONISATION PULSES FOR AN INTERNAL COMBUSTION ENGINE

Abstract: Synchronisation pulses are generated by identifying the second of two pulses of the same sense in a pulse train of positive going and negative going pulses. A first pulse sequence is generated which switches from a first level to a second level in response to a positive going pulse and from the second level to a first level in response to a negative going pulse. A synchronisation pulse is generated in response to each pulse of said same sense only when the level of the first pulse sequence indicates that a pulse of said same sense has just occurred.

Description: Apparatus for generating synchronisation pulses for an internal combustion engine This invention relates to apparatus for electronically generating synchronisation pulses for an internal combustion engine. In an internal combustion engine having a fuel injection system or some other operation which must be synchronised with engine rotation, it is neces¬ sary to generate a timing signal identifying the rota¬ tional position of the engine for controlling the operation. The timing signal is usually in the form of periodically generated synchronisation pulses which occur in relation to the top dead centre position of a specified engine cylinder. In many known systems the synchronisation pulses are derived from a voltage signal produced by a detector or sensor which indicates the engine speed and crankshaft position. For example the synchronisation pulses may be derived from the voltage signal produced by a crank¬ shaft transmitter. This voltage signal typically consists of a series of alternate positive and negative pulses generated as the crankshaft rotates, with an additional pulse being generated at a certain reference position, e.g.; the top dead centre position of the first cylinder. In one known system the crankshaft transmit- - 0 - ter is placed adjacent a slotted or toothed disc which rotates with the crankshaft. The transmitter produces alternate positive and negative pulses as the teeth pass it. A magnet is provided at the reference posi¬ tion and thus an extra pulse is generated each time the magnet passes the sensor. The voltage signal from the crankshaft trans¬ mitter thus consists of a series of alternate negative and positive pulses with two consecutive pulses of the same sense at regular intervals. It is possible to generate, from the crank¬ shaft transmitter voltage, a pulse sequence which switches from a first level to a second level in re- - εponse to a negative going pulse and from the second level to the first level in response to a positive going pulse. This pulse sequence is hereinafter re¬ ferred to as the negative/positive evaluation signal. This has been achieved using an integrated circuit together with a number of external components and has been used in many hybrid electronic ignition devices. Suitable circuitry for generating such a pulse sequence is described in detail in DE-OS 3208262. It is desirable to generate the synchronisation pulses from the crankshaft transmitter voltage using as little as possible additional circuit¬ ry. In hybrid devices only a limited space can be made available for implementing the circuit. This means that all functions additionally needed must be incorporated into existing or new integrated compo¬ nents. It is obviously advantageous, to incorporate additional functions into existing components wherever possible. It has been proposed to utilise the circuitry for generating the negative/positive evaluation signal for generating the synchronisation pulses. However, the previous proposals have required modifications to the integrated circuit. The present invention provides apparatus for identifying the second of two pulses of the same sense in a pulse train of positive going and negative going pulses comprising means for generating a first pulse sequence which switches from a first level to a second level in response to a positive going pulse and from the second level to the first level in response to a negative going pulse; and means for generating a synchronisation pulse in response to each pulse of said same sense only when the level of the first pulse sequence indicates that a pulse of said same sense has just occurred. Preferably the synchronisation pulse genera¬ tion means is enabled and disabled m response to changes of level in the first pulse sequence. Thus, the synchronisation pulse generation means is only enabled when the first pulse sequence is at said level indicating that a pulse of said same sense has oc¬ curred. The present invention may thus be very simply accommodated m a known circuit for generating a nega¬ tive/positive evaluation signal. The evaluation signal is simply used to control a further pulse generator for generating synchronisation pulses. The two plush generators may be incorporated in the same integrated circuit. An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a diagram of a circuit embodying the present invention and Figure 2 shows the waveforms of voltages at different places in the circuit of Figure 1 on parallel time axes. The crankshaft transmitter voltage is applied to the input GE1 of an integrated circuit 10 along line 11 via resistor R1. The waveform of the voltage at point A in the circuit is shown in Figure 2. The circuitry comprising connections GE1 , F1 , GA1 of the integrated circuit and the external components R1 , R2, R3, R4; C1 , C2, C3 and D1 produces the nega¬ tive/positive evaluation signal at point B. An output waveform is produced at B which switches from a first level to a second level when the voltage at A drops below a first threshold level and switches from the second level back to the first level when the voltage at A rises above a second threshold level. In the illustrated example, the integrated circuit includes two constant current generators connected between GE1 and a Schmitt trigger whose output is connected to GA1. The input at F1 is a control input for the constant current generators. The generation of the synchronisation pulses is implemented by resistors R5, R6, R7, a capacitor C4 and connectors GE2, F2 and GA2 of the integrated cir¬ cuit. As with GE1 , GA1 and Fl , two constant current generators are connected between GE2 and a Schmitt trigger whose output is connected to GA2. F2 is the control input for the constant current generators. The output from the terminal GA1 of the integrated circuit 10, i.e. the negative/positive evaluation signal, is fed back to the input F2 along a line 12 via resistor R5. Capacitor C4 operates to differentiate the crankshaft transmitter voltage applied to the terminal GE1. The differentiated signal from the capacitor is applied along a line 13 to the terminal GE2 via the junction of resistors R6 and R7 which form a potential divider. Referring to Figure 2, the crankshaft trans¬ mitter voltage consists of a series of alternate posi¬ tive and negative pulses with two consecutive negative pulses at regular intervals. The negative/positive evaluation signal switches from high potential to low potential when the crankshaft transmitter voltage drops below a certain negative potential and from low poten¬ tial to high potential when the crankshaft transmitter voltage rises above a certain positive potential. This switching is brought about by the Schmitt trigger. Thus, the second of two consecutive negative pulses from the transmitter has no effect on the nega¬ tive/positive evaluation signal because at this stage the Schmitt trigger is already off. The output voltage of the capacitor at point C in the circuit is shown in Figure 2. The output from the terminal GA2 at point D in the circuit is also shown in Figure 2. Referring to the region marked X in the capacitor output waveform, the voltage output from terminal GA2 switches from high to low potential when the capacitor voltage drops below a first predeter¬ mined level and from low to high potential when the capacitor voltage rises above a second predetermined level. The circuit of Figure 1 distinguishes the second of two negative pulses from the first by actuat¬ ing terminal GA2 only after GA1 has gone to low poten¬ tial. Referring to the region marked Y in the capaci¬ tor output waveform it can be seen that by the time GA1 switches to low potential the capacitor voltage has already risen above the first predetermined level and so GA2 does not switch to low potential. The detailed operation of the circuit is as follows: when GA1 is at high, the consequent input at F2 drives constant current sources at the input of GE2 into conduction to such an extent that the current of the differentiated pulse from GE1 via C4 cannot cause GE2 to switch. If GA1 is at low potential, the con¬ stant current sources are almost cut off by F2. This switching-off process can be extended by an additional capacitor C5 shown in dotted lines, if required. The operation point for GE2 is then determined by the voltage at the junction between resistors R6 and R7. If C4 is correctly dimensioned, GA2 switches to low with the next negative edge at GE1 i.e. the next nega¬ tive pulse from the transmitting as shown in Figure 2. If the falling edges of negative pulses and rising edge with positive are steeper than their asso¬ ciated rising and falling edges respectively, it is possible to switch GA2 only at the steeper edges by appropriate dimensioning of C , R6, R7. Under certain circumstances it may be neces¬ sary to insert a further diode D2, shown in dotted lines in Figure 1, between lines 12 and 13 for a de¬ fined switching to high of GA2 with the positive pulse. The circuit described above has a number of advantages over previously proposed arrangements. Firstly, the previous proposals all require additional hardware expenditure, for example flip flops and ana¬ logue amplifiers. Because space in hybrid devices is limited this necessitates development of new integrated cir¬ cuits or reworking of existing integrated circuits. The present invention saves time and cost on reworking and development since existing functions of the inte¬ grated circuit can be utilised. The circuit is particularly versatile since the differing edge steepnesses can be utilised by appropriate dimensioning of the components.

Claims: CL I S : 1. Apparatus for identifying the second (x) of two pulses of the same sense in a pulse train of posi¬ tive going and negative going pulses comprising means (GA1 ) for generating a first pulse sequence (B) which switches from a first level to a second level in re¬ sponse to a positive going pulse and from the second level to the first level in response to a negative going pulse; and means (GA2) for generating a synchronisation pulse (D) in response to each pulse of said same sense only when the level of the first pulse generation means indicates that a pulse of said same sense has just occurred. 2. Apparatus as claimed in claim 1 in which the synchronisation pulse generation means is enabled and disabled in response to changes of level in the first pulse sequence. 3. Apparatus as claimed in claim 1 or 2 in which the train of pulses is conveyed to the synchronisation pulse generation means via a differentiation means (C4). 4. Apparatus as claimed in claim 3 in which the differentiation means comprise a capacitor. 5. Apparatus as claimed in claim 3 or 4 in which the synchronisation pulse generation means is arranged when enabled to switch from a first level to a second level when the capacitor output voltage falls below a first predetermined value and to switch from the second level to the first when the capacitor output voltage rises above a second predetermined level. 6. Apparatus as claimed in any preceding claim in which the means for generating a first..pulse se¬ quence and the means for generating the εynchronrsa-tion pulses are incorporated in an integrated circuit. 7. Apparatus as claimed in any preceding claim wherein the means for generating the first pulse se¬ quence and the means for generating the synchronisation pulses each comprise constant current generators con¬ nected to a threshold switching device. 8. Apparatus as claimed in claim 7 in which the first pulse sequence is used to control the constant current generators of the means for generating the synchronisation pulses. 9. Apparatus as claimed in claim 7 or 8 in which the constant current generators and the threshold switching devices are incorporated in an integrated circuit. 10. Apparatus as claimed in claim 7 , 8 or 9 in which the threshold switching devices comprise Schmitt triggers.

Inventors: HUESER KLAUS, HUESER, KLAUS
Applicants: BOSCH GMBH ROBERT, ROBERT BOSCH GMBH
Application year: 1988
Main classification: F02D37
IPC codes: F02D41, F02P7