TECHNICAL FIELD The present invention relates to a synchronizing system for internal combustion engines, which may be applied in particular to the high-pressure- electronic injection system of high-speed, direct-injection diesel engines. BACKGROUND ART

As is known, electronic injection systems comprise a control system which, to regulate the controlled variables involved, must be synchronized with the engine for it to know the exact engine stroke and angular position of the crankshaft at all times.

When the engine is turned off (ignition key in the off position) , the crankshaft continues turning by force of inertia, so that, when the engine is turned on,, the angular position of the crankshaft is unknown and the engine must be synchronized.

This is done using two pulse wheels fitted respectively to the drive shaft and camshaft and each cooperating with a respective sensor for detecting the

tooth sequence on the respective wheel and generating a corresponding electric signal. The pulse wheel fitted to the drive shaft presents a number of teeth equally spaced about the periphery of the wheel with the exception of an untoothed portion corresponding to a gap of two teeth and which represents a reference or zero by which to count the teeth on the wheel. Conversely, the pulse wheel fitted to the camshaft generally comprises only two teeth separated by an angular distance of, say, 90°.

As each engine cycle corresponds to two turns of the drive shaft, the angular position of the-drive shaft alone is not enough for determining the engine stroke, so that the signals of both pulse wheels are needed for synchronizing the engine. At present therefore, when the engine is started up, the signals generated by both pulse wheels are detected for at least two complete turns of the drive shaft to determine the presence of the pulses generated by the teeth on the camshaft wheel. Such a solution therefore involves a certain amount of delay due, as stated, to the drive shaft necessarily effecting at least two complete turns.

Moreover, being related to engine speed, the amplitude of the pulse wheel signals at low startup engine speed is so low as to be unusable for identifying the teeth, thus requiring a further delay of roughly half a turn of the shaft for the engine to be synchronized.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a synchronizing system permitting faster identification of the engine stroke when the engine is started up.

According to the present invention, there is provided a synchronizing system for an internal combustion engine, comprising a first pulse wheel fitted to the drive shaft and presenting a number of equally spaced teeth with the exception of at least one untoothed portion; a second pulse wheel fitted to the camshaft and comprising at least one tooth; -and a first and second transducer for said first and second pulse wheels respectively, for generating a respective electric signal presenting a pulse corresponding to detection of each tooth on the relative pulse wheel; characterized in that said first and second pulse wheels are positioned in a predetermined manner in relation to each other. BRIEF DESCRIPTION OF DRAWINGS

A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows the pulse wheels of the synchronizing system according to the present invention;

Figure 2 shows the electric signals corresponding to the Figure 1 pulse wheel readings.

BEST MODE FOR CARRYING OUT THE INVENTION

Figure 1 shows the two pulse wheels of the system according to the present invention. Number 1 indicates the pulse wheel (also referred to as the drive pulse wheel) fitted to the drive shaft 2 of a high-speed, direct-injection diesel engine (not shown) , and which, in the example shown, comprises 58 teeth 3 (one every 6°) , and an untoothed portion 4 corresponding to a gap of two teeth and constituting a start reference for the tooth count. An inductive type sensor or pickup 5 is positioned facing drive wheel 1, for detecting the tooth sequence of wheel 1 and generating an electric signal which is filtered and clipped to give signal- S _M (Figure 2) characterized by a sequence of pulses (corresponding to teeth 3) interrupted solely (signal portion 6) at untoothed portion 4.

Number 9 indicates the pulse wheel (also referred to as the cam pulse wheel) fitted to the camshaft 8, and which presents, in known manner, only two teeth 10, 11 separated, for example, by an angular distance of 90° in rotation direction A. Cam wheel 9 presents a sensor 12 similar to sensor 5, for generating a signal which is processed as for signal S.. to give signal S (Figure 2) presenting only two pulses 13, 14 corresponding to teeth 10, 11. In the embodiment shown, the engine (not shown) presents a 1-3-4-2 timing sequence, and the top dead center position at the end of the compression stroke of each cylinder corresponds to the positioning of teeth

N. 23 and 53 of drive wheel 1 opposite sensor 5. Since, as already stated, each engine cycle corresponds to two turns of the drive shaft, it follows that, when tooth N. 23 is positioned opposite sensor 5, the engine alternately presents the third and second cylinder in the compression top dead center position (stroke TDC3 or TDC2) ; whereas, when tooth N. 53 is positioned opposite sensor 5, the engine alternately presents the first and fourth cylinder in the compression top dead center position (stroke TDCl or TDC4) . In practice, if in one turn the passage of tooth N. 23 past" sensor 5 corresponds to the top dead center position of the third cylinder (TDC3) , the subsequent passage of tooth N. 53 in the same turn corresponds to the top dead center position of the fourth cylinder (TDC4) ; and, in the next turn, the passage of tooth N. 23 corresponds to the top dead center position of the second cylinder (TDC2) , and the passage of tooth N. 53 corresponds to the top dead center position of the first cylinder (TDCl) , as shown in Figure 2. To determine whether the passage of tooth N. 23 corresponds to the top dead center position of the third or second cylinder when the engine is started up, use must therefore be made of the signal generated by sensor 12 of cam wheel 9 for which, having a period twice that of drive wheel 1, the position of the pulses corresponding to teeth 10, 11 is related solely to the position of the engine cylinders.

According to the present invention, to speed up

synchronization when the engine is started up, cam wheel 9 is arranged in a precise angular position with respect to drive wheel 1. More specifically, pulse wheels 1 and 9 are so fitted that tooth 10, which precedes tooth 11 by 90° in rotation direction A of cam wheel 9, is detected by sensor 12 when one of the first ten teeth of drive wheel 1 moves past sensor 5, as shown in Figure 2. Upon startup, the synchronizing procedure provides that the processing system receiving signals S _M and S correlated to the signals of sensors 5 and 12 be switched to standby awaiting portion 6 of ^" signal S _M ; and, upon detection of portion 6 (passage of untoothed portion 4 past sensor 5) , the system switches to standby awaiting pulse 13 corresponding to the passage of tooth 10 of cam wheel 9. If pulse 13 is detected within a time lapse corresponding to ten pulses of signal S„, this means the next top dead center position (passage of tooth N. 23) corresponds to TDC3; conversely, the next passage of tooth N. 23 corresponds to TDC2. The system thus provides for exactly determining the stroke of the engine (and so activating the right injection sequence) with a delay corresponding at most to a rotation of 420° (one full turn plus angle α corresponding to the first ten teeth of drive wheel 1) . Figures 1 and 2 also show the fuel injection regions 15 which may be controlled effectively by virtue of synchronizing the engine as described above, and which are defined by the detection of teeth 16, 27 and

teeth 46, 57 respectively.

The synchronizing system described therefore provides for rapidly detecting the engine stroke and hence rapidly synchronizing the engine, as well as for minimizing startup time and attainment of the steady-state condition of the engine.

Moreover, the system described involves no additional expense by virtue of employing conventional pulse wheels and software procedures which may be implemented easily and cheaply on existing elements.

Clearly, changes may be made to the- system as described and illustrated herein without, however, departing from the scope of the present invention. In particular, the cam wheel may present one tooth instead of two, seeing as the second tooth, though offering a greater margin of safety in some situations, is not necessarily required by the synchronizing procedure described; and, though described with reference to a four-cylinder engine, the system according to the present invention may also be applied equally as well to five- or six-cylinder engines.