FR2566839A1 - SENSOR FOR DETECTING THE PASSAGE OF A PISTON OR PISTON GROUP OF AN INTERNAL COMBUSTION ENGINE BY THE POSITION OF THE HIGH DEATH POINT - Google Patents

Abstract

The sensor contains a rotary element (10) which can rotate synchronously with the drive shaft and has a plurality of detectable reference marks (12, 13), of which each is assigned to a piston or a group of pistons (1, 4; 2, 3), and a fixed terminal unit (11), assigned to the rotary element (10), for detecting the passage of each reference mark (12, 13) and generating a corresponding predetermined signal. The rotary element (10) has a further detectable reference mark (14), which is arranged next to a reference mark (12) which is assigned to a predetermined piston or a predetermined group of pistons (1, 4).

Description

The present invention relates to a sensor allowing

  both to detect the displacement of a piston or group of pistons of an internal combustion engine to the position of the point

dead high.

  In particular, the invention relates to a sensor of the type comprising: a rotary element which can rotate in synchronism with the drive shaft and having several detectable references each associated with a respective piston or group of pistons, and a fixed terminal instrument associated with a rotating element used to detect the passage of each of the references

  and producing a corresponding predetermined electrical signal.

  A conventional sensor of this type, used in relation

  tion with a four-cylinder four-stroke internal combustion engine, is shown schematically in Figure 1. In this

  drawing, the rotary element is designated by 10 and the ter-

  minal is designated by 11. The detectable references are consti-

  killed by teeth 12, 13 diametrically opposite. In the embodiment shown in FIG. 1, the tooth 12 is associated with the pistons 1 and 4, while the tooth 13 is associated with the pistons 2 and 3. The rotary element 10 is mounted so that the tooth 12 passes in front the terminal instrument 11 when the pistons 1 and 4 are at top dead center (or at a predetermined advance or delay angle

  relative to the movement to top dead center).

  FIG. 2 shows, as a function of time t., The typical trend of the signal which can be obtained at the output of the terminal instrument 11: this signal S comprises a succession of pulses, which are each associated with the passage of a tooth 12 or 13 in front of the terminal instrument 11. In this signal, it is impossible to distinguish the pulses associated with the displacement of the pistons 1, 4 until the top dead center with respect to the pulses

  associated with the displacement of the pistons 2, 3 to top dead center.

  In other words, the conventional sensor represented in FIG. 1 does not make it possible to make a difference in the "row" of cylinders

  in which the pistons move to top dead center.

  This is a problem for electronic ignition systems

static distribution.

  The object of the invention is to produce a sensor of the type indicated above, which is designed so as to allow additional information to be obtained in a very simple and very easy manner concerning the "row" in which the

  pistons move to top dead center at some point.

  The object according to the invention is obtained by means of a sensor which is distinguished in that the rotary element has

  an additional detectable reference which is placed on the

  setting the reference associated with a predetermined piston or group of pistons.

  The following description, intended as an illustration

  tration of the invention, aims to give a better understanding of its characteristics and advantages; it is based on the appended drawings, among which: FIGS. 1 and 2, already described, illustrate a sensor according to the prior art and the electrical signal which can be obtained using this sensor, and FIGS. 3 and 4, which will be described below, respectively represent an embodiment of the sensor according to the invention and the trend of the electrical signal which can be obtained

  using this sensor as a function of time.

  FIG. 3 shows a sensor according to the invention associated, for example, with the shaft of a four-stroke four-cylinder engine. According to the invention, the rotary element 10 has an additional reference, which is for example an additional tooth 14, adjacent to the tooth 12. Preferably, the additional tooth 14 is placed so as to be angularly offset behind the

  reference tooth 12, in operation.

  FIG. 4 illustrates the signal SS which can be obtained using the terminal instrument 11 of FIG. 3: this

  signal has respective cycles of pulses A, C and B pro-

  produced by the passage of teeth 12, 14 and 13 opposite the instrument

  terminal 11, in the direction of rotation of the arrow F of

Figure 3.

  The duration T1 separating a pulse A from the pulse

  following C sion and the duration T2 separating a pulse C from the im

  next drive B must always be different. Therefore

  quent, it is possible to distinguish the pulse A (relative to the pair of cylinders 1 and 4) from a pulse B (relative to the pair of cylinders 2 and 3) by simple comparison of the durations T1

and T2.

  As stated above, these durations must generally

  actually be different from each other. Their report is cons-

  both when the motor drive shaft rotates at a constant angular speed. The ratio of these times can vary when the drive shaft (and therefore the rotary element 10)

  is subject to angular acceleration or deceleration The posi-

  tion of tooth 14 must therefore be such that, for the maximum angular acceleration expected, the duration T1 is in all cases different from the duration T2 (it is, in this example, less

at this time).

  While reference has been made to a four-cylinder four-stroke engine in the embodiments explained above, those skilled in the art will immediately understand that the application of the sensor according to the invention is not limited to such an engine, but allows, in general, to distinguish the piston or group of pistons of an engine moving to top dead center. In addition, the detectable references can be of a very different nature from the teeth represented by means of a nonlimiting example. Thus, they could for example be constituted by notches, inserts made of a material having magnetic characteristics different from the material constituting the rotary element 10, etc. In addition, each piston or group of pistons can have several angularly equidistant references which

are associated.

  - Of course, those skilled in the art will be able to ima-

  giner, from the sensors whose description has just been given

  by way of illustration, in no way limiting, various other

  variants and modifications not departing from the scope of the invention.

Claims (2)

R E V E N D I C A T I 0 N S   1. Sensor intended to detect the displacement of a   piston or group of pistons (1, 4; 2, 3) of a combustion engine   internal position up to the top dead center position, comprising: a rotary element (10) which can rotate in synchronism with the drive shaft and having several detectable references (12, 13) each associated with a piston or respective piston group (1, 4; 2, 3), and   a fixed terminal instrument (11) associated with summer-   rotatable (10) and used to detect the passage of each of the   references (12, 13) and to produce a corresponding predetermined signal   laying, characterized in that the rotary element (10) has an additional detectable reference (14) placed in the vicinity of a reference   (12) associated with a predetermined piston or group of pistons (1, 4).   2. Sensor according to claim 1, characterized in that the additional detectable reference (14) is placed   so as to be angularly offset from said reference   rence (12) associated with the predetermined piston or group of pistons (1, 4) finished, in use.