GB2054097A - Shaft coupling for control of fuel injection timing - Google Patents

Abstract

An automatic control device for the timing of injection in an internal combustion engine comprises a body (1) including an outer member (2) rotatable by the engine and a hub (7) rotatably driven by the body and for connection to the injection pump and means carried by the body capable of changing the relative angular position between the body and the hub in accordance with the rotational speed of the engine, which means comprises a centrifugal mass (9) pivotally connected to the body by means of a pin (12) through the intermediary of a bush (11), the arrangement being such that the bush (11) is free to rotate both with respect to the pin (12) and also with respect to the centrifugal mass (9). This duplication of bearing surfaces minimises adverse effects in tie event of a seizure of one of the bearings due to a high temperature in use. <IMAGE>

Description

SPECIFICATION Control device for fuel injection The present invention refers to a device for the automatic control of the timing of the injection in internal combustion engines with injection.

Known devices of the above type generally comprise a body intended to be rotated by the drive shaft, a hub rotatably driven by the body and intended to be mounted on the shaft of the injection pump of the engine, and control means dependent upon centrifugal effect for changing the relative angular position betweein the body and the hub when the angular speed of the drive shaft changes.

The applicant has for some time been producing a device of the type specified alone in which the control means comprises a pair of centrifugal masses, each pivotallyconnected to a pin carried by the body through the intermediary of a bush.

In such devices each of the bushes is stressed in relation to a portion of its sliding surface by a high load variable in both magnitude and direction. This load, due to the reaction torque of the injection pump shaft, or to the centrifugal force acting on the centrifugal mass, or to the force of reaction of a return spring associated with the centrifugal mass, induces a rise in temperature and a corresponding increase in the value of the coefficient of friction in the area where the bush slides. This often causes the phenomenon of seizing up, which irreparably damages the sliding surfaces which are in contact.

The purpose of the present invention is to provide a device of the above mentioned type which avoids the aforesaid disadvantage.

According to the present invention, there is provided a device for the automatic control of the timing of the injection in an internal combustion engine with injection comprising a body adapted to be rotated by a drive shaft of the engine, a hub rotatably driven by the said body, and intended to be mounted on the shaft of the injection pump of the engine and control means carried by the body and capable of changing the relative angular position between the body and the hub when the angular speed of the drive shaft is altered, which comprises at least one centrifugal mass pivotally connected to the body through the intermediary of a bush on a pin carried by the body characterised in that said bush is supported in a rotating manner both with respect to the pin and with respect to the centrifugal mass.

This arrangement avoids risk of seizing up.

Under normal operating conditions sliding occurs in relation to the inside wall of the bush, between the bush and the pin carried by the body of the device. When, following a rise in temperature the bush tends to jam on the pin carried by the body of the device, however, the bush begins to turn its outside wall with respect to the centrifugal mass, thus preventing the phenomenon of seizing Up.

The invention will be further apparent from the following description with reference to the accompanying drawings, which show, by way of example only, one form of control device embodying the invention.

Of the drawings Fig. 1 is a front view partly in section of the control device; Fig. 2 is a sectional view on line Il-Il of Fig. 1; and Fig. 3 illustrates diagrammatically on a larger scale part of the device shown of Fig. 1 Referring now to the drawings, it will be seen that the control device comprises a body 1, commonly called "a cage" comprising two coaxial annular members 2 and 3 joined together by a plurality of bolts 4. The body 1 is intended to be attached in known manner to the shaft of an internal combustion engine so as to be rotated thereby. Members 2 and 3 comprising the body 1 have hubs 5 and 6 coaxial and in alignment with each other, inside of which a hub 7 is rotatably mounted. The hub 7 is intended to be fixed to the shaft of the injection pump associated with the internal combustion engine.The inside wall of hub 7 has a truncated conical portion 7a into which it is intended that a corresponding truncated conical portion of the end of the injection pump shaft should engage. A nut 8 intended to be screwed onto a threaded end portion of the injection pump shaft so as to bring about the engagement of the truncated conical portion of the shaft with the truncated conical portion 7a of the hub 7 is provided.

The control device further comprises two centrifugal masses 9 and 1 0 (one of which is illustrated with a broken line in Fig. 1), each pivotally mounted by means of a bush 11 on a pin 12 having screwed ends 1 2a and 1 2b fixed respectively to the members 3 and 2 of the body 1 by means of nuts 13.

Each of the centrifugal masses 9 and 10 is additionally provided with a pin 14 having a narrower portion 1 4a in the centre, bounded by two flat parallel surfaces 1 4b capable of sliding respectively on the opposed faces of a groove 1 5 in associated fork member 1 6 integral with the hub 7.

Each of the centrifugal masses 9 and 10 is also provided with resilient return means 1 7 interposed between a member 1 8 mounted on the outside wall of hubs 5 and 6 so as to be able to rotate about the axis of the device, and a member 1 9 (see Fig. 1) provided with a seat 1 9a in which a pin 20 carried by the centrifugal mass engages.

The device shown is partly filled with lubricating oil through a port 21 in a closure member 22 mounted on the body 1.

In accordance with the invention each of the bushes 11 is free to rotate relative to both its associated pin 1 2 and its associated centrifugal mass. The resulting advantages will become clear from the following description of the operation of the device with reference to Figure 3.

While the engine is running the body 1 is.

rotated as are the centrifugal masses 9 and 10 through the pins 12, which are fixed on body 1.

The rotation of the centrifugal masses 9 and 10 is transmitted to the hub 7 fixed on the shaft of the injection pump through the engagement of the pins 14 in the grooves 1 5 of the forked members 16 carried by the hub 7. In this way a connection between the drive shaft and the shaft of the injection pump associated with the motor is established.

Naturally, when the angular speed of the drive shaft changes due to centrifugal effect the position of the centrifugal masses 9 and 1 0 alters.

In particular, when this angular speed rises, the centrifugal masses tend to rotate towards the outside of the axis of pins 12, bringing about a traverse of each pin 14 in the interior of the groove 1 5 of the corresponding forked member 16. Because this groove is rectilinear, the shift of pin 14 in the groove induces a rotation of the forked member 1 6 with respect to the axis of the device, causing a change in the relative angular position between body 1, connected to the drive shaft, and hub 7, connected to the injection pump shaft. The alteration in this angular position hence brings about an alteration in the timing of injection.

When the angular speed falls the resilient means 1 7 cause a rotation of the centrifugal masses 9 and 10 towards the inside about the axes of the corresponding pins 12 and a shifting of the pins 14 in grooves 1 5 and a rotation of hub 7 with respect to body 1 in the opposite direction.

Figure 3 illustrates diagrammatically one centrifugal mass of the control device.

While the device is operating, pin 12 carried by body 1 of the device transmits through bush 11 to centrifugal mass 9 a force F which changes in magnitude and direction.

Suppose that centrifugal mass 9 is in the position shown in broken line in Fig. 3, pin 12 must transmit to centrifugal mass 9 a force F1 whose direction coincides with that of the straight line joining the centres of the pins 12 and 14 and whose magnitude is equal to the reaction torque of the injection pump shaft (which is rotated by centrifugal masses 9 and 10 through the engagement of pins 14 in fork members 16) divided by the distance d between the said direction and the axis of the device. Centrifugal mass 9 is furthermore subjected to the force of reaction Fm of resilient means 17, acting in relation to pin 20, and to the centrifugal force (not shown) acting on its centre of gravity. Force Fm and the centrifugal force give rise to a force F2 applied in relation to the axis of pin 12. The resultant of forces F1 and F2 is force F.

Taking the critical case from the point of view of the stresses, in which only one centrifugal mass transmits the rotation to the injection pump shaft, force F1 would become force F3 of double intensity, because of which the resultant force transmitted by pin 12 to centrifugal mass 9 through bush 11 would become the force indicated F4 in Fig. 3.

During the rotation of the injection pump shaft, the reaction torque of that shaft varies, for which reason force F1 exhibits an intensity periodically variable between a minimum and a maximum value. In consequence, the resultant F therefore varies both in intensity and direction, covering an angular portion 1 a of bush 1 This stress tends to induce a rise in temperature and a consequent rise inthe coefficient of friction in relation to the sliding surfaces of the bush.

In known devices the bush 11 is mounted on pin 12 and slides with respect to centrifugal mass 9, or is mounted on centrifugal mass 9 and slides in relation to pin 12. In either case the above mentioned increase in temperature and coefficient of friction can cause seizing up of the sliding surfaces.

In the device according to the present invention, bush 11 is capable of sliding both in relation to pin 12 and the centrifugal mass 9. In normal operating conditions the sliding surface of bush 11 is that of less diameter, that is the inside wall in contact with pin 12. With increase in the temperature, the coefficient of friction in relation to the inside wall of bush 11 reaches a value such that the bush itself begins to slide on the outside wall in contact with centrifugal mass 9 instead of on its inside wall, avoiding the phenomenon of seizing up.

It will be appreciated that it is not intended to limit the invention to the above example only, many variations such as might readily occur to one skilled in the art being possible without departing frbm the scope thereof, as defined in the appended claims.

Claims (2)

1. A device for the automatic control of the timing of the injection in an internal combustion engine with injection comprising a body adapted to be rotated by a drive shaft of the engine, a hub rotatably driven by the said body; and intended to be mounted on the shaft of the injection pump of the engine and control means carried by the body and capable of changing the relative angular position between the body and the hub when the angular speed of the drive shaft is altered which comprises at least one centrifugal mass pivotally connected to the body through the intermediary of a bush on a pin carried by the body, characterised in that said bush is supported in a rotating manner both with respect to the pin and with respect to the centrifugal mass.

2. A device for the automatic control of the timing of an injection in an internal combustion engine with injection substantially as described herein with reference to and as illustrated by the Figures of the accompanying drawings.