GB2079405A - Timing device for speed-sensitive variation of the relative rotary position of two rotary members - Google Patents

Abstract

The timing device comprises compression springs (7,8) each biassed between a pair of guiding pieces (3,4). One guiding piece (3,4) of each pair is fixed to a primary rotary member (1), and the other guiding piece (5,6) of each pair is fixed to a secondary rotary member (2). As rotary speed increases, fly-weight (9) guided between the guiding pieces (4,5 or 3,6) move outwardly against the bias of the springs so as to alter the relative rotary position of the primary and secondary members (1,2). In order to reduce wear and friction each fly- weight (9) has two members (11,12) freely rotatable relative to each other. One rotatable member (11) is in rolling contact with one guiding piece (3) and the other rotatable member (12) is in rolling contact with the other guiding piece (6). <IMAGE>

Description

SPECIFICATION Timing device for speed-sensitive variation of the relative rotary position of two rotary members The present invention relates to a timing device for speed-sensitive variation of the relative rotary position of two coaxially-arranged rotary members, e.g.

shafts.

Timing devices are required, e.g. for commercial vehicles, not only to match the start of fuel delivery to the engine speed in high-speed Diesel engines, but also to adjust the firing point in other internal combustion engines in order to vary the fuel delivery or injection timing as a function of speed.

Timing devices of the aforementioned type generally consist (see German Specification 27 27 121) of a primary member driven by a crankshaft and a secondary member fixedly connected to the shaft of an injection pump. The primary and secondary members are mutually adjustable in such a manner that fuel injection is advanced as engine speed increases.

The adjustment is effected by means of flyweights which, as they move radially outwards as a function of rotary speed inside a casing forming the primary members force apart two guiding pieces against the bias of a spring. One of the guiding pieces is fixedly attached to the primary member and the other is fixedly attached to the secondary member. The fly-weights themselves are substantially disc-shaped, and slide between respectively curved side faces of the guiding pieces.

Because of its compact and relatively low-cost design, this type of timing device has found wide acceptance in a great variety of versions.

However, a disadvantage of such a timing device is that there is a wide scatter of adjusting characteristics caused mainly by friction, but also by the macro and micro-structure of the sliding faces on the guiding pieces and the fly-weights. Specially where static friction has to be overcome at the start of the centrifugal motion, when the centrifugal force is still small, undesirably wide scatter tends to occur with unacceptable discrepancies between actual values and desired values. Moreover, the performance of the timing device tends to be considerably affected in long-term operation as a result of the frinctional wear.

Although the negative influence of the surface form structure can be controlled by adopting highprecision, but also high-cost, machining, it is not possible - due to production-related scatter - to maintain the friction coefficient within such narrow limits that the negative influence of friction on the timing characteristic is kept at an acceptable level.

Thus, an exact start of delivery over the full engine speed range cannot be attained with timing devices of the conventional type operating as explained above. With a view to obtaining high economy, low smoke emission and a long service life it is, however, absolutely necessary in Diesel engines to provide accurate timing of the start of fuel delivery. Moreover, recent legislation in some countries calling for compliance of the specified emission levels has made it necessary to provide accurate control of the timing of the start of fuel delivery.

An object of the present invention is to provide a timing device in which both the friction between the guiding pieces and the fly-weights is reduced to a minimum and poor operation - due to surface form structure deficiencies on the above-mentioned part is obviated.

The invention provides a timing device for speedsensitive variation of the relative rotary position of two co-axially arranged primary and secondary rotary members for varying the injection or ignition timing in an internal combustion engine, the device comprising resetting springs biassed between guiding pieces fixed to the primary member and respective guiding pieces fixed to the secondary member so as to bias against the centrifugal force exerted by fly-weights guided between the guiding pieces as rotary speed increases, wherein each fly-weight has two members freely rotatable relative to each other, of which one rotatable members bears against the guiding piece fixed to the primary member and the other rotatable member bears against the guiding piece fixed to the secondary member so that there is rolling contact between the fiy-weights and guiding pieces.

Contrary to the timing devices of the aformentioned type used hitherto, the fly-weight in the timing device according to the invention is no longer a simple solid cylinder or a simple disc, but it consists of at least two discs which are freely rotatable relative to each other, provision being made by appropriate selection of the diameter and/or contacting faces on the guiding pieces to have one of the discs contact the guiding piece connected to the primary member (e.g. a camshaft) whereas the other bears against the guiding piece connected to the secondary member (e.g. a pump shaft). This feature enables both parts to roll on the mating surfaces of the guiding pieces, so that the above-mentioned drawbacks are avoided.

Two embodiments of the invention will now be described with reference to the accompanying drawings, wherein: Figure 1 is a partially sectioned plan view of a timing device according to the invention, Figure 2 is a section taken along the line Il-Il of Figure 1, Figure 3 is a sectional view of a fly-weight for use in the timing device of Figure 1,and Figure 4 is a view similar to Figure 3 of a different fly-weight.

In Figures 1 and 2, a drive gear 1 of a camshaft accomodates the parts required for the timing device. The drive gear 1 represents the primary member of the timing device. The gear 2 to be adjusted will, in the following, be referred to as the secondary member of the timing device.

Four guiding pieces 3, 4, 5 and 6 in the form of segment levers are supported inside the primary members 1. The guiding pieces 3 and 4 are firmly fixed in the camshaft gear 1, whereas the guiding pieces 5 and 6 are attached to the secondary member 2.

Compression springs 7 and 8, the compression of each of which is adjustable by means of a nut, act on the segement levers 3, 4, 5 and 6 so as to cause their contact faces to approach each other. Fly-weights 9, which are arranged between these contact faces, are forced radially inwards by the contact faces as a function of the pressure of the springs 7 and 8. The fly-weight 9 at the top of Figures 1 and 2 is shown in an initial position, whereas the fly-weight at the bottom is shown in an intermediate position.

The general method of working of such a timing device is known. It should, however, be pointed out that, when the fly-weights move radially outwards, they force the guiding pieces 4, 5 and 3,6 apart against the force of the springs 7 and 8, thereby adjusting the secondary member 2 relative to the primary member 1 in an anti-clockwise direction in the embodiment shown.

Figure 2 shows the general construction of the fly-weights 9. In order not to encumber this figure with too many reference numerals, one of the fly-weights 9 is shown in a somewhat modified form in detail in Figure 3. It should be noted that in Figure 3 the parts of the guiding pieces 3 and 5 adjacent the fly-weight are shown in an exploded view; in a working condition, they are forced by the springs 7 and 8 directly against the individual discs of the fly-weights, the construction of which will now be explained.

Each fly-weight 9 consists of a central pin 15 onto which a spacer 13 is fixedly mounted. Two discs 11 are then pressed onto the sides of the spacer 13 and are non-rotatably connected to the central pin 15, for example, by caulking. A central disc 12 is arranged between the two discs 11, and is freely rotatable on a roller bearing 14. The central disc 12 is somewhat narrower than the spacer 13 so as to ensure free rotation of the central disc 12 between the side discs 11.

In such an arrangement, the side discs 11 of the fly-weight 9 bear against the guiding piece 3 fixed to the camshaft wheel, whereas the central disc 12 bears against the guiding piece 6 attached to the secondary member 2. Thus, as the individual discs move radially outwards, they can roll on the respective contact faces of the guiding pieces so that sliding friction is avoided (cf. Figure 1).

A comparison of Figures 2 and 3 shows that the diameter of the individual discs may be equal (Figure 2), or may differ (Figure 3). Since the two parts are freely rotatable relative to each other, the diameter is not a factor which affects the working and in particular, satisfactory rolling motion. It is only necessary to form the contact faces of the guiding pieces 3 to 6 in a manner such that the mating guiding piece is actuated by the related surface area of the fly-weight; for example, in the embodiment of Figure 3, the guiding piece 3 contacts the side descs 11, and the guiding piece 6 contacts the central disc 12.

Of course, it is possible to make the diameter of the central disc 12 smaller than that of the side discs 11. The corresponding guiding piece would then have to be provided with a guiding land registering in the space between the side discs 11.

In Figure 4 the fly-weight comprises two discs 11' and 12' arranged side by side and freely rotatably mounted on a common pin 15'. Disc 11' contacts the guiding piece 3', whereas the disc 12' cooperates with the guiding piece 6'. Both discs 11' and 12' are mounted via roller bearings 14' on the central pin 15'.

Various modifications may be made to the embodiments. For instance, the side discs 11 of Figures 2 and 3 may be rotatably mounted on the pins 15. The central disc 9 may in special cases be guided by means of a simple plain bearing or a ball bearing. In the embodiment of Figure 4, it is also possible to omit the bearing for one of the discs and to have that disc fixedly mounted on the pin 15'. The other disc may, alternatively, be guided only by a plain bearing.

In each case, the desired advantage is obtained, in that no sliding friction occurs on the interface between the fly-weight and contact face of the guiding pieces which would erratically and detrimentally affect the working of the timing device.

Claims (9)

1. A timing device for speed-sensitive variation of the relative rotary position of two co-axially arranged primary and secondary rotary members for varying the injection or ignition timing in an internal combustion engine, the device comprising resetting springs biassed between guiding pieces fixed to the primary member and respective guiding pieces fixed to the secondary member so as to bias against the centrifugal force exerted by fly-weights guided between the guiding pieces as rotary speed increases, wherein each fly-weight has two members freely rotatable relative to each other, of which one rotatable member bears against the guiding piece fixed to the primary member and the other rotatable member bears against the guiding piece fixed to the secondary member so that there is rolling contact between the fly-weights and guiding pieces.

2. A timing device as claimed in claim 1, wherein each fly-weight comprises at least two discs, of which at least one disc is freely rotatable on a central pin.

3. Atiming device as claimed in claim 2, wherein each fly-weight comprises two discs fixedly mounted on a central pin, and a central disc rotatably mounted on a spacer on the pin between the said two discs.

4. A timing device as claimed in claim 3, wherein the central disc is mounted on a roller bearing mounted on the spacer.

5. A timing device as claimed in claim 3, wherein the central disc is mounted on a plain bearing mounted on the spacer.

6. A timing device as claimed in any one of claims 1 to 5, wherein the freely-rotatable parts have the same diameter.

7. Atiming device as claimed in any one of the preceding claims, wherein the bias of the resetting springs is adjustable by nuts.

8. Atiming device as claimed in any one of the preceding claims, wherein the primary member is driven by the engine crankshaft and the secondary member is fixed to a shaft of an injection pump.

9. A timing device substantially as herein described with reference to any one of the embodiments shown in the accompanying drawings.