GB2066986A

GB2066986A - A hydraulic automatic device for the injection advance of a diesel engine

Info

Publication number: GB2066986A
Application number: GB8000150A
Authority: GB
Original assignee: Renault Vehicules Industriels SA
Current assignee: Renault Trucks SAS
Priority date: 1980-01-03
Filing date: 1980-01-03
Publication date: 1981-07-15
Also published as: GB2066986B

Abstract

The device comprises a hub 7 fixed to the pump camshaft and a casing 8 fixed to the drive pinion of the pump. Two rollers 9 and 10 in the casing bear on the ramps 13 and 14 of pistons 11 and 12 of which the position is a function of the speed of rotation, owing to two inertia blocks 30 and 31 thrust by the pistons and controlling a slide valve 25 regulating the pressure in chambers 15, 16 behind the pistons. Movement of the rollers by the piston ramps causes relative angular displacement between the hub and casing. <IMAGE>

Description

SPECIFICATION A built-in hydraulic automatic device for advancing the injection of a diesel engine The present invention concerns a built-in automatic device for the hydraulic advance of a diesel engine injection pump.

On a diesel engine, it is known that high drive forces must be applied to the crankshaft of the fuel injection pump. These forces are all the greater when it is a question of large modern diesel engines fitted to industrial vehicles. However, it is essential to introduce a variable angular displacement into the drive transmission of the injection pump shaft, this variation having to take into account the momentary operating conditions of the engine in order to carry out the control of the injection advance.

Mechanical automatic devices for controlling the injection advance are known. These devices do not stand up well to high drive forces and therefore are falling out of use in the case of large diesel engines.

Several types of hydraulic automatic devices for controlling the injection advance are known, and these do not have the disadvantage of the mechanical devices. The hydraulic devices are generaliy found in the form of a coupling sleeve, and are in all cases bulky and complicated. These devices are all the more costly in that they complicate the fitting of the injection pump.

The invention aims at achieving a hydraulic automatic device for the injection advance which allows injection pumps known as "flanged" to be fitted, that is to say, injection pumps which fit directly to the engine by means of a mounting flange, the pump shaft drive being made directly, through, for example, a conical sleeve, and without the intervention of a coupling sleeve.

The invention aims at achieving a device of the aforementioned type which may be incorporated in a drive system constituted, for example by a gear in the timing case of the diesel engine, this gear engaging with another gear mounted on the camshaft or on the crankshaft of the diesel engine.

The invention has therefore the aim of achieving a device of the aforementioned type which may be built into the diesel engine and housed inside the timing case of the said engine.

A A hydraulic automatic device for injection advance according to the invention, mainly for the injection pump of a diesel engine, is constituted by a revolving assembly co-axial with the camshaft of the injection pump and it is characterised in that it comprises: -a hub fixed to the injection pump camshaft; -a casing which is fixed to the drive pinion of the injection pump, which surrounds the hub, and which carries internally at least one roller parallel to the axis of the casing but situated away from this axis; -in connection with each roller of the casing, a piston of which the axis is at right angles to the axis of the device, each piston being fitted to slide in a blind boring in the hub and comprising a lateral bearing ramp which acts with the corresponding roller of the casing;; -a hydraulic circuit comprising within the hub at least one distributor of which the slide valve is operated by an eccentric inertia block which is able to move mainly under the action of centrifugal force, this distributor regulating the pressure in the chambers defined behind the pistons.

According to an additional characteristic of the invention the device includes at least one spring which acts between the hub and the casing to hold each roller of the casing against the ramp of the corresponding piston.

According to an additional characteristic of the invention the ramp of each piston is located near to the front of the said piston and slopes towards the axis of the piston, towards its front, this ramp being in addition, sufficiently inclined in relation to a transverse plane of the piston for the transmission of movement between the piston and the roller to be irreversible, that is to say, so that the piston cannot slide under the action of the thrust of the roller, no matter how strong it may be.

According to an additional characteristic of the invention, the inertia block which operates the slide valve is subject to the action of one of the pistons in the hub by means of a coil spring which is co-axial with this piston and which is compressed between this piston and the inertia block, the axis of the piston and the axis of the slide valve being parallel and lying on opposite sides of the pivot in the hub on which the inertia block is fitted so as to swing, this pivot itself being parallel to the axis of the device.

According to an additional characteristic of the invention, the main axis of the inertia block is closely perpendicular to the axis of the piston which acts on this inertia block.

According to an additional characteristic of the invention the front face of the piston acting on the inertia block is tilted towards this inertia block, and the hydraulic distributor is arranged so as to make the pressure in the chamber defined behind the piston increase when the inertia block moves away from the distributor, the pivot on which the inertia block swings extending between the axis of the piston and the centre of gravity of the inertia block.

According to an additional characteristic of the invention, the rear chamber of each piston is permanently connected to a feed of fluid under pressure, as well as to a fluid escape orifice which the slide valve can block progressively when the inertia block moves away from the distributor.

According to an additional characteristic of the invention, the feed of fluid under pressure comprises a revolving seal fitted to one end of the hub.

According to an additional characteristic of the invention, the device comprises two diametrically opposite inertia blocks of which only one is connected with the distributor slide valve.

The attached drawings given by way of non-limiting example, will allow the characteristics of the invention to be better understood.

Figure 1 is a side view of a diesel engine fitted with a hydraulic automatic device for advancing the injection according to the invention.

Figure 2 is a front view of the same engine.

Figure 3 is a section Ill-Ill (Fig. 2) in which the engine is shown only close to the device according to the invention.

Figure 4 is a front view of the device according to the invention.

Figure 5 is a section IV-IV (Fig. 7).

Figure 6 is an enlarged portion of Fig. 5 showing the hydraulic distributor of the device.

Figure 7 is a section VII-VII (Fig. 5) Figure 8 is a side view of the device according to the invention.

Figures 9 and 10 are views corresponding respectively to Figs. 7 and 8, showing a manufacturing variant of the device according to the invention.

Figures 1 1 and 12 are part diagrammatic views corresponding to Fig. 5 and showing the operation of the device.

There is shown in Fig. 1 in a simplified way a diesel engine fitted with a device according to the invention. In question is a six cylinder engine fitted with an injection pump 1 and a timing case 2. The pump 1 is known as "flanged", which means that it carries a circular fixing flange 3 by means of which it is attached to the engine. This attachment is carried out directly, without the intervention of a coupling sleeve, and the drive pinion 4 of the pump 1 camshaft is located inside the timing case 2, this pinion 4 engaging with a pinion 5 driven by the crankshaft of the engine (Fig. 2).

The device according to the invention is constituted by a compact revolving assembly of which the axis 6 is identical with that of the camshaft of the pump 1. This device comprises mainly on the one hand a hub 7 which is fixed to the camshaft of the pump, and on the other hand a casing 8 which is attached to the pinion 4 (see Figs. 3 to 8).

The casing 8, which encloses the hub 7, carries internally two rollers 9 and 10 which are diametrically opposite, parallel to the axis 6. and situated some distance from this axis 6.

These rollers 9 and 10 are associated with, respectively, pistons 11 and 1 2 of which the axes are at right angles to the axis 6, each piston having a lateral bearing ramp 1 3 or 1 4 which works in conjunction with the corresponding roller, and being mounted to slide in a blind bore in the hub 7. The ramps 1 3 and 1 4 are sufficiently inclined in relation to a transverse plane through the corresponding pistons for the transmission of movement between the pistons and the rollers to be irreversible, that is to say, so that the pistons cannot slide under the action of the thrust of the rollers no matter how strong it may be.

The pressure chambers 1 5 and 1 6 formed behind the pistons 11 and 1 2 are in communication with an annular passage 1 7 into which is fed a fluid under pressure. This feed comprises a revolving seal 1 8 fitted on one end of the hub 7, a calibrated radial hole 1 9 drilled into the hub 7, and a delivery pipe 20 for fluid under pressure, as well as a channel 21 which extends longitudinally in the hub 7 between the hole 1 9 and the annular passage 17.

The annular passage 1 7 likewise communicates with a bore 22 lying parallel to the pistons 11 and 1 2 in the hub 7, and enclosing a distributor 23 comprising a fixed cap 24 and a slide valve 25 (Fig. 6). The cap 24 carries radial openings 26 which may either be blocked by a cylindrical rear extension 27 of the slide valve 25, when this slide valve moves forward in the direction of the arrow 28, or open into an annular throat 29 in the slide valve when the latter moves rearward.

Since the slide valve 25 is tubular, with some radial openings 25aand 25bwhich open on the one hand into the throat 29 and on the other to the outside at the front of the cap 24, the throat 29 is always connected to the outlet. The hydraulic fluid which escapes simply falls back into the timing case 2.

Finally the device comprises two inertia blocks 30 and 31 which are diametrically opposite and of which the main axes are closely perpendicular to the axes of the pistons 11 and 1 2. The inertia block 30, which is under the action of the piston 11, is mounted to swing about a pivot 32 in the hub 7. The pivot 32 is parallel to the axis of the device. A coil spring 33, co-axial with the piston 11, is compressed between one end of the inertia block 30 and the bottom of a blind bore 34 hollowed in the piston 11. The other end of the inertia block 30 is able to push the front face of the slide valve 25 backwards.

The axis of the piston 11 and the axis of the slide valve 25 lie on opposite sides of the pivot 32, whilst the centre of gravity of the inertia block 30 lies between the pivot 32 and the geometrical axis of the slide valve 25. The inertia block 31, which is subject in the same way to the action of the piston 12, is mounted in an identical manner to the inertia block 30. This inertia block 31 is not in contact with any slide valve, unlike the inertia 'block 30, but the unbalance caused by this dissymmetry is entirely negligible. Taking ac count of the very small mass of the slide valve 25 in relation to the mass of the inertia block 30, the centrifugal force acting on this slide valve is insignificant, and need not be taken into account in the operation of the device.

Two return springs 36 are permanently stretched between the hub and the casing, in the front of the device (Fig. 4), to hold the rollers 9 and 10 constantly bearing against the ramps 1 3 and 14.

It will be seen that the whole of this com pact device is really built into the drive pinion 4. This pinion may be fitted with a toothed ring applied to the periphery of the casing 8 (see Figs. 7 and 8), but the teeth may be also cut directly on the outside of the casing 8 (Figs. 9 and 10).

Fig. 3 shows well the simplicity of fitting and maintenance: by removing the inspection cover 38 in the timing case 2 there is immedi ate access to the whole of the device and to the locking bolt 39 by means of which the camshaft 40 of the pump 1 is locked into the hub 7. The camshaft 40 is fixed in this hub by means of a conical sleeve 41.

The operation is as follows: When the system is at rest, that is to say, when centrifugal forces have not yet any action on the inertia blocks 30 and 31, the latter are subject only to the action of the springs 33. Thus, taking account of the posi tion of extreme swing in which the inertia block 31 is held, the slide valve 25 is pressed inwards and the distributor connects the pres sure chambers 1 5 and 16 to the outlet. The pistons 11 and 1 2 remain at rest.

From a certain speed of rotation of the pinion 4. the inertia blocks move outward under the effect of centrifugal force (Fig. 11), and the freed slide valve moves outwards (arrow 42). which causes the pressure in the chambers 1 5 and 1 6 to rise. Immediately the two pistons 11 and 1 2 move forward (arrow 43), which has the consequences of: creating a certain angular displacement between the hub and the casing. since the rollers 9 and 10 O "climb" the ramps 1 3 and 1 4 of the pistons; -increasing the compression of the springs 33. The springs 33 oppose the cen trifugal force by bringing the centre of gravity of the inertia blocks back inwards (Fig. 12, arrows 44).The inertia blocks then return to their starting positions, pressing the slide valve 25 into the cap 24 and making the pressure in the chambers 1 5 and 1 6 fall once more.

In fact, 3 balance is rapidly reached be tween the oil pressure in the chambers 1 5 and 1 6, the tension of the springs 33, and centrifugal force. The establishment of this balance causes immobilisation of the pistons 11 and 1 2 at an intermediate point in their sliding movement, that is to say, by a certain angular displacement between the hub 7 and the casing 8. Thus to each speed of rotation there correspond a certain angular displacement of the said components and a certain advance of the injection.

It will be seen that it is possible to establish a law giving the value of the angular displacement in relation to the travel of the pistons by varying the profile of the ramps 1 3 and 14.

This allows the size of the error of position of the pistons in relation to their travel to be reduced.

It is possible to modify the law for injection advance by changing the stiffness of the springs 33. By changing the initial calibration of the springs 33, the beginning of the development of ignition advance is modified.

The straight ramps 1 3 and 14 may also be replaced by ramps which allow a law of advance to be obtained which is not directly proportional to the speed of rotation of the pump camshaft.

The device according to the invention has the following main advantages: -the hydraulic and mechanical arrangement allowing the pistons to be moved by a pressure of oil which is in relation to the speed of rotation is such that the operation is simple and free from oscillation phenomena or risk of breakdown. In particular, no use is made of small springs which are too fragile and difficult to calibrate.

-the angular indexing obtained is both precise and stable in relation to the speed of rotation.

owing to the operation being irreversible the force component acting on the pistons and arising from the high and irregular drive couple of the injection pump is not able to move the pistons 11 and 1 2. This allows great stability of operation to be obtained. In particular, it is useless to close the hydraulic circuit after each movement of the pistons 11 and 12, the latter having no need to remain supported by a hydraulic cushion since the control is irreversible.

-the operation is very progressive and free from oscillations such as those due to repeated opening and closing of a slide valve, -the fluid under pressure used is advantageously, but not necessarily, the lubrication oil of the engine. From the point of view of the dependability of operation, the oil-tightness is not of paramount importance, from the fact that the device is located inside the timing case of the engine. All leaks are automatically collected.

-the injection pump is fixed in cantilever, by means of the fixing flange: this particularly simple and practical mounting reduces the bulk of the assembly, and avoids the use of any other fixing device of the pump to the engine block.

Claims

1. A hydraulic automatic device for injection advance, mainly for a diesel engine injection pump, constituted by a revolving assembly co-axial with the camshaft of the injection pump and characterised in that it comprises: -a hub fixed to the injection pump camshaft; -a casing which is fixed to the drive pinion of the injection pump, which encloses the hub, and which carries internally at least one roller parallel to the axis of the casing but situated away from this axis; -in association with each roller of the casing, a piston of which the axis is at right angles to the axis of the device, each piston being fitted to slide in a blind boring and carrying a lateral bearing ramp, which works in conjunction with the corresponding roller of the casing;; -a hydraulic circuit having, in the hub, at least one distributor of which the slide valve is operated by an eccentric inertia block capable of displacement mainly under the action of centrifugal force, this distributor controlling the pressure in the chambers formed behind the pistons.

2. A device according to Claim 1, characterised in that it comprises at least one spring which acts between the hub and the casing so as to keep each roller of the casing constantly bearing against the ramp of the corresponding piston.

3. A device according to either one of Claims 1 and 2, characterised in that the ramp of each piston is situated near the front end of the said piston, this ramp being in addition sufficiently inclined in relation to a transverse plane of the piston for the transmission of movement between the piston and the roller to be irreversible, that is to say that the piston cannot slide under the action of the thrust of the roller, no matter how strong it may be.

4. A device according to any one of the preceding claims, characterised in that the inertia block which operates the slide valve is subject to the action of one of the pistons in the hub through a coil spring which is co-axial with this piston and which is compressed between this piston and the inertia block, the axis of the piston and the axis of the slide valve, being parallel and lying on opposite sides of a pivot in the hub on which the inertia block is mounted to swing, this pivot being itself parallel to the axis of the device and being located between the axis of the piston and the centre of gravity of the inertia block.

5. A device according to Claim 4, characterised in that the main axis of the inertia block is closely perpendicular to the axis of the piston which acts on this inertia block.

6. A device according to either one of Claims 4 and 5, characterised in that the front face of the piston which acts on the inertia' block through the spring is turned towards this inertia block, the hydraulic distributor being arranged in such a way as to make the pressure in the chamber formed behind the piston increase when the inertia block moves away from the distributor.

7. A device according to Claim 6, characterised in that the rear chamber associated with each piston is permanently connected to a feed of fluid under pressure, as well as to a fluid escape orifice which the slide valve can progressively block when the inertia block moves away from the distributor.

8. A device according to any one of the preceding claims, characterised in that the feed of fluid under pressure comprises a revolving seal fitted to one end of the hub and a calibrated hole provided in the hub, the fluid return being carried out directly into the timing case in which the device is located.

9. A device according to any one of the preceding claims, characterised in that it comprises two diametrically opposite inertia blocks, of which only one is in contact with the slide valve of the distributor.

10. A device according to any one of the preceding claims, characterised in that the teeth of the drive pinion are directly attached to the casing, these teeth being either fixed to the outside of the case or cut directly into the external surface of the casing.

11. A hydraulic automatic device for injection advance constructed and arranged substantially as herein described with reference to Figs. 1 to 8, 11 and 12 or Figs. 1 to 8, 11 and 1 2 as modified by Figs. 9 and 10 of the accompanying drawings.