GB2200973A

GB2200973A - Damping device for a centrifugally controlled injection timing device

Info

Publication number: GB2200973A
Application number: GB08801207A
Authority: GB
Inventors: Wendelin Klugel; Frank Thoma
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1987-01-23
Filing date: 1988-01-20
Publication date: 1988-08-17
Anticipated expiration: 2008-01-20
Also published as: GB2200973B; IT8819073A0; GB8801207D0; IT1215704B; DE3701852C1

Abstract

The invention relates to a hydraulically operating damping device in a centrifugally controlled injection timing device consisting of a primary and a secondary part, with centrifugal weights 9, 10 which, when the engine r.p.m. change, move against the force of return springs, of which at least one contains in a cylindrical recess 14 closed radially outwards a damping piston 15 secured in a radial direction on the primary side which on a torque action retards the displacement movement of the centrifugal weight 10. <IMAGE>

Description

Damping Device For A Centrifugally Controlled Injection Timing Device The invention relates to a damping device for a centrifugally controlled injection timing device with centrifugal weights adapted to be disposed between a primary part driven by the crankshaft of an internal combustion engine and a secondary part rigidly connected with the pump shaft of a fuel injection pump, said weights being movable against the force of - a return spring when the r.p.m. that is, the revolutions per minute of the engine speed change.

As is well known, mechanically-operating injection timing devices are used in the diesel engines of the present day for setting the beginning of the injection or the beginning of the delivery. The timing devices effect, as the r.p.m. of the engine increase, a relative movement between the secondary part on the injection pump side and the primary part on the drive side. The centrifugal weights which in this arrangement are under the action of centrifugal force and slide outwardly radially against the direction of the force of springs move the secondary part against the primary part in the direction of earlier start of delivery.

From DE-OS 3400812 an injection timing device of this type is known, the two half-moon--shaped centrifugal weights of which have in each case a cylindrical recess with a damping device. This has a damping piston guided in the recess of the centrifugal weight which bears on the inner peripheral surface of the primary part, and as a result of a movement of the centrifugal'weight caused by the centrifugal force, it is pressed contrary to the force of a spring into a recess filled with oil through a throttle opening. Damping is therefore effective as the r.p.m. increase.

It has now been found that when mounted on the engine the secondary part, as opposed to the primary part of the timing device, is excited into vibrations which are caused by the irregularity of the engine and in particular by the torque peaks occurring at the injection pump. The vibrations cause undesirable random oscillations of the inception of injection and at worst damage to the injection timing device.

The present invention seeks to provide a device which reduces or eliminates the adverse effects of the vibrations.

According to the invention there is provided a damping device for a centrifugally controlled injection timing device with centrifugal weights adapted to be disposed between a primary part driven by the crankshaft of an internal combustion engine and a secondary part rigidly connected with the pump shaft of a fuel injection pump, said weights.being movable against the force of a return spring when the r.p.m. changes, of which centrifugal weights at least one has a cylindrical recess for housing a damping piston, the damping device also having an oil supply which leads via a throttling port to an oil pressure spaced formed by the recess and delimited by the damping piston, wherein the recess comprises a blind bore closed radially outwards and the damping piston is secured in the radial direction on the primary side and, when a torque effect occurs, prevents the displacement movement of the centrifugal weight.

By means of the steps according to the invention the vibrations arising on the secondary side, particularly during the injection processes as a result of the high torque peaks, are damped, i.e. the oil buffer above the damping piston damps the movement of the centrifugal weight.

Preferably, the damping piston comprises a hollow piston with a bottom part facing the pump shaft and which contains the throttling port adapted to be connected with the oil supply. m this case, the bottom part may have an annular groove into which a securing bolt fixed on the primary side engages. The bottom part may be guided in a recess of a bushing rotatably mounted concentrically with the pump shaft, said bushing being at the same time the boss of a driving chain wheel.

The bushing may have a flat portion facing the centrifugal weight on which the bottom portion of the damping piston bears in seal-tight manner supported by the force of a spring. The spring may be prestressed in the starting position of the centrifugal weights and applies a load on the one hand on the bottom of the blind hole and on the other hand on the bottom portion of the damping piston.The bushing may have a radial oil feed bore into which the throttling port opens.

A non-return valve closing the throttling port may be arranged in the piston, via which the damping chamber only is fillable, though outflow from the damping chamber takes place via a throttle port opening out into a pressure-free space of the injection timing device.

The centrifugal we,ight, when the r.p.m. changes, may slide on the one hand along a guide track on the primary side extending parallel with the axis of the damping piston, and on the other hand along a guide track, concavely curved, on the secondary side.

The centrifugal weight may be constructed as a roller and is in linear contact with the guide tracks. The centrifugal weight on the primary side may be curved in such a manner that the radius of curvature is smaller than that of the guide track. Embodiments of the invention will now be described by way of example with reference to the drawings in which: Figure lis an injection timing device with integral damping device in cross-section; Figure 2is on an enlarged scale a detail of the construction shown in Figure 1, Figure 3is a further embodiment with a damping piston supported by the force of a spring, and Figure 4shows in enlarged representation a detail of the construction shown in Figure 3 with a non-return valve.

Figure 1 shows an injection timing device 1, centrifugally controlled, intended for an air-compressing fuel injection reciprocating engine with a hydraulically operating damping device 2. The timing is composed of a primary part 3 driven by the crankshaft of the internal combustion engine, and of a secondary part 5 rigidly connected with the pump shaft 4 of an injection pump.

between the primary and the secondary part there are provided diametrically oppositely situated centrifugal weights 10, 11, constructed in the manner of rollers and sliding along guide tracks 6, 7 and 8, 9 which weights, as the r.p.m. of the engine and the centrifugal force increase, are pressed radially outwards against the direction of force of return springs 12, 13, move the secondary part 5 relative to the primary part 3 by some degrees of angle, and displace the injection time in the direction of advance. The concavely curved guide tracks 6, 9 on the secondary side are disposed opposite the flat guide tracks 7, 8 on the primary side.

The damping device 7 is housed in the centrifugal weight 10. Also, in a cylindrical recess 14 which is open towards the pump shaft 4 and is constructed in the form of a blind bore, there is a hollow damping piston 15, the open side of which faces the bottom of the blind bore 16 and the bottom part 17 of which faces the pump shaft 4.

In the position of the damping piston 15 shown in Figures 1 and 2 the bottom part 17 only protrudes out of the blind bore; said bottom part is guided in a matching recess 18 of a bushing 19 rotatably mounted concentrically with the pump shaft 4; the bushing is at the same time the boss of a driving chain wheel 20. A securing bolt 21 rigidly inserted in the bushing 19 engages into an annular groove 22 on the bottom part 17, so that the damping piston 15 is screwed in the radial direction (Figure 2).

The hollow space formed by the damping piston is in connection via a central throttling port 23 in the bottom part 17 and via a radial oil feed bore 24 extending in the bushing with the engine oil circuit.

The further throttle port 25 provided in the bottom part 17 is used for ventilation purposes and, together with the throttling port 23, acts as a damping throttle.

In Figure 3 the damping device 2 is housed in a larger centrifugal weight mass. By this means an additional damping effect is achieved through the relatively great bearing face of the centrifugal weight 10, the sliding surface 26 of which on the primary side is constructed level, as is the guide track 7, and of which the secondary sliding surface 27 has a convex shape, with a radius of curvature which is smaller than that of the associated guide track 6.

In the damping piston 15 a spring 28 is provided which bears, on the one hand, on the bottom of the blind hole 16 and, on the other hand, on the bottom part 17 of the damping piston 15 and, under all conditions of operation of the internal combustion engine, applied the damping piston 15 seal-tightly on a flat portion 29 of the bushing 19. By means it is ensured that the damping space is filled -with oil. The thrbttling hole 25 serves also for ventilation purposes and acts as a damping throttle.

Figure 4 shows a damping piston 15 with integrated non-return valve 30 the ball 32 of which, pressed by a spring onto the valve seat, closes, as a valve closure member, the throttle hole 23.

Ball 32 only allows the oil to flow into the damping chamber via the throttle port 23. A reversal of flow is prevented byA the spring-loaded ball 32. damping is determined only by the flowing out of the throttle port 25 into a pressure-free space 33 of the timing device.

With the use of the non-return valve 30 high damping forces are achievable with a rapid filling of the damping chamber.

Claims

1. A damping device for a centrifugally controlled injection timing device with centrifugal weights adapted to be disposed between a primary part driven by the crankshaft of an internal combustion engine and a secondary part rigidly connected with the pump shaft of a fuel injection pump, said weights being movable against the force of a return spring when the r.p.m. changes, of which centrifugal weights at least one has a cylindrical recess for housing a damping piston, the damping device also having an oil supply which leads via a throttling port to an oil pressure spaced formed by the recess and delimited by the damping piston, wherein the recess comprises a blind bore closed radially outwards and the damping piston is secured in the radial direction on the primary side and, when a torque effect occurs, prevents the displacement movement of the centrifugal weight.

2. A damping device according to Claim 1, wherein the damping piston comprises a hollow piston with a bottom part facing the pump shaft and which contains the throttling port adapted to be connected with the oil supply.

3. A damping device according to Claim 2, wherein the bottom part has an annular groove, into which a securing bolt fixed on the primary side engages.

4. A damping device according to claim 2 or 3, wherein the bottom part is guided in a recess of a bushing rotatably mounted concentrically with the pump shaft, said bushing being at the same time the boss of a driving chain wheel.

5. A damping device according to claim 2 or 3, wherein the -bushing has a flat portion facing the centrifugal weight on which the bottom portion of the damping piston bears in seal-tight manner supported by the force of.a spring.

6. A damping device according to claim 5, wherein the spring is prestressed in the starting position of the centrifugal weights and applies a load on the one hand on the bottom of the blind hole and on the other hand on the bottom portion of the damping piston;

7. A damping device according to claim 4, wherein the bushing has a radial oil feed bore into which the throttling port opens.

8. A damping device according to. any one of the preceding claims, wherein in the damping piston a nonreturn valve closing the throttling port is arranged, via which the damping chamber only is fillable, though outflow from the damping chamber takes place via a throttle port opening out into a pressure-free space of the injection timing device.

9. A damping device according to any one of the preceding claims, wherein the centrifugal weight, when the r.p.m. changes, slides on the one hand along a guide track on the primary side extending parallel with the axis of the damping piston, and on the other hand along a guide track, concavely curved, on the secondary side.

10. A damping device according to any one of the preceding claims, wherein the centrifugal weight is constructed as a roller and is in linear contact with the guide tracks.

11. A damping device according to any one of the preceding claims, wherein the centrifugal weight is on the primary side curved in such a manner that the radius of curvature is smaller than that of the guide track.

12. A damping device for a centrifugally controlled injection timing device with centrifugal weights adapted to be disposed between a primary part driven by the crankshaft of an internal combustion engine and a secondary part rigidly connected with the pump shaft of a fuel injection pump, said weights being movable against the foree of a return spring when the r.p.m. changes, substantially as described herein with reference to and as illustrated in the accompanying drawings.