GB2151333A

GB2151333A - Hydraulic injection timing mechanism for a fuel injection pump

Info

Publication number: GB2151333A
Application number: GB08431237A
Authority: GB
Inventors: Karlheinz Hoffman; Guenter Seiler; Frank Thoma
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1983-12-15
Filing date: 1984-12-11
Publication date: 1985-07-17
Also published as: FR2556779B1; IT8423892A1; GB8431237D0; DE3345343C2; DE3345343A1; GB2151333B; FR2556779A1; IT8423892A0; IT1178705B

Abstract

A hydraulic adjusting mechanism for a fuel injection pump (2), which mechanism controls the injection timing of the pump depending on various operating parameters of a self- igniting internal combustion engine, consists of a primary element (6) driven from the drive shaft of an internal combustion engine and a secondary element (5) rigidly connected to the camshaft (4) of the injection pump (2), of which elements the primary element (6) connected to a hydraulic oil supply (14) is provided with a control element (10) which, when subjected to pressure, can be displayed axially in opposition to the force of return springs. The primary element (6), which is in the form of a driver with external toothing, serves as a housing for the control element (10) which consists of a piston (8) and sliding blocks or parts (9), and the pin-like sliding block or part of which has an inclined or acute-angled face (9a) which in constant contact with the adjacent face of a cooperating piece (12) mounted in the secondary element (5). A compact design is possible with this adjusting mechanism. <IMAGE>

Description

SPECIFICATION Hydraulic injection timing mechanism for a fuel injection pump This invention relates to a hydraulic injection timing mechanism for a fuel injection pump of an internal combustion engine.

Current exhaust emission laws make it necessary to adjust the injection timing depending on engine speed, load and other operational conditions instead of, as hitherto, using centrifugal injection timing gear which made it possible for an injection timing adjustment, which was predetermined by centrifugal force, to be dependent on the speed of the internal combustion engine.

German Offenlegungsschrift 3209 813 discloses an adjusting mechanism for a fuel injection pump which controls or regulates fuel injection depending on various operating parameters of the internal combustion engine.

In this design a secondary element contains a ring-shaped piston which, when seen in crosssection, is wedge-shaped and, when subjected to pressure, operates slides provided with inclined faces and eccentric plates cooperating with these slides on a primary element in such a manner that an axial movement of the hydraulic piston or control element can be converted into a radial movement of the slides and a relative movement is effected between the primary and secondary elements by way of eccentric plates.

A hydraulic adjusting mechanism for varying the injection timing in an internal combustion engine is also known from British Patent Specification No. 1,218,026, in which a bush-shaped control element engages, on the one hand, with a shaft end of the secondary element, which is in the form of a hydraulic head, and, on the other hand, with a sleeveshaped coupling element by way of internal and external helical gearing, the coupling element in this case combining with the drive shaft to form the primary element.

The object underlying the present invention is to provide a hydraulically operated adjusting mechanism for a fuel injection pump which makes a compact design possible and the adjusting elements of which cooperate in such a manner that a reduced friction and, thus also more rapid response characteristics are obtained when the secondary element is adjusted relative to the primary element. In addition, the influence of centrifugal forces is to be avoided.

According to the invention, there is provided a hydraulic adjusting mechanism for a fuel injection pump, which mechanism controls the injection timing of the pump in dependence on various operating parameters of a self-igniting internal combustion engine, the adjusting mechanism comprising a primary element which is driven by the drive shaft of the inernal combustion engine, and a secondary element which is rotatable relative to the primary element and rigidly connected to the fuel injection pump, one of said elements being connected to a hydraulic oil supply having a control element which, when subjected to pressure, can be displaced axially in oppostion to the force of return springs and which consists of a piston and slidable part, said slidable part having an inclined face which is in constant contact with an adjacent face of a cooperating piece arranged in the other of said elements and, when in its operative direction, lies in the peripheral direction of the adjusting mechanism, wherein, in an adjusting mechanism in which the primary element is formed by a driver having external toothing, this driver is provided as a housing for the control element, the slidable part of which, being directly connected to the piston, is pin-shaped and guided so as to be longitudinally displaceable in the driver.

In addition to a compact design for the adjusting mechanism, the invention also includes a simple conversion of the movement between the adjusting element of the primary element and the cooperating piece of the secondary element to be achieved.

A particularly favourable embodiment of the invention in which the inclined face slides along the needle bearing of the cooperating piece allows precise injection timings to be effected because of the extremely low frictional forces. In addition, the provision of only one hydraulic piston results in an adjusting mechanism design which is advantageous from the production engineering viewpoint.

Embodiments of the invention will now be described in more detail, by way of example and with reference to the accompanying drawings, in which: Figure 1 shows a longitudinal section of a hydraulic adjusting mechanism, Figure 2 shows a sectional view of the adjusting mechanism taken along the line ll-ll in Fig. 1, Figure 3 is a partial longitudinal section of another embodiment of the adjusting mechanism, Figure 4 shows a portion of the adjusting mechanism of Fig. 3 rotated through 90 , in which the adjustment-effecting elements have surfaces in contact with one another, Figure 5 shows an embodiment in which the adjustment-effecting elements have line contact, Figure 6 shows a further embodiment of the adjusting mechanism, in longitudinal section, and Figure 7 shows a section from the adjusting mechanism of Fig. 6 which has been rotated through 90 .

A hydraulic adjusting mechanism 1, which controls the injection timing of the injection pump 2 depending on various operating para meters of a self-igniting internal combustion engine, consists essentially of a primary ele ment 3 driven by the drive shaft or crankshaft of the internal combustion engine, and of a secondary element 5 which is arranged coaxially with the primary element and is connected to the camshaft 4 of the injection pump 2.

The primary element 3 is composed of a chain wheel 6 and a cover 7 which, together, form a housing, and also of a control element 10 consisting of a piston 8 and slidable parts 9.

The disc-shaped piston 8 illustrated in Fig.

1 is guided by its piston element 8a so as to be axially displaceable in a central recess 11 in the cover 7, and its piston flange 8b serves as a supporting flange for the three slidable parts 9 which are distributed uniformly in the peripheral direction and are axially displaceable in the chain wheel. The supporting flange 8b is outwardly curved on its sliding face 8c in order to prevent the piston 8 from jamming.

The pin-like slidable parts 9 are wedgeshaped and lie with their inclined faces 9a in contact with associated cooperating pieces 1 2 arranged in the secondary element 5 of the adjusting mechanism 1. The inclined face 9a of the slidable part 9, when in its operative direction, runs in the peripheral direction of the primary element 3. Each cooperating piece 1 2 is formed by a pin which extends radially in the secondary element 5 and is secured in position in the radial direction and the free section of which, between the clamped pin ends 1 2a, is enclosed by a needle bearing 1 3 which serves as a bearing surface 1 3a for the inclined face 9a of the slidable part 9.

The primary element 3 is connected to a hydraulic oil supply (not shown) through a line 14 connected to the cover 7. The piston 8 which can be operated by a pressure medium and which, together with the cover 7, forms a working chamber 15, adjusts the secondary element 5 for the purpose of advancing or retarding the ignition timing when subjected to pressure by the slidable parts 9 engaging on the respective cooperating pieces 1 2 in opposition to the force of return springs 1 6 (Fig. 2). With this compact design adjustments are effected in an absolutely jerk-free and consequently very precise manner because of the use of the needle bearing and the line contact associated with such use.

Fig. 3 shows an embodiment in which there are provided pistons 8 which are equal in number to the three cooperating pieces 1 2 and which have a hollow design and guide the inserted sliding pieces 9 in their hollow interiors 1 7. The cooperating piece 12 is designed in one piece and is non-rotatably mounted in the secondary element 5 axially parallel to the camshaft. The cooperating piece 1 2 is provided with an inclined face 18 which is adapted to match that of the slidable part 9 (Fig. 4).

In this embodiment feed channels 1 9 for the operating medium run through the primary element 3 to the various working chambers 15.

The embodiment shown in Fig. 5 differs from that in Figs. 3 and 4 in that the piston and slidable part form a compact constructional unit 20, the inclined face 9a of this unit 20 sliding along the cooperating piece 12, which is in the form of a pin, when it is subjected to pressure. This cooperating piece 1 2 is identical to the design according to Figs.

1 and 2, but it can be designed without the needle bearing 1 3-as shown-just as in the case of the embodiment of Figs. 6 and 7 in which the piston 8 and slidable part 9 are again designed in one piece, but are connected to one another by a piston rod 21 which is longitudinally displaceable with respect to the chain wheel 6.

The adjusting mechanisms 1 according to Figs. 1 to 7 can each have two, three or four control elements 10 and cooperating pieces 1 2 which are equidistatly spaced from one another in the peripheral direction. In addition, the control elements 10 can be arranged in the secondary element 5 and the cooperating pieces 1 2 in the primary element 3.

In order to minimize the sudden change of pressure stage when the piston is first lifted, very small abutments 22 are provided on the piston or on the wall of the primary element lying opposite the piston.

Claims

1. A hydraulic adjusting mechanim for a fuel injection pump, which mechanism controls the injection timing of the pump in dependence on various operating parameters of a self-igniting internal combustion engine, the adjusting mechanism comprising a primary element which is driven by the drive shaft of the internal combustion engine, and a secondary element which is rotatable relative to the primary element and rigidly connected to the fuel injection pump, one of said elements being connected to a hydraulic oil supply having a control element which, when subjected to pressure, can be displaced axially in opposition to the force of return springs and which consists of a piston and a slidable part, said slidable part having an inclined face which is in constant contact with an adjacent face of a cooperating piece arranged in the other of said elements and, when in its operative direction, lies in the peripheral direction of the adjusting mechanism, wherein, in an adjusting mechanism in which the primary element is formed by a driver having an external toothing, this driver is provided as a housing for the control element, the slidable part of which, being directly connected to the piston, is pjn-shaped and guided so as to be longitudinally displaceable in the driver.

2. A mechanism according to Claim 1, wherein the control element consists of three slidable parts which are uniformly distributed in the peripheral direction and which are operatively associated with cooperating pieces.

3. A mechanism according to Claim 1 or Claim 2, wherein the axially displaceable piston is disc-shaped and has a piston flange acting as a supporting flange for the slidable parts, and a piston element projecting into a recess in a cover of the primary element, the piston flange combining with the cover to form a pressure chanmber connected to said hydraulic oil supply.

4. A mechanism according to any one of Claims 1 to 2, wherein each cooperating piece is formed by a radially extending pin which is enclqsed by a needle bearing cooperating with the inclined face of the associated slidable part and is rigidly mounted with its free ends located in the secondary element.

5. A mechanism according to Claim 1 or Claim 2, wherein the control element has three pistons which are axially displaceable with respect to the driver and can be subjected to pressure, each one of which is hollow, and the associated pin-shaped slidable part, which is arranged so that its inclined face slides on an inclined face of the cooperating piece mounted in the secondary element is guided in the respective hollow space.

6. A mechanism according to Claim 1 or Claim 2, wherein the piston and slidable parts are combined to form a constructional unit and the inclined face bears against the cooperating piece formed by a pin, the pin ends being mounted in the secondary element.

7. A mechanism according to Claim 1 or Claim 2, wherein each piston has a piston rod which is longitudinally displaceable in the dirver and at the free end of which there is provided the slidable part having an inclined face which bears against the cooperating piece formed by a pin, the pin ends being rigidly mounted in the secondary element.

8. A hydraulic adjusting mechanism for a fuel injection pump, substantially as hereinbefore described and with reference to Figs. 1 and 2 of Figs. 1 and 2, modified as shown in Figs. 3 and 4, or Figs. 5, 6 or 7 of the accompanying drawings.