GB2065831A

GB2065831A - Injection timer for internal combustion engines

Info

Publication number: GB2065831A
Application number: GB8039799A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-12-15
Filing date: 1980-12-12
Publication date: 1981-07-01
Also published as: JPS6016750Y2; JPS5699026U; DE2950544C2; DE2950544A1; GB2065831B

Abstract

An injection timer (5) for an internal combustion engine varies the angular position of the output shaft (11) relative to the drive shaft (8) at least in dependence upon rotational speed. The adjusting mechanism of the timer (5) comprises two pairs (26) of eccentrics each of which comprises an adjusting eccentric (27) and a compensating eccentric (28). The adjusting eccentrics (27) are each connected by means of a respective transmission element (35) to two hydraulically operable adjusting pistons (31) which are disposed parallel to one another. For the purpose of varying the instant of injection, the adjusting eccentric (27) is rotatable by the changes in the position of the adjusting pistons (31) effected by the hydraulic medium, (engine fuel), and the pressure of the hydraulic medium is controlled in dependence upon the rotational speed and/or further operating parameters (load, temperature). <IMAGE>

Description

SPECIFICATION Injection timer for internal combustion engines The invention relates to injection timers for internal combustion engines.

An injection timer is already known (Swiss Patent Specification No. 331,948) in which the angular position of an output or driven shaft relative to a drive shaft is variable by two servooperated adjusting pistons which are accommodated within the timer and which act radially outwardly. One of the adjusting pistons incorporates a centrifugal-force-operated control valve spool which operates against the force of a return spring and which controls the position of the adjusting piston. The adjusting movements are transmitted by way of rocker arms which abut against adjusting blocks connected to the output shaft, and the positive connection between the rocker arm and the adjusting blocks is maintained by helical compression springs in addition to being maintained by the drive torque.In this timer, the timing of the injection operation is controllable exclusively in dependence upon rotational speed, and the fluctuations in torque caused by the cam drive of the injection pump cannot be fully damped by the helical compression springs.

Owing to the fact that travel is transmitted directly by the adjusting mechanism comprising the rocker arms, these fluctuations in torque lead to angular oscillations and thus to momentary angular variations between the driving member and the driven member, which in turn lead to undesirable high load-dependence of the adjustment in addition to loud drive noise. The disadvantages which have been described also lead to rapid wear on the transmission parts and thus to a change in the instant of injection, this being inadmissible owing to the increased requirement with respect to the quality of the exhaust gas, particularly in modern engines. If the working capacity is to be increased with a given oil pressure, this can only be effected by increasing the diameter of the piston, although this is disadvantageous in that it leads to a larger overall length of the timer.

German Patent Specification No. 1,022,419 and German Offenlegungsschrift No. 27 25 414 describe centrifugal-force-operated injection timers in which the flyweights act upon the adjusting eccentrics of eccentrics pairs which are each formed by an adjusting eccentric and a compensating eccentric and which serve as an adjusting drive. The construction of the eccentrics is such as to result in a one-way action, i.e. the torque being transmitted between the driving and driven members cannot itself turn the eccentrics and thereby affect the injection timing. Such injection timers are consequently insensitive to load surges, resulting in smaller dependence upon load and consequently are less prone to wear than the timer described initially and also cause less noise.However, these timers which are only operated by centrifugal force are also only controllable in dependence upon rotational speed and their working capacity is limited by the size of the flyweights and the installation space for the return springs.

An injection timer in accordance with the invention comprises rotatable and coaxial driving and driven members which are angularly adjustable relative to one another by means of an adjusting mechanism which has two pairs of eccentrics, each pair consisting of an adjusting eccentric and a compensating eccentric, and two pairs of adjusting pistons, which are slidably received in respective bores in a rotatable piston carrier and which are actuatable by the pressure of an hydraulic medium against a restoring force, the two pistons of a pair being disposed parallel to one another and coupled to a respective one of the adjusting eccentrics by means of a respective one of two transmission elements, such that the relative angular positions of the driving and driven members are adjusted by the piston by virtue of the adjusting mechanism, all the adjusting pistons being guided in the piston carrier within one plane lying at right angles to the longitudinal axis of the timer.

By virtue of the fact that the pairs of eccentrics are combined with the adjusting pistons which act upon the adjusting eccentrics in pairs and which are actuatable by the pressure of the hydraulic medium, it is possible to manufacture an injection timer which, with small external dimensions, has an increased working capacity, generates only a small amount of noise, has only a small amount of dependence upon load, and has a long service life.

The control pressure of this timer can be regulated or controlled outside the timer in a separate control device and thus can also be adapted to the increased demands made on modern engines in dependence upon the rotational speed and upon one or several operating parameters.

Advantageously, the centrifugal force of the transmission members and the adjusting pistons produces a speed-dependent basic adjusting characteristic on which the hydraulically controlled adjusting characteristic is superimposed.

In a preferred embodiment of the injection timer, the piston carrier is maintained on a guide part of the driven member. Satisfactory guidance is thus ensured, and a construction of the injection timer results which is easy to oversee and which is simple to mount and to adjust. If each transmission element includes a balance beamlike member to which three connection pins for the two pistons and the adjusting eccentric are attached, the installation space which lies in the same plane, and which is located adjacent the adjusting pistons, can be utilised to an optimum extent, so that, with satisfactory mountability and possibility of adjustment, the springs acting on the transmission element and providing the return force can be of correspondingly strong construction.

Further operating parameters in addition to the rotational speed can be processed by an external control device which provides the hydraulic pressure, without having to vary the overall size or type of construction of the timer itself.

The invention is further described, by way of example, with reference to the drawings, in which: Figure 1 is a longitudinal section through an injection timer, taken approximately along the line I-I of Figure 2, Figure 2 is a fragmentary detail cross section taken approximately along the line Il-Il of Figure 1,and Figure 3 is a cross section taken along the line Ill-Ill of Figure 2.

The injection timer 5 is fitted to a fuel injection pump 6 (only partially illustrated) for diesel engines and is in the form of a closed front mounted injection timer and is coupled to a drive shaft 8 of the engine by way of a coupling 7 indicated by dash-dot lines. It will be appreciated that, alternatively, the injection timer can be in the form of an open built-in injection timer for fitting into a closed drive housing or into the gearbox of the engine if, for exampie, the injection timer is provided in a known manner with a gearwheel (not illustrated) serving as drive member.

As will be described in detail hereinafter, the illustrated injection timer 5 serves to vary the relative angular positions of two coaxial shafts at least in dependence upon rotational speed, that is to say, a driving shaft and a driven shaft, the driven shaft either at the same time being the camshaft of the injection pump or being an intermediate shaft coupled thereto, and the instant of injection or the commencement of delivery by the fuel injection pump being varied in dependence upon a predetermined natural law by varying the relative angular positions of the two shafts.

In the preferred embodiment illustrated in Figures 1 to 3, the drive shaft 8 is bolted by means of the coupling 7 to a housing 10 constituting the driving member of the timer. A driven member 12 of the timer is secured to a camshaft 11 of the fuel inection pump 6 by means of a cap nut 15 and comprises a flange 1 2a and an adjusting hub 1 2b.

The hub 1 2b serves as a guide member for a piston carrier 14. The driven member 12 is prevented from turning relative to the shaft 11 by means of a key 13.

An adjusting disc 19 provided with two plane parallel side faces 17 and 18 is inserted into a recess 1 6 in the housing 10 and is rigidly connected to the housing 10 by means of bolts 21 (see Figures 2 and 3). An annular-groove-like cavity 24 is formed by one side face 17 of the adjusting disc 19 and a recess 23 in the housing 10 and encloses the flange 1 2a, whereby to form an axial and radial bearing for the housing 10, the coupling 7 being mounted on the end face 1 Oa of the housing.

The flange 1 2a, which may be regarded as a part of the driven camshaft 11 is coupled to the housing 10 by means of two pairs 26 of eccentrics rotatably mounted in the adjusting disc 19, each pair of eccentrics comprising an adjusting eccentric 27 and a compensating eccentric 28 received eccentrically in the adjusting eccentric 27. The compensating eccentrics 28 are each journalled to the support flange 1 2a by means of a pin 29 and serve to compensate for the height of the arc which the centre points of the adjusting pins 29 would reach if they were to turn about the centre points of the adjusting eccentrics 27 in the absence of compensating eccentrics 28.This rotary movement of each of the adjusting eccentrics 27 is effected by two respective adjusting pistons 31 (see Figure 2) which are guided parallel to one another, that is to say, they are guided in diametrically opposite pairs in the piston carrier 14, and which are operable by the pressure of an hydraulic medium. The adjusting pistons 31 are guided in an oil-tight manner in parallel, radially outwardly directed cylindrical bores 34 in the piston carrier 14 and are moved outwardly away from the adjusting hub 1 2b against the force of return springs 33 in conformity with the pressure of the hydraulic medium controlled by a control device 32 (see Figure 3). The adjusting eccentrics 27 are turned by way of transmission members 35 which act eccentrically upon the adjusting eccentrics 27.All the adjusting pistons 31 are guided within a plane 40 (indicated by a dash-dot line) which lies at right angles to the longitudinal axis 5a of the timer 5.

Each of the transmission members 35 (see Figure 3) comprises an intermediate element 36, like a balance-beam, which is provided with three spaced connection pins 37 and 38, the two connection pins 37 being held in the associated adjusting pistons 31, and the third connection pin 38 being fitted into the corresponding adjusting eccentric 27. Thus, the lifting movement of the adjusting pistons 31 effected against the restoring force of the timer and of the return springs 33 is converted by a tractive force in the intermediate member 35 to the rotary movement of the adjusting eccentric 27 required for timing the injection operation. Compensating movements can be effected both at the mounting of the piston carrier 14 on the hub 1 2b and by clearance in the transverse bores 31 a provided in the adjusting pistons 31 to accommodate the two pins 37.The four compression springs 33 which acts upon the outermost ends 36a of the intermediate elements 36, and which serve as return springs, have a restoring effect and also a stabilizing effect. They determine the steepness of the basic characteristic, but only influence the timing conditionally when the supply of hydraulic medium to the adjusting pistons 31 is regulated externally in the control device 32. As is indicated by the arrows on the control device 32, closedloop control of this kind can be effected in dependence upon the rotational speed n, the load Q or an operating temperature T, and the actual value of the angle a: of adjustment characterising the instant of injection. The associated source of pressure is only indicated and is designated 39.

Alternatively, instead of closed-loop control via the hydraulic medium fed to the adjusting pistons 31, the control device 32 can control the valve of the pressure of the hydraulic medium in accordance with the operating parameters of the engine (open-loop control), and the adjusting pistons 31 are then displaced in conformity with the restoring force of the return springs 33 and in proportion to the pressure and the simultaneously effective centrifugal force of the transmission members 35 and adjusting pistons 31. The adjusting eccentrics 27 are thus correspondingly turned. In the case of open-loop control, the characteristic of the compression springs 33 substantially determines the shape of the adjusting characteristics or of the adjusting curves.The adjusting characteristic has to be relatively flat for stable behaviour of the timer, this being achieved by correspondingly stiff springs.

The maximum stroke H of the adjusting pistons 31, and thus the maximum adjustment of the mutual angular positions of the housing 10, serving as the driving member, and the camshaft 11 is limited by an interior peripheral wall 1 Ob of the housing 10 against which the adjusting pistons 31 abut when they are in their outermost end positions.

The hydraulic medium is fed from the pressure source 39 to the adjusting pistons 31 through a pressure line 42 which is connected externally to a support flange 41 of the injection pump 6, the pressure level of the hydraulic medium being controlled or regulated by the control device 32.

The engine fuel flowing into the interior of the timer 5, and serving as the hydraulic medium, flows through a passage arrangement 43 in the support flange 41 and in the adjusting hub 1 2b into the regions of the cylindrical bores 34 which form the pressure chambers for the adjusting pistons 31.

When in their illustrated starting positions, the angled ends 36a of the intermediate members 36 abut against one another under the initial stressing force of the return springs 33, whereby the starting angular position of the housing 10, serving as the driving member, is determined relative to the camshaft 11, serving as the output shaft.

Each of the return springs comprises a set of compression springs 33 clamped between spring abutments 92 and 93 at the outermost ends 36a of the intermediate elements 36. The spring abutments 92 are bush-like and are in each case secured to the ends 95a of a spacer rod 95 which holds the compression springs 33 together, and the spring abutments 93 are received by the drilled ends 36a, bent at right angles of the intermediate elements 36 and are also bush-like.

The mode of operation of the injection timer in accordance with the invention will now be described with reference to the embodiment illustrated in Figures 1 to 3.

When the adjusting pistons 31 are in their starting positions illustrated in Figures 1 to 3, the housing 10, serving as the driving member, assumes a predetermined angular position relative to the driven member 12 which is attached to the camshaft 11, serving as an output shaft. If it is desired to advance the instant of injection with increasing rotational speed, the associated adjustment is preprogrammed in the control device 32, and, controlled by the control device 32, the pressure of the hydraulic medium, delivered by the pressure source 39 is conducted through the conduit 42 and below the adjusting pistons 31 and adjusts the latter radially outwardly in addition to the speed-dependent centrifugal force already existing, until, with corresponding turning of the adjusting eccentric 27, the flange 1 2a of the driven member 12, and thus the camshaft 11, have been turned through the desired angle a of adjustment relative to the housing 10 or relative to the drive shaft 8. The control fluid conducted below the adjusting pistons 31 is regulated upon measuring the actual value of the angle a of adjustment, until the desired value and the actual value are equal, so achieving a closed-loop control.

Alternatively, however, the pressure of the hydraulic medium fed through the conduit 42 can be controlled directly in dependence upon the rotational speed n and further operating parameters such as the load Q and operating temperatures T, and the restoring force of the return springs 33 can be opposingly varied. In this case, at the non-loaded instant, that is to say, upon a change in direction of the force of the torque surges, the adjusting pistons 31 assume a position which is determined by the equilibrium between the restoring force of the return springs 33 and the adjusting force which comprises the centrifugal force and the hydraulic pressure and which is transmitted by the pistons 31, so achieving an open-loop control. The adjusting eccentrics 27 have then been turned by a predetermined amount which corresponds to the desired angular adjustment of the housing 10 relative to the camshaft 11. This relative angular adjustment leads to the change in the commencement of delivery or instant of injection on the diesel engine dependent upon the described operating parameters.

Claims

1. An injection timer for an internal combustion engine, comprising rotatable coaxial driving and driven members which are angularly adjustable relative to one another by means of an adjusting mechanism which has two pairs of eccentrics, each pair consisting of an adjusting eccentric and a compensating eccentric, and two pairs of adjusting pistons which are slidably received in respective bores in a rotatable piston carrier and which are actuable by the pressure of an hydraulic medium against a restoring force, the two pistons of a pair being disposed parallel to one another and coupled to a respective one of the adjusting eccentrics by means of a respective one of two transmission elements, such that the relative angular positions of the driving and driven members are adjusted by the pistons by virtue of the adjusting mechanism, all the adjusting pistons being guided in the piston carrier within one plane lying at right angles to the longitudinal axis of the timer.

2. An injection timer as claimed in claim 1, in which each transmission element has three connection pins disposed parallel to the longitudinal axis of the timer, two such pins being respectively associated with the two pistons of the respective pair and the third pin being associated with the respective adjusting eccentric.

3. An injection timer as claimed in claim 2, in which said two connection pins of the transmission element which are associated with the adjusting pistons are inserted into these pistons at right angles to the longitudinal axes thereof and the third connection pin extends into the respective adjusting eccentric, the transmission element further comprising an intermediate member via which the third connection pin is connected to the first two connection pins.

4. An injection timer as claimed in claim 3, in which each intermediate member is balancebeam-like and its outermost, mutually oppositely located ends are subjected to said return force which is exerted by return springs.

5. An injection timer as claimed in claim 4, in which each return spring comprises a set of compression springs clamped between spring abutments.

6. An injection timer as claimed in claim 5, in which one end, bent at right angles, of each intermediate member serves as a respective one of the abutments for the compression springs.

7. An injection timer as claimed in any preceding claim, in which the piston carrier is mounted on a guide part of one of said driving and driven members.

8. An injection timer as claimed in claim 7, in which the piston carrier is mounted on a part of the driven member.

9. An injection timer as claimed in any preceding claim, in which said pressure of the hydraulic medium is dependent upon rotational speed and at least one further operating parameter and is determinable by a control device located outside the timer.

10. An injection timer as claimed in claim 9, in which the relative angular position between the driving and driven members is fed back to the control device.

11. An injection timer constructed and adapted to operate substantially as herein described with reference to and as illustrated in the drawings.