Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1987-11-16
1991-09-24
Miller, Carl S.
Internal-combustion engines
Charge forming device
Fuel injection system
123502, 123506, 417462, F02M 3900
Patent
active
050505580
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention starts from a fuel injection pump. In a known fuel injection pump disclosed by GB-A-2,086,080, the lower end of the distributor is designed as a piston carrier and the rollers are mounted in guides of a roller-carrier part by means of their roller tappets. A cam drive of the pump pistons consists of a cam ring which is mounted fixed in place in the pump casing, that is to say the stationary part of the cam drive. It is the roller-carrier part which is driven to rotate, this being connected via a toothing of the drive shaft of the fuel injection pump. This drive shaft is coupled, on its end face, to the end face of the distributor on the same side as the piston-carrier part. The injection-effective feed stroke of the pump pistons is controlled by means of a solenoid valve, a relief channel of the pump working space being closed by means of an electromagnetic valve for the start of injection (injection start), and this valve being opened again in order to determine the end of injection. Where a stationary cam is concerned, the disadvantage of this type of control is that the length of the cam flank driving the pump pistons must serve both for calculating the injection time and for calculating the injection start. This means that, when the injection start is late and the fuel injection quantity is large, the limits of the operating capacity of such a fuel injection pump are reached just when this fuel injection pump has to feed a large number of cylinders of an internal-combustion engine per revolution, high injection pressures have to be generated and high rotational speeds are to be brought about, as is required in modern direct-injection diesel engines. Since there are limits to the steepness of the cams, the length of the cam flank cannot be increased to any extent desired. Also the assembly of such pumps involves a high outlay. The roller tappets are guided in slots which open towards the upper part of the pump casing, so that the roller-carrier part must be exactly in line with the pump casing to ensure that the roller tappets run perfectly. Moreover, the roller-carrier part is also not guided radially, so that it is exposed not only to torsional vibrations, but also to certain tilting vibrations from the drive side of the drive shaft. Moreover, the coupling of the distributor to the drive shaft is rigid and does not allow any error in the alignment of the axes.
Particularly on radial piston pumps of the type in which the part of the cam drive carrying the cam contact surface is driven to rotate, while the piston carrier is stationary, according to German Offenlegungsschrift 301,039, it is difficult to adjust the injection start. In the fuel injection pump known from this publication, the injection start is adjusted by varying the relative position of the distributor in relation to the rotary-driven part of the cam drive which sets this distributor in rotary movement. But the disadvantage of this is that, when such a fuel injection pump is used for the purpose already described above, in practice a large part of the cam flank has to be reserved for adjusting the injection start, thus restricting the capacity of a fuel injection pump when the internal-combustion engine has a large number of cylinders to be fed.
SUMMARY OF THE INVENTION
The fuel injection pump in accordance with the invention, has pump pistons and rollers driving the pump pistons which are guided in constructional parts, which are separated from one another and which are coupled to one another so as to allow misalignments in the radial and axial directions. The advantage of this is that the forces generated by the cam drive as a result of the running of the rollers over the cam contact surface are not transmitted, for example, to the piston-carrier part in such a way that the latter is loaded to such an extent that its guide becomes jammed. On the contrary, a special coupling allows the coupled part to follow with only low reaction, thus increasing the operating capacity of the fuel injection
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Brunel Andre
Duplat Gerard
Leblanc Jean
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