Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1993-01-05
1995-02-07
Cross, E. Rollins
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9031, F01L 134
Patent
active
053868072
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a device for adjusting the rotational angle relationship of a camshaft to a drive wheel or element of an internal combustion engine.
An adjustment device for continuously adjusting the angular relationship of a camshaft for actuating gas exchange valves of an internal combustion engine relative to its drive element is known, comprising a servomotor which is actuated by a pressurized medium, in particular a hydraulic medium, and which has working chambers whose enclosed volumes can be increased or reduced by predetermined volume amounts during an adjustment.
In an adjustment device known from EP-A-0 163 046, two hydraulic servomotors are provided on a diameter of a part connected to the camshaft and each of these is equipped with a servopiston which acts via a roller on a ramp which is located on a drive gearwheel radially surrounding the part connected to the camshaft. The two servomotors are separately subjected to pressure and the pressure is controlled by separate valves. The servomotors are triggered by a valve arrangement in such a way that the outwardly moved piston of one servomotor is subjected to pressure and the working space of the other, opposite servomotor is relieved so that the piston of this servomotor can deflect following the ramp. In the case of uneven pressure in the servomotors, the servopiston is displaced and the roller acts both on the ramp of the drive wheel and on the shaft. This angular adjustment can take place in both directions.
Although the oil pressure source present in an internal combustion engine for lubrication purposes can be employed as the drive means for adjusting the camshaft, it only generates a relatively low pressure and is also limited with respect to the delivery volume per unit time. Furthermore, the additional pressurized medium consumption is substantial so that the use of a larger oil pressure source is necessary. A separate high pressure pump, on the other hand, requires more components and energy consumption. In addition, the device proposed is also complicated because two separate magnetic valves or a three-position valve must be employed in order to trigger the two servomotors.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide.
The invention is based on the object of providing a device which permits, for a minimum pressurized medium requirement, a continuous, i.e. rapid advance or retardation, dependent on a characteristic map, of the camshaft relative to the camshaft drive wheel, even in the lower rotational speed range.
According to the invention, the adjustment device continuously adjusts an angular orientation of a camshaft of an internal combustion engine relative to a
The invention is based on the knowledge that the alternating torque on a camshaft relative to the camshaft drive wheel can well be used for an advance or retardation in the upper rotational speed range, the pressure peaks arising due to the torque fluctuations being used as an additional pressure source for setting purposes. In the lower rotational speed range, on the other hand, an additional auxiliary force has to be employed in order to compensate appropriately for the difference occurring, in this rotational speed range, between the necessary pressure force and the actually occurring pressure force due to the torque fluctuations so that a sufficiently rapid adjustment of the camshaft can be realized.
In addition to a hydraulic servomotor necessary for the adjustment, the device according to the invention has, therefore, pump means. An additional adjustment component is generated, particularly in the lower rotational speed range of the internal combustion engine, by this pump means which, according to the invention, is embodied as a ball piston pump and, located in the drive system of the camshaft, forms a complex unit with the hydraulic servomotor means.
In accordance with a preferred embodiment of the invention, a two-cylinder ball piston pump with a two strike cam is provided. The pump is symmetri
REFERENCES:
patent: 4895113 (1990-01-01), Speier et al.
patent: 5056477 (1991-10-01), Linder et al.
patent: 5170755 (1992-12-01), Kano et al.
patent: 5172659 (1992-12-01), Butterfield et al.
patent: 5189999 (1993-03-01), Thoma
Cross E. Rollins
Lo Weilun
Robert & Bosch GmbH
Striker Michael J.
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