Internal-combustion engines – Starting device – Compression relieving type
Reexamination Certificate
1999-05-13
2001-05-01
Dolinar, Andrew M. (Department: 3747)
Internal-combustion engines
Starting device
Compression relieving type
Reexamination Certificate
active
06223708
ABSTRACT:
The subject matter of the present invention is an automatic decompression system for an internal combustion engine, especially a one-cylinder diesel engine, with at least one outlet and one inlet valve, which are activated by a camshaft with at least one cam, wherein the outlet valve is lifted during starting to reduce the cranking resistance and with further features according to the preamble of claim
1
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From the prior art there are known devices which reduce the cranking resistance during starting of internal combustion engines. Most are semi-automatic devices which lift the outlet valve by a few tenths of one millimeter by a manually operated lever and, after one working cycle during reversing start or after several working cycles during hand-cranked start, switch from decompression to compression by means of a restoring or latching mechanism. Also known from the prior art are decompression devices which, under centrifugal control, lift only one of the valves (inlet or outlet valve) by a few tenths of one millimeter for a specified, short angular range around ignition TDC and, when a specified crankshaft speed is reached, switch again from decompressed to compressed condition. Yet another starting aid operating under centrifugal control is known from European Patent EP 0515183 A1. Because of the rigid connection between flyweight and bow-shaped member, a relatively large installation space is needed this device. The object of the present invention is therefore to provide an easy-to-make, low-cost automatic decompression system which operates completely automatically by purely mechanical regulation and needs only a small installation space. This object is achieved by the automatic decompression system of the present invention. Therein there is provided for lifting the outlet valve at speeds below a switching speed for changeover from decompression to compression a fully automatic lifting device, which effects lifting of the outlet valve from the valve seat. In this way the lifting device effects lifting of the valve as long as the camshaft is rotating more slowly than a specified switching speed. This leads advantageously to reduction of the cranking resistance during starting, whereby the internal combustion engine is started either manually by reversing cable or by crank or electrically by means of a small starter motor. Above the switching speed the lifting device is inactive, and so the valve is not lifted and thus full compression takes place. Furthermore, the invention provides that the lifting device is equipped with a bow-shaped member, pivoted in articulated relationship, disposed between the cam and a cam disk, which bow-shaped member has two articulated arms and a crosspiece joining them, and which at speeds below the switching speed occupies in the cam plane an engaged decompression position, in which it projects beyond the cam base circle, and which can be disengaged into a neutral position in the cam-disk plane when the switching speed is reached. This bow-shaped member is designed such that it can swivel around a rotary pivot disposed in a plane parallel to the cam plane and, in fact, in such a way that the bow-shaped member is engaged in the cam plane with the crosspiece disposed transverse to the articulated arms and projects beyond the cam base circle when the camshaft is turning slowly or is stopped. By this space-saving arrangement, the valve is slightly lifted from its closed position, or in other words raised from the valve seat, as long as it is controlled by the cam in the region of the crosspiece. After the specified switching speed has been reached, a restoring force is exerted on the articulated arms, causing swiveling movement of the bow-shaped member, whereby the crosspiece is disengaged into the cam-disk plane. Hereby there is created in simple manner with purely mechanical means a completely automatic decompression system, which has only a small space requirement in the assembly chamber. Furthermore, the invention provides that, for speed-dependent control of the engagement and disengagement process of the bow-shaped member for decompression or compression respectively, there is provided at least one flyweight held in a specified rest position by a pretensioning spring and subjected in radial direction to inward pressure. The mass of this flyweight is dimensioned such that it occupies its outermost radial position against the pressure of the spring at the defined switching speed, or in other words such that it bears against a stop in this position. In addition, the pretensioning spring ensures that the flyweight when in rest position is held in a specified position regardless of gravitational forces. In dimensioning the mass of the flyweight as a function of switching speed, the pretensioning force of the spring must be taken into consideration. By the coupling of the flyweight mechanism with the bow-shaped member pivoted in articulated relationship, engagement and disengagement of the bow-shaped member as a function of switching speed is achieved in simple manner.
In this connection an advantageous embodiment of the invention provides that the inside radius of one of the flyweights is shaped as a ramp to engage the bow-shaped member against the resistance of a disengaging spring. In this structural embodiment, the turning knuckle of the bow-shaped member is disposed approximately at the height of the longitudinal axis of the camshaft parallel to the cam plane. For this purpose the articulated arms are provided with a lever arm extending to the crosspiece and a lever arm extending from the joint in the direction opposite the crosspiece. The lever arm is loaded by the disengaging spring, whereby the bow-shaped member is held in its disengaged position as long as the flyweight occupies its outermost radial position at speeds above the switching speed. At speeds of rotation below the switching speed, the ramp-like face of the inside radius of the flyweight bears against the crosspiece, causing the bow-shaped member to be held in its engaged position against the pretension exerted by the disengaging spring.
A further advantageous embodiment of the present invention provides that the flyweight is coupled with the bow-shaped member via a driver disposed on the articulated arm. In this embodiment, the driver, designed as a lever, is coupled directly with a driving arm of the flyweight. When the switching speed is reached, the flyweight drives the driver to the extent that the bow-shaped member tilts outward to its disengaged position and becomes positioned in the cam-disk plane. Below the switching speed, the driving arm holds the bow-shaped member in its engaged position, in which the crosspiece is disposed in the cam plane.
Finally, it is advantageous for two bow-shaped flyweights to be provided, which are coupled with each other by a joint. Hereby the influence of gravitational forces is advantageously eliminated by the restraining effect of two opposite flyweights. Thereby it is possible to achieve very low switching speeds, which is advantageous in particular for reversing starts.
Another advantageous embodiment of the invention provides that lifting in decompression position takes place in a specified crank-angle range of approximately 90° by appropriate arc length of the bow-shaped member. This is the range available after closing of the inlet valve and before attainment of ignition TDC or after ignition TDC and before opening of the outlet valve. For reasons of valve-play adjustment capability, a range without valve lift must be provided at ignition TDC.
Furthermore, it is advantageous for the switching speed to be between 300 and 600 rpm, preferably 400 rpm. By selecting such a switching speed, manual starting is still possible even at extremely low temperatures, or the engine can be turned with a low-power starter.
Finally, an advantageous embodiment provides that the control cam is provided with a slot to accommodate the bow-shaped member in engaged position. Hereby the bow-shaped member retains its specified position and is protected fr
Griebl Udo
Kampichler Guenter
Dolinar Andrew M.
Helfgott & Karas P.C.
Motorenfabrik Hatz GmbH & Co. KG
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