Electronic protection system for a battery-less diesel engine

Abstract: A protection system for a diesel engine of battery-less operation comprises a normally unenergized solenoid valve (104) for fuel flow shutoff; a current generator (3) able to provide sufficient current for energizing said solenoid valve down to below a certain predetermined engine r.p.m.; a decompression device (8) which comes automatically into operation at a rotational speed at least equal to said predetermined engine r.p.m.; and a control centre for receiving signals from at least one transducer for an engine operating parameter, for comparing said signal with a limiting alarm signal, and for energizing said solenoid valve with a predetermined delay.

Description: Modern internal combustion engines are designed for increasingly severe operating conditions, and consequently need to be adequately protected against operating abnormalities. To prevent irreparable engine damage, certain selected operating parameters have long been noted, the exceeding of which is an indication of danger and results automatically in engine stoppage. All known protection systems use either switches to interrupt the electrical supply to otto engines or solenoid valves to interrupt fuel feed to diesel engines. Said switches or solenoid valves are operated electrically under the control of an electronic system which processes the signals of the various transducers present on the engine, to indicate when the selected parameters exceed their acceptable safety values. More than one parameter is generally monitored simultaneously, such as for example an operating temperature, the lubricating oil pressure, the lubricating oil level and the maximum r.p.m. If the engine is permanently coupled to a power machine, the engine safety system must also be sensitive to maloperation of the power machine and to situations of danger for third parties which can occur during the use of the machine. An essential condition for the operation of safety and control systems is the availability of electrical energy, which means that they cannot be applied to diesel engines of battery-less operation. Diesel engines generally of small dimensions and hence of low cost exist which for reasons of strength, reliability and economy, are battery-less. Such small engines are started by a self-winding cable system which acts on the flywheel, and do not comprise any electrical generator. They can be stopped only manually, by shutting off the fuel flow, and hence in addition to not being protectable against operating abnormalities, they cannot even be coupled to power machines the operation of which can give rise to dangerous situations, in that there is no way of stopping them automatically. Attempts to provide these small engines with an independent current generator have been unsuccessful, in that the generator ceases to deliver current when the engine r.p.m. falls below a certain value, at which point as the safety devices are no longer under electrical operation the engine immediately returns to normal working. The GB-A-2145858 discloses a System for monitoring some parameters of a Diesel engine, comprising an electronic circuit energized by a current generator. The electronic circuit receives some signals from the engine, compares said signals with stored limiting alarm signals parameters and shuts off the fuel delivery by de-energizing the normally energised solenoid valve for the fuel flow. The de-energising of the shut off solenoid valve results in the engine stop. For this type of battery-less diesel engine, stoppage systems are however known which use as the energy source the pulsating pressure within the engine crankcase or the lubricating oil pressure. These systems have however proved totally unpractical both because of their complication and because of the fact that only one engine parameter can be monitored at a time. They comprise external connections to pressure or vacuum circuits with possible unfavourable influence on engine reliability. The object of the present patent is to remedy said situation by providing an automatic system for halting battery-less diesel engines when certain operating parameters are exceeded. Said object is attained according to the invention by automatically decompressing the engine combustion chamber below a certain r.p.m. This can be achieved for example by using a valve-lifting device which comes into operation when the engine r.p.m. falls below a predetermined value, to act in combination with a current generator which ensures the availability of a sufficient current quantity at least until the valve-lifting device comes into automatic operation. The merits and operational and constructional characteristics of the invention will be more apparent from the detailed description of a preferred embodiment thereof given hereinafter by way of non-limiting example with reference to the accompanying drawings. Figure 1 is a partly sectional side view of the engine camshaft in the configuration representing normal rotational speed; Figure 2 is a view in the direction II of Figure 1; Figure 3 is a partly sectional side view of the engine camshaft in the configuration representing rotational speed less than the predetermined r.p.m. for automatic decompression; Figure 4 is a view in the direction IV of Figure 3; Figure 5 is a section on the line V-V of Figure 3, with its upper part complete; Figure 6 shows the electrical schematic of the invention. The figures show a small single-cylinder diesel engine 1, to the drive shaft 2 of which there is connected a current generator 3 (Figure 6). By means of gears 4, 5, the drive shaft 2 operates in the usual manner the camshaft 6, which comprises an exhaust cam 61 and an intake cam 62. On the camshaft 6 there is keyed a centrifugally operating device 7 which operates a decompression device or valve-lifting device 8. The device 7 comprises two levers 71 and 72 pivoted respectively at 73 and 74, those ends thereof close to the pivotal points being constrained to each other by a tooth 76 inserted into a fork 77, such that they approach and withdraw from each other in a symmetrical manner. Both the levers are provided with a sized weight 78 and are maintained in a position of mutual approach by a spring 79. The free end of the lever 72 is shaped to provide a tooth 721 arranged to rest against a stop 9 limiting the opening travel of the levers 71 and 72, and a recess 722 which receives as an exact fit the end of an appendix 81 which operates the valve-lifting device 8. The appendix 81 extends perpendicularly from a pin 82, which is parallel to the camshaft 6 and is mounted on the periphery of the low part of the exhaust cam 61. The pin 82 has a semi-cylindrical end which, when the engine is under normal working and the lever 72 rests against the stop 9, has its flat portion 821 lower than the lowest contour of the exhaust cam 61, enabling the tappet 10 of the exhaust valve 11 to rest on the cam and hence allowing the valve 11 to be closed. When the engine r.p.m. falls below a certain value, the lever 72 approaches the centre, to drag the pin 82 into rotation via the appendix 81, so that the cylindrical portion 822 of the pin end projects beyond the low contour of the cam 61, and prevents the tappet 10 from resting on the cam. Under these conditions the exhaust valve can no longer be closed, and the engine stops for lack of compression. The spring 79 is rated such that the aforedescribed valve-lifting device comes automatically into operation at engine speeds of less than between about 200 and 400 r.p.m. The electrical characteristics of the current generator 3 ensure delivery of virtually constant current at speeds in the region of 200 r.p.m. The aforedescribed combination results in the attainment of the objects of the invention. In this respect, the generator 3 powers a control unit 100 to which the various transducers for the monitored parameters are connected, such as the oil pressure transducer 101, the temperature transducer 102, and the oil level transducer 103 (Figure 6). The control centre receives the signals from at least one transducer for an engine operating parameter, compares said signal with a limiting alarm signal and, with a predetermined delay, energizes the solenoid valve 104 to interrupt fuel feed. The solenoid valve 104 is normally unenergized and open, and closes to intercept fuel flow only if energized. The operation of the solenoid valve 104 is slightly delayed to enable the engine to reach normal working when started. As a consequence the engine r.p.m. decreases, and when it falls below the predetermined value between 200 and 400 r.p.m., the automatic decompression or valve-lifting device 8 halts the engine even if in the meantime the solenoid valve 104 has reopened due to current insufficiency. The invention is not limited to the aforedescribed embodiment, and modifications and improvements can be made thereto without leaving the scope of the following claims.

Claims: A protection system in a diesel engine of battery-less operation, having a cam (61) and an exhaust valve, comprising a normally unenergised solenoid valve (104) for fuel flow shutoff; a current generator (3) able to provide sufficient current for energising said solenoid valve above a certain predetermined engine speed; a decompression device (8) which comes automatically into operation at an engine speed at least equal to said predetermined engine speed; and a control centre for receiving signals from at least one transducer for an engine operating parameter, for comparing said signal with a limiting alarm signal, and for energising said solenoid valve with a predetermined delay. A protection system as claimed in claim 1, characterized in that said automatic decompression device (8) comprises a pin (82) which is mounted on the contour of the low part of that cam which controls the engine exhaust valve, is parallel to the cam axis and is provided with a semi-cylindrical end which can assume two positions, in one of which the flat part of the semi-cylindrical end is below the contour of the low part of the cam, and in the other of which the rounded part projects beyond said contour. A protection system as claimed in claim 2, characterised in that said pin is provided with a perpendicular appendix (81) engaged in a recess (722) of a lever (72) which can swing by centrifugal force, against a spring (79) about an axis parallel to the cam axis and rigid with the camshaft, said lever being able to assume a position close to the camshaft axis and a position distant from the camshaft axis, in accordance with the rating of the spring and the engine rotational speed.3. A protection system as claimed in claim 1, characterised in that said predetermined speed is at least 200 r.p.m.

Inventors: LOMBARDINI GIORGIO, LOMBARDINI, GIORGIO
Applicants: LOMBARDINI FAB IT MOTORI SPA, LOMBARDINI FABBRICA ITALIANA MOTORI S.P.A.
Application year: 1996
Main classification: F02D17
IPC codes: F01L13, F02D17