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(12) United States Patent ao) Patent No.: us 6,318,332 Bi
Kern et al. (45) Date of Patent: Nov. 20,2001
(54) METHOD FOR MONITORING ADEQUATE OIL LUBRICATION OF AN INTERNAL COMBUSTION ENGINE AND AN INTERNAL COMBUSTION ENGINE FOR CARRYING OUT THE METHOD
(75) Inventors: Eckhart Kern; Werner Wallrafen, both of Hofheim; Joachim Acht, Frankfurt; Volker Wehrmeyer,
Konigstein, all of (DE)
(73) Assignee: Mannesmann VDO AG (DE)
( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 0 days.
(21) Appl. No.: 09/461,789
(22) Filed: Dec. 15, 1999
(30) Foreign Application Priority Data
Dec. 22, 1998 (DE) 198 59 337
(51) Int. C I. F01M 11 10
(52) U.S. CI 123/196 S; 123/196 R
(58) Field of Search 123/196 S, 196 R;
(56) References Cited
U.S. PATENT DOCUMENTS
4,599,888 7/1986 Hufton, et al. .
4,859,864 * 8/1989 Smith 250/577
4,913,108 4/1990 Sougawa, et al. .
5,326,447 * 7/1994 Fletcher 204/401
5,814,214 * 9/1998 Chun 210/130
5,922,969 * 7/1999 Haar 73/861.02
FOREIGN PATENT DOCUMENTS
3931497A1 9/1989 (DE) . 0039244A1 4/1981 (EP) . 0816839A1 6/1997 (EP) .
* cited by examiner
Primary Examiner—-Willis R. Wolfe
Assistant Examiner—-Jason Benton
(74) Attorney, Agent, or Firm—David M. Thimmig; Mayer, Brown & Piatt
To monitor adequate oil lubrication of an internal combustion engine, air bubbles in the oil flow are detected by means of a sensor arranged in an oil line of a pressure circulation lubrication system and connected to an electronic evaluation system. These air bubbles are an early indicator of inadequate lubrication of the internal combustion engine.
42 Claims, 2 Drawing Sheets
METHOD FOR MONITORING ADEQUATE
OIL LUBRICATION OF AN INTERNAL
COMBUSTION ENGINE AND AN INTERNAL
COMBUSTION ENGINE FOR CARRYING
OUT THE METHOD 5
BACKGROUND OF THE INVENTION
The invention relates to a method for monitoring adequate oil lubrication of an internal combustion engine, in particular that of a vehicle, by means of a sensor arranged in an oil 10 line of a pressure circulation lubrication system and connected to an electronic evaluation system. The invention also relates to an internal combustion engine for carrying out this method.
Proper functioning of the pressure circulation lubrication 15 system is of decisive importance to the service life of internal combustion engines. If the oil film on the cylinder walls breaks down, the engine overheats very rapidly and this rapidly leads to serious engine damage. Currently, adequate oil lubrication of internal combustion engines is 20 monitored only indirectly by sensors which measure the pressure in the oil line. If the pressure falls due, for example, to failure of the oil pump or a leak in the oil circuit, the driver receives a warning signal. In addition, the oil level in the oil pan is often monitored by means of a sensor in order to 25 ensure that there is always a sufficiently large supply of oil.
It has been found in practice, however, that an oil pressure drop can often only be detected when serious engine damage has already occurred due to inadequate lubrication. Monitoring the oil level in the oil pan does not ensure an adequate 30 oil supply either. Owing to dynamic driving states, e.g. when driving round a relatively long bend, when driving on a slope or during acceleration, the oil level in the oil pan can shift to such an extent that the oil pump draws in air instead of oil and, as a result, lubrication temporarily ceases and 35 inadequate lubrication occurs.
The problem underlying the invention is to develop a method for monitoring adequate oil lubrication of an internal combustion engine by means of which a warning can be given as early as possible if there is a risk of inadequate 40 engine lubrication. The intention is furthermore to develop an internal combustion engine which operates in accordance with such a method.
SUMMARY OF THE INVENTION
According to the invention, the first-mentioned problem is solved by virtue of the fact that gas bubbles in the oil flow of the oil line are detected by means of the sensor and the electronic evaluation system.
By means of such a method, it is possible to generate a 50 warning even if air is temporarily being drawn in with the oil owing to dynamic driving states or if very slight leaks, through which air enters the system, occur in the intake region of the oil circuit. The risk of inadequate engine lubrication is thereby detected in good time. A warning 55 signal can be generated even before engine lubrication ceases. The method according to the invention is not limited to use with motor vehicles. The risk that air will be drawn in owing to dynamic traveling states is very great in the case of ships, for example, when large waves occur, or in the case 60 of sailing ships operating simultaneously under engine power and under sail because the sails can often lead to a pronounced and prolonged tilt. With motorized aircraft too, there is the risk of an inadequate supply of lubricant due to dynamic flying states. 65
The further away the sensor is from the lubrication points of the internal combustion engine, the earlier a warning
signal can be generated when there is a risk of inadequate engine lubrication. It is therefore advantageous if the sensor is arranged in an oil intake line upstream of an oil pump of the pressure circulation lubrication system.
If a somewhat lower detector speed—i.e. a shorter time between detection and the arrival of the bubbles in the cylinders of the engine—is acceptable, it is, however, also possible for the sensor to be arranged downstream of the oil pump and downstream of an oil filter arranged downstream of the oil pump. This has the advantage that the sensor responds even to air bubbles which enter the oil flow upstream of the sensor owing to leaks in the oil filter or, for example, the oil line.
The sensor for detecting air bubbles can vary widely in design. It would be possible, for example, to monitor the translucence of the oil flow with an optical sensor. The sensor is of particularly simple configuration if a sensor operating on the thermoelectric principle is used. Such sensors are already common for level monitoring and can therefore be obtained at relatively low cost. The sensor is of simple construction and is therefore particularly suitable for large-scale manufacture if, as is advantageous, it has a temperature-dependent wire resistor. The operational reliability and durability of the sensor is particularly high if, as is preferred, it has a thermistor.
It is likewise possible to resort to sensors commonly used for level monitoring if, in accordance with another development of the method according to the invention, a capacitive sensor is used as a sensor to detect changes in the dielectric constant of the oil flow passing the sensor.
A particularly advantageous development of the method consists in the sensor being arranged at the level of the minimum permissible oil level in an oil pan of the internal combustion engine, and the electronic evaluation system being used to detect when the oil level in the oil pan falls below the minimum with the internal combustion engine stationary, in addition to detecting bubbles with the internal combustion engine running. This allows the sensor to be used for a dual purpose, namely, on the one hand, to monitor engine lubrication with the internal combustion engine running and, on the other hand, to monitor the oil level with the internal combustion engine stationary.
To determine a filling level and the presence of air bubbles, it is advantageous if a constant current is allowed to flow through the resistance body for a defined period of time for each measurement of the oil level, and the voltage drop at the beginning and the end of energization is determined.
For continuous monitoring of an oil flow with regard to the presence of bubbles, it is advantageous if a constant current is allowed to flow through the resistance body for the continuous detection of bubbles, and at the same time the signal fluctuations of the voltage are determined for the purpose of ascertaining the concentration of gas bubbles.
It is also possible to use a mechanically operating sensor for the method according to the invention if a sensor operating with a dynamic pressure flap which can be deflected by the oil flow is used as the sensor. Here, use is made of the fact that the inertia forces acting on the dynamic pressure flap are lower due to air bubbles in the oil flow, with the result that the flap is then deflected to different degrees.
A sensor of relatively low accuracy of response is sufficient if the sensor is arranged above an approximately horizontal region of the oil line, in the upper region of a flow stagnation space connected in the lower region to the oil line. This gives rise to an integrating effect. Small air