EP1910652A2

EP1910652A2 - Method for detecting the oxidation level of an engine oil and for recommending an oil change

Info

Publication number: EP1910652A2
Application number: EP06778948A
Authority: EP
Inventors: Sébastien GAUCHARD; Michel Bleusse
Original assignee: Peugeot Citroen Automobiles SA
Current assignee: PSA Automobiles SA
Priority date: 2005-06-10
Filing date: 2006-06-08
Publication date: 2008-04-16
Also published as: WO2006131686A2; FR2886976A1; WO2006131686A3

Abstract

The invention relates to a device for optimizing the maintenance of a motor vehicle comprising means for determining, over time, at least one derivative of the lubricating oil at the entrance to the engine and means for notifying the driver when this derivative reaches a predefined threshold.

Description

The present invention claims the priority of the French application 0551567 filed on June 10, 2005 whose content (description, claims, drawings) is incorporated herein by reference,

The present invention generally relates to the lubrication systems of internal combustion engines and more particularly to a method for estimating the oxidation level of a motor oil and recommend draining wisely.

In recent years, the many improvements in both internal combustion engines and lubricating oils have significantly spaced the frequency of oil changes recommended by the manufacturer for optimal operation of the vehicle. Nevertheless, the automotive clientele remains sensitive on this point and expresses a persistent desire to further reduce the frequency of oil changes.

Most often, the recommendations of the manufacturers are based on relatively empirical basic criteria such as the mileage traveled and / or the time elapsed since the last emptying. However, the wear of an engine oil certainly depends on the mileage traveled but also, and especially, the conditions in which these kilometers were traveled, in particular the type of journey (urban cycle, motorway, etc.), speed the vehicle and the type of conduct adopted by the driver.

To better take into account some of these parameters, we have proposed algorithms that weight the factor by the temperature of the oil. Nevertheless, these algorithms only estimate the supposed wear of the oil and not its actual wear essentially related to its oxidation. However, this actual wear also depends on extrinsic parameters that are very difficult to take into account. For example, the speed with which an engine oil deteriorates also depends on the quality of the oil used. If the algorithms are based on the hypothesis of the use of a relatively poor quality oil (low fluidity), users who favor quality are encouraged to replace a low-oxidized oil. Another factor to take into account is the refreshing of the oil by top-up. Indeed, it is well known that the frequency of oil changes can be reduced if the volume of oil is increased. And indeed, many vehicles are nowadays equipped with oil tank with increased capacity compared to what existed a few years ago. Nevertheless, it is clear that such an increase in the volume of the tank to limits, both in terms of congestion and acceptability by customers sensitive to the cost of replacing the entire volume of oil. But many users get a similar effect by adding small amounts ^of oil "fresh" regularly between two charging operations. Again, this contributes to a lower degradation of the oil and therefore to the possibility of a spacing of oil changes, a possibility that certainly can not be taken into account by an algorithm based on a simple model like those mentioned above.

The wear of a motor oil is mainly related to its oxidation which has four direct consequences: the increase in the viscosity of the oil, the increase in the acidity of the oil, the formation of deposits , varnish and sludge and blackening of the oil. These factors are used, alone or in combination, by laboratory techniques based on sampling. Clearly, these techniques are not suitable for individual vehicles and per se, are not a solution to the demand for simplified maintenance.

It therefore remains a need for a simple way to recommend a drain in a timely manner, taking into account the actual state of oxidation of the lubricating oil.

According to a first variant of the invention, this object is achieved by a device for optimizing the maintenance of a motor vehicle comprising means for determining a derivative over time of the pressure of the lubricating oil. motor input and means for alerting the driver when said derivative (s) reach predefined thresholds.

The implementation of the invention thus assumes the acquisition of the lubricating oil pressure at the engine inlet, at a known temperature and means for calculating the drift of this pressure over time. Note that the scale from here considered is that time of the operating time of the engine véhicuie, time does not flow when the engine is ^at standstill.

[0011] In an embodiment of ^the invention more particularly preferred, this measurement is made under conditions of constant temperature and engine speed. Preferably, these conditions are chosen outside the starting phase of the engine, and this pressure measurement is preferably carried out when the temperature reaches for example a minimum of 50 ^° C. and when the engine rotates at least 1500 rpm. On the other hand, it is desirable that these reference points are not too high in order to be reached on a majority of the journeys made by the vehicle, in particular not imposing an engine speed that would not be systematically achieved if the vehicle is essentially used. for courses in urban areas.

The method according to the invention is based on the study of a derived function, it can predict the evolution of the viscosity and therefore to recommend a drain for example before having traveled a thousand kilometers again, without broadcast a threatening message that could unnecessarily alert some drivers.

In a more particularly preferred embodiment of the invention, the drift of the viscosity gradient is also calculated, which makes the alerts more robust, especially avoiding the disturbance during oil replenishments.

Other details and advantageous features of the invention appear from the embodiment described below with reference to the accompanying drawings in which:

_* Figure 1 is a schematic view of the lubrication system of an engine;

_* Figure 2 is a simplified model of the lubrication circuit at constant speed and iso temperature oil;

_* Figure 3 shows the relationship between the viscosity of an oil and engine inlet pressure;

_* Figure 4 shows the evolution of the viscosity of the lubricating oil according to the mileage traveled for different types of oil; ® 5 shows the change in viscosity, and the viscosity gradient, depending on the distance traveled after a complete renewal of ^the lubricating oil;

_* Figure 6 shows the evolution of the viscosity, and the viscosity gradient in the first hours after a drain corresponding to the circled part of Figure 5;

_* Figure 7 is a view similar to Figure 5 wherein there is shown more of the shape of the second derivative of the function of the viscosity versus time.

[0015] There is shown in Figure 1 a diagram of a lubrication system ^of an engine. An oil pump 1 sucks the oil from the housing not shown here through a strainer ^2, the oil is supplied to an oil filter 3 and an exchanger 4 for cooling. The clean oil is cooled and is fed to the main boom 5 for pressure distribution to the different elements to be lubricated. A discharge valve 8 makes it possible to regulate the oil pressure whatever the speed of rotation of the engine.

[0018] This distribution ^is effected according to a first circuit 7 to the mechanical parts contained in the casing of the engine block, in particular the pins of the crankshaft (8 nozzles) and the crossheads.

By a second lubrication circuit, the oil is also directed to the bodies of the cylinder head, via the rise to the cylinder head 9, to lubricate in particular the bearings of the camshaft and the hydraulic pushers (nozzles 10). ). In this figure, is also schematized the solenoid valve 11 which feeds the camshaft dephaser.

[0018] In general, the main ramp ^is equipped with a pressure switch for example at position 12 which generates an alarm signal if the pressure falls below a certain critical pressure, ie if the engine ^is no longer lubricated. This ^alarm signal is typically relayed to the level of the dashboard by a bright red light directing the driver to stop the vehicle in the most promptly. This pressure switch is of the all-or-nothing type and in fact, rarely triggers before the stop lubrication causes a break engine.

According to the invention, the main ramp is also equipped with a pressure sensor (which may optionally play more the function of the pressure switch),

If we consider the simplified diagram of the lubrication circuit as shown in Figure 2, in the event of a closed discharge valve, it can be summarized as having an oil sump 20, an oil pump 21, an oil filter 22, engine pressure drops 23 and a discharge valve 24. The main ramp 25 corresponds to the duct between the filter 22 and the engine,

If the closed discharge valve is assumed, the pressure at the engine inlet, in other words in the main ramp 25, is a resultant of the oil flow at the outlet of the pump 21, the pressure drop of the engine and the viscosity of the oil. According to the invention, a pressure sensor is thus placed in the main ramp 25.

The flow generator is typically a volumetric type pump. For a given speed and oil temperature, the pump is therefore designed to provide a fixed output flow. Assuming that the pump performance drift (whereas its wear) is much slower than ^the oxidation of the oil, it can be assumed that the flow rate is a constant for the conditions of engine speed and temperature fixed.

The engine pressure losses are assumed to constant at engine speed N and oil temperature T constant. Thus, the inlet pressure can be considered as a direct image of the viscosity of the oil, as represented in FIG. 3 which shows the evolution of the viscosity as a function of the pressure in the main ramp. In a first approximation, this function can be considered as affine, that is to say that the viscosity is assumed to be proportional to the pressure in the main ramp.

[viscosity - K * wmpe pressure) _rv

The evolution of the oil pressure in the main ramp is itself a reflection of the evolution of this viscosity. The knowledge of the temperature of ^oil, pressure in the manifold and engine speed are therefore the only éiéments necessary for evaluating the oil viscosity. As indicated above, the pressure can be measured by a pressure sensor. The temperature is either determined by the system in known manner, or also measured by a temperature sensor also placed in the ramp. The engine speed must be known at all times, but this data is generally already available because necessary especially for the control of the injection.

Figure 4 illustrates the evolution of the viscosity of the oil according to the mileage traveled. With a basic oil H1, taking as kilometer zero the mileage corresponding to the last oil change, it is observed that the viscosity is initially almost constant, then increases significantly to exceed a maximum reference viscosity tolerated. When the mileage K1 is reached, it is desirable to renew the oil. Another oil, such as, for example, the oil H2, while at the same time having a viscosity similar to the viscosity of the oil H1, can age better and allow a higher oil content. K2 kiiorπagerie higher than K1. Note that ^the term "other type ^of oil" also covers the case of an oil subjected to another type of pipe, and which will have a different aging because the driver is not necessarily the intrinsic quality of the oil used . An oil of a lower grade (initially more viscous) is based on its aging n ^authorize a city even less.

[0026] Patent application US 2004/0211246 proposes to ^use this affine relation pressure / viscosity for generating a warning to the driver when the oil is worn. However, this application does not take into account another factor illustrated in Figure 4 that the deterioration is not identical ^to an oil to another. The temperature behavior (and in particular the reduction in viscosity with increase in temperature) depends on an oil to ^the other. A more viscous cold oil is not necessarily a problem if its hot viscosity remains below a certain threshold. The measurement by the derivative as according to the invention, on the other hand makes it possible to overcome this problem. For example, in the case of oil H2, the viscosity remains good for longer than ^with the other two oils but the degradation is very marked. Conversely, in the case of ^oil H3, the limit viscosity is reached faster but does not significantly increases right after. Delay the oil change after the alarm indicator is triggered is less dangerous in practice with the oil H3 with ^oil H2 yet intrinsically better.

The present invention obviates this problem by not only considering the value of the pressure (and therefore indirectly the viscosity) but also the derivative over time of this pressure.

[0028] In a first variant of the invention, can be measured repeatedly, for example every 5 minutes, the pressure value and the engine speed and the ^oil temperature at the time of this measurement. These measures provide an entire set of values which can be extracted representative values, for example the corresponding points at an average engine speed (typically between 1500 and 2500 rpm) and an average temperature (typically between 50 ⁰ C and 150 ⁰ C. .. note that these values are preferably such ^that they are reached on most journeys made by the vehicle even if the vehicle is used almost exclusively in the urban cycle is, however, avoid choosing too low a temperature - which risks be routinely exceeded in the hot season, or too low a regime that can suffer disturbances independent of the wear of the oil.

[0029] In a second variant of the invention, the pressure value measured n ^'is stored only if it meets the steady conditions and temperature. This variant is preferred insofar as it makes it possible to avoid an excessive increase in the mass of stored data.

If one chooses to place in known conditions T, N and which occur repeatedly in the life of a vehicle, for example an engine speed of 2000 rpm, and a temperature of 80 ° C, observed as shown in Figure 5 that when the critical viscosity (denoted Threshold 0) is reached, the first derivative (gradient with respect to time or mileage) corresponds to a stage where the first derivative of the viscosity is substantially constant and above ^of a certain critical threshold here noted SeuïM.

According to a first embodiment of the invention, the emptying alert can therefore be triggered if

~> Seιul 1 Q

In a second variant of the invention, an additional criterion is imposed, namely that the first derivative must not be negative.

Indeed, following a supply of new oil due to a drain, in the first hours of operation of the engine, the oil is subjected to shear forces which cause an initial decrease in its viscosity. This is what is shown in Figure 6 shows the change in viscosity and viscosity gradient during this initial "running in" phase ^of oil. Note that a similar phenomenon of decreasing the viscosity of the oil also occurs due to an extra filling, and again the second criterion ^eliminates unnecessary alerts. During the catch-up phase, when the viscosity of the oil starts to increase again, the value of the first derivative becomes positive again, but remains lower than the value Threshold 1 (the curves are given only to illustrate the various phenomena and the values slopes should not be interpolated from one figure to ^the other).

It is also advantageous to calculate the second derivative of the evolution of the viscosity over time. Indeed, as shown schematically in FIG. 7, when the viscosity is greater than a critical value Seuil__G, the derivative is greater than SeuiM and the second derivative is smaller than a third critical value Seuil_2. This value Threshold__2 is reached when the oxidation of the oil begins to stabilize.

It is therefore advantageous to set a new criterion for an emptying alert, namely

- d ² i (. Cos cos ity L) ^ Seui .l, 2 ώ ²

Advantageously, this critical value Threshold 2 does not depend on the type of lubricant used by the customer, which makes the method much more robust.

The observation of FIG. 7 further shows that the representative curve of the second derivative has an extremum and is decreasing in the zone corresponding to the stabilization of the first derivative. To avoid untimely alerts, it is therefore desirable to check that we are in the decreasing part of the curve, which is to prohibit an alert if the third derivative is positive (a criterion which in fact can be substituted for the two criteria on the first derivative mentioned above, namely non-negative slope and at least equal to the Threshold).

[0038] As the description given above spring, the ^oxidation of ^the state of observation method lubricating oil supplied according to the invention is not only based on the actual state of oxidation oil but is not affected by the type of oil used by the customer or by punctual contributions ^of new oil.

Moreover, knowledge of the second derivative, and the sign of the third derivative allows to calculate the rate of degradation of the oil and therefore to announce in advance when a drain will become desirable. A recommended stop light may thus be lit if the system observes a too rapid degradation of the oil, then recommending the driver to stop the vehicle before the engine has actually been damaged.

It should be noted that the pressure values measured by the pressure sensor can also be used as absolute references, for example to alert the driver if the pressure becomes greater than the limit pressure allowable by the engine or if, on the contrary, the pressure is below a floor value

(In this case, the pressure sensor is used as a pressure switch). In other words, as soon as the engine inlet pressure deviates from the recommended range for optimal engine operation, an alert can be activated.

The invention thus provides a robust method, inexpensive and reliable.

Claims

Device for ^optimizing maintenance ^of a automobiie vehicle comprising means for determining, at a temperature and a reference engine speed, at least one derivative over time of the pressure motor inlet in the lubricating oil and means for alerting the driver when said derivative reaches a predefined threshold.

Device according to Claim 1, characterized in that the said reference temperature is between 50 ^° C. and 150 ° C. 3. Device according to Claim 1, characterized in that the said reference engine speed is between 1500 and 2500 revolutions per minute. .

4. Device according to one of the preceding claims, characterized in that one of the derivatives is the first derivative corresponding to the pressure gradient over time. 5. Device according to claim 4, characterized in that the alert is actuated only if the pressure gradient is more positive.

8. Device according to one of the preceding claims, characterized in that one of the derivatives is the second derivative of the evolution of the pressure of the lubricating oil at the engine inlet and in that said means for alerting the driver are actuated only if in addition said second derivative is less than reference threshold Threshold__2.

7. Device according to claim 8, characterized in that it further comprises means for calculating the third derivative of the evolution of the pressure of the lubricating oil at the engine inlet and in that said means for alerting the engine driver are only actuated if in addition said third derivative has a negative value.

8. Device according to one of claims 6 to 7, characterized in that it further comprises means for calculating the moment when the viscosity of the oil will reach a critical value and to alert the driver accordingly.

9. Device according to any one of the preceding claims, characterized in that the value of the pressure of the lubricating oil at the engine inlet is used to actuate an alarm if this value deviates from an optimum operating range. of the motor.