FR2956075A3 - Method for determining temperature of mechanical coupling unit of axles of transmission system of motor vehicle, involves determining current temperature of mechanical coupling unit by calculation utilizing temperature estimation model - Google Patents

Abstract

The method involves determining initial temperature of a mechanical coupling unit by temperature measurement, and determining current temperature of the mechanical coupling unit by calculation utilizing the initial temperature and a temperature estimation model. The temperature of the mechanical coupling unit is temperature of a friction unit i.e. mechanical coupling unit disc. Temperature of an electromagnetic coil of an actuator (14) of the mechanical coupling unit is measured. An independent claim is also included for a computer implemented program having a set of instructions for executing a temperature determining method.

Description

The present invention relates to the estimation of the temperature of a mechanical coupling means. The invention also relates to a system for estimating the temperature of a mechanical coupling means. It still relates to a control system of an actuator including such a temperature estimation system. It also relates to a transmission system comprising such a control system and / or estimation. It still relates to a motor vehicle comprising such a transmission system.

The invention applies to a vehicle equipped with a four-wheel drive system. The transmission system is in mechanical connection with a motor (or torque source) driving the vehicle. The transmission system mainly comprises a first wheel axle and a second wheel axle, the first and second axles being connected by mechanical coupling means (coupler). The first axle is driven by default by the engine and the second axle is driven optionally via the mechanical coupling means. The transmission system also comprises a system for controlling the state of the mechanical coupling means. The control system may include means for selecting the operating mode of the transmission system and a calculator.

The objective of this type of vehicle is to improve performance such as performance and safety.

It is known to use a mechanical coupling means controlled clutch type to allow the drive of the second axle. Such a mechanical means of coupling makes it possible to define a maximum transmittable torque, that is to say, it returns to a sliding operation when one tries to transmit a torque greater than the transmittable torque. MS \ REN170FR.dpt The operating temperature of a mechanical coupling means of this type has a direct impact on the value of the transmissible torque, and therefore on its performance. Indeed, the clutch can transmit more or less torque depending on its level of heating, for the same driving instruction. Indeed, the control setpoint allows for example to control an actuator modifying the pressure exerted by the friction discs of the mechanical coupling means on each other, so that at each value of the control setpoint corresponds a pressure contact discs against each other and therefore, at a given temperature, a maximum torque transmittable by the mechanical coupling means.

The mechanical coupling means also has a maximum temperature threshold above which it can no longer transmit torque and deteriorates (fusion of the friction elements). Conversely, a very cold clutch can transmit a much larger torque than that corresponding to the steering setpoint that determines its state. This can lead to a shift between the desired transmissible torque threshold (thanks to a control setpoint of the mechanical coupling means) and the transmissible torque threshold actually obtained. This offset may cause a deterioration of the drive train in the case of low temperatures of the coupling means. Indeed, the mechanical coupling means can, in this case, transmit a much larger torque than that can bear downstream other transmission members. At normal temperature corresponding to a temperature range for which the control setpoint of the mechanical coupling means is valid, the mechanical coupling means could not transmit such a large torque and the transmittable torque would be limited to an acceptable value for the transmission members. transmission downstream of the coupling means. MS \ REN170FR.dpt This phenomenon of variation of the torque transmissible by the coupling means as a function of its temperature is illustrated by the graph of FIG. 5 on which are represented, on the abscissa, the temperature of the coupling means and, on the ordinate, the maximum torque transmissible by the mechanical coupling means.

The temperature of the mechanical coupling means can be either measured by means of a sensor or estimated by the use of a heating model, for example a numerical calculation model.

It is particularly difficult to implement a temperature sensor on the friction discs of the mechanical coupling means or in their vicinity, these being in motion relative to a housing and with respect to each other in certain operating phases. In addition, the use of a numerical calculation model saves the expense of a temperature sensor.

It is therefore preferred to use a heating model to determine the temperature of the mechanical coupling means. However, this use poses a major problem: it is necessary to determine an initial temperature of the mechanical coupling means before carrying out the determination of the temperature by the use of the heating model. Knowing the temperature of the mechanical coupling means before implementing the use of the model makes it possible to adequately limit the torque that can be transmitted by the mechanical coupling means. It is very difficult, if not impossible, to choose an arbitrarily predetermined temperature. Indeed, the motor vehicle can be used in very variable temperature conditions depending on the geographical region where it is and depending on the season. In addition, the temperature of the mechanical coupling means may be a function of the operating history of the coupler. Thus, the temperature may vary depending on the previous use of the vehicle. This will result in a difference in temperature between a vehicle that has been immobilized overnight in the garage and a vehicle that has recently completed a cross-country run. The temperature may be relatively high when the vehicle is reused after a brief period of non-use having for example lasted only a few minutes.

Document JP 2007139129 discloses a method of estimating the temperature of a mechanical coupling means from the sliding of the clutch.

Document GB 2 233 419 discloses a method for determining the temperature of an electromagnetic clutch from the measurement of the voltage and the supply current of an electric coil of this clutch.

The object of the invention is to provide a temperature determination method making it possible to remedy the problems mentioned above and to improve the determination methods known from the prior art. In particular, the invention proposes a determination method that is simple to implement and that makes it possible to provide an accurate temperature value in order to make the operation of an axle coupling means of a motor vehicle of the four-wheel-drive type more reliable.

According to the invention, the method makes it possible to determine the temperature of a mechanical coupling means of the first and second axles of a transmission system of a motor vehicle. The method comprises: a first initial phase for determining an initial temperature of the mechanical coupling means by measuring a temperature, and MS \ REN170FR.dpt a second phase for determining the current temperature of the mechanical calculation coupling means using the initial temperature and a temperature estimation model.

The temperature of the mechanical coupling means may be the temperature of a friction member, in particular a disk, of the mechanical coupling means. In the first determination phase, it is possible to measure the temperature of an electromagnetic coil of an actuator of the mechanical coupling means. The temperature measurement can be deduced from measurements of the current and the supply voltage of the electromagnetic coil. The second determination phase can implement an iterative calculation.

The second determination phase may continue to be implemented after the immobilization of the motor vehicle and after the ignition of the motor vehicle. The second determination phase may be terminated when a delay, triggered by the immobilization of the motor vehicle, has elapsed or when the calculated temperature of the mechanical coupling means becomes lower than a threshold temperature value or when the derivative relates to time. the calculated temperature of the mechanical coupling means becomes lower than a threshold cooling value. The invention also relates to a data storage medium readable by a computer on which is recorded a computer program comprising computer program code means for implementing the steps of the method defined above. According to the invention, the system for determining the temperature of a mechanical coupling means of the first and second axles of a transmission system of a motor vehicle is characterized in that it comprises hardware and / or software for implementing the method defined above. The material and / or software means may comprise a module for determining an initial temperature of the mechanical coupling means by measuring a temperature and a module for determining the current temperature of the mechanical calculation coupling means using the initial temperature and a model of temperature estimation.

According to the invention, the motor vehicle comprises a determination system defined above. Computer program comprising a computer program code means adapted to perform the steps of the method according to one of claims 1 to 7, when the program runs on a computer.

The appended drawing represents, by way of example, an embodiment of a temperature determination method according to the invention and an embodiment of a temperature determination system according to the invention.

Fig. 1 is an embodiment of a temperature determination system according to the invention.

Fig. 2 is a diagram illustrating an example of a temperature measurement procedure.

Fig. 3 is a diagram of a first example of means used to determine the temperature. Figure 4 is a diagram of a second example of means used to determine the temperature.

FIG. 5 is a graph representing, on the abscissa, the temperature of the coupling means and, on the ordinate, the maximum torque transmissible by the mechanical coupling means.

The temperature determination method according to the invention makes it possible to estimate the temperature of a mechanical coupling means of the electromagnetic clutch type. It uses a temperature sensor, for example comprising an electromagnetic coil 16 of an actuator 14 for controlling the operation of the mechanical coupling means by allowing discs to move away from and closer to the mechanical coupling means.

In particular, the temperature determination method makes it possible to determine the temperature of a mechanical coupling means used in a transmission system of the four-wheel drive type, and in particular of the four-wheel drive type of a motor vehicle. The transmission system 15 mainly comprises a first axle of wheels connected by a first differential itself connected to a drive motor of the motor vehicle via a gearbox and a second axle of wheels connected by a second differential, the first differential. being connected to the second differential via a mechanical coupling means. The transmission system also comprises a control system of the actuator for controlling the state of the mechanical coupling means. Thus, the first and second axles are or are not coupled according to the state of the mechanical coupling means. The first axle is by default driven by the drive motor of the motor vehicle, MS \ REN170FR.dpt the second is in turn driven or not depending on the state of the mechanical coupling means.

The temperature determination method comprises two phases. In the first phase, an initial temperature representative of the actual temperature of the mechanical coupling means, in particular the friction discs thereof, is preferably determined by measurement. The accuracy of the determination method depends on the accuracy of determination of the initial temperature. It makes it possible to adjust the control of the actuator 14 in order to obtain the transmissible couples expected. Thus, the use of a precise initial temperature makes it possible to protect the drive train of the vehicle from possible over-torques in use at low temperatures and to protect the mechanical overheating coupling means 15 in use at a high temperature. In addition, in case of low temperature, taking into account an increased temperature difference makes it possible to push back a little further reaching the temperature limit in case of heating the clutch due to a slip of the first axle. . In the latter case, the clutch can be used longer before its limit heating. In the first phase, the estimation of the temperature must be done at the start of the vehicle, "cold" or at rest for several minutes in the case of the use of an electromagnetic coil of the actuator 14 to estimate the temperature. temperature. Indeed, the heat energy released by the clutch disks may take some time to reach the electromagnetic coils, according to the architecture of the mechanical coupling means and the thermal inertia of its organs. The initial temperature is stored in an electronic memory.

In the second phase, the temperature of the mechanical coupling means, in particular the temperature of the friction discs of the mechanical coupling means in MS \ REN170FR.dpt using the initial temperature value, is preferably calculated by calculation. The calculation uses a model, for example a numerical model, in particular a model based on a power or energy balance made at the level of the mechanical coupling means. The model can take into account the speed difference existing between the first and second axles and the value of the mechanical torque transmitted by the mechanical coupling means. A model similar to that described in JP 2007139129 can be used. The calculated temperature value is regularly stored in the electronic memory initially used to store the initial temperature value. The model advantageously takes into account the architecture of the mechanical coupling means and the thermal characteristics of its various members.

When starting the motor vehicle, to determine the temperature of the mechanical coupling means, it is first implemented the first phase of the determination process, but it must be ensured that it has elapsed a sufficient time long to overcome the risk of error that may be due to the architecture of the mechanical coupling means and / or the heat inertia of its organs. An engine stall can thus represent a problematic case. Indeed, if just after stalling of the engine, it is restarted and it resets the temperature determination process by implementing the first phase described above, there is a strong risk that the initial temperature measured (that the electromagnetic coil) is not representative of the actual temperature of the friction discs of the mechanical coupling means. To remedy this problem, it is preferable to continue to implement the second phase of the temperature determination process for a certain time after the immobilization of the vehicle and even after it is put out of contact. This time can be predetermined, for example between 5 and 30 minutes and preferably set at 10 minutes, for example. This time can also be determined indirectly: it can for example be expected that the estimated temperature (according to the method MS \ REN170FR.dpt object of invention) becomes lower than a temperature threshold (for example 50 ° C) or that the derivative by relative to the time of the estimated temperature becomes less than a cooling threshold (for example -1 ° C.min-1).

In a preferred embodiment of the first phase, the objective is to determine the temperature of the mechanical coupling means by measuring the temperature of a coil of the actuator. The coil is for example made of a copper wire. It is possible to determine the resistivity of the coil from the resistivity of the copper, the length and the section of the wire constituting the coil. The resistivity of copper at 20 ° C is well known. The following formulas linking the coil resistance and the temperature thereof are then obtained: Rt = R (200C) • (1 + tempco (T-20 ° C)) RT = RT (20 ° C) tempco i + 20 ° C with: RT the resistance of the coil at the temperature T (0) R (200G) the resistance of the coil at 20 ° C (0) T the temperature of the coil (° C) tempco the coefficient thermal resistance The temperature estimate of the friction discs is based on the coil and is based on an evaluation of the electrical resistance of the coil. This resistance is a known function, for a given material, of the temperature of the coil. The coil is composed of an electrical conductor (eg copper) wound in turns. This electromagnet is powered (by a voltage source or by a current source). Noting u the voltage across the coil, and i the current flowing in the coil. The coil 16 is modeled by a resistor R 18 in series with MS \ REN170FR.dpt an inductance L 17 as shown in Figure 2. The values of the resistor and the inductance are unknown. The phase of measuring the temperature of the coil comprises the following steps: 1. Measuring the voltage u across the coil and the current flowing in the coil; 2. Calculate the electrical resistance R of the coil. One method is to wait until the voltage u and the current i have stabilized (the main dynamic comes from the unknown inductance L, in practice, for the targeted applications, less than a second is needed for stabilization); R is then R = u / i. Another approach consists of jointly estimating R and L, for example under transient conditions (by applying a voltage step and measuring the current several times); 3. Calculate the AT temperature variation according to the formula: ÈT = (RxS / L / pO-1) / a; 4. Calculate the temperature according to the formula: T = TO + ETE.

with: a: temperature coefficient of the resistivity in ° C- '; p0: resistivity of the material, given at a temperature TO (in 0m); L: the length of the conductor of the coil (in m); S: the conductor section of the coil (in m2); AT: the temperature variation defined by T-T0.

The values p0 and a are known for the materials constituting the coils. For example, for copper, the following numerical values can be used: p0 = 1.7.10_ $ 0.m, and a = 3.9.10-3 ° C-1 for a reference TO temperature of 20 ° C. MS \ REN170EN.dpt30 In one example, consider a coil of copper wire with a diameter of 0.5 mm (r = 0.25mm). The average diameter of the coil is 5mm. There is L = 10m of wire, about 300 turns. The section S is S = rrxr2 = 2.10-7 m2. We measure a resistance of 1.03 0, this corresponds to a temperature variation of ETE = 49 ° C. The temperature of the coil is therefore T = 20 + 49 = 69 ° C.

The process according to the invention makes it possible in particular to estimate the temperature over a range of from -20 ° C. to + 80 ° C. to a few degrees. As shown in FIG. 3, in the case of an embodiment with analog-to-digital converters 22, 23 (to obtain the values of the voltage u and of the current i), the equation giving AT is a type law. refines the resistance. It can be written as follows: ÈT = axR + b where a = S / (LxpO xa) and b = -1 / a (a and b are pre-calculated or calculated during a calibration phase). The temperature is calculated in a calculation module 24.

In the particular case of an embodiment with analog-digital converter and current source, the measurement of the voltage u is sufficient to know R, since R = u / i and that i is imposed by the current source. Since many coil control systems are powered by current sources, this particular case is of economic interest.

In the case of an analog embodiment as shown in Figure 4, the equation giving AT can be translated by a gain and an offset. These two operations can be performed by means of operational amplifiers, the offset being the addition of a constant value b (adder assembly 21) and the gain consisting of the multiplication by a constant a (amplifier 20). A very simple analog embodiment is possible in the case where the coil is supplied by a generator 19 of constant current: in this case, the voltage u across the coil is directly MS \ REN170FR.dpt proportional to the resistance (R unknown) . The temperature is then given by an affine function of this resistance, therefore of this voltage.

The assemblies of FIG. 3 or 4 are for example used in a module 11 for determining an initial temperature of the mechanical coupling means by measuring a temperature, this module forming part of a system 10 for determining the temperature of mechanical means for coupling the first and second axles of the transmission system of the motor vehicle shown in FIG.

This temperature determination system 10 comprises, in addition to the first module 11, a second module 12 for determining the current temperature of the mechanical calculation coupling means using the initial temperature value supplied by the first module and a model for estimating the temperature. temperature. The first and second modules operate as described above. They include, for example, software programs.

An estimated temperature is provided, at the output of the temperature estimation system, in particular, at the output of the second module, to a third module 13 for defining laws and control strategies of the actuator, this third module transmitting to the actuator a control setpoint, for example a torque setpoint.

The temperature estimation method according to the invention has the following advantages: 1. it allows an estimation of the sensorless temperature at the level of the friction members, 2. it makes it possible to make the temperature estimation more precise, 3. it allows the adaptation of a four-wheel drive transmission control strategy in the starting phase, 4. it protects the drive train of the vehicle against wear, MS \ REN170FR.dpt in particular against the over-couples. MS \ REN170FR.dpt

Claims (12)

1. A method for determining the temperature of a mechanical coupling means of the first and second axles of a transmission system (15) of a motor vehicle, comprising: a first initial phase of determining an initial temperature mechanical coupling means for measuring a temperature, and a second phase for determining the current temperature of the mechanical calculation coupling means using the initial temperature and a temperature estimation model. 2. Determination method according to claim 1, characterized in that the temperature of the mechanical coupling means is the temperature of a friction member, in particular a disk, of the mechanical coupling means. 3. Determination method according to claim 1 or 2, characterized in that, in the first determination phase, the temperature of an electromagnetic coil (16) of an actuator (14) of the mechanical coupling means is measured. 4. Determination method according to the preceding claim, characterized in that the temperature measurement is deduced from measurements of the current (i) and the voltage (u) of supply of the electromagnetic coil (16). 5. Determination method according to one of the preceding claims, characterized in that the second determination phase implements an iterative calculation. MS \ REN170EN.dpt 15 6. Determination method according to one of the preceding claims, characterized in that the second determination phase continues to be implemented after the immobilization of the motor vehicle and after the ignition of the motor vehicle. 7. Determination method according to the preceding claim, characterized in that the second determination phase is completed when a delay, triggered by the immobilization of the motor vehicle, is overdue or when the calculated temperature of the mechanical coupling means becomes less than one. threshold temperature value or when the derivative compared to the time of the calculated temperature of the mechanical coupling means becomes less than a threshold cooling value. 8. Data storage medium readable by a computer on which is recorded a computer program comprising computer program code means for implementing the steps of the method according to one of the preceding claims. 9. System (10) for determining the temperature of a mechanical coupling means of the first and second axles of a transmission system (15) of a motor vehicle, characterized in that it comprises material means and / or software implementation of the method according to one of claims 1 to 7. 10. System (12) for determining according to claim 9, characterized in that the hardware and / or software means comprise a module (11) for determining an initial temperature of the mechanical coupling means by measuring a temperature and a temperature. module (12) for determining the current temperature of the mechanical calculation coupling means using the initial temperature and a temperature estimation model. MS \ REN170FR.dpt Motor vehicle comprising a determination system (10) according to claim 9 or 10. Computer program comprising a computer program code means adapted to perform the steps of the method according to one of claims 1 to 7, when the program runs on a computer. MS \ REN170FR.dpt