WO2007148031A2

WO2007148031A2 - Device and method for generating a datum value for a vcr system

Info

Publication number: WO2007148031A2
Application number: PCT/FR2007/051507
Authority: WO
Inventors: Emmanuel Devaud; Gwennaël Favennec; David Gerard; David Racher; Charlie Rambert
Original assignee: Renault S.A.S.
Priority date: 2006-06-23
Filing date: 2007-06-22
Publication date: 2007-12-27
Also published as: FR2902834B1; FR2902834A1; WO2007148031A3

Abstract

The invention relates to a device for generating variable compression ratios for an internal combustion engine, comprising a computer (2) controlling an actuator (3) that generates a compression ratio in the engine, the computer (2) comprising a map (21) and receiving engine speed and engine torque, or effective pressure, data in order to generate a first compression ratio datum (211) and a first processing means (22) for processing said first compression ratio datum (211) that generates a second compression ratio datum (221) equal to a mean of earlier first compression ratio datums (211). The invention is essentially characterized in that the computer (2) further comprises a second processing means (23) converting said second compression ratio datum (221) into a hysteresis datum (231) which is sent to the actuator (3) so that it can generate said compression ratio.

Description

DEVICE AND METHOD FOR SETTING GENERATION FOR

VCR SYSTEM

The present invention relates to a setpoint generation device for a VCR system of an internal combustion engine and a method implemented by this device.

More specifically, the present invention relates to a device for generating variable compression ratio, which can vary between maximum and minimum values, for an internal combustion engine, said device comprising a computer controlling an actuator generating a compression ratio in the engine, said calculator comprising a map and receiving data of engine speed and engine torque, or effective pressure, to generate, consequently, a first compression ratio setpoint, and a first processing means of said first compression ratio setpoint generating a second compression ratio setpoint, equal to an average of first previous compression ratio setpoints, for controlling an actuator generating a compression ratio.

Such a device is known from the prior art especially in the automotive industry. Indeed, in an effort to comply with increasingly stringent antipollution standards on automotive engines, car manufacturers have had to reduce the pollutant emissions of their engines. These pollutant emission reductions had to be made without neglecting the performance and consumption of the engines concerned. Systems based on variable compression ratio (later called VCR systems) have made gains in consumption or depollution, as appropriate. For example, on a gasoline engine, a VCR system allows, at full load, to reduce the compression ratio to prevent rattling, and increase the partial load compression ratio to optimize the engine performance. On diesel engines, a VCR system allows, for example, high load to have a low compression ratio to limit the NO _x emission, and fable load to have a strong compression ratio to limit the emission of HC, CO and CH ₄ . In a VCR system, the compression ratio is varied through the use of an actuator whose position is varied according to control signals issued by a computer. However, there are several principles concerning VCR systems for modifying a compression ratio, for example the geometry of the piston, the position of the cylinder head or the position of the piston can be varied.

US 6,666,177 discloses a system for varying the highest compression ratio as a function of the operating point of the engine in which the actual compression ratio is adjusted from a knock sensor which detects when the compression ratio is too high.

US 6,915,766 discloses a method of generating a compression rate setpoint from a map connecting engine speed and engine torque measurements to a target compression ratio. This instruction is then reprocessed to avoid rattling problems so as to define a period during which this instruction is not applied.

US 6,412,453 discloses a method for generating a compression ratio setpoint from a measurement of engine speed, engine load, and mapping linking these measurements to a desired compression ratio.

If it appears that the use of a cartography receiving measurements of engine speed and engine torque is widely exploited. It seems nevertheless that none of the documents presented above prejudge the sizing of the actuator. None of these documents seek to limit the use of the actuator of the VCR system and therefore the power consumed by it. Indeed, according to the teaching of the documents mentioned above, the generations of compression rate instructions assume that in all situations where a compression ratio is set, the actuator can reach it, which can cause very strong voltages on one actuator. Moreover, these documents do not mention the compression ratio instructions that last less than one second, the realization of which is then of no real interest from the point of view of the performance / consumption / pollution ratio, but which generates strong constraints on 1 Actuator since the movement of the actuator can not vary as fast as this type of short compression rate setpoints.

In this context, the present invention therefore aims to provide a method and a compression rate setpoint generation device for reducing the force supported by the actuator according to the compression ratio.

To this end, the device of the present invention, moreover in accordance with the generic definition given in the preamble above, is essentially characterized in that the computer further comprises a second processing means transforming said second rate setpoint. of compression in a hysteresis setpoint which is sent to the actuator to generate said compression ratio.

According to a preferred embodiment of the invention the first processing means is a filter, preferably a "low-pass" filter allowing the low frequency signals to pass.

According to another embodiment, the actuator (3) is provided with a braking means enabling the actuator (3), when maintained in a stationary position, not to consume power. In this case, the computer may further comprise a power control means of the actuator allowing, when the power consumed by the actuator reaches a predetermined threshold, to limit this power, for example by immobilizing the actuator or in it transmitting a compression ratio setpoint requiring a power lower than the threshold power.

In addition, according to this embodiment, the power regulation means may comprise a calculation means determining the power required by the actuator to apply the setpoint and an arbitration means between the power determined in the calculation means and the power currently used by the actuator.

Also, according to another embodiment, the device may further comprise means for measuring the engine temperature which will send a signal representative of the temperature to the computer.

According to another embodiment, the computer further comprises a switching means transmitting, as a function of the engine temperature, the setpoint after arbitration or a maximum, or near, setpoint to the actuator so that it generates said compression. According to another of its aspects, the invention also relates to an internal combustion engine comprising a variable compression ratio generating device according to any one of the embodiments of the present invention.

According to yet another of its aspects, the invention relates to a method for generating a variable compression ratio of a variable compression ratio (VCR) internal combustion engine that can vary between maximum and minimum values of compression ratio , the method comprising a first step for setting the compression ratio at or near its maximum value, and a second step during which a computer, receiving data of engine speed and engine torque or effective pressure, generates, at a means of mapping, a first compression ratio setpoint which is then processed by means of a first processing means in order to generate a second setpoint equal to an average of previous first setpoints, and the method being characterized in that this second instruction is converted, by means of a second processing means, into a hysteresis setpoint which makes it possible to control an actuator so that it gen era said compression ratio.

According to a preferred embodiment of this aspect of the invention, the first step takes place during a starting phase of the engine and the second step that follows is triggered when a predetermined threshold of engine temperature is reached.

According to another embodiment of this aspect of the invention, the first step takes place during a motor start phase and the second step that follows after a predetermined time is triggered. According to a preferred embodiment of this aspect of the invention, the second setpoint is generated by means of a slope saturation.

According to another embodiment of this aspect of the invention, the second setpoint is generated by means of a filter, preferably a "low-pass" filter allowing the low-frequency signals to pass.

According to a preferred embodiment of this aspect of the invention, the method further comprises a power control operation of the actuator comprising measuring the power consumed by the actuator and maintaining it at a threshold or lower value. fixing the associated compression ratio.

Other features and advantages of the invention will emerge clearly from the description which is given below, for information only and not limiting.

Figure 1 schematically shows a variable compression ratio generation device for an engine according to an embodiment of the present invention.

FIG. 2 schematically represents a computer according to a first embodiment of the present invention. Figure 3 schematically shows a computer according to a second preferred embodiment of the present invention.

FIG. 1 represents a preferred embodiment of a variable compression ratio generation device 1 comprising a computer 2 and an actuator 3 which is connected to a conventional VCR 4 kinematic system controlling a piston 5. The device 1 also comprises a means for measuring the engine speed 6, for example a sensor located on the crankshaft 7, and a means for estimating or measuring the engine torque (not shown), or the effective pressure, for example by a sensor or by estimating the quantity of air at 1 admission.

When the engine is running, the computer 2 receives data concerning the engine speed and the engine torque, or the effective pressure, and according to these data, the computer 2 will send a control signal a to the actuator 3. The actuator 3 receiving the control signal a will change its position. This movement actuates the VCR 4 kinematic system so as to modify the compression ratio, overall or per cylinder. Indeed, in this embodiment, by changing position, the actuator 3 modifies the top dead center (TDC) and bottom dead center (PMB) of the piston 5 which will vary the compression ratio in the engine. According to other embodiments of the present invention, the displacement of the actuator 3 may, for example, vary the position of the cylinder head or the geometry of the piston.

In addition, the device 1 comprises an engine temperature sensor (not shown), this sensor can, for example, measure the temperature of the engine coolant, representative of the engine temperature and then informs by means of a signal the computer the engine temperature.

In this embodiment, the actuator 3 sends a signal b to the computer. This signal b may be representative of the position of the actuator 3 or the power consumed by the actuator 3. Thus, in some cases, it is possible to measure and regulate the power consumed by the actuator 3. This embodiment has a "modified kinematic" VCR system, it is understood that the present invention also includes any other type of known VCR system. When starting a vehicle according to a preferred embodiment of the invention, the method comprises two distinct steps. In a first step, the compression ratio that can generally vary between a maximum value and a minimum value is set at its maximum value, or as close to it as possible.

The start-up phase is started when the engine is started and stops, preferably when the engine temperature has reached a certain threshold. Nevertheless, other parameters are likely to determine the end of the start-up phase, for example, a predetermined time.

The start-up phase is followed by a second step, called the nominal phase, which will end with the stopping of the engine. FIG. 2 diagrammatically represents a first embodiment of the method for generating a compression ratio in the computer 2 during the nominal phase. The computer 2 receives data concerning the engine speed 21a and the engine torque 21b, or the effective pressure, and comprises a map 21 which makes it possible to associate with each pair of values (engine speed, engine torque) or (engine speed, pressure effective) a compression ratio value. Thus, thanks to the map 21, the computer generates a first compression ratio setpoint, called the raw rate setpoint 211. The number of compression ratios available on the map 21 can be two, but is not limited to number, independently of the possibilities of the actuator 3. The Gross rate setpoint 211 is sent directly to a first processing means 22, for example a low-pass filter, which converts the raw rate setpoint 211 into a second compression ratio setpoint, called the filtered rate setpoint 221. The filter low pass 22 operates to generate a set value equal to the average of the value of the filtered raw set point and of all the values of the raw setpoints prior to the filtered setpoint received in a predetermined period of time, for example one minute . However, the filtered rate setpoint 221 can be obtained by other means, for example rather than passing the raw setpoint 211 through a filter 22 it is possible to use a slope saturation, that is, say to slow down the gross setpoint variation, for example, by means of an algorithm, to obtain the filtered rate setpoint 221. The filtered rate setpoint 221 is then subjected to at least one hysteresis in a second processing means 23, in order to This hysteresis setpoint is then sent to the actuator 3 so that it can generate the compression ratio representative of the setpoint 231.

FIG. 3 schematically represents a second embodiment of the method of generating a compression ratio in the computer 2 during the nominal phase. In this second embodiment, the VCR system of the device shown in FIG. 1 has a "blocking" mode of operation, that is to say that no power is consumed or supplied by the actuator. when he has to maintain a position. The computer 2 receives data concerning the engine speed 21a and the engine torque 21b, or the pressure effective, and includes a map 21 which allows to associate each pair of values (engine speed, engine torque) or (engine speed, effective pressure) a compression ratio value. Thus, thanks to the map 21, the computer generates a first compression ratio setpoint, called the raw rate setpoint 211. The number of compression ratios available on the map 21 can be two, but is not limited to number, independently of the possibilities of the actuator 3. The raw rate setpoint 211 is sent directly to a first processing means 22, for example a low-pass filter, which converts the raw rate setpoint 211 into a second rate setpoint. of compression, called filtered rate setpoint 221. The low-pass filter 22 operates to generate a value set equal to the average of the value of the filtered raw setpoint and all the values of the raw setpoints prior to the filtered setpoint received in a predetermined period of time, for example one minute. However, the filtered rate setpoint 221 can be obtained by other means, for example rather than passing the raw setpoint 211 through a filter 22 it is possible to use a slope saturation, that is, say to slow down the gross setpoint variation, for example, by means of an algorithm, to obtain the filtered rate setpoint 221. The filtered rate setpoint 221 is then subjected to at least one hysteresis in a second processing means 23, in order to The hysteresis setpoint is then sent to a regulating means 27, where it is the subject of a specific treatment in a calculation means. 24 in which a power necessary for the performance of this rate of compression is determined. Subsequently, this power value 241 is compared with the power currently consumed with the actuator in an arbitration means 25, for example by means of a second mapping. Indeed, at each moment the actuator 3 emits a signal b representative of the power that it consumes. This signal may represent, for example, an electric current or a pressure in the case of an electric or hydraulic actuator, respectively. When the power consumed by the actuator reaches a predetermined value, considered as a maximum value of power reasonably consumed, the compression ratio will be fixed either at its current value, which means immobilization of the actuator 3, or at the value hysteresis setpoint if the latter contributes to reducing the power consumed by the actuator 3.

Thus, after comparison, the arbitration means 25 emits an instruction called "after arbitration" 251 representative of the hysteresis setpoint or the compression ratio currently used as appropriate. This setpoint is sent in a switching means 26 depending on the phase in which the motor is located, if the motor is in the starting phase, a maximum compression ratio, or close to this value, will be sent to the actuator, if the engine is in nominal phase, the setpoint after arbitration 251 is transmitted to the actuator so that it can generate the appropriate compression ratio.

Claims

A variable compression ratio generating device, capable of operating between maximum and minimum values, for an internal combustion engine, said device comprising:

- A computer (2) controlling an actuator (3) generating a compression ratio in the engine, said computer (2) comprising a map (21) and receiving data of engine speed and engine torque, or effective pressure, to generate consequently, a first compression ratio setpoint (211), and a first processing means (22) of said first compression ratio setpoint (211) generating a second compression ratio setpoint (221) equal to an average first prior compression ratio setpoints (211), the device being characterized in that the computer (2) further comprises a second processing means (23) transforming said second compression ratio setpoint (221) into a setpoint d hysteresis (231) which is sent to the actuator (3) to generate said compression ratio.

2. Device according to claim 1, wherein the first processing means (22) is a "low pass" filter passing low frequency signals.

3. Device according to claim 1 or 2 wherein the actuator (3) is provided with a braking means allowing the actuator (3), when maintained in the stationary position, not to consume power.

4. Device according to claim 3, wherein the computer (2) further comprises a power control means (27) of the actuator (3) allowing, when the power consumed by the actuator (3) reaches a predetermined threshold, to regulate this power.

5. Device according to claim 4, wherein the power control means (27) comprises a calculating means (24) determining the power required for the actuator (3) to apply the instruction (231) and a means of arbitration (25) between the power (241) determined in the calculation means (24) and the power (b) currently used by the actuator (3).

6. Device according to one of the preceding claims, further comprising a means for measuring the engine temperature.

7. Device according to claim 6, wherein the temperature measuring means sends a signal representative of the temperature to the computer (2).

8. Device according to claim 7, wherein the computer (2) further comprises a switching means (26) transmitting, as a function of the engine temperature, the setpoint after arbitration (251) or a maximum setpoint, or close, the actuator (3) to generate said compression ratio.

An internal combustion engine comprising a compression rate variation device (1) as claimed in any one of the preceding claims.

A method of generating a variable compression ratio of a variable compression ratio (VCR) internal combustion engine that can vary between maximum and minimum values of compression ratio, the method comprising: a first step for setting the compression ratio at, or near, its maximum value, and a second step during which a computer (2), receiving data of the engine speed and of the engine torque or of the effective pressure, generates, by means of a map (21), a first compression ratio setpoint (221) which is then processed by means of a first processing means (21) to generate a second setpoint (221) equal to an average of the previous first setpoints (211), and the method being characterized in that said second setpoint (221) is converted, by means of a second processing means (22), into a hysteresis setpoint (231) for controlling an actuator (3) to generate said compression ratio.

11. The method of claim 10, wherein the first step takes place during a motor start phase and the second step that follows is triggered when a predetermined threshold of engine temperature is reached.

12. The method of claim 10, wherein the first step takes place during a motor start phase and triggers the second step that follows after a predetermined time.

13. Method according to one of claims 10 to 12, wherein the second setpoint (221) is generated by means of a slope saturation.

14. Method according to one of claims 10 to 12, wherein the second setpoint (221) is generated by means of a "low-pass" filter (22) passing the low frequency signals.

The method according to one of claims 10 to 14, further comprising a power control operation of the actuator comprising measuring the power consumed by the actuator and maintaining it at a threshold value or lower by setting the associated compression ratio.