EP1474303B1 - Method of controlling a compressor driven by the engine of a vehicle - Google Patents

Abstract

The invention relates to a method of controlling a compressor which is driven by the engine of a vehicle and which supplies at least one compressed air tank. The compressor is activated or de-activated according to a comparison which is made between the value of the pressure in the tank(s) and the pre-determined conjunction and disjunction pressure thresholds, depending on the sign of the engine torque. If the range of torque is positive there are multiple conjunction and disjunction pressure thresholds which are determined according to the vehicle speed estimation or measurement.

Description

Technical area

The invention relates to the field of the automotive industry in the broad sense, and more specifically to the sector of industrial vehicles whose braking uses pneumatic means. The invention more specifically relates to a method of controlling the air compressor which is driven by the vehicle engine, and which supplies the compressed air reservoir (s). The process according to the invention makes it possible in particular to optimize the production of compressed air depending in particular on the different modes of operation of the vehicle.

Previous techniques

In general, trucks or more generally industrial vehicles have a braking system that uses pneumatic energy. Thus, the motor drives an air compressor associated with it, and which delivers a quantity of pressurized air to one or more storage tanks. These compressed air tanks in turn feed the braking circuit as well as other specific circuits performing particular functions. These functions include pneumatic suspension devices as well as systems of servitude and assistance to the operation of the gearbox or clutch system.

In general, the compressor is controlled by mechanical means associated with the compressor. More precisely, the compressor delivers compressed air to a regulation and distribution module comprising mechano-pneumatic members which interfere with the configuration of the pneumatic circuit of the compressor. Thus, this control module is arranged in such a way that the compressor stops supplying pressurized air when the pressure in the tank reaches a predetermined threshold, called the "disjunction threshold". In practice, this disjunction can be obtained by venting the compressor exhaust. In more sophisticated systems, the disjunction is achieved by connecting the intake and exhaust of the compressor. Conversely, the The compressor resumes supplying pressurized air when the pressure in the tank reaches a low threshold, called "conjunction pressure". In this case, the regulation and distribution module ensures the connection between the exhaust of the compressor and the tanks. The conjunction and disjunction thresholds are generally set by construction of the regulation and distribution module, and more precisely by the adjustment of various valves, springs, valves and other section ratios.

More advanced systems have already been proposed, including that described in WO 98/07588. More specifically, the mechanism described in this document takes into account various operating parameters of the vehicle to ensure optimum production of compressed air. Indeed, when the vehicle operates in engine braking mode, the fuel consumption is zero, and it is advantageous then to use a portion of the engine braking torque to ensure a production of compressed air. Thus, the pressure setpoint, and more precisely the disjunction threshold, applied to the compressor is higher when the engine torque is negative, corresponding to a motor brake phase.

Thus, the production of air is increased in the phases where the energy to drive the compressor does not cause any fuel consumption. This additional air production is advantageous for providing mechanical braking in addition to engine braking.

Conversely, when the motor exerts a positive torque, the pressure set point is set at a lower level so as to limit the fuel consumption. The pressure setpoint is set to ensure a sufficient production of compressed air so that the braking functions in particular are properly ensured.

Among the systems other than braking, operating with the aid of pneumatic energy, mention may be made of air suspension systems. The system of Air suspension operates in two different modes depending on whether the speed is high or low. Thus, when the speed is low, the air suspension system can provide a height adjustment of the chassis. This control function requires a relatively high pressure level to obtain satisfactory response times. The altitude setting of the chassis is not done at high speed, so the pressure level that is needed at high speed is less than the level of pressure needed at low speed.

The object of the invention is to take into account these different operating modes to ensure the optimization of the value of the pressure setpoint delivered to the compressor.

Presentation of the invention

The invention therefore relates to a method of controlling a compressor driven by the engine of a vehicle, and which supplies at least one compressed air tank. The compressor can be activated or deactivated based on the comparison of the value of the pressure in the reservoir (s) with respect to different predetermined conjunction and disjunction thresholds. These predetermined thresholds may be functions of the sign of the engine torque in particular.

According to the invention, in the range where the torque is positive, the thresholds of conjunction and disjunction pressure are multiple and determined according to the measurement or estimation of the speed of the vehicle. In other words, when the vehicle is running, the pressure delivered by the compressor varies with the speed of the vehicle. The setpoint, that is to say the thresholds of conjunction and disjunction of the compressor, are different depending on whether the vehicle is low or high speed. Thus, the air pressure from the compressor is regulated within ranges of values that are different depending on the speed and torque of the engine.

In practice, the pressure thresholds can be determined by comparing the speed of the vehicle with a predetermined speed threshold. In other words, when the vehicle is at a speed below a predetermined threshold, the pressure reference range, that is to say the compressor conjunction and disjunction thresholds are set to a first pair of values. Conversely, when the vehicle is traveling at a speed greater than the predetermined speed threshold, the conjunction and disjunction thresholds are then set to a different pair of values.

In practice, the pressure thresholds are set to higher values when the vehicle speed is below the predetermined speed threshold. In other words, the pressure delivered by the compressor is higher when the vehicle is at low speed, which allows a supply of the reservoir at a pressure sufficient to ensure optimum operation of the various systems including air suspension systems ensuring altitude control of the chassis.

In addition, the energy consumption of the compressor is higher at low speed, the range in which the engine is not running at full speed, so that this additional consumption does not disturb the operation of the vehicle. In this way, the pressure is regulated in a range of values as high as possible, to make the most of the possibility of using part of the energy of the heat engine without influencing the traction performance, and thus benefit from a reserve of maximum pneumatic energy. Conversely, at high speed, the pressure is regulated in a range of lower values, so that the consumption of the compressor is slightly reduced, and does not too strongly reduce the power available for the traction function.

In practice, the speed threshold making it possible to differentiate the two operating modes of the compressor can advantageously be chosen as being the speed threshold beyond which the specific altitude control function of the chassis of the pneumatic suspension system is inhibited.

Advantageously in practice, the high pressure threshold determined when the torque is positive and the speed below the predetermined speed threshold, can be identical to the high pressure threshold determined when the torque is negative. In other words, the compressor disjunction threshold can be the same for the motor brake energy recovery phases, and for the low speed traction phases.

The invention therefore also relates to a device for regulating a compressor driven by the engine of a vehicle and supplying one or more compressed air tanks.

• ■ des moyens pour activer ou désactiver le compresseur en fonction de la comparaison de la valeur de la pression dans le ou les réservoirs par rapport à des seuils prédéterminés ;
• ■ des moyens de mesure de la pression dans le ou les réservoirs ;
• ■ des moyens pour mesurer ou estimer le signe du couple du moteur ;
• ■ des moyens pour faire varier les seuils de pression prédéterminés.

Such a device comprises:

• Means for activating or deactivating the compressor according to the comparison of the value of the pressure in the reservoir (s) with respect to predetermined thresholds;
• ■ means for measuring the pressure in the reservoir or reservoirs;
• Means for measuring or estimating the sign of the engine torque;
• Means for varying the predetermined pressure thresholds.

According to the invention, the device also comprises means for evaluating or estimating the speed of the vehicle and means for varying the predetermined pressure thresholds in the range where the engine torque is positive.

In practice, the different predetermined pressure thresholds are set in software. An electronic control unit regulates and controls the compressor and is informed of the speed of the vehicle and the engine torque, to ensure the adjustment of the thresholds according to the invention.

Brief description of the figures

• La figure 1 est un schéma illustrant les différents éléments intervenants dans le procédé conforme à l'invention.
• La figure 2 est un diagramme illustrant l'évolution dans le temps de la vitesse et de la pression délivrée par le compresseur, en fonction des différentes phases de fonctionnement.

The manner of carrying out the invention as well as the advantages which result therefrom will emerge from the description of the embodiment which follows, in support of the appended figures in which:

• Figure 1 is a diagram illustrating the various elements involved in the process according to the invention.
• FIG. 2 is a diagram illustrating the evolution over time of the speed and the pressure delivered by the compressor, as a function of the different operating phases.

Way of realizing the invention

FIG. 1 illustrates a particular but nonlimiting embodiment, implementing the method according to the invention. Thus, it is possible to identify in FIG. 1 the compressor (1) which delivers the compressed air to a regulation and distribution module (9) on which the cartridge of the desiccator (2) is mounted. This compressor (1) is driven by the motor (3). The interaction between the regulation module (9) and the compressor (1) is represented by the arrow (13). The configuration of the pneumatic circuit connected to the compressor, and in particular the action on the exhaust of the compressor is performed by various control means, including pneumatic or electrical.

The regulation and distribution module (9) delivers compressed air via lines (4) to one or more tanks (5), the number of which can vary according to the vehicle, without departing from the scope of the invention. These tanks (5) are connected to different circuits shown schematically. It can be the braking circuit (6) as well as the supply circuit of the air suspension system (7) or the supply of the compressed air trailer. The tanks can also supply other pneumatic circuits (8) performing various functions among which mention may be made of the parking brake or parking brake, as well as various systems of servitudes connected to the gearbox or clutch mechanism.

Mention may also be made, among systems operating with the aid of pneumatic energy, of the movement-taking or PTO systems, or else of the differential locking system, inter-wheel or inter-bridge, or concerning the box. transfer. This list is of course not exhaustive.

According to the invention, the control of the compressor (1) is provided by means of an electronic control unit (10) which can form a separate element, providing only the management and operation of the compressor, but which can also be integrated into a more global system for the electronic management of other functions within the vehicle. In the illustrated form, the electronic control unit is flanged on the regulation and distribution module (9). Nevertheless, the electronic control unit can also be geographically distant from the module (9).

In the illustrated form, this electronic control unit has a plurality of electrical outputs (11) delivering electrical signals to the compressor (1). These two electrical outputs make it possible to inform the compressor of the pressure threshold levels corresponding to the disjunction thresholds and the conjunction of the compressor. However, other modes of communication between the compressor and the control unit (10) can be envisaged. Thus, the pressure thresholds corresponding to the different modes of operation can be programmed within the compressor by mechanical construction arrangements. The control control unit can inform the compressor of the current control mode, thus transmitting a binary type information between the control unit (10) and the compressor (1) .The communication between the electronic control unit and the the control module (9) is not limited to the exchange of electrical signals, but the invention also covers variants using pneumatic or other signals.

In the illustrated form, the vehicle comprises a computer bus (12) through which various information exchanged between the control units present in the vehicle passes. Thus, information relating to the speed as well as the sign of the torque of the motor (3) can be conveyed via this bus (12) to the control unit (10) controlling the compressor. (1).

The tanks (5) are designed to work up to stabilized pressures of the order of 12.5 bar. The pneumatic energy requirements of the various elements consuming compressed air are variable. Thus, the braking circuit of the various axles of the trailer generally operates at a pressure of about 8.5 bar maximum. The air suspension system (7) operates with a maximum pressure of about 12.5 bar. This pressure is required for the operation of the suspension system to ensure control of the altitude of the chassis, also called "up and down" system of the chassis.

This function is used in particular when connecting the trailer and docking. This altitude control function of the chassis is inhibited when the vehicle is running, and its speed is above a predetermined threshold, typically close to 10 km / h. Beyond this speed, the air suspension system provides level control of low amplitude, and an air pressure of less than 10 bar is then sufficient.

Among the other systems using pneumatic energy, the different servitudes generally operate at maximum pressures of the order of 8.5 bars. The supply of compressed air to the trailer is also carried out at a pressure of the order of 8.5 bars.

The operation of the compressor according to the invention can be understood in support of FIG. 2 which illustrates the evolution of the different set point thresholds applied to the compressor as a function of the operating phases.

Thus, at the start of the engine, corresponding to the instant t ₀ , the tank (5) is at atmospheric pressure, and the overpressure is equal to 0 bars. With the vehicle stationary and the engine torque being positive, the compressor is driven so that the pressure thresholds are relatively high. More precisely, the compressor is driven in such a way that the pressure can rise up to the high disjunction value (D _H ) close to 12.5 bar. As soon as the pressure reaches (D _H ), the compressor is tripped.

After this disjunction, a regeneration phase of the desiccator cartridge (2) automatically engages. This regeneration consumes a quantity of compressed air which results in a slight decrease in pressure. Depending on the air consumption of the different systems (6, 7, 8) the pressure continues to decrease slightly. As soon as the pressure reaches the low threshold, corresponding to the disjunction threshold, the compressor is then reactivated, so that the compression re-increases.

This operating mode "at low speed" continues after starting the vehicle, corresponding to the time t ₁ , and as long as the speed remains below the predetermined threshold V ₀ .

At time t ₂ , when the speed exceeds the threshold V ₀ , the pressure thresholds are then automatically changed to lower values (D _B , C _B ) corresponding to operation in "high speed" mode. The pressure is then regulated analogously to the mode mentioned above, in the range defined between the two values D _B and C _B.

Subsequently, at time t ₃ , the engine torque becomes negative, corresponding to a braking phase by engine brake. The fuel injection rate is zero. The electronic control unit (10) analyzes this information and modifies the pressure regulation thresholds accordingly to operate the compressor in "energy recovery" mode. The new pressure set point is set to a value D _H corresponding to the disjunction threshold for the "low speed" mode described above. Nevertheless, this pressure setting could be set to a different value without departing from the scope of the invention. Thus, when the pressure reaches this high threshold D _H , the compressor is disjunct during the regeneration phase of the desiccant cartridge (2). The compressor is then re-activated so that the pressure reaches the high threshold D _H and this as long as the system is in "energy recovery" mode.

The pressure in the air tank is then maintained at a maximum level without the engine consuming fuel. It will be observed that, advantageously, the energy consumed by the compressor contributes to slowing down the vehicle. In this phase of engine braking, the various pneumatic systems (6, 7, 8) can consume compressed air, which lowers the pressure in the tanks (5).

At time t ₄ , the motor torque becomes positive again. Since the speed of the vehicle is greater than the predetermined threshold V ₀ , the compressor operates according to the mode called "high speed" described above.

From time t ₅ , the vehicle is in engine braking until it stops, the compressor is then regulated according to the "energy recovery" mode described above. The passage of the speed below the predetermined threshold V ₀ has no effect, since the torque remains negative.

• il permet de réduire la consommation en carburant lié à la production d'énergie pneumatique, et ce par une optimisation des phases lors desquelles le compresseur est sollicité ;
• il permet d'améliorer les fonctions de stockage et de distribution d'air comprimé aux différents organes consommateurs embarqués sur le véhicule ;
• il garantit des niveaux de pression d'air suffisant à ces organes consommateurs ;
• il permet d'augmenter la durée de vie des composants impliqués dans le système de gestion de l'air comprimé et notamment la cartouche du dessiccateur.

It follows from the foregoing that the control method according to the invention has many advantages and in particular:

• it makes it possible to reduce the fuel consumption related to the production of pneumatic energy, and this by an optimization of the phases in which the compressor is requested;
• it makes it possible to improve the functions of storage and distribution of compressed air to the various consumer bodies on board the vehicle;
• it guarantees sufficient air pressure levels for these consumer organs;
• it makes it possible to increase the life of the components involved in the compressed air management system and in particular the dryer cartridge.

Claims (6)

1. A method of controlling a compressor (1) driven by the engine (3) of a vehicle and supplying at least one compressed-air reservoir (5), in which the compressor (1) is started or stopped depending on a comparison between the value of the pressure in the reservoir(s) (5) and various predetermined connection and disconnection pressure thresholds, depending on the sign of the engine torque, which method is characterized in that the range where the engine torque is positive, there are multiple connection and disconnection pressure thresholds (D_H, C_H, D_B, C_B) determined as a function of the measurement or estimate of the speed of the vehicle.
2. The method as claimed in claim 1, characterized in that in the range in which the torque is positive, the pressure thresholds are determined by comparing the speed of the vehicle with a predetermined speed threshold (V₀).
3. The method as claimed in claim 2, characterized in that in the range in which the torque is positive, the pressure thresholds (D_H, C_H) are higher when the speed of the vehicle is less than the predetermined speed threshold (V₀).
4. The method as claimed in claim 1, characterized in that the upper pressure threshold D_H determined when the torque is positive and the speed less than the predetermined speed threshold, is identical to the upper pressure threshold determined when the torque is negative.
5. A device (10) for regulating a compressor driven by the engine of a vehicle and supplying at least one compressed-air reservoir, comprising:

   • means for starting or stopping the compressor (1) depending on a comparison between the value of the pressure in the reservoir(s) (5) and various predetermined connection and disconnection pressure thresholds;

   • means for measuring the pressure in the reservoir(s) (5);

   • means for measuring or evaluating the sign of the torque of the engine (3);

   • means for varying the predetermined pressure thresholds;

   characterized in that it also comprises means for evaluating or estimating the speed of the vehicle, and means for varying the predetermined connection and disconnection pressure thresholds in the range in which the torque is positive.
6. The device as claimed in claim 5, characterized in that the means for varying the predetermined pressure thresholds in the range in which the torque is positive are built into a computer program.

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