FR2889259A3 - Common fuel supply rail for motor vehicle, has piston housed in pressurized fuel receiving chamber and moved towards front or rear for varying volume of chamber in continuous and progressive manner to vary pressure in chamber - Google Patents

Abstract

The rail has a piston (26) housed in a pressurized fuel receiving chamber (20) and presenting a lateral face (28) with cylindrical form complementary to cylindrical form of an inner lateral face (31) of the rail. The piston is moved towards the front or rear for varying the volume of the chamber in a continuous and progressive manner in order to vary the pressure in the chamber. The piston slides within the chamber along the direction of an axis (16) and is guided to the end of the chamber by a rear rod (32) sliding in an extended housing (34) of rear part of the chamber. Independent claims are also included for the following: (1) a vehicle comprising a common fuel supply rail (2) a method for controlling a common fuel supply rail (3) a method for controlling an engine.

Description

The invention relates to common fuel supply ramps for

vehicle engine.

  It is known to supply a motor vehicle diesel engine with injectors connected to a common rail or common rail containing pressurized fuel, itself fed by a pump connected to the fuel tank.

  During transient pressure ramps related to the passage from one operating point of the engine to another, the pressure in the ramp must go up or down to reach the new pressure setpoint.

  The increase in pressure is achieved by increasing the flow delivered by the pump but the achievement of the new set point then requires a certain time especially if the engine speed, and thus the speed of rotation of the pump, is low.

  A pressure drop in the ramp is achieved by creating a leak using a high pressure actuator if it is installed on the application concerned. If the application does not have this actuator, the low pressure actuator located at the inlet of the pump is closed so that the pump no longer delivers. The pressure drop in the ramp is then due to the quantities of diesel fuel that are injected into the engine and the leakage of the injectors towards the reservoir. Here too, the achievement of the new directive requires a certain amount of time. But when the driver of the vehicle lifts his foot off the accelerator pedal, the injection is cut off. On the other hand, some injectors have almost zero static leakage. Therefore, in the case of a foot lift on an engine that uses this type of injector, the pressure drop in the ramp can take a long time. Conversely, during re-acceleration, the desired pressure level in the ramp is not necessarily reached quickly.

  It is also understood that the lower the volume of the ramp, the more transient pressure regimes will be brief. However, on the other hand, the increase in the volume of the ramp makes it possible to limit the pressure drops during the injection (which improves the performance of the engine) and the pressure oscillations in the tubes (which limits the interactions between the injections ). The volume of the ramp is a compromise between the speed of reaching the transient and the pressure reserve necessary for the proper functioning of the system to limit pressure drops and dampen the interactions between the injectors.

  An object of the invention is to provide a ramp whose transient conditions are short and also limiting the pressure drop during injection and the pressure oscillations in the tubes.

  For this purpose, there is provided according to the invention a common fuel supply system for a vehicle which comprises a member arranged to vary a fuel pressure.

  Thus, the ramp can be given a relatively small volume to limit the duration of the transient conditions while maintaining better control of the pressure inside the ramp in the interest of engine performance.

  The ramp according to the invention may also have at least one of the following characteristics: the member extends in a fuel reception chamber of the ramp; - The member is movably mounted in the ramp; - The member is slidably movable; the member forms a piston; and - the ramp comprises a first chamber portion into which at least two injector ducts open, and a second chamber portion in which the organ is received, the two parts succeeding one another in a longitudinal direction of the ramp and having different dimensions in a direction perpendicular to this longitudinal direction.

  According to the invention, a vehicle comprising a ramp according to the invention is also provided.

  Also provided according to the invention is a method of controlling a common vehicle fuel supply ramp, in which a member of the ramp is actuated to vary a fuel pressure.

  Advantageously, the organ is moved.

  Finally, according to the invention, a method of controlling an engine in which the above-mentioned method according to the invention is implemented is provided.

  Advantageously, it actuates a fuel supply pump of the ramp, concomitantly with the actuation of the organ.

  Advantageously, the member is moved in a first direction, then an operating parameter of the pump is modified and the member is moved in the opposite direction.

  Other features and advantages of the invention will become apparent in the following description of two preferred embodiments given by way of non-limiting example with reference to the accompanying drawings in which: - Figure 1 is a schematic view of a circuit injection of an engine comprising a ramp according to the invention; and FIGS. 2 and 3 are two views in longitudinal section of two embodiments of the ramp according to the invention intended to form part of the engine of FIG. 1.

  With reference to FIG. 1, the injection circuit 2 comprises a fuel tank 4 into which a high-pressure pump 6 draws fuel and delivers it by means of a high-pressure tube 8 towards a common rail 10. The latter is in direct communication with several parallel high pressure tubes 12 communicating with respective injectors 14. The tubes 12 and the injectors 14 are here four in number.

  Referring to Figure 2, in a first embodiment, the ramp 10 has a generally elongate shape of axis 16 and is cylindrical in revolution about this axis. It has a chamber 20 for receiving pressurized fuel in which opens a conduit 22 communicating with the tube 8 and four conduits 24 communicating with the respective tubes 12.

  The ramp comprises a member for varying the pressure in the chamber 20. In the present example, this member comprises a piston 26 or needle, housed in the chamber 20 and having a shape complementary to the latter. Thus, the piston has a cylindrical side face 28 complementary to the cylindrical shape of the inner side face 31 of the ramp. The piston 26 defines by its flat front face 30 perpendicular to the axis 16 one of the walls of the chamber 20. The piston 26 is slidably movable inside the chamber in the direction of the axis 16 and is guided for this purpose by a rear rod 32 sliding in an elongated housing 34 of the rear end of the chamber.

  The ramp comprises means for actuating the piston to cause it to move forwards or backwards. These means may comprise, depending on the case, an electric motor, a hydraulic cylinder, a magnetic actuator or an actuator of another type. These means are controlled by the engine control computer according to instructions determined by the latter, in particular pressure instructions depending on engine speed and instructions given by the driver of the vehicle.

  The displacement of the piston 26 makes it possible to vary the volume of the chamber 20 in a continuous and progressive manner between the most advanced position of the piston which defines the minimum volume of the chamber and the most retracted position which defines the maximum volume of the chamber. .

  This displacement also makes it possible to vary the pressure in the ramp according to Hooke's law: = -B. AVN0 where: - B is the compressibility module of the fluid which is in this case a fuel such as diesel fuel; - Vo is the initial volume of the chamber; LV is the volume variation resulting from the displacement of the piston; and - L P is the pressure variation in the ramp resulting from the change in volume.

  Thus, when it is desired to increase the fuel pressure prevailing in the ramp, the piston is displaced in such a way as to reduce the volume of the ramp (AV is therefore negative), which makes it possible to reach rapidly the new pressure and pressure setpoint. accelerate the transitional regime. Conversely, to lower the pressure in the ramp, the volume of the ramp is increased by means of the piston (AV is therefore positive) and the same advantages are obtained.

  Each of these pressure variations is effected by means of a very fast movement of the piston.

  Once the new pressure setpoint reached, it controls the piston to bring it back slowly, that is to say, less quickly than the aforementioned displacement, in the neutral position so that it is ready to intervene during the next transient regime. The neutral position of the piston will for example be a position in which it can move on a predetermined forward stroke and a predetermined backward stroke. Preferably, it will be a position midway between its most advanced position and its most remote position.

  When slowly returning the piston to its neutral position, it will be possible to simultaneously control the delivery of the pump to maintain a constant fuel pressure in the ramp, equal to the new pressure setpoint. Thus, when the piston is moved back to increase the volume, the pump speed will be increased concomitantly. Conversely, when the piston is reduced by decreasing the volume of the ramp, the pump speed will be lowered concomitantly.

  As can be seen, the piston can also be advantageously used to accelerate the pressure rise time of the rail when starting the engine. Thus, when the engine is stopped, before it starts, the piston is positioned in its most advanced position so as to give the chamber 20 a minimum volume. Once the start and the pressure setpoint reached, it gradually moves the piston to the neutral position, resulting in a gradual increase in the volume of the chamber.

  A second embodiment of the ramp 11 has been illustrated in FIG. 3. This time, the chamber 20 has a front part 36 and a rear part 38 both of cylindrical shape with an axis 16. However, the diameter of the part Rear 38 measured perpendicularly to this axis is larger than the diameter of the front portion 36, the two parts being separated by a shoulder 40. The ducts 22 and 24 open into the front portion 36 while the piston 26 is housed in the part rear 38 having a corresponding diameter. Due to this difference in section, a movement of the piston identical to the displacement carried out in the case of FIG. 2 induces a rise or fall in the pressure in the front portion 36 which is greater than in the case of FIG. There is no difference in section. This further reduces the duration of the transient pressure regimes in the ramp. Conversely, transients of the same duration can be achieved with lower displacements of the piston, which may be of interest in view of the congestion constraints of the ramp.

  In the case where the seal between the piston and the part of the ramp in which it slides is not perfect, it is possible to put in communication the compartment of the ramp located at the rear of the piston with the tank 4 by means of a conduit 50 for returning to the tank 4 the fuel that would arrive in this compartment. However, it will be advantageous to minimize fuel leakage at this level.

  As can be seen, the ramp according to the invention makes it possible to vary the volume and the pressure of the or each chamber so as to accelerate the pressure transients while maintaining a sufficient ramp volume.

  Of course, we can bring to the invention many changes without departing from the scope thereof.

  The invention can be applied to the case of a ramp having a spherical shape or a different shape. It can also be applied to the case of a non-cylindrical piston. Each time, the movement of the piston in the ramp allows to vary its volume even if the inner shape of the ramp and the outer shape of the piston are not complementary.

Claims (12)

  1. Common rail (10, 11) fuel supply for vehicle, characterized in that it comprises a member (26) arranged to vary a fuel pressure.   2. Ramp according to the preceding claim, characterized in that the member (26) extends into a chamber (20) for receiving fuel from the ramp.   3. Ramp according to any one of the preceding claims, characterized in that the member (26) is movably mounted in the ramp.   4. Ramp according to any one of the preceding claims, characterized in that the member (26) is slidably mounted.   5. Ramp according to any one of the preceding claims, characterized in that the member (26) forms a piston.   6. Ramp according to any one of the preceding claims, characterized in that the ramp (11) comprises a first portion (36) of chamber (20) into which at least two injector ducts (24) open, and a second part (38) of chamber in which the member (26) is received, the two parts succeeding one another in a longitudinal direction of the ramp and having different dimensions in a direction perpendicular to this longitudinal direction.   7. Vehicle, characterized in that it comprises a ramp according to any one of the preceding claims.   8. A method of controlling a common vehicle fuel supply ramp (10, 11), characterized in that a member (26) of the ramp is actuated to vary a fuel pressure.   9. Method according to the preceding claim, characterized in that one moves the member (26).   10. A method of controlling an engine characterized in that it is in accordance with one of claims 8 or 9.   11. Method according to the preceding claim, characterized in that it actuates a pump (6) for supplying the ramp (10, 11) with fuel, concomitantly with the actuation of the member (26).   12. Method according to any one of claims 10 or 11, characterized in that one moves the member (26) in a first direction, then changes an operating parameter of the pump (6) and moves the member (26) in opposite directions.