Controlling fuel pressure in an injection system

Abstract

Method for controlling a pressure (32, 34) in an injection system (14) for an engine (12) of a vehicle (10), the method comprising the steps: Determine whether the vehicle (10) is decelerating; Reducing the delivery rate of a high-pressure pump (16) that supplies the injection system (14) with fuel; Reducing the pressure in the injection system (14) to a standstill pressure (p S ) by means of an idle operation of the engine (12); characterized by Estimating a standstill time (t1) during which the vehicle (10) comes to a standstill; Reducing the delivery rate of the high-pressure pump (16) before the standstill time (t1) is reached, so that at the standstill time (t1) the standstill pressure (p S ) is achieved in the injection system (14).

Description

Field of the invention

[0001] The invention relates to a method, a computer program and a computer-readable medium for controlling a pressure in an injection system for an engine of a vehicle. Background of the invention

[0002] In order to save fuel, vehicles can be equipped with a so-called automatic start / stop system, which automatically switches off the engine when the vehicle is stationary and automatically starts it again when the vehicle continues driving.

[0003] In vehicles with high-pressure injection systems, such as diesel vehicles, it can be advantageous if the pressure in the injection system is below an idle pressure (for example, approximately 500 bar) when starting the engine, for example, to ensure a defined and thermodynamically optimal engine start. For this purpose, the residual pressure in the injection system can be further reduced during engine shutdown (for example, to approximately 300 bar).

[0004] Especially for commercial vehicles, the injection systems are usually designed to be capable of running in emergency situations. This means that pressure control valves are installed that ensure a certain minimum injection pressure (for example, approximately 900 bar) so that the vehicle can still be operated in the event of a malfunction. This pressure is usually higher than the idle pressure, so the injection pressure must be reduced, for example, via the injection systems themselves, to reach the idle pressure.

[0005] DE 10 2006 000 396 A1 discloses a control device for a direct-injection engine that injects fuel directly into each combustion chamber, as well as a control method therefor. The device comprises a pressure sensing device, a device for setting the target fuel pressure, a fuel pressure control device, and a stop determination device. The high-pressure pump is a piston pump with a cam that drives the piston. A fuel pressure control valve regulates the fuel quantity. The ECU executes routines to establish the target fuel pressure and determines whether engine shutdown is imminent. If shutdown is imminent, the target fuel pressure is set lower to prevent fuel leaks during stoppage.

[0006] DE 10 2008 007 668 A1 discloses a method and device for controlling a fuel metering system by regulating the fuel pressure depending on the operating state of the internal combustion engine. When the engine is switched off, the fuel pressure is controlled to a specific value. Under certain conditions, the fuel pressure is controlled to a different value. In particular, a distinction is made as to whether the engine is switched off using the control element or the start-stop control. This ensures that the rail pressure in the high-pressure area of ​​the common rail system is available more quickly upon restart. The method comprises queries and steps for controlling the actuator in order to adjust the fuel pressure accordingly. The fuel pressure is adjusted depending on various conditions, such as the operating state of the engine and the signals from the control element and the start-stop control.

[0007] DE 10 2009 017 472 A1 discloses a method for reducing the fuel pressure in a returnless fuel supply system of an internal combustion engine, particularly with direct injection, to a desired pressure level. When the engine is requested to shut down, the system is automatically switched to pressure reduction mode to prevent unnecessarily high fuel pressure and reduce the risk of fuel leakage. The engine control system adapts by first reducing the fuel pressure before interrupting injection. This allows for a longer delivery of engine torque, which can be compensated for by other measures. With direct injection, injection continues until the desired pressure level is reached. The fuel pump is controlled accordingly to prevent additional fuel from being supplied. Summary of the invention

[0008] The object of the invention is to reduce the fuel consumption of a vehicle with an internal combustion engine.

[0009] This object is achieved by the subject matter of the independent claims. Further embodiments of the invention emerge from the dependent claims and the following description.

[0010] One aspect of the invention relates to a method for controlling pressure in an injection system for a vehicle engine. For example, the engine may be a diesel engine that can be supplied with fuel by a high-pressure pump via a high-pressure injection system.

[0011] According to one embodiment of the invention, the method comprises the steps of: determining whether the vehicle is decelerating; reducing the delivery rate of a high-pressure pump that supplies fuel to the injection system; and reducing the pressure in the injection system to a standstill pressure by means of idling the engine.

[0012] For example, an electronic control unit can determine whether a vehicle driver has taken their foot off the accelerator or, more generally, whether the driver desires deceleration. A desired deceleration can also be determined from current vehicle data, such as the current speed.

[0013] The flow rate of the high-pressure pump can be reduced by closing a suction control valve at the pump inlet. It is possible to reduce the flow rate of the high-pressure pump to zero.

[0014] The pressure in the injection system can initially be reduced using a pressure control valve between the high-pressure pump and the injection system. Fuel is then directed back to the inlet of the high-pressure pump via the pressure control valve. This pressure control valve can be designed to maintain a predefined minimum pressure.

[0015] Furthermore, the pressure in the injection system can be reduced by releasing fuel from the injection system via injections into the engine.

[0016] The method further comprises the steps of: estimating a standstill time at which the vehicle comes to a standstill; and reducing the delivery rate of the high-pressure pump before the standstill time is reached, such that the standstill pressure in the injection system is reached at the standstill time. In this way, the engine can be switched off precisely when the vehicle comes to a standstill, or at least shortly thereafter, since a standstill pressure is already present in the injection system at this time or shortly thereafter, with which the engine can be restarted later. In this way, fuel can be saved, since it is not necessary to continue running the engine to reduce the pressure in the injection system after the vehicle has come to a standstill.

[0017] In particular, the recuperation phases used in hybrid and / or start / stop vehicles to save fuel do not need to be significantly affected. This avoids prolonging the engine run-on time when the vehicle is stationary, which is also relevant to fuel consumption.

[0018] According to one embodiment of the invention, the downtime is estimated based on an average deceleration since the vehicle began decelerating. To ensure sufficient accuracy in predicting the time until the vehicle comes to a standstill, the average deceleration can be recalculated with an appropriate resolution.

[0019] According to one embodiment of the invention, the method further comprises the step of determining a period of time required to reduce the pressure of the injection system to the standstill pressure by means of idle operation. The delivery rate of the high-pressure pump can be reduced at a time that is (essentially exactly) before the determined period of time before the standstill time. In other words, the period of time required to reduce the pressure can be subtracted from the estimated standstill time to determine the time to reduce the pressure in the injection system.

[0020] According to one embodiment of the invention, the period is calculated based on a volume of the injection system and an injection volume of fuel during idle operation. For example, if the high-pressure pump no longer delivers fuel, a volume of fuel can be calculated that must be delivered via the injection system to reduce the pressure to the desired value, i.e., the idle pressure.

[0021] According to one embodiment of the invention, the method further comprises the step of: operating the engine in overrun mode and / or recuperation mode during a period in which the vehicle is decelerating, such that the pressure in the injection system is reduced to a minimum injection pressure defined by a pressure control valve. In this case, the minimum injection pressure is the pressure from which the pressure in the injection system is to be reduced to the standstill pressure. To bring the engine into idle mode, the engine can then be disconnected from the drivetrain when the delivery rate of the high-pressure pump is reduced.

[0022] According to one embodiment of the invention, the method further comprises the step of: operating the engine in an idle mode during a period in which the vehicle is decelerating, such that the pressure in the injection system is reduced to an idle pressure. The engine may be disconnected from the driveline when the vehicle begins to decelerate. In this case, the idle pressure is the pressure from which the pressure in the injection system is to be reduced to the standstill pressure.

[0023] In both cases, the engine is disconnected from the drivetrain before the vehicle comes to a stop. This procedure allows the clutch timing to be advanced.

[0024] A further aspect of the invention relates to a computer program which, when executed on a processor, instructs the processor to perform the steps of the method as described above and below. The method can be implemented in a vehicle by providing a suitable software function for displaying or timing the injection pressure reduction in a control unit. The injection hardware does not need to be modified.

[0025] A further aspect of the invention relates to a computer-readable medium on which such a computer program is stored. The computer-readable medium can be, for example, a ROM, EPROM, or FLASH memory. It is also possible for the computer-readable medium to be a floppy disk or a hard disk.

[0026] A further aspect of the invention relates to a control unit for controlling a pressure in an injection system, which is designed to carry out the method as described above and below. For example, the control unit can have a processor designed to execute the above-mentioned computer program.

[0027] Another aspect of the invention relates to a vehicle, for example a commercial vehicle such as a truck, excavator, or bus. However, it is also possible for the vehicle to be a passenger car.

[0028] According to one embodiment of the invention, the vehicle comprises an engine, an injection system for injecting fuel into the engine, a high-pressure pump for supplying the injection system with fuel, and a control unit, as described above and below.

[0029] The engine can, for example, be a diesel engine that includes a common rail injection system as the injection system.

[0030] Furthermore, the vehicle can be a hybrid vehicle with an electric motor, which can be used as a generator, for example, in the vehicle's recuperation mode.

[0031] In summary, the method or the control unit can enable vehicles with a conventional commercial vehicle injection system to reduce the pressure in their injection system to the value required for engine restart by targeted injection pressure reduction before engine stop phases. Short description of the characters

[0032] In the following, embodiments of the invention are described in detail with reference to the accompanying figures. Fig. 1 schematically shows a vehicle according to an embodiment of the invention. Fig. 2 shows a diagram explaining a method for controlling a pressure in an injection system of a vehicle according to an embodiment of the invention. Fig. 3 shows a further diagram explaining a method for controlling a pressure in an injection system of a vehicle according to an embodiment of the invention.

[0033] In principle, identical or similar parts are provided with the same reference symbols. Detailed description of implementation examples

[0034] Fig. Figure 1 schematically shows a vehicle 10 comprising an internal combustion engine 12 as the drive, which can be supplied with fuel via an injection system 14. For this purpose, the vehicle 10 has a high-pressure pump 16 that can deliver fuel under high pressure into the injection system 14.

[0035] The injection system 14 can inject fuel into the engine 12. The amount and timing of the injection can be used to determine how much fuel is delivered to the engine per unit of time by the injection system.

[0036] The pressure in the injection system 14 can be regulated via a pressure control valve 18, located between the high-pressure pump and the injection system. To equalize the pressure, fuel from the injection system 14 can be returned to the low-pressure circuit upstream of the high-pressure pump 16 via the pressure control valve 18. The pressure control valve 18 is designed such that a minimum injection pressure is maintained even when the pressure control valve 18 is open. This ensures that the vehicle 10 remains operational even if the pressure control valve 18 is defective.

[0037] A suction control valve 20 located at the inlet of the high-pressure pump can be used to adjust the amount of fuel delivered by the high-pressure pump 16. The more the suction control valve 20 is closed, the more the delivery capacity of the high-pressure pump 16 decreases.

[0038] In addition to the internal combustion engine 12, the vehicle may also include an electric motor 22, which, like the internal combustion engine 12, may be coupled to a drivetrain 24 of the vehicle 10. In other words, the vehicle 10 may be a hybrid vehicle.

[0039] A programmable controller 26 of the vehicle 10 with a processor can control the injection system 14, the pressure control valve 18, the high-pressure pump 16, and the suction control valve 20. The controller can perform a method for controlling the fuel pressure in the injection system 14, as described with reference to the following two figures.

[0040] The Fig. 2 shows in the upper part a diagram with the speed 30 of the vehicle 10 versus time t, which describes a start / stop operation of the vehicle 10.

[0041] Before time t0, the vehicle travels at a constant speed v1. At time t0, the driver of vehicle 10 begins to brake. The vehicle decelerates between times t0 and t1, coming to a stop at time t1, and the engine 12 of vehicle 10 is turned off. Later, at time t2, the driver presses the accelerator pedal to accelerate the vehicle 10 again, and the engine 12 is restarted at time t2. After a starting and idling phase between times t2 and t3, the vehicle 10 begins to move off and accelerate again at time t3.

[0042] The control unit 26 is designed to determine that the vehicle 10 should be decelerated. For this purpose, current vehicle data, such as a determined position of the accelerator pedal lever or the brake pedal lever, can be used.

[0043] From the overrun transition of the vehicle 10 at time t0, ie during the deceleration, the average deceleration of the vehicle 10 is estimated by the control unit 26 from further current vehicle data, such as the current speed. From the average deceleration, the control unit 26 can then determine the period Δt v until the vehicle 10 comes to a standstill at time t1. This calculation can be repeated regularly after time t0 to account for a changing current deceleration.

[0044] In the lower area the Fig. 2 a diagram with the pressure 32 in the injection system 14 of the vehicle 10 versus time t.

[0045] While the vehicle 10 is moving at the constant speed v1, the injection system 14 has a pressure p1 of, for example, approximately 1,100 bar.

[0046] After the time t0, when an intended deceleration of the vehicle has been detected, the engine 12 then remains in overrun mode (ie remains coupled to the drive train 24) and the pressure 32 in the injection system 14 is reduced by the control unit 26 as far as possible, as is possible with the pressure control valve 18, ie to the minimum injection pressure p M , which can be around 900 bar, for example.

[0047] Alternatively or additionally, the vehicle 10 may be in recuperation mode by using the electric motor 22 as a generator to convert kinetic energy into electricity via the drive train 24.

[0048] From the current pressure 32 in the injection system 14 and known (predetermined) data of the injection system, such as the fuel volume present in the injection system and the fuel volume injected when the engine 12 is idling, the control unit 26 determines the period Δt P , which is necessary to reduce the pressure 32 in the injection system 14 to a desired (predetermined) standstill pressure p S to reduce.

[0049] The standstill pressure p S corresponds to the pressure 32 with which the engine 12 is to be shut down at time t1 and then subsequently restarted at time t2. p S can be determined thermodynamically optimally for engine restart and is, for example, approximately 300 bar.

[0050] For example, the period Δt P = 3.6 sec at an initial pressure at the minimum injection pressure p M of 900 bar, a final pressure at standstill pressure pS of 300 bar, a volume of the injection system 14 of 70 cm 3 , and an injection volume of 20 mm 3 at 6 cylinders and 600 rpm.

[0051] From the period Δt P and the time t1 at which the vehicle 10 is likely to come to a standstill, the control unit determines the time t S = t1 - Δt P , from which the pressure 32 in the injection system 14 is to be reduced, so that at time t1 the desired pressure p S When calculating t S Delay times, which can arise, for example, due to finite switching times, can also be taken into account.

[0052] At time t SThe control unit 26 reduces the delivery rate of the high-pressure pump 16 (for example, completely to 0) by closing the suction control valve 20 accordingly, and disconnects the engine 12 from the drive train 24, so that the engine 12 operates at idle. Through idle injections, the pressure 32 in the injection system 14 is now increased to a defined, applicable desired value p S reduced.

[0053] In order to separate the vehicle thrust from the engine idling required for pressure reduction as much as possible and thus to enable the recuperation process, which is possible in hybrid vehicle applications depending on the topology, to a large extent, the engine idling is only started at the latest possible time t S requested and executed before the vehicle comes to a standstill at time t1.

[0054] If the deceleration is aborted before the vehicle comes to a standstill at time t1, the correct injection pressure for continued driving or acceleration is always guaranteed up to a certain point, since the pressure reduction to the standstill pressure p S only at the latest possible time t S shortly before vehicle 10 comes to a standstill.

[0055] In the Fig. For comparison, Figure 2 shows another possible pressure curve 34 for the pressure in the injection system 14, which occurs when the engine is idling during deceleration.

[0056] This process is in the Fig. 3, which is a diagram analogous to the Fig. 2 represents.

[0057] In contrast to the process of Fig. 2, shortly after time t0, at which a desired deceleration is detected, the motor 12 is disconnected from the drivetrain 24 (for example, by disengaging a clutch). The vehicle then enters a so-called coasting mode ("free rolling"), in which free rolling with the clutch disengaged can occur without recuperation. The motor 12 is then idling.

[0058] As a result, the pressure 34 drops to an idle pressure p during the beginning of the deceleration phase L , which can be, for example, 600 bar. The injection pressure 34 is therefore initially adjusted via the injection to the applied idle pressure p L reduced by the control unit 26 opening the pressure control valve 18 and operating the engine 12 in idle mode.

[0059] Analogous to the Fig. 2, the control unit 26 now determines the time periods Δt V , Δt P ' and the time t S', whereby the current pressure from which we assume is now the idle pressure pL.

[0060] The period Δt P ' before the predicted vehicle standstill or engine stop at time t1, the pressure reduction to p S by the control unit 26, for example by setting the desired pressure at time t S ' the suction control valve 20 is closed.

[0061] Additionally, it should be noted that "comprising" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. Furthermore, it should be noted that features or steps described with reference to one of the above embodiments may also be used in combination with other features or steps of other embodiments described above. Reference signs in the claims are not to be considered as limitations.

Claims

[1] Method for controlling a pressure (32, 34) in an injection system (14) for an engine (12) of a vehicle (10), the method comprising the steps: Determining whether the vehicle (10) is decelerating; Reducing the delivery rate of a high-pressure pump (16) which supplies the injection system (14) with fuel; Reducing the pressure in the injection system (14) to a standstill pressure (p S ) by means of an idling operation of the engine (12); characterized by Estimating a standstill time (t1) at which the vehicle (10) comes to a standstill; Reducing the flow rate of the high-pressure pump (16) before the standstill time (t1) is reached, so that at the standstill time (t1) the standstill pressure (p S ) in the injection system (14). [2] Method according to claim 1, wherein the standstill time (t1) is estimated based on an average deceleration since the start of the deceleration of the vehicle (10). [3] The method according to claim 1 or 2, further comprising the step: Determining a period (Δt P , Δt P '), which is necessary to reduce the pressure (32, 34) in the injection system (14) to the standstill pressure (p S ) to reduce; wherein the delivery rate of the high-pressure pump (16) at a time (t S , t S ') which is before the determined period before the downtime. [4] Method according to claim 3, wherein the period (Δt P , Δt P ') is calculated based on a volume of the injection system (14) and an injection volume of fuel during idle operation. [5] Method according to one of the preceding claims, further comprising the steps: Operating the engine (12) in overrun mode and / or recuperation mode during a period in which the vehicle (10) decelerates, so that the pressure (32) in the injection system (14) drops to a minimum injection pressure (P M ) defined by a pressure control valve (18); Disconnecting the engine (12) from a drive train (24) when the delivery rate of the high-pressure pump (16) is reduced. [6] Method according to one of claims 1 to 4, further comprising the steps: Disconnecting the engine (12) from a driveline (24) while the vehicle (10) is decelerating; Operating the engine (12) in an idle mode during a period in which the vehicle (10) is decelerating, so that the pressure (34) in the injection system drops to an idle pressure (p L ) is reduced. [7] A computer program which, when executed on a processor, directs the processor to perform the steps of the method according to any one of the preceding claims. [8] A computer-readable medium having stored thereon a computer program according to claim 7. [9] Control device (26) for controlling a pressure (32, 34) in an injection system (14), which is designed to carry out the method according to one of claims 1 to 6. [10] Vehicle (10), comprising: an engine (12), an injection system (14) for injecting fuel into the engine (12); a high-pressure pump (16) for supplying the injection system (14) with fuel; and a control device (26) according to claim 9.

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