EP0668965B1

EP0668965B1 - Control system for high-pressure fuel injection system for an internal combustion engine

Info

Publication number: EP0668965B1
Application number: EP94926233A
Authority: EP
Inventors: Riccardo Buratti; Paolo Tubetti
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1993-09-03
Filing date: 1994-09-02
Publication date: 1998-12-09
Anticipated expiration: 2014-09-02
Also published as: EP0668965A1; ITTO930645A0; DE69415140T2; JP3865767B2; IT1261574B; DE69415140D1; WO1995006813A1; JPH08503052A; ITTO930645A1

Abstract

An injection control system including a number of maps for determining various injection control quantities (Q, P, ANT, ET) on the basis of power demand (Vα) and engine speed (N). In the steady-state condition, fuel injection quantity (Q) is first calculated; injection pressure (P) and advance (ANT) are calculated on the basis of fuel injection quantity; and injection time (ET) is calculated on the basis of fuel injection quantity and injection pressure. Injection pressure is closed-loop controlled (30) by controlling the duty cycle of the supply current of a pressure regulating solenoid valve (7) connected to a high-pressure pump (6).

Description

TECHNICAL FIELD

The present invention relates to an injection control system for internal combustion engine high-pressure injection systems.

BACKGROUND ART

A high-pressure injection system substantially comprises a fuel tank, and a high-pressure injector supply circuit in turn comprising a pump for supplying fuel at high pressure to a manifold in turn supplying a number of injectors. The pump presents a pressure regulating solenoid valve for supplying fuel at a predetermined pressure.

The EP-A-501 463 discloses a common rail high pressure fuel injection system, which comprises a fuel tank, and a high-pressure injector supply circuit in turn comprising a pump for supplying fuel at high pressure to a manifold in turn supplying a number of injectors. The pump presents a pressure regulating solenoid valve for supplying fuel at a predetermined pressure. The fuel pressure is PID feed-back controlled using the input from a pressure sensor by controlling the on time of a solenoid valve. One table is used for determining the fuel injection quantity as a function of engine parameters.

For best vehicle performance in terms of power, consumption, smoke level, exhaust and drivability, operation of the engine must be controlled to ensure the right quantity of fuel is injected at each injection with the right timing and pressure. Injection pressure in particular affects several injection parameters, such as fuel injection quantity for a given injection time; the fuel injection plan (volume per unit of time); fuel atomization; jet penetration; actual injection time; and duration of the electric signal; which parameters greatly affect engine performance, especially in terms of output, exhaust, noise level and drivability.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide an injection control system for electronically controlling fuel injection quantity, injection advance (timing) and injection pressure with a high degree of resolution and flexibility, and as a function of the state of the engine (as indicated by speed, temperature, pressure and load values) and of power demand (as indicated by the position of the accelerator pedal).

According to the present invention, there is provided an injection control system for internal combustion engine high-pressure injection systems, comprising a number of injectors for injecting fuel at high pressure on the basis of injection control quantities; characterized in that it comprises regulation generating means for generating values regulating the injection control quantities on the basis of engine parameters; and control means for controlling the injection control quantities on the basis of said regulating values, according to claim 1.

BRIEF DESCRIPTION OF DRAWINGS

A preferred non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1 shows an overall diagram of the hydraulic system of an injection system to which the control system according to the present invention is applied;

Figure 2 shows a detail of the pressure regulator of the Figure 1 system;

Figures 3-6 show block diagrams illustrating control of the controlled quantities according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A general description will now be given, with reference to Figure 1, of a high-pressure injection system for internal combustion engines. The system, indicated by 1, comprises a tank 2 at atmospheric pressure, connected by a delivery line 5 to a radial-piston pump 6 presenting a pressure regulating solenoid valve (or pressure regulator) 7 connected by drain line 8 to tank 2.

Pump 6 feeds the fuel at high pressure along line 11 to a manifold 10 which provides for distributing the fuel to the injectors and damping any fluctuation in pressure caused by the action of the pump and opening of the injectors. Manifold 10 consists of a steel body in the form of a parallelepipedon and in which is formed a cylindrical cavity extending along the length of the manifold and connected to line 11 by a central hole 12. Manifold 10 also presents four holes 13 spaced along the length of the manifold and connected to four high-pressure (up to 1500 bar) supply conduits 14 of four injectors 15 of an engine 16. Each injector 15 is also connected to a conduit 17 for recirculating the drive valve operating fuel into tank 2.

Manifold 10 is fitted at one end with a known pressure sensor 18.

Pressure regulator 7 is conveniently formed as shown in Figure 2, and comprises a body 20 defining a conical seat 21 for a spherical shutter 22. By means of a push rod 23, shutter 22 is subjected to the combined force of a spring 24 and a solenoid 25 which cooperates with a core 26 integral with a rod 27 in turn integral with push rod 23. Varying the current supply to solenoid 25 regulates the force exerted on spherical shutter 22 in the closing direction and, hence, the output pressure of pump 6.

Pressure is regulated by supplying solenoid 25 with a current whose duty cycle is modulated at a fixed oscillation frequency (PWM - Pulse Width Modulation - technique) and using a closed regulating loop which takes into account the actual pressure measured by pressure sensor 18, as shown in the Figure 3 diagram described below.

A description will now be given of the control system according to the present invention, which is based on the observation that each instant in the operation of the engine is characterized by a given engine speed and load (torque). As load is in turn related to the quantity of fuel injected at each injection, controlling the fuel injection quantity therefore provides for regulating the power of the engine.

The relationship between load and the quantity of fuel injected at each point in the operation of the engine may be determined by bench testing the engine and simultaneously measuring load and fuel consumption. Bench testing also provides for determining the best injection pressure, injection advance and injection time adjustments and so obtaining control maps as a function of load and engine speed, i.e. as a function of fuel injection quantity and engine speed.

According to the present invention, operation of the engine is controlled using such maps. That is, on determining power demand by the user and the fuel quantity required for meeting it, the control system determines, by means of the maps, the adjustments to be made for ensuring correct operation of the engine.

The fuel injection quantity Q is calculated as shown in Figure 3. More specifically, during startup, a map 40 is used, having as inputs engine speed N and the temperature of the engine (e.g. of the coolant) or of the oil in the case of air-cooled engines. As such, output QO is in no way limited, and is independent of the position of the accelerator pedal.

At steady speed, a quantity QCARB is first calculated by means of a map 42 called a regulating map (by virtue of performing the same function as a normal mechanical pump regulator) and having as inputs engine speed N and a quantity Va related solely to the position of the accelerator pedal. If the closed-loop idling speed control is activated and engine speed is below a given threshold value, a parallel calculation is made of the fuel quantity QCMIN required to sustain the engine at zero power demand and low engine speed. QCMIN is calculated by means of a proportional-integral closed-loop control algorithm based on the error between a target idling speed and engine speed N; and, as a function of the error, a calculation is made of the fuel quantity QCMIN required to restore the target speed. The control algorithm is represented in Figure 3 by idling speed control block 43. Subsequently, the QCARB value is compared with QCMIN in block 44 to give a value Q1 corresponding to the greater of the two.

To control the smoke level at the exhaust when accelerating - as required by turbosupercharged diesel engines, due to the delay in adaptation of the supercharge pressure caused by the high degree of inertia of the turbosupercharger - provision is made for limiting the fuel quantity; which limitation is calculated by means of a smoke limiting map 45 having as inputs the air intake QA at each cycle, measured by means of a device at the intake, and engine speed N. The output QCMAX of map 45 is compared with Q1 in block 46 to give a value Q2 corresponding to the lesser of the two.

The fuel quantity is finally limited by means of a one-dimensional (power limiting) map 47 having engine speed N as the input and in which are stored the maximum acceptable fuel quantities at high power (fully pressed accelerator pedal). The output QCPOW of map 47 is compared with Q2 in block 48 to select the lesser of the two values, which represents the steady-state fuel injection quantity Q3. Quantity Q3 is used during steady-state operation, as shown schematically in Figure 3 by switch 41 which represents, ideally, selection of value QO or Q3 according to the operating condition of the engine (startup or steady state). Figure 3 of course merely illustrates the operating principle of the two processing operations performed respectively in the startup/steady-state condition, in that Q0 and Q3 are never calculated simultaneously, and switch 41 is purely indicative of enabling by the type of processing operation performed.

As already stated, fuel quantity Q is used for regulating the engine, comprising regulation of injection pressure, injection advance and injection time, which will now be described with reference to Figures 4, 5 and 6 respectively.

As shown in Figure 4, the injection pressure regulating system, indicated as a whole by 30, is a closed-loop type, and comprises a pair of

maps

31, 32 for calculating a reference pressure correlated to the state of the engine. More specifically, map 31 provides for calculating steady-state reference pressure P_R1 on the basis of engine speed N and fuel injection quantity Q (corresponding to steady-state value Q3 calculated as described with reference to Figure 3); while map 32 provides for calculating startup reference pressure P_R2 as a function of engine temperature T and engine speed N, to take into account the requirements of the engine at different startup temperatures.

Via an ideal switch 33, the outputs of

maps

31, 32 are connected selectively to the noninverting input of an error comparator 34, the inverting input of which is connected to the output of a filter 35 supplied with a signal correlated to the actual pressure measured by sensor 18 fitted to manifold 10.

The output of comparator 34, presenting error signal E, is connected to the input of a regulating element 36 and to a memory 37 whose output is also connected to regulating element 36. On the basis of the error between the reference and actual pressures, and of a proportional-integral control algorithm, regulating element 36 provides for controlling the duty cycle of the supply current to solenoid 25 (Figure 2). In practice, the output of regulating element 36 is connected to memory 37, and also controls an actuator 38 supplying solenoid 25.

The output of sensor 18 is conveniently read every 5 ms; the read pressure signal is filtered by filter 35 and compared with the reference pressure value from

map

32 or 31, depending on whether the engine is in the startup or steady state respectively; the error E between the actual and reference pressure values is supplied to regulator 36 and to memory 37 which stores it for use in the following cycles; and regulator 36 calculates the duty cycle on the basis of a proportional-integral algorithm.

More specifically, the regulating element determines a new duty cycle percentage value (ranging from 1 to 99%) which in turn affects the force generated by solenoid 25 on spherical shutter 22. In -particular, the sign and value of error E determine the amount by which the duty cycle is varied, which in turn provides for so varying pressure as to achieve the required pressure value (set by the maps). When the duty cycle of the current supply to solenoid 25 is increased, this increases the force exerted on shutter 22 and hence the pressure inside the hydraulic circuit (conduits 11, 14, manifold 10). Similarly, a reduction in the duty cycle provides for a reduction in pressure.

Injection advance is determined as shown in Figure 5. More specifically, during startup, injection advance is determined by means of a map 50 (startup advance map) having as inputs engine speed N and engine temperature T, and generating an output value ANT0.

At steady speed, injection advance is calculated by means of two maps: a base map 51 and a correction map 52. Base map 51 presents as inputs fuel injection quantity Q (corresponding to steady-state value Q3 calculated as described with reference to Figure 3) and engine speed N, and generates a base advance value normally used for high-temperature operation of the engine; while correction map 52 presents as inputs engine speed N and engine temperature T, and provides, as a function of the input quantities, for determining an advance correction for low-temperature operation of the engine.

Outputs ANT1 and ANT2 of

maps

51 and 52 are added in adding block 53 to give a value ANT3 which is used during steady-state operation as shown schematically in Figure 5 by switch 54 which represents, ideally, selection of the ANT0 or ANT3 value, depending on the operating condition (startup or steady state) of the engine.

Injection time ET is determined as shown in Figure 6. More specifically, during startup, injection time is determined as a function of fuel injection quantity Q (corresponding to value Q0 in Figure 3) and pressure P (output of filter 35 in Figure 4) measured just prior to injection, by means of a map 60 (startup ET map) supplying an output value ET0. If ET0 equals zero, no fuel is injected; if ET0 is above a maximum permissible value (e.g. 3000 µs), injection time is limited to the maximum permissible value (in a manner not shown in Figure 6).

At steady speed, injection time is determined as a function of fuel injection quantity Q (corresponding to value Q3 in Figure 3) and pressure P measured just prior to injection, by means of a map 61 supplying an output value ET1. In this case also, if ET1 equals zero, no fuel is injected (cut-off condition); and the maximum injection time is limited to a maximum permissible value (e.g. 1500 µs) in a manner not shown.

In this case also, the ET0 and ET1 values are calculated selectively, depending on whether the engine is in startup or the steady state, as shown schematically by switch 62.

The control system described thus provides for adapting the controlled injection variables to the operating condition of the engine, for ensuring the best values of the various injection parameters, such as atomization, jet penetration and injection plan, for each condition.

The system described also provides for a high degree of reliability, and may be implemented using easy-to-implement software with no major alterations to the injection system.

Injection pressure in particular, which is of vital importance for controlling the other quantities, is closed-loop controlled to ensure the best values are achieved at all times.

Clearly, changes may be made to the system as described and illustrated herein, for example, all the regulations described may be refined to take into account particular operating conditions of the engine.

Claims

An injection control system (30) for internal combustion engine high-pressure injection systems (1), comprising a number of injectors (15) for injecting fuel at high pressure (P) on the basis of injection control quantities (Q, P, ANT, ET); and regulation generating means (31, 32, 40-48, 50-53, 60, 61) for generating values regulating the injection control quantities (Q, P, ANT, ET) on the basis of engine parameters (N, Vα, T, QA); and control means (34-38) for controlling the injection control quantities on the basis of said regulating values; and pressure detecting means (18) for detecting an actual injection pressure value; and error detecting means (34) for generating an error signal related to the difference between a reference pressure value and said actual injection pressure value; said error signal being supplied to said regulating means (36-38) to obtain an injection pressure value equal to said reference pressure value; characterized in that it comprises first and second memory means (31, 32) for calculating the reference pressure value, having respective inputs supplied with signals relative to engine parameters; and switching means (33) having an output connected to said regulating means (36-38), and which selectively connect said first and second memory means to said regulating means according to the operating condition of said engine, said first and second memory means (31, 32) respectively relate to a steady-state and a startup condition of the engine; said engine parameters comprising engine speed and fuel injection quantity for said first memory means, and engine speed and engine temperature for said second memory means.
A system as claimed in Claim 1, comprising a solenoid valve (7) for regulating the pressure of a high-pressure pump (6) supplying said injectors (15); characterized in that said control means comprise regulating means (36-38) for varying the duty cycle of the supply current of said solenoid valve.
A system as claimed in Claim 1 or 2, wherein said injection system comprises a manifold (10) interposed between said pump (6) and said injectors (15); characterized in that said pressure sensor (18) fitted to said manifold (10).
A system as claimed in any one of the foregoing Claims from 1 to 3, characterized in that said error detecting means comprise a comparator (34) having a first input connected to the output of said pressure detecting means (18), and a second input connected to said generating means (31, 32); and said regulating means comprise a proportional-integral regulator (36).
A system as claimed in Claim 4, characterized in that it comprises third memory means (37) having inputs connected to said error detecting means (34) and said regulator (36), and an output connected to said regulator; said third memory means storing preceding error signals.
A system as claimed in Claim 4 or 5, characterized in that it comprises filter means (35) interposed between said pressure detecting means (18) and said comparator (34).
A system as claimed in any one of the foregoing Claims from 1 to 6, characterized in that said regulation generating means comprise startup generating means (40) for generating a first fuel injection quantity value as a function of engine speed and engine temperature; regulating generating means (42) for generating a second fuel injection quantity value as a funtion of engine speed and power demand; closed-loop control means (43) for controlling a minimum quantity as a function of engine speed and engine temperature; smoke limiting generating means (45) for generating an acceleration smoke limiting value as a function of air intake and engine speed; power generating means (47) for generating a power limiting value as a function of engine speed; first selecting means (44) for selecting the greater of said second value and said minimum quantity; second selecting means (46) for selecting the lesser of the output of said first selecting means and said acceleration smoke limiting value; and third selecting means (48) for selecting the lesser of the output of said second selecting means and said power limiting value.
A system as claimed in Claim 7, characterized in that said regulation generating means comprise startup advance generating means (50) for generating a first advance value as a function of engine temperature and engine speed; base advance generating means (51) for generating a second advance value as a function of fuel injection quantity and engine speed; correction generating means (52) for generating a correction value as a function of engine temperature and engine speed; and correcting means (53) for adding said second advance value and said correction value.
A system as claimed in Claim 7, characterized in that said generating means comprise startup injection time generating means (60) for generating a first injection time value as a function of fuel injection quantity and injection pressure; and steady-state injection time generating means (61) for generating a second injection time value as a function of fuel injection quantity and injection pressure.
A system as claimed in any one of the foregoing Claims, characterized in that said generating means comprise memorized maps.