WO1989007195A1

WO1989007195A1 - Process for metered injection of fuel

Info

Publication number: WO1989007195A1
Application number: PCT/DE1989/000012
Authority: WO
Inventors: Anton Karle
Original assignee: Robert Bosch Gmbh
Priority date: 1988-01-28
Filing date: 1989-01-11
Publication date: 1989-08-10
Also published as: DE3802418A1

Abstract

In a process for metered injection of fuel in a distributor-type fuel injection pump, the metered quantity of fuel is governed by the duration of closure of a solenoid valve (29) arranged in a connecting line between the working and discharge chambers of the pump. The duration of closure of the solenoid valve (29) is determined from the ratio of a theoretical angle of rotation of the pump piston (14) for the injection stroke, calculated in function of engine operating parameters, and a constant angle of rotation covered by a measurement window evaluated over time, multiplied by the flow time measured in the measurement window. To determine changes in engine speed between the time of evaluation of the measurement window and the injection of fuel, a metering window covering an identical angle is evaluated over time during the injection of fuel and a correction factor is calculated from the ratio of the metering and measurement window times and used to correct the measured duration of closure of the solenoid valve (29) during the next piston stroke.

Description

Method of metering fuel injection quantity

State of the art

The invention relates to a method for metering the fuel injection quantity in a fuel injection pump of the distributor type for internal combustion engines of the type defined in the preamble of claim 1.

Such a method with transformation of certain delivery strokes of the pump piston representing angles of rotation of the pump piston into a closing time for the solenoid valve is described in the German patent application P 37 21 352.0. In order to record the instantaneous speed of the pump piston and thus the instantaneous speed of the internal combustion engine when metering the injection quantity, a defined measurement window immediately before the start of injection is evaluated and thus the time for the required injection quantity, the required closing time of the solenoid valve is calculated.

As studies have shown, however, the instantaneous speed between the measurement window and the actual metering changes during engine operation of the internal combustion engine, and thus the basis for calculating the metering time, so that a considerable error can occur during metering. For this purpose, reference is made to FIG. 1 of the drawing, in which the speed curve of the crankshaft (a) and camshaft (b) of a four-cylinder engine is included

Distributor fuel injection pump over the angle of rotation of the pump piston at an average speed of 1200 rpm and an average load is shown. The different speed curve on the crankshaft and camshaft is caused by the unavoidable vibration of the belt connecting the camshaft to the crankshaft. The diagram clearly shows that there is a drop in speed of approx. 70 rpm between the speed in the measuring window and the speed during metering. The closing time of the solenoid valve calculated on the basis of the instantaneous speed prevailing in the measuring window is therefore too small with regard to this drop in speed at the moment of metering. The insufficient fuel metering leads to a further drop in engine speed. Overall, a positive feedback effect sets in, which is due to the imprecise

Fuel metering leads to a significant drop in engine speed.

Advantages of the invention

The inventive method with the characterizing features of claim 1 has the advantage that speed changes between the time of the calculation of the closing time and the actual metering and the calculated closing time of the check valve is extended or shortened in accordance with the amount of the speed drop or the speed increase. The correction or weighting factor is indeed based on measurements during the previous injection stroke of the injection

Pump piston determined, but changes in speed between two stroke periods of the pump piston - in contrast to speed change within the stroke period of the pump piston between the measurement window and metering are negligible. For this purpose, reference is made to FIG. 1 of the drawing, where a total of three of four stroke periods are shown during one revolution of the pump piston. The minima and maxima of the speed curve as well as the measurement window and the metering pulses are each 90 ° apart, based on a rotation of 360 ° of the pump piston. It can clearly be seen that the speed is approximately constant at the same points in the individual stroke periods. In the method according to the invention, the drop in speed between the measuring window and the actual metering in each stroke period is compensated for by the fact that the

Throughput time of the measuring window determined closing time of the check valve is corrected with the ratio of the angular velocity in the measuring window to the angular velocity during the metering. Since the speed drop until metering

Angular velocity decreases, the closing time of the check valve is extended in the correct way and thus counteracts the speed reduction. Since the instantaneous speeds are almost constant at the same points in successive injection strokes of the pump piston at a constant mean speed, no error is made in that the correction factor is determined in the immediately preceding injection stroke. Do measurement windows and metering windows be made with regard to the span they span

Angle of rotation of the same size, so you can as a correction or Instead of the ratio of the angular velocities, the weighting factor directly uses the ratio of the throughput time of the metering window to the throughput time of the measurement window.

One could consider compensating the metering error caused by the change in speed in the known method - in contrast to the method according to the invention - by using the speed curve - for example according to FIG. 1 of the drawing - to obtain a correction factor V as the ratio of the amount of speed in the measuring window and the amount of the speed during the metering pulse and thus multiplies the closing time of the check valve determined in the measurement window on the basis of the throughput time measurement. However, this presupposes the recording of such speed curves for a large number of average speeds, which can be done, for example, in a test bench measurement of the engine or the internal combustion engine, and their reproducibility.

However, the method according to the invention also has significant advantages over such a correction method. On the one hand, there is no need to record a map (application) formed from the large number of speed curves. On the other hand, such speed errors are also detected, which arise from the scatter of specimens of the internal combustion engine. In contrast to this, only typical characteristic maps can be stored due to the measurement outlay in the method outlined and can generally be used for all fuel injection pumps to correct the closing time of the check valve. Individual deviations from these maps are not taken into account. Finally, in the method according to the invention, changes in speed caused by more or less large belt lots between the crankshaft and camshaft also do not lead to errors in the metering of the fuel injection quantity. For this purpose, reference is made to FIG. 2 of the drawing, in which the same diagram as in FIG. 1 is shown, but for a loose belt between crankshaft (a) and camshaft (b). In comparison to Fig. 1, the enlarged is clearly

Speed drop between the area of the measuring window and the area of the actual metering can be seen, which here is about 80 rpm. This speed difference could not be compensated for by means of a stored map as described above. In the method according to the invention, however, such speed differences are also detected by individual speed measurements for each fuel metering and the metering duration is corrected accordingly.

By the specified in the further claims 3-6

A device for carrying out the method according to the invention can be implemented at a

Advantageously implement fuel injection pump of the distributor type.

drawing

The invention is explained in more detail in the following description with reference to an embodiment shown in the drawing. Show it:

Fig. 1 each has a diagram of the speed curve and 2 on the angle of rotation on the crankshaft (a) and camshaft (b) of a four-cylinder engine with

Distributor injection pump with fixed (Fig. 1) or loose (Fig. 2) belt for coupling the crankshaft and camshaft,

Fig. 3 is a schematic diagram of a fuel injection pump of the distributor type for a four-cylinder internal combustion engine,

4 shows a longitudinal section of a specific embodiment of the fuel injection pump in FIG. 3,

Fig. 5 in temporal assignment excerpt diagrams of the time course of the

Cam lift curve (a) on the cam drive of the fuel injection pump in Fig. 3 or 4, the output signal (b) of an angle wheel sensor for defining measurement and metering window, the control voltage (c) on the solenoid valve and

Movement strokes (d) of the solenoid valve in the fuel injection pump according to FIG. 3 or 4.

Description of the embodiment

In the fuel injection pump of the distributor type shown schematically in FIG. 3 and in longitudinal section in FIG. 4, a bushing 12 is arranged in a bore 10 of a housing 11, in the cylinder bore 13 of which a pump piston 14 in a known manner a reciprocating and at the same time rotating movement executes. The pump piston 14 is driven by a cam drive 15 via a shaft 16 which rotates synchronously with the speed of the internal combustion engine supplied with fuel by the fuel injection pump. A pump working space 17 is delimited from the end face of the pump piston 14 and communicates with a pump via a supply channel 18

Low-pressure fuel chamber or suction chamber 19 in the housing 11 of the fuel injection pump is connected. The suction chamber 19 is supplied with fuel via a feed pump 20, which is seated on the shaft 16 in a rotationally fixed manner. The feed pump 20 is supplied via a feed line 21 from a fuel, not shown

Aspirates fuel tank. From the pump work room 17 is distributed via a distributor opening 22, which opens at the circumference of the pump piston 14 and is permanently connected to the pump working chamber 17 via an axial channel 23, and distributes the fuel with appropriate rotation of the pump piston 14 to pressure lines 24 (FIG. 3). The

Pressure lines 24 lead via non-return valves 25 to injection nozzles 26 of the internal combustion engine. The number of pressure lines 24 supplied by the distributor opening 22 corresponds to the number of injection nozzles 26 to be supplied by the internal combustion engines. An equal number of cams 27 are provided in the cam drive 15. In the four-cylinder internal combustion engine shown here as an example of an internal combustion engine, each with one injection nozzle per combustion cylinder, there are a total of four pressure lines 24, four injection nozzles 26 and four cams 27 in the cam drive 15. The angle of rotation of the cams in the cam drive 15 is 90 °. In the end region of the pump piston 14 facing the pump work chamber 17, longitudinal grooves 28 on the circumference of the pump piston 14, which are open towards the end face and thus towards the pump work chamber 17, are provided, via which a connection between the supply channel 18 and the pump work chamber 17 is established during the suction stroke of the pump piston 14.

The bushing 12 and the end face of the pump piston 14 which delimits the pump working space 17, a solenoid valve 29 is screwed into the bore 10 (FIG. 4), so that the pump working space 17 can be closed off or relieved from the valve member of the solenoid valve 29. as shown schematically in Fig. 3, this is as

2/2-way valve designed solenoid valve 29 connected to the suction chamber 19. Depending on the switching position of the solenoid valve 29, the pump working space 17 is thus closed or connected to the suction space 19. The solenoid valve 29 is designed so that in the de-energized rest position Connection to the suction chamber 19 is established and the pump working chamber 17 is closed in the energized working position. The solenoid valve 29 is controlled by a control unit 30, which contains a control computer 31 which, depending on operating parameters of the internal combustion engine, such as speed, load, position of the accelerator pedal, temperature and the like, calculates the fuel injection quantity required for optimal operation of the internal combustion engine. A certain fuel injection quantity requires a certain delivery stroke of the pump piston 14 and, given cam tracks of the cams 27 in the cam drive 15, a certain angle of rotation φ _{Q of} the pump piston 14. The assignment of the operating parameters to the effective angle of rotation φ _{Q of} the pump piston 14 or the shaft 16 is shown in so-called Characteristic maps are stored so that the control computer 31 can determine the corresponding angle of rotation φ _Q from these characteristic maps on the basis of the operating data supplied to it.

Since the control device 31 for controlling the solenoid valve 29 cannot process angles of rotation but only times, a so-called angle-time system 32 is provided, with the aid of which the control computer 31 converts the determined injection-effective angle of rotation φ _{Q of} the pump piston 14 into a period of time corresponding to its speed can convert. The angle-time system 32 consists of an angle wheel 33, which is coupled in a rotationally fixed manner to the shaft 16 (FIG. 4), and of a sensor 34, which senses the angular position of the angle wheel 33. The bevel gear 33 initially has four tooth pairs 35, 36 which are evenly distributed over the circumference, the teeth of which are offset by approximately 10 ° relative to one another on the circumference of the bevel gear 33. Each pair of teeth 35, 36 spans a measuring window over a rotation angle of approximately 10 ° of the pump piston 14, in which the transit time of a point on the circumference of the pump piston 14 is determined through the measuring window. The The measuring window is opened as soon as the sensor 34 detects the passage of the first tooth 35 and closes again as soon as the sensor 34 detects the passage of the second tooth 36 of each pair of teeth 35, 36. Accordingly, two occur in the output signal of sensor 34

Voltage pulses as shown in Fig. 5b. The output signal of the sensor 34, which can be designed as a field plate, Hall sensor, inductive sensor or eddy current sensor, is fed to the control computer 31, which measures the throughput time T _{M of} the angular gear 33, ie the time between the two voltage pulses. The measurement can be carried out, for example, by a simple counter, which is clocked at a fixed counting frequency and started with the first voltage pulse of the measuring window and stopped with the second voltage pulse of the measuring window. Since the constant rotation angle φ _{0 of} the measuring window is known to the control computer 31, it can determine the closing time T _{Q of} the solenoid valve 29 from the injection angle φ _Q determined from the characteristic diagrams and the throughput time T _M

determine.

By driving the drive shaft 16, the pump piston 14 is rotated and, as a result of the rotating cams 27 rolling on a roller ring 39, leads alongside the

Rotary motion a reciprocating pump movement. If the pump piston 14 is located on the falling flank of the cam elevation curve (FIG. 5 a), it carries out a suction stroke in a known manner, in which the pump working space 17 is filled with fuel from the suction space 19. After passing through the bottom dead center position, the pump piston 14 is moved by the rising cam curve of the following cam 27 in an upward stroke, the so-called. Conveying stroke, driven. If the connection to the suction chamber 19 is interrupted, the fuel displaced by the pump piston 14 is conveyed via the distributor opening 22 into one of the pressure lines 24, with which the distributor opening 22 is connected in accordance with the rotational position of the pump piston 14.

The delivery of the fuel delivered under high pressure into the pressure lines 24 to the injection nozzles 26 is determined by the solenoid valve 29, which is energized by the control unit 30 at the start of delivery FB and thereby

Pump working space 17 completes opposite the suction space 19. After the closing time T _Q calculated by the control computer 31 within the computing time T _R after measuring the measuring window time T _M , the energization of the solenoid valve 29 is stopped by the control device 30. This returns to its rest position and connects the pump work space 17 to the suction space 19. At this moment, the high pressure in the pump work space 17 collapses and the remaining fuel delivered by the pump piston 14 is passed through the opened solenoid valve 29 until the top dead center position of the pump piston 14 is reached pushed out into the suction space 19. During the subsequent downward movement of the pump piston 14, the pump working space 17 is refilled with fuel as described above. The funding period is designated in Fig. 5a with FD. Due to the unavoidable switching times of the solenoid valve 29, this does not exactly match the time at which the solenoid valve 29 is energized or de-energized. The voltage pulses for energizing the solenoid valve 29 are shown in FIG. 5c, while the stroke movement of the valve member of the solenoid valve 29 can be seen in FIG. 5d.

In Fig. 1, the speed curve measured with an engine running at the average speed of 1200 rpm is over shows the angle of rotation, curve a representing the speed curve on the crankshaft and curve b representing the speed curve on the camshaft. The speed curve on the camshaft corresponds to the speed curve on the pump piston 14 via the rotation angle φ of the pump piston 14. The diagram shows the measurement window in which the throughput time T _{M is} measured by the angle-time system 32. A few angular degrees later, in the area of the delivery stroke of the pump piston 14, the injection takes place during the delivery period FD, referred to in the diagram as a metering pulse. It can clearly be seen that during the measurement of the throughput time T _M in the measuring window the instantaneous speed is much higher than during the injection in the metering pulse. As a result, the throughput time T _M measured at a higher speed leads to an error in the metering of the metered injection quantity. This error is now compensated for by the following procedure:

By means of the relative angle-time system 32, a further measurement window, the so-called metering window, is defined over a fixed rotation angle φ _{0 of} the pump piston 14 of likewise approximately 10 °. For this purpose, the angular gear receives 33 pairs of teeth 37, 38, which are in turn offset from one another by an angle which results from dividing 360 ° by the number of combustion cylinders, in the example with four cylinders at 90 °. Each pair of teeth 37, 38 is in turn assigned to a cam 27 of the cam drive 15. With regard to the cam elevation curve, the tooth pairs 37, 38 are arranged such that the sensor 34 senses the passage of the tooth pair 37, 38 during the injection stroke of the pump piston 14, that is to say when the fuel injection takes place when the solenoid valve 29 is closed. In the output signal of the sensor 34, two voltage pulses defining the metering window therefore occur during the delivery period FD, as is shown in FIG. 5b. in the control computer 31 the time interval is now the two pulses, the transit time T _Z through the metering window, determined. A correction or weighting factor K according to the ratio of the throughput time T _Z through the metering window and the throughput time T _M through the measurement window

calculated. With this correction factor K, the closing time T _Q determined in the measuring window in the immediately following stroke period of the pump piston 14 by the control device 30 on the basis of the renewed measurement of the throughput time T _M according to Eq. (1) multiplied according to

T _Q * = K. T _Q (3)

This results in the corrected metering time T _Q *, in which the change in speed between the measurement window and the actual fuel injection is taken into account, so that the metered amount of fuel is precisely matched to the speed at the moment of metering.

If the metering window is not stretched over the same angle of rotation φ _OM (here approx. 10 °) as the measuring window, but rather over a different angle of rotation φ _OZ , this must be taken into account in the correction factor K. The

Correction factor K is then calculated from the ratio of the angular velocities in the measuring window (ω _M ) and in the metering window (ω _Z )

With

and

As can easily be seen, if φ _OM = φ _OZ = φ _O , the correction factor K results again according to Eq. (2).

Claims

Expectations

1.Method for metering the fuel injection quantity in a fuel injection pump of the distributor type for internal combustion engines, in which the quantity of fuel conveyed for injection during the delivery stroke of a pump piston which is rotated and at the same time axially oscillating by a cam drive is injected by the closing duration (T _Q ) of a check valve, in particular one Solenoid valve is fixed, which is arranged in a relief line, which connects a pump work space delimited by the pump piston with a relief space, in particular a fuel-filled pump interior, and in which an injection-effective delivery stroke of the pump piston for determining the closing time (T _Q ) of the check valve Corresponding target rotation angle (φ _Q ) of the pump piston as a function of operating parameters of the internal combustion engine, such as speed, load, Accelerator pedal position and the like, calculated, preferably determined from a map, the throughput time (T _M ) measured by a measuring window spanned before the delivery stroke of the pump piston over a constant angle of rotation (φ _OM ) of the pump piston, and this with the ratio of the desired angle of rotation (φ _Q ) and measuring window rotation angle (φ _OM ) is multiplied, characterized in that in the area of the delivery stroke of the pump piston (14) a metering window is spanned over a constant rotation angle (φ _OZ ) of the pump piston (14) and the throughput time (T _Z ) is measured by it and that a weighting factor (K) is formed from the ratio of the angular velocity (ω _M ) in the measuring window and the angular velocity (ω _Z ) in the metering window, with which the closing time (T _Q ) calculated for the following delivery stroke of the pump piston (14) Check valve (29) is corrected.

2. The method according to claim 1, characterized in that the metering window and the measuring window are spanned over an equally large constant angle of rotation (φ _O ) of the pump piston (14) and the weighting factor (K) as a ratio of the throughput time (T _Z ) in the metering window and the throughput time (T _M ) is calculated in the measuring window.

3. Device for performing the method according to

Claim 1 or 2, characterized by an angular gear (33) rigidly coupled to the pump piston (14), the angular position of which is sensed by a fixed sensor (34), and in that the sensor signal is fed to a control device (30) with a control computer (31) is, which determines the metering window throughput time (T _Z ) and the measurement window throughput time (T _M ) and the Closing time (T _Q ) of the check valve (29) is calculated.

4. The device according to claim 3, characterized in that the angle wheel (33) for defining the measuring window and the metering window per stroke period of the pump piston carries a pair of teeth (35,36 or 37,38), the teeth (35,36 or 37, 38) are offset from one another by the constant angle of rotation (φ _O ) of the windows on the circumference of the angular gear (33), and that the sensor (34) is designed such that it generates a voltage pulse when each tooth (35 - 38) is rotated past generated.

5. Apparatus according to claim 4, characterized in that the teeth associated with the measuring window or metering window (35, 36 or 37, 38) are offset from one another by approximately 10 °.

6. Device according to one of claims 3-5, characterized in that the sensor (34) works inductively or e.g. is designed as a Hall sensor or eddy current generator.