EP0305736B1 - Control device for the glow plugs of a self-igniting combustion engine - Google Patents

Description

The invention relates to a method for controlling glow plugs of a self-igniting internal combustion engine. EP-A 0 018 257 describes a method for controlling glow plugs of a self-igniting internal combustion engine. This document describes a device for controlling glow plugs of a diesel engine. The device comprises an electronic control unit which controls various relays which release the current flow through the glow plugs. The power supply to the glow plugs is controlled depending on the temperature and the speed of the internal combustion engine. This device allows three different annealing processes, which are referred to as pre-annealing, annealing and post-annealing.

Another method for controlling glow plugs is described in DE-OS 36 24 664 published on 28-1-88. Thereafter, it is known to control glow plugs of a diesel engine with a duty cycle dependent on the battery voltage. The disadvantage of this method is that the selection of the parameters or information used in the control of the glow plugs is limited.

It is not possible with this device to take into account the effect of the amount of fuel injected on the temperature of the glow plugs. As a result, precise control of the glow plug temperature that is desired is not possible. With small injection quantities, the temperature required for optimal combustion is not reached. On the other hand, damage to the glow plugs cannot be ruled out with high injection quantities.

In contrast, the method according to the invention with the features of the main claim has the advantage that when the glow plugs are activated, relevant data present in the engine control unit, in particular the fuel quantity injected, are taken into account. As a result, the power supplied to the glow plugs and thus their operating temperature can be optimally adjusted. Advantageous further developments and improvements of the method specified in the main claim are possible through the measures listed in the subclaims. It is particularly advantageous that the duty cycle when controlling the glow plugs can be easily adapted to changes in the vehicle electrical system voltage.

• Figur 1 ein Blockschaltbild einer Motorsteuerung mit einer Schnittstelle;
• Figur 2 ein bei der Ansteuerung der Glühkerzen als Steuerbefehl dienendes Datenwort;
• Figur 3 zwei Impulsdiagramme von Datenbits und
• Figur 4 eine Tabelle zur Erläuterung von Datenworten.

An embodiment of the method is explained in more detail with reference to the figures. Show it:

• Figure 1 is a block diagram of a motor controller with an interface;
• FIG. 2 shows a data word that serves as a control command when activating the glow plugs;
• Figure 3 shows two pulse diagrams of data bits and
• Figure 4 is a table for explaining data words.

In the method according to the invention for controlling glow plugs, an interface is used which is between an electronic engine control MS, e.g. an electronic diesel control unit (EDC) and a glow system or a glow time control unit of an internal combustion engine.

FIG. 1 shows a block diagram of a motor control MS with an interface 1 and a glow system, of which only driver stages 2, glow plug monitoring 3 and overcurrent detection 4 are shown here for better clarity. The driver stages 2 serve to control a number of glow plugs, possibly also to control one or more glow plug control displays designed as a control lamp.

The interface 1 has a microprocessor MP which controls the driver stages 2 and which is connected to the glow plug monitoring 3 and the overcurrent detection 4. In addition, the interface on the input side is provided with a level converter 5, with which the data word output by the motor controller MS is converted to the levels required for the microprocessor MP. An input filter can also be contained in the level converter 5, with which unwanted interference signals can be eliminated. Correspondingly, a converter 6 is provided for the transmission of data words from the microprocessor MP to the motor control MS, which converts the level appropriately. Finally, a clock generator 7 and a switching device 8 are connected to the microprocessor MP, with which the microprocessor can be switched on and off and reset.

To control the glow plugs, a data word, as shown in FIG. 2, is transmitted serially to the interface 1 by the engine control MS. The data word has a start bit which indicates the start of the data word and a stop bit which indicates the end of the data word. There are 8 data bits D0 to D7 between the start and stop bit. D0 to D4, as can be seen from FIG. 4, determine the duty cycle with a resolution of approximately 3%. A preheat indicator lamp L1 (not shown here) can be controlled by data bit D5, for example. A diagnosis call can be made via data bit D6. D7 can be provided for further special tasks, for example for controlling a second lamp L2. The lamp L2 is activated, for example, when the vehicle is ready to start.

The following applies to the statement of data bits D5 and D6: if D5 assumes the logical value "1", the preheat indicator lamp is switched on, otherwise it is switched off. Accordingly, a diagnosis is requested in the event that D6 assumes the logical value "1".

Each of the 8 data bits can have a pulse curve shown in FIG. 3, the upper pulse curve with a pulse duration of T / 8 representing a logical "0" and the lower pulse curve with the pulse duration T / 2 representing a logical "1". Because a pulse is also transmitted at logic "0", each of the data bits can be used simultaneously as a synchronization bit.

To transmit a data word, in the present case 64 ms are required for data bits D0 to D7 and 1 ms each for the start and stop bit. The transmission of the data word from the engine control MS to the glow time control device (GZS) is preferably carried out every 200 to 300 ms.

It is assumed in the following that two relays R1 and R2, not shown here, are provided for driving the glow plugs, the relay R1 serving as the main relay for the power supply and the relay R2 for bridging a series resistor connected upstream of the glow plugs. When activating the glow plugs, the duty cycle is varied by changing the duty cycle of relay R2, while relay R1 remains switched on or energized.

The method according to the invention is explained in more detail below with reference to the figures:
The data available in the engine control, such as vehicle electrical system voltage, engine temperature, fuel injection quantity, etc., are available to the glow system or the glow time control device during operation of a motor vehicle; they can be optimally used to control the glow plugs. On the basis of the data, these methods can also be used to distinguish between individual annealing processes that are independent of one another or decoupled from one another, preferably pre-annealing, annealing, afterglowing and intermediate annealing.

Before the start of a glow process, the on-board electrical system or battery voltage U_Batt is detected and this voltage value is compared with a predetermined parameter U_GLmax. In order to avoid that the glow plugs are overloaded, no glow process is initiated if the vehicle electrical system voltage is too high, namely at voltages above the value U_GLmax.

The individual annealing processes should be dealt with chronologically:
After it has been determined that the on-board electrical system voltage does not exceed a predetermined value, after the control unit supply voltage is switched on, a preheating process is initially initiated for a preheating time T_V, in which both the relay R1 and the relay R2 are constantly energized. The preheat time T_V is a function of the engine temperature T_M and the battery voltage U_Batt. This function is stored in a three-dimensional map.

The preheating process is ended when the preheating time T_V has expired.

During the preheating, the speed of the internal combustion engine is detected and the preheating process also ends before the preheating time has elapsed when the so-called start release speed has been reached.

During the preheating, the control lamp L1 indicating the preheating process is activated or switched on. It is switched off again when the preheating time T_V has expired or when a certain engine start speed N_St of, for example, 800 rpm for a time T_VSt of e.g. 10 s is exceeded.

After the preheating time T_V has elapsed, the preheating process for a safety glow time T_S at the longest is followed by a glowing process in which the power supplied to the candles is limited by the fact that the relay R2 has a fixed period duration T_p specified in the glow time control device and one in the engine control (EDC ) the duty cycle T_G to be determined is clocked. In contrast, R1 remains fully energized during the safety glow period T_S.

A duty cycle T_G1 is stored in the motor controller and is only maintained during the specified period T_p. It was determined by tests with the usual battery voltage U_Batt1. It is stored as a function of the fuel injection quantity M_E and the engine speed N in a map.

wobei mit R_v der Vorwiderstand und mit R_k der Kerzenwiderstand bezeichnet wird.For any voltages U_Batt deviating from U_Batt1, the duty cycle is corrected according to the following equation after the period T_p has elapsed:

where R _v denotes the series resistor and R _k the candle resistance.

It should be noted that the duty cycle T_G determined in this way is only valid for the period T_p specified when measuring T_G1.

The glow process is ended when either the safety glow time T_S has expired or the engine has reached the start throwing speed.

dargestellt.If the start discharge speed is reached either during preheating or during annealing, an afterglow process is initiated which is maintained during an afterglow time T_M. The afterglow time is a function of the engine temperature T_M and is characterized by a characteristic curve $\text{T\_M = f (T\_M)}$

shown.

und aus der Spannungskorrektur ermittelt. Auch während des Nachglühens ist das Relais R1 dauernd angezogen, während das Relais R2 getaktet betrieben wird.As with the glow process, the permissible power P_KE supplied to the candle and the duty cycle T_G become from the map $\text{T\_G = f (M\_E, N)}$

and determined from the voltage correction. Relay R1 is also continuously energized during afterglow, while relay R2 is operated clocked.

The power supplied to the candles depends on the engine or combustion chamber temperature. With a higher load on the motor and the resulting higher temperature, the candles are switched on shorter, i.e. the energy supply is reduced. Thereby thermal overloads are avoided. Since the temperature of the combustion chamber cannot rise abruptly when the gas is accelerated, the energy supplied to the candles need not be withdrawn immediately. Rather, it is withdrawn with a delay - corresponding to the slowly rising combustion chamber temperature.

The reverse is true for gas withdrawal, i.e. for reducing the fuel injection quantity: The temperature of the combustion chamber gradually drops as the load decreases; the energy supply to the candles increases with a certain delay when the load is reduced.

It follows from this that the actually implemented duty cycle T_G * transmitted from the motor control MS to the interface 1 follows the determined duty cycle T_G with a certain delay, here a first-order delay. This delay time is designated T_VG and is in the range from 1 to 3 s, for example.

Finally, another annealing process can be distinguished: intermediate annealing. This process is initiated when the engine is idling, that is, when the speed falls below a predetermined speed N_Sch or a predetermined injection quantity M_Sch, and when the engine is cold, namely when the engine temperature T_M falls below a predetermined temperature value T_MSch. Relay R1 is continuously energized and relay R2 is clocked with a fixed duty cycle T_GZ at a period T_p. The period is known from the annealing process described above.

Here too - as with glow and afterglow - a voltage correction of the duty cycle is carried out. The duty cycle determined during intermediate annealing based on the voltage correction is compared with the duty cycle required during afterglow and the larger of the two values is used (maximum value selection).

It follows from FIG. 4 that a diagnosis is always requested when the data bits D0 to D4 all assume the value "0", that is, when the relays R1 and R2 are not activated. In this way, the engine control system makes diagnostic requests to the glow time control device before the glow period T_V and the afterglow time T_N. Regardless of this, a diagnosis request can be made via data bit D6.

The method described here is designed in such a way that every diagnostic request from the engine control MS to the glow time control device must be answered. After the diagnosis request, the motor control sends a logical "1". In response to this request, the transmission line leading to the motor control is temporarily set to zero potential in the glow time control device. The motor controller evaluates the times during which the transmission line is at zero potential. The following table shows that two cases can be distinguished: Motor control differentiates the errors reported from the glow time control or not. The two cases are distinguished in the table by a double, dashed horizontal line.

Instead of the relays R1 and R2 mentioned in the explanation of the method for controlling glow plugs, semiconductor switches can also be used. They have the advantage that they can be clocked much faster than relays, so that clock frequencies above 16 Hz can also be achieved. The human eye then no longer perceives flickering of the vehicle's electrical lighting devices due to the inertia when the high candle currents are switched on and off. This means that the relay R 1 and the series resistor can also be omitted.

Because the information available in the motor control is used in the described method, various signal input connections that are otherwise provided can be omitted:

The NTC in the glow time control unit is replaced by a cooling water temperature signal from the engine control; the load switch or the load potentiometer on the fuel injection pump or on the accelerator pedal is replaced by load information in the engine control system based on the injection quantity and the speed, and the starter signal by speed information such as minimum or start release speed.

In addition, the information about the on-board electrical system voltage in the glow time control device is used to change the duty cycle. Finally, it is possible to report the errors of the glow time control detected during the diagnosis back to the engine control via the interface and to save them there.

Claims (12)

1. Method for actuating glow plugs of an internal combustion engine with auto-ignition, an electric engine control, a glow time control and an interface arranged between the engine control and the glow time control, individual glow processes which are isolated from one another being distinguished, characterized in that during at least one of the individual glow processes the supply of power to the glow plugs is controlled at least as a function of the fuel injection quantity.
2. Method according to Claim 1, characterized in that distinctions are made between a preglow process, a glow process, a postglow process and an intermediate glow process, the preglow process being initiated after the engine control is switched on and being terminated after a preglow time (T_V) has expired or when a start completion speed is reached, the glow process being initiated after termination of the preglowing and being maintained at maximum for a prescribable time (T_S) until the start completion speed is reached, the glow process being followed by the postglow process for a postglow time (T_N) after the starting speed is reached, and an intermediate glow process being initiated when the engine is cold, when the speed drops below a prescribed lower speed (N_Sch) and/or when the fuel injection quantity drops below a prescribed lower fuel injection quantity (M_Sch).
3. Method according to Claim 2, characterized in that during preglowing a continuous current flows through the glow plugs.
4. Method according to Claim 3, characterized in that during the preglow process a display device (L1) is activated and is inactive when the preglow time (T_V) has expired or if a prescribed engine starting speed (N-St) is exceeded for a prescribed time (T_VSt).
5. Method according to Claim 2, characterized in that during the glow process the power fed to the glow plugs is limited in that an intermittent current is directed through the glow plugs.
6. Method according to Claim 5, characterized in that during the glow process the current fed to the glow plugs is initially clocked during a period (T_p) prescribed in the glow system with a pulse duty factor (T_G1) which is determined by the engine control and depends on the fuel injection quantity (M_E) and the engine speed (N), and in that during this process a pulse duty factor (T_G) which is adapted to the instantaneous supply voltage (U-Batt) is determined and used.
7. Method according to Claim 6, characterized in that during the postglow process the power fed to the glow plugs is limited.
8. Method according to Claim 7, characterized in that during the postglow process the current fed to the glow plugs is sampled with a pulse duty factor (T_G*).
9. Method according to Claim 2, characterized in that during intermediate glowing the glow plugs are actuated with an intermittent current.
10. Method according to Claim 9, characterized in that during the intermediate glow process the current fed to the glow plugs is clocked with a fixed pulse duty factor (T_GZ) during a period of (T_p), in that, during this process, a correction of the pulse duty factor is performed in accordance with the instantaneous supply voltage (U_Batt), and in that the maximum value determined during postglowing and during intermediate glowing is selected as pulse duty factor.
11. Method according to one of Claims 1 to 10, characterized in that the information necessary for the respective glow process is transmitted serially from the engine control to the glow systems, at least the pulse duty factor to be used instantaneously being transferred in a data word.
12. Method according to Claim 11, characterized in that additional information for controlling at least one display device and/or supplementary information is transmitted with the data word.

Images