DE19732630A1 - Method for starting a diesel engine and drive system with a diesel engine - Google Patents

Abstract

The invention relates to a method for starting a diesel engine (1), comprising the following steps: no thermal auxiliary starting agent needs to be used in a range of low temperatures up to the lowest acceptable temperature or at least above a low threshold temperature; the diesel engine (1) is speeded by means of an electrical starter (4) up to a sufficiently high number of TPM to ignite the fuel without preliminary use of a thermal auxiliary starting agent; the diesel engine (1) starts. The invention also pertains to a corresponding propulsion system.

Description

The present invention relates to a method for starting a Diesel engine and a drive system with a diesel engine.

The willingness to start of diesel engines takes on low temperatures doors down. On the one hand there is an increase in the friction torque responsible. On the other hand, leakage and heat losses decrease when compressing the air, the final compression pressure and the com final pressure temperature from. Traditionally, diesel engines therefore equipped with thermal starting aids. The Temperature limit from which the starting aids are used generally depends on depending on the engine type. So directly injecting diesel engines with one-piece combustion chamber (in the following called the "DI motors") due to lower heat losses better starting behavior than front and swirl chamber engines, which have a divided combustion chamber.

Starting aids are usually used for small-volume DI Engines and engines with a split combustion chamber glow plugs used. The glow plug of the candle protrudes into the combustion chamber or the chamber of the engine. In addition to glow plugs, there are also glow plugs (in the narrower sense) common, d. H. Glow plugs with exposed glow wire. The thermal is based on large-volume diesel engines Start-up assistance often involves preheating the intake air With the help of electrically heated heating plugs or heating flanges (see Kraftfahrtechnisches Taschenbuch, 22nd ed. 1995, VDI-Ver lag, Düsseldorf, pp. 538-540).  

From DE 195 32 135 A1 a drive system with a Automatic start-stop is known, in an advantageous manner Designing an electric starter up an internal combustion engine drives to reach the idle speed. This serves the Internal combustion engine after a stop using the electric Bring starters directly to idle speed.

The object of the present invention is an improved method to specify a diesel engine to start and a corresponding To provide drive system.

In terms of method, this object is achieved according to claim 1 by a method for starting a diesel engine, which comprises the following steps:

• - It is also in the range of low temperatures up to lowest permissible temperature or at least one low limit temperature not from a thermal start made use of tools,
• - The diesel engine gets deeper at least in this area Temperatures on an electric starter brought high speed to ignite the fuel without With the help of a thermal booster system is sufficient,
• - the diesel engine starts.

In terms of the device, this object is achieved according to claim 8 by a drive system with:

• - A diesel engine that is not a thermal starting aid has or is controlled so that a thermal Starting aids not or at least not above one low limit temperature is used,
• - an electric starter and
• - a control system which initiates the starter, - possibly above the low limit temperature - the diesel engine on one Bring high speed to ignite the fuel without prior use of a thermal starting aid is sufficient.

It has been recognized that a significant portion of the startup problems are related to low temperatures from cooling due to compression heated air from the cold cylinder walls. Building the invention is based on the idea that through a Shortening the contact time between air and cylinder walls achieved a significant improvement in the misfire start behavior can be. The shorter contact time is in turn due to a achieved faster starting speed. For example, at one Tripling the starting speed compared to the conventional one Initially, the contact time in the cylinder was a third of the conventional one value. According to the invention, the compression takes place when starting more in the adiabatic range, so that for the Auto ignition of the fuel also requires the limit temperature achieved at low temperatures by compression alone becomes. The use of thermal jump starters, such as Glow plugs or air preheaters in the intake tract can thereby completely or at least above a low limit temperature is eliminated. In terms of device, the diesel engine therefore has no thermal starting aid or it is controlled that a starting aid, if any, does not exist or only above it the low limit temperature is used. Preferential wise is also on any other indirect preheating of the Motors, e.g. B. in the form of cooling water heating (possibly above the low limit temperature). The diesel engine points therefore preferably no such device for indirect Preheat on or is controlled so that such a device not to start or only above the low limit temperature ratur is used. Some engine designs can a post-heating device (e.g. an after-glow device) is pre-selected be seen in the first time after starting the diesel engine is operated to better combustion in the warm-up phase bring about. Such heating after the start is not considered To understand "using a thermal starting aid". Accordingly, a drive system with glow plugs or the like, the is controlled so that the glow plugs are heated only after starting are, not as "having thermal starting aids" ver  stood. Afterheating of this type is not particularly advantageous carried out and there is no post-heating device.

The method and drive system according to the invention have the following advantages:

• - which are traditionally used for preheating or air preheating The required waiting time does not apply (at least above the low limit temperature), which makes starting faster can be done. This serves traffic safety (in danger situation in which the engine is switched off quickly Driving is required) and increases the comfort at Die sel vehicles;
• - With the saving of the conventional thermal Jump start system saves a considerable amount of effort accompanying;
• - The amount of energy required to start is less, which is a smaller dimensions of the starter battery allowed.

Overall, the present invention thus makes a contribution on road safety, environmental protection and increasing the Driving comfort and to reduce effort in diesel vehicles. It can thus be used for the further spread of diesel vehicles contribute.

In the subclaims are more detailed explanations and advantageous Refinements specified:

According to claims 2 and 9, what is advantageous is defined is to be understood by "low limit temperature" a temperature that is below one of the following values 0 ° C, -5 ° C, -10 ° C, -15 ° C, -20 ° C, -25 ° C, -30 ° C. These temperatures are well below the limit from which conventional Diesel systems annealing is no longer required. The in the "lowest permissible temperature" specified in independent claims of the drive system is typically below the above Values for the low limit temperature (e.g. at -35 ° C).  

According to claims 3 to 5, it is further defined what is advantageously to be understood by "high speed" in the range of low temperatures, namely a speed of 400 min ^-1 or more, preferably 600 min ^-1 or more, more preferably 800 min ^-1 or more. The maximum speed at the lowest temperature will typically not exceed 1500 min ^-1 .

Claims 6 and 10 relate to the point in time from which in the course of Starting process fuel is injected. This is what happens advantageous only after reaching the speed required for the self ignition of the fuel is necessary. This saves fuel and min changes the smoke development.

According to claims 7 and 11, the diesel engine is preferably a small-volume engine with a displacement of less than 3000 cm ³ , particularly preferably a displacement of less than 2000 cm ³ . This type of engine is used in particular in passenger cars and small commercial vehicles with a total weight of less than 3.5 t. In such engines, the cooling in the combustion chamber is particularly pronounced, and the elimination of thermal starting aids achieved by the invention, at least above the low limit temperature, is therefore particularly advantageous here.

According to claim 12, it is the starter of the drive systems around an electrical that acts as a starter / generator Machine that runs continuously. According to claim 13, the Re relative speed from electrical machine to diesel engine in the starter and the same in generator mode, d. H. the gear ratio between the electric machine and the internal combustion engine is constant.

Such machines are for generator operation at high speeds designed. For starter operation, they have to be able to, high Applying torques. They are to achieve the he required high starting speed. According to Claim 14 is an electric starter inverter-controlled induction machine. Under "Rotary field machine ne "is understood to mean a machine in which a magnetic rotation  field occurs that rotates through 360 ° and takes the runner with it. The inverter provides alternating or three-phase current with freely adjustable frequency, amplitude and Phase ready. According to claim 15 is required to start Energy at least partially a capacitor storage (e.g. a so-called intermediate circuit storage), whose preload according to claim 16 can be temperature dependent. According to claim 17 becomes the energy to start at least partially a battery taken.

Refinements and features, the preceding or following described in connection with the procedure apply of course also in connection with the drive system revealed (and vice versa).

The invention is now based on exemplary embodiments and attached schematic drawings explained in more detail. In the Show drawing:

Figure 1 is a schematic representation of a drive system with a diesel engine.

Fig. 2 is an illustration of the relationship between start rotation speed and temperature;

Fig. 3 is a flow chart for starting the diesel engine in the cold state at low temperature.

The drive system of FIG. 1 is z. B. intended for a motor vehicle, such as a passenger car. It has a direct-injection diesel engine with a small cubic capacity (e.g. 1500 cm ³ ) 1 , which outputs torque via a drive shaft 2 , a clutch 3 and other (not shown) parts of a drive train to the drive wheels of the vehicle. The diesel engine 1 is equipped with no glow device and no preheater for the suction air. It also has no device for heating the cooling water when the engine is stopped. In other (not shown) designs such devices are available, but are only used above a low limit temperature. On the drive shaft 2 serving as a starter / generator electric machine 4 , here an asynchronous three-phase machine, is arranged. It has a rotor 5, which is seated directly on the drive shaft 2 and is connected to it in a rotationally fixed manner, and a z. B. on the housing of the diesel engine 1 supported stand 6 . The (not shown) winding of the stator 6 is fed by an inverter 7 with electrical currents and voltages of practically freely adjustable amplitude, phase and frequency. It is a DC link inverter ter, which from a substantially constant DC link voltage with the help of electronic switches z. B. cuts out sine-weighted width-modulated pulses, which - averaged by the inductance of the electrical machine 4 - lead to almost sinusoidal currents of the desired frequency, amplitude and phase.

The inverter is essentially made up of a machine-side DC-AC converter 7 a, a DC voltage intermediate circuit 7 b and a DC-DC converter 7 c. The latter is coupled to a vehicle electrical system 8 and an electrical system long-term storage 9 , here a conventional lead-sulfuric acid battery. The vehicle electrical system 8 and the vehicle electrical system battery 9 are at a low voltage level, e.g. B. 12 or 24 volts. In contrast, the intermediate circuit 7 b is at an increased voltage, which is advantageously in the range between 200 and 400 volts. In other embodiments, the increased voltage is at the top of the low voltage range, approximately 36 volts. In the intermediate circuit 7 b is a Kurzzeitspei cher, here a capacitor memory 10 is connected, which keeps the voltage in the intermediate circuit even with a steep slope increasing current consumption - which is present when pulses are generated by the converter 7 a - approximately constant. In other embodiments (not shown), the short-term memory is formed by a short-term battery (ie a quickly dischargable battery).

The electrical machine 4 and the inverter 7 are laid out so that they have the required torque and the power to directly drive the drive shaft 2 (z. B. the crankshaft) of the diesel engine 1 to the required high speed.

The electrical machine 4 can function as a generator, for example, after the start-up process, ie supply electrical energy. The converter 7 c is trained as a bidirectional converter. He can on the one hand, if the electric machine 4 is operated as a motor and is fed from the on-board electrical system battery 9 , bring electrical energy from the on-board electrical system battery 9 into the intermediate circuit 7 b, and on the other hand, if it is operated as a generator, energy from the Intermediate circuit 7 b for feeding the consumers of the on-board electrical system 8 and the on-board electrical system battery 9 .

The capacitor store 10 can also serve as an energy store for all or part of the energy required for the starter operation. The capacitor store 10 can be charged in different ways: one possibility is to keep the capacitor store 10 charged even when the diesel engine 1 is switched off: when the diesel engine 1 is operating, that is to say when the electrical machine 4 is operating as a generator, it is charged anyway. When the engine comes to a standstill, the unavoidable minor charge losses from battery system battery 9 are continuously recharged. The start can then follow without waiting. In another possibility, reloading is dispensed with. The capacitor store 10 then discharges when the engine is idle for a prolonged period, and is only charged from the vehicle electrical system battery 9 before starting. In both cases, the total energy required to start the capacitor 10 need not be stored. Part of this can also be removed from the on-board electrical system battery 9 during the starting process. In other (not shown) embodiments, a special energy storage device coupled to the intermediate circuit 7 b (for example a capacitor storage device or a short-term battery) takes over the storage of all or part of the starting energy. If a thermal starting aid is used at low temperatures, it is advantageously also fed from the capacitor store 10 . In embodiments (not shown), the starter 4 and possibly the thermal starting aids are supplied in whole or in part from a battery, e.g. B. the on-board electrical system battery 9 .

A higher-level control unit 11 controls the starting process by controlling the inverter 7 , specifically the converter 7 a and the converter 7 c. It gives the converter 7 a amplitude, phase and frequency of the three-phase voltage to be generated. The converter 7 c gives the amount of current, the current direction for motor operation and, if applicable, the amount of voltage increase (if the on-board electrical system battery 9 energy is removed). To start the diesel engine 1 , the control unit 11 controls the electric machine 4 via the inverter 7 in such a way that the drive shaft 2 is driven to a high speed sufficient to ignite the fuel, with no use being made of a thermal starter system.

The speed to which the diesel engine 1 is driven by the electrical machine 4 can be a temperature-independent size, which is so high that at the lowest temperatures occurring (or at the low limit temperature) safe starting is guaranteed. However, the speed is advantageously selected (at least in a sub-area) depending on the temperature. To detect the engine and outside temperature, an engine temperature sensor 12 a and an outside temperature sensor 12 b are seen before.

Fig. 2 illustrates the dependence of the starting speed (ie the speed required for self-ignition, at which fuel is injected) on the temperature. To simplify the engine and outside temperature are assumed to be the same; Different values of these temperatures are taken into account by a corresponding map. The dependency drawn is such that the starting speed drops from a maximum (eg 400 min ^-1 ) at the lowest temperature with increasing temperature. Above a certain temperature (here 10 ° C) it is kept constant, so it is in this area by an amount increasing with increasing temperature above the minimum required speed value. This setting of a minimum speed serves for starting comfort. A further temperature-dependent parameter (not illustrated in more detail here) can be the starting time, ie the time with which the diesel engine 1 is driven at the starting speed until fuel is injected. The start time is longer at low temperatures than at high ones, ie their temperature dependence is similar to the relationship shown in FIG. 2. When charging the capacitor memory 10 , these temperature dependencies are taken into account by the charge level is set in a variable manner at least so high that a safe start is guaranteed at the respective temperature. Depending on whether the capacitor 10 is permanently charged or is only charged shortly before the start, the control unit 11 ensures a permanent recharge or one-time charge from the on-board electrical system battery to the above-mentioned minimum charge level before the actual starting process. When using a battery as an energy source, its capacity and power are selected sufficiently to ensure starting with the required starter speed at all temperatures (possibly above the limit value).

In the method according to FIG. 3, in step S1 it is first queried whether a command to start the diesel engine 1 has been given. In the mode of operation with continuous recharging, previous steps (not shown) ensure that the capacitor store 10 is sufficiently charged to be able to start the diesel engine 1 safely at the present temperature conditions without using thermal starting aids. These process steps include a measurement of the temperatures, a determination of the charge level required for safe starting at measured temperature values, for. B. with the help of a stored in the control unit 11 map similar to FIG. 2, and reloading the capacitor memory 10 to the required level. This sequence of procedural steps is repeated continuously while the engine is at a standstill. When operating with a single charge, this sequence is carried out once after the start command. In step S2, the temperatures are then measured (if this has not already happened immediately beforehand) and the start speed and start duration required for safe starting at the measured temperature values, for. B. with the help of a stored in the control unit 11 Kenn field. Without using thermal starting aids (step S3), the crankshaft 2 of the diesel engine 1 is then driven by the electric starter 4 at the previously determined starting speed in step S4. After the predetermined start time has elapsed, fuel injection begins in step S5. In the subsequent step S6, the diesel engine starts by auto-ignition without having been made use of a thermal starting device Ge, even at the lowest occurring operating temperatures. In embodiments with limit temperature, this method is modified in such a way that it is also determined in step S2 whether and if so for how long a thermal starting aid is to be operated. The starting aid is then operated in step S3.

Reference list

1

Diesel engine

2nd

drive shaft

3rd

clutch

4th

electric starter

5

runner

6

Stand

7

Inverter

7

a converter

7

b DC link

7

c DC converter

8th

Wiring system

9

Vehicle battery

10th

Capacitor storage

11

Control unit

12th

a temperature sensor

12th

b Temperature sensor

Claims (17)

1. Method for starting a diesel engine ( 1 ) with the following steps:

• no thermal starting aid is used even in the range from low temperatures to the lowest permissible temperature or at least above a low limit temperature,
• - The diesel engine ( 1 ) is brought in this area lower temperatures by an electric starter ( 4 ) to a high speed, which is sufficient to ignite the fuel without prior use of a thermal starting aid,
• - The diesel engine ( 1 ) starts.

2. The method of claim 1, wherein the deep Limit temperature is below one of the following values: 0 ° C, -5 ° C, -10 ° C, -15 ° C, -20 ° C, -25 ° C, -30 ° C. 3. The method according to claim 1 or 2, in which the electric starter ( 4 ) drives the diesel engine ( 1 ) in the region of lower temperatures to a speed of 400 min ^-1 or more. 4. The method according to claim 3, wherein the electrical star ter ( 4 ) drives the diesel engine ( 1 ) in the range of low temperatures to a speed of 600 min ^-1 or more. 5. The method according to claim 4, wherein the electrical star ter ( 4 ) drives the diesel engine ( 1 ) in the range of low temperatures to a speed of 800 min ^-1 or more. 6. The method according to any one of claims 1 to 5, wherein the injection of the fuel into the combustion chamber of the diesel engine ( 1 ) takes place only after reaching the speed to ignite the fuel from reaching. 7. The method according to any one of claims 1 to 6, wherein a diesel engine ( 1 ) is used, which is small and in particular is designed for use in passenger cars and small-duty vehicles. 8. Drive system, in particular for a motor vehicle, with

• - A diesel engine ( 1 ) which has no thermal starting aid or which is controlled so that a thermal starting aid above a low limit temperature is not used,
• - An electric starter ( 4 ) and
• - A controller ( 11 ) which causes the starter ( 4 ) to bring the diesel engine ( 1 ) to a high speed, which is sufficient to ignite the fuel without prior use of a thermal starting aid.

9. Drive system according to claim 8, wherein the low-lying Limit temperature is below one of the following values: 0 ° C, -5 ° C, -10 ° C, -15 ° C, -20 ° C, -25 ° C, -30 ° C. 10. Drive system according to claim 8 or 9, wherein the injection of the fuel into the combustion chamber of the diesel engine ( 1 ) takes place only after reaching the speed sufficient to ignite the fuel. 11. Drive system according to one of claims 8 to 10, wherein the diesel engine ( 1 ) is small in volume and is designed in particular for use in passenger cars and small commercial vehicles. 12. Drive system according to one of claims 8 to 11, wherein the electrical starter ( 4 ) is designed as a starter / generator which runs continuously with the diesel engine ( 1 ). 13. Drive system according to claim 12, wherein the relative rotational speed of the electric starter ( 4 ) to the diesel engine ( 1 ) is fixed. 14. Drive system according to one of claims 9 to 13, wherein the electrical starter ( 4 ) is an inverter-controlled three-phase machine. 15. Drive system according to one of claims 9 to 14, in which the energy required for starting is at least partially taken from a capacitor store ( 10 ). 16. Drive system according to claim 15, wherein the precharging of the capacitor store ( 10 ) takes place as a function of temperature. 17. Drive system according to one of claims 9 to 16, in which the energy required to start at least partially is taken from a battery.