DE19732741A1 - Starting procedure for two stroke engine - Google Patents

Abstract

During the starting sequence for a two stroke IC engine a control system monitors the air temperature in the inlet manifold, the throttle valve setting and the temperature and speed of the engine. The fuel injection is controlled to include a flushing process and a fuel injection rate matched to the starting requirements. As soon as the engine fires the starting sequence is stopped and the engine runs normal. The system provides for a shorter starting sequence for a warm engine.

Description

State of the art

The invention is based on a starting method for one Two-stroke gasoline engine with at least one pulse air actuated feed pump supplied high pressure direct injection, with at least one sensor to determine the Dros selflap position, the intake air temperature, the engine speed number and the engine temperature and with one the sensor information processing and at least one fuel injector control grounding electronic control unit

A fuel pump device for an internal combustion engine operating on the two-stroke principle is known from the unpublished DE 196 31 286.8. The fuel pumping device, which is part of a high-pressure injection system, is shown below with its diaphragm piston pumps in FIG. 2. In combination with the high-pressure injection system, the diaphragm piston pumps cause problems when starting or restarting warm or hot two-stroke engines. Gas bubbles from evaporated fuel that collect in the diaphragm piston pumps delay the fuel injection and thus the starting process.

Advantages of the invention

The starting method according to the invention can be used for two-stroke Otto motors are used, each with at least one Sensor for determining the throttle valve position, the intake air temperature, engine speed and engine temperature and with a processing the sensor information and min least an electronic valve controlling an injection valve device. With the help of these sensors the Start process monitored.

During the starting process, the ignition is switched on and a positive starter detection a flushing of the fuel systems over a predetermined number of engine revolutions open injector. After that, the engine temperature compared with a predetermined threshold and in the event that the engine temperature is higher than that Threshold, the flushing process by a few more engine revs prolonged. Then the fuel pressure builds up in the injection system, the injection valve via several others Engine revs locked. After opening the injection valve The engine acceleration is tils for an injection duration with a target engine acceleration and the engine speed with an idle speed reduced by a threshold speed compared, the injection duration in the event that the Mo Torist acceleration is smaller than the engine target acceleration and the engine speed is lower than that around the threshold value speed reduced idle speed from cycle to cycle increased by a predetermined period of time.  

With this starting strategy, the existing sensors each the current operating state summarizes and according to the rinsing process timed and the injection duration per start phase is regulated. In this way the starting process is especially during a hot combustion engine shortened in time. That either spares the star battery or the muscle strength of the hand or foot starter operating person.

drawings

Further details of the invention emerge from the here not cited claims and the character descriptions.

Fig. 1 two-stroke small engine with direct petrol injection;

Fig. 2 fuel injection system for high pressure direct injection

Fig. 3 flow chart for the engine starting process.

Description of the embodiment

Fig. 1 shows a two-stroke small engine with a fuel supply system and a number of sensors, which are desirable, among other things, for engine control and regulation.

The two-stroke engine ( 1 ) has two sensors ( 12 ) and ( 13 ) on an intake manifold ( 4 ). The sensor ( 12 ) is a potentiometer that sits on the shaft of the throttle valve ( 5 ) and detects the throttle valve position. In front of the throttle valve ( 5 ), the intake air temperature sensor ( 13 ) is arranged. On the crankcase ( 2 ) sits a speed sensor ( 14 ) and spatially above this is an engine temperature sensor ( 15 ) on the cylinder wall ( 3 ) be fastened. All sensors ( 12-15 ) are connected to a controller ( 11 ).

In the cylinder head ( 17 ), a spark plug ( 6 ) and an injection valve ( 8 ) is screwed. The spark plug ( 6 ) is connected to the control ( 11 ), inter alia, via an ignition coil ( 7 ). The injection valve ( 8 ) also connected to the control unit is supplied with fuel from a fuel tank ( 9 ) via a filter ( 10 ) and two series-connected diaphragm piston pumps ( 90 ) and ( 20 ). The diaphragm piston pumps are pneumatically connected to the crankcase ( 2 ) via an impulse air line ( 16 ).

The diaphragm piston pumps ( 90 ) and ( 20 ) arranged between the fuel tank ( 9 ) and the injection valve ( 8 ) are shown in FIG. 2 in the form of a functional diagram. The device formed from two pumps connected in series can generate an injection pressure of approximately 20.10 ⁵ Pa. The first pump is arranged as a prefeed pump ( 90 ) between the filter ( 10 ) and a second so-called high-pressure pump ( 20 ). The pre-feed pump ( 90 ) is a double diaphragm pump with a diaphragm ( 91 ) and a diaphragm ( 92 ) loaded with fuel. Both diaphragms ( 91 , 92 ) are in contact via a coupling rod ( 93 ) and each have their outer side supported by spring elements ( 94 , 95 ) against the pump housing. The space between the two membranes ( 91 , 92 ) is ventilated with ambient air. A suction ( 96 ) and a pressure valve ( 97 ) are arranged in front of the side of the diaphragm ( 92 ) which is acted upon by fuel.

The second diaphragm piston pump ( 20 ) sucks the fuel supplied by the prefeed pump ( 90 ) via a suction valve ( 61 ). The fuel drawn into a compression chamber ( 51 ) into which a pump piston ( 22 ) is immersed. The fuel displaced there flows via a pressure valve ( 71 ) into a fuel pressure accumulator ( 73 ) and, for example, to an electrically controlled injection valve ( 8 ). On the pressure side, some of the fuel escapes via a pressure relief valve ( 80 ) z. B. in the fuel tank ( 9 )
The pump piston ( 22 ) protrudes with its rear end into the space ( 23 ) of the pump housing, which is pneumatically connected to the crankcase ( 2 ) of the internal combustion engine ( 1 ) operating according to the two-stroke principle via the impulse air line ( 16 ). In this pulse air space ( 23 ), the pump piston ( 22 ) is pressed via a spring element ( 25 ) against a diaphragm ( 41 ) reinforced with a diaphragm plate ( 42 ). On the back of the membrane ( 41 ) is a surrounding air space ( 33 ), in which a spring element ( 35 ) is also arranged. This spring element ( 35 ) counteracts the other Fe derelement ( 25 ). Both prestressed Federele elements ( 25 , 35 ) hold the membrane ( 41 ) in a central position, provided that the same air pressure is present on both sides of the membrane ( 41 ).

Flowing the pulse air with positive pressure in the pulse pressure chamber (23) moves as illustrated in FIG. 2, Mem brane (41) downward, wherein the spring element (25), piston pump (22) readjusts the diaphragm (41) and the Federele element ( 35 ) is further tensioned. The diaphragm piston pump ( 20 ) sucks fuel into the compression chamber ( 51 ) via a suction valve ( 61 ). As soon as the excess pressure drops, the partially relaxing spring element ( 35 ) pushes the pump piston ( 22 ) into the compression chamber ( 51 ). The fuel flows via the pressure valve ( 71 ) to the injection valve ( 8 ) and / or to the fuel pressure accumulator ( 73 ). The compression stroke extends beyond the central position of the diaphragm ( 41 ) because the negative pressure now prevailing in the crankshaft housing has an effect on the diaphragm ( 41 ) towards the end of the stroke. The membrane ( 41 ) is sucked upwards.

As the pulse air pressure rises, the pumping movement of the pump piston ( 22 ) repeats.

The diaphragm piston pumps ( 20 , 90 ) react due to their inherently harmful space to gas bubbles in the fuel delivered. The gas bubbles occur, for example, after the hot two-stroke engine ( 1 ) is switched off. A part of the fuel in the fuel system evaporates due to the engine waste heat. In the event of a hot start, the gas bubbles hinder the delivery effect of the diaphragm piston pumps, in particular the high pressure pump ( 20 ). As a result, fuel is injected too little and / or irregularly, so that the two-stroke engine ( 1 ) runs "shaking" or out of round and switches off several times if necessary.

To prevent this, the two-stroke engine ( 1 ) is started with a special strategy. It is presented in a flow chart in FIG. 3. The strategy does not require any design changes to the fuel system or the engine.

After switching on the ignition, the control unit ( 11 ) initiates a start detection. For this purpose, the engine speed is detected by the sensor ( 14 ). If the engine ( 1 ) is stopped at this time, the crankshaft is rotated - for example with the help of a starter - over a predetermined number of m ₁ engine revolutions and the fuel system is thus flushed. In this process, the air and vapor bubbles are displaced, which can occur after switching off in the fuel system, preferably in the line to the injection valve ( 8 ), in the high-pressure accumulator ( 73 ) and in the high-pressure pump ( 20 ). The fuel system is flushed via the pre-feed pump ( 90 ) connected directly to the tank ( 9 ). Here, the injection valve ( 8 ) is open. It is controlled in the engine cycle range "open overcurrent" and "close outlet". In this phase, there is no back pressure in the combustion chamber, which means that the fuel system is virtually flushed without pressure.

After the m ₁ engine revolutions, the temperature T _M measured on the cylinder wall ( 3 ) with the engine temperature sensor ( 15 ) is compared with a predetermined temperature threshold value T _S. If the difference is positive - it means a hot start - further flushing operations are carried out over m ₂ engine revolutions. The number of engine revolutions is, for example, proportionally dependent on the level of the temperature difference T _M -T _S. Here too, the injection valve ( 8 ) is open during flushing.

In the next step, the injection valve ( 8 ) remains closed for m ₃ engine revolutions. During these revolutions, the fuel pressure required for engine operation is built up. In this case, the number of engine revolutions is, for example, a constant that is based on empirical values. Alternatively, it can also be a function of various operating parameters.

After the required pressure build-up, the injection will be pulses or the injection time t _i t _i corresponding to the selected -Kennfeld. Basic parameters for the injection duration are the throttle valve angle α detected by the sensor ( 12 ) and the engine speed n _m . The intake air temperature T _A and the engine temperature T _M serve as correction variables, for example.

At the same time, it is concluded from the interpretation of the engine run-up whether the injection quantity determined via the injection duration t _i and the storage pressure corresponds to a predetermined target value. As long as the actual engine acceleration (δn / δt) _{n is} not a target engine acceleration (δn / δt) _{n, should} correspond and, in addition, the engine speed n _{M is} below the idling speed n _L minus a speed threshold n _S , the storage pressure does not yet have that of the pressure relief valve ( 80 ) reached a set value. To compensate, the injection duration t _{i is} increased from cycle to cycle by the value Δt _is until the target engine acceleration (δn / δt) _n, and the idling speed n _L minus a speed threshold n _{S have been} reached.

From now on the control takes place via the t _i map.

Claims (3)

1.Starting procedure for a two-stroke gasoline engine with a high-pressure direct injection supplied via at least one pulse air-operated feed pump, with at least one sensor each for determining the throttle valve position, the intake air temperature, the engine speed and the engine temperature, and with an electronic control unit that processes the sensor information and controls at least one injection valve Control unit as marked by

• - That after the ignition is switched on and a positive starter identification (n _M = 0), the fuel system is flushed over a predetermined number of m _i engine revolutions with the injection valve ( 8 ) open,
• - That the engine temperature T _{M is} compared with a predetermined threshold value T _S and in the event that the engine temperature T _{M is} greater than the threshold value T _S , the flushing process is extended by m ₂ engine revolutions,
• - That the fuel pressure build-up in the injection system, the injection valve ( 8 ) is blocked for a further m ₃ revolutions,
• - That after opening the injection valve ( 8 ) with an injection duration t _i the actual engine acceleration (δn / δt) _{n, is} with the target engine acceleration (δn / δt) _n, and the engine speed n _m with a threshold value speed n _S reduced Idle speed n _{L are} compared, the injection duration t _i in the event that the actual engine acceleration (δn / δt) _{n is} less than the target engine acceleration (δn / δt) _n, and the engine speed n _{M is} less than that the idle speed n _L reduced by the threshold speed n _{S is} increased from cycle to cycle by a time period t _is .

2. Starting method according to claim 1, characterized in that the m ₂ engine revolutions of the first flushing of the fuel system are a function of the engine temperature T _M. 3. Starting method according to claim 1, characterized in that the target engine acceleration (δn / δt) _{n, is} a function of the engine temperature T _M and the intake air temperature T _A.