Method for starting an internal combustion engine, device and computer program product

Abstract

The invention relates to a method for starting an internal combustion engine for a motor vehicle, said internal combustion engine having at least two cylinders, a valve drive with at least one inlet valve and at least one outlet valve for each of the cylinders, wherein at least the closing times of the inlet valves can be variably adjusted, and a direct injection system, in particular a gasoline direct injection system, the starting process being initiated by a direct injection and ignition in one of the cylinders. During a starting process, the closing time of at least one inlet valve differs from at least one of the other cylinders dependent on at least one current state value.

Claims

1. A method for starting an internal combustion engine for a motor vehicle, said internal combustion engine having at least two cylinders, a valve drive with at least one inlet valve and at least one outlet valve for each of the cylinders, wherein at least closing times of the inlet valves can be variably adjusted, and a direct injection system, the starting process being initiated by a direct injection and ignition in one of the cylinders, characterized in that, during the starting process, the closing time of the at least one inlet valve of one cylinder differs from the at least one valve of the other cylinders dependent on at least one current state value; wherein a rotational speed (n) of the internal combustion engine is detected during the start-up process as one of the at least one current state values and a lubricant condition (T.sub.S) of the internal combustion engine is acquired as another of the at least one current state values, and during the startup process, changing the closing times of the intake valves of the other cylinders to a later time when the detected rotational speed (n) is less than an expected speed and changing the closing times of the intake valves of the other cylinders to an earlier time when the detected rotational speed (n) is greater than the expected speed; wherein the lubricant condition (TS) of the internal combustion engine is a viscosity of the lubricant of the internal combustion engine acquired via a sensor.

2. The method according to claim 1, characterized in that an ambient temperature (T.sub.0) is acquired as one of the at least one current state value.

3. The method according to claim 1, characterized in that an ambient pressure (p.sub.0) is acquired as one of the at least one current state value.

4. The method according to claim 1, characterized in that an engine temperature (T.sub.M) is ascertained as one of the at least one current state value.

5. The method according to claim 1, characterized in that the closing time of the at least one inlet valve is selected as a function of the at least one state value acquired, such that a decompression for the starting process occurs in the corresponding cylinder.

6. A device for operating an internal combustion engine having at least two cylinders, a valve drive with at least one inlet valve and at least one outlet valve for each of the cylinders, wherein at least closing times of the inlet valves can be variably adjusted, and a direct injection system, the device comprising a control device configured to, during a starting process, adjust a closing time of at least one inlet valve different from at least one valve of the other cylinders dependent on at least one current state value; wherein a rotational speed (n) of the internal combustion engine is detected during the start-up process as one of the at least one current state values and a lubricant condition (T.sub.S) of the internal combustion engine is acquired as another of the at least one current state values, and during the startup process, changing the closing times of the intake valves of the other cylinders to a later time when the detected rotational speed (n) is less than an expected speed and changing the closing times of the intake valves of the other cylinders to an earlier time when the detected rotational speed (n) is greater than the expected speed; wherein the lubricant condition (TS) of the internal combustion engine is a viscosity of the lubricant of the internal combustion engine acquired via a sensor.

7. A non-transient computer readable medium containing a computer program product which carries out the method according to claim 1 when the program is executed on a control device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in greater detail below with the aid of the drawings.

(2) In the drawings:

(3) FIG. 1 shows an advantageous method for starting an internal combustion engine in a flow diagram;

(4) FIG. 2 shows a first exemplary embodiment of a starting process and

(5) FIG. 3 shows a second exemplary embodiment of the starting process.

DETAILED DESCRIPTION

(6) In a simplified flow diagram, FIG. 1 shows a method for starting an internal combustion engine which has at least two cylinders, in the present example six cylinders, and a valve drive, wherein the valve drive has at least one inlet valve and at least one outlet valve for each of the cylinders and wherein at least the closing time of the inlet valves can be variably adjusted. The internal combustion engine further comprises a gasoline direct injection system, by means of which fuel can be directly introduced into the cylinders. An ignition device, in particular a spark plug, is furthermore associated with each of the cylinders in order to ignite the fuel introduced into the respective cylinder.

(7) The internal combustion engine is to be put into operation by means of a direct start or, respectively, a decompression start, wherein fuel is injected into a cylinder, the piston of which is located statically in the expansion phase, and ignition is initiated. The ensuing combustion introduces a rotational movement into the crankshaft of the internal combustion engine by means of the piston. The cylinder first ignited shall be denoted below as the start cylinder.

(8) In order to ensure an optimal start of the internal combustion engine, the advantageous method provides that, when starting said engine, the closing time of at least one inlet valve differs from at least one of the succeeding cylinders, i.e. from one of the cylinders which is after the start cylinder, in the firing order dependent on at least one current state value. In particular, the closing times of the inlet valves of the first and second cylinder succeeding in the firing order are changed dependent on at least one current state value. In so doing, a base control time for the corresponding inlet valve is initially assumed, which would ensure an optimal starting process under optimal operating conditions. This base control time is changed respectively corrected by taking into account the current state value so that the corresponding inlet valve closes earlier or later, whereby the decompression occurring in the respective cylinder is adapted. The base control time is preferably deposited in an engine control device as a function of the switch-off position of the internal combustion engine and is available as a starting position for further steps of the method. Provision is made in the present embodiment for a so-called offline correction or, respectively, adaptation of the closing time of the inlet valves to initially be carried out, as it is exemplarily depicted in FIG. 1 in a flow diagram. Because optimal staring conditions are generally not present, provision is made in the offline correction for the closing times to be changed respectively corrected dependent on ambient conditions and state conditions of the internal combustion engine, which can be acquired when said internal combustion engine is shut down. In a first step S1, the start cylinder, in which the starting process is to be initiated, is initially determined as a function of the switch-off position of the internal combustion engine. As a result, it can be determined in which succeeding cylinders the closing times of the inlet valves are to be changed. In the internal combustion engine comprising six cylinders, it is, for example, no longer necessary from the fourth cylinder onwards or, respectively, from the third succeeding cylinder to carry out a decompression; thus enabling the method to revert back to the normal closing times here. A change in the closing times for the first and the second succeeding cylinder takes place however according to the advantageous method. This will be described below in greater detail.

(9) An ambient pressure p0 and/or an ambient temperature T.sub.0 is initially acquired. In step S2, the closing time is changed or the base control time of the corresponding inlet valve is corrected as a function of the ambient pressure p0 and/or ambient temperature T.sub.0. The ambient pressure and the ambient temperature determine the charge for the initial combustion as well as the compression work to be achieved by the succeeding cylinders. Provision is, for example, made for the closing time of the corresponding inlet valve to be moved backwards respectively delayed in the event of a high ambient pressure in order to cope with the increased compression work.

(10) An engine temperature is furthermore determined, a coolant temperature T.sub.W being acquired for this purpose by means of a corresponding sensor. In step S3, the respective closing time is correspondingly further changed, i.e. shifted to an earlier or later point in time, as a function of the engine temperature T.sub.M that was acquired as stated above. The temperature T.sub.M has an effect on the friction in the internal combustion engine and therefore also on the rotational speed curve during start-up. If the closing time is correspondingly changed as a function thereof, the decompression of the succeeding cylinders can be further optimized in order to ensure a good start-up of the internal combustion engine.

(11) Provision is furthermore made for a lubricant condition T.sub.S from a lubricant of the internal combustion engine, in particular motor oil, to be acquired. A viscosity of the lubricant is particularly acquired as the lubricant condition T.sub.S, said viscosity changing with the mileage on the internal combustion engine due to abrasion, carbonization and/or fuel ingress. In step S4, the closing point of the respective inlet valve is likewise corrected as a function of the lubricant condition T.sub.S because the condition of the lubricant likewise has an effect on the friction of the internal combustion engine. This can be taken into account when optimizing the decompression of the corresponding cylinder by means of the advantageous method in order to ensure an optimal start-up.

(12) Following the corrections carried out in steps S2, S3 and S4, the starting time up to achieving a certain minimum rotational speed of the internal combustion engine and/or the minimum rotational speed during the compression strokes of said internal combustion engine are, for example, measured. With these values, signs of wear in the internal combustion engine, which likewise effect the decompression start, can then be taken into account by means of an adaptation function in step S6, such as, for example, an engine friction which changes over the service life of the engine and/or the so-called blow-by behavior. The steps S2, S3 and S4 can, of course, also be carried out in an order that is different from the one presented here.

(13) Whereas the closing times of the inlet valves are determined prior to start-up of the internal combustion engine during the offline correction, an adaptation and change of the closing times of the inlet valves are provided during the starting process that has already been initiated in the online correction which is described below and can additionally or alternatively take place to the offline correction. In so doing, the rotational speed n of the internal combustion engine is monitored during the starting process. To this end, the FIGS. 2 and 3 each show a diagram in which the rotational speed n of the internal combustion engine is plotted over the time t. A rotational speed curve of an optimal respectively planned start-up curve of said internal combustion engine is thereby depicted by a first curve n.sub.0.

(14) In the first exemplary embodiment according to FIG. 2, the actually acquired start-up curve n.sub.S has lower rotational speeds, which are caused by an insufficient decompression of the succeeding cylinders and lead to an aborted start-up.

(15) It is however clear already at the beginning of the starting process that the acquired rotational speed n.sub.S deviates from the expected rotational speed n.sub.0 and has lower values. If this is detected during a starting process, the closing times of the inlet valves of the succeeding cylinders are changed to a later point in time or, respectively, a greater decompression of the succeeding cylinders is adjusted according to the advantageous method. As a result, the start-up time of the internal combustion engine is in fact lengthened overall by the value t.sub.1, as is plotted in FIG. 2. Nevertheless, the starting process can be saved respectively ensured as is depicted by the resulting rotational speed n.sub.SK.

(16) As a result of the greater decompression, the start-up is still saved because the rotational speed n during the compression of the respective succeeding cylinder does not drop as dramatically as with unchanged closing times.

(17) FIG. 3 shows a rotational speed curve n.sub.B which is improved in comparison to the expected rotational speed curve n.sub.0 and which leads to higher rotational speeds than expected already at the beginning of the starting process. In this case, the start-up curve can be accelerated still further by the respective cylinder charge being built up faster than was originally planned at the beginning of rotation. To this end, the closing times of the inlet valves of the succeeding cylinders are shifted to an earlier point in time so that the succeeding cylinders are less strongly decompressed in a planned manner as originally by means of the base control time. As a result, the internal combustion engine is accelerated faster and the resulting rotational speed n.sub.BK reaches the minimum rotational speed faster. The start-up time is thereby shortened by the value t2 plotted in FIG. 3.