Motor vehicle e.g. small-size car, start-up phase controlling method, involves starting fuel injection process at time after synchronization time, where time of start of clutch lies before synchronization time

The invention relates to a method for controlling the start-up process of motor vehicles which are driven by an internal combustion engine with internal combustion and have an automatically actuated clutch, the internal combustion engine being accelerated from a standstill by a starter, the engagement process of the clutch starting from a predefined one

Limit speed can be started to initiate the start-up process, and is started at a point in time after a synchronization point in time with the injection process.

The term synchronization means that the engine control system can recognize the absolute angle at which the crankshaft of the internal combustion engine is currently located. This includes information about the part of the cycle in which the individual cylinders are located. Because of the sensors that are usually used, this is only possible after a certain angle has been covered after the crankshaft has moved for the first time.

The functions of motor vehicles are being automated to an increasing extent. This applies, for example, to the process of starting motor vehicles. If a motor vehicle is to start from a standstill with the engine at a standstill, it is necessary to first start the internal combustion engine and then engage the clutch in order to establish the frictional connection between the internal combustion engine and the drive wheels. The critical factor here is the length of time that elapses between the initiation of the start-up process and the start of the acceleration of the motor vehicle. The acceptance of automated systems by drivers depends largely on whether objective criteria, such as dead time, noise or jerking, can be minimized and subjective ones

Optimize criteria.

In conventional systems, the internal combustion engine is first accelerated by the starter without carrying out an injection so as not to worsen the exhaust gas limit values ​​through the emission of unburned hydrocarbons. The first injection process is carried out after a synchronization point in time at which, on the one hand, the phase position of the piston or the valves are in a permissible range and, on the other hand, the engine speed is already high enough to ensure safe combustion. From the first active injection it can be assumed that the internal combustion engine is delivering a positive torque. Then the clutch engagement process begins, so that after a short dead time, torque can be transmitted to the drive wheels of the motor vehicle and the acceleration process begins. The total time up to the start of the acceleration of the motor vehicle depends essentially on the time that elapses from the start of the process to the time of synchronization. This time period in turn depends on the power of the starter, the moment of inertia and the frictional torque of the internal combustion engine, the required speed at the time of synchronization and the phase position of the internal combustion engine at the beginning of the process.

The object of the present invention is to minimize the time until the start of the power transmission and thus the acceleration of the motor vehicle by optimizing the control of the starting process and in particular the engagement of the clutch.

According to the invention, this is achieved in that the point in time of the start of the engagement process of the clutch is before the point in time of synchronization.

What is essential to the present invention is the knowledge that with a suitable design of the system components, the engine speed at the time of synchronization is significantly higher than the limit speed at which a successful starting process is possible. In the method according to the invention, the internal combustion engine is therefore initially accelerated with the clutch fully disengaged up to a first speed which is above the minimum speed required for a starting process. As the clutch begins to be engaged, the speed of the internal combustion engine drops, while the acceleration of the motor vehicle begins at the same time. The control takes place in such a way that the speed at the time of synchronization is still high enough to successfully complete the start process. The internal combustion engine in this way then delivers an excess of torque which, on the one hand, increases the speed and, on the other hand, further accelerates the motor vehicle. The method according to the invention makes it possible to bring the start of the acceleration process of the motor vehicle forward and thus to achieve a significantly faster response behavior.

A particularly smooth start-up behavior can be achieved if the end of the clutch engagement process is after the synchronization point in time. That way will

AT 412 861 B achieves that the first ignition of the internal combustion engine takes place at a point in time when the clutch still has a certain amount of slip, so that the torque surges at this point in time are largely absorbed by the clutch.

In a particularly advantageous variant of the method according to the invention, it is provided that the clutch is open at the beginning of the start-up process, ie when the internal combustion engine is at a standstill. Alternatively, however, it is also possible that the clutch at the beginning of the starting process, ie When the internal combustion engine is at a standstill, the gearbox of the motor vehicle is in neutral, after which the clutch is opened at a first point in time, then a gear is engaged at a second point in time, after which the engagement process of the clutch is started at a third point in time and then the injection process is started at a synchronization point in time. The advantage of this variant of the method is that the clutch does not have to be kept in the open state, even in the case of longer standstill times.

It is particularly preferred if, at the start of the injection process, the engine speed is at least 100 min¹ is above a limit speed at which a safe starting process is possible. In this way, a safe starting process can be guaranteed in all operating conditions.

Furthermore, the present invention relates to a device for controlling the start-up process of a motor vehicle, which is equipped with an internal combustion engine with internal combustion and an automatic clutch, the device being designed to control a starter in order to accelerate the internal combustion engine from standstill and with a to start the clutch engagement process at a predetermined engine speed in order to initiate the start-up process, as well as to to start the injection process at a synchronization point in time. According to the invention, this device is characterized in that the device defines the start of the engagement time of the clutch before the synchronization time. The engine control device according to the invention shortens the time until the start of the acceleration process.

The present invention also relates to a motor vehicle having an internal combustion engine, an automatic clutch and a control device for controlling the starting process, as described above. The present invention can be applied particularly advantageously to a motor vehicle that is equipped with a starter generator. This is an electric machine that is coupled to the drive train and that can be used both as a starter and as a generator.

In order to be able to determine the optimum synchronization point in time, it is particularly preferred if the device for controlling the start-up process is connected to both a camshaft sensor and a crankshaft sensor. In this way it can be decided with certainty in which cylinder the first injection and thus ignition takes place.

Particular advantages result if the gearbox of the motor vehicle is designed as an automatic gearbox. In particular, it is advantageous if the gearbox is designed as a sequential gearbox. In this way, as described above, without

If the driver intervenes, a starting process can be carried out in which a closed clutch is assumed, which is first opened in order to engage a gear and then the actual engagement process is carried out. A particularly favorable variant of the invention provides that the motor vehicle is equipped with an automatic parking brake that is coupled to the control of the starting process. Such an automatic parking brake is an auxiliary brake that is activated when the vehicle is stationary and remains activated until the drive train has sufficient torque to start the acceleration process. With such an automatic parking brake, starting on a hill is possible without any problems even without special measures by the driver.

In order to cope with the various load situations when starting up, it can be cheaper

Way an inclination sensor can be provided which is connected to the device for controlling the start-up process. This inclination sensor measures the inclination of the vehicle body in the longitudinal direction and can thereby determine, if necessary, that a start-up process is to be carried out uphill.

Another relevant load situation is when the vehicle is heavily loaded. In these cases, the internal combustion engine decelerates more strongly

AT 412 861 B

The beginning of the engagement process of the clutch is to be expected, so that the beginning of the engagement process has to be shifted slightly backwards. This situation can be determined by comparing the current engine torque with a previously calibrated torque that characterizes the state of a vehicle that is unloaded except for the driver and has just been moving. This moment can be determined from the start of the clutch engagement by the drop in the speed of the internal combustion engine. Since the loading of the vehicle generally does not change or changes only rarely during a journey, the previously determined value can be used as an estimate until a new value is determined.

The particular advantage of the solution according to the invention arises in motor vehicles that are equipped with an automatic start-stop system. Such an automatic start-stop system switches off the internal combustion engine when the motor vehicle is at a standstill or when there is no momentary request and starts it automatically when a corresponding driver request is detected.

The invention is explained in more detail below with reference to the exemplary embodiment shown in the figures.

1 shows a diagram that explains a first variant of the method according to the invention, FIG. 2 shows a diagram that explains a second variant of the method according to the invention, FIG. 3 schematically shows the essential components of the drive train of a motor vehicle according to the invention in a first variant and 4 shows a further variant embodiment of the drive train.

In the diagram of FIG. 1, the engine speed n is plotted over time t. At time t = 0, the internal combustion engine is at a standstill, and it is assumed that the signal to start the internal combustion engine and to drive off is given after a corresponding driver request is detected, which is expressed, for example, by depressing the accelerator pedal. The use of the starter increases the speed n of the internal combustion engine 1. When a predetermined speed n! is reached, the clutch 2 begins to engage and the torque transmission to the drive wheels 4 begins. A drive torque is transmitted from the internal combustion engine 1 to the wheels 2 via the slipping clutch 2. The speed n of the internal combustion engine 1 ultimately drops to a value n as a result of the torque transmission₂ from, but is kept at the height selected for the start-up process by a suitable device in the control of the drive train. This value n₂ is always above the minimum speed n_min, generally also lie above the idle speed. The predictability of the system behavior ensures that the minimum speed n_min is not fallen below.

At time t_s, which is shortly after the point in time, the first injection takes place, and the internal combustion engine 1 begins to deliver a positive torque. At time t_ee, the night_sync, the engagement process of clutch 2 is complete and direct power transmission is established.

The variant embodiment of the method of FIG. 2 differs from that of FIG. 1 in that the clutch is initially engaged up to time t. The gearbox is in neutral so that no power transmission takes place. Between the times L and t₂ the clutch is opened so that a control command can be given to the automatic gearbox to engage first gear. From the time te_S. the method proceeds analogously to that of FIG. 1.

The course of the clutch actuation is shown below the tn diagram of FIG. 2, where o denotes the open state of the clutch and e denotes the engaged state.

3 shows schematically in a first variant the essential components of the drive train of a motor vehicle according to the invention. An internal combustion engine 1 is connected to an automatic gearbox 3 via an automatically actuated clutch 2. The gearbox 3 drives the drive wheels indicated schematically with 4 via a drive train, indicated here only by 10. A crankshaft 50 starter generator 9 is provided upstream of the clutch 2 and is used, among other things, to start the internal combustion engine 1. A further clutch 12 is optionally provided between the internal combustion engine 1 and the crankshaft starter generator 9, which enables the vehicle to be operated purely electrically. With this embodiment variant, both the method according to FIG. 1 and the method according to FIG. 2 can be implemented.

In the embodiment variant of FIG. 4, a starter generator 9 is parallel to the gearbox 3

AT 412 861 B arranged. A first belt drive 5 is arranged upstream of the gearbox 3 and a second belt drive 6 is arranged downstream of the gearbox 3. The belt drives 5 and 6 are connected via clutches 7, 8 to the electric machine 9, which serves as a starter generator. With an appropriate design of the gearbox 3, the clutches 7, 8 can also be designed as synchronizer rings, or can be replaced by such.

Since the clutch 2 is arranged upstream of the belt drive 5, only the method of FIG. 2 can be implemented with such an embodiment variant. By opening the clutch 2 at time t₂ the transmission of the torque from the starter generator 9 to the internal combustion engine is interrupted, so that the speed n after the time t₂ begins to sink.

It is obvious to the person skilled in the art that there is the possibility of carrying out a method according to FIG. 1 through appropriate modifications, even with a similar embodiment variant.