DE10255180B4 - Method for controlling the startup of a supercharged engine - Google Patents

Abstract

A method for controlling the startup of a supercharged engine, in particular a small-volume high-loading engine, which is associated with an automatic transmission with a hydrodynamic torque converter, characterized in that after starting the engine and after switching the transmission in the first gear at idle speed and when applied of the engine in the direction of full load, the internal pressure of the converter is lowered to a value at which targeted cavitation occurs in the converter, so that in this state, the identifier of the converter is shifted to a lower pump receiving torque and that upon reaching the speed at which a sufficient charge pressure from Turbocharger is built to almost reach the speed for full load, the internal pressure of the converter is raised back to the normal value.

Description

The present invention relates to a method for controlling the starting of a supercharged engine, in particular a small-volume high-loading engine, which is associated with an automatic transmission with a hydrodynamic converter.

Since the introduction of automatic transmissions, hydrodynamic transducers have been the link between an engine and the actual transmission. Due to the slippage, a converter enables a comfortable smooth starting and at the same time dampens rotational irregularities of the internal combustion engine. On the other hand, the torque increase due to the principle provides a large starting torque.

A hydrodynamic converter according to the prior art consists of an impeller, a turbine wheel, the reaction member in the form of a stator and the fluid necessary for torque transmission, usually an oil.

The impeller, which is driven by the motor, puts the oil in the converter in a circular flow. This oil flow hits the turbine wheel and is deflected there in the direction of flow. In the hub area, the oil leaves the turbine and reaches the stator, where it is deflected again and thus fed to the impeller in the appropriate direction of flow. The reversal creates a moment at the stator whose reaction torque increases the turbine torque, whereby the ratio of turbine torque to pump torque is referred to as torque increase.

The larger the speed difference between pump and turbine, the greater is the torque increase, which has the maximum size when the turbine is stationary. As the turbine speed increases, the torque increase decreases.

If the turbine speed reaches 75 to 85 of the pump speed, the torque increase becomes 1, d. H. the turbine torque is equal to the pump torque.

The stator, which is supported on the transmission housing via the freewheel and the stator shaft, runs freely in this state in the flow and the freewheel is overrun. From this point on, the converter works as a pure fluid coupling. During the conversion, the stator is stationary and is supported by the freewheel on the housing.

Hydrodynamic converters can be designed in one or more stages. The number of stages is defined by the number of turbine wheels to which a stator is assigned. The stator is in this case blocked via a freewheel in one direction and freely overrun in the other direction, the Leitraddurchströmung can be centrifugal or centripetal.

Furthermore, constructions are known in which the angle of the Leitradschaufel can be changed so as to adapt the Wandlerkennung the operating point. In automatic transmissions are often used for cost and space reasons single-stage converter with centripetal flowed through non-adjustable stator.

Such a configuration may still have disadvantages in operation. An automatic gearbox with hydrodynamic converter shows depending on the identifier a more or less strong creep torque at low speeds and at standstill. In addition, the engine is required a moment at standstill, which leads to an increase in fuel consumption. In addition, in supercharged engines, the transmission absorption torque counteracts the rapid engine run-up, resulting in a sluggish engine torque build-up. This condition can be accommodated by using soft transducers, i. H. Converters are used with soft identifiers, which somewhat favor the engine run-up, but also show a deteriorated operating efficiency and a higher power loss.

Methods are also known for controlling the lockup clutch of an automatic transmission during the starting process of a vehicle, which use an electronic transmission control unit with calculation unit and an electric pressure actuator. The lockup clutch is said to be open or deactivated when no torque is being transmitted through the lockup clutch; In contrast, in the activated state, the piston of the torque converter lock-up clutch is pressurized, wherein one or more friction disks are pressed against the resulting piston force and a corresponding transmission torque is generated. However, the control of the lockup clutch is problematic in certain driving situations, including the starting of a vehicle with an automatic transmission, in which a soft hydrodynamic converter is used.

To overcome these difficulties, was already in the DE 197 05 956 C1 a method for controlling a torque converter lockup clutch of an automatic transmission during the starting process of a vehicle by means of an electronic transmission control unit with calculation unit and an electric pressure actuator proposed with a controlled converter clutch throughout Driving range, especially at a starting, from 0 km / h in the activated or regulated state can be operated. For this purpose, a reworking function for influencing slip during startup is started when it is determined in a first differentiation function that a starting gear is engaged and an additional predefined starting condition is fulfilled, whereby for slip influencing own control parameters and an own setpoint slip characteristic map, which determines the relationship between nominal slip , Turbine speed and motor torque determined to be used; the processing function is processed until it is determined in a distinguishing function that a specifiable abort criterion is met or it is determined in a subordinate discriminating function that a predefinable end criterion is fulfilled.

If an internal combustion engine is charged with exhaust gas, then the air mass supplied to the engine by the supercharging is directly dependent on the rotational speed of the exhaust gas turbine. The speed up of the exhaust gas turbine always takes place with a certain time offset to the power requirement of the driver, which feels the undesirable slow build up of the output torque of the vehicle as a "turbo lag".

In conjunction with converter automatic transmissions, the starting weakness of a motor vehicle with a supercharged engine can be positively influenced by the characteristic of the torque converter. This takes place in that the hydraulic power transmission can be mechanically bridged via the bridging clutch provided in the converter, in order to reduce the slip losses during operation at higher vehicle speeds. The hydrodynamic torque transmission ensures a smooth start-up process with high comfort. However, a disadvantage for the starting dynamics is that the engine speed must run high against the torque converter's torque. Added to this are the other drag torques that are also present in the powertrain as losses. Since the pick-up torque of a high torque gain transducer (soft transducer recognition) is lower than that of a low torque gain transducer (hard transducer recognition), the starting weakness can be partially compensated, but at the expense of poorer engine speed performance due to the soft identification.

To avoid this disadvantage has already been in the DE 100 23 053 A1 a control system for a transmission with a torque converter or a hydrodynamic coupling proposed in a motor vehicle having at least one torque in the starting of the motor vehicle clutch or brake, the starting power of the motor vehicle is controlled by a arranged in the transmission slipping clutch or brake as a function of a driver's request including parameters of the torque converter, or the hydrodynamic coupling.

The design of a transducer as a starting element depends essentially on the intended use. Significant variables here are the Anfahrwandlung, the pump pick-up torque and the speed of rotation. The selection of the appropriate transducer is made via a transducer cooperation diagram, i. H. a representation of the converter parabolas and the static full-load engine torque over the speed performed. It is important to ensure that the converter map is not too far away from the best values of the engine consumption map.

However, in low-voluminous supercharged engines, this selection no longer works because the run-up behavior of these engines is based on the suction curve until sufficient exhaust gas volume and resulting boost pressure are present and the torque approaches or approaches the static engine characteristic. H. that the motor is hindered or held fast by a converter recognition corresponding to the maximum engine torque. For this reason, converters with a lower pump absorption torque must be used for such small-volume high-loading engines and in particular for their start-up. However, these converters are too soft in the main driving range, resulting in large differential speeds, whereby the fuel consumption increases, the power loss is greater and the load of the lockup clutch also increases.

The DE 19 64 560 A discloses a hydrodynamic transmission comprising a torque converter and a torque converter upstream, modulatable friction clutch. The pressure prevailing in the torque converter can be controlled so that the braking capacity of the torque converter is reduced, but the torque converter can resume torque transmission in a very short time.

In the DE 24 56 792 A1 An apparatus for controlling the working pressure in hydrodynamic torque converters will be described. A pressure reduction in the torque converter is caused when an instantaneous value of a speed signal is below a reference voltage.

The DE 100 23 053 A1 discloses a control system for a transmission with a hydrodynamic torque converter, comprising at least one in the starting process of the motor vehicle torque conducting clutch or brake, wherein the starting power of the vehicle on the at least one slipping, torque in the starting process of the motor vehicle clutch or brake as a function of the driver's request, including parameters of the converter is regulated.

Object of the present invention is to provide a method for dynamic starting even for small-volume high-turbocharged engines with a hard converter.

Based on a method of the type mentioned in more detail, the solution of this problem is carried out with the features specified in the characterizing part of the patent claim.

According to the invention, it is thus provided that, after starting the engine and after switching the transmission into the first gear at idle speed and when the motor is loaded in the direction of full load, the internal pressure of the converter is lowered to a value at which cavitation specifically occurs in the converter, thus In this state, the identifier of the Wandles is shifted to a lower pumping torque and that upon reaching the speed for the full load, the internal pressure of the converter is increased again to the normal value.

Thus, the method according to the invention fulfills the function of a traction aid with harder converter recognition, with the advantage that the starting behavior and the acceleration is improved, that the NBS function can be represented cost-effectively, that lower power losses occur in the converter both at its standstill and during startup, that the heat input into the transmission is reduced, that the fuel consumption is reduced, that the lamella load in the converter clutch is reduced and that the number of converter detections is reduced, whereby the logistics costs and finally the costs can be reduced.

In the following the invention will be explained in more detail with reference to the drawing, in which the inventive method is shown schematically. Show it:

1 a schematic representation of a hydrodynamic converter and

2 a schematic diagram of the speed and pressure over time.

1 shows purely schematically a hydrodynamic torque converter for the automatic transmission of a motor vehicle, which is well known to those skilled in the art, so that a more detailed description need not be discussed here. P is the impeller, T is the turbine wheel and L is the stator, while p_Zulauf and p_Ablauf designate oil-carrying lines for the supply of the hydrodynamic torque converter.

Out 2 goes out the inventive method. After starting a small-volume high-turbocharged engine, it runs at idling speed, ie idle. Now, the transmission is turned on in the first gear, according to which in the position indicated by Pos. 1 on the abscissa t the driver acts on the engine in the direction of full load, ie the accelerator pedal passes. At this time, the internal pressure of the converter p is lowered in the direction of a lower pump receiving torque via one of the two oil-carrying lines p_Zulauf or p_Ablauf, so that the motor can run up almost freely, as shown by the curve n-An. At the point in time indicated in item 2, the engine speed reaches the value at which sufficient boost pressure from the turbocharger can be established to reach almost full engine torque full load. At this time, the internal pressure P of the converter is raised again to the normal level, so that the starting operation can be continued as usual.

The same principle can also be applied when the vehicle is at a standstill in order to keep the engine droop and thus the loss low, or to replace a complex mechanical representation of the function "neutral at standstill".

• n

  rotation speed

  p

  internal pressure

  p_Zulauf

  oil-carrying pipe

  p_Ablauf

  oil-carrying pipe

  n-Tu

  Turbine speed

  L

  stator

  P

  impeller

  T

  turbine

Claims (1)

A method for controlling the startup of a supercharged engine, in particular a small-volume high-loading engine, which is associated with an automatic transmission with a hydrodynamic torque converter, characterized in that after starting the engine and after switching the transmission in the first gear at idle speed and when applied of the engine in the direction of full load, the internal pressure of the converter is lowered to a value at which targeted cavitation occurs in the converter, so that in this state, the identifier of the converter is shifted to a lower pump receiving torque and that upon reaching the speed at which a sufficient boost pressure of Turbocharger is built to nearly the speed for full load too reach, the internal pressure of the converter is raised back to the normal value.

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