WO2000050254A1

WO2000050254A1 - Method for co-ordinating the switch between a stoichiometric and a lean mixture of an otto engine with gear shift of an automatic transmission

Info

Publication number: WO2000050254A1
Application number: PCT/DE2000/000482
Authority: WO
Inventors: Walter Janach
Original assignee: Robert Bosch Gmbh
Priority date: 1999-02-22
Filing date: 2000-02-22
Publication date: 2000-08-31

Abstract

The switch (A, B) from a stoichiometric (S) to a lean (M) air-fuel mixture in an Otto engine is carried out simultaneously with the switch from a lower (T) to a higher gear (H) in an automatic transmission, whereby the switch is triggered by releasing the acceleration pedal. The traction force (Z) is thus reduced more significantly than by a gear shift alone. Fuel consumption can thereby be reduced by additional dethrottling. The switch (B, A) from a lean (M) to a stoichiometric mixture (S), triggered by strongly pressing on the accelerator pedal, is carried out simultaneously with automatic downshifting to the next lower gear (T).

Description

Process for coordinating the switchover between the stoichiometric and lean mixture of an Otto vehicle engine with the gear change of an automatic transmission

The invention relates to a gasoline engine for vehicles, which is operated alternately with a stoichiometric or lean air-fuel mixture and an associated automatic transmission, in particular a method for coordinating the switch between stoichiometric and lean mixture with the automatic gear change of the transmission.

As is known, the operation with a lean air-fuel mixture is used in an Otto vehicle engine, in practice about 50%

Excess air, to reduce fuel consumption at partial load by dethrottling. The excess air enables the same torque to be generated with less throttling and thus less loss than with a stoichiometric mixture. For higher loads, in particular full load, the engine, on the other hand, is operated without excess air, ie stochiometrically, or even with excess fuel, ie a rich mixture.

When switching from one type of mixture to the other, the intermediate area with excess air should be avoided, because this is where nitrogen oxide emissions are greatest and cannot be reduced in a three-way catalytic converter. This means that when switching between the stoichiometric and lean mixture, the excess air suddenly jumps from zero to about 50%, which leads to a sudden drop in torque by about a third if the throttle valve is not changed. The change in torque associated with switching between stoichiometric and lean mixture is now compensated for by a simultaneous automatic adjustment of the throttle valve, so that both effects on the torque are even pick up and the driver feels practically no change in traction. The effort required for this is considerable.

On the other hand, it is characteristic of each gearbox based on the graded gear ratios of the individual gears that each gear change causes the tractive force to change with the engine torque remaining the same. For example, before an overtaking maneuver, the driver shifts down to a lower gear in order to obtain greater traction and thus greater acceleration.

In practical driving, fuel-efficient driving in a high gear with low engine speed, relatively high part load and low throttling often conflicts with the need for greater traction power reserve in a lower gear

Acceleration when suddenly needed. In automatic transmissions, this conflict of objectives is resolved by driving at the highest possible gear at constant driving speed and part load and only shifting down to a lower gear when the accelerator pedal is pressed hard.

The aim of the invention is to coordinate the changeover between the stoichiometric and lean mixture of an Otto vehicle engine with the gear change of an associated automatic transmission in a new way in such a way that both processes contribute to a greater reduction in fuel consumption than all of them . The invention also enables a larger traction reserve when shifting down into a lower gear. The Übermmaus allows the invention to dispense with the torque compensation described above when changing the mixture by adjusting the throttle valve. The method according to the invention consists in that when the tractive force required for the vehicle decreases, for example during the transition from acceleration to travel at a constant speed, the system also switches from stoichiometric to lean mixture at the same time as the automatic change to the next higher gear of the manual transmission. The result of both measures together is a greater dethrottling than by shifting on its own and is comparable to an upshift by two gear steps, for example from third directly to fifth gear. The greater dethrottling shifts the operating point of the engine closer to the consumption optimum, with a corresponding reduction in fuel consumption but also in the available tractive power reserve. This is not a problem because the automatic manual transmission immediately shifts down one gear by strongly pressing the accelerator pedal and, according to the invention, the switch to stoichiometric mixture takes place at the same time. As a result of the combined effect of both measures, the tractive power reserve increases massively, such as when shifting down by two gear steps without changing the mixture composition.

Because the change in torque resulting from the switch between stoichiometric and lean mixture coincides according to the invention with the shifting process of the automatic transmission, its effect is merely an increase in the thrust force change that occurs in any case, such as when shifting over two gear stages, and is not perceived by the driver as disturbing. Therefore, the torque change associated with the mixture changeover does not need to be compensated for by adjusting the throttle valve, which is a simplification.

In summary, the method according to the invention enables coordination of the changeover between stoichiometric and lean mixture with the gear change of an automatic one Manual transmission both a more economical driving style through increased dethrottling as well as a larger traction reserve when shifting down into a lower gear.

The invention is explained below using an exemplary embodiment with the aid of a figure.

The single figure shows a graphical representation of the tractive force (Z) of the vehicle as a function of the driving speed (V) for two different gear ratios, both for stoichiometric and lean air-fuel mixture. The two curves marked (S) represent the tensile force (Z) that can be achieved without throttling for a stoichiometric or rich mixture of. The two curves (M) apply to a mixture that is leaned with excess air. With both types of mixture (S) and (M) the engine torque and thus the tractive force (Z) can be reduced by throttling (D).

From the figure it can be seen that as a result of the different gear ratios, for example with the third gear (T) at lower speed (V) greater tractive forces (Z) are achieved than with the fourth gear (H) at higher speed (V) . The figure and the explanations below apply mutatis mutandis to other gear stages of the manual transmission, for example for second and third gear or fourth and fifth gear. The greatest tractive force (Z) is achieved in each individual gear with the throttle valve fully open and a stoichiometric (S) or even rich air-fuel mixture and can be reduced by throttling (D). When operating with a mixture that has become leaner due to excess air, the tractive force (Z) drops by around a third on the curves (M) when the throttle valve is fully open and can in turn be further reduced by throttling (D). The inventive method is that the Driver request for a decrease in the tractive force (Z), for example when transitioning from full load acceleration (S) in third gear (T) to driving at constant speed, simultaneously with the automatic change to fourth gear (H) also from stoichiometric ( S) is switched to lean mixture (M). The automatic and simultaneous changeover (A, B) of both processes is triggered by the driver withdrawing the accelerator pedal. In the opposite direction, starting from constant speed (V) with low tractive effort (Z) and lean mixture (M) in higher gear (H), triggered by a strong push on the accelerator pedal, the gearshift to the next lower gear (T) takes place simultaneously with the switchover (B, A) to a stoichiometric mixture (S), accompanied by a correspondingly strong increase in the tensile force (Z).

The practical implementation takes place according to the invention by coordinating the functions controlling the mixture changeover in an electronic engine control with the corresponding functions in the electronics of the automatic transmission control, preferably in a single overall electronics unit integrating both the engine and the transmission functions.

When driving, there are also situations in which the method according to the invention cannot be used, for example the brief interruption of the tractive force during the automatic gear change and the overrun when braking with an engine.

Claims

claims

1. A method for coordinating the changeover between stoichiometric and lean air-fuel mixture of a gasoline engine and the gear change of an automatic transmission in a vehicle, characterized in that the changeover (A, B) from stoichiometric mixture (S) to lean mixture (M) , and vice versa (B, A), simultaneously with the change from a lower gear (T) to a higher gear (H) of the automatic transmission, and vice versa (H, T).

2. The method according to claim 1, characterized in that the changeover (A, B) from stoichiometric mixture (S) to lean mixture (M) and the simultaneous change to a higher gear (H) are triggered by a depression of the accelerator pedal by Driver.

3. The method according to claim 1, characterized in that the

Switching (B, A) from lean mixture (M) to stoichiometric (S) or rich mixture and the simultaneous change to a lower gear (T) are triggered by a strong push on the accelerator pedal by the driver.

Method according to claims 1 to 3, characterized in that when switching from the stoichiometric (S) to the lean mixture (M) or vice versa, there is no presentation of the throttle valve for constant aging of the engine torque.