Method and arrangement for determining the storage capacity of a catalytic converter

• US 5,335,538 A
• Filed: 08/31/1992
• Issued: 08/09/1994
• Est. Priority Date: 08/30/1991
• Status: Expired due to Term

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Schneider, Erich, Schnaibel, Eberhard, Blischke, Frank
• Primary Examiner(s): RAEVIS, ROBERT R
• Application Number:
  US07/937,411
• Time in Patent Office: 708 Days
• Field of Search: 73/118.1, 60/277, 340/438, 364/424.03, 364/424.05, 364/431.01
• US Class Current: 73/114.75
• CPC Class Codes: F01N 11/007 the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus
• CPC Class Codes: F01N 2550/02 Catalytic activity of catalytic converters
• CPC Class Codes: F01N 2900/0422 measuring the elapsed time
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

The invention is directed to a method for determining the storage capacity of a catalytic converter of an internal combustion engine with the aid of a first signal from an oxygen-indicating first probe mounted forward of the catalytic converter and a second signal from an oxygen-indicating second probe mounted rearward of the catalytic converter. The first and second signals show the change from rich to lean and vice versa and the method includes the steps of: determining the storage capacity as a quantity proportional to the time-dependent integral of an integration variable; starting the integration at a time point at which said first signal changes from rich to lean or vice versa; and, ending the integration after a time interval. The method does not need a special test operation of the engine to determine the storage capacity of the catalytic converter. Instead, the method can be carried out in any steady-state operating condition for which the probe rearward of the catalytic converter regularly indicates jumps from rich to lean and vice versa. The invention is also directed to an arrangement for carrying out the invention.

Claims

1. A method for determining a value SPV for the oxygen storage capacity of a catalytic converter in the exhaust gas flow of a motor vehicle equipped with a control apparatus, the method comprising the steps of:

providing a first signal λ

_-- V from an oxygen-indicating first probe mounted upstream of said catalytic converter with said first signal λ

_-- V showing the change from rich to lean and vice versa;

providing a second signal λ

_-- H from an oxygen-indicating second probe mounted downstream of said catalytic converter with said second signal λ

_-- H likewise showing the change from rich to lean and vice versa;

determining said value SPV in said control apparatus by integrating an integration variable with said integration variable being the product Δ

λ

_-- V(t)·

LM(t);

starting the integration at a time point T_-- 0 at which said first signal changes from rich to lean or vice versa; and

,

ending the integration after a time span t_-- S with said time span t_-- S being dependent upon a measured phase shift time t_-- PS of said first and second signals of said probes and from the gas running time t_-- GV and t_-- GKH, wherein;

Δ

λ

_-- V(t)=λ

_-- V(t)-1=instantaneous deviation of the lambda value of 1;

LM(t)=air mass flow in the engine;

t_-- S=t_-- PS-(t_-- GV+t_-- GKH)=direction of the integration;

t_-- PS=measured phase shift time of the signals of said first and second probes;

t_-- GV=k1/LM=gas running time from said first probe to the upstream end of the catalytic converter;

t_-- GKH=k2/LM=gas running time from said upstream end of said catalytic converter to said second probe downstream of said catalytic converter; and

,

k1 and k2=constants dependent upon the arrangement of said probes and the volume of said catalytic converter.

2. The method of claim 1, wherein the variable k3·

Δ

λ

_-- V(t)·

LM(t) is used as said integration variable with the constant k3 being indicative of the oxygen content the air.

3. The method of claim 1, wherein said LM(t) is set for the entire integration to the value LM(T_-- 0) at the start of the integration procedure.

4. The method of claim 1, wherein the integration is carried out as a sun, nation over discrete values of the integration variable with these values being formed in the spacing of a fixed scanning time interval t_-- AT and the number n of the sun, hands being determined as an integer component of the fraction t_-- S/t_-- AT.

5. An arrangement for determining a value SPV for the storage capacity of a catalytic converter in the exhaust gas flow of a motor vehicle, the arrangement comprising:

an oxygen-indicating first probe mounted forward of the catalytic converter for supplying a first signal λ

_-- V;

an oxygen-indicating second probe mounted rearward of the catalytic converter for supplying a second signal λ

_-- H;

said first and second signals showing the change from rich to lean and vice versa;

a time-determining apparatus connected to said probes for receiving said signals to determine therefrom a storage time interval t_-- S according to the equation;

space="preserve" listing-type="equation">t.sub.-- S=t.sub.-- PS-(t.sub.-- GV+t.sub.-- GKH)

wherein;

t_-- PS=measured phase shift time of the signals of said first and second probes;

t_-- GV=k1/LM=gas running time from said first probe to the forward end of the catalytic converter;

t_-- GKH=k2/LM=gas running time from said forward end to said second probe; and

,

k1 and k2=constants dependent upon the arrangement of said probes and the volume of said catalytic converter;

said time-determining apparatus including an integration unit for computing the time-dependent integral of an integration variable Δ

λ

_-- V(t)·

LM(t) to thereby produce said value SPV for said oxygen storage capacity;

means for beginning said integration at time point T_-- 0 at which said first signal changes from rich to lean or vice versa; and

,

means for ending said integration after a time interval t_-- S and said time integral being proportional to the storage capacity, wherein;

Δ

λ

_-- V(t)=λ

_-- V(t)-1;

LM(t)=air mass flow into the engine and therefore also into the catalytic converter.