Engine control system

• US 4,535,740 A
• Filed: 05/31/1984
• Issued: 08/20/1985
• Est. Priority Date: 06/03/1983
• Status: Expired due to Fees

• Current Assignee: Ford Motor Company
• Original Assignee: Ford Motor Company
• Inventors: Ma, Thomas T.
• Primary Examiner(s): Dolinar, Andrew M.
• Application Number:
  US06/615,632
• Time in Patent Office: 446 Days
• Field of Search: 123/435, 123/425, 123/480, 123/486, 123/416, 123/417
• US Class Current: 123/435
• CPC Class Codes: F02B 1/04 with fuel-air mixture admission into cylinder
• CPC Class Codes: F02P 5/1455 by using a second control of the closed loop type dependent on pinking F02P5/152
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

The invention describes a control system in which open loops control the mixture strength and spark timing by means of look-up tables (14, 12) stored in a computer and a closed loop (16, 18, 20, 24) with much greater response time corrects the air fuel ratio to compensate for long term drift in the open loops under the control of an ionization sensor sensitive to the duration of the burn period. The ionization sensor output is used only in operating ranges where its output accurately reflects the burn period duration.

Consequently, the high speed response of an open loop is achieved at the same time as the long term stability of a feedback loop sensitive to the burn period duration.

Claims

1. An internal combustion engine in which the ignition timing and the fuel-to-air ratio are determined by an open loop control system including tables (12,22,14) stored in a microcomputer, the tables providing signals indicating predetermined settings of the ignition timing and the fuel to air ratio in dependence upon sensed parameters and in which a closed loop control circuit (16,18,20,24) incorporating an ionisation sensor disposed within a combustion chamber is provided for sensing a burn period duration and applying a correction to one of the signals derived from the tables stored in the microcomputer in dependence upon the sensed burn period duration, characterised in that the closed loop applies a correction to the signal for regulating the fuel-to-air ratio and has a response time substantially greater than the response time of the open loop, and in that changes in the correction effected by the closed loop are permitted only when the engine is operating within a predetermined range for which the operation of the ionisation sensor is accurately representative of the burn period duration.

2. An engine as claimed in claim 1, wherein several alternative tables are stored in the microcomputer and means are provided for latching the correction signal under different engine loads and speeds and comparing the latched off-sets, the table selection being changed in response to an excessive difference between the latched values, whereby to select maps more appropriate to the prevailing burning characteristics of the fuel.

3. An engine as claimed in claim 1 or 2, characterised in that the ionisation sensor is constituted by the spark plug of a cylinder, means being provided to monitor the impedance of the plug gap immediately after ignition has taken place.