Interface for Coupling an Analyzer to a Distributorless Ignition System

This invention utilizes apparatus described and claimed in U.S. Pat. No. 5,068,613 filed Oct. 11, 1988, entitled METHOD AND APPARATUS FOR GENERATING DISPLAY WAVEFORMS IN WASTED SPARK IGNITION SYSTEMS, in the names of K. A. Kreft, M. Dikopf and T. D. Loewe, and is related to application Ser. No. (651,077), filed Feb. 1, 1991, entitled A METHOD OF DERIVING A PRIMARY CLOCK, in the names of T. D. Loewe and D. M. Oles, all of which are assigned to Sun Electric Corporation.

This invention relates generally to ignition analyzers for automotive engines and particularly to an interface unit for coupling an ignition analyzer, such as the Sun Electric Corporation Model MCA 3000, to automotive engines having distributorless ignition systems.

In distributorless ignition systems, individual pairs of spark plugs are connected by a common ignition coil and are fired simultaneously, with one firing resulting in a real firing event and the other firing resulting in a wasted firing event. The real firing event occurs on the compression stroke. The wasted firing event occurs on the exhaust stroke and contributes no power to the engine. With the arrangement, a single ignition coil is used for each pair of spark plugs which are fired with opposite polarity voltages. The voltage during the wasted firing event is typically one third of the voltage during the real firing event. For a four cylinder engine, two individual ignition coils are required and for a six cylinder engine, three are required. A major difficulty is that it is not readily known whether a spark plug experiences a real firing event or a wasted firing event since each spark plug is fired during both the compression and the exhaust strokes of each engine cylinder cycle. The above-mentioned copending application Ser. No. 256,168 describes a system that determines the real and wasted firing events by using a pair of pickup clamps, each of which is coupled to the spark plug wires having secondary voltages of like polarity, in conjunction with a #1 cylinder secondary pickup clamp.

Difficulties often arise because of the crowded conditions under the hood of a modern day automobile and because of the engine design. Often it is not possible to access all of the spark plug wires of like polarity with a single pickup clamp. In the above-mentioned system in U.S. Pat. No. 5,068,613, the two pickup clamps are designed to couple spark plug wires having the same signal polarity. In an automobile engine where that is physically impossible with the pickup clamps, the present invention solves a need.

With the invention, the engine type is entered into the interface unit via a keypad. A so-called vehicle personality module or card is installed to interconnect with the vehicle connector. The personality module provides level matching for signals going between the vehicle and a logic cell array (LCA). The LCA is in communication with a ROM memory that stores spark plug polarity and pattern information for a variety of different engines, configures a solid state input switch such that an appropriate polarity signal is outputted for a particular spark plug wire, irrespective of the signal input polarity received by the signal pickup clamp. The particular wires that are to be grouped in each pickup clamp are identified for the technician via a display device. A #1 cylinder pickup clamp is installed on the #1 cylinder spark plug wire and provides #1 cylinder clock information to the LCA. As mentioned, in accordance with the U.S. Pat. No. 5,068,613, the secondary signals are sorted into wasted and real firing event groups and the real firing event (power) #1 signal is determined. Thus the interface of the invention permits the engine analyzer to be used with distributorless ignition systems of many different types.

A principal object of the invention is to provide a novel interface for coupling an engine analyzer to a distributorless ignition system.

Another object of the invention is to provide an analyzer interface that simplifies a technician's job.

A further object of the invention is to provide an interface for a distributorless ignition system and an engine analyzer that does not require like polarity secondary signals to be grouped together in the same pickup clamp.

These and other objects and advantages of the invention will be apparent upon reading the following description in conjunction with the drawing, the single FIGURE of which is a simplified block diagram of the inventive interface coupled to a distributorless ignition system.

Referring to the drawing, an engine 10, illustrated as having four cylinders, has an associated distributorless ignition system 11 that supplies secondary or firing voltages, via a plurality of spark plug wires 12, 13, 14 and 15, to corresponding ones of a group of four spark plugs 16. A pair of secondary voltage pickup clamps 18 and 20 is provided, with each clamp encircling a pair of spark plug wires and responding to secondary voltage signals thereon. A cylinder #1 pickup clamp 22 is coupled to the #1 spark plug wire on engine 10 for picking up the #1 cylinder secondary voltage. Secondary pickup clamp 18 is coupled to a buffer amplifier 24 and secondary pickup clamp 20 is coupled to a buffer amplifier 26. The outputs of the buffer amplifiers are coupled to a semiconductor input switch 28 which produces a pair of outputs, one having all of the positive polarity firing event which are supplied to a balance amplifier 30 and the other having all of the negative polarity firing events which are supplied to an inverter 32. Balance amplifier 30 is a variable gain amplifier that balances the levels of the signals from input switch 28 since some are processed by inverter 32. The outputs of balance amplifier 30 and inverter 32 (both positive) are coupled to a pattern switch 34 and to a secondary waveform switch 36. The outputs of pattern switch 34 are also coupled to secondary waveform switch 36 and to a pair of sample-and-hold circuits 38 and 40, respectively. The sample-and-hold circuits function to elongate or stretch out the very short duration secondary ignition voltages from pattern switch 34. The sample-and-hold circuits 38 and 40 are in turn coupled to a comparator 42 which develops an output that reflects the largest amplitude signal. The output of comparator 42 is applied to a logic arrangement 44. The output of secondary waveform switch 36 supplies a variable gain amplifier 46, the output of which provides the secondary waveforms to an engine analyzer (not shown).

The programmable logic cell array 50 includes a plurality of input and output connections and is coupled to logic circuit 44. LCA 50 is readily available ("off the shelf") under the designation XILINX PRE 2064. LCA 50 is also coupled to input switch 28, to pattern switch 34, to secondary waveform switch 36 and to comparator 42. The #1 cylinder clock signal is applied through a wave shape circuit 84 to LCA 50. LCA 50 obtains a timing clock corresponding to the #1 cylinder signal (or other selected cylinder) from waveshape circuit 84. As fully disclosed in the above-mentioned U.S. Pat. No. 5,068,613, the real and wasted firing events are determined based upon the magnitude of the signals from pattern switch 34 and coordinated with the #1 cylinder signal so that the real and wasted firing event signals are all determined by LCA 50. LCA 50 outputs a signal, corresponding to the real #1 cylinder firing event, to a trigger loop circuit 52 which provides the trigger signal for the engine analyzer. LCA 50 is also in communication with a primary signal processor 54 which is coupled to the primary signal processing circuitry of the engine analyzer. An adapter 56 is coupled to LCA 50 and communicates with a bidirectional bus 57. Adapter 56 is commonly referred to as VIA (versatile interface adapter) and is an IC of the type RC 522. The bus 57 in turn is coupled to a microprocessor control unit (CPU) 58, a programmable interval timer 60, a display device 62, a user-operated keypad 64 and a serial communications arrangement 66, the latter of which permits communications with the host engine analyzer or other computer. CPU 58 is coupled to LCA 50, as is programmable interval timer 60. A ROM 90 is accessible to CPU 58 and includes the spark plug location and signal polarity information for each of the various engine types. As mentioned, this information is made available to LCA 50 via CPU 58 and keypad 64. Lastly, the vehicle personality module is coupled to LCA 50. As mentioned, this module is adapted to be intercoupled with a vehicle connector 88 that is resident on the particular vehicle under test. The vehicle personality module may contain information particular to the particular vehicle, group of vehicles or type of vehicle and may be used by the technician to obviate the entry of engine type data into LCA 50 via the keypad. In the preferred embodiment, the personality module contains interface circuitry (i.e. level shifting) to couple the vehicle signals to the analyzer. The personality module thus is capable of bringing an enhanced degree of automation to the engine analysis process and in the preferred embodiment, enables the MCA 3000 to perform comprehensive tests on the engine.

A separate rapid test circuit feature is also shown for conducting secondary only testing operations relatively quickly. The rapid test sequence is automatically accessed in the absence of a vehicle personality module. Such a test, in which the secondary waveforms are viewed and analyzed, provides a gross analysis of engine performance and may obviate more detailed tests or point out particular tests that should be performed. In the rapid test only the secondary pickup clamps 18 and 20 and the trigger pickup clamp 22 are installed (along with a battery connection, not shown). This arrangement consists of an adder 68 that is supplied with the outputs of the input switch 28 and, which in turn, supplies a pair of differentiators 70 and 72. The outputs of the differentiators are applied to respective threshold detectors 74 and 76 which supply respective monostables 78 and 80. One output of monostable 78 is also supplied as an input to monostable 80. The monostable outputs are applied to the R and S inputs of an RS flip-flop 82, the output of which is coupled to LCA 50. The purpose of this arrangement is to develop a pseudo primary "points open" and "points closed" clock signal to drive the digital logic circuitry since LCA 50, in the rapid test arrangement, is not provided with any primary information. The pseudo clock signal enables the LCA to determine the real and wasted sparks and therefore to perform very fundamental secondary voltage checks to determine the gross operating parameters of the engine.

A pair of square wave pulses is developed by detectors 74 and 76. The monostables have different timing cycles, with monostable 78 being about 2.4 ms and monostable 80 being about 1.15 ms. The 2.4 ms square wave is used to block the negative pulse resulting from ringing of the secondary firing event waveform. This arrangement is claimed in copending application Ser. No. 651,077.