Ignition system

A modular electronic ignition system for use in internal combustion engines is provided using latching Hall effect sensing devices. Two permanent magnets are affixed to a non-ferrous member mounted to the camshaft which extends through a seal in the timing cover. A sensing module comprising the Hall effect devices is arranged annularly or angularly about the magnet containing member and senses the magnetic field as the magnets pass the Hall effect devices. Dwell time is controlled by the angular distance at which the magnets are placed from each other. The output of the Hall effect devices drives application specific integrated circuits which provide low level switching of ignition coil primaries. The modular design allows for a low part count, a simplified EMI shielding arrangement, and easy removal and replacement of system components.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to ignition systems for use in 
internal combustion engines and more particularly to an ignition system 
for use in internal combustion engines employing magneto-responsive solid 
state sensing devices. 
2. Description of the Prior Art 
Ignition of the fuel to air mixture in internal combustion engines by 
electric spark has been achieved in many ways. Regardless of the system 
implemented, there exists the fundamental necessity to provide and deliver 
a high voltage pulse to the spark plugs with sufficient energy content to 
create an electric arc between center electrodes and ground electrodes of 
the spark plugs. In addition, the high voltage pulse must be delivered to 
each spark plug at the appropriate time and for an appropriate duration of 
time. Modern systems typically have sensor or triggering means that sense, 
via an angular position of a crankshaft, when a piston in a particular 
cylinder is entering a power stroke in the engine cycle and relay that 
information in some manner. Processing circuitry with high voltage, high 
current switching means is used to energize a primary coil of an ignition 
coil and a secondary coil delivers a high tension pulse to the spark 
plugs. One drawback to the known systems is that it is necessary that all 
the ignition processing circuitry be RF shielded. Poor shielding can lead 
to system malfunction or complete failure, particularly in those systems 
that require microprocessors. High tension wires, i.e. spark plug wires, 
must also be shielded so as not to affect ignition processing circuitry as 
well as other electronic devices such as car stereos, car phones, and the 
like. 
As stated, sensing and triggering means exist that sense the angular 
position of an engine's crankshaft either directly or indirectly. 
Presently, inductive sensing means are most often implemented. Inductive 
sensing requires that a magnetic field at the sensor change. Although a 
change in magnetic flux induces a voltage in a conductor, 
magneto-responsive devices are not always "inductive" in that sense. A 
magnetic field may be used to effect sensor output in which the magnitude 
and not a change in flux of the field causes a sensor output to change. 
Hall effect elements, and the devices in which they are used, are examples 
of magneto-responsive solid-state devices that do not work on the 
principle of rate of change induced voltage. Instead, a magnetic field 
perpendicular to the flow of current causes a difference in electric 
potential throughout a conductor or semiconductor. The resulting voltage 
is referred to as the Hall voltage. The output voltage of a sensor of this 
type as effected by the Hall voltage is independent of the rate of change 
of the magnetic field being sensed. 
The advantages of using a Hall effect device, versus other magnetic means 
for crank angle sensing, include: (1) smallest package size; (2) low cost; 
(3) minimum parts count; (4) sharp trigger response; (5) good resistance 
to environmental effects. 
Latching Hall effect devices provide an advantage in that timing intervals 
can be set with two very small permanent magnets. This contrasts with more 
involved external means of extending the response of non-latching devices 
that are known. The prior art teaches the use of a single Hall effect 
device, namely a bipolar two-output Hall device, that is spaced between a 
pair of opposing permanent magnets. Dual magnetic flux fields of the same 
magnitude are generated at the Hall effect device which cancels the effect 
on the device. A crankshaft mounted disk carries metallic tabs in specific 
relation to shunt the magnetic field between one and then the other of the 
magnets and the Hall effect device at predetermined intervals which allows 
the device to be actuated by the remaining magnetic field at the sensor. 
One of the outputs of the bipolar Hall device, depending on which field is 
shunted, relays the sensor output to one of two input channels of a 
microprocessor. The related output channel of the microprocessor is input 
to a related coil driver, ignition coil, and then the spark producing 
means of two of four cylinders. The dwell time, i.e., the time for which a 
primary coil is energized to saturation before the collapse of the 
magnetic field in the ignition coil and thereby inducing a high voltage 
pulse in the secondary coil which is grounded through the spark plugs, is 
determined by the length of a metallic tab. The longer the tab, the longer 
the Hall effect device produces a Hall voltage, which, by way of some 
intermediate circuitry, energizes the primary coil. Similarly, a single 
magnet and two single output Hall effect devices are taught and function 
in a like fashion. In both cases, the sensor is arranged to sense the 
angular position of the crankshaft in direct relation to the crankshaft's 
rotation. Because the crankshaft makes two complete revolutions per power 
stroke in a given cylinder in four stroke cycle engines, the ignition coil 
or coils are fired twice during one complete engine cycle for a particular 
cylinder. One of the firings is delivered between exhaust and intake 
strokes and is of no benefit. In fact, this doubles the necessary burden 
of the system. 
Also known in the art is a solid state ignition system utilizing a 
non-latching Hall effect switch as a means of advancing and retarding the 
ignition timing. The Hall effect switch is activated by a D.C. biasing 
voltage which is induced in a coil by permanent magnets carried on the 
rotatable member of a small, single cylinder, magneto fired engine. The 
use of the Hall effect switch in this application differs greatly from 
that previously described. 
Examples of the above-described devices may be found in U.S. Pat. Nos.: 
4,155,340; 4,508,092; 4,406,272; 5,158,056; 5,014,005; 4,903,674; 
3,556,068; 2,768,227; 4,918,569; 5,113,839; 3,587,549; 2,811,672; and 
3,621,827. Additionally, French Patent 2,422,044 and U.S. Pat. Nos. 
2,675,415 and 2,462,491 may be of interest. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
solid state, contactless ignition system for internal combustion engines. 
A further object of this invention is to provide an improved solid state, 
contactless ignition system for internal combustion engines, having a 
simpler, more reliable design. 
It is another object of this invention to provide an improved solid state, 
contactless ignition system for internal combustion engines, of modular 
form to permit removal and replacement of the system components quickly 
and easily. 
It is yet another object of this invention to provide an improved, solid 
state, contactless ignition system for internal combustion engines, having 
a simplified EMI shielding arrangement. 
Briefly, these and other objects may be achieved by a system which employs 
inductive sensing using four Hall effect latching integrated circuits, two 
camshaft mounted miniature permanent magnets, four application specific 
integrated circuit coil driver devices, and two modular snap-on firing 
modules. 
Other objects and features of the present invention will be apparent from 
the following detailed description of the preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to the Figures, wherein like reference characters indicate 
like elements throughout the several views and, in particular, with 
reference to FIG. 1, the front view of an internal combustion engine is 
depicted with the solid state ignition system according to the present 
invention. A sensing module SM is depicted which is attached to a "timing 
cover" TC with two retaining screws RS1 and RS2, which penetrate cover TC 
through two adjustment slots AS1 and AS2 in module SM flange. Module SM 
may be rotated clockwise or counterclockwise by loosening screws RS1 and 
RS2 and applying force to a timing tang TT affixed to a cover SMC of 
module SM. Rotating module SM causes an advancement or retardation of the 
ignition timing as will be shown. Also depicted are two firing modules 
FM1,3 and FM 2,4. More precisely, it is the firing module covers MC1 and 
MC2 that are shown in FIG. 1 which are similar in appearance to 
conventional valve covers and snap onto the cylinder heads CH1 and CH2. 
Covers MC1 and MC2, and the components housed by and attached thereto, 
make up modules FM1,3 and FM2,4 which are identical and interchangeable. 
The components that make up modules FM1,3 and FM2,4, and the functions 
thereof, will be explained in conjunction with FIGS. 2, 6, 7 and 8. 
Referring now to FIG. 2, which depicts firing module FM1,3, according to 
the invention with the internal components being shown with dashed 
outlines, module FM1,3 comprises a dual coil driver circuit board CB1, two 
ignition coils IC1 and IC3, two spark plug towers PT1 and PT3, firing 
module cover MC1, sensor output receiving terminal ST, as well as wire 
conducting means between the components as required. The wire conducting 
means have been omitted from FIG. 2 for clarity. The sensor output signal 
from module SM is transmitted to terminal ST via a shielded conductor (not 
shown). The sensor output signal is transmitted from terminal ST to 
circuit board CB1 which contains two application specific integrated 
circuits CD1 and CD3, hereafter referred to as ASIC coil drivers, which 
provide low level switching for the primary coils of coils IC1 and IC3. 
Output from circuit board CB1 drives coils IC1 and IC3 which in turn 
provide a high voltage output via high voltage leads to two spark plug 
terminals (not shown). The high voltage leads are secured to the spark 
plug terminals through towers PT1 and PT3. Electrical contact between the 
leads and the spark plug terminals is maintained under spring pressure. 
All high voltage components, as identified above, are contained within 
cover MC1, which by means of contact to the engine structure, provides EMI 
shielding which satisfies EMC requirements worldwide. Said EMI shielding 
cannot be defeated when module FM1,3 is properly attached to the cylinder 
head (not shown). It should be again noted that module FM2,4 is identical 
and operates identically for the remaining two cylinders of the present 
embodiment of the invention. 
Referring now to FIG. 3, which depicts an expanded side view of a camshaft 
magnet adapter MA and module SM. The module SM's circuit board SB, which 
contains four identical latching Hall effect integrated circuit devices 
and related circuitry, later described, is shown as is cover SMC. The 
advantages of using a Hall effect device, versus other magnetic means for 
crank angle sensing, include: (1) smallest package size; (2) low cost; (3) 
minimum parts count; (4) sharp trigger response; (5) good resistance to 
environmental effects. 
Latching Hall effect devices provide an advantage in that timing intervals 
can be set with two very small permanent magnets. This contrasts with more 
involved external means of extending the response of non-latching devices 
that are known. Also shown is adapter MA to which are affixed two 
miniature permanent magnets, N and S. Magnets N and S are mounted at 90 
degrees to each other at the outer edge of adapter MA. The poles of 
magnets N and S at the outer edge of adapter MA differ; N is the north 
pole and S is the south pole. Adapter MA is mounted to an extension of 
camshaft CS, which protrudes through a sealed opening in cover TC. As will 
be seen in later Figures, adapter MA, circuit board SB, and cover SMC are 
all aligned in concentric relation with necessary operating clearance 
provided between adapter MA and circuit board CB. 
Referring now to FIG. 4, which depicts a front view of circuit board SB, 
adapter MA, devices HA1 through HA4 and related circuitry, again magnets N 
and S are shown at 90 degrees to each other with N being North pole 
outwardly arranged and S being south pole outwardly arranged. For 
clockwise rotation of the camshaft CS at a constant speed, any one of the 
devices, HA1 through HA4, will therefore experience the magnetic field of 
magnet N and then that of S at shorter intervals then between S and N. 
Devices HA1 through HA4 are arranged at 90 degree intervals near the inner 
edge of circuit board SB. All have identical related circuitry which will 
be explained in detail in reference to FIG. 5 which follows. 
Referring now to FIG. 5, which is a schematic of the components of one of 
the four identical sensing circuits mounted to circuit board SB, the 
circuit shown comprises an A3185E solid state latching Hall effect 
integrated circuit HA1, and a 250 ohm resistor R1. A regulated voltage 
source 5 VS is connected to pin 1 of the solid state latching Hall effect 
integrated circuit HA1, as well as one side of resistor R1. Pin 2 is 
grounded. The remaining side of resistor R1 is connected to the output of 
HA1 at pin 3. The output of HA1 at pin 3 is connected to the firing 
circuit not shown. In the present embodiment, this regulated source 
maintains 5 volts at pin 1 of the solid state latching Hall effect 
integrated circuit HA1, which provides a biasing voltage to HA1. Resistor 
R1 is used to hold the voltage at pin 3 of the solid state latching Hall 
effect integrated circuit HA1 high when the solid state latching Hall 
effect integrated circuit HA1 is in an off state. 
Referring now to FIG. 6, which is a functional electrical diagram of the 
complete sensing and firing elements necessary for one cylinder, adapter 
MA is depicted with magnets N and S. An arrow is shown to indicate 
clockwise rotation. The sensing circuit previously described in reference 
to FIG. 5 is shown here generally as sensing circuit SC. ASIC CD1, 
VB921ZVSP coil driver power 1C, is a proprietary design of SGS-Thomson 
Microelectronics, and is comprised of resistors R2 and R3, zener diode D1, 
diode D2, vertical current flow power trilington transistor Q1 and 
integrated control circuit UD1. Ignition coil IC1 containing primary coil 
WP1, and secondary coil WS1 are shown, as are capacitors C1 and C2, and 
transient voltage suppressor TVS1. A voltage source VS is connected to one 
side of primary coil WP1, the other side of which is switched to ground by 
ASIC CD1. 
It should be understood that the following explanation concerning the 
operation of the ignition system according to the instant invention, in 
reference to FIG. 6, applies to the remainder of the sensor and firing 
circuits identically. Because the operation of the ignition system is 
repetitive in nature, the explanation to follow will assume an arbitrary 
starting point. For that reason, adapter MA will be assumed to be rotating 
clockwise as indicated and magnet N will be assumed to be proximate to the 
solid state latching Hall effect integrated circuit HA1. The field of 
magnet N causes the solid state latching Hall effect integrated circuit 
HA1 to release the output at pin 3 from ground. Upon doing so, 5 volts are 
applied to the output at pin 3. The 5 volts are applied to the ASIC coil 
driver CD1 closing transistor Q1 causing the low side of coil WP1 to be 
grounded. As a result, current then flows through WP1 and a magnetic field 
builds in coil IC1. The field is allowed to build until such time as 
device HA1 is once again activated by the presence of an opposing magnetic 
field. This quality distinguishes latching Hall effect devices from 
non-latching Hall effect devices, which do not maintain the operative 
state of the device in the absence of an actuating field incident of the 
device. 
As magnet S passes the solid state latching Hall effect integrated circuit 
HA1, the output of the solid state latching Hall effect integrated circuit 
HA1 at pin 3 is grounded. Transistor Q1 is driven to the off state. With 
transistor Q1 open, current flow in WP1 ceases and the field acquired in 
coil IC1 collapses. A high tension voltage is induced in the secondary 
coil, WP2, which is grounded through a spark plug. The resulting arc 
between the plug's electrodes ignites the charge in the cylinders. Diodes 
D1 and D2 are for circuit protection. D1 provides collector voltage 
clamping, D2 dampens flyback spikes generated by collapse of the coil 
field and UD1 amplifies, controls and provides coil current limiting. The 
coil IC1 is not energized again until the passing of N at which point the 
cycle repeats as previously described. Transient voltage suppressor TVS1 
and capacitors C1 and C2 are optional and serve to reduce noise in the 
system. 
In a second embodiment (not shown), field effect transistors, driven by 
high speed drivers, are used for low level switching for the primary 
coils. It should be noted that, while a preferred embodiment of the 
invention would use the ASIC coil drivers previously discussed, many 
systems are known which are capable of providing low level switching of 
the primary coils. 
It should be appreciated that, although the magnets have been described as 
being placed at 90 degrees to each other in the instant invention, the 
annular distance between magnets N and S determines the dwell time, which 
may appropriately be desired less than that which would result in the 
system as described above. Furthermore, the passing of magnet S, and the 
ignition of the charge in a given cylinder shortly thereafter, corresponds 
generally to the point in time when a piston has reached top dead center, 
or the accepted number of degrees before top dead center, in anticipation 
of a power stroke. Therefore, the annular distance between sensors should 
be equal regardless of the number of cylinders a particular engine 
utilizing such a system as has been described above may have. It should 
also be understood that by rotating module SM relative to the camshaft's 
angular position, the timing of the spark to all cylinders is either 
advanced or retarded equally. 
A contactless and distributorless ignition system has been described, 
possessing many desirable qualities. The use of latching Hall effect 
devices allows for a simplified sensing arrangement and method of dwell 
control. By sensing the rotational position of the camshaft, a spark is 
provided to each cylinder only once during a cycle rather than twice, 
thereby relieving the system of an unnecessary burden. The system is 
essentially comprised of only four basic components, a non-ferrous adapter 
with two permanent magnets affixed to a camshaft which extends through a 
seal in the timing cover, a sensing module, and two identical firing 
modules. This modular design allows for easy removal and replacement of 
the components which may reduce the time and cost of repair. Further, 
because all high tension components are RF and EMI shielded by the firing 
module cover, individual shielding for many components is avoided and the 
wiring necessary for the system is reduced. Also, because the circuitry is 
well protected from outside elements and the firing modules and sensing 
module employ very simple, solid covers, the entire engine may be 
externally cleaned easily, without affecting the ignition system's 
operation. 
Although the present invention has been fully described in connection with 
the preferred embodiment thereof with reference to the accompanying 
drawings, it is to be noted that various changes and modifications are 
apparent to those skilled in the art. Such changes and modifications are 
to be understood as included within the scope of the present invention as 
defined by the appended claims, unless they depart therefrom.