State of the Art
[0001] The invention relates to a glow plug controller for a combustion engine. The
US 6, 009, 369 A1 discloses a glow plug controller with improved functionality and diagnostics.
Advantages of the invention
[0002] The glow plug controller and the method of controlling the glow plug controller,
with the features of the independent patent claims have the below advantages:
[0003] Introducing offsets in the PWM frequency, results in spreading the energy contained
in the spikes appearing on the power lines of the glow plugs, bringing down the peak
energy level in a measuring widow and hence bringing down the peak level of the Electro
Magnetic Interference (EMI) in the measuring window. The reduced EMI from the glow
plugs will improve the smooth operation of the glow plugs and also ensure safe operations
with other electronic devices in the proximity.
[0004] Further improvements and/or advantages are realised by the features of the dependent
patent claims.
[0005] The glow plug controller uses a known PWM generator which generates a plurality of
PWM signals which are sequential in time.
[0006] The jitter generator used to vary the frequency of the PWM signals uses a pre-stored
table containing the offsets for the PWM frequencies which is simple.
Brief description of the drawings
[0007] The embodiments of the invention are shown in the drawing and are described in detail
in the description.
- Figure 1
- Shows schematic of a glow plug controller
- Figure 2
- Shows the graphs of the PWM signals and the current signal for PWM signals with 50%
duty cycles
- Figure 3
- Shows the graphs of the PWM signals and the current signal for PWM signals which have
more than 50% duty cycles
- Figure 4
- Shows the current and energy graphs
- Figure 5
- Shows the PWM signals, current and energy graphs with jitter
Description of the embodiments
[0008] Shown in Figure 1 is a glow plug controller 10 receiving engine parameters 18 and
delivering PWM signals 31 to 34 to glow plugs 20 to 23 respectively. The glow plug
controller 10 further comprises a computation means 12, a sequencing means 14 and
a jitter generator 16. The number of PWM signals and the glow plugs may vary depending
upon the engine requirements.
[0009] The computation means 12 receives the engine parameters 18 such as engine temperature,
ambient air temperature and pressure, fuel quantity to be injected, intake mass air
flow, exhaust gas characteristics, exhaust gas recirculation characteristics etc.
to calculate the effective voltage and the timing information 15 for each of the PWM
signals 31 to 34. The effective voltage and the timing information 15 are supplied
to the sequencing means 14.
[0010] The sequencing means 14 receives the effective voltage and the timing information
15 and using the same, generates a plurality of PWM signals 31, 32, 33 and 34 which
are delivered to the glow plugs.
[0011] The PWM signals 31, 32, 33 and 34 are continuous in time and have a frequency F.
Each of the PWM signals 31, 32, 33 and 34 comprise PWM pulses of time duration T which
is 1/F. The time duration T includes both on time and off time of the PWM pulse.
[0012] The jitter generator 16 when activated by the sequencing means 14 generates different
offsets for the time duration T of the PWM signals. Different offsets are added to
T in positive and negative directions, keeping the original T at the centre. For example
if the original T of the PWM signal is 40 millisecond, different offsets are added
to it to generate modified T, for example, of durations 37 msec, 38 msec, 39 msec,
40 msec, 41 msec, 42 msec and 43 msec. The original T is kept at the centre and other
values are at equal steps to its left and right sides. The jitter generator may compute
the offsets dynamically or it may contain a pre-computed table containing the different
time durations of the PWM signals for different conditions. To generate PWM pulses
of varying time durations, the frequency of the PWM signal is varied so that the rising
edge of the PWM pulses keep shifting in both directions. The movement of the rising
edges of the PWM pulses is like adding jitter to the original PWM signal. This jitter
reduces the peak energy measured in a window on the power lines thereby reducing the
Electro Magnetic Interference EMI. The working of the invention is explained in detail
in subsequent paragraphs.
[0013] The glow plugs 20 to 23 get energised when the PWM signals have high level and get
de-energised when the PWM signals have low level. The glow plugs 20 to 23 get heated
up when they are energized and help in igniting the fuel injected into the combustion
chambers which are not shown.
[0014] The glow plugs and the glow plug controllers are already known as state of the art.
Glow plugs are used to bring the engine temperatures to an operating level where the
air and fuel mixture ignites easily on compression, in the diesel combustion engines.
Diesel engines are substantially different from the standard spark ignition internal
combustion engines. The diesel engine does not have a sparking device such as a standard
spark plug. Fuel is ignited when fuel and hot compressed air are mixed in the engine
cylinders. For this ignition to occur efficiently, the engine must be brought to a
temperature at or above a given minimum operating temperature because a cold diesel
engine will not achieve ignition.
[0015] Glow plugs are used as heaters to heat the diesel engine prior to initial start up.
These glow plugs serve to bring the diesel engine to an efficient operating temperature
before the engine is started. Ideally glow plugs will rapidly bring a diesel engine
to a desired starting temperature. After the engine has started, the glow plugs operate
for sufficiently long time to maintain desired engine temperature until engine self-heating
reaches an efficient sustainable point. The glow plugs also enable the engine to run
smoothly during an initial period and minimize emissions. Once an engine can sustain
its operating temperature, the glow plug is turned off.
[0016] The glow plugs are also used in different engine running conditions to help the ignition
of the air fuel mixture or to bring the temperature of the exhaust gases to a predefined
value, for example, when the engine needs to run in re-generation mode where the soot
in the exhaust pipe needs to be burnt.
[0017] The temperature of the glow plugs is controlled by controlling the voltage supplied
to the glow plugs and also the duration of the voltage supplied to the glow plugs.
The computation of the timing requirements is normally done by a glow plug controller
based on the engine parameters. The glow plugs are supplied with power from the battery
of the vehicle.
[0018] The computation means 12 in Fig. 1 receives the engine parameters 18 and based on
the engine parameters 18, the computation means computes the temperature requirements
of the glow plugs and also the timing information. The temperature requirement of
the glow plugs is then converted into the effective voltage required for each of the
glow plugs to attain the required temperature. The computed effective voltage values
and the timing information are supplied to the sequencing means 14. Based on the effective
voltage required for each of the glow plugs and the timing information, the sequencing
means generates a PWM signal for each of the glow plugs.
[0019] Figure 2 shows the PWM signals generated by conventional state of the art glow plug
controllers. The PWM signals shown in the graphs 2A, 2B, 2C and 2D are generated by
the sequencing means 14, the X axis of the graphs representing the time t and the
Y axis representing the voltage V. Each of the PWM signals 2A, 2B, 2C and 2D control
one of the glow plugs 20 to 23. Here as an example the duty cycles of the PWM signals
are taken as 50%. The PWM signals are sequential, i.e. at t1 the on period of the
first PWM starts. At t2, the on period of first PWM signal ends and the on period
of second PWM starts. At t3, the on period of second PWM signal ends and the on period
of third PWM signal starts. At t4, the on period of third PWM signal ends and the
on period of fourth PWM signal starts. The cycle keeps repeating as long as the glow
plugs are operational. Four glow plugs are shown only as an example but the number
of glow plugs may vary based on the engine.
[0020] The graph 2E shows the current waveform as observed on the power lines supplying
power to the glow plugs for the above case where the duty cycles of the PWM signals
are 50%. From t1 to t2, only glow plug 20 is on, from t2 to t3 only glow plug 21 is
on. So from t1 to t3 the current is constant at a level I1. From t3 onwards, at any
given time two glow plugs are on. So the current drawn is twice, i.e. 12, constantly.
[0021] Figure 3 shows the PWM signals generated by conventional state of the art glow plug
controllers where the PWM signals have more than 50% duty cycle. For such cases the
current drawn will not be constant as there will be overlap of on-periods of different
PWM signals at different time slots.
[0022] The graph 3A, 3B, 3C and 3D are similar to the graphs in Fig. 2, the only difference
being the duty cycles of PWM signals in Fig.3 are more than 50%. The graph 3E shows
the current waveform as observed on the lines supplying power to the glow plugs for
the above case where the duty cycles of the PWM signals are more than 50%. Here from
t1 to t3 current remains at I1, from t3 to t5 current is at 12, at t5 a small spike
appears for a small duration where the current is at I3 because three glow plugs have
on periods. Similarly at t7, for a small duration of the time the current is at level
13. The cycle repeats as long as the glow plugs are operational.
[0023] The measurement of current in a measuring window W is shown in graph 3E. The part
is blown in the figure 4 graph 4A.
[0024] Fig. 4 graph 4A shows the measurement of current in the measuring window W where
the spike appears, the X axis representing the time t and the Y axis representing
the current 1.
[0025] The graph 4B shows the energy representation of the graph 4A. During the window a
peak level in the energy is observed which corresponds to the spike in the current.
The peak energy also represents the Electro Magnetic Interference caused by the glow
plug during the measuring window as the EMI is directly proportional to the energy.
[0026] All the electronic devices which cause EMI need to adhere to safety standards wherein
the EMI caused by them should be below a limit, the limit being prescribed by the
governing authorities, for safe operations of the electronic devices in proximity
of each other. So each electronic device undergoes an EMI test before it is declared
as fit for use.
[0027] The glow plugs also cause the EMI because of rapid changes in the current drawn by
them from the power supply of the vehicle when the spikes occur. So the glow plugs
undergo the EMI test before they are declared safe for use.
[0028] Here the invention proposes a method to reduce the peak level of the EMI by varying
the frequency of the PWM signals.
[0029] In Fig. 5 the graph 5A shows a normal PWM signal where the frequency of the PWM signal
is constant, the X axis representing the time and the Y axis representing the voltage.
The frequency of the PWM signal is F and the time duration of one PWM pulse is T,
the T being 1/F.
[0030] The graph 5B shows the PWM signal wherein the T of the PWM pulse is varied by varying
the frequency F of the PWM signal. The frequency is varied by adding small steps of
positive and negative offsets to the frequency F as explained earlier. The resulting
PWM signal is shown with dotted lines in graph 5B.
[0031] The variation of the frequency of the PWM signals is achieved using the jitter generator
16. The jitter generator 16 has a table where different values of T are stored for
different frequencies for the PWM signals. The jitter generator 16 when activated
provides to the sequencing means, the offsets to be used for the PWM signals based
on the current frequency of the PWM signals and also based on engine parameters. The
jitter generator may also calculate the offsets in real time.
[0032] The graph 5C shows the current in the window 'W' where a spike is observed because
of the overlap of on periods of different glow plugs. The position of the spike keeps
shifting to left and right because of the variation in frequency of PWM signals.
[0033] The graph 5D shows energy analysis of the graph 5C. Because of the variations in
the frequency of PWM signals, the energy contained in the spike gets distributed over
a wide range of frequency components, in the measuring window W. The distribution
of the energy results in reduction of peak energy level when the frequency of the
PWM signal is varied. The reduction of peak energy in the window W will directly reduce
the peak EMI level as the EMI is directly proportional to the energy.
[0034] Using the invention, the glow plugs have a reduced EMI level in a given measuring
widow and may easily meet the safety standards set for EMI tests for the glow plugs.
[0035] In the embodiment described above, the glow plug controller has its own microcontroller
and has computation means. In another embodiment, the glow plug controller can be
realised in an engine control unit which controls the engine.
[0036] While at least one exemplary embodiment has been presented in the foregoing description,
it should be appreciated that a vast number of variations exist. It should also be
appreciated that the exemplary embodiments are only examples, and are not intended
to limit the scope, applicability, or configuration of the invention in any way. Rather,
the foregoing detailed description will provide those skilled in the art with a convenient
road map for implementing the exemplary embodiment, it should be understood that various
changes can be made in the function and arrangement of the elements without departing
from the scope of the invention.
1. A glow plug controller (10) for vehicles, the said glow plug controller adapted to
receive engine parameters (18) to generate at least one PWM signal (31, 32, 33, 34)
deliverable to at least one glow plug (20, 21, 22, 23), the said glow plug controller
(10) characterised by a jitter generator (16) adapted to vary the frequency of the PWM signals (31, 32,
33, 34) by introducing an offset in the frequency.
2. A glow plug controller (10) according to claim 1 wherein the glow plugs (20, 21, 22,
23) receive power from the battery through power lines.
3. A glow plug controller (10) according to claim 1 wherein the on periods of the PWM
signals (31, 32, 33, 34) are in a sequential order with respect to time.
4. A glow plug controller (10) according to claim 1 wherein the on periods of the PWM
signals overlap with each other based on the duty cycles of the PWM signals.
5. A glow plug controller (10) according to claims 1, 2, 3 and 4 wherein the overlaps
of the on periods of the PWM signals cause spikes in the current on the power lines.
6. A glow plug controller (10) according to claim 1 and 5 wherein the jitter generator
(16) introduces a jitter in the frequency of the PWM signals (31, 32, 33, 34) by varying
the frequency of the PWM signals (31, 32, 33, 34) thereby causing a distribution of
energy contained in the spikes, bringing down the peak energy level in a measuring
window around the spikes.
7. A glow plug controller (10) according to claim 1 is a part of an engine control unit.
8. A method to operate a glow plug controller (10), the said method comprising the steps:
- receiving engine parameters (18)
- generating at least one PWM signal (31) for at lease one glow plug (20) in dependence
of the engine parameters (18)
- adding a jitter to the PWM signals (31, 32, 33, 34) by varying the frequency used
to generate PWM signals (31, 32, 33, 34) whenever spikes appear in the current measurement
in a measuring window, thereby reducing the peak level of the energy in the measuring
window.
Amended claims in accordance with Rule 137(2) EPC.
1. A glow plug controller (10) for vehicles, the said glow plug controller adapted to
receive engine parameters (18) to generate a set of PWM signals (31, 32, 33, 34) deliverable
to a set of glow plugs (20, 21, 22, 23) respectively, the said glow plug controller
(10) characterised by a jitter generator (16) adapted to vary the frequency of the PWM signals (31, 32,
33, 34) by introducing an offset in the frequency when the on periods of PWM signals
overlap.
2. A glow plug controller (10) according to claim 1 wherein the glow plugs (20, 21,
22, 23) receive power from the battery through power lines.
3. A glow plug controller (10) according to claim 1 wherein the on periods of the PWM
signals overlap with each other based on the duty cycles of the PWM signals.
4. A glow plug controller (10) according to claims 1, 2, 3 and 4 wherein the overlaps
of the on periods of the PWM signals cause spikes in the current on the power lines.
5. A glow plug controller (10) according to claim 1 and 5 wherein the jitter generator
(16) introduces a jitter in the frequency of the PWM signals (31, 32, 33, 34) by varying
the frequency of the PWM signals (31, 32, 33, 34) thereby causing a distribution of
energy contained in the spikes, bringing down the peak energy level in a measuring
window around the spikes.
6. A glow plug controller (10) according to claim 1 is a part of an engine control unit.
7. A method to operate a glow plug controller (10), the said method comprising the steps:
- receiving engine parameters (18)
- generating a set of PWM signal (31, 32, 33, 34) for a set of glow plugs (20, 21,
22, 23) in dependence of the engine parameters (18)
- adding a jitter to the PWM signals (31, 32, 33, 34) by varying the frequency used
to generate PWM signals (31, 32, 33, 34) whenever spikes appear in the current measurement
in a measuring window, thereby reducing the peak level of the energy in the measuring
window.