Electrical Description of EGM
Status September 2003 (EvoBus-Service / AFT)
Page: 52 of 83
3.4.3
Proportional valve actuation
To actuate external actuators and switching devices (e.g. turbocharger, gas pressure regulator, fan etc.),
four proportional valve connections are provided in the EGM-C1 sample. The valve current is controlled by
means of PWM with intelligent low-side drivers with a diagnostic function, however without current
measurement.
On the M 447 hLAG only the output Prop 1 boost pressure control is currently used.
Data for Prop 1:
Valve current:
I
Nom
= 2 A (over entire temperature range)
PWM frequency:
f
PWM
= approx. 120 Hz
PWM resolution:
< 1%
The outputs Prop3 and Prop4 are used for the low-side actuation of various fan systems. On the ÜSTRA
natural-gas Citaro the fans are actuated by a separate controller. The outputs Prop3 and Prop4 are not in
use.
3.4.4
Lambda heating actuation
The CNG engine control unit permits the connection of a broadband lambda probe, model LSU, for the
lambda control. The nominal temperature of the measuring probe is around 750 °C. As the exhaust-gas
temperature of natural-gas lean engines is considerably loser, an electrical probe heater is required.
According to the manufacturer, these new types of probes, produced in planar technology do not permit
charging with a heater voltage of 24 V. Therefore, a switching controller is integrated in the control unit
which supplies a low, load-dependent heater voltage of approx. 11 V. The heater current is continuously
measured and lies at approx. 1.1 A in the steady state.
Data for lambda heater
Heater voltage:
11 V
±
0.5 V
Heater current:
I
Nom
= 1.1 A (dependent on exhaust-gas temperature)
Min. switch-on duration:
10 ms
Resistance:
2
Ω
< R < 10
Ω
(dependent on exhaust-gas temperature)
3.4.5
High-pressure cut-off valve actuation
The high-pressure cut-off valve of a natural-gas engine is comparable to the fuel pump of a petrol engine.
Through actuation the gas injection system is supplied with fuel. For safety reasons, this valve is supplied
by Ter. 15 and energised on the control unit side with low-side actuation. As these valves have a high-
resistance design, a switching output state is sufficient.
Data for Gas_OFF:
Valve current:
I
Nom
= 2 A (over entire temperature range)
3.4.6
Ignition module actuation
The ignition modules are actuated powerlessly via a six-channel driver output stage. Each channel
controls the closing and firing angle of one cylinder. The actuation principle is shown in the following
illustration.
