Engine brake control apparatus and method

An electronic microcomputer based engine brake control device and a method for controlling an engine compression brake is disclosed. An algorithm for enabling engine brake operation includes monitoring a brake enable switch, engine RPM, engine fueling rate, cruise control or power takeoff system activation state, throttle position, manifold pressure and clutch pedal position. Engine brake operation is fully automatic and operates in a safe manner according to the disclosed algorithm.

FIELD OF THE INVENTION 
This invention relates generally to an improved engine brake control 
apparatus and method and more particularly to an electronic control unit 
for monitoring a variety of input signals corresponding to operating 
conditions and enabling engine brake operation only when the input signals 
meet predetermined conditions. 
BACKGROUND OF THE INVENTION 
Adequate and reliable braking for large vehicles, particularly tractor 
trailer vehicles, is assisted by devices known as engine brakes or engine 
compression brakes. An engine brake system utilizes the energy required to 
compress air in the cylinders of the engine to brake the vehicle. The drag 
put on the drive line by the engine when placed in the compression braking 
mode can serve to slow the vehicle more rapidly, when used in conjunction 
with the disc or drum brakes of the vehicle. 
With the advent of electronic controls for use with internal combustion 
engines, the sophistication of control strategies increases. Specifically, 
when an engine control module or ECM is responsible for monitoring a host 
of parameters in supplying a variety of control signals to various 
devices, the ECM should prevent operation of engine compression braking 
when certain operating conditions exist. 
One known engine brake controller device is shown in Meistrick et al., U.S. 
Pat. No. 4,664,070. The device disclosed therein includes a compression 
release-type engine retarder having a hydro-mechanical valve actuating 
mechanism operated by an electronic controller which responds to throttle 
position, actuation of the brake pedal, and other manual or automatic 
control or inputs. Other patents showing electrical controllers for 
operating compression release engine retarding systems include Meistrick, 
U.S. Pat. No. 4,592,319, and Sickler, U.S. Pat. No. 4,572,114. 
Tart, Jr. et al., U.S. Pat. No. 4,742,806, discloses an engine braking 
system including an on/off switch and switches connected to other 
parameters such as clutch throttle position which, when in a favorable 
position, allow the system to operate, but when in an unfavorable 
position, the system is disabled. Furuhashi, U.S. Pat. No. 4,401,073, 
Matsunaga, U.S. Pat. No. 4,640,241, and Gravestock, U.S. Pat. No. 
4,655,187 disclose electronic fuel control systems which include various 
inputs and outputs. Muir, U.S. Pat. No. 3,525,317, discloses a 
multiple-position switch actuated by a throttle pedal so that the position 
of the throttle pedal provides actuation in a multiple stage fashion of 
the engine compression braking system disclosed therein. 
A control strategy for preventing operation of engine braking except when 
certain operating conditions and parameters are satisfied will provide 
more efficient and safer operation of engine braking. 
SUMMARY OF THE INVENTION 
A compression brake control device for use with a vehicle having an engine, 
a clutch, a transmission, a compression brake apparatus having a brake 
input and activated in response to signals supplied to the brake input, 
and a throttle control device, the brake control device according to one 
aspect of the present invention comprises fuel metering means for 
controlling fuel delivery to the engine, the fuel metering means including 
a fuel signal input, the fuel metering means supplying fuel to the engine 
in accordance with signals supplied to the fuel signal input, throttle 
position sensor means for sensing the position of the throttle control 
device, the throttle position sensor means producing a throttle signal 
corresponding to the position of the throttle control device, pressure 
sensor means in fluid communication with the intake manifold of the 
engine, the pressure sensor means producing a pressure signal 
corresponding to intake manifold pressure, control circuit means for 
supplying a fueling signal to the fuel signal input in accordance with the 
throttle signal, RPM sensor means for producing an RPM signal 
corresponding to engine RPM, and brake circuit means for supplying a 
braking signal to the brake input of the compression brake apparatus in 
accordance with concurrence of the following conditions: the RPM signal is 
greater than a predetermined RPM limit; the throttle signal is below a 
predetermined throttle limit; the fueling signal is below a predetermined 
fueling limit; and the pressure signal is below a predetermined pressure 
limit. 
A method for activating and deactivating a compression brake in an internal 
combustion having a throttle control according to another aspect of the 
present invention includes the steps of (a) detecting a throttle control 
position below a predetermined throttle limit, (b) detecting an intake 
manifold pressure below a predetermined pressure limit, (c) detecting an 
engine speed above a predetermined RPM limit, (d) detecting a fuel 
metering signal corresponding to a fueling rate below a predetermined 
fueling limit, and activating the compression brake only when the 
conditions in steps (a), (b), (c), and (d) are concurrently satisfied. 
One object of the present invention is to provide an improved engine brake 
control device. 
Another object of the present invention is to provide an engine brake 
control device which monitors and senses a plurality of inputs and 
operating conditions and tests whether a predetermined combination of 
input conditions and operating conditions exist prior to activating the 
compression brakes. 
A further object of the present invention is to provide safety lockout 
conditions for preventing activation of the engine brakes under certain 
circumstances wherein operation thereof would endanger the driver of the 
vehicle or other persons in nearby vehicles. 
These and other objects of the present invention will become more apparent 
from the following description of the preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
For the purposes of promoting an understanding of the principles of the 
invention, reference will now be made to the embodiment illustrated in the 
drawings and specific language will be used to describe the same. It will 
nevertheless be understood that no limitation of the scope of the 
invention is thereby intended, such alterations and further modifications 
in the illustrated device, and such further applications of the principles 
of the invention as illustrated therein being contemplated as would 
normally occur to one skilled in the art to which the invention relates. 
Referring now to FIG. 1, an engine brake control device 10 according to the 
present invention is shown. The engine brake control device 10 includes an 
engine control module or ECM 12. ECM 12 is a microcomputer including ROM, 
RAM, EEPROM, analog I/O and digital I/O. Connected to the ECM 12 are a 
variety of input and output devices which form a part of the engine 
control system. Devices which are controlled by ECM 12 include fuel 
shutoff valve 14, cylinder select device 18, engine brake relay 16, and 
fuel injectors 30. Cylinder control devices for activating compression 
braking of individual pairs of cylinders designated as blocks 24, 26 and 
28 are indirectly controlled by ECM 12 when relay 16 is energized. A 
variety of input signals are supplied to digital and analog inputs of ECM 
12, which inputs correspond to operating conditions of the vehicle. More 
particularly, switches SW1 and SW2 provide input signals to the ECM 12 
representing the operator's request for power takeoff (PTO) and cruise 
control operation. Switch SW1 provides set/coast and resume/acceleration 
input signals while SW2 is the activation signal indicating that power 
takeoff operation or cruise control operation is desired. Switches SW1 and 
SW2 are dual function switches in that while the vehicle is moving down 
the road the switches act or function as cruise control operation 
switches, and while the vehicle is stationary and a particular fixed speed 
of engine operation is desired to run a power takeoff device, such as a 
cement mixer truck, the ECM 12 will determine that the vehicle is not 
moving and that the driver is requesting power takeoff operation rather 
than cruise control operation. 
Switch SW3 is mechanically coupled to brake pedal 32 via linkage 34. 
Likewise, switch SW4 is mechanically coupled via linkage 38 to clutch 
pedal 36. Switches SW3 and SW4 supply logic signals to ECM 12 
corresponding to the position of pedals 32 and 36, respectively. 
Accelerator pedal 40 is mechanically coupled to potentiometer P1 via 
linkage 42. Wiper W1 of potentiometer P1 is electrically connected to an 
analog to digital or A/D input of ECM 12. RPM and engine position sensor 
22 includes a tone wheel or gear tooth detection sensor (a variable 
reluctance or Hall effect device sensor) and corresponding signal 
conditioning circuitry for producing a signal representative of engine 
RPM. The signal produced by RPM sensor 22 is an analog signal. 
Alternatively, the signal produced by sensor 22 may be a digital pulse 
train. 
Boost pressure sensor 20 is mounted on the engine and in fluid 
communication with the intake manifold of the engine. Where a typical 
heavy duty truck engine includes a turbocharger for increasing intake 
manifold pressure, an intake manifold sensor or boost pressure sensor 20 
is utilized to monitor one operating condition of the engine. The boost 
pressure sensor 20 produces an analog signal which is supplied to an A/D 
input of ECM 12. Engine brake switch SW5 is a double-pole, single-throw 
switch located in the driver's cab compartment. Switch SW5 provides two 
separate functions when actuated. First, switch SW5 provides an input 
signal to ECM 12 indicating that the driver of the vehicle desires engine 
brake operation. Additionally, switches SW5 and SW6, when enabled, supply 
power (12 VDC) to relay 16, and thus enable engine brake operation when 
ECM 12 has energized relay 16. As a further safeguard, switch SW6 is 
included in the system design to prevent activation of the cylinder select 
block 18 in the event the contacts of relay 16 become welded together and 
will not open. Thus, key switch SW6 prevents activation of cylinder select 
device 18. 
Fuel injectors 30, of which there are six, are activated via six control 
signals represented by signal bus 31. Resistors R1-R5, and resistor R7 
provide pull down functions well known in the art for maintaining the 
logic inputs of ECM 12 at a logic low state to prevent floating of the 
inputs of ECM 12 to a logic high state under high impedance conditions or 
switch "open" conditions. 
Referring now to FIG. 2, a flow-chart for the engine brake control 
algorithm according to the present invention is shown. ECM 12, in addition 
to its other functions of providing fuel injection signals to the fuel 
injectors 30 and monitoring other operating conditions of the vehicle, 
also is responsible for periodically monitoring the conditions associated 
with engine brake operation and activating the engine braking apparatus 
when certain predetermined conditions exist. Typically, ECM 12 executes 
the algorithm depicted in FIG. 2 many times a second so that a continuous 
monitoring of inputs and resulting control of outputs occurs in a real 
time fashion. Specifically, the algorithm for enabling engine brake 
operation includes monitoring the brake enable switch SW5 at step 100 for 
a request for engine brake operation. If the switch is on, or closed, then 
step 102 is next executed. However, if switch SW5 is open, program flow 
continues with step 116 where ECM 12 will deactivate the compression 
braking apparatus by de-energizing relay 16 and energize the fuel shutoff 
valve 14 to enable fuel to be supplied to the fuel injectors 30. At step 
102, the engine speed as detected through sensor 22 is tested to see if it 
is above or below 1000 RPM. If below 1000 RPM, program execution will 
continue at step 104. If engine speed is above 1000 RPM (or an alternate 
yet suitable predetermine speed) at step 102, then program execution 
continues with step 116. 
ECM 12 examines the contents of memory locations which correspond to the 
rate or level of fueling of the engine at step 104. The fueling rate data 
recalled from memory is indicative of and enables a determination of the 
duty cycle of the pulse width modulated signals supplied to the injectors 
30. In particular, the fuel injectors 30 receives the pulse width 
modulated signals produced by ECM 12. If the pulse width modulated signals 
supplied to the fuel injectors 30 are all less than a predetermined duty 
cycle, i.e. such as an 8 percent or lower duty cycle signal, then program 
execution will continue at step 106. However, if the duty cycle of the 
fuel signals is greater than a predetermined duty cycle percentage, which 
may range anywhere from 8 to 22 percent or higher, then program execution 
will continue with step 116. At step 108, ECM 12 checks the throttle 
position via a test of the voltage from wiper W1, to determine if the 
throttle is at or below a predetermined minimum position corresponding to 
a predetermined voltage. If the sensed voltage at W1 is at or below a 
predetermined throttle minimum voltage then program execution continues at 
step 110. If the wiper W1 voltage is not at or below the throttle minimum 
voltage, i.e. the driver has depressed and displaced the accelerator 
pedal, then program execution continues with step 116. At step 110, ECM 12 
checks the input signal from boost pressure sensor 20 to determine if the 
intake manifold pressure is within a predetermined range (a valid signal 
indicating the sensor is functioning properly) and below a predetermined 
pressure limit or if the engine brake is presently active or operating. If 
either or both of these logic conditions are satisfied, then program 
execution will continue at step 112. If neither of the dual conditions of 
step 10 are satisfied, then program execution continues with step 116. At 
step 112, ECM 12 monitors the input signal from switch SW4 to determine 
whether the driver of the vehicle has depressed the clutch pedal 36. If 
switch SW4 indicates the clutch pedal has been depressed, then program 
execution continues with step 116. If at step 112 the clutch is released, 
i.e. switch SW4 is closed, then program execution continues with step 113. 
At step 113, the signal from the intake manifold pressure sensor or boost 
sensor 20 is analyzed by ECM 12 for out of range conditions, i.e. the 
sensor is producing a signal indicative of a defective sensor. If the 
sensor 20 is producing an out of range signal, it is desired that engine 
braking remain operational if all other conditions in steps 100-112 are 
currently satisfied for engine brake operation. Therefore, if the sensor 
20 signal is out of range, a predetermined "sensor defective" delay is 
executed by ECM 12 before program execution continues at step 114. 
Alternatively, if the sensor 20 signal is within a range which indicates 
the sensor if functioning normally, then program execution continues at 
step 114 after step 113. At step 114, ECM 12 delays a period of time 
before supplying a signal to relay 16 activating relay 16, and thus 
activating cylinder select device 18. Cylinder select device 18 controls 
cylinder control blocks 24, 26 and 28 to enable three separate levels of 
engine braking operation. Optionally, ECM 12 can deenergize fuel shutoff 
valve 14 at step 114 to prevent additional fuel from flowing to fuel 
injectors 30. If relay 16 is deenergized before execution of step 114, 
then ECM 12 delays activation of relay 16 at step 114 for a predetermined 
"activation" period of time (up to several seconds) to expend fuel in the 
system or engine after de-energizing valve 14. Similarly, when the state 
of relay 16 is changed from deenergized to energized, a predetermined 
"deactivation" time delay is executed by ECM 12 at step 116 after 
deactivating compression braking before valve 14 is energized to allow the 
vehicle brake hydraulics (not shown) to mechanically release the drive 
train before fueling begins. After steps 114 or 116, program execution 
continues with step 100 wherein the host of conditions necessary for 
engine braking operation are again checked. In this manner, an algorithm 
enabling engine brake operation is continuously operating and allows fully 
automatic operation or activation of the engine brakes which provides 
increased convenience to the driver of a heavy duty truck. 
Referring now to FIG. 3, a more detailed block diagram of the engine brake 
control device 10 according to the present invention is shown. Like 
components of FIG. 1 are identified with like designations in FIG. 3. 
System componentry located in the cab area A includes clutch switch SW4, 
brake switch SW3, engine brake on/off switch SW5 and cruise control 
switches SW1 and SW2. Accelerator position sensor assembly P1 corresponds 
with potentiometer P1 of FIG. 1. Vehicle key switch SW6 is also shown. 
Cylinder selection device 18 and engine brake relay 16 are also shown 
located in the cab area A while cylinder control devices 24, 26 and 28 are 
attached to the engine (indicated by broken line B). In addition, other 
components of this system include an idle validation switch SW7 and an 
idle/diagnostics INC/DEC switch SW8. A tachometer output 50 is provided in 
the cab area as well as a data link 52 which enables connection to an 
external diagnostics device. Fault lamps 53 provide an indication to the 
driver of various engine operating or fault conditions detected by ECM 12. 
A diagnostic test input 54 is also provided in the cab area for entering 
input information with regard to diagnostics. 
Systems closely associated with and attached to the engine of the vehicle 
are contained within the broken line B. Sensors which provide operating 
condition information to ECM 12 include boost pressure sensor 20, engine 
speed/position sensor 22, vehicle speed sensor 56, oil temperature sensor 
58, ambient air pressure sensor 60, manifold air temperature sensor 62, 
coolant temperature sensor 64, oil pressure sensor 66, and coolant level 
switch 68. 
Device which are subject to control by ECM 12 include wastegate solenoid 
70, fuel shutoff valve 14, and fuel injectors 30. Also shown are a vehicle 
fuel tank 72, a fuel filter 74, a fuel supply pump 76, a battery 78, a 
fuse 80, and fan clutch solenoid 82 controlled by ECM 12. Lastly, ECM 12 
is located within fuel cooler 84 to provide a temperature controlled 
environment for ECM 12. 
The system depicted in FIG. 3 corresponds with the electronic controls 
designed and manufactured by Cummins Electronics and Cummins Engine of 
Columbus, Ind. The device 10 is sold and marketed under the trade name 
CELECT by Cummins Engine. 
While the invention has been illustrated and described in detail in the 
drawings and foregoing description, the same is to be considered as 
illustrative and not restrictive in character, it being understood that 
only the preferred embodiment has been shown and described and that all 
changes and modifications that come within the spirit of the invention are 
desired to be protected.