Engineering Test Report
Evaluate the new Banks SpeedBrake and compare downhill retarding effect to stock and a traditional valve style exhaust brake.
The late model GM (and Ford) diesel pickup truck engines are equipped with variable geometry turbochargers. The design of the turbo includes vanes that can be manipulated to change the dynamics of the exhaust flow past the turbine wheel. The control of these vanes is managed by the ECU and by intercepting signals, independent positioning of the vanes is possible.
Diesel engines lack the drop throttle braking characteristics exhibited by gasoline engines due to their lack of an intake throttle valve. However, engine braking can be induced by introducing a restriction in the exhaust flow, causing an increase in exhaust back pressure acting against the piston during the exhaust stroke. Traditionally this effect has been achieved using a valve assembly mounted downstream of the turbine wheel.
The Banks SpeedBrake takes exhaust braking to a new and intelligent level by capturing control of the turbine vanes and closing them to a predetermined safe position when engine braking is desired. By combining manipulation of the turbine vanes with specific control of gear selection and torque converter clutch application, auxiliary braking becomes much more effective than is possible with a simple valve assembly. Furthermore, additional control features allow for variable manipulation used to control downhill speed to a specific set point.
The SpeedBrake has various operating modes and settings that allow the user to optimize the function for individual preferences and conditions:
Banks SpeedBrake Modes
The SpeedBrake has three operating modes; ON, SPEED CONTROL and OFF. In the ON mode, the SpeedBrake will activate and fully close the turbocharger vanes to achieve maximum braking. In SPEED CONTROL mode, the SpeedBrake varies the position of the turbocharger vanes and selects an appropriate gear in order to maintain a pre-selected target speed. In the OFF mode, the vehicle will behave as if the SpeedBrake is not present.
Strength Settings
While in the ON mode, there are three strength selections available; HIGH, medium (MED) and LOW. The purpose of these settings is to allow for variations in vehicle weight as well as user preference. The HIGH strength setting achieves the highest level of braking activity by aggressively downshifting the transmission. This setting is recommended for heavily loaded vehicles or whenever aggressive braking behavior is desired. The MED strength setting achieves a moderate level of braking activity by slightly delaying transmission downshifts. This setting is recommended for moderately loaded vehicles. The LOW strength setting achieves a lower level of braking activity and is recommended for lightly loaded or unloaded vehicles. The LOW setting may also be appropriate for stop-and-go driving.
Speed Selection
While in the SPEED CONTROL mode, the SpeedBrake will act by controlling the user-selected speed, similar to the function of a vehicle’s cruise control. There are two methods available for speed selection. The target speed can be increased or decreased from its current value in increments of 1 MPH, or the user can select from three different speed presets, which are user adjustable. For example, when traveling down a 6% grade with a heavy load, 50 MPH may be an appropriate speed for safe descent. With 50 MPH selected as the target speed, the SpeedBrake will act to maintain 50 MPH and no less. If the target of 50 MPH cannot be met after the SpeedBrake has taken all possible actions to do so, an advisory message to the driver will display on the Vehicle-User Interface (VUI), instructing the use of the foot brake to help slow the vehicle.
Foot Brake Activation
Since the SpeedBrake is an auxiliary braking device, the user may select options that provide the best interface method for individual driving style or vehicle load conditions. The use of the foot brake will have varied influence on overall braking depending on the SpeedBrake mode that is selected. A selection checkbox allows the user to either ENABLE or DISABLE the Foot Brake Activation feature.
Foot Brake Activation Disabled
When ON mode is selected and Foot Brake Activation is disabled, braking will occur any time that the driver releases the accelerator pedal, regardless of whether or not the foot brake is used. When SPEED CONTROL mode is selected, any use of the foot brake will have no impact on SpeedBrake activity.
Foot Brake Activation Enabled
When ON mode is selected and Foot Brake Activation is enabled, the SpeedBrake will only become active if the foot brake is applied. Once the driver releases the foot brake, SpeedBrake will deactivate. In this condition, the foot brake pedal effectively becomes an “On” switch for the SpeedBrake. Only slight pedal pressure is required to activate the SpeedBrake. Some drivers will find that this method of brake activation is preferable to constant brake activity.
When SPEED CONTROL mode is selected and Foot Brake Activation is enabled, the SpeedBrake will effectively switch to ON mode, closing the turbo vanes to provide maximum braking and downshifting the transmission according to the selected Strength setting. (Note: This change in braking conditions will not change the VUI display.) Depending on the vehicle speed and the selected target speed, the driver may or may not notice any difference in SpeedBrake functionality. For example, if the target speed is 50 MPH and the actual vehicle speed is 60 MPH, the SpeedBrake will be selecting maximum braking strategy in an attempt to slow the vehicle down, therefore when the foot brake is applied, there will be no noticeable increase in SpeedBrake activity. However, if the actual vehicle speed is only 45 MPH, lower than the target speed, the SpeedBrake will not be providing any braking effect. Therefore, when the foot brake is applied, braking activity will become much greater and the driver will feel an increase in braking effect. This condition is useful when the driver has selected the SPEED CONTROL mode and conditions require the vehicle to slow down or stop, such as approaching a highway off-ramp.
Vehicle-User Interface (VUI)
The VUI provides two-way communication between the user and the vehicle. During normal operation, the VUI will display vehicle speed, current braking effort (indicative of vane position), transmission temperature, engine coolant temperature, operating gear, braking mode, target speed and system status. A System Menu is available to the user that allows for a variety of adjustment selections, some of which have already been discussed.
System Status Indicator/On Screen Alerts
The System Status Indicator is used in conjunction with On Screen Alerts and will inform the user of any important messages. Under normal conditions, the indicator will be highlighted green and will have a green check mark in it. The user has the option of setting warning alerts if either coolant or transmission temperature exceed a preset value. In such a case, the System Status Indicator will be highlighted red and a warning message will appear. This warning is also accompanied by an audible alarm. The threshold temperature values are user adjustable from 180 to 250 degrees and the audible alarm volume may be set to low, medium, high or silent. The status indicator will also communicate any faults that may be detected in the SpeedBrake circuitry, allowing for quick and easy troubleshooting.
OBDII Scan Tool Capability
Because the SpeedBrake is integrated with the vehicle’s communication system, it can also serve as an OBDII scan tool. If a check engine light should appear on the dash, the user can use the SpeedBrake to read, interpret and clear the codes.
Test Vehicle
A 2006 Chevrolet Silverado 4x4 Crew Cab Short Bed with the LBZ Duramax engine, single rear wheel with Allison 6-speed automatic transmission was used as the test vehicle. The results of this testing are representative of both the LBZ and the LMM. A weight trailer was added to the vehicle bring Gross Combined Weight (GCW) to approximately 18,500 lbs. Testing was conducted on CA-HWY 138 near the intersection of CA-HWY 2. The test location consists of approximately 1 mile of 6.16% grade.
Test Method
As the vehicle crests the top of the hill, speed is maintained at 55 MPH. Drive is the selected gear. As needed to maintain consistent speed, the driver lifts off the accelerator pedal which determines the beginning of the test. As the vehicle descends the hill, terminal velocity is noted. All tests were conducted with Tow/Haul mode active. The foot brake is purposely not applied during descent except to prevent unsafe speeds and runaway conditions. Speed is noted at the end of 1 mile.
Data Acquisition
A GPS-based data acquisition system was used to measure speed along with other parameters.
Stock
When the vehicle is in Drive with Tow/Haul mode active, the approach conditions to the test hill result in a gear selection of 5th. As the vehicle begins to descend the hill, it immediately begins to accelerate. With no application of the foot brake, the vehicle shifts into 6th gear at approximately the 1/3 mile mark. By about ½ mile, the vehicle is traveling at 70 MPH. To maintain safety, the driver applies the foot brake and slows the vehicle to 68 MPH. At this point, the Tow/Haul mode strategy intervenes and shifts the transmission to 4th gear. Vehicle speed still increases and reaches 70 MPH by about the ¾ mile mark. The foot brake is again applied and vehicle speed is slowed to 65 MPH. At this point the Tow/Haul strategy allows for a downshift to 3rd gear. This allows for vehicle speed to be maintained at 65 MPH for the duration of the run.
PacBrake
The PacBrake is a mechanical valve that installs in the exhaust system about 3 feet behind the turbocharger. It requires cutting into the exhaust system and welding to join the pieces together. A compressor is mounted under the hood and wiring is run into the cab of the vehicle for the activation switch. It does not include any electronic management and relies on the Tow/Haul mode to enhance its functionality. As with the stock run, the vehicle is in 5th gear at the top of the hill. Although braking activity is initiated, the vehicle continues to accelerate. At a little past the halfway mark, the vehicle shifts into 6th gear. By the end of the run, vehicle speed is 68 MPH, an increase of 13 MPH.
BD
Like the PacBrake, the BD brake is a mechanical valve that installs in the exhaust system about 3 feet behind the turbo and requires cutting and welding for installation, and a compressor and wiring is installed. It also includes no electronic management and relies on the Tow/Haul mode to enhance its functionality. Braking behavior was nearly identical to the PacBrake, with a final speed of 70 MPH, 15 MPH over stock.
Banks SpeedBrake
The first benefit that becomes obvious about the SpeedBrake is its ease of installation compared to the PacBrake and BD. It is entirely electronic and installs with a few simple underhood connections. No modification to the exhaust system is required. A single communication wire runs from the SpeedBrake module through the firewall to the VUI. (Note: If the SpeedBrake is being installed on a vehicle with a Banks diesel tuner, the two units simply interface with each other under the hood and under the dash. No additional wiring needs to be installed through the firewall.) The entire installation is non-intrusive and does not require any cutting or splicing of wires.
The first test of the SpeedBrake was performed in the Speed Control mode with a set target speed of 50 MPH. As with the previous runs, the vehicle starts the decent in 5th gear. But as soon as the driver lifts his foot from the accelerator, the SpeedBrake begins braking activity by closing the turbine vanes and downshifting the transmission to 3rd gear. This quickly brings the vehicle down to its target speed of 50 MPH. Once the target speed is achieved, the SpeedBrake varies the position of the turbine vanes such that speed is maintained at 50 for the duration of the run.
The next test of the SpeedBrake was performed in the Brake ON mode with the Strength setting on HIGH. This evaluates the SpeedBrake’s maximum braking capability. As in all the previous runs, the test begins with the vehicle in 5th gear. Like the previous run while in Speed Control mode, the transmission is shifted into 3rd and the vehicle quickly begins to decelerate. But since the ON mode does not have a target speed, the vehicle continues to decelerate and shifts clear down into 1st gear. By ¾ of the way down the hill, the vehicle is traveling at 15 MPH. This is a speed reduction of 40 MPH.
Conclusion
The SpeedBrake outperforms the competitive products by leaps and bounds in its basic braking function, and adds new dimension to the capabilities of an exhaust brake. The Speed Control mode is only possible with the type of electronic sophistication offered by the Banks SpeedBrake.
