The disclosed subject matter relates to a motor vehicle, such as a truck vehicle, which is propelled by an internal combustion engine which has an engine brake.
Some internal combustion propulsion engines of motor vehicles, such as diesel engines, typically run unthrottled. In an unthrottled diesel engine, air from an intake manifold enters through an open cylinder intake valve of a respective engine cylinder into the cylinder during an intake downstroke of a piston which reciprocates within the cylinder. The piston is coupled by a connecting rod to a crankshaft of the engine which is in turn coupled through a drivetrain to drive wheels which propel a motor vehicle.
As the engine cycle for a cylinder transitions from an intake downstroke to a compression upstroke, the cylinder intake valve operates from open to closed. Because a cylinder exhaust valve remains closed during the piston's compression upstroke, intake valve closing causes a volume of air which has entered the cylinder during the piston downstroke to be trapped in the cylinder. As the piston upstrokes, it compresses the trapped volume of air, elevating the air's temperature in the process. When diesel fuel is injected into the cylinder at or near engine top dead center (TDC), it is ignited by the hot compressed air to run the engine and propel the vehicle.
When a driver of the vehicle releases the vehicle's accelerator pedal, the engine ceases to deliver torque to the vehicle's drive wheels and instead, rotation of the drive wheels acting through the vehicle's drivetrain uses kinetic energy of the moving vehicle to compress the trapped air. Some of the energy used to compress the air is recovered as the compressed air expands during an ensuing downstroke, but over an engine cycle, the effect is to decelerate the vehicle.
An engine which has a compression release braking mechanism, sometimes simply called a compression release brake, functions to release the hot air which has been compressed by an engine piston during a compression upstroke into an exhaust manifold of the engine by opening a cylinder exhaust valve at or near TDC. Release of the hot compressed air prevents its energy of expansion from being used during an ensuing downstroke to oppose engine braking
When activated after a driver of a moving vehicle has released the accelerator pedal, a compression release brake enables an engine to provide a significant increase in vehicle deceleration when compared with deceleration which would occur without compression release braking
Therefore, when a motor vehicle is in motion after having been accelerated by its engine, and a driver of the vehicle releases the accelerator pedal while the drive wheels of the vehicle continue to be coupled to the engine through the vehicle's drivetrain, the engine begins to act as a brake by becoming a load which is driven by the drive wheels acting through the drivetrain, and as a result, the vehicle decelerates. If the engine has a compression release brake, the vehicle will decelerate more quickly when the compression release brake is activated. Several configurations for compression release brake activation are known.
One configuration comprises an on-off switch which can be operated by a driver for activating and de-activating the compression release brake.
Another configuration is activation of the compression release brake upon the driver releasing the accelerator control pedal.
Still another configuration is activation of the compression release brake upon the driver depressing a service brake pedal after having released the accelerator pedal.
A selector switch may be used to enable particular sets of engine cylinders to be selected for engine braking
One general aspect of the disclosed subject matter relates to a motor vehicle comprising an internal combustion engine which is accelerated by a driver of the vehicle depressing an accelerator pedal to deliver torque through a drivetrain to drive wheels to propel the vehicle along an underlying road surface, and service brakes which are applied by the driver depressing a brake pedal to brake the vehicle.
The engine comprises cylinders within which pistons reciprocate to propel the vehicle by delivering torque to the drive wheels when fuel is being combusted within the cylinders, but when the engine is not delivering torque to the drive wheels as the vehicle travels on an underlying road surface, the drive wheels act through the drivetrain to apply torque to the engine.
The engine further comprises an intake system through which air enters the cylinders to support combustion, an exhaust system through which exhaust resulting from combustion leaves the cylinders, and an engine brake.
When the drive wheels act through the drivetrain to reciprocate the pistons, activation of the engine brake dissipates energy of air which a respective piston has compressed within at least one cylinder during an upstroke by causing the compressed air to be released into the exhaust system rather than to expand during an ensuing downstroke.
A controller enables activation of the engine brake to occur in a selected one of multiple activation types which include an activation type in which an algorithm is repeatedly executed to select between Service Brake Latched Engine Brake activation and Latched Engine Brake activation.
The foregoing summary is accompanied by further detail of the disclosure presented in the Detailed Description below with reference to the following drawings which are part of the disclosure.
Engine 12 has a number of cylinders into which fuel is injected by fuel injectors to combust with air which has entered the cylinders through an intake system 18. Exhaust resulting from combustion leaves the cylinders through an exhaust system 20.
Pistons reciprocate within the cylinders to propel truck vehicle 10 by delivering torque to drive wheels 16 through drivetrain 14 when fuel is being combusted within the cylinders, but when engine 12 is not delivering torque to drive wheels 16 as truck vehicle 10 travels on an underlying road surface, the vehicle is decelerated by drive wheels 16 acting through drivetrain 14 to apply torque to engine 12 using kinetic energy of the moving truck vehicle.
Engine 12 also has a compression release engine brake 22. When the rotating drive wheels 16 act through drivetrain 14 to decelerate truck vehicle 10, activation of compression release engine brake 22 dissipates energy of air which a respective piston has compressed within at least one cylinder by causing air which the respective piston has compressed during an upstroke to be released into exhaust system 20 rather than to expand during an ensuing downstroke during which the energy of expansion would counteract the torque being applied to the engine by drive wheels 16. In that way activation of compression release engine brake 22 enables engine 12 to be more efficient as a brake for decelerating truck vehicle 10.
Engine 12 is accelerated by a driver of truck vehicle 10 depressing an accelerator pedal 24 of an engine accelerator. Truck vehicle 10 has a brake pedal 26 which a driver depresses to operate foundation brakes of a service brake system at drive wheels 16 and at front steered wheels 28.
The example illustrated by truck vehicle 10 is that of a highway tractor having a fifth wheel 30 to which a trailer (not shown) can be coupled for towing by truck vehicle 10.
A controller 32 which may be contained in an engine electronic control unit (engine ECU) comprises an executable algorithm 34 (
Latched Engine Brake activation activates compression release engine brake 22 upon release of accelerator pedal 24.
Service Brake Latched Engine Brake activation activates compression release engine brake 22 upon depression of brake pedal 26 after accelerator pedal 24 has been released.
Algorithm 34 represents one of several selectable options for engine brake activation. Each option is uniquely identified by a particular value of a programmable parameter in controller 32. The particular one of the options which is enabled is selected by programming its unique value in controller 32. A user of truck vehicle 10, such as a customer who has purchased the vehicle from a manufacturer or manufacturer's agent, can perform the programming by a user input.
When executed, algorithm 34 first determines if it is has been selected for enablement (Step 36 in
If Step 36 determines that a different option has been selected, algorithm 34 ceases to execute further until its next iteration.
However if Step 36 determines that the automatic selection option between Latched Engine Brake activation and Service Brake Latched Engine Brake activation has been programmed in controller 32, algorithm 34 continues to execute by performing a Step 38 which initializes Service Brake Latched Engine Brake activation as an initial default setting.
Algorithm 34 then continues by executing a Step 40 which evaluates the load on engine 12 and the grade of the road on which truck vehicle 10 is traveling. Certain conditions such as bobtailing and total vehicle weight, including that of any towed vehicle, affect the load on engine 12. Weight (i.e. mass) of truck vehicle 10, including that of any towed vehicle, is one example of a parameter indicative of load on engine 12. That weight is used in the example described here. The absolute value of the grade of the road on which truck vehicle 10 is traveling is evaluated with respect to a road grade threshold which is itself a function of the elevation relative to sea level (altitude) of truck vehicle 10. Environmental barometric pressure is an example of a parameter which may be used for measuring elevation, and is used as the present example. Using the absolute value of road grade accounts for both uphill and downhill grades.
Only if Step 40, by answering NO, determines that both a) vehicle mass is greater than a vehicle mass threshold and b) grade of road on which truck vehicle 10 is traveling is greater than the road grade threshold, is a total vehicle traveling distance accumulator then incremented (Step 42 in
A Step 46 which follows Step 42 sets an upper limit on total accumulated vehicle traveling distance. A Step 48 which follows Step 44 sets a lower limit on total accumulated vehicle traveling distance.
After any incrementing or decrementing of total accumulated vehicle traveling distance, a Step 50 is performed. Step 50 evaluates the total accumulated vehicle traveling distance with respect to a total accumulated traveling distance threshold which is itself a function both of elevation of truck vehicle 10 relative to sea level and of grade of road on which truck vehicle 10 is traveling (i.e. is both altitude- and road grade-based). The result of the evaluation is used to select between Latched Engine Brake activation (reference numeral 52) and Service Brake Latched Engine Brake activation (reference numeral 54).
The algorithm repeatedly iterates at an appropriate iteration rate as truck vehicle 10 travels along a road. Total accumulated vehicle traveling distance incrementally accumulates provided that the vehicle is traveling on uphill and downhill road grades whose absolute values are greater than the road grade threshold and that vehicle mass is concurrently greater than the vehicle mass threshold. Otherwise, total accumulated vehicle traveling distance decrements, such as during travel on relatively flat ground (less than road grade threshold) or at light engine load (less than engine load threshold).
Total accumulated vehicle traveling distance is compared with the total vehicle traveling distance threshold which is different at different elevations. When total accumulated vehicle traveling distance is not greater than the vehicle traveling distance threshold (answer NO to Step 50), the initialized Service Brake Latched Engine Brake activation continues as the engine brake activation type. When total accumulated vehicle traveling distance is greater than the total vehicle traveling distance threshold (answer YES to Step 50), the initialized Service Brake Latched Engine Brake activation is discontinued and is replaced by Latched Engine Brake activation.
Road grade and vehicle weight can be provided by any suitable source such as a transmission control module or an alternative control module like smart cruise.
By automatically configuring engine brake activation based on road grade and on engine load, as measured by vehicle weight as in the present example, a vehicle may exhibit better driving performance and better overall fuel economy. Faster brake activation (Latched Engine Brake activation) will occur automatically when a vehicle is operating in situations which call for it because there is no delay due to the driver moving the foot from the accelerator pedal to the brake pedal. In other situations after the accelerator pedal has been released, it may be premature to activate the engine brake, and so engine brake activation by depressing the brake pedal is left to the discretion of the driver (Service Brake Latched Engine Brake activation).
Road grade input 64, vehicle mass input 66, environmental barometric pressure input 68, and total accumulated vehicle traveling distance input 70 are inputs to Traveling Distance Accumulation sub-strategy 76.
Road grade input 64 and environmental barometric pressure input 68 are inputs to Mode Selection Threshold Determination sub-strategy 78.
An output 82 of Traveling Distance Accumulation sub-strategy 76 and an output 84 of Mode Selection Threshold Determination sub-strategy 78 are inputs to Decision To Select Mode sub-strategy 80.
Decision To Select Mode sub-strategy 80 provides the two outputs, Latched Engine Brake activation output 72 and Service Brake Latched Engine Brake activation output 74.
The output of logic function 86 is one input to a two-input AND logic function 92. The other input to function 92 is an output of a logic function 94 which evaluates environmental barometric pressure data at input 68 and road grade data at input 64.
Because a measurement of road grade may be either positive or negative, its absolute value is determined by an absolute value function 96 and that is then used by logic function 94 to select an output from either a first look-up table 98 which is based on larger absolute values of road grade or a second look-up table 100 which is based on smaller absolute values of road grade.
Each look-up table is populated with binary logic values (i.e. “1” and “0”) representing a population of altitude-compensated road grades some of which (logic value “1”) have been predetermined as being sufficiently steep to call for total accumulated vehicle traveling distance to be incremented and the remainder of which (logic value “0”) not to call for total accumulated vehicle traveling distance to be incremented.
AND logic function 92 consequently provides a logic “1” output only when both an altitude-compensated road grade is greater than an altitude-compensated road grade threshold and vehicle mass is greater than a vehicle mass threshold. Otherwise, AND logic function 92 provides a logic “0” output. When AND logic function provides a logic “1” output, total accumulated vehicle traveling distance is incremented, and when AND logic function provides a logic “0” output, total accumulated vehicle traveling distance is decremented.
An incrementer/decrementer 102 provides both an increment input 104 and a decrement input 106 to a selection function 108. Function 108 selects the increment input to cause an increment to be added to total accumulated vehicle traveling distance when AND logic function 92 is providing a logic “1” output, and selects the decrement input to cause a decrement to be subtracted from total accumulated vehicle traveling distance when AND logic function 92 is providing a logic “0” output.
A limiting function 110 stops further incrementing of total accumulated vehicle traveling distance when total accumulated vehicle traveling distance equals a positive upper accumulation limit and also stops further decrementing when total accumulated vehicle travel distance equals a lower accumulation limit such as zero, thereby preventing the total accumulated vehicle traveling distance from becoming a negative number. The output of sub-strategy 76 thereby becomes the total accumulated vehicle travel distance which will be provided at input 70 when algorithm 34 next iterates.
A look-up table 114 contains a correlation of each of various combinations of environmental barometric pressures and road grades with a value of total accumulated vehicle distance traveling threshold. The environmental barometric pressures in table 114 span a range typical of a high altitude range where pressure is low.
The value of environmental barometric pressure data at input 68 is used by a logic function 116 to select the appropriate look-up table 112 or 114 to provide a total accumulated vehicle traveling distance threshold at an output 118.
Logic function 116 evaluates environmental barometric pressure data at input 68 with respect to an environmental barometric pressure threshold, which is defined by a range which lies between a Low Pressure Threshold 120 and a High Pressure Threshold 122. When environmental barometric pressure becomes greater than High Pressure Threshold 122, logic function 116 outputs a logic “0”. When environmental barometric pressure becomes less than Low Pressure Threshold 120, logic function 116 outputs a logic “1”. This provides hysteresis which avoids occasional excessively frequent switching of the output which might occur if a single value were used for the environmental barometric pressure threshold. Hence, when environmental barometric pressure becomes less than Low Pressure Threshold 120, table 114 is used, and when environmental barometric pressure becomes greater than High Pressure Threshold 122, table 112 is used.
A global vehicle distance accumulator determines whether truck vehicle 10 is traveling and measures accumulated distance traveled. Accumulated vehicle traveling distance is calculated based on vehicle speed, software execution time, and some metric unit conversion constant. The front end of Traveling Distance Accumulation sub-strategy 76 embodies an internal distance accumulator which increments on the basis of distance traveled between iterations of algorithm 34 when both vehicle mass is greater than the vehicle mass threshold and road grade is greater than the road grade threshold.