Patent Application
20070192010
This invention relates generally to motor vehicles that, in addition to having foundation brakes, have mechanisms in their powertrains that can be operated to decelerate a moving vehicle independently of foundation brakes. The invention further relates to a system and method for determining if braking torque that is potentially available by operating such mechanisms is sufficient to fully satisfy a braking request, thereby making application of the foundation brakes unnecessary.
A motor vehicle, especially a large one like a heavy truck or highway tractor, may be equipped with one or more mechanisms in its engine/powertrain that when operated can apply a load on the engine/powertrain for decelerating the vehicle. Examples of such mechanisms are devices like exhaust brakes, engine brakes, and driveline retarders. Downshifting of a transmission can also decelerate a vehicle.
The ability to decelerate a vehicle is also a function of vehicle weight. The heavier a vehicle, the greater the kinetic energy that must be dissipated in order to decelerate it.
All large motor vehicles have foundation brakes that are the primary means for decelerating them. Foundation brakes apply friction forces to rotating wheels, creating torque that opposes wheel rotation, and also generating heat that raises brake temperature. That torque creates forces at the interfaces between the wheels' tires and road surface that oppose the direction of vehicle motion along the road, thereby decelerating the vehicle. Every application of the foundation brakes contributes to wear of brake linings or brake pads.
A system and method that can mitigate brake temperature rise and reduce such wear even in what may seem fairly small ways can be meaningful to the operation of commercial vehicles like large trucks and highway tractors. The use of engine/powertrain mechanisms is one possibility for accomplishing this, but insofar as the inventors are aware, there exists no effective system or method for doing so, especially a system and method that can integrate the operation of various braking mechanisms with foundation brakes while taking into account the substantial difference in vehicle weight between unloaded and fully loaded conditions.
Certain motor vehicles (commonly called hybrids) have energy storage means, such as air tanks and/or storage batteries, that capture kinetic energy to decelerate a moving vehicle (such method of deceleration sometimes being called regenerative braking). If sufficient energy can be captured to satisfy a deceleration request, foundation brakes need not be applied. A system and method that can integrate the operation of various engine/powertrain braking mechanisms with foundation brakes, while taking into account the substantial difference in vehicle weight between unloaded and fully loaded conditions, in manners as herein contemplated by the inventors, would typically give precedence to regenerative braking. When a braking request cannot be satisfied by regenerative braking alone, or when the on-board energy storage means cannot accept more energy for storage, then the use of engine/powertrain braking mechanisms that do not store energy becomes appropriate before foundation brakes need be applied. Only when such mechanisms cannot satisfy a deceleration request does application of foundation brakes become necessary.
The present invention relates to a novel adaptive deceleration control that integrates the operation of various braking mechanisms with foundation brakes while taking into account the substantial difference in vehicle weight between unloaded and fully loaded conditions. The invention contemplates avoiding the use of the foundation brakes when relatively light decelerations are requested by the driver of a vehicle and instead using mechanisms present in the engine/powertrain to provide appropriate braking for light decelerations. Light decelerations can be performed in this way over an initial portion of the range of depression of the brake pedal when operated by the driver. Depressions of the brake pedal beyond this initial range cause the foundation brakes to be applied.
As alluded to above, the inventors contemplate that the use of such energy-dissipating mechanisms will not be considered by a control system when a vehicle is a hybrid, if regenerative braking alone can satisfy a deceleration request.
Operation of various braking mechanisms that are part of a vehicle powertrain is requested when evaluation of a deceleration request discloses that operation of one or more of such mechanisms can satisfy the request, thereby precluding the need to apply foundation brakes. Brake pedal depression beyond a range within which the mechanisms are potentially capable by themselves of satisfying the request, causes foundation brake application so that a fault that does not result in braking by the mechanisms will cause the foundation brakes to be applied when the driver, sensing lack of braking, depresses the pedal beyond the range.
One generic aspect of the present invention relates to a motor vehicle comprising a chassis comprising wheels on which the vehicle travels, at least some of which are driven by an internal combustion engine through a powertrain. A brake system for braking the wheels comprises an actuator that is operated by a driver of the vehicle to brake the vehicle by selective operation of foundation brakes at the wheels and of one or more mechanisms in the powertrain capable of applying braking torque to driven wheels.
A sensor associated with the actuator discloses vehicle deceleration request data corresponding to a vehicle deceleration request by the driver. A processor executes an algorithm that compares vehicle deceleration request data from the sensor with data representing vehicle deceleration that is potentially obtainable by operating one or more of the mechanisms in the powertrain. Operation of the one or more mechanisms is requested when the comparison discloses that operation of the one or more the mechanisms can satisfy the request.
A further generic aspect of the invention relates to the system that embodies the sensor and algorithm.
A still further generic aspect of the invention relates to the method that is embodied in the vehicle and system.
Braking that is performed in accordance with the invention gives more consistent brake pedal operation that is less affected by the vehicle load, meaning that when a vehicle is traveling at a given speed, a given amount of brake pedal displacement will consistently produce essentially the same deceleration independent of load.
One of the benefits of such operation occurs during a situation where a vehicle is lightly loaded and traveling at a speed where an ABS braking system would not come into play. The inventive system and method would be effective to decelerate the vehicle in a manner that does not lock the wheels, thereby avoiding wear that tends to make tires out-of-round when rotating wheels suddenly lock.
Because certain principles of the invention take vehicle weight into account, the same benefit is realized in a like situation where the vehicle is instead heavily, rather than lightly, loaded. It is believe that this attribute can contribute to improved safety because braking will be more consistent over a range of loads while brake temperature rises that might otherwise occur can now be avoided.
The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows.
ESC 12 comprises a processor that communicates with processors of each ECU 14, 16, 18 to control braking of vehicle 10 in accordance with brake request data from sensor 20 as processed by an algorithm 30 that is programmed in ESC 12 and that will be explained with reference to
Algorithm 30 iterates at a rate sufficiently fast to track changes in brake pedal position as signaled by sensor 20. The algorithm begins at a start 32, shown in
A step 36 processes the data value for brake pedal position, the data value for vehicle speed, and the data value for vehicle weight to determine a data value for brake force that must be applied to the moving vehicle in order to satisfy the request. That brake force can be equated to brake torque that needs to be applied to the vehicle's wheels.
The vehicle chassis comprises wheels on which the vehicle travels. Those wheels may vary in number and typically include driven wheels and non-driven wheels. Driven wheels are those that are coupled through a powertrain to an internal combustion engine. Various aspects of engine operation are controlled by engine ECU 14. Various aspects of transmission operation are controlled by transmission ECU 16.
Non-driven wheels are those that lack coupling through the powertrain to the engine. Depending on the specific vehicle powertrain configuration, certain wheels that are typically considered non-driven wheels may temporarily become driven wheels. It is also possible that driven wheels may be temporarily placed in non-driven relation with the engine, such as when the transmission is placed in neutral.
All wheels of a vehicle typically have foundation brakes that are typically drum- and/or disc-brakes, actuated either hydraulically or pneumatically to brake the wheels by friction through ABS ECU 18.
The next series of steps in algorithm 30 determine if the vehicle engine/powertrain has certain mechanisms other than foundation brakes that can be operated to brake the engine/powertrain. In this embodiment, such devices include: an engine exhaust brake that can increase engine back pressure by restricting exhaust flow; an engine brake, commonly known as a “Jake” brake, that is associated with the engine exhaust valves to cause them to open in the vicinity of top dead center and vent charge air that has been compressed in an engine cylinder during the immediately preceding compression stroke so that the energy of compression is not returned to the engine crankshaft during the ensuing downstroke; and a driveline retarder that may take any of several different forms to impose additional load on the engine. Any controllable device or mechanism that will produce drivetrain losses resulting in vehicle deceleration can serve as a retarder during certain operating conditions. For example, an engine cooling fan that can be selectively connected to and disconnected from the engine could be used as a retarder during certain conditions. Other devices and mechanisms include air intake throttle valves, electrical loads, and energy storage devices that are not associated with hybrid vehicle operation.
Other mechanisms in the powertrain may also be present for braking driven wheels. If a vehicle has a transmission that is capable of being shifted automatically, downshifting of the transmission can exert braking on the engine/powertrain to slow the vehicle. Some transmissions have transmission retarders that are similar to engine retarders in that they can be operated to apply a load to the engine/powertrain via the transmission without downshifting. Downshifting offers the possible advantage of more effective deceleration because it makes the engine accelerate to a higher speed that will operate any accessory loads directly driven by the engine at increased speed, thereby increasing their energy dissipation.
With the needed brake force having been determined by step 36, potential resources, such as those just mentioned, for providing the increased load on the engine/powertrain required to meet the needed brake force can be ascertained and evaluated.
A step 38 determines if an exhaust brake is present in the engine exhaust system. If so, a step 40 determines the brake force that the exhaust brake could apply at the current engine speed (RPM) to decelerate the vehicle if the exhaust brake were to be operated. A step 42 then compares the results of steps 36 and 40 to determine if operation of the exhaust brake would be sufficient by itself to satisfy the brake request. If so, the exhaust brake is operated, as shown by a step 44, and the current iteration of the algorithm ends (reference numeral 46).
The exhaust brake is operated by ESC 12 communicating to engine ECU 14 data representing the extent to which the exhaust brake should be applied. Engine ECU 14 contains an appropriate exhaust brake control strategy for operating the exhaust brake in accordance with the brake request.
Had step 38 determined that no exhaust brake was present, the algorithm would have skipped steps 40 and 42 and instead performed step 48 shown in
The engine brake is operated by ESC 12 communicating data to engine ECU 14 for causing the engine ECU to act on two cylinders. Engine ECU 14 contains an appropriate control strategy for acting on the selected engine cylinders.
Had step 52 determined that engine brake action on two cylinders was insufficient to satisfy the brake request, the algorithm would have continued with a step 56 to determine if engine brake action on four cylinders would be sufficient to fully satisfy the brake request. Step 56 compares the result of step 36 and the result of step 50 based on four cylinders being used for engine braking. If step 56 discloses that four cylinders are adequate, the engine brake acts on them, as shown by a step 58, and the current iteration of the algorithm ends. The engine brake is operated by ESC 12 communicating data to engine ECU 14 for causing the engine ECU to act on four cylinders.
Had step 56 determined that engine brake action on four cylinders was insufficient to satisfy the brake request, the algorithm would have continued with a step 60 to determine if engine brake action on six cylinders would be sufficient to fully satisfy the brake request. Step 60 compares the result of step 36 and the result of step 50 based on six cylinders being used for engine braking. If step 60 discloses that six cylinders are adequate, the engine brake acts on them, as shown by a step 62, and the current iteration of the algorithm ends. The engine brake is operated by ESC 12 communicating data to engine ECU 14 for causing the engine ECU to act on six cylinders.
As the reader can appreciate, this example has assumed a six-cylinder engine.
Had step 42 determined that full operation of the exhaust brake would be insufficient to fully satisfy the deceleration request, then the algorithm would have continued at step 48 and the algorithm would have proceeded to execute as described above. Had any of steps 52, 56, and 60 determined that the engine brake could satisfy the deceleration request from sensor 20, the engine brake would have been applied to the appropriate extent without the exhaust brake being operated.
If an iteration of the algorithm reaches step 60 and that step determines that the engine brake cannot satisfy the deceleration request, then
If step 64 determines that operation of both brakes is insufficient to satisfy the request, or if step 48 determines that an engine brake is not present, then a step 68 determines if a driveline retarder is present. If so, a step 70 determines the brake force that such the retarder could apply to decelerate the vehicle if it were to be operated. A step 72 then compares the result of step 36 and the result of step 70 to determine if operation of the retarder would provide sufficient brake force to fully satisfy the brake request. If so, the retarder is applied, as shown by a step 74, and the current iteration of the algorithm ends. Application of the retarder will occur without application of the exhaust brake or the engine brake.
If step 72 had determined that operation of the retarder by itself would be insufficient to satisfy the deceleration request, then a step 76 determines if concurrent operation of the exhaust brake, of the engine brake and of the retarder would be able to satisfy the deceleration request. If so, then a step 78 causes all three to be operated in appropriate ways to provide the needed braking force, and the current iteration of the algorithm ends.
Had step 76 determined that operation of the exhaust brake, of the engine brake and of the retarder would be unable to satisfy the deceleration request, then a step 80 (see
If step 80 determines that an automatic transmission is present, then a step 84 determines how much brake force could be gained if the transmission were to be downshifted one gear and if such downshifting would provide at least enough braking force to satisfy the deceleration request. If that is the case, then a step 88 initiates the downshift, and the current iteration of the algorithm ends. The downshift occurs without the exhaust brake, the engine brake, or the retarder being operated.
If step 84 determines that such downshifting would not by itself provide at least enough braking force to satisfy the deceleration request, a step 90 initiates the downshift, but that is followed by a step 92 that subtracts the engine brake force from the requested force, and the algorithm returns to step 38 to continue through the various steps as already described to provide additional braking. Because a downshift accelerates the engine, more braking force can be obtained from powertrain braking/retarding devices, but because the downshift satisfied some of the request, the portion that was satisfied must be subtracted from the request to avoid excess brake force, and that is the reason for step 92 which provides the difference as the basis for the next iteration beginning at C in
From this description, one can see that the use of various powertrain mechanisms is based on a hierarchy.
The traces 110, 112, and 114 in
The traces 116 and 118 in
As mentioned earlier, the adaptive deceleration control of the present invention strives to use available engine/powertrain mechanisms for braking, instead of foundation brakes, when relatively smaller deceleration requests requesting relatively light braking are issued by sensor 20. For accomplishing this, sensor 20 is calibrated in a particular way in relation to travel of brake pedal 22, as explained with reference to
Over an initial portion of the range of brake pedal travel in the direction of increasing depression of the brake pedal, the foundation brakes are not applied. This is the range between the solid and broken line positions of pedal 22 in
If sensor 20 is a potentiometer, pedal travel from 0% to 10% of its range moves the potentiometer wiper over its full range of travel, with the wiper remaining at 100% of its range of travel as pedal travel increases beyond the initial 10% of its range of travel. This is portrayed by trace 100 in
As also mentioned earlier, the data value for the amount of pedal travel as processed by ESC 12 is understood as a request to decelerate the vehicle at a deceleration corresponding to that data value. Because vehicle weight is a factor in accelerating and decelerating a vehicle, vehicle weight needs to be at least approximately known in order for algorithm 30 to be effective in invoking engine/powertrain braking that will result in the requested deceleration.
For a motor vehicle having an air suspension, on-board electronics technology can provide cost-efficient measurement of vehicle weight, especially when the use of measured weight is shared among various systems to provide various performance improvements. Data representing vehicle weight is used in the data processing that occurs during step 36 of algorithm 30. Measurement of vehicle weight can be made using sensors associated with a vehicle's air suspension.
In a vehicle such as a straight truck or highway tractor, measurement of weight is quite straightforward. Two pressure sensors, one for the front suspension, the other for the rear suspension, may be sufficient. Air pressure is adjusted to reference (frame to axle distance), and the measured pressure defines weight. Four pressure sensors, two at the front and two at the rear, may also be used.
In a tractor-trailer combination, a trailer having air suspension allows associated sensors to provide trailer weight. Measuring weight involves inflation of suspension to reference displacement and measurement of pressure.
A trailer lacking air suspension requires a different method. Tare weight of the tractor is measured prior to trailer attachment. Assuming that tare weight of the trailer is known, a uniformly loaded trailer weight is approximated from weight on the tractor's fifth wheel by an understanding of trailer wheel location and consequent center of gravity (CG) 1
Because the sum of distances x2+x3+x4 is a known parameter and distance x2 is readily resolved=½(x3+x4). This is the CG of M2 which consequently allows solution for opposing king pin force F where the center of rotation for F is at the center of the tandem trailer axles. King pin force F is measured via suspension system air pressure at the tractor rear axles.
The braking required when the foundation brakes are not being applied and travel of pedal 22 is within the initial 10% range is generally proportional to the request from sensor 20 and the vehicle weight. However, an air brake valve is always operated in correlation with a specific pedal displacement. For a vehicle operating at or near gross weight, the load is preferably adjusted such that M1=M2 resulting in substantially the same weight applied to King Pin (or tractor driven wheels) as is applied to the trailer wheels.
For a vehicle not loaded to gross weight, the center of gravity of the load may vary depending upon factors such as unloading sequence. With air suspension on the trailer, load weight is the sum of the weight on the tractor drive wheels plus the weight on trailer wheels.
If the trailer does not have air suspension (part load) the user may enter distance x1 into the truck on-board computer, and the distribution of the load from a grid layout. The estimated distribution then allows calculation of M1 vs M2
Further, the user may enter location of the tractor fifth wheel, since if the fifth wheel is not centered, some load will be shifted to the front axles (1 in.->˜2% weight shift).
In the absence of air suspension, gross weight of a tractor-trailer combination can be ascertained by any suitably appropriate way, many of which are known in the industry and utilize the know relationship between force, mass, and acceleration. Acceleration can be measured directly and/or mathematically calculated from velocity change over time; force can be calculated from engine torque.
While a presently preferred embodiment of the invention has been illustrated and described, it should be appreciated that principles of the invention apply to all embodiments falling within the scope of the following claims.
