Patent Application
20150057850
The present invention relates to railway maintenance vehicles, including but not limited to, self-propelled vehicles designed for applying or removing rail fasteners, such as spikes, inserting or removing rail anchors, tie plates, ties and other railway maintenance tasks using tampers and regulators. More specifically, the present invention relates to a propulsion control system for such devices.
Conventional railway maintenance vehicles are propelled by an internal combustion engine that powers a hydraulic system. Hydraulic motors are connected to at least one set of drive wheels, for example, by a chain drive that drives at least one of front and rear axles. Most conventional railway maintenance machines are propelled through power delivery to one of two axles. Each axle is connected to two flanged rail-engaging wheels, as is well known in the art.
Due to their operation in outdoor conditions, railway maintenance machines are exposed to a variety of weather conditions, including rain, snow and ice. Further, it is common for environmental obstacles to cover the rails from time to time, such as weeds, cut grass, spilled contents from rail cars, or the like. Such obstacles and/or the environmental conditions impede the traction of rail wheels on the rails. Quite often, the railway maintenance vehicles experience traction difficulties when exposed to the above conditions, which are made worse when driven over uneven or hilly terrain.
In some cases, as such obstacles are encountered by the railway maintenance vehicle, the drive wheels spin relative to the rails, and the vehicle is unable to keep up with other machines in the maintenance gang, or is unable to effectively reach its desired destination. More hydraulic fluid is pumped to the motor(s) driving the spinning wheel, thereby wasting energy, and increasing the difficulty for the operator to regain propulsion control of the vehicle. Thus, there is a need for developing an improved system and method of an automatic propulsion control operation.
The present disclosure is directed to an improved control system and method for a railway maintenance vehicle having an automatic propulsion control system operating under the following control logic. The speed, as in revolutions per minute (RPM) for each of the front and rear axles of the vehicle is monitored. In addition to the aforementioned axle sensor setup, an additional non-axle sensor could be used in conjunction with the axle sensors. This sensor may be attached to a non-powered wheel that contacts the rail, and be mounted anywhere on the machine. This sensor could be used to provide true vehicle speed, and each axle could then be compared to that value to determine if the axle is slipping. In the event the RPM of one axle is sensed to be greater than that of the other axle, the system determines that slipping is occurring. Alternatively, if the difference in RPM between the two axles exceeds a preset threshold, then slipping is also detected.
Once slipping is detected, the control system, which is connected to the hydraulic drive system that powers the slipping axle, reduces power to the slipping axle, by setting the motor at the slipping axle to zero or minimum torque, thereby stopping the axle from further slipping, and decreasing the RPM of the slipping axle. While the slipping axle is going to zero torque, the fluid to the corresponding motor(s) is reduced. It is contemplated that each axle is powered by a corresponding drive motor and a pump associated with the hydraulic drive system. To achieve the slowdown of the slipping axle, the drive motor for the slipping axle is set to the zero or minimum torque condition by adjusting the motor's displacement. The term “displacement” generally refers to a volume of fluid transferred from an inlet to an outlet in one revolution. As for a non-slipping axle, the pump's displacement is reduced (e.g., by at least 50%) to accommodate the reduced torque in the motor of the slipping axle. This arrangement avoids the vehicle from gaining its speed while slipping.
Next, the power to the slipping axle is gradually increased. Optionally, as the power to the drive axle is gradually increased, the drive motor and the associated pump powering the drive axle is gradually or intermittently energized, to prevent the drive wheels from slipping.
In another situation, when the control system detects application of a brake pedal in the maintenance vehicle, corresponding wheels of the vehicle are typically locked up by pressurized brake pads, and the RPM of the stopping axle(s) becomes zero while the vehicle with locked-up wheels is skidding or sliding along a railroad track. However, during the skidding action of the vehicle, an actual current speed of the vehicle has not yet reached zero, even if the drive motor is in the zero or minimum torque condition due to the motor's zero or minimum displacement. When the brake pedal is subsequently released, if the vehicle speed exceeds a preset velocity, damage to the engine parts is likely to occur when a vehicle speed has not yet been reduced to zero. This is because the spinning motor(s) act as hydraulic pumps, and in turn the pumps act as hydraulic motors. To coordinate the engine speed with the vehicle speed, the control system adjusts displacement of at least one of the motors and the pumps to compensate for the actual current speed of the vehicle by reducing the displacement for the stopping axle(s). As a result, when the drive motor is reactivated, the hydraulic drive system recovers from the zero or minimum displacement without causing damage to the engine parts during and after the skidding action.
In one embodiment, a propulsion control system is provided for controlling a hydraulic drive system of a railway maintenance vehicle, and includes an axle monitoring module configured for receiving and monitoring a first signal received from a first rotation sensor, and a second signal received from a second rotation sensor, the first signal being associated with a first axle of the vehicle, and the second signal being associated with a second axle of the vehicle. Also included are a speed comparison module configured for calculating a delta value representing a difference between the first and second signals by comparing values of the first and second signals, and generating a speed control signal based on the comparison; a speed control module configured for receiving the speed control signal, and generating a power signal for controlling an amount of power applied to at least one of the first and second axles based on the speed control signal; and an actuation control module configured for receiving the power signal, and performing a power allocation function for controlling a speed or power of the hydraulic drive system that controls at least one of the first and second axles based on the power signal.
In another embodiment, a method for controlling a hydraulic drive system of a railway maintenance vehicle is provided, and includes receiving and monitoring a first signal received from a first rotation sensor, and a second signal received from a second rotation sensor, the first signal being associated with a first axle of the vehicle, and the second signal being associated with a second axle of the vehicle; calculating a delta value representing a difference between the first and second signals by comparing values of the first and second signals, and generating a speed control signal based on the comparison; receiving the speed control signal, and generating a power signal for controlling an amount of power applied to at least one of the first and second axles based on the speed control signal; and receiving the power signal, and performing a power allocation function for controlling a speed or power of the hydraulic drive system that controls at least one of the first and second axles based on the power signal.
In yet another embodiment, a propulsion control system is provided for controlling a hydraulic drive system of a railway maintenance vehicle, includes an axle monitoring module configured for receiving and monitoring a first signal received from a first rotation sensor, and a second signal received from a second rotation sensor, the first signal being associated with a first axle of the vehicle, and the second signal being associated with a second axle of the vehicle. Also included are a speed comparison module configured for comparing an actual current speed of the vehicle and at least one of the first and second signals, and generating a speed control signal based on the comparison when a brake of the vehicle is applied; a speed control module configured for receiving the speed control signal, and generating a power signal for controlling an amount of power applied to at least one of the first and second axles based on the speed control signal; and an actuation control module configured for receiving the power signal, and performing a power allocation function for controlling a speed or power of the hydraulic drive system that controls at least one of the first and second axles based on the power signal, and selectively initiating a dynamic braking based on the actual current speed of the vehicle.
Referring now to
Although the children modules residing in their respective parent modules are shown, the broad teachings of the present system can be implemented in a variety of forms. Thus, while this disclosure includes particular examples and arrangements of the modules, the scope of the present device should not be so limited since other modifications will become apparent to the skilled practitioner.
In addition to the ECM 12, the PCS 10 further includes a plurality of rotation or RPM sensors 14, a database 16, and a hydraulic drive system 18. Mounted on a vehicle body (not shown) near an axle shaft (not shown), each RPM sensor 14 detects a rotational speed of an associated axle in revolutions per minute (RPM). In addition to the aforementioned axle sensor setup, an additional non-axle sensor could be used in conjunction with the axle sensors. This sensor may be attached to a non-powered wheel that contacts the rail, and be mounted anywhere on the machine. This sensor could be used to provide true vehicle speed, and each axle could then be compared to that value to determine if the axle is slipping. Preferably, at least two RPM sensors 14 respectively independently detect the rotational speeds of front and rear axles of the maintenance vehicle, and generate associated RPM signals. For example, a first signal RPM1 is associated with a first or front axle, and a second signal RPM2 is associated with a second or rear axle. It is contemplated that either one of the front or rear axles can be a drive axle, or both axles can be drive axles.
All relevant speed information on the axles can be stored in the database 16 for retrieval by the ECM 12, for example, as a data storage device and/or a machine readable data storage medium also carrying computer programs or nodules. At least one drive motor 20 and at least one pump 21, preferably hydraulic, are connected to the hydraulic drive system 18 for driving at least one of the front and rear axles of the maintenance vehicle. Thus, for purposes of the present application, “power” refers to the flow of hydraulic fluid for driving the drive motor 20.
Also included in the ECM 12 is an interface module 22, which provides an interface between the ECM 12, the RPM sensors 14, the database 16, and the hydraulic drive system 18. The interface module 22 also controls operation of, for example, the hydraulic drive system 18, and other related system devices, services, and applications. The other devices, services, and applications may include, but are not limited to, one or more software or hardware components, as are known in the art. The interface module 22 also receives signals, which are communicated to the respective modules, such as the ECM 12 and its children modules.
Regarding the children modules, an axle monitoring module 24 is provided for receiving the first and second signals RPM1, RPM2 from the RPM sensors 14, and respectively monitoring the rotational speeds of the first and second axles. More specifically, the axle monitoring module 24 receives the RPM signals RPM1, RPM2 from the RPM sensors 14 via the interface module 22, and transmits the RPM signals to a speed comparison module 26 for further processing. When the speed comparison module 26 receives the RPM signals RPM1, RPM2, both signal values are compared for calculating a delta value representing a difference between the RPM signals. As described in further detail below, the speed comparison module 26 performs an analysis of the RPM signals, and generates a speed control signal CTL for controlling the motor 20 and the pump 21 of the hydraulic drive system 18. A speed control module 28 receives the speed control signal CTL from the speed comparison module 26, and generates a power signal P for controlling an amount of power applied to at least one of the first and second axles based on the control signal CTL. A detailed description of the power signal P is provided below in relation to
In one embodiment, the speed comparison module 26 compares an actual current speed VCURR of the vehicle and at least one of the first and second RPM signals RPM1, RPM2, and generates a speed control signal based on the comparison when a brake 32 of the maintenance vehicle is applied. Exemplary friction values for steel wheels on steel rails can range from 0.05 to 0.78. As known in the art, it is assumed that the lower the friction value, the longer distance it will take to stop the vehicle. It is also assumed that kinetic friction (i.e., sliding friction) is lower than static friction (i.e., wheels rolling). Consequently, it takes longer to stop the vehicle when the wheels are locked up and sliding along the railroad track. When the vehicle applies the friction brake to stop by locking up the wheels, a kinetic friction condition occurs, and thus generates a longer stopping distance.
An important aspect of the present ECM 12 is that the vehicle utilizes the hydraulic system 18 for generating a shorter braking distance by employing the greater static friction than the kinetic friction. This is achieved by increasing the motor displacement and decreasing the pump displacement. It is beneficial because the wheels are not locked up, and the static friction condition is generated for providing a shorter stopping distance for the vehicle. The pump and motor displacement is controlled by the operator (e.g., accelerator pedal) and control software. The higher the pump displacement, the more fluid flow can be delivered into the motors 20. The motor displacement affects the speed and torque of the vehicle. The higher the displacement of the motors, the higher torque on the wheels is generated, but the lower RPM of the wheels is maintained at a constant pump flow and pressure. Conversely, the lower the motor displacement, the lower torque on the wheels is generated, but the higher RPM of the wheels is maintained at the constant pump flow and pressure.
As an example, when the speed comparison module 26 detects the application of the brake 32 in the maintenance vehicle depending on the duration of the application of the brake, corresponding wheels of the vehicle are typically locked up by pressurized brake pads (not shown), and the motor 20 is operated at a zero or minimum displacement. Immediately after the brake 32 is applied, the speed comparison module 26 waits for a predetermined time period (e.g., a 0.5 second delay) for scanning the vehicle speed at least once. The zero displacement generally refers to a condition in which the motor 20 is free-wheeling and provides zero or minimum torque for moving the maintenance vehicle. However, although the RPM of the stopping axle(s) becomes zero, the locked-up wheels keep skidding or sliding on a railroad track due to the inertia of the moving vehicle. During the skidding action of the vehicle, the actual current speed VCURR of the vehicle has not yet reached zero even if the drive motor 20 is in the zero or minimum torque condition due to the motor's zero or minimum displacement.
When the brake 32 is subsequently released, the vehicle speed may not yet have been reduced to zero. To accommodate the vehicle speed and to prevent an engine speed from exceeding preset levels, the speed control module 28 adjusts the displacement of at least one of the motor 20 and the pump 21 to compensate for the actual current speed VCURR of the vehicle. In a preferred embodiment, the actual current speed VCURR of the vehicle is determined based on the RPM of the wheels during a predetermined time period. Alternatively, the RPM of the wheels can be scanned multiple times to validate the actual current speed VCURR of the vehicle.
The actuation control module 30 controls an amount of the hydraulic fluid delivered to the drive motor 20 of the stopping axle based on the actual current speed VCURR of the vehicle. For example, if the vehicle decelerates when the brake 32 is released (e.g., an accelerator is not engaged by the operator), then a dynamic braking is selectively initiated by the actuation control module 30 based on the actual current speed VCURR of the vehicle. However, if the vehicle accelerates when the brake 32 is released (e.g., the accelerator is engaged by the operator), then the actuation control module 30 gradually increases the amount of the hydraulic fluid delivered to the drive motor 20, or decrease the motor displacement to accommodate the acceleration of the vehicle. As a result, when the drive motor 20 is reactivated, the hydraulic drive system 18 recovers from the zero or minimum displacement without causing damage to the engine parts.
Referring now to
The method begins at step 100. In step 102, the axle monitoring module 24 receives the first signal RPM1 from the associated RPM sensor 14, and monitors the rotational speed of the associated first axle (Axle1). Simultaneously, in step 104, the axle monitoring module 24 receives the second signal RPM2 from the associated RPM sensor 14, and monitors the rotational speed of the associated second axle (Axle2). In step 106, the speed comparison module 26 compares values of the RPM signals RPM1, RPM2. In step 108, the speed comparison module 26 calculates a delta value representing a difference between two RPM signals RPM 1, RPM2. An exemplary delta value ΔRPM may be an absolute value defined as provided by expression 1.
ΔRPM=|RPM1−RPM2| (1)
In step 110, the speed comparison module 26 performs an analysis of the RPM signals, and generates the speed control signal CTL for controlling the motor 20. More specifically, if the delta value ΔRPM is greater than a predetermined threshold value, then the speed control signal CTL is generated based on the RPM signals RPM1, RPM2, such as the delta value ΔRPM, and control proceeds to step 114. Otherwise, control proceeds to steps 102 and 104. An exemplary speed control signal CTL may be defined as provided by expression 2.
CTL=f{RPM1,RPM2} (2)
Similarly, in step 112, the speed comparison module 26 determines which of the RPM signals RPM1, RPM2 has a greater value. If a value of the first signal RPM1 is greater than a value of the second signal RPM2, then the speed control signal CTL is generated based on the RPM signals RPM1, RPM2, such as the delta value ΔRPM, and control proceeds to step 114. Otherwise, control proceeds to steps 102 and 104.
In step 114, the speed control module 28 receives the speed control signal CTL from the speed comparison module 26, and generates the power signal P based on the control signal CTL. More specifically, the power signal P is generated for reducing and/or temporarily cutting power to the motor 20 that controls the first axle (Axle1), such that the actuation control module 30 allocates less power to the motor 20 than a previous power level based on the power signal P. It is also contemplated that instead of the first axle (Axle1), the motor 20 can control the second axle (Axle2) or both first and second axles simultaneously. Alternatively, separate motors may be designated for the respective first and second axles to suit the situation.
In step 116, the actuation control module 30 determines whether the motor 20 is operated at zero displacement, which generally refers to a condition that the motor is free-wheeling and provides zero torque for moving the maintenance vehicle. If the motor 20 is at zero or minimum displacement, control proceeds to step 118. Otherwise, control repeats step 116 at a predetermined interval until the motor 20 is operated at or minimum zero displacement.
In step 118, the speed control module 28 generates the power signal P for gradually increasing the power to the motor 20 that controls the first axle (Axle1) based on at least one of the speed control signal CTL and a status of the motor MOTOR (e.g., whether the motor is operated at zero displacement). As a result, the actuation control module 30 gradually increases power applied to the motor 20 using the hydraulic drive system 18 based on the power signal P.
In step 120, in addition to this gradual power increase applied to the motor 20, the speed control module 28 optionally generates a first auxiliary power signal P′ for applying or delivering pulsing power to the first axle (Axle1). As another option, in step 122, the speed control module 28 generates a second auxiliary power signal P″ for applying gradual or pulsing power to corresponding brakes 32 of the first axle (Axle1). An exemplary power signals P, P′, P″ (
P,P′,P″=f{CTL,MOTOR} (3)
In step 124, the speed comparison module 26 compares the value of the first signal RPM1 with a predetermined RPM value for generating the speed control signal CTL based on this comparison. If the value of the first signal RPM1 is greater than or equal to the predetermined RPM value, control proceeds to step 128. Otherwise, control proceeds to step 126. Similarly, in step 126, the speed comparison module compares the value of the first signal RPM1 with the second signal RPM2 for generating the speed control signal CTL based on this comparison. If the value of the first signal RPM1 is within a predetermined percentage value of the second signal RPM2, control proceeds to step 128. Otherwise, control proceeds to step 118.
In step 128, the speed control module 28 receives the speed control signal CTL and generates the power signal P based on the speed control signal CTL so that the actuation control module 30 maintains the power level of the motor 20 based on the power signal P. Control ends at step 130.
While a particular embodiment of the present propulsion control system has been described herein, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the present disclosure in its broader aspects and as set forth in the following claims.
This application claims priority under 35 USC 119(e) from U.S. Provisional Application Ser. No. 61/867,825 filed Aug. 20, 2013.
| Number | Date | Country | |
|---|---|---|---|
| 61867825 | Aug 2013 | US |
