ASPHALT DISTRIBUTOR WITH MULTISPEED MOTOR

Abstract

An asphalt distributor has a multispeed hydraulic motor mechanically driving an asphalt pump. The asphalt distributor has a controller for controlling the flow rate of asphalt being sprayed. The controller has a gain for controlling the flow rate. During a transition when the speed of the multispeed hydraulic motor changes, the gain has a value for the transition. Beneficially, the asphalt distributor has a wider than conventional asphalt spraying flowrate over which it provides a consistent spray. A method for controlling the flowrate involves adjusting, preferably dynamically, the value of the gain during the transition.

Claims

1. An asphalt distributor for spraying asphalt onto the ground, the asphalt distributor comprising: a multispeed hydraulic motor having a first speed and a second speed, an asphalt pump mechanically driven by the multispeed hydraulic motor, a controller for controlling the flow rate of asphalt being sprayed, the controller having a gain for controlling the flow rate, the gain having a value for the first speed, a value for the second speed, and a value for a transition for a change in speed between the first and second speeds, the value for the transition being different from the value for the first speed and the value for the second speed.

2. The asphalt distributor of claim 1 further comprising an engine and a hydraulic pump driven by the engine wherein the controller changes the flow rate of hydraulic fluid pumped by the hydraulic pump for achieving the desired asphalt flow rate.

3. The asphalt distributor of claim 1 wherein the transition has a predetermined duration.

4. The asphalt distributor of claim 1 wherein the transition ends when the relative error is below 5%.

5. The asphalt distributor of claim 1 wherein the value for a transition for a change in speed between the first and second speeds is the transition for a change in speed from the first speed to the second speed and the gain for controlling the flow rate further comprising a value for a transition for a change in speed from the second speed to the first speed.

6. The asphalt distributor of claim 1 wherein the gain is selected from a proportional gain, an integral gain and a derivative gain.

7. The asphalt distributor of claim 1 wherein the value of the gain during the transition is dynamically adjusted.

8. The asphalt distributor of claim 7 wherein the dynamic adjustment of the gain comprises an increase in the proportional gain of the controller.

9. The asphalt distributor of claim 8 wherein the increase in the proportional gain is a function of the relative error and the increase increases as the relative error increases.

10. The asphalt distributor of claim 7 wherein the dynamic adjustment of the gains comprises a decrease in an integral gain of the controller.

11. The asphalt distributor of claim 10 wherein the decrease in the integral gain is a function of the relative error and the decrease increases as the relative error decreases.

12. A method of controlling the flowrate of an asphalt pump driven by a multispeed hydraulic motor during a transition for a speed change of the motor, the method comprising adjusting a gain of a controller controlling the flowrate during the transition.

13. The method of claim 12 wherein adjusting the gain comprises increasing a proportional gain of the controller relative to the proportional gain for the speed that the speed is being changed to.

14. The method of claim 12 wherein adjusting the gain comprises decreasing an integral gain of the controller relative to the integral gain for the speed that the speed is being changed to.

15. The method of claim 12 further comprising measuring the flowrate of the asphalt pump and calculating the relative error of the flowrate based on the measured flowrate.

16. The method of claim 15 wherein adjusting a gain comprises dynamically adjusting a proportional gain of the controller as a function of the relative error.

17. The method of claim 15 wherein adjusting a gain comprises dynamically adjusting an integral gain of the controller as a function of the relative error.

18. The method of claim 12 wherein adjusting the gain comprises adjusting the value of the gain relative to the value of the gain for the speed to which the speed is being changed.

19. The method of claim 18 further comprising terminating the transition after a predetermined duration followed by controlling the flowrate of the asphalt pump using the value of the gain for the speed to which the speed was changed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a perspective view of an asphalt distributor.

[0023] FIG. 2 is a schematic view of the distributing apparatus of the asphalt distributor of FIG. 1.

[0024] FIG. 3 is a flowchart illustrating an algorithm programmed in the controller shown in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

[0025] In an embodiment of the invention, an asphalt distributor 10 is provided. Fluid distributor 10 includes a motorized vehicle 12 (shown in phantom), typically a truck, having a cab 14, one or more side view mirrors 15, two or more axles 16, a chassis 18, and a tank or vessel 20 mounted to chassis 18. Tank 20 is used to store the asphalt to be distributed, i.e., sprayed. Tank 20 may be heated by a heater 21 of any suitable kind. Heater 21 is shown schematically as an electric heater.

[0026] Fluid distributor 10 has an engine 22 (shown schematically), which drives a transmission 24 (shown schematically) and a power take off 28. Engine 22 may be any suitable engine such as an internal combustion engine, diesel or gasoline, or an electric motor. Transmission 24 may be any suitable transmission for driving one or more axles 16, such as a manual transmission or an automatic transmission. Transmission 24 is connected to a power takeoff 28. Engine 22 drives transmission 24 which drives power take off 28, which in turn drives a hydrostatic transmission 29. Alternatively, engine 22 can drive hydrostatic transmission 29 via a front crank shaft for a manual or automatic transmission.

[0027] Hydrostatic transmission 29 includes a hydraulic drive pump 30, a multi-speed hydraulic motor 32, and an optional gear box 34. Hydraulic drive pump 30 pumps hydraulic fluid which causes hydraulic motor 32 to rotate thereby driving gear box 34. Hydraulic drive pump 30 is an axial piston motor having a continuously adjustable swashplate. Gear box 34 is used to convert the rate of rotation from .sub.2 to .sub.3. Typically gear box 34 is fixed such that the ratio of .sub.2 to .sub.3 is fixed. Hydraulic motor 32 may be any suitable multi-speed motor including an axial piston motor having an adjustable swashplate, such as the Bosch Rexroth A10. Hydraulic motor typically has 2 speeds, but can have more speeds.

[0028] Hydrostatic transmission 29 is connected to and drives asphalt pump 36, typically via gear box 34. Pump 36 may be of any suitable type. Preferably, it is of constant displacement, metering type such as a gear pump. Pump 36 draws fluid from tank 20 via an intake port 38 having an intake valve 40.

[0029] Asphalt pump 36 pumps asphalt from tank 20 to an asphalt distribution system 42 located at the rear end of vehicle 12. Working from the end backwards, asphalt distribution system 42 has spray nozzles 44 (or outlets) for spraying the asphalt, control valves 46, spray bar 48, and conduit/piping system means 50. Spray nozzles 44 are arranged on spray bar 48, typically uniformly spaced along spray bar 48. Spray bar 48 may be extendable or fixed. Fixed spray bars have a length that typically is approximately the same as or narrower than vehicle 12. Extendable spray bars of any suitable design are designed to extend beyond the width of vehicle 12 in operation, but to retract to be at or less than the width of vehicle 12 for ease of transportation. As shown, spray bar 48 is extendable having pivotal end portions 48a and 48b and a central portion 48c. Pivotal end portions are sometimes called spray bar wings. Alternatively, spray bar 48 could be a variable width spray bar having central portion 48c and end portions that move in and out in several positions. End portion 48a is shown in the extended position with spraying occurring in FIG. 1 while end portion 48b is shown in the retracted position with no spraying occurring. Central portion 48c is shown spraying. Spray bar 48 may be located at the front end or the rear of vehicle 12. Flow of asphalt to spray nozzles 44 is controlled by control valves 46. In one embodiment, there are three spray nozzles 44 per foot of spray bar 48 and one control valve 46 per spray nozzle 44. Other arrangements are also contemplated, such as one valve 46 controlling the flow through three spray nozzles 44. Fluid distribution system 42 has the necessary conduit, whether tubing, hoses, piping or mixtures thereof for connecting distribution system 42 together.

[0030] Asphalt distributor 10 has a control panel 52 for controlling the distribution of asphalt. Control panel 52 is typically located in cab 14 so that the operator of asphalt distributor 10 can drive vehicle 12 while controlling the distribution of asphalt via control valves 46. Asphalt distributor 10 has a controller 54 for controlling the flowrate of asphalt. Controller 54 measures the flowrate from pump 36 by a flowmeter 56 based on any suitable method. The flowmeter need not be located at the location shown in FIG. 2. Preferably, flowmeter 56 measures the flowrate using a proximity sensor in asphalt gear pump 36 to count teeth in asphalt gear pump 36 passing by the proximity sensor as the axle of hydraulic motor rotates or indirectly by measuring .sub.3 or .sub.2 using an encoder disk with an optical sensor. Controller 54 controls the flowrate of asphalt pump 36 by adjusting the flowrate of drive pump 30, typically by adjusting the angle of its swashplate. Any suitable controller may be used including a P, PI or a PID controller, which may be computer-based. If a P, PI, or PID controller is used, its gain(s) may be tuned by any suitable method such as the Ziegler-Nichols methods. K.sub.P, K.sub.I, and K.sub.D denote the proportional, integral and derivative gains. It may not be necessary for all the gains to be non-zero. Controller 54 may also control the opening and closing of valves 46 and calculate the desired flowrate based on the number of valves open and the desired application rate.

[0031] In addition to having gains, controller 54 has programming to provide an even flowrate when the speed of motor 32 changes. When motor 32 is a two-speed motor, the programming preferably implements algorithm 70 shown in FIG. 3. For purposes of explaining algorithm 70, motor 32 will be assumed to be in its high speed and the discussion will start at step 72. At step 72, controller 54 (which is assumed to be a PID or a digital equivalent of a PID controller) is in the high flowrate mode, which means that it is using gain(s) tuned to achieve proper control for high flowrates, e.g., K.sub.P,high, K.sub.I,high, and K.sub.D, high. In high flowrate mode, controller 54 calculates the error, which is the difference between the desired flowrate (or flowrate setpoint) and the measured flowrate. The error and the gains are then used to adjust the flowrate of hydraulic fluid produced by drive pump 30 as is conventional for a PID controller.

[0032] At step 74, controller 54 checks the flowrate and compares it to the change point for changing to the low flowrate mode. If the flowrate is above the low change point, the algorithm returns to step 72. If not, controller 54 causes the speed of motor 32 to change to low in step 76 (or to initiate the change to low speed) thereby initiating a transition to low speed. Essentially simultaneously to step 76, e.g., immediately before or after, optionally in step 78, controller 54 starts a timer at 0. In step 80, controller 54 calculates the absolute relative error denoted as E.sub.rel in equation 1 below.

E.sub.rel=|q.sub.SPq|/q.sub.SP(eq. 1)

where q.sub.SP is the desired flowrate or setpoint and q is the measured or calculated flowrate.

[0033] In step 82, scaling factors SF.sub.P and SF.sub.I are calculated for gains K.sub.P and K.sub.I of controller 54 based on equations 2 and 3 below.

SF.sub.P=(S.sub.max,PS.sub.min,P)*E.sub.rel+S.sub.min,P(eq. 2)

SF.sub.I=(S.sub.max,IS.sub.min,I)*E.sub.rel+S.sub.min,I(eq 3)

where S.sub.max represents the most that the scale factor SF can be assuming a maximum error of 100%; S.sub.min represents the minimum that the scale factor SF can be, i.e, the scale factor when the absolute relative error is 0. The value of the scale factor maximums and minimums are based in part on the inventors' insight into the process including that the integral gain should generally be reduced as the integral term has less relevance when the speed of hydraulic motor 32 changes, especially initially.

[0034] In step 84, new gains are calculated based on the scale factors as set forth in equations 4 and 5 below.

K.sub.Pscaled=SF.sub.P*K.sub.P,low(eq. 4)

K.sub.Iscaled=SF.sub.I*K.sub.I,low(eq. 5)

[0035] K.sub.P,low and K.sub.I,low represents the normal gains in low flowrate mode (step 90), i.e., outside any transition. Of course, steps 80, 82 and 84 can be combined in a single step or two steps. As can be seen, the gains are dynamically adjusted by a linear function of the relative error in step 84.

[0036] The new gains, K.sub.Pscaled and K.sub.Iscaled, are then used by controller 54 instead of K.sub.P,low and K.sub.I,low in step 86 to correct the flowrate in the ordinary manner. It is contemplated that if derivative control is used that its gain could be zero or minimized during the transition in a way similar to the integral gain or increased.

[0037] In step 88, controller 54 checks to see if the criterion or criteria for ending the transition period has occurred. One criterion can be whether the timer (or elapsed time of the transition period) has reached a target to account for the time that it takes the motor to change speed. Another criterion can be whether the error is below a certain threshold, for example 10%, or more preferably 5%. Other suitable criteria are possible. The criteria may be used in combination in various ways, e.g, two criteria have to be met before ending the transition period or either of two criteria have to be met before ending the transition period.

[0038] If the criterion or criteria are not satisfied then the next step is step 80 and the transition period continues until the criterion or criteria are satisfied.

[0039] If the criterion or criteria are satisfied then the next step is step 90 thereby ending the transition to low flowrate mode. At step 90, controller 54 is in the low flowrate mode, which means that it is using gain(s) tuned to achieve proper control for low flowrates. In low flowrate mode, controller 54 use the error and gains K.sub.P,low and K.sub.I,low to adjust the flowrate of hydraulic fluid produced by drive pump 30 as is conventional for a PID controller.

[0040] Conceivably, another criterion for ending the transition to low speed mode could be whether the flowrate setpoint is above the high change point (use of this criterion is not shown in FIG. 3). If this criterion is met, the algorithm could go to step 94.

[0041] At step 92, controller 54 checks the flowrate and compares it to the change point for changing to high flowrate mode. If the flowrate is below the high change point, the algorithm returns to step 90. The high change point is usually different and higher than the low change point to avoid a situation where the motor is having to change speed frequently. If not, controller 54 causes the speed of motor 32 to change to high in step 94 (or to initiate the change to high speed) thereby initiating a transition to high speed. Essentially simultaneously to step 94, e.g., immediately before or after, optionally in step 96, controller 54 starts a timer at 0. In step 98, controller 54 calculates the absolute relative error denoted as E.sub.rel. In step 100, scaling factors SF.sub.P and SF.sub.I are calculated for gains K.sub.P and K.sub.I of controller 54 based on equations 2 and 3, but note that the value of constants S.sub.max,P, S.sub.min,P, S.sub.max,I and S.sub.min,I may be different between steps 100 and 82.

[0042] In step 102, new gains are calculated based on the scale factors as set forth in equations 6 and 7 below.

K.sub.P,scaled=SF.sub.P*K.sub.P,high(eq. 6)

K.sub.I,scaled=SF.sub.I*K.sub.I,high(eq. 7)

[0043] K.sub.P,high and K.sub.I,high represents the normal gain in high flowrate mode (step 72), i.e., outside any transition. Of course, steps 98, 100 and 102 can be combined in a single step or two steps. As can be seen the gains are dynamically adjusted by a linear function of the relative error in step 102.

[0044] The new gains, K.sub.P,scaled and K.sub.I,scaled, are then used by controller 54 instead of K.sub.P,high and K.sub.I,high in step 104 to correct the flowrate in the ordinary manner. It is contemplated that if derivative control is used that its gain could be zero or minimized during the transition in a way similar to the integral gain or increased.

[0045] In step 106, controller 54 checks to see if the criterion or criteria for ending the transition period has occurred similar to step 88. If elapsed time is a criterion, the elapsed time target for step 106 can be different than the one for step 88 because the amount of time to change speed can vary depending on the speed. If the criterion or criteria are not satisfied then the next step is step 98 and the transition period continues until the criterion or criteria are satisfied.

[0046] If the criterion or criteria are satisfied then the next step is step 72, previously discussed, thereby ending the transition to high flowrate mode.

[0047] Conceivably, another criterion for ending the transition to low speed mode could be whether the flowrate setpoint is above the low change point (use of this criterion is not shown in FIG. 3). If this criterion is met, the algorithm could go to step 94.

EXAMPLE

[0048] Experimentation was performed on an asphalt distributor having a Rexroth A10 hydraulic motor. It was found that much better performance could be achieved using a multispeed hydraulic motor versus a single speed motor over a wide range of flowrates avoiding sprayers to not overlap properly or for the spray to surge. The following settings for the transition from low to high flowrate were found empirically to give excellent results. [0049] S.sub.max,P=5 [0050] S.sub.min,P=1 [0051] S.sub.max,I=4 [0052] S.sub.min,I=0

[0053] Criteria for ending transition was an elapsed time of 100 ms.

[0054] If E.sub.rel is 25% or 0.25, the scale factors have the following values.

SF.sub.P=(51)*0.25+1=2.0

SF.sub.I=(40)*0.25+0=1.0

[0055] If E.sub.rel is 10% or 0.1, the scale factors have the following values.

SF.sub.P=(51)*0.1+1=1.4

SF.sub.I=(40)*0.1+0=0.4

[0056] If E.sub.rel is 1% or 0.01, the scale factors have the following values.

SF.sub.P=(51)*0.01+1=1.04

SF.sub.I=(40)*0.01+0=0.04

[0057] If E.sub.rel is 0% or 0.00, the scale factors have the following values.

SF.sub.P=(51)*0.00+1=1.00

SF.sub.I=(40)*0.00+0=0.00

[0058] As can be seen, the gains vary based on the value of E.sub.rel. For values of E.sub.rel below 0.25, the effect is to decrease the integral gain, K.sub.I. For all values of E.sub.rel except zero, the proportional gain is increased. For all practical values of the relative error, SF.sub.P is higher than SF.sub.I. This is because, pursuant to the inventors' insight, the integral term has less importance during the transition to low flowrate mode.

[0059] The following settings for the transition from low to high flowrate were found empirically to give excellent results. [0060] S.sub.max,P=1 [0061] S.sub.min,P=1 [0062] S.sub.max,I=0 [0063] S.sub.min,I=0

[0064] Criteria for ending transition was an elapsed time of 500 ms.

[0065] If E.sub.rel is 25% or 0.25, the scale factors have the following values.

SF.sub.P=(11)*0.25+1=1

SF.sub.I=(00)*0.25+0=0.0

[0066] If E.sub.rel is 1% or 0.01, the scale factors have the following values.

SF.sub.P=(11)*0.01+1=1

SF.sub.I=(00)*0.01+0=0.0

[0067] As can be seen, SF.sub.P is always 1 and SF.sub.I is always 0 during the transition from high to low speed. This is because, pursuant to the inventors' insight, the integral term has less importance during transitions.

[0068] Relative error, E.sub.rel is defined as the absolute value of the error, i.e., actual value minus the target value, divided by the target value.

[0069] While the invention has been described with respect to certain embodiments, as will be appreciated by those skilled in the art, it is to be understood that the invention is capable of numerous changes, modifications and rearrangements, and such changes, modifications and rearrangements are intended to be covered by the following claims.