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Title:
METHOD AND APPARATUS FOR THE OPTIMUM BLENDING OF LUBRICATING BASE OILS AND AN ADDITIVE
United States Patent 3826904
Abstract:
A method and apparatus for enabling the computation of a minimum cost blend of lubricating oil base stocks, wherein a viscosity index improver additive is included. System includes measurement of viscosity and related data at two separate concentrations of the additive where such concentrations are in the range from about 1 percent to about 10 percent of the additive with a given base oil. Data obtained are used in non-linear formulae to provide bases for calculating optimum blends to obtain particular specifications with minimum cost.


Inventors:
Leonard, John M. (Houston, TX)
Lewis Jr., John S. (Huntsville, AL)
Application Number:
05/295060
Publication Date:
07/30/1974
Filing Date:
10/04/1972
Assignee:
Texaco Inc. (New York, NY)
Primary Class:
Other Classes:
208/DIG.1, 700/36, 700/265
International Classes:
G01N33/28; (IPC1-7): G01N25/46; F23M5/00
Field of Search:
235/151
View Patent Images:
US Patent References:
Primary Examiner:
Morrison, Malcolm A.
Assistant Examiner:
Wise, Edward J.
Attorney, Agent or Firm:
Whaley, Thomas Ries H. C. G.
Parent Case Data:


CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation as to all subject matter common to U.S. application, Ser. No. 90,244, now abandoned, filed Nov. 17, 1970 by John M. Leonard et al., and assigned to Texaco Inc., assignee of the present invention, and a continuation-in-part for all additional subject matter.
Claims:
What is claimed is

1. A system for controlling the blending of base oils and an additive, to achieve a desired blend having predetermined characteristics, being provided to blending means, comprising means for controlling the quantities of base oils and additive being provided to the blending means to be blended in accordance with control signals, means for providing signals corresponding to the predetermined characteristics for a desired blend of base oils and the additive, means for providing signals corresponding to the economic values of the base oils, memory means for storing values of different combinations of the base oils and the additive quantities, means connected to the value signal means, to the memory means and to the characteristic signal means for selecting a desired combination of base oil and additive quantities in accordance with the economic value signals and the characteristic signals and providing signals corresponding thereto to the control means as control signals so as to achieve the desired blend of base oils and the additive.

2. A system as described in claim 1 in which the selecting means includes means connected to the memory means for controlling the memory means to provide signals corresponding to quantities of base oils & additive for different combination thereof comprising different blends in an iterative manner, means connected to the memory means and to the value signal means for providing a signal corresponding to the cost of a combination of the quantities represented by the signals provided by the memory means in accordance with the economic value signals and the following equation: ##SPC8##

3. A system as described in claim 2 in which the predetermined characteristics are the H value, the pour blend value PBV, and ASTM color blend value, the flash point blend value BV and the aniline point blend value and the determining means includes means receiving direct current voltages corresponding to terms h, a and b for the different base oils and l, associated with the following equations, and connected to the memory means for providing a signal corresponding to H for a present combination of base oils quantities in accordance with the following equation: ##SPC9##

Description:
BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns lubricating oil blending in general. More particularly, it relates to an improved method of blending lubricating oils where the blend includes a viscosity index improver additive.

2. Description of the Prior Art

Heretofore, in the blending of lubricating oil base stocks, to obtain desired specifications there was no particular difficulty because the blend viscosities were proportional to the percentage amounts of the base stocks by making use of the so-called "H-value" used in determining the viscosity index. However, it was found that where such blends included therein one of more viscosity index improvement-type additives, the resulting blend was not predictable. Thus, it was found that additives of the sort mentioned could not be blended on the basis of a predetermined viscosity index for the additive, since the "H-value" would vary in a non-linear manner with the amount of additive and the particular base oil with which it was blended. Pour points also varied non-linearly with the amount of additive and the base oil used.

Consequently, it is an object of this invention to provide a method and system for predetermining a particular blend of base oils with a viscosity index improver additive, so as to provide predetermined characteristics for the resulting blend.

SUMMARY OF THE INVENTION

A system controls the blending of base oils and an additive to achieve a desired blend oil having predetermined characteristics at minimum cost. The system includes apparatus which controls the quantities of base oils and additive being provided to a blending tank in accordance with control signals. A circuit provides signals corresponding to the predetermined characteristics to a network. The network provides the control signals to the apparatus in accordance with the characteristic signals.

The objects and advantages of the invention will appear hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawings wherein two embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustration purposes only and are not to be construed as defining the limits of the invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified block diagram of a control system, constructed in accordance with the present invention, controlling apparatus shown in schematic form, for the blending of base oils with an additive.

FIGS. 2, 3, 4 and 7 are detailed block diagrams of the programmer, the xi signal means, the constraint control means and the blending control means, respectively, shown in FIG. 1.

FIGS. 5 and 6 are detailed block diagrams of the Hi network and the BVi network, respectively.

FIG. 8 shows another embodiment of the present invention in which a general purpose digital computer is used to control the blending of base oils with an additive.

FIG. 9 is a non-linear graph illustrating the non-linear relationship of a base oil mixture and the percentage of additive in the mixture.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Lubricating oils are often blended in order to meet predetermined specifications, e.g., those called for to meet a customer's desires. Heretofore, that could be accomplished in a straightforward manner since the characteristics of the blend varied in proportion with the volume-fraction of the base oils of the blend. However, it was found that the addition of a viscosity index improver additive created conditions such that the linear blending of the base stocks of lubricating oils could no longer be carried out with an expectation of providing a predetermined blend viscosity or viscosity index. It was found that the viscosity index improver additive did not act as a lubricating oil in that its own viscosity H-value was not a constant but varied according to the base oil or oils in the blend. It was also discovered that the pour point depressant effects of the VI improver additive varied according to the base oil or oils in the blend. Thus, a relationship between the viscosity and pour point of a blend of base oils and the viscosity and pour point of that blend with a viscosity index improver additive could not be defined.

It may be noted that the above-mentioned "H-value" is an element in the formula for calculating the viscosity index of any given oil. The formula is given and explained in the "Standard Method for Calculating Viscosity Index from Kinematic Viscosity" of the American Society for Testing and Materials under the fixed designation D2270. Such Standard is published by the Society with an annual issue.

Another approach to the problem was to assume a constant H-value for a particular additive over a limited range of viscosity of a base oil blend. However, this was found not to work since it appeared that the effect of the additive on the viscosity of several different base oil blends, each of which blends had the same viscosity, indicated that the assumed or pseudo H-values were not usable.

It was discovered that if the viscosities of a particular lubricating oil base stock at standard temperatures, e.g., 100°F and 210°F, were measured under two separate percentage mixtures with the additive, a predetermined relationship could be expressed for each base oil. Such relationship follows a curve of the general form as illustrated in FIG. 9. This could be represented by the following equation:

(ΔH)i = Hi - hi = ai (1 - e -b x ) (1)

wherein Hi is the viscosity "H-value" of a given base oil-additive combination; and hi is the viscosity H-value of the base oil aone; ai and bi are constants; and xl is the volume-fraction of the additive; and e is the natural log base.

Since the hi is known or can be readily determined for each base oil, the H-value of a base oil i with any volume-fraction xl of a given additive, from 0.0 to somewhat above 0.06, could be predicted by the following equation:

Hi = hi + ai (1 - e -b x ) (2)

These base oil-additive combinations can then be treated as separate components in a blend, each with H-value Hi. The viscosity H-value of a blend of n base oils with a given concentration xl of an additive is thus calculated by ##SPC1##

where xi (i = 2, 3, . . . ., n) is the volume-fraction of base oil i in the blend. The blend H-values at 100°F and 210°F may then be used in the Standard formula noted above to calculate a predetermined blend viscosity and viscosity index.

It will be understood that throughout this disclosure the abbreviation "VI" stands for viscosity index.

It was also discovered that the pour point of each base oil mixed with the additive would have a predetermined relationship which follows the general form similar to that for the H-value, as illustrated in FIG. 9, except that the pour point decreases with increasing additive dosage. Consequently, if the pour points of the base oil-additive mixtures using two separate percentages, e.g., with 3 and 6 percent of the additive, was also measured, such data could be converted to form a blending equation comparable to the H-value equation for viscosity.

Thus, using calculations similar to those made for viscosity, the pour blending value (PBV) of any blend of base oils with volume-fraction xl of the additive could be found by using the following equation: ##SPC2##

where PBV is the pour blending value of a blend with volume-fraction xl of additive; (pbv)i is the pour blending value of base oil i; and where ci and di are constants calculated for base oil i.

With respect to other characteristics of a blend of base oils with a VI improver additive included, such as flash point, aniline point, and ASTM color, there was found to be no significant change because of the additive. Consequently, linear blending values previously developed for such property of each base oil could be used to predetermine these characteristics of blends. The characteristic blending value of a blend containing volume-fraction xi of base oil i (i = 2, 3, . . . ., n) could thus be found by the equation: ##SPC3##

where BV is the characteristic blending value of a blend; (BV)i is the corresponding property blending value for base oil i; and xl is the volume-fraction of the additive in the blend, as above.

The resulting expressions, e.g., (3), (4) and (5) above, allow prediction of the viscosities at 100°F and 210°F (and hence VI), plus pour point, flash point, aniline point, and ASTM color of any blend of base oils with a VI improver. It is to be noted that the entire relationship of the constituents of a blend with an additive may be derived from data taken at only two additive levels for each base oil. It will be appreciated that conventional and/or stardard equipment (not shown) may be employed in carrying out the measurements of the properties. As pointed out above, the measurements are made using each of two different percentage amounts of an additive in therange from about 1 to about 10 percent mixed with each base oil individually. Actual percentage amounts of an additive that were used in carrying out the invention were 3 and 6 percent.

The entire lube oil blending procedure and system lends itself to use with a computer in order to find the minimum-cost blend which meets a given set of characteristic specifications. Using a digital computer, a skilled programmer could write a program using non-linear constraints so as to minimize the cost function which would be expressed in the form: ##SPC4##

subject to contraints (i.e. specifications) expressed in forms such as the following:

The viscosity constraints HL and HU would be: ##SPC5##

The pour constraints PBVL and PBVU would be: ##SPC6##

and each additional specification would have constraints BVL and BVU of the form ##SPC7##

where C is the total cost of a blend; Ci is the cost of a constituent base oil i; and xi is the volume-fraction of base oil i in the blend, as in previous expressions; and where H, PBV and BV are characteristics; and the other terms used in the expressions (7), (8) and (9) are all the same as in previous expressions. Some typical specification characteristics are gravity, flash point, etc.

Referring to FIG. 1, base oils A, B and C from storage facilities (not shown) are provided to a blending tank 1 through lines 2, 3 and 4. For convenience, the following example disclosing the present invention will show the use of three base oils, although there is no restriction on the number of base oils that may be blended in tank 1 to provide a blend oil. The flow rate of a base oil is directly related to the quantity of that base oil in the final blend oil. The flow rate of the base oil A in line 2 is controlled by a valve 6 receiving a signal from a flow recorder controller 8. Flow recorder controller 8 receives a signal corresponding to the flow rate of base oil A in line 2 from a flow rate sensor 10. The set point of flow rate controller 8 is positioned to a desired flow rate, as hereinafter described, which will provide the desired portion of base oil A for a desired blend oil in blending tank 1. Flow recorder controller 8 provides the signal to valve 6 in accordance with the difference between the flow rate signal from sensor 10 and the position of its set point so that the flow rate in line 2 assumes the desired flow rate.

Similarly the flow rate of base oil B in line 3 is controlled by the cooperation of a valve 6A, a flow rate sensor 10A and a flow recorder controller 8A. The quantity of base oil C entering tank 1 is also controlled in a similar manner by a valve 6B and flow recorder controller 8B and a flow rate sensor 10B. Elements having a number and a suffix are connected and operate in a similar manner to those elements having the identical number without a suffix.

A viscosity improver additive is also provided to tank 1 through a line 11. A valve 6C, a flow recorder controller 8C and a sensor 10C cooperate to control the flow rate of the additive in line 11. A direct current voltage VA sets the set point in controller 10C to a position corresponding to the predetermined flow rate.

Although, for purposes of illustration, the flow rate of the additive and base oils are shown as being controlled by flow recorder controller cooperating valves and flow sensors, it would be obvious to one skilled in the art that the flow rates can be controlled using meters, valves, differential control counters and digital-to-analog converters. Such a control method is discussed in an article by Mr. J. J. Jiskoot in the Oct., 1968 issue of the Chemical and Process Engineering at page 87.

The set points of flow recorder controllers 8, 8A and 8B are controlled in accordance with equations 6, 7, 8 and 10. In this regard, a programmer 12, which is shown in detail in FIG. 2, provides control pulses EA through EE to Xi signal means 14 through 14C, respectively. Xi signal means 14 through 14C cooperate to provide signals E2 through E2C, respectively, which correspond to the quantities of base oils A, B and C, and the additive, respectively, for a particular blend oil. The providing of signals E2 through E2C may also be done by various types of memory means, in which various combinations of base oils A, B and C have been stored, that would replace programmer 12 and Xi signal means 14 through 14C.

Referring now to FIGS. 1, 2 and 3, signals E2 through E2C are developed as follows. An operator activates a switch 20 in programmer 12 receiving a direct circuit voltage V1. Switch 20 may be a conventional type "momentary on" type of switch. Voltage V1 passed by switch 20 triggers a flip-flop 24 to a set state. A flip-flop provides a high level direct current output when in a set state and a low level direct current output when in a clear state. The high level output from flip-flop 24 causes an AND gate 26 to pass timing pulses from a clock 27 to a counter 30. Counter 30 counts the timing pulses and its content is decoded by a logic decoder 31 to provide a plurality of outputs to a corresponding plurality of one shot multivibrators 35. One shot multivibrators 35 provide a plurality of control pulses EA through EE and a reset pulse E1. Reset pulse E1 occurs when counter 30 is full. Reset pulse E1 resets flip-flop 24 to a clear state thereby disabling AND gate 26. When disabled AND gate 26 blocks the timing pulses from clock 27 to prevent further counting by counter 30. Reset pulse E1 also resets counter 30 to a zero count. Programmer 12 provides reset pulse E1 to other portions of the control system as hereinafter disclosed.

Each pulse passed by AND gate 26 triggers a time delay one shot multivibrator 36 to provide a time delay pulse. The time delay pulse allows calculating networks to complete the calculation before triggering another one shot multivibrator 37 to provide a pulse. The pulse from multivibrator 37 is inverted by an inverter 38 to provide an inhibiting pulse E6.

FIG. 3 shows in detail Xi signal means 14 which includes a plurality of conventional type electronic switches 40 through 40D. The number of switches correspond to the number of combinations of base oils A, B and C and additive that is expected to be utilized. For example, if more base oils than base oils A, B and C were desired for blending, then more switches are needed because there would be more possible blend combinations of the various base oils.

Direct current voltages i.e., B through VF, provided by a conventional type direct current voltage source not shown, correspond to predetermined quantities of base oil A for different blend oils. For a count of one, electronic switch 40 receiving voltage VB is activated by pulse EA from programmer 14, to provide voltage VB as signal E2. Similarly, pulse EA causes signal means 14A, 14B, 14C to provide other direct current voltages corresponding to the quantities of base oils B & C standard the additive necessary for that particular blend oil to be provided as signals E2A, E2B and E2C. Similarly, pulses EB, EC, ED the range and EE will render switches 40A, 40C and 40D, respectively, conductive in turn to provide direct current voltages VC through VF respectively as base oil A quantity signal E2. In a similar manner signal means 14A, 14B, 14C are also controlled to provide corresponding direct current voltages so that at any one time signals E2 through E2C correspond to quantities of base oil A, B and C and the additive required to make a particular blend oil. In essence, signal means 14, 14A, 14B, and 14C, along with the voltage source, comprise memory means storing signals corresponding to quantities of base oils A, B and C and the additive for different blend oils.

Although a particular blend oil has been defined by signals E2, E2A and E2B it does not necessarily follow that the particular blend oil is acceptable or that the particular blend oil, if acceptable, is the most economical blend oil obtainable.

Referring to FIGS. 1, 4 and 5, control means 42 determines if a particular blend oil, as defined by signals E2, E2A, E2B and E 2C meets the various constraints imposed on a blend oil and more particularly the characteristics defined by equations 3, 4 and 5. Constraint control means 42 includes an H constraint circuit 44, a pour constraint circuit 45, a flash point constraint circuit 46, an aniline constraint circuit 47 and an ASTM color constraint circuit 48. Constraint circuits 44 through 48 provide a plurality of direct current outputs to an AND gate 50. Each constraint circuit will provide a high level output when a parameter, being monitored by the constraint circuit, is within upper and lower constraint limits and a low level output when the monitored parameter is not within the constraint limits. When all parameters are within their constraint limits, AND gate 50 provides an output E3 at a high level output as signal E3 and a low level output as signal E3 when any or all of the constraint circuits outputs are at a low level.

Signals E2, E2A, E2B, E2C are applied to Hi networks 55, 55A and 55B, respectively, providing signals E4, E4A and E4B, respectively, corresponding to the H values for blend oils A, B and C, respectively. In network 55, a multiplier 56 multiplies direct current voltage V3 corresponding to the term b2, with signal E2C from signal means 14C to provide a signal corresponding to the term b2 Xl. The signal from multiplier 56 is applied to a unity gain inverting amplifier 57. A logarithmic amplifier 58 provides an output corresponding to the logarithm of a direct current voltage V4 which corresponds to the term e in equation 3. A multiplier 63 multiplies the output from amplifiers 57, 58 to provide a signal corresponding to the term -b2 Xl log e to an antilog circuit comprising an operational amplifier 64 having a function generator 65 as a feedback network. Function generator 65 may be of the type manufactuered by Electronic Associates under their Part Number PC12. Thus, the output from amplifier 64 corresponds to the term e-b X .

The output from amplifier 64 is subtracted from a direct current voltage V5, corresponding to the term 1 in equation 3, by subtracting means 70. A multiplier 71 multiplies the output from subtracting means 70 with a direct current voltage V6, corresponding to the term a2. Summing means 72 sums the output from multiplier 71 with a direct current voltage V7, corresponding to the term h2 in equation 3, to provide a signal to another multiplier 73. A divider 74 divides signal E2 with a signal from subtracting means 75 corresponding to the term l - Xl, to provide an output to multiplier 73. Subtracting means 75 subtracts signal E2C from voltage V5. Multiplier 73 multiplies the output from summing means 72 and divider 74 to provide signal E4.

Similarly networks 55A and 55B operate on signals E2A, E2B, E2C, respectively, to provide signals E4A and E4B.

In circuit 44, summing means 80 sums signals E4, E4A and E4B to provide a signal E5 corresponding to the H value for base oil A with direct current voltages V9 and V10 corresponding to predetermined upper and lower constraint limits, respectively. Comparator 81 provides a high level output when voltage V9 is more positive than signal E5 and a low level output when V9 is not more positive than signal E5. Comparator 81A provides a high level output when signal E5 is more positive than voltage V10 and a low level output when signal E5 is not more positive than voltage V10 so that when H is within the constraint limits, comparators 81, 81A provide high level outputs which cause an AND gate 82 to provide a high level output to AND gate 50. When the H value exceeds the upper constraint limit, signal E5 is more positive than voltage V9 causing comparator 81 to provide a low level output which disables AND gate 82 causing it to provide a low level output to AND gate 50. Similarly, when the H value is less than the lower constraint limit signal E5 is not more positive than voltage V10 which causes comparator 81A to provide a low level output which has the same effect as when comparator 81 provided a low level output.

Pour constraint circuit 45 is similar to constraint circuit 44. Pour constraint circuit 45 utilizes PBVi networks in place of the Hi networks 55 through 55D in constraint circuit 45. The PBVi circuits are similar to the Hi networks with the difference being that the direct current voltages received correspond to the constants c and d instead of a and b and the PBVi network has summing means instead of having subtracting means 70 which sums the output from the operational amplifier with a direct current voltage corresponding to PBVi.

Constraint circuits 46, 47 and 48 are identical with each other and are similar to constraint circuit 44. The difference between constraint circuits 46, 47 and 48 are constraint circuit 44 is that constraint circuit 44 uses Hi networks 55 through 55B while constraint circuits 46, 47, 48 use PVi networks in lieu of networks 55 through 55B. Referring to FIG. 6, there is shown a BVi network. A divider 88 divides signal E2 with a signal from subtracting means 90. Means 90 subtracts signal E2 from voltage V5. A multiplier 89 multiplies the signal from divider 88 with a direct current voltage V10 which corresponds to the blend value of a particular characteristic, which by way of example may be the ASTM color, for base oil A to provide a signal corresponding to a particular BVi value.

Referring now to FIGS. 1 and 7, programmer 12 provides reset pulse E1 to blending control means 90 which also receives signals E2, E2A and E2B from Xi signal means 14, 14A and 14B, respectively, and signal E3 from constraint control means 42. Blending control means 90 provides signals E10, E10A and E10B corresponding to desired set point positions for flow recorder controllers 8, 8A and 8B, respectively, to set their set points to control the blending of base oils A, B and C with the additive in tank 1. Multipliers 93, 93A and 93C in blending control means 90 provides signals corresponding to the cost for the different component portions of a particular blend oil. Multiplier 93 multiplies direct current voltages V11 and V12 corresponding to Xl and Cl, the cost of the additive, to provide a cost signal. Similarly, direct current voltages V13, V14 and V15 corresponding to economic values of base oils A, B and C, respectively, are multiplied with signals E2, E2A and E2B, respectively, by multipliers 93A, 93B and 93C, respectively, to provide cost signals. Summing means 94 sums the cost signals from multipliers 93 through 93C to provide a blend oil cost signal E12 corresponding to C in equation 6.

Signal E12 is applied to a conventional type analog-to-digital converter 98 which provides digital signals, corresponding to signal E12, to a plurality of AND gate 99. Signal E3 is also provided to AND gates 99 to partially enable those gates. When AND gates 99 receive a transfer pulse as hereinafter explained, the digital signals from converter 98 are transferred to a storage register 100.

Storage register 100 effectively stores the minimum cost signal. This is accomplished by applying outputs from storage register 100 to a conventional type digital-to-analog converter 101 which provides an analog signal E14 corresponding to the content of register 100. Signal E14 is applied to an electronic switch 107 and to a comparator 108. Electronic switch 107 is in effect a single pole double throw switch receiving a direct current voltage V16. Voltage V16 has an amplitude larger than the amplitude of a typical cost signal E12. Comparator 108 receives voltage V17 which substantially corresponds to a zero value so that when the content of storage 100 is zero comparator 108 provides a high level signal to electronic switch 107. Electronic switch 107 passes voltage V16 to a comparator 112 when comparator 108 provides a high level signal and signal E14 when comparator 108 provides a low level signal.

The use of switch 107, comparator 108 and voltages V16 and V17 is necessitated by the initial condition of storage register 100. Since the object of register 100 is to store the minimum cost signal, when register 100 initially has a zero content it is impossible to enter any cost signal into register 100 but for the operation of switch 107 and comparator 108.

An AND gate 113 controls an electronic switch 114 receiving signal E12 from converter 98 and direct current voltage V16 in accordance with signal E3 and inhibiting pulse E6. Switch 114 passes signal E12 and blocks voltage V16 when signal E3 is at a high level and inhibiting pulse E6 is absent. Switch 114 blocks signal E12 and passes voltage V16 when signal E3 is at a low level or inhibiting pulse E6 is present.

During the initial phase of the operation, comparator 112 goes to a low level in response to voltage V16 being greater than a passed signal E12 from switch 114.

A one shot multivibrator 118 is triggered by the change to a low level in the output from comparator 112 to provide a reset pulse to an AND gate 121 which is controlled by signal E3. When switch 114 blocks signal E12, comparator 112 output would go to a low level causing one shot multivibrator 118 to provide a reset pulse which would erroneously reset register 100 and other registers if AND gate 121 was not there. However, AND gate 121 is disabled by the low level of signal E3 and blocks such an erroneous pulse.

The pulse provided by one shot multivibrator 118 passes through AND gate 121 and is applied to another one shot multivibrator 119 and to register 100 through an OR gate 120. Register 100 is reset by the pulse while one shot multivibrator 119 is triggered by the trailing edge of the pulse to provide a transfer pulse to AND gates 99. AND gates 99 in response to the transfer pulse and a high level signal E3 enters the digital signals from converter 98 into register 100.

Now signal E14 from converter 101 is greater than voltage V17 causing the output from comparator 108 to go to a low level. The low level output from comparator 108 causes switch 107 to pass signal E14 to comparator 112 and to block voltage V16. Comparator 112 now effectively compares the present blend oil cost, as represented by signal E12, with the previous minimum blend oil cost as represented by signal E14. When the present cost is less than the previous minimum cost, comparator 112 output goes to a low level causing the previous minimum cost stored in register 100 to be replaced by the present cost.

At this time, it would be appropriate to explain the effect of inhibiting pulse E6. Without AND gate 113, voltage V16 and inhibiting pulse E6 and with signal E3 controlling switch 114 directly, a condition in which successive lower blend oil costs occurred would cause all but the first lower cost to be lost. Under that condition, the output of comparator 112, already providing a low level output due to the first lower cost condition, cannot change to a lower level and therefore cannot trigger one shot multivibrator 118. However, as previously stated, the presence of inhibiting pulse E6 causes switch 114 to provide voltage V16 to comparator 112. Since voltage V16 is greater than signal E14, comparator 112 output goes to a high level. Now, when the next successive cost is lower than the next preceding cost, comparator 112 output will change from a high level to a low level triggering one shot multivibrator 118.

Where the present cost is greater than the minimum cost, comparator 112 output remains at a high level and does not trigger one shot multivibrator 118. Since one shot multivibrator 118 is not triggered, the minimum cost remains stored in register 100. When all the costs for different blend oils have been computed, storage register 100 will contain the minimum cost.

Concurrent wth storing of the minimum cost in register 100, it is necessary that the quantities of base oils A, B & C and the additive comprising the blend oil having the minimum cost be stored in registers. The pulse from one shot multivibrator 118, passed by AND gate 121 resets a storage register 128 in set point signal means 130. Signal E2 is applied to a conventional type analog-to-digital converter 131 which provides corresponding digital signals to a plurality of transfer AND gates 135. AND gates 135 are fully enabled by the pulse provided by one shot multivibrator 119 so that when a particular cost signal is transferred to storage register 100, signal E2 corresponding to the quantity of base oil A contributing to that particular cost is also transferred to storage register 128. Thus, at any time the content in register 128 corresponds to the quantity of base oil A in the blend oil that has the minimum cost.

Register 128 provides a plurality of outputs to transfer AND gates 140, wich are connected to storage register 141. Reset pulse E1 from programmer 12 resets registers 100 and register 141. Pulse E1 also triggers a one shot multivibrator 142 causing it to provide an enabling pulse to AND gates 140 causing them to transfer the content of registers 128 to 141. Register 141 holds the content corresponding to the quantity of base oil A in the minimum cost blend oil until the operation is repeated.

The signals stored in register 141 correspond to a quantity and must be converted to a flow rate control signal. A conventional digital-to-analog converter 150 converts the outputs from register 141 to an analog signal. A multiplier 151 multiplies the signal from converter 150 with a conversion signal E60 to provide signal E60. Summing means 152 sums x1 through x4 signals from signal means 130-130C, respectively, to provide a sum signal to a divider 153. Divider 153 divides a direct current voltage V59 with the sum signal to provide signal E60.

Set point signal means 130A, 130B, 130C provides signal E10 and E10A, respectively, in a similar manner to that of the set point signal means 130 so that valves 6 through 6C are controlled to allow the proper rates of the base oils & additive to achieve a minimum cost blend oil.

Although an analog computer has been used to describe the present invention, it would be obvious to one skilled in the art to use a general purpose digital computer so that the present invention is not restricted to an analog computer but also encompasses digital computer control as well as hybrid digital and analog control systems. Referring to FIG. 8, a general purpose digital computer 140 provides digital outputs to digital-to-analog converters 141-141C which converts the digital outputs to signals E10 through E10C, respectively. Computer 140 is programmed in a conventional manner to provide the digital outputs as follows:

1. Store in the computer memory values for different quantities of base oils A, B and C & the additive.

2. Store in the computer memory, equations 3 through 6.

3. Store in the computer memory, predetermined values for a, b, c, d, h, phv, ASTM color bv, flash point bv and aniline point bv for each base oil.

4. Store predetermined limits for H, PBV, ASTM color BV, flash point BV and aniline point BV.

5. Store the costs c1, c2 and c3 of base oils A, B and C, respectively, in the memory.

6. Select a first combination of base oil and additive quantities.

7. Calculate H using equation 3, PBV using equation 4 and the ASTM color BV, flash point BV and aniline point BV using equation 6 in accordance with the selected base oils quantities values and the stored values of a, b, c, d, h, pbv, AST, color bv, flash point bv and aniline point bv.

8. Compare the calculated values of H, PBV, ASTM color BV, last point BV and aniline BV with their respective limits stored in the memory.

9. If any of the calculated values are not within the limits, repeat steps 6 through 8 and 9 or 10, whichever is applicable, for the next blend combination of base oil quantities.

10. If all of the calculated values are within the limits, calculate the cost of the blend combination.

11. If there is no minimum cost, store the present cost and blend combination quantities values and select a next combination of blend oil quantities values and repeat steps 7 through 11.

12. If there is a stored minimum cost, compare the present cost with the stored cost.

13. If the stored cost is less than the present cost, select a next combination of base oils quantities values and repeat steps 7 through 12.

14. If the stored cost is not less than the present cost, store the present cost and the blend combination quantities values associated with the present cost.

15. Select a next combination of blend oils quantities values and repeat steps 6 through 14 until all of the different combination of quantities values have been processed, at that time the digital signals corresponding to the stored values of quantities of base oils and additive are provided as the digital outputs.

The apparatus of the present invention as heretofore described controls the blending of base oils with an additive to achieve a blend oil meeting predetermined characteristics. The apparatus also computes the cost for difference blend oils and effectively controls the blending of the base oils and additives to achieve the blend oil meeting the predetermined specifications but also having a minimum cost. The apparatus may be an analog computer specifically arranged to solve the equations heretofore described or it may be a general purpose digital computer program to solve the equations and to provide outputs controlling the blending of the base oils and additives.