Method of and apparatus for the combined detection of speed varying energy level wheel slip detection and determination of wheel slip intensity of a railway vehicle brake system

A method of and an apparatus for controlling wheel slip in a railway vehicle brake system which includes: determining whether the axle rate is in the slippage range, and generating a first output logical signal indicative thereof; comparing the axle rate and the first output logical signal to determining an energy summation value indicative of the wheel/axle set's loss of energy due to braking wheel slippage, and generating an energy summation signal indicative thereof; determining an energy loss limit and generating an energy loss limit signal at which wheel slippage has little potential for self correction; comparing the energy summation signal and the energy loss limit signal to generate a second logical output signal indicative of whether the wheel/axis set is in a slip condition that needs correction; comparing the axle rate signal, the energy summation signal and the second logical output signal to generate a wheel slip intensity signal; converting the wheel slip intensity signal to a command signal; and utilizing the command signal in a force modulation interface to vary the rate of braking force reduction.

FIELD OF THE INVENTION 
This invention relates, in general, to a wheel slip control system for a 
passenger transit railway and/or other similar type vehicles, and, more 
specifically, this invention relates to both a method and apparatus which 
includes a combination of wheel slip control detection and wheel slip 
intensity determination. By including a wheel slip intensity 
determination, the system is a full range detection system that allows 
fast through slow breakaway wheel slip detection. The system lends itself 
to microprocessor applications, and is well suited to use with pattern 
recognition adhesion adaptive wheel control systems. 
BACKGROUND OF THE INVENTION 
It has been found that, when the brakes of a transit vehicle of a railway 
train consist are applied, the braking force must be properly controlled 
in order to safely and efficiently slow down and/or stop the vehicle or 
train at a station or the like. For a given running surface condition, the 
force between the wheel tread and the running surface or track increases 
during the initial stages of slippage. As slippage increases the slip 
value moves toward the a critical wheel slip value. When the value of the 
wheel slip increases beyond such critical slip value, the force between 
the wheel tread and the running surface decreases. It will be appreciated 
that stable and effective braking occurs when the slip value is either 
equal to or less than the critical slip value. Thus, when a slip value 
becomes greater than the critical slip value, the braking becomes unstable 
and can result in a sudden wheel lockup which can not only cause excessive 
wheel and running surface wear and wheel flattening, but will increase the 
actual stopping distance. Accordingly, in the braking operation, it is 
advantageous to detect an incipient wheel lockup by continuously 
monitoring the wheel slip value between the wheel tread and the running 
surface and in order to reduce and/or control the braking force being 
applied to the extent necessary to achieve the maximum possible braking 
effort without causing wheel lockup. 
A prior art type wheel-slip control system is shown and disclosed in U.S. 
Pat. No. 4,491,920, issued on Jan. 1, 1985, entitled "Rate Polarity Shift 
Wheel-Slip Control System", which is assigned to the assignee of the 
present invention, and the teachings therein are incorporated herein by 
reference thereto in the present application. Briefly, the wheel-slip 
control in that patented system is for a multiple-truck vehicle and 
includes a speed sensor for generating signals representative of the 
velocity of each of the wheel axle units. A differentiator is connected to 
each of the speed sensors for differentiating the velocity signals to 
obtain a rate signal. A rate determining circuit determines the most 
negative-going rate signal of each of the wheel axle units of each truck. 
A plurality of deceleration threshold and rate direction detectors and 
data processing logic initiate a brake force reduction action on the truck 
experiencing a wheel slip, and a positive logic "OR" gate senses a 
polarity shift in the most negative rate signal to cause the data 
processing logic to reapply a braking action. 
A more recent prior art wheel-slip control system is shown and disclosed in 
our U.S. Pat. No. 4,941,099, issued on Jul. 10, 1990, entitled "Electronic 
Adhesion Adaptive Wheel Slide Protection Arrangement Function", which is 
also assigned to the assignee of this invention, and is also incorporated 
herein by reference thereto. Pursuant to that patented system, a distinct 
and separate speed varying rate detection circuit and an energy storage 
slip detection circuit are provided, with the speed varying rate detection 
circuit being a part of a primary wheel slip detection system, while the 
energy storage slip detection circuit is a part of a synchronous wheel 
slip detection system. Each detection circuit is interfaced with its own 
separate pattern recognition logic, which are then tied together through a 
relatively complex brake force modulation scheme. 
Accordingly, the above patented system uses two separate detection systems, 
with each detection system requiring a separate slip control logic, which 
then must be tied together with a rather complex force modulation scheme. 
In addition, the above described patented system uses a single energy 
storage level set point which limits the effectiveness of the system to a 
particular speed range, and is, therefore, normally used only for fast 
breakaway slippage, and is sometimes prone to over sensitivity. 
SUMMARY OF THE INVENTION 
The present invention provides an apparatus and process for a wheel slip 
control detection and combines therewith, a wheel slip intensity 
determination function. By measuring and incorporating the variable energy 
storage slip value, as opposed to utilizing a predetermined set point, a 
full range detection system results for fast through slow breakaway wheel 
slip detection. By combining the two functions, the variable energy 
storage factor also minimizes the possibility of over sensitivity. 
Incorporation of a wheel slip intensity determination function also allows 
the force reduction modulation to be calibrated to the intensity of the 
wheel slippage without the need for complex force modulation logic. By 
combining the two functions, the system requires only one slip control 
logic and thereby reduces the necessary hardware and/or software code 
needed to implement the detection logic. Although the process can be 
implemented through use of discrete circuits, it readily lends itself to 
microprocessor applications, and is well suited for use with a number of 
different types of slip control logic including both simple and complex 
wheel slip control logic schemes, and can be adapted to a variety of force 
modulation systems. 
In a system using a variable force reduction rate approach, for example, 
the apparatus will include a rate band detector responsive to an axle rate 
signal and a preset deceleration rate level, to produce a first output 
logical signal of "0" or "1" and an energy summation means responsive to 
the output logical signal of the rate band detector to produce an energy 
summation output signal. An energy constant means is also provided, which 
is responsive to an axle speed signal to produce an energy constant signal 
defining an energy loss limit having a numerical value no greater than 
zero, and a slip detector, responsive to the energy summation signal and 
the energy constant signal to produce a second logical signal of "0" or 
"1". A wheel slip intensity detector is also provided which is responsive 
to the axle rate signal, the energy summation output signal and the second 
logical signal, to produce a wheel slip intensity output signal having a 
value of "0" if the second logical output signal is "0", and if the second 
logical signal is "1", this intensity output signal will have a value 
equal to the axle rate signal. Lastly, a release rate determination means 
is provided which is responsive to the wheel slip intensity output signal 
to convert the wheel slip intensity output signal to a command signal 
which is used to vary the rate of braking force reduction. 
OBJECTS OF THE INVENTION 
It is, therefore, one of the primary objects of the present invention to 
provide a method of and an apparatus for a new and improved wheel slip 
detection system for controlling the braking system on a passenger transit 
railway and/or other similar type vehicle. 
Another object of the present invention is to provide a method of and an 
apparatus for providing a combination system of speed varying energy level 
wheel slip detection and wheel slip intensity determination in a system 
for controlling the brake system on a passenger transit railway and/or 
other similar type vehicle, which permits fast through slow breakaway 
wheel slip detection. 
A further object of the present invention is to provide a method of and an 
apparatus for combining a speed rate detection function and storage slip 
detection function within a single system for controlling a brake system 
on a passenger transit railway and/or other similar type vehicle which is 
not prone to over sensitivity. 
Still another object of the present invention is to provide a method of and 
an apparatus for combining a speed rate detection function and storage 
slip detection function within a single system for controlling a brake 
system on a passenger transit railway and/or other similar type vehicle 
which is effective over any speed range. 
A further object of the present invention is to provide a method of and an 
apparatus for combining a speed rate detection function and storage slip 
detection function within a single system for controlling a brake system 
on a passenger transit railway and/or other similar type vehicle which 
minimizes the logic necessary and reduces the hardware and/or software 
needed to implement the detection logic. 
A still further object of the present invention is to provide a method of 
and an apparatus for combining a speed rate detection function and storage 
slip detection function within a single system for controlling a brake 
system on a passenger transit railway and/or other similar type vehicle 
which does not require the incorporation therein of a complex force 
modulation logic. 
Still another object of the present invention is to provide a method of and 
an apparatus for combining a speed rate detection function and storage 
slip detection function within a single system for controlling a brake 
system on a passenger transit railway and/or other similar type vehicle 
which can be used with a number of different types of wheel slip control 
logic, and can be adapted to a variety of force modulation approaches. 
In addition to the numerous objects and advantages described with 
particularity above, various other objects and advantages of the instant 
invention will become more readily apparent to those persons who are 
skilled in the passenger transit brake control art from the following more 
detailed description of the invention, particularly, when such description 
is taken in conjunction with the attached drawing and the appended claims.

BRIEF DESCRIPTION OF A PRESENTLY PREFERRED AND ALTERNATIVE EMBODIMENTS OF 
THE INVENTION 
Prior to proceeding with the more detailed description of the invention, it 
should be noted that although the invention will be described as a system 
utilizing a variable force reduction rate approach, which includes a rate 
band detector, an energy summation means, an energy constant means, a slip 
detector, a wheel slip intensity detector, and a release rate 
determination means, it should be understood that any such detectors and 
means can be readily used by persons skilled in the art whether electronic 
or otherwise, and that such a person skilled in the art could apply this 
approach to other force modulation systems. In addition, the terms 
"device" or "means" as used herein may be either a discrete electrical or 
electronic circuit or a portion of a microprocessor. 
It should be further noted that the system, according to the present 
invention, is intended to be used as a system for controlling the barking 
forces on any given wheel/axle combination being monitored. Pursuant to 
conventional prior art practices, any such wheel/axle combination being 
monitored will be provided with an individual speed pickup (not shown) 
which will provide an axle speed signal indicative of the rotational speed 
of the wheel/axle being so monitored. It is this axle speed signal which 
is utilized to activate the system of this invention. 
The presently preferred embodiment of this invention utilizes a number of 
process input and output signals to achieve effective vehicle brake 
control with respect to a particular wheel/axle set being monitored. As 
noted above, one of these signals is the axle speed signal 10, provided by 
the speed pickup (not shown). Another of one these signals is the axle 
rate signal 12, which is the acceleration/deceleration of the wheel/axle 
set being monitored for slippage. This axle rate signal 12 is developed by 
the invention from the differentiation of the axle speed signal 10 which 
is externally supplied to the inventive unit by an outside source, namely 
the speed pickup (not shown) as noted above. The axle speed signal 10 and 
axle rate signal 12 may be generated in a manner similar to that shown and 
disclosed in the above-noted U.S. Pat. No. 4,491,920. 
With reference to the drawing, the presently preferred embodiment of this 
invention which utilizes a variable force reduction rate approach includes 
a rate band detector 14 which receives the above-noted axle rate signal 
12. As previously noted, the axle rate signal 12 is the 
acceleration/deceleration rate of the wheel/axle being monitored for 
slippage, and is developed from the differentiation of the axle speed 
signal 10 externally supplied by speed pickup (not shown). The rate band 
detector 14 is adapted to receive the axle rate signal 12, and compare it 
to a deceleration rate level, which is programmed into the rate band 
detector 14 and is set to be indicative of the border line between a 
deceleration rate that the vehicle could actually produce without wheel 
slippage and any deceleration rate that is in the wheel slippage range. As 
a result of such comparison, the rate band detector 14 produces a first 
output logical signal 16 which will have a numerical value of "0" or "1". 
If the input axle rate signal 12 is less than or equal to -5.2 MPHPS 
(miles per hour per second) the output will be a logical signal 16 of "1". 
If the input axle rate signal 12 is greater than -5.2 MPHPS the output 
will be a logical signal 16 of "0". An output logical signal 16 of "1" 
indicates that the axle deceleration is in the slippage range, while an 
output logical signal 16 of "0" indicates that the axle deceleration is 
not in the slippage range. 
In addition to the above, an energy summation means 18 is also provided 
which is responsive to the output logical signal 16 and the axle rate 
signal 12, to produce an energy summation output signal 20, which is equal 
to "SUM". The energy summation means 18 is adapted to receive the axle 
rate signal 12 and add it to +5.2 MPHPS and then to include the value into 
a memory within the energy summation means 18. If the rate band detector 
14 indicates that the axle deceleration is in the slippage range, the 
value of the summation will be carried into the next program cycle. The 
value in the memory of the energy summation means 18, will be set to 0 if 
the input from the rate band detector 14; i.e., output logic signal 16, 
indicates that the axle deceleration is not in the slippage range. 
Accordingly, the value in the memory of the energy summation means 18 is 
representative of the wheel/axle set's loss of energy due to braking wheel 
slippage, and will be either 0 or a negative value. The more negative the 
value, the greater the energy loss. The energy summation output signal 20, 
as a function of the two input signals 12 and 16 to such energy summation 
means 18, will vary as follows: If the logical signal 16 is a logical "1", 
the mathematical process that will occur is 
EQU SUM=SUM+(axle rate+5.2 MPHPS) 
On the other hand, if the logical signal 16 is a logical "0", then 
EQU SUM=0 
In addition to the above, the system of this invention also includes the 
function of determining an energy constant, or an energy constant 
determination means 22 responsive to the axle speed signal 10 to produce 
an energy constant signal 24 defining an energy loss limit. As previously 
noted, the axle speed signal 10 is externally supplied by the speed pickup 
(not shown) and is a value representative of the speed of the wheel/axle 
set being monitored. The input speed signal 10 is used to compute the 
energy constant signal 24, and utilizes an equation which defines the 
energy loss limit at which wheel slippage has little potential for self 
correction. As the vehicle speed increases, the energy loss limit becomes 
greater as the nature of wheel to rail slippage would dictate. The energy 
constant signal 24 will always have a negative value, and as the axle 
speed increases; i.e. axle speed signal 10 increases, the value of the 
energy constant signal 24 will become more negative. Accordingly, the 
energy constant signal 24 is defined in terms of the input signal (axle 
speed signal 10) as follows: 
EQU Energy constant signal=-0.0053(axle speed**2)-8, and has a numerical value 
which is always negative. 
A slip detector 26, is also provided within the inventive system which is 
responsive to the energy summation signal 20 and the energy constant 
signal 24 to produce a second logical signal 28 of "0" or "1". As 
previously noted, the energy summation signal 20 will be a negative number 
or zero, while the energy constant signal 24 will always have a negative 
value, which becomes more negative with increasing axle speeds. On the 
basis of comparing these two values, the slip detector 26 produces a slip 
enable output signal 28, which indicates to all other logic functions 
connected thereto, that the axle is in a slip condition that must be 
corrected, and functions as follows: If the energy summation signal 20 is 
less than or equal to the energy constant signal 24, the second logical 
signal 28 will be a logical "1". If the energy summation signal 20 is 
greater than the energy constant signal 24, the second logical signal 28 
will be a logical "0". 
A wheel slip (w/s) intensity detector 30 is also provided which is 
responsive to axle rate signal 12, the energy summation signal 20 and the 
second logical signal 28, to produce a wheel slip intensity output signal 
32. The wheel slip intensity detector 30, is adapted to hold in memory the 
axle deceleration rate at the point where slip is detected. If the axle 
rate signal 12 is negative, it is decelerating, and the more negative the 
rate, the faster breakaway of the slip; i.e., lower intensity, and 
accordingly the lower the intensity output signal 32. On a typical system, 
the axle rate value indicating the intensity, could theoretically be 
anywhere between -5.2 MPHPS and -25.6 MPHPS. If the input energy summation 
signal 20 is zero, then the intensity output signal 32 will be zero. If 
the input energy summation signal 20 is not zero, then the following will 
result: If the input second logical signal 28 transitions from a logical 
"0" to a logical "1", then the intensity output signal 32 will equal the 
input axle rate (i.e., axle rate signal 12). If the input second logical 
signal 28 remains constant in either state, positive or negative, or 
transitions from a logical "1" to a logical "0", then the intensity output 
signal 32 will remain unchanged from the previous determination. The 
overall effect of this function is that the intensity output signal 32 
will be either 0 or the axle deceleration rate value at the time the 
second logical signal transitions from a logical "0" to a logical "1". 
A release rate determination means 34 is also provided which is responsive 
to the wheel slip intensity detector 30, i.e., wheel slip intensity output 
signal 32, to convert the wheel slip intensity output signal 32 to a 
command signal 36 which is then utilized to vary the rate of braking force 
reduction through a brake force modulation interface 38. The wheel slip 
intensity signal 32 will be either a numerical 0 or a numerical value 
between -5.2 MPHPS and -25.6 MPHPS. The lower this value (more negative), 
the faster the breakaway slow breakaway wheel slip is more effectively 
controlled by a slow brake force reduction. On the other hand 
effectiveness and wheel protection make a rapid brake force reduction an 
imperative for fast breakaway wheel slips, 
While a number of different devices can he utilized as a brake force 
modulation interface 38 to he responsive to the command signal 36 to vary 
the brake force reduction, for purposes of example, a variable flow 
modulation valve can he utilized for this purpose, If such a flow 
modulation valve is used, the release rate determination means 34 will 
convert the wheel slip intensity signal 32 to command signal 36 which is a 
varying current signal used to drive the variable flow modulation valve, 
The variable flow modulation valve operates in the following manner: 
##STR1## 
The input to the release rate determination means 34 from the wheel slip 
intensity detector, i.e., intensity output signal 32, will be either 0 or 
an axle rate signal 12 in the range from -5.2 MPHPS to -25.6 MPHPS. With 
regard to the above described variable flow modulation valve, if the input 
(intensity output signal 32) is 0, the output command signal 36 will be 
630 mA current (a lap condition). If the input intensity output signal is 
in the -5.2 to -5.6 MPHPS range, the following equation is used to 
determine the output command signal 36: 
EQU Output Command Signal=-7.84* Input+799.23. 
Accordingly, the variable flow modulation valve will control the brake 
force reduction through the variable command signal 36 provided in the 
form of a variable mA current signal. 
While a number of presently preferred embodiments of the invention have 
been described in detail above with reference to the attached drawing 
Figure, it should be understood that the embodiments described are an 
example of apparatus as may be used in a variable force reduction rate 
approach, and a number of modifications and/or other adaptations of the 
present invention may be made by persons who are skilled in the passenger 
transit type braking art utilizing different types of slip control logic 
and a variety of other force modulation systems without departing from 
either the spirit of the invention or the scope of the appended claims.