Loose wheel detection
The disclosed invention makes use of a wheel speed signal to detect a wheel anomaly such as a loose wheel or a wheel with zero pressure. The wheel speed signal is used as a basis to determine a first and a second detection signal. A further basis for determining the first and second detection signals are a first and second reference signal, respectively. The anomaly of e.g. a loose wheel is detected, according to the teaching of the invention if at least one of the detection signals exceeds a threshold. In particular, the disclosure relates to methods, systems and computer program products to achieve the mentioned objective.
1. A method of detecting a loose wheel of a vehicle, comprising:
obtaining a wheel speed signal t(n) from a wheel sensor selected from the group consisting of magnetic wheel sensors and optical wheel sensors indicative of a wheel speed of a wheel of a vehicle,
determining a first detection signal on the basis of the wheel speed signal t(n) and a first reference signal, wherein determining the first detection signal comprises estimating an imperfection signal {circumflex over (δ)} 1 from the wheel speed signal t(n), which imperfection signal {circumflex over (δ)} 1 being indicative of an imperfection of the wheel speed signal t(n) as compared to the actual wheel speed of the wheel of the vehicle,
determining a second detection signal on the basis of the wheel speed signal t(n) and a second reference signal,
determining that the wheel of the vehicle is a loose wheel if at least one of the following conditions is met:
the first detection signal exceeds a first detection threshold,
the second detection signal exceeds a second detection threshold.
2. The method of claim 1 , wherein
the wheel speed signal t(n) is obtained from a wheel speed sensor comprising the wheel sensor sensing the wheel speed of the wheel of the vehicle, and
estimating the imperfection signal {circumflex over (δ)} 1 comprises estimating a sensor imperfection value {circumflex over (δ)} 1 indicative of the sensor imperfection of the wheel speed sensor.
3. The method of claim 2 , wherein the sensor imperfection value {circumflex over (δ)} 1 is a weighted average of sensor imperfection values y(n) of previous and current revolutions n of a rotary element of the wheel speed sensor.
4. The method of claims 3 , wherein estimating the imperfection signal {circumflex over (δ)} 1 comprises a step of low pass filtering according to the following filter relation:
LP
:
δ
^
l
=
(
1
-
μ
)
δ
^
l
+
μ
y
(
n
)
,
wherein
y
(
n
)
=
2
π
T
LAP
(
n
)
(
t
(
n
)
-
t
(
n
-
1
)
)
-
2
π
L
,
wherein {circumflex over (δ)} 1 is an estimation value of the sensor imperfection, μis a forgetting factor of the filter, t(n) and t(n−1) is the wheel speed signal, L is the total number of teeth of the rotary element and T LAP (n) is the duration of a complete revolution of the rotary element ( 5 ).
5. The method of claim 1 , wherein determining the first detection signal comprises determining an imperfection-corrected wheel speed signal ε(n) from the wheel speed signal t(n) and the imperfection signal {circumflex over (δ)} 1 .
6. The method of claim 1 , wherein determining the first detection signal comprises at least one of the following:
computing a first variance within a finite time window,
computing a difference to the first reference signal,
computing a first cumulative sum according to the following relation:
CUSUMCounter( n+ 1)=min(max(CUSUMCounter( n )+α( n )−Drift,0),CounterLim it),
wherein Drift and CounterLim it are tuning parameters.
7. The method of claim 1 , wherein computing the second detection signal comprises at least one of the following:
band pass filtering the wheel speed signal,
computing a second variance within a finite time window,
computing a difference to the second reference signal,
computing a second cumulative sum according to the following relation:
CUSUMCounter( n+ 1)=min(max(CUSUMCounter( n )+α( n )−Drift,0),CounterLim it),
wherein Drift and CounterLim it are tuning parameters.
8. The method of claim 1 , wherein at least one of the first or second reference signals is a constant.
9. The method of claim 1 , wherein at least one of the first or second reference signals is determined on the basis of a wheel speed signal indicative of a wheel speed of a further wheel of a vehicle.
10. A non-transitory computer program product including program code configured to, when executed in a computing device, carry out a method of detecting a loose wheel of a vehicle, comprising:
obtaining a wheel speed signal t(n) from a wheel sensor selected from the group consisting of magnetic wheel sensors and optical wheel sensors indicative of a wheel speed of a wheel of a vehicle,
determining a first detection signal on the basis of the wheel speed signal t(n) and a first reference signal, wherein determining the first detection signal comprises estimating an imperfection signal {circumflex over (δ)} 1 from the wheel speed signal t(n), which imperfection signal {circumflex over (δ)} 1 being indicative of an imperfection of the wheel speed signal t(n) as compared to the actual wheel speed of the wheel of the vehicle,
determining a second detection signal on the basis of the wheel speed signal t(n) and a second reference signal,
determining that the wheel of the vehicle is a loose wheel if at least one of the following conditions is met:
the first detection signal exceeds a first detection threshold,
the second detection signal exceeds a second detection threshold.
11. A system to detect a loose wheel, comprising a processing unit, the processing unit configured to
obtain a wheel speed signal t(n) from a wheel sensor selected from the group consisting of magnetic wheel sensors and optical wheel sensors indicative of a wheel speed of a wheel of a vehicle,
determine a first detection signal on the basis of the wheel speed signal t(n) and a first reference signal,
determine a first detection signal on the basis of the wheel speed signal t(n) and a second reference signal,
determine that the wheel of the vehicle is a loose wheel if at least one of the following conditions is met:
the first detection signal exceeds a first detection threshold,
the second detection signal exceeds a second detection threshold;
wherein the processing unit comprises at least one of the following:
an imperfection estimation section, configured to obtain the wheel speed sensor signal, the imperfection estimation section being configured to estimate an imperfection signal {circumflex over (δ)} 1 from the wheel speed signal t(n), which imperfection signal {circumflex over (δ)} 1 being indicative of an imperfection of the wheel speed signal t(n) as compared to the actual wheel speed of the wheel of the vehicle,
an imperfection signal correction section,
a band pass filter, configured to obtain the wheel speed sensor signal,
a variance computing section,
a cumulative sum determining section,
a decision section, configured to determine the presence or absence of a loose wheel.
12. The system according to claim 11 , wherein the system further comprises a wheel speed sensor comprising the wheel sensor for sensing the wheel speed of the wheel of the vehicle.