Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
1999-10-28
2001-01-16
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C180S065600, C180S065700, C180S065800, C180S170000, C180S400000, C477S034000, C280S093500
Reexamination Certificate
active
06175793
ABSTRACT:
This invention relates to improvements in gearbox monitoring systems, especially, but not exclusively, for use in combination with a reduction gearbox in an electric power steering system.
It is known, in the art to provide power assistance to a steering system by employing an electric motor which drives the steering column through a reduction gearbox, typically comprising a gearbox housing and a gearset in the form of a toothed reduction wheel and a worm wheel. In operation, electric signals passed to a control unit from a torque sensor mounted on the steering column are used to control the drive of the electric motor.
In this kind of safety critical application, and indeed in any similar application which employs a gearbox, it is important to avoid jamming in the gearbox. This condition may arise if foreign matter is present in the gearbox, or if damage or excessive wear occurs to the teeth of the gearset. Jamming can prevent the rotation of the gears in the gearbox, and results in an unsafe operational state.
Because of the possible safety implications of jamming in the gearbox, designers have in the past taken several steps to prevent such an occurrence. Gearboxes have often been over-engineered to prevent excessive wear, and long term testing has typically been used to study the wear pattern of the gears. Other steps have been directed towards reducing the amount of unwanted material within the gearbox, minimising the possibility of a piece of material becoming free.
A difficulty with these prior solutions is that they are both expensive and time-consuming to implement. Furthermore, there is still no guarantee that a jam will not occur.
According to a first aspect of the present invention, we provide a gearbox monitoring apparatus for use in combination with a gearbox which provides a connection between an input shaft and an output shaft, said gearbox monitoring apparatus comprising:
a first position sensing means and a second position sensing means, said first and second position sensing means generating a respective first and second output signal, said first output signal being representative of the angular position of the input shaft and said second output signal being representative of the angular position of the output shaft;
a torque signal generating means which generates a third output signal representative of the torque carried by the gearbox; and
signal processing means adapted to receive said output signals, said signal processing means being adapted to produce a difference signal representative of the difference between the angular position of the input shaft and the output shaft from the first and second output signals, and in which said signal processing means is adapted to divide the difference signal values into two steams corresponding to the third output signal representative of negative torques and positive torques respectively and to process said two streams of output signals to produce one or more modified output signals representative of the wear in the gearbox.
This monitoring apparatus is advantageous in that it enables the wear in the gearbox to be monitored during operation. Preferably, the input shaft comprises a driven shaft driven by a motor.
Preferably, the gearbox monitoring apparatus may be used in combination with a gearbox in an electric power assisted steering system. In this case, there are two inputs, one manual and one powered, which are combined using the gearbox to produce a single boosted output. The manual input is the side of the steering column shaft connected to the steering wheel, and the powered input is driven by the motor. The output shaft torque is used to turn the road wheels.
The torque signal generating means may comprise a torque sensor. Alternatively, the gearbox torque may be inferred as a function of measured parameters such as the motor drive current, velocity and acceleration. In the case of an electric power steering system, the gearbox torque signal may be generated by measuring the driver imposed torque using a torque sensor sited between the driver's steering wheel and the gearbox, along with measurements of the steering column position, velocity and acceleration.
Preferably, the gearbox monitoring apparatus produces a modified output signal which comprises a first modified output signal representative of the backlash and a second modified output signal representative of the compliance of the gearset within the gearbox. The first modified output signal may be produced by correlating the signals from the first and second position sensors at different torque values. The second modified output signal may also be produced by correlating the signals from the first and second position sensors at different torque values.
Some gearboxes have been found to have a backlash that increases slowly as the gearteeth wear, but to have compliance that hardly varies at all over the life of the system. For these gearboxes, it has been found that it is possible to rely upon a fixed preset value of gearbox compliance which can be multiplied by the motor torque to produce the second modified output signal value for different torques. This simplifies the calculation by making an assumption about gearbox compliance.
Such a monitoring apparatus is advantageous over the prior art as it allows imminent failure of the gearbox to be predicted before it occurs and, in any event, enables a jamming situation to be readily identified.
The gearbox monitoring apparatus may also include a speed sensor which generates a fourth output signal representative of the rotational speed of the output shaft. In a power-assisted steering system, this would therefore produce a measure of the rotational speed of the steering column. A single sensor could be used to provide both the third output signal (torque) and the fourth output signal (speed).
The gearbox monitoring apparatus may also include a trigger means adapted to generate a trigger signal in response to a trigger stimulus. The trigger means determines the timing of the measurements made by the sensing means. Preferably, a dataset of output signals is produced in response to each trigger signal, the dataset comprising a single output from each sensor. The trigger stimulus may be a set position of the input shaft or output shaft for example, in which case a dataset of values will be produced every time the shaft passes the set position. Alternatively, the trigger stimulus may be a clock signal, with datasets produced on each clock pulse. Preferably, each of the sensors produce a continuous output signal which is sampled by the signal processing means on each trigger signal.
In a preferred embodiment, the trigger stimulus may be the movement of a motor rotor magnetic pole past a Hall effect sensor. This is advantageous in, for example, an electric power steering system as it enables the existing motor control circuitry to be employed to generate the trigger stimulus, thus reducing cost and reducing complexity. If a clock signal is used, it should be of a sufficient frequency that at least two events occur within the fastest revolution of the input shaft or motor to prevent the system loosing track of position.
The output signals forming the dataset are preferably synchronised so that they each represent the state of the respective measurands at an instant in time determined by the trigger signal. This can be done by making the measurements simultaneously in time, or may be performed by employing time domain interpolation to generate effectively simultaneous measurements.
The gearbox monitoring apparatus may further include a warning means adapted to produce a warning signal in the event that the modified output signals produced by the signal processor indicate a jam has occurred or is likely to occur. A fault alleviation means may also be provided. The warning signal may be in the form of an audio/visual or haptic signal. Most preferably, the warning signal comprises vibrating the output shaft by exciting the motor in a clockwise and anti-clockwise direction using an alternating frequency curren
Beaulieu Yonel
Cuchlinski Jr. William A.
Tarolli, Sundheim, Covell Tummino & Szabo L.L.P.
TRW Lucas Varity Electric Steering Ltd.
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