Engine torque sensor

An optical sensing system is used to measure engine torque. A pair of patterns are formed on a driveshaft between a transmission and axle differential. The patterns are spaced apart from one another by a predetermined distance and are formed about the circumference of the driveshaft. Lasers and photo receivers are used to scan the patterns as the driveshaft rotates. Data from the photo receives is used to determine the angle of twist on the driveshaft which is proportional to the engine torque. The torque for each cylinder can be measured by generating a torque profile for every two revolutions of the driveshaft. The torque profile is read in 120 degree increments for a six cylinder engine and in 90 degree increments for an eight cylinder engine, for example.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for measuring the output torque of automotive engine. Specifically, a sensing system includes components mounted to a driveshaft that are used to measure the twist of the driveshaft under load to determine engine torque.

2. Related Art

Engine torque is a critical parameter that allows a vehicle to accelerate. For heavy duty vehicles, there are acceleration and overall torque output requirements that need to be met in order to satisfactorily perform designated duty cycles. As more auxiliary loads are run off of vehicle engines, torque losses frequently occur causing poor engine performance. These auxiliary loads such as air conditioning, alternators, generators, power steering, or power take-offs consume a portion of the engine torque that would normally satisfy the acceleration and output torque requirements. Thus, it is very important to be able to accurately measure engine torque.

There are different types of engines such as gas and diesel engines, for example. Engines typically have a number of cylinders that are driven by a common crankshaft. In a gas powered internal combustion engine, the cylinders each have a piston, a spark plug, and a connecting rod that interconnects the piston and the crankshaft. A fuel system supplies fuel to each of the cylinders, which is ignited by the spark plug to generate power or output torque. Typically a processor or other similar apparatus is used to control the fuel supply to the engine. If the torque for each cylinder could be measured, a closed torque control system could be utilized to provide independence from auxiliary loads. A closed system that separately identifies each cylinder torque can ease tolerances on fuel injection components because adjustments are easily made in the fuel control system.

Several different methods have been used to measure engine torque, however, there is no simple method for determining an individual torque for each engine cylinder. One method for measuring engine torque has a sensor mounted on the engine to generate a signal with different amplitudes for each engine cylinder. This results in a complex signal that is difficult to translate. Another method determined torque by using engine speed changes. Another method has a sensor mounted in the engine that utilizes Hooke's law to determine an engine output torque but the output is not used to determine torque for each cylinder.

It is the object of the present invention to provide a simple and effective apparatus and method for calculating engine torque on a cylinder by cylinder basis that overcomes the deficiencies outlined above. Further, this method will allow the fuel system to be easily adjusted to compensate for auxiliary loads.

SUMMARY OF THE INVENTION

In a disclosed embodiment of this invention, a system for measuring engine torque includes an engine having an engine output shaft operatively connected to a driveshaft to provide driving input to an axle differential. A portion of a sensor assembly is mounted to the driveshaft to measure the twist of the driveshaft. Preferably a portion of the sensor assembly is mounted on the driveshaft between a transmission and the axle differential. A processor determines engine torque based on driveshaft twist measure and can control predetermined engine parameters based on the torque signal.

In a preferred embodiment, the sensor assembly includes a position target supported on the driveshaft. The position target is comprised of a first specified pattern and a second specified pattern spaced apart from the first specified pattern by a predetermined distance. The first and second specified patterns have reflective and non-reflective surfaces placed on the driveshaft. Preferably, the first and second specified patterns are comprised of a plurality of spaced apart lines having variable thicknesses compared to each other. The lines are placed about the circumference of the driveshaft parallel to a longitudinal axis. A first laser is aimed at the first specified pattern and a second laser is aimed at the second specified pattern. A first photo receiver is mounted adjacent to the first laser to receive a first reflected beam from the first specified pattern and a second photo receiver is mounted adjacent to the second laser to receive a second reflected beam from the second specified pattern. The processor compares data from the first photo receiver to data from the second photo receiver to determine driveshaft twist, which is proportional to the engine torque.

In one embodiment, the engine includes a plurality of cylinders actuated by rotation of a crankshaft. A torque profile is generated as the driveshaft rotates. Peaks in the profile are monitored so that an individual torque value can be assigned to each of the cylinders.

A method for measuring engine torque includes the following steps. A portion of a sensor assembly is mounted on the driveshaft, the twist of the driveshaft is measured, and engine torque is determined based on the twist measurement. Preferably, the twist is optically measured with at least one laser and photo receiver. Additional steps include forming a first specified pattern on the driveshaft, forming a second specified pattern on the driveshaft at a predetermined distance from the first specified pattern, scanning the first specified pattern with a first laser, receiving a first reflected beam from the first laser with a first photo sensor, scanning the second specified pattern with a second laser, and receiving a second reflected beam from the second laser with a second photo sensor.

The preferred method includes measuring the twist of the driveshaft multiple times during each revolution of the driveshaft to form a torque profile and reading the torque profile at 120 degree increments for two revolutions to individually assign torque values to each cylinder in a six cylinder engine. Optionally, the torque profile is read at 90 degree increments for two revolutions to individually assign torque values to each cylinder in an eight cylinder engine.

The subject apparatus provides a simple method for determining engine torque for each cylinder. As a result, adjustments can easily be made to the fuel control system for the engine to provide the desired torque level while accommodating auxiliary loads.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

Referring to the drawings,FIG. 1shows a schematic overview of a vehicle driveline. The driveline includes an engine10having a plurality of cylinders12that are operably connected to a crank shaft14. Preferably, the engine10is a six (6) or eight (8) cylinder engine, however, engines having more or less cylinders could also utilize this unique method and apparatus. The engine10can be a diesel or gas engine, the operation of both of which are well known in the art and will not be discussed in detail.

Typically, the engine has an output shaft16that is coupled to a flywheel18mounted between the engine10and a transmission20. The transmission20can be a manual or automatic transmission and includes a transmission output shaft22that is coupled to a driveshaft24to provide driving input torque to an axle differential26. The differential26is used to drive vehicle wheels28.

A sensor assembly, shown generally at30, includes components that are mounted on the driveshaft24between the transmission20and the differential26. The sensor30generates a signal32that is transmitted to a computer or microprocessor34to determine cylinder12by cylinder12torque. A timing mechanism36, separate from or incorporated into the microprocessor34, can be used to facilitate the determination of the individual cylinder torques. The cylinder torque information is used to adjust the performance of a fuel control system38that supplies fuel to the engine10.

For short lengths, position accuracy has to be measured repeatabley within microseconds. Laser sensing of position allows this goal to be achieved. In the preferred embodiment, the sensor assembly30uses a laser system40to optically sense the angle of twist in the driveshaft24. This twist angle, according to Hooke's law, is proportional to the amount of torque need to generate the twisting of the driveshaft24and is dependant upon the type of material used for the driveshaft24. The laser system40can be mounted to one of the non-rotating driveline components or can be mounted to a vehicle structure, such as a frame or chassis member42.

The sensor assembly20further includes a position target44supported on the driveshaft24. The laser system40utilizes at least one laser46to generate a beam to scan the target44. The beam is reflected back and received by at least one photo receiver48mounted adjacent to the laser46.

As shown more clearly inFIG. 2, the position target44is comprised of a first specified pattern50and a second specified pattern52. Both patterns50,52include reflective and non-reflective surfaces placed on the driveshaft24. This can be implemented in any of various ways including black and white striped patterns using paint (evenly spaced bar codes), or black anodize and then machined polished surfaces. The first pattern50is placed at a first location and the second pattern52is spaced apart from the first pattern50by a predetermined distance D1.

In order to accurately measure the twist of the driveshaft24, the laser system40includes a first laser46athat generates a beam that scans the first pattern50and a second laser46bthat generates a beam that scans the second pattern52. The first beam is reflected back and received by a first photo receiver48aand the second beam is reflected back and received by a second photo receiver48b. The signals from the photo receivers are sent to the microprocessor34and are compared to each other and used to determine the angle of twist for the driveshaft24. With the appropriate known electronics, this signal can be measured in nanoseconds. The receiving photo sensors have to have sufficient response to insure this. Preferably, phototransistors with a response time of 10 nanoseconds or less are utilized. Additionally, the laser beam should be sufficiently narrow to work with the patterns50,52.

As can be seen inFIG. 2, when the driveshaft24is not under load, a normal non-stressed line56is shown extending along the length of the driveshaft24. When a torque T is applied to the driveshaft24, a stress line58is shown that deviates from the non-stressed line56by a twist angle A. This deviation is caused by the driveshaft24twisting under load. The patterns50,52, the lasers46a,46b, the photo receivers48a,48b, and the microprocessor34are used to determine this angle of twist A. This will be discussed in further detail below.

Once the angle of twist A is determined the engine output torque can also be derived from Hooke's law. Further, if the lasers46continuously scan the patterns50,52a torque profile can be generated. This profile will include peak torques that correspond to a specific engine cylinder12. As discussed above, the processor34can optionally utilize a timing mechanism36to determine which cylinders are firing at which peak torques in the profile to assign an individual torque value to each of the cylinders12.

Any type of laser or photo receiver known in the art can be used to measure the angle of twist. Further, the operation of lasers and photo receivers are well known and will not be discussed in detail.

Preferably, the first50and second52specified patterns are comprised of a plurality of spaced apart lines60having variable thicknesses compared to each other, see FIG.3. The driveshaft24defines a longitudinal axis62and the lines60are placed about the circumference of the driveshaft24parallel to the longitudinal axis62.

The required hardware signal processing is shown inFIGS. 4A-D.FIG. 4Ashows a laser beam64moving from a non-reflective surface66to a reflective surface68. The light reflected back into the photo receiver48is a convolution of the light beam and the reflective surface. The resulting signal will be a slow starting ramp, shown inFIG. 4B, which will increase gradually until the center of the beam64passes the edge of the reflective surface68. After this occurs, the output will approach a steady-state.

The actual threshold position can be measured by differentiating the incoming signal, shown inFIG. 4C, and identifying the zero crossovers70of signals (positive to negative thresholds), shown in FIG.4D. This processing can be performed inexpensively with simple analog circuitry well known in the art.

In order to assign an individual torque to each engine cylinder12, the torque should be measured more than once per revolution of the driveshaft24. In order to accomplish this, an index must be placed in the position target44. As shown inFIG. 5, each specified pattern50,52includes an index line72that has a greater thickness than the other lines60in the patterns50,52. With the addition of an index72, it is possible to break the position target44into two patterns50,52, discussed above. The indices72of the two patterns50,52should be aligned along the driveshaft24and any offset can be removed by calibration.

The patterns50,52are used to determine the individual cylinder torques. This may be performed when the transmission20is in direct drive (1:1 gear ratio) at the angles for individual cylinder firings. For a six-cylinder engine this angle is 120 degrees and for an eight-cylinder engine this angle is 90 degrees. At these angles the torque measured is relatively constant and the torque profile for each cylinder is shown every two (2) driveshaft24revolutions.

The cylinder torque is maximum at one point during its respective firing angle, after which the torque slowly decays. The cylinder torque is also affected by the compression effort on neighboring cylinders12. The engine crankshaft14position and the position of the maximum cylinder torque must be determined in order to select a target line60closest to the peak torque position.

The bar pattern inFIG. 5is one of many that can be used. In this pattern, the index72is a double bar, i.e. the index72is twice as thick as the other lines or bars60. The index72includes a rising edge74and a falling edge76. For all of the following bars60only a rising edge78is counted. The number of target bars60should be a multiple of twelve (12) to accommodate both six (6) and eight (8) cylinder12engines10. If possible, one degree resolution is preferred.

The torque values will be derived from each bar set50,52. The twist angle A will be calculated as follows. First a delta time will be determined, i.e., a time difference for measurements from corresponding bars between the patterns (ΔTime=time_bar_N—1−time_bar _N—2). Then the measured angle A is calculated by dividing the delta time by the time different between similar measurements (angle=(ΔTime)/(last_time_bar_N—1−last_time_bar_N—2). Next a corrected torque angle TA is calculated by utilizes a correction factor to remove the offset between the indices72, (torque_angle=angle−offset_bar_N). Finally, the torque is determined by multiplying the torque angle by a constant (torque_N=torque_constant*torque_angle). The torque constant is dependent upon various driveshaft material properties such as shaft thickness, type of material, stiffness, and modulus of material, for example.

In order to calibrate and correct for the offset between corresponding bars in the first and second patterns50,52, the driveshaft24needs to be rotating and the transmission20must be in neutral, i.e., the driveshaft24cannot be under load. This relieves the torque so that there is no stress on the driveshaft24. Offset angle=(time_bar—1−time_bar—2 )/(time_bar—1−last_time_bar—1). The accuracy of this angle can be increased by using the average of many samples.

To measure cylinder to cylinder variations, the transmission20must be in a 1:1 gear ratio. The torque value for each cylinder12is repeated every two (2) driveshaft24revolutions. The peak value for each cylinder12is the value that is preferably used. This value can be identified from the engine timing and fueling of a particular cylinder by finding the peak torque output during that period. When this technique is applied, engine balancing can be accomplished for smoother running.

As discussed above, the method for measuring engine torque includes patterns50,52on the driveshaft24, measuring the twist of the driveshaft24, and determining engine torque based on the twist measurement. Preferably, the patterns50,52are formed on the driveshaft between the transmission20and axle differential26. Indices72are formed in the patterns50,52to establish baseline references for each pattern50,52so that accurate calibration can be performed.

The twist/torque of the driveshaft24is measured multiple times during each revolution of the driveshaft24to form a torque profile. The torque profile is read at 120 degree increments for two revolutions to individually assign torque values to each cylinder12in a six cylinder engine. The torque profile is read at 90 degree increments for two revolutions to individually assign torque values to each cylinder12in an eight cylinder engine.

The subject apparatus provides a simple method for determining engine torque for each cylinder. As a result, adjustments can easily be made to the fuel control system for the engine to provide the desired torque level while accommodating auxiliary loads.

Although a preferred embodiment of this invention has been disclosed, it should be understood that a worker of ordinary skill in the art would recognize many modifications come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.