Stormrider
.040 Over
Found some interesting read on Throttle Position Sensors...
POTENTIOMETERS
Potentiometers are variable resistance sensors that typically consist of a resistor with a lead on each end and a wiper that slides across the surface of the resistor. By applying a calibrated voltage to one side of the resistor and grounding the other side, we can measure the position of the wiper by measuring the voltage as measured at the wiper's point of contact. The farther the wiper goes toward the ground side of the resistor, the lower the output voltage will be. And as the wiper moves toward the powered side, the voltage will increase. Since these sensors need to be grounded on one end, they are connected to the ECU via three wires calibrated input voltage, ground, and signal out. Isolating them from the rest of the electrical system helps reduce noise and other stray signals that might be conducted through the vehicle’s electrical system or chassis. Variable resistors are great for measuring the motion of mechanical pieces (especially rotation). This makes them ideal for use to measure throttle position, or EXUP-style valve position. You can also find them in most float-type airflow sensors as found on old Kawasaki’s and many Japanese im0ort cars of the 1980's.
The advantages of the potentiometer are many; they have been around for decades and can be sourced cheaply and easily. Response characteristics can be tailored quite easily to suit the requirements put forth by the designer of the system. They can measure fairly small changes in position with good accuracy. And there are many manufacturers capable of making such devices, meaning there is basically no chance of running into a supply problem at any point. In addition, there are different grades and qualities of potentiometers for different prices. It is also possible to make them redundant (with two resistive tracks and two wipers) to help ensure a valid measurement.
The disadvantages primarily center on the potentiometer’s mechanical nature. They are prone to wear over time, wiper contact area can degrade, and readings can be inconsistent due to dirt or worn bits of resistor track getting in the way. Potentiometers have a finite useful lifespan and should probably be replaced on high-mileage vehicles to ensure best power, emissions, and drivability, especially at or near closed throttle, where street vehicles spend most of their life.
There are other alternatives to potentiometers, but they are not currently being used on motorcycles. These alternate sensor types are typically solid-state, which makes them hardier for the long term; however, some alternatives require support electronics to process the signals into a form usable by the ECU. Between the increased cost of production and the cost of the support electronics, it is currently the position of the industry that potentiometers are a more cost-effective method of reaching sensing goals, while maintaining good long-term reliability. The automobile world is rapidly changing to special, variable-output Hall-effect devices (called non-contact rotary position sensors), which are more stable and precise than potentiometers. This is a likely future development for motorcycles, as well. Cars even use them for drive-by-wire technology, which is a technology likely to be adopted as well someday by motorcycles.
THROTTLE POSITION SENSOR
This has long been one of the most important sensors on an EFI system. Even systems that don't ever use throttle position (which is also known as alpha, describing the throttle angle) for primary mapping of fuel delivery will still have a TPS. And since nearly all motorcycle (and automotive) applications use butterfly style throttle plates to control intake air density and throttle the engine's power output, I'll just be describing how a TPS works in relation to butterfly-type throttle(s).
A TPS is a well-calibrated potentiometer that attaches to the end of the throttle shaft and measures alpha (throttle angle). Since there are no other mechanical parts inside the potentiometer housing (like the return spring used in the VAF), they can be sealed against dirt and corrosion. They are substantially hardier than the potentiometers used in VAF sensors, but they do eventually wear out. The automotive world has largely abandoned them in favor of Hall-effect rotation sensors, but even the remaining automotive potentiometers far exceed the quality and longevity of most current motorcycle potentiometers. Due to the shorter lifespan of motorcycles, this is a cost/benefit ratio that is found acceptable by the manufacturers at this time. We may see even better quality sensors on bikes in the future.
Now the amount of airflow that the throttle plate allows is not linear with its angle. In other words, the difference between 1 degree and 2 degree open is much greater in terms of delta airflow (rate of airflow change) than the difference between 50 degrees and 51 degrees open. It has a non-linear response; small changes near closed throttle make a much bigger difference in airflow than small changes near wide-open throttle. This is one of the disadvantages of the TPS; it does not respond linearly to changes in actual airflow. However, this can be all but eliminated by using a potentiometer with a logarithmic response curve, which will more closely match actual delta airflow. This has advantages and disadvantages from a programming perspective, and many automotive applications use a linear potentiometer for its predictable behavior when faced with aging and temperature changes.
Since some systems require a very precise measurement of small changes in alpha, their potentiometers are available with multiple resistive tracks and better coupling to the wiper arm. These benefits combine to make for a more reliable and precise reading, in addition to delivering a longer life for the component. The downside, of course, is the increased price of such a sensor.
POTENTIOMETERS
Potentiometers are variable resistance sensors that typically consist of a resistor with a lead on each end and a wiper that slides across the surface of the resistor. By applying a calibrated voltage to one side of the resistor and grounding the other side, we can measure the position of the wiper by measuring the voltage as measured at the wiper's point of contact. The farther the wiper goes toward the ground side of the resistor, the lower the output voltage will be. And as the wiper moves toward the powered side, the voltage will increase. Since these sensors need to be grounded on one end, they are connected to the ECU via three wires calibrated input voltage, ground, and signal out. Isolating them from the rest of the electrical system helps reduce noise and other stray signals that might be conducted through the vehicle’s electrical system or chassis. Variable resistors are great for measuring the motion of mechanical pieces (especially rotation). This makes them ideal for use to measure throttle position, or EXUP-style valve position. You can also find them in most float-type airflow sensors as found on old Kawasaki’s and many Japanese im0ort cars of the 1980's.
The advantages of the potentiometer are many; they have been around for decades and can be sourced cheaply and easily. Response characteristics can be tailored quite easily to suit the requirements put forth by the designer of the system. They can measure fairly small changes in position with good accuracy. And there are many manufacturers capable of making such devices, meaning there is basically no chance of running into a supply problem at any point. In addition, there are different grades and qualities of potentiometers for different prices. It is also possible to make them redundant (with two resistive tracks and two wipers) to help ensure a valid measurement.
The disadvantages primarily center on the potentiometer’s mechanical nature. They are prone to wear over time, wiper contact area can degrade, and readings can be inconsistent due to dirt or worn bits of resistor track getting in the way. Potentiometers have a finite useful lifespan and should probably be replaced on high-mileage vehicles to ensure best power, emissions, and drivability, especially at or near closed throttle, where street vehicles spend most of their life.
There are other alternatives to potentiometers, but they are not currently being used on motorcycles. These alternate sensor types are typically solid-state, which makes them hardier for the long term; however, some alternatives require support electronics to process the signals into a form usable by the ECU. Between the increased cost of production and the cost of the support electronics, it is currently the position of the industry that potentiometers are a more cost-effective method of reaching sensing goals, while maintaining good long-term reliability. The automobile world is rapidly changing to special, variable-output Hall-effect devices (called non-contact rotary position sensors), which are more stable and precise than potentiometers. This is a likely future development for motorcycles, as well. Cars even use them for drive-by-wire technology, which is a technology likely to be adopted as well someday by motorcycles.
THROTTLE POSITION SENSOR
This has long been one of the most important sensors on an EFI system. Even systems that don't ever use throttle position (which is also known as alpha, describing the throttle angle) for primary mapping of fuel delivery will still have a TPS. And since nearly all motorcycle (and automotive) applications use butterfly style throttle plates to control intake air density and throttle the engine's power output, I'll just be describing how a TPS works in relation to butterfly-type throttle(s).
A TPS is a well-calibrated potentiometer that attaches to the end of the throttle shaft and measures alpha (throttle angle). Since there are no other mechanical parts inside the potentiometer housing (like the return spring used in the VAF), they can be sealed against dirt and corrosion. They are substantially hardier than the potentiometers used in VAF sensors, but they do eventually wear out. The automotive world has largely abandoned them in favor of Hall-effect rotation sensors, but even the remaining automotive potentiometers far exceed the quality and longevity of most current motorcycle potentiometers. Due to the shorter lifespan of motorcycles, this is a cost/benefit ratio that is found acceptable by the manufacturers at this time. We may see even better quality sensors on bikes in the future.
Now the amount of airflow that the throttle plate allows is not linear with its angle. In other words, the difference between 1 degree and 2 degree open is much greater in terms of delta airflow (rate of airflow change) than the difference between 50 degrees and 51 degrees open. It has a non-linear response; small changes near closed throttle make a much bigger difference in airflow than small changes near wide-open throttle. This is one of the disadvantages of the TPS; it does not respond linearly to changes in actual airflow. However, this can be all but eliminated by using a potentiometer with a logarithmic response curve, which will more closely match actual delta airflow. This has advantages and disadvantages from a programming perspective, and many automotive applications use a linear potentiometer for its predictable behavior when faced with aging and temperature changes.
Since some systems require a very precise measurement of small changes in alpha, their potentiometers are available with multiple resistive tracks and better coupling to the wiper arm. These benefits combine to make for a more reliable and precise reading, in addition to delivering a longer life for the component. The downside, of course, is the increased price of such a sensor.
