Are the hybrid gas pedals involved in all this?
#2
01-29-2010, 07:12 PM
Re: Are the hybrid gas pedals involved in all this?
This is long. I got on a roll. Sorry if it's boring, or a repeat of other threads.
Pretty much all modern cars, hybrid or not, are drive-by-wire, or electronic throttle, ie no mechanical cable connection between the pedal and the throttle plate. But there's way more than that.
First off, Prius' were accelerating suddenly a long time ago:
http://www.phoenixnewtimes.com/2009-...dly-wild-ride/
http://www.safetyresearch.net/toyota...rce-documents/
The thing about Toyota's Synergy drive is that it has no true neutral. In a standard automatic you have a clutch plate and other clutch packs that can physically separate the engine torque and stored energy in the transmission from the axles/drive wheels. So the engine can rev away all it wants and no power goes to the wheels in Park or Neutral. What the Synergy drive has is called 'pseudo-neutral' or 'Prius Neutral' in the hybrid biz. The torque sources in the powertrain; the engine, traction motor and generator, are always attached to the output shaft that goes directly to the wheels. In one sense it's an elegant and simple transmission. But put another way, there's no way to disconnect the drive wheels from the torque inputs. What feels like traditional Park or Neutral is just the two electric machines counteracting the torque of the engine. The Prius transmission is an input-split hybrid, meaning there's one planetary gearset with each of the three torque sources attached to the ring, sun and planet carrier sections of the gearset. The software controls are critical to managing all three and deliver the correct output, like an orchestra. And the folks who say, just put it in neutral? Well, the PRNDL selector is by-wire, too, on many cars. I don't know 100% if the 2nd gen Prius has PRNDL-by-wire, but I'm pretty sure the 2010 does. So increasingly the gear selector is not a mechanical selector anymore, either. Then there are stability control systems, brake assist, and adaptive cruise control that take active control of your throttle, brakes, and steering if conditions warrant. And that start-stop button that takes 3 seconds of constant pressure to shut the motor off. Basically, the driver is being further and further removed from direct control of the modern car. And the software controls are taking on more of the decision making. Like it or not, that's how it is and it's only going to get worse. The challenge for the car companies is to develop robust, independent, error-checking micros that make sure the primary vehicle control algorithms and sensor inputs didn't just go out to lunch and are making bad calculations, which lead to bad things. And the error-checking security algorithms have to be accurate and fast...in all weather conditions...at all altitudes...in all driving environments. It's a huge challenge, and it's not something that can be band-aided on later. It has to be there from the start of the controls design. Otherwise, inevitably, conditions will line up and there will be 'hole' where the system loses control. The Prius traction motor can generate around 100 instantaneous horsepower. Also, low rolling resistance tires that are great for mileage in dry pavement, but are lousy in bad weather conditions. Now there are a lot of Prius' out there and most of them have been very reliable. And there are plenty of other car makers that have had controls glitches that have led to surges, stalls, startling bumps, etc. I'm just trying to point out that the drive for ever-increasing efficiency and mileage have led to really complex vehicles. Not to mention all the amenities we like today, like bluetooth, satellite radio, nav, park assist, etc. that add even more complexity.
Pretty much all modern cars, hybrid or not, are drive-by-wire, or electronic throttle, ie no mechanical cable connection between the pedal and the throttle plate. But there's way more than that.
First off, Prius' were accelerating suddenly a long time ago:
http://www.phoenixnewtimes.com/2009-...dly-wild-ride/
http://www.safetyresearch.net/toyota...rce-documents/
The thing about Toyota's Synergy drive is that it has no true neutral. In a standard automatic you have a clutch plate and other clutch packs that can physically separate the engine torque and stored energy in the transmission from the axles/drive wheels. So the engine can rev away all it wants and no power goes to the wheels in Park or Neutral. What the Synergy drive has is called 'pseudo-neutral' or 'Prius Neutral' in the hybrid biz. The torque sources in the powertrain; the engine, traction motor and generator, are always attached to the output shaft that goes directly to the wheels. In one sense it's an elegant and simple transmission. But put another way, there's no way to disconnect the drive wheels from the torque inputs. What feels like traditional Park or Neutral is just the two electric machines counteracting the torque of the engine. The Prius transmission is an input-split hybrid, meaning there's one planetary gearset with each of the three torque sources attached to the ring, sun and planet carrier sections of the gearset. The software controls are critical to managing all three and deliver the correct output, like an orchestra. And the folks who say, just put it in neutral? Well, the PRNDL selector is by-wire, too, on many cars. I don't know 100% if the 2nd gen Prius has PRNDL-by-wire, but I'm pretty sure the 2010 does. So increasingly the gear selector is not a mechanical selector anymore, either. Then there are stability control systems, brake assist, and adaptive cruise control that take active control of your throttle, brakes, and steering if conditions warrant. And that start-stop button that takes 3 seconds of constant pressure to shut the motor off. Basically, the driver is being further and further removed from direct control of the modern car. And the software controls are taking on more of the decision making. Like it or not, that's how it is and it's only going to get worse. The challenge for the car companies is to develop robust, independent, error-checking micros that make sure the primary vehicle control algorithms and sensor inputs didn't just go out to lunch and are making bad calculations, which lead to bad things. And the error-checking security algorithms have to be accurate and fast...in all weather conditions...at all altitudes...in all driving environments. It's a huge challenge, and it's not something that can be band-aided on later. It has to be there from the start of the controls design. Otherwise, inevitably, conditions will line up and there will be 'hole' where the system loses control. The Prius traction motor can generate around 100 instantaneous horsepower. Also, low rolling resistance tires that are great for mileage in dry pavement, but are lousy in bad weather conditions. Now there are a lot of Prius' out there and most of them have been very reliable. And there are plenty of other car makers that have had controls glitches that have led to surges, stalls, startling bumps, etc. I'm just trying to point out that the drive for ever-increasing efficiency and mileage have led to really complex vehicles. Not to mention all the amenities we like today, like bluetooth, satellite radio, nav, park assist, etc. that add even more complexity.
Last edited by KC135R; 01-29-2010 at 07:23 PM.
#3
01-31-2010, 10:39 AM
Re: Are the hybrid gas pedals involved in all this?
The Highlander Hybrid uses "drive by wire" for the the accelerator pedal, the brake pedal, and the gear shift selector.
The "brake by wire" system however, has a direct hydraulic backup from the brake pedal to the brake cylinders on the wheels if the electronics fail.
The gear shift selector does have a cable connected to the trans-axle that mechanically engages a pawl to prevent movement when in park. This probably will not help help much when the vehicle is at speed.
Below is some background on the throttle by wire system in the Highlander and and other Toyota vehicles and the failure management strategy Toyota employs.
Toyota throttle-by-wire system
In Toyota's throttle-by-wire system, dual accelerator position sensors, each calibrated with a different scale, send data to the engine control module (ECM), which compares the signals to check for errors. In the event of an error in the signal from one of the position sensors, the ECM can switch off the throttle-control servomotor and modulate power through the fuel-injection and ignition systems. The ECM also considers input from the traction-, stability-, and anti-theft-control systems when directing the throttle, ignition, and fuel-injection systems.
Toyota developed an all-electric throttle-by-wire system for its Lexus LS430 luxury flagship that it has also deployed in its near-luxury ES300 and mainstream Camry family sedan. The benefits of eliminating the throttle cable include improved NVH because there is no cable penetrating the firewall. The system also allows for simplified traction-, stability-, and cruise-control systems.
"Consumers don't always do (what's) best with the throttle," said Paul Williamsen, Curriculum Development Manager at Toyota Motor Sales, U.S.A. Toyota's throttle-by-wire system analyzes the driver's actions and interprets intentions to produce better driveability and stability, while reducing emissions, especially when the engine is cold.
"We gain better overall control," Williamsen added.
It also simplifies "shift-shock" control by letting the computer ease off the throttle for smooth automatic upshifts.
An obstacle to fielding throttle-by-wire has been the need for a backup system. Earlier Toyota systems used a conventional cable as the backup, but under normal conditions throttle position was handled electronically. Several years of experience with that system on the Toyota Supra, V8-equipped Tundra, Land Cruiser, and LX430 models emboldened Toyota to eliminate the cable. "After a number of years of offering this, we've got the data on what the failure rate is," said Williamsen. "It is pretty low."
That doesn't mean that a backup system isn't needed, but it did show that a physical cable wouldn't be required. The new system uses a pair of accelerator position sensors, each with a different scale, so that the signals from the two can be compared for their differences and checked for accuracy, not just for a loss of signal from one sensor.
A servomotor moves the throttle to the desired position, and redundant throttle position sensors report the results. If one of the pedal position sensors fails, the car can still be driven, and the check engine warning light is illuminated. If both sensors fail, engine control is lost, and the engine will only idle.
Toyota has designed an interesting failure mode that lets the car be driven to safety if the throttle position sensors fail. The throttle assembly has two return springs, one of which holds the throttle open slightly in the absence of control by the servo. "You get a gap of about 0.5 mm (0.02 in) on each side of the butterfly," said Williamsen. That doesn't sound like much, but the area is actually reasonably large, so the engine can produce about one-quarter its maximum power.
Having a run-away engine is no better than having an idle engine, but the engine-management computer can control engine output through other means. By altering the fuel-injection duration and the ignition timing in response to input on the gas pedal, the car responds to the driver's demand for power.
"It gives an amazing impression of throttle response, even as the throttle doesn't move," Williamsen said. "At speeds below 48 km/h (30 mph), you might not even notice it much."
This failure mode is adequate for getting home from across town, but isn't well suited to highway driving, and should be used only to get off a highway at the earliest opportunity. "In town it will limp home pretty effectively, but it would have a hard time maintaining highway speeds," he said.
The "brake by wire" system however, has a direct hydraulic backup from the brake pedal to the brake cylinders on the wheels if the electronics fail.
The gear shift selector does have a cable connected to the trans-axle that mechanically engages a pawl to prevent movement when in park. This probably will not help help much when the vehicle is at speed.
Below is some background on the throttle by wire system in the Highlander and and other Toyota vehicles and the failure management strategy Toyota employs.
Toyota throttle-by-wire system
In Toyota's throttle-by-wire system, dual accelerator position sensors, each calibrated with a different scale, send data to the engine control module (ECM), which compares the signals to check for errors. In the event of an error in the signal from one of the position sensors, the ECM can switch off the throttle-control servomotor and modulate power through the fuel-injection and ignition systems. The ECM also considers input from the traction-, stability-, and anti-theft-control systems when directing the throttle, ignition, and fuel-injection systems.
Toyota developed an all-electric throttle-by-wire system for its Lexus LS430 luxury flagship that it has also deployed in its near-luxury ES300 and mainstream Camry family sedan. The benefits of eliminating the throttle cable include improved NVH because there is no cable penetrating the firewall. The system also allows for simplified traction-, stability-, and cruise-control systems.
"Consumers don't always do (what's) best with the throttle," said Paul Williamsen, Curriculum Development Manager at Toyota Motor Sales, U.S.A. Toyota's throttle-by-wire system analyzes the driver's actions and interprets intentions to produce better driveability and stability, while reducing emissions, especially when the engine is cold.
"We gain better overall control," Williamsen added.
It also simplifies "shift-shock" control by letting the computer ease off the throttle for smooth automatic upshifts.
An obstacle to fielding throttle-by-wire has been the need for a backup system. Earlier Toyota systems used a conventional cable as the backup, but under normal conditions throttle position was handled electronically. Several years of experience with that system on the Toyota Supra, V8-equipped Tundra, Land Cruiser, and LX430 models emboldened Toyota to eliminate the cable. "After a number of years of offering this, we've got the data on what the failure rate is," said Williamsen. "It is pretty low."
That doesn't mean that a backup system isn't needed, but it did show that a physical cable wouldn't be required. The new system uses a pair of accelerator position sensors, each with a different scale, so that the signals from the two can be compared for their differences and checked for accuracy, not just for a loss of signal from one sensor.
A servomotor moves the throttle to the desired position, and redundant throttle position sensors report the results. If one of the pedal position sensors fails, the car can still be driven, and the check engine warning light is illuminated. If both sensors fail, engine control is lost, and the engine will only idle.
Toyota has designed an interesting failure mode that lets the car be driven to safety if the throttle position sensors fail. The throttle assembly has two return springs, one of which holds the throttle open slightly in the absence of control by the servo. "You get a gap of about 0.5 mm (0.02 in) on each side of the butterfly," said Williamsen. That doesn't sound like much, but the area is actually reasonably large, so the engine can produce about one-quarter its maximum power.
Having a run-away engine is no better than having an idle engine, but the engine-management computer can control engine output through other means. By altering the fuel-injection duration and the ignition timing in response to input on the gas pedal, the car responds to the driver's demand for power.
"It gives an amazing impression of throttle response, even as the throttle doesn't move," Williamsen said. "At speeds below 48 km/h (30 mph), you might not even notice it much."
This failure mode is adequate for getting home from across town, but isn't well suited to highway driving, and should be used only to get off a highway at the earliest opportunity. "In town it will limp home pretty effectively, but it would have a hard time maintaining highway speeds," he said.
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tigerhonaker
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06-18-2006 06:22 PM
2007, cabling, cars, control, disconnect, drivebywire, electronics, gas, highlander, hybrid, pedal, pedals, pressure, prius, return, spring, throttlebywire, toyota
