BUG*PWR
RIP, Gone But Not Forgotten
- Joined
- Aug 25, 1999
- Location
- Plymouth, CT .
With gas engines so efficient today, why would VW bother to build a diesel? For lots of reasons. First, this is no slouch--the 1.9L 90 hp turbocharged and intercooled four can propel you to 111 mph and has a remarkably flat torque curve with a peak of 149 ft. lbs. at a thoroughly useable 1,900 rpm, providing a 0-30 time equivalent to that of the European GTI's 16-valve gasoline burner (it's also just about as quiet). After all, a high fun-to-drive quotient is part of the Wolfsburg company's image.
A related reason VW is offering the TDI is product differentiation. Volkswagen has always cultivated the idea that its cars aren't like the great mass of personality-challenged vehicles out there, and that owning one means you're just a little above the ordinary.
Our recent El Nino experience and fears of global warming--which is almost certainly being made worse by excessive burning of fossil fuels and its attendant CO2 production--are making mpg numbers important again. What's the TDI's score? How about 48 mpg on the highway, or 700 miles on a tankful? And it emits 20% less CO2 than a gas engine. It's clean, too, meeting all U.S. regs (including those of California).
How they do it
All this was accomplished through the application of thoroughly modern technology beginning with electronically controlled injection, boost, EGR, and glow plug on-time. The computer gets the info it needs from numerous sensors, including those for MAF, MAP, ECT, TP, IAT, and fuel temperature, then decides which of 25 maps is appropriate.
As you know, most car diesels use pre-combustion or swirl chambers to provide a smoother burn and cut noise and vibration. But direct injection, as found on heavy-duty diesels, is maybe 20% more efficient. In the TDI, the electronics allow fuel to be injected directly into the combustion chamber in two stages, which vastly softens operation. A unique inlet swirl port and five-hole injectors that make a nice mist contribute, too.
Diesel injection pump outlet pressures are always high, but for automotive applications those of the TDI are especially so--13,775 psi on automatic New Beetles (the nozzles blow off at 3,190 psi, which is enough to give you a diesel tattoo if you're not careful using your pop tester).
Another smoothness enhancement is the intake manifold flap. In any diesel, compression is so high that it tends to stop the pistons abruptly during shut-down, which causes the characteristically unpleasant shudder. This vacuum-operated flap cuts off intake air upon command from the ECM, thus lowering psi and allowing a kinder, gentler finish.
Tech details
You've probably never seen a catalytic converter on a diesel before, but the TDI has one. While it helps a little on HC and CO, its big job here is knocking down NOx. Speaking of NOx, the EGR includes a cooler to reduce the temperature of the recycled gases by as much as 122°F, which helps its efficiency.
As you should know, diesels don't make enough vacuum to operate the brake booster, EGR valve, etc., so the TDI gets a camshaft-driven vane-type vacuum pump.
The timing belt replacement interval is every 40K miles. This is definitely a hitter, so you'd better keep after your customers about this job as a way to avoid megabuck repairs. Just as in the original Rabbit diesel, a special tool is available to lock the injection pump hub in place while you R&R the belt (a setting bar holds the cam). Never, ever loosen or remove the hub from the pump shaft.
For ecology's sake, the TDI has a cartridge-type oil filter element. You just unscrew the housing cap (which also opens a drain that lets the oil in the housing run back into the pan) and lift out the old element. A 10,000-mile change interval is given in the owner's manual, but we suggest you use your own judgment in recommending a realistic fluid maintenance program.
If you hate valve cover oil leaks--something water-cooled VWs had plenty of--you'll like the New Beetle. The cast magnesium head cover has a bonded gasket, which keeps it perfectly positioned.
The alternator on stick TDIs features a freewheel disc, which works only during cecel when the glow plugs are operating and there's a big electrical load. It cuts out the charging system and allows the rotor to freewheel. Something else that's unique to manual trans versions is a second set of glow plugs that are used to heat the coolant.
If the other automakers decide to come out with competing diesels to address environmental concerns, the fuel crunch-era predictions of the predominance of this type of engine might just come true--a quarter-century late. http://www.autotruck.net/ms/archives/1998/898/898bug.asp
------------------
It ain’t the horsepower it’s the Torque !
.
..........|
........-^-
....-/_____\-
...(O\__o__/O)
...[#]oxxxo[#]
A related reason VW is offering the TDI is product differentiation. Volkswagen has always cultivated the idea that its cars aren't like the great mass of personality-challenged vehicles out there, and that owning one means you're just a little above the ordinary.
Our recent El Nino experience and fears of global warming--which is almost certainly being made worse by excessive burning of fossil fuels and its attendant CO2 production--are making mpg numbers important again. What's the TDI's score? How about 48 mpg on the highway, or 700 miles on a tankful? And it emits 20% less CO2 than a gas engine. It's clean, too, meeting all U.S. regs (including those of California).
How they do it
All this was accomplished through the application of thoroughly modern technology beginning with electronically controlled injection, boost, EGR, and glow plug on-time. The computer gets the info it needs from numerous sensors, including those for MAF, MAP, ECT, TP, IAT, and fuel temperature, then decides which of 25 maps is appropriate.
As you know, most car diesels use pre-combustion or swirl chambers to provide a smoother burn and cut noise and vibration. But direct injection, as found on heavy-duty diesels, is maybe 20% more efficient. In the TDI, the electronics allow fuel to be injected directly into the combustion chamber in two stages, which vastly softens operation. A unique inlet swirl port and five-hole injectors that make a nice mist contribute, too.
Diesel injection pump outlet pressures are always high, but for automotive applications those of the TDI are especially so--13,775 psi on automatic New Beetles (the nozzles blow off at 3,190 psi, which is enough to give you a diesel tattoo if you're not careful using your pop tester).
Another smoothness enhancement is the intake manifold flap. In any diesel, compression is so high that it tends to stop the pistons abruptly during shut-down, which causes the characteristically unpleasant shudder. This vacuum-operated flap cuts off intake air upon command from the ECM, thus lowering psi and allowing a kinder, gentler finish.
Tech details
You've probably never seen a catalytic converter on a diesel before, but the TDI has one. While it helps a little on HC and CO, its big job here is knocking down NOx. Speaking of NOx, the EGR includes a cooler to reduce the temperature of the recycled gases by as much as 122°F, which helps its efficiency.
As you should know, diesels don't make enough vacuum to operate the brake booster, EGR valve, etc., so the TDI gets a camshaft-driven vane-type vacuum pump.
The timing belt replacement interval is every 40K miles. This is definitely a hitter, so you'd better keep after your customers about this job as a way to avoid megabuck repairs. Just as in the original Rabbit diesel, a special tool is available to lock the injection pump hub in place while you R&R the belt (a setting bar holds the cam). Never, ever loosen or remove the hub from the pump shaft.
For ecology's sake, the TDI has a cartridge-type oil filter element. You just unscrew the housing cap (which also opens a drain that lets the oil in the housing run back into the pan) and lift out the old element. A 10,000-mile change interval is given in the owner's manual, but we suggest you use your own judgment in recommending a realistic fluid maintenance program.
If you hate valve cover oil leaks--something water-cooled VWs had plenty of--you'll like the New Beetle. The cast magnesium head cover has a bonded gasket, which keeps it perfectly positioned.
The alternator on stick TDIs features a freewheel disc, which works only during cecel when the glow plugs are operating and there's a big electrical load. It cuts out the charging system and allows the rotor to freewheel. Something else that's unique to manual trans versions is a second set of glow plugs that are used to heat the coolant.
If the other automakers decide to come out with competing diesels to address environmental concerns, the fuel crunch-era predictions of the predominance of this type of engine might just come true--a quarter-century late. http://www.autotruck.net/ms/archives/1998/898/898bug.asp
------------------
It ain’t the horsepower it’s the Torque !
.
..........|
........-^-
....-/_____\-
...(O\__o__/O)
...[#]oxxxo[#]
