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Old 03-08-2014, 04:51 PM   #1 (permalink)
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Phantom Blot (Spökplumpen in swedish) - '75 Saab 96 V4
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Coasting booster (adding av tiny diesel engine)

This idea may not be the most successful solution to improve fuel consumption but I can build the concept almost for fre "Scrapheap Challenge-style". I have been practising Pulse & Glide (accelerating/coasting) together with engine shutdown in city traffic, saving some fuel. About 50% of my travel TIME is in city traffic with a lot of traffic lights, the rest is highway where I go maximum 80km/h (50mph).

My idea is to use a tiny diesel engine, a 12hp@3200 rpm 600cc two-cylinder industrial Kubota in two ways, -as a "coasting booster" that hopefully will extend the time between accelerations, but also as the main engine for slow city traffic. A larger diesel, preferably a small turbo diesel, as the only engine would offcourse be a much better solution but I have to satisfy with what I have in my garage. A great bonus with an extra power unit is that I don't have to worry about expensive towing if my old scrappy Saab 96 V4 breaks down on the highway.

The concept:

The little Kubota will (almost) fit in the trunk together with the hydrostatic transmisson I got together with the engine. Hydrostatics have poor efficiency (85-90% in my case) but that may not hurt too bad in city traffic where a lot of the time is spent idling at the traffic lights. Together with a weak engine the continous variable transmission may also be superior to a stepped gearbox. Since the fuel consumption at idle is extremely low on such a tiny diesel I don't need to bother about shutting down the engine at the traffic lights. The diesel will have an alternator big enough to run LED rear- & headlights, heating fan and rear window defroster. There will also be an electric coolant pump and the diesel will share radiator with the Saab's petrol engine. This will not only save weight but also keep the big engine warm until next time it's needed.

The output from the diesel will be through a 5:th wheel out through the rear of the car. It will be a small 10" or 12" wheel with a pneumatic, electric or hydraulic cylinder to lift the wheel when it's not needed. This design may look a bit silly but a major advantage is that I can design the entire diesel unit as "cargo" instead of having to pay a lot of money and effort to get it legally approved as a modification to the car.

I expect to get a maximum speed of about 40-50km/h from the diesel and hydrostatic transmission, but the 12 horsepowers is also about half or two thirds of what's needed to KEEP my highway cruising speed of 80km/h (50mph). Att highway I simply bypass the hydrostatic transmission with a direct gear between the engine and the 5:th wheel to get highest possible efficiency.

The Saab's petrol engine will offcourse be needed for acceleration from 50 to 80 but then I can hopefully shut it down a lot longer than without the help from the little diesel.

To make the design as simple as possible there may actually be two little wheels sticking out from the trunk, -one for the highway direct drive (via a V-belt), one from the hydrostatic transmission for city driving. The highway wheel can be spring-loaded to the ground continously since it will be disengaged by slacking off the V-belt, but the city-wheel must be possible to quickly lift up from the driving seat.

12hp@3200 rmp is a low figure also for a 600cc engine. Perhaps it can easily be adjusted to give a bit more since it's an industrial engine? I suppose the same or similar engines may have been made for other purposes such as boats where a bit more wear can be tolerated in exchange for more power.

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Old 03-08-2014, 05:26 PM   #2 (permalink)
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If you have a scan gauge, you could monitor how much horsepower is required to keep up with traffic or speed limits. This will tell you if the little diesel power plant will do the job. Might need to account for the hydrostatic drive losses and extra weight of the engine and 5th wheel.
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Old 03-09-2014, 12:19 PM   #3 (permalink)
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Phantom Blot (Spökplumpen in swedish) - '75 Saab 96 V4
90 day: 52.77 mpg (US)
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My Saab 96 is from 1975 and has carburettor but I'm planning to build myself a fuel computer. (been planning that for a year...)

My previous crazy-eco-project was a little Fiat 127 from 1980 from which I removed two of it's four pistons and saved 10-15% fuel without changing my average speed. The engine was quite worn out, produced 48 hp as new so my guess is that it gave no more than 23. Compared with how it was geared, my driving style and marching speed I roughly estimate the engine put out 17hp most of the time. That car weighted perhaps 150 kilos less than the Saab but I soon found that weight is not a major factor. I suppose the aerodynamics of the Saab is superior to the Fiat so my final guess is that the Saab could do quite well with only 20-25hp to reach my wanted 80 km/h.

12hp will defininitely NOT keep the car at 80, the interesting thing to find out is if it will extend the coasting time enough to make P&G less annoying and reduce total fuel consumption enough to compensate for the awkward driving...

I definitely think that the little diesel can be used for city traffic and if I can reach the maximum speed limit of 50 km/h or only 35 doesn't matter so much. A hydrostatic transmission (or any other CVT) can possibly make stop & go driving in dense traffic a lot nicer.

My first test will however be to see how much the diesel can help P&G in higher speed. It will be quite easy to build such a prototype to hang from the rear bumper. I don't think it's worth only the fuel savings in city traffic to have about 100 kg extra in the trunk all the time.

A little turbo would be nice!
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Old 04-18-2018, 11:14 AM   #4 (permalink)
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Phantom Blot (Spökplumpen in swedish) - '75 Saab 96 V4
90 day: 52.77 mpg (US)
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Long time have passed, but I still carry this crazy idea around, and it have evolved slowly so I felt like sharing my ideas now:

I still love the Saab classics 96 and 95 from the 1960's and what's new since my last post is that I have got two Saab 95 station wagons and an old scrappy trailer to experiment with. I intend to modify the trailer so heavily inly a steel tube or two will remain, but it's a much cheaper way through bureaucracy and regulations to get a street legal DIY trailer.

I plan to use the entire front suspension and transmission from another Saab 95/96 and attach it to a telescopic towbar (poor english?) so I can change the wheel base between the car's rear axle and the trailer's wheels. The retracted position is the normal driving mode where the trailer is firmly attached to a pair of higher mounting points that makes the entire structure rigid to act as a whole six-wheel car. The extended position is simply what's needed to make the trailer street legal. -I must be able to drive the trailer in the usual manner with the hitch-ball as the only mechanical connection to the car, but it's allowed to have a retractable towbar to make parking and storage more compact. (so "oops, i forgot to extend the towbar before driving away, sorry!")

The little Kubota 600cc two-cylinder diesel is still en engine I want to use in the trailer, with a V-belt connection to the Saab gearbox permanently mounted on the trailer frame and driveshafts. -Nothing prevents me from building a street-legal trailer with driveshafts and gearbox, but the engine will be mounted later as "payload".



To improve aerodynamics the roofline of the Saab 95 may be slightly modified in the rear, and the windshield can be replaced by a Saab 96 rear window turned 90 degrees for a better fit. This looks really good with the Ecomodder aerodynamic template! The trailer will have an aerodynamic body shell that when retracted fits perfectly to the rear of the car. (this will off course look silly in the extended position...)

Since the trailer will be quite light and is not intended for carrying extra cargo it can have soft suspension to barely carry it's own weight. I guess progressiv suspension like air bellows may be a good choise since there will probably be some heavy forces to handle while driving up and down ramps/slopes and over bumps. The attachment points to the car must be rigid as well. (I don't intend to go offroad driving with this machine, even if it will practically be a 4x4, or rather a 4x6...)

If I make the aerodynamic shell lightweight and removable I can put it on hinges and flip it upwards while parking with the trailer attached in the retracted position to save some valuable space in lenght.

If I use the front suspension of another old Saab it's possible to have a low-speed mode where the trailer wheels can steer freely, and be locked in straight position at higher speeds. I guess the entire six-wheeler will be very stable at the highway this way and still be easy to turn without sliding in city traffic. (while reversing with the trailer, it's wheels must either be locked straight or steered by an electric motor, or else they will quickly steer to full stop in either direction)

So, what do you think? How crazy am I?
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1975 Saab 96 V4, carburetted stock engine. Usually below 4,5 L100 = above 53 mpg (us) by Burn & Glide with engine shut-off. http://ecomodder.com/forum/em-fuel-l...vehicleid=8470
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Old 04-18-2018, 12:12 PM   #5 (permalink)
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Pretty crazy!

I too have had fantasies of having a little engine to putt around with in traffic. I wouldn't go as far as having it be liquid cooled and tap into the main engine coolant, I would just have a simple system with an air cooled engine.

I wish we got V4 cars here, we only get them in bikes.
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Old 04-18-2018, 01:27 PM   #6 (permalink)
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I dunno about the efficiency of your Saab's engine, but the thermal efficiency of the engine in my Insight is almost certainly much greater than that of any small engine. They're usually pretty bad. So, running full-tilt, it would probably have higher running costs than pulse and glide using your big engine.
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Old 04-18-2018, 01:57 PM   #7 (permalink)
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Sure this project sounds quite ambitious, and maybe even crazy. But anyway, why don't you just perform a Diesel swap instead?

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