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Posts filed under ‘Technical Curiosities’

Technical Curiosities:
The Hydraulic Cooling Fan

November 7, 2011 by Matt

Hydro Hydraulic Drive Fan Motor Cooling Radiator

I first ran across this one when I was doing the 7M-to-1JZ engine swap in my old Supra Turbo. Before the thought of a swap had even entered my mind, I remember puzzling over pictures of Japanese-market-only Supra engine bays fitted with the 1JZ-GTE from the factory, wondering why they seemed to have not one, but two power steering fluid reservoirs (yes, I sit and ponder things like that). I couldn’t figure it out, but when I finally had my hands on one and was lining up my ducks for the swap, I quickly discovered the reason for the extra container of hydraulic fluid: The car was fitted with a hydraulically-powered cooling fan.

In almost every instance, car engine cooling fans are powered one of two ways: Either directly by the engine off the front of the water pump pulley, or electrically using a large-ish motor. Typically, longitudinal (front-to-back) engines feature direct-drive, whereas engines mounted in a transverse (sideways) fashion, with their accessory belts rotating perpendicular to the ideal orientation for a direct-drive cooling fan, receive electric units. However, in a handful of cars, the engineers decided to grant the cooling fan its own, dedicated hydraulic circuit for motive purposes. In addition to the 1JZ-GTE in my ’89-’92 Supra application (the 1JZ was directly-driven in other Toyotas), the ’92-’96 Toyota Camry V6, Lincoln LS and ’99-’04 Jeep Grand Cherokee all featured hydro fans.

The disadvantages are obvious, but not outright deal-breakers for sensible and careful engineers: The setup adds another layer of complexity to the engine, with more parts to fail, and another fluid level for the owner/mechanic to check and service. As with Audi’s UFO brakes, the rarity of the solution means added expense for parts.

Hydro Hydraulic Drive Fan Motor Cooling Radiator 1JZ 1JZ-GTE 1JZGTE 1JZGTTE 1JZ-GTTE Parts Diagram Schematic Pump

There are some distinct advantages, though: The decoupling, as it were, of the fan from the engine gives the developers some leeway in term of radiator and accessory placement. The hydraulic drive can draw more power from the engine than an electric fan, and thus move more air through the radiator for more effective cooling. And compared to a directly-driven unit, the hydro fan’s speed isn’t dependent on engine speed—the solenoid that controls the flow of hydraulic fluid through the fan motor can opt to run the fan on high speed as the engine idles, for example, or completely freewheel the fan on the highway.

In the final analysis, if you can accept a little added complexity under the hood, the hydro fan combines the best qualities of both directly-driven and electric cooling fans: high power and flexibility, respectively. It’s a wonder to me that it hasn’t been more widely adopted.

Editor’s note: This post is part of an ongoing series spotlighting obscure automotive engineering solutions. Read the other installments here:


Technical Curiosities:
The Laycock de Normanville Overdrive

October 29, 2011 by Matt

Laycock de Normanville Overdrive OD Gearbox Transmission

This one was used on a pretty wide variety of cars, but I had to include it because of the name. I mean, c’mon. How I could I not write a post about an automotive component with a name like that? It’s awesome.

Invented by a Briton, one Edgar de Normanville, and manufactured by automotive supplier Laycock Products, the unit basically consisted of a solenoid-activated planetary gearset residing between the standard manual transmission and driveshaft, offering a reduction in gear ratio at the driver’s command. At the press of a button or flip of a switch (depending on the car) in the cockpit, the overdrive would engage and lower the engine speed relative to the driveshaft, markedly improving fuel economy.

Advantages? Transmission development has always been pricey, and as fuel economy began to become a priority for automakers, the idea of a fuel-saving external add-on to an existing 3- or 4-speed manual transmission was an appealing one. Not only that, but the nature of the Laycock Overdrive meant that it could be engaged at any time, even in the lower gears, effectively doubling the number of ratios at a driver’s disposal. A 4-speed tranny became an 8-speed, for instance.

Downsides? Added complexity, mainly. The solenoid in particular could be finicky on higher mileage cars, and frequently the overdrive unit had its own fill and drain plug separate from the “main” transmission, requiring a unique maintenance interval. As all-in-one 5-speeds with integrated overdrive became de rigeur, the Laycock Overdrive faded from the scene.

Laycock de Normanville Overdrive OD Gearbox Transmission Diagram Schematic

I first learned about it from its presence on the Volvo M46 4-speed + overdrive transmission. Installed from the factory on Volvo 240s and later 740s, it’s one of only two manual transmissions (the proper 5-speed M47 being the other) available stateside for those of us interested in a bolt-in manual swap for a Volvo 200-, 700- or 900-series. Remarkably, up until the late ’80s, the Laycock Overdrive was fitted to a wide variety of cars, not just Volvos: Jaguars, MGs, Austin Healeys, Alpines and Triumphs, among others, were available with the unit. Not too shabby for an obscure bit of engineering with a funny name.

Editor’s note: This post is part of an ongoing series spotlighting obscure automotive engineering solutions. Read the other installments here:


Technical Curiosities: Audi’s UFO Brakes

October 21, 2011 by Matt

Audi V8 200 200q20v 20v ATE UFO Brake Brakes Calipers

I love weird engineering. As much as I might be cursing on any given Sunday afternoon leaning over the engine bay of a car featuring said weird engineering, shaking my fist at the gods as I ask why the automaker couldn’t have assembled the car the “normal” way, I’ll always admire manufacturers who march to the beat of their own drum. Whether it’s an all-encompassing philosophy or a random decision here or there, automakers who deviate from conventional wisdom will always command my attention.

Today we embark on a new series of posts highlighting technical esoterica, or unique solutions to engineering challenges in the automotive world. Sometimes there are plausible justifications for off-the-beaten-path decisions automotive engineers make, but sometimes it seems like automakers just want to do things their own way for the sake of being different. Either way, let’s dive in.

The year was 1989. Audi was introducing its top-of-the-line Mercedes- and BMW-fighter, its V8. Built on a stretched version of its 100/200 mid-size chassis, Audi stuffed a brand new, all-aluminum, 3.6l, DOHC 32-valve V8 (oddly enough) under the hood, paired it with its first automatic quattro drivetrain and decked the whole car out in appropriately luxurious trappings. In spite of the added bulk over the run-of-the-mill 100/200, the big V8 moved the car along as a respectable clip. Braking prowess, however, was another area Audi wanted its new luxury flagship to have sporting credentials. But instead of simply giving the V8 larger front brakes, they decided to do something a bit different.

Constrained by a maximum wheel size of 15 inches, Audi enlarged the swept area of the brakes, and thus their potential stopping power, by “flipping” the caliper inside the disc, creating their “UFO” brakes, so called because of the resemblance of the disc carrier and its heat-dissipating holes to a stereotypical alien spacecraft:

Audi V8 200 200q20v 20v ATE UFO Brake Brakes Calipers

This move allowed the diameter of the disc to fill the inside of the road wheel, without having to allow for a caliper positioned on the perimeter of the disc, as is the case with every other disc brake system.

Did it work? By all accounts, it did—when operating as designed, compared to “regular” disc brakes engineered to fit the same 15″ wheel diameter, the UFO brakes provided tremendous bite and resistance to fade. The system gave the V8 (and ’91 200 Turbo quattro, to which it was also fitted) braking capability commensurate with its accelerative abilities.

Did it have downsides? Most definitely. UFO brakes weren’t shared with any other automaker, and failed to benefit from economies of scale in manufacturing; replacement rotors and calipers are quite expensive. Improperly maintained, the rotors can warp; an often-prescribed “solution” involves multiple consecutive panic stops from highway speeds. Allegedly, this can straighten out the rotors and eliminate the shimmy. And perhaps the most significant bummer for those concerned about appearance, especially when exposed by thin-spoke aftermarket wheels, to the uninitiated UFO brakes have the decidedly downmarket appearance of steel wheels.

Regardless of its engineering justifications, disadvantages or even its benefits, Audi’s experiment with UFO brakes appeals for the simple reason that the automaker tried something different. Kudos to them.

Editor’s note: This post is part of an ongoing series spotlighting obscure automotive engineering solutions. Read the other installments here: