Hydristor

Key takeaways

Hydristor belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Hydristor to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Hydristor from memory before moving on to harder problems.

Reference excerpt

Hydristor is a joining of the words 'hydraulic' and 'transistor'. The device invented by Tom Kasmer in 1996 and is based on the dual pressure balanced hydraulic vane pump invented by Harry F. Vickers in 1925.

Vane pump details The Vickers design included an elliptic chamber which confined the radial motion of the vanes nested in the rotor slots. As the rotor and vanes turn, each vane is first pushed radially inward followed by a maximum radial extension and that happens twice per revolution. The displacement of the fixed device is calculated by determining the difference in vane extension between minimum and maximum, times the axial length of the vanes and rotor. This multiplies to an area subject to the hydraulic pressure in the device whether used as a motor or a pump. Then an average of the minimum and maximum extensions establishes a 'radius of motion' for the pressurized equivalent pressure/force area. of each vane which passes one of the 4 axial sealing areas. What happens is that this equivalent area patch travels through the circumference or the equivalent linear distance resulting from rotating the 'radius of motion' through one complete revolution of 360 degrees. The elliptic chamber is called a 'cam ring' by the industry. As a vane moves into, say, a maximum extension, and then rotates into a minimum extension region of the cam ring, it passes through a gradual transition from maximum to minimum followed by a gradual transition back to maximum and this happens twice per revolution. In order to prevent oil under pressure from bypassing the vanes, 4 sealing areas are created by means of 4 kidney shaped ports located in the transition areas between minimum and maximum. The spaces between the kidney ports are called the sealing areas and this port system is located at either, or both axial ends of the rotor and vanes. The configuration of the ports and sealing areas are such that the space between any two adjacent vanes is slightly less than the coverage of the sealing area. In other words, as the vanes rotate through the sealing area, for a small amount of rotation, both adjacent vanes are within the sealing area. As the rotation continues, the first vane in line leaves the sealing area, but not before the next vane in succession is firmly in the sealing region. The effect is to prevent the exchange of oil from any two adjacent chambers located on either side of a given sealing area and the oil can only be interchanged by the actual rotation of the rotor and vanes. This is the pumping mechanism for the historical vane pump or motor. The term 'pressure balanced' comes from the fact that pressure in any chamber is matched by the same pressure in the diametrically opposite chamber and the hydraulic radial side thrust calculated by a 'side view area' and the two forces are opposite and cancel; hence the name 'pressure balanced'.

Hydristor details

There are several problems with the historical design. The vane tips radially contact the cam ring elliptic surface and cause a significant friction as the rotor and vanes turn. This friction is both pressure dependent and speed squared dependent due to RPM-squared centripetal forces. The speed is limited to about 6-7,000 RPM and the pressure is limited to about 2,500 PSI. Another pressure-related problem is that the pressure forces into the axial rotor to stationary kidney endplate clearance and buckles the device ends thus increasing fluid blowby referred to as 'volumetric efficiency'. Typically, vane pumps and motors have two external ports but there are actually two separate sets of chambers which form two separate pumps and motors. The internal plumbing is y-connected to create only two external ports. For the Hydristor. a 'concentric nesting of endless metal belts' replaces the fixed elliptic cam ring. And, all the vane tips contact the inner surface of the belt. The historical friction of the vane tips now causes the belt set to rotate at approximately the same speed as the rotor and vanes, but there is a very slight 'walking behind' of the vane contact area and there is a very slight speed slippage which results in the inner belt wear being spread out and this results in much longer belt life. Also, the belt set now confines the pressure and speed-squared forces like a pressure vessel and the potential speed of operation is very much higher. The result of all this is to raise both the operating pressure and the operating speed and this amounts to a 10 times increase in hydraulic packaging density and similar decrease in weight per unit power.

Related patents There are 4 US and international patents on this device:

US6022201 - Hydraulic vane pump with flexible band control - filled May 14, 1997 US6527525 - Hydristor control means - filled Feb 8, 2001 US6612117 - Hydristor heat pump - filled Feb 20, 2002 US7484944 - Rotary vane pump seal - filled Aug 11, 2004

Hydristor efficiency The fixed relationships of the elliptic cam ring are replaced by 4 curved surface (cupped) movable pistons located at the 4 sealing areas, at 12,3,6, and 9 o'clock like the face of a clock. The curvature of each piston rides on a 'hydrodynamic oil bearing' similar to hydroplaning tires in the wet and this virtually eliminates metal-to-metal contact and friction. The first Hydristor achieved almost 95% efficiency overall and the present designs are in the 97+% range. If the 4 pistons are positioned equidistant from the center of rotation, no oil is expressed or accepted by any of the kidney ports. This is called 'neutral'. For a clockwise rotation, if 3 and 9 pistons are moved inward with 6 and 12 moving outward, all moving an equal amount, then a device displacement in proportion to the piston movement is created. If the 6 and 12 pistons were moved in with 3 and 9 moving equally out, then all the oil flows reverse. Since the piston positions are infinitely variable, any possible displacement between zero and + or - maximum displacement can be created. If two such Hydristor units are packaged face-to-face with the 4 port kidney plate between them, an infinitely variable transmission is formed. This transmission can select any ratio in the forward direction and in the reverse direction without the need for any gears.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Hydristor

Start with the simplest possible case. Write down what Hydristor claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Hydristor before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Hydristor ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Hydristor

In research: Hydristor appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Hydristor in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Hydristor is common in secondary-school and first-year university syllabi. It links to neighbouring topics Automotive transmission technologies, Mechanisms (engineering), Pumps, so understanding it makes those chapters shorter.
In everyday life: Look for Hydristor outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Hydristor in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hydristor means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Hydristor out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hydristor in simple terms?

Hydristor is a joining of the words 'hydraulic' and 'transistor'. The device invented by Tom Kasmer in 1996 and is based on the dual pressure balanced hydraulic vane pump invented by Harry F.

Why does Hydristor matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Hydristor?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Hydristor.