From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Article from 'The Motor' magazine describing the Lentz transmission gear system.
Identifier | ExFiles\Box 136\4\ scan0003 | |
Date | 14th November 1911 | |
14th November, 1911. 735 The Motor LENTZ TRANSMISSION GEAR.—Contd. is being poured in; the said vent holes, of course, being afterwards plugged. With the engine running then, we now have the oil in this forward casing being churned round and round, but as all the communicating ports between the forward casing and the rear casing are closed by the distributor valves, nothing happens except that the oil continues to be churned up. Now, however, we take the change-speed lever in hand and move it to the first-speed position. This action operates the two distributor valves (they are merely duplicated for convenience), and opens the rear port connecting between the rear pump itself in the forward casing, and the main body of the back-axle casing. Now, therefore, a volume of oil approximately equivalent to the pumping area of the rear pump, is forced through to the back-axle casing, but as soon as it gets there it has to mix with the other oil already there, and. of course, filling up all the space between the transmission blades which form the but-ment against which the pressure is now conveyed. Each cardan shaft constituting the drive to the back axle is connected to what, for the want of a better term, we will designate as a differential-butment piston—a term through the use of which probably many of our readers will not obtain a very concise idea of its construction. Therefore, we will endeavour to explain a little further. The action of the pumps has been explained already, and it has also been stated that the construction of these said pumps is quite similar to the transmitting portions of the mechanism in the back axle, and if one imagines one of these pumps instead of acting as a pump to force the fluid has the fluid forced against it, then it will be seen that it is driven instead of driving. Therein lies the crux of the whole situation. The discharge of oil from the forward cylindrical casing to the rear one is brought to a bifurcated discharge orifice, and finds its way to each differential piston in such proportions as the resistance to the drive in each wheel varies. Thus there is no actual differential gear provided, although at the same time a differential action takes place automatically when necessary. The position which we have been considering can be taken as the low gear, in which a small quantity of oil is pumped for a given number of revolutions of the engine; consequently, the speed of the drive resulting from this small quantity of oil being forced against the transmitting gear is slow, with, however, a corresponding increase of pressure. Another movement of the gear lever and the next port is open to communicate with the back axle driving mechanism, and as the area of this port is larger, the quantity of oil pumped for the same given engine speed is proportionately greater, and, therefore, the speed is increased again. The same train of argument applies with the third port; that is to say, the largest one, a still larger quantity of oil being put in circulation between the front and the back chambers for a given number of engine revolutions, and consequently the speed increases. For the fourth speed, ports Nos 1 and 2 are brought into communication together, whilst for the fifth and top speed the whole volume of oil, which can be pumped by the three pumps in combination, is passed directly through to the back axle. It will be seen, therefore, that this transmission gear can give practically as many speeds as the designer chooses to allow for, as the addition of another pump or two would permit a combination approaching very close to the infinitely variable drive. It must be understood that both in the case of the pumps and the differential pistons the vanes move in and out through the medium of a cam track, the bases of the said vanes being provided with rollers mounted on pins, running in this said cam track. As the one vane commences its return movement from its maximum eccentricity, the blade nearest to it is just assuming its maximum movement radially, and, consequently, at once takes up the drive or transmission of the drive, as the case may be. For reversing, the oil is simply allowed to enter the rear casing in the opposite direction. Then, again, there is another feature, as the oil is utilized for braking purposes, the oil outlet from the differential pistons being contracted, which, it is claimed, gives an absolutely safe and reliable brake under all conditions. One other item requires a few words before we summarize the claims for consideration possessed by this new invention, and that is the clever way in which leakage of oil is guarded against. In addition to the careful packing of the various faces, etc., all such parts are arranged to be in connection with the suction chamber of the pumps, so that the oil around the shafts emanating from the gear casing proper is placed under a slight vacuum, or, at any rate, a tendency in that direction, and thus, instead of being inclined to leak, its tendency, we are told, is in the reverse direction. If one should wish, whilst driving, to “ de-clutch,” there is a simple piece of apparatus to permit one so to do, as a small safety valve is provided, which not only allows the free use of any of the forward speeds, the reverse and the brake, but is also a safety valve for starting, sudden braking, and changing speeds, etc., should the pressure, through any conceivable cause, become excessive. By operating this safety valve when on any of the gears, one has an ordinary free-wheel position. With regard to the claims made on behalf of this gear, it is stated to be very efficient, and also simple and silent. Wear and tear are said to be reduced to a negligible quantity; the maximum of reliability is claimed to be attained, and also economy, on account of the simplicity of the apparatus. Obviously, as regards its application, it can very easily be adapted to most types of cars or, for that matter, to many other purposes. We may, perhaps, make a few remarks on these claims, although, in justice to the gear, we should point out that we could not obtain quite as full information of it at the Show (where it was exhibited on the stand of Messrs. Charron Cars, 33, Wardour Street, London, W.) as we should have liked to have done, and possibly there may have been a misunderstanding somewhere; for instance, in the case of efficiency, we were told that this had been proved to be as high as 83 per cent. in a number of tests. Whilst not in the slightest way doubting the bona fides of the statement—as a statement—it would certainly be a very pleasurable surprise for us to find that hydraulic gear of any description could be constructed to give as high an efficiency as this. It is, of course, obvious that all the parts are running in oil, and, therefore, under favourable conditions, but, on the other hand, with a hydraulic Image Captions: The three pumps (which are mounted on ball bearings) are shown with one of the vanes of each. The pump to the left is the slow speed, the middle one the second, and the one on the right the third speed. One of the two distributor valves for permitting or stopping the flow of oil from the pumps to the rear casing. Drawing out the portion with the slots cut in it, has the effect of partially rotating one, two, or all the valves as the desired combination necessitates. Stamp Text: ROLLS-ROYCE, LIMITED. ORDER OFFICE. D23 14 NOV. 1911 DERBY. | ||