| Free-piston
propulsion system with infinitely adjustable hydrostatic converter |
| The basic structure
of this propulsion system consists of two modules: a two-stroke free-piston
engine and a hydrostatic converter system. |
Free-piston engines have a history of at least 150 years.
They have most recently been used mainly as compressors for air and for
gases.
Trials with the use of free-piston engines as vehicle propulsion systems,
in some cases in combination with hydraulic systems, and in others in combination
with linear electric motors, are currently being conducted in a number
of countries.
The advantages of the free-piston engine can essentially be found in
its lower weight, higher efficiency achieved by increasing combustion
pressure,
reduced piston friction, and improved combustion, since piston motion
is not tied to the sinusoidal pattern of the crankshaft.
Tests completed
up to now have indicated a significant reduction in consumption
and emissions.
|
| These developments, coupled with advances in electronic control and regulation
technologies, open up new applications for hydraulics, particularly in
terms of the infinitely adjustable conversion of pressure and volume across
a broad range. |
| Backbone |
| The central items are the piloted telescopic pump, which permits a significantly
higher conversion (transmission) of pressure and volume with a high efficiency
and low weight, and recuperation of braking energy by means of hydraulic
accumulators. Both of these factors reduce control complexity, response
time and weight most significantly compared, for example, to hybrid propulsion
systems. |
It can be stated, by way of summary, that the advantage of this oscillating,
infinitely adjustable engine can be found in its significantly reduced
weight and size, low moving masses and parts, and in the low friction levels
inherent in the system.
High-loss transformation of rotary to oscillating and back to rotary motion
is avoided. The practically constant frequency of the combustion propulsion
system in the optimum characteristics field range, combined with increase
of pressure in the combustion chamber and free acceleration of the combustion
piston, make it possible to anticipate a higher efficiency for the combustion
propulsion system as a whole. |
| The combination of
free-piston propulsion system, high degree of conversion for the hydraulic
system, and recuperation of the braking energy, with automatic shut-down
when the vehicle is stationary, promise a significant reduction in consumption
for the vehicle propulsion system, combined with a significant simultaneous
reduction in emissions. |
| Matching of output to vehicle size can be accomplished either by means
of variation of piston diameter and stroke in the free-piston propulsion
system, or via multiple installation of identical propulsion systems. |
| Key to Diagram LET 07 |
(please click on the drawing to enlarge it) |
The Engine Housing (1) contains a permanently connected pair of Combustion
Pistons (2) which oscillate within the motor housing. The system operates
on a two-stroke cycle, with the currently active piston at any time compressing
the intake air in the Chamber (3) after ignition. The pistons transmit
the combustion pressure by means of the Hydraulic Pistons (8) rigidly connected
to them via the Fluid Columns (10) to the Telescopic Pistons (11).
Fresh air flows via the Port (3.1) into the Chamber (3). From here, the
compressed air passes via the Valve (4) into the Pressure Reservoir (5),
which is connected to the hydraulically operated Inlet Valves (6). The
combusted mixture leaves via the Duct (3.2) and passes to the exhaust system. |
| Connected to
the Fluid Columns (10) in each case are the FC accumulators. These permit
the combustion piston an acceleration pattern which diverges from sinusoidal
motion, in order to achieve improved combustion and thus lower emissions.
The piston motion decelerates toward the end of the piston stroke as
a result of the increasing compression pressure on the opposing side.
This promotes the expulsion of the combusted mixture. |
The fluid columns act on the reciprocating Telescopic Pumps (11). The
two outer cup pistons are fixed to one another via an Eccentric (13). An
integrated rotary motion is thus generated to drive the Plain Rotary Slide
Valve (14) and Auxiliaries (28), such as the injection pump, the alternator,
cooling-water pump, etc. The engine can thus also be started via an electrical
starter motor.
The Rotary Valve (14) with the connected auxiliaries acts as a flywheel,
achieving a uniform reciprocating motion of the telescopic pumps and a
defined end position for the combustion piston. |
(please click on
the drawing to enlarge it) |
The Adjusting Piston (12) is used to control the delivery rate of the
Pump (11). When all annular pistons are extended, the cup piston pumps
the minimum delivery flow against a high pressure, resulting from the ratio
of the areas of the annular and the base surface. The maximum delivery
rate occurs when all pistons are retracted.
Positioning of the Piston (12) is accomplished by means of the electronically
controlled Proportional Valve (15). At a constant engine output, this moves
the Adjusting Piston toward lower volume/higher pressure or higher volume/lower
pressure, as a function of rolling resistance. |
| An extremely large transmission ratio of pressure and delivery flow,
i.e., of torque and speed of rotation, can be achieved at the wheel of
the vehicle via the number of telescopic pistons and their distribution
across area. |
| An HS accumulator for smoothing of volumetric flow is connected to High-pressure
Line H. The Isolating Valve (16) is located upstream. The high-pressure
flow ultimately passes via the mechanically actuated Three-Position Valve
(24) for Forwards/Reverse/Idle to one or more Hydraulic Motors (25). |
When the Engine (25) is acting as a pump due to the impetus of the vehicle,
the electronically controlled Pressure Valve (18) can be used to raise
or lower the pressure in the Low-pressure Line N, thus making braking intensity
variable.
If pressure in N increases, Accumulator BS will be charged via the Three-Position
Valve (27). In this phase, the combustion propulsion system switches to
minimum output, the Pump (11) supplies an adjusted flow, and Accumulator
HS is disabled. The intake volume comes from Low-pressure Accumulator NS.
The combustion propulsion system is also switched off when the vehicle
is stationary. When the vehicle moves off again, Accumulator BS is discharged
into High-pressure Line H for acceleration, and Low-pressure Accumulator
NS is charged. The combustion propulsion system switches in again on the
basis of travel-state setting, and the telescopic pump adjusts correspondingly. |
| The output from the combustion propulsion system is controlled via metering
of the fuel. The flow of fuel determines the initial pressure in the hydraulic
system. The pump delivery rate adjusts until approximate equilibrium of
forces is achieved in the pump. |
| Networking of all components of the engine is accomplished electronically.
The input for the control system is generated by sensors for fluid pressure,
take-off speed, position of the combustion pistons, position of the telescopic
pump, position of the valves and Output Monitor E. |
| The output signals are transmitted to the engine elements
by means of a program drafted in accordance with the requirements of each
particular vehicle. |
| Output Monitor E controls the fuel injection rate and acts as an electronic
multiplier of the product of oil pressure and take-off speed, or of torque
and vehicle speed. |
The following known components of a hydraulic system are not described
here in more detail:
17 Oil-cooler
19 Pressure valve, low-pressure setting
20 Electric motor
21 Top-up pump, leakage compensation
22 Pressure limitation N
23 Pressure limitation H
26 Fluid reservoir
29 Leakage compensation, fluid columns |
LEHLE GmbH
Technik & Design
robert.lehle@lehle-gmbh.de
fax: +49 (0) 7034 26661
Teckstrasse 37
D-71116 Gärtringen
Germany
Registered: HRB 3902
Amtsgericht Böblingen
VAT-Nr.: DE811926159 |
