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DE-102025146966-A1 - Fuel injector for a miniature diesel engine

DE102025146966A1DE 102025146966 A1DE102025146966 A1DE 102025146966A1DE-102025146966-A1

Abstract

Injection nozzle (10) for a miniature diesel engine, at least comprehensively: - a housing (1) with a bore (9); - a nozzle needle (4) which is guided in the bore (9); - a spring (3) by which the jet needle (4) is supported on the housing (1), - that at least one seal (8) is arranged in the housing (1) at an end area of the bore (9); - that the jet needle (4) has a valve plate (7) at one end; - that the spring (3) is supported on a shoulder (9.2) in the housing (1) and on an element connected to a shaft of the jet needle (4) and - that the preload of the spring (3) causes the valve plate (7) to rest against the seal (8) from the outside. characterized by - that the nozzle needle (4) has at least one guide shoulder (5) at one end, wherein the diameter of the guide shoulder (5) is selected such that it can pass through the bore in the seal (8); - that a constriction (6) is provided on the nozzle needle (4) between the guide shoulder (5) and the valve plate (7) and - that the seal (8) is made of a thermoplastic material.

Inventors

  • Erfinder gleich Anmelder

Assignees

  • Christoph Wallscheid

Dates

Publication Date
20260513
Application Date
20251113
Priority Date
20241113

Claims (7)

  1. Injection nozzle (10; 10') for a miniature diesel engine, comprising at least: - a housing (1; 1') with a bore (9; 9'); - a nozzle needle (4; 4') guided in the bore (9; 9'); - a spring (3; 3') by which the nozzle needle (4; 4') is supported on the housing (1; 1'); - that at least one seal (8; 8') is arranged in the housing (1; 1') at an end region of the bore (9; 9'); - that the nozzle needle (4; 4') has a valve disc (7; 7') at one end; - that the spring (3; 3') is supported on a shoulder (9.2) in the housing (1; 1') and on an element connected to a shaft of the nozzle needle (4; 4'), and - that the valve disc (7; 7') bears against the seal (8; 8') from the outside due to the preload of the spring (3; 3'). characterized in that - the nozzle needle (4; 4') has at least one guide shoulder (5; 5') at one end, the diameter of the guide shoulder (5; 5') being selected such that it can pass through the bore in the seal (8; 8'); - that a constriction (6; 6') is provided on the nozzle needle (4; 4') between the guide shoulder (5; 5') and the valve disc (7; 7'), and - that the seal (8; 8') is made of a thermoplastic material.
  2. Injector nozzle (10; 10') after Claim 1 , characterized in that the seal (8; 8') is made of PEEK.
  3. Injector nozzle (10; 10') after Claim 1 or 2 , characterized in that the spring (3; 3') is supported on a shoulder (9.2; 9.2') in the housing (1; 1') and on a spring plate (2; 2') which is connected to the jet needle (4; 4').
  4. injector (10) after one of the Claims 1 until 3 , characterized in that an upper annular surface of the seal (8) is fully supported on a shoulder (9.4) of the bore (9) in the housing (1) and is received with its outer circumference without play in an annular groove in the housing (1).
  5. Injector nozzle (10; 10') after Claim 4 , characterized in that the spring travel and spring constant of the spring (3; 3') on the one hand and the modulus of elasticity and the geometry of the seal (8; 8') on the other hand are coordinated in such a way that the valve plate (7; 7') bearing against the seal (8; 8') causes a compression of the seal (8; 8') supported in the housing (1; 1') such that its inner circumference engages in the constriction (6; 6') as long as there is no overpressure in the bore (9; 9').
  6. Injector nozzle (10') after one of the Claims 1 until 5 , characterized in that - the seal (8') comprises a wide head (8.1') and a comparatively slender, cylindrical sealing section (8.4'); - the housing (1') is in two parts with a housing upper part (1.1') and a housing lower part (1.2'), wherein these are connected to each other via a thread and wherein the head (8.1') of the seal (8') can be clamped between the housing upper part (1.1') and the housing lower part (1.2'), and - that the spring (3') is supported on the head (8.1').
  7. Injector nozzle (10') after one of the Claims 1 until 6 , characterized in that an annular channel is formed between the nozzle needle (4') and the cylindrical sealing section (8.4') through which fuel can reach the lower end of the injection nozzle (10').

Description

The invention relates to an injection nozzle for a miniature diesel engine having the features of the preamble of claim 1. A miniature diesel engine is defined as an internal combustion engine with a diesel combustion process and a maximum displacement of 20 cubic centimeters. Today's injection systems for diesel engines are mostly common rail systems, with the pump and (injection) nozzle as a single unit (PDE), or with the pump and injector separated by a pressure line. Despite different methods of pressure control, all these systems ultimately share a purely hydraulically controlled nozzle needle as a common feature. The known operating principle of the nozzle needle and nozzle body (see 1 ) corresponds to a hydraulically controlled valve, whereby at the time of injection a pressure chamber F is pressurized with the corresponding injection pressure. The pressure acting on a nozzle needle shoulder D causes a lifting movement against a pressure bolt B and a compression spring A, which lifts the nozzle needle C out of its sealing seat E, and the pressure is relieved. Once the pressure is released, the closing force of the compression spring A predominates, and the nozzle needle is pressed back into its sealing seat E. The internally lapped nozzle body G, made of high-quality steel, is paired with an externally lapped nozzle needle C in such a way as to achieve extremely tight tolerances of 0.002 mm. This is necessary to prevent lateral migration of the nozzle needle C in its sealing seat and to ensure that the nozzle needle C completely lifts off the sealing seat. The injectors available today cannot be used effectively in a miniature diesel engine with a displacement of just a few cubic centimeters, as the minimum injection quantity is already far too high and would lead to exceeding the smoke limit and overloading the engine. From the EP 1 988 278 B It is known that a valve body opens outwards due to applied fuel pressure. The valve body is pressed against a sealing surface within a tubular housing by spring force, against the direction of fuel flow. This sealing surface corresponds to the conical shape of the valve body head. The opening of the valve, and thus the injection process, is controlled by an electromagnetic valve. From the EP 1 734 251 A1 as well as EP 1 717 437 A1 A similarly designed, outward-opening injection valve is also described. Here, too, the nozzle opening is electromagnetically controlled. The object of the present invention is to create an injection nozzle for an internal combustion engine with a diesel combustion process with a displacement of a few cubic centimeters, and thus to enable or optimize the operation of a miniature diesel engine. This problem is solved by an injection nozzle having the features of claim 1. In the injection nozzle according to the invention, at least one annular seal is arranged in the housing at one end region of a bore. A nozzle needle has at one end at least a guide shoulder, a subsequent constriction, and finally a valve disc. The diameter of the guide shoulder is selected such that it can pass through the bore in the seal, but the valve disc at the end cannot. The nozzle needle is supported by a spring against a shoulder in the housing and against an element connected to a shaft of the nozzle needle. Due to the spring preload, the valve disc rests against the seal from the outside. The injection nozzle according to the invention makes it possible to introduce even the smallest quantities of fuel into highly compressed air with sufficient atomization. This makes it possible to manufacture an internal combustion engine with a diesel combustion process and a maximum displacement of 20 cubic centimeters. In practice, the injection nozzle according to the invention, installed in a diesel engine with a displacement of 13.5 cubic centimeters, has proven its reliability. This allows for a cold start with diesel fuel in a very small engine. The advantages of low fuel consumption and minimal smoke emission result during operation. Further advantages of the injection nozzle according to the invention are the avoidance of the extremely complex manufacturing processes necessary in the prior art, such as lapping and subsequent pairing, as well as automatic wear compensation of the valve seal. Similarly, the purely hydraulic control via fuel pressure eliminates the need for complex regulation using electromagnetic or piezoelectric actuators. This allows the The entire fuel injection system, designed to fit the engine's tiny geometries, can be built very compactly and, moreover, requires no electricity. Even though the injector nozzle according to the invention makes low-emission and effective combustion possible in the smallest geometries, it is not excluded to apply the sealing principle of the invention to larger designs as well. The invention is described below with reference to the embodiments shown in the drawings. The figures show a cross-sectional view of: