DE4119657A1 - Electromagnetically adjustable radial compressor for exhaust turbo-supercharger - has blades fitted to spring-biased inner coaxial shaft subject to progressive attraction by external electromagnet - Google Patents

Abstract

Turbine blades (61) are fixed to an inner shaft (60) around which an outer shaft (63) carries the broadened surfaces (64) of a supercharger rotor and the turbine wheel (62). The inner shaft (60) is urged by a spring (70) towards one axial end position. The blades (61) are moved by an electromagnet (72,73) whose north-seeking pole opposes that of a permanently magnetised ring (71) fixed to the outer shaft (63). The spring (70) is compressed progressively as the energisation of the electromagnet (72,73) increases. ADVANTAGE - Supercharging pressure is continuously adjustable at any given rotational speed by contactless setting of compressor blade dia.

Description

The invention relates to an electromagnetically adjustable Radial compressors and their application in exhaust gas turbochargers.

Exhaust gas turbochargers have so far been almost exclusively regulated via the exhaust gas flow of the internal combustion engine (bypass control) or via the adjustment of the turbine guide vanes takes place. (cf. automotive engineering Paperback / Bosch; 20th ed .; Düsseldorf 1987).

Such a regulation is for stationary operation along the full load line Particularly favorable above the engine speed.

For non-stationary operation in automotive internal combustion engines that have a wide range Have speed range and at any engine speed with full and part load are operated, but is also evident in these control methods a weakness specific to exhaust gas turbochargers.

The exhaust gas turbocharger (ATL) has a weakness in non-stationary operation on, which is known as "turbo lag".

If you want from the partial load range (low Exhaust gas temperature, low exhaust gas volume) in the full load range (high Exhaust gas temperature, high exhaust gas volume), then the engine speaks only delayed to, because the ATL has to "run up" to get the required one Build up boost pressure.

Given the geometry of the turbine, the build-up behavior of the turbine characterized by the gas volume.

The turbine pressure ratio p₃ / p₄ of the pressure p₃ before the turbine and the pressure p₄ behind the turbine is therefore a function of the exhaust gas mass m₃ and the exhaust gas temperature T₃.

The turbine power P _T obeys the equation:

P _T = m _{T *} C _{pa *} T₃ _* (1- (p₄ / p₃) ^{((K-1) / K)} ) _* η _T

With
m _T = exhaust gas mass
C _pa = specific heat
T₃ = temperature in front of the turbine
p₃ = pressure in front of the turbine
p₄ = pressure behind the turbine
K = isentropic exponent
η _T = turbine efficiency

The compressor power P _v obeys the equation:

P _v = (m _{v *} ψ _{v *} u₂²) / (2 _* η _v )

With
m _v = air mass
ψ _v = pressure digit
η _v = compressor efficiency
u₂ = peripheral speed of the compressor wheel

According to the laws of similarity for turbomachines, the torque M _{v of} the compressor obeys the equation:

M _v = λ _* ϑ _* D⁵ _* ω²

With
λ = coefficient of performance
ϑ = spec. Fluid weight
D = diameter of the compressor wheel (blade diameter)
ω = angular velocity of the impeller

Since the ATL has a power balance between turbine and compressor power, the equilibrium equation applies when the friction power P _{R is taken} into account:

P _v = P _T -P _R

With changed gas pressure p₃ in front of the turbine by:
a) Changing the gas mass by changing the engine speed or changing the throttle valve position (gasoline engine)
and or
b) Change in the exhaust gas temperature by changing the fuel supply per cylinder stroke
changes the turbine pressure ratio p₃ / p₄ and the gas mass m₃ or the gas temperature T₃ in the equation of the turbine power.

The compressor performance is, however, completely, especially from the exhaust gas temperature independently.

The speed is therefore in the partial load range (reduced exhaust gas temperature) of the ATL decrease and thus generate a lower boost pressure.

If the engine load remains unchanged, the reduced boost pressure in the Part load range is only a subordinate role in the fast The delay makes a transition to a higher engine load noticeably noticeable due to the startup behavior of the ATL.

A reduction in the moment of inertia of the lug can only bring minor improvements.

Studies by KKK show that the moment of inertia is halved of the trolley by using ceramic rotors instead of metal rotors only reduces the "ramp-up time" by approx. 30%. (cf. B. Engels / "Improving the transient behavior of exhaust gas turbochargers" / seminar "Development of combustion processes for direct injection Diesel engines "of the Technical Academy Wuppertal; Nuremberg 1990)

The invention seeks to remedy this. The invention as it is characterized enables a non-contact Adjustment of the diameter of the compressor blades for a given Compressor speed, the power consumption and the boost pressure are infinitely variable change and so in turbochargers over a large part of the operating range of internal combustion engines a constant speed of the turbocharger maintain.

This is achieved in that the adjustment of the compressor blades is done so that the compressor capacity so available standing turbine power is adjusted to a desired speed is maintained.  

Fig. 1 and 2, the explanation of the compressor control according to the invention are used at a Angasturbolader.

The outer sections of the loader blades 61 are fixed to an inner shaft 60 .

Around the inner shaft ( 60 ) is the outer shaft 63 , on which the widened side surfaces 64 of the supercharger wheel and the turbine wheel 62 are fixed.

By axially displacing the inner shaft 60 relative to the outer shaft 63 , the blades 61 are drawn into slots in the side surfaces 64 and the radial diameter between the side surfaces is changed. The inner shaft and outer shaft are thus connected in a rotationally fixed but axially displaceable manner.

By axially relative adjustment of the two shafts is the loader diameter changeable.

This turbocharger is set electromagnetically and without contact.

The inner shaft 60 is pressed into the one end position relative to the outer shaft 63 with a spring 70 . A permanent magnet ring 71 is fixed to the outer shaft, the north pole of which lies in the axial direction against the north pole of an electromagnet 72, 73 which is fixed to the housing and is ring-shaped around the soft iron end of the inner shaft. The blade setting can be determined by adjusting the strength of the electromagnet.

The stronger the attraction of the electromagnet, the more the soft iron end of the inner shaft 60 is drawn into the electromagnet. At the same time, however, the north pole of the electromagnet repels the north pole of the permanent magnet 70 fixed on the outer shaft.

So it becomes an axial displacement force opposite the spring force generated between the inner and outer shaft without touching and therefore friction between rotating elements and housing is necessary becomes. The inner and outer shaft come into the relative position, in the magnetic force and spring force are in balance.

Fig. 1 shows the setting for maximum force of the electromagnet, Fig. 2 for minimum force.

Since the blades on turbochargers are connected, you only get the outer ones Move sections.

The regulation then takes place as follows:

Suppose that you want to optimize an "ATL startup procedure". Then one becomes a constant speed n₀ of the ATL over the entire operating range of the engine. In this case it plays Mass moment of inertia of the running gear does not matter when the load changes more.

Such an adjustment solely by changing the compressor diameter becomes clear due to the equilibrium equation of the ATL.

The ATL can be equipped with a "waste gate" for better adjustments be a part of the exhaust gas flow from a certain exhaust gas volume bypassed the turbine.

In the partial load range, the compressor diameter is then reduced to such an extent that the reduced turbine power P _T at the desired rotor speed n₀ is in equilibrium with the friction power P _R and the reduced compressor power P _v .

If you want to suddenly increase the engine power (generated during loader tests this sudden load change at constant engine speed by sudden Opening a throttle valve), then you will simultaneously with the Opening the throttle valve or, in the case of diesel engines, increasing the injection quantity increase the compressor diameter.

This leads to a sudden increase in boost pressure p₂ and suddenly increased charge density ₂.

Of course, the increased power consumption of the compressor have a braking effect on the running gear. But there is so much rotational energy in the train saved that this sudden increase in compressor output lead to a gradual decrease in speed would, analogous to the ramp-up behavior of previous ATL.

This drop in the rotor speed is prevented by the then increased turbine output.

With an ATL according to this concept, it is therefore not sluggish Give reaction by starting up.

Such an ATL, which reacts quickly to load changes is therefore particularly suitable for motors in transient operation suitable, such as B. automotive engines.

The advantages of the concept compared to known adjustable ATL are:
- Fundamental improvement of the transient behavior by eliminating the "run-up" of the ATL during load changes
- no interference in the hot exhaust gas flow
- No dependence of the supercharger speed on the turbine power
- Charge control integrated in the electronic engine management
- Run-up behavior after overrun can be improved by minimizing the compressor performance.

Claims (3)

1. Radial compressor for heat engines, in which the effective diameter of the compressor blades 61 is carried out by axially displacing the blades or part of the blades or the side surfaces 64 of the compressor wheel, characterized in that with the help of a housing-fixed electromagnet 72, 73 and a fixed connection to the rotor 70 to generate a restoring force via the setting of the strength of the electromagnet, the setting of the effective blade diameter of the compressor is carried out. 2. radial compressor under claim 1, characterized, that it is the compressor of an exhaust gas turbocharger. 3. radial compressor under claim 2, characterized, that it is controlled so that the power consumption of the compressor so adapted to the available power of the turbine is that the running gear has a desired speed.