GB2027935A

GB2027935A - Propulsion plant with a diesel engine and hydrodynamic transmission

Info

Publication number: GB2027935A
Application number: GB7927762A
Authority: GB
Original assignee: MTU Friedrichshafen GmbH; MTU Motoren und Turbinen Union Friedrichshafen GmbH
Current assignee: Rolls Royce Solutions GmbH
Priority date: 1978-08-10
Filing date: 1979-08-09
Publication date: 1980-02-27
Also published as: GB2027935B; FR2435602B3; DE2835041C2; FR2477225A2; DE2835041A1; FR2477225B2; FR2435602A1

Abstract

The designing of the propulsion plant is to be so effected that at the rated engine speed and at the maximum power consumption (11) of the circulating pumps of the hydrodynamic transmission the transmission power input coordinated with the rated engine output is received by the transmission. With a relatively low power consumption (12 to 14) by the circulating pumps, means are provided so that the action of an engine speed governor is modified to control the power plant to achieve relatively high transmission driving speeds by increasing the engine speed above the rated engine speed without exceeding the rated engine output, with a corresponding reduction in the fuel-injection rate. <IMAGE>

Description

SPECIFICATION Propulsion plant with diesel engine and hydrodynamic transmission The invention relates to a propulsion plant, for example for vehicles, in which a diesel engine drives the pumps for the circuits of a hydrodynamic transmission directly or via a geared transmission stage, the power consumption of which, depending on the speed ratio between the transmission output speed and transmission driving speed, exhibits a curve varying respectively when plotted against the transmission driving speed.

In designing such propulsion plants normally the rated output and rated rpm of the diesel engine is co-ordinated with a mean power consumption of the pumps for the circuits at the different speed ratios.

This designing has the result that at speed ratios with low power consumption by the pumps, the engine speed increases with a simultaneous reduction in engine power effected by the governor. At speed ratios with relatively high power consumption by the pumps, the engine has its speed of rotation lowered, whereby the engine power is likewise reduced. Accordingly, the full rated output of the engine is available only at the speed ratio on which the design is based. At all other speed ratios a reduction in this rated output has to be taken into consideration.

According to the invention there is provided a propulsion plant, for example for vehicles, in which a diesel engine drives the pumps for the circuits of a hydrodynamic transmission directly or via a geared transmission stage, the power consumption of which, depending on the speed ratio between the transmission output speed and transmission driving speed, exhibits a curve varying respectively when plotted against the transmission driving speed, the hydrodynamic circuits and/or of the geared transmission stage being designed such that at the speed ratios with the highest power consumption by the pumps and at the rated engine speed the transmission is able to receive a transmission power input coordinated with the rated engine output, and there being means for controlling the plates such that relatively high transmission driving speeds for speed ratios with relatively low power consumption by the pumps are achieved by increasing the engine speed above the rated engine without exceeding the rated engine output, with a corresponding reduction in the fuel-injection rate.

As a result of this design of the propulsion plant and mode of operation of the diesel engine, the hitherto existing reduction in transmission output torque is completely eliminated by the reduced output at the transmission input occurring almost over the entire transmission output speed range.

It is merely a prerequisite in this respect that the diesel engine can be operated above its rated rpm.

By reducing the fuel-injection rate at these overspeeds, the combustion chamber pressures and propulsion-unit loads occurring at the admissible rated output are not exceeded.

Another advantage lies in the fact that in selecting the gearing ratio at the transmission input it is possible to proceed more liberaliy than hitherto, since even with an inaccurately matching transmission ratio either the power reduction caused hitherto by the downward adjustment or that caused by lowering the engine speed does not take place. In this way it is possible to use an often already existing inaccurately matching gearing ratio and it is possible to avoid a delay in the deadline for supplying the transmission, caused by the production of a new gearing ratio.

By way of example, one embodiment of a propulsion plant according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows the characteristic curves of a propulsion plant of conventional design; Figure 2 shows the characteristic curves of a propulsion plant in a design according to the invention.

Figure 3 shows diagrammatically a governor for a speed-regulated diesel engine.

In the drawings the power consumption of the pump in the circuit of a hydrodynamic transmission is plotted against the transmission driving speed for different, for example selected, speed ratios between transmission output speed and transmission driving speed. The curve 11 represents in this case the maximum power consumption of the pump, the curves 12 and 13 respectively medium power consumption and the curve 14 the minimum power consumption of the pump.

In addition to the power consumption of the circulating pump of the transmission, an engine power curve 15 with a regulating curve 16 in a conventional design is plotted in Figure 1. The full rated engine power can be reached only at point 17 in the power consumption curve 13 of the pump and, therefore, only at the speed ratios co-ordinated with this power consumption curve. All all other speed ratios, i.e. almost throughout the operating range of this circuit, it is necessary to take into account power reductions caused by lowering the engine speed (points 18, 19) or by downward adjustment (point 20), which power reductions have a detrimental effect on the development of the transmission output torque.

Figure 2 illustrates the design according to the invention of a propulsion plant. The engine power curve 21 reaches at point 22 the curve 11 forthe maximum power consumption of the pump of the hydrodynamic circuit. At this point the engine reaches its rated rpm which, normally, corresponds to the transmission driving speed. Higher transmission driving speeds for speed ratios with low power consumption of the pump are attained by increasing the engine speed above the rated engine speed (points 23 to 25). By correspondingly decreasing the fuel-injection rate any exceeding of the rated engine output is thus prevented. The final downward adjustment takes place in accordance with the regulating curve 26.

In order to arrive at the characteristic curves of Figure 2 from the characteristic curves of Figure 1 in a completed drive plant an alteration in the dimen sions of the hydrodynamic circuits and/or in the gear-wheel transmission stage and an alteration in the governor characteristic of the diesel engine is necessary. If, for example, the maximum admissible engine speed with fuel injection amounts to 1500 rpm and if the hydrodynamic circuits of the gearing require 3000 rpm according to curve 13, corresponding to a speed ratio between transmission output speed and transmission driving speed, to take up the mean transmission input power available at this engine speed, then the gear-wheel stage must have a transmission ratio of 3000:1500 = 2.0, in the hitherto conventional design.

For the design according to the invention the transmission input power should be taken as a basis at a speed ratio corresponding to curve 11) between transmission output speed and transmission driving speed. The transmission input power of curve 11 is, at 3000 rpm, considerably higher than the power made available by the engine. The rotation speed of the circuits must, therefore, be decreased to 2700 rpm, for example, so that the new transmission ratio of the gear-wheel stage amounts to 2700:1500= 1.8.

Instead of an alteration in transmission ratio a corresponding alteration in the dimensions of the hydrodynamic circuits may also be effected.

Through one of these measures or a combination of both it is brought about that the diesel engine reaches its maximum permissible engine speed at full fuel injection already at point 22 (Figure 2).

If the power requirements vary according to the curves 12 to 14 then the speed of the diesel engine must be increased. In order to keep the load on the engine within admissible limits a corresponding reduction in the fuel-injection rate must occur.

Figure 3 shows schematically a governor for a speed-regulated diesel engine. The governor shaft 40 is driven by the diesel engine, and fly-weights 41 adjust the governor sleeve 42 in a known way against the force of a governor spring 43. The pre-stressing of the governor spring can be varied by a desired-value lever 44 for setting different regulating/desired speeds of rotation.

The governor sleeve 42 adjust via a lever 45 a control rod or rack of an injection pump 49, the control rod being divided into two halves 47/48 by a spring element 46. The desired-value lever 44 can act upon the control rod half 47 from a predetermined setting via a stop member 50 connected to the spring element 46.

The desired-value lever 44 is shown in three positions. In position 51 (solid line) for no-load speeds of rotation and in position 52 (chain line) for medium speeds of rotation, the desired-value lever 44 exerts no influence on the position of the control rod. The injection pump is controlled in a conventional way by the governor.

Upon setting a desired-value speed of rotation which exceeds the speed of rotation of point 22 in Figure 2, e.g. position 53 (broken line), the desiredvalue lever 44 presses to an increasing extent the spring element 46 and with it the control rod half 47 via the stop member 50 away from the full-load position and thus reduces the admission. This takes place in opposition to the position of the governor sleeve and is made possible by the spring element 46.

Claims

1. A propulsion plant, for example for vehicles, in which a diesel engine drives the pumpsforthe circuits of a hydrodynamic transmission directly or via a geared transmission stage, the power consumption of which, depending on the speed ratio between the transmission output speed and transmission driving speed, exhibits a curve varying respectively when plotted against the transmission driving speed, the hydrodynamic circuits and/or of the geared transmission stage being designed such that at the speed ratios with the highest power consumption by the pumps and at the rated engine speed the transmission is able to receive a transmission power input coordinated with the rated engine output, and there being means for controlling the plant such that relatively high transmission driving speeds for speed ratios with relatively low power consumption by the pumps are achieved by increasing the engine speed above the rated engine speed without exceeding the rated engine output, with a corresponding reduction in the fuel-injection rate.

2. A propulsion plant substantially as hereinbefore described with reference to and as shown In Figure 3 of the accompanying drawings.