GB2140506A

GB2140506A - Starting piston engines

Info

Publication number: GB2140506A
Application number: GB08314484A
Authority: GB
Inventors: Thomas Albert Parkin
Original assignee: British Shipbuilders
Current assignee: British Shipbuilders
Priority date: 1983-05-25
Filing date: 1983-05-25
Publication date: 1984-11-28
Also published as: GB8314484D0; GB2140506B

Abstract

Large marine diesel engines can be started by supplying compressed air sequentially to the engine cylinders. In a known arrangement, the air is fed from a manifold 26 to the respective cylinders via pneumatically-actuated valves 28 which are actuated in sequence by an engine-driven pneumatic distributor 34. The valves 28 are heavy and thus sluggish in operation, especially when closing. To take account of this sluggish operation, the invention provides for the signal to each valve 28 to close that valve to be advanced with respect to engine position as the engine speed increases. Preferably, the signal to each valve 28 to open that valve is also advanced, but to a lesser extent than the closing signal. <IMAGE>

Description

SPECIFICATION Starting piston engines This invention relates to a method and an installation for starting piston engines.

A known way of starting large marine diesel engines is to supply compressed air in turn to the engine cylinders via pneumatically actuated valves so that the engine is run up to a speed at which fuel can be admitted to cylinders to fire the engine. The pneumatically actuated valves are controlled by, for example, a camshaft-driven pneumatic distributor which distributes air to the air start valves to cause them to open and close in the correct sequence and at generally the correct time.

In view of the large size of engine with which such a starting system is generally used, the valves must be capable of handling high flow rates of air at high pressure. The valves must therefore be of heavy construction, and consequently are sluggish in operation, especially in closing. It has been noted that, at an engine speed at which firing can be commenced, the valves may close about 100" of crank angle after the crank angle at which they close when the engine is turning very slowly. With such delays in closing of the air starting valves, the engine exhaust valves may open before the air starting valves have closed, with a consequent waste of compressed air.

In accordance with the present invention, the signal to the or each air starting valve to close that valve is caused to be advanced with respect to engine position upon increasing engine speed.

Thus, the present invention takes account of the sluggishness of the air starting valve with a view to ensuring that the valve closes at an appropriate crank angle whether the engine is turning very slowly or has reached a speed at which firing can be commenced. Therefore, the present invention enables a saving in consumption of compressed air and accordingly savings in the size and cost of reservoirs for the compressed air and the energy required to compress the air.

The air starting valves are usually not so sluggish in opening as they are in closing. In accordance with a preferred feature of the present invention, the signal to open the air start valve is either supplied at a predetermined engine position or is preferably supplied at an engine position which is advanced with increasing engine speed, but to a lesser extent than the corresponding advance of the signal to close the valve. Thus, preferably, the difference in engine position between supplying the signals to open and close the air start valve is decreased with increasing engine speed.

A specific embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which; Figure 1 is a schematic drawing of a pneumatic part of a dual engine starting installation employing selectably the present invention and the known method; and Figure2 is a schematic drawing of control circuitry used with the pneumatic part of the installation shown in Figure 1.

Firstly a description will be given with reference to Figure 1 of the known starting installation. In this case air lines 10, may be connected directly to air lines 14,16, respectively, without the provision of change-over valves 18,20.

A remotely actuable manifold valve 22 is con nected between a reservoir 24 of compressed air at approximately 31 bar and a manifold 26. For each cylinder A, B, C, etc. of the engine, a remotely actuable start valve 28 is connected between the manifold 26 and the respective cylinder. The installation can receive three pneumatic signals from an operating station, viz. an "initiate" signal on line 10/14, an "ahead" signal on line 30 and an "astern" signal on line 32. The initiate signal is fed to the manifold valve 22 to cause pressurising of the manifold 26 to 31 bar. The ahead and astern signals are fed to a rotary pneumatic distributor 34 which is driven in synchronism with the engine camshaft.If an ahead signal is present on line 30, the distributor 34 distributes the signal sequentially with a predetermined timing dependent upon camshaft angle and with a predetermined sequence via lines 12/16 to the air start valves 28 to cause the valves 28 to open and close to pressurise the engine cylinders A, B, C, etc.

in a predetermined sequence to cause rotation of the engine in an ahead direction. Alternatively, if an astern signal is present on line 32, the distributor 34 distributes the signal in the reverse sequence to cause the engine to rotate in the opposite, astern direction. The signal on each line 12/16 to each air start valve 28 begins at one predetermined constant crank angle and finishes at another predetermined constant crank angle, and thus the difference in crank angle between each signal beginning and finishing is also constant.

The valves 28 are, by necessity of their construction, sluggish. They take a significant, constant time to open upon receipt a signal on line 12/16 and a longer, constant time to close once the signal is removed from line 12/16. Since the times taken to open and close the valves 28 do not reduce with increasing engine speed, they have a marked effect on the timing of the valves 28 (with respect to crank angle) as the engine speed increases, the opening of the valves becoming retarded, and the closing of the valves becoming even more retarded, as engine speed increases, with the consequent disadvantages described above.

To alleviate these disadvantages, the modifications now described are made. Each air starting valve 28 is fed from the manifold 26 by a respective solenoid valve 36 via lines 38,40, 16, the changeover valves 20 being switched to connect lines 40 ratherthan lines 12 to lines 16. Referring now also to Figure 2, the solenoid valves 36 are electrically actuated by a microprocessor 42 via respective relays 44 or equivalent solid state devices. Conveniently, the manifold valve 22 is also fed by a solenoid valve 46, actuated by a relay 48 driven by the MPU 42. The pneumatic line 50 connecting the solenoid valve 46 to the supply 24 may include a turning gear interlock 52 to prevent starting of the engine if the turning gear is engaged.

An opto-electronic angle encoder 54 or other suitable device is driven by or in synchronism with the engine camshaft 56 and produces binary coded electrical signals which are fed to the MPU 42. From these signals the absolute crankicamshaft angle of the engine can be determined. The MPU is also connected to an isolation switch 58, which is opened when the engine is to be started using the known system to disable the MPU controlled starting programme. Furthermore, the MPU is arranged to receive "ahead" or "astern" signals on electrical lines 60, 62, and is also provided with RAM and ROM. All inputs to and outputs from the MPU are connected via opto-isolators.

The MPU is programmed to operate as follows: 1. Upon receipt of an "ahead" or "astern" signal on line 60 or 62, the MPU checks the state of the isolation switch 58 and also checks the angle encoder 54 to determine whether or not the engine is turning. if the switch 58 is open, or if the engine is turning, then the program is terminated. If the switch is closed and the engine is stationary, then: 2. The MPU operates relay 48 to open solenoid valve 46, open the manifold valve 22 and pressurise the manifold 26.

3. The MPU selects an "ahead" or "astern" firing order array from memory dependent upon whether an ahead or astern signal was received at stage 1.

4. From the shaft encoder signal and selected firing order array, the MPU determines which engine cylinder should be pressurised initially and operates the appropriate relay 44 to cause that cylinder to be pressurised.

5. From the shaft encoder signal and the signal read during stage 4, the MPU determines whether the engine has turned in the correct direction. If it has not turned or has turned in the wrong direction, then all relays 44, 48 are de-activated and the program returns to stage 2 and repeats a maximum of two more times, and then if the engine still does not turn in the correct direction, the program is terminated. If, however, the engine has turned in the correct direction, then: 6. The MPU continues cyclicly reading the shaft angle encoder signal, the firing order array and an "advance" memory, and by comparison with the last read encoder signal and the MPU clock can determine which relays 44 to open and close and when, dependent upon camshaft angle and camshaft speed, in order to pressurise the correct engine cylinders at the appropriate time and for the appropriate period. Stage 6 continues for a predetermined time sufficient normally for the engine to reach sufficient speed for firing to begin, and then the program is terminated.

The function of the advance memory used in stage 6 is to cause the crank angle at which each relay 44 is opened to be advanced with increasing engine speed in order to counteract the effect of the sluggishness in closing of the respective air start valve 28. Further, advance memory is preferably also used to cause the crank angle atwhich each relay 44 is closed to be advanced to a lesser extent upon increasing engine speed on account of the sluggishness in opening of the respective air start valve 28.

Claims

1. A starting installation for a piston engine, comprising for the or each cylinder a remotely actuable valve for communicating that cylinder intermittently with a supply of compressed gas to turn the engine, and further comprising a control arrangement having means to detect the engine position and speed and having further means to provide a signal to the or each valve to cause that valve to open and close with engine rotation, the control arrangement including means to advance with respect to engine position the signal to the or each valve to close that valve as engine speed increases.

2. An installation as claimed in Claim 1, wherein the control arrangement further includes means to advance with respect to engine position the signal to the or each valve to open that valve upon increasing engine speed to a lesser extent than the advance of the signal to close that valve.

3. An installation as claimed in Claim 1, wherein the control arrangement is such that the timing of the signal to the or each valve to open that valve is independent of engine speed.

4. A starting installation for a marine piston engine substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

5. A marine piston engine fitted with an installation as claimed in any of Claims 1 to 4.

6. A method of starting a piston engine, wherein compressed gas is supplied intermittently to the or each engine cylinder via a or a respective remotely actuable valve to cause the engine to turn, wherein a or a respective signal is supplied intermittently to the or each valve to cause that valve to open and close to cause said intermittent supply of compressed gas, and wherein the signal supplied to the or each valve to cause that valve to close is advanced with respect to engine position upon increasing engine speed.

7. A method as claimed in Claim 6, wherein the timing of the signal supplied to the or each valve to cause that valve to open is independent of engine speed, or is advanced with respect to engine position upon increasing engine speed to a lesser extent than the advance of the signal to close that valve so that the difference in engine position between supply of the signals to open and close that valve reduces with increasing engine speed.

8. A method of starting a marine piston engine substantially as hereinbefore described with reference to the accompanying drawings.