WO2008104780A1

WO2008104780A1 - Camshaft drive

Info

Publication number: WO2008104780A1
Application number: PCT/GB2008/000675
Authority: WO
Inventors: Keith M. Macaskill
Original assignee: Dakota Ltd Gibraltar
Priority date: 2007-02-28
Filing date: 2008-02-28
Publication date: 2008-09-04
Also published as: GB2447034A; GB0703900D0

Abstract

A drive means for a camshaft is constituted by a drive motor (4) and control means (5, 6) for controlling the output speed of the drive motor in dependence upon the rotational speed of an associated crankshaft (1).

Description

Camshaft Drive

This invention relates to a drive means for a camshaft of an internal combustion engine, and to an internal combustion engine including such a camshaft drive.

An internal combustion engine utilises the principal that thermal energy which is released when fuel is burnt is converted into mechanical energy. An internal combustion engine usually has a plurality of cylinders (typically four cylinders, six cylinders or eight cylinders), in each of which a combustible mixture of air and fuel (either petrol or diesel) is compressed and ignited. The gases which are formed in each cylinder by the combustion expand and thrust an associated piston downwards, acting through a connecting rod to impart rotary motion to a crankshaft. The spent burned gases must then be removed from each of the cylinders, and replaced by a fresh fuel/air mixture. Control of the entry of air/fuel into the cylinders and exhaustion of spent burnt gases is controlled by inlet and outlet valves provided on the cylinders, and the operation of the valves is controlled by one or more camshafts driven by the crankshaft.

The or each camshaft is typically driven by the crankshaft via a timing chain, a belt, or by direct gearing. In each case, approximately fifteen to twenty percent of the power produced by the engine is spent operating the valves via the camshaft(s).

An aim of the invention is to provide a camshaft drive which requires a smaller power input from the crankshaft, thereby to improve the efficiency of the engine, to provide better fuel economy, and to reduce engine emissions.

The present invention provides a drive means for a camshaft, the drive means being constituted by a drive motor and control means for controlling the output speed of the drive motor in dependence upon the rotational speed of an associated crankshaft.

In a preferred embodiment, the drive means further comprises a plurality of transducers associated with the crankshaft, and a sensor associated with the control means, the arrangement being such that the control means controls the output speed of the motor in dependence upon the rotational speed of the crankshaft as determined by the number of transducer output signals sensed by the sensor in a predetermined time.

The motor may be an electric motor or an hydraulic motor.

The invention also provides an internal combustion engine comprising a plurality of cylinders whose pistons are drivably engageable with a crankshaft, and at least one camshaft for operating inlet and outlet valves associated with the cylinders, wherein the or each camshaft is driven by drive motor means, and control means are provided for controlling the output speed of the drive motor means in dependence upon the rotational speed of the crankshaft.

Preferably, the control means is a microprocessor provided with a sensor for detecting signals output by a plurality of transducers mounted for rotation with the crankshaft.

Advantageously, the transducers are equidistantly spaced around the circumference of the crankshaft.

In a preferred embodiment, there are two camshafts and a single drive motor drivably engageable therewith. Alternatively, there are two camshafts, each of which is provided with a respective drive motor.

The invention will now be described in greater detail, by way of example, with reference to the drawings, in which:-

Figure 1 is a schematic representation of a first camshaft drive constructed in accordance with the invention;

Figure 2 is a schematic representation of a second camshaft drive constructed in accordance with the invention;

Figure 3 is a schematic representation of a modified form of the camshaft drive of Figure 2; and Figure 4 is a schematic representation of another modified form of the camshaft drive of Figure 2.

Referring to the drawings, Figure 1 shows a crankshaft 1 of an internal combustion engine (most of which is not shown), and a pair of camshafts, of which only the toothed drive gear wheels 2 are shown. The camshafts drive the inlet and outlet valves (not shown) of the cylinders (not shown) of an internal combustion engine. The drive gear wheels 2 are in drivable engagement with a driven gear wheel 3 attached to the output shaft of an electric motor 4. The output speed of the motor 4 is controlled by a microprocessor 5.

A plurality of transducers 6 are positioned equidistantly around the circumference of the crankshaft 1 , and a sensor (not shown) associated with the microprocessor 5 is positioned to sense output signals from the transducers as the crankshaft rotates. The microprocessor 5 can, therefore, calculate the rotational speed of the crankshaft 1 by counting the number of output signals from the transducers 6 per unit time. Usually, each camshaft should rotate at half the speed of the crankshaft 1 , and the microprocessor 5 is programmed accordingly to effect this control of the camshaft. The motor 4 is powered by either the battery (not shown) or the alternator (not shown) associated with the internal combustion engine.

Figure 2 shows a modified camshaft drive which is basically similar to that of Figure 1 , but utilises individual hydraulic motors 14 associated with each of the camshafts. Each hydraulic motor 14 is provided with an output gear wheel 15 which meshes with the drive gear wheels 2 of the camshafts. A respective small electric pump (not shown) is associated with each of the hydraulic motors 14. The camshaft drive of Figure 2 operates in the same way as the camshaft drive of Figure 1. This arrangement does, however, have an advantage in that the electric pumps needed to drive the hydraulic motors 14 can be quite small, and so can be operated with a smaller current than the electric motor 4 of Figure 1 , thereby providing a further reduction in the power needed to drive the camshafts.

Figure 3 shows a modified version of the camshaft drive of Figure 2. Here, the associated internal combustion engine (not shown) has a single camshaft (not shown). The camshaft is driven by a hydraulic motor 24 whose output gear wheel (not shown) meshes with a drive wheel (not shown) of the camshaft. The hydraulic motor 24 is connected to a compressor pump and oil reservoir 25 via pipes 26 and 27, each of which is provided with a one-way valve 26a, 27a. The compressor pump 25 is powered by an electric motor (not shown) which, in turn, is controlled by a microprocessor 28 which is similar to the microprocessor 5 of the embodiments of Figures 1 and 2. As with those embodiments, the microprocessor 28 calculates the rotational speed of the associated crankshaft (not shown) by counting the number of output signals from transducers (not shown) positioned around the crankshaft in a similar manner to the way in which the sensors 6 are positioned around the crankshaft 1 of the embodiments of Figures 1 and 2. The one-way valves 26a, 27a ensure that the pressure of hydraulic fluid supplied to the pump 25 by the motor 24 remains substantially constant.

The embodiment of Figure 4 is similar to that of Figure 3, in that a compressor pump and oil reservoir 25 is supplied with hydraulic fluid from a hydraulic motor 24 via pipes 26, 27 controlled by one-way valves 26a, 27a. As with the embodiment of Figure 3, the hydraulic motor 24 is associated with a single camshaft (not shown) of an associated internal combustion engine. The main difference between the embodiment of Figure 4 and that of Figure 3 is that the compressor pump 25 is directly driven by a belt drive 28 from a crank pulley 29 associated with the crankshaft (not shown) of the internal combustion engine. In this embodiment, therefore, there is no need for either a microprocessor or sensors associated with the crankshaft.

It will be apparent that modifications could be made to the camshaft drives described above. In particular, the sensors of the embodiments of Figures 1 to 3 could be associated with the ignition system of the associated internal combustion engine. Moreover, for a diesel engine, the sensors could be provided on the fuel injection devices, or be associated with the injection pump.

It will be apparent that each of the camshaft drives described above has the advantage of a reduced power loss. Another important advantage is that the drive to the camshafts is infinitely variable, so that control of the valve timings is also infinitely variable. These advantages lead to a better fuel economy and a reduction in engine emissions.

Claims

1. A drive means for a camshaft, the drive means being constituted by a drive motor and control means for controlling the output speed of the drive motor in dependence upon the rotational speed of an associated crankshaft.

2. A drive means as claimed in claim 1, further comprising a plurality of transducers associated with the crankshaft, and a sensor associated with the control means, the arrangement being such that the control means controls the output speed of the motor in dependence upon the rotational speed of the crankshaft as determined by the number of transducer output signals sensed by the sensor in a predetermined time.

3. A drive means as claimed in claim 1 or claim 2, wherein the motor is an electric motor.

4. A drive means as claimed in claim 1 or claim 2, wherein the motor is an hydraulic motor powered by an electric pump.

5. A drive means as claimed in any one of claims 1 to 4, wherein the drive motor has a output drive gear wheel drivably engageable with a complementary gear wheel fixed to the camshaft.

6. A drive means as claimed in any one of claims 1 to 4, wherein the drive motor has an output drive gear wheel in drivable engagement with respective gear wheels fixed to each of two camshafts.

7. An internal combustion engine comprising a plurality of cylinders whose pistons are drivably engageable with a crankshaft, and at least one camshaft for operating inlet and outlet valves associated with the cylinders, wherein the or each camshaft is driven by drive motor means, and control means are provided for controlling the output speed of the drive motor means in dependence upon the rotational speed of the crankshaft.

8. An engine as claimed in claim 7, wherein the control means is a microprocessor provided with a sensor for detecting signals output by a plurality of transducers mounted for rotation with the crankshaft.

9. An engine as claimed in claim 8, wherein the transducers are equidistantly spaced around the circumference of the crankshaft.

10. An engine as claimed in any one of claims 7 to 9, wherein there are two camshafts and a single drive motor drivably engageable therewith.

11. An engine as claimed in anyone of claims 7 to 9, wherein there are two camshafts, each of which is provided with a respective drive motor.

12. An engine as claimed in any one of claims 7 to 9, wherein there is a single camshaft and a single drive motor drivably engageable therewith.

13. An engine as claimed in any one of claims 10 to 12, wherein the or each motor is an electric motor.

14. An engine as claimed in any one of claims 10 to 12, wherein the or each motor is an hydraulic motor driven by an electric pump.

15. An engine as claimed in claim 15 when appendant to claim 12, wherein the hydraulic motor is fluidly connected to the pump by inlet and outlet pipes, each of which is provided with a one-way valve.

16. An engine as claimed in claim 7, wherein a drive motor drivably engages a single camshaft, the motor being an hydraulic motor driven by an electric pump, and the pump being directly driven from the crankshaft by a belt drive.

17. An engine as claimed in claim 16, wherein the hydraulic motor is connected to the pump by inlet and outlet pipes, each of which is provided with a one-way valve.