GB2536760A

GB2536760A - A hot gas pulse generator and a turbocharger testing apparatus including same

Info

Publication number: GB2536760A
Application number: GB1521435.6A
Authority: GB
Inventors: Charles Capon Geoff; Witt Dennis; Copeland Colin; Akehurst Sam
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2015-12-04
Filing date: 2015-12-04
Publication date: 2016-09-28
Anticipated expiration: 2035-12-04
Also published as: DE102016121974A1; GB2536760B; GB201521435D0

Abstract

A hot gas pulse generator 10 (100, fig.3) is disclosed having a closed chamber 12 (112, fig.3) arranged for connection to a source of hot pressurised gas via an inlet valve 11 (111, fig.3) and arranged to supply pulses of hot pressurised gas to a turbocharger 20 being tested via an outlet valve 13 (113, fig.3). By varying the frequency of opening of the outlet valve 13 variations in engine speed can be simulated. The volume of the chamber 12 can be changed by either moving a plug 15 (115, fig.3) in a cylinder 16 (116, fig.3) partially defining the chamber 12 or by using different height plugs 15. In either case the magnitude of the hot gas pulse supplied to the turbocharger 20 is changed when the volume of the chamber 12 is changed thereby simulating different engine throttle opening states. A turbo charger testing apparatus and method of use is also disclosed.

Description

Intellectual Property Office Application No. GII1521435.6 RTM Date:26 May 2016 The following terms are registered trade marks and should be read as such wherever they occur in this document: Kratzer Automation Intellectual Property Office is an operating name of the Patent Office www.gov.uk/ipo -1 -A Hot Gas Pulse Generator and a Turbocharger Testing Apparatus including same This invention relates to turbochargers for internal combustion engines and, in particular, to an apparatus for testing a turbocharger in order to establish the operating characteristics of the turbocharger.

Determining the performance characteristics of turbochargers is essential to the matching and optimisation of such turbomachines when applied to diesel and gasoline internal combustion engines.

Traditionally commercial turbocharger testing apparatus (turbocharger gas stands) utilise natural gas burners and are arranged to produce a steady flow of hot pressurised gas to a turbocharger to be tested. A typical turbocharger test stand is capable of producing a hot mass gas flow of up to approximately 0.3 kg/s, uses between 5 and 350kW of power, produces a pressurised hot gas flow of up to 0.8MPa (8 bar) and can generate a hot gas temperature of up to 120000.

However, in use, a reciprocating internal combustion engine provides a highly unsteady pulsating flow to the turbocharger turbine and the performance of a turbocharger obtained under these non-steady state conditions is significantly different from the performance obtained under steady flow conditions using a conventional steady flow turbocharger gas stand.

In addition, if the frequency of exhaust pulses reduces, by, for example reducing engine operation from four cylinders to three cylinders then the flow of exhaust gas to the turbine of a turbocharger will become even more pulsating and unsteady and so the use of a conventional steady flow turbocharger gas stand becomes even less representative of in use conditions. -2 -

Therefore there is a need to provide an apparatus capable of producing a highly pulsating gas flow to a turbine of a turbocharger that can accurately replicate typical flow conditions found during use of an engine.

It is an object of this invention to provide a hot gas pulse generator and a turbocharger testing apparatus capable of producing a pulsating flow of gas to a turbocharger for 10 evaluating the performance of a turbocharger.

Accordingly there is provided a hot gas pulse generator for providing a pulsed supply of hot gas to a turbocharger for testing purposes, the pulse generator being arranged to receive a supply of hot pressurised gas from a source of hot pressurised gas and adapted for connection to a turbocharger to be tested wherein the pulse generator comprises a body defining at least one closed volume chamber, at least one inlet valve to control the flow of gas from the source of hot pressurised gas into the cylinder, at least one outlet valve to control the flow of gas from the at least one cylinder to the turbocharger being tested and a valve control means to control the opening and closing of the at least one inlet and outlet valves to simulate the supply of pulsed exhaust gas from an engine to the turbocharger.

In an embodiment, the valve control means is operable to change the frequency of gas pulses supplied to the turbocharger being tested.

Further, the valve control means may be operable to increase the frequency of gas pulses supplied to the turbocharger being tested at a rate representative of an accelerating engine.

In an embodiment, the valve control means is operable to reduce the frequency of gas pulses supplied to the turbocharger being tested at a rate representative of a decelerating engine.

In an embodiment, the volume of the closed volume 5 chamber is changeable to alter the magnitude of the gas pulse provided to the turbocharger.

In a further embodiment, the volume of the closed chamber is changeable between a minimum volume providing a 10 low magnitude gas pulse state and a maximum volume providing a high magnitude gas pulse state.

In an aspect, there is provided a turbocharger testing apparatus comprising a pulse generator as previously described and a hot pressurised gas generator arranged to supply hot pressurised gas to the pulse generator.

In an embodiment, the apparatus further comprises an electric motor and an electronic controller to control the operation of the electric motor wherein the inlet and outlet camshafts are both rotated by the electric motor in response to a control signal from the electronic controller.

The electronic controller may be operable to control 25 the electric motor to vary the frequency of pulses provided by the pulse generator between a minimum frequency and a maximum frequency representative of an engine.

In an aspect, there is provided a method of testing a turbocharger comprising the steps of:- (a) Attaching the turbocharger to a pulse generator of a turbocharger testing apparatus as claimed in any of claims 10 to 14; and (b) Operating the turbocharger testing apparatus 35 to produce hot gas pulses of known pulse magnitude at different frequencies to simulate the frequency and magnitude of exhaust gas pulses from an engine. -4 -

The method may further comprise the step of:- (c) Changing the pulse magnitude and repeating step (b) to simulate the frequency and magnitude of exhaust gas pulses when the engine is operating in a different state.

Further steps may include: (d) Changing the pressure of the hot gas supplied to the pulse generator and repeating steps (b) and (c); An (e) Changing the temperature of the hot gas supplied to the pulse generator and repeating the steps (b), (c) and (d).

The invention will now be described by way of example with reference to the accompanying drawing of which:-Fig.1 is a schematic representation of a turbocharger testing apparatus in accordance with a second aspect of the invention showing a first embodiment of a pulse generator constructed in accordance with a first aspect of the invention showing the pulse generator in a low magnitude pulse generating state; Fig.2 is a representation similar to Fig.1 but showing the pulse generator in a high magnitude pulse generating state; Fig.3 is an end view of a second embodiment of a pulse generator constructed in accordance with the first aspect of the invention showing the pulse generator in a medium magnitude pulse generating state; Fig.4 is a schematic plan view of the pulse generator shown in Fig.3 showing a valve control means used _ 5 _ to control opening and closing of inlet and outlet valves forming part of the pulse generator; Fig.5 is an exploded view of the pulse generator shown in Figs.3 and 4 in a partially assembled condition; and Fig.6 is a chart showing various combinations of pulse frequency, pulse magnitude and hot gas temperature for simulating a single cylinder four stroke engine.

With particular reference to Figs.1 and 2 there is shown a turbocharger testing apparatus 1 comprising a source of pressurised hot gas in the form of a hot gas generator 2 and a pulse generator 10 (indicated by a broken line on Figs.1 and 2) arranged to receive hot pressurised gas from the hot gas generator 2 and supply it to a turbine 21 of a turbocharger 20 to be tested. The turbocharger 20 also includes a compressor 22 that is driven by the turbine 21 as is well known in the art.

The hot gas generator 2 is of a similar design and construction as that normally used in a conventional Turbocharger Test Stand. Such hot gas generators are commercially available from KRATZER AUTOMATION AG of Gutenberg Strasse 5, Unterschleissheim, Germany.

The pulse generator 10 comprises a body 17 defining a cylinder 16 in which is located a plug 15. The plug 15 and the cylinder 16 define in the case of this example a single closed volume chamber 12. It will be appreciated that the pulse generator in other embodiments could have more than one cylinder, plug and chamber.

The pulse generator 10 is connected to the hot gas generator 2 by a supply conduit 3 that is connected to the pulse generator 10 via an inlet valve 11. The inlet valve 11 controls the flow of gas from the hot gas generator 2 into the chamber 12 to which it is connected via an inlet port 4.

Opening and closing of the inlet valve 11 is controlled by an electronically controlled electrical actuator 32. The electronically controlled actuator 32 is operatively connected to an electronic controller 30 and the operation of the electronically controlled actuator 32 is controlled by the electronic controller 30.

An outlet valve 13 is used to control the flow of hot gas from the chamber 12 to the turbine 21 of the turbocharger 20 being tested. Opening and closing of the outlet valve 13 is controlled by an electronically controlled electrical actuator 34. The electronically controlled actuator 34 is operatively connected to the electronic controller 30 and the operation of the electronically controlled actuator 34 is controlled by the electronic controller 30.

The outlet valve 13 is connected to the chamber 12 via an outlet port 5 and to the turbocharger 20 via a turbocharger supply conduit 6. Gas flows out from the turbine 21 via an exhaust conduit 7 to atmosphere.

It will be appreciated that there could be more than one inlet valve controlling the flow of hot gas into the chamber and/or more than one outlet valve controlling the flow of hot gas from the chamber to the turbocharger.

It will be appreciated that the electrical actuators 32, 34 are required to operate in the vicinity of hot gas and that they are either water cooled from a supply of cooled water and/ or connected to the respective inlet and outlet valves 11, 13 by heat insulating linkages. -7 -

The temperature and pressure of the hot gas supplied by the hot gas generator 2 is measured as indicated schematically by the use of the reference numeral 31 on Figs.1 and 2.

Various sensors are provided to measure the operation of the turbocharger 20 such as, for example and without limitation, rotational speed of the turbocharger 20, hot gas pressure upstream and/or downstream of the turbine 21, hot gas temperature upstream and/or downstream of the turbine 21, mass flow rate of the hot gas entering and/or leaving the turbine 21, mass flow rate of the compressed air produced by the compressor 22, temperature of the air flowing in and/or out from the compressor 22, pressure of the air flowing in and/or out of the compressor. These sensors are indicated schematically on Figs.1 and 2 by the reference numeral 25.

In Fig.1 the plug 15 is positioned high in the cylinder 16 so that the volume of the chamber 12 is at a minimum volume designed to simulate a closed throttle state of an engine whereas in Fig.2 the plug 15 is positioned low in the cylinder 16 so that the volume of the chamber 12 is at a maximum volume designed to simulate a wide open throttle state of an engine.

When the volume of the chamber 12 is set to a minimum value it is said to be in a low magnitude gas pulse state and the magnitude of the gas pulses supplied to the turbine 30 will be at a minimum.

When the volume of the chamber 12 is set to a maximum value it is said to be in a high magnitude gas pulse state and the magnitude of the gas pulses supplied to the turbine 35 will be at a maximum. -8 -

The volume of the chamber 12 is therefore changeable between the low-magnitude gas pulse state and the high magnitude gas pulse state in order to simulate various throttle opening positions of an engine.

In the case of the example shown in Figs.1 and 2 the plug 15 is shown displaceable between high in cylinder 16 and low in cylinder 16 positions and it will be appreciated that an actuator (not shown) such as, for example and without limitation, a crank similar to that used in a conventional reciprocating piston engine is provided to effect such movement of the plug 15.

In an alternative embodiment the plug 15 can be mounted in a fixed position in the cylinder 16 and a number of plugs of differing height can be used to produce the change in chamber volume. For example and without limitation, there may be a low chamber volume plug of diameter 0.05m and height 0.075m; a medium chamber plug of diameter 0.05m and height 0.06m and high chamber volume plug of diameter 0.05m and height 0.045m.

Operation of the turbocharger testing apparatus 1 is as follows.

A turbocharger 20 to be tested is attached to the turbocharger supply conduit 6 ready for testing.

The volume of the chamber 12 is set to simulate a desired engine throttle position.

The hot gas generator 2 is started and controlled to produce a hot gas flow of known pressure and temperature such as, for example, 750°C and 0.8MPa (8 Bar).

The inlet and outlet valves 11 and 13 are then operated to produces hot gas pulses to the turbocharger 20 of a known _ 9 _ frequency to simulate operation of an engine operating at a particular rotational speed.

The response of the turbocharger to this set of operating parameters is then recorded and the frequency of the hot gas pulses supplied to the turbocharger 20 is changed by controlling the opening and closing of the inlet and outlet valves 11 and 13. It will be appreciated that in order to increase the frequency of the hot gas pulses the frequency at which the outlet valve 13 has to be opened is increased and vice-versa.

The frequency of the pulses of hot gas supplied to the turbocharger 20 is changed through a range of frequencies between a minimum frequency and a maximum frequency chosen to represent the expected exhaust gas pulses from an engine when operating between chosen minimum and maximum rotational speeds such as, for example, idle speed and maximum permitted operating speed. It will be appreciated that acceleration of an engine can be simulated by increasing the frequency of pulses from the pulse generator 10 over time at a rate corresponding to an expected increase in frequency of pulses from an engine when it is accelerating. It will be further appreciated that a slowing engine can be simulated by decreasing the frequency of pulses from the pulse generator 10 over time a rate corresponding to an expected decrease in frequency of pulses from an engine when it is slowing.

After a full sweep of pulse frequencies has been completed either the volume of the chamber 12 can be changed and the process be repeated or the pressure or temperature of the hot gas supplied from the hot gas generator can be changed before repeating the sweep of pulse frequencies.

In most cases the frequency of opening of both the inlet and the outlet valve 11 and 13 are changed to vary the -10 -frequency of hot gas pulses supplied to the turbocharger 20 because such an arrangement better simulates the operation of an engine. However, it will be appreciated that the frequency of opening of the inlet valve 11 need not be varied if the chamber 12 can be filled with hot gas to the required pressure quickly enough using a single frequency.

By using the pulse generator 10 and the turbocharger testing apparatus 1 in this way permits turbocharger performance maps to be generated referencing various frequencies, chamber volumes (pulse magnitudes), hot gas pressures and hot gas temperatures. Such maps can be used when evaluating the suitability of a turbocharger for a new engine application to establish whether the turbocharger has the characteristics required for the proposed application.

For example, a three dimensional turbocharger map referencing pulse frequency versus pulse magnitude and hot gas pressure can be generated for use as an application guide tool.

It will also be appreciated that data produced by turbocharger testing can be arranged in tabular form that can be saved in an electronic processor or apparatus in the form of one or more look-up tables.

Fig.6 shows in tabular form one non-limiting example of the test results that can be generated when using a turbocharger testing apparatus in accordance with this invention. In the example provided the pulse frequency is varied from 5 hertz to 70 hertz for three chamber volumes referred to as high, medium and small and for three different hot gas supply pressures of 0.4MPa, 0.6MPa and 0.8MPa. The chosen combination of pulse frequency, pressure and pulse magnitude is representative of a typical range of engine operating conditions.

It will be appreciated that the inlet and outlet valves 11 and 13 need not be operated by electronically controlled actuators and that other means such as for example mechanical cams (such as described hereinafter with respect to Figs.3 to 5) could be used to operate the inlet and outlet valves 11 and 13.

Irrespective of the type of valve actuation used, the valve actuation must be sufficiently powerful to open and/or close the inlet and outlet valves 11 and 13 when they are subject to the high gas pressures required for turbocharger testing.

It will be further appreciated that the inlet and outlet valves 11 and 13 and other components of the pulse generator 10 are subject to high temperatures representative of engine exhaust gas temperatures such as, for example, temperatures up to 100000 and so must be made of materials able to withstand high pressure at such a high temperature.

Although the invention has been described with reference to an embodiment in which a single electronic controller 30 is used to control the operation of the inlet and outlet valves 11 and 13 and to collect data from the sensors 25, 31 it will be appreciated that there could be several electronic units provided and that the control of the pulse generator 10, the control of the hot gas generator 2 and the acquisition of data from the sensors 25, 31 could be performed by separate electronic devices.

With reference to Figs.3 to 5 there is shown a pulse generator 100 having three cylinders 116 designed to simulate the operation of a three cylinder four stroke internal combustion engine.

As before the pulse generator 100 forms part of a turbocharger testing apparatus comprising a source of -12 -pressurised hot gas such as a hot gas generator (not shown) and the pulse generator 100. As before the pulse generator 100 is arranged to receive a supply of hot pressurised gas from the hot gas generator and supply hot gas pulses to a turbocharger (not shown) to be tested.

As previously referred to, the hot gas generator can be of a similar design and construction as that normally used in a conventional Turbocharger Test Stand such a hot gas generator of the type commercially available from KRATZER AUTOMATION AG of Gutenberg Strasse 5, Unterschleissheim, Germany.

The pulse generator 100 comprises a body 117 defining three cylinders 116 in each of which is fitted a plug 115.

The plugs 115 and the cylinders 116 define in the case of this example three closed volume chambers 112 of which only one is shown in Fig.3.

A cylinder head 140 which, in the case of this example is in the form of a modified existing cylinder head from an engine, is attached to an upper end of the body 117 via an adaptor plate 102. Each of the plugs 115 is secured in position to a base plate 101 by a threaded fastener 119.

The base plate 101 is secured to the body 117 sometimes referred to as a cylinder block by a number of long threaded fasteners (not shown) that, in the case of this example, extend through apertures in the cylinder head 140 and adaptor plate 102. It will be appreciated that in other embodiments alternative fastening means can be used to secure the cylinder head 140 to the body 117.

In the case of the example shown the height of the plugs 116 has been chosen such that a large chamber volume is produced when the plugs 115 are in position in the cylinders 116. This will produce a high magnitude pulse -13 -when hot gas is flowed through the chambers 112 thereby simulating an engine wide open throttle state.

Alternative plugs are also available for use in vary 5 the volume of the chambers 112 so as to permit various engine throttle opening states to be simulated.

For example and without limitation, there may be a low volume chamber plug of diameter 0.06m and height 0.09m; a medium chamber plug of diameter 0.06m and height 0.075m and the high chamber volume plug of diameter 0.06m and height 0.056m shown in Figs.3 and 5.

When the volume of the chambers 112 are set to a minimum value the pulse generator is said to be in a low magnitude gas pulse state and the magnitude of the gas pulses supplied to the turbocharger will be at a minimum.

When the volume of the chambers 112 are set to a maximum value the pulse generator is said to be in a high magnitude gas pulse state and the magnitude of the gas pulses supplied to the turbocharger will be at a maximum.

The volume of the chambers 112 are therefore changeable between the low-magnitude gas pulse state and the high magnitude gas pulse state by inserting different height plugs 115 in the cylinders 116 and securing them in position to the base plate 101 in order to simulate various throttle opening positions of an engine.

As with the first embodiment moveable plugs could alternatively be used that are displaceable in the cylinders 116 by suitable actuators such as, for example and without limitation, a crankshaft and connecting rod arrangement.

The pulse generator 100 is connected to the hot gas generator by a supply conduit (not shown) that is connected -14 -to an inlet manifold 132 of the pulse generator 100 via a flange 133.

The pulse generator 100 can be connected to the turbocharger to be tested by a turbocharger supply conduit (not shown) that is connected to an outlet manifold 134 of the pulse generator 100 via a flange 135. However, in other cases where the turbocharger is of a close coupled type, the turbocharger can be connected directly to the flange 135 of the outlet manifold 134.

Hot gas from the hot gas generator enters the chambers 112 of the pulse generator 100 via, in the case of this example, three inlet ports 103 defined in the cylinder head 140. Although in the case of this example each of the chambers 112 is supplied with hot gas via a single respective inlet port 103, it will be appreciated that, each chamber 112 could alternatively be supplied with hot gas through more than one inlet port.

The flow of hot gas from each inlet port 103 into the associated chamber 112 is controlled, in the case of this example, by a single inlet valve 111 there being three inlet valves 111 in total. It will however be appreciated that there could be more than one inlet valve arranged to control the flow of hot gas to each chamber 112 particularly if more than one inlet port is provided per chamber 112.

Each of the inlet valves is in the form of a conventional poppet valve 111 that is held closed by a respective helical valve spring 145 and is opened by a valve actuator in the form of a respective cam 142 mounted on a inlet camshaft 141. As is well known in the art, an inlet valve shim 143 is interposed between each of the inlet cams 142 and the inlet valve 111 that it operates.

-15 -The inlet camshaft 141 is rotated by an electric motor 152 in response to a control signal from a controller 130.

Hot gas from the pulse generator 100 exits the chambers 112 of the pulse generator 100 via, in the case of this example, three outlet ports 105 defined in the cylinder head 140. Although in the case of this example each of the chambers 112 is connected to a single respective outlet port 105, it will be appreciated that, each chamber 112 could be connected to more than one outlet port.

Hot gas flows in use from the chambers 112 through the outlet ports 105 to the outlet manifold 134 and from there to the turbocharger being tested.

The flow of hot gas through each outlet port 105 into the outlet manifold 134 is controlled, in the case of this example, by a single outlet valve 113 there being three outlet valves 113 in total. It will however be appreciated that there could be more than one outlet valve arranged to control the flow of hot gas from each chamber 112.

Each of the outlet valves is in the form of a conventional poppet valve 113 that is held closed by a respective helical valve spring 146 and is opened by a valve actuator in the form of a respective cam 144 mounted on a outlet camshaft 147. As is well known in the art, an outlet valve shim 145 is interposed between each of the outlet cams 144 and the outlet valve 113 that it operates.

The outlet camshaft 147 is rotated by an electric motor 154 in response to a control signal from the controller 130.

It will be appreciated that by using two electric 35 motors 152, 154 to control the opening of the inlet and outlet valves 111 and 113 the phasing and duration of the -16 -inlet and outlet valves 111 and 113 can independently be controlled.

By varying the rotational speed of the two electric motors the frequency of hot gas pulses supplied to the turbocharger being tested can be changed between minimum and maximum frequencies to simulate various operating speeds of an engine.

However it will be appreciated that both of the camshafts 141, 147 could alternatively be driven by a single electric motor. If a single electric motor is used the phasing of the inlet and outlet valves could be adjuster using a convention cam phase adjusting mechanism.

As before, the temperature and pressure of the hot gas supplied by the hot gas generator will be measured and various sensors (not shown) are provided to measure the operation of the turbocharger so as to provide the required data for evaluating its performance.

These sensors could include, for example and without limitation, rotational speed of the turbocharger, hot gas pressure upstream and/or downstream of the turbocharger, hot gas temperature upstream and/or downstream of the turbocharger, mass flow rate of hot gas entering and/or leaving the turbocharger, mass flow rate of compressed air produced by the turbocharger, temperature of the air flowing in and/or out from the turbocharger, pressure of the air flowing in and/or out of the turbocharger.

Operation of the turbocharger testing apparatus is much as before.

A turbocharger to be tested is attached to the flange on the outlet manifold 134 ready for testing.

-17 -The volume of the chambers 112 is set to simulate a desired engine throttle position by fixing in position plugs 115 of the required height.

The hot gas generator is started and controlled to produce a hot gas flow of known pressure and temperature.

The inlet and outlet valves 111 and 113 are then operated to produces hot gas pulses to the turbocharger of a known frequency to simulate operation of an engine operating at a particular rotational speed.

The response of the turbocharger to this set of operating parameters is then recorded and the frequency of the hot gas pulses supplied to the turbocharger is changed by the electronic controller 130 which changes the rotational speed of the electric motors 152, 154 thereby controlling the frequency of opening and closing of the inlet and outlet valves 111 and 113. It will be appreciated that in order to increase the frequency of the hot gas pulses the frequency at which the outlet valves 113 are opened has to be increased and vice-versa.

In most cases the frequency of opening of the inlet and the outlet valves 111 and 113 of each chamber 112 are both changed to vary the frequency of hot gas pulses supplied to the turbocharger because such an arrangement better simulates the operation of an engine. However, it will be appreciated that the frequency of opening of the inlet valves 111 need not be varied if the chambers 112 can be filled with hot gas to the required pressure quickly enough.

The frequency of the pulses of hot gas supplied to the turbocharger is changed through a range of frequencies between a minimum frequency and a maximum frequency chosen to represent the expected exhaust gas pulses from an engine when operating between chosen minimum and maximum rotational -18 -speeds such as, for example, idle speed and maximum permitted operating speed.

After a full sweep of frequencies simulating acceleration or deceleration of an engine has been completed the process is repeated for a different hot gas pressure or for a different hot gas temperature.

The volume of the chambers 112 is then changed by replacing plugs 115 of one height with plugs 115 of a different height. It will be appreciated that although three sets of plug of differing height are referred to herein there could be more or less sets of plugs.

After completing testing the turbocharger for various combinations of pulse frequency, pulse pressure, pulse magnitude and hot gas temperature one or more turbocharger performance maps can be generated referencing various frequencies, chamber volumes (pulse magnitudes), hot gas pressures and hot gas temperatures.

For example and without limitation a three dimensional turbocharger map referencing pulse frequency versus pulse magnitude and hot gas pressure can be generated.

In one particularly economical embodiment of a hot gas pulse generator, a conventional cylinder head was adapted to receive a pressurized steady hot gas flow from a turbocharger gas stand and produce hot gas pulses representative of engine exhaust pulses.

The use of an existing cylinder head design was advantageous in that it was representative of a typical exhaust valve and exhaust manifold flow path to a turbocharger turbine. The intake valves used were replaced with valves able to withstand the high gas temperatures present at the inlet to the pulse generator. The use of -19 -intake valves manufactured from the same or a similar material to that conventionally used for exhaust valves solved this problem.

The control of the cams used to operate the inlet and outlet valves was provided by using a single electric motor using conventional camshaft phaser technology to drive both inlet and outlet camshafts.

However, servo control of the camshafts using separate electric motors for the inlet and outlet camshafts would be readily useable.

The inlet and outlet valves were operated using a conventional return spring and cam arrangement. However, the spring rate used for the inlet valves was uprated to prevent the inlet valves blowing open when subject to the pressurised hot gas from the hot gas generator. The use inlet valve springs having a spring rate of 450N/m were found to be effective in preventing unintentional opening of the inlet valves.

The replacement of the conventional spring and cam valve actuation mechanism with a desmodromic mechanism would 25 be possible and would potentially overcome the problem of unintentional inlet valve opening.

It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to one or more embodiments it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

-20 -Claims 1. A hot gas pulse generator for providing a pulsed supply of hot gas to a turbocharger for testing purposes, the pulse generator being arranged to receive a supply of hot pressurised gas from a source of hot pressurised gas and adapted for connection to a turbocharger to be tested wherein the pulse generator comprises a body defining at least one closed volume chamber, at least one inlet valve to control the flow of gas from the source of hot pressurised gas into the cylinder, at least one outlet valve to control the flow of gas from the at least one cylinder to the turbocharger being tested and a valve control means to control the opening and closing of the at least one inlet and outlet valves to simulate the supply of pulsed exhaust gas from an engine to the turbocharger.
2. A pulse generator as claimed in claim I wherein the valve control means is operable to change the frequency 20 of gas pulses supplied to the turbocharger being tested.
3. A pulse generator as claimed in claim 2 wherein the valve control means is operable to increase the frequency of gas pulses supplied to the turbocharger being tested at a rate representative of an accelerating engine.
4. A pulse generator as claimed in claim 2 wherein the valve control means is operable to reduce the frequency of gas pulses supplied to the turbocharger being tested at a rate representative of a decelerating engine.
5. A pulse generator as claimed in any of claims 1 to 4 wherein the volume of the closed volume chamber is changeable to alter the magnitude of the gas pulse provided to the turbocharger.

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6. A pulse generator as claimed in claim 5 wherein the volume of the closed chamber is changeable between a minimum volume providing a low magnitude gas pulse state and a maximum volume providing a high magnitude gas pulse state.
7. A pulse generator as claimed in claim 6 wherein, in the low magnitude gas pulse state, the pulse generator produces a gas flow to the turbocharger representative of an engine throttle closed state.
8. A pulse generator as claimed in claim 6 wherein, in the high magnitude gas pulse state, the pulse generator produces a gas flow to the turbocharger representative of an engine wide open throttle state.
9. A pulse generator as claimed in any of claims 1 to 8 wherein the at least one inlet valve is a poppet valve actuated by a cam on an inlet camshaft and the at least one outlet valve is a poppet valve actuated by a cam on an outlet camshaft.
10. A turbocharger testing apparatus comprising a pulse generator as claimed in any of claims 1 to 9 and a hot pressurised gas generator arranged to supply hot pressurised gas to the pulse generator.
11. An apparatus as claimed in claim 10 when dependant upon claim 9 in which the apparatus further comprises an electric motor and an electronic controller to control the operation of the electric motor wherein the inlet and outlet camshafts are both rotated by the electric motor in response to a control signal from the electronic controller.
12. An apparatus as claimed in claim 11 wherein the electronic controller is operable to control the electric motor to vary the frequency of pulses provided by the pulse -22 -generator between a minimum frequency and a maximum frequency representative of an engine.
13. An apparatus as claimed in claim 10 when dependant upon claim 9 in which the apparatus further comprises first and second electric motors and an electronic controller to control the operation of the first and second electric motors wherein the inlet camshaft is rotated by the first electric motor in response to a control signal from the electronic controller and the outlet camshaft is rotated by the second electric motor in response to a control signal from the electronic controller.
14. An apparatus as claimed in claim 13 wherein the electronic controller is operable to control the electric motors to vary the frequency of pulses provided by the pulse generator between a minimum frequency and a maximum frequency representative of an engine.
15. A method of testing a turbocharger comprising the steps of:- (a) Attaching the turbocharger to a pulse generator of a turbocharger testing apparatus as claimed in any of claims 10 to 14; and (b) Operating the turbocharger testing apparatus to produce hot gas pulses of known pulse magnitude at different frequencies to simulate the frequency and magnitude of exhaust gas pulses from an engine.
16. A method as claimed in claim 15 wherein the method further comprises the step of:- (c) Changing the pulse magnitude and repeating step (b) to simulate the frequency and magnitude of exhaust gas pulses when the engine is operating in a different state.

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17. A method as claimed in claim 16 wherein the method further comprises repeating step (c) until a full range of pulse magnitudes and frequencies has been simulated.
18. A method as claimed in claim 16 or in claim 17 wherein the method further comprises the step of:- (d) Changing the pressure of the hot gas supplied to the pulse generator and repeating steps (b) and (c).
19. A method as claimed in claim 18 wherein the method further comprises the step of:- (e) Changing the temperature of the hot gas supplied to the pulse generator and repeating the steps (b), (c) and (d).
20. A hot gas pulse generator substantially as described herein with reference to the accompanying drawing.
21. A turbocharger testing apparatus substantially as 20 described herein with reference to the accompanying drawing.
22. A method of testing a turbocharger substantially as described herein with reference to the accompanying drawing.