GB2078984A - Dynamometers - Google Patents

Abstract

A dynamometer for testing internal combustion engines has an input coupling 112 rotatable about an axis 126 and arranged for connection tot e engine to be tested. An hydraulic pump 109 is driven from the input coupling and is fixed to a manifold 114 connected via a load cell to the dynamometer frame 101. A fixed manifold 125 is mounted on the frame 101 and is connected to the pump manifold 114 by conduits 122, 123, 124. The conduits are pivoted to the pump manifold 114 at the axis 126, which intersects the respective conduit axes. Thus, the forces resulting from the fluid under pressure in the conduits and in the pump manifold act through the input coupling axis 126 and do not exert any turning moment about this axis. Accordingly, the forces result from the fluid pressure do not affect the measurement of the load applied by the engine being tested, so that the accuracy of the dynamometer is greatly improved. <IMAGE>

Description

SPECIFICATION Improvements in or relating to dynamometers The present invention relates to dynamometers, for instance of the regenerative type. Such dynamometers may be used for testing internal combustion engines.

According to the invention, there is provided a dynamometer comprising an input coupling rotatable about an axis for connection to an engine to be tested, an hydraulic pump arranged to be driven from the input coupling, a fixed manifold, and a plurality of conduits interconnecting the pump and the fixed manifold and arranged so that fluid pressure in the conduits produces no turning moment aboutthe input coupling axis.

Preferably, the pump is coaxial with the input coupling. Preferably, the pump is provided with a pump manifold defining a plurality of chambers and the conduits are arranged to enter into the respective chambers with their axes passing through the input coupling axis, the conduits being pivoted to the pump manifold about the input coupling axis, for instance by means of O-rings.

Preferably, the pump manifold is fixed at one end to the pump and is pivotably mounted, for instance by a trunnion bearing coaxial with the input coupling axis, at its other end to a fixed frame of the dynamometer.

Preferably, the pump manifold is connected via a load cell to the fixed frame of the dynamometer.

Preferably, the conduits extend from the pump manifold manifold on opposite sides of the input coupling axis.

Preferably, the conduits extend in parallel in a first direction from the pump manifold and a further conduit extends in the opposite direction to a fixed member with its axis passing through the input coupling axis, the further conduit being pivoted to the pump manifold about the input coupling axis.

Preferably, the further conduit is pivoted at its ends to the pump manifold and to the fixed member by means of respective O-rings.

Preferably, the further conduit is arranged to communicate with the plurality of chambers in the pump manifold via passageways and there is provided a shuttle valve arranged to allow the further conduit to communicate with the chamber containing fluid at the highest pressure.

Preferably, there are a plurality of hydraulic pumps disposed around the input coupling axis and arranged to be driven from the input coupling, the fixed manifold having fluid input and output chambers disposed coaxially with the input coupling axis, the plurality of conduits connecting the input and output sides of the pumps with the input and output sides, respectively, of the fixed manifold chambers, the conduits being further arranged in relation to the input and output chambers of the fixed manifold so that the forces resulting from fluid pressure in the conduits during operation of the dynamometer act substantially through the inlet coupling axis and the resultant thereof has a substantially zero component in a plane transverse to the input coupling axis.

Preferably the pumps are connected to the input coupling via a load splitting gearbox which is pivotable about the input coupling axis and is connected to a fixed frame of the dynamometer by a load cell.

Preferably the pumps are equiangularly spaced about the input coupling axis. In the case where two pumps are provided, the pumps are disposed on opposite sides of the input coupling axis with their longitudinal axes in a horizontal plane. The pumps are preferably of the same type and are arranged to be driven by the load splitting gearbox or other means at the same speed. The conduits may extend radially with respect to the input coupling axis from the fixed manifold to the pumps. The inlet and outlet chambers of the fixed manifold may be spaced apart longitudinally of the input coupling axis.

Preferably, there are a plurality of manifolds disposed around the input coupling axis, the plurality of conduits connecting the pump to the manifolds and being further arranged so that the forces resulting from fluid pressure in the conduits during operation of the dynamometer act substantially through the inlet coupling axis and the resultant thereof has a substantially zero component in a plane transverse to the input coupling axis.

Preferably, two manifolds are provided on opposite sides of the input coupling axis and the conduits between the pump and the manifolds and between the manifolds extending radially with respect to the input coupling axis.

Preferably, the fixed manifold is hydraulically connected to one or more further hydraulic pumps mechanically connected to an AC motor.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figures 7a and lb show a trunnion mounted regenerative dynamometer; Figure 2 is a plan view of the part of the dynamometer shown in Figure la; Figure 3 is an end view of the part of the dynamometershown in Figure 1a; Figure 4 is a side view of the part of the dynamometer shown in Figure 1a; Figure 5 is a side cross-sectional view of part of a dynamometer which may be used with the part shown in Figure 1b; Figure 6 shows on the left side a front view of the part of the dynamometer of Figure 5 and on the right side a part-sectional view on the line A-A of Figure 5; Figure 7is a part-sectional view on the line C-C of Figure 5;; Figure 8 is a cross-sectional view on the line C-C of Figure 6; Figure 9 is a cross-sectional view of a modified dynamometer similar to that of Figure 5; and Figure 10 is a cross-sectional view on the line D-D of Figure 9.

A regenerative dynamometer as shown in the accompanying drawings comprises a first part (Figure 1a) for connection to an engine to be tested, such as a petrol or diesel engine for a vehicle, and a second part (Figure 1b) including an A.C. motor. The two parts are connected together by high pressure pipe work.

The first part comprises a base 1 on which are mounted brackets 2. An input coupling 3 is rotatably mounted on the front bracket 2 and is connected to the input of a load splitting gearbox 4, which is pivotally mounted between the brackets 2. The gearbox 4 is provided at one side with a bracket 5 which is pivotally connected to one end of a dynamometer load cell 6 whose other end if pivotally connected to another bracket 7 fixed to the base 1.

The gearbox 4 has two output shafts which are connected to two hydraulic pumps/motor 8 so as to drive the two pumps in the same rotary directions.

The pumps/motors are provided with respective pump manifolds 9, which are connected together by tie rods 10 and which are hydraulically connected to a fixed manifold 11 by conduits 12.

The second part of the regenerative dynamometer comprises a frame 13 which supports an hydraulic pump 14 connected to an A.C. motor 15. As an alternative, more than one hydraulic pump may be provided and may be connected to the A.C. motor 15 by means of a load splitting gearbox. An hydraulic oil tank 16 is provided in the frame 13 and includes filters, heat exchangers, and the like. The hydraulic pump 14 is connected to the fixed manifold 11 by means of high pressure pipes 17.

An engine to be tested is connected to the input coupling 3 and drives the hydraulic pumps/motors 8 via the gearbox 4. Hydraulic oil is pumped by the pumps/motors 8 via the pump manifolds 9, the fixed manifold 11, and the pipes 17 to the hydraulic pump 14so that a closed hydraulic circuit is provided. The pump 14 drives the A.C. motor 15. During testing, the A.C. motor 15 may be driven or may be used in a generator mode so that a controlled load is applied to the engine to be tested. Pivoting of the gearbox 4 causes a load corresponding to the load on the engine to be tested to be applied to the load cell 6.

The input coupling 3 has a rotational axis 18 extending longitudinally of the first part of the dynamometer. The gearbox 4 is thus pivotable about the axis 18 and is generally symmetrical with respect thereto. In particular, the outputs of the gearbox 4 and the hydraulic pumps/motors 8 connected thereto are disposed symmetrically with respect to the axis 18 and with their longitudinal axes generally parallel thereto and in a common horizontal plane therewith. Each of the pumps/motors 8 has an inlet and an outlet connected to the respective pump manifold 9. The manifolds 9 have inlet and outlet chambers for hydraulic oil spaced apart longitudinally with respect to the corresponding pump axis.

Similarly, the fixed manifold 11, which is fixed to the base 1, has longitudinally spaced inlet and outlet chambers disposed at the same respective distances from the front of the base 1 as the inlet and outlet chambers of the pump manifolds 9. The inlet and outlet chambers of the pump manifolds 9 are connected to the inlet and outlet chambers, respec tivelyofthefixed manifold 11 by the conduits 12, which extend horizontally between the pump manifolds 9 and the fixed manifolds 11. In particular, the longitudinal axes of the conduits 12 extend through the longitudinal axis of the inlet and outlet chambers of the fixed manifold 11, which latter axis is coaxial with the input coupling axis 18.The conduits 12 are sealed at their ends to the manifolds 9 and 11 by means of O-rings, which allow a small degree of angular movement of each conduit end with respect to the corresponding manifold.

In use, when an engine to be tested is coupled to the input coupling 3, the engine drives the gearbox 4 which in turn drives the hydraulic pumps/motors 8.

The gearbox divides the drive provided by the engine to be tested and supplies this to the hydraulic pumps/motors 8, which are connected in parallel so as to provide a sufficiently large load absorption capacity. Hydraulic oil pumped by the pumps/ motors 8 is supplied to the pump manifolds 9, which have chambers defining passages conducting the inlet and outlet hydraulic oil to and from the horizontal plane containing the input coupling axis 18. The chambers of the pump manifolds 9 at this plane then pass horizontally toward the axis 18 and communicate with the conduits 12, which in turn conduct hydraulic oil to and from the chambers of the fixed manifold 11. The fixed manifold chambers conduit the oil generally downwardly to outlets 19, which communicate with the pipes 17.

The longitudinal axes of the conduits 12 all pass through the axis 18, so that the pressure acting in the conduits 12 during use of the dynamometercreates a force at the fixed manifold 11 which similarly acts through the axis 18. Thus, there exists no turning moment on the gearbox 4 with respect to the fixed manifold 11,so that the passage of the high pressure hydraulic oil through the conduits 12 does not affect pivotal deflection of the gearbox 4, which is measured in the dynamometer cell 6. Also, because the longitudinal axes of the conduits 12 are coplanar and the hydraulic oil pressure in the conduits from each of the pump manifolds 9 is substantially equal, there exists no resultant force due to the hydraulic oil pressure in a plane transverse to the input coupling axis 18.Accordingly, accuracy of measurement by the dynamometer is substantially unaffected by the high pressure hydraulic oil flow through the dynamometer. This is of great advantage as the actual deflection at the load cell 6 caused by testing an engine amounts to only several thousandths of an inch, the corresponding deflection of the conduits 12 being of the order of one thousandth of an inch.

Thus, if the force and turning moment resulting from the flow of high pressure hydraulic oil between the pumpsimotors 8 and the fixed manifold 11 were not neutralized as described above, the very large hydraulic pressures involved could result in substantial errors in measurement, especially at low loading of the engine to be tested. Accordingly, the arrangement described hereinbefore is capable of greatly improved accuracy, especially at low loadings of the engine to be tested.

An alternative arrangement within the scope of the present invention includes a single hydraulic pump/ motor driven by an input coupling and coaxial therewith. The pump/motor is provided with two manifolds, for instance symmetrically disposed generally in a vertical plane through the input coupling axis. Conduits extend from the pump/motor to both manifolds and between the two manifolds. The pump inlet and outlet may, for instance, be substantially coaxial with the input coupling axis, the conduits extending radially from this axis in opposite directions to each other. Similarly, the conduits between the two manifolds extend in a straight line with their axes crossing the input coupling axis.

Thus, forces resulting from the high pressure hydraulic oil in the conduits act through the input coupling axis so that no residual turning moment exists. The resulting forces acting in opposite directions with respect to the input coupling axis can also be balanced so that no net force exists in a plane transverse to the input coupling axis. For instance, the conduits connected to the lower pressure side of the pump/motor may be provided with some form of restriction in order to increase the pressure of the fluid therein so as to balance the forces acting through the input coupling axis.

In order to calibrate the dynamometer, a known load may be applied to the input coupling with the result thereof from the load cell 6 being monitored.

The vertical positions of the pump manifolds 9 may then be adjusted with respect to the fixed manifold 11 until the output from the load cell 6 corresponds to the known correct value. If necessary, measurements may be taken at different input loadings. Such loadings would normally be of a relatively low level so that the effect of the calibrational adjustment may more easily be determined. When the calibration has been completed, the relative adjustment of the pump manifolds 9 is fixed.

Figures 5 to 8 show part of a dynamometer comprising a frame 101 having front and rear upstanding brackets 102 and 103, respectively. The front bracket 102 has mounted therein a bearing comprising inner and outer races 103 and 104 and a plurality of rolling elements 105 disposed therebetween. The outer race 103 is fixed to the front bracket 102 and the inner race 104 is fixed to a housing 106 in which are provided two bearing assemblies 107. The housing 106 is rigidly connected by means of bolts 108 to an hydraulic pump/motor 109.

The pump/motor 109 has a shaft 110 to which is fixed a spline gear 111. The spline gear 111 meshes with internal splines in an axial bore of an input coupling 112. The input coupling 112 is provided with a plurality of holes 113 for connection to an output shaft of an engine to be tested.

The pump/motor 109 is rigidly connected to one end of a manifold 114 whose other end has an annular extension 115. The annular extension 115 is provided with an inner race 116 of a trunnion bearing which further comprises an outer race 117 fixed to the rear bracket 103 and a plurality of rolling elements 118.

The manifold 114 has formed therein three cham bers 119, 120, and 121.The chambers 119 and 120 are connected via respective passage-ways disposed laterally in the manifold 114 to the inlet and outlet sides of the pump/motor 109 as illustrated in Figure 7. The chamber 121 similarly communicates with the pump/motor 109 and is provided for bleeding off any fluid escaping from within the pump/motor 109 for the purpose of cooling. The various passage-ways between the pump/motor 109 and the manifold 114 are sealed by means of gaskets or O-rings as shown in Figure 7.

Three tubular pipes 112,123 and 124 enter the chambers 119, 120 and 121, respectively, at their upper ends and are connected to corresponding chambers provided in a fixed manifold 125 attheir lower ends. The upper ends of the pipes 122, 123 and 124 extend through and just beyond the axis 126 of the input coupling 112 and the pump/motor 109. The upper ends of the pipes 122, 123 and 124 are sealed to the manifold 114 by means of O-rings 127 provided in annular grooves formed in the manifold 114. The planes of the O-rings 127 pass through the input coupling axis 126, which extends across the diameters of the O-rings so that the axes of the pipes 122,123 and 124 intersect the input coupling axis 126. The manifold 114 has conically tapered surfaces 128 tapering outwardly and downwardly from the grooves in which the O-rings 127 are provided.Thus, the pipes 1.22, 123 and 124 are able to pivot slightly in the manifold 114 at their upper ends about the O-rings 127 so that the pipe axes always intersect the input coupling axis 126.

The manifold 114 is rigidly connected to one end of an arm 129 which extends laterally of the input coupling axis 126. At its other end, the arm 129 is connected by means of a bearing 130 to an upper bracket 131 which is fixed to the top of a load cell 132. The lower end of the load cell 132 is connected via a bracket 133 and a another bearing 134 to the frame 101.

The dynamometer part shown in Figures 5 to 8 may be used as part of a regenerative dynamometer in place of the part shown in Figure 1a. The output shaft of an internal combustion engine to be tested is connected to the input coupling 112 and the chambers of the fixed manifold 125 are connected via high pressure pipe work to the pump 14 connected to the AC motor 15. The lower ends of the pipes 122, 123 and 124 are sealed to the chambers of the manifold 125 by means of O-rings and are pivotable thereto in the same way as the pivoting and sealing arrangements at the upper end of the pipes. Alternatively, they may be fixed at this end.

During testing of the engine, its output shaft drives the input coupling 112 which drives the input shaft 110Ofthe pump/motor 19 via the splined gearing 111. Fluid to and from the pump/motor passes via the chambers 119, 120 ofthe manifold 114 and via the pipes 122, 123 and the fixed manifold 125 to the pump 14 and the AC motor 15 so that a load can be put on the engine being tested. The load causes the pump/motor 109 to try to pivot about the input coupling axis, which in turn tries to cause turning of the arm 129 so that a load is placed on the load cell 132. The load cell 132 provides a signal which can be used to determine the torque and/or power of the engine being tested.

The pivoting by the manifold 114 as a result of the engine load does not cause the pipes 122, 123 and 124 to pivot also in the fixed manifold 25. According iy, the fluid in the chambers 119, 120 and 121 and in the pipes 122, 123 and 124 is under very high pressure during operation of the dynamometer but the forces resulting from the high pressure fluid always act through the input coupling axis 126.

Accordingly, these forces resulting from the fluid pressure exert no turning moment on the manifold 114, so that they have no effect on the load supplied to the load cell 132 via the arm 129. Thus, the accuracy of the dynamometer is not impaired. In this respect, although the pivoting of the manifold 114 at the loads produced by internal combustion engines to be detected is only relatively small, the hydraulic fluid in the chambers and pipes 119 and 124 is at such a high pressure that very large forces result which could have a substantial effect on the reading obtained by the dynamometer, thus impairing its accuracy. However, these forces always act through the input coupling axis 126, so that no additional loading is placed on the load cell 132, which therefore only measures the load supplied by the engine to be tested.The front ball-bearing and the reartrunnion bearing allow the pump/motor 109 and the manifold 1 14to pivot about the input coupling axis while preventing vertical movement thereof as a result of the fluid pressure forces acting through the input coupling axis 126.

According to a modification of the embodiment shown in Figures 4to 8, the pipes to the manifold 114 may be arranged to extend from either side of the coupling axis in such a way that the net force acting through this axis is zero. In this case, the "0" ring can no longer be on the input coupling axis.

Figures 9 and 10 of the accompanying drawings show part of another dynamometer constituting a further preferred embodiment of the invention.

Those parts of the embodiment of Figures 9 and 10 which have already been described with reference to Figures 5 to 8 are referred to by the same reference numerals and will not be described further.

As shown in Figure 9, the pipes 123 and 124 are spaced apart by a greater distance than the corresponding pipes 123 as shown in Figure 5. Afurther pipe 135 is disposed between the two pipes 122 and 123 and extends away from the input coupling axis 126 in the opposite direction. The further pipe 135 is tubular and its axis intersects the input coupling axis 126 at its lower end. The lower end of the further pipe 135 is also provided with an "0" ring 136 defining a plane through which the input coupling axis 126 passes as shown in Figures 9 and 10. The manifold 114 has a conically tapered surface 137 tapering outwardly and upwardly from the grooves in which the O-ring 136 is provided. The further pipe 135 is thus able to pivot slightly in the manifold 114 at its lower end about the O-ring 136 so that the pipe axis always intersects the input coupling axis 126.

The upper end of the further pipe 135 enters a bridge piece 138 and is sealed thereto by means of another O-ring 139. The bridge piece 138 has a tapered surface 40 which tapers outwardly and downwardly so that the further pipe 135 can pivot slightly in the bridge piece 138 at its upper end. The bridge piece 138 is elongate transversely to the input coupling axis 126 and is fixed at its ends to the fixed manifold 125 by means of a pair of struts 141 and spacers 142.

The further pipe 135 is connected buy a bore 143 formed in the manifold 114to another bore 144 formed in the manifold 114 and containing a shuttle valve 145. The bore 144 communicates with one of the passages 146 from the pump leading to one of the pipes 122 and 123. The bore 144 communicates via a further bore 147 in the manifold 114 with another passage 148 which leads from the pump 109 to the other of the pipes 122 and 123.The embodiment shown in Figures 9 and 10 of the accompany- ing drawings differs from that shown in Figures 5 to 8 of the accompanying drawings in that, when the dynamometer is in use, the shuttle valve 145 is deflected by the fluid in the passages 146 and 148 and moves to a position such that the further pipe 135 communicates via the bore 143 with the one of the passages 146 and 148 which contains fluid at the higher pressure. Figure 10 illustrates the position of the shuttle valve 145 such that the further pipe 135 is in communication with the passage 146. The fluid in the further pipe 135 thus exerts a pressure resulting in a force which passes through the input coupling axis 126, the bridge piece 138 serving to provide a reaction to this force at the upper end of the further pipe 135.This force thus acts through the input coupling axis 126 but in the opposite direction to the forces resulting from fluid pressure in the pipes 122 and 123, and so tends to reduce the net force acting transversely to the input coupling axis 126. Further, because the further pipe 135 is disposed between the pipes 122 and 123, the turning moment in the vertical plane through the input coupling axis 126 is also substantially reduced. The load on the trunnion bearings is thus substantially relieved by the provision of the pipe 135. However, because the lower end of the further pipe 135 can pivot slightly by means of the O-ring but is such that its axis always intersects the input coupling axis 126, the provision of the further pipe 135 has no substantial effect on measurements obtained by the dynamometer as the force resulting from the fluid pressure in the further pipe 135 does not exert any turning moment about the input coupling axis 126.

Claims (22)

1. A dynamometer comprising an input coupling rotatable about an axis for connection to an engine to be tested, an hydraulic pump arranged to be driven from the input coupling, a fixed manifold, and a plurality of conduits interconnecting the pump and the fixed manifold and arranged so that fluid pressure in the conduits produces no turning moment about the input coupling axis.

2. A dynamometer as claimed in claim 1, in which the pump is coaxial with the input coupling axis.

3. A dynamometer as claimed in claim 1 or 2, in which the pump is provided with a pump manifold defining a plurality of chambers and the conduits are arranged to enter into the respective chambers with their axes passing through the input coupling axis, the conduits being pivoted to the pump manifold about the input coupling axis.

4. A dynamometer as claimed in claim 3, in which the conduits are pivoted and sealed to the pump manifold by means of respective O-rings.

5. A dynamometer as claimed in claim 3 or 4, in which the pump manifold is fixed at one end to the pump and is pivotably mounted at its other end to a fixed frame of the dynamometer.

6. A dynamometer as claimed in claim 5, in which the pump manifold is mounted to the fixed frame by means of a trunnion bearing which is coaxial with the input coupling axis.

7. A dynamometer as claimed in any one of claims 3 to 6, in which the pump manifold is connected via a load cell to a or the fixed frame of the dynamometer.

8. A dynamometer as claimed in any one of claims 3 to 7, in which the conduits extend from the pump manifold on opposite sides of the input coupling axis.

9. A dynamometer as claimed in any one of claims 3 to 7, in which the conduits extend in parallel in a first direction from the pump manifold and a further conduit extends in the opposite direction to a fixed member with its axis passing through the input coupling axis, the further conduit being pivoted to the pump manifold about the input coupling axis.

10. A dynamometer as claimed in claim 9, in which the further conduit is pivoted at its ends to the pump manifold and to the fixed member by means of respective O-rings.

11. A dynamometer as claimed in claim 9 or 10, in which the further conduit is arranged to communicate with the plurality of chambers in the pump manifold via passageways and there is provided a shuttle valve arranged to allow the further conduit to communicate with the chamber containing fluid at the highest pressure.

12. A dynamometer as claimed in claim 1, in which there are a plurality of hydraulic pumps disposed around the input coupling axis and arranged to be driven from the input coupling, the fixed manifold having fluid input and outputchambers disposed coaxially with the input coupling axis, the plurality of conduits connecting the input and output sides of the pumps with the input and output sides, respectively, of the fixed manifold chambers, the conduits being further arranged in relation to the input and output chambers of the fixed manifold so that the forces resulting from fluid pressure in the conduits during operation of the dynamometer act substantially through the input coupling axis and the resultant thereof has a substantially zero component in a plane transverse to the input coupling axis.

13. A dynamometer as claimed in claim 12, in which the pumps are connected to the input coupling via a load splitting gear-box which is pivotable about the input coupling axis and is connected to a fixed frame of the dynamometer by a load cell.

14. A dynamometer as claimed in claim 12 or 13, in which the pumps are equiangularly spaced about the input coupling axis.

15. A dynamometer as claimed in claim 14, in which two pumps are provided and are disposed on opposite sides of the input coupling axis with their longitudinal axes in a horizontal plane.

16. A dynamometer as claimed in any one of claims 12 to 15, in which the pumps are of the same type and are arranged to be driven at the same speed.

17. A dynamometer as claimed in any one of claims 12to 16, in which the conduits extend radially with respect to the input coupling axis from the fixed manifold to the pumps.

18. A dynamometer as claimed in any one of claims 12 to 17, in which the inlet and outlet chambers of the fixed manifold are spaced apart longitudinally of the input coupling axis.

19. Adynamometer as claimed in claim 1, in which there are a plurality of manifolds disposed around the input coupling axis, the plurality of conduits connecting the pump to the manifolds and being further arranged so that the forces resulting from fluid pressure in the conduits during operation of the dynamometer act substantially through the inlet coupling axis and the resultant thereof has a substantially zero component in a plane transverse to the input coupling axis.

20. A dynamometer as claimed in claim 19, in which two manifolds are provided on opposite sides of the input coupling axis, the conduits between the pump and the manifolds and between the manifolds extending radially with respect to the input coupling axis.

21. A dynamometer as claimed in any one of the preceding claims, in which the fixed manifold is hydraulically connected to one or more further hydraulic pumps mechanically connected to an AC motor.

22. A dynamometer substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.