Abstract:
In July of 2004 KTH Racing will attend at the Formula Student event in England. The Formula Student event is a competition between schools that has built their own formula style race cars according to the Formula SAE rules. In January of 2004 the Formula Student project started at KTH involving over seventy students. The aim of this thesis work is to design the suspension and steering geometry for the race car being built. The design shall meet the demands caused by the different events in the competition. The design presented here will then be implemented into the chassis being built by students participating in the project. Results from this thesis work shows that the most suitible design of the suspension is a classical unequal length double A-arm design. This suspension type is easy to design and meets all demands. This thesis work is written in such a way that it can be used as a guidebook when designing the suspension and steering geometries of future Formula Student projects at KTH.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates generally to vehicle powertrain mounting systems, and more particularly to a vehicle powertrain mounting system including a magnetorheological hydraulic mount and to a method for controlling such a mount in such a system.  
       BACKGROUND OF THE INVENTION  
       [0002]     A vehicle powertrain includes a vehicle engine and a vehicle transmission. One example of a conventional vehicle powertrain mounting system includes five mounts each attached to the vehicle powertrain and to one or more vehicle weight-supporting members (such as a vehicle frame, a vehicle subframe, or a vehicle body). The first mount is a conventional hydraulic mount attached to a rear portion of the powertrain. The second mount is a conventional hydraulic mount attached to a front portion of the powertrain. The third mount is an elastomeric mount attached to a side portion of the powertrain. A fourth mount is an upper torque strut (restrictor) attached to the powertrain above the center of gravity of the powertrain. A fifth mount is a lower torque strut (restrictor) attached to the powertrain below the center of gravity of the powertrain. The first through third mounts carry loads and the fourth through fifth mounts react engine torque caused by a change in rotational speed of the vehicle engine.  
         [0003]     It is known to replace a conventional hydraulic mount with a magnetorheological (MR) hydraulic mount (also called an MR-fluid hydraulic mount) to carry loads. MR hydraulic mount systems, which involve various designs and which are well known in the art, include an MR fluid whose damping effect is varied by changing the electric current to an electric coil which is positioned to magnetically influence the MR fluid and hence the damping effect of the MR fluid.  
         [0004]     What is needed is an improved vehicle powertrain mounting system including a magnetorheological hydraulic mount and to a method for controlling such a mount in such a system.  
       SUMMARY OF THE INVENTION  
       [0005]     In a first embodiment of the invention, a vehicle powertrain mounting system includes a vehicle powertrain and a first magnetorheological (MR) mount. The vehicle powertrain includes a vehicle engine. The first MR hydraulic mount operatively connects the vehicle powertrain to a vehicle weight-supporting member. The first MR hydraulic mount is positioned to carry load and is positioned to react vehicle engine torque during a change in rotational speed of the vehicle engine.  
         [0006]     In a second embodiment of the invention, a vehicle powertrain mounting system includes a vehicle powertrain, a first magnetorheological (MR) mount, and a controller. The vehicle powertrain includes a vehicle engine. The first MR hydraulic mount operatively connects the vehicle powertrain to a vehicle weight-supporting member. The first MR hydraulic mount is positioned to carry load and is positioned to react vehicle engine torque during changes in rotational speed of the vehicle engine. The first MR hydraulic mount includes a first electric coil. The controller controls electric current to the first electric coil. The controller supplies electric current to the first electric coil during bounce of the vehicle engine, and/or the controller supplies electric current to the first electric coil during a change in rotational speed of the vehicle engine.  
         [0007]     A method of the invention is for controlling a magnetorheological (MR) hydraulic mount of a vehicle powertrain mounting system for a vehicle powertrain including a vehicle engine. The MR hydraulic mount operatively connects the vehicle powertrain to a vehicle weight-supporting member. The MR hydraulic mount is positioned to carry load and is positioned to react vehicle engine torque during changes in rotational speed of the vehicle engine. The MR hydraulic mount includes an electric coil. The method includes the step of supplying electric current to the electric coil during bounce of the vehicle engine. The method also includes the step of supplying electric current to the electric coil during a change in rotational speed of the vehicle engine.  
         [0008]     Several benefits and advantages are derived from one or more of the embodiments and method of the invention. Using an MR hydraulic mount positioned to carry load and positioned to react vehicle engine torque during changes in rotational speed of the vehicle engine allows such MR hydraulic mount to replace more than one conventional mount in a conventional powertrain mounting system. In one example, the MR hydraulic mount replaces a load-carrying conventional hydraulic mount operatively connected to a rear portion of the vehicle powertrain and eliminates using upper and lower torque strut (restrictor) conventional mounts. 
     
    
     SUMMARY OF THE DRAWINGS  
       [0009]      FIG. 1  is a side-elevational schematic diagram of a first embodiment of the powertrain mounting system of the invention including a first magnetorheological (MR) hydraulic mount;  
         [0010]      FIG. 2  is a side-elevational schematic diagram of a second embodiment of the powertrain mounting system of the invention including first and second magnetorheological (MR) hydraulic mounts; and  
         [0011]      FIG. 3  is block diagram of a method for controlling an MR hydraulic mount of a powertrain mounting system such as that shown in the first embodiment of  FIG. 1 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]     Referring now to the drawings,  FIG. 1  shows a first embodiment of the present invention. A first expression of the first embodiment of  FIG. 1  is for a vehicle powertrain mounting system  110  comprising a vehicle powertrain  112  and a first magnetorheological (MR) hydraulic mount  114 . The vehicle powertrain  112  includes a vehicle engine  116 . The first MR hydraulic mount  114  operatively connects the vehicle powertrain  112  to a vehicle weight-supporting member  118 . The first MR hydraulic mount  114  is disposed to carry load and is disposed to react vehicle engine torque during a change in rotational speed of the vehicle engine  116 .  
         [0013]     In one employment of the first expression of the first embodiment of  FIG. 1 , the vehicle engine  116  is a transverse-mounted vehicle engine.  
         [0014]     In an example of the first expression of the first embodiment of  FIG. 1 , the vehicle powertrain mounting system  110  also includes a non-MR hydraulic mount  120  operatively connected to a front portion  122  of the vehicle power train  112  and an elastomeric mount  124  operatively connected to a side portion  126  of the vehicle powertrain  112 . In this example, the first MR hydraulic mount  114  is operatively connected to a rear portion  128  of the vehicle powertrain  112 , and the first MR hydraulic mount  114 , the non-MR hydraulic mount  120 , and the elastomeric mount  124  are the only mounts operatively connected to the vehicle powertrain  112 .  
         [0015]     In one illustration of the first embodiment of  FIG. 1 , the first MR hydraulic mount  114  is the primary mount operatively connected to the vehicle powertrain  112  which reacts vehicle engine torque during a change in rotational speed of the vehicle engine  116 . In this illustration, the first MR hydraulic mount  114  reacts more vehicle engine torque during a change in rotational speed of the vehicle engine than any other mount operatively connecting the vehicle powertrain  112  to a vehicle weight-supporting member. In one arrangement of the first embodiment of  FIG. 1 , the vehicle powertrain  112  is devoid of any torque-strut operative connection to a vehicle weight-supporting member.  
         [0016]     In a second embodiment shown in  FIG. 2 , the vehicle powertrain mounting system  210  also includes a second MR hydraulic mount  215  operatively connecting the vehicle powertrain  212  to a vehicle weight-supporting member (such as member  218  or a different vehicle weight-supporting member, not shown). The second MR hydraulic mount  215  is disposed to carry load and is disposed to react vehicle engine torque during changes in rotational speed of the vehicle engine  216 . Examples of vehicle weight-supporting members include, without limitation, a vehicle frame, a vehicle subframe, and a vehicle body.  
         [0017]     In one variation of the second embodiment of  FIG. 2 , the vehicle powertrain mounting system  210  also includes an elastomeric mount  224  operatively connected to a side portion  226  of the vehicle powertrain  212 . In this variation, the first MR hydraulic mount  214  is operatively connected to a rear portion  228  of the vehicle powertrain  212 , the second MR hydraulic mount  215  is operatively connected to a front portion  222  of the vehicle powertrain  212  and the first and second MR hydraulic mounts  214  and  215  and the elastomeric mount  224  are the only mounts operatively connected to the vehicle powertrain  212 .  
         [0018]     A second expression of the first embodiment of  FIG. 1  is for a vehicle powertrain mounting system  110  comprising a vehicle powertrain  112 , a first magnetorheological (MR) hydraulic mount  114 , and a controller  130 . The vehicle powertrain  112  includes a vehicle engine  116 . The first MR hydraulic mount  114  operatively connects the vehicle powertrain  112  to a vehicle weight-supporting member  118 . The first MR hydraulic mount  114  is disposed to carry load and is disposed to react vehicle engine torque during a change in rotational speed of the vehicle engine  116 . The first MR hydraulic mount  114  includes a first electric coil  132 . The controller  130  controls electric current to the first electric coil  132 . The controller  130  supplies electric current to the first electric coil  132  during bounce of the vehicle engine  116  and/or during a change in rotational speed of the vehicle engine  116 .  
         [0019]     In one employment of the second expression of the first embodiment of  FIG. 1 , the vehicle engine  116  is a transverse-mounted vehicle engine.  
         [0020]     In one example of the second expression of the first embodiment of  FIG. 1 , the vehicle powertrain mounting system  110  also includes a non-MR hydraulic mount  120  operatively connected to a front portion  122  of the vehicle powertrain  112  and an elastomeric mount  124  operatively connected to a side portion  126  of the vehicle powertrain  112 . In this example, the first MR hydraulic mount  114  is operatively connected to a rear portion  128  of the vehicle powertrain  112 , and the first MR hydraulic mount  114 , the non-MR hydraulic mount  120 , and the elastomeric mount  124  are the only mounts operatively connected to the vehicle powertrain  112 .  
         [0021]     In the second embodiment of  FIG. 2 , the vehicle powertrain mounting system  210  also includes a second MR hydraulic mount  215  operatively connecting the vehicle powertrain  212  to a vehicle weight-supporting member (such as member  218  or a different vehicle weight-supporting member, not shown). The second MR hydraulic mount  215  is disposed to carry load and is disposed to react vehicle engine torque during changes in rotational speed of the vehicle engine  216 . The second MR hydraulic mount  215  includes a second electric coil  233 , and the controller  230  controls electric current to the second electric coil  233 . The controller  230  supplies electric current to the second electric coil  233  during bounce of the vehicle engine  216  and/or during a change in rotational speed of the vehicle engine  216 . The controller  230  also controls electric current to the first electric coil  232 . The controller  230  supplies electric current to the first electric coil  232  during bounce of the vehicle engine and/or during a change in rotational speed of the vehicle engine  216 .  
         [0022]     In one variation of the second embodiment of  FIG. 2 , the vehicle powertrain mounting system  210  also includes an elastomeric mount  224  operatively connected to a side portion  226  of the vehicle powertrain  212 . In this variation, the first MR hydraulic mount  214  is operatively connected to a rear portion  228  of the vehicle powertrain  212 , the second MR hydraulic mount  215  is operatively connected to a front portion  222  of the vehicle powertrain  212 , and the first and second MR hydraulic mounts  214  and  215  and the elastomeric mount  224  are the only mounts operatively connected to the vehicle powertrain  212 .  
         [0023]     In one illustration of the second embodiment of  FIG. 2 , the first and second MR hydraulic mounts  214  and  215  are the primary mounts operatively connected to the vehicle powertrain  212  which react vehicle engine torque during a change in rotational speed of the vehicle engine  216 . In this illustration, the first and second MR hydraulic mounts  214  and  215  each react more vehicle engine torque during a change in rotational speed of the vehicle engine than any other mount operatively connecting the vehicle powertrain  212  to a vehicle weight-supporting member. In one arrangement of the second embodiment of  FIG. 2 , the vehicle powertrain  212  is devoid of any torque-strut operative connection to a vehicle weight-supporting member.  
         [0024]     A method of the invention is shown in block-diagram form in  FIG. 3  and is for controlling a magnetorheological (MR) hydraulic mount  114  (also called a first MR hydraulic mount) of a vehicle powertrain mounting system  110  for a vehicle powertrain  112  including a vehicle engine  116 . The MR hydraulic mount  114  operatively connects the vehicle powertrain  112  to a vehicle weight-supporting member  118 . The MR hydraulic mount  114  is disposed to carry load and is disposed to react vehicle engine torque during changes in rotational speed of the vehicle engine  116 . The MR hydraulic mount  114  includes an electric coil  132  (also called a first electric coil). The method includes steps a) and b). Step a) is labeled “Supply Current To Coil During Bounce” in block  134  of  FIG. 3 . Step a) includes supplying electric current to the electric coil  132  during bounce of the vehicle engine  116 . Step b) is labeled “Supply Current To Coil During Change In Engine Speed” in block  136  of  FIG. 3 . Step b) includes supplying electric current to the electric coil  132  during a change in rotational speed of the vehicle engine  116 .  
         [0025]     It is noted that the damping effect provided by the MR hydraulic mount  114  is increased with an increase in the magnitude of the electric current supplied to the electric coil  132 , as can be appreciated by the artisan. In one employment of the method of  FIG. 3 , the vehicle engine  116  is a transverse-mounted vehicle engine. Examples of a vehicle weight-supporting member  118  include, without limitation, a vehicle frame, a vehicle subframe, and a vehicle body.  
         [0026]     In one implementation of the method of  FIG. 3 , step a) supplies electric current to the electric coil  132  during bounce of the vehicle engine  116  at or above, but not below, a bounce threshold magnitude. In this implementation, step b) supplies electric current to the electric coil  132  during a change in rotational speed of the vehicle engine  116  at or above, but not below, a rotational-speed threshold magnitude.  
         [0027]     In one extension of the method of  FIG. 3 , the MR hydraulic mount  114  has a longitudinal axis  138 , and there is also included the step of determining a magnitude of a bounce of the vehicle engine  116  along the longitudinal axis  138 . In one construction, the longitudinal axis  138  is substantially vertically aligned (i.e., substantially vertically aligned when the vehicle, not shown, is on a level horizontal surface). In one variation, bounce of the vehicle engine  116  is determined from the signal output of a position sensor, a velocity sensor, or an accelerometer, as is within the capabilities of those skilled in the art. In one modification, the signal output is filtered to control specific vibration frequencies of any vehicle components that could influence the engine bounce and/or torque reaction.  
         [0028]     In the same or a different extension of the method of  FIG. 3 , there is also included the step of determining a magnitude of a change in rotational speed of the vehicle engine  116 . In one variation, such change is determined from a change in the fore-aft position of the vehicle engine  116  relative to the vehicle frame, subframe or body. In another variation, such change is determined from a prediction of such change based on throttle position, braking, engine RPM (revolutions per minute), gear shifting, etc., and changes therein, as is within the capabilities of those skilled in the art.  
         [0029]     In one application of the method of  FIG. 3 , the magnitude of the electric current supplied to the electric coil  132  in steps a) and b) depends on the magnitude of the bounce and/or the magnitude of the change in rotational speed. In one variation, when both bounce and change in rotational speed of the vehicle engine  116  are present, the magnitude of the supplied electric current depends on the magnitude of the bounce or the magnitude of the change in rotational speed having the greater effect on vehicle performance, as can be appreciated by the artisan. In the same or a different application, a different magnitude of electric current is supplied to the electric coil for compression than for extension of the MR hydraulic mount  114 .  
         [0030]     Several benefits and advantages are derived from one or more of the embodiments and method of the invention. Using an MR hydraulic mount positioned to carry load and positioned to react vehicle engine torque during changes in rotational speed of the vehicle engine allows such MR hydraulic mount to replace more than one conventional mount in a conventional powertrain mounting system. In one example, the MR hydraulic mount replaces a load-carrying conventional hydraulic mount operatively connected to a rear portion of the vehicle powertrain and eliminates using upper and lower torque strut (restrictor) conventional mounts.  
         [0031]     The foregoing description of several embodiments and a method of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise form and steps disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.