Zeroshift move up a gear with HBM data logging
Zeroshift Ltd., a company based in the UK, has developed revolutionary new transmission technology that facilitates a completely instantaneous change in gear ratio with no interruption of torque to the driving wheels. Zeroshift has developed the system using HBMs MGCplus data logger in their development vehicles and with catman®Easy software as their data analysis tool.
In order to develop the system for its wide range of applications, a large number of driveline parameters variables need to be closely monitored during the gearshift; such as engine and vehicle speeds, driveline torques, actuator position and clutch and throttle pedal positions etc.
Therefore Zeroshift makes good use of the multi-channel MGCs. Working with OEMs and Tier 1s means that Zeroshift have access to the vehicles CAN (Controller Area Network) data, therefore the ability to read CAN channels directly into the logger is a big advantage.
Zeroshifts Chief Engineer Adam Huckstep, ‘Zeroshift, as its name suggests, has the ability to change gear instantaneously. Therefore our data logger needs to be able to acquire data at extremely fast rates to be able to capture the change in engine and transmission speed and torque during a gearshift, and to track the position of the actuation system. With a shift that’s over in a few milliseconds, we need logging rates well into the kilohertz for all our acquired channels to really see what’s going on.’
Business Development Manager, Ray Heath, explains that they also make great use of the PC card data logging function.
‘Our test vehicles are regularly driven by customers and potential clients who don’t want to be starting and stopping data loggers on their test drive. However the data from different drivers and driving styles is useful for our engineers, so the PC card data storage function allows us to trigger the data logger for example on key-on, or on an engine speed threshold, and capture all the data of the drive.’
The future of transmission technology
The Zeroshift principle is relatively simple in concept: the new gear is engaged whilst the previous gear is still driving, eliminating the break in torque (head nod) experienced in conventional manual and automated manual transmissions during a gearshift. As the new gear takes up the drive the previous gear is automatically disengaged, leaving the vehicle to continue driving in the new gear.
Figure 1 illustrates the arrangement of bullets and dogs and gears. The blue and red bullets appear identical, however their ramp and engagement faces point in opposite directions providing a bullet face on either side of the dog teeth and hence transmitting torque from the gear mesh to the hub via either the driven or overrun set of bullets.
Figure 2 illustrates the process of making a ‘Zeroshift’ (shifting gear without a delay in applied torque to the driven wheels). An up-shift from gear one to gear two is detailed below, and illustrates how the geometry of each set of bullets makes it possible to achieve a seamless gearshift.
Starting in neutral, figure 2(a) shows both sets of bullets (blue and red) positioned midway between the gear 1 and gear 2. Torque generated by the engine is transmitted to the transmission output shaft via the dog teeth. Since neither set of bullets are locked to a gear, the vehicle is in neutral.
To select first gear, both bullet sets are moved onto gear one dog teeth via an actuator. Figure2(b) shows the blue bullets engaging onto gear one, which is driving in a clockwise direction.
The red bullets lock onto the overrun side of gear one dog teeth (figure 2c). In the event of the driver breaking, the direction of torque is reversed and instead runs in the anti-clockwise direction. In this case the red bullets will take up drive and slow the vehicle down.
Assuming the driver is accelerating and wants to change from gear 1 to gear 2, the unloaded bullets (in this case the red bullets), are free to move. The loaded bullets (blue), are locked to gear one since the retaining force (due to the torque acting on the retention angle) between the bullet face and dog tooth is greater than the axial force generated by the actuator as depicted in figure 2(d).
Gear 2 rotates with greater angular speed than gear 1 (both in the clockwise direction). As the red bullets engage onto the dog teeth the drive taken up on its bullet face pushes the hub (figure 1), at the new speed. Notice that in figure 2(e), both red and blue bullets are engaged at the same time. This is the point of Zeroshift.
Now the hub is moving at a speed dictated by gear 2, the blue bullets are overdriven and come loose from the gear 1 dog teeth (figure 2f).
The blue bullets are now free to move. Figure 2(g) shows a dog tooth on gear 1 making contact with the ramp face of the blue bullets thus firing it into position to act as the over-run gear on gear 2 (figure 2(h)). Even though both gear 1 and gear 2 are rotating in the clockwise direction, gear 1 is running slower with reference to a point on gear 2.
Notice that the red bullets are now the driven bullets (formerly the overrun bullets) and the blue bullets are the overrun bullets (formerly the driven bullets).
Figure 3 and 4 are graphs obtained by HBM data logging equipment and from simulation respectively. The smooth speed curve obtained by Zeroshift transmission is clear. Uninterrupted torque to the driven wheels allows positive acceleration through gearshifts. The simulation results on figure 4 compare the speed traces of identical cars. The car with the AMT requires a break in torque to its driven wheels and hence loses positive acceleration during the gearshift.
For more information about Zeroshift visit the website www.zeroshift.com