Rx 400h Heading For Police Duty in the UK
21 August 2005
 |
| Rx 400h in police livery. |
Testdriven. Lexus is kitting out the Rx 400h hybrid for police trials in the UK.
The acceptance of the hybrid into police trials highlights the increasing optimization of the hybrid platform for power. Although a number of cities in the US, for example, are mandating some percentage of hybrid or alternative fuel vehicle purchases, most often those mandates exclude emergency response vehicles—e.g., the police—aside from administrative transport.
The RX 400h uses an enhanced version of the Hybrid Synergy Drive system that combines the 3.3-liter V6 gasoline engine with a high-torque electric drive motor-generator plus a rear electric drive motor-generator to provide on-road all-wheel drive (AWD) capability.
 |
| The front power unit of the Rx 400h. |
A good deal of the performance of the vehicle is due to the design of its front power unit.
The Lexus hybrid uses a water/oil cooled, AC synchronous type motor of a high-efficiency DC, brushless design operating on AC current. A rotor constructed from stacked, electromagnetic steel plates and Neodymium permanent magnets arranged in a V configuration combine to maximize drive torque and power output.
This, combined with a boost in power supply voltage to 650V, a significant increase in motor rotation speed to a maximum of 12,400 rpm and the adoption of a planetary gear to amplify torque through motor speed reduction increases power output by approximately 2.48 times that of the Prius motor, despite the respective units being of near identical size.
The power output of 123 kW (167 hp) and 333 Nm of torque currently gives the power unit the highest output per unit of weight and volume in the world.
A rear-axle 650V electric motor that kicks in when the vehicle needs 4WD spins at up to 10,752 rpm and generates a maximum output of 50 kW (67 hp) and 130 Nm of torque.
The combined full hybrid system delivers 268 hp (200 kW). [Lexus initially published a figure for combined axle torque of 3,500 lb-ft. Likely a typo, although it has not published a combined system torque number since. Further discussion of the toque number is below in the comments section.]
The luxury hybrid accelerates from zero to 60 mph in 7.3 seconds—about 0.5 seconds quicker than the RX 330. (Earlier post.)
The Hampshire police will be the first force to test the hybrid SUV under full police specification and under police operational conditions. Initial trials in the Hampshire force went very well.
We have already received positive feedback from our officers after an initial trial and know that the vehicle’s performance was outstanding, with quick acceleration and more than adequate response throughout the range of the electronic gearbox. We eagerly await the fully equipped model when we will be able to put it through its paces and gauge the performance under police operational conditions.
—John Bradley, Hampshire Police Fleet Manage
Does it really have 3,500 lb-ft of torque? That's not a typo? Holy...
Posted by: Mikhail Capone | 21 August 2005 at 10:24 AM
Lexus has stated that the system can put out 3500 lb-ft of torque, and yes, that is Lexus' typo, repeated all over the web. I'm guessing they meant 350 total, but whether that refers to the 2WD or 4WD version is unclear. Lexus does not give a total powertrain torque rating in their technician service info, nor on their website. Combined horsepower is stated as 268, whether 2WD or 4WD.
The 3MZ-FE engine puts out a maximum of 212 lb-ft of torque. MG2 can is rated at 246 lb-ft, and the optional MG-R (4WD version) is rated at 96 lb-ft.
212 plus 246 plus 96 = 554, but this does not, however, add up to 554 lb-ft in the real world, as electric motor ratings are a rating of maximum capability, which is dependent on motor control, battery SOC, etc. plus Toyota's desire to protect the system by not running the bejeezus out of it.
Posted by: Jack | 21 August 2005 at 11:37 AM
There's also the fact that the torque curves of electrical motors and ICEs are very different, I suppose...
Posted by: Mikhail Capone | 21 August 2005 at 01:26 PM
Toyota does say 3,500 ft-lbs of torque in a press release from earlier this year. The towing capacity for the RX400h is 3,500 lbs -- perhaps that's where the lines got crossed.
http://lexus.com/models/rx_hybrid/specifications.html
Looking around the Web, I'm not seeing any definitive figures for combined torque.
Posted by: Joseph Willemssen | 21 August 2005 at 01:43 PM
Thanks for the underlying motor info, Jack!
Posted by: Mike | 21 August 2005 at 01:44 PM
If the car is in low gear the 3500 ft/lb at the wheel is quite reasonable.
Posted by: tom | 21 August 2005 at 01:50 PM
"If the car is in low gear the 3500 ft/lb at the wheel is quite reasonable."
Not true. There's only 554 lb/ft total to play with. 3500 lb/ft of torque would snap the axles. Hell, 1000 lb/ft of torque would probably break them. For comparison, a military Hummer H1 (not the gentrified H2) with a high-torque turbodiesel puts out a maximum 520 lb/ft of torque, which is about 15% of the 3500 figure.
In addition (expanding on my earlier post), a comparison or combination of electric and fuel-based horsepower and torque specs cannot, unfortunately, be accurately made, for the following reasons:
Maximum horsepower and torque specs for a fueled engine reflect the highest numbers seen at any time during dyno testing. In other words, peak output.
Horsepower and torque specs for electric motors (and if the output is given in kilowatts, that can be converted to horsepower, as 746 watts = 0.746 kW = one hp) reflect, on the other hand, what the motor can put out under continuous load. Unlike fueled engines, electric motors can produce a peak output of eight to ten times their rated (continuous load) output.
To make things even more confusing, the rated output of an electric motor does not normally reflect its output once it is installed in a battery-powered electric drive system. The motor controller, which is the inverter assembly in today's hybrids, will be programmed to permit a certain percentage of maximum output at full load. And that's assuming, of course that the battery is fully charged; the percentage out output allowed will of course drop as battery state-of-charge falls, and rise again with SOC. Such control, coupled with the elegant simplicity of the electric motor itself, combine to provide a component that, when properly designed, will likely last the life of the car.
Other factors, such as ambient temperature, motor temperature, and so on, affect the equation, but that's probably enough for now.
By the way, if anyone finds it odd that the Lexus RX400h hybrid, and not the less costly Highlander hybrid, is being trialled for police duty, it's because the Highlander is not sold in the UK.
Posted by: Jack | 21 August 2005 at 03:52 PM
"By the way, if anyone finds it odd that the Lexus RX400h hybrid, and not the less costly Highlander hybrid, is being trialled for police duty, it's because the Highlander is not sold in the UK."
Thanks for the info. I was wondering about that and figured that maybe the Lexus had better handling characteristics than the Highlander.
Posted by: Mikhail Capone | 21 August 2005 at 06:46 PM
Give me a break. Not to break the Hybrid chatter, but a 2.5turbo subaru legacy outback would have better performance, offroad capability(lexus advices customers not to take the RX400h offroad), and have the same fuel economy without the hybrid complexity and cost. The RX400h is stilla gas guzzler. The police is using this for trials because of the image. Now what about those smart police cars I see on the streets of london?
Posted by: Tman | 22 August 2005 at 09:12 AM
"but a 2.5turbo subaru legacy outback would have better performance, offroad capability(lexus advices customers not to take the RX400h offroad), and have the same fuel economy without the hybrid complexity and cost."
400h - 31 city/27 hwy/29 combined
Legacy turbo - 19 city/25 hwy/21 combined
Also, where does Lexus advise its customers not to take it offroad? And I didn't realize that police vehicles in Hampshire need significant offroad capabilities.
Posted by: Joseph Willemssen | 22 August 2005 at 09:30 AM
WHAT??
How do come off saying 29mpg is the same fuel econemy as 21mpg? That's a difference of 38%! Moreover a cop's drive cycle is probably closer to a city drive cycle, where the difference is 63%.
I am assuming they need a large SUV for some reason. Do brittish cops like donuts as much as american cops do?
Posted by: LochDhu | 22 August 2005 at 01:05 PM
Nothing pisses me off more than seeing cops sitting around in the guzzling crown-vics doing paper work, eating donuts and drinking coffee or whatever -- just sitting there with the engine idling for very long periods of time. In fact I've never seen a cop car that was turned off, even with no police in the vehicle, such as at road checks. The HSD will save them a LOT of fuel by shutting off the engine when they just sit there, as they seem to do an awful lot. Cop cars are expensive anyways, so no real additional expense by going to this model or the HH, hopefully it will work well enough that they implement something similar over here.
Posted by: Schwa | 22 August 2005 at 08:37 PM
Torque inceases with every gear reduction. If the differential ratio is 4:1 and low gear is 2.5:1 then the torque at the wheel would be 10 times the engine torque. Since the wheel speed would be 1/10 engine speed the HP at the wheel would equal engine HP minus friction losses in the drivetrain. Archimedes figured this out 2300 years ago! Learn a little basic physics before commenting again.
Posted by: tom | 23 August 2005 at 08:00 AM
Torque increases with every gear reduction. If the differential ratio is 4:1 and low gear is 2.5:1 then the torque at the wheel would be 10 times the engine torque. Since the wheel speed would be 1/10 engine speed the HP at the wheel would equal engine HP minus friction losses in the drivetrain. Archimedes figured this out 2300 years ago! Learn a little basic physics before commenting again.
Posted by: tom | 23 August 2005 at 08:01 AM
Cop cars are expensive became people tend to ram into them and shoot at them and stuff... thats also why they are heavy. They tried lighter cop cars and the result was alot more dead cops.
Posted by: wintermane | 23 August 2005 at 11:31 AM